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Title: An Introduction to Entomology: Vol. III (of 4) - or Elements of the Natural History of the Insects
Author: Spence, William, Kirby, William, 1817-1906
Language: English
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*** Start of this LibraryBlog Digital Book "An Introduction to Entomology: Vol. III (of 4) - or Elements of the Natural History of the Insects" ***
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[Illustration: _Printed by H. Howard, RA._
_Engraved by W. T. Fry._
_William Kirby. M.A. F.R. L.S. &c_
_Published by Longman & C^o. London, July, 1825_.]
AN
INTRODUCTION
TO
ENTOMOLOGY:
ELEMENTS
OF THE
_NATURAL HISTORY OF INSECTS:_
WITH PLATES.
BY WILLIAM KIRBY, M.A. F.R. AND L.S.
RECTOR OF BARHAM,
AND
WILLIAM SPENCE, ESQ. F.L.S.
VOL. III.
_LONDON:_
PRINTED FOR
LONGMAN, REES, ORME, BROWN, AND GREEN,
PATERNOSTER ROW.
1826.
PRINTED BY RICHARD TAYLOR,
SHOE LANE, LONDON.
ADVERTISEMENT.
The publication of the concluding volumes of the "Introduction
to Entomology" has been unavoidably delayed by the continued ill
health of one of the Authors, which has devolved upon the other a
considerable increase of labour, and demanded a greater expenditure
of time than would otherwise have been required: for though Mr.
SPENCE put every facility in Mr. KIRBY'S power, and had drawn up a
rough copy of every Letter belonging to his department; yet, as most
of them had been written several years ago, many curious facts, and
a great variety of interesting information subsequently derived from
various sources, were necessarily to be inserted, and the whole to be
prepared for the press.
When the thousands of objects that were to be examined, and many of
them repeatedly, in composing the Letters on the External Anatomy
of Insects, are considered, it will not appear surprising if some
errors should have crept in; especially as Mr. KIRBY was deprived of
the effectual help formerly derived from the acumen, learning, and
judgement of his esteemed coadjutor, by his lamented and protracted
indisposition: but it is hoped that these errors will be found of
minor importance, and not to affect any general principles advanced.
The same remarks are also in part applicable to the Anatomical and
Orismological Tables (VOL. III. p. 354-393, and VOL. IV. p. 257-354),
which were drawn up by the Authors jointly many years ago, before any
other portion of the work was composed, but which have, especially
the former, required considerable alterations and additions in
consequence of subsequent observations and information.
It will not be amiss here to state, in order to obviate any charge
of inconsistency in the possible event of Mr. KIRBY'S adverting in
any other work to this subject, that though on every material point
the authors have agreed in opinion, their views of the _theory of
instinct_ do not precisely accord. That given in the second and
fourth volumes is from the pen of Mr. SPENCE.
It was originally intended, as mentioned in the Preface, to have given
a complete list of Entomological works, of which a large portion was
drawn up; but the great length to which more important matters have
extended, has rendered necessary the intire omission of this list,--an
omission in some degree compensated by the catalogue of _Authors
quoted_, which comprises most of the standard Entomological works.
ERRATA.
Page. Line.
29 27, _for_ Pseudo-c_o_rdia _read_ Pseudo-c_a_rdia.
33 7, _for_ 1/12 _read_ 1-1/2.
35 7 and elsewhere, _for_ Gigas _read_ grandis.
46 16, _for_ number and situation _read_ in some respects.
98 6, _for_ Furtina _read_ Jurtina.
121 note^d, _for c read c´._
135 note^b, _for_ XXIV. _read_ XXIII.
137 note^a, _for_ 17 _read_ 18.
251 4, _for_ ten _read_ nine.
378 10, } _for_ frœnum _read_ frænum.
359 21, }
422 note^b, _for_ a´ _read_ a´´.
425 note^b, _for_ b´´ _read_ b´.
471 1, _dele_ Pelecotoma.
10, _for_ orbicular _read_ subtriangular.
512 antepenult. _After_ genera _insert_ except in some _Acridæ_, as
_A. viridissima_.
562 note^c, _for_ πνεω _read_ πνυμι.
606 5, _for_ Heteropterous _read_ Homopterous.
DIRECTIONS TO THE BINDER.
The Synoptical Table of the Nomenclature of the Parts of the External
Crust of Insects should be placed opposite to page 354.
Plates VI-XX. should be placed in this Volume, and the remainder in
the Fourth.
It is however suggested to Purchasers, that in binding complete Sets
of the Work, a separate Volume may be formed of the Synoptical Table,
the Plates and their Explanations, and the Indexes.
CONTENTS OF VOL. III.
Letter. Page.
XXVIII. Definition of the Term _Insect_ 1-51
XXIX. States of Insects. _Egg state_ 52-104
XXX. The same Subject continued. _Larva
state_ 105-237
XXXI. The same Subject continued. _Pupa
state_ 238-290
XXXII. The same Subject continued. _Imago
state_ 291-347
XXXIII. External Anatomy of Insects. _Terms
and their Definition_ 348-393
XXXIV. The same Subject continued. _The Head
and its Parts_ 394-528
XXXV. The same Subject continued. _The
Trunk and its Parts and Organs_ 529-697
XXXVI. The same Subject continued. _The Abdomen
and its Parts_ 698-720
NOTICE RESPECTING VOL. I. AND II.
It being judged expedient, since the publication of the last Edition
of the first and second Volumes of this Work, to adopt a new plan
with respect to the reference letters of the Plates, the Reader is
requested to make the following corrections in those Volumes.
VOL. I.
Page. Note.
125 ^e, _for_ f, d _read_ a´´.
273 ^a, _for_ a _read_ _a_.
395 ^a, _for_ 29, 30 _read_ 13.
VOL. II.
244 ^c, _for_ a _read_ _a_.
319 ^b, _for_ 10 _read_ 14.
348 ^a, _for a read e´´´._
353 ^a, _for_ 7--. _read_ 16--.
366 ^b, _for a read s´´, v´´´._
^c, _for b read t´´._
405 ^a, _for_ 1.8. aa _read_ 18. _c_†.
^b, _for_ bb _read_ _q´´´_.
406 ^e, _for_ bb _read_ _C´´_.
407 ^e, _for_ cc _read_ _C´´ C´´_, which represent the bundles of
muscles in connexion with the drums. In the above
figure the mirror is the part directly under those
bundles.
AN
INTRODUCTION
TO
ENTOMOLOGY.
LETTER XXVIII.
_DEFINITION OF THE TERM_ INSECT.
What is an insect? This may seem a strange question after such
copious details as have been given in my former Letters of their
history and economy, in which it appears to have been taken for
granted that you can _answer_ this question. Yet in the scientific
road which you are now about to enter, to be able to define these
creatures technically is an important first step which calls for
attention. You know already that a butterfly is an insect--that
a fly, a beetle, a grasshopper, a bug, a bee, a louse, and flea,
are insects--that a spider also and centipede go under that name;
and this knowledge, which every child likewise possesses, was
sufficient for comprehending the subjects upon which I have hitherto
written. But now that we are about to take a nearer view of them--to
investigate their anatomical and physiological characters more
closely--these vague and popular ideas are insufficient. In common
language, not only the tribes above mentioned, but most _small_
animals--as worms, slugs, leeches, and many similar creatures, are
known by the name of _insects_. Such latitude, however, cannot be
admitted in a scientific view of the subject, in which the class
of insects is distinguished from these animals just as strictly as
beasts from birds, and birds from reptiles and amphibia, and these
again from fishes. Not, indeed, that the just limits of the class
have always been clearly understood and marked out. Even when our
correspondence first commenced, animals were regarded as belonging
to it, which since their internal organization has been more fully
explained, are properly separated from it. But it is now agreed on
all hands, that an earthworm, a leech, or a slug, is not an insect;
and a Naturalist seems almost as much inclined to smile at those who
confound them, as Captain Cook at the islanders who confessed their
entire ignorance of the nature of cows and horses, but gave him to
understand that they knew his sheep and goats to be birds.
You will better comprehend the subsequent definition of the
term _Insect_, after attending to a slight sketch of the chief
classifications of the animal kingdom, more especially of the
creatures in question, that have been proposed. That of Aristotle
stands first. He divides animals into two grand sections,
corresponding with the _Vertebrata_ and _Invertebrata_ of modern
Zoologists: those, namely, that have blood, and those that have it
not[1]:--by this it appears that he only regarded _red_ blood as
real blood; and probably did not suspect that there was a true
circulation in his _Mollusca_ and other white-blooded animals. His
_Enaima_, or animals that have blood, he divides into _Quadrupeds_,
_Birds_, _Fishes_, _Cetacea_, and _Apods_ or reptiles; though
he includes the latter, where they have four legs, amongst the
quadrupeds[2]; and his _Anaima_, or animals without blood, into
_Malachia_, _Malacostraca_, _Ostracoderma_, and _Entoma_. The
first of these, the _Malachia_, he defines as animals that are
externally fleshy and internally solid, like the _Enaima_; and
he gives the _Sepia_ as the type of this class, which answers to
the _Cephalopoda_ of the moderns. The next, the _Malacostraca_,
synonymous with the _Crustacea_ of Cuvier and Lamarck, are those,
he says, which have their solid part without and the fleshy within,
and whose shell will not break, but splits, upon collision[3]. The
_Ostracoderma_, corresponding with the _Testacea_ of Linné, he also
defines as having their fleshy substance within, and the solid
without; but whose shell, as to its fracture, reverses the character
of the _Malacostraca_. He defines his last class _Entoma_, in Latin
_Insecta_, with which we are principally concerned, as animals whose
body is distinguished by _incisures_, either on its upper or under
side, or on both, and has no solid or fleshy substance separate, but
something intermediate, their body being equally hard both within and
without[4]. This definition would include the _Annelida_ and most
other _Vermes_ of Linné, except the _Testacea_, which accordingly
were considered as insects by those Zoologists that intervened
between Aristotle and the latter author. The Stagyrite, however, in
another place, has expressly excluded all _apods_[5]. From other
passages in his works, it appears that he regarded the _Vermes_, &c.
either as _larvæ_, or as produced spontaneously and not _ex ovo_[6].
This definition of an insect, though partly founded on misconception,
as well as his primary division of animals in general, is by no means
contemptible. If you look at a bee or a fly, you will observe at first
sight that its body is _insected_, being divided as it were into three
principal pieces--head, trunk, and abdomen[7]; and if you examine
it more narrowly, you will find that the two last of these parts,
especially the abdomen, are further subdivided. And this character
of _insection_, or division into segments, more or less present in
almost every insect[8], is not to be found (with the exception of the
_Crustacea_, which Aristotle distinguishes by the nature of their
integument and its contents) in any of the other classes into which he
divided animals without blood. It was on account of this most obvious
of their characters, that these little creatures were in Greek named
_Entoma_, and in Latin _Insecta_; and from the former word, as you
know, our favourite science takes the name of _Entomology_.
Pliny adhering to the definition of Aristotle, as far as it relates
to the _insection_ of the animals we are speaking of, expressly
includes _Apods_, as well as _Aptera_, amongst them[9]; and in
this was followed, without any attempt at improvement, by all the
entomological writers that intervened between him and the great
Aristotle of the moderns, Linné.
This illustrious naturalist, aware of the incorrectness of the
primary divisions of the animal kingdom founded upon the presence or
absence of blood, establishes his system upon the structure of the
heart, and upon the temperature and colour of the circulating fluid.
He divided animals into two great _sections_ or _sub-kingdoms_, each
comprising two _classes_. His _first_ section included those having
a heart with _two_ ventricles, _two_ auricles, and _warm_ and red
blood, viz. the _Mammalia_ or beasts, and the _Aves_ or birds. His
_second_, those having a heart with _one_ ventricle, _one_ auricle,
and _cold_ and red blood, namely, the classes _Amphibia_, which
included reptiles, serpents, &c. and _Pisces_ or fish. His _third_,
those having a heart with _one_ ventricle and _no_ auricle, and _cold
white_ sanies in the place of blood, namely, his classes _Insecta_ et
_Vermes_, including the _Invertebrate_ animals of Lamarck. Thus the
first of Aristotle's great divisions he increased by the addition of
a new and very distinct class, the _Amphibia_, by which some ground
was gained in the science; but as much was lost by his compressing
the four classes of which the last consisted into two, by which
the natural classes of _Cephalopoda_ and _Crustacea_ merged under
_Insecta_ and _Vermes_. Linné was not aware of the extraordinary
fact, that the _Cephalopoda_ have three hearts; and that though the
_Crustacea_ and _Arachnida_ have a circulation, _Insects_ have none,
or he would never have taken this retrograde step.
Indeed Linné's definition of an _Insect_ is, in many most material
points, inapplicable, not only to the _Crustacea_, but to many other
animals included under that denomination. This will appear evident
from a very slight examination. Thus it runs: "_Polypod animalcula,
breathing by lateral spiracles, armed every where with an osseous
skin, whose head is furnished with movable sensitive antennæ_[10]."
Now of this definition only the first member can be applied to the
whole class which it is meant to designate; for the entire genus
_Cancer_ L., which, with some others, forms the class _Crustacea_ of
the moderns, does not respire by _spiracles_ at all, but by _gills_;
and the same in some degree may be said of spiders, scorpions, &c.
With the last member of the definition Linné himself must have been
aware that a large number of what he conceived to be insects were at
variance, as mites, spiders, and many other of his apterous tribes:
though from some very recent observations of M. Latreille[11],
there seems some ground for thinking, that in these the antennæ
are represented by the mandibles, palpi, &c.[12], and to the soft
flexible, coriaceous or membranous skin of a vast number of insects,
the term _cutis ossea_ is by no means applicable.
Evident as these incongruities are, when the Herculean task which
Linné imposed upon himself, and the vastness and variety of his
labours, are considered, they become very venial. Indeed, unless he
had divided his class _Insecta_ into two or more, it was impossible
to define it intelligibly to ordinary readers, otherwise than nearly
in the terms which he actually employed; and these characters,
restricted and amended by qualifying clauses, are still those to
which recurrence must be had in a popular definition of the class,
when separated as it ought to be from the _Crustacea_ and _Arachnida_.
Pennant, Brisson, and other zoologists, who, attending to _nature_
rather than _system_, saw the impropriety of uniting a crab or a
lobster in the same class with a bee or a beetle, long since assigned
the _Crustacea_ their ancient distinct rank. "But these changes,"
as Latreille observes[13], "being only founded upon _external_
characters, might be deemed arbitrary; and to fix our opinion, it was
necessary to have recourse to a decisive authority--the _internal_
and comparative organization of these animals." It results from the
observations of the most profound comparative anatomist of our age,
M. Cuvier, that the _Crustacea_ and _Arachnida_ differ from insects
properly so called, and particularly from those that are furnished
with wings, in having a complete system of circulation, a different
mode of respiration, and that they have a more perfect organization.
Influenced by these motives, both Cuvier and Lamarck have considered
them as forming two classes separate from insects. Treviranus, led by
considerations founded on the organs of circulation, of respiration,
and of generation, is of opinion that spiders and scorpions ought
to form one class with the _Crustacea_: he observes, however, that
the nervous system of all three is very dissimilar; and that in an
arrangement founded on this circumstance, the organs of motion, and
the external shape, even spiders and scorpions must be placed in
different classes[14].
It is to be observed with regard to the _Arachnida_ of the French
school, that the class as laid down by them includes several
animals that have no circulation, and breathe by _tracheæ_, of
which description are the mites (_Acarus_ L.), and the harvest-men
(_Phalangium_ L.) &c.; and therefore it has been divided into two
orders, _Pulmonaria_ and _Tracheana_; but if the definition from
the internal organization be adhered to, the latter should either
remain with the class _Insecta_, or form a new one by themselves. Yet
the animals that compose the _Trachean_ order of _Arachnida_, their
external form considered, are certainly much more nearly related to
the spiders and scorpions than to any members of the class _Insecta_
at present known. This circumstance, perhaps, may seem to throw some
doubt upon the modern system of classification.
I must further observe, that the assertion of Treviranus, which appears
to intimate that the respiration of the _pulmonary Arachnida_ is the
same with that of the _Crustacea_, is not quite correct, since in
the latter the _branchiæ_ or gills are _external_, and in the former
_internal_, the air entering by spiracles before it acts upon them[15].
It may not be amiss in this place to lay before you the principal
points in which the _Crustacea_ and _Arachnida_ agree with _Insecta_,
and also those in which they differ.
The _Crustacea_ agree with _Insecta_ in having a body divided into
segments, furnished with jointed legs, compound eyes, and antennæ.
Their nervous system also is not materially different, and they
are both oviparous. They differ from them in having the greater
insections of the body less strongly marked; in the greater number
of legs on the trunk, the anterior ones performing the office of
maxillæ: in their eyes usually on a moveable footstalk: their
palpigerous mandibles; and their four antennæ at least in the great
majority. But the principal difference consists in the internal
organization and the fountains of vitality; for the _Crustacea_ have
a double circulation, the fountain of which is a heart in the middle
of their thorax[16]. They have too a kind of gizzard and liver,
at least the _Decapods_[17], and their respiration is by gills.
Genuine insects terminate their existence after they have laid their
eggs[18]; but the _Crustacea_ live longer, and lay more than once.
The _Arachnida_ will be found to differ from insects more widely than
even the _Crustacea_. They agree in their jointed legs and palpi;
immoveable eyes; and in being covered with a coriaceous or corneous
integument: but they differ in having a system of circulation;
gills instead of tracheæ; their organs of generation double; and
the females lay more than once in their lives. Their head also is
not distinct from the trunk as in insects; they have no compound
eyes; and their antennæ, if we admit the opinion on this head of MM.
Latreille and Treviranus, that they have representatives of these
organs, differ totally in structure, situation, and use, from those
of the great body of insects. In the _Araneidæ_ or Spiders, their
body seems to have no segments or incisure but that which separates
the abdomen from the trunk; and in the _Scorpionidæ_ they are
observable only in the abdomen. Other particulars might be enumerated
in which these two classes differ from insects; but these will be
sufficient to convince you that Aristotle and MM. Cuvier and Lamarck
were justified in separating them.
The two last-mentioned authors made further improvements in Zoology.
The latter, from the consideration of the general structure of animals,
perceiving that Aristotle's _Enaima_ were distinguished from his
_Anaima_, by being built as it were upon a vertebral column, very
judiciously changed the denomination, which was indeed improper, of
"_The Philosopher's_" two sub-kingdoms, into that of _Vertebrata_
or animals that have a vertebral column, and _Invertebrata_ or those
that have no vertebral column. These he distributes into three primary
divisions according to their supposed degrees of _intelligence_--Thus:
* _Apathetic Animals._ 1. INFUSORIA.
2. POLYPI.
3. RADIATA.
4. VERMES.
** _Sensitive Animals._ (_Epizoaria._)
5. INSECTA.
6. ARACHNIDA.
7. CRUSTACEA.
8. ANNELIDA.
9. CIRRHIPEDA.
10. MOLLUSCA.
*** _Intelligent Animals._ 11. PISCES.
12. REPTILIA.
13. AVES.
14. MAMMALIA.[19]
Profiting by the light afforded by the Aristotelian system, this
eminent zoologist improved, we see, upon that of Linné, by resolving
his _Insecta_ into three classes, and his _Vermes_ into seven,
interposing the Linnean _Insecta_ between the four first and three
last, in which he was not so happy, since as to _sense_ insects should
certainly occupy the place he has here assigned to the _Mollusca_.
In the work from which I have taken this statement of Lamarck's
system, that acute writer has given a sketch of another method of
arrangement, in which he has made the first deviation from the beaten
track of an unbroken and unbranching series. In the Supplement to
the first volume, he has distributed the _Invertebrata_ in a double
subramose series--one consisting of _articulate_, and the other of
_inarticulate_ animals[20].
Upon Lamarck's system, most of the modern ones, with some variation,
are founded. There is one, however, by a learned countryman of ours,
that is more unique, _sui generis_, and I may add profound, than any
that has yet appeared. I am speaking of that, you will perceive, of
which our friend Mr. Wm. MacLeay has given a detailed statement in
his _Horæ Entomologicæ_. In this he goes even far beyond what Lamarck
has attempted in the above sketch, and substantiates his claim to be
considered as one of those original thinkers, _rari nantes in gurgite
vasto_, that do not appear every day. The following are the principal
bases of his system.
1. That all natural groups, whether kingdoms or any subdivision of
them, return into themselves; a distribution which he expresses by
circles.
2. That each of these circles is formed precisely of _five_ groups,
each of which is resolvable into five other smaller groups, and so on
till you reach the extreme term of such division.
3. That proximate circles or larger groups are connected by the
intervention of lesser groups, which he denominates _osculant_.
4. That there are relations of analogy between the corresponding
points of contiguous circles.
This system he has represented by tables of circles inscribed with
the five primary divisions of each group. His first table exhibits a
general view of organized matter as distributed in the animal and
vegetable kingdoms--Thus:
[Illustration]
Our learned author here divides the animal kingdom into what may be
denominated five sub-kingdoms or provinces, in three of which (with
the exception of the _Crustacea_ and _Arachnida_ belonging to his
_Annulosa_) no circulation of blood is visible, but which obtains in
the rest. These he names--
1. ACRITA, consisting of the _Infusory Animals_, the _Polypi_, the
_Corallines_, the _Tæniæ_, and the least organized of the _Intestinal
Worms_.
2. RADIATA, including the _Jelly-fish_, _Star-fish_, _Echini_, and
some others.
3. ANNULOSA, consisting of _Insecta_, _Arachnida_, and _Crustacea_.
4. VERTEBRATA, consisting of _Beasts_, _Birds_, _Reptiles_,
_Amphibia_, and _Fishes_.
5. MOLLUSCA, including the numerous tribes of _shell-fish_,
_land-shells_, _slugs_, &c., which, from their mucous or gelatinous
substance, from their nervous system and the imperfection of their
senses, return again to the _Acrita_, though connected with the
_Vertebrata_ by having a heart and circulation.
His next set of circles shows the sub-division of these five
sub-kingdoms into classes--Thus:
[Illustration]
In this scheme the _osculant_ classes are those placed between the
circles. In the _Mollusca_ circle two classes are still wanting
to complete the quinary arrangement of that sub-kingdom. I am not
sufficiently conversant with the details of the animal kingdom
at large to hazard any decided opinion upon Mr. MacLeay's whole
system, or to ascertain whether all these classes are sufficiently
distinct[21]. My sentiments with regard to those of the _Annulosa_ I
shall state to you hereafter.
Upon a future occasion I shall consider more at large the station
to which insects seem entitled in a system of invertebrate animals,
which will not accord exactly with that assigned by MM. Cuvier and
Lamarck. But I am now in a field in which I have no intention to
expatiate further, than as it is connected with the subject of the
present letter. I shall therefore confine myself in what I have
more to say to the definitions of _Insecta_ that have been given by
modern authors, beginning with that of the zoologist last mentioned.
Insects form a part of his _second_ group, which he terms _sensitive_
animals (_animaux sensibles_), which group he thus defines: "_They
are sentient, but obtain from their sensations only perceptions of
objects--a kind of simple ideas which they cannot combine to obtain
complex ones._ Charact. _No vertebral column; a brain, and most
commonly an elongated medullary mass; some distinct senses; the
organs of movement attached under the skin: form symmetrical, by
parts, in pairs_[22]." This division of animals, from the kind and
degree of sense and intelligence that they possess, seems rather
fanciful than founded in nature, since many insects show a greater
portion of them than many vertebrate animals. Compare in this
respect a _bee_ with a _tortoise_[23]. Lamarck divides his group
of _animaux sensibles_ into two sections, namely, _Articulated_
animals, exhibiting segments or articulations in all or some of their
parts; and _Inarticulatcd_ animals, exhibiting neither segments
nor articulations in any of their parts. _Insecta_, _Arachnida_,
and _Crustacea_, belong to the first of these sections, which he
defines as "_those whose body is divided into segments, and which are
furnished with jointed legs bent at the articulations_[24]." INSECTA
he defines--"_Articulate animals, undergoing various metamorphoses,
or acquiring new kinds of parts--having, in their perfect state,
six feet, two antennæ, two compound eyes, and a corneous skin. The
majority acquiring wings. Respiration by spiracles_ (stigmates), _and
two vascular opposite chords, divided by plexus, and constituting
aeriferous tracheæ, which extend every where. A small brain at the
anterior extremity of a longitudinal knotty marrow, with nerves. No
system of circulation, no conglomerate glands. Generation oviparous:
two distinct sexes. A single sexual union in the whole course of
life_[25]." ARACHNIDA he defines--"_Oviparous animals, having at
all times jointed legs, undergoing no metamorphosis, and never
acquiring new kinds of parts. Respiration tracheal or branchial: the
openings for the entrance of the air spiraculiform (stigmatiformes).
A heart and circulation beginning in many. The majority couple
often in the course of life_[26]." I shall next add his definition
of CRUSTACEA: "_Oviparous, articulated, apterous animals, with a
crustaceous integument more or less solid, having jointed legs; eyes
either pedunculate or sessile, and most commonly four antennæ, with a
maxilliferous mouth seldom rostriform; maxillæ in many pairs placed
one over the other; scarcely any under-lip; no spiraculiform openings
for respiration; five or seven pair of legs; a longitudinal knotty
marrow terminated anteriorly by a small brain. A heart and vessels
for circulation. Respiration branchial with external branchiæ,
sometimes hid under the sides of the shell of the thorax, or shut
in prominent parts; sometimes uncovered, and in general adhering to
particular legs or to the tail. Each sex usually double_[27]."
I have given Lamarck's definitions of these three classes, all
considered as _Insecta_ by Linné, that by comparing them together
you may be better enabled to appreciate the system of this author.
On looking over the characters of the _Arachnida_ as here given,
you will see at once that it consists of heterogeneous animals--for
in fact he includes in this class not only the _Trachean Arachnida_
of Latreille, but the _Ametabolia_ of Dr. Leach, or the _Hexapod_
Aptera, and the _Myriapoda_.
I shall next copy for you Latreille's latest definition of _Insecta_
and _Arachnida_.
"INSECTA: _A single dorsal vessel representing the heart: two
trunks of tracheæ running the whole length of the body, and opening
externally by numerous spiracles; two antennæ; very often upper
appendages for flight, indicating the metamorphosis to which the
animal is subject when young; legs most commonly reduced to
six._ ARACHNIDA: _Distinguished from_ Crustacea _by having their
respiratory organs always internal, opening on the sides of the
abdomen or thorax to receive the respirable fluid. Sometimes these
organs perform the office of lungs, and then the circulation takes
place by means of a dorsal vessel, which sends forth arterial, and
receives venose branches. Sometimes they are tracheæ or air-vessels,
which, as in the class_ Insecta, _replace those of circulation. These
have only the vestige of a heart, or a dorsal vessel alternately
contracting and sending forth no branch. The absence of antennæ,
the reunion of the head with the thorax, a simple trachea but
ramified and almost radiating, serve to distinguish these last_
Arachnida, _or the most imperfect of insects, which respire only by
tracheæ_[28]." Under this head he observes--"Of all these characters,
the most easy to seize and the most certain would doubtless be,
if there were no mistake in it, that of the absence of antennæ;
but later and comparative researches, confirmed by analogy, have
convinced me, that these organs, under particular modifications it
is true, and which have misled the attention of naturalists, do
exist[29]:" and he supposes, from the situation and direction of
the _mandibles_ of the _Arachnida_, corresponding with that of the
_intermediate_ pair of _antennæ_ in _Crustacea_, that they really
represent the latter organs. If this supposition be admitted, their
use is wholly changed; the palpi, in fact, executing the functions of
antennæ, which probably induced Treviranus to call them _Fühlhörner_
(_Feelinghorns_). Perhaps these last may be regarded as in some sort
representing the _external_ antennæ of the _Crustacea_? With regard
to _Insecta_, their antennæ seem to disappear in the _Pupiparæ_
Latr., or the genus _Hippobosca_ L.
The above definitions of the _Arachnida_ by these two celebrated
authors, appear to me the reverse of satisfactory. When we are told
of animals included in it, that some breathe by gills and others by
tracheæ, that some have a heart and circulation and others not, we
are immediately struck by the incongruity, and are led to suspect
that animals differing so widely in the fountains of life ought
not to be associated in the same class. A learned zoologist of our
own country, Dr. Leach, seems to have made a nearer approach to a
classification in accordance with the internal organization, by
excluding from _Arachnida_ the _Acari_ and _Myriapoda_.
Sub-kingdom ANNULATA Cuv.
* Gills for respiration. _Classes._
_Legs sixteen:_ Antennæ two or four 1 CRUSTACEA.
** Sacs for respiration.
_Legs twelve:_ Antennæ none 3 ARACHNÖIDEA.
*** Tracheæ for respiration.
a. No Antennæ.
4 ACARI.
b. Two Antennæ.
_Six thoracic legs:_ Abdomen also bearing legs 2 MYRIAPODA.
_Six thoracic legs:_ No abdominal legs 5 INSECTA[30].
Mr. MacLeay, on whose system I shall now say a few words, divides
his sub-kingdom _Annulosa_ into five classes, namely, _Crustacea_,
_Ametabola_, _Mandibulata_, _Haustellata_, _Arachnida_. From
the _Crustacea_ he goes by the genus _Porcellio_ Latr. to
_Iulus_[31], which begins his _Ametabola_: these he connects with
the _Mandibulata_, by _Nirmus_, which he thinks approaches some of
the corticarious _Coleoptera_[32]. This class he appears to leave
by the _Trichoptera_ Kirby, and so enters his _Haustellata_ by the
_Lepidoptera_[33], and leaves it again by the _Diptera_ by means of
the _Pupiparæ_ Latr., especially _Nycteribia_, connecting this class
with the _Arachnida_, which he enters by the Hexapod _Acari_ L.[34],
and these last he appears to leave by the _Araneidæ_, and to enter
the _Crustacea_ by the Decapods[35]: thus making good his circle
of classes, or a series of Annulose animals returning into itself.
Mr. MacLeay's whole system upon paper appears very harmonious and
consistent, and bears a most seducing aspect of verisimilitude; but
it has not yet been so thoroughly weighed, discussed, and sifted, as
to justify our adopting it _in toto_ at present: should it, however,
upon an impartial and thorough investigation, come forth from the
furnace as gold, and be found to correspond with the actual state
of things in nature, my objections, which rest only upon some parts
of his arrangement of _Annulosa_, would soon vanish. Some of those
objections I will state here, and some will come in better when I
treat of the Systems of Entomology. My first objection is, that his
_Ametabola_, _Mandibulata_, and _Haustellata_, approach much nearer
to each other than they do to the other two classes of his circle,
or than even these last to each other; so that under this view it
should primarily consist of _three_ greater groups, resolvable, it
may be, into five smaller ones. My next objection is, that he has
also considered the _Trachean_ and _Pulmonary_ Arachnida as forming
_one_ class. Whether an animal breathes by gills or tracheæ, or has
a circulation or not, is surely as strong a reason for considering
those so distinguished as belonging to different classes, as the
taking of their food by suction or by manducation is, for separating
others to the full as much or more nearly related as to their
external structure. But of this more hereafter. I cannot help, as a
last objection, lamenting that our learned author has rejected from
his system a term consecrated from the most remote antiquity, and
which, even admitting his arrangement, might have been substituted
for _Annulosa_, a name borrowed by Scaliger from Albertus Magnus,
neither of whom, in Entomology, is an authority to weigh against
Aristotle, from whom we derive the term _Insecta_, in Greek Εντομα.
As Fabricius did not alter Linné's _class_ Insecta, but merely broke
up his _orders_ into new ones, which he named classes, I shall give
you a detail of the alterations he introduced into the science in a
future letter.
Having stated what my predecessors have done in classification, I
shall next proceed to lay before you my own sentiments as to--_What
is an insect._ Since our correspondence commenced, the _Arachnida_,
principally on account of their internal organization, have been
excluded from bearing that name, carrying with them, as we have seen,
several tribes, which as yet have not been discovered to differ
materially in that respect from the present _Insecta_: for the sake,
therefore, of convenience and consistency, that I may, as far as the
case will admit, adhere to the Horatian maxim
---- Servetur ad imum
Qualis ab incepto processerit et sibi constet,
I shall regard as _Insects_ all those _Annulosa_ that respire by
tracheæ[36] and have no circulation, considering the _Trachean
Arachnida_ and the _Myriapoda_ for the present as sub-classes,
the one bordering upon the _Arachnida_, and the other upon the
_Crustacea_. Some of these I am ready to own seem separated by an
interval sufficiently wide from the _Hexapods_, which may be regarded
as more peculiarly entitled to the denomination of _Insects_. The
most striking differences will be found in the coalition of the head
with the trunk in some (_Phalangidæ_), and the disappearance of the
annulose form of the body in others (_Acarus_ L.), so that the legs
only are jointed[37]. Yet an approach to such structure may be traced
in some Hexapods; for instance, the coalition of the head and trunk in
_Melophagus_, Latr., and that of the trunk and abdomen in _Sminthurus_,
Latr.[38] The _Myriapoda_ exhibit other remarkable differences; though
their head and trunk are distinct, the former antenniferous, and their
body annulose, the abdomen as well as the trunk is furnished with
legs, sometimes amounting to hundreds; but even to this a tendency
has been observed in some Hexapods[39]. If you examine a specimen
of _Machilis polypoda_, an insect related to the common sugar-louse
(_Lepisma saccharina_), you will find that the abdomen is furnished
with a double series of elastic appendages, which, being instruments
of motion, may be regarded as representing legs. It is worthy of
notice, that the _Myriapoda_ when first disclosed from the egg have
never more than _six_ legs[40], and keep acquiring additional pairs
of them and additional segments to their abdomen as they change their
skins: and it is equally remarkable, that many Hexapods are subject to
a law in some degree the very reverse of this, having many abdominal
legs in their first state, and losing them all in their last. The
union of the head with the trunk in the _Trachean Arachnida_ has
been regarded as almost an unanswerable argument, in spite of their
different internal organization, for including them in the same class
with the _Pulmonary Arachnida_; but the case of _Galeodes_, which,
though furnished with gills, (as an eminent Russian Entomologist Dr. G.
Fischer is reported to have discovered,) implying also a circulation,
and evidently belonging to the last-mentioned class, has nevertheless
a distinct thorax consisting of more than one piece, to which are
affixed only six legs[41], proves that even this circumstance possesses
no weight when set against the organization. If it was a difference in
this respect, that proved the _Crustacea_ classically distinct from
_Insecta_--that likewise was the principal reason for the separation
also of the _Arachnida_--it seems to follow that it ought also to
furnish an argument equally cogent for considering the _Trachean
Arachnida_, as well as the _Myriapoda_, distinct from the _Pulmonary_.
Another difference between the tribes in question is that of their
_metamorphosis_; and this appears to have had great weight with
Lamarck, inducing him to include in his _Arachnida_, not only the
_Tracheans_ and _Myriapods_, but even the apterous _Hexapods_, except
_Pulex_, or the _Anoplura_ and _Thysanura_ of modern authors. But the
metamorphosis alone, unless supported by the internal organization,
will I think scarcely be deemed a sufficient reason for separating
from each other tribes agreeing in that respect, and placing them
with others with which they disagree. The metamorphosis in some
of the Hexapods (_Lepidoptera_) consists in the loss of legs, the
acquisition of wings, a great change in the oral organs and in the
general form; in others (some _Coleoptera_), in the acquisition only
of wings and a change of shape, the oral organs remaining much the
same; in others again (_Curculio_ L.), in the acquisition of six legs
and wings and a change of form; in the flea, in the acquisition of
six legs and a change of form only; in the _Orthoptera_, _Hemiptera_,
&c. in the mere acquisition of wings; in the _Libellulidæ_, in
the loss of the mask that covers the mouth and the acquisition of
wings; in the _Diptera_, in the acquisition of six legs, wings, a
change of the oral organs and of the form; in some of the _Octopods_
(_Acarus_ L.), in the acquisition of a pair of legs; and in others
(_Phalangium_ and _Aranea_ L.), solely in a modification of them as
to their proportions; in the _Myriapods_, the alteration that takes
place in this respect is considerable; a large number of pairs of
legs is acquired and many additional abdominal segments, and the
proportion which the abdomen bears to the whole insect is quite
altered. In all these cases there is a change more or less, either
partial or general, of the original shape or organs of the animal;
and with regard to their metamorphosis, there is a greater difference
between a young and adult _Iulus_ than between a young and adult
_grasshopper_ or _bug_: so that if the metamorphosis, _per se_, be
assumed as a principal regulator of the class, the grasshopper or bug
have as little claim to belong to it as the _Iulus_.
M. Lamarck lays considerable stress upon another character--That
_Insecta_ engender only once in the course of their lives, and
_Arachnida_ more than once. But this, if examined, will be found to
be confined chiefly to the _Pulmonary Arachnida_, the _Tracheans_
following the law of _Insecta_ in this respect[42].
You may perhaps object that the bringing of the Trachean _Arachnida_
and the _Myriapoda_ into the class _Insecta_ will render the
approximation of them to a natural arrangement more difficult,
since it will be impossible at the same time to connect the
_Myriapods_ with the _Crustacea_, and the _Trachean_ with the
genuine _Arachnida_. I admit the validity of your objection, but
by no arrangement of insects in a simple series can we attain this
object: the difficulty, however, may perhaps be obviated in this way.
The distribution of organized matter, to adopt Mr. Wm. MacLeay's
metaphor[43], begins in a dichotomy, constituting the animal and
vegetable branches of the great tree of nature, and from these two
great branches, by means of infinite ramifications, the whole system
is formed, and, what is remarkable, these branches unite again so
as to represent a series returning into itself, a discovery due to
the patient investigation and acumen of our learned friend just
mentioned. Now, in considering the _Aptera_ order, we find at first
setting out from the Hexapods, a dichotomy, where the _Anoplura_
Leach branch off on the one side, and the _Thysanura_ Latr. on the
other--the former, by means of the _Pediculidæ_, taking their food
by suction, particularly _Phthirus_ Leach, or the Morpion (in which
the segments of the trunk and abdomen become indistinct[44]) approach
the _Octopods_ by the hexapod _Acari_ L.--the latter by _Machilis
polypoda_ tending towards the _Myriapods_. In the Octopod branch a
further dichotomy takes place, from which you proceed on one side to
the _Araneidæ_ in the _Arachnida_, by _Phalangium_, &c.; and in the
other by _Chelifer_, &c. to _Scorpio_. Again, the _Myriapod_ branch
also divides, going by the _Iulidæ_ to one branch of the _Isopod
Crustacea_, and by the _Scolopendridæ_ to another.
But there is another view of this subject before alluded to, which
may be repeated here, and which seems to prove that the types of
form in one natural group or class are reproduced in another; this
appears to result from the following parallel series:
_Neuropterous_ _Aptera._ _Arachnida._ _Crustacea._
_Larvæ._
Psocus Hexapoda Galeodes Larunda.
Myrmeleon _Phalangium_ Aranea {Decapoda
{ brachyura.
Octopoda
Panorpa? _Chelifer_ Scorpio {Decapoda
{ macroura.
{ _Thalassina
{ Scorpio_
{ especially.
Ephemera Myriapoda ***** Isopoda.
No type representing the _Myriapoda_ has yet been discovered in the
_Arachnida_ class; but I have little doubt of its existence. You will
observe that the analogies between the larvæ of the _winged_ orders
and the _Aptera_ were first noticed by Mr. W. MacLeay[45]. It is
probable that these parallel series of representatives of each other
might be increased, as well as the numbers in the respective columns.
What I have said will, I trust, sufficiently justify me for making
at present no more material alterations in the classification I
long since proposed to you[46]; I shall, therefore, now proceed
to define the objects I consider as _Insecta_; but I shall first
observe--that as Latreille considers the _branchiopod Crustacea_
or _Entomostraca_ of Müller as entitled to the denomination of
_Crustaceo-Arachnida_[47]; so his _Trachean Arachnida_ might be
called _Arachnida-Insecta_, and his _Myriapoda_, _Crustaceo-Insecta_.
_Sub-kingdom_--ANNULOSA[48].
_Class_--INSECTA.
_First Definition--From their_ external _Organization_.
BODY--divided into Head--Trunk--Abdomen.
HEAD.--Principal seat of the organs of sensation.
_Organs of sight._ Immoveable eyes, simple or compound, varying
in number.
_Organs of hearing_ uncertain, probably connected with the
antennæ.
_Organ of taste._ Ligula or palate within the mouth, accompanied
by the _organs of manducation_--a pair of mandibles and maxillæ
and an upper and lower lip, or their representatives.
_Organs of touch._ Principally two jointed antennæ or their
representatives, and four jointed feelers--two maxillary and
two labial.
TRUNK. Principal seat of the organs of motion.
_Organs of walking, running, or jumping._ Six or eight jointed
thoracic legs, in pairs.
_Organs of flight._ Four wings or their representatives, mostly
with branching nervures containing air-vessels; found in the
majority of the class.
_Organs_ (_external_) _of respiration._ A double set of lateral
spiracles, some for expiration.
ABDOMEN. Principal seat of the organs of generation.
_Organs of motion._ In the _Myriapods_ many pairs of acquired
legs; in the _Thysanura_ elastic ventral or caudal appendages.
_Organs of respiration._ A double series of lateral spiracles for
inspiration in the majority; in some only a single series, and
in others only a single pair.
_Organs of generation_ those common to the _Vertebrata_, but
retractile within the body, attended usually by various anal
appendages, particularly a forceps in the males, and an
ovipositor in the females.
_Second Definition--From their_ internal _Organization_.
SENSATION.
_Nervous System._ A small brain usually subbilobed, crowning a
knotty double medullary chord; nerves proceeding from the brain
and other ganglions to all parts of the body.
CIRCULATION.
_Heart_ replaced by a simple alternately contracting dorsal vessel
or pseudocardia, without arteries or veins, but filled with a
white cold sanies.
RESPIRATION.
_Lungs_ replaced by tracheæ, which receive the air from the
spiracles, and distribute it by bronchiæ infinitely ramified. #/
DIGESTION.
_Liver and biliary vessels_ in most replaced by from 2 to + 150
floating hepatic filaments opening into the space between the two
skins of the intestinal canal below the pylorus.
GENERATION.
_Internal organs. Males_--Vasa deferentia, and vesiculæ seminales,
and the other ordinary organs. _Females_--Ovary usually
bipartite, with palmate lobes; genital organs single and mostly
anal; one sexual union impregnates the female for her life.
_Development_. In their passage to their adult state, after they
have left the egg, _insects_ undergo several simultaneous changes of
their integument or successive moults, and the majority assume three
distinct forms, with distinct organs, which appear as rudiments in
their second state, and are completely developed in their last.
* * * * *
In defining the _Arachnida_ I shall only mention those particulars in
which they differ from _Insectæ_ in their external anatomy.
_Class_--ARACHNIDA.
BODY.
HEAD and Trunk usually not separated by a suture.
_Eyes_. Two to eight, not lateral.
_Mandibles_ cheliform or unguiculate, representing the interior
pair of the antennæ of the _Crustacea_.
_Palpi_ pediform or cheliform.
_Trunk_. Legs eight or their representatives: tibiæ mostly
consisting of two joints.
ABDOMEN with from two to eight spiracles.
SENSATION.
_Nervous System_. A small bilobed brain crowning a double, knotty,
medullary chord; nerves proceeding from the brain and other
ganglions to all parts of the body.
CIRCULATION.
_Heart_ unilocular, inaurite, with a system of circulation by
arteries and veins; blood a cold white sanies.
RESPIRATION.
_Lungs_ replaced by internal gills receiving the air by spiracles.
DIGESTION.
_Liver_, consisting of conglomerate glands, and enveloping the
intestines[49]; hepatic ducts.
GENERATION.
_Genital organs_ double, ventral; more than one sexual union in the
course of life.
The external characters in this class are the same almost in
every respect as those which distinguish the _Phalangidæ_, the
whole difference consisting almost in the systems of circulation,
respiration, and digestion. Perhaps some future anatomist may
discover in the tribe just mentioned, that there is a nearer
agreement between them and the _Arachnida_ in these systems than is
at present suspected, which would prove them true _Arachnida_. I am
inclined to think that _Phrynus_ and _Gonyleptes_, &c. breathe by
branchial spiracles; but having no opportunity of examining living
specimens, I dare not speak with any confidence on the subject.
* * * * *
Having thus given you a view of the most important diagnostics by
which what we have all along called _Insects_ may scientifically be
distinguished from other invertebrate animals, it may not be without
use, if, under this head, I take a more _popular_ and familiar view
of the subject, and say something upon those distinctions which may
attract the attention of the more common observer.
The notion of diminutive size, particularly as compared with
vertebrate animals, seems more frequently attached to the idea of
an insect than any other; and this notion is generally correct,
for one insect that is bigger than the least of the above animals,
thousands and thousands are vastly smaller: but there exist some
that are considerably larger, whether we take length or bulk into
consideration, and this in almost every order. To prove this
most effectually, and that you may have a synoptical view of the
comparative size of the larger insects of the different orders and
tribes, I now lay before you a table of the dimensions of such of
the largest as I have had an opportunity of measuring, including
particularly those giants that are natives of the British isles.
Explanation of Table:
Column A - Length Inches
B - Breadth Inches
C - Expansion of Wings Longitudinal Inches} See note in table
D - Expansion of Wings Transverse Inches }
_Order and | _Species._ | A | B | C | D |
Family._ | | | | | |
| | | | | |
COLEOPTERA. | | | | | |
| | | | | |
CICINDELIDÆ |_Manticora grandis_ |1-5/8 | 7/10| | |
| | | | | |
ANTHIADÆ |_Anthia sexguttata_ |1-7/8 | 7/10| | |
| | | | | |
CARABIDÆ |_Carabus scabrosus_ |1-3/4 | 8/10| | |
| | | | | |
DYTISCIDÆ |_Dytiscus latissimus_|1-1/2 |1 | | |
| | | | | |
STAPHYLINIDÆ |_Staphylinus olens_ |1-1/2 | 5/10| | |
| Br. | | | | |
| | | | | |
HYDROPHILIDÆ |_Hydrophilus piceus_ |1-3/4 | 7/8 | | |
| Br. | | | | |
| | | | | |
BUPRESTIDÆ |_Buprestis grandis_ |2-1/2 |1 | | |
| | | | | |
|--------- _bicolor_ |2-5/12| 3/4 | | |
| | | | | |
DYNASTIDÆ |_Dynastes Hercules_ |4-1/2 |2-1/2 | | |
| |Horns | | | |
| |Incl. | | | |
| | | | | |
|_Megasoma Actæon_ K. |4-1/4 |2-1/4 | | |
| |Horns | | | |
| |Incl. | | | |
| | | | | |
CETONIADÆ |_Goliathus giganteus_|3-7/10|1-9/10| | |
| | | | | |
LUCANIDÆ |_Lucanus Cervus_ Br. |2 | 7/10| | |
| |Mands.| | | |
| |Incl. | | | |
| | | | | |
TENEBRIONIDÆ |_Tenebrio grandis_? |1-7/10| 7/10| | |
| | | | | |
BRENTIDÆ |_Brentus_ N. S. Mus. |2-1/10| 2/12| | |
| MacLeay | | | | |
| | | | | |
CALANDRIDÆ |_Calandra_ N. S. Mus.|3-5/8 |1 | | |
| MacLeay | | | | |
| | | | | |
BRACHYCERIDÆ |_Brachycerus apterus_|1-5/8 | 7/8 | | |
| | | | | |
|_Brachycerus_ |2 | 9/10| | |
| _Toxicophagus_ | | | | |
| Burch. | | | | |
| | | | | |
PRIONIDÆ |_Prionus grandis_ |6-1/2 |2-3/8 | | |
| | | | | |
|---- _cervicornis_ |5-1/2 |1-5/8 | | |
| |Mands.| | | |
| |Incl. | | | |
| | | | | |
|Do. |4-1/4 | | | |
| |Mands.| | | |
| |Excl. | | | |
| | | | | |
|---- _coriarius_ Br. |1-6/10| 7/10| | |
| | | | | |
LAMIADÆ |_Lamia grandis_ |2-3/4 |1 | | |
| | |nearly| | |
| | | | | |
CHRYSOMELIDÆ |_Chrysomela_ N. S. |1-1/4 | 3/4 | | |
| MacLeay | | | | |
| | | | | |
HISPIDÆ |_Alurnus grossus_ |1-3/10| 6/10| | |
| | | | | |
EROTYLIDÆ |_Erotylus grandis_ |1-6/10| 6/10| | |
| |nearly| | | |
| | | | | |
| | | | | |
DERMAPTERA. | | | | | |
| | | | | |
|_Labidura gigantea_ |1-1/4 | | | |
| Br.? |nearly| | | |
| |Forcs.| | | |
| |Incl. | | | |
| | | | | |
|_Forficula_ N. S. N. |1-4/5 | 2/5 | | |
| Holl. | | Do. | | |
| | | | | |
| | | | | |
ORTHOPTERA. | | | | | |
| | | | | |
BLATTIDÆ |_Blatta gigantea_ |2-5/8 |1-1/2 | | |
| | | | | |
|---- N. S. MacLeay |3-3/10|1-1/2 | | |
| | | | | |
PHASMIDÆ |_Phasma grandis_ |7 | 7/8 | | |
| |about | | | |
| | | | | |
|---- _australensis_ |8-1/2 | 3/4 |7-1/2 |2-3/4 |
| K. | | | | |
| | | | | |
ACHETIDÆ |_Gryllotalpa |1-3/4 | | | |
| vulgaris_ Br. | | | | |
| | | | | |
LOCUSTIDÆ |_Locusta Dux_ |4-3/8 | |8-1/4 |2 |
| | | | | |
CONOCEPHALIDÆ|_Acrida viridissima_ |2-1/10| | | |
| Br. | | | | |
| | | | | |
| | | | | |
HEMIPTERA. | | | | | |
* | | | | | |
| | | | | |
FULGORIDÆ |_Fulgora laternaria_ |3 | |5-6/10|2 |
| |nearly| | | |
| | | | | |
CICADIADÆ |_Cicada_ N. S. N. |2-1/10| |5-1/2 | |
| Holland |Wings | | | |
| |Excl. | | | |
| | | | | |
** |Do. |2-8/10| | | |
| |Wings | | | |
| |Incl. | | | |
| | | | | |
NEPIDÆ |_Belostoma grandis_ |3 | |5-6/10|1-3/10|
| | | | | |
LYGEIDÆ |_Lygæus Pharaonis_ |2 |1 | | |
| | | | | |
| | | | | |
LEPIDOPTERA | | | | | |
* | | | | | |
| | | | | |
PAPILIONIDÆ |_Papilio Remus_ | | |8-3/4 |3-5/8 |
| | | | | |
|---- _Priamus_ |2-1/2 | |7-6/10|3 |
| | | | | |
|---- _Machaon_ Br. |1 | |3-1/2 |1-1/2 |
| | | |nearly|Tail |
| | | | |Excl. |
| | | | | |
NYMPHALIDÆ |_Morpho Teucer_ |1-7/10| |7-1/2 |4-1/2 |
| | | | | |
SPHINGIDÆ |_Sphinx_ N. S. Brazil|2-1/2 | 7/10|6-1/2 | |
** | | | | | |
| | | | | |
SPHINGIDÆ |_Sphinx Atropos_ Br. |2 | 5/8 |4-3/4 |1-1/2 |
*** | | | | | |
| | | | | |
BOMBYCIDÆ |_Attacus Atlas_ |1-3/4 | |8-3/4 |5-1/2 |
| | | | | |
|_Gastropacha |1-1/4 | |3-1/2 |1-1/4 |
| quercifolia_ Br. |nearly| | | |
| | | | | |
NOCTUIDÆ |_Erebus Strix_ |2 1/4 | |10-3/4|3-1/4 |
| | | | | |
| | | | | |
NEUROPTERA. | | | | | |
| | | | | |
AGRIONIDÆ |_Agrion lineare_ |5-1/2 | |5 | |
| | | | | |
ÆSHNIDÆ |_Anax Imperator_ |3-1/3 | | | |
| Leach--Br. | | | | |
| | | | | |
MYRMELEONIDÆ |_Myrmeleon |2 | |5 | |
| libelluloides_ | | | | |
| | | | | |
SEMBLIDÆ |_Corydalis cornuta_ |2-3/4 | |5-1/4 | |
| |Mands.| | | |
| |Incl. | | | |
| | | | | |
|Do. |2 | | | |
| |Mands.| | | |
| |Excl. | | | |
| | | | | |
| | | | | |
HYMENOPTERA. | | | | | |
| | | | | |
SCOLIADÆ |_Scolia cyanipennis_ |2 | | | |
| | | | | |
POMPILIDÆ |_Pompilus ocellatus_ |2-1/8 | |3-1/2 | |
| | | | | |
VESPIDÆ |_Cyclostoma grandis_ |2 | | | |
| N. S. K. China | | | | |
| | | | | |
XYLOCOPIDÆ |_Xylocopa Nigrita_ |1-5/8 | | | |
| | | | | |
| | | | | |
DIPTERA. | | | | | |
| | | | | |
TIPULIDÆ |_Tipula sinuata_ Br. |1-3/8 | |2-1/2 | |
| | | | | |
ASILIDÆ |New Gen. Brazil. |1-3/4 | | | |
| | | | | |
MUSCIDÆ |_Echinomyia grossa_ |3/4 | | | |
| Br. | | | | |
| | | | | |
TABANIDÆ |_Tabanus_ N. S. Mus. |1-1/8 | | | |
| Drury | | | | |
| | | | | |
|---- _bovinus_ Br. |1 | | | |
| |nearly| | | |
| | | | | |
| | | | | |
APTERA. | | | |_Expansion of|
* | | | | Legs_ |
| | | | Inches. |
| | | | |
SCOLOPENDRIDÆ|_Scolopendra_ N. S. |13 |7/8 | |
| Mus. MacLeay | | | |
** | | | | |
| | | | |
IULIDÆ |_Iulus_ N. S. Do. |5-1/2 |8/10 | |
| | | | |
PHALANGIDÆ |_Gonyleptes_ N. S. | 3/8 | | 6 |
| Brazil | | | |
| | | | |
_Class._ | | | | |
| | | | |
ARACHNIDA. | | | | |
| | | | |
SCORPIONIDÆ |_Scorpio_ N. S. |7 | | |
| MacLeay |nearly| | |
| |Chelæ | | |
| |Excl. | | |
| | | | |
ARANEIDÆ |_Mygale_ N. S. Do. |3 |1-1/2 | 11 |
From this table you see that several insects included in it exceed
some of the smallest _Vertebrata_ in bulk. In the _Mammalia_, the
_Sorex Araneus_, called by the common people here the Ranny, is
not more than two inches long excluding the tail; and the _Mus
messorius_, or harvest-mouse, peculiar to the southern counties of
England, is still more diminutive: so that to these little animals,
the larger _Dynastidæ_, _Goliathi_, and _Prioni_, &c., appear giants,
and may compete with the mole in size. Even some of the beetles
of our own country, as the great _Hydrophilus_, the stag-beetle,
&c., are more bulky than the two first-named quadrupeds. Amongst
the birds, many _Picæ_, _Passeres_, &c., yield to several insects
in dimensions, and their wings when expanded do not extend so far
as those of not a few _Lepidoptera_. The great owl-moth of Brazil
(_Erebus Strix_) in this respect is a larger fowl than the quail.
Those beautiful little creatures, the humming-birds (_Trochilus_ L.),
the peculiar ornament and life of tropical gardens, which emulate the
most splendid butterflies in the brilliancy of their plumage, are
smaller than a considerable number of insects in almost every order,
and even than some of those that are natives of Britain. Various
reptiles also are much inferior in size to many of the insects of the
above table. The smallest lizard of this country would be outweighed
by the great British beetles lately mentioned, and the mole-cricket
(_Gryllotalpa vulgaris_); and some of the serpent tribe are smaller
than the larger _Scolopendræ_ and _Iuli_. Amongst the _fishes_ also,
though some are so enormous in bulk, others in this respect yield
the palm to several insects. The _minnow_ and the _stickleback_ that
frequent our own pools and streams are considerably inferior in size
to some of our water beetles.
In looking over the table, and comparing the different species that
compose it with each other, you will perceive that the largest
insects of the two sections of _Hemiptera_, of the _Lepidoptera_
as to their _body_ merely, of the _Hymenoptera_ and _Diptera_, in
general size fall considerably short of those of the other orders;
and that certain individuals of the _Orthoptera_ and _Aptera_ bear
away the palm in this respect from all the rest. In the _Coleoptera_
the giants, with the exception of the _Goliathi_, are chiefly to
be found amongst the timber devourers in the _Lamellicorn_ and
_Capricorn_ tribes. Of orthopterous insects the _Phasmidæ_ present
the most striking examples of _magnitude_; and in the _Neuroptera_,
the _Agrionidæ_ of great _length_.
It is worthy of remark here, that although the tropical species
of a genus usually exceed those of colder climates in size, the
_Gryllotalpa_ of Brazil is very considerably smaller than that of
Europe: whether this is the case with the rest of the cricket tribe I
have not had an opportunity of ascertaining. The _Lepidoptera_, though
often remarkable for the vast expansion of their "sail-broad vans," if
you consider only their bodies, never attain to gigantic bulk. Even
the hawk-moths (_Sphinx_ L.), though usually very robust, make no
approach to the size of the great beetles, or the length of some of
the spectres (_Phasma_) and dragon-flies (_Agrionidæ_). With regard
to the superficial contents of their wings, a considerable difference
obtains in different species where they expand to the same length--for
the _secondary_ wings are sometimes smaller than the _primary_, and
sometimes they equal them in size. In some instances, also, the latter
although long are narrow, and in others they are nearly as wide as
long: regard, therefore, should be had to their expansion both ways.
In the _Hymenoptera_ and _Diptera_, the principal giants are to be
found in the predaceous or blood-sucking tribes, as _Scolia_, the
_Sphecidæ_, _Pompilidæ_, _Vespidæ_, &c., belonging to the former order;
and the _Asilidæ_ and _Tabanidæ_ to the latter. The true and false
humble bees (_Bombus_ and _Xylocopa_) and the fly tribe (_Muscidæ_),
though they sometimes attain to considerable size, scarcely afford
an exception to this observation. Amongst the _Aptera_ none of the
_Hexapods_ strike us by their magnitude, and few of the _Octopods_,
though the legs of some of the _Phalangidæ_ inclose a vast area. That
in the table would with them describe a circle of six inches diameter,
though its body is little more than a quarter of an inch in length.
The _Myriapods_ exceed most insects in the vast elongation of their
body, which with their motion gives them no slight resemblance to the
serpents. In the class _Arachnida_, the bird-spiders (_Mygale_) are
amongst the principal giants, nor do the _Scorpions_ fall far short of
them--both of them when alive often alarming the beholder as much by
their size as by their aspect.
But as I have before observed, generally speaking, one of the most
remarkable characters of the insect world, is the little space
they occupy; for though they touch the vertebrate animals and even
quadrupeds by their giants, yet more commonly in this feature they go
the contrary way, and by their smallest species reach the confines
of those microscopic tribes that are at the bottom of the scale of
animal life. I possess an undescribed beetle, allied to _Silpha
minutissima_ E. B.[50], which, though furnished with elytra, wings,
antennæ, legs, and every other organ usually found in the order it
belongs to, is absolutely not bigger than the full stop that closes
this period. In several other coleopterous genera there are also very
minute species, as in _Cryptophagus_, _Anisotoma_, _Agathidium_,
&c. I know no _orthopterous_ insect that can be called extremely
minute, except that remarkable one found on the Continent in the
nests of ants, the _Blatta Acervorum_ of Panzer[51], but now called,
I believe, _Myrmecophilus_: nor indeed any in the _Hemiptera_,
_Neuroptera_, and _Diptera_, that approach the extreme limits of
visibility: but in the _Lepidoptera_, the pygmy _Tinea occultella_
is almost invisible except in flight, being scarcely thicker than
a horse's hair, and proportionably short; indeed, many others of
those lovely Lilliputians, the subcutaneous _Tineæ_, decorated with
bands of gold and silver, and studded with gems and pearls, that in
larger species would dazzle the beholder's eye, are in size not much
more conspicuous. In the _Hymenoptera_ order, _Ichneumon Punctum_ of
Dr. Shaw, which forms so striking a contrast to his giant _Phasma
dilatatum_, being placed together in the same plate; and another
that I possess, under the trivial name of _Atomos_, would elude the
searching eye of the entomologist unless when moving upon glass.
Linné named the tribe of parasites to which these belong, _Minuti_,
on account of their generally diminutive size. But these little
minims, under the superintendence of Providence, are amongst the
greatest benefactors of the human race, since they keep within due
bounds the various destroyers of our produce.
The number of minute species of insects seems greatly to exceed
that of large ones, at least in Europe, of which it may be asserted
probably with truth, that two-thirds are under a quarter of an inch
in length, and one-third not exceeding much a duodecimal of it. It
might hold good perhaps in _Coleoptera_, _Hymenoptera_, _Diptera_,
and _Aptera_: but in _Orthoptera_, _Hemiptera_, _Neuroptera_, and
especially _Lepidoptera_, a large proportion would be found to exceed
three lines in length. Neither can it be affirmed of extra-European
species, of those at least preserved in cabinets, amongst which it
is rare to find an insect less than the fourth of an inch long.
This, however, must probably be attributed to the inattention of
collectors, who neglect the more minute species.
* * * * *
Though size forms a pretty accurate distinction between insects and
the great bulk of _vertebrate_ animals, it affords less assistance in
separating them from the _invertebrate_ classes, which are of every
size, from the monstrous bulk of some _Cephalopoda_ (cuttle-fish) and
_Mollusca_ (shell-fish, &c.) to the invisible infusory animalcule:
but external characters, abundantly sufficient for this purpose,
may be drawn from the general covering, substance, form, parts, and
organs of the body. As I shall enter into pretty full details upon
this subject when I come to treat of the external anatomy of insects,
I shall here, therefore, only give such a slight and general sketch
of the distinctions just mentioned, as will answer the end I have in
view. I must here repeat what I have before observed, and what it is
necessary that you should always bear in mind, namely, that at the
limits of classes and of every other natural group, the characters
begin to change, those peculiar to the one group beginning gradually
to disappear, and those of the other to show themselves; so that it
is impossible almost to draw up a set of characters so precise as
exactly in every respect to suit all the members of any natural group.
Whichever way we turn our eyes on the objects of creation,
above--below--athwart, _analogies_ meet us in every direction, and it
appears clear, that the Book of Nature is a Book of Symbols, in which
one thing represents another in endless alternation. And not only
does one animal, &c. symbolize another, but even between the parts
and organs of one set of animals there is often an _analogy_ as to
their _situation_ and _use_, when there is little or no _affinity_ as
to their _structure_--or again, the analogy is in their _situation_,
without affinity in either structure or use. Thus certain parts in
one tribe represent other certain parts of another tribe, though
as to their structure there is often a striking disagreement. This
is particularly observable between the vertebrate and invertebrate
animals. I shall therefore, in my remarks on the general and
particular structure of insects, contrast it in its most important
points with that of the first-mentioned tribe.
The first thing that strikes us when we look at an insect is its
outside _covering_, or the case that incloses its muscles and internal
organs. If we examine it attentively, we find that it is not like the
skin of quadrupeds and other _Vertebrata_, covering the whole external
surface of the body; but that in the large majority it consists of
several pieces or joints, in this respect resembling the skeleton
of the animals just named; and that even in those in which the body
appears to have no such segments, as in many of the Mites (_Acarus_
L.), they are to be found in the _limbs_. This last circumstance,
to have externally jointed legs, is the peculiar and most general
distinction by which the _Insecta_ of Linné, including the _Crustacea_,
may always be known from the other invertebrate animals[52].
If we proceed further to examine the _substance_ of this crust or
covering, though varying in hardness, we shall find it in most
cases, if we exclude from our consideration the shells of the
_Mollusca_, &c., better calculated to resist pressure than that of
the majority of animals that have no spine. In all the invertebrate
tribes, indeed, the muscles, there being no internal skeleton, are
attached to this skin or its processes, which of course is firmer
than the internal substance; but in insects it is very often rigid
and horny, and partially difficult to perforate, seldom exhibiting
that softness and flexibility which is found in the cuticle of birds
and most quadrupeds. From this conformation it has been sometimes
said, that insects carry their _bones_ on the _outside_ of their
body, or have an _external_ skeleton. This idea, though not correct
in all respects, is strictly so in this--that it affords a general
point of support to the muscles, and the whole structure is erected
upon it, or rather I should say within it. The difference here
between _Insects_ and the _Vertebrata_ seems very wide; but some of
the latter make an approach towards it. I allude to the Chelonian
Reptiles (_Testudo_ L.), in which the vertebral column becomes
external or merges in the upper shell. The _cyclostomous_ fishes also
are not very wide of insects as to their integument. But on this
subject I shall be more full hereafter.
The _forms_ of insects are so infinitely diversified that they almost
distance our powers of conception: in this respect they seem to
exceed the fishes and other inhabitants of the ocean, so that endless
diversity may be regarded as one of their distinctions. But on all
their variations of form the Creator has set his seal of symmetry; so
that, if we meet with an animal in the lower orders in which the parts
are not symmetrical, we may conclude in general that it is no insect.
But it is by their _parts_ and _organs_ that insects may be most
readily distinguished. In the _vertebrate_ animals, the body is
usually considered as divided into _head_, _trunk_, and _limbs_,
the _abdomen_ forming no part of the skeleton; but in the _insect_
tribes, besides the organs of sense and motion, the body consists of
_three_ principal parts--_Head_, _Trunk_, and _Abdomen_--the _first_,
as was before observed, bearing the principal organs of _sense_ and
_manducation_; the _second_ most commonly those of _motion_; and the
third those of _generation_--the organs of respiration being usually
common to both trunk and abdomen. These three primary parts,--though
in some insects the head is not separated from the trunk by any
suture, as for instance in the _Arachnida_; and in others, head,
trunk, and abdomen form only _one_ piece, as in some mites,--still
exist in all, and in the great majority they are separated by
incisures more or less deeply marked: this is particularly visible in
the _Hymenoptera_ and _Diptera_, which, in this respect, are formed
upon a common model; and in the rest, with the above exceptions, it
may be distinctly traced.
The _head_ of insects is clearly analogous to that of vertebrate
animals, except in one respect, that they do not breathe by it. It
is the seat probably of the same senses as _seeing_, _hearing_,
_smelling_, _tasting_--and more peculiarly perhaps of that of
_touch_. The _eyes_ of insects, though allowed on all hands to be
organs of _sight_, are differently circumstanced in many particulars
from those of the animals last mentioned; they are fixed, have
neither iris nor pupil, are often compound, and are without eyelids
to cover them during sleep or repose; there are usually two compound
ones composed of hexagonal facets, but in some instances there
are four; and from one to three simple in particular orders. The
_antennæ_ of insects in some respects correspond with the _ears_
of the animals we are comparing with them; but whether they convey
the vibrations of sound has not been ascertained: that they receive
pulses of some kind from the atmosphere I shall prove to you
hereafter--so that if insects do not _hear_ with them in one sense,
they may, by communicating information, and by _aëroscopy_, to use
Lehman's term, not directly in his sense[53], supply the place of
ears, which would render them properly analogous to those organs.
That in numbers these remarkable organs are _tactors_ is generally
agreed, but this is not their _universal_ use. That insects _smell_
has been often proved; but the organ of this sense has not been
ascertained. What has improperly been called the _clypeus_, or the
part terminating the face above the upper lip (_labrum_), is in the
situation of the _nose_ of the _Vertebrata_, and therefore so far
analogous to it, and in some cases even in form: I therefore call it
the _nose_. Whether this part represents the nose by being furnished
with what answer the purpose of _nostrils_, residing somewhere at or
above the suture that joins it to the upper lip, I cannot positively
affirm; but from the observations of M. P. Huber, with regard to the
hive-bee, it appears that at least these insects have the organ of
the sense in question somewhere in the vicinity of the mouth, and
above the tongue[54]: analogy, therefore, would lead us to look for
its site somewhere between the apex of the nose and the upper lip;
and in some other cases, which I shall hereafter advert to, there is
further reason for thinking that it actually resides at the apex of
the nose. The organ of _taste_ in insects, though some have advanced
their _palpi_ to that honour, is doubtless in some part within the
mouth analogous in a degree to the tongue and palate of the higher
animals. The organs of manducation, in what may be deemed the most
perfect description of mouth, consist of an _upper lip_ closing the
mouth above, a pair of _mandibles_ moving horizontally that close its
upper sides, and a _lower lip_ with a pair of _maxillæ_ attached to
it, which close the mouth below and on the under sides, both labium
and maxillæ being furnished with jointed moveable organs peculiar
to annulose pedate animals, called palpi. In some tribes these
organs assume a different form, that they may serve for suction;
but though in many cases some receive an increment at the expense
of others, and a variation in form takes place, none, as M. Savigny
has elaborately proved, are totally obliterated or without some
representative[55]. The organs now described, except the upper lip,
are formed after a quite different type from those of _Vertebrata_,
with which they agree only in their oral situation and use.
The second portion of the body is the _Trunk_, which is interposed
between the head and abdomen, and in most insects consists of three
principal segments, subdivided into several pieces, which I shall
afterwards explain to you. I shall only observe, that some slight
analogy may perhaps be traced between these pieces and the vertebræ
and ribs of vertebrate animals, particularly the Chelonian reptiles.
This is most observable in _Gryllus_ L. and _Libellula_ L., in which
the lateral pieces of the trunk are parallel to each other[56]. In
the _Diptera_ and many of the _Aptera_ most of these pieces are not
separated by sutures. Each of the segments into which the trunk is
resolvable bears a pair of jointed _legs_, the first pair pointing
to the _head_, and the two last to the _anus_. These legs in their
composition bear a considerable analogy to those of quadrupeds,
&c., consisting of _hip_, _thigh_, _leg_, and _foot_; but the last
of these, the foot or _Tarsus_, is almost universally monodactyle,
unless we regard the _Calcaria_ that arm the end of the tibia, as
representing fingers or toes, an idea which their use seems to
justify. _Acheta monstrosa_ and _Tridactylus paradoxus_, however[57],
exhibit some appearance of a phalanx of these organs. They differ
from them first in number, the thoracic legs being invariably _six_
in all insects, with the exception of the _Octopods_ or most of the
_Trachean Arachnida_, which have usually _eight_. In the _Myriapods_,
though there are hundreds of _abdominal_ legs, only six are affixed
to the _trunk_. Next they differ with regard to the _situation_ of
their legs; for though the anterior pair or arms are analogous in
that respect, the posterior pair are not, since in _quadrupeds_
these legs are placed _behind_ the abdomen, but in _insects before_
it--in fact, in the former the legs may be considered as placed at
each end of the body, excluding only the head and tail, but in the
latter in the middle. Though they correspond with those of quadrupeds
in being in _pairs_ or opposite to each other, yet their direction
with respect to the body is different, the legs of quadrupeds, &c.
being nearly straight, whereas in insects they are bent or form
an angle, often very obtuse at the principal articulations, which
occasions them to extend far beyond the body, and when long to
inclose a proportionally greater space. The _wings_ are the organs
of motion with which the upper side of the trunk is furnished; and
these, though they are the instruments of flight, are in no other
respect analogous to those of birds, which replace the anterior legs
of quadrupeds, but approach nearer, both in substance and situation,
to the fins of some fishes, and perhaps in some respects even to
the leaves of plants. M. Latreille is of opinion, That the four
wings or their representatives replace the four thoracic legs of the
decapod _Crustacea_[58]. Upon this opinion, which shows great depth
of research and practical acumen, I shall have occasion to express
my sentiments when I come to treat more at large on the anatomy of
the trunk and its members; at any rate they do not replace the two
anterior pair of legs of the hexapod _Aptera_. When merely used as
wings, they commonly consist of a fine transparent double membrane,
strengthened by various longitudinal and transverse nervures, or
bones as some regard them, accompanied by air-vessels, of which more
hereafter, as well as of their kind and characters. I shall only
observe, that insects are known from all other winged animals, by
having _four_ wings, or what represent them, and this even generally
in those that are supposed to have only a pair. Another peculiarity
distinguishes the trunk of insects that you will in vain look for
in the vertebrate animals--these are one or two pair of lateral
_spiracles_ or breathing pores. Though the respiratory sacs, &c. of
birds are almost as widely dispersed as the tracheæ and bronchiæ
of insects[59], yet their respiration is perfectly pulmonary, and
nothing like these pores is to be discovered in them.
The principal peculiarity of the third part of the body, the
_abdomen_, is its situation behind the posterior pair of thoracic
legs, and its rank as forming a distinct portion of what represents
the skeleton. In most insects it is so closely affixed to the
posterior part of the trunk as to appear like a continuation of
it, but in the majority of the _Hymenoptera_ and _Diptera_, and in
the _Araneidan Arachnida_, or spiders, it is separated by a deep
incisure; and in the first-mentioned tribe is mostly suspended to
the trunk by a footstalk, sometimes of wonderful length and tenuity.
In the _Mammalia_ the _male_ genital organs are partly external;
but in insects as well as in many of the vertebrate animals, except
when employed, they are retracted within the body. This part is the
principal seat of the respiratory pores or spiracles, many having
eight in each side, while others have only one.
* * * * *
Such are the principal external characters which distinguish
_Insecta_ and _Arachnida_, or what we have heretofore regarded as
insects, to which here may be added another connected with their
internal organization. The union of the sexes takes place in the
same manner as amongst larger animals; and the females with very
few exceptions, more apparent than real, are oviparous. They are,
however, distinguished by this remarkable peculiarity already alluded
to, that, except in the case of the _Arachnida_, one impregnation
fertilizes all the eggs they are destined to produce. In most cases,
after these are laid, the females die immediately, and the males
after they have performed their office, though they will sometimes
unite themselves to more than one female. One other circumstance may
be named here--that no genuine insect or Arachnidan has yet been
found to inhabit the ocean.
Before I conclude this letter, it is necessary to apprize you, that
every thing which it contains relative to the characters of insects,
has reference to them only in their _last_ or perfect state, not in
those preparatory ones through which you are aware that the majority
of them must pass. The peculiar characteristics of them in these
states--in the _egg_, the _larva_, and the _pupa_, will be the
subjects of my next letters, which will be devoted to a more detailed
view of the metamorphosis of insects than I gave you before when
adverting to this subject[60].
FOOTNOTES:
[1] Εναιμα, Αναιμα. _Hist. Animal._ l. i. c. 6.
[2] _Hist. Animal._ l. i. c. 5, 6: compare 1. v. c. 3 and 33, and _De
Partibus Animal._ l. iv. c. 1 and 11.
[3] Το δε σκληρον αυτων ου σθραυσον αλλα φλασον.
[4] _Hist. Animal._ l. iv. c. 1.
[5] Εντομα πολυποδα μεν γαρεσι παντα. _De Part. Animal._ l. iv. c. 6.
[6] _Hist. Animal._ l. iv. c. 19.
[7] The insection that distinguishes these parts, the abdomen
especially, is most visible in the majority of the _Hymenoptera_ and
_Diptera_ orders; next in some _Coleoptera_, as the _Lamellicorn_
tribes, &c. and the _Lepidoptera_. Latreille is of opinion, that the
two last segments of the thorax in some insects are represented by the
first of the abdomen, and that the upper half segment of this part in
_Coleoptera_ also represents the same. Latr. _De quelques Appendices,
&c._ _Annales Générales des Sciences Physiques._ A Bruxelles, vi.
livrais, xviii. 14. In fact, in the _Lepidoptera_, when the abdomen is
separated from the trunk, this segment usually remains attached to the
latter. In the _Myriapods_, the trunk is to be distinguished from the
abdomen only by its bearing the three first pair of legs.
[8] There is no general rule without exceptions, and no character is
so universal as to be distinctly exhibited by every member of a class
or other natural group. Thus, in the majority of the _mites_ (_Acarus_
L.) the body is marked by no segments, and the only articulation or
incision is in the legs, palpi, &c. But as the exception does not
make void the rule, so neither does the extenuation or absence of
some primary character at its points of junction with others, in some
individuals, annihilate the class or group.
[9] _Hist. Nat._ l. xi. c. 1.
[10] Animalcula polypoda, _spiraculis_ lateralibus respirantia, cute
ossea cataphracta; _antennis_ mobilibus sensoriis instruuntur. _Syst.
Nat._ ed. 12. i. 533.
[11] Quoted by Mr. Wm. MacLeay in his very remarkable and learned work
_Horæ Entomologicæ_, in which he inclines to the same opinion. 383.
[12] Treviranus (_Ueber den innern Bau der Arachniden_, &c. 22.)
always calls the palpi of spiders "_Fülhörner_." In _Scorpio_ he
regards them as palpi (_Palpen_).
[13] _N. Dict. d'Hist. Nat._ xvi. 181.
[14] Treviranus, _ut supra_, 48. For the nervous system of scorpions,
see _t._ i. _f._ 13; and for that of spiders, _t._ v. _f._ 45.
[15] PLATE XXIX. FIG. 2. Treviranus, _t._ i. _f._ 1.
[16] Cuvier _Anat. Comp._ iv. 407.
[17] _N. Dict. d'Hist. Nat._ ix. 190.
[18] The females of _Dorthesia_, however, a genus related to
_Coccus_, are said to survive laying their eggs. _N. Dict. d'Hist.
Nat._ ix. 553.
[19] _Anim. sans Vertebr._ i. 381.
[20] _Anim. sans Vertebr._ i. 457.
[21] The number _five_, which Mr. MacLeay assumes for one basis
of his system as consecrated in _Nature_, seems to me to yield
to the number _seven_, which is consecrated both in _Nature_ and
_Scripture_. Metaphysicians reckon _seven_ principal operations of
the mind; musicians _seven_ principal musical tones; and opticians
_seven_ primary colours. In Scripture the abstract idea of this
number is--_completion_--_fullness_--_perfection_. I have a notion,
but not yet sufficiently matured, that Mr. MacLeay's _quinaries_ are
resolvable into _septenaries_.
[22] _Anim. sans Vertebr._ i. 381.
[23] See on this point MacLeay, _Hor. Entomolog._ 209--.
[24] _Anim. sans Vertebr._ iii. 243.
[25] _Ibid._ iii. 245.
[26] _Anim. sans Vertebr._ iii. 245.
[27] _Ibid._
[28] _Des Rapports généraux, &c. des Anim. invertebr. artic., Ann. du
Mus._
[29] _Ibid._ _Hor. Entomolog._ 383.
[30] Leach in _Entomologist's Useful Compendium_, by Samouelle, 75.
[31] _Hor. Entomolog._ 348.
[32] _Ibid._ 354.
[33] _Ibid._ 373.
[34] _Ibid._ 381.
[35] _Ibid._ 389.
[36] There is some reason for thinking, though the octopod and myriapod
insects breathe by tracheæ, that there is no small difference in the
distribution of these organs. The _Trachean Arachnida_ have only a pair
of spiracles, from which the tracheæ must _radiate_, if I may so apply
the term, in order to convey the necessary supply of air to every part
of the body. _Scutigera_, as far as I can discover, has only a _single_
series of _dorsal_ spiracles (see PLATE XXIX. FIG. 20)--an unusual
situation for them: in these also, to attain the above end, each
trachea must also radiate, so as to supply each part of the segment
it is in. Those of _Iulus_, according to the observations of Savi
(_Osservaz. per servire alla Storia di una Specie de Iulus_, &c. 15--),
consist of bundles of parallel tracheæ. Perhaps these circumstances
would warrant the considering of these _Arachnida_ and the _Myriapoda_
as primary classes? The genus _Galeodes_ is said to breathe by gills
similar to those of the _Araneidæ_, which structure, probably, carries
with it a system of circulation, and exhibits a _third_ type in the
_Arachnida_, with four palpi, six legs, and a distinct thorax. This
genus, then, is the corresponding point in the _Arachnida_ to the
_Hexapod Aptera_, as the _Scorpions_ are to the _Cheliferidæ_ or
Pseudo-Scorpions, and the _Araneidæ_ to the other _Octopods_; and these
analogies furnish a strong proof, that the _Tracheans_ belong rather to
_Insecta_ than _Arachnida_. Comp. _N. Dict. d'Hist. Nat._ xxvi. 445;
and _Description de six Arachnid. nouv._ &c. par Leon Dufour, 16.
[37] Mr. MacLeay observes with regard to the _Tardigrade_, described
by Spallanzani and Dutrochet, that "it proves that an animal may
exist without antennæ or distinct annular segments to the body, but
having two eyes and six articulate legs." (_Hor. Entomolog._ 350--.)
Many _Acari_ prove the same thing. De Geer, vii. _t._ vii. _f._ 14.
[38] De Geer, vii. _t._ iii. _f._ 8.
[39] _Hor. Entomolog._ 351.
[40] De Geer, _Ibid._ 571, 583. _t._ xxxvi. _f._ 20, 21.
[41] Dufour _ubi supra._ _Hor. Entomolog._ 382.
[42] Male _Insecta_ in some instances engender more than once. Mr.
MacLeay sen. has observed this with regard to _Chrysomela Polygoni_,
and I have noticed it in _Bombyx Mori_.
[43] _Hor. Entomolog._ 134. 200.
[44] _Zoolog. Miscell._ iii. _t._ 146. In this figure the segments
are made much more distinct than they are in my specimen.
[45] _Hor. Entomolog._ 422--.
[46] See above, VOL. I. 4th Ed. p. 66. Note^a.
[47] Surely the denomination ought to have been
_Arachnido-Crustacea_, since the learned author considers them as
belonging to the _Crustacea_ class.
[48] It may not be without use to give here a short definition of the
_Annulosa_; I mean excluding the _Vermes_, which Mr. W. MacLeay has
included; and the _Annelida_, which Latreille has made the fifth of
his Annulose classes. _Ann. du Mus._ 1821.
_Annulosa._ Animal invertebrate, oviparous; external integument
of a firmer consistence than the internal substance,
serving as a general point of attachment to the
muscles; _eyes_ immoveable; _legs_ more than four,
jointed.
CLASSES.
1. _Crustacea._ Gills external; more than eight legs.
2. _Arachnida._ Gills internal; spiracles; eight legs.
3. _Insecta._ Tracheæ; spiracles; six to eight thoracic legs.
[49] What L. Dufour regards as the liver in _Scorpio_ (_N. Dict.
d'Hist. Nat._ xxx. 421.) Treviranus looks upon as an Epiploon
(_Fettkörper_) both in _Scorpio_ and _Aranea._ 6. _t._ i. _f._ 6. A
A. _t._ ii. _f._ 24. _dd._ Hepatic ducts: _t._ i. _f._ 6. ii. _t._
ii. _f._ 24. β. β. β. β.
[50] _S. minutissima_ of Marsham is synonymous with _Dermestes
atomarius_ De Geer, _Scaphidium atomarium_ Gyllenh., and _Latridius
fascicularis_ Herbst., but surely arranging with none of these
genera, being sufficiently distinguished from them and every other
insect by its singular capillary wings. In my cabinet it stands under
the name of _Trichopteryx_ K.
[51] Panz. _Fn. Germ. Init._ lxii. 24. Comp. _Hor. Entomolog._
Addenda, &c. 523.
[52] The _Annelida_ have, however, sometimes _jointed_ organs, which
facilitate their progressive motion whether vermicular or undulatory;
but they cannot be deemed legs, since they neither support the body
nor enable it to walk, &c. Latreille _Anim. invertebr._ Artic. 126.
_Ann. du Mus._ 1821.
[53] _De Antennis Insect._ ii. 65.
[54] _Nouv. Obs. sur les Abeilles_, ii. 376--. It appears from
M. Huber's experiment, that it was only when the hair-pencil,
impregnated with the oil of turpentine, was presented "près de la
cavité, _au dessus de l'insertion de la trompe_," that the bee was
sensible of the odour.
[55] _Anim. sans Vertebr._ I. i. Mem. i.
[56] PLATE VIII. FIG. 10-14; IX. FIG. 6-8.
[57] Coquebert _Illust. Ic._ iii. _t._ xxi. _f._ 3.
[58] _Hor. Entomolog._ 413--.
[59] _N. Dict. d'Hist. Nat._ xxviii.; compare 104 and 110.
[60] See above, VOL. I. Ed. 4. p. 63--.
LETTER XXIX.
_STATES OF INSECTS._
EGG STATE.
On a former occasion I gave you a general idea of what has been called,
perhaps not improperly, the _metamorphosis_ of insects[61]; but since
that time much novel and interesting speculation on the subject has
employed the pens of many eminent Physiologists; and besides this, the
doctrine then advanced of successive developments has been altogether
denied by a very able Anatomist, Dr. Herold, who, with a hand, eye, and
pencil, second only to those of Lyonnet, has traced the changes that
gradually take place in the structure of the cabbage-butterfly (_Pieris
Brassicæ_) on passing through its several states of larva, pupa, and
imago. It is necessary, therefore, that previously to considering
separately and in detail the _states_ of insects, I should again call
your attention to this subject, and endeavour to ascertain whether Dr.
Herold's hypothesis rests upon a solid foundation; or whether that
adopted from Swammerdam by all the most eminent Entomologists and
Physiologists since his time can be maintained against it.
I shall first give you a short abstract of the new hypothesis.
According to Dr. Herold--_The successive skins of the caterpillar,
the pupa-case, the future butterfly, and its parts and organs, except
those of sex which he discovered in the newly excluded larva, do
not preexist as germes, but are formed successively from the_ rete
mucosum, _which itself is formed anew upon every change of skin from
what he denominates the_ blood, _or the chyle after it has passed
through the pores of the intestinal canal into the general cavity of
the body, where, being oxygenated by the air-vessels, it performs the
nutritive functions of blood. He attributes these formations to a_
vis formatrix (Bildende Kraft).
_The caul or epiploon_ (Fett-masse), _the_ corps graisseux _of
Reaumur, &c., which he supposes to be formed from the superfluous
blood, he allows, with most physiologists, to be stored up in the
larva, that in the pupa state it may serve for the development of
the imago. But he differs from them in asserting that in this state
it is destined to two distinct purposes--first, for the production
of the muscles of the butterfly, which he affirms are generated from
it in the shape of slender bundles of fibres;--and secondly, for
the development and nutrition of the organs formed in the larva, to
effect which, he says, it is dissolved again into the mass of blood,
and being oxygenated by the air-vessels, becomes fit for nutrition,
whence the epiploon appears to be a kind of concrete chyle_[62].
Need I repeat to you the hypothesis to which this stands
opposed--_That every caterpillar at its first exclusion contains
within itself the germe of the future butterfly and of all its
envelopes, which successively presenting themselves are thrown off,
till it appear in perfection and beauty, with all its parts and
organs, when no further development takes place._
I believe you will agree with me, when you have read and considered
the above abstract of Dr. Herold's hypothesis, that in it he
substitutes a name for knowledge, talks of a _vis formatrix_ because
his assisted eye cannot penetrate to the primordial essence or state
of the germes of being, and denies the existence of what he cannot
discover[63]. From ancient ages philosophers have done the same, to
conceal their own ignorance of causes under a sounding name, when
they have endeavoured to penetrate within the veil of the _sanctum
sanctorum_, which it is not permitted to vain man to enter. This
has occasioned the invention, not only of the term in question, but
of many others, as little meriting the appellation of _Signs of
ideas_; such as _Plastic Nature_, _Epigenesis_, _Panspermia_, _Idea
seminalis_, _Nisus formativus_, &c. But upon this subject you cannot
do better than consult what the learned Dr. Barclay has said in his
admirable work _On Life and Organization_[64], in which he has placed
the inanity, the _vox et præterea nihil_, of such high-sounding
terms in their true light. The processes of nature in the formation
and development of the _fœtus in utero_, of the chick in the egg,
of the butterfly in the caterpillar, we in vain attempt fully to
investigate; yet we can easily comprehend that pre-existent germes,
by the constant accretion of new matter in a proper state, may be
gradually developed, but we find it impossible to conceive how, by
the action of second causes, without the intervention of the first
cause, the butterfly should be formed in the caterpillar, unless it
preexists there as a germe or fœtus. "Is it not clear," asks Dr.
Virey in his lively manner, "as Blumenbach and other Physiologists
maintain, that there is a formative power, a _nisus formativus_,
which organizes the embryo? Admirable discovery!" says he, "which
teaches us that the fœtus forms itself because it forms itself! As
if you should affirm that the stone falls because it falls[65]!"
Had Dr. Herold considered what Bonnet says with as much good sense
as modesty, he would never have imagined that his discovering the
organs of the butterfly one after the other at certain periods in
the caterpillar, was any sound argument against their preexistence
and coexistence as germes. "Organs," says that amiable and excellent
Physiologist, "that have no existence as to us, exist as they respect
the embryo, and perform their essential functions; the term of their
becoming visible is that which has been erroneously mistaken for
the period of their existence[66]." This has been Dr. Herold's grand
error; he mistook the commencement of the _appearance_ of the organs
of the butterfly for that of their _existence_, and yet the early
appearance of the sexual organs ought to have led him to a conclusion
the reverse of that which he has adopted.
Dr. Virey has observed with great truth--that "Every being has a
peculiar and unique nature, which would be impossible if the body was
composed of parts made at several intervals, and without a uniform
power that acts by concert[67]:" and every Physiologist acquainted
with the history of insects that undergo a _complete_ metamorphosis
will allow, that their developments and acquisition of new parts and
organs take place according to a _law_ which regulates the number,
kind, and times of them, differing in different species, and which
has had an invariable operation, since the first creation, upon every
sound individual that has been produced into the world.
In consequence of this law, one species changes its skin only _four_
times, and another _five_ or _six_;--in some cases the first skins
shall be covered or bristled with hairs or spines, and the last
be naked and without arms;--that which forms the case of the pupæ
shall differ in form and substance from the preceding skins, varying
in both respects in different species; and finally the butterfly
shall invariably follow, when no other change but the last mortal
one shall take place. Can this law, so constantly observed, be the
result of a _blind_ power? Or are we to suppose that the Deity
himself is always at work to _create_ the necessary organs in their
time and place? Is it not much more consonant to reason and the
general analogy of nature, to suppose that these parts and organs
exist in embryo in the newly-hatched caterpillar, and grow and
are successively developed by the action of the nutritive fluid?
In the pupa of many _Diptera_ the inclosed animal, even under the
microscope, appears without parts or organs, like a mere pulp;
but Bonnet tells us, that if boiled, all the parts of the pupa
appear[68], which proves the preexistence of these parts even when
not to be discerned, and that nothing but the evaporation of the
fluids in which they swim is wanted to render them visible.
Mr. William MacLeay has with great truth observed: "The true
criterion of animal as well as vegetable perfection is the ability
to continue the species[69];" and in their progress to this state
certain changes take place in the parts and organs of _all_ animals
and vegetables: there is, therefore, an analogy in this respect
between them; and this analogy also furnishes another argument
against Dr. Herold's hypothesis, as we shall presently see. These
changes are of three kinds: In the vegetable kingdom, at least in
the phænogamous classes, there is a succession of developments
terminating in the appearance of the generative organs, inclosed
in the flower; in this kind the integuments, or most of them,
are usually _persistent_. In insects and other annulose and some
vertebrate animals, there is a succession of spoliations, or
simultaneous changes of the whole integument, till the animal appears
in its perfect form with powers of reproduction; in this kind the
integuments are _caducous_.--In man and most of the vertebrate
animals there is a gradual action of the vital forces in different
organs till they are fitted for reproduction; accompanied, as
progress is made to the adult state, by the acquisition of certain
organs, &c. as of teeth, horns, pubes, feathers, &c.[70] Let us
now consider a little in detail the analogies that appear to exist
between the second and the first and third kinds. I shall first
consider the latter as the least obvious. That able, judicious, and
learned physiologist, Dr. Virey, has pointed out no inconsiderable
resemblance between the metamorphosis of the insect, and the changes,
which he denominates a metamorphosis by metastasis, to which most
vertebrate animals are subject. In them, he observes, a state
analogous to the _larva_ state begins at the exclusion of the fœtus
from the womb; it is deprived of teeth, and its viscera are only
accommodated to milk: in the cornute species the horns are in embryo:
the digestive system now preponderates, and the great enjoyment is
_eating_. A second state, in a degree analogous to that of _pupa_,
commences at the period of dentition--the teeth now produce another
modification in the intestinal canal, which becomes capable of
receiving and digesting solid food: during this period the vital
forces are all tending to produce the perfect state of the animal;
and in this state, in man especially, the individual is _educated_
and fitted to discharge the duties of active life. Again, analogous
to the _imago_ state is the age of puberty, in which the complete
development of the sexual powers takes place in both sexes, and the
animal has arrived at its acme, and can continue its kind[71]: now
the digestive powers diminish in their activity, and love reigns
paramount. When this state is fully attained, no further or higher
change is to be expected, and the progress is soon towards decay and
the termination of the animal's mortal career. So we see that in fact
man and other _mammalia_, though they do not simultaneously cast
their skins like the insect; or pass into a state of intermediate
repose, before they attain the perfection of their nature, like the
caterpillar; have their three _states_, in each of which they acquire
new parts, powers, and appetites.
But a more striking analogy has been traced between the insects
that undergo a complete metamorphosis and the _vegetable_ kingdom;
for though the _primary_ analogy seems to be between the _Polypus_
and the _Plant_, yet the _secondary_ one with the _Insect_ is not
by any means remote. There are circumstances to which I shall have
occasion hereafter to call your attention, which afford some ground
for supposing, that the substance of the insect and the vegetable
partakes of the same nature, at least approximates more nearly, than
that of the insect and the vertebrate animal; and every one who
has observed these little creatures with any attention, will have
observed amongst them forms and organs borrowed as it were from the
kingdom of Flora; and _vice versâ_ the Botanist, if he makes the
comparison, will find amongst his favourite tribes many striking
resemblances of certain insects. But the analogy does not stop here;
for the butterfly and the plant appear to have been created with
a particular reference to each other, both in the epoch of their
appearance and the changes that take place in them. Thus, as Dr.
Virey has observed, the caterpillar is simultaneous with the leaf
of the tree or plant on which it feeds, and the butterfly with the
flowers of which it imbibes the nectar[72]. Swammerdam, I believe,
was the first who noticed the analogy between the _changes_ of
the insect and the vegetable, and has given a table in which he
has contrasted their developments, including other animals that
undergo a metamorphosis[73]: an idea which has been generalized
by Bonnet[74], and adopted and enlarged by Dr. Virey[74]. A state
analogous to that of the _larva_ in the insect begins in the plant
when it is disclosed from the seed, or springs from its hybernaculum
in the bulb, &c., or is evolved from the gemma; integument after
integument, often in various forms, as cotyledon, radical, cauline,
or floral leaves, expands as the stem rises, all which envelopes
incase the true representative of the plant, the fructification, as
the various skins do the future butterfly. When these integuments
are all expanded, the fructification appears inclosed by the calyx
or corolla as the case may be, in which the generative organs are
matured for their office--this is the bud, which is clearly analogous
to the _pupa_ state of the insect. Next the calyx and corolla expand,
the impregnation of the germen takes place, and the seed being
ripened, and dispersed by the opening of the seed-vessel or ovary of
the plant, the individual dies: thus the _imago_ state of the insect
has its representative in the plant. "If we place," says Dr. Virey,
"here the egg of the insect, next its caterpillar, a little further
the chrysalis, and lastly the butterfly--what is this but an animal
stem--an elongation perfectly similar to that of the plant issuing
from the seed to attain its blossoming and propagation?"[75]
There being, therefore, this general analogy in their progress to
that state in which they can continue their species between every
part of animated nature, it holds good, I think, that the same
analogy should take place in their developments. If the adult man
or quadruped, &c. is evidently an evolution of the fœtus, as from
microscopical observations it appears that they are[76], if the
teeth, horns, and other parts, &c. to be acquired in his progress to
that state are already in him in their embryos, we may also conclude
that the butterfly and its organs, &c. are all in the newly-hatched
caterpillar. Again, if the blossom and its envelopes are contained
in the gemma, the bulb, &c. where they have been discovered[77],
it follows analogically that the butterfly and its integuments all
preexist in its forerunner.
Perhaps after this view of the objections to Dr. Herold's hypothesis,
it will not be necessary to say much with regard to the argument
he draws from the change of organs--the loss of some and the
acquisition of others--since this may readily be conceived to be the
natural consequence of the vital forces tending more and more to the
formation of the butterfly, and the withdrawing of their action more
and more from the caterpillar; I shall not, therefore, enter further
into the question, especially since the change of organs will come
more regularly under our notice upon a future occasion.
Winged insects, many branchiopod _Crustacea_, and the Batracian
reptiles, have been observed by Dr. Virey to bear some analogy to the
_mammalia_, _aves_, &c. in another respect. In leaving their egg,
they only quit their first integument, answering to the _chorion_ or
external envelope of the human fœtus; they therefore still continue
a kind of fœtus, so to speak, more or less enveloped under other
tunics, and principally in their _amnios_, or the covering in which
the fœtus floats in the _liquor amnii_[78]. This the butterfly does
in the pupa case; and its birth from this, under this view, will be
the true birth of the animal. In the human subject, the ova upon
impregnation are said to pass from the ovary through the Fallopian
tube into the uterus. In the insect world, upon impregnation, the
eggs pass first from the ovaries into the oviduct, answering to the
Fallopian tube, which in them terminates in the _ovipositor_, or
the instrument by which the parent animal conveys the eggs to their
proper station: there is, therefore, nothing properly analogous to
the uterus in the insect, and the substance upon which the larva
feeds upon exclusion answers the purpose of a placenta.
After this general view of the most modern theories with regard to
the _metamorphosis_ of insects, I shall in the present and some
following letters, treat separately of the different states through
which these little beings successively pass.
* * * * *
The first of these is the _Egg state_, the whole class of insects
being strictly oviparous. Some few tribes indeed bring into the
world living young ones, and have on that account been considered
as _viviparous_, but incorrectly, for the embryos of none of these
are nourished, as in the true viviparous animals, within a uterus
by means of a placenta, but receive their development within true
eggs which are hatched in the body of the mother. This is proved
by the observations of Leeuwenhoek, who found eggs in the abdomen
of a female scorpion[79]; and of Reaumur, with regard to the
flesh-fly (_Musca carnaria_) and other viviparous flies as they
have been called[80]. A similar mode of production takes place in
vipers and some other reptiles, which have hence been denominated
_ovo-viviparous_, to distinguish them from the true viviparous
animals--the class _Mammalia_. By far the larger portion of
insects is oviparous in the ordinary acceptation of the term. The
ovo-viviparous tribes at present known are scorpions; the flesh-fly
and several other flies; a minute gnat belonging to Latreille's
family of _Tipulariæ_[81]; some species of _Coccus_; some bugs
(_Cimicidæ_)[82]; and most _Aphides_, which last also exhibit the
singular fact of individuals of the same species being some oviparous
and others ovo-viviparous, the former being longer in proportion than
the latter.--Bonnet, however, is of opinion that the eggs of the
first are not perfect eggs, but a kind of cocoon, which defends the
larva, already formed in some degree, from the cold of winter[83].
When excluded from the body of the mother, or from the egg, as has
been before observed, some insects appear nearly in the form of
their parents, which, with a very slight alteration, they always
retain; others, and the greater number, assume an appearance totally
different from that of their parents, which they acquire only after
passing through various changes. It is to these last, which have
chiefly engaged the attention of Entomologists, that the title of
metamorphoses has been often restricted. As, however, those insects
which undergo the slightest change of form, as spiders do, undergo
_some_ change, and almost all insects cast their skins several
times[84] before they attain maturity, Linné and most Entomologists,
till very recently, have regarded the whole class as undergoing
metamorphoses, and as passing through _four_ different states, viz.
the Egg--the Larva--the Pupa--and the Imago.
It is obvious, however, that in ovo-viviparous species _three_ states
of their existence only come under our cognizance, as these, being
hatched in the body of the mother, come forth first under the form of
larvæ. There is even one tribe of insects which presents the strange
anomaly of being born in the _pupa_ state. This is the Linnean
genus _Hippobosca_ (_Pupipara_ fam. Latr.), to which our forest-fly
belongs, the females of which lay bodies so much resembling eggs,
that they were long considered as such until their true nature was
ascertained by Reaumur (most of whose observations were confirmed
by De Geer), who, from their size, which nearly equals that of
the parent fly--from their slight motion when first extruded--from
spiraculiform points which run down each side of them--and lastly,
from their producing not a larva, as all other insects' eggs do,
but perfect flies in the winged state--inferred, and doubtless with
reason, that they are not real eggs, but pupæ, or larvæ just ready
to assume the pupa state, which, however strange it may seem, have
passed the egg and larva states in the body of the mother[85].
Insects, therefore, as to their mode of birth, may be divided into--
I. _Ovo-viviparous_, subdivided into--
1. _Larviparous_, coming forth from the matrix of the mother in
the state of larvæ, as the Scorpion (_Scorpio_), the Flesh-fly
(_Musca_), the Plant-louse (_Aphis_), &c.
2. _Pupiparous_, continuing in the matrix of the mother during
the larva state, and coming forth in that of _pupa_, as the
Forest-fly (_Hippobosca equina_), the Sheep-louse (_Melophagus
ovinus_), the Bat-louse (_Nycteribia Vespertilionis_), &c.
II. _Oviparous_. All other insects.
Our business for the remainder of this letter will be with the latter
description of these little animals.
The unerring foresight with which the female deposits her eggs
in the precise place where the larvæ, when excluded, are sure to
find suitable food; and the singular instruments with which, for
this purpose, the extremity of their abdomen is furnished, have
been noticed in a former letter[86], and those last mentioned will
be adverted to in a future one. I shall now, therefore, confine
myself to other circumstances connected with the subject, arranged
for the sake of order under several distinct heads, as--their
_exclusion_--_situation_--_substance_--_number_--_size_--_figure_--
_colour_--and _period of hatching_.
i. _Exclusion._ The exclusion or extrusion of the impregnated eggs
takes place, when, passing from the ovary into the oviduct, they are
conducted by means of the ovipositor, in which it terminates, to
their proper situation. By far the greater number of insects extrude
them _singly_, a longer interval elapsing between the passage of each
egg in some than in others. In those tribes which place their eggs
in groups, such as most butterflies and moths, and many beetles,
they pass from the ovaries usually with great rapidity; while in the
_Ichneumonidæ_, _Sphegidæ_, _Œstri_, and other parasitic genera,
which usually deposit their eggs singly, an interval of some minutes,
hours, or perhaps even days, intervenes between the extrusion of
each egg. One remarkable instance of the former mode I noticed in
my letter on the _Perfect Societies_ of Insects[87]; another may
be cited, to which you may yourself be a witness--I allude to that
common moth, vulgarly called the _Ghost (Hepialus Humuli)_, which
lays a large number of minute black eggs, resembling grains of
gunpowder, and ejects them so fast that, according to De Geer, they
may be said to _run_ from the oviduct, and are sometimes expelled
with the force of a popgun[88]. A Tetrapterous insect, the genus of
which is uncertain, is said, when it is taken, to discharge its eggs
like shot from a gun[89]. And a friend of mine, who had observed with
attention the proceedings of a common crane-fly (_Tipula_), assured
me that several females which he caught projected their eggs to the
distance of more than ten inches.
A few _Diptera_ extrude them in a sort of chain or necklace, each
egg being connected by a glutinous matter with that which precedes
and follows it. In a small species of a genus allied to _Psychoda_
(a kind of midge), which one season was abundant in a window of my
house, this necklace is composed of eggs joined by their sides, not
unlike those strung by children of the seeds of the mallow[90]. Other
_Tipulidæ_ on the contrary extrude their eggs joined end to end,
so as to resemble a necklace of oval beads. _Beris clavipes_ and
_Sciura Thomæ_, two other flies, produce a chain about an inch long,
consisting of oval eggs connected, in an oblique position, side by
side; an arrangement very similar prevails in the ribband of eggs
which drop from some of the _Ephemeræ_[91].
These eggs, like those of the insects first mentioned, though
connected, are expelled in succession; but other tribes, as the
_Libellulidæ_, with the exception of _Agrion_, many _Ephemeræ_,
_Trichopterous_ insects, &c. expel the whole at once, as it were
in a mass. In those first mentioned they are gummed together in an
oblong cluster[92]. In one _Ephemera_ mentioned by Reaumur[93], they
formed two oblong masses, each containing from three to four hundred
eggs, and three and a half or four lines long. These animals as soon
as their wings are developed eject these masses by two orifices,
and are aided in the process by two vesicles full of air, wherever
they happen to alight or to fall; in most instances it is the water,
their proper element, that receives them, but the animal does not
appear to know the difference between a solid and a liquid, and
seems only anxious how to free herself from a burthen that oppresses
her; all has been contrived that an insect so short-lived may finish
her different operations with the utmost celerity: the term of her
existence would not have admitted the leisurely extrusion of such a
number of eggs in succession[94]. Some _Trichoptera_, or May-flies,
as _Phryganea grandis_ L., exclude their eggs in a double packet,
enveloped in a mass of jelly, (a circumstance often attending the
eggs that produce aquatic larvæ,) upon the leaves of willows[95].
A similar double packet in the year 1810 I observed appended to
the anus of a black species with long antennæ, probably _Phryganea
atrata_ F.[96] Upon taking several of the females I was surprised to
find in the above situation a seemingly fleshy substance of a dirty
yellow. At first, from its annular appearance, I conceived it to be
some parasitic larva, but was not a little surprised upon pulling
it away that it was full of globular transparent dusky eggs: it was
about two lines and a quarter in length and nearly one in breadth.
Being bent double it was attached to the animal by the intermediate
angle, and when unfolded was constricted in the middle[97]. Each
half, which was roundish, had about ten sharp transverse ridges, the
interstices of which appeared as if crenated, an appearance produced
by the eggs which it contained. Upon more than gentle pressure it
burst and let out the eggs. Though resembling the packet of _P.
grandis_ in shape and other circumstances, it was nothing like
jelly, but had rather a waxy appearance, and seems to have been
covered by a membrane: so that the excluded larvæ must probably have
eaten their way out of it. I have still by me, in 1822, specimens of
these egg-packets, which, after the lapse of so many years, retain
their original form and colour. It is not improbable that other
species extrude their eggs in a similar case. Scopoli says of _P.
bicaudata_ L., that the female carries about under her belly her eggs
united into a globe, like _Lycosa saccata_[98]. The eggs of _Geometra
Potamogata_ F. are also enveloped in a gelatinous substance, and the
mass is covered with leaves[99].
Insects of the _Diptera_ order also, like frogs and toads, commit
their eggs to the water imbedded in masses of jelly. Dr. Derham
describes two different kinds of them, in one of which the eggs were
laid in parallel rows end to end, and in another in a single row,
in which the sides were parallel[100]. But the most remarkable and
beautiful specimen of this kind that I ever saw was one that, many
years ago, I took out of a pond at Wittersham in Kent, from which I
requested a young lady to make the drawing I send you[101]. The mass
of jelly, about an inch and a quarter long, and rather widest in the
middle, was attached by one end to some aquatic grass, and from one
end to the other ran a spiral thread of very minute eggs, the turns
of the screw being alternately on each side.
The mode of exclusion of the eggs of the _Blattæ_, which are engaged
for a whole week in the business of oviposition, is very singular:
the female deposits one or two large suboviform capsules, as large as
half their abdomen, rounded on one side, and on the other straight
and serrated, which at first is white and soft, but soon becomes
brown and hard. This egg-case, as it may be called, contains sixteen
or eighteen eggs arranged in a double series, and the cock-roaches
when hatched make their escape through a cleft in its straight
side, which shuts so accurately when they have quitted it, that at
first it appears as entire as before[102]. The insects of the genus
_Mantis_ also, or what are called the _praying insects_, when they
deposit their eggs, eject with them a soft substance, which hardens
in the air and forms a long kind of envelope resembling parchment,
in which the eggs are arranged also in a double series. And the
Locusts (_Gryllus Locusta_ L.) are said by Morier[103] to deposit in
the ground an oblong substance, of the shape of their abdomen, which
contains a considerable number of eggs arranged neatly in rows. The
peristaltic motion observed in the females of some insects during
oviposition has been before described[104].
ii. _Situation._ Under this head I include the situation in which the
female insect places her eggs when extruded, whether she continues her
care of them and carries them about till they hatch, or whether she
entirely deserts them, placing them either without a covering within
reach of their food, or enveloping them in hair or otherwise protecting
them from accident or the attack of enemies. I shall consider them
under two views: _first_, as depositing their eggs in _groups_, whether
covered or naked; and _secondly_, as depositing them _singly_.
1. Those that deposit their eggs in _groups_ are first to be
considered. I shall begin with those that protect them with some kind
of _covering_.
I have already mentioned in a former letter[105] the silken bag with
which _Lycosa saccata_ Latr., a kind of spider, surrounds her eggs, and
in which she constantly carries them about with her, defending them to
the last extremity. Many other spiders, indeed nearly the whole tribe,
fabricate similar pouches, but of various sizes, forms, texture, and
colours. Some are scarcely so big as a pea, others of the size of a
large gooseberry; some globular, some bell-shaped; others, the genus
_Thomisus_ Walck. in particular, depressed like a lupine; some of a
close texture like silk; others of a looser fabric resembling wool:
some consisting of a single pellicle, but most of a double, of which
the interior is finer and softer[106]; some white; others inclining
to blue; others again yellow or reddish; most of them are of a whole
colour, but that of _Epeira fasciata_ is gray varied with black[107].
And while the parent spider of some kinds (the _Lupi_) always carries
her egg-bag attached to her anus, others hold them by their palpi and
maxillæ; and others suspend them by a long thread, or simply fasten
them in different situations, either constantly remaining near them
(the _Telariæ_), or wholly deserting them (the _Retiariæ_). The eggs of
one of these last Lister describes as often fixed in a very singular
situation--the cavity at the end of a ripe cherry; and thus, as he
expresses it--"_Stomachi maxime delicatuli quoties hanc innocuam buccam
non minus ignoranter quam avide devorarunt_[108]."
Herman informs us, that the species of the genus _Chelifer_ carry
their eggs in a mass under their belly[109].
Madam Merian gives an account of two species of _Blatta_, which
she affirms carry an egg-pouch about with them--one species (_B.
gigantea?_) she describes as carrying its eggs in a globular pouch of
web like certain spiders, and the other in a brown bag, which, when
alarmed, it drops and makes off[110]. But this admirable paintress of
natural objects was not always correct in her statements[111]: it seems
very improbable, from the habits of those species of which we know the
history, that any of them should spin a pouch of web for their eggs.
The only insects certainly known to spin an egg-pouch like the
spiders, are the _Hydrophili_, a kind of water-beetles. Some of
these, as _H. lividus_, carry them about with them, like _Lycosa
saccata_, attached to the under side of their body, as M. Miger
observed[112]; and others when they are finished desert them. That of
the great water-beetle (_Hydrophilus piceus_) was long ago described
and figured by Lyonnet[113]; and a more detailed account of it has
since been given by M. Miger[114]. In form it somewhat resembles a
turnip when reversed, since it consists of a pouch of the shape of
an oblate spheroid, the great diameter of which is three quarters
of an inch; and the small, half an inch, from which rises a curved
horn, about an inch long and terminating in a point[115]. The animal
is furnished with a pair of anal spinners, which move from right to
left, and up and down, with much quickness and agility: from these
spinners a white and glutinous fluid appears to issue, that forms
the pouch, which it takes the animal about three hours to construct.
The exterior tissue is produced by a kind of liquid and glutinous
paste, which by desiccation becomes a flexible covering impermeable
to water; the second, which envelops the eggs, is a kind of light
down of great whiteness, that keeps them from injuring each other.
The tissue of the horn is of a silky nature, porous and shining, and
greatly resembling the cocoons of _Lepidoptera_. This part, contrary
to what Lyonnet supposes, appears calculated to admit the air, the
water soon penetrating it when submerged. At its base is the opening
prepared for the egress of the larvæ, when hatched, which is closed
by some threads, that, by means of the air confined in the cocoon or
pouch, hinder the water from getting in[116]. This nidus does not
float at liberty in the water till after the eggs are hatched, the
parent animal always attaching it to some plant. By means of this
anomalous process for a beetle, which this insect is instructed by
Providence thus to perfect, the precious contents of its little ark
are secured from the action of the element which is to be the theatre
of their first state of existence, from the voracity of fishes, or
the more rapacious larvæ of its own tribe, until the included eggs
are hatched, and emerge from their curious cradle.
I shall next amuse you with a few instances, in which the Allwise
Creator instructs the parent insect, instead of defending her eggs
with a covering furnished by her internal organs, to provide it from
without, either from her own body or from some other substance.
Most commonly, indeed, the female leaves her cluster of eggs without
any other covering than the varnish with which in this case they are
usually besmeared. Either they are deposited in summer and will soon be
hatched, or they are of a substance calculated to encounter and resist
the severities of the season. But many species, whose eggs are more
tender or have to resist the cold and wet of winter, defend them in the
most ingenious manner with a clothing of different kinds of substance.
_Cassida viridis_, a tortoise beetle, Rösel tells us, covers her
group of eggs with a partially transparent membrane. _Arctia Salicis_
F., a moth, common on willows, wholly conceals hers with a white
frothy substance, which when dry is partly friable and partly
cottony, and being insoluble in water effectually protects them from
the weather[117]. The female of _Lophyrus Pini_ (a saw-fly), having
by means of her double saw made a suitable longitudinal incision
in the leaf of a fir, and placed in it her eggs in a single row
end to end, stops it up with a green frothy fluid mixed with the
small pieces of leaf detached by her saws, which when dry becomes
friable: a necessary precaution, since these eggs are extremely
brittle[118]. _Arctia chrysorhœa_, _Hypogymna dispar_, and several
other moths, surround theirs with an equally impervious and more
singular clothing--_hair_ stripped from their own bodies. With this
material, which they pluck by means of their pincer-like ovipositor,
they first form a soft couch on the surface of some leaf: they then
place upon it successively layers of eggs, and surround them with a
similar downy coating, and when the whole number is deposited cover
the surface with a roof of hairs, which cannot be too much admired;
for those used for the interior of the nest are placed without order,
but those employed externally are arranged with as much art and skill
as the tiles of a roof, and as effectually keep out the water, one
layer resting partly on the other, and all having the same direction,
so that the whole resembles a well-brushed piece of shaggy cloth or
fur. When the mother has finished this labour, which often occupies
her for twenty-four hours, and sometimes even twice that period, her
body, which before was extremely hairy, is almost wholly naked--she
has stripped herself to supply clothing to her offspring, and
having performed this last duty she expires. The female moths which
thus protect their eggs are often furnished with an extraordinary
quantity of hair about the anus for this express purpose; and Reaumur
conjectures, that the singular anal patch of scales resembling those
of the wings, but considerably larger, which is found in the female
of _Lasiocampa Pityocampa_, is destined for the same purpose[119].
Reaumur had once brought to him a nidus of eggs clothed still more
curiously: they surrounded a twig in a spiral direction, like those
of _Lasiocampa Neustria_, but were much more numerous, and were
thickly covered with fine down, not pressed close, but standing off
horizontally, which assumed much the same appearance as a fox's tail
would if twisted spirally round a branch[120].
A procedure nearly similar was observed by De Geer in some species of
Aphides (_A. Alni_ and _A. Pruni_), which covered their eggs with a
white cottony down detached from their belly by means of their hind
legs[121]. In this case, however, the eggs were separately coated
with the down, but there was no general covering to the group.
Several insects make the leaves and other parts of plants serve as
coverings for their eggs. _Tenthredo Rosæ_ L., a saw-fly, and other
species of the same genus, with their saws make an incision in the
green twigs of shrubs and trees, and fill it with a line of eggs
placed end to end, taking care that, as the eggs grow after they are
laid, they are placed at such distances as to leave room for their
expansion[122]. _Rhynchites Bacchus_, a brilliant weevil, well known
to the vine-dressers for the injury it does[123], rolls with much art
the leaves of the vine, so as to form a cavity, in which it places
its eggs; other species practise similar manœuvres; and some probably
place their young progeny in the interior of twigs, making an opening
for that purpose with their rostrum--at least, I once saw _Rhynchites
Alliariæ_ L. with its rostrum plunged up to the antennæ in the twig of
a crab-tree. Others of this tribe, as we know, place their eggs in the
interior of fruits and grain, as the nut, acorn, and common weevils.
It is probable that most of the above coverings serve another
purpose besides the protection of the eggs from wet and cold--that
of sheltering them from the action of too great light, which, as Dr.
Michellotti by numerous experiments has ascertained, is fatal to
the included germe[124]. On this account it is perhaps that so many
insects fasten their eggs to the under side of leaves. Those exposed
in full day have usually an opaque and horny texture.
Some insects are spared all trouble in providing a covering for their
eggs, their own bodies furnishing one in every respect adapted to
this purpose. Not to mention the _Onisci_, or wood-lice, since they
rather belong to the _Crustacea_, which have a four-valved cell under
the breast, in which they carry their eggs, as the kangaroo does
its young in its abdominal pouch, the whole body of the female of
those strange animals the _Cocci_ becomes a covering for her eggs,
which it incloses on every side. To make this intelligible to you,
further explanation is necessary. You must have noticed those singular
immovable tortoise-shaped insects, which are such pests to myrtles and
other greenhouse plants. These are the young of a species of _Coccus_
(_C. Hesperidum_ L.), and _their_ history is that of the whole race.
Part of them never become much bigger than the size of which you
ordinarily see them, and when full-grown disclose minute two-winged
flies, which are the males. The size of the females, which glue
themselves to a twig or leaf as if lifeless, now augments prodigiously,
and the whole body, distended with the thousands of eggs which it
includes to the bigness of a large pea, without any vestige of head or
limb, resembles a vegetable excrescence or gall-apple rather than an
insect. If you remove one of them, you will perceive that the under
part of its abdomen is flat and closely applied to the surface of the
branch on which it rests, only a thin layer of a sort of cotton being
interposed between them. In laying her eggs the female _Coccus_ does
not, like most insects, protrude them beyond her body into day-light;
but as soon as the first egg has passed the orifice of her oviduct,
she pushes it between her belly and the cottony stratum just mentioned,
and the succeeding eggs are deposited in the same manner until the
whole are excluded. You will ask how there can be found space between
the insect's belly and the cotton, to which at first it was closely
applied, for so large a mass of eggs? To comprehend this, you must
consider that nearly the whole contents of its abdomen were eggs; that
in proportion as these are extruded a void space is left, which allows
the skin of the under side of the body to be pushed upwards, or towards
that of the back, affording room between it and the cottony web for
their convenient stowage. If you examine the insect after its eggs are
all laid, you will find that they have merely changed their situation;
instead of being on the upper side of the skin forming the belly, and
within the body, they now are placed between it (now become concave
and nearly touching the back) and the layer of cotton. As soon as the
female _Coccus_ has finished her singular operation she dies; but her
body, retaining its shape, remains glued upon the eggs, to which it
forms an arched covering, effectually protecting them, until they are
hatched, from every external injury. Some species lay so many eggs,
that the abdomen is not sufficiently large to cover the whole mass,
but merely one side of it, the remainder being enveloped in cottony
web[125].
* * * * *
I am next to consider the situation of those eggs that are excluded
by the mother in groups _without any_ other _covering_ than the
varnish with which they are usually besmeared in their passage from
the oviduct. The females only place them upon or near the food
appropriated to the young larvæ, to which they adhere by means of
the varnish just mentioned. These groups consist of a greater or
less number; and when the eggs are hatched by the heat of the sun,
the larvæ begin to disperse and attack with voracity the food that
surrounds them. It is thus that most butterflies and moths attach
their eggs to the stems, twigs, and leaves of plants; that the lady
birds (_Coccinellæ_), the aphidivorous flies (_Syrphi_ &c.), and
the lace-winged flies (_Hemerobii_), deposit them in the midst of
plant-lice (_Aphides_); that the eggs of some flesh-flies are gummed
upon flesh; those of crickets and grasshoppers buried in the earth;
those of gnats and other Tipulidans set afloat upon, or submerged in,
the water.
Frequently the whole number of eggs laid by one female is placed in
one large group, more commonly, however, in several smaller ones,
either at a distance from each other on the same plant, or on distinct
plants. The object in the latter case seems to be, in some instances,
to avoid crowding too many guests at one table, in others to protect
the unhatched eggs from the voracity of the larvæ first excluded, which
would often devour them if in their immediate neighbourhood.
In the disposition of the eggs which compose these groups much
diversity prevails. Sometimes they are placed without order in
a confused mass: more frequently, however, they are arranged
in different, and often in very beautiful modes. The common
cabbage-butterfly (_Pieris Brassicæ_) and many other insects place
theirs upon one end, side by side, so as, comparing small things with
great, to resemble a close column of soldiers, in consequence of which
those larvæ which, on hatching, proceed from the upper end, cannot
disturb the adjoining eggs. Many indeed have a conformation purposely
adapted to this position, as the hemisphærical eggs of the puss-moth
(_Cerura Vinula_), which have the base by which they are gummed
membranous and transparent, while the rest is corneous and opaque. The
same ready exit to the larva is provided for in the oblong eggs of the
emperor moth (_Saturnia Pavonia_), which are piled on their sides in
two or more lines like bottles of wine in a bin[126].
Where the larva does not emerge exactly from the end of the egg other
arrangements take place. The whirlwig-beetle (_Gyrinus natator_) and
the saw-fly of the gooseberry &c. (_Tenthredo flava_ L.) dispose
theirs end to end in several rows; the former upon the leaf of some
aquatic grass, the rows being parallel[127], the latter gummed to the
main nerves of gooseberry or currant leaves, the direction of which
they follow[128].
But the lackey-moths (_Lasiocampa Neustria_, _castrensis_, &c.)
adopt a different procedure. As their eggs, which are laid in the
autumn, are not to be hatched until the spring, the female does not,
like most other moths, place them upon a leaf, with which they might
be blown by the winter's storms far from their destined food, but
upon the twig of some tree, round which she ranges them in numerous
circles. If you examine your fruit-trees, you can scarcely fail
to find upon the young twigs collections of these eggs, which are
disposed with such admirable art, that you would take them rather
for pearls, set by the skilful hand of a jeweller, than for the eggs
of an insect. Each of these bracelets, as the French gardeners
aptly call them, is composed of from 200 to 300 pyramidal eggs
with flattened tops[129], having their axes perpendicular to the
circumference of the twig to which they are fastened, surrounding it
in a series of from fifteen to seventeen close spiral circles, and
having their interstices filled up with a tenacious brown gum, which,
while it secures them alike from the wintry blast and the attack
of voracious insects, serves as a foil to the white enamel of the
eggs that it encompasses. It is not easy to conceive how these moths
contrive to accomplish so accurately with their tail and hind feet an
arrangement which would require nicety from the hands of an artist;
nor could Reaumur, with all his efforts and by any contrivance,
satisfy himself upon this head. He bred numbers of the fly from the
egg, and supplied the females after impregnation with appropriate
twigs; but these, as though resolved that imprisonment should not
force from them the secret of their art, laid their eggs at random,
and made no attempt to place them symmetrically[130].
This illustrious Entomologist was more successful in discovering
the mode in which another insect, the common _gnat_, whose group of
eggs is, in some respects, as extraordinary as that last described,
performs its operations. The eggs of this insect, of a long
phial-like form, are glued together, side by side, to the number of
from 250 to 300, into an oblong mass, pointed and more elevated at
each end, so as considerably to resemble a little boat in shape.
You must not here suppose that I use the term _boat_ by way of
illustration merely; for it has all the essential properties of a
boat. In shape it pretty accurately resembles a London wherry, being
sharp and higher, to use a nautical phrase, fore and aft; convex
below and concave above; floating, moreover, constantly on the keel
or convex part. But this is not all. It is besides a _life-boat_,
more buoyant than even Mr. Greathead's: the most violent agitation
of the water cannot sink it; and what is more extraordinary, and a
property still a desideratum in our life-boats, though hollow it
never becomes filled with water, even though exposed to the torrents
that often accompany a thunder-storm. To put this to the test, I
yesterday (July 25, 1811) placed half a dozen of these boats upon the
surface of a tumbler half full of water; I then poured upon them a
stream of that element from the mouth of a quart bottle held a foot
above them. Yet after this treatment, which was so rough as actually
to project one out of the glass, I found them floating as before upon
their bottoms, and not a drop of water within their cavity.
This boat, which floats upon the surface of the water until the
larvæ are disclosed, is placed there by the female gnat. But how?
Her eggs, as in other insects, are extruded one by one. They are so
small at the base in proportion to their length that it would be
difficult to make them stand singly upright on a solid surface, much
more on the water. How then does the gnat contrive to support the
first egg perpendicularly until she has glued another to it--these
two until she has fixed a third, and so on until a sufficient number
is fastened together to form a base capable of sustaining them in
their perpendicular position? This is her process. She fixes her four
anterior legs upon a piece of leaf, or a blade of grass, and projects
her tail over the water. She then crosses her two hind legs, and in
the inner angle which they form, retains and supports the first laid
egg, as it proceeds from the anus. In like manner she also supports
the second, third, &c., all of which adhere to each other by means of
their glutinous coating, until she feels that a sufficient number are
united to give a stable base to her little bark; she then uncrosses
her legs, and merely employs them to retain the mass until it is of
the required size and shape, when she flies away, and leaves it to
its fate floating upon the water[131].
It may not be out of place to mention here a remarkable circumstance
which not seldom attends a kind of water-scorpion (_Naucoris_ F.)
occasionally to be met with in collections of Chinese insects. Its
back is often covered with a group of rather large eggs, closely
arranged; but whether these are its own eggs or those of some large
species of water-mite (_Hydrachna_ Maïll.) has not been clearly
ascertained. On the former supposition, the ovipositor must be
remarkably long and flexile to enable the animal to place the eggs
on its back. In confirmation of the latter it may be observed, that
the species of the genus _Hydrachna_ usually attach their eggs to the
body and legs of aquatic insects, as for instance _H. abstergens_ to
the water-scorpion (_Nepa cinerea_), &c.[132]
2. After having thus laid before you some of the procedures of those
insects that usually deposit their eggs in groups, either naked or
defended by coverings of various kinds, I next proceed to a rapid
survey of those of the species that commonly deposit them _singly_.
Some of these, as for instance the Admiral Butterfly (_Vanessa
Atalanta_), glue each egg carefully to its destined leaf by alighting
on it for a moment. Another butterfly (_Hipparchia Hyperanthus_)
whose caterpillar is polyphagous, drops hers at random on different
plants. In general it may be observed, that all those larvæ which
live in solitude, as in the interior of wood, leaves, fruits, grain,
animals, &c., proceed from eggs laid singly by the female, which
is usually provided with an appropriate instrument for depositing
them in their proper situation. Thus the nut-weevil (_Balaninus
Nucum_ Germ.) and also that of the acorn (_B. Glandium_) pierce a
nut or an acorn with their long beak, and then deposit in the hole
an egg, from which proceeds the maggot that destroys those fruits.
Leeuwenhoek asserts that the common weevil (_Calandra granaria_)
adopts the same process, boring a hole in every single grain of
corn before it commits an egg to it, and at the same time, by this
manœuvre, prepares a small quantity of flour to serve for the food
of the tender grub when it is first hatched[133]. It is probable
that the Rhyncophorous or weevil tribe in general chiefly use their
beaks for the purpose of depositing their eggs in different vegetable
substances, and perhaps principally in fruit or grain. The tribe of
gall-flies (_Cynips_) on the contrary, whose economy, detailed in a
former letter[134], interested you so much, bore an opening for the
egg with their spiral oviduct, which also conveys it.
Another large tribe of insects depositing their eggs singly, are those
which feed upon the bodies of other animals, into the flesh of which
they are either inserted, or placed so as speedily to find their way
into it. Some of these introduce them into _living_ animals, and then
leave them to their fate, as the _Ichneumons_ and gad-flies: others
deposit them along with the _dead_ body of an insect interred in a
hole, often prepared with great labour, as the different species of
sand-wasps (_Sphecidæ_), spider-wasps (_Pompilidæ_), &c.: the manners
of the latter of these tribes have been already adverted to[135], and
those of the _Ichneumonidæ_ will come more fully under consideration
when I treat of the _diseases_ of insects.
A similar labour in providing suitable habitations for their eggs
is undergone by various other insects whose larvæ live chiefly on
vegetable food, some inserting their egg within the substance the
larva devours, as those that prey on timber, twigs, roots, or the
like, and others on its surface. One would suppose at first, that the
exceedingly small egg which produces the subcutaneous larvæ would, by
the parent moth, be imbedded in the substance of the leaf which is
to exhibit hereafter their serpentine galleries: but this is not the
case, for she merely glues it on the outside; at least such was the
situation of the only egg of these very minute moths Reaumur had ever
an opportunity to observe[136].
Other insects, belonging to the tribe which lay their eggs singly, bury
them in the ground. Of this description are many of the lamellicorn
insects, the dung-chafers (_Scarabæidæ_ MacLeay) particularly, which,
inclosing their eggs in a pellet of dung, deposit them in deep
cylindrical cavities. Concerning the proceedings of some of these, as
well as of the whole race of bees, wasps, &c., which all lay single
eggs, I have before detailed to you many interesting particulars[137].
I must not conclude this subject without observing, that the female
_Pycnogonidæ_, an osculant tribe between Insects and _Crustacea_, carry
their eggs upon two pair of false legs[138].
iii. _Substance._ From this long dissertation on the _situation_
of the eggs of insects and matters connected with it, I pass on to
their _substance_ or their external and internal composition, giving
at the same time some account of the embryo included in them. The
eggs of insects, like those of birds, consist in the first place
of an external coat or shell, varying greatly, as to substance, in
different genera. Most commonly, particularly in those which deposit
their eggs in moist situations, as in dung, earth, and the like, it
is a mere membrane, often thin and transparent, and showing, as in
spiders, all the changes that take place in the inclosed embryo,
as the formation of the head, trunk, and limbs[139]. This membrane
is sometimes so delicate as to yield to the slightest pressure,
and insufficient to protect the included fluids from too rapid
an evaporation, if the eggs be exposed to the full action of the
atmosphere. In most _Lepidoptera_, and several other tribes, this
integument is considerably stronger, in those moths whose eggs are
exposed throughout the winter, as _Lasiocampa Neustria_, &c., so
hard as not to yield easily to the knife. Even in these, however,
its substance is more analogous to horn or a stiff membrane than
to the shell of the eggs of birds. Nothing calcareous enters into
its composition, and it is not perceptibly acted upon by diluted
sulphuric acid. The eggs of birds are lined by a fine membrane; but
I have examined several of those of insects, and have been able to
discover nothing of the kind in them. I will not, however, affirm
that it does not exist, though the shell of the insect egg appears
more analogous to the membrane that lines that of the bird than to
the outside shell itself.
Within this integument is included a fluid, on the precise nature
of which, except that it is an aqueous whitish fluid, few or no
observations have been made, or indeed are practicable; but it is
reasonable to suppose, that like the white and yolk of the bird's
egg, it serves for the development of the organs of the germe of the
future insect.
But few observations are recorded that relate to the embryo included
in the egg. It is stated, that it is invested with an extremely fine
and delicate pellicle--supposed by some analogous to the _Chorion_
and _Amnios_ of the human fœtus, though others think the shell of the
egg to correspond with the _Chorion_, and the successive integuments
of the larva with the _Amnios_[140]. When the egg is first laid,
nothing indeed is to be seen in it but the fluid just mentioned;
the first change in this fluid is the appearance of the head of
the embryo, more particularly in _Coleoptera_, of two points, the
rudiments of the mandibles, and of those apertures into the tracheæ
which I have called spiracles[141]; the little animal we may suppose
then assumes its form and limbs. The embryo is usually so folded in
the egg that the head and tail meet[142], and the head, annuli, and
other parts of the larva are often visible through the shell[143].
Swammerdam even saw the pulsation of the great dorsal vessel through
the shell of the egg of _Oryctes nasicornis_.
Under this head I must notice another singular circumstance peculiar
I believe to the eggs of insects, that sometimes, though rarely, they
are covered with down or hair. Those of a singular little hemipterous
insect, of a genus I believe at present undescribed, the ravages
of which upon the larch have been before noticed[144], are covered
by a downy web, as is the case with the animal itself. De Geer has
described the eggs of a bug, not uncommon in this country (_Pentatoma
juniperina_ Latr.), which are reticulated with black veins, in which
very short bristles are planted[145]. I possess also a nest of brown
eggs, probably of a species of the same genus, found upon furze,
which appear to be covered with very short downy hairs. The top of
these is flat, and surrounded by a coronet of short bristles, each
surmounted by a small white ball, so as to wear the appearance of
a beautiful little _Mucor_. But hairy eggs are not confined to the
Hemiptera Order, for, according to Sepp, those of the figure-of-eight
moth (_Bombyx cæruleocephala_) are of this description[146].
iv. _Number._ The fertility of insects far exceeds that of birds,
and is surpassed only by that of fishes[147]. But the number of
eggs laid by different species, sometimes even of the same natural
family, is extremely various. Thus the pupiparous insects may be
regarded as producing only a single egg; _Musca Meridiana_ L., a
common fly, lays two[148], other flies six or eight; the flea twelve;
the burying beetle (_Necrophorus Vespillo_[149]) thirty; May-flies
(_Trichoptera_ K.) under a hundred; the silk-worm moth about 500;
the great goat-moth(_Cossus ligniperda_) 1,000; _Acarus americanus_
more than 1,000[150]; the tiger-moth (_Callimorpha Caja_) 1,600; some
Cocci 2,000, others 4,000; the female wasp at least 30,000[151];
the queen bee varies considerably in the number of eggs that she
produces in one season, in some cases it may amount to 40,000 or
50,000 or more[152]; a small hemipterous insect, resembling a little
moth (_Aleyrodes proletella_ Latr.) 200,000. But all these are left
far behind by one of the white ants (_Termes fatale_ F. _bellicosus_
Smeath.)--the female of this insect, as was before observed[153],
extruding from her enormous matrix not less than 60 eggs in a minute,
which gives 3,600 in an hour, 86,400 in a day, 2,419,200 in a lunar
month, and the enormous number of 211,449,600 in a year: probably she
does not always continue laying at this rate; but if the sum be set
as low as possible, it will exceed that produced by any other known
animal in the creation.
v. _Size._ The size of the eggs is in proportion to that of the
insect producing them, though in some instances small ones produce
larger eggs than those laid by bigger species. Thus the eggs of
many _Aptera_, as those of that singular mite _Uropoda vegetans_,
and of the bird-louse found in the golden pheasant, are nearly as
large, it is probable, as the parent insect; while those of the
ghost-moth (_Hepialus Humuli_) and many other _Lepidoptera_, &c.
are vastly smaller. This circumstance perhaps depends principally
on the number they produce: the majority of them, however, are
small. The largest egg known, if it be not rather an egg-case,
is that of a spectre insect (_Phasma dilatatum_), figured in the
Linnean Transactions[154], being five lines in length and three
in width, which probably approaches near the size of that of some
humming-birds. The largest egg of any British insect I ever saw was
that of the common black rove-beetle (_Staphylinus olens_) sent me by
Mr. Sheppard--this is a line and half long by a line in width. But
we do not often meet with insect-eggs exceeding a line in length. A
vast number are much smaller: those of Ephemeræ are more minute than
the smallest grains of sand[155], and some almost imperceptible, as
those of the subcutaneous moths, to the naked eye. Commonly the eggs
laid by one female are all of the same size; but in several tribes,
those containing the germe of the _female_ are larger than those that
are to give birth to a _male_. This appears to be the case with those
of the Rhinoceros beetle (_Oryctes nasicornis_[156]), and according
to Gould with those of ants[157]. As the female in a vast number
of instances is much bigger than the male, it is not improbable
that this law may hold very extensively. It is stated, however, by
Reaumur[158], that the reverse of this takes place in the eggs of the
hive-bee, those that are to produce males being larger than the rest.
Another peculiarity connected with the present head is the
augmentation in bulk which takes place, after exclusion, in the eggs
of the great tribe of saw-flies (_Tenthredo_ L.), the gall-flies
(_Cynips_ L.), the ants (_Formica_ L.) and the water-mites
(_Hydrachna_ Maïll. _Atax_ F.). Those of the two former, which are
usually deposited in the parenchymous substance of the leaves, or of
the young twigs, of various plants, imbibe nutriment in some unknown
manner, through their membranous skins, from the vegetable juices
which surround them[159], and when they have attained their full size
are nearly twice as large as when first laid. Except in the eggs of
fishes, whose volume in like manner is said to augment previously
to the extrusion of the young, there is nothing analogous to this
singular fact in any other of the oviparous tribes of animals, the
eggs of which have always attained their full size when they are laid.
It is to M. P. Huber that we are indebted for the knowledge of the
fact that the eggs of _ants_ grow after being laid, a circumstance
favoured probably by the moist situation in which the workers are
always careful to keep them. By an accurate admeasurement he found
that those nearly ready to be hatched were almost twice as big
as those just laid[160]. A similar observation was made on the
red eggs of a water-mite (_Hydrachna abstergens_) by Rösel, who
conjectured that they draw their means of increase from the body of
the water-scorpions (_Nepæ_), of which they form so singular an
appendage[161], which opinion is confirmed by De Geer, who observes
that when the water-scorpions are covered by an unusual number of the
eggs of the water-mites, they grow weak and languid, and endeavour
to rid themselves of their parasitic appendages[162]. It is most
probable that the mite lately named (_Uropoda vegetans_), which is
often found planted as it were upon the bodies of various beetles, by
means of a long pedicle, through which, as the fœtus by an umbilical
chord and placenta, it derives its nutriment from the above animals,
is at first so fixed in the egg state, though before it is disengaged
from the pedicle it is hatched, since it is often found with its legs
displayed and quite active--this is the more probable, as the eggs of
the water-mite are fixed by a pedicle to the animals to which they
are attached[163]. I have met with a remarkable instance, in which
pedunculated eggs seem to draw nutriment from the _mother_, which
brings the pedicle still near to the nature of the umbilical chord.
Those of the small hemipterous insect which infests the larch before
alluded to, are attached to the anal end of the mother by a short
foot-stalk not longer than the egg.
Dr. Derham seems to have observed, that the eggs of some _Diptera_,
of the tribe of _Tipulidæ_, also increase in size before the larva
is excluded[164]. It seems to me likely enough, that in this and
many of the above cases in which the egg is supposed to grow, it is
rather an extension of the flexile membrane that forms their exterior
proportioned to the growth of the included embryo from food it finds
within the egg, than from any absorption from without.
vi. _Shape._ We are accustomed to see the eggs of different species
of oviparous animals so nearly resembling each other in form, that
the very term _egg-shaped_ has been appropriated to a particular
figure. Amongst those of birds, with which we are most familiar,
the sole variations are shades of difference between a globular and
oval or ovate figure. The eggs of insects, however, are confined by
no such limited model. They differ often as much, both as to their
shape, sculpture, and appendages, as one seed does from another; and
it is not improbable that, if duly studied, they would furnish as
good indications of generic distinctions as Gærtner has discovered in
those of plants. Their most usual form indeed is globular, oval, or
oblong, with various intermediate modifications. We meet with them
ovate, or of the shape of the common hen's egg, flat and orbicular,
elliptical, conical, cylindrical, hemispherical, lenticular,
pyramidal, square, turban-shaped, pear-shaped, melon-shaped,
boat-shaped, of the shape of an ale-stand, of a drum, &c.[165], and
sometimes of shapes so strange and peculiar, that we can scarcely
credit their claim to the name of eggs. Thus the eggs of the gnat
are oblong and narrow, or nearly cylindrical, having at the top a
cylindrical knob[166], so as to give them the precise form of the
round-bottomed phial sometimes used by chemists: those of the common
water-scorpion (_Nepa cinerea_) are oblong, and at the upper end are
surrounded by a sort of coronet, consisting of seven slender rays or
bristles of the length of the egg[167], so as to resemble somewhat
the seeds of _Carduus benedictus_ (_Cnicus acarna_[168]) of the
old botanists. One would think this spinous circlet a very awkward
appendage to bodies which are to be gradually extruded through the
fine membranous ovaries and oviduct which inclose them: but they are
so admirably packed, the unarmed end of each egg fitting closely
into the space inclosed by the spines of the one next below it,
or, rather, the spines which are moveable, embracing it closely,
that not only is no room lost, but the ovaries are perfectly secure
from injury. The eggs of another species of this tribe (_Ranatra
linearis_) have only two of these spines or bristles--they are
inserted in the stem of a water-rush (_Scirpus_) or other aquatic
plant, so as to be quite concealed, and are only to be detected
by the two bristles which stand out from it[169]. The eggs of the
beautiful lace-winged flies (_Hemerobius_), those golden-eyed insects
so serviceable in destroying the plant-lice (_Aphides_[170]), are
still more singular. Those of _H. Perla_ are oval, and each of them
attached to a filiform pedicle not thicker than a hair, and seven or
eight times as long as the egg. By this pedicle (which is supposed
to be formed by a glutinous matter attached to one end, which the
female draws out by abstracting her ovipositor with the egg partly
in it from the leaf, to which she has previously applied it, to a
proper length, when the gluten becoming sufficiently solid she wholly
quits the egg,) the eggs are planted in groups of ten or twelve on
the surface of leaves and twigs, from which they project like so many
small fungi, to some of which they have a remarkable resemblance.
When the included larva has made its way out of them by forcing open
the top, they look like little vases, and were actually once figured
by a Naturalist, as we learn from Reaumur, as singular parasitic
flowers growing upon the leaves of the elder, for the origin of which
he was extremely puzzled to account[171]. Eggs similarly furnished
with a pedicle are also laid by other insects; but as most of these
have been before alluded to, it is not necessary to describe them
here[172]. The cause of these differences of form is for the most
part concealed from us: in many instances it may perhaps be referred
to that will to vary forms, and so to glorify his wisdom[173] and
power, independently of other considerations, which, as Dr. Paley
has well remarked[174], seems often to have guided the Great Author
of Nature. But in some cases the end to be answered is sufficiently
evident. The long footstalks of the eggs of the _Hemerobius_ just
mentioned, there can be little doubt, are meant to place them out
of the reach of the hosts of predaceous insects which roam around
them, from whose jaws, thus elevated on their slender shaft, they are
as safe as the eggs of the tailor bird in its twig-suspended nest
from the attack of snakes. Reaumur has described the eggs of a kind
of fly, common upon the excrements of the horse and other animals
(_Scatophaga vulgaris_ Latr.), or one related to it, that requires
to be immersed in the dung to which it is committed, on which the
future grubs are to feed. He found that if not thus surrounded with
moisture, they infallibly shrivelled up and came to nothing; but it
is equally necessary that they should not be wholly covered: if they
were, the young larva would be suffocated at its first exit from the
egg. In what way is this nice point secured? In this manner. Each
egg is provided at its upper end, at which the animal when hatched
comes out, with two diverging horns[175]; these prevent it from being
stuck into the excrement, in which the female deposits the eggs one
by one, more than three-fourths of its length: and when examined they
resemble not badly, as Reaumur remarks (except that their colour is
white), a parcel of cloves stuck into a pudding, as they are neatly
inserted at due distances in the disgusting mass[176]. The French
Naturalists found these eggs in swine's dung; I have observed them
in cow-dung. Latreille thinks that the bristles above described
attached to the eggs of _Nepa_ and _Ranatra_ have a similar use,
as the female plunges them all but these bristles into the stems
of aquatic plants[177]: but may not this have something to do with
their oxygenation? Reaumur has figured another egg of a dipterous
insect which has a longitudinal wing or lateral margin attached to
it, giving it the form of an oblong square, the object of which,
he conceives, is to give a greater surface by which it may be more
firmly fixed to the substance against which the fly attaches it[178].
Besides these more striking variations in figure, their surface,
though often smooth, is frequently curiously and most elegantly
_sculptured_, a circumstance that distinguishes the eggs of no other
oviparous animals. Some, as the margined egg just mentioned, are only
sculptured on one side, the other being plain; or, as those of the
Tusseh silk-worm[179] (_Attacus Paphia_) and other _Bombyces_, which
have orbicular depressed eggs with a central cavity above and below,
have their circumference crossed with wrinkles corresponding with
the rings of the inclosed embryo[180]. Others again are sculptured
all over. Of these, in some, the sculpture of the two sides is not
symmetrical, as in those of a fly figured by Reaumur[181]: but
in general there is a correspondence in this respect between the
different parts of the egg. In those elegant ones before alluded
to of some bird-louse attached to the golden pheasant, the shell
resembles the purest wax, and is scored with longitudinal striæ,
each distinguished by a series of impressed points, which give it
a beautiful appearance of net-work. In the others, as in a common
butterfly (_Hipparchia Ægeria_) and moth (_Geometra cratægata_),
the whole surface is covered with hexagonal reticulations[182].
Others, as those of another butterfly (_Hipparchia Hyperanthus_),
are beset with minute granules or tubercles[183]. Others again, like
those of the cabbage and hawthorn butterflies (_Pieris Brassicæ_ and
_Cratægi_), are remarkable for beautiful longitudinal ribs, often
connected by elevated lines crossing them at right angles[184]; and
in some, as in another butterfly (_Hipparchia Jurtina_), crowned by
imbricated scales[185]. Many other minor differences in this respect
might be noticed, but these will suffice to give some idea of the
infinite variety exhibited in this respect by these little atoms. If
the Creator has wrought them with so much art and skill, can it be
beneath his reasonable creatures to examine and admire them, that
they may glorify those attributes which they serve to illustrate?
Some eggs after exclusion occasionally become slightly corrugated:
Malpighi supposed that this occurs only when the eggs are barren,
having observed that those of the moth of the silk-worm which preserved
their plumpness always produced caterpillars, while those which
lost their original rotundity and became wrinkled were constantly
unprolific. Bonnet, however, found exactly the reverse take place
in another moth[186], so that these appearances are scarcely to be
depended upon. Kuhn asserts, that a virgin female of the puss-moth
(_Cerura Vinula_) having begun to lay eggs, which were yellow above,
green below, and depressed, he introduced to her an hour afterwards a
male, and some minutes subsequently to the union, she again deposited
eggs, which were wholly of a dark brown and convex[187].
vii. _Colour_. The colour of the eggs of insects is as various as
their shape and sculpture. They are very often white, those of some
spiders like minute pearls[188]; some are yellow, as those of the
silk-worm; others orange, such are the eggs of the bloody-nosed
beetle (_Timarcha tenebricosa_); others again of a golden hue;
sometimes they are of a sanguine red. I remember once being much
surprised at seeing the water at one end of a canal in my garden as
red as blood: upon examining it further I found it discoloured by
an infinite number of minute red eggs, belonging probably to some
dipterous insect of the Tipulidan tribe. There are also eggs of every
intermediate shade between red and black; some again are blue and
others green. They are not always of whole colours, for some are
speckled like those of many birds, of which I can show you specimens,
that are also shaped like birds' eggs; these I think were laid by a
common moth (_Odenesis potatoria_); others are banded with different
colours--thus the blue eggs of the lappet-moth (_Gastropacha
quercifolia_) are encircled by three brown zones[189]; others are
brown with a white zone[190].
Many eggs assume a very different colour after being laid a few
days. In general upon their first exclusion they are white. Those
of the chameleon-fly (_Stratyomis Chamæleon_) which I once found in
great numbers, arranged like tiles on a roof one laid partly over
another, on the under side of the leaves of the water-plantain,
from white become green, and then change to olive green. Those of
the hemipterous enemy of the larch, more than once mentioned in
this letter, are first mouse-coloured, then they assume a reddish
hue, and lastly a blackish one. Those of the gnat from white in a
short time assume a shade of green, in a few hours they are entirely
green, and at length become gray[191]. Those of the silk-worm,
which at first are of a yellow or sulphur colour, acquire a violet
shade. The eggs of that rare moth _Endromis versicolor_, are at
first sulphur-coloured, then green, next rose-coloured, and lastly
blackish. The colour of almost all eggs changes when they are near
hatching; but this change depends more frequently upon the colour of
the included larva, which appears through the transparent shell of
the egg, than upon any actual alteration in the egg itself.
viii. _Period of hatching._ The general rule for the hatching
of the eggs of insects is the absorption by the embryo of all
the superabundant moisture included in them; but the time varies
according to the state of the atmosphere, to the action of which they
are subjected. Like those of other animals, they require a certain
degree of heat for the due evolution of the included larva. This
heat in much the greater number of instances is derived from the
temperature of the air, but often also from other sources. The eggs
of the gad-fly tribe are hatched principally by the heat of the body
of the animal to which they are committed; and doubtless the vital
heat of various larvæ, small as it may be, must contribute something
to the hatching of the eggs deposited in them by various Ichneumons.
In the fermenting bark in which the instinct of the rhinoceros
beetles (_Oryctes nasicornis_ &c.) impels them to place theirs, the
dung which the _Scarabæidæ_ select for that purpose, and the decaying
vegetables chosen by many other insects, a degree of artificial heat
must exist: and the eggs, or rather egg-like pupæ, of the spider-fly
of the swallow (_Ornithomyia Hirundinis_) are hatched by the heat of
those birds which sit upon them along with their own eggs.
Fabricius says, "Insects never sit upon their eggs[192];" but
certainly, as I formerly related to you[193], the female earwig does
this, and one would be induced to suppose, from the circumstance of
the young ones following their mother, as chickens do the hen, that
_Pentatoma grisea_ (_Cimex_ Linn.), formerly mentioned, may do the
same[194].
With these exceptions, the eggs of all insects are hatched by
atmospheric heat alone, the variations in which determine the more
speedy or more tardy disclosure of the included insect. The eggs
of such species as have several broods in the year, as the nettle
butterfly (_Vanessa Urticæ_) when laid in summer are hatched in a
few days; but if not laid till the close of autumn, they remain
dormant through the winter, and are only hatched at the return of
spring. That this difference is to be attributed to the influence
of heat has been often proved by experiment: the autumnal eggs if
brought into a warm room may be hatched as soon as those laid in
the height of summer. Silk-worms' eggs naturally are not hatched
till they have been laid six weeks, but in countries where they are
reared, the women effect their exclusion in a much shorter period
by carrying them in their bosoms: yet to retard their hatching with
particular views is in many circumstances impossible. When the heat
of the atmosphere has reached a certain point, the hatching cannot
be retarded by cellars; and M. Faujas has remarked, that in June the
silk-worm's eggs would hatch in an ice-house[195].
The period of exclusion does not, however, depend solely upon
temperature: the hardness or softness of the shell, and possibly
differences in the consistence of the included fluid, intended to
serve this very purpose, cause some eggs to be hatched much sooner
than others exposed to the same degree of heat. Thus the eggs of many
flesh-flies are hatched in twenty-four hours[196]; those of bees
and some other insects in three days; those of a common lady-bird
(_Coccinella bipunctata_) in five or six days; those of spiders in
about three weeks; those of the mole-cricket in a month; while those
of many _Lepidoptera_ and _Coleoptera_ require a longer period for
exclusion. The hard eggs of _Lasiocampa Neustria_ and _castrensis_,
noticed above, remain full nine months before being hatched[197], as
do those of another moth (_Hypogymna dispar_), which, though laid
in the beginning of the warm month of August, do not send forth the
included caterpillar till the April following[198]. We know no more
of the cause of this difference than of that which takes place in
the period of exclusion of the eggs of the different species of birds.
Some eggs change considerably both their form and consistence
previously to being hatched. M. P. Huber found that those of
different species of ants when newly laid are cylindrical, opaque,
and of a milky white; but just before hatching their extremities are
arched, and they become transparent with only a single opaque whitish
point, cloud, or zone, in their interior[199]. An analogous change
takes place in the eggs of many spiders, which just before hatching
exhibit a change of form corresponding with that which the included
spider receives when its parts begin to be developed, the thin and
flexible skin of the egg moulding itself to the body it incloses[200].
In proportion as the germe included in the egg is expanded, it
becomes visible through the shell when transparent: this is
particularly the case with spiders, in which, as was before observed,
every part is very distinctly seen. At length, when all the parts
are consolidated so as to be capable of motion, which in spiders
takes place in four or five days after they begin to be visible in
the egg, the animal breaks the pellicle by the swelling of its body
and the movement of its legs, and then quits it, and disengages
all its parts one after the other[201]. In general, at least where
the shell is harder than that of spiders, insects make their way
out by gnawing an opening with their mandibles in the part nearest
their head, which, when the shell is very strong (as in _Lasiocampa
Neustria_, &c.), it is often several hours in accomplishing[202].
In many instances, however, the larva is spared this trouble, one
end of the egg being furnished with a little lid or trap-door, which
it has but to force up, and it can then emerge at pleasure: such
lids are to be found in the eggs of several butterflies and moths,
as _Satyrus Mæra_, _Saturnia pavonia major_, &c. and the common
louse[203]. In those exquisitely elegant eggs, before described, of
some kind of bird-louse (_Nirmus_) found adhering to the base of the
neck feathers of the golden pheasant[204], there is a lid or cap of
this kind of a hemispherical form terminating in a tortuous style.
Those of a species of bug (_Pentatoma_ Latr.), found by our friend
the Rev. R. Sheppard, besides a convex lid are furnished with a
very curious machine, as it should seem, for throwing it off. This
machine is dark-brown, of a corneous substance, and of the shape of
a cross-bow[205], the bow part being attached to the lid or pushing
against it, and the handle, by means of a membrane, to the upper end
of the side of the egg.
When the included animal has made its way out of the egg, it enters
upon a new state of existence, that of _Larva_, to which I shall
direct your attention in the following letter.
FOOTNOTES:
[61] The word μεταμορφοω, and its derivative μεταμορφωσις, are not
extant in any Greek writer before the date of the New Testament.
They are used to express any _external_ change of form or colour,
and metaphorically an _inward_ change and progressive improvement of
the mind. Comp. Matth. xvii. 2. Ælian. _Var. Hist._ l. i. c. 1. Rom.
xiii. 2. 2 Cor. iii. 18. They are, therefore, not improperly applied,
as some have supposed, to the changes of insects.
[62] _Entwickelungsgeschichte der Schmetterlinge_ 12-27. 105--.
[63] Dr. Virey's observations under the article _Embryo_ (_N.
Dict. d'Hist. Nat._ x. 195.) deserve here to be considered. "Il
y a donc quelque chose au dessus de l'intelligence humaine dans
cette formation des êtres; en vain on veut l'approfondir, c'est
un abime dans lequel on ne voit que la main de Dieu. A quoi bon
s'appesantir sur le mystère de la formation des êtres, sans esperance
de l'expliquer? Ne vaut-il pas mieux observer les opérations de la
nature autant qu'il est permis à l'œil humain de les appercevoir?"
[64] § xiv.
[65] _N. Dict. d'Hist. Nat._ x. 193.
[66] _Œuv._ v. 279. "Il n'est pas exact de dire que le cœur, la tête,
et la moelle épinière, sont formés les premiers dans les fœtus des
animaux à sang rouge et vertébrés," says Dr. Virey; "mais il faut
dire seulement que tel est l'ordre dans lequel ces organes commencent
à devenir visibles." _N. Dict. d'Hist. Nat._ x. 196.
[67] _Ibid._ 193.
[68] _Œuvr._ viii. 315.
[69] _Hor. Entomolog._ 446.
[70] See on this subject _N. Dict. d'Hist. Nat._ xx. article
_Metamorphosis_.
[71] _N. Dict. d'Hist. Nat._ xx. 349--.
[72] _N. Dict. d'Hist. Nat._ xx. 348.
[73] _Bibl. Nat._ Ed. Hill. ii. 138.
[74] _Œuvr._ v. 283--.
[75] _N. Dict. d'Hist. Nat._ xx. 355.
[76] Leeuwenhoek discovered in the incipient fœtus of a sheep, not
larger than the eighth part of a pea, all the principal parts of the
future animal. _Arc. Nat._ I. ii. 165, 173.
[77] Bonnet, _Œuvr._ v. 284.
[78] _N. Dict. d'Hist. Nat._ xx. 352.
[79] Select Works by Hoole, i. 132. The fact is confirmed by M. L.
Dufour, who, having opened the abdomen of a female scorpion, found in
the midst of some eggs nearly mature a little scorpion a quarter of
an inch long; it lay without motion, with its tail folded under the
body. _N. Dict. d'Hist. Nat._ xxx. 426.
[80] Reaum. iv. 425--.
[81] _Ibid._ 428--. _t._ xxix. _f._ 10, 11.
[82] Busch, a German author, affirms that many _Cimicidæ_ are subject
to this law. _Schneid._ i. 206.
[83] Quoted in Huber _Fourmis_, 208. Some reptiles also are at one
time oviparous, and at another ovo-viviparous. _N. Dict. d'Hist.
Nat._ xii. 568.
[84] I say _almost_ all insects, because the larvæ of _Hymenoptera_
and _Diptera_ are supposed not to undergo this change. _N. Dict.
d'Hist. Nat._ xx. 365.
[85] Reaum. vi. _Mém._ xiv. De Geer, vi. 280.
[86] See VOL. I. Lett. xi.
[87] See VOL. II. p. 36.
[88] De Geer i. 494--.
[89] Called by M. l'Abbé Preaux, who observed it near Lisieux in
Normandy, _Mouche Baliste._ _N. Dict. d'Hist. Nat._ xxi. 442.
[90] PLATE XX. FIG. 20.
[91] Reaum. vi. 509. _t._ XLV. _f._ 11, 12.
[92] Reaum. vi. 434.
[93] _Ibid._ vi. 494.
[94] The vesicles, which Reaumur thinks may be pulmonary vesicles,
as well as assisting in the extrusion of the masses of eggs, he has
figured _t._ xliv. _f._ 10. _u u._
[95] De Geer ii. 534. _t._ xiii. _f._ 13.
[96] Coquebert _Illustr. Ic. t._ i. _f._ A. B.
[97] PLATE XX. FIG. 25.
[98] _Ent. Carniol._ 269. _n._ 705.
[99] Reaum. ii. 401.
[100] In Raii _Hist. Ins._ 264.
[101] PLATE XX. FIG. 24.
[102] Goeze _Naturf._ xvii. 183--. _t._ iv. _f._ 16-19. Comp. _N.
Dict. d' Hist. Nat._ iii. 475. and xix. 239. De Geer iii. 533.
[103] _Second Journey through Persia_, 100--.
[104] See VOL. II. p. 36.
[105] VOL. I. p. 359--.
[106] Latr. _Hist. Nat. des Fourmis_, 334. _N. Dict. d'Hist. Nat._
ii. 284.
[107] Lister _De Aran._ Tit. 13, 14. _N. Dict. d'Hist. Nat._ ii. 284.
[108] Lister _Ibid._ 56. Tit. 15.
[109] _N. Dict. d'Hist. Nat._ xxvi. 447.
[110] _Ins. Surinam, t._ i.
[111] A striking instance of this may be seen in her forty-ninth
plate, in which she has clapped the rostrated head of _Fulgora
laternaria_ upon the body of a _Cicada_ Latr., affirming it to be the
former fly in its previous state! This might be a trick upon her.
[112] _N. Dict. d'Hist. Nat._ xv. 489.
[113] _Lesser_ L. i. 300.
[114] _Annales du Muséum_, xiv. 441.
[115] _Lesser_ L. i. _t._ ii. _f._ xvi.
[116] Miger _Ann. du Mus._ ubi supr. Comp. _N. Dict. d'Hist. Nat._
xv. 482--.
[117] De Geer i. 192.
[118] Ibid. ii. 982.
[119] Reaum. ii. 97. 159.
[120] Ibid. 107--. _t._ iii. _f._ 15.
[121] De Geer iii. 48. 51.
[122] Reaum. v. 122.
[123] See above, VOL. I. p. 196. 202.
[124] _Journ. de Phys. Philos. Mag._ ix. 244.
[125] Reaum. iv. _Mem._ i.
[126] Rösel, ix. 157. _t._ 265?
[127] Ibid. iii. 197.
[128] See above, VOL. I. p. 195.
[129] PLATE XX. FIG. 14.
[130] Reaum. i. 95-- _f._ 1-13.
[131] Reaum. iv. 615--. _t._ xliv. _f._ 2-7.
[132] _N. Dict. d'Hist. Nat._ xv. 445. Rös. iii. 156.
[133] _Epist._ 1687.
[134] VOL. I. p. 448--.
[135] See above, VOL. I. p. 344--.
[136] Reaum. iii. 8--.
[137] VOL. I. 349--. 371--.
[138] _N. Dict. d'Hist. Nat._ xxviii. 271.
[139] De Geer vii. 194.
[140] Compare _N. Dict. d'Hist. Nat._ xvi. 246. with xx. 352-; but as
the _Amnios_ immediately envelops the fœtus, the pellicle seems most
analogous to it, and the shell to the _Chorion_.
[141] Swamm. _Bibl. Nat._ ed. Hill. l. 133. a. Comp. _N. Dict.
d'Hist. Nat._ xvi. 246.
[142] Swamm. _Ibid._
[143] Sepp. iv. _t._ iii. _f._ i. _c._ v. _t._ iv. _f._ 2.
[144] See above, VOL. I. p. 208: it is there called an _Aphis_, but
it is a distinct genus.
[145] De Geer iii. 245. _t._ xiii. _f._ 20-22.
[146] Sepp. iv. _t._ xiii. _f._ 2. 3.
[147] The sturgeon is said to lay 1,500,000 eggs, and the cod-fish
9,000,000.
[148] Reaum. iv. 392.
[149] See above, VOL. I. p. 350.
[150] De Geer vii. 159.
[151] See above, VOL. II. p. 109.
[152] Ibid. 159. 166.
[153] Ibid. 36--.
[154] iv. _t._ xviii. _f._ 4. 5.
[155] De Geer ii. 638.
[156] _Bibl. Nat._ i. 132. b.
[157] Gould 36.
[158] Reaum. v. 477.
[159] Ibid. iii. 579. v. 121.
[160] _Fourmis_, 69--.
[161] Rösel iii. 152.
[162] De Geer vii. 145.
[163] Ibid. 123--. See above, VOL. I. p. 393.
[164] Raii _Hist. Ins._ 265.
[165] Eggs of various shapes are given PLATE XX. FIG. 3-23. See
also Brunnich. _Entomologia_ 4. _N. Dict. d'Hist. Nat._ xvi. 245.
Reaum. ii. _t._ iii. iv. xiv. xxvi. xxvii. &c.
[166] PLATE XX. FIG. 18.
[167] PLATE XX. FIG. 23. Swamm. _Bibl. Nat. t._ iii. _f._ 7, 8. In a
specimen I opened of this insect the bristles converged so as to form
a kind of tail to the egg.
[168] Darwin _Phytolog._ 512.
[169] Geoffr. _Ins. Par._ i. 480. _t._ x. _f._ 1. _b. c._
[170] See above, VOL. I. p. 261.
[171] Reaum. iii. 386--. _t._ xxxii. _f._ 1. _t._ xxxiii. _f._ 5.
[172] I allude to _Ophion luteum_ F. (_Ichneumon_ L.) Vol. i.
Ed. 3. p. 269, figured PLATE XX. FIG. 22; and the _Hydrachnæ_ or
_Trombidia_. See above, and De Geer vii. 145.
[173] From this circumstance called πολυποικιλος σοφια by the
Apostle, _Ephes._ iii. 10.
[174] _Nat. Theol._ 11th Ed. 375.
[175] PLATE XX. FIG. 19. _a a._
[176] Reaum. iv. 376--. _t._ xxvii. _f._ 9, 10.
[177] _Hist. Nat. gen. et partic. des Crust. et Ins._ xii. 282.
[178] Reaum. iv. 381. _t._ xxvi. _f._ 19, 20.
[179] Roxburgh in _Linn. Trans._ vii. 34.
[180] Some of the _Noctuæ_ have similar eggs, as _N. Lappa._ Sepp iv.
_t._ iii. _f._ 1. _c._
[181] Reaum. _ubi supr. f._ 22, 23.
[182] PLATE XX. FIG. 6. 8.
[183] PLATE XX. FIG. 5.
[184] Ibid. FIG. 3. 4. 7. 9. &c.
[185] Ibid. FIG. 15.
[186] Bonnet _Œuvr._ ii. 9.
[187] _Naturf._ xiii. 229.
[188] _N. Dict. d'Hist. Nat._ xvi. 245.
[189] Reaum. ii. 286.
[190] PLATE XX. FIG. 11. Sepp _t._ iv. _f._ 2.
[191] Reaum. iv. 617.
[192] _Philos. Ent._ 76.
[193] See above, VOL. I. 358--.
[194] See above, VOL. I. Ibid.
[195] Young's _France_, ii. 34. This author asserts, that no art will
hatch the eggs of the common silk-worms the first year, or that in
which they are laid; but that there is a sort brought from Persia,
which are hatched three times a year, and which will hatch in fifteen
days in the proper heat. In 1765, it is said, the common sort hatched
in the first year. _Ibid._ 226--.
[196] In the _N. Dict. d'Hist. Nat._ xii. 564. the eggs of the
flesh-fly are said to hatch in two hours. This is true I believe in
very warm weather.
[197] Brahm. 310.
[198] Rimrod _Naturf._ xvi. 131.
[199] _Fourmis._ 69.
[200] De Geer vii. 195.
[201] Ibid. 196.
[202] Reaum. ii. 167.
[203] Brahm. 249. Rösel. iv. 130. Swamm. _Bibl. Nat. t._ i. _f._ 2.
[204] By Mr. White, jun. cordwainer at Ipswich.
[205] PLATE XX. FIG. 16. _a._
LETTER XXX.
_STATES OF INSECTS._
LARVA STATE.
The _Larva_ state is that in which insects exist immediately after
their exclusion from the egg (or from the mother in ovo-viviparous
species), in which they usually eat voraciously, change their skin
several times, and have the power of locomotion, but do not propagate.
Almost all larvæ, at their birth, are for a time in a very feeble
and languid state, the duration of which differs in different
species. In most it continues for a very short time, a few minutes
or perhaps hours, after which they revive and betake themselves to
their appropriate food. In others, as in the generality of spiders,
this debility lasts for seven or eight days, and in some species
even a month, during which the young ones remain inactive in the
egg-pouch[206], and it is not till they have cast their first skin
that their active state of existence commences.
All larvæ may be divided into two great divisions:--
I. Those which in general form more or less resemble the
perfect insect.
II. Those which are wholly unlike the perfect insect.
I shall begin by calling your attention to the characters of the
_first_ of these divisions: the second, which is by far the most
numerous, will be afterwards considered.
I. The _first_ division includes the larvæ of _Scorpions_, _Spiders_,
_Cockroaches_, _Grasshoppers_, _Lanthorn-flies_, _Bugs_, &c.; or
generally, with the exception of the _Flea_ and _Crustacea_, the
whole of the _Linnean_ Orders _Aptera_ and _Hemiptera_. All these
larvæ, however remotely allied in other respects, agree in the general
similarity which they bear to the perfect insects which proceed from
them. The most acute entomologist, untaught by experience, could
not even guess what would be the form of the perfect insects to be
produced from larvæ of the _second_ division, while they can recognise
the form of the spider, the cricket, the cockroach, the bug, and the
frog-hopper, in that of the larvæ. There are, however, differences in
the degrees of this resemblance, according to which we may, perhaps,
divide this tribe in their second state as follows:--
i. Those that resemble the perfect insect, except in the
relative proportions and number of some of their parts.
ii. Those which resemble the perfect insect, except that they
are apterous, or not yet furnished with organs of flight.
i. Spiders, _Phalangia_, scorpions, lice, _Poduræ_, sugar-lice
(_Lepisma_), mites, centipedes, millepedes, &c. come under the
_first_ subdivision. The larvæ of the first six tribes here mentioned
differ at their birth from the perfect insect, only in size and the
proportions of their parts. Thus the larvæ of spiders have their
legs of a different relative length from that which they subsequently
acquire; and the palpi in the males, which previously to the
discoveries of Treviranus were regarded as their sexual organs, are
not yet fully developed[207]: and a similar difference takes place in
the legs of _Phalangia_. The general form too of the body undergoes
slight alterations, and the colour very considerable ones, with each
change of the skin--a change to which all these tribes are subject.
The larvæ of the three last-mentioned tribes (the mites, centipedes,
and millepedes) differ from the perfect insect not only in the
proportion but also in the number of their parts. Leeuwenhoeck states
(and De Geer confirms his assertion, extending it to other species of
mites[208]), that the common cheese-mite, which in its perfect state
has _eight_ legs, when first excluded from the egg has but _six_, the
third pair being wanting[209]. Some however are born with _eight_
legs, for instance _A. eruditus_ of Schrank, which he saw come from
the egg itself with that number[210]. Others again have never more
than six legs: this is the case with Latreille's genera--_Caris_,
_Leptus_, _Atoma_, and _Ocypetes_ of Dr. Leach[211]. In the centipedes
(_Scolopendridæ_) and millepedes (_Iulidæ_) differences still more
remarkable, as I have stated in a former letter, have been observed
by De Geer; these animals, in their progress to the perfect state,
not only gain several additional pairs of _legs_, but also several
additional _segments_ of the body. This illustrious Entomologist found
that _Pollyxenus lagurus_ (_Scolopendra_ L.) was born a hexapod,
with but three segments and as many pairs of feet, but successively
acquired five additional segments with other appendages, and nine
more pairs of feet[212]. A species of millepede (_Iulus terrestris_
L.), which he also traced from its birth, and which begins the world
at first with only eight segments and six feet, by a successive
development at length acquires, in its perfect state, 50 segments
and not less than 200 feet[213]. The nature of these very singular
accretions, which Latreille and Mr. Wm. MacLeay have also observed
in the centipedes[214], seems not well understood. If, as is most
probable, though De Geer could not find any exuviæ[215], the larvæ
cast a skin before each change, they do not essentially differ from
the metamorphosis of other insects. The legs that these insects thus
acquire are affixed to the abdomen, the six that they set out with
being attached to the part representing the trunk, so that the former
may be regarded as analogous to the prolegs of caterpillars. These
animals therefore, as I have before intimated, invert the order of
Nature, and from _perfect_ degenerate into _imperfect_ insects.
ii. If you examine the _cockroach_, _cricket_, or _grasshopper_, in
different stages of their growth, you will find that the larva does
not vary essentially from the perfect insect, except in wanting wings
and elytra. The case is the same in almost all the Linnean genera
of the modern order--_Hemiptera_; and with _Raphidia_, _Termes_,
and _Psocus_, in the _Neuroptera_. Some of these, however, exhibit
slighter discrepancies in the proportion of some of their parts,
but without affecting the general resemblance. Thus the larvæ of
the common ear-wig have at first only _eight_, and subsequently
_nine_ joints to their antennæ, whereas the perfect insect has
_fourteen_[216]; and the forceps is quite different, resembling
rather two straight styles than what its name implies. In those
also of many bugs (_Coreus marginatus_ F. &c.), the joints of the
antennæ are of a shape dissimilar to that which obtains in the
perfect insect. In that of the common water-scorpion, the anal
air-tube, which is so long in the imago, is scarcely visible[217]. In
the _Cicada_ tribe, so celebrated for their song[218], neither the
larva nor the imago have the enormous thigh armed below with strong
teeth, the tibiæ terminating in a fixed incurved claw, probably for
the purpose of digging the holes into which they retire till they
disclose the fly, which distinguish the pupæ of some species, and is
particularly conspicuous in one commonly brought from China[219].
These often exhibit also other minor differences.
II. In treating of the second great division of larvæ, those that
are wholly unlike the parent insect,--which includes, with few
exceptions[220], the whole of the Linnean orders, _Coleoptera_,
_Lepidoptera_, _Hymenoptera_, _Diptera_, the majority of the
_Neuroptera_, _Coccus_ and _Aleyrodes_ in _Hemiptera_, and the genus
_Pulex_ in _Aptera_,--I shall advert to their characters, under
several distinct heads; and to avoid unnecessary circumlocution, I
shall in what follows wholly leave out of consideration the _first_
division already explained, and use the term _larvæ_ with reference
only to those of the _second_. The heads under which I propose to
treat of them are: The _substance_ of their body, its _parts_,
_shape_, or figure, _clothing_, _colour_. Also the _Economy_ or mode
of life of these creatures: their _food_, _moultings_, _growth_,
_age_, _sex_, and their preparations for assuming the _Pupæ_.
i. _Substance_, with the exception of the head and six fore-feet,
which are usually corneous, the exterior integument or skin of larvæ
is commonly of a membranous texture, and the body is of a much softer
consistence than in the perfect insect. In those, however, of some
_Staphylinidæ_ and other _Coleoptera_, the dorsal part of the three
first pieces, which represent the trunk of the perfect insect, is
hard and horny. Some also have their whole skin coriaceous, as the
tortoise-shell butterfly (_Vanessa polychloros_); and some few, as
the wire-worm (_Elater segetum_), and other _Elateres_, very hard.
I possess a very remarkable larva from Brazil, from the extreme
flatness of its body, and from its having cavities to receive its
legs when unemployed, probably living under bark, the skin of which
is still harder than that of the grub of the Elaters. Perhaps it
has to resist great pressure; and on that account is gifted with
this quality, so seldom to be met with in other kinds of larvæ.
The interior of the body of these animals is generally of a softer
consistence than in the perfect insect. Their intestines, and other
internal organs, are usually wrapped in a voluminous substance of
a fatty nature, which is regarded as analogous to the _epiploon_,
_omentum_, or _caul_, which envelops the viscera of quadrupeds, &c.,
and is called by Reaumur the _corps graisseux_. The use of this
general flexibility of larvæ is obvious; for, their bodies being
mostly long and narrow, a hard rigid covering would have been very
inconvenient, and a considerable impediment to their motions. When
a caterpillar is feeding, it has occasion to apply its body to any
part of the margin of a leaf so as to support itself by its prolegs,
and when moving it wants to give it all the curves that are necessary
to enable it to avoid obstacles, and thread its way through the
sinuous labyrinths which it must often traverse. On the other hand,
the hardness of the substance of its head affords a strong fulcrum
to the muscles which keep its powerful jaws in constant play. The
larvæ, indeed, of some _Diptera_ have a membranous head; but their
mandibles, which serve also as legs, are not grinders, but merely
claws, the muscles of which require less powerful support[221]. Under
this head it may be proper to observe, that generally larvæ are
opaque; but some, as those of ants, and a few _Lepidoptera_[222],
are diaphanous. That of _Corethra crystallina_ (_Tipula_ De Geer) is
so beautifully transparent as to resemble a piece of crystal, and
scarcely to be distinguished from the water in which it lives[223].
ii. _Parts._ The body of each larva consists of the _head_, including
its different organs, and of the _succeeding segments_, of which the
three first may usually be denominated the _trunk_, and have the
six anterior feet, when present, attached to their under side: the
remainder is the _abdomen_. The latter includes in some species a
variable number of membranous feet, as well as various appendages
affixed usually to its tail and sides. No larva is ever furnished
with wings[224]. Each of these greater divisions, and the organs
which they include, require separate consideration.
1. _Head._ This, as was lately observed, is exteriorly of a horny
substance, or at least harder than the rest of the body, in most
larvæ; and on this account, though rarely separated from it by any
visible distinct neck[225], is, if the larva be of a tolerable
size, distinguished at the first view. In those of many Dipterous
insects, however, the head is covered with the same flexible
membranous skin with the rest of the body, from which it is often
scarcely to be distinguished. In these, except that it contains the
organs of manducation, it wears no more the appearance of a head
than any other segment of the body, and scarcely so much as the last
or anal one. The head of these larvæ is also remarkable for another
peculiarity,--that it is capable of being extended or contracted,
and assuming different forms at the will of the insect: a property
which the head of no superior animal can boast. It is probable that
there is a considerable variety in the shape and circumstances
of the heads of larvæ; but since, with the exception of those of
_Lepidoptera_, they have had less attention paid to them than they
deserve (indeed in a vast number of cases, from the difficulty of
meeting with them, these variations, except in a few instances,
have not been described), I will here mention a few of the most
remarkable. The head of the young larva at its first exclusion from
the egg is usually the most dilated part of the body, but it does not
often continue so. In that of _Cicindela campestris_, however,--the
beautiful green beetle sometimes found in sandy banks,--and also
in several caterpillars of _Lepidoptera_, it is much larger than
any of the following segments[226], which, in conjunction with the
animal's formidable jaws, gives it a most ferocious appearance. In
some lepidopterous larvæ the head is of the same diameter with the
rest of the body, but in insects in general it may, I think, be
stated as less; and occasionally it bears no proportion whatever
to it. This is the case with the subcortical one from Brazil lately
mentioned. It is more commonly longer than broad; but in some, as in
the larvæ of carrion beetles (_Silphæ_), the reverse of this takes
place. Its shape varies from triangular to orbicular, the mouth of
the animal forming the vertex of the triangle. In some larvæ of
_Hemerobii_, however, the head is narrowest behind. That of the grub
of a gnat noticed above (_Corethra crystallina_) forms a kind of
sharp horn or claw, terminating the body anteriorly[227]. The contour
of the head of larvæ is usually intire and unbroken; but in the
caterpillars of some _Lepidoptera_, as the butterfly called the grand
admiral (_Vanessa Atalanta_), the Glanville fritillary (_Melitæa
Cinxia_), &c. it is divided into two lobes[228]. In the Brazil flat
larvæ it is trilobed, each lateral lobe being divided into three
smaller ones: in which circumstance it somewhat resembles the head
of some subcortical _Cimicidæ_. Although the part we are treating
of is generally without _horns_, yet in some tropical butterflies
of the tribe of _Nymphales_, it is singularly armed with them. Thus
_Papilio Anchises_ is distinguished, according to Madame Merian[229],
by two in the occiput, which it has the power of retracting. In
the purple highflier (_Apatura Iris_), a British species, the two
lobes of the head, I am informed, terminate behind in two horns; as
they do likewise in the brilliant _Morpho Menelaus_[230], the lobes
assuming the form of a pear, and the horn representing the stalk.
In a caterpillar I found amongst Mr. Francillon's larvæ, the head
is bilobed, with a very long recurving subcapitate subramose spine.
In _Satyrus Cassiæ_, the head is armed with three occipital stout
spines[231]. The larva of _Nymphalis Amphinome_ Latr. (_Limenitis_
F.) is crowned with a coronet of eight occipital stout acute spines,
the intermediate ones being the longest[232]; and that of _Morpho
Teucer_ has a similar coronet, consisting of only seven blunt _rays_,
seemingly, rather than spines[233]. With regard to the articulation
of the head with the trunk, it is generally by its _whole_ diameter;
but in some instances, only by a _part_ of it. This is the case with
one of a sphinx figured by Mad. Merian[234]; and I have another,
probably belonging to the nocturnal _Lepidoptera_ (_Phalæna_
L.)[235]. In both these, the head is vertical and triangular; and in
the latter (which is a remarkable creature, the tail itself being
more like a head, and furnished with what resemble two prominent
black eyes) the vertex of the triangle is considerably higher than
the back of the animal. Whatever may be the clothing of the body,
the head is usually _naked_. Sometimes, however, it is itself beset
with very small simple spines, as in the butterfly of the mallow
(_Hesperia Malvæ_); or with longer compound ones, such as are found
on the rest of the body. This is the case with one of a butterfly
named by Rösel _Papilio morsa_. The most common _colour_ of the head
of larvæ, where it differs from the rest of the body, is a darker or
lighter reddish brown, or piceous. This is particularly observable
in those of Coleopterous insects, but it is very commonly in other
tribes of the same hue. Sometimes, amongst the _Lepidoptera_, the
head is of a different colour from the rest of the body; especially
where a contrast renders it striking. I can show the caterpillar of
some insect, probably of the hawk-moth tribe (_Sphingidæ_), from
Georgia, remarkable for the length of its anal spine, in which the
body is black, and the head red: another has a white head and a
brown body. In the larvæ of some _Lepidoptera_, _Coleoptera_, and
_Diptera_, the head can be wholly or nearly withdrawn within the
first segment of the body. This may be readily seen in that of the
common glow-worm; and that of a small gnat (_Tipula replicata_
De Geer) withdraws it so completely that the anterior margin of
that segment closes the orifice, so that the animal appears to
have no head[236].--The parts of the head which require distinct
consideration are, the _eyes_, _antennæ_, and the _mouth_: consisting
of various organs, which will be specified. Some of these parts
and organs are peculiar to larvæ of one order, others to those of
another, and some are furnished with them all.
_Eyes._ The larvæ of many insects have no eyes. Those with antennæ
which terminate in a lamellated clava (_Scarabæus_ L.), and
capricorn beetles also (_Cerambyx_ L.), amongst the _Coleoptera_,
are without them, and probably several others; and amongst the
_Diptera_, all those with a membranous or variable head. Those of the
remaining orders, with the exception, perhaps, of some _Hymenoptera_
and _Lepidoptera_, are furnished with these organs; and in the
_Coleoptera_ all the predaceous tribes, as well as most of those that
are herbivorous or granivorous, and the Gnats and other Tipulidans
(_Tipulariæ_ Latr.) in the _Diptera_, are also distinguished by
them. In the larvæ of the dragon-flies (_Libellula_ L.), and other
_Neuroptera_, they are composed of many facets as in those of the
perfect insect, from which they differ chiefly in being smaller.
But in the other insects of this description they are simple, and
resemble those of the _Arachnida_, and many aptera. These simple
eyes vary in their number, in different genera and tribes, from one
to six on each side of the head. Thus the larva of _Telephorus_,
and the saw-flies, has only _one_[237]; that of _Cicindela three_,
the two posterior ones being large with a red pupil surrounded by
a paler iris, which adds to the fierce aspect of this animal; and
the anterior one very minute. Those of the tortoise-beetles also
(_Cassida_) have _three_[238]; of _Staphylinus, four_; of _Timarcha_
(the bloody-nosed beetle) _five_; of _Carabus_, and the _Lepidoptera_
in general, _six_. In the last they are of different sizes, and
generally arranged in a circle: in that of _Hemerobius_ there are
five in a circle, with one central one[239]. The appearance of
these globules, which are often not visible but under a powerful
lens, is so different from that of the eyes of a butterfly or moth,
or other perfect insect, that it has been doubted whether they
actually perform the office of _eyes_, but without reason. They
occupy the usual station of those organs, being situated in many
instances upon a protuberance which appears to incase them; and seem
of a construction closely analogous to that of the eyes of spiders,
and the _stemmata_ or _ocelli_ of _Hymenoptera_, which have been
satisfactorily proved to be organs of vision. In the larva of a moth
not yet ascertained to exist in this country, _Attacus Tau_, and
probably other species, the eyes, after the skin has been changed a
few times, are no longer to be seen[240].
_Antennæ._ Most larvæ are provided with organs near the base of the
mandibles, which from their situation and figure may be regarded
as antennæ. Fabricius has asserted that the larvæ of the saw-flies
(_Tenthredo_ L.) have no antennæ; but in this he was mistaken, for
though very short, they are discoverable in them, as he might have
learned by consulting De Geer[241]. In the majority of _Neuropterous_
larvæ, they almost precisely resemble those of the perfect insect.
In all the rest they are very different. The antennæ of Coleopterous
larvæ are usually either filiform or setaceous, consisting of four
or five joints, nearly equal in length. Those of Lepidopterous
larvæ are commonly conical, as are those likewise of _Chrysomela_
and _Coccinella_ &c. amongst the _Coleoptera_, and very short,
composed of two or three joints, of which the last is much thinner
than the first, and ends in one or two hairs or bristles. These
antennæ the larva has the power of protruding or retracting at
pleasure. Lyonnet informs us, that the caterpillar of the great
goat-moth (_Cossus ligniperda_) can draw the joints of its antennæ
one within the other, so as nearly to conceal the whole[242]. The
larva of the common gnat has two long incurved setaceous antennæ,
fringed with hairs at some distance from their apex, which consist
only of a single joint[243]. The greater number of Dipterous larvæ,
however, all indeed except the Tipulidans (_Tipulariæ_ Latr.), and
many belonging to the _Coleoptera_ and _Hymenoptera_ orders (as
those of _Curculio_, _Apion_, _Apis_, &c.), are wholly deprived of
antennæ. It is a general rule, that the antennæ of larvæ are shorter
than the same organs in the perfect insect, the tribe _Ephemerina_
perhaps affording the only example in which the reverse of this takes
place[244].
_Mouth._ All larvæ have a mouth situated in the head, by which they
receive their food, and furnished with one or more instruments for
the purpose of mastication and deglutition. These instruments, in all
the orders except _Lepidoptera_, some _Neuroptera_ and _Diptera_,
bear a general resemblance to the same parts in the perfect insect.
In larvæ of the Coleopterous, Lepidopterous, and Hymenopterous
orders, we can distinguish for the most part an upper and under lip;
two pairs of jaws answering to the mandibulæ and maxillæ; and two,
four, or six palpi[245]: and some of these instruments may be found
in most _Diptera_. Each of these parts require separate notice.
_Upper-lip_ (LABRUM). The mouth of almost all larvæ, except some of
the order _Diptera_, are provided with a distinct _upper-lip_, for
retaining their food during mastication. As the construction of this
part does not widely differ from that of the perfect insect, which will
hereafter be more fully described, it is only necessary to observe,
that it is usually a transverse moveable plate, attached posteriorly to
the nasus (_clypeus_ F.), and situated just above the mandibles[246].
_Upper-jaws_ (MANDIBULÆ). The most usual figure of these, which are of
a hard horny consistence[247], is that of two slightly concave, oblong,
or triangular plates, often at their lower extremity of considerable
thickness, and of very irregular form, the base of which is filled
with powerful muscles, and planted in the side of the mouth so as to
move transversely. The other extremity can be made to meet or diverge
like the claws of pincers, and are divided into one or more tooth-like
indentations, by means of which the food of the larva is cut[248].
This is their construction in the larvæ of all _Lepidoptera_, and in
many of those of the other orders. They frequently, however, assume
a different form, though their situation is always the same. Thus
in the larvæ of the capricorn beetles (_Cerambyx_ L.) and of other
wood-boring species, they are shaped like the half of a cone, the inner
sides of which, applying close to each other, form a pair of powerful
grindstones, capable of comminuting the hardest timber[249]. M. Cuvier
has observed, with regard to the mandibulæ of those of stag-beetles
(_Lucanus_), that besides their teeth at the extremity, they have
towards their base a flat striated molary surface; so that they both
cut and grind their ligneous food[250]. It seems to have escaped
him, that a similar structure takes place in many perfect insects of
the lamellicorn tribe, as I shall hereafter show you. In the larvæ
of the water-beetles (_Dytiscus_ L.), ant-lions (_Myrmeleon_ L.),
and lace-winged flies (_Hemerobius_ L.), they resemble somewhat the
forceps at the tail of an ear-wig, being long and incurved; and, what
is more remarkable, hollow and perforated at the end, so as to serve
as a channel for conveying into the larva's mouth the juices of the
prey which by their aid it has seized. Reaumur even asserts, that the
larva of _Myrmeleon_ has no other entrance into its throat than through
these tubular mandibles[251]. That of the rove-beetles (_Staphylinus_
L.), and of many other Coleopterous genera, have these organs of this
forcipate construction, without being perforated[252]. In the larva of
the carnivorous flies, and many other _Diptera_, are two black incurved
subulate parts, connected at the base, and capable of being protruded
out of, and retracted into, the head, through the skin of which they
are usually visible. As I informed you in a former letter[253],
these mandibles are used for _walking_ as well as _feeding_: they
are parallel to each other, and are neither formed for cutting nor
grinding like the mandibles of other insects, but merely detach
particles of food by digging into it and tearing the fibres asunder.
In this operation they are probably assisted by an acutely triangular
dart-like instrument of a horny substance, which in some species
(_Musca vomitoria_) is placed between the two. In others this part is
wanting. Some Dipterous larvæ have two similar mandibles, but instead
of being parallel, they are placed one above the other; others (_Musca
domestica_ and _meridiana_) have but one such mandible, and some have
no perceptible mandible of any kind. The mandibles of the larva of the
crane-flies (_Tipula_), which are transverse and unguiform, do not act
against each other, but against two other fixed, internally concave and
externally convex, and dentated pieces[254].
_Under-jaws_ (MAXILLÆ). These are a pair of organs, usually of a
softer consistence, placed immediately under the upper-jaws; but as
they are usually so formed and situated as not to have any action
upon each other, it is probable that in general they rather assist
in submitting the food to the action of the mandibulæ, than in the
comminution of it. In Lepidopterous larvæ they appear to be conical
or cylindrical (at least in that of the cossus so admirably figured
by Lyonnet[255]), and to consist of two joints; which may, I imagine,
be analogous to the upper and lower portions of which the maxillæ of
perfect insects usually consist. The last of these joints is surmounted
by two smaller jointed palpiform organs. If any part of the maxillæ can
act upon each other, it is these organs or palpi; but it is evident
they are not calculated for mastication, although they may assist in
the retention of the substance to be masticated. In a figure given
by Reaumur of the under side of the head of another lepidopterous
larva (_Erminea Pomonella_), the maxillæ consist of a single joint,
and appear to be crowned by chelate palpi[256]: a circumstance
which is also observable in that of a common species of stag-beetle
(_Lucanus parallelipipedus_), the weevil of the water-hemlock (_Lixus
paraplecticus_[257]), and other insects. In general the maxillæ of
larvæ are without the lobe or lobes discoverable in those of most
perfect insects, this part being usually represented by a kind of
nipple, or palpiform jointed process, strictly analogous to the
interior maxillary palpi of the predaceous coleoptera; but in most
of the lamellicorn beetles the lobe exists in its proper form[258],
as it does likewise in that of the capricorn-beetle before noticed
(_Callidium violaceum_[259]). In the former instance, it is armed with
spines or claws; but in the latter it is unarmed, and rounded at the
end. In the larva of _Cicindela campestris_, the base of the maxilla
runs in a transverse direction from the mentum, to which, as is usually
the case, it is attached. From this at right angles proceeds the lobe,
from the outer side of which the feeler emerges; and the inner part
terminates in an unguiform joint, ending in two or three bristles. The
structure in the larvæ of water-beetles (_Dytiscus_ L.) is different,
for they appear to be without maxillæ[260]; but the case really seems
to be, that these organs are represented by the first joint of what M.
Cuvier calls their _palpi_[261]; from which proceed the real palpi, the
interior one being very short, and consisting only of a single joint.
These maxillæ of larvæ were regarded by Reaumur and other writers as
parts of the under-lip, on each side of which they are situated; and
indeed, as well as those in the perfect insect, they form a part of
the same machine, being connected by their base with the mentum, which
is part of the labium, but they are clearly analogous to the maxillæ
of the imago. They are not to be found in the larvæ of many Dipterous
insects, and perhaps in some species belonging to other orders. In some
Neuropterous larvæ, as those of the _Libellulina_ MacLeay, the maxillæ
are of a substance quite as solid and horny as the mandibles, which in
every respect they resemble[262].
_Under-lip_ (LABIUM). Between the two maxillæ in the larvæ of most
of the insects under consideration is a part termed by Reaumur the
middle division of the under-lip, but which is in fact analogous to
the whole of that organ in the _imago_. This organ varies in shape,
being sometimes quadrangular, often conical, &c. Interiorly it is
frequently connected with a more fleshy protuberance, called the
tongue by Reaumur[263], and supplying the place of the _ligula_ in
the perfect insect. On each side of the apex of the under-lip is a
minute feeler, and in the middle between these in the _Lepidoptera_
and many others, is a filiform organ, which I shall call the
_spinneret_ (_Fusulus_), through which the larva draws the silken
thread employed in fabricating its cocoon, preparatory to assuming
the pupa state, and for other purposes[264]. This organ is found
only in those larvæ which have the power of spinning silk; that
is, in all _Lepidoptera_, most _Hymenoptera_, _Trichoptera_, some
_Neuroptera_, and even a _Dipterous_ insect[265]. This tube, Lyonnet
had reason to believe, is composed of longitudinal slips, alternately
corneous and membranous, so as to give the insect the power of
contracting its diameter, and thus making the thread thicker or
smaller. There is only a single orifice at the end, which is cut
obliquely, somewhat like a pen, only with less obliquity, and without
a point, the opening being below, so as to be conveniently applicable
to the bodies on which the larva is placed. Reaumur conceived that
this spinneret had two orifices; but Lyonnet ascertained this to be
a mistake, the two silk tubes uniting into one before they reach the
orifice. From the contractile nature of the sides and the form of the
orifice, combined with the power the insect has of moving it in every
direction, results the great difference which we see in the breadth
and form of the threads, some being seven or eight times as thick as
others, some cylindrical, others flat, others channelled, and others
of different thickness in different parts[266]. In the larvæ of many
_Diptera_ the under-lip is merely a small tubercle, which can be
protruded from the insect's mouth by pressure[267].
One of the most remarkable prepensile instruments, in which the art and
skill of a DIVINE MECHANICIAN are singularly conspicuous, and which
appears to be without a parallel in the insect world, may be seen in
the under-lip of the various species of dragon-fly (_Libellula_ L.).
In other larvæ this part is usually small and inconspicuous, and
serves merely for retaining the food and assisting in its deglutition;
but in these it is by far the largest organ of the mouth, which when
closed it entirely conceals; and it not only retains but actually
seizes the animal's prey, by means of a very singular pair of jaws
with which it is furnished. Conceive your under-lip (to have recourse,
as Reaumur on another occasion[268], to such comparison,) to be horny
instead of fleshy, and to be elongated perpendicularly downwards[269],
so as to wrap over your chin and extend to its bottom,--that this
elongation is there expanded into a triangular convex plate[270],
attached to it by a joint[271], so as to bend upwards again and fold
over the face as high as the nose, concealing not only the chin and the
first-mentioned elongation, but the mouth and part of the cheeks[272]:
conceive, moreover, that to the end of this last-mentioned plate are
fixed two other convex ones, so broad as to cover the whole nose and
temples[273],--that these can open at pleasure, transversely like a
pair of jaws, so as to expose the nose and mouth, and that their inner
edges where they meet are cut into numerous sharp teeth or spines,
or armed with one or more long and sharp claws[274]:--you will then
have as accurate an idea as my powers of description can give, of the
strange conformation of the under-lip in the larvæ of the tribes of
_Libellulina_; which conceals the mouth and face precisely as I have
supposed a similar construction of your lip would do yours. You will
probably admit that your own visage would present an appearance not
very engaging while concealed by such a mask; but it would strike
still more awe into the spectators, were they to see you first open
the two upper jaw-like plates, which would project from each temple
like the blinders of a horse; and next, having by means of the joint
at your chin let down the whole apparatus and uncovered your face,
employ them in seizing any food that presented itself, and conveying
it to your mouth. Yet this procedure is that adopted by the larvæ
provided with this strange organ. While it is at rest, it applies
close to and covers the face. When the insects would make use of it,
they unfold it like an arm, catch the prey at which they aim by means
of the mandibuliform plates, and then partly refold it so as to hold
the prey to the mouth in a convenient position for the operation of
the two pairs of jaws with which they are provided. Reaumur once found
one of them thus holding and devouring a large tadpole;--a sufficient
proof that Swammerdam was greatly deceived in imagining earth to be
the food of animals so tremendously armed and fitted for carnivorous
purposes. Such an under-lip as I have described is found in the tribe
of dragon-flies (_Libellulina_); varied, however, considerably in its
figure in the different genera. In the larva of _Libellula_ Fab.,
such as _Libellula depressa_, &c. it is of the shape above described;
so exactly resembling a mask, that if Entomologists ever went to
masquerades, they could not more effectually relieve the insipidity of
such amusements and attract the attention of the _demoiselles_, than
by appearing at the supper table with a _mask_ of this construction,
and serving themselves by its assistance. It would be difficult, to
be sure, by mechanism to supply the place of the muscles with which
in the insect it is amply provided: but Merlin, or his successor, has
surmounted greater obstacles. In the larva of the Fabrician _Æshnæ_
(_Libellula grandis_, &c. L.), this apparatus is not convex but flat:
so that, though it equally conceals the face, it does not so accurately
resemble a mask; and the jaws at its apex are not convex plates, but
rather two single conical teeth[275]. It is, as to its general shape,
similarly constructed in _Agrion_ Fab. (_L. Virgo_, &c. L.); but the
first joint is more remarkably elongated, the jaws more precisely
resemble jaws than in any of the rest, and are armed with three long,
very sharp teeth: between them also there is a lozenge-shaped opening,
through which, when the apparatus is closed, is protruded a circular
sort of nipple, apparently analogous to the ligula[276]. _Libellula
ænea_, L., which is the type of another tribe (_Cordulia_ Leach), has a
mask somewhat different from all the above, the jaws being armed with
a moveable claw and an internal tooth[277]. You will admire the wisdom
of this admirable contrivance, when you reflect that these larvæ are
not fitted to pursue their prey with rapidity, like most predaceous
animals; but that they steal upon them, as De Geer observes[278], as
a cat does upon a bird, very slowly, and as if they counted their
steps; and then, by a sudden evolution of this machine, take them as
it were by surprise, when they think themselves safe. De Geer says, it
is very difficult for other insects to elude their attacks, and that
he has even seen them devour very small fishes[279]. As these animals
are found in almost every ditch, you will doubtless lose no time in
examining for yourself an instance of so singular a construction.
_Feelers_ (PALPI). In the orders _Diptera_ and _Hymenoptera_ are
many larvæ in which these organs have not been certainly discovered;
yet Reaumur in that of a common fly (_M. meridiana_ L.) found four
retractile nipples[280] which seem analogous to them; and Latreille
has observed, that below the mandibles of those of ants are four
minute points, two on each side[281]: but in all other larvæ their
existence is more clearly ascertained. The _maxillary_ palpi vary
in _number_, many having _two_ on each maxilla and others only
_one_. In the perfect insect the former is one of the distinguishing
characters of the predaceous beetles (_Entomophagi_ Latr.), but in
the larvæ it is more widely extended; since even in the caterpillars
of _Lepidoptera_ the inner lobe of the maxilla which represents this
feeler is jointed, which is precisely the case with the beetles
just named. Cuvier has observed this circumstance in the larva of
the stag-beetle[282]; and it belongs to many other _Coleoptera_
that have only a pair of maxillary palpi in the perfect state. The
_labial_ palpi are always two, emerging usually one on each side from
the apex of the under-lip. With regard to the _form_ of the palpi,
those of the _Lepidoptera_ are mostly conical; in other orders they
are sometimes setaceous and sometimes filiform. Their termination
is generally simple, but sometimes the last joint is divided. They
are for the most part very short, and the labial shorter than the
maxillary. The latter never exceed _four_ joints[283], which seems
the most natural number; and the former are limited to _three_. Both
vary between these numbers, and _one_ joint. The joints, though
commonly simple, are sometimes branched. This is the case with one I
met with in considerable numbers upon the Turnip, in October 1808,
the second joint of the palpi of which sends forth near the apex an
internal branch. In the larva of the _Cossus_, as Lyonnet informs
us[284], the joints of the palpi are retractile, so that the whole of
the organ may be nearly withdrawn.
* * * * *
After thus describing the _head_ of larvæ, and its principal organs,
we must next say something upon the remainder of the body, or what
constitutes the
2. _Trunk and Abdomen_: which I shall consider under one article.
These are composed of several _segments_ or rings, to which the
feet and other appendages of the body are fixed. The form of these
segments, or that of their vertical section, varies considerably: in
many _Lepidoptera_, the wire-worm, &c., it would be nearly circular;
in others a greater or less segment of a circle would represent it;
and in some, perhaps, it would consist of two such segments applied
together. Their lower surface is generally nearly plane. Their most
natural _number_, without the head and including the anal segment, is
twelve: this they seldom exceed, and perhaps never fourteen. The three
first segments are those which represent the _trunk_ of the perfect
insect, and to which the six anterior legs when present are affixed. In
general, they differ from the remaining segments only in being shorter,
and in many cases less distinctly characterized; but in Neuropterous
larvæ, those of _Dytisci_, and some other _Coleoptera_, they are longer
than the succeeding ones, and pretty nearly resemble the trunk of the
animal in its last state. The surface of the trunk and abdomen will be
considered under a subsequent head; I shall not, therefore, describe it
here. The _conformation_ of the different segments varies but little,
except of the terminal one, or tail, which in different larvæ takes
various figures. In most, this part is obtuse and rounded; in others
acute or acuminate; in others truncate; and in others emarginate, or
with a wider sinus, and with intermediate modifications of shape which
it would be endless to particularize. In some, also, it is simple and
unarmed; in others beset with horns, spines, radii, and tubercles of
different forms, some of which will come under future consideration.
The parts connected with the trunk and abdomen which will require
separate consideration, are the _legs_, the _spiracles_, and various
_appendages_.
_Legs._ It may be stated generally that the larvæ of the orders
_Coleoptera_, _Lepidoptera_, and _Neuroptera_, have legs; and that
those of the orders _Hymenoptera_ and _Diptera_ have none. This must
be understood, however, with some exceptions. Thus the larvæ of some
_Coleoptera_, as the weevil tribes (_Curculio_ L.) have no legs,
unless we may call by that name certain fleshy tubercles besmeared
with gluten, which assist them in their motions[285]; while those
of _Tenthredo_ and _Sirex_ in the order _Hymenoptera_ are furnished
with these organs. At present I know no Dipterous larva that may be
said to have _real_ legs, unless we are to regard as such certain
tentacula formed upon a different model from the legs of other
larvæ[286]. Rösel has, I think, figured a Lepidopterous apode. No
Neuropterous one has yet been discovered.
The legs of larvæ are of two kinds; either horny and composed of
joints, or fleshy and without joints[287]. The first of these, as
I observed in a former letter[288], are the principal instruments
of locomotion, and the last are to be regarded chiefly as props and
stays by which the animal keeps its long body from trailing, or by
which it takes hold of surfaces; while the other legs, or where there
are none, the annuli of its body, regulate its motions. The former
have been commonly called _true legs_ (_pedes veri_), because they
are persistent, being found in the perfect insect as well as in the
larva; and the latter _spurious legs_ (_pedes spurii_), because they
are caducous, being found in the larva only. Instead of these not
very appropriate names, I shall employ for the former the simple term
_legs_, and for the latter _prolegs_ (_propedes_)[289].
The legs, when present, are always in number _six_, and attached by
pairs to the underside of the three first segments of the trunk. They
are of a horny substance, and consist usually of the same parts as
those of the perfect insect; namely, _coxa_, _trochanter_, _femur_,
_tibia_, and _tarsus_, suspended to each other by membranous ligaments:
these parts are less distinctly marked in some than in others. Thus in
the legs of a caterpillar, or the grub of a capricorn-beetle, at first
you would think there were only three or four joints besides the claw;
but upon a nearer inspection, you would discover at the base of the
leg the rudiments of two others[290], in the latter represented indeed
by the fleshy protuberance from which the legs emerge. In the larvæ of
the predaceous _Coleoptera_, the hip and trochanter are as conspicuous
nearly as in the perfect insect; and the tarsus, which still consists
of only a single joint, is armed with two claws[291]. In those of the
_Neuroptera_ order, in which all the joints are very conspicuous, the
tarsi are jointed, as well as two-clawed[292]. The legs of larvæ are
usually shorter than those of the perfect insect, and scarcely differ
from each other in shape, for they all gradually decrease in diameter
from the base to the apex. This is the most usual conformation of
them in Lepidopterous, Hymenopterous, and some Coleopterous larvæ,
(those of the capricorn-beetles are very short and minute, so as to be
scarcely visible,) in which they are so small as to be concealed by the
body of the insect[293]. In Neuropterous larvæ, however, and several
_Coleoptera_, as those of _Dytiscus_, _Staphylinus_, _Coccinella_, &c.,
they more resemble the legs of the perfect insect, the joints being
more elongated, and the femoral one projecting beyond the body[294].
You will find no other than true legs in most Coleopterous,
Neuropterous, and Hymenopterous larvæ. But those of the saw-flies
(_Tenthredo_ L.), and all caterpillars, have besides a number of
_prolegs_: a few Dipterous larvæ also, are provided with some organs
nearly analogous to them. These _prolegs_ are fleshy, commonly
conical or cylindrical, and sometimes retractile protuberances,
usually attached by pairs to the underside of that part of the body
that represents the abdomen of the future fly[295]. They vary in
conformation and in number; some having but one, others as many as
eighteen.
With regard to their _conformation_, they may be divided into two
principal sections: first, those furnished with terminal claws; and
secondly, those deprived of them. Each of which may be divided into
smaller sections, founded on the general figure of the prolegs, and
arrangement of the claws or hooks.
i. The prolegs of almost all Lepidopterous larvæ are furnished
with a set of minute slender horny hooks, crotchets, or _claws_,
of different lengths, somewhat resembling fish-hooks; which either
partially or wholly surround the apex like a pallisade. By means
of these claws, of which there are from forty to sixty in each
proleg, a short and a long one arranged alternately, the insect is
enabled to cling to smooth surfaces, to grasp the smallest twigs to
which the legs could not possibly adhere: a circumstance which the
flexible nature of the prolegs greatly facilitates[296]. Claws nearly
similar are found on the prolegs of some _Dipterous_ larvæ[297],
but not in any of those of the other orders. These last, however,
are seldom either so numerous, or arranged in the same manner, as
in caterpillars. When the sole of the foot is open, the claws with
which it is more or less surrounded are turned outwards, and are in a
situation to lay hold of any surface; but when the animal wishes to
let go its hold, it begins to draw in the skin of the sole, and in
proportion as this is retracted, the claws turn their points inwards,
so as not to impede its motion[298].
The prolegs with claws may be further divided into four different kinds.
1. In the larvæ of the great majority of butterflies and moths they
assume the form of a truncated cone, the lower and smaller end of which
is expanded into a semicircular or subtriangular plate, having the
inner half of its circumference beset with the claws above mentioned;
and, from its great power of dilating and contracting, admirably
adapted for performing the offices of a foot. Jungius calls these legs
_pedes elephantini_[299]; and the term is not altogether inapplicable,
since they exhibit considerable resemblance to the clumsy but
accommodating leg and foot of the gigantic animal he alludes to.
2. The larvæ of many minute moths, particularly of the Fabrician
genera _Tortrix_ and _Tinea_--those which live in convoluted leaves,
the interior of fruits, &c., as well as the _Cossus_, and some
other large moths,--have their prolegs of a form not very unlike
those of the preceding class, but shorter, and without any terminal
expansion; the apex, moreover, is wholly, instead of half, surrounded
with claws[300]; the additional provision of which, together with a
centrical kind of nipple capable of being protruded or retracted,
in some measure, though imperfectly, supplies the place of the more
flexible plate-like expansion present in the first class.
3. The third class is composed of a very few _Lepidopterous_ larvæ
which have their prolegs very thick and conical at the base, but
afterwards remarkably slender, long, and cylindrical, so as exactly to
assume the shape of a wooden leg[301]. These, as in the first class,
are expanded at the end into a flat plate: but this is wholly circular,
is surrounded with claws, and has also in the middle a retractile
nipple, as in the preceding class. In _Cossus_, at least in an American
species (_Cossus Robiniæ_), described by Professor Peck[302], the anal
prolegs have the claws only on their _exterior_ half.
4. The remaining description of unguiferous prolegs, if they may
not rather be deemed a kind of tentacula, are those of certain
_Diptera_, provided with no true legs; which differ from the three
preceding classes, either in their shape, or the arrangement of their
claws. In one kind of those remarkable larvæ, which from their long
respiratory anal tubes Reaumur denominates "_rat-tailed_," that of
_Elophilus pendulus_, there are fourteen of these prolegs, affixed
by pairs to the ventral segments, the twelve posterior ones of which
are subconical, and truncate at the apex, which is surrounded with
two circles of very minute claws, those of the inner being much more
numerous and shorter than those of the exterior circle; while the
anterior pair terminate in a flat expansion, and in shape almost
exactly resemble those of a mole[303]. The prolegs of the larvæ of
a kind of gnat called by De Geer _Tipula amphibia_, and of _Syrphus
mystaceus_ F., (_Musca plumata_ De Geer,) are nearly of a similar
construction, but in the last are armed with three claws only[304].
Long moveable claws also distinguish the singular prolegs before
described[305] of another gnat (_Tanypus maculatus_ Meig., _Tipula_
De Geer). The case-worms (_Trichoptera_ K.) and some others, have two
prolegs at the anus, each furnished with a single claw[306].
ii. The prolegs _deprived_ of _claws_ are found in the larva of the
Hymenopterous tribe of saw-flies (_Tenthredo_ L.), in those of some
_Lepidoptera_ (_Hepialus_ F. &c.), and in some few Coleopterous and
Dipterous genera. Those of the former are of the shape of a truncated
cone, and resemble the second class of unguiculate prolegs, except
in the defect of claws. In the latter they are a mere retractile
nipple-like protuberance, in some species so small as scarcely to be
perceptible. In all they aid in progressive motion; but it is by laying
hold of surfaces, and so enabling the body more readily to push itself
forward by annular contraction and dilatation, and not by taking steps,
of which all prolegs are incapable: to assist in this purpose the
protuberance sometimes secretes a gluten[307], which supplies the place
of claws. Some larvæ have the power of voluntarily dilating certain
portions of the underside of their body, so as to assume nearly the
shape and to perform the functions of prolegs. In a Coleopterous (?)
subcortical one from Brazil, before alluded to, there are four round
and nearly flat areas in each ventral segment of the abdomen, but the
last very little raised above the surface, and rough, somewhat like a
file; and besides these, the base of the anal segment has ten of these
little rough spaces, but of a different shape, being nearly linear,
placed in a double series, five on each side. Doubtless these may be
regarded as a kind of _prolegs_, which enable the animal to push
itself along between the bark and the wood[308].
In considering, in the next place, the _number_ and _situation_ of
the prolegs, it will contribute to distinctness to advert to these
circumstances as they occur in the different orders furnished with
these organs.
To begin with the _Lepidoptera_.--Lepidopterous larvæ have either
ten, eight, six, or two prolegs, seldom more[309], and never fewer.
Of these, with a very few exceptions, two are attached to the last
or anal, and the rest, when present, to one or more of the _sixth_,
_seventh_, _eighth_, and _ninth_ segments of the body: none are ever
found on the fourth, fifth, tenth, or eleventh segments.
1. Where _ten_ prolegs are present, as is the case in by far the
greatest proportion of Lepidopterous larvæ, there is constantly an
anal pair, and a pair on each of the four intermediate segments just
mentioned.
2. In caterpillars, which like those of a few species of the genera
_Sphinx_, _Pyralis_, and of the _Bombycidæ_, &c. have _eight_ legs,
they are placed in _three_ different ways. In those which have an
anal pair, the remaining six are in some fixed to the sixth, seventh,
and eighth; in others, to the seventh, eighth, and ninth segments. In
those which, like _Cerura Vinula_, and several other species of the
same family, have no anal prolegs; the whole eight emerge from the
sixth, seventh, eighth, and ninth segments.
3. The Hemigeometers, as _Noctua Gamma_, &c. have only _six_ legs:
namely, an anal pair, and two ventral ones, situated on the eighth
and ninth segments.
4. The larvæ of the Geometers (_Geometræ_ F.) have but _four_
prolegs; of which two are anal, and two spring from the ninth
segment. It should be observed, however, that the larvæ of
Hemigeometers, and even of some of those that have ten prolegs, where
the four anterior ones are much shorter than the rest, move in the
same way as the Geometers. This even prevails in a few where these
organs are all of equal length.
5. Many of the larvæ of _Tinea_ L. which live in the interior of
fruits, seeds, &c., have but _one_ pair of prolegs, which are
attached to the anal segment.
6. The larvæ of Haworth's genus _Apoda_ (_Hepialus Testudo_
and _Asellus_ F.), remarkable for their slug-like shape and
appearance, move by the aid of two lateral longitudinal pustule-like
protuberances, which leave a trace of a gummy slime in their course.
_Hymenoptera._--The larvæ of the different tribes of _Tenthredo_ L.,
almost the only Hymenopterous insects in which prolegs are present,
have a variable number of these organs; some sixteen, as the saw-fly
of the willow (_T. lutea_ L.), and this is the most numerous tribe
of them, including the modern genera, _Cimbex_ F., _Pterophorus_,
&c. Others have fourteen, as that of the cherry (_T. cerasi_ L.);
and many others with only nine joints to their antennæ. A third
class have only twelve, as that of the rose (_T. Rosæ_ L.), but
this contains but few species. The last class contains those that
have no prolegs at all, but only the six horny ones appended to the
trunk. Of this tribe, the caterpillars of which have a very different
aspect from the preceding, are those of the genus _Lyda_ F. (_T.
crythrocephala_ L.)[310]. Two of the prolegs are anal, and the rest
intermediate, and none are furnished with claws. This circumstance,
in conjunction with the greater number of prolegs, except in the
case of _Lyda_, will always serve as a mark to distinguish these
_fausses chenilles_, as the French call the larvæ of saw-flies, from
true _caterpillars_. The _dorsal_ prolegs of a species of _Cynips_
described by Reaumur have been before noticed.
_Coleoptera._--The larvæ of insects of this order are so little known
or attended to, that no very accurate generalization of them in this
respect is practicable. Many of them, in addition to their six horny
legs, have a proleg at the anus; which in many cases appears to be
the last segment of the abdomen, forming an obtuse angle with the
remainder of it, so as to support that part of the body, and prevent
it from trailing; and in some instances, as in _Chrysomela Populi_,
a common beetle, secreting a slimy matter to fix itself[311]. In the
larvæ of _Staphylinidæ_ this proleg is very long and cylindrical;
in that of _Cicindela_ it is shorter, and in shape a truncated cone
rather compressed; it is very short, also, in those of the _Silphæ_
that I have seen. In the wire-worm (_Elater Segetum_) it is a minute
retractile tubercle, placed in a nearly semicircular space, shut
in by the last _dorsal_ segment, which becomes also ventral at the
anus. This space is in fact the last ventral segment. This seems
characteristic of the genus[312]. From the underside of the body of
the common meal-worm (_Tenebrio Molitor_), at the junction of the two
last segments, when the animal walks, there issues a fleshy part,
furnished below with two rather hard, long, and moveable pediform
pieces, which the animal uses in walking[313]. In the larva of
another beetle, whose ravages have been before noticed, under the
name of the cadelle[314] (_Trogosita mauritanica_), a pair of prolegs
are said to be found under the anal segment; and in that of the
bloody-nose beetle (_Timarcha tenebricosa_), that segment is bifid.
That of the weevil of the common water-hemlock (_Lixus paraplecticus_
F.) exhibits a singular anomaly: prolegs occupy the usual station
of the true legs, being attached to the three segments representing
the trunk[315]. This insect, however, does not appear to use them
in moving. A pair in each of the twelve segments of the body are
found in the grub of another weevil (_Hypera Rumicis_ Germ.), the
nine last pair being the shortest, which all assist the insect in
walking[316]. But the greatest number of prolegs is to be found in
the Brazil subcortical larva lately mentioned. Besides the six horny
legs of the trunk, this remarkable animal has four prolegs on each
of the seven intermediate abdominal segments, and five on each side
of the base of the last, making the whole number of prolegs, if so
they may be called, amount to forty-four: a far greater number than
is to be found in any larva at present known. When I wrote to you
upon the motions of insects, I informed you that some larvæ moved
by means of legs upon their back[317], but I was not then aware that
any were furnished with them both on the back and the belly at the
same time. By the kindness of Mr. Joseph Sparshall of Norwich, a very
ardent and indefatigable entomologist, I am in possession of the
larva of _Rhagium fasciatum_, a timber-feeding beetle. This animal
on the ten intermediate segments of the underside of the body, which
in the centre form a fleshy protuberance, has on it a double series
of rasps, as it were, consisting each of two rows of oblique oblong
prominences; and on the seven intermediate _dorsal_ segments there
are also in the centre seven rasps of three or four rows each, of
similar prominences: so that this animal at the same time can push
itself along both by dorsal and ventral prolegs. It is worthy of
observation, that a pair of these rasps is between the second and
third pair of true legs.
_Diptera._--The larva of a little gnat, _Tipula stercoraria_ De
Geer[318] (_Chironomus_ Meig.?), drags itself along by the assistance
of a _single_ tubercle, placed on the underside of the first
segment of the body, which the animal has the power of lengthening
or contracting[319]. That of another beautiful _Chironomus_ (_C.
plumosus_), remarkable for the feathered antennæ of the male[320],
has _two_ short prolegs, or pediform but not retractile tentacula in
the same situation[321]. Others, as that of _Tanypus maculatus_,
&c. have _two pairs_, one attached to the anal and the other to the
first segment[322]. _Tipula amphibia_ De Geer in this state has _ten_
prolegs, placed by pairs on the fourth, fifth, eighth, ninth, and
tenth _dorsal_ segments[323]; and _Scæva Pyrastri_ F., one of the
aphidivorous flies, has not fewer than _forty-two_, arranged in a
sextuple series, seven in each row[324].
It may not be useless to close this long description of the _legs_ of
larvæ with a tabular view of them, founded chiefly upon these organs;
which afford very obvious marks of distinction.
I. Larvæ without legs.
i. With a corneous head of determinate shape (coleopterous and
hymenopterous _apods_--_Culicidæ_, some _Tipulidæ_, &c.
amongst the _Diptera_).
ii. With a membranaceous head of indeterminate shape (_Muscidæ_,
_Syrphidæ_, and other _Diptera_).
II. Larvæ with legs.
i. With legs only, and with or without an anal proleg
(_Neuroptera_, and many _Coleoptera_).
1. Joints short and conical (_Elater_, _Cerambycidæ_,
&c.).
2. Joints long and subfiliform (_Staphylinus_,
_Coccinella_, _Cicindela_, &c.).
ii. Prolegs only (many _Tipulidæ_, and some subcutaneous
Lepidopterous larvæ, &c.).
iii. Both legs and prolegs (_Lepidoptera_, _Tenthredinidæ_, and
some _Coleoptera_).
1. Without claws (_Tenthredinidæ_, &c.).
2. With claws (_Lepidoptera_, &c.).
I should next say something upon the spiracles, or breathing-pores,
or any other external apparatus for the purpose of _respiration_,
in larvæ; but I think it will be best to reserve the consideration
of these for a subsequent Letter. We will therefore conclude this
detailed description of their parts in their first state, with some
account of their other.
iii. _Appendages._ The generality of larvæ have no other
external organs than those already described; but in several
of them we observe various kinds of retractile ones and
others--protuberances--horn-like processes--rays, &c.; which, though
not properly coming either under any of the above _parts_, or under
the _clothing_ of these animals, yet require to be noticed. Upon
these I shall now enlarge a little.
You must have observed upon the back of the last segment but one
of the caterpillar of the silk-worm a horn-like process, rising at
first nearly perpendicularly, and then bending forward. A similar
horn, though confined in the genus _Bombyx_ to the silk-worm and a
few others, if we may believe Madame Merian, who, however, often
makes great mistakes, is found in the beautiful caterpillar of one
of the largest and finest moths that we know (_Erebus Strix_[325]),
the glory of the _Noctuidæ_, and in most of those of the hawk-moths
(_Sphinx_ F.) [_S. Porcellus_, _Vitis_, and a few others excepted; in
some of which, as _S. Labruscæ_, &c., this anal horn is replaced by
a gibbosity, and in others, as _S. Œnotheræ_, by a callous eye-like
plate[326]] in the same situation, but much longer[327], and
commonly curving backwards over the tail[328]. Sometimes, however,
as in _S. ocellata_ and _S. Stellatarum_, it is perfectly straight.
These organs towards the apex are horny, and often end in a sharp
point; nearer the base they are fleshy. They are without any true
joint[329], yet the insect can elevate or depress them at pleasure.
Under a lens, they usually appear covered with spinous eminences,
arranged like scales. The use of these horns is quite unknown:
Goedart fancies that they secrete a potent poison, and are intended
as instruments of defence; but both suppositions are altogether
unfounded. It has been remarked, that the body of those caterpillars
which have these horns, is firmer, and yields less to the touch
than that of those which have no such appendages[330]. The larva of
a small timber-devouring beetle (_Lymexylon dermestoides_ F.) has,
like the above caterpillars, a long horn, and in the same situation:
it has also a singular protuberance on the first segment[331]. Upon
some other caterpillars, as in _Bombyx Stigma_ F., a singular pair of
horn-like appendages arises from the back of the second segment of
the body, excluding the head. In a tawny-coloured one from Georgia,
with a transverse row of short black spines on each segment, these
horns are half an inch long, black, covered with spinous eminences,
rather thickest at the base, and terminate in a little knob. They
appear to articulate with the body at the lower extremity. I have
another species, black, with narrow longitudinal yellow stripes, in
which these horns are of equal thickness at base and apex, but with
the same terminal knob. _Danais Archippus_ has a pair of tentacula
at the head, and another pair, but shorter, at the tail; and _D.
Gylippus_ has, besides these, two in the middle of the body[332].
We are equally ignorant of the use of the upright horn found upon the
back of the fourth segment in the larva of some moths (_Noctua Psi_,
and _tridens_ F.) which is of a construction quite different from that
of those last described. It is cylindrical, slightly thinner at the
apex, which is obtuse, fleshy, incapable of motion, of a black colour,
and about two lines long. On the same segment, also, in the case-worms
(_Trichoptera_ K.) are three fleshy conical eminences, which the animal
can inflate or depress, so that they sometimes totally disappear,
and then in an instant swell out again. When retracted, they form a
tunnel-shaped cavity, varying in depth[333]. Reaumur conjectured that
these eminences were connected with respiration, and one circumstance
seems in favour of this conjecture, that this segment has not the
respiratory threads observable in the subsequent ones. Latreille
mentions certain fleshy naked eminences placed upon the ninth and tenth
segments of some hairy caterpillars, which, like those just mentioned,
the animal can elevate more or less. They are often little cones;
but when it would shorten them, the summit is drawn in, and a tunnel
appears where before there was a pyramid[334].
In a former Letter I gave you a short account of the remarkable
Y-shaped, as it should seem, scent-organs (_Osmateria_) of the
beautiful caterpillar of the swallow-tailed butterfly (_Papilio
Machaon_ L.), and others of the _Equites_[335]; I will now speak
of them more fully. That found in the former is situated at the
anterior margin at the back of the first segment, close to the head,
from which at first view it seems to proceed. At the bottom it is
simple, but divides towards the middle, like the letter Y, into two
forks, of a fleshy substance[336], which it can lengthen, as a snail
does its horns, to five times their ordinary extent, or retract
them within the stalk, so as wholly to conceal them. Sometimes it
protrudes one fork, keeping the other retracted; and often withdraws
the whole apparatus for hours together under the skin, and its place
is only marked by two tawny-coloured dots, so that an ordinary
spectator would not suspect the existence of such an instrument[337].
Unfortunately this larva is rare in this country, so that I can
scarcely flatter you with the hope of seeing this curious organ in
a living specimen[338], unless you choose to import a parcel of its
eggs from the south of Europe, where it is common. This you will
think rather a wild proposition; but why should not Entomologists
import the eggs of rare insects, as well as botanists the seeds of
rare plants? But if you will be satisfied with the dissection of a
dead specimen, I have several, done by the ingenious Mr. Abbott of
Georgia, in which this part is well exhibited[339].
Another small caterpillar, as it should seem, of a geometer, prepared
by the same gentleman, exhibits a pair of similar horns on the fifth
and sixth segments: in these the common base from which the fork
proceeds is very short and wide, and each branch grows gradually more
slender from the base to the apex, where it is involute. Whether
these are retractile, or whether they correspond with those of _P.
Machaon_ in their nature and use, cannot be ascertained from a dead
specimen: as they belong to a larva of a quite different tribe of
_Lepidoptera_, the probability is, that they essentially differ. Two
globose retractile vesicles issue from the ninth and tenth segments
of those of _Arctia chrysorrhea_, &c.[340]
A great number of Lepidopterous larvæ, particularly those which are
smooth and of a moderate size, have between the under-lip and fore-legs
a slender transverse opening, containing a teat-like protuberance of
the same construction as the furcate horn of the caterpillar of the
beautiful mountain-butterfly, _Parnassius Apollo_; and, like that, can
either be wholly retracted and concealed, or by pressure be extended
to the length of one of the legs. In some larvæ this part is of a
subhemispherical figure, generally single, but sometimes double. It is
commonly, however, more slender and conical; and when of this shape, it
is sometimes quadruple[341]. The use of this part is not very clearly
known: some have supposed it to be a second spinneret, and to be of use
in fabricating the cocoon; but it is more probable that it secretes
some other kind of fluid, and is connected with defence.
The singular organ in a similar situation, evidently for that
purpose, with which the puss-moth endeavours to annoy its assailants,
has been described in a former Letter, to which I refer you[342].
Bonnet, who was the first that discovered this organ, ascertained
that it might be cut off without injury to either larva or imago. He
also remarked in a caterpillar found in the wild succory (_Cichorium
Intybus_) another short, black, needle-shaped organ between the
conical part just described and the under-lip[343]. De Geer mentions
a remarkable fleshy horn-like style, which issues from the lower
side of the first segment, between the head and the legs of the
case-worms (_Trichoptera_): he does not describe it as retractile, or
it might be regarded as analogous to those of _Lepidoptera_ similarly
situated, that I have just noticed[344]. In that of the emperor-moth
(_Saturnia Pavonia_), there are perforated tubercles, which when the
animal is molested spirt forth a transparent fluid[345].
The horn-like appendage of the puss-moth (_Cerura Vinula_) is
situated at the tail of the insect, and is composed of two distinct
cylindrical diverging branches, each about four lines long, not
united at the base. Each of these is hollow, and includes a smaller
cylindrical piece, which can be protruded at pleasure, and withdrawn
again, as a pencil within its case; or, rather, as the horns of a
snail. The two outer horns are tolerably firm, moveable at their
base, and beset with black spines; the interior tentacula are
fleshy, moveable in every direction, and in full-grown larvæ of a
rose colour. The animal seldom protrudes them, unless in some way
disturbed; and frequently it approximates the two outer cases so
closely that they resemble a single horn. It appears to use these
inner horns, when protruded, as a kind of whip to drive away the
flies, especially the Ichneumons, that alight upon its body. When
touched in any place, it will unsheath one of them, and sometimes
both, and with them strike the place where it is incommoded[346]. A
similar organ is found in some other _Bombycidæ_, as _B. Tau_ and
_Furcula_ F. Reaumur mentions a caterpillar that to this kind of
tail added the resemblance of two ears, or two cylindrical bodies,
terminating in a point, which emerged from the first segment behind
the head[347]. In another observed by the same author, the legs were
replaced by a single horn, but which did not appear to send forth
an internal one: from the back of its fourth segment also emerged a
single conical or pyramidal fleshy eminence or cleft, terminating in
two points[348]. Some of the tropical butterflies also, as may be
seen in the figures of Madame Merian, have two diverging anal horns
instead of anal prolegs; but it does not appear that they incase
tentacula[349]. Wherever these caudal horns are found, the above
prolegs are wanting[350]. Two conical anal horns also distinguish
the caterpillar of one of the moths called _Prominents_, _Notodonta
camelina_; but these are not terminal, but on the back of the last
segment but one[351]. In that of another British moth, _N. ziczac_
F., there are three dorsal prominences, one near the anus, and two
more in the middle[352]. Some Geometers (_G. fuliginosa_, &c.) have
two erect horns on the eleventh segment, and others (_G. syringaria_,
&c.) two recurved ones on the eighth[353]. I must not here omit to
mention the curious hooks emerging from two tubercles on the back
of the eighth segment of the ferocious larva of that beautiful
tiger-beetle, the _Cicindela campestris_ L., not uncommon on warm
sunny banks. This animal with incessant labour, as we are informed
by M. Desmarets, digs a cylindrical burrow, to the enormous depth,
the size of the animal considered, of eighteen inches. To effect
this, it carries out small masses of earth upon its large concave
head; and having often occasion to rest in ascending this height, by
means of these hooks[354] it fixes itself to the sides of its burrow,
and, having finally arrived at its mouth, casts off its burthen.
When these insects lie in wait for their prey, their head, probably
in conjunction with the first segment of the body, accurately stops
the mouth of the burrow, so as to form an exact level with the
surrounding soil; and thus careless insects, walking over it without
perceiving the snare, are seized in a moment and devoured[355].
Another kind of appendage, which is found in some larvæ, is the organ
employed by them to carry the excrement; with which, instead of letting
it fall to the ground, they form a kind of umbrella to shelter and
probably conceal them. All the tortoise-beetles (_Cassida_ L.) have
instruments for this purpose, as well as an Indian genus (_Imatidium_
Latr.) very nearly related to them. This instrument is a kind of fork,
half as long as the body, consisting of two branches, growing gradually
smaller from the base to the summit, where they terminate in a very
fine point, of a substance rather horny, and attached to the body near
the anal orifice. They are armed on the outside with short spines,
from the base for about a third of their length. When this fork, as it
usually is, is laid parallel to the back, with its points towards the
head, the anal aperture points the same way. When the animal walks, the
fork points the other way, and is in the same line with the body, and
the anus assumes a prone position[356].
The larvæ of a genus of flies (_Volucella_ Geoffr.) remarkable for
inhabiting the nests of humble bees, are distinguished on their upper
side by six long, diverging, pointed, membranous radii; placed in a
semicircle round the anus[357]: what the particular use of these organs
may be, has not been conjectured. Another in my collection has only
four upper radii, but below the anus are two fleshy filiform tentacula.
One of a Tipulidan described by Reaumur, has also four upper teeth;
but instead of two subanal tentacula, has six[358]. The singular larva
of another of this tribe (_Chironomus plumosus_) has on the two
last segments four long, fleshy, filiform, flexible tentacula, often
interlaced with each other; which, according to the same illustrious
author, are used by the animal to fix its caudal extremity, like
the geometers, that the other end may be at liberty. Besides these
organs round the anus, it has also four other oval ones, of uncertain
use: not to mention the two prolegs, which M. Latreille thinks are
air-tubes[359]. Jointed anal organs are observable in other larvæ:
those in that of a saw-fly described by De Geer (_Lyda_ F.) consist
of three joints[360]; in that of _Hister cadaverinus_, a carnivorous
beetle, of two[361]. The larva as well as the pupa and imago of
_Ephemera_ is furnished with three long diverging multiarticulate
tails, which are probably useful as a kind of rudder to assist and
direct their motions. That of the smaller dragon flies (_Agrion_ F.)
is furnished with three long vertical laminæ, by moving which, as fish
do their tails, from side to side, the animal makes its way in the
water[362]. That singular one, also, with a hooked head, figured by
Reaumur, has a single swimming lamina, or fin, shaped like a fan, and
placed in a vertical position under the tail[363].
The whole circumference of the body in some coleopterous larvæ,--for
instance, in that of the tortoise-beetle lately mentioned,--is
surrounded with appendages like rays. These are sometimes simple, rough
with very short spinous points[364]; but I have a dipterous larva,
in which these radii themselves are beautifully pinnated by a fringe
of longish spines on each side. Reaumur has described the grub of a
beetle, the genus of which is uncertain, and which feeds upon the larva
of _Aleyrodes Proletella_, whose body is margined on each side by eight
triangular fleshy mammular processes, terminating each in a bristle,
which give it a remarkable aspect[365]. The curious scent-organs with
which the larva of _Chrysomela Populi_ is fringed have been before
fully described; and therefore I shall only mention them here[366].
In the larvæ of the lace-winged flies (_Hemerobius_), and ant-lions
(_Myrmeleon_), the anus is furnished with a small fleshy retractile
cylinder, from which proceeds the silken thread that forms the cocoon
inclosing the pupa[367]. Providence has many different ways of
performing the same operation. From the structure of the oral organs
of these animals, the silk could not conveniently be furnished by the
mouth; the Allwise Creator has therefore instructed and fitted them
to render it by a spinneret at the other extremity of the body.
The respiratory anal appendages of many Dipterous larvæ will be
fully described in a subsequent Letter: I shall therefore now only
further observe upon this subject, that although there is seldom any
alteration in the form of these appendages &c. in the same species,
the caterpillars of two moths (_Cerura Vinula_ and _Attacus Tau_),
however, are exceptions. The former, when young, has two hairy
projecting ear-like protuberances, which it entirely loses, as I have
myself observed, before it assumes the pupa; and the latter, in like
manner, after its third change of skin, is deprived of its bent
thorn-like points which attend it when young[368]. It is remarkable
that these last larvæ, when just excluded from the egg, are also
entirely destitute of these appendages; they soon, however, appear,
from slight elevations which mark their situation, and rapidly
acquire their usual form[369]. Changes of a similar kind, hitherto
unobserved, may probably take place in other species.
iii. _Figure._ I am next to consider the general figure or shape of
larvæ. All of them, with but few exceptions[370], agree in having a
body more or less constricted at intervals into a series of rings
or _segments_; usually in number, _twelve_; often nearly equal in
length, but sometimes in this respect very dissimilar[371]. The general
outline or shape of the body is extremely various: most frequently
it approaches to cylindrical, as in most of the caterpillars of
_Lepidoptera_, and of the Hymenopterous tribe of saw-flies (_Tenthredo_
L.). The next most common figure is that more or less oblong or oval
one, sometimes approaching to conical, found in many of the larvæ
usually called grubs; such as those of the weevil (_Curculio_ L.) and
of the capricorn (_Cerambyx_ L.), and other coleopterous tribes; of
bees, and all Hymenopterous insects but the saw-flies; and also of a
large number of flies (_Diptera_). In some the figure approaches to
fusiform, as in most of the moths of the Fabrician genus _Lithosia_.
In others, as in those of the water-beetles (_Dytiscus_, &c.), it
approaches to an obovate shape, being widest towards the head, and
terminating in a point at the anus. In others, again, it is linear; an
example of which is that of _Staphylinus_. Some are convex, and others
gibbous, above, and flat underneath; as those of _Silpha_, _Chrysomela_
and many other beetles. Others are flat, both above and below, and
depressed like a leaf; a remarkable instance of which has been before
noticed[372]. Some are very long, as those of most _Lepidoptera_;
others very short, as that of the ant-lion (_Myrmeleon_). Many other
peculiarities of form in individuals might be instanced; but a dry
enumeration of these would be of no great use to you. They can only be
advantageously learned by the study of good figures, and by watching
the actual metamorphosis of the singularly-formed larvæ that you meet
with.
Instead, therefore, of any further specification of individual forms,
I shall now endeavour to give you, as far as my own knowledge of them
and the information I can collect from other sources will enable me,
a larger and more general view of the kinds of larvæ; for analytical
inquiries lose half their value and importance unless we proceed to
apply them synthetically, by forming, if possible, into groups the
objects with which we are individually acquainted.
Partial attempts at a synthetical arrangement with regard to the
larvæ of _Lepidoptera_ and the saw-flies (_Tenthredo_ L.) have been
made both by Reaumur and De Geer. M. Latreille also has recently
given a _Tableau méthodique et général_ of articulated animals
furnished with jointed legs, considered in their first state[373].
The former of these is chiefly founded upon the number of the
prolegs, and the latter upon the metamorphosis, prolegs, habits,
head, and parts of the mouth, without any other notice of the
configuration. Mr. Wm. MacLeay, who, though young in years, is old in
science and critical acumen, has started a perfectly new hypothesis
upon this subject. In the progress of his inquiries into the natural
arrangement of animals, particularly of _insects_ in the _Linnean_
sense, he has been the first to observe, that the relation which
organized objects bear to each other is of two kinds; one of real
_affinity_, and the other only of _analogy_, or resemblance. This
important distinction, upon which I shall enlarge in a future Letter,
when I come to treat of Systems of Entomology, he has applied, in
a way quite original, to larvæ in general, but more particularly
to those of the _Coleoptera_ order. For the basis of his system he
assumes a relation of analogy between the _larvæ_ of Insects that
in the progress of their metamorphosis assume wings, and those that
do not, which form his class _Ametabola_, so that the prototypes
of the former shall be found amongst the latter[374]. But though
Mr. MacLeay appears to consider the analogy between these two as
_primary_, he extends it in a _secondary_ sense to the _Crustacea_,
at least in several instances[375]. Upon this occasion he very
judiciously remarks, that "in terming larvæ _Chilognathiformes_
or _Chilopodiformes_, it is not meant that they are _Scolopendræ_
or _Iuli_, or even near to them in affinity; but only that they
are so constructed that certain analogical circumstances attending
them strongly remind us of these _Ametabola_[376]." This remark you
will bear in mind while I am treating of this subject. It should
seem from another part of the same paragraph, that the comparison
which our learned Physiologist recommends, is between the _young_
of the _Ametabola_ and the larvæ of the corresponding groups of
_Coleoptera_. This must be understood to refer chiefly to the young
of the _Chilopoda_ and _Chilognatha_, since they approach nearer
to them in that state, having then only six legs; but the rest of
the _Ametabola_ should certainly be brought to this comparison in
their adult state: and even the two former orders in that state
more strongly resemble numerous coleopterous larvæ, than when they
are young and much shorter. I before called your attention to the
remarkable circumstance that contrasts very many larvæ of Hexapod
insects that become winged in their perfect state with adult
_Myriapoda_: namely, that in one the progress to this state is by
losing their prolegs and shortening their body; while in the other,
the reverse of this takes place, numerous prolegs and additional
segments being gained before they arrive at maturity[377]. As the
multiplication of organs is a sign of imperfection, it may be
affirmed of the former of these tribes, that their progress is
towards greater perfection; while that of the other may be called a
degradation. As larvæ may be regarded as a stepping-stone by which
approach is made from the apterous to the winged tribes of Insects,
it seems most consistent with general analogy that each should
connect with the other in that state in which the resemblance is
greatest. Now the _Myriapoda_ resemble larvæ, as we have just seen,
most when in their _adult_ state; therefore the comparison should be
between larvæ and adult _Myriapoda_.
Mr. MacLeay divides _coleopterous_ larvæ into five tribes thus
characterized:--
1. _A carnivorous hexapod larva, with an elongate linear flattened
body, having a large head armed with two sharp falciform mandibles,
and furnished with six granular eyes on each side._ This kind he
denominates _Chilopodiform_, as having for its type in the _Ametabola_,
_Scolopendra_ L. The examples he gives are _Carabus_ and _Dytiscus_.
2. _A herbivorous hexapod larva, with a long and almost cylindrical
body, so fashioned that the posterior extremity being curved under
the breast, the animal when at rest necessarily lies like an IULUS
on its side._ This tribe he denominates _Chilognathiform_, from
_Iulus_ L. His examples are, the larvæ of _Petalocerous_ insects, as
_Scarabæus_ L., _Lucanus_ L. &c.
3. _An apod larva, having scarcely the rudiments of antennæ, but
which is furnished instead of feet with fat fleshy tubercles; which,
when continued along the back and belly, give the animal a facility
of moving in whatever way it may be placed._ These he denominates
_Vermiform_, from certain of the _Vermes intestina_ and _Mollusca_ of
Linné which he has associated with his _Annulosa_[378]. His examples
are, _Curculio_ L. and _Cerambyx_ L.
4. _A hexapod and distinctly antenniferous larva, with a subovate
rather conical body, of which the second segment is longer and of
a different form from the others, so as to give the appearance
of a thorax._ His denomination for these is _Anopluriform_, from
_Pediculus_ L., forming Dr. Leach's _Anoplura_. His examples are,
_Coccinella_ and _Chrysomela_ L.
5. _A hexapod antenniferous larva of an oblong form, having like
the former vestiges of a thorax, besides two or more articulated or
inarticulated setaceous or corneous appendages to the last segment of
the abdomen._ This tribe he calls _Thysanuriform_, from _Lepisma_ and
_Podura_ L., forming M. Latreille's order _Thysanura_. His example is
_Meloe_ with a note of interrogation[379].
The system here stated, of naming and characterizing larvæ from the
resemblance and analogy, in many cases very striking, that they bear
to the apterous tribes, is a very happy and original one, and does
its author great credit; yet I think in some instances, as I shall
soon have occasion to point out to you, the application of it is
not so happy as the first idea. But this is always the case when a
new law of nature is discovered; the proper application of it is
gradually developed, and it does not at all detract from the merit of
the first discoverer, that all the bearings of such law do not strike
him as it were intuitively.
Having, however, got the vantage-ground afforded by this discovery
of my friend, let us see if by standing upon it we cannot get a
tolerable generalization of the larvæ of all orders of insects
that undergo a metamorphosis. But first I must observe, that as in
the perfect animals, so in their larvæ, the different groups are
connected by certain _transition_ species, exhibiting characters
common to two or more of them; and likewise that in many cases, which
you will see as we proceed, the analogy is as strong or stronger
between them and the _Crustacea_ (and in a few instances _Arachnida_,
and even _Mollusca_) than the _Ametabola_. My denominations,
therefore, will be taken from those tribes where the analogy appears
to me the most striking, and not from the _Ametabola_ alone.
I shall begin by drawing up for you a list of the Primary forms
that I seem to have observed, and their characters; and then going
through the orders, shall give you the examples of each, with such
observations upon them as the case may require.
_Primary Forms of Larvæ._
APTERA. ARACHNIDA. CRUSTACEA.
ANOPLURIFORM. ARANEIDIFORM. ISOPODIFORM.
THYSANURIFORM. ONISCIFORM.
CHILOPODIFORM. IDOTEIFORM.
CHILOGNATHIFORM. AMPHIPODIFORM.
STOMAPODIFORM.
MOLLUSCA. ANNELIDA. DECAPODIFORM.
BRANCHIOPODIFORM.
LIMACIFORM. VERMIFORM.
_Characters._
1. _Anopluriform._ Carnivorous; hexapod; antenniferous:
with a shortish oblong depressed body, and distinct
thoracic shield. Example: _Psocus_, _Coccinella_, most
_Hemiptera_[380].
2. _Thysanuriform._ Polyphagous; hexapod; antenniferous: body
with segments of trunk distinctly marked; anus often
furnished with setæ or mucro. Ex. _Meloe_[381]? _Thrips_,
_Aphis_.
3. _Chilopodiform._ Carnivorous; subhexapod; antenniferous: body
depressed, elongate, linear, with falcate acute mandibles,
a distinct thoracic shield, and an anal proleg. Ex.
_Cicindela_[382]? _Carabus_ L.
4. _Chilognathiform._ Herbivorous; body subcylindrical,
elongate, linear; no thoracic shield; often many prolegs,
sometimes a retractile one, and sometimes none.--Ex.
_Elater_, _Petalocera_, most _Lepidoptera_, _Tenthredo_
L.[383]
5. _Vermiform._ Polyphagous; apod or hexapod: with very short
legs; antennæ nearly obsolete; body fleshy, plicate, with
sides often plicato-papillose; no distinct thoracic shield.
Ex. _Curculio_ L., _Cerambyx_ L., _Musca_ L., and many other
_Diptera_[384].
6. _Araneidiform._ Carnivorous; hexapod: body very short;
mandibles long, suctorious; animal lying in wait for its
prey in a pitfall it has prepared; motion retrogressive. Ex.
_Myrmeleon_ L.[385] _Cicindela_?
7. _Isopodiform._ Saprophagous; hexapod; antenniferous, with
longer antennæ: body oblong; thoracic shield distinct; anus
styliferous or laminiferous. Ex. _Blatta_ L. _Silpha_ L.?
8. _Onisciform._ Herbivorous; polypod; antenniferous: body
short, oblong, depressed, margined. Ex. _Erycina_, _Lycæna_,
in the _Lepidoptera_, and some species of _Tenthredo_ L.[386]
9. _Idoteiform._ Subcortical; hexapod; antennæ obsolete: body
much depressed, with the last segment elongate, terminating
in three or more mucros. Ex. Larva from Brazil. Perfect
insect at present unknown.
I have placed this larva, which was described above[387], amongst
crustaceous forms, because of the remarkable resemblance which the
last segment of the body bears to that of the _Idoteidæ_; but I do it
with considerable hesitation, since in other respects its type seems
to be in the _Ametabola_. In its want of antennæ, very short legs,
and ventral asperities, it resembles some of the _Vermiform_ larvæ;
in its small head, distinct thoracic shield, and oblong shape, it
approaches the _Anopluriform_; and in its very depressed body, but
not at all in other respects, the _Chilopodiform_. At any rate, it
appears of a primary Type.
10. _Læmodipodiform._ Herbivorous; hexapod; antenniferous, with
long antennæ: body elongate, subcylindrical; second segment
of the trunk the longest; anterior pair of legs distant from
the other two. Ex. _Phasma_.
11. _Amphipodiform._ Herbivorous; hexapod; antenniferous, with
long antennæ: body shortish, compressed, saltatorious. Ex.
_Gryllus_ L.[388]
12. _Stomapodiform._ Carnivorous or saprophagous; hexapod;
antenniferous, with long antennæ: body elongate,
subdepressed, with raptorious hands, and abdomen wider than
the trunk; in aquatic species furnished with lateral gills.
Ex. _Mantis_, _Ephemera? Sialis?_
13. _Decapodiform._ Carnivorous; hexapod; antenniferous: body
elongate, narrow, convex, compressed, tapering towards the
tail; tail with natatorious laminæ. Ex. _Dytiscus_ L.,
_Agrion_ F.[389]
14. _Branchiopodiform._ Carnivorous?; aquatic; apod;
antenniferous: head distinct: body transparent, flexile,
furnished with a respiratory tube just above the tail. Ex.
_Culex_[390].
15. _Limaciform._ Herbivorous; apod, or with very short legs:
body ovate or obovate, slimy. Ex. _Apoda_ Haw., _Tenthredo
Cerasi_ L.
The above are the principal forms that appear to me _Primary_ (though
some doubt may rest upon the ninth and tenth); and probably others will
hereafter be discovered, since at present our knowledge of the larvæ
of most of the Orders is very limited. And now having given you this
generalization of them, as far as they are known to me, I shall next,
in a slight survey of those of the different orders, lay before you
what I have further to observe upon this subject.
_Coleoptera._ The _Anopluriform_ coleopterous larvæ, according to
Mr. W. MacLeay's view of them, include both those of _Coccinella_
L., _Chrysomela_ L., and _Cassida_ L.; but this appears to me to
admit of further consideration. With regard to the two former--those
of _Coccinella_ are carnivorous, those of _Chrysomela_ herbivorous;
the first is also usually more flat and depressed. As to the latter,
_Cassida_[391], it seems to me to belong to a peculiar type,
distinguished not only by its radiated margin, but by the remarkable
deflected anal fork on which it carries its excrement. At present I
know no analogous form amongst the apterous tribes; I must therefore
leave this without a denomination. Perhaps the larva of _Hispa_ or
_Alurnus_, when known, will throw light upon this subject. The larva
of _Endomychus_ agrees with that of _Coccinella_.
There are very few known larvæ that approach to a true
_Thysanuriform_ type in this order: that most celebrated is the
one supposed to belong to _Meloe_; but the claim of this to be so
considered, is, as we have seen, rather dubious. Should this point
at last be satisfactorily ascertained, it will probably carry with
it the whole tribe of vesicatory beetles. But even this animal in
its _general_ structure is _anopluriform_: the only circumstance
that gives it any analogy to the _Thysanura_ being its anal setæ.
Mr. William MacLeay is inclined to regard some of the larvæ of the
_Malacodermi_ Latr., but which of them he does not state, as probably
belonging to the tribe in question[392]. Those of _Lampyris_ and of
_Telephorus_, as described and figured by De Geer[393], appear to me
intermediate between the _Anopluriform_ and _Chilopodiform_ Types:
they have no anal setiform or styliform appendages, their mandibulæ
are falcate, and their habits seem carnivorous.
Examples of _Chilopodiform_ coleopterous larvæ are more numerous.
Of this description are those of _Gyrinus_, _Cicindela_, _Carabus_,
and _Staphylinus_. That of the first, indeed, appears to be the
most perfectly _Scolopendriform_ of any yet known; yet the gills
or respiratory laminæ, a pair of which issues from each abdominal
segment, and two pair from the last[394], prove that there is no
slight analogy between it, and indeed many other aquatic larvæ,
and the _Stomapoda_ amongst the _Crustacea_. A remarkable instance
of analogy with the _Decapoda_ of the same _Class_ is presented
by the larva of _Dytiscus_, &c. which Mr. MacLeay considers as
_Chilopodiform_, but which exhibits no other resemblance to
_Scolopendræ_ than in its predaceous habits and threatening aspect.
Its convex, compressed, tapering body, terminating in setæ or laminæ,
is certainly much more like that of a shrimp or a prawn; to which
the older Entomologists thought it was akin[395], and after which
they named it. As Mr. MacLeay's object was, to take all his forms
from the _Ametabola_, perhaps these larvæ will best fall in with his
_Chilopodiform_ type; though in the general form of their body they
most represent a section (_Lepisma_ L.) of the _Thysanura_.
_Chilognathiform_ forms are equally numerous in the Coleoptera with
the preceding. The wire-worm, or larva of _Elater Segetis_, as to
shape best represents the full-grown _Iulus_[396], and those of the
_Petalocera_ (_Scarabæus_ L., _Lucanus_ L.) the young one.
The most abundant of all forms in this order, is, I think, the
_Vermiform_, upon which I have nothing further to remark.
With regard to _Crustaceous_ forms in _Coleoptera_, besides the
_Decapodiform_ just noticed, I possess two specimens of larvæ of
_Silphidæ_ which seem to exhibit a considerable analogy with the
_Isopodous Crustacea_, one rather convex and the other flatter, so
as to give the idea of an _Armadillo_ and of an _Oniscus_.
_Strepsiptera._ Larva _Vermiform_.
_Dermaptera._ Larva _Thysanuriform_. Type _Podura_ or _Sminthurus_.
_Orthoptera._ Mr. MacLeay considers the larvæ of this Order as
primarily _Thysanuriform_[397], though he allows the resemblance
between them and _Amphipoda_ to be particularly striking[398]. For
my own part, their prototypes appear to me to be in the _Crustacea_,
and their analogical relations to the _Thysanura_ much more distant.
I trust this will appear to you the reverse of dubious in a progress
through the Crustaceous Orders. I begin with the _Isopoda_. Take the
larva of a _Blatta_, and place it between a _Lepisma_, or _Machilis_,
and an _Oniscus_, or _Porcellio_; you will find that in shape and
width, and the form of its anal styles, it resembles the latter
much more than it does the former, with which it possesses scarcely
any character in common, except its multiarticulate antennæ. It is
remarkable, that amongst the _Blattidæ_ we meet with species that
represent both the _Oniscidæ_ and _Armadillo_ or _Glomeris_[399], the
latter being more convex than the former. In their habits the Blattæ
certainly agree with _Lepisma_; and Dumeril, who thought the latter and
_Podura_ subject to a metamorphosis, imagined they were related[400].
The Spectres of Stoll (_Phasma_ F.) are so strikingly analogous
to another crustaceous tribe, the _Læmodipoda_, particularly the
genus _Caprella_, that Montagu gave one species the Trivial name of
_Phasma_[401]. The jumping _Amphipodiform_ Crustacea are represented
extremely well by _Gryllus_ L., and the _Stomapodiform_, particularly
_Squilla Mantis_, by _Mantis_. The resemblance in this last instance
is so very striking, that it cannot escape the eye of the least
intelligent observer. Orthopterous insects may perhaps one day
be discovered analogous to the two other crustaceous orders, the
_Decapods_ and _Branchiopods_; but at present I know of none of that
description.
_Hemiptera._ The larvæ of this order, which in general resemble the
perfect insect, except that they have no wings, seem most commonly to
belong to the _Anopluriform_ type[402]; but the _Aphides_, _Chermes_,
and _Thrips_ may, I think, be regarded as more analogous to the
genera _Podura_ and _Sminthurus_ in the _Thysanura_[403]. I have
some suspicion that the _Nepidæ_, _Naucoris_, and the remipedes,
_Notonecta_, _Sigara_, &c. may find their prototypes amongst the
_Crustacea_; but my confined knowledge of the latter does not enable
me to point to any individual genera or tribes that they may be
presumed to represent.
_Neuroptera._ As the kinds of larvæ of the different tribes
composing this order, as it now stands, are very various, it is to
be expected that the analogical forms they represent are equally
so. The _Libellulina_ MacLeay (whose metamorphosis that gentleman
has denominated _subsemicomplete_, a term warranted by their
losing in their perfect state the mask before described[404]) in
their oral organs, particularly by their galeate _maxilla_ and
distinct _ligula_[405], have some relation to the _Orthoptera_, the
prototypes of whose larvæ we have found amongst the _Crustacea_:
probably, therefore, those of the tribe in question lurk in that
class; a suspicion that receives strong confirmation from the larva
of _Agrion_[406], which in its tapering body and anal natatorious
laminæ represents a shrimp. The larvæ of that very peculiar and
distinct tribe, the _Ephemerina_, appear to be intermediate between
the _Stomapodiform_ and _Thysanuriform_ types. Their natatory
respiratory abdominal laminæ seem copied from the former, and their
anal diverging setæ from the latter[407]. The _Myrmeleonina_, as
well in their general form as in their motions and habits, present
a most singular analogy with the tribe of spiders, as does also in
some respect that of _Cicindela_. With regard to _Panorpa_, which
Mr. MacLeay remarks is related to _Myrmeleon_[408], and is a most
ferocious insect[409], as its larva has not yet been discovered,
nothing certain respecting its analogical form can be asserted; but
should it, like the male fly, represent the scorpion, both orders
of _Arachnida_ will have their representatives in the class we are
considering. The _Corydalina_, as far as the larva of _Hemerobius_
instructs us, is _Chilopodiform_, but with a tendency to the
_Araneidiform_ Type. The _Ametabola_ also furnish the prototype
of the next tribe, the _Termitina_, which, as is evident both
from _Psocus_ and _Termes_, are perfectly _Anopluriform_. The
_Sialina_, or _Plicipennes_ of Latreille, excluding _Trichoptera_
Kirby, appear to me to be intermediate between the _Chilopodiform_
and _Stomapodiform_ Types, and not without some relation to the
_Thysanuriform_. Their pediform, jointed, respiratory abdominal
appendages, their head and falcate mandibles, seem copied from
the first tribe. The same appendages considered as organs of
respiration, and their taper forks, are moulded upon the plan of the
_Stomapodiform Crustacea_, and the long seta which terminates the
abdomen is upon the _Thysanuriform_ plan[410].
_Trichoptera._ The larvæ of this order appear also to be constructed
upon a double plan. The respiratory threads observable in both the
upper and under sides of the abdomen connect it with the _Stomapoda_,
and its cylindrical elongate body with _Chilognathiform_ types in the
_Lepidoptera_[411].
_Lepidoptera._ The great majority of larvæ in this order are
_Chilognathiform_, but there are exceptions to this remark. Those
of the _Geometræ_ recede from this type, both in their motions and
the distance and number of their legs. In both these respects they
represent the _Læmodipoda_ in the _Crustacea_[412]. Other caterpillars
are _Onisciform_; and a third sort seem to leave the _Annulose_ type,
and imitate that of the _Mollusca_, and one is figured by Madame
Merian[413] which appears to tend even to the _Chilopodiform_ type.
_Hymenoptera._ In this order the larvæ of the saw-flies, _Tenthredo_
L., are in general _Chilognathiform_, though some are _Onisciform_,
others _Limaciform_, and those of _Lyda_ F. (_Cephaleia_ Jur.) and
_Sirex_[414] have a _Vermiform_ tendency, and are a stepping-stone to
those of the rest of the order, which are all _Vermiform_ and apods.
_Diptera._ The majority of this order may be set down as _Vermiform_,
though it is not improbable that some of them bear an analogy to
animals that appear far removed from the _Annulosa_. Thus, the larva
of _Stratyomis Chameleon_ seems to exhibit no small resemblance to
some of the _Polypi vaginati_ in the _Acrita_ subkingdom of Mr. W.
MacLeay[415]. That of _Culex_ and some others is constructed on a
quite different type from the rest, and seems to possess some analogy
to the _Branchiopod Crustacea_.
Though some of these analogies are more striking than others, yet
in almost all that I have stated there is that kind of resemblance
that could not be the result of what is called mere chance; and Mr.
MacLeay, by first pointing out this plan of the All-wise Creator,
and by laying down the doctrine of _analogies_ in general, as
distinguished from _affinities_ in the animal kingdom, has furnished
the believer with a new argument against those attacks of the
infidel, that would render null those proofs of the wisdom and
goodness of the Author of nature with which the animal and vegetable
creation furnish us; by affirming most absurdly, and under the
most stultifying blindness of mind, that the _creatures_ were in a
manner their own _creators_, their wants under local circumstances
stimulating them to efforts that in a long course of years produced
all the different forms and organizations that are now to be found
in our globe. The affinities and close connexion of beings with
each other, so that the ascent from low to high is usually by
the most gentle gradations, is the circumstance on which they
build this strange and impious theory. But the fact, that certain
animals of one tribe were created with a view to certain animals
of another, so as to present a striking aspect of correspondence,
parallel almost with that of type and antitype, without any real
affinity or approximation;--this triumphantly proves a Power above
and without them, who has associated them not only in a complex
chain of affinities, but has caused them to represent and figure
each other, even when evidently far removed, so as to give a mutual
correspondence and harmony to the whole, which could be produced only
by a Being infinite in power and wisdom, who made all things after a
general preconceived plan and system.
iv. We are now to consider the _clothing_ with which larvæ are
furnished. Many are quite naked, and smooth or rough only with granular
elevations or tubercles orderly arranged; but a very considerable
number, especially of the _Lepidoptera_ order, are clothed with hair
or bristles of different kinds, in greater or less abundance, and
arranged in different modes; and a proportion still smaller have their
skin beset with spines or a mixture of spines and hairs. Lyonnet found
that the hairs of the caterpillar of the great goat-moth (_Cossus
ligniperda_) were hollow, though not to the apex: probably this is the
case with those of other larvæ, as well as with their spines. In this
instance they were set, he observes, in a corneous ring, or very short
cylinder, elevated a little above the skin. The hair passes through
this ring, and appears to be rooted in a soft integument, which clothes
the skin within, and upon which the nerves form a reticular tissue,
some of which he thinks he has even seen enter the root of the hairs,
which perhaps are organs of touch[416].
Of the pilose larvæ, some, like most of those of the smaller moths
(_Geometra_, _Tortrix_, _Pyralis_, &c.), have merely a few scattered
short hairs, scarcely perceptible except through a lens: others
(_Odenesis potatoria_, _Lasiocampa Rubi_) are covered with down
more or less thick: in others (_Eriogaster lanestris_, _Lasiocampa
Neustria_) the hair is slenderer, and more like wool; the body of
two species which I purchased from the collection of Mr. Francillon
is covered with woolly hairs, so long as to give them the appearance
of a shock-dog; and Madam Merian has figured a similar one, which
she could not bring to the perfect state[417]. The hairs of many
_Bombycidæ_, known commonly by the name of _hairy caterpillars_, as
_Arctia erminea_, &c. are stiffer, resembling bristles; sometimes,
as in _Arctia chrysorhea_, mixed with shorter ones. The hairs either
spring immediately from the skin (_Noctua Aceris_, _leporina_), or,
as is more general, proceed only from certain tubercular elevations,
usually subhemispherical, but sometimes conical; of which a number
varying from four to twelve are found on each segment of different
species. They seem to issue from these tubercles, as little diverging
streams from the rose of a watering-pot. In both cases, they form
a coating usually so dense as to conceal the body, but sometimes
more thinly set, and admitting the skin to be seen more or less
between them. In a caterpillar of the beautiful _Arctia ocularia_,
the hairs are set upon tubercles alternately nearer the anterior and
posterior margin of each segment, so as to form a dense band, the
rest being naked; and in the lovely green and black one of _Saturnia
Pavonia_, each tubercle bears but six hairs, diverging like a star,
the central one being the longest and capitate, so that the chief
part of the body appears naked. This diverging position of the
hairs is most common in the thick-clothed larvæ also, but many have
them placed differently: thus, in those of _Callimorpha Caja_ and
_Arctia villica_[418] they are all directed towards the tail, like
the quills of a porcupine: in some others the anterior ones point
towards the head: in that of _Eriogaster Quercus_ half of the tuft
of hairs of each tubercle is directed downwards, the other half
upwards: in that of _Arctia Salicis_ all the hairs point downwards,
so that the belly is thickly covered, while the back is bare. Another
variation is, that the hairs of half the tubercle are sometimes
very long, while those of the other half are very short, and even
of a different colour[419]. In the larva of Tussuck moths (_Laria
pudibunda_, _fascelina_, &c.) the hairs are collected into tufts of a
singular appearance, those on the intermediate segments of the back
being quite level at the top, so as to resemble so many brushes;
while those on the first and last segments are longer, and composed
of feathered hairs converging to a point at their extremity, like a
common camel-hair-pencil[420]. This last mode of arrangement prevails
also in the larva of _Noctua Aceris_; but in this the pencils
are shorter, exactly wedge-shaped, and distinguished by another
particularity, that of springing directly from the skin, and not
from a tubercle. This is also the case with the large caterpillars
of _Odenesis potatoria_, which has a double row of short bundles of
black hairs on the back, intermixed with larger ones: at each end of
the body is a pencil of converging hairs, and the sides are spotted
with bundles of white ones, which with longer tawny ones are bent
downwards, so as to cover the sides of the creature[421]. Some have
the anterior aigrettes disposed like the arms of a cross, of which
the body of the caterpillar is the stem[422]. But not only is there
considerable variety in the general arrangement of the hairs that
clothe our little larvæ, the hairs themselves differ much in their
kind and structure, of which I will now, before I proceed to consider
spines, give you some account. Several of them are feathered like the
plumes of a bird: this is the case with those of _Morpho Idomeneus_,
on each segment of the body of which are three blue tubercles, like
so many little turquois beads, from each of which proceeds a long
black plume[423]. Other hairs terminate in a club; those of the larva
of _Noctua Alni_, a specimen of which I possess taken in England,
are flat and incrassated at the apex, something like the antennæ of
some _Sphingidæ_. Mad. Merian has figured the caterpillar of another
moth which feeds upon the Papaw-tree (_Carica Papaya_) with similar
hairs[424]. But the most remarkable larva for the shape of its hairs
is that of _Anthrenus Musæorum_, the little pest of our cabinets,
which I noticed in a former letter[425]. All the hairs of its body
are rough with minute points; but those of six diverging long tufts
or aigrettes, laid obliquely on the anal extremity of the body, which
the animal when alarmed erects as a porcupine does its quills, are
of a most singular structure: every hair is composed of a series
of little conical pieces, placed end to end, the point of which is
directed towards the origin of each hair, which is terminated at the
other extremity by a long and large conical mass, resembling somewhat
the head of a pike[426].
Besides the one lately mentioned, other caterpillars are rendered
striking by the brilliant colour of the tubercles from which their
hairs emerge. A remarkable instance of this is the thick large
caterpillar of a Bombyx, which feeds upon the _Psidium pyriferum_,
or white Guava, figured by Madame Merian. This caterpillar, which
is white, with transverse black stripes, and which has two singular
long converging curved bunches of hairs near the tail, is splendidly
adorned on each side with fifty red tubercles, shining like coral,
from which proceed six or seven long diverging hairs. Leeuwenhoeck
took these tubercles for eyes[427]. Another figured by the same
lady, who mistakes it, with her usual inaccuracy, for the larva of
a _Lygæus_ F., and which seems by her description to be between
the _onisciform_ and _limaciform_ types, has the apparently fleshy
mamillæ that project from its sides and back crowned with little
hairy red globes, which give the animal a most singular and unique
appearance[428]. Having thus described some of the principal modes in
which the All-wise Creator has decked and defended these creatures
with _hairs_, I shall next give you a short account of the _spines_
with which he has armed others. The spinous larvæ are principally
_lepidopterous_, and more particularly conspicuous in some tribes of
the genus _Papilio_ L., though some saw-flies and _Diptera_ are also
distinguished by them. _Vanessa Io_[429], _Atalanta_ and _Urtica_,
_Argynnis Paphia_, _Urania Leilus_, and many other Butterflies, &c.
are clothed with long sharp points, which claim the denomination
of spines, rather than that of hairs or bristles; being horny and
hard, and so stiff at the point as readily to pierce the skin. Those
of the last-mentioned species, Madame Merian says, are as stiff
as iron-wire[430]. They are sometimes entirely _simple_, and look
like spikes rather than spines, as in the caterpillar of _Nymphalis
Amphinome_ and _Morpho Menelaus_[431]; but ordinarily they are beset
with _hairs_, or more commonly with shorter spines, which often give
them the appearance of plumes, as in _Urania Leilus_ just mentioned:
sometimes these lateral spines are so long as to have the appearance
of a branch of a tree; this is strikingly the case with a small
caterpillar which Captain Hancock brought from Brazil; its body is so
thickly planted with spines of this description, that it absolutely
wears the appearance of a forest or thicket in miniature. A singular
circumstance attends the spines of this species: in many cases a
smaller and very slender hair-like spine issues from them, resembling
a sting; and this accounts for an observation of Abbott's, that many
American caterpillars _sting_ like a nettle, raising little white
blisters on the skin when accidentally or slightly touched[432].
Lewin has described the caterpillar of a moth found in New Holland,
which he names _Bombyx vulnerans_, that, like these Americans, has
also the power of wounding, but in a different way. It darts out,
he says, when alarmed by the approach of any thing, from as many
knobs or protuberances in its back eight bunches of little stings,
with which it inflicts a very painful and venomous wound[433].
The caterpillar of _Papilio Protesilaus_ F., if Madame Merian's
account and figure of it are correct, has its body armed with hairy
spines, the extreme point of which is surmounted by a star-shaped
appendage[434]. Those of a few saw-flies (_Tenthredo Pruni_ L.), and
another figured by Reaumur[435], are covered with a little forest of
spines without lateral branches, but divided into a fork at the apex.
Some spines are merely rough, with very short points, as those round
the head, which give so terrific an appearance to the caterpillar
of the _Bombyx regalis_, of some proceedings of which I gave you an
account in one of my former letters[436].
I must now say something upon the _arrangement_ of these spines.
Though in a few instances so thickly set as entirely to conceal
the body of the animal, as in the case of the Brazil one lately
mentioned, yet generally speaking, even when they are most numerous,
they permit the skin to be distinctly seen. Their arrangement is
various, though always orderly: in the majority they are planted
singly, but in some caterpillars in bundles. In that of _Saturnia
Io_, on each segment there are six bundles of longish, quill-shaped,
sharp, slender, diverging spines, which also appear to sheath aculei.
Madame Merian has figured this larva, or one very near it, as the
grub of a _Euglossa_[437], with which, though she affirms she traced
it to the fly, it can have no connection. With regard to _number_,
some larvæ have only four spines on each segment; others five, others
again six, and others seven, or even eight: they are planted on the
sides and back only, never on the belly. They are often more numerous
on the intermediate than on the anterior and posterior segments;
but sometimes the reverse of this takes place; in that of _Attacus
Erythrinæ_ only the head and tail are armed with spines, the rest of
the body being without any[438]; and in that of _Morpho Teucer_ there
is only a single spine on the four intermediate segments[439]. They
are usually all nearly of equal length; but in some cases those of
the head and tail are much longer than the rest, and remarkably so
in the caterpillar of _Urania Leilus_, also beautifully plumose, and
gracefully waved[440]. Those in the second and third segments are
much longer than any of the rest in that of _Bombyx regalis_; which
circumstance gives it the terrific appearance lately alluded to. In
the family to which _Argynnis Paphia_ belongs, the larva is adorned
with two on the back of the first segment twice as long as the rest,
and resembling at first sight two antennæ.
The spines, as well as the hairs of the new skin, are concealed
under the old one, and not incased in its spines; but Bonnet
ascertained, that if cut off very closely, the larva sometimes died
in consequence, whilst no such result followed a similar operation on
hairy larvæ. We learn from Reaumur[441], that some spinous larvæ of
saw-flies (_Tenthredo_ L.) lose their spines at the last change of
their skin; and from Madame Merian, that that of _Attacus Erythrinæ_
before mentioned loses also at the same period the six tremendous
black spikes that arm its black and yellow larvæ. The grubs of ants
that are destined to pass the winter in the larva state are hairy,
but are not so in summer[442]. The spines found in the grubs of some
gad-flies (_Œstrus_ L.) are of a different kind from those above
described, being very minute triangular flat plates, arranged in
different and contrary directions[443], and serving the insect merely
to change its place and fix itself[444].
Two other kinds of clothing, if so they may be called, neither
coming under the description of _hairs_ nor _spines_, are found
in some other larvæ, not only amongst the _Lepidoptera_, but also
in some of the other orders. _Nymphalis Populi_ and others of the
same family have larvæ furnished on the back of each segment with
cylindricoconical processes of a fleshy substance, obtuse at the apex
and surrounded with capitate hairs. In that of _N. Sybilla_, which
has on each segment two fleshy protuberances, they are bifurcate or
trifurcate, and also encircled at the base with a hairy tuft[445].
Others, as those of _Melitæa Artemis_, _Cynthia_, &c. have each
segment beset on the back with from seven to nine fleshy, pubescent,
wedge-shaped protuberances; two larger ones projecting over the
head. Under this head, too, may be noticed, the glutinous secretion
which clothes the grub of _Cionus Scrophulariæ_, a little weevil;
and of _Tenthredo Cerasi_ L. a saw-fly, and that waxy or powdery
substance which transpires through the skin of the larvæ of several
_Aphides_, _Chermes_, _Cocci_, _Hylotoma ovata_ F., &c. The _Aphis_,
whose extensive ravages of our apple-trees (_A. lanata_) were before
described to you[446], is covered and quite concealed by this kind
of substance, so that the crevices in the bark which they inhabit
look as if they were filled, not with animals, but with cotton. The
insect, also, that forms those curious galls produced upon the spruce
fir, and which imitate its cones (_Chermes Abietis_ L., _Aphis_ De
Geer) secretes a similar substance. In these and other cases of the
same kind, this matter seems to be, if I may so speak, wire-drawn
through numerous pores in certain oval plates in the skin, more
depressed than the rest of the back, arranged regularly upon the
segments, and exhibiting minute tuberosities. When young, these
animals have more of this secretion than when more advanced: it then
hangs from their anal extremity in locks[447].
But the insects most remarkable for a covering of this nature are
those _Coccidæ_ of which Bosc has made a genus under the name of
_Dorthesia_. De Geer is the first author that notices them, and has
given a description and figure of one species under the name of
_Coccus floccosus_[448]. It was discovered by Modeer upon some sere
fir-leaves in a thick bed of moss. Panzer has figured a second found
upon _Geranium sanguineum_, which from the figure appears distinct
from De Geer's, under the name of _Coccus dubius_[449]. Fabricius
regards this as synonymous with the _Dorthesia characias_ of Bosc,
inhabiting _Euphorbia characias_ in South Europe[450]. Olivier found
a species upon the bramble[451]. I once took one, which appears to
differ in some respects from the preceding species, upon _Melampyrum
cristatum_, and our indefatigable friend Mr. Sheppard has sent me
another, on what plant found I do not remember, which does not agree
with any that I have mentioned. The body of the animals of this genus
is covered by a number of cottony or waxy laminæ which partly cover
each other, and are arranged usually in a triple series: in De Geer's
figure the series appears quadruple, the lateral ones being placed
obliquely. The anterior one in my specimen covered the head, and
they are all canaliculate. Above the anus are four diverging ones:
the whole are of the most dazzling whiteness. When these laminæ are
removed, the body appears divided into segments.
With respect to those larvæ which imitate slugs by the viscid
covering that besmears them and issues from their pores, we learn
from Professor Peck that this exudation takes place as soon as they
are hatched; that the animal retains its humidity although exposed
to the fiercest heat of the sun, and that at the last moult the
skin becomes quite clean, and free from all viscidity[452]. It is
probable that the other limaciform larvæ are similarly circumstanced.
Madame Merian has figured an _onisciform_ one, the legs of which, she
says, are covered with a viscid skin: this produced a _Noctua_. Those
of _Papilio Anchises_ also are slimy, and adhere to each other[453].
v. Amongst other qualities which attach to larvæ, we must not
omit to say something concerning their _Colour_. For though those
which live in darkness, in the earth, in wood, in fruits, &c. are,
with few exceptions[454], of an uniform whitish colour, yet such
as are exposed to the influence of the light are usually adorned
with a vast variety of tints, sometimes the most vivid that can be
imagined. That the white colour of the former may be attributed to
the absence of light is proved by an experiment of M. Dorthes, who
having forced some to live under glasses, exposed to the light, found
that they gradually became brown[455]. To attempt any classification
of coloured larvæ would be in vain, since they are tinged with
almost every possible shade that can be conceived, of many of which
it would be difficult to find examples elsewhere; and infinitely
diversified as to the arrangement and figure of their multiform
markings and spots. A few general remarks, therefore, are all that
you will expect on this head. Many are of one uniform colour; while
a variety of tints, very different, and very vivid and distinct,
ornament others. Sometimes they are distributed in longitudinal rays
or bands, at others in transverse ones. Sometimes they are waved or
spotted, regularly or irregularly; at others they are sprinkled in
dots, or minute streaks, in every possible way. Various larvæ are
of the colour of the plant on which they feed, whence they are with
difficulty discovered by their enemies. Thus, a large proportion of
_Lepidoptera_ are green of different shades, sometimes beautifully
contrasted with black bands; a circumstance which renders the
caterpillars of two of our finest insects of this order as lovely as
the fly: I mean that of _Papilio Machaon_ and _Saturnia Pavonia_.
Very frequently the larvæ of quite different species resemble each
other so exactly, in colour as well as shape, as scarcely to be
distinguishable: this sometimes takes place even where they belong
to different genera, as in those of _Bombyx versicolor_ a moth, and
_Smerinthus Populi_ a hawk-moth. And it sometimes happens, very
fortunately for distinguishing allied species, that where the perfect
insects very nearly resemble each other, the larvæ are altogether
dissimilar. Thus, the female of _Pieris Rapæ_ is so much like the
same sex of _Pieris Brassicæ_, that it might be taken for a variety
of it, did not the green caterpillar of the one, and the spotted one
of the other, evince the complete distinction of these butterflies.
_Noctua Lactuca_, _N. umbratica_, and several other species of the
same tribe, which includes _N. Absinthii_, _Verbasci_, _Chamomillæ_,
_Abrotani_, are so extremely alike, that the most practised eye
can scarcely discover a shade of difference between them, though
their larvæ in colour and markings are constantly distinct[456].
The markings of species belonging to the same family are usually
different; but in some cases the latter may be prejudged from the
former. The larvæ of many of the genus _Sphinx_ L., for example,
have their sides marked by oblique streaks running from the back
in a direction towards the head; and by this last circumstance
they are distinguished from those of _Bombyx versicolor_, _Attacus
Tau_, and others of the same tribe, which have also lateral oblique
striæ, but running from the back towards the tail[457]. The colours
of individual larvæ of the same species are usually alike, but in
_Sphinx Elpenor_ and some others they vary exceedingly. Many, like
those of _Lasiocampa Rubi_, _Saturnia minor_, &c., are of one colour
when first disclosed, and assume others quite different in riper age.
Just previously to _changing their skin_, the tints of most larvæ
become as dull and obscure, as they are fresh and vivid when the
change has fully taken place; and in some instances the new skin is
quite differently marked from the old one. This is remarkably the
case with the last skin of some of the larvæ of the genus _Tenthredo_
L., which is entirely different from all the preceding ones. As
people when they advance far in years usually become more simple
in their dress than when they were young, so the larvæ in question
change an agreeably variegated skin for one of a uniform and less
brilliant colour[458]. Madame Merian has observed with respect to
_Attacus Erythrinæ_, that its caterpillar is at first yellowish,
with nine black striæ on each side: when arrived at one third of its
size, they become orange; the striæ are obliterated, and in their
place a round black spot appears on each of the eight intermediate
segments[459]. Mr. Sheppard has remarked to me, that the skin of that
of _Sphinx Ligustri_, after being under ground four days, was changed
from a vivid green to a dull red. Very rarely, however, it becomes of
a more brilliant hue just before entering the pupa state: thus, that
of another hawk-moth (_Smerinthus Tiliæ_) changes to a bright violet;
and the yellow hairs of that of _Laria pudibunda_ then become of a
lovely rose colour. And here I may observe, that the hairs and spines
also, of larvæ, vary greatly in colour. They are to be met with
brown, black, red, yellow, violet, white, &c. De Geer found, that
in the larva of _Cimbex nitens_ the two sides of the body were of a
different colour, the left being of a deep green, whilst the right
side and the rest of the body were paler[460]; but as he saw only
a single individual, this was probably an accidental circumstance.
Though the caterpillars, as I lately said, of one of the most
beautiful butterflies and moths that inhabit Britain contend with
the perfect insect in loveliness, yet in general no judgement can be
formed of the beauty of the future fly from the colour of the larva;
and the young Aurelian must not flatter himself always with the hope,
because the caterpillar excites admiration by its colours and their
arrangement, that the butterfly or moth it is to produce will do the
same; nor ought he to despise and overlook a sombre or plain-coloured
individual of the former, under the idea that it will produce one
equally plain of the latter, for it often happens that the splendid
caterpillar gives a plain butterfly or moth, and _vice versâ_. De
Geer, however, gives us two instances of conformity between the
colours of the caterpillar and those of the future moth; the one is
that of the common currant-moth (_Phalæna G. grossulariata_ L.),
the caterpillar of which is white, ornamented with several black
spots varying in size. At the two extremities it is yellowish, with
a longitudinal ray of the same colour on each side, the head and
legs being black. These colours are all to be found in the fly, the
ground of its wings being white ornamented with many black spots of
different sizes. Its upper wings are traversed by a yellowish band;
and towards their base is a spot of the same colour. Its body is
yellowish, with black spots; but the head and legs are black[461].
The other is that of a green caterpillar, which gives a green moth,
figured by Reaumur (_Pyralis prasinaria_ Fab.)[462]. Sometimes, also,
the sex of the future perfect insect may be predicted from the colour
it exhibits in its first state: thus, the brown caterpillars of
_Noctua Pronuba_ produce males, and the green ones females[463]. The
sexes, also, of _N. exoleta_ and _Persicariæ_ differ in that state.
vi. To the full account of the _Food_ of insects given in a former
letter[464], which had reference chiefly to their larva state,
it is only necessary in this place to add a few particulars not
there noticed. Many larvæ when first excluded, as those of _Pieris
Cratægi_, &c. devour the shells of the eggs from which they have
proceeded[465]; and others (_Cerura Vinula_, _Sphinx Euphorbiæ_,
_Noctua Verbasci_), though their usual food is of a vegetable nature,
eat with great apparent satisfaction the skins which they cast from
time to time, not leaving even the horny legs. This strange repast
seems even a stimulating dainty, which speedily restores them to
vigour, after the painful operation by which they are supplied with
it. Under this head it will not be out of place to mention, that some
larvæ of insects, which feed only on the juices of animals, or the
nectar and ambrosia of flowers, have no anal passage, and of course
no feces. This is said to be the case with the grubs of bees, wasps,
the larvæ of _Myrmeleon_, &c.[466]
vii. You will require no stimulus to induce you to attend to the
subject I am next going to enter upon,--the _Moulting_, namely,
of Larvæ; or their changes of skin. This, indeed, is a subject
so replete with interest, and which so fully displays the power,
wisdom, and goodness of the Creator, affording at the same time such
large occasion for nice investigation, that a pious and inquisitive
mind like yours cannot but be taken with it. In the higher orders
of animals, though the _hairs_ of quadrupeds and the _feathers_ of
birds are in many cases annually renewed, the change, or scaling
and increment of the _skin_, is gradual and imperceptible; no
simultaneous rejection of it, in which it is stripped off by the
animal itself like a worn shirt, being observable, till you descend
in the scale to the Serpent tribe[467], which at certain periods
disengage themselves from their old integument, and start forth with
that new and deadly beauty so finely described by the Mantuan bard:--
"So from his den, the winter slept away,
Shoots forth the burnished snake in open day;
Who, fed with every poison of the plain,
Sheds his old spoils and shines in youth again:
Proud of his golden scales rolls tow'ring on,
And darts his forky _tongue_[468], and glitters in the sun."
PITT.
In these the new skin, I imagine, is formed under the old from the
_rete mucosum_; but in _insects_, as I formerly stated[469], since the
time of Swammerdam it has generally been believed by entomologists,
that the larva includes a series of cases or envelopes, one within
the other, containing in the centre the germe of the future perfect
insect, whose development and final exclusion take place only when
these cases have been successively cast off. This hypothesis, as was
explained to you on a former occasion[470], has been controverted by a
late writer, Dr. Herold; who affirms that the skins of caterpillars are
also successively produced out of the _rete mucosum_. I have however,
I hope, satisfied you that the old system is most consonant to nature
and probability: but as we are now to enter at large upon the _Moults_
of insects, it will not be without use if I add a few additional
reasons which seem to me still further to prove the correctness of
Swammerdam's system, as far as it relates to that subject. With regard
to the mere formation of the skin from the _rete mucosum_, were this
the whole question few would hesitate to adopt the sentiments of M.
Herold; but when we come to consider further--that the number of moults
of individuals of the _same_ species is always the same, and that it
varies in _different_ species, and takes place at certain periods,--we
begin to suspect that something more than the mere formation of a new
skin upon an old one being cast is to be accounted for; and that the
law which prescribes its own definite number of skins to each species,
must begin to act in the primordial formation of the larva. Again,
the _hairs_ observable in the higher animals do not take their origin
from the epidermis solely, but are planted below it in the _rete
mucosum_, or deeper[471]; so that the change of skin does not affect
them; but in the larvæ of insects they are a continuation of that
integument, since, when the moult takes place, they always remain on
the rejected skin[472]: this is the case, also, even with spines. If
you shave a caterpillar ready to change its skin, either partially or
generally, you will find that the parts in the new skin that correspond
with those that are denuded, are equally hairy with those that were
not[473]; and if you pay attention to the new-clad animal, you will
find further, that the hairs never grow after a moult. From hence it
follows, that the _hairs_ have their place and take their whole growth
between the new skin and the old[474]. Whether the _spines_, simple or
compound, lately described to you, that arm some larvæ are similarly
circumstanced, seems not as yet to have been ascertained; but as the
spinous ones of certain _Tenthredines_ L. and _Lepidoptera_ at their
last moult have no spines, the presumption is, that, whether incased
or not, they are mere appendages of the skin on which they appear.
A new set of hairs, therefore, and probably of spines in spinous
larvæ, accompanying each skin, and these varying very much in size,
composition, &c. though a new membrane may be admitted to be formed
from an action in the _rete mucosum_ without a pre-existent germe of
it, it seems not easy to conceive how these hairs and spines can spring
up and grow there, each according to a certain law, without existing
previously as a kind of _corculum_ or _punctum saliens_; and that the
germes of the tubercles, in which the hairs are so generally planted,
according to a certain arrangement and in a given number, should also
pre-exist, seems most consonant to reason. These and the several skins
may all co-exist in their primordial germes, and remain beyond the
discovery of our highest powers of assisted vision, till a certain
period when they may first enter the range of the microscope-aided eye.
It does not therefore follow, because these _primordia semina rerum_
are not discoverable, that therefore they may not exist. Our faculties
and organs are too limited and of too little power to enable us to see
the essences of being.
Upon the supposition that the hypothesis of Swammerdam is the true
one, we may imagine that the envelope that lies within all the rest is
that which covers the insect in its pupa state. Above this are placed
several others, which successively become external integuments. These
changes or casting of the skin in larvæ, analogous, as before observed,
to that of serpents, are familiar to every breeder of silk-worms, in
which _four_ such changes occur: the first at the end of about _twelve_
days from its birth, and the three next each at the end of _half_ that
time from the moulting which preceded it. With some exceptions[475],
similar changes of the skin take place in all larvæ, not however in
the same number and at the same periods. Most indeed undergo this
operation only three or four times; but there are some that moult
oftener, from five up to eight (_Arctia villica_), nine (_Callimorpha
Dominula_), or even ten times; for so often, M. Cuvier informs us,
the caterpillar of the tiger-moth (_Callimorpha Caja_) casts its
exuviæ. It has been observed that the caterpillars of the day-flying
_Lepidoptera_ (_Papilio_ L.) usually change only _three_ times, while
those of the night-flying ones (_Phalæna_ L.) change _four_[476]. The
periods that intervene between each change depend upon the length of
the insect's existence in the larva state. In those which live only a
few weeks or months, they are from eight to twenty days; while in those
that live more than a year, as the cockchafer, &c. they are probably
proportionably longer: though we know very little with regard to the
moult of any insects besides the _Lepidoptera_.
A day or two previously to each change of its skin, the larva ceases
eating altogether; it becomes languid and feeble, its beautiful
colours fade, and it seeks for a retreat in which it can undergo
this important and sometimes dangerous and even fatal operation in
security. Here, either fixing itself by its legs to the surface on
which it rests, or, as is the case with many caterpillars, by its
prolegs, to a slight web spun for this purpose, it turns and twists
its body in various directions, and alternately swells and contracts
its different segments. The object of these motions and contortions
seems to be, to separate the exterior skin, now become dry and rigid,
from the new one just below it. After continuing these operations for
some hours, resting at intervals without motion, as if exhausted by
their violence, the critical moment arrives: the skin splits in the
back, in consequence of the still more violent swelling of the second
or third segment: the opening thus made is speedily increased by a
succession of swellings and contractions of the remaining segments:
even the head itself often divides into three triangular pieces, and
the inclosed larva by degrees withdraws itself wholly from its old
skin. All larvæ, however, do not force their way through this skin
in precisely the same place. Thus, those of the hawthorn butterfly
(_Pieris Cratægi_), according to Bonnet[477] make their way out by
forcing off what may be called their skull, or the horny part of
their head, without splitting the skin, which remains entire; others
have been observed to make their way out at the side and the belly.
Reaumur noticed the larva of _Zygæna Filipendulæ_, previously to its
last moult, actually biting off and detaching several portions of its
old skin; and before this, drops of a fluid resembling water were
seen to exude from it[478].
The skin when cast is often so entire, that it might be mistaken
for the larva itself; comprising not only the covering of the main
trunk with the hairs which clothed it, but of the very skull, eyes,
antennæ, palpi, jaws, and legs; which, if examined from within, are
now found to be hollow, and to have incased, like so many sheaths,
similar parts in the new skin. That the feet of the newly-coated
larva were actually sheathed, as fingers in a glove, in the same
parts of the exuviæ, may be proved by a very simple experiment: if
a leg of one just ready to cast its skin be cut off, the same limb
will be found mutilated when that change has ensued. The anal horns,
also, of the larvæ of the hawk-moth (_Sphinx_ L.) and other similar
protuberances, are incased in each other in like manner; but hairs
are laid flat between the two skins, and contribute considerably
towards their more easy separation. Thus, if you saved the skins cast
by the larva of _Callimorpha Caja_, for instance, you would appear to
have ten different specimens of caterpillars, furnished with every
external necessary part, and differing only in size, and the colour
perhaps of the hairs, and all representing the same individual.
But further changes than this take place. Swammerdam says, speaking
of the moult of the grub of _Oryctes nasicornis_, a beetle common
in Holland, but not satisfactorily ascertained to inhabit Britain,
"Nothing in all nature is in my opinion a more wonderful sight than
the change of skin in these and other the like worms. This matter,
therefore, deserves the greatest consideration, and is worthy to be
called a specimen of nature's miracles; for it is not the external
skin only that these worms cast, like serpents, but the throat and a
part of the stomach, and even the inward surface of the great gut,
change their skin at the same time. But this is not the whole of
these wonders; for at the same time some hundreds of pulmonary pipes
within the body of the worm cast also each its delicate and tender
skin. These several skins are afterwards collected into eighteen
thicker, and, as it were, compounded ropes, nine on each side of the
body, which, when the skin is cast, slip gently and by degrees from
within the body through the eighteen apertures or orifices of the
pulmonary tubes before described, having their tops or ends directed
upwards towards the head. Two other branches of the pulmonary
pipes that are smaller, and have no points of respiration, cast a
skin likewise." ... "If any one separates the cast little ropes or
congeries of the pulmonary pipes with a fine needle, he will very
distinctly see the branches and ramifications of these several pipes,
and also their annular composition[479]."--Bonnet makes a similar
observation with regard to _caterpillars_; but he appears to have
observed it more particularly, at least the change of the intestines,
previously to the metamorphosis of the insect, when he says with the
excrements it casts the inner skin of the stomach and viscera[480].
Both these great men appear to have recorded the result of their
own actual observations with regard to the proceedings of two very
different kinds of insects; the one the grub of a beetle, and the
other the caterpillars of _Lepidoptera_. The account of the former is
given quite in detail, as that of a person who is describing what he
has actually _seen_: yet by a later and very able physiologist, Dr.
Herold, it is affirmed that the inner skin of the intestinal canal
is never cast, that canal constantly retaining its two skins. He
further affirms, that they are only the _large_ trunks of the Tracheæ
that cast their skins, none being detached from their _smaller_
ramifications[481]. When men so eminent for their anatomical skill
and nicety, and for their depth and acumen, disagree, the question
must be regarded as undecided till further observations throw
sufficient weight into one scale or the other.
The larva which has undergone this painful process is at first
extremely weak: all its parts are soft and tender; even the corneous
ones, as the head and the legs, are then scarcely more than membranous,
and are all bathed with a fluid, which, before the moult, intervenes
between the two skins, and facilitates their separation[482]: and
it is only after some _hours_, or in some cases even _days_, during
which it lies without motion, that this humidity evaporates, all its
parts become consolidated, and it recovers its strength sufficiently
to betake itself to its wonted food. Its colour, too, is usually at
first much paler than before, and its markings indistinct, until their
tints have been enlivened by exposure to the air, when they become
more fresh, vivid, and beautiful to appearance than ever. When a few
meals have invigorated its languid powers, the renovated animal makes
up for its long abstinence by eating with double voracity. . A similar
preparatory fast, and succeeding state of debility, accompany every
change of the larva's skin. Each time except the last, the old skin is
succeeded by a new one, with few exceptions, similar to the one it has
discarded. Previously to the final change, which discloses the pupa, it
quits the plant or tree on which it had lived, and appears to be quite
unsettled, wandering about and crossing the paths and roads, as if in
quest of some new dwelling. It now abstains from food for a longer time
than before a common moult, empties itself copiously, and as I have
just said, if Swammerdam and Bonnet are to be depended upon, casts the
skin that lines the stomach and intestines, as well as that of the
Tracheæ.
I have observed above, that all larvæ, with few exceptions, change
their skins in the manner that I have described. These exceptions
are principally found in the order _Diptera_, of which those of
the Linnean genera _Musca_, _Œstrus_, and probably all that, like
the maggot of the common flesh-fly, have membranous contractile
heads, never change their skin at all, not even preparatory to their
becoming pupæ. The skin of the pupa, though often differing greatly
in shape from that of the larva, is the same which has covered this
last from its birth, only modified in figure by the internal changes
that have taken place, and to which its membranous texture readily
accommodates itself. The larvæ of the Dipterous genera _Tipula_,
_Culex_, and those which have corneous heads, like other larvæ
change their skins several times previously to becoming pupæ[483].
The grubs, also, of bees, wasps, ants? and probably many other
_Hymenoptera_, do not change their skin till they assume the pupa,
nor the larva of the female _Coccus_[484].
If you feel disposed to investigate the reasons of that law of the
Creator which has ordained that the skins of the higher animals shall
be daily, and imperceptibly, and as it were piece by piece renewed,
while those of insects are cast periodically and simultaneously,--the
proximate cause must be sought for in the nature of the two kinds
of skin, the one being more pliable and admitting a greater degree
of tension than the other, and being so constructed as to scale off
more readily. If, ascending higher, you wish to know why the skins
of insects are so differently circumstanced from our own, the most
apparent reason is, to accommodate the skin to the very rapid growth
of these animals, which a gradual and slower change would have
impeded too much, or the skin have suffered constant dilapidation
and injury; therefore their Beneficent Creator has furnished them
with one which will stretch to a certain point, and during a certain
period, and then yield to the efforts of the inclosed animal, and be
thrown aside as a garment that no longer fits the wearer.
viii. And this leads me to a subject to which I am desirous now to
bespeak your attention,--the _Growth_, I mean, and size of Insects in
this state. As to _size_, larvæ differ as much as insects in their
perfect state: these last, however, never grow after their exclusion
from the pupa, while larvæ increase in bulk in a proportion, and
often with a rapidity, almost without a parallel in the other tribes
of animals. Thus Lyonnet found, that the caterpillar of the great
goat-moth (_Cossus ligniperda_ F.) after having attained its full
growth is at least 72,000 times heavier than when it was first
excluded from the egg[485]; and of course had increased in size in
the same proportion. Connected with the size of larvæ, is the mode
in which their accretion takes place. This, with respect to the more
solid parts, as the head, legs, &c., is not, as in other animals,
by gradual and imperceptible degrees, but suddenly and at stated
intervals. Between the assumption of a new skin and the deposition of
an old one, no increase of size takes place in these parts, while the
rest of the body grows and extends itself, till, becoming too big for
these solid parts, nature restores the equilibrium between them by a
fresh moult[486], in which the augmentation of bulk, especially in
these parts, is so great, that we can scarcely credit the possibility
of its being cased in so small an envelope. Malpighi declares, that
the head of a silk-worm that has recently cast its skin is four times
larger than before the change[487]. It is very probable, also, that
when the outer skin becomes rigid, it confines the body of the larva
within a smaller compass than it would expand to if unconfined, so
that, when this compression is removed, the soft and elastic new
integument immediately swells out, and the animal appears all at
once much larger than it was before the moult. In fact, the proximate
cause of the rupture and rejection of the old skin is the expansion
of the included body, which at length becomes so distended as to
split its envelope, aided, indeed, as before described, by the
contortions of the creature itself.
The larvæ most notorious for the _rapidity_ of their growth are those
of _Musca carnaria_ and other flesh-flies: some of which Redi found
to become from 140 to more than 200 times heavier in twenty-four
hours[488]: an increase of weight and size in so short a time truly
prodigious, but essential for the end of their creation--the rapid
removal of dead and putrescent animal matter. As the skins of these
larvæ are never changed, we may conclude, if the cause of the change
of skin in other larvæ above surmised be accurate, that their skins
are more contractile and capable of a greater degree of tension than
those of larvæ that are subject to moulting. And two peculiarities
observable in them confirm this idea: in the first place, their head
is not hard and corneous, as that of the others, but capable of being
shortened or lengthened; and in the next, their breathing-pores are
not in the sides, but at the extremities of the body, while in the
_moulting_ larvæ there are two in almost every segment, which must form
so many callous points that impede the stretching of the skin to the
utmost. The hairs, spines, and tubercles, that are so often found on
caterpillars, must also form so many points of resistance that prevent
that full extension of the integument which it might otherwise admit.
There is not always that proportion between the size of larvæ and of
the insects that proceed from them that might have been supposed,
some small larvæ often producing perfect insects larger than some of
those proceeding from such as are of greater size.
ix. As insects often live longest in the state we are treating of,
I shall say something next upon the _age_ of larvæ, or the period
intervening between their exclusion from the egg and their becoming
pupæ. This is exceedingly various, but in every case nicely adapted
to their several functions and modes of life. The grubs of the
flesh-fly have attained their full growth, and are ready to become
pupæ, in _six_ or _seven_ days; the caterpillar of _Argynnis Paphia_,
a butterfly, in _fourteen_ days; the larvæ of bees in _twenty_ days;
while those of the great goat-moth (_Cossus ligniperda_) and of the
cockchafer (_Melolontha vulgaris_) live _three_ years, or at least
survive three winters, before the same change. That of another
lamellicorn beetle (_Oryctes nasicornis_ F.) is said to be extended
to _four_ or _five_; that of the wire-worm (_Elater segetum_) to
_five_. That of the stag-beetle (_Lucanus Cervus_) is affirmed by
Rösel to be extended to _six_ years; but the most remarkable instance
of insect longevity is recorded by Mr. Marsham in the _Linnean
Transactions_[489]. A specimen of _Buprestis splendida_, a beautiful
beetle never before found in this country, made its way out of a deal
desk in an office in London in the beginning of the year 1810, which
had been fixed there in the year 1788 or 1789; so that according to
every appearance it had existed in this desk more than twenty years.
Ample allowance being made for its life as a pupa, we may conclude
that it had existed as a larva at least half the above period. The
grubs of the species of the genus _Cynips_ L. attain their full size
in a short time; but they afterwards remain five or six months in the
gall before they become pupæ[490].
With few exceptions it may be laid down, that those larvæ which live
on dead animals, in fungi, in dung, and in similar substances, are of
the shortest duration in this state; and that those which live under
the earth, on the roots of grass, &c. and in wood, the longest: the
former becoming pupæ in a few days or weeks, the latter requiring
several months, or even years, to bring them to maturity. The larvæ
which live on the leaves of plants seem to attain a middle term
between the one and the other,--seldom shorter than a few weeks, and
rarely longer than seven or eight months. Aquatic larvæ appear to be
subject to no general rule: some, as the larvæ of _Gnats_, becoming
pupæ in two or three weeks; and others, as those of the _Ephemeræ_,
which are thus compensated for their short life as flies, in as
many years[491]. The cause of all these differences is obviously
dependent on the nature of the food, and the purposes in the economy
of creation to which the larvæ are destined.
x. The last part of the history of larvæ relates to their _Preparations
for assuming the pupa state_. When they have acquired their full size,
after having ceased to take food, by a copious evacuation they empty
the intestinal canal, even rejecting the membrane that lines it and
the stomach[492]; their colours either change totally, or fade; and
they make themselves ready for entering upon a new stage of their
existence. Some merely rest in a state of inactivity in the midst of
the substances in which they feed, as if conscious of their inability
to select any safer abode. Of this description are most Coleopterous,
Hymenopterous, and Dipterous larvæ, that feed under ground, or in the
interior of trees, fruits, and seeds.
But a still larger tribe, those which feed on leaves, animals, &c.
act as if more sensible of the insecurity of this to them important
epoch. They are about to exchange their state of vigour and activity
for a long period of deathlike sleep. The vigilant caution which
was wont to guard them from the attack of their enemies will be
henceforward of no avail. Destitute of all the means of active
defence, their only chance of safety during their often protracted
night of torpor must arise from the privacy of their place of repose.
About this, therefore, they exhibit the greatest anxiety. Many, after
wandering about as if bewildered, retire to any small hole on the
surface of the earth, covering themselves with dead leaves, moss, or
the like, or to the chinks of trees, or niches in walls and other
buildings, or similar hiding-places. Many penetrate to the depth of
several inches under ground, and there form an appropriate cavern
by pushing away the surrounding earth; to which they often give
consistence by wetting it with a viscid fluid poured from the mouth.
The larvæ of other insects undertake long and arduous journeys in
search of appropriate places of shelter. Those of flesh-flies, now
satiated with the mass of putridity in which they have wallowed,
leave it, and conceal themselves in any adjoining heap of dust.
The grubs of the gad-fly (_Œstrus_) creep some of them out of the
backs of cattle, in tumours of which they have resided, and suffer
themselves to fall to the earth; while others, which have fed in the
stomach of horses, quit their hold, and by a still more extraordinary
and perilous route are carried through the intestines the whole
length of their numerous circumvolutions, and are discharged at the
anus. And without enumerating other instances, various aquatic larvæ,
as that of a common fly (_Elophilus pendulus_), &c. leave the water,
now no longer their proper element, and betake themselves to the
shore, there to undergo their metamorphosis.
Most of these, having reached their selected retreat, require no other
precaution; but another large tribe of larvæ have recourse to further
manœuvres for their defence before they assume the pupa. Those of
the aphidivorous flies (_Syrphus_ F. &c.), of the various lady-birds
(_Coccinella_ L.), and tortoise-beetles (_Cassida_ L.), &c. fix
themselves by the anus with a gummy substance to the leaves or twigs
under which they propose to conceal themselves during their existence
in that state. Others previously suspend themselves by a silken thread
fixed to the tail, or passing round the body; by which also, when
become pupæ, they are afterwards pendent in a similar position; and
lastly, a very great number of larvæ wholly inclose themselves in cases
or cocoons, composed of silk and various other materials, by which
during their state of repose they are protected both from their enemies
and the action of the atmosphere. As these two last-mentioned processes
are extremely curious and interesting, I shall not fear tiring you by
entering into some further detail respecting them: explaining _first_
the mode by which larvæ _suspend_ themselves, both before and after
they are become pupæ, by silken threads; and _next_, the various
_cases_ or _cocoons_ in which others inclose themselves, and their
manner of operating in the formation of them.
1. The larvæ which suspend themselves and their pupæ, with the
exception of the tribe of _Alucitæ_, and some _Geometræ_ of the family
of _G. pendularia_, _punctaria_, &c. are almost all _butterflies_[493].
No others follow this mode. They may be divided into two great
classes--those which suspend themselves _perpendicularly_ by the
_tail_, and those which suspend themselves _horizontally_ by means of
a thread girthed round their _middle_. In both cases it should be
observed, that the suspension of the pupa is the object in view; but as
the process is the work of the larva, this seems the proper place for
explaining it. To begin with the _first_ case.
You are aware that all _lepidopterous_ larvæ have the faculty of
spinning silk threads from their mouths, and it will readily occur
to you that it is by means of these threads that they suspend
themselves. But how? How is a caterpillar to hang itself by the
tail to threads spun from the mouth? Even suppose this difficulty
overcome, others still greater remain. Suppose the caterpillar to be
suspended by its tail,--this is but a preparatory operation,--what
is required is, that the pupa shall hang in the same position:
now when you take into consideration that it is incased _within_
the skin of the larva, and without feet or other external organs;
that it has to extricate itself from this skin; to hang itself
in its place, and to detach the skin from the threads which hold
it--this will appear no trifling task. Indeed at first view it seems
impossible. Country-fellows for a prize sometimes amuse the assembled
inhabitants of a village by running races in sacks: take one of the
most active and adroit of these, bind him hand and foot, suspend him
by the bottom of his sack with his head downwards, to the branch
of a lofty tree; make an opening in one side of the sack, and set
him to extricate himself from it, to detach it from its hold, and
suspend himself by his feet in its place. Though endowed with the
suppleness of an Indian juggler, and promised his sack full of gold
for a reward, you would set him an absolute impossibility: yet this
is what our caterpillars, instructed by a beneficent Creator, easily
perform. Their manœuvres I shall now endeavour to explain.
When the caterpillar has selected the under-side of the leaf or
other object to which it purposes suspending itself, its first
process is to spin upon it a little hillock of silk consisting of
numerous loosely interwoven threads; it then bends its body so as to
insinuate the anal pair of prolegs amongst these threads, in which,
by a slight exertion, the little crochets which surround them[494]
become so strongly entangled as to support its weight with ease. It
now suffers the anterior part of the body to fall down, and it hangs
perpendicularly from its silken support with its head downwards. In
this position it remains often for twenty-four hours, at intervals
alternately contracting and dilating itself. At length the skin is
seen to split on the back near the head, and a portion of the pupa
appears, which by repeated swellings acts like a wedge, and rapidly
extends the slit towards the tail. By the continuance of these
alternate contractions and dilatations of the conical pupa, the skin
of the caterpillar is at last collected in folds near the tail, like
a stocking which we roll upon the ancle before withdrawing it from
the foot. But now comes the important operation. The pupa, being much
shorter than the caterpillar, is as yet at some distance from the
silken hillock on which it is to be fastened; it is supported merely
by the unsplit terminal portion of the latter's skin. How shall it
disengage itself from this remnant of its case, and be suspended in
the air while it climbs up to take its place? Without arms or legs
to support itself, the anxious spectator expects to see it fall to
the earth. His fears, however, are vain; the supple segments of the
pupa's abdomen serve in the place of arms. Between two of these,
as with a pair of pincers, it seizes on a portion of the skin; and
bending its body once more, entirely extricates its tail from it.
It is now wholly out of the skin, against one side of which it is
supported, but yet at some distance from the leaf. The next step it
must take is to climb up to the required height. For this purpose
it repeats the same ingenious manœuvre, making its cast-off skin
serve as a sort of ladder, it successively with different segments
seizes a higher and a higher portion, until in the end it reaches the
summit, where with its tail it feels for the silken threads that are
to support it. But how can the tail be fastened to them? you ask.
This difficulty has been provided against by Creative Wisdom. The
tail of the pupa is furnished with numerous little hooks pointing in
different directions[495], as well adapted to the end in view as the
crochets of the larva's prolegs, and some of these hooks are sure to
fasten themselves upon the silk the moment the tail is thrust amongst
it. Our pupa has now nearly completed its labours; it has withdrawn
its tail from the slough, climbed up it, and suspended itself to the
silken hillock--manœuvres so delicate and perilous, that we cannot
but admire that an insect which executes them but once in its life,
should execute them so well: nor could it, as Reaumur has well and
piously observed, had it not been instructed by a GREAT MASTER. One
more exertion remains: it seems to have as great an antipathy to
its cast-off skin, as one of us should, when newly clothed after
a long imprisonment, to the filthy prison garments we had put off.
It will not suffer this memento of its former state to remain near
it, and is no sooner suspended in security than it endeavours to
make it fall. For this end--it seizes, as it were with its tail, the
threads to which the skin is fastened, and then very rapidly whirls
itself round, often not fewer than twenty times. By this manœuvre
it generally succeeds in breaking them, and the skin falls down.
Sometimes, however, the first attempt fails: in that case, after a
moment's rest, it makes a second, twirling itself in an opposite
direction; and this is rarely unsuccessful. Yet now and then it is
forced to repeat its whirling, not less than four or five times:
and Reaumur has seen instances where the feet of the skin were so
firmly hooked, that after many fruitless efforts the pupa, as if in
despair, gave up the task and suffered it to remain[496]. After these
exertions, it hangs the remainder of its existence in this state
until the butterfly is disclosed.
We are now to consider the _second_ mode of suspension, in which
larvæ by means of a silken girth round their middle, fix themselves
_horizontally_ under leaves, &c. These follow the same process with
that of those last described, in spinning a small hillock of silk to
which they fasten their hind legs; and if the operation concerned
the larva state alone, this would be sufficient, as by means of this
support, and of their prolegs, they could easily retain themselves
in a horizontal position. But these larvæ act as if they foresaw
the assumption of a state in which they will be deprived of legs.
It is the suspension of the forthcoming pupa that is the object
in view; and though this can be hung by the tail in the same way
with those of the first class, yet it is plain that it cannot be
retained in a horizontal position, which for some unknown reason is
essential to it, without some support to its anterior extremity. It
is necessary for the larva, therefore, not only to fix its posterior
legs amongst a collection of silken fibres, but to spin a _girth_
of the same material round its body. This girth, though apparently
of a single thread, will be found on examination to be composed of
several, often as many as fifty or sixty; and is fastened on each
side of the body of the larva about the middle, to the surface under
which it is placed. Three different modes of fixing these girths
are adopted by the caterpillars of different butterflies. Some, as
those of the common cabbage-butterfly (_Pieris Brassicæ_), which have
remarkably pliable bodies, bend them almost double on one side, then
fix the thread and carry it over to the other in the same position,
repeating this operation as often as is necessary. Others, as that
of _Lycæna Argus_ and many more of the _Papiliones Rurales_ and
_Urbicolæ_ L., which have a short and more rigid body, after having
bent the head on one side so as to fix one end of the thread, bring
themselves into a straight position, and, by a manœuvre not easily
described, contrive to introduce the head under the thread, which
they then bend themselves to fasten on the other side, pushing it
to its proper situation by the successive tension and contraction
of their segments. But the most curious mode, though indeed that
which seems most natural, is adopted by the caterpillar of the
beautiful swallow-tail butterfly (_Papilio Machaon_) and others of
the same family. This first forms the loop which is to serve for
its girth, and then creeps under it. But the difficulty it has to
surmount is, to keep itself from being entangled in the fifty or
sixty fine distinct threads of which the girth is composed, and to
preserve them all extended so as to be able to introduce its body
beneath them. For this purpose it makes use of the two first pair of
its fore-legs, employing them as a woman does her hands in winding
a skein of cotton, to collect and keep all the threads of its card
unentangled and properly stretched; and it is often with great
difficulty, towards the end of the process, that it prevents them
from slipping off. When a sufficient number of threads is completed,
the animal bends its head between its legs, and insinuates it under
the collected loop, which by its annular contraction it easily pushes
to the middle of the body.
In about thirty hours after the larvæ which girth themselves have
finished their operations, the skin splits, and the pupa disengages
itself from it by those contractions and dilatations of its segments
which have been before described, pushing the exuviæ in folds to
the tail, by different motions of which it generally succeeds in
detaching them. One would have thought there would be considerable
difficulty in slipping the skin past the girth; but this, according
to Reaumur, seems to be easily effected[497].
If you are desirous of witnessing for yourself the manœuvres by
which these curious modes of suspension are effected, you may be
readily gratified. It is only necessary to collect and feed until
their metamorphosis the black spinous caterpillars of the common
peacock-butterfly (_Vanessa Io_), which in most places may be found
upon nettles, or those of the _Pieris Brassicæ_, which swarm in
cabbages or brocoli in every garden. The former will exhibit to you
a specimen of _vertical_, the latter of _horizontal_ suspension. It
should be observed, however, that to hit the precise moment when
these processes are going on, it is necessary to feed a considerable
number of the larvæ of each kind; some one of which, if you watch
them narrowly when they have attained their full growth, you will
scarcely fail to surprise in the act.
I must observe here, that although the vertical and horizontal are
the two principal positions in which caterpillars suspend themselves,
yet that others are inclined at various angles; and some are attached
with less art, appearing only to be fastened by some part of their
abdomen to the body upon which they are fixed[498].
2. The larvæ whose procedures I am in the next place to describe,
are those which, previously to assuming the pupa state, inclose
themselves in _cases_ or _cocoons_ of different materials. For the
sake of method, I shall divide these into two great classes: _First_,
those which form their cocoons entirely or principally of _silk_; and
_secondly_, those which form them chiefly of _other substances_.
To begin with the _first_. The larvæ which inclose themselves in
_silken_ cocoons are chiefly of the Lepidopterous tribes of _Bombycidæ_
and _Noctuidæ_; but a few _Geometræ_ (_G. papilioniaria_, _lactearia_,
&c.); most of the _Hymenoptera_; some _Coleoptera_, as certain of the
weevil tribe (_Hypera Arator_, _Rumicis_ Germ.), and those brilliant
beetles frequenting aquatic plants constituting the genus _Donacia_ F.;
the Neuropterous genera _Hemerobius_ and _Myrmeleon_; _Mycetophila_
and a few others in the _Diptera_; and _Pulex_ in the _Aphaniptera_
fabricate coverings of the same material. In all, with the exception
of _Myrmeleon_ and _Hemerobius_ (and perhaps _Hypera Rumicis_, &c.?)
which have their spinning apparatus at the extremity of the abdomen,
the silken thread employed in forming these coverings proceeds from
the middle part of the under-lip, as before explained; and is in fact
composed of two threads gummed together as they issue from the two
adjoining orifices of the spinner.
Of the larvæ which inclose themselves in _silk_, the most familiarly
known is the silk-worm: the cocoon of this consists exteriorly of a
thin, transparent, gauze-like coating, through the interstices of
which can be seen an inner, smaller, oval ball of a more close and
compact texture. The whole is in fact composed of one single thread,
but arranged in two distinct modes. To form the _exterior_ envelope,
which is merely the scaffolding by means of which the inner and
more solid covering is constructed, the caterpillar, after fixing
upon a space between two leaves or twigs or angles suitable for
its purpose, begins by glueing one end of its thread to one of the
adjoining surfaces. This thread it next conducts to another part and
then fastens, repeating this process and interlacing it in various
directions, until it has surrounded itself with a slight and loosely
spun netting. In the centre of this, when contracted into a space
sufficiently small, it lays the foundation of the _interior_ cocoon.
Fixing itself by its prolegs to some of the surrounding threads, it
bends its body, and by successive motions of its head from side to
side spins a layer of silk on the side opposite to it: when this
is of the requisite thickness, the larva shifts its position, and
repeats the same process in another quarter, covering each layer
in turn with a new one until the interior cavity is reduced to the
size desired. Thus, the silken thread which forms this new cocoon is
not, as might have been supposed, wound circularly as we wind the
thread of a ball of cotton; but backwards and forwards in a series
of zigzags, so as to compose a number of distinct layers. Malpighi
could distinguish six of these layers[499], and Reaumur suspects
there is often a greater number[500]. The former found the length of
the thread of silk composing them when wound off, without including
the exterior case, to be not less than 930 feet[501]; but others have
computed it at more than a thousand[502]: consequently the threads
of five cocoons united would be a mile in length. Estimating by the
weight,--the thread of a pound of cocoons, each of which weighs about
two grains and a half, would extend more than 600 miles[503], and
such is its tenuity, that the threads of five or six cocoons require
to be joined to form one of the thickness requisite in the silk
manufacture. It is the continuous thread of the inner cocoon which is
most valuable; the outer loose coating from its irregularity cannot
be wound off, and is known in commerce by the name of _floss silk_.
Manœuvres in their general principle similar to those of the
silk-worm are followed by most of those larvæ which inclose
themselves in silken cocoons. Many species, however, adopt variations
in the mode of procedure all of which it would be tedious to
particularize, but some of them are worth mentioning. The larvæ of
_Tortrix prasinana_, and other species of moths which form cocoons
resembling a reversed boat, arrange their threads in layers, so as to
construct two parallel walls gradually inclining towards the top and
ends, where they finally force them to approach each other by means
of an apparatus of silken cables[504]. And the larva of _Saturnia
Pavonia_, though it forms the base of its flask-shaped cocoon by
spinning like the silk-worm a number of interwoven zigzags, places
the threads which compose the interior funnel-like opening of the
apex nearly straight, parallel to each other, and converging towards
the same point in the centre[505].
These last, as well as almost all larvæ, constantly remain in the
_inside_ of the cocoon during its construction. But De Geer has given
us the history of a minute caterpillar of a species of moth (_Tinea_
L.) which feeds on the under side of the leaves of the _Rhamnus
Frangula_, or Black Alder, that actually weaves half of its cocoon
on the _outside_. This cocoon, which is very small, is beautifully
fluted, consisting of several longitudinal cords, with the intervals
filled by fine net-work, and shaped like a reversed boat[506]. The
animal begins by laying the foundations of one of the ends of
her cocoon, she adds new threads to this small beginning, and so
proceeds. As the work advances she retreats backwards, and her body
is situated nearly in the same line with the cocoon she has begun,
and quite _out_ of it; she only touches with her head and legs its
anterior margin. When half the cocoon, or rather of its exterior
layer, is finished, she suspends her operations for some moments. She
then for the first time introduces her head _into_ this demi-cocoon,
and turns herself in it by doubling her supple body, and passing
one part over the other, so that at last she manages to bring her
tail into the pointed end of the cocoon, the head and the anterior
half of her body remaining without. Thus situated, she commences her
operations afresh. At a distance from the margin of the demi-cocoon,
equal to its length, she begins to spin the pointed end of the other
moiety, the length of her body serving her as a measure that enables
her to begin at the proper distance from it. This new portion she
spins in the same manner as the other; but as she is prevented by the
demi-cocoon in which the posterior part of her body is lodged from
retreating backwards, she contracts her body more, which answers the
same purpose. When the new work is so advanced that she can no longer
contract her body, she bends the anterior part of it considerably,
and reverses her head. When the distance between the margin of the
two halves of the cocoon is very small, so as no longer to admit the
head between them, in order to unite them she is obliged to have
recourse to another manœuvre. Withdrawing her head, she extends
silken longitudinal threads between the two margins, and thus unites
them. This part is more clumsy, and not so regular as the rest
of the cocoon, so that the point of union is always discoverable.
These caterpillars do not always divide the cocoon into two _equal_
portions, for often they will finish three quarters of the cocoon
before they enter it, and begin at the other end[507].
The general rule is,--that each larva spins for itself a separate
cocoon; but amongst those of _Arctia chrysorhea_ and others which
live in society, two or three sometimes begin their operations so
close together that they are under the necessity of forming one
common cocoon, which serves for a covering to the whole number.
The same thing happens to silk-worms, the double or treble cocoons
of which are called _Dupions_ by the breeders. The larvæ of some
Ichneumons, besides forming each its separate cocoon, spin a joint
cottony covering for the whole[508], which is effected thus:--After
they leave the caterpillar they have devoured, they fix themselves
side by side at a little distance from it, and begin to spin each a
cocoon; and in order to defend its end and side that is not covered
by others, they spin further an envelope of loose silk, and thus this
exterior covering is formed.
The size, figure, colour, substance, and texture of silken cocoons
are extremely various. Their _size_ indeed is usually proportioned
to that of the included larva or pupa; yet it is by no means always
so. Some large caterpillars spin cocoons so small, that the observer
can hardly conceive how they can be contained in so narrow a compass:
_Eriogaster Catax_ is a moth of this description[509]. And others
smaller in size lodge themselves in apartments apparently much
more spacious than necessary. The transparent hammock-like cocoons
of _Hepialus Humuli_ and _Arctia villica_, two other moths, would
contain several of their pupæ. I possess one in which the pupa is
suspended in the centre, that is ten times its size, and not very
short in dimensions of that of _Attacus Paphia_, a giant silk-moth.
The largest cocoon I ever read or heard of, is that thus described by
Mr. Hobhouse in his _Travels_: "Depending," says he, "from the boughs
of the pines, near the Attic mountain Parnes, and stretching across
from tree to tree so as to obstruct our passage, were the pods,
_thrice as big as a turkey's egg!_ and the thick webs of a chrysalis,
whose moth must be far larger than any of those in our country."[510]
If this statement is correct, and I am not aware that there is any
reason for doubting it, the cocoon must be vastly larger than the
pupa, or the moth it produced would far exceed in size any yet known.
Perhaps, however, as this gentleman is probably no entomologist,
what he took for a cocoon might be a nidus, in which many larvæ were
associated, of the nature of those formerly described[511].
With regard to _figure_, the majority are like those of the
silk-worm, of a shape more or less oval or elliptic: some, however,
vary from this. That of _Lasiocampa Rubi_ is oblong. I have one from
New Holland somewhat resembling an acorn, fixed to the twigs of
some tree or shrub, of a very close silk, and covered by a circular
operculum, which the animal pushes off when it assumes the imago;
this is ovate or conico-ovate; others again are globose[512]; others
are conical[513], as that of _Gastropacha quercifolia_; others
almost fusiform[514] (_Odenesis potatoria_). Reaumur received
one from Arabia which was nearly cylindrical[515]. Those of _T.
prasinana_ before noticed, and many other _Tortrices_, are shaped
like a reversed boat[516]; that of _Saturnia Pavonia_ and others of
the same tribe, like a Florence flask with a wide and short neck. The
cocoon of _Lygæna Filipendulæ_ resembles a grain of barley. Another
cocoon in my cabinet, of very slight network, is shaped something
like an air-balloon. But the most remarkable one for its form and
characters, is one that I received from the rich cabinet above
quoted. This, which is of an unusually close texture, is suspended by
a thread more than two inches long from the point of a leaf; it then
swells into a perfect cone, at the base about four-fifths of an inch
in diameter and half an inch in length, and covered with scattered
setiform appendages: from the centre of the base projects a large
hemispherical protuberance, which terminates in a long stalk, much
thicker than the thread that suspends the cocoon. There is commonly
no difference between the shape of cocoons spun by larvæ which are
to give birth to different sexes of the same species. The silk-worm
cocoons, however, which will produce _male_ moths, have more silk at
the ends, and consequently are more round than those which are to
produce _females_: but the difference is not striking.
The most usual _colour_ of silken cocoons is white, yellow, or brown,
or the intermediate shades. The whites are very pure in the general
envelope of some species of _Ichneumonidæ_, and yellows often very
brilliant. But besides these more general colours, some cocoons are
black[517], some few blue or green, and others red[518]. Sometimes
the same cocoon is of two different colours. Those of certain
parasites of the tribe of _Ichneumones minuti_ L. the motions of one
of which I noticed on a former occasion[519], are alternately banded
with black or brown and white, or have only a pale or white belt in
the middle, which gives them a singular appearance. In both cases
the difference in colour depends upon the different tints with which
the silky gum is imbued in the reservoirs: the first portion of it
is white, and with this the larva first sketches the outline of its
cocoon, and then thickens the layers of silk considerably in those
parts where the white bands appear: when these are finished, its
stock of white silk is exhausted, and the remainder of the interior
of the cocoon is composed of brown silk[520]. The circular operculum
above mentioned as covering an acorn-shaped cocoon, is paler than
the latter, and also ornamented by a zone within the margin of deep
brown. The pale cocoon also of _Attacus Paphia_ is veined with silk
of a deep red.
I have very little to say on the _substance_ of the silk of cocoons.
Though that of the silk-worm is composed of such a slender thread, that
of many others is still finer, scarcely yielding in tenuity to the
spider's web. On the other hand, the silk of the cocoons of _Saturnia
Pavonia_ and of several foreign species is as thick as a hair.
With regard to the _texture_ of their cocoons--in some, as in that
of the silk-worm, the threads are so slightly glued to each other,
as to separate with facility; but in that of the emperor-moth just
mentioned they are intimately connected by a gummy matter, furnished,
as Reaumur conjectures, from the anus[521], with which the whole
interior of the cocoon is often plastered. Some, as that of the
silk-worm, are composed of an exterior loose envelope, and an inner
compact ball; others have no exterior covering, the whole cocoon
being of an uniform and thick texture. The larva of _Cossus Robiniæ_
Peck, in spinning its cocoon, makes the end next the opening to the
air, by which the imago is to emerge, of a slighter texture than
the rest of it[522]. The exterior case is sometimes, as in _Laria
pudibunda_, very closely woven, so as to resemble a real cocoon[523]:
its form is usually adapted to that of the inner one; but in some
which fix them under flat surfaces (_Laria fascelina_, _Callimorpha
Caja_,) it resembles a hammock[524]. Cocoons of a close texture have
generally no orifice in any part; but that of _Eriogaster lanestris_
is spun with openings, as if bored from without, the use of which,
however, does not seem to have been ascertained[525].
Many silken cocoons are of so close a fabric, as, when finished,
entirely to conceal the included insect; but a very considerable number
are of a more open texture, composed of a much smaller quantity of
silk, and that woven so loosely, that the larva or pupa may always
be discovered through it. Of this description are the cocoons of
_Hypogymna dispar_, _Arctia Salicis_, &c., which consist only of a few
slight meshes. Those of some others resemble gauze or lace[526]. Of
the first description is one in my cabinet before alluded to, shaped
somewhat like an air-balloon; the meshes are large and perfectly
square. The pupa hangs in the centre, fixed by some few slight threads
which diverge from it to all parts of the cocoon--so that it looks as
if it was suspended in the air, like Mahomet's coffin, without support.
Of the second description is a black one with very fine and nearly
circular meshes: the threads that form these are thick, and seem to be
agglutinated. In our own country, the cocoons of some beetles, as of
_Hypera Arator_, _Galeruca Tanaceti_, and of some little _Tineæ_, also
resemble gauze. Many of the larvæ, however, which spin these cocoons,
whose thinness is probably attributable to the smallness of their stock
of silk, seem anxious for a more complete concealment; and therefore
commonly either hide them between leaves tied together, in some with
a certain regularity, in others without art[527]; or thicken their
texture, and render it opaque, by the addition of grains of earth[528],
or of other materials with which their bodies supply them. These are
principally of two kinds. The larvæ of _Lasiocampa Neustria_, _Arctia
Salicis_, &c. after spinning their cocoons, cast from their anus three
or four masses of a soft and paste-like matter, which they apply with
their head all round the inside of the cavity; and which, drying in a
short time, becomes a powder that effectually renders it opake. This
is not, as might be conjectured, an excrement, but a true secretion,
evidently intended for this very purpose: and, according to Reaumur,
a similar powder, but white, derived from the varicose intestines, is
used by the caterpillars of _Gastropacha quercifolia_, &c.[529] The
other material, which is still more frequently employed, and which is
occasionally mixed with the former, is the _hair_ which everyone has
observed to cover so thickly the bodies of some caterpillars. This,
after spinning a sufficient envelope, they tear, or in some instances
cut off with their mandibles, and distribute all round them, pushing
it with their head amongst the interstices of the silk, so as to make
the whole of a regular thick texture. After this process, which leaves
the body completely denuded, and often seems to give them great pain,
they conclude by spinning another tissue of slight silk, in order to
protect the forthcoming pupa from the surrounding prickly points. It
should be observed, however, that though many hairy larvæ, as those
of _Noctua Aceris_, _Arctia Caja_, and others, employ their hairs in
the composition of their cocoons, the rule is not general, several
never making any such use of them. Nor do all that do so employ them
distribute them in the same manner as those above described, which
rarely attempt to arrange them in any regular position. Reaumur has
noticed a small hairy caterpillar that feeds on lichens, which is more
methodical: this actually places its hairs upright, side by side, as
regularly as the pales in a palisade, in an oval ring around its body,
connecting them by a slight tissue of silk, which forces them to bend
into a sort of roof at the top; and under this curiously-formed cocoon
assumes its state of pupa[530]. Some larvæ make so much hair and so
little silk enter into the composition of their cocoons, that on the
first inspection they would be pronounced wholly composed of it[531];
others, thickening the interior of their cocoon with hair, line the
whole with a viscid matter like varnish[532].
The larvæ of some saw-flies (_Tenthredo_ L.) are remarkable for
inclosing themselves in a double cocoon, in which the inner is not,
as in the silk-worm &c., connected with the outer, but perfectly
distinct from it. Some species, as _T. Rosæ_ (_Cryptus_ Jur.), which
have but a small stock of silk, compose the outer cocoon of thick
silken cords crossing at right angles, and forming an oval net;
which at the same time that it protects them effectually from the
ants, which are always ready to attack them, demands much less silk
than a covering of a closer texture. But the tender nymph itself
requires to be inclosed in a case of a softer and more delicate
substance; and accordingly the inner cocoon is composed of fine silk,
woven so closely that the threads are scarcely perceptible under a
microscope[533]. Reaumur mentions a hymenopterous larva belonging
to Latreille's _Fossores_ (_Sphex_ L.) which thickened its cocoon
with the legs, wings, and other relics of the flies which it had
devoured[534]: trophies--like the drinking-cups of some savages, made
of the skulls of their enemies, or the skull pyramid near Ispahan--of
its powers of devastation.
It is a general rule, that those larvæ which spin cocoons, never
in ordinary circumstances become pupæ without having thus inclosed
themselves. An exception, however, is met with in the larva of
a species of ant noticed by De Geer (_Formica fusca_ L.), some
of the individuals of which inclose themselves in cocoons; while
others neglect this precaution, and undergo their metamorphosis
uncovered[535]. Rösel also made nearly the same observation on the
larva of the flea[536].
I must say something with regard to the _situation_, often very
remote from their place of feeding, in which larvæ fabricate their
cocoons. A very considerable number, probably the majority, form
them either partially (_Arctia lubricipeda_) or wholly under ground;
others beneath dead leaves, moss, or in the chinks of the trees;
others within the wood in substances on which they have fed; the
larva of _Cossus_ leaves in these a communication with the open air
by which the imago emerges; and a large number attach them to the
leaves and branches of trees and plants; the cocoon of _Donacia
fasciata_(?) is fastened by one side to the roots or surculi of
_Typha latifolia_. There is usually nothing very remarkable in
the mode of fixing them, the exterior threads being merely gummed
irregularly to different portions of the objects which support them.
But some effect this with greater art. I have one from New Holland,
very long, which is suspended from a twig by a long riband, as it
were, which entirely girths the twig. The larva of the magnificent
silk-moth, _Attacus Paphia_, actually forms a solid silken stalk
to its cocoon, an inch and half in length and a line in diameter,
fastened by the other extremity to a twig, which it closely surrounds
as if with a ring, at first sight resembling a fruit of a very
singular appearance[537]. I have specimens of this cocoon with both
stalk and ring. A bell-shaped cocoon fastened by a foot-stalk, but
of softer consistence, to a blade of grass, found by Mr. Sheppard, I
can also show you; and my friend Mr. Wilkin had a similar one out of
the late Mr. Hudson's collection. Most larvæ spin their cocoons in
solitude: some of those, however, which live in society do it close
together under their common tent.
There are other cocoons that should be noticed here, such as those
formed by the larva of _Zygæna Filipendulæ_, and some _Bombyces_,
saw-flies (_Tenthredo_ L.), and beetles (_Curculio_, _Donacia_ F.),
&c. These are formed of a substance which seems more analogous to gum
than silk, yet furnished from the silk reservoirs, and usually present
the appearance externally of parchment or membrane. That of the insect
first mentioned is coated, however, with a slight interior silken
lining; as indeed are almost all cocoons, of whatever substance.
* * * * *
The _second_ class, into which I have divided larvæ that inclose
themselves in cocoons, includes those which form their coverings
not solely or principally of silk, but in which other materials are
mixed more or less. The cocoons of some of these larvæ are merely
composed of a few leaves slightly tied together, either irregularly,
or arranged, particularly when they are of a linear figure, with
considerable symmetry. The grubs of many beetles, as of the
rose-beetle, _Cetonia aurata_, &c., prepare themselves a cocoon,
composed of earth, pieces of rotten wood, and any substances within
their reach: which they fasten together with a glutinous secretion.
The same material is employed by others in forming a cocoon wholly
of earth; which is sometimes, as that of the stag-beetle, _Lucanus
Cervus_, exceedingly hard; at others, as that of some moths, _Noctua
ambigua_, &c, so slight as to fall to pieces as soon as touched[538].
Other cocoons are formed of grains of earth. Reaumur has given a
very interesting account of the procedures of a larva in repairing
one of these cocoons, from which he had broken off the top when just
completed. Without quitting the interior of the walls that remained,
it put out its head from the breach, and for more than an hour
employed itself in selecting one by one grains of earth, which it
conveyed with its mandibles and deposited within its case: it next
spun all round the opening threads of silk, to which it attached
grains of earth taken from the previously-stored heap, uniting them
compactly by means of other silken threads. After employing three
hours in this laborious process, the industrious little mason had
reduced the diameter of the breach to a few lines. Reaumur was very
curious to know how it would fill up this orifice, which would no
longer admit the protrusion of its head outside the walls, as in
its previous operations. He concluded, that while the rest of the
cocoon was exteriorly formed of earth, this opening would be merely
closed with silk. He was mistaken, however: the artist knew how to
vary its manœuvres, and make its vault of one uniform texture. It
spun across the opening a little net of silk, between the meshes of
which it thrust grains of earth so dexterously that they projected
as far as the outer surface, retained there probably by silken
lines previously attached and fastened within. It then finished its
habitation by fortifying the inside of the orifice with another layer
of earth[539]. The ant-lion (_Myrmeleon_) spins a globular cocoon
with its anus, which it covers with grains of sand[540]. One that I
took in the forest of Fontainebleau, in the quarry that produces the
crystallized sandstone called the _Fontainebleau fossil_, was covered
with large and shining grains. Instead of the grains of earth or sand
employed by these larvæ, those of another tribe substitute grains
of stone detached from the softer walls, upon whose lichens they
previously feed, which they unite into solid oval cocoons[541]. Those
of a fourth form their cocoons of patches of short moss arranged with
the roots downwards, and forming a vault, as it were, of verdant
turf, admirably adapted for concealment[542]. The larvæ of some moths
form their cocoons of irregular pieces of bark tied together with
silk, and resembling when completed a knotty protuberance of the twig
on which they are fixed. That of _Pyralis tuberculana_ constructs a
pannier-shaped one of the parenchyma of the leaves of plants[543].
All these cocoons, however, must yield in point of singularity of
construction, materials, and ingenuity, to one formed by a small
caterpillar, described by the illustrious naturalist lately quoted,
which feeds upon the oak. This cocoon is wholly composed of small
rectangular strap-shaped pieces of the fine upper skin, or epidermis
of the twig upon which it rests, regularly fastened to each other
in a longitudinal direction with very slender silken cords. But the
mode of its construction is even more remarkable than the substance
of which it is fabricated. The caterpillar's first process is to
form its slips of bark into two flat triangular wing-like pieces,
projecting opposite to each other from each side of the twig,
somewhat like the feathers of an arrow. It does not, perhaps, require
any great degree of intelligence in a larva to give its cocoon the
usual oval form, when it begins to arrange its materials in that
shape from the very first, and round so good a mould as its own bent
body; but we surely must admit that it is a task to which no stupid
artist would be competent, to form first a multitude of strap-shaped
laminæ into two triangular plates, and then to bend these plates
into a case resembling the longitudinal section of a cone, with an
elliptical and protuberant base,--the figure which the cocoon of this
insect assumes. All the minutiæ of the manœuvres which it employs in
this nice operation could not be comprehended without a more diffuse
explanation than I have here room to give: suffice it to say, that
the caterpillar fastens silken lines to each exterior opposite and
longer side of the laminæ, and by applying all the weight of its
body forces them to bend and approach each other, in which position
it secures them by other shorter lines. It next repeats the same
process with the upper and shorter sides of the plates; which when
joined form the base of the cocoon. Both these tasks are accomplished
in less than an hour, and the seams are so nicely joined as to be
imperceptible. A fine inner tapestry of silk, covering all the
asperities of the exterior walls, concludes its labours[544]. It
is to be lamented that Reaumur was unacquainted with the moth that
proceeds from the pupæ inclosed in these ingenious cocoons; which
being small, and precisely of the same colour as the bark of the
twig that supports them, are not to be discovered but by a very
narrow inspection. It would seem, however, to be _Noctua Strigula_
of Berkhausen, _Pyralis strigulalis_ of Hubner[545]. The larva, he
informs us, is found in May: its body is flatter than common, of
a yellowish flesh-colour, clothed with tufts of red hair on each
segment, and furnished with fourteen feet. Should this description
enable you to detect it upon your oaks, a view of its ingenious
procedures would amply repay you for the trouble of seeking for it.
The larvæ of _Cerura vinula_, _Stauropus Fagi_, and several other
moths, form their cocoons of grains of wood gnawed from the trees on
which they feed. These grains they masticate, mixed with a glutinous
fluid secreted from the mouth, into a paste, which forms a covering
of an uniform smooth texture, and so hard as not readily to yield
to a knife. Of a substance apparently nearly similar is composed
the cocoon of a weevil related to _Liparus Pini_; which with its
inhabitant was given me by the ingenious Mr. Bullock. A little moth,
whose ravages have been before noticed[546], lines the interior of
the grain of barley, of which it has devoured the contents, with
silk; divides it into two apartments, into one of which it pushes the
excrement it had voided, and in the other assumes the pupa[547].
These, and the other larvæ mentioned above, commonly form their
cocoons of the substances I have indicated; but when by any cause
they are prevented from access to them, they often substitute such
other materials as are at hand. Reaumur fed a larva that formed its
cocoon of minute fragments of paper, which with its mandibles it
had cut from the piece that covered the glass vessel that contained
it[548]: and the same circumstance happened to Bonnet.
Upon a former occasion I described to you the cases of various kinds
formed and inhabited by the insects of the _Trichoptera_ Order
(_Phryganea_ L.) commonly called case-worms[549]. As these serve
for the pupa as well as the larva, they may be regarded as a kind
of cocoon. I shall not repeat here what I then said; but having
purchased from the collection of the late Mr. Francillon some that
seem to belong to this or some cognate tribe, that are of a curious
construction, I shall give you some account of two or three of
them in this place. The first is not quite three inches long, of a
sublanceolate shape, but rather widest towards one end. It consists
of an internal tough and thick bag or cocoon, of a silk resembling
fine wool of a dirty white colour, which is closely covered
transversely by pieces of the stalk of a plant, about three-fourths
of an inch in length, and crossing each other at an obtuse angle.
The next is thicker and shorter: the internal bag is just covered
with small fragments of wood like sawdust; over these are fastened
irregularly, short stout pieces of a pithy stick or stalk, and the
whole is clothed with a very close-woven ash-coloured web. It seems
difficult to conceive how the inclosed animal could contrive to
cover her habitation with this web without going wholly out of it.
The third is the most curious and remarkable of all. It is nearly
six inches long, and about four-fifths of an inch in diameter. It
consists of a bag of thick cinereous silk web, to which are fastened,
in a sextuple series, pieces of stick about an inch long, the end of
one mostly resting upon the base of another: between each series a
space of about three-tenths of an inch intervenes, but at the apex
they all converge. This probably imitates the branch or stem of some
tree or plant, in which the leaves are linear, and diverge but little
from the stem. A label upon it states its country to be New Holland.
I suspect the inhabitants of the two last cocoons to be terrestrial
animals: the first is probably a true aquatic case-worm.
* * * * *
The same purpose for which the cocoons above described serve, is
answered in the case of numerous _Dipterous_ insects, by a humble and
less artificial contrivance--the skin, namely, of the larva; which,
as was before observed[550], is never cast, but, when the insect is
about to enter into the pupa state, assumes a different form and
colour; becomes of a thicker and more rigid texture; and defends the
included pupa, which is separate from it, till its exclusion. In
this case the mouth of the larva is constantly different from that
of the perfect insect, or at least has not with it those relations
as to number and kind of organs, which have been observed in the
mouth of other larvæ compared with the insects that they produce.
The animal, immediately after it is clothed with this skin, if it
is opened, exhibits only a soft gelatinous pulp, in the surface of
which the exterior organs of the adult insect cannot yet be detected.
Nature requires more time for their elaboration, or at least for
the appearance of their outline, and to consolidate them. This pulp
first takes an oblong form (_Boule allongée_ Reaum.), and afterwards
that of the insect it is destined to give birth to[551]. The skin of
the larva also serves for a cocoon to the pupæ of male _Cocci_[552].
The grub of the genus _Anthrenus_, so destructive to our cabinets
of natural objects[553], when it assumes the pupa does not quit
its skin, but only splits it open longitudinally on the back, and
when it becomes an imago makes its exit through the orifice[554].
Some Lepidopterous larvæ even (_Alucita pentadactyla_, _Callimorpha
rosea_, &c.) assume the pupa state within their last skin[555].
* * * * *
When a larva has finished its cocoon,--which with some species, that
proceed so earnestly as though they had not a moment to lose, is the
work of a few hours, of others about two or three days,--after a
certain interval it casts its last skin, which is usually suffered to
remain in the cocoon (but which one moth, _Geometra lacertinaria_,
ejects through an opening purposely left in its bottom), and the pupa
makes its appearance[556]. This interval is exceedingly various. Most
larvæ assume the pupa state within a few days after they have formed
their cocoons; but some not for several weeks, or even months. The
caterpillar of _Bombyx cæruleocephala_, according to Rösel, lies
three weeks in the cocoon before this change is effected; those of
many _Pupivora_ and _Diplolepariæ_ Latr., according to Reaumur,
six months[557]; that of _Phalæna urticata_ nine months[558]; and
that of _Cimbex lutea_, according to De Geer, sometimes eighteen
months[559]. Brahm observes, that such larvæ of the double-brooded
moth, _Hepialus Testudo_, as form their cocoons in autumn, do not
become pupæ until the following spring; while those which form them
in summer undergo this change in a few days[560]. From this fact
it might be conjectured, that the degree of heat prevailing at
the time the insect incloses itself determines the period of the
pupa's appearance; but this supposition seems contradicted by what
Reaumur observed of a brood of the larvæ of _Phalæna urticata_, just
mentioned, which, though they formed themselves cocoons in September,
did not become pupæ till the June following[561]. I am unable,
therefore, to assign any plausible cause for these extraordinary
variations. The difficulty of comprehending how animals before so
voracious can live so long without food may be partly surmounted, by
adverting to the circumstance of its having attained its full growth,
and laid up a store of nutriment for the development of the perfect
insect. It is consequently no more wonderful that it should not have
need of any further supply without casting off its upper integument,
than that it should not eat after having done so and become a pupa.
FOOTNOTES:
[206] De Geer vii. 197.
[207] De Geer vii. 197.
[208] Ibid. 85.
[209] _Epist._ lxvii. 1694. 390.
[210] _Enum. Ins. Austr._ 575.
[211] _N. Dict. d'Hist. Nat._ i. 74.
[212] De Geer vii. 576.
[213] Ibid. 584.
[214] _Considerat. Géner._ 21. _Horæ Entomolog._ 353.
[215] De Geer, _Ibid._ Mr. W. MacLeay observes of the _Chilopoda_, or
Centipedes, that they moult in the manner of _Crustacea. ubi supr._ 352.
[216] De Geer iii. 549. The figure of the forceps in De Geer (Ibid.
_t._ xxv. _f._ 21) is not quite correct. The styles do not taper to a
point, but are filiform and acute.
[217] Compare De Geer iii. _t._ xviii. _f._ 2 and 12. _q._
[218] See above, VOL. II. p. 401.
[219] PLATE XVI. FIG. 4. _c._ Reaum. v. _t._ xix. _f._ 16. De Geer
_ubi supr._ _t._ xxxii. _f._ 26. According to Reaumur, the larva as
well as the pupa of _Chermes Ficus_ has wing-cases (iii. 353).
[220] These are in the female sex of some _Coleoptera_, as
_Lampyris_, &c. which retain in the perfect state nearly the same
form which they had when larvæ. The larvæ of some _Staphylini_ are
not very dissimilar in form to the perfect insect.
[221] The larvæ described in the first Section, which resemble the
imago, are usually covered with a skin not materially different from
that of the insect in that state.
[222] Huber _Fourmis._ 73; _N. Dict. d'Hist. Nat._ vi. 250.
[223] Reaum. v. 40. _t._ vi. _f._ 4-15.
[224] Müller, the Danish zoologist, relates, that he once met with a
papilio which, with the true wings of the genus, had a head without
antennæ or tongue, furnished with mandibles; and, in short, that of a
true caterpillar. It was a female, which deposited eggs that proved
barren. If this solitary instance was not a mistake, is it possible
that some parasitic larva had devoured only the inclosed head of the
butterfly, or so injured it that it could not reject the hard skin of
the larva, and yet not be destroyed?
[225] The only larvæ which have a visible distinct neck are those
of some _Dytisci_, _Staphylini_, and a few others, in which this
part is quite distinct: proving the erroneousness of the opinion of
those German entomologists, who consider the thorax as analogous to
the neck of other animals, and hence call it _Halsschild_. In some
lepidopterous larvæ, however, as in that of _Pieris Brassicæ_, though
no visible neck presents itself, one is very perceptible when the
insect stretches the head forward considerably. Reaum. i. 460.
[226] PLATE XVII. FIG. 13.
[227] Reaum. v. _t._ vi. _f._ 7. _i. c._
[228] In fact, in almost all Lepidopterous larvæ the head may be
regarded as divided into two lobes or eye-shaped portions, which
include in the angle formed by their recession anteriorly from each
other, the nasus (_clypeus_ F.), the labrum, and other instruments of
manducation. Posteriorly these lobes generally come into contact; but
I have a specimen in which there is a narrow space between them.
[229] _Ins. Surinam._ _t._ xvii.
[230] _Ins. Surinam. t._ liii.
[231] _Ibid. t._ xxxii.
[232] _Ibid. t._ viii.
[233] _Ibid. t._ xxiii.
[234] _Ibid. t._ xiv.
[235] I purchased this singular caterpillar from the collection of
the late Mr. Francillon, with his other exotic larvæ; but without any
indication of the fly to which it belonged.
[236] De Geer vi. 352.
[237] De Geer iv. 66. ii. 922.
[238] De Geer v. 170.
[239] De Geer says, he could not make out the number of eyes of
the larva of the whirlwig (_Gyrinus_): probably, as in that of
_Dytiscus_, there are six. iv. 362. 385.
[240] Pez. 188.
[241] ii. 923, _t._ xxxvi. _f._ 1, _b b._ Fabr. _Philos. Ent._ 60.
[242] Lyonnet 41. _t._ ii. _f._ 1. c.
[243] De Geer vi. 307.
[244] Ibid, ii. _t._ xvi. Comp. _f._ 2 _a a_ with _f._ 14 _a a_.
[245] In the larva of _Cicindela_ there are _six_ palpi, as in the
perfect insect.
[246] Lyonnet, _t._ i. _f._ 7. E. In the larva of _Callidium
violaceum_, however, this part is of a singular shape, being
orbicular. Kirby _Linn. Trans._ v. _t._ xii. _f._ 12. _a_.
[247] It is affirmed (_N. Dict. d'Hist. Nat._ vii. 333) that the
larvæ of those _Coleoptera_ that live in carcases have mandibles
almost membranous: those, however, of that of _Silpha rugosa_ are
horny and hard.
[248] Lyonnet, _t._ ii. _f._ 1. D D, and _f._ 2, 3, 4.
[249] Kirby in _Linn. Trans._ v. _t._ xii. _f._ 7 _b._
[250] Cuvier _Anat. Comp._ iii. 322.
[251] Reaum. vi. 340.
[252] The larva of _Cicindela campestris_ has mandibles of this
description. PLATE XVII. FIG. 13. _c´._
[253] See above, VOL. II. 275--.
[254] Reaum. v. 9. _t._ i. _f._ 4. _c c._ _l l._
[255] _Traité Anatom._ _t._ ii. _f._ 1. H H.
[256] Reaum. ii. _t._ 40. _f._ 4.
[257] De Geer v. 229.
[258] Ibid. iv. _t._ xi. _f._ 16. _p p._
[259] _Linn. Trans_. v. _t._ xii. _f._ 10.
[260] Cuvier _Anat. Comp._ iii. 323.
[261] De Geer iv. _t._ xv. _f._ 9. _b b._ The exterior and interior
palpi are both represented in this figure.
[262] Reaum. vi. _t._ xxxvii. _f._ 5. _e e._
[263] Ibid. i. 125.
[264] PLATE XXI. FIG. 9. The organ with which the larvæ of
_Hemerobius_, _Myrmeleon_, and _Hydrophilus_, spin their cocoons, is
situated in the _anus_. The spinneret of the _Cossus_ is figured by
Lyonnet _Anatom._ _t._ ii. _f._ 1. I. and _fig. 9_.
[265] De Geer vi. 370. This species (_Tipula Agarici seticornis_ De
Geer) has two separate spinnerets. _t._ xx. _f._ 8. _m m._
[266] Lyonnet 55--.
[267] Reaum. iv. 166.
[268] Reaum. v. 155.
[269] Ibid. vi. _t._ xxxvii. _f._ 7. _b p._
[270] Ibid. _m e e_.
[271] Ibid. _f._ 6. _p._
[272] Ibid. Compare _f._ 4 with _f._ 6, 7.
[273] Ibid. _t._ xxxvi. _f._ 12. _s u e_.
[274] Ibid. _n e_, and xxxviii. _f._ 7, _d c._; De Geer ii. _t._ xix.
_f._ 17. _d g._
[275] Reaum. vi. _t._ xxxvii. _f._ 4-6. 8.
[276] Ibid. _t_. xxxviii. First joint _f._ 8. _b f p._; jaws _f._ 7.
_c d._; opening _o_, Ligula, _f._ 6. _l._
[277] De Geer ii. _f._ 17. Jaws _g g_; claw _d_; tooth _h_.
[278] Ibid. 674.
[279] Ibid. ii. 674.
[280] Reaum. iv. 376.
[281] _N. Dict. d'Hist. Nat._ xii. 64.
[282] _Anat. Comp._ iii. 322.
[283] At first in the _Dytisci_ they appear to have five joints;
but, as I before observed, the first joint must be regarded as
representing the maxilla.
[284] Lyonnet _Anatom._ 55, 58.
[285] De Geer v. 203.
[286] De Geer iv. 5. Legs of this kind are figured PLATE XXIII. FIG. 7.
[287] In the larva, however, of _Sialis_, or some kindred genus, in
which, like those of _Scolopendra_, the prolegs are jointed, a pair
distinguishes each abdominal segment. See Reaum. iv. _t._ xv. _f._ 1,
2. Compare De Geer ii. _t._ xxiii. _f._ 11.
[288] See above, VOL. II 286--.
[289] Ibid. 288.
[290] Lyonnet _Anatom._ _t._ iii. _f._ 8. _Coxa_ B. _Trochanter_ C.
_Femur_ D. _Tibia_ E. _Tarsus_ F. _Claw_ G.
[291] De Geer iv. _t._ xiii. _f._ 20; and _t._ xv. _f._ 16.
[292] Ibid. ii. _t._ xvi. _f._ 5, 6, 7. _d e_: and _t._ xix. _f._ 4.
_c f g h_.
[293] The larva of a scarce moth (_Stauropus Fagi_. See PLATE XIX.
FIG. 4) is an exception to this. The first pair of its legs are of
the ordinary stature, but the two next are remarkably long, and so
thin and weak as to be unable to bear the body. Pezold. 119. Another
minute caterpillar described by Reaumur has the third pair of the
legs apparently fleshy and singularly incrassated at the apex into a
pyriform figure, terminated by a pair of claws. This conformation is
for some particular purpose in the economy of the animal, since they
are the most busily employed of all in arranging the threads of her
web. Reaum. ii. 258. In the larva of a geometer (_Geometra lunaria_)
the third pair are remarkably long. Illig. _Mag._ 402. In that of
another moth, according to Kuhn (_Naturf._ xvi. 78. _t._ iv. _f._
3), the third pair of the fore-legs is remarkably incrassated, being
twice as thick and long as the other pair, though consisting of the
same number of joints, the last of which has claws.
[294] On the legs and prolegs see also what is said above, VOL. II.
p. 286--.
[295] In some few instances these legs are dorsal. Ibid. 281.
[296] The claws or crotchets, though general, are not universal, in
Lepidopterous larvæ. An exception is furnished to the rule by the
singular _limaciform_ ones of _Hepialus Testudo_ and _Asellus_ of
Fabricius, two moths forming Haworth's genus _Apoda_, which have no
distinct prolegs, but in their stead a number of small transparent
shining tubercles without claws. The larva also of one of the
subcutaneous moths first discovered by De Geer in the leaves of the
rose (i. 446), but whose history is fully given by Goeze, _Naturf._
xv. 37-48, (who has satisfactorily ascertained that it is the true
larva of a _Tinea_ of Linné, but of a different habit from that of
most subcutaneous ones), has no true legs, and eighteen prolegs
without any claws. Another subcutaneous larva, for the history of
which we are indebted to M. Godeheu de Riville, is according to him
entirely deprived of legs of any kind (Bonnet ix. 196--.); as is
another of the same tribe that feeds on the poplar, an account of
which is given by Goeze _Naturf._ xiv. 105.
[297] PLATE XXIII. FIG. 7. See also below, p. 137.
[298] Lyonnet _Anatom._ 84. _t._ iii. _f._ 11, 12.
[299] _Hist. Vermium_, 130.
[300] PLATE XXIII. FIG. 1.
[301] PLATE XXIII. FIG. 18.
[302] _Account of Locust-tree Insects_, 69.
[303] Reaum. iv. 443. _t._ xxx. _f._ 6. _l l._ _t._ xxii. _f._ 6. _l l._
[304] De Geer vi. 383. and 137. _t._ viii. _f._ 8, 9.
[305] See above, VOL. II. p. 278. De Geer _ubi supr._ 376.
[306] Reaum. iv. 184. _t._ xv. _f._ 12. _c c._
[307] De Geer v. 203.
[308] See above, p. 110, 114.
[309] Some few subcutaneous larvæ have more, as that, before
mentioned, observed by De Geer in the leaves of the rose; which has
eighteen prolegs, and no true ones.
[310] De Geer ii. _t._ xl. _f._ 15, 16. Bergman has added to these
four classes of the larvæ of saw-flies, a fifth; the insects
belonging to which, he affirms, though they have sixteen prolegs,
are without the anal pair. Ibid. 931. But as neither De Geer nor
Reaumur ever met with one of this description, it is probable he was
mistaken. Reaumur thought he had seen one with eighteen prolegs upon
_Erysimum alliaria_ (v. 91), but he does not speak positively.
[311] De Geer v. 288.
[312] De Geer iv. 157.
[313] Ibid. v. 36. _t._ ii. _f._ 11.
[314] See above, VOL. I. p. 171.
[315] De Geer v. 228.
[316] Ibid. 233.
[317] See above, VOL. II. p. 281.
[318] De Geer vi. 388.
[319] Ibid. 389.
[320] Reaum. v. _t._ v. _f._ 10.
[321] Ibid. 31. This larva has also a pair of pediform processes at
the anus, surrounded at the end with claws (_t._ v. _f._ 4, 5, _s
s_), which he saw the animal use in locomotion; but which he suspects
to be respiratory organs (Ibid. 33), which Latreille asserts they
are. _Gen. Crust. et Ins_. iv. 249.
[322] De Geer Ibid. _t._ xxiv. _f._ 15-17.
[323] Ibid. 383.
[324] Ibid. 111. _t._ vi. _f._ 14-16.
[325] Merian _Ins. Sur. t._ xx.
[326] _Ibid. t._ xxxiv.
[327] I have a caterpillar, I believe from Georgia, in which this
horn is nearly an inch long, filiform, slender, and tortuous.
[328] PLATE XVIII. FIG. 12. _c._
[329] That of _Sphinx Iatrophæ_ L. appears to be jointed, at least it
is moniliform. Merian _Surinam. t._ xxxviii. Compare also _t._ iii.
[330] _N. Dict. d'Hist. Nat._ vi. 252.
[331] Schellenberg _Entomolog. Beytr. t._ 1.
[332] Smith's _Abbott's Insects of Georgia, t._ xiii.
[333] De Geer ii. 507. _t._ xi. _f._ 16. _m n. t._ xiv. _f._ 7.
[334] _N. Dict. d'Hist. Nat._ vi. 256.
[335] See above, VOL. II. p. 244--.
[336] PLATE XIX. FIG. 1. _a._
[337] Reaum. i. _t._ xxx. _f._ 2. _N. Dict. d'Hist. Nat._ xxiv. 490,
497--.
[338] Ray says he found it feeding on common fennel, about Middleton
in Yorkshire: _Lett._ 69. The indefatigable Mr. Dale recently found
many in the neighbourhood of Whittlesea-mere, feeding on _Selinum
palustre_. It will also eat the wild carrot.
[339] This gentleman was remarkable for the admirable manner in which
he prepared caterpillars, so as scarcely to differ from life.
[340] Reaum. i. 92.
[341] Bonnet ii. 84--. iii. 1.
[342] See above, VOL. II. 251--.
[343] Bonnet ii. 88.
[344] De Geer ii. 507. _t._ xi. _f._ 16. _c._
[345] Rös. iv. 162.
[346] De Geer i. 322--. See PLATE XIX. FIG. 2. _a a._
[347] Reaum. ii. 275. _t._ xxii. _f._ 3.
[348] Ibid. 276. _t._ xxii. _f._ 4, 5.
[349] _Ins. Surinam. t._ vii. _Nymphalis Amphinome_ xxiii. _Morpho
Teucer t._ xxxii. _Papilio Cassiæ_.
[350] This is not, however, universally the case, for the caterpillar
of a Geometer described by Reaumur (ii. 363. _t._ xxix. _f._ 8.) (_G.
amatoria_) has a pair of fleshy anal horns, terminating, it should
seem from his figure, in a minute hook that the animal uses as a
forceps; which has at the same time the anal legs, of which indeed
these horns seem to be appendages.
[351] Sepp. iv. _t._ l. _f._ 6-8.
[352] PLATE XIX. FIG. 5. _a b._ Sepp. iv. _t._ xxi. _f._ 4-7.
[353] Rös. iii. 69.
[354] PLATE XVII. FIG. 13. _c._
[355] _N. Dict. d'Hist. Nat._ vii. 95.
[356] De Geer v. 170-- _t._ v. _f._ 19-23. Compare Reaum. iii. 235--.
[357] PLATE XIX. FIG. 11. _a._ De Geer vi. 137. Reaum. iv. 482.
[358] Reaum. iv. _t._ xiv. _f._ 9, 10.
[359] Reaum. v. 32. _t._ v. _f._ 3-5. Latr. _Gen. Crust. et Ins._ iv.
249.
[360] De Geer ii. 1031. _t._ xl. _f._ 13, 14. _k k._
[361] _N. Dict. d'Hist. Nat._ x. 430.
[362] De Geer ii. 697. _t._ xxi. _f._ 4, 5. _b b b._
[363] Reaum. v. _t._ vi. _f._ 7. _n._
[364] PLATE XVIII. FIG. 2.
[365] Reaum. ii. _t._ xxv. _f._ 20.
[366] See above, VOL. II. p. 245--.
[367] Reaum. iii. 384. vi. 366. _t._ xxxii. _f._ 7, 8.
[368] Rös. iii. _t._ lxviii. _f._ 1. Meinecken _Naturf._ vi. 120.
[369] Ibid. xiii. 175.
[370] In the larva of _Tenthredo Cerasi_ L., and some others, no
traces of segments are to be seen; and in many coleopterous and
dipterous ones the folds of the skin prevent the segments from being
distinctly perceptible.
[371] Reaum. ii. 361. In the larva of a small common moth often met
with in houses (_Aglossa pinguinalis_), every segment is divided
into two parts, and underneath has two deep folds, by means of which
these two parts can separate to a certain point, or approach again,
according to circumstances. Thus Providence has enabled them to
prevent their spiracles from being stopped by the greasy substances
on which they often feed. _N. Dict. d'Hist. Nat._ i. 208.
[372] See above, p. 110.
[373] _N. Dict. d'Hist. Nat._ xvii. 329.
[374] _Hor. Entomolog._ 285. 397--. 422. 462--. &c.
[375] _Ibid._ 399-401.
[376] _Hor. Entomolog._ 423.
[377] See above, p. 23.
[378] The _Intestinaux cavitaires_ of Cuvier, and the _Epizoaria_ of
Lamarck. See _Hor. Entomolog._ 286--.
[379] _Hor. Entomolog._ 422. comp. 463. Mr. MacLeay's idea of the
larva of _Meloe_ is taken from the animal which Frisch, Goedart, and
De Geer imagined to be such; but upon this opinion there rest great
doubts. (See Kirby _Mon. Ap. Angl._ ii. 168, and Latreille _N. Dict.
d'Hist. Nat._ xx. 109.) At p. 464 he gives also _Mordella_ and many
_Heteromera_ as having Thysanuriform larvæ. He thinks, that probably
that of _Clerus_ is of the same description; to which he suspects
that many of Latreille's _Malacoderma_ likewise belong.
[380] PLATE XVIII. FIG. 1. as to the thoracic shield.
[381] _May_ 27, 1822. This day, T. Allen, Esq. F.L.S. brought me in a
phial a vast number of the little insect which Goedart, Frisch, and De
Geer took for the larva of _Meloe Proscarabæus_, which he found on the
leaves of _Achillea Millefolium_. These little animals were coursing
each other with wonderful velocity over the sides of the phial. To
assist them in their motions, they applied to the surface of the glass
the end of their abdomen, using it, like many larvæ of _Coleoptera_,
as a seventh leg. This circumstance excited a suspicion in the minds
of both Mr. MacLeay sen., then visiting me, and myself, that after all
they might be _coleopterous_ larvæ. One, amongst other circumstances,
however, seemed to militate strongly against this opinion; namely, that
in this infinite number none appeared to differ in _size_.
[382] PLATE XVII. FIG. 13.
[383] Ibid. FIG. 12.; PLATE XVIII. FIG. 4, 11, 13, &c.
[384] PLATE XVIII. FIG. 3, 9.
[385] PLATE XIX. FIG. 8.
[386] _Ibid._ FIG. 3. Reaum. v. 97. _t._ xii. _f._ 17, 18.; De Geer
ii. 1004. _t._ xxviii. _f._ 12.
[387] See above, p. 110, 114, 138, 142.
[388] PLATE XVIII. FIG. 7.
[389] PLATE XVIII. FIG. 5.
[390] PLATE XIX. FIG. 9.
[391] PLATE XVIII. FIG. 2.
[392] _Hor. Entomolog._ 465.
[393] De Geer iv. 66. _t._ ii. _f._ 5-8.
[394] Ibid. _t._ xiii. _f._ 16-19. A very singular larva, which preys
upon that of _Aleyrodes proletella_ Latr., if Reaumur's figure be
correct (ii. _t._ xxv. _f._ 18-20), is of a perfect _Chilopodiform_
type, the abdominal legs being represented by a tubercle crowned by
a bristle: yet even this, which turns to a minute beetle (Ibid. _f._
21), has some tendency to the _Anopluriform_ type.
[395] "Squilla _insectum a_ squilla _pisce parum differt_." Mouffet,
319.
[396] A remarkable difference obtains between the larva of the
wire-worm and that of _Elater undulatus_. In the former, the last
segment is longer than the preceding one, terminating in a small
acute mucro at the apex, with a deep cavity, perhaps a spiracle, on
each side, at the base. In the latter, this segment is shorter than
the preceding one, forming above a nearly circular plate; the margin
of which is a little elevated, and armed on each side with three
teeth, and at the apex with a pair of furcate recurved horns, and
without any basal spiracle. De Geer iv. 156. _t._ v. _f._ 25. I have
a similar larva, but not the same species.
[397] _Hor. Entomolog._ 397.
[398] _Ibid._ 399.
[399] _Ibid._ 438. Note *.
[400] _Traité Element._ ii. 35. _n._ 577.
[401] _Trans. Linn. Soc._ vii. 66. _t._ vi. _f._ 3.
[402] Compare De Geer iii. _t._ xi. _f._ 3. and _t._ xvii. _f._ 14. &c.
[403] Ibid. _t._ i. _f._ 4, 9. _t._ ii. _f._ 15. _t._ ix. _f._ 4.
[404] See above, p. 125--.
[405] Compare PLATE VI. FIG. 6. with FIG. 12 _c_, _d_, _d_.
[406] De Geer ii. _t._ xxi. _f._ 4, 5.
[407] Swamm. _Bibl. Nat. t._ xiii. _f._ 1.
[408] _Hor. Entomolog._ 438.
[409] See above, VOL. II. p. 256.
[410] De Geer ii. _t._ xxiii. _f._ 9-14. Comp. Reaum. iv. _t._ xv.
_f._ 1, 2.
[411] De Geer ii. _t._ xiv. _f._ 7. &c. The caterpillar of _P. G.
Scratiotata_ L. like those of _Phryganeæ_, has these respiratory
threads. _Ibid._ i. _t._ xxxvii. _f._ 2-6. De Geer has described the
larva of a _Phryganea_ L. which is without any respiratory threads,
ii. 569. _t._ xv. _f._ 10.
[412] _Hor. Entomolog._ 401. Montagu in _Linn. Trans._ vii. 67.
[413] _Ins. Surinam. t._ xxviii. Compare _Ibid._ _t._ xix. right-hand
figure.
[414] PLATE XVIII. FIG. 10.
[415] Swamm. _Bibl. Nat. t._ xxxix. PLATE XIX. FIG. 13.
[416] Lyonnet 69--.
[417] _Surinam_, _t._ lvii. right-hand figure.
[418] Sepp iv. _t._ ii. _f._ 3. _t._ xvi. _f._ 2, 3.
[419] _N. Dict. d'Hist. Nat._ vi. 254.
[420] PLATE XIX. FIG. 6. One of these larvæ was taken at Melville
Island. See Parry's _Voyage_, Appendix No. x. 37.
[421] Sepp. iv. _t._ viii. _f._ 4. Some species have three, others
four, and others even five of these brushes. _N. Dict. d'Hist. Nat._
vi. 255.
[422] _Ibid._ Merian _Eruc._ xxxiv. upper left hand figure.
[423] Merian _Ins. Surinam_. _t._ lx.
[424] _Ibid._ _t._ xl.
[425] See above, VOL. I. p. 238.
[426] De Geer iv. 207. _t._ viii. _f._ 4-6.
[427] _Ins. Sur._ _t._ xix. right hand caterpillar.
[428] _Ibid._ xli.
[429] PLATE XVIII. FIG. 13.
[430] _Ins. Sur._ _t._ xxix.
[431] _Ibid._ _t._ vii. liii.
[432] Smith's _Abbott's Ins. of Georg._ Pref. vi.
[433] _Prodromus Entomology._
[434] _Ins. Sur._ _t._ xliii. The figure represents only the two
spines near the head as thus circumstanced.
[435] Reaum. v. _t._ xii. _f._ 8, 14. PLATE XVIII. FIG. 11.
[436] See above, VOL. II. p. 238. This, with _B. imperatoria_, &c. in
the modern system, should form a genus.
[437] _Ins. Sur._ _t._ xlviii. right hand figure.
[438] _Ibid._ _t._ xi.
[439] _Ibid._ _t._ xxiii.
[440] _Ibid._ _t._ xxix.
[441] Reaum. v. 95.
[442] Huber _Mœurs des Fourmis_, 79.
[443] See above, VOL. II. p. 276--.
[444] Reaum. v. 72. _t._ ix. _f._ 2-4.
[445] Rös. _t._ 211.
[446] See above, VOL. I. p. 29, 198--.
[447] De Geer iii. 111. Comp. 121. It would be as well to adopt the
French word _flocon_, instead of locks or flocks, which strictly mean
very different things.
[448] vii. 604. _t._ xliv. _f._ 26.
[449] _Fn. Germ. Init._ xxxvi. 21.
[450] _Syst. Rhyng._ 311. 29.
[451] _N. Dict. d'Hist. Nat._ ix. 554.
[452] _Natural History of the Slug-worm_, 7.
[453] _Ins. Surinam._ _t._ xv. xvii.
[454] The larvæ of _Carabus_ L. form one, being generally black.
[455] _Annales de Chimie_ ii.
[456] _Wien. Verz._ 219.
[457] _Wien. Verz._ 4.
[458] Reaum. v. 92.
[459] _Ins. Surinam._ _t._ xi.
[460] ii. 1017.
[461] De Geer i. 57.
[462] _Ibid._ 58. Reaum. i. _t._ xxxix. _f._ 13, 14.
[463] De Geer ii. 400.
[464] See above, VOL. I. _Letters_ xii. xiii.
[465] Bonnet (ii. 18) mentions, that the young larvæ of a butterfly
(_Pieris Cratægi_), after devouring the exuviæ of the eggs from which
they were hatched, gnawed those which were not so: not, however,
so as to destroy the included animal, but rather to facilitate its
egress. Those also of _Coccinella bipunctata_ which I lately bred
from the egg, as soon as hatched began to devour the unhatched ones
around them, which they seemed to relish highly. I am inclined to
believe, however, that this unnatural procedure was to be attributed
to the circumstance of the female not having had it in her power to
place her eggs in the midst of _Aphides_, their proper food.
[466] _N. Dict. d'Hist. Nat._ xx. 359.
[467] In the human species, after certain fevers a simultaneous
and total moult, if the term may be so applied, takes place. I
experienced this myself in my boyhood; when convalescent from
_Scarlatina_, the skin of my whole body, or nearly so, peeled off.
[468] The translator, more ignorant of natural history than his
author, has turned the "_linguis_ micat ore trisulcis" of Virgil,
into "darts his forky _sting_."
[469] VOL. I. p. 70.
[470] See above, p. 52--.
[471] Cuvier _Anat. Comp._ ii. 596. _N. Dict. d'Hist. Nat._ xxvi. 165.
[472] Cuvier _Ibid._ 624.
[473] Reaum. i. 182.
[474] _N. Dict. d'Hist. Nat._ vi. 290.
[475] Those Diptera whose metamorphosis is coarctate (VOL. I. p. 67),
bees, the female _Cocci_, &c. do not cast their skin in the larva
state. Reaum. iv. 364. _N. Dict. d'Hist. Nat._ xx. 365.
[476] _N. Dict. d'Hist. Nat._ vi. 289. xx. 372. Cuvier _Anat. Comp._
ii. 548. M. Cuvier (_Ibid._ 547.) asserts, that most _Papiliones_ and
_Bombyces_ moult _seven_ times.
[477] _Œuvr._ ii. 71.
[478] Reaum. ii. 75.
[479] _Bibl. Nat. E. Trans._ i. 135. col. B. _t._ xxvii. _f._ 6.
[480] _Œuvres_, viii. 303.
[481] _Entwickelungsgeschichte_, &c. 34, 88. Swammerdam on the
contrary affirms, that "on the hinder part of the cast skin where
it is twisted and complicated, whoever accurately examines the skin
itself may still observe the coat that was cast by the _intestinum
rectum_." _Ubi supr._ 136. col. A.
[482] _N. Dict. d'Hist. Nat._ vi. 290
[483] Reaum. iv. 604.
[484] Ibid. 364. _N. Dict. d'Hist. Nat._ xx. 365. Huber _Fourmis_ 78.
M. Huber does not say expressly that the grubs of ants do not change
their skin; but his account seems to imply that they change it only
previously to their metamorphosis.
[485] Lyonnet 11.
[486] _N. Dict. d'Hist. Nat._ vi. 290.
[487] _De Bombycibus_, 68.
[488] _Opusc._ i. 27.
[489] _Linn. Trans._ x. 399.
[490] _N. Dict. d'Hist. Nat._ vii. 129.
[491] As the larvæ of Ephemeræ usually live in the submerged part of
the banks of rivers, perhaps they may be regarded as following the
economy of subterranean _terrestrial_ larvæ.
[492] A caterpillar nearly answering to the description of that of
_Bombyx camelina_, which I found upon the hazel, after a few days
produced sixteen grubs of some _Ichneumon_. At first these grubs
were green, but they became gradually paler; and after a day or two
became pupæ. But I mention this circumstance here for another reason:
upon examining them after this last occurrence, I observed that they
adhered to the lid of the box in which I kept the larva, arranged
somewhat circularly; and at a little distance from the anus of each
was a pea-green mass, consisting of about eight oval granules, which
appeared like so many minute eggs. These were the excrement evacuated
by each grub previously to its becoming a pupa. The appearance of
this little group, with their verdant appendage, formed a curious
spectacle: they are still pupæ, July 30, 1822.
[493] Except some species of _Polyammatus_ Latr. (_Thecla_,
_Argynnis_ F.), _P. Argiolus_, _Corydon_, &c., and _Hesperia Rubi_,
_Betulæ_ F., &c. Some of the larvæ of the former become pupæ within
the stalk of some plant, or partly under the earth: those of the
latter usually in a leaf to which the abdomen is fastened by various
threads. These last are the _rouleuses_ of the butterfly-tribe,
living, like some moths, in leaves that they have rolled up. _N.
Dict. d'Hist. Nat._ xxiv. 499.
[494] PLATE XXIII. FIG. 1. _a._
[495] PLATE XXIII. FIG. 8. _a._
[496] Bonnet is of opinion that this twirling process is not with any
view to get rid of the exuviæ, but is caused only by the irritation
occasioned by the spines of the skin of the caterpillar when they
touch that of the pupa. _Œuv._ ii. 109.
[497] For the above account see Reaum. i. _Mem._ x. xi.
[498] _N. Dict. d'Hist. Nat._ vi. 291--.
[499] _De Bombyc._ 24.
[500] i. 498.
[501] _De Bombyc._ 43.
[502] _N. Dict. d'Hist. Nat._ vi. 294.
[503] Lesser. L. ii. 150, note 22. Boyle says an English lady found
that the silk of a single cocoon would extend 300 English leagues or
900 miles. But this must be a mistake.
[504] Reaum. i. 555--.
[505] PLATE XVII. FIG. 5. _b._
[506] De Geer i. _t._ xxxii. _f._ 3-6.
[507] De Geer i. 463--.
[508] Reaum. ii. _Mem._ xi. Comp. De Geer ii. 162. Reaum. ii. 424.
[509] _B. Catax_--Pupa arcte folliculata. _Fab._
[510] _Travels in Greece_, 285.
[511] See above, VOL. I. p. 476--.
[512] Merian _Surinam._ _t._ xv.
[513] Reaum. ii. _t._ xxiii. _f._ 5.
[514] Sepp. iv. _t._ viii. _f._ 5.
[515] Reaum. i. _t._ xliv. _f._ 2.
[516] PLATE XVII. FIG. 7.
[517] I have a black one from Mr. Francillon's cabinet.
[518] _N. Dict. d'Hist. Nat._ vi. 294.
[519] See above, VOL. II. p. 298--.
[520] Reaum. ii. 436.
[521] Reaum. i. 503.
[522] Peck on _Locust-tree Insects_, 69.
[523] Bonnet ii. 260.
[524] Sepp. iv. _t._ ii. _f._ 4.
[525] Brahm. _Ins. Kal._ 289.
[526] PLATE XVII. FIG. 8.
[527] The thick cocoons of _Attacus Paphia_, _Polyphemus_, &c. are
also thus fastened between leaves.
[528] Merian _Europ._ ii. _t._ ix.
[529] Reaum. ii. 284.
[530] Ibid. i. 524.
[531] Bonnet ii. 297.
[532] Ibid. ix. 181.
[533] Reaum. v. 102.
[534] Ibid. iv. 269.
[535] De Geer ii. 1084. Comp. Ray _Hist. Ins._ Præf. xi. It is the
opinion of M. P. Huber, that in this case the _naked_ pupæ are
deprived of their cocoons by the neuters: he states, indeed, that
he has often seen them pulled off by them, and also by those of
_F. canicularia_; and he seems to think that these larvæ are never
developed. _Mœurs des Fourmis_, 84. note 1.
[536] II. viii. 16.
[537] _Linn. Trans._ vii. _t._ ii. _f._ 5, 6.
[538] _Wien. Verz._ I possess a cocoon of this kind from New Holland,
even now quite solid, and retaining its form. No silk appears to have
been used in its composition.
[539] Reaum. i. 579.
[540] Ibid. vi. 368.
[541] Ibid. i. 542.
[542] Ibid. 543.
[543] _Linn. Trans._ i. 196.
[544] Reaum. i. 545--.
[545] _Pyral._ 8. 3. _t._ iii. _f._ 16.
[546] See above, VOL. I. p. 172--.
[547] Reaum. ii. 491.
[548] Reaum i. 540.
[549] See above, VOL. I. 167--. II. 264.
[550] See above, VOL. I. p. 67.
[551] _N. Dict. d'Hist. Nat._ xvi. 269--. xxii. 76.
[552] Reaum. iv. 32. The author here quoted asserts that the grub
of _Ichneumon Larvarum_ L. retains its skin, which, he says, is
so transparent that the form of the nymph can be seen through it.
Ibid. ii. 447. De Geer, however, found that this really did cast its
skin, which is so transparent as to be scarcely visible, by pushing
it gradually towards the anus, where it soon dries up and cannot
then be discovered. De Geer ii. 893--. According to Rösel the same
circumstance attends the transformation of _Coccinella renipustulata_
Illig. (_C. Cacti_ Ent. Brit.), which at first perplexed him not
a little. It is probable that in this case the retention of the
skin was accidental; for some of the grubs of a _Mycetophila_, the
transformation of which I observed, became pupæ within their last
skin, while others wholly disengaged themselves from it. The cause of
this variation, I conjectured, arose from the former being too weak
to extricate themselves from the skin.
[553] See above, VOL. I. p. 238. _Byrrhus Musæorum_ belongs to this
genus.
[554] _N. Dict. d'Hist. Nat._ ii. 161.
[555] _Pezold._ 102.
[556] De Geer i. 339--.
[557] Reaum. ii. 423, and iii. 497.
[558] Ibid. i. 605.
[559] De Geer ii. 941.
[560] Brahm _Insek._ 72.
[561] Reaum. _ubi supra._
LETTER XXXI.
_STATES OF INSECTS._
PUPA STATE.
We have now traced our little animals through their egg and larva
states, and have arrived at the third stage of their existence, _the
Pupa State_. This, to include all, can only be defined,--that state
intervening between the larva and imago, in which the parts and organs
of the perfect insect, particularly those of sex, though in few cases
fully developed, are prepared and fitted for their final and complete
development in the last-mentioned state; and in which the majority of
these animals are incapable of locomotion, or of taking food.
Pupæ, like larvæ, may be separated into two great divisions:--
I. Those which, in general form, more or less resemble the larvæ
from which they have proceeded.
II. Those which are wholly unlike the larvæ from which they have
proceeded.
I. To the first division belong, with some exceptions[562], the
_Dermaptera_, _Orthoptera_, _Hemiptera_, and most _Aptera_, with the
neuropterous tribes of _Libellulina_, _Ephemerina_, and the genus
_Termes_, in the class _Insecta_; and the majority of the _Arachnida_.
This, like the first division of larvæ, may be subdivided into two
corresponding smaller sections; the first including those pupæ which
resemble the larvæ, except in the relative proportion and number of
some of their parts; and the second those that resemble them, except in
having the rudiments of wings, or of wings and elytra.
i. The first subdivision will include the pupæ, if they may be so
called[563], of insects of the _Aptera_ order, and of the class
_Arachnida_: as, lice, _Poduræ_, _Lepismidæ_, centipedes, millipedes,
mites, harvest-men, spiders, scorpions, &c. These mostly differ from
their larvæ only in that the relative length or number of their legs,
the number of the segments of the body in some, or the development
of their palpi, more nearly approach the characters of the perfect
insect; and in that while in their larva state they have two or
more skins to cast, previously to their assumption of the imago, in
their pupa state they have but one. In fact, this last circumstance
is the only one which, strictly speaking, characterizes the pupæ
of this subdivision; as the changes which take place in the number
and proportion of the organs are partly produced with each change
of the larva's skin. And hence, as it is not easy to ascertain what
number of skins a spider, for example, has yet to cast, and as
both the larva and pupa differ so little from the perfect insect,
it is very difficult to determine in what state insects of this
division are. From this difficulty has probably arisen the too great
multiplication of species in some of these tribes, particularly the
_Arachnida_, the larva and pupa having been mistaken for perfect
insects. The pupæ of this subdivision were named by Linné _complete_,
from the near resemblance which they bear to the imago.
ii. The second subdivision will include the pupæ of the _Dermaptera_,
_Orthoptera_ and _Hemiptera_ orders, with few exceptions; as
likewise the _Libellulina_, _Ephemerina_, and _Termitina_? amongst
the _Neuroptera_: including the well-known tribes of earwigs,
cockroaches, crickets, grasshoppers, locusts, lanthorn-flies,
froghoppers (_Cicada_ L.), bugs, plant-lice, dragon-flies, day-flies,
white ants, &c. Of these, as in the former subdivision, the pupæ
are equally capable of eating and moving with the larvæ, which they
resemble, except in having the rudiments of wings, or of wings
and elytra. The pupæ of the three orders first enumerated differ
from those of the _Neuroptera_ in resembling the perfect insect in
most instances, both as to shape and the organs for taking their
food; and in all other respects, except in not having their wings
and elytra fully developed[564]. The resemblance of the pupæ of
the _Libellulina_ and _Ephemerina_ to the perfect insects is more
distant, and the above organs in the two states are very dissimilar;
for the pupæ of the former are furnished with a prehensory mask
similar to that of the larvæ before described[565], which the perfect
insect has not; and those of the latter with the usual oral organs
of masticating insects, of which the imago has scarcely the rudiments.
I have applied the term _rudiments_ to the wings and elytra in
this state, not in a strict sense, but merely to denote their
appearance; for in fact the wings, &c. are complete, but only folded
up longitudinally and transversely, and inclosed in membranous
cases, which when the last change takes place remain attached to
the puparium or pupa-case. The tegmina or hemelytra in this state
usually cover the wings, and the upper wings the under; but in the
_Libellulina_ both are usually visible. Though commonly very small
compared with the instruments of flight in the perfect insect, some
of these rudiments, contrasted with the majority, are of considerable
magnitude. This is the case with those of some species of _Chermes_,
as we learn from De Geer[566].
II. The second grand division comprises by far the largest number of
pupæ: those of all _coleopterous_, _strepsipterous_, _lepidopterous_,
_hymenopterous_, _dipterous_, and _aphanipterous_, and by far the
majority of _neuropterous_ insects, as well as the _hemipterous_ genus
_Aleyrodes_, and one sex of _Coccus_ of the same order. These pupæ,
however, though agreeing in the circumstance of being unlike the larvæ
from which they proceed, differ from each other in several respects,
and require to be divided into three great sections, as under:--
i. Those pupæ in which the _parts_ of the future insect, being
folded up under a membranous skin closely applying to each, are
distinctly _visible_. To this head belong generally, the pupæ
of _coleopterous_[567] and _hymenopterous_ insects; those of
the _neuropterous_ genera _Myrmeleon_ and _Hemerobius_, &c.;
the _Trichoptera_; amongst the _Diptera_, _Culex_, _Tipula_ L.,
_Tabanus_, _Bombylius_, &c.; and that of the flea (_Pulex_). These
were the _incomplete_ pupæ of Linné.
ii. Those pupæ in which the _parts_ of the future insect, being
folded up under a harder skin, are _less_ distinctly _discoverable_.
To this subdivision belong the pupæ of all _Lepidoptera_, and of them
alone. These are what Linné termed _obtected_ pupæ.
iii. Those pupæ which are inclosed in the thick and opaque skin of
the larva, through which no _trace_ of the perfect insect can be
_discovered_. These, which Linné termed _coarctate_ pupæ, include a
large proportion of the _dipterous_ genera; as _Œstrus_ L., _Musca_
L., _Empis_ L., _Conops_ L., &c. &c.[568]
I shall next advert, chiefly to the pupæ of the grand division last
described, under the distinct heads of _substance_, _figure_, and
_parts_; _colour_, _age_, _sex_, _motions_, and _extrication of the
perfect insect_.
* * * * *
i. As to their _substance_--at first interiorly all pupæ consist of
a milky fluid, in which the unformed members of the future perfect
insect may be said to float, and in which they may be discerned,
and separated with the point of a pin[569]. In proportion as
these acquire consistency, and are more and more developed by the
absorption of the surrounding fluid, they occupy its place, and fill
up the cavity of the puparium. The rest of this fluid passes off
by transpiration[570]. Reaumur is of opinion that it is from the
epiploon, or _corps graisseux_, that this matter is prepared, which
he regards as analogous to the white of an egg[571]. In _coarctate_
pupæ the included animal, or the pulp that contains its germes (in
which the limbs and body at first are not discernible), fills at
this period the whole skin-cocoon; but in proportion as the above
evaporation takes place, and the consolidation of the body and parts
proceeds, it shrinks at each end, so that when near assuming the
imago, a considerable cavity appears both at the head and tail of
the cocoon[572]. At this period of its existence, from the quantity
of fluid included in the puparium, the animal weighs usually
considerably more than it does when become a perfect insect[573].
The _exterior_ integument or _skin_ of pupæ, which is usually lined
with a very thin white pellicle, is of different consistence in
different orders. In the _Coleoptera_ and _Hymenoptera_ it is,
with a few exceptions, of a soft and membranous texture; in the
_Lepidoptera_ (especially those that are not defended by cocoons),
and _Diptera_, it is more rigid and harder, being either coriaceous
or corneous. Lepidopterous pupæ, however, are not excluded from
the last skin of the larvæ with this hard covering. At the moment
of this change the envelope is nearly as soft and membranous as
in the order first mentioned. But they are besides covered with
a viscous fluid, which appears to ooze out, chiefly from under
the wings, and which very soon drying, forms the exterior hard
shell[574]. At first the antennæ, wings, and legs, like those of
_Coleoptera_ and _Hymenoptera_, can be each separated from the body;
and it is only after these parts have been glued together by the
fluid just mentioned, which takes place in less than twenty-four
hours[575], that they are immoveably attached to the body of the
pupa, as we usually see them. In fact, the essential difference
between incomplete and obtected pupæ seems to be, that in the former
the limbs and body are only covered each with a single membranous
integument, whereas in the latter they are besides glued together by
a substance which forms an additional and harder envelope. It is not
easy to explain the alteration that takes place in the texture of the
skin of such _dipterous_ pupæ as retain the skin of the larva. In the
latter this is generally a transparent and very fine membrane: yet
the very same integument becomes to the pupa an opaque and rigid case.
The surface of the skin of the greater number of pupæ is smooth,
but in those of many _Papilionidæ_ it is rugose and warty: this
you may see, particularly in that of _Papilio Machaon_. In many of
the hawkmoths (_Sphinx_ L.) it is covered with impressed puncta.
In _Attacus Io_ the upper side of the channels that separate the
intermediate segments of the abdomen are curiously striated with
transverse striæ, formed of very minute granula, the lower side
being transversely sulcated. In some few instances, as in _Arctia
Salicis_, _Laria pudibunda_ and _fascelina_, the skin of the pupa is
clothed with hair[576]: as is also that of _Hesperia Bixæ_, according
to Madame Merian[577]. De Geer has described a little beetle under
the name of _Tenebrio lardarius (Latridius_ Latr., _Corticaria_
Marsh.), the pupa of which is beset with very fine hairs, terminating
in a spherical or oval button[578].
ii. I shall include under the same head both the _figure_ or shape,
and _parts_ of pupæ, as the latter in most kinds are either the same
or nearly the same as those of the larva, or merely incasing those of
the imago, so as not to require that detailed notice that I judged
necessary when treating of the parts of larvæ.
With regard to _incomplete_ pupæ, nothing further can be said of their
extremely various _figure_, than that it has a general resemblance
to that of the perfect insect. The head, trunk, abdomen, and their
respective external organs, are alike visible in both; but in the
pupæ, the latter, instead of occupying their natural situation, are
all closely folded under the breast and abdomen: or, as in the case
of the long ovipositors of some Ichneumons, laid along the back. In
a specimen of some coleopterous insect now before me, the following
is the order of the arrangement of the parts:--The head is inflexed;
the mandibulæ are open; between them are seen the labium and labial
palpi; these appear to cover and conceal the maxillæ, and the maxillary
palpi extend on each side beyond them; the antennæ pass above the
thighs of the two anterior pair of legs, and then turning down over
the breast between them and the posterior legs, repose upon the base
of the wings; which also are turned down between the intermediate and
posterior pair of legs, and rest upon the latter; the tibiæ are bent
in and folded upon the thigh, and the tarsi turn outwards[579]. In
another coleopterous species, the wings and elytra are placed under
the hind-legs. In _Hymenopterous_ pupæ the antennæ appear usually to
lie between the legs[580]. In many _Tipulæ_ the long legs are bent
into three folds in the pupæ; but the tarsi are extended, and lie
close to each other, the anterior pair being the shortest[581]. In a
specimen belonging to this tribe in my cabinet, which I think contained
_Ctenocera pectinicornis_, the six leg-cases are of the same length,
exactly parallel and adjacent, and being annulated wear the appearance
of tracheæ[582]. These parts have each their separate case, so that a
pin may be introduced between them and the body: which cases, as well
as the general envelope, are usually formed of a fine soft transparent
membrane; but sometimes, as in the lady-bird (_Coccinella_), the
tortoise-beetle (_Cassida_), the crane-fly (_Tipula_), &c. it is harder
and more opaque, so that though it is usually easy for a practised
Entomologist from an examination of the pupa, particularly in the
_Hymenoptera_, to predict to what genus the insect to be disclosed
from them will belong, yet in these cases the organs being not so
conspicuous, a less experienced examiner might be perplexed, and unable
to come to a conclusion.
Although _hymenopterous_ pupæ have usually no parts but what are
afterwards seen in the perfect insect, this is not the case with
several _coleopterous_ and _dipterous_ ones, which are furnished with
various temporary appendages, indispensable to them to bring about
their final change, or for other purposes. Thus, the pupa of the male
of _Lucanus Cervus_ has two short, jointed anal processes[583]. That of
_Hydrophilus caraboides_ has a pedunculated lunulate one; and moreover,
the sides of the abdominal segments, and the top of the thorax, are
beset with hairs, which are not seen in the perfect insect[584]. The
abdomen of many, also, is armed with spines. That, the arrangement of
whose organs I lately described, has a quadruple series in the back of
this part; viz. on each of the first five segments, 3, 2, 2, 3. The
five first ventral segments also have on each side three spines; the
inner are incurved, the intermediate nearly upright, and the outer
one recurved. These spines, except those of the innermost ventral
series, terminate in a bristle. In another coleopterous species the
back part of the head is armed with a pair of lateral spines, and
that of the thorax with three processes, the external ones armed with
a single spine, and the intermediate one with a pair. De Geer has
figured the pupa of an _Asilus_, the head of which is armed with eight
spines--two robust ones in front, and three smaller ones, connected at
the base on each side. The abdominal segments, also, are fringed with
spines[585]. The abdomen of the pupa of _Ctenocera pectinicornis_ is
armed with several strong conical spines, pointing mostly towards the
tail, which is likewise the case with that of _Tipula lunata_[586].
As the above pupæ are usually subterranean or subcortical, the spines
assist in pushing them out of the ground, &c. The respiratory horns
that proceed from the thorax of the pupæ of many of the aquatic gnats
will be noticed in another place. Those of _Corethra culiciformis_ and
of some other aquatic gnat-like _Diptera_, have their anus furnished
with a pair of oars, or natatory laminæ, by which they rise to the
surface[587].
The figure of _obtected_ pupæ, or chrysalises, is more uniform.
They are commonly obtuse at the anterior extremity, and gradually
contracted to a point at the posterior, or tail. The outline usually
inclines to a long oval or an ellipse; but in some, as _Attacus Io_
and _Luna_, the pupa is shorter and more spherical. In _Geometra
sambucaria_ it represents an elongated cone, and in _Hepialus_ it is
nearly cylindrical. In the butterfly tribe (_Papilio_ L.) the outline
is frequently rendered angular by various protuberances.
In all these pupæ may be distinguished the following parts:--_first_,
the _Head-case_ (_Cephalo-theca_), or anterior extremity; _secondly_,
the _Trunk-case_ (_Cyto-theca_), or intermediate part; and _thirdly_,
the _Abdomen-case_ (_Gastro-theca_).
1. The _Head-case_ covers and protects the _head_ of the
inclosed imago. From its sides behind proceed the antennæ-cases
(_Cera-theca_); and before from the middle, the tongue-case
(_Glosso-theca_). Just below the base of the antennæ-case you may
discern the eye-cases (_Ophthalmo-theca_), surrounded on their inner
side by a crescent-shaped lævigated piece, which may perhaps transmit
some light to the inclosed prisoner.
2. The _Trunk-case_, divided into the _thorax_, or _upper_ surface,
extending from the head to the dorsal segments of the abdomen,
and consisting of three pieces, answering to the _prothorax_,
_mesothorax_, and _metathorax_ of the perfect insect: the first
answering to the prothorax small, the second covering the mesothorax
very large, and the two next representing the metathorax, at first
appearing to belong to the abdomen, but having no spiracle; and
the breast (_pectus_) or under-surface reaching from the head to
the ventral abdominal segments, from which proceed the wing-cases
(_Ptero-theca_) and leg-cases (_Podo-theca_), which organs, with the
antenna-cases and tongue-case, entirely cover, or rather form, the
breast. The arrangement of the whole is as follows:--The wing-cases,
which are more or less triangular, and exhibit the larger nervures of
the wings, are a lateral continuation of the mesothorax, which turn
downwards from the sides of the breast, and cover, or replace, the
three first ventral segments of the abdomen. The _antenna-cases_,
united to the anterior portion of the head just behind the eye-cases,
repose immediately next to those of the wings running parallel with
their inner margin. Then follow the legs, the tibiæ forming an angle
with the thigh, and the case of the anterior pair being innermost,
and representing the breast-bone in the pupa. The tongue lies over
the forelegs, except in the case of some sphinxes, which I shall
notice afterwards: so that the glosso-theca covers both them and it.
3. The abdomen-case consists of _nine_ segments when viewed on the
back, and of only _six_ when viewed below; so that it might be said
to have ten dorsal and six ventral segments: but the fact is, that
the place of the three anterior ventral segments, or rather ventral
portions of the segments, (for they form complete rings without any
lateral suture,) are replaced by the wings and other organs: in
consequence of this, the fourth segment, which is less covered than
the three first, at its posterior margin forms an annulus or ring. In
counting the abdominal segments of a pupa, you must be careful not to
include the piece that represents the _metathorax_, which looks as if
it belonged to the abdomen[588]. In the pupæ of _butterflies_ you will
discover evident traces of _ten_ dorsal segments; but in many _moths_,
and some _hawk-moths_, you will perceive at first only _eight_, or
even _seven_, but a closer examination will enable you to discover
the line that marks out the others; and if you divide the puparium
longitudinally, and inspect its internal surface, you will see very
visible sutures between them. The intermediate segments are sometimes
separated from each other and the preceding and subsequent ones by deep
channels. In the pupa of _Papilio Machaon_ there is one such channel
between the third and fourth segments. In _Bombyx regalis_ the channel
is between the sixth and seventh, and in _B. imperatoria_ there are
three, namely, a channel between the third and fourth, and fourth and
fifth, and fifth and sixth segments. The way in which insects with an
exserted sting fold it in the pupa seems not to have been noticed; but
from an observation of De Geer upon one species of _Ichneumon_, it
appears to be turned up over the back of the abdomen[589].
These little animals, thus swathed and banded, exhibit no unapt
representation of an Egyptian mummy; though Lamarck applies the term
_Mumia_ to _incomplete_ pupæ[590], to which it seems less happily
applicable.
Chrysalises, as to the modifications of their general figure, may
be conveniently divided into two great classes: _first_, those that
have no angular projections, the anal mucro of some excepted, on
different parts of their body; and _secondly_, those which have such
projections. Each of these classes affords variations in its peculiar
characters which require to be noticed.
1. The first of these are called _angular_ pupæ[591], and are
confined to the _Butterfly_ or diurnal tribes. In some the head
projects into one short conical protuberance: this you may see in the
chrysalis of the common cabbage butterfly (_Pieris Brassicæ_), and
others of the same genus[592]; in the brimstone-butterfly (_Colias
Rhamni_[593]), and in the beautiful purple emperor or high-flier
(_Apatura Iris_ F.[594]): though in this last it is not conspicuous.
But the most remarkable instance of a single eminence from the head
is exhibited by the pupa of a tropical butterfly (_Morpho Idomeneus_
Latr.), figured by Madame Merian. In this the head projects into a
long incurved obtuse horn[595]. In others the head is armed with
two mucros, or conical eminences. This is the case with the common
butterfly of the nettle (_Vanessa Urticæ_ F.[596]), and with that of
the beautiful _Papilio Machaon_[597]. In these the prominences are
trigonal. These processes, which in some, as in the peacock-butterfly
(_Vanessa Io_), stand upright[598], and in others diverge (_Papilio
Machaon_), form the eye-cases of the included imago; and in their
outer base is planted the crescent-shaped piece I lately mentioned,
which seems intended to convey light into it. In many the prothorax,
besides a lateral angular projection, has in the middle another
triangular or trigonal one, somewhat resembling a Roman nose; on
each side of which is a smaller elevated black point: so that it
requires no great stretch of imagination to find out in it a sort of
resemblance to the human face, which, though not quite so striking
as honest Goedart figures it[599], is however very considerable.
In the pupa of _Morpho Menelaus_, figured by Madame Merian[600],
this nasiform prominence of the prothorax is extended into a long
arched horn, reaching to the middle of the abdomen. The pupa of the
silver-washed fritillary (_Argynnis Paphia_ F.), and others of the
same genus, exhibit beneath this nasiform prominence a very deep
depression, itself beset with one or more series of smaller angular
elevations. The back of the abdomen is often furnished with two rows
of protuberances, in some species larger, in others smaller[601];
sometimes sharp and conical, and sometimes flat, and in some
instances resembling the fins of fishes[602]. These bosses usually
decrease in size towards the tail.
2. The second kind of chrysalises are denominated _conical_[603].
These, which include the _crepuscular_ and _nocturnal Lepidoptera_,
and the butterflies with _onisciform_ larvæ, have no protuberances,
and are less variable in their form--their anterior extremity being
almost constantly oval and rounded, and their posterior conical and
acute. An exception to this form is met with in the pupa of a moth
long celebrated (_Lasiocampa Pithyocampa_)[604], which has the head
acute and the tail obtuse, and armed with two points[605]. Another
occurs in that of the Cossus, which has two points on the head,
by which it makes an opening in its cocoon: when it assumes the
imago, one of these is placed below the other[606]. And some few
have the anterior end nearly flat instead of rounded. The pupa of
the orange-tip butterfly (_Pieris Cardamines_) seems intermediate
between the angular and conical kinds: it is somewhat boat-shaped,
and distinguished by a fusiform process from the head and tail[607].
Other modifications of the usual figure are met with, but are for the
most part so slight as not to require notice. One or two, however,
should not be passed over. The pupæ of many hawk-moths (_Sphinx_
L.) have the anterior piece of the head-case elongated into a sort
of cylindrical proboscis, which is incurved beneath the breast: you
will find this formation in _S. Convolvuli_ and _Ligustri_[608]. In
some, as in a species figured by Madame Merian, that feeds upon the
_Annona squamosa_, it is rolled up like a serpent in many folds[609].
In _Noctua Linariæ_ the tongue-case turns upwards, and is prominent
laterally beyond the body[610]. This singular appendage is one of
those beautiful instances of compensating contrivances, as Dr.
Paley calls them, which perpetually occur in the insect tribes. The
tongue of these hawk-moths is of very great length, often three
inches, while the pupa itself is scarcely two; it could not possibly,
therefore, have been extended at length, as it is in common cases,
but is coiled up within the above protuberance. When the tongue is
but a little longer than the breast, the ordinary plan is adhered to,
but the apex of the breast projects a little over the abdomen into
a sort of nose, in which the end of the tongue is contained. This
conformation may be seen in the pupa of _Noctua Gamma_, _Verbasci_,
and many other species. Sometimes, as in _N. Linariæ_ F., this
projection is recurved into a short horn.
I have before adverted to the _adminicula_ or short spines looking
towards the anus, with which the dorsal segments of the abdomen of
some pupæ are armed; and by which, when the time for their exclusion
is arrived, they are enabled to push themselves upwards or outwards
from their several places of confinement[611]: you will find these
in the pupa of the great goat-moth (_Cossus ligniperda_); and in the
cylindrical pupa of the moth called the ghost (_Hepialus Humuli_
F.) there are two rows of sharp triangular spines on the back of
each segment. These are not laid flat, but, as they do also in
the _Cossus_, form an acute angle with the body; which gives them
greater power of resistance. Those that constitute the row nearest
the base of the segment are longer than the anterior row, the middle
spines than the lateral ones. The first and last segment are without
them, and the last segment but one has a sharp ventral transverse
ridge, armed with many sharp teeth[612]. The abdominal spines lately
mentioned, of semicomplete pupæ, are also _adminicula_.
The tail of this description of pupæ is in many instances armed with
a mucro, or sharp point, emerging from its upper side. You will
see this in most hawk-moths. In the pupa of _Hesperia Proteus_ the
mucro is truncate at the apex; in that of _Bombyx imperatoria_ it
is long, and terminates in two diverging points. In the majority
of chrysalises of both descriptions the tail is acute, and usually
furnished with hooks of different kinds. These are so various in
shape and number, &c. that they would probably afford good characters
for discriminating many allied species. In some there are but two or
three, in others five or six, in others they are more numerous[613].
Sometimes they are quite straight[614], but most commonly recurved,
so as to form a hook. The hawk-moths, and a few others, as _Bombyx
Pini_, _Cerura Vinula_, &c., have no anal hooks whatever. Under this
head I shall observe, that in many conical pupæ below the anal angle
or mucro, is the appearance of a vertical foramen or passage: this is
particularly conspicuous in _Hepialus_, in which it is surmounted by
a bifid ridge, and has under it a pair of minute black tubercles.
A pretty accurate judgement of the division to which the perfect
insect when disclosed will belong, may usually be formed from the
figure of its _chrysalis_. All the _angular_ ones, with scarcely
any exception, inclose _butterflies_. The converse, however, does
not hold; for some that are not angular, as those of _Parnassius
Apollo_ and _Mnemosyne_, and most of the Linnean _Plebeii urbicolæ_,
also inclose flies of that description. With these exceptions, all
_conical_ chrysalises give birth to _moths_ or _hawkmoths_. An idea
even of the family or genus under which the perfect insect will
arrange, may be generally formed from the figure of the chrysalis;
less distinctly, however, in the conical or rounded, than in the
angular kinds, in which the prominences of the head and trunk, as
before explained, usually vary in different families. Even the sex
of some moths may be judged from the pupæ: those of females being
thicker; and those also of the females that have no wings, or only
the rudiments of them, will of course vary somewhat from the ordinary
form: but there is a still more striking difference in that of
_Callimorpha? vestita_ F., and others of the singular tribe before
noticed[615], called by the Germans _Sacktrager_ (sack-bearers), from
the sack-like cases in which the larva resides. The females of these
having not only no wings, but no antennæ, and legs not longer than
those of the larva, their pupa more resembles that of a _dipterous_
than of a _lepidopterous_ insect, it being not easy to determine
which is the head and which the tail[616].
In these too we can often learn from the outline of the wing-cases,
whether the inhabitant of the chrysalis has these organs indented
or intire. If the former, the margins of these cases are sinuate,
as in that of _Vanessa C. album_; if the latter, they are intire,
as in _Pieris Brassicæ_. Even in conical pupæ,--the size, the shape
of the antennæ, which may be distinguished through the skin that
covers them, and slight modifications of the ordinary form,--give
indications of the genus of the included insect sufficiently
conclusive to a practised eye.
The true figure of _coarctate_ pupæ when they are mature, the parts
of the future fly being very visible, and each being included in a
separate case[617], is that of those that belong to the _incomplete_
division; but as this is a character not cognizable without dissection,
it is customary, in speaking of pupæ of this description, to refer
solely to the shape of the exterior covering, which is in fact a cocoon
formed of the dried skin of the larva moulded into a different form.
In this sense the figure of coarctate pupæ is extremely various. The
majority of them are more or less oval or elliptical, without any
distinct parts, were it not that they usually retain traces of the
segments which composed the larva's body[618]. Of this figure are the
pupæ of the common cheese-maggot[619], and many other flies. Others
(_Sepedon_ Latr.) have the pupa shaped like a boat. That of _Scæva
Pyrastri_ F. assumes the figure of a flask; or, according to Reaumur's
more accurate comparison, of a _tear_[620]. The tail of many of these
pupæ, particularly of aquatic species, is elongated into a sort of
beak, either simple or forked, or is beset with spines variously
arranged. The pupa of _Stratyomis Chamæleon_, and other allied species,
differs from all the rest of this subdivision in retaining the exact
form of the larva[621]; and hence constitutes an exception to the
general character of our second great Division.
iii. There is much less variety in the _colour_ of pupæ than in that
of larvæ. The majority of coleopterous and hymenopterous pupæ are
white, or whitish; of lepidopterous and dipterous, brown of various
shades, often verging on black in the former and on red in the latter.
The angular lepidopterous ones, however, are more gaily decorated.
Some, _Pieris Brassicæ_, are of a greenish yellow, marked with spots
of black; others are of a uniform green, _Apatura Iris_, _Pieris
Cardamines_; others, reddish, _Vanessa C. album_; others again red
with black spots, _Urania Leilus_[622]. A still greater number shine
as though gilded with burnished gold--either applied in partial
streaks, _Vanessa Cardui_; or covering the entire surface, _Vanessa
Urticæ_. It was from this gilded appearance in some _obtected_ pupæ
that the terms _Chrysalis_ and _Aurelia_ were applied to the whole.
The alchemists mistook this for real gold; and referred to the case as
an argument in favour of the transmutation of metals. But Reaumur has
satisfactorily shown, that in this instance the old proverb is strictly
applicable--"All is not gold that glitters." He found that this
appearance is owing to the shining white membrane immediately below
the outer skin, which being of a transparent yellow gives a golden
tinge to the former; in the same way that tinfoil, when covered with a
yellow varnish, assumes the metallic appearance which we see in gilt
leather. He mentions, too, that for the production of this effect--it
is essential that the inner membrane be moist: whence may be explained
the disappearance of the gilding as soon as the butterfly is ready to
escape from the pupa. The shade of colour in these gilded chrysalises
is various: some are of a rich yellow, like pure gold; others much
paler; and some nearly as white as silver. That of _Hipparchia Cassiæ_
F. is red with silver spots[623].
Though by far the greater number of the chrysalises of moths are of
an uniform chestnut, brown, or black,--a few are of other colours;
as that of _Geometra alniaria_, which is of a glaucous blue; of
_Noctua sponsa_, lilac; and of _Noctua pacta_, of a lovely blue,
caused by a kind of bloom, like that of a plum, spread upon a brown
ground. A similar bloom is found on that of _Parnassius Apollo_, and
on the anterior part of that of _Platypterix cultaria_ and _sicula_;
in which last, Kliemann observed it to the be renewed when rubbed
off[624] Many pupæ have the sheaths of the wings of a different
colour from that of the rest of the body; a few are variegated with
paler streaks or bands, as _Clostera Anastomosis_, which has two red
longitudinal stripes down its dark-brown back; and that of the common
gooseberry and currant moth, which may be found in every garden, has
alternate rings of black and yellow[625].
A few pupæ vary in their colour, as the painted lady-butterfly
(_Vanessa Cardui_), some of which are light-brown with gray streaks
and golden dots, others wholly of a golden yellow or brown, others of
a light green[626].
Almost all at their first assumption of the pupa state have a
different colour from that which they take a few days afterwards.
This last they retain until the disclosure of the perfect insect;
except some that have transparent skins, which a few days previously
to this period exhibit the colours of the included animal.
iv. There is as great variety in the length of the _age_ of Insects
in their pupa as in their larva state. Some species continue in it
only _two_ or _three days_ (_Aleyrodes Chelidonii_ Latr., _Tinea
proletella_ L.); others, as many _weeks_, or _months_, or even
_years_. Each, however, has in general a stated period, which in
ordinary circumstances it neither much exceeds nor falls short
of. The only general rule that can be laid down is--that _small_
pupæ continue in that state a shorter time than those of _larger_
bulk. Thus, amongst coleopterous genera, the more minute species of
_Curculio_ L.; amongst the _Hymenoptera_, the _Ichneumones minuti_
L.; amongst the _Lepidoptera_, the subcutaneous tribes; and the
majority of the _Diptera_,--remain as pupæ only a few days or weeks:
while the larger species in all these orders commonly exist in the
same state several months--many even upwards of _two_ years. There
are, however, numerous exceptions to this rule; for some large pupæ
are disclosed in a much shorter time than some others not a twentieth
part of their bulk.
The reasons both of the rule and of the exceptions to it are
sufficiently obvious. And first, as to the rule:--If you open a pupa
soon after its assumption of that state, you will find its interior
filled with a milky fluid, in the midst of which the rudiments of its
future limbs and organs, themselves almost as fluid, swim. Now the
end to be accomplished during the pupa's existence is, the gradual
evaporation of the watery parts of this fluid, and the development of
the organs of the inclosed animal by the absorption and assimilation
of the residuum. Reaumur, by inclosing a pupa in a stopped glass
tube, collected a quantity of clear and apparently of pure water,
equal to eight or ten large drops, which had evaporated from it, and
was condensed against the sides of the tube, and it was found to have
lost an eighteenth part of its weight[627]. It is plain, therefore,
that this necessary transpiration, other circumstances being alike,
must take place sooner in a _small_ than in a _large_ pupa. Next, as
to the exceptions:--Since the more speedy or more tardy evaporation
of fluids depends upon their exposure to a greater or less degree
of heat, we might _à priori_ conclude, that pupæ exposed to a high
temperature would sooner attain maturity, even though larger in bulk,
than others exposed to a low one:--and this is the fact. The pupa
of a large moth, which has assumed that state in the early part of
summer, will often disclose the perfect insect in twelve or fourteen
days; while that of an Ichneumon, not one hundredth part of its size,
that did not enter this state till late in autumn, will not appear as
a fly for seven or eight months. But this is not the whole. The very
same insect, according as it has become a pupa at an earlier or later
period of the year, will at one time live but a few weeks, at another
several months, in that state. Thus, if the caterpillar of _Papilio
Machaon_, one of those which has annually a double brood, becomes
a pupa in July, the butterfly will appear in _thirteen days_: if
not until September, it will not make its appearance until the June
following; that is, not in less than _nine_ or _ten months_: and the
case is the same with the pupæ of _Noctua Psi_, and of a vast number
of other insects. To put beyond all doubt the dependence of these
remarkable variations on temperature merely, it was only necessary
that they should be effected, as Lister long ago advised[628], by
artificial means. This Reaumur accomplished. In the month of January
he placed the chrysalises of several moths and butterflies, which
would not naturally have been disclosed until the following May,
in a hothouse: the result was, that the perfect insects made their
appearance in less than a fortnight, in the very depth of winter;
and by other numerous and varied experiments he ascertained, that in
this heated atmosphere five or six _days_ hastened their maturity
more than as many _weeks_ would have done in the open air. The
disclosed insects were in every respect perfect, and the females,
after pairing, laid their eggs, and then died, just as if they had
not been thus prematurely forced into existence. The converse of this
experiment equally succeeded:--by keeping pupæ the whole summer in an
icehouse, Reaumur caused them to produce the fly one full year later
than their ordinary period[629].
This extraordinary fact leads us to a very singular and unexpected
conclusion--that we have the power of lengthening or shortening the
life of many insects at pleasure; that we can cause one individual to
live more than twice as long as another of the same species, and _vice
versâ_. Had Paracelsus made this discovery, it would have led him to
pursue his researches after the elixir of immortality with redoubled
confidence, and would have supplied him with an argument for the
possibility of prolonging the life of man beyond its usual term, which
his sceptical opponents would have found some difficulty in rebutting.
Even the logical Reaumur seems inclined to infer from it, that this
object of the alchemists was not so chimerical as we are wont to
conclude[630]. He confesses, however, if it were to be attained only
by the same process as effects the extension of an insect's life--by
prolonging its state of torpor and insensibility,--that few would
choose to enjoy it on such conditions. The man of pleasure, blunted
by excess of use to all modern stimuli, might perhaps not object to a
sleep of a hundred years, in the hope of finding something new under
the sun when he waked; and an ardent astronomer would probably commit
himself with scientific joy to a repose as long and as sound as that
of the seven sleepers, for the chance of viewing his predicted return
of a comet, on stepping out of his cave: but ordinary mortals would
consign themselves to the perils of so long a night with reluctance,
apprehending a fate no better than what befel the magician, who
ordered himself to be cut in small pieces and put in pickle, with the
expectation of becoming young again[631].
The duration, then, of an insect's existence in the pupa state,
depends upon its bulk, upon the temperature to which it is exposed,
and upon a combination of these two circumstances. This experiment
appears very simple. We seem to ourselves to have accomplished what
is so often undertaken in vain--to have found an entrance into the
cabinet of Nature, and to have made ourselves masters of the contents
of one of the pages of her sealed and secret book. We deceive,
ourselves, however: this book, when it seems most legible, is often
interlined with _sympathetic inks_, if I may so speak, which require
tests unknown to us for their detection. If you lay up a considerable
number of the pupæ of a moth now called _Eriogaster lanestris_,
the larva of which is not uncommon in June on the black-thorn,
selected precisely of the same size, and exposed to exactly the same
temperature, the greater number of them will disclose the perfect
insect in the February following; some not till the February of the
year ensuing, and the remainder not before the same month in the
third year[632]. Mr. Jones of Chelsea, a most acute lepidopterist,
in one of his excursions captured a female of _Arctia mendica_,
another moth, which laid a number of eggs, thirty-six of which
produced caterpillars: all these fed, spun their cocoons, and went
into the pupa state in the usual manner, but at the proper season
only twelve produced the fly. As this was no uncommon circumstance,
he concluded that the rest were dead: to his great astonishment,
however, in the next season twelve more made their appearance; and
the following year the remainder burst into life, equally perfect
with the foregoing[633]. In this extraordinary result, which also
occasionally has been observed to take place in the emperor-moth
(_Saturnia pavonia_), the privet-hawkmoth (_Sphinx Ligustri_), and
that of the spurge (_S. Euphorbiæ_)[634], and other species,--it is
clear that something besides mere size and temperature is concerned:
for, these circumstances being precisely alike, one pupa arrives
at maturity in six months, and another of the same brood requires
between two and three years. We can guess, that the end which the
All-wise Creator has in view, in causing this remarkable difference,
is the prevention of all possibility of the destruction of the
species. _Eriogaster lanestris_ and _Arctia mendica_, &c., for
instance, are doomed, for some reason unknown to us[635], to be
disclosed from the pupa in the cold and stormy months of February
and March, almost every day of which in certain years is so ungenial
that few insects could then survive exposure, much less deposit their
eggs and ensure the succession of a progeny. Now, were all these to
make their appearance in the perfect state in the _same_ year, it
might happen that the whole race in a particular district would be
destroyed. But this possibility is effectually guarded against by the
beautiful provision under consideration, it being very improbable
that three successive seasons should be throughout unfavourable;
and without such occurrence, it is clear that some of the race of
this moth will be preserved. In the case of other moths, whose pupæ
though disclosed in the summer are governed by the same rule, the
prevention of the extinction of the species, by any extraordinary
increase in a particular year of their natural enemies, seems the
object in view[636]. But though the intention be thus obvious, the
means by which it is effected are impenetrably concealed. What
physiologist would not be puzzled with the eggs of a bird, of which
one-third should require for their hatching to be sat upon only a
fortnight, another third a month, and the remainder six weeks? Yet
this would be an anomaly exactly analogous to that observed by Mr.
Jones with respect to the pupæ of _A. mendica_. Reaumur found that
when the skin of pupæ was varnished, so as to prevent absorption,
the appearance of the fly happened nearly two months later than in
ordinary circumstances. Are we to conjecture that those of the moth
just mentioned, or of _E. lanestris_, that are latest matured, from
a greater degree of viscidity in the fluid that forms them[637],
have thicker and more impervious skins than those disclosed at an
earlier period? Or are we to refer the difference to some unknown
peculiarity of organization? On any supposition, the fact remains
equally wonderful; and I know of none the illustration of which is
more worthy of the patient investigation of the physiologist.
As the period of maturity of the perfect insect is thus in some cases
not fixed even to years, and as in many it seems dependent upon such
variable causes; nothing appears more improbable than that it should
ever be so strictly determined, that even the week in which the fly
will leave its pupa-case can be pretty accurately predicted. Such,
however, is the fact with regard to the _Ephemera_ so interestingly
described by Reaumur, the myriads of which that issue from the banks
of the Seine all appear in two or three days, somewhere between the
10th and 18th of the month of August[638] in every year; at which
time the fishermen regularly expect them. A like regularity attends
the appearance of those described by Swammerdam, which every year,
for three days about the feast of St. John, issue in clouds from the
Rhine[639]--Not only is the week fixed, but in several instances
even the hour. The Ephemeræ observed by Reaumur appear at no other
time than between _eight_ and _ten_ o'clock in the _evening_; and so
unalterably is their exclusion fixed, that neither cold nor rain can
retard it. Between these hours, in the evenings on which they appear,
you may see them fill the air, but an hour before or after, you will
in vain look for one[640]. So also the silkworm-moth and the hawkmoth
of the evening primrose (_Sphinx Œnotheræ_) constantly break forth
from the pupa at _sunrise_: and the hawkmoth of the lime (_Smerinthus
Tiliæ_) as certainly at _noon_[641]. Schroeter states, that of
sixteen specimens of the death's-head-hawkmoth (_S. Atropos_) which
he bred, every one was disclosed between _four_ and _seven_ o'clock
in the _afternoon_[642].
Before I conclude this head, I must observe, that after a caterpillar
or gnat has spun its cocoon, it sometimes remains for a considerable
period before it incloses itself in the pupa-case, and casts off the
form of a larva. Thus the little parasite (_Ichneumon glomeratus_
L.) that destroys the caterpillar of the common cabbage-butterfly,
remains a larva in its cocoon for many months, but it becomes a
perfect insect a few days after it has put on its puparium[643]; and
the caterpillars of the great goat-moth (_Cossus ligniperda_), if
they spin their cocoon in the autumn, remain in it through the winter
in the larva state; whereas, if they inclose themselves in the month
of June, they assume the pupa, so as to appear as flies in three or
four weeks[644]. It is not therefore easy to state precisely the age
of those pupæ which are produced from larvæ that spin cocoons.
v. I have not much to say with regard to the _sex_ of pupæ. The male
is probably to be distinguished from the female by being smaller; but
in the first great division of pupæ, those which resemble the larvæ,
and are locomotive, the female in numerous cases may be known by the
Ovipositor, or instrument for depositing her eggs in their proper
station: and the male also has his anal instruments. Sometimes in
this state the animal is so matured, as to be capable of continuing
its kind. I have found the pupæ both of a _Gryllus_ L. and of a
_Cimex_ L. _in coitu_.
vi. Though the pupæ of the second great division are usually not
locomotive, yet I must not omit some notice of their _motions_. As the
legs of insects in this state are folded within a common or partial
integument, of course none of the pupæ now under consideration,
with the exception of those of the _Trichoptera_ order, can walk:
_coarctate_ ones are even incapable of the slightest motion, and
exhibit no symptom whatever of animation. Some of those that are
termed _incomplete_, however, and most chrysalises, have the power of
communicating to their bodies a slight movement, extending more or
less in different species, which is effected by the abdominal segments
solely. The latter, during the first twelve hours of being pupæ, when
their skin is soft, frequently turn themselves, that the side on which
they lie may not be flattened; afterwards by far the majority merely
wriggle or twist their abdomen when touched, or in any way incommoded
or disturbed. We learn from De Geer, that the pupa of the ghost-moth
(_Hepialus Humuli_), the cocoon of which is more than twice the
length of the chrysalis, moves in it from one end to the other[645].
Bonnet observed one of a moth (perhaps _Lasiocampa Quercus_), which
alternately fixed itself at the top and bottom of its spacious and
obliquely-fixed cocoon; descending slowly, but ascending as quickly,
and almost in the same manner, as a chimney-sweeper in a chimney[646].
The pupa of the weevil of the water-hemlock (_Lixus paraplecticus_)
will move from one end of the interior of a branch to another by
means of its _adminicula_, aided by the motion of its abdominal
segments[647]. But the most locomotive of pupæ of the second division
are those of gnats, and many Tipulidans, which pass this state in the
water. These will move from the bottom to the surface, and back again,
with great facility and velocity. I have before mentioned several other
motions of pupæ[648], which I shall not repeat here, by which they
extricate themselves from their several places of intermediate repose,
before they leave the puparium: if the imago were to be disclosed in
the interior of a tree, or in the earth, its wings would be materially
injured in forcing its way out. The object of several of the above
motions may be to alarm insects that might attack these defenceless
beings. The twirling motion in particular, formerly noticed[649], in
some species, by causing a rustling against the sides of the cocoon,
makes a considerable noise--so singular in that of a red underwing-moth
(_Noctua pacta_), that Rösel tells us, (who by the by was more timid
than becomes a philosopher,) that the first time he heard it, he had
nearly thrown away the box that contained it, in his fright[650].
vii. We are next to consider _The extrication of the perfect insect
from the puparium, or pupa-case, and from the cocoon_. The period
when the pupa has attained maturity, and the inclosed insect is ready
to burst the walls of its prison, may be often ascertained. Just at
this time the colour frequently undergoes an alteration, the golden
or silver tint of the gilded chrysalises vanishes; and those which
are transparent, usually permit the form and colours of the insect
within and the motions of their limbs to be distinctly seen through
them. In the _Libellulina_ the eyes become more brilliant[651]. The
mature pupæ of the moth lately mentioned (_Eriogaster lanestris_)
have a particular swell of the abdominal segments, not apparent in
those that are to continue till another season, or longer[652]. Those
of the case-worms (_Trichoptera_) push off the grates from the cases
which they have hitherto inhabited, and swim about[653]. Other signs
and motions doubtless predict the approach of this great change in
other species, which have not been recorded.
The mode in which insects make their way out of the _puparium_
differs in different orders. In _obtected_ pupæ, the struggles of
the included butterfly or moth first effect a longitudinal slit down
the middle of the thorax, where there is usually a suture for the
purpose. The slit rapidly extends along the head, and down the parts
which compose the breast, and the insect gradually withdraws itself
from its case. It is not, however, from the outer skin merely that it
has to disengage itself, but also from a series of inner membranous
cases, which separately inclose the antennæ, proboscis, feet, &c., as
a glove does the fingers; and similar cases inclose the parts of the
perfect insect in pupæ of all the other orders. This is sometimes a
work of difficulty, but ordinarily it is effected with ease.
_Incomplete_ and _semicomplete_ pupæ undergo nearly the same process,
save that in them the body is not swathed up in a common case; and
therefore they have only to liberate themselves from the partial
cases that envelop the several parts of their body.
In _coarctate_ pupæ, as those of _Muscidæ_, _Syrphidæ_, _Œstridæ_, &c.,
the process is different. Their outer-case is ordinarily more rigid
and destitute of the sutures, which in the former tribes so easily
yield to a slight effort. Yet in these, at the anterior end under
which the head of the fly lies, and from which it always issues, there
is commonly a sort of lid, joined by a very indistinct suture to the
rest, which can be pushed off, leaving a sufficient opening for the
egress of the insect. In the pupæ of many of this tribe this lid is
composed of two semicircular pieces, which can be separately removed.
Many species seem to be able to force off the lid of their puparium, by
merely pushing against it with their heads: but the common flesh-fly
and many other _Muscidæ_, which are perhaps too feeble to effect this,
or whose puparia are stronger than ordinary, are furnished with a very
remarkable apparatus for this express and apparently sole purpose.
They are gifted with the power of introducing _air_ under the middle
part of the head, to which the antennæ are fixed, and of inflating
that part into a sort of membranous vesicle as big as the head itself;
by the action of which against the end of the pupa-case, the lid is
soon forced off. So powerful is this singular lever, that it is even
sufficient to rupture the fibrous galls in which the pupæ of the
gay-winged _Tephritis Cardui_[654] are inclosed. That it is designed
by Creative Wisdom to answer this sole purpose seems proved, from its
disappearing soon after the disclosure of the fly, whose head shortly
becomes all alike hard. Reaumur suspects that it may also be intended
to promote the circulation of the insect's fluids; but to me his
reasons appear not conclusive[655]. In one instance a mode still more
unexpected obtains. The illustrious naturalist just named found that
the fly which proceeded from one of the rat-tailed grubs (_Elophilus_
Latr.) had actually the power of completely reversing its situation in
its narrow case; and that it then employed its _tail_ in pushing off
the lid, which other species remove by means of their _heads_[656].
The extrication of insects whose pupæ are above ground, like those
of butterflies, many beetles, flies, &c., is comparatively a simple
operation. But what, you will ask, becomes of those species whose pupæ
are concealed deep in the earth, or in the heart of the trees on which
their larvæ have fed? Of this you shall be informed.--_Coleopterous_
insects disclosed from pupæ thus circumstanced, wait until their
organs have acquired strength, and their elytra are sufficiently
hardened to protect their filmy wings from damage in forcing their way
through the earth or wood which covers them. Thus _Oryctes nasicornis_,
a rhinoceros beetle common on the Continent, is a full _month_ before
it reaches the surface of the earth, after quitting its puparium. But
it is evident that no delay would enable _lepidopterous_ or _dipterous_
insects, which are without elytra, to make their way out of such
situations, without irreparable injury to their delicate wings. Many
of these, therefore, while still within the hard case of the pupa,
have the precaution, a few days previously to their exclusion, to
force themselves up to the surface of the earth, or, when they reside
in the interior of trees, to the entrance of their hole. This is
effected by a successive wriggling of the abdominal segments, which
in several species, of the _Coleoptera_, _Lepidoptera_, and _Diptera_
orders, for this purpose, as has been more than once observed[657], are
furnished with sharp points (_adminicula_), admitting a progressive,
but not a retrograde motion. The puparia of the great goat-moth
(_Cossus ligniperda_) may be often seen projecting from orifices in
willow-trees; and those of the common crane-fly (_Tipula oleracea_)
from the surface of the earth, to which they have thus made their way
from a depth of several inches.
In all the preceding instances the exclusion of the perfect insect
is complete, as soon as it has withdrawn itself from the puparium.
But to a very large number, even after this is effected, the arduous
task still remains of piercing the cocoons of leaves, of thick
silk, of tough gum, or even of wood, in which the pupæ are incased.
We can readily conceive how the strong jaws of _coleopterous_ and
_hymenopterous_ species may be employed to release them from their
confinement. But what instruments can be used for this purpose by
_moths_ in a state of great debility, whose mouth has nothing like
jaws--merely a soft membranous proboscis? How shall the silkworm-moth
(_B. Mori_) force its way through the close texture of a silken
ball, through which the finger could not be easily pushed? Or the
puss-moth (_Cerura Vinula_) pierce the walls of its house of glue
and wood, which scarcely yield to the knife? You will not doubt
that these difficulties have been foreseen by INFINITE WISDOM, and
provided against by INFINITE POWER. The egress of moths from their
cocoons is secured in two ways;--either by some peculiarity in the
first construction of the cocoon by the caterpillar, or by some
process which the pupa or perfect insect is instructed to perform. As
examples of each, several curious instances may be cited.
The larva of the moth which about 1760 made such havoc in the
province of Angoumois in France, becomes a pupa in the interior of
the grain of wheat which it has excavated; but the opening by which
it first entered is not bigger than a pin's point, and is quite
insufficient for the egress of the moth. How, then, is the latter to
force its way through the tough skin which surrounds it? The larva,
previously to assuming the pupa state, gnaws out a little circular
piece at that end of the grain where the head of the future moth
would lie, taking care not to detach it entirely. At this little
door, which is sufficient to protect it from intruders, the moth
has but to push, when it falls down, and leaves a free passage for
its exit. A contrivance almost similar is adopted by a caterpillar
which feeds in the interior of the heads of a species of teazel
(_Dipsacus_ L.), for a minute and interesting history of which we are
indebted to Bonnet. This caterpillar previously to its metamorphosis
actually cuts a circular opening in the head, sufficiently large
for the egress of the future moth; but to secure this sally-port
during its long sleep, it artfully closes it with fibres of the
teazel, closely but not strongly glued together[658]. Another small
caterpillar described by the same author, resides in the leaf of
an ash curiously rolled up into a cone, and then assumes the pupa,
which is inclosed in a silken cocoon, ingeniously suspended by two
threads like a hammock in the middle of its habitation, and of so
slight a texture that it presents no obstacle to the extrication of
the moth. It is the closely-joined sides of its leafy dwelling that
form a barrier, which, were it not for the precaution of the larva,
would be impenetrable to so small and weak an animal. The little
provident creature, before its change to a pupa, gnaws in the leaf a
round opening, taking care not to cut through the exterior epidermis.
This door is to serve the moth for its exit, like that formed by
the wheat-caterpillar. But in proportion to its bulk its verdant
apartment is of considerable size. How then shall the moth know the
exact place where its outlet has been traced? How, without a clue,
shall it discover in its dark abode the precise circle which requires
only a push to throw it down? Even this is foreseen and provided
against. Out of twenty positions in which its hammock might have
been slung, the caterpillar has been directed so to place it, that
the silken cord that suspends the head is fastened close to the side
of the door which it has previously constructed; and the moth, guided
by this _filum ariadneum_, at once makes its way out of an apartment
which, but for this contrivance, might have been to it a labyrinth as
inextricable as that of Minos[659].
The mode in which other caterpillars provide for their extrication,
when become moths, from their silken cocoons, is not less ingenious.
Those of _Eriogaster lanestris_ (of which I have lately said so much,)
and others, form oblong cocoons, which, viewed externally, you would
at the first glance assert were of one solid piece: but on examining
them more narrowly, you perceive one end of them to be a distinct
lid, of a size large enough to permit the moth to issue out; and that
it is kept in its place by a few slight threads, easily broken by
pressure from within[660]. A few pages back[661] I mentioned a cocoon
formed by the larva of _Tortrix prasinana_, of the shape of a boat
reversed, composed of two inclined walls fastened together at the
top and ends. In constructing this cocoon, it firmly glues to each
other the top and one end, so as to form an impermeable suture; but
the other end, at which the moth is to issue, though externally it
seems as strong as the rest, is merely drawn close by a slender thread
or two fastened on the inside, and easily broken from within. And,
what is particularly singular in the construction of this ingenious
habitation, the sides forming the end last mentioned, though originally
requiring force to draw them into their required position, become
so elastic as to close again when the moth has passed between them
and made her escape; the cocoon preserving its usual shape, even when
deprived of its inhabitant[662]. A similar cocoon is constructed by
another leaf-rolling caterpillar, that of _Tortrix chlorana_[663]. Many
similar proofs of contrivance in the construction of silken cocoons
might be adduced, but I shall confine myself to one more only--I mean
that furnished by the flask-shaped brown one of _Saturnia Pavonia_,
and some other moths. If you examine one of these cocoons, which are
common enough in some places on the pear-tree or the willow, you will
perceive that it is generally of a solid tissue of layers of silk
almost of the texture of parchment; but at the narrow end, or that
which may be compared to the neck of the flask, that it is composed of
a series of loosely-attached longitudinal threads, converging, like so
many bristles, to a blunt point, in the middle of which is a circular
opening[664]. It is through this opening that the moth escapes. The
silk of its cocoon is of so strong a texture and so closely gummed,
that had both ends been similarly closed, its egress would have been
impracticable; it finds, however, no difficulty in forcing its way
through the aperture of a sort of reversed funnel, formed of converging
threads that readily yield to pressure from within. But an objection
will here probably strike you. You will ask, Is not this facility of
egress purchased at too dear a rate? Must not a chrysalis in an open
cocoon be exposed to the attacks of those ichneumons of which you
have said so much, and of numerous other enemies, which will find
admittance through this vaunted door? Our caterpillar would seem to
have foreseen your dilemma; at least, under heavenly guidance, she
has guarded against the danger as effectually as if she had. If you
cut open the cocoon longitudinally, you will see that within the
exterior funnel-shaped end, at some distance she has framed a second
funnel, composed of a similar circular series of stiff threads, which,
proceeding from the sides of the cocoon, converge also to a point, and
form a sort of cone exactly like the closed peristome of a moss; or,
to use a more humble though not less apt illustration, like the wires
of certain mousetraps[665]. In this dome not the slightest opening is
left, and from its arched structure it is impenetrable to the most
violent efforts of any marauders from without; whilst it yields to
the slightest pressure from within, and allows the egress of the moth
with the utmost facility. When she has passed through it, the elastic
threads resume their former position, and the empty cocoon presents
just the same appearance as one still inhabited. Rösel relates with
amusing naïvété how this circumstance puzzled him the first time he
witnessed it: he could scarcely help thinking that there was something
supernatural in the appearance of one of these fine moths in a box
in which he had put a cocoon of this kind, but in which he could not
discover the slightest appearance of any insect having escaped from
it, until he slit it longitudinally[666]. But from an observation of
Meinecken, it appears that these converging threads serve a double
purpose; being necessary to compress the abdomen of the moth as it
emerges from the cocoon, which forces the fluids to enter the nervures
of the wings, and give them their proper expansion. For he found, that
when the pupa is taken out of the cocoon, the moth is disclosed at the
proper time, but remains always crippled in its wings; which never
expand properly, unless the abdomen be compressed with the finger and
thumb, so as to imitate the natural operation[667].
I am next to give you some account of the _second_ mode in which the
release of the perfect insect from its cocoon is effected--that,
namely, wherein its own exertions chiefly accomplish the work. I
shall from a large number select only a few instances. The texture
of the cocoon of the silkworm-moth is uniform in every part, and the
layers of silk are equally thick at both ends. The moth makes its
way out by cutting or breaking these threads at the end opposite
to its head: an operation which, as it destroys the continuity of
the silk, those who breed these insects are particularly careful
to guard against, by exposing the cocoon to heat sufficient to
destroy the included pupa. The question is--What instruments does
the moth employ to effect this? And this we are not able to answer
satisfactorily. Malpighi asserts that the animal first wets the
silk with a liquid calculated to dissolve the gum that connects the
threads, and then employs its lengthened head to push them aside and
make an opening[668]. But, as Reaumur has observed, besides that
so obtuse a part as the head of a moth is but ill fitted to act as
a wedge, we find the threads not merely pushed to each side, but
actually cut asunder. He therefore infers that the eyes, which are
the only hard organs of the head, are the instruments by which the
threads are divided--their numerous minute facets serving the purpose
of a fine file[669]. It should be observed, however, that Mr. Swayne
confirms Malpighi's assertion, that the silkworm does not cut, but
merely pushes aside, the threads of its cocoon; and he informs us
that he has proved the fact, by unwinding a pierced cocoon, the
thread of which was entire[670]. Yet Reaumur's correctness cannot be
suspected: and he affirms, that from observation there can scarcely
be a doubt that most of the threads are broken[671]; which is further
confirmed in an account of the breeding of silk-worms published in
the _American Philosophical Transactions_: in which it is expressly
stated, that cocoons out of which the fly has escaped, cannot be
wound[672]. Analogy, it must be confessed, is against Reaumur's
opinion; since other kinds of silkworms make their escape by means
of a _fluid_. Thus we are informed by Dr. Roxburgh, that _Attacus
Paphia_, when prepared to assume the imago, discharges from its
mouth a large quantity of liquid, with which the upper end of the
case is so perfectly softened, as to enable the moth to work its way
out in a very short space of time,--an operation which, he says, is
always performed in the night[673]. Perhaps the two opinions may be
reconciled, by supposing the silkworm first to moisten and then break
the threads of its cocoon. In those that are of a slighter texture,
a mere push against the moistened end is probably sufficient: and
hence we find in so many newly disclosed moths the hair in that part
wet, and closely pressed down[674]. If it be apparently difficult
for the silkworm-moth to effect an opening in its cocoon, how much
harder must seem the task of the puss-moth (_Cerura Vinula_) to
pierce the solid walls of its wood-thickened case? Here the eyes
are clearly incompetent; nor could any ordinary fluid assist their
operation, for the gum which unites the ligneous particles is
indissoluble in _aqueous_ menstrua. You begin to tremble for the
fate of the moth incarcerated in such an impervious dungeon--but
without cause: what an _aqueous_ solvent cannot effect, an _acid_ is
competent to: and with a bag of such acid our moth is furnished. The
contents of this she pours out as soon as she has forced her head
through the skin of the chrysalis, and upon the opposite end of the
cocoon. The acid instantly acts upon the gum, loosens the cohesion
of the grains of wood, and a very gentle effort suffices to push
down what was a minute ago so strong a barrier. How admirable and
effectual a provision! But there is yet another marvel connected
with it. Ask a chemist, of what materials a vessel ought to be to
contain so potent an acid: he will reply,--of glass. Yet our moth
has no glass recipient: her bottle is a membranous bag; but of so
wonderful a fabric as not to be acted upon by a menstruum which a
gum, apparently of a resinous nature, is unable to resist! This fact
can only be explained by the analogous insensibility of the stomach
to the gastric juice, which in some animals can dissolve bone,--and
it is equally worthy of admiration. In both cases, the vitality of
the membranous or fleshy receptacle secures it from the action of the
included fluid; but _how_--who shall explain?
Ordinarily it is the moth that breaks the cocoon; but in the goat-moth
and many _Tortrices_ it is the pupa itself that performs the work,
either wholly or partially. The pupa of the former is for this purpose
furnished with sharp points upon the head, capable of effecting this
object[675]. The locust-moth, another species of _Cossus_ (_C. Robiniæ_
Peck), whose history has been admirably detailed by Professor Peck,
has a different process. "In the silk-moth," says he, "and all others
which I have had opportunity to observe, the chrysalis bursts _in_ the
cocoon, and the fluid which surrounded the new insect in it escaping
at the same time, so weakens or dissolves the fibre and texture of
the silk, that the moth is able to extricate itself, leaving the
chrysalis behind it; but this is not the manner in the locust-moth.
After remaining till all its parts are fully grown and it is ready to
quit its prison, a certain quantity of exercise is necessary, to break
the ligaments which attach the moth to the shell of the chrysalis, and
to loosen the folds of the abdomen. In taking this exercise, it can
only move the abdomen in various directions: as one side of the rings
is moved forward, the hooks in the serrated lines above mentioned (the
_adminicula_) take hold of the silk, and prevent their sliding back;
the next flexure brings forward the opposite side of the rings, which
are prevented by the points on that side from slipping back in the
same manner, and the chrysalis is forced out of the slightly woven
extremity of the cocoon, and through the silk-lined cavity, till it is
protruded for about one-third of its length out of the opening in the
bark, and into the air[676]."
An exception to the general rule--that the rupturing of the cocoon is
the business of the inclosed insect itself--is met with amongst ants;
the workers of which not only feed the young, but actually make an
aperture in their cocoons, cutting the threads with their mandibles
with admirable dexterity and patience, one by one, at the time they
are ready to emerge, the precise period for which these indefatigable
nurses are well aware of, that they may meet with no obstacle. Without
this aid, the young ant would be unable to force its way through the
strong and dense coating of silk that infolds it[677]. And a proceeding
somewhat akin to this was observed by the Hon. Captain Percy, R.N., who
himself related it to me. Being fond of the study of insects, he was
in the habit of attending to their motions; and in the beginning of
September 1821 noticed those of a number of female _Tipulæ_, probably
_T. oleracea_ L., busily engaged in depositing their eggs amongst the
roots of grass. While observing these proceedings, he at the same time
saw one quitting its pupa-case, which had already by its own efforts
got its head, thorax, and anterior legs out of it. It was then joined
by two _male_ flies; which, with their anal forceps and posterior legs
taking hold of the pupa-case, appeared with their mouths and anterior
legs to push the little prisoner upwards, moving her backwards and
forwards; and as they kept raising her, shifting their hold of the
skin till she was entirely extricated, when they left her to recover
her strength by herself. Probably the extreme length of the two pair
of hind-legs of these animals may render such assistance necessary for
their extrication.
There remains yet to be explained under this head the manner in
which the perfect insect is excluded from certain aquatic pupæ; such
as those of _Phryganeæ_, gnats, and one of those _Tipulidæ_ that
resemble gnats. These pupæ (perhaps that they may be safe from the
attack of birds) are destined to remain during the greater part of
their existence in this state at the bottom of the water. But it is
obvious that if the perfect insects were there to be disclosed, their
wings would be wetted, and they would be drowned. It is the provision
by which this result is obviated that now calls for your attention.
You have already been told that the larvæ of _Phryganeæ_ inclose
themselves in cases of different materials, open at each end[678]. You
have also learned, that in becoming pupæ, they secure each end of their
cases with a grating of silk[679]. When that change has occurred, they
remain motionless at the bottom of the water. Now how are these pupæ,
encased in tubes of a greater specific gravity than the surrounding
fluid, to make their way to the surface when the time has arrived
for their becoming denizens of the air? This they accomplish in the
following manner:--The pupa is furnished with two strong exterior
moveable mandibuliform processes, and has the power of moving its four
anterior legs and antennæ while in the pupa-case. With these temporary
_jaws_ it makes an opening in one of the silken doors of its case,
forces its way out at that end, and then by moving its legs, the cases
of which in some species are ciliated for this very purpose, swims to
the surface, where its skin splits, and discloses the included insect.
That these jaws are given for the express and exclusive purpose of
being thus applied, seems undeniable. The pupa eats nothing--they are
therefore in every other point of view superfluous. They are given to
it alone of all other similar pupæ, because unnecessary to all others;
and they are cast off along with the rest of the puparium, the perfect
insect having no vestige of jaws[680].
The _gnat_ has to undergo its change on the surface of the water--How
is it to accomplish this without being wetted? In the pupa state
they usually remain suspended with the posterior end of the body
turned downwards: but when the period for its change is arrived,
it stretches it out upon the surface, above which its thorax is
elevated. Scarcely has it been a moment in this position, than,
swelling out the interior and anterior parts of the thorax, it
causes it to split between the two respiratory horns. Through this
opening the anterior part of the gnat then emerges. As soon as the
head and trunk are disengaged, it proceeds with its labour, and gets
out more and more; elevating itself so as to appear in the puparium
like a mast in a boat. As it proceeds, the mast is more and more
elevated and lengthened, till it becomes nearly perpendicular--just
as the mast of a boat is gradually raised from a nearly horizontal
to a vertical position: at this period a very small portion of the
abdomen remains in the puparium. Neither its legs nor wings are of
any use in maintaining it in this position. The latter are too soft,
and, as it were, folded; and the former are stretched out along
the abdomen--the segments of this last part are the only agents.
The observer who sees how the little boat gradually sinks, and how
its margin approaches the water, forgets the mischievous insect it
contains, which at another time he would crush without remorse, and
becomes interested for its fate; especially should wind agitate the
water. A very little is sufficient to drive about rapidly the little
voyager, since it catches the wind in some degree as a sail. If it
should be upset, it would be all over with it;--and numbers do thus
perish. The gnat, after having fixed itself thus perpendicularly,
draws first its two anterior legs out of their case, and moves them
forward, and next the two intermediate ones; then inclining itself
towards the water, it rests its legs upon it, for water is to them a
soil sufficiently firm and solid to support them, although surcharged
with the weight of the insect's body. As soon as it is thus upon the
water, it is in safety; its wings unfold themselves and are dried,
and it flies away. All this is the work of an instant[681].
The pupæ of _Chironomus plumosus_ proceed from those red worm-like
larvæ so common throughout the summer in tubs of rain-water, &c.,
described by Reaumur[682]. They are not inclosed in cases, but are of
a greater specific gravity than the water at the bottom of which they
reside, until within a few hours of the exclusion of the fly. They have
the power of swimming, however; and by moving the tail alternately
backwards and forwards, can slowly raise themselves to the top of
the water. But here occurs a difficulty. For the extrication of the
imago it is necessary that they should remain quietly suspended at
the surface; and moreover that the thorax, in which the opening for
its exit is to be made, should be at least level with it: and this is
precisely what takes place. If you watch one of these pupæ when it
ascends from the bottom, you will see that as soon as it has reached
the top it remains suspended there motionless; and that its thorax
is the highest part of the body, and level with the surface. Now the
question is, in what way this is accomplished? How can a pupa of
greater specific gravity than water, remain suspended without motion at
its surface? and how can its thorax, which is at its heaviest end, be
kept uppermost?--By a most singular and beautiful contrivance, which I
shall explain; the more particularly because it has escaped Reaumur,
and, as far as I know, all other entomological observers. The middle of
the back of the thorax has the property of repelling water--apparently
from being covered with some oily secretion. Hence, as soon as the pupa
has once forced this part of its body above the surface, the water is
seen to retreat from it on all sides, leaving an oval space in the
disk, which is quite dry. Now though the specific gravity of the pupa
is greater than that of water, it is but so very slightly greater, that
the mere attraction of the air to the dry part of the thorax, when once
exposed to it, is sufficient to retain it at the surface; just as a
small dry needle swims under similar circumstances. That this is a true
solution of the phænomenon, I am convinced by the result of several
experiments. If, when the pupa is suspended at the surface, a drop of
water be let fall upon the dry portion of the thorax, it instantly
sinks to the bottom,--the thorax, which belongs to the heaviest half,
being the lowest; and if the pupa be again brought to the surface, so
that the fluid is repelled from its disk, it remains suspended there
without effort, as before. Just previously to the exclusion of the fly,
the dry part of the thorax is seen to split in the middle. The air
enters, and forms a brilliant stratum resembling quicksilver, between
the body of the insect and its puparium; and the former pushing forth
its head and forelegs, like the gnat, rests the latter upon the water,
and in a few seconds extricates itself wholly from its envelope.
Before I close this letter, I must state a fact connected with the
subject of it that deserves to be recorded. It is a general rule,
that _one_ pupa-case incloses only _one_ insect; but Kleesius, a
German entomologist, asserts that he had once _two_ specimens of
_Gastropacha quercifolia_ produced from _one_ pupa; which was large,
being full two inches long, and one thick.
FOOTNOTES:
[562] In the _Hemiptera_ the male _Cocci_ (Reaum. iv. 32.) and
_Aleyrodes_ (Ibid. ii. 311.) belong to the second division.
[563] The terms _larva_ and _pupa_, applied to the insects of this
subdivision, are perhaps not strictly proper.
[564] The larvæ and pupæ of many of the _homopterous_ section of
_Hemiptera_ differ often from the imago, not only in their fore-legs
(PLATE XVI. FIG. 4.), but also in other respects. I have the larva of
a _Centrotus_ from Canada, given me by Dr. Bigsby, which has a long
anal process or tail.
[565] See above, p. 125--.
[566] iii. 135.
[567] The pupæ of _Cassida_, _Imatidium_, &c. seem to vary somewhat
from this type, the upper part being neither membranous nor
exhibiting distinctly the form of the inclosed imago.
[568] The following arrangement of pupæ is perhaps in some respects
better than that above given. But it is scarcely possible to propose
one free from objections.
I. Capable of eating and walking.
i. Like the perfect insect, except in proportion and number of
parts.
1. Except in proportion (_Lice_, _Poduræ_, _Mites_,
_Spiders_, _Scorpions_, &c).
2. Except in proportion and number (_Centipedes_,
_Millepedes_).
ii. With rudiments of the organs of flight.
1. With oral organs resembling those of the perfect insect
(_Hemiptera_).
2. With oral organs differing from those of the perfect
insect (_Libellula_ L., _Ephemera_ L.).
II. Incapable of eating and walking.
i. Incomplete pupæ.
ii. Obtected.
iii. Coarctate.
Lamarck divides the pupæ of insects that undergo a metamorphosis into
three kinds, which he names--_Chrysalis_, _Mumia_, and _Nympha_.
i. _Chrysalis._ Under this denomination he includes all inactive pupæ
inclosed in an opaque puparium which entirely conceals them. These he
further subdivides into two kinds.
1. _Chrysalis signata._ This term is synonymous with the _Pupa
obtecta_ of Linné, or the _Chrysalis_ of _Lepidoptera_ and some
_Diptera_.
2. _Chrysalis dolioloides._ Equivalent to the _Pupa coarctata_ Linn.
peculiar to those _Diptera_ that assume this state in the skin of the
larva.
ii. _Mumia._ All inactive pupæ which are covered by a transparent
skin, through which all the parts of the inclosed imago may be seen,
subdivided also into two.
1. _Mumia coarctata._ Corresponding with the _Pupa incompleta_ Linn.,
which includes the _Coleoptera_ and most of the _Hymenoptera_.
2. _Mumia pseudonympha_, confined to the Pupa of _Phryganea_ and some
others. This might be named _Pupa subincompleta_.
iii. _Nympha._ Under this denomination are included all insects that
undergo only a partial metamorphosis, and are active in their pupa
state, corresponding with the _Pupa semicompleta_ Linn. and also
_subsemicompleta_ MacLeay. See _Anim. sans Vertebr._ iii. 285--.
M. Latreille has started an ingenious idea on this subject with
regard to these kinds of metamorphosis, which comprehends both larva
and pupa under a distinct denomination: as thus--
1. _Demilarve_ and _Deminymph_, synonymous with the _Semicomplete
Metamorphosis_. 2. _Larve_ and _Nymph_, answering to _Incomplete
Metamorphosis_. 3. _Caterpillar_ and _Chrysalis_, answering to
_Obtected Metamorphosis_. 4. _Vermilarve_ and _Pupa_, answering to
_Coarctate Metamorphosis_. _N. Dict. d'Hist. Nat._ xvi. 272.
[569] _N. Dict. d'Hist. Nat._ vii. 57.
[570] De Geer ii. 105.
[571] Reaum. ii. 428--.
[572] Swamm. _Bibl. Nat._ Engl. Tr. ii. 32. _t._ xli. _f._ 2. Comp.
Reaum. iv. _t._ xxv. _f._ 1.
[573] _Ibid._ i. 144.
[574] Reaum. i. 355.
[575] _N. Dict. d'Hist. Nat._ ubi sup. 59.
[576] PLATE XVI. FIG. 14. _N. Dict. d'Hist. Nat._ vii. 59.
[577] _Ins. Surinam._ _t._ xliv.
[578] De Geer v. 47. _t._ ii. _f._ 29-31.
[579] In the pupa of _Hydrophilus piccus_ (Lesser L. _t._ ii. _f._
13, 14), the arrangement of the parts is nearly the same, but the
tarsi are not reflexed.
[580] _Ibid._ _f._ 9, 10. De Geer ii. _t._ xxxii. _f._ 5. Reaum. v.
_t._ xxxvi. _f._ 14.
[581] Reaum. _Ibid._ _t._ ii. _f._ 9.
[582] The legs of _Tipula replicata_ L. are placed in a similar way.
De Geer vi. _t._ xx. _f._ 12. _l._
[583] Rös _t._ 81.
[584] _Ibid._ _t._ 95.
[585] De Geer vi. 237. _t._ xiv. _f._ 8.
[586] Reaum. v. _t._ ii. _f._ 7. The anal and ventral spines of
_Tipula replicata_ are also remarkable. De Geer vi. _t._ xx. _f._ 14.
[587] De Geer _Ibid._ 377. _t._ xxiii. _f._ 8, 9. _n._ Reaum. v. 42.
_t._ vi. _f._ 9. _m n._
[588] The caterpillar consists of twelve segments (Lyonnet _t._ i.
_f._ 4, 5), excluding the head; on each of which, except the 2d,
3d, and 12th, there is a pair of spiracles. The chrysalis usually
exhibits an analogy to this structure, though the first, second, and
last pair of spiracles are more or less obsolete in most.
[589] De Geer ii. 847. _t._ xxix. _f._ 7. _a b._
[590] _Animaux sans Vertebres_, iii. 287.
[591] _N. Dict. d'Hist. Nat._ vii. 57.
[592] Sepp ii. _t._ i. _f._ 4. _t._ ii. _f._ 4. _t._ iv. _f._ 5.
[593] PLATE XVI. FIG. 12.
[594] PLATE XVI. FIG. 10.
[595] _Ins. Surinam. t._ lx. It is singular that the chrysalis of its
congener, _Morpho Teucer_, which she figures _t._ xxiii., exhibits no
such process. The larvæ also widely differ.
[596] PLATE XVI. FIG. 11.
[597] Sepp ii. _t._ iii. _f._ 5.
[598] Sepp i. _t._ vii. _f._ 5.
[599] _De Insectis_, ed. Lister. _t._ 1.
[600] _Ins. Surinam. t._ liii.
[601] Sepp i. _t._ ii. _f._ 6.
[602] _N. Dict. d'Hist. Nat._ vii. 60.
[603] _Ibid._ 57.
[604] See above, VOL. I. p. 131.
[605] Reaum. ii. 158. _t_. viii. _f_. 4, 5.
[606] Lesser L. i. 160. note. _t._ ii. _f._ 19.
[607] _N. Dict. d'Hist. Nat._ xxvi. 165. Reaum. i. 347. Rösel says
this is present only in some individuals. I. ii. 47.
[608] PLATE XVI. FIG. 13. _a._
[609] _Ins. Surinam. t._ iii.
[610] De Geer ii. 433. _t._ viii. _f._ 4. _t._
[611] See above, VOL. II. p. 300.
[612] This description was taken from a _puparium_ in my own cabinet;
it is similarly described by De Geer i. 490. _t._ vii. _f._ 2.
[613] PLATE XXIII. FIG. 8, 9.
[614] _Kliemann Beitrage_, 304.
[615] See above, VOL. I. 464.
[616] Von Scheven in _Naturf._ stk. xx. 64. _t._ ii. _f._ 4.
[617] PLATE XVII. FIG. 2. Lesser L. _t._ ii. _f._ 26.
[618] PLATE XVII. FIG. 1. Lesser L. _t._ ii. _f._ 24, 25.
[619] Whether M. Meigen has separated this fly generically from others,
I am not aware: in my catalogue it stands under the name of _Tyrophaga_.
[620] Reaum. iii. 376. _t._ xxxi. _f._ 7.
[621] Ibid. iv. 318. _t._ xxiii. _f._ 1-4. xxv. _f._ 1.
[622] _Ins. Surinam._ _t._ xxix.
[623] _Ins. Surinam._ _t._ xxxii. Lister imitated the gilding of
_Chrysalises_ by putting a small piece of a black gall in a strong
decoction of nettles: this produced a scum, which when left on
cup-paper, he says, will exquisitely gild it.--Ray's _Letters_, 87. 90.
[624] _Beitrage_, 181.
[625] Sepp. pt. ii. _t._ ii. _f._ 4.
[626] Rösel. I. i. 61. ii. 5.
[627] Reaum. i. 383.
[628] Lister's _Goedart_. 122.
[629] Reaum. ii. 10--.
[630] Ibid. 24.
[631] This is a legend of Virgil, of which an account is given in
_The Lay of the Last Minstrel_, Note xv. 12mo ed. 1822, p. 257.
[632] Haworth _Lepidopt. Britann._ i. 125. An instance is recorded
in Scriba's Journal, in which a pupa was not disclosed until the
_fourth_ year. B. i. st. iii. 222. Pezold. 170.
[633] Marsham in _Linn. Trans._ x. 402.
[634] Meinecken found, that of several pupæ of _Saturnia pavonia_,
some kept all winter in a room heated daily by a stove, and others
in a cold chamber, some of both parcels appeared in March (none
earlier), and some of both had not appeared in July, though evidently
healthy. _Naturf._ viii. 143.
[635] The exclusion of certain moths, &c. from the pupa is probably
regulated by the time their eggs require to be hatched, and the
appearance of the leaves that constitute their appropriate food.
[636] Mr. Marsham makes a similar observation in _Linn. Trans._, ubi
supr.
[637] See above, p. 245.
[638] The appearance of them sometimes continues to near the end of the
month: it began on the 19th, when Reaumur observed them. vi. 480. 488.
[639] _Bibl. Nat._ E. Transl. i. 103--.
[640] Reaum. vi. 486.
[641] Brahm. 423. 421.
[642] _Naturf._ xxi. 75.
[643] Reaum. ii. 423.
[644] De Geer ii. 370. It is not certain, however, that De Geer did
not, in this instance, mistake the winter habitation of a larva for
a cocoon intended to shelter the future chrysalis; since Lyonnet
informs us that they spin a habitation to pass the winter in. _Traité
Anatomique_, &c. 9.
[645] De Geer i. 490. _t._ vii. _f._ 3, 4.
[646] _Œuv._ ii. 1.
[647] De Geer v. 229.
[648] VOL. II. 300--.
[649] VOL. II. 298--.
[650] I. iv. 101.
[651] Reaum. vi. 407.
[652] Haworth _Lepidopt. Britann._ i. 127.
[653] De Geer ii. 566.
[654] Reaum. iii. _t._ xlv. _f._ 12-14.
[655] For this whole account, see Reaum. iv. Mem. viii.
[656] Ibid. 472.
[657] See above, p. 255--. and VOL. II. p. 301--.
[658] Bonnet, _Œuv._ ii. 169.
[659] Bonnet, _Œuvr._ ii. 207.
[660] Rös. I. iv. 209. _t._ lxiii. ccxii.
[661] See above, p. 217.
[662] Bonnet, _Œuvr._ ii. 229.
[663] De Geer ii. 477.
[664] Sepp. iv. _t._ xi. _f._ 8.
[665] PLATE XVII. FIG. 5. N.B. Sepp's figure represents the
_exterior_ funnel; and this, which exhibits the cocoon divided
longitudinally, the _interior_ one, or dome.
[666] Rös. I. iv. 31.
[667] _Naturf._ viii. 133.
[668] _De Bombyc._ 29.
[669] Reaum. i. 624.
[670] _Trans. of the Society of Arts_, vii. 131.
[671] Reaum. _ubi supr._
[672] ii. 359.
[673] _Linn. Trans._ vii. 35.
[674] Pezold. 171.
[675] Lyonnet 16.
[676] _Some Notice of the Insect which destroys the Locust-trees_,
70. This Memoir is in some American periodical work, of which I have
not the title.
[677] Huber _Fourmis_ 82.
[678] VOL. I. p. 467.
[679] VOL. II. p. 264.
[680] De Geer ii. 519.
[681] Reaum. iv. 610--.
[682] Ibid. v. 30--. _t._ v. _f._ 1-10. See above, p. 153--.
LETTER XXXII.
_STATES OF INSECTS._
IMAGO STATE.
When the insect has quitted the exuviæ of the pupa, it has attained
the last stage of its existence. It is now termed an _Imago_, or
perfect insect; and is capable of propagation.
Just after its exclusion, it is weak, soft, and languid: all its
parts are covered with moisture; and, if a winged insect, its wings
have so little the appearance, either in shape, size, or colour,
which they are about to assume, that it might be taken for a
mutilated abortion, rather than an animal in the most vigorous stage
of life. If it be a beetle, its elytra, instead of covering the
back of the abdomen, are folded over the breast: their substance is
soft and leathery, and their white colour exhibits no traces of the
several tints which are to adorn them. If the insect be a butterfly
or a moth, the wings, instead of being of their subsequent amplitude,
and variegated and painted with a variety of hues and markings, are
in large species scarcely bigger than the little finger nail, falling
over the sides of the trunk, and of a dull muddy colour, in which no
distinct characters can be traced. If the excluded insect be a bee
or a fly, its whole skin is white and looks fleshy, and quite unlike
the coloured hairy crust which it will turn to in an hour or two; and
the wings, instead of being a thin, transparent, expanded film, are
contracted into a thick, opaque, wrinkled mass.
These symptoms of debility and imperfection, however, in most
cases speedily vanish. The insect, fixing itself on the spoils of
the pupa, or some other convenient neighbouring support, first
stretches out one organ, and then another: the moisture of its skin
evaporates, the texture becomes firm, the colours come forth in all
their beauty; the hairs and scales assume their natural position;
and the wings expanding, extend often to five or six times their
former size--exhibiting, as if by magic, either the thin transparent
membranes of the bee or fly, or the painted and scaly films of
the butterfly or moth, or the coloured shells of the beetle. The
proceedings here described I witnessed very recently with regard
to a very interesting and beautiful butterfly, the only one of its
description that Britain has yet been ascertained to produce--I mean
_Papilio Machaon_. The pupa of this being brought to me by a friend
early in May this year (1822), on the sixteenth of that month I had
the pleasure to see it leave its puparium. With great care I placed
it upon my arm, where it kept pacing about for the space of more than
an hour; when all its parts appearing consolidated and developed, and
the animal perfect in beauty, I secured it, though not without great
reluctance, for my cabinet--it being the only living specimen of this
fine fly I had ever seen. To observe how gradual, and yet how rapid,
was the development of the parts and organs, and particularly of the
wings, and the perfect coming forth of the colours and spots, as the
sun gave vigour to it, was a most interesting spectacle. At first
it was unable to elevate or even move its wings; but in proportion
as the aërial or other fluid was forced by the motions of its trunk
into their nervures, their numerous corrugations and folds gradually
yielded to the action, till they had gained their greatest extent,
and the film between all the nervures became tense. The ocelli, and
spots and bars, which appeared at first as but germes or rudiments
of what they were to be, grew with the growing wing, and shone forth
upon its complete expansion in full magnitude and beauty.
To understand more clearly the cause of this rapid expansion and
development of the wings, I have before explained to you that these
organs, though often exceedingly thin, are always composed of two
membranes, having most commonly a number of hollow vessels, miscalled
nerves, running between them[683]. These tubes, which, after the
French Entomologists, I would name _nervures_, contribute as well
to the development of the wings, as to their subsequent tension. In
the pupa, and commonly afterwards, the two membranes composing the
organs in question do not touch each other's inner surface, as they
afterwards do: there is consequently a space between them; and being
moist, and corrugated into a vast number of folds like those of a
fan, but transverse as well as longitudinal, and so minute as to be
imperceptible to the naked eye, the wings appear much thicker than
in the end. Now as soon as the insect is disclosed, a fluid enters
the tubes, and being impelled into their minutest ramifications,
necessarily expands their folds; for the nervures themselves are
folded, and as they gradually extend in length with them, the moist
membranes attached to them are also unfolded and extended. In
proportion as this takes place, the expanding membranes approach each
other, and at last, being dried by the action of the atmosphere, become
one. To promote this motion of the fluid, seems the object of the
agitations which the animal from time to time gives to its unexpanded
wings. That a kind of circulation, or rather an injection of an aqueous
fluid into these organs, actually takes place, may be ascertained by
a very simple experiment. If you clip the wings of a butterfly during
the process of expansion, you will see that the nervures are not only
hollow, but that, however dry and empty they may subsequently be found,
they at that time actually contain such a fluid[684]. Swammerdam, who
appears to have been the first physiologist that paid attention to
this subject, was of opinion that an aëriform as well as an aquiform
fluid contributes to produce the effect we are considering. He had
observed that, if a small portion be cut off from the wing of a bee,
a fluid of the latter kind exuded from its vessels in the form of
pellucid globules, becoming insensibly drops--which he concluded
proved the action of the latter; and he noticed, also, that the wings
were furnished with tracheæ, which were at that time distended by the
injected air; whence he justly surmised, that the action of the _air_
was also of great importance to produce the expansion of the wing[685].
And Jurine found that every nervure contains a trachea, which,
proceeding from the interior of the trunk in a serpentine direction,
follows all the ramification of the nervure, though it does not fill
it[686]. Though Reaumur attributes the expansion of the wings chiefly
to an _aqueous_ fluid, yet he suspects that the _air_ on some occasions
contributed to it[687].
The wings of the other tribes of insects probably differ from the
_Lepidoptera_ in the manner in which they are folded. It should seem
from Reaumur's description, that those of some flies, instead of
the straight transverse folds of the former, have angular or zigzag
folds[688]; which equally shorten the wing. Many _Hymenoptera_ have
wings without any nervures except the marginal. We may conjecture that
these are more simply folded, so as to render their expansion more
easy; but even in these wings there are often tracheæ, which appear as
spurious nervures, and help to effect the purpose we are considering.
The operation of expanding their wings, in by far the larger number
of insects, takes place gradually as described above; and, according
to their size, is ended in five, ten, or fifteen minutes; in some
butterflies half an hour, in some even an hour. A few species, such
as _Sphinx Œnotheræ_ F., require several hours, or even a day, for
this operation; and, from the distance to which they creep before
it has taken place, a considerable degree of motion seems requisite
for causing the necessary impulse of the expanding fluids[689]. In
a few genera, however, as the gnat, the gnat-like Tipulidæ, and
the Ephemeræ, this process is so rapid and instantaneous, that the
wings are scarcely disengaged from the wing-cases before they are
fully expanded and fit for flying. These genera quit the pupa at the
surface of the water, from which, after resting upon it for a few
moments, they take flight: but this would evidently be impracticable,
and immersion in the fluid, and consequent death, would result, were
not the general rule in their case deviated from.
Some species of the last of these genera, _Ephemera_, are
distinguished by another peculiarity, unparalleled, as far as is
known, in the rest of the insect world. After being released from
the puparium, and making use of their expanded wings for flight,
often to a considerable distance, they have yet to undergo another
metamorphosis. They fix themselves by their claws in a vertical
position upon some object, and withdraw every part of the body, even
the legs and wings, from a thin pellicle which has inclosed them,
as a glove does the fingers; and so exactly do the exuviæ, which
remain attached to the spot where the Ephemera disrobed itself,
retain their former figure, that I have more than once at first
sight mistaken them for the perfect insect. You can conceive without
difficulty how the body, and even legs, can be withdrawn from their
cases; but you must be puzzled to conjecture how the wings, which
seem as thin, as much expanded, and as rigid as those of a fly, can
admit of having any sheath stripped from them; much less how they
can be withdrawn, as they are, through a small opening at the base
of the sheath. The fact seems to be, that though the outer covering
is rigid, the wing inclosed in it, notwithstanding it is sometimes
more than twenty-four hours before the change ensues, is kept moist
and pliable. In proportion, therefore, as the insect disengages
itself from the anterior part of the skin, the interior or real
wings become contracted by a number of plaits into a form nearly
cylindrical, which readily admits of their being pulled through the
opening lately mentioned; and as soon as the insect is released from
its envelope, the plaits unfold, and the wing returns to its former
shape and dimensions. Thus our little animal, having bid adieu to its
shirt and drawers, becomes, but in a very harmless sense, a genuine
_descamisado_ and _sansculotte_. It does not seem improbable, that
the pellicle we have been speaking of is analogous to that which,
in addition to the outer skin, incloses the limbs of _Lepidoptera_,
&c. in the pupa state, but which they cast at the same time with the
puparium, and leave adhering to it[690].
The body of newly-disclosed insects commonly appears at first of its
full size; but the aphidivorous flies (_Syrphus_ F. &c.), and some
others, in about a quarter of an hour after leaving the pupa become
at least twice as large as they were at their first appearance: this
apparent sudden growth, which is also noticed by Goedart, Reaumur
found to depend upon the expansion of the previously compressed
segments of the animal by means of the included air[691]. Both in this
instance and in that of insects whose wings only require expansion, the
size of the _imago_ often so greatly exceeds that of the _pupa_, that
we can scarcely believe our eyes that it should have been included in
so contracted a space. The pupa of one of the beautiful lace-winged
flies (_Hemerobius Perla_) is not so big as a small pea, yet the body
of the fly is nearly half an inch long, and covers, when its wings and
antennæ are expanded, a surface of an inch square[692].
When the development of the perfect insect is complete, and all
its parts and organs have attained the requisite firmness and
solidity[693], it immediately begins to exercise them in their
intended functions; it walks, runs, or flies in search of food; or
of the other sex of its own species, if it be a male, that it may
fulfill the great end of its existence in this state--the propagation
of its kind. Previously to thus launching into the wide world, or at
least immediately afterwards, almost all insects discharge from their
intestines some drops of an excrementitious fluid, often transparent,
and sometimes red. I have before related to you the alarm that this
last circumstance has now and then produced on the minds of the
ignorant and superstitious[694]. Whether this excrement is produced
indifferently both by males and females I cannot positively assert;
but a circumstance related by Jurine affords some ground for a
suspicion that it is peculiar to the latter. A specimen of a female
of _Lasiocampa Rubi_, when killed emitted some of this fluid, which
dropped upon the floor: this appeared to attract the males to the
apartment in which it happened, and to the very spot--from whence it
may be conjectured, that the scent of the fluid brought them there,
and that the use of it is to bring the sexes together soon after
exclusion from the pupa[695].
The colour, sculpture, and other peculiarities which distinguish
insects in this state I shall consider at large in another letter,
when I treat of their external parts and organs. Under the present
head I shall confine myself to pointing out the characters by which
the _sexes_ of many species are distinguished from each other;
as likewise the _duration of their life_ in their perfect state;
together with the circumstances on which this duration depends.
I. _Sexual Distinctions._ The first general rule that may be laid down
under this section is,--That among insects, contrary to what mostly
occurs in vertebrate animals, the _size_ of the female is almost
constantly larger than that of the male. Even in the larva and pupa
states, a practised eye can judge, from their greater size, which
individuals will become females. There are, however, some exceptions
to this rule. Thus amongst the _Coleoptera_, the male _Dynastidæ_,
remarkable for their horns, as you may see in _D. Alocus_, _Antæus_,
_Actæon_, &c., as likewise those of _Lucanus_, are larger than the
unarmed females[696]. In the _Neuroptera_ the female _Libellulidæ_ are
sometimes sensibly smaller, and never larger, than their males[697]. In
the _Hymenoptera_ the male of the hive-bee, but more particularly that
of _Anthidium manicatum_ and other bees of that genus, is much more
robust than the other sex[698]. In the _Diptera_, the same difference
is observable in _Syrphus Ribesii_, and some other aphidivorous
flies, and also in _Scatophaga stercoraria_[699]. And amongst the
_apterous_ tribes, we are informed by De Geer that the male of
_Argyroneta aquatica_, which builds an aërial palace in the bosom of
the waters[700], usually exceeds the female in bulk[701]. The reason of
this rule seems in some degree connected with the office of the female
as a mother, that sufficient space may be allowed for the vast number
of eggs she is destined to produce; and it is when impregnation has
taken place, and the eggs are ready for extrusion, that the difference
is most sensible. In the majority of cases this sexual disproportion
is not very considerable, but in some few it is enormous. Reaumur
mentions a beetle, of which he intended to give the history, the male
of which is so small compared with the female, that a bull not bigger
than a sheep, or even a hare, set by the side of the largest cow, would
aptly contrast with them. This little beetle, he says, has wings and
elytra, while the giant female has no vestige of either, having the
upper surface of its body naked and membranous[702]. The species to
which this illustrious Naturalist here alludes, does not appear to
have been ascertained. The female of many gall-insects (_Cocci_) is so
large in comparison with the male, that the latter traverses her back
as an ample area for a walk[703]. But this is nothing compared with
the prodigious difference between the sexes of _Termes fatale_, and
other species of white ants, whose males are often many thousand times
less than the females, when the latter are distended with eggs[704].
Accidental differences in the size of the sexes sometimes arise: as
when the female larva has, from any cause, been deprived of its proper
supply of food, it will occasionally be less than the male. De Geer
has stated a circumstance with respect to the _Aphides_ that produce
galls, that should be mentioned under this head--the first, or _mother_
female, is larger than any of her progeny ever become[705].
The second observation that may be generally applied to the sexes of
insects is, that, size excepted, there is a close resemblance between
them in other respects. But to this rule the exceptions are very
numerous, and so important that it is necessary to specify examples
of each under distinct heads.
i. In some species the sexes are either partly or wholly of a
different _colour_. Thus, in the order _Coleoptera_, the elytra of
the male of _Rhagium meridianum_ F. are testaceous, and those of the
female black. _Leptura rubra_ of Linné, with red elytra, is the
female of his _L. testacea_, in which they are testaceous. _Cantharis
dermestoides_ of the same author is the other sex of his _Meloe
Marci_; one of which is chiefly testaceous, and the other black:
which seems to have so misled Linné, that he placed them in different
genera. One more instance in this order, the female of _Cicindela
campestris_, as was first observed to me by our friend Sheppard, has
a black dot on each elytrum, not far from its base near the suture,
which the male has not.
Amongst the _Orthoptera_, the male _Locustæ_ F., as Professor
Lichtenstein has informed us[706], have a fenestrated ocellus, which
is not to be found in the other sex. I was once attending to the
proceedings of a Hemipterous species, _Pentatoma oleracea_ Latr.,
which I found in union: the paired insects had white spots, but
another individual was standing by them, in which the spots were
of a sanguine hue. I mention this by the way only--the spots in
the prolific sexes being of the same colour: but might not the red
spotted one be a neuter?
The sexes of many _Lepidoptera_ likewise differ in their colour. I
must single out a few from a great number of instances. The males of
_Lycæna Argus_ F. have the upper surface of their anterior wings of a
dark blue, while in the female it is wholly brown. The wings of the
former sex of _Hypogymna dispar_ are gray, clouded with brown; but
those of the latter are white, with black spots. In the brimstone
butterfly (_Colias Rhamni_), which is one of the first that appear in
the spring, the wings of the male are yellow--of the female whitish.
In the common orange-tip (_Pieris Cardamines_ F.), one sex has not
the orange tip to the upper wings: and, to name no more, the male of
_Lycæna dispar_, one of our rarest and most beautiful butterflies,
has only a single black spot in the disk of its fulgid wings; while
in the other sex, the primary pair have nine, and the secondary are
black, with a transverse orange fascia near the posterior margin.
But the most remarkable difference in this respect observable in the
insects of the order in question, takes place in a tribe, of which
only one species is certainly known to inhabit Britain--I mean the
_Papiliones Equites_ of Linné: what he has called his _Trojani_ and
_Achivi_ in some instances have proved only different sexes of the
same species. Mr. MacLeay's rich cabinet affords a singular instance
confirming this assertion;--a specimen of a Papilio is divided
longitudinally, the right hand side being male, and the left hand
female. The former belongs to _P. Polycaon_, a Grecian, the latter to
_P. Laodocus_, a Trojan. An instance of two _Grecians_ thus united is
recorded in the _Encyclopédie Méthodique_, as exhibited in a specimen
preserved in the Museum of Natural History at Paris; which on the
right hand side is _P. Ulysses_, on the left _P. Diomedes_[707].
In the _Neuroptera_, the _Libellulidæ_ are remarkable for the
differences of colour in the sexes. In the common _Libellula
depressa_, which you may see hawking over every pool, the abdomen
of the male is usually slate-colour, while that of his partner is
yellow, but with darker side-spots. Reaumur, however, noticed some
males that were of the same colour with the females[708]. Schelver
observed, when he put the skins of _Libellula depressa_ into water,
that the colours common to both sexes were in the substance of the
skin, and remained fixed; while those that were peculiar to one
could be taken off with a hair-pencil, and coloured the water: which
therefore were superficial, and, as it were, laid on[709]. The yellow
males, therefore, that Reaumur observed, were probably such as had
the superficial blue colour which distinguishes them washed off. In
_Calepteryx Virgo_ Leach, the former are of a lovely silky blue, and
the latter green. In _Agrions_ F. nature sports infinitely in the
colours of the sexes.
In the order _Hymenoptera_ there are often differences equally great;
the sexes of many of the Ichneumons and Saw-flies are of quite
different colours. The former tribe Linné has divided into sections,
from the white annulus observable in the antennæ of some, and from
the colour of their scutellum: but these are often merely sexual
characters[710]. The male of _Anthophora retusa_ Latr., a kind of
wild bee, is wholly black, the female wholly gray, and of so very
different an aspect that they were long regarded as distinct species;
a mistake which has likewise occurred with regard to the sexes of
_Osmia cærulescens_, another bee, of which the male has a bronzed and
the female a violet abdomen[711]. The nose of male _Andrenæ_ Latr.
is often yellow, or white, as in _A. hæmorrhoidalis_--when that of
the female is black[712]. The _labrum_ also is often of a different
colour in the sexes, as in _Ceratina_ Latr.
In the _Diptera_, _Aptera_, _Arachnida_, &c., I am not aware of any
striking difference in the colours of the sexes.
ii. The sexes of insects vary (but more rarely than in colour) in
their _sculpture_ also, and _pubescence_. Thus the elytra of the
females of many of the larger water-beetles (_Dytiscus_) are deeply
furrowed, while those of the males are quite smooth and level[713].
The thorax of the female in several species of _Colymbetes_ of the
same tribe, as _C. Hybneri_ and _transversalis_, on each side has
several tortuous impressed lines or scratches, like net-work, which
are not to be discovered in the male. _Hyphydrus gibbus_ Latr.,
which differs solely from _H. ovalis_ (_Dytiscus ovalis_ Illig.) in
being thickly covered with minute impressed puncta, is, from the
observation of the Rev. R. Sheppard, the other sex of this last,
with which he has taken it coupled; and it is by no means improbable
that _Hydroporus picipes_ (_Dytiscus punctatus_ Marsh.) and _H.
lineatus_,--between which, as Gyllenhal has justly observed, the same
difference only exists,--are in like manner sexual varieties. With
respect to _pubescence_, I have not much to say. Another aquatic
beetle, _Acilius sulcatus_ Leach, has not only its elytra sulcated,
but the furrows of these, and a transverse one of the thorax, are
thickly set with hair; while the male is smooth, and quite naked.
Particular care seems to have been taken by the Creator, that when
all the above inhabitants of the water are paired, the male should be
able to fix himself so firmly, by means of his remarkable anterior
tarsi, (which I shall afterwards describe,) and these asperities,
&c. in the upper surface of his mate, as not to be displaced by the
fluctuations of that element, the reluctance of the coy female, or
any other slighter cause.
In a moth called the ghost (_Hepialus Humuli_), the posterior tibia
of the male is densely bearded, but not of the female[714].--Some
_Hymenoptera_, as _Ammophila_ Kirb. and _Stigmus_ Jurine, have
the upper lip of the male clothed with silver pile, while that
of the female is not so ornamented. The legs of some bees are
distinguished in the sexes by a difference in their _clothing_. That
observable in those of the hive-bee has been before noticed[715].
In _Andrena_ of Latreille[716] the posterior tibia of the female is
covered externally with a dense brush of hairs, for collecting the
pollen; and the posterior legs at their base have a curled lock of
hair--which are not to be found in the male[717]. In _Dasypoda_,
_Melecta_, _Anthophora_, _Centris_, _Epicharis_, &c. of the same
author, the first joint of the tarsus of the female, and in
_Xylocopa_ almost the whole tarsus, is also similarly signalized from
that of the other sex. In _Bombus_, as in the hive-bee, the posterior
tibiæ of the females and neuters are furnished with a basket of hairs
for carrying their pollen paste, which you will in vain look for in
the male[718]. The latter, however, in some species of this tribe are
distinguished from the former by the longer hairs of their legs, but
not in the posterior ones. Thus, in _Anthophora retusa_ the first
joints of the intermediate tarsus are bearded internally with a thin
fringe of long hairs, and the first externally with a triangular one
of short ones at the apex: but what is most remarkable, the last or
unguicular joint, which in almost every other bee is naked, is on
both sides fringed with long hairs[719]. In that remarkable genus
_Acanthopus_ Illig., of which the male only is known, the first and
last joint of the intermediate tarsus have a dense external brush
of stiff hairs, which probably is also a sexual character[720].
Another sexual kind of clothing is exhibited by the females of those
bees that have their labrum or upper-lip inflexed (_Megachile_
Latr.)[721]. Their abdomen is covered underneath with a brush of
stiff hairs, involved in which they carry the pollen they collect.
In the males of some of this tribe, as of _M. Willughbiella_, the
first four joints of the anterior tarsus on their inner side have a
long dense fringe of incurved hairs[722]: a circumstance also to be
found in the same sex of _Xylocopa latipes_, in which the claw-joint
also is bearded[723]. In _Andrena_ Latr. the last dorsal segment of
the abdomen of the same sex is fringed, while that of the male is
naked[724]. In the humble-bees (_Bombus_), the mandibles of the male
are bearded with curled hairs, while those of the females and neuters
are without them. Some bees, as _Andrena_ and _Halictus_ Latr., have
the anus of the female bearded, and that of the male naked: in some
_Bombyces_ the reverse takes place.
iii. With regard to the general _shape_ of their body, the male and
female usually resemble each other: but there are some exceptions to
this rule. The male of the hive-bee is much thicker and more clumsy
than either the female or the worker; but in _Halictus_ Latr. the
males are nearly cylindrical in shape, and very narrow; while the
other sex are oblong or ovate, especially their abdomen: and in
_Andrena_ Latr. the former are much slenderer than the females, and
of a more lanceolate shape. But a still more striking difference
in this respect between the sexes is exhibited by some species of
the genus _Ptinus_ F., in which the male is long and slender, and
the female short and thick. This, in more than one instance, has
occasioned them to be mistaken for distinct insects: thus, _P.
Lichenum_ and _P. similis_, _P. ovatus_ and _P. testaceus_, of Mr.
Marsham, are mere sexual varieties. But the most entire abalienation
of shape at present known, is that which distinguishes the male from
the female _Coccus_; these are so completely dissimilar as scarcely
to have any part in common. In _Bombyx vestita_ F., and others of
the same family, while the males are of the ordinary conformation of
the order, the females are without even the slightest rudiments of
wings; they have no antennæ, the legs are extremely short, not longer
than those of the caterpillar; and the body is entirely destitute
of scales, so that they altogether assume the exact appearance of
hexapod larvæ[725]. A conformation nearly similar takes place in the
female of _Tinea Lichenella_; but in this the feet are longer, and
the anus is furnished with a long retractile ovipositor[726].
iv. In many cases, the structure of particular _parts_ and _organs_
of the body differs in the sexes. As the facts connected with this
part of our present subject are extremely numerous and various,
it will be convenient to subdivide it, and consider the sexual
characters that distinguish--the _Head_, _Trunk_, and _Abdomen_ of
insects, and their several appendages.
1. The _Head_. This part in some females is considerably larger than
it is in the male. This is the case with the ants, and several other
_Hymenoptera_; while in some _Andrenæ_, as _A. hæmorrhoidalis_, and
_Staphylinidæ_, as _St. olens_, that of the male is the largest. But
in none is the difference more conspicuous than in the stag-beetle
(_Lucanus_); in which genus the male not only exceeds the female
in the length of his mandibles, but also greatly in the size and
dimensions of his head. In the _Apion_ genus, the rostrum of the
female is generally longer and slenderer than that of her mate; and
in _Brentus_, the rostrum of one sex (probably the male) is long
and filiform, while in the other it is thick and short. This is
particularly visible in _B. dispar_ and _maxillosus_[727], &c.
One of the most striking distinctions of the males in this part of
their body, are those threatening horns, usually hollow, with which
the heads of many of the male lamellicorn insects and some others
are armed, and which give them some resemblance to many of the
larger quadrupeds. Many are _unicorns_, and have their head armed
with only a _single_ horn; which in some, as in _Oryctes_ Illig.,
_Dynastes Endymion_[728], &c. is very short; in others, very long,
as in _Dynastes Enema_, _Pan_, _Elephas_[729]. In one, again, it
is thick and robust; as in the clumsy _Dynastes Actæon_[730]: in
another very slender, as in _Onthophagus spinifer_[731]. With respect
to its direction in _Elephastomus proboscideus_ MacLeay, it is
horizontal[732] and straight; in _Phaleria cornuta_ horizontal and
broken, or the apex turning outwards and forming an angle with the
base[733]; in _Dynastes Hercules_ horizontal, and recurved at the
apex[734]; in _D. Actæon_, _Elephas_, and _Typhon_, recurving from
the base. In _Geotrupes dispar_ it is recurved, so that its point
exactly coincides with that of the porrected thoracic horn, with
which it forms a kind of forceps[735]. In _Copris lunaris_ F. and
_Diaperis horrida_, the horn is nearly upright[736]. In _Onthophagus
Xiphias_ it is dilated at the base, and reclining upon the thorax;
and at the apex attenuated, and bending forwards, or nodding.
In _Passalus cornutus_ it rises a little, and then bends wholly
forwards. In _Dynastes Milon_, a most remarkable beetle, it slopes
backwards in a waving line[737]; and in _Onthophagus spinifer_ it is
recurved and reclining.--In speaking of the direction of the horn,
you must recollect that it will vary in proportion as the head varies
from a horizontal position: so that an upright horn will become
inclined or reclined, as the head bends forwards or backwards; but
I speak of it as it appears when the head is horizontal. Again,
it varies in its teeth or branches. In _Dynastes Hercules_ it is
armed with several teeth. In _D. Elephas_ and _Actæon_ it has only
one large one at its upper base[738]. In _D. Milon_ it is serrated
above. In _D. Alcides_, _Tityus_, _Ægeon_, _Copris lunaris_, &c. the
horn is unarmed and simple at the apex. In _D. Oromedon_, _Gedeon_,
_Enema_, _Actæon_ and congeners, it is bifid. In some the horn is at
first a broad lamina or ridge, which terminates in two branches, as
in _Onthophagus Vacca_. In this the branches are straight; but in
another undescribed species in my cabinet (_O. Aries_ Kirby, MS.)
they are first bent inwards, and then at the apex a little recurved:
and in _D. dichotomus_ it is divided into two short branches, each of
which is bifid[739]. Other males emulate the bull, the he-goat, or
the stag, in having a _pair_ of horns on their head. In _Onthophagus
Taurus_, these arms in their curvature exactly resemble those of
the first of these animals[740]. In _Goliathus pulverulentus_, the
straight, robust, diverging, sharp horns are not unlike those of some
of the goat or gazel tribe. I have a beautiful little specimen in my
cabinet, (I believe collected by Mr. Abbott of Georgia,) in which the
horns have a lateral tooth, or short branch, like those of a stag;
and which I have therefore named _O. cervicornis_. In _O. Vacca_,
_Camelus_, &c. the horns are very short, and nearly perpendicular. In
the male of _Copris Midas_, the two longer perpendicular horns have
a deep cavity between them, which, together with its black colour,
give it a most demoniac aspect; so that you would think it more aptly
representative of a Beelzebub or _Beelzebul_ than a Midas[741],
or than _Phanæus Beelzebul_ MacL. A similar cavity is between the
occipital horns of _Diaperis hæmorrhoidalis_ Payk. Some species of
_Rynchænus_, as _R. Taurus_, have a pair of long horns upon the
rostrum of the male, the rudiments only of which are to be traced
in the female[742]. Other species go beyond any known quadrupeds in
the number of horns that arm their heads. Thus _Ditomus calydonius_
Bonelli, belonging to _Carabus_ L., has _three_ equal horns[743]. The
same number distinguishes _Onthophagus Bonasus_; but the intermediate
one is very short. In _Goliathus Polyphemus_ the middle horn, on
the contrary, is much longer and thicker than the lateral ones, and
forked at the apex; so that it looks as if it had four of these
weapons[744]. A little _Diaperis_ (_D. viridipennis_ F.), a native
of _Carolina_, has four horns upon the head of the male; namely,
two long ones on the occiput, and two short dentiform ones on the
nose. In a species nearly related to this, sent me by Professor Peck
from New England, there is a cavity between the two occipital horns.
The same number distinguishes _Onthophagus quadricornis_ (_Copris_
F.). The _situation_ also of the horns varies: In some it is in the
_middle_ of the head, as _Oryctes nasicornis_, _Copris lunaris_,
&c.: in others, as in _Onthophagus nuchicornis_, _Xiphias_, &c. it
is a process of the _occiput_ or hind-head; and in _O. Oryx_ F. the
two horns proceed from the _anterior_ part of the head. In the other
sex, in insects the head of whose males is armed with horns, they are
usually replaced by mere tubercles, or very short elevations, as you
may see in the female of _Copris lunaris_; or by transverse ridges,
as in the _Onthophagi_: or else the head is without arms, and quite
smooth, as in _Diaperis_, _Phaleria_, &c. What may be the use of
these extraordinary appendages, as well as those on the thorax, and
in some cases on the abdomen, (which I shall mention afterwards), to
the males, has not yet been ascertained. Whether the individuals of
this sex are more exposed to the attack of birds and other enemies,
in consequence of being more on the wing than the females, and are
therefore thus provided with numerous projecting points for defence,
is a question worth considering[745]. It is the only probable
conjecture on the _cui bono_ of these arms that I can at present
make. Under this head I ought to notice the remarkable membranous
process of an obovate shape, which like an umbrella covers the head
of _Acheta umbraculata_ F.[746] Whether the sharp curved horns which
arm this part in another _Acheta_ figured by Stoll[747], in an
incumbent posture, with their point towards the mouth, are a sexual
distinction, we are not informed,--probably they are.
The _organs_ of the head also present many sexual distinctions.
The upper lip (_labrum_) in _Halictus_ Latr., a tribe of wild bees,
in the female is furnished with an inflexed appendage, which is not
discoverable in that of the male[748]; and the shape of this lip in
_Sphecodes_ Latr. differs in the sexes[749]. Perhaps the horn or
tubercle observable on this part of some female _Nomadæ_ F.[750] may
be wanting in the male.
The under-lip (_labium_)--taken in a restricted sense for that
central part from which emerge the labial palpi, and which is often
considered as the mentum,--does not offer any striking variations in
the sexes. One, however, is of importance, as it helps to prove which
are the true female _Lucani_. In the male the labium is emarginate,
in the female it is intire. This may be seen both in _L. Cervus_
and _femoratus_, and probably in other species. The sculpture also
is different, the lip being smooth in the former and covered with
excavated _puncta_ in the latter. The tongue (_lingua_ or _ligula_)
of the sexes is usually the same; except in the hive-bee, in which
that of the neuters is longer than that of the male and female.
The upper-jaws (_mandibulæ_), however, often afford striking sexual
characters. The enormous protended ones of the common stag-beetle
(_Lucanus Cervus_) attract the attention of the most incurious
observer; and these are now generally allowed to be of this
description. Geoffroy and Mr. Marsham, indeed, have asserted that
they have taken _in coitu_ those with long mandibles: but as these
males are pugnacious, and attack each other with great fury, as Mr.
Sheppard informs me, it is not improbable that these gentlemen may
have mistaken a _battle_ for an _amour_: since not only have those
with long mandibles been often taken united with those that have short
ones[751], but the same difference obtains in the sexes of other
species. This is particularly observable in _Lucanus femoratus_, of
which I received from Brazil many specimens agreeing in every respect
except in this, that one had short and the other very long mandibles.
These organs vary in different specimens, as to the number of their
teeth and branches. They are singularly robust in _L. Alces_[752]; but
in none more threatening than in _L. Elephas_[753], in which they curve
outwards and downwards. In Mr. W. MacLeay's genus _Pholidotus_, they
are almost parallel to each other, and curve downwards; in _Lucanus
nebulosus_ Kirby, they assume a contrary direction[754]; as they do
likewise in _Lamprima_ Latr.[755] In _Lucanus Capreolus_ the points
close over each other[756]. In _Lethrus_ F. in the female, but not
the male, the mandible is armed below with a long incurved horn. In
_Lucanus serricornis_ they form a complete forceps[757]. In _Siagonium
quadricorne_ Kirby[758] the mandible is furnished at its base with an
exterior horn, which is probably a sexual distinction. The male of
_Synagris cornuta_, a kind of wasp, is still more conspicuous in this
respect; for from the upper side of the base of its straight slender
mandibles proceed a pair of crooked, decurved, tortuous, sharp horns,
not only longer than the mandible, but than the head itself[759].
Many sexual differences are observable in the mandibles of the various
tribes of bees (_Anthophila_ Latr.). Thus, in _Colletes_ Latr. the
_male_ mandible is more distinctly bidentate at the apex than the
female[760]: in _Sphecodes_ Latr. and others, the reverse of this takes
place[761]. Where these organs in both sexes are toothed at the apex,
they often vary in the number of teeth. Thus, the female of _Megachile
centuncularis_ Latr. has four teeth at the apex of its mandible, while
the male has only two[762]. In _M. Willughbiella_, though the mandibles
of both sexes have four teeth, yet those of the male are sharp, and
the two external ones the longest; while those of his mate are obtuse,
and all nearly equal in length[763]. In _Anthidium manicatum_ Latr.,
the former has only three teeth, while the latter has five[764].
The differences in this respect in the hive-bee have been before
noticed[765]; those of the humble-bees (_Bombus_ Latr.) are strikingly
distinguished from each other; the female mandible being very stout and
wide, constricted in the middle, and furrowed on its outer surface; and
the male, on the contrary, very slender at the apex, dilated at the
base, and without furrows[766].
Of all the organs of the head, none seem so little subject to _sexual_
variation as the under-jaws (_maxillæ_)[767]. I can bring forward only
one striking instance of it, and some degree of doubt rests even upon
that. In the genus _Nemognatha_ of Illiger, the maxillæ of the male are
elongated, narrow, setiform, and often involute or spiral, like those
of a bee or a butterfly. But that this is peculiar to the males is at
present only surmised[768]. I possess several species of the genus, all
of which are distinguished by long maxillæ; though in some they are as
long as the body, and in others scarcely half that length. _Gnathium_
Kirby is similarly characterized[769].
The _maxillary palpi_ occasionally differ in the sexes. In _Cerocoma_
those of the female are filiform, while the two intermediate joints
of those of the other sex are much thicker than the first and
the last[770]. In _Hylæcetus_ and _Lymexylon_, those of the male
are still more remarkable: they are pendent, the last joint very
large, and laciniated so as to form a tuft[771]. The female ones
grow gradually larger towards the end, but are not at all divided
there[772]. The palpi of male spiders are of a very different
structure from those of the other sex, terminating in a very complex
incrassated piece, which has been supposed to contain the organ
of generation; but this, according to Treviranus, is a mistaken
idea--that organ being, as usual, to be found in the abdomen[773]. In
the common gnat the palpi of the male are as long as the proboscis,
consist of five joints, and at the end are tufted with hairs; while
those of the female are scarcely one-fourth of its length, have only
three joints, and are not tufted. Whether the _labial palpi_ in any
genus differ in the sexes, I cannot affirm with certainty: I have
not, however, observed any such variation in them.
I shall next mention some organs of the head, in which the difference
between the sexes is often very striking and peculiar. You will
readily conjecture that I am speaking of the _antennæ_. And here
the advantage seems wholly on the side of the males: since in them
these wonderful instruments of unknown sensations are not only more
complex, but usually more elegant, than those of the other sex. You
will pardon me, therefore, if I enlarge a little more than ordinary
upon a subject so full of interest, and say something upon the
differences observable between the sexes--in the shape, magnitude,
and length, number of articulations, ramification and plumage, and
individual joints of their antennæ.
With regard to their _shape_, variations are sometimes observable
between the antennæ of the sexes; but this principally occurs in the
_Hymenoptera_ order. For instance, those of _Chelostoma maxillosa_,
a small bee that deposits its eggs in little holes in posts and
rails, are clavate in the female and filiform in the male[774]--a
circumstance that distinguishes in some degree those of _Sphecodes_,
_Halictus_, and _Andrena_ of Latreille, three other genera of
wild-bees[775]. In _Dinetus_ Jur. the male antennæ are moniliform at
the base, and filiform at the apex; the female, on the contrary, are
entirely filiform[776].
The antennæ of the sexes also sometimes differ in _magnitude_ and
_length_. This is the case in the three genera of wild bees just
mentioned; those of the female being thicker than those of the male,
while these last are longer than the former. But in this tribe
the males of the Fabrician genus _Eucera_ are most remarkable for
their long antennæ[777]. With regard to the different length of
these organs in the sexes, no insects are more distinguished than
some species of the capricorn-beetles (_Cerambyx_ L.). In _Lamia
Sutor_ the male antennæ are twice the length of the female; and in
another Brazilian species in my cabinet, related to _L. annulata_
(_Stenocorus_ F.), they are thrice their length. Some of the
_Anthribi_ F. approach the _Cerambycidæ_, not only in some other
characters, but also in this circumstance:--thus the antennæ of _A.
albinus_, a native of Britain, are vastly longer in the male than in
the female; and in _A. cinereus_ (_Macrocephalus_ Oliv.)[778], which
I suspect to be of the former sex, they are as long nearly as is
usual in the tribe just named, called in France capricorn-beetles.
I may here observe, that sometimes in the sexes a difference is also
to be found in the _direction_ or flexure of their antennæ. Thus in
_Scolia_ F., _Pepsis_ F. &c., in the males the antennæ are nearly
straight, but in the females convolute or subspiral. The reverse
of this takes place in _Epipone spinipes_, a kind of wasp, and its
affinities; and _Systropha_ Illig., a kind of bee: for in these the
male antenna is convolute at the apex[779], and the female straight.
In the various tribes of bees (_Anthophila_ Latr.), these organs in
the latter are what is denominated _broken_, the main body of the
antenna forming an angle with the first joints: but in the former
this does not take place.
The antennas of the sexes do not always agree in the _number_ of
joints. In the bees, and many other _Hymenoptera_, the male has
one more joint than the female; as is the case also in _Œdemera
notata_ (_Cantharis acuta_ Marsh.). In _Pteronus Laricis_, a kind of
saw-fly, the latter has only sixteen joints in its antennæ, while the
former has twenty-four[780]. In _Rhipicera marginata_, a beetle, the
beautiful antennæ of the male consist of thirty-two joints, while the
female has no more than eleven! In _Chelonus_ Jur. the male, on the
contrary, has the smallest number of joints, namely sixteen; while
the female has twenty-five[781].
In nothing do the sexes differ more materially than in the
_ramification_ of these organs, and their _plumage_. By attending
to this, you may often detect the sexes in an instant; since the
antennæ of the males in numerous instances are much more complex than
those of the females. For what end the Creator has so distinguished
them is not quite clear; but most probably this complex structure
is for the purpose of receiving from the atmosphere information of
the station of the female. A tendency to branching will be found in
the antennæ of some males, in tribes where these organs are usually
perfectly simple in both sexes. Thus, in the male of _Chelostoma
maxillosa_,--mistaken for another species by Linné, which he names
_Apis florisomnis_,--the intermediate joints on their inner side
project into an angle[782]; and those of the same sex of the common
hornet, by means of a central sinus, have two obtuse teeth on each.
With regard to more direct ramifications, some male antennæ terminate
in a fork, or two branches. This is the case with _Hylotoma furcata_
Latr., a saw-fly[783]; and the peacock-louse (_Nirmus Pavonis_
Herm.)[784]. Others, again, have three lateral branches, as in
_Eulophus_ Geoffr. a little parasite, the male antennæ of which send
forth a hairy external and rather long branch, from the base of the
fourth, fifth, and sixth joints[785]. In _Elater flabellicornis_
L., the eight last joints are flabellate, or elongated and flat,
resembling the sticks of a fan in the male[786]; in the female they
are shorter, and more properly may take their denomination from the
teeth of a comb. In _Lampyris Latreillii_ Kirby, the antennæ of the
former are flabellate on both sides, while those of the latter are
little more than serrate[787]. These organs are extremely beautiful
in the males of the _Rhipiceræ_ of Latreille. In _R. marginata_ K.
they consist of thirty-two joints, from thirty of which issues a
branch, the first very short, but the rest gradually increasing in
length as they approach the middle of the antenna; then gradually
decreasing to the end, so as to represent an expanded fan[788]. But
in none are they altogether so remarkable as in those moths that
Linné denominates _Bombyces Attaci_, and some others. In these, in
the males, these organs in their contour are lanceolate, and every
joint is furnished with a couple of parallel equal branches on each
side[789]. In the females these branches are shorter on the whole,
and alternately one long and one short; but in some, as _Saturnia
Pavonia_, there is only one short branch or tooth on each joint in
this sex[790]. In _Bombyx regalis_ &c. only the first part of the
antenna is so branched; and those of the female are setaceous and
without branches. In _B. versicolor_, &c. there is only one branch
from each side on every joint; those of the female being much shorter
than those of the male. The latter sex of _Pteronus Laricis_ Jur., a
saw-fly, afford an example of a different structure, the antennæ on
one side sending forth a branch from every joint but the two first;
but on the other side, the nine or ten last joints also are without
a branch. The female antenna is serrated[791]. In another of this
tribe, _Pterygopterus cinctus_ Klug, the male antenna resembles a
single-toothed comb, being branched only on one side: that of the
female, like the former instance, is serrated[792]. Whether the
remarkable antennæ that distinguish the known individuals of the
genus _Phengodes_ (_Lampyris plumosa_ F.) is a sexual character
has not been ascertained; but it is not improbable that it may be,
as in other _Lampyridæ_. A pair of delicate flexile and almost
convolute plumose branches proceeds from the apex of each joint
except the basal ones, which have something the air of cirri, and
give a more than usual degree of lightness and elegance to these
organs[793]. Other antennæ, especially in the _Diptera_ order,
assume an appearance of _plumes_--not from the branches that proceed
from them, but from the fine long hairs that beset and adorn them.
These are universally indications of the male sex, those of the
females being generally comparatively naked. If you take the common
gnat, you will find that the antennæ of one individual are thickly
fringed on each side, and tufted at the end with fine long hairs,
while in the other only four or five placed at intervals in a
whorl are to be perceived[794]. In _Chironomus_ Meig., a kind of
_Tipula_ L., resembling a gnat, the male antennæ are beset on all
sides with the finest hairs, and resemble a beautiful plume[795],
while the females to the unarmed eye appear naked. Even in some
_Hymenoptera_, the antennæ of the males are thus feathered, in a less
degree: for instance, in _Hylotoma_ Latr.[796] Whether the tufts and
fringes which ornament, in a remarkable manner, the antennæ of many
_Cerambycidæ_[797], are sexual characters, is not certainly known.
We are now to consider other sexual differences in these organs,
resulting from the size or configuration of one or more _individual
joints_. To begin with the first joint, or scapus. In many of
the _Hymenoptera_, particularly the _Anthophila_ Latr., this is
elongated, and the remaining joints form an angle with it in the
females: while in the other sex it is much shorter, and in the
same line with the rest of the antennæ; and in _Hylæus dilatatus_
(_Melitta dilatata_ Kirby) the first joint in the male is dilated and
shaped something like a patella[798]. In _Malachius bipustulatus_,
&c. the sex just mentioned is peculiarly distinguished by a white
excrescence on the first four joints of the organs in question,
most conspicuous in the second and fourth. The antennæ of male
_Cerocomæ_ are not very different[799]. Mr. Marsham has described
a little _Haltica_ under the name of _Chrysomela nodicornis_, from
a peculiarity of the same sex not to be found in the other. The
fourth joint is very large and obtriangular; in the female it is
merely longer than the rest. In _H. Brassicæ_ and _quadripustulata_
the fifth joint is larger and longer than all but the first in the
male, in their females it is only longer. In some moths (_Herminia_
Latr., _Crambus_ F.) there is also a knot in the middle of the male
antennæ[800]. In _Noterus_, a water-beetle, the six intermediate
joints are thicker than the rest, beginning from the fourth, and the
last but one ends internally in a truncated tooth. The fifth and
two following joints in the male antennæ of _Meloe_ are larger than
the rest, which distinguishes them, as well as a remarkable bend
observable at that part[801].
Variations of the kind we are considering are also observable in
the _clava_, or knob, in which antennæ often terminate. You have
doubtless observed that the lamellated clava of the antennæ of
the common cockchafer is much longer and more conspicuous in some
individuals than in others--the long clava belongs to the male[802].
In another species, _M. Fullo_, that of this sex is nine or ten
times the length of that of the other. In _Colymbetes serricornis_,
a water-beetle, the male has a serrated clava of four joints. In
_Dorcatoma dresdensis_[803], and also _Enoplium damicorne_, two
beetles, it is nearly branched in the male, but much less so in
the female. In a little destructive beetle, common in our houses
(_Attagenus Pellio_), in the latter it is very short, but in the
former it is very long, and nearly formed by a single joint. In
_Eurhinus_ Kirby, a New Holland genus of the weevil-tribe, in
the male the last joint, also, is much longer than it is in the
female[804]. These examples will give you some idea of the principal
variations that take place in the antennæ of the sexes, and of the
wonderful diversity of forms in this respect to which mere sexuality
gives rise amongst insects.
In the _eyes_, or _stemmata_, this diversity is less remarkable.
Latreille has described two ants, _Formica contracta_ and _coeca_, in
the neuter of which he could discover no eyes[805]: in the former,
the female, however, had large ones. The male he appears not to
have known, but it probably was not destitute of these organs; of
the latter he was acquainted only with the workers. The neuter of
_Myrmica rubra_, another ant, has no ocelli or stemmata, although the
male and female are provided with them[806]. They are discoverable
only in the former sex of that singular insect related to the ants,
_Mutilla europæa_. Other insects differ in the _size_ of the eyes
of their sexes. In the hive-bee, and some _Ephemeræ_, the eyes of
the drone or male are much larger than those of the worker and
female, and also meet at the vertex, having their stemmata below the
conflux; whereas in these latter they are widely distant[807]. In
_Stratyomis_, _Tabanus_, and many other two-winged flies, the _male_
eyes meet at some point below the stemmata, and above the antennæ.
In the former they touch more at an angle; for the vertex forming
a narrow isosceles triangle, and for the anterior part of the face
one nearly equilateral: while those of the _female_ are separated
by a considerable interval. In _Heptatoma_ and _Hæmatopota_ in that
sex, a similar interval obtains; while in the other, after forming a
minute short triangle, they unite for a considerable space, and then
diverging, form the face. This is also the case in _Tabanus_; but in
the female, the space that intervenes between the posterior part of
the eyes is much narrower than in these two cognate genera of the
horse-flies. In some others of this order, as _Musca_ Latr., the eyes
of the male do not touch, but approach posteriorly much nearer to
each other than those of the other sex. In a few instances the sexes
vary even in the number of their eyes, as well as the size. This
occurs in some species of _Ephemera_ L. (_E. diptera_, &c.), in which
the male, besides the common lateral ones, has two large and striking
intermediate eyes, that sit upon vertical pillars or footstalks[808].
2. The _Trunk_. The thorax of many coleopterous males, especially
of the _Dynastidæ_ and _Copridæ_ amongst the petalocerous tribes,
exhibits very striking differences from that of the female. In
many _Lucani_ the lateral angle is more prominent. In _Anthia_
it is bilobed posteriorly, while in the last-mentioned sex it is
entire[809]. In _Phanæus carnifex_ MacLeay (_Copris_ F.) it is
elevated into a plane triangular space, with the vertex of the
triangle pointing to the head; but in the female it is convex, with
an anterior abbreviated transverse ridge[810].
In a large proportion terrific _horns_, often hollow, like those
of the head lately noticed, arm the thorax of the male, of which
you will usually only discover the rudiments in the other sex. In
the first place, some are _unicorns_, or armed only with a _single_
thoracic horn, which frequently, in conjunction with the thorax
itself, not a little resembles a tunnel reversed: of this description
are _Dynastes Hercules_, _Tityus_, _Gedeon_, _Enema_, &c.[811] In
the three first this horn is porrected, or nearly in the same line
with the body; but in the last, and _D. Pan_, it forms an angle with
it; and in _D. Ægeon_ it is nearly vertical[812]. In _D. Hercules_
it is very long; in _D. Alcides_[813] and _Tityus_ very short; in
the two last, and in _Oxytelus tricornis_ which is similarly armed,
it is undivided at the apex; but in _D. Gedeon_, _Pan_, _bilobus_,
&c.[814] it is bifid or bilobed. It is usually rather slender, but
in _D. Chorinæus_[815] and _bilobus_, it is very stout and wide.
In _D. claviger_ it is hastate at the apex[816]. In _D. hastatus_
it is short and truncated[817]. Others, again, have _two_ thoracic
horns. In _Copris nemestrinus_ these are discoidal, diverging, and
inclining forwards[818]. In _Phanæus floriger_[819] they are lateral,
triangular, and incline towards each other, with, as it were, a
deep basin between them. In _P. splendidulus_ they sink into two
longitudinal ridges, most elevated posteriorly, with an intervening
valley[820]. In _P. bellicosus_ they are posterior, compressed,
truncated, and emarginate at the apex, and include a basin[821]. In
_Copris Sabæus_ they are merely two acute prominences[822].--_Three_
horns distinguish the thorax of many. In _D. Aloeus_[823] and its
affinities, they are arranged in a triangle, whose vertex is towards
the head. In _D. Antæus_[824] these horns are nearly equal in
length, and undivided at the apex. In _D. Titanus_[825] the anterior
horn is longer than the rest, and bifid at the apex; in _D. Atlas_
and _Endymion_[826], both of which have a horn on the head, it is
much shorter. In others, as in _Megasoma_ Kirby, the vertex of the
triangle is towards the anus. In _M. Typhon_[827] it is longer than
the anterior ones, and bifid at the apex; in _M. lanigerum_ they
are equal in length[828]. In _M. Elephas_ and _Actæon_[829] it is
merely an elevation of the thorax; in the last almost obsolete. In
_Geotrupes Typhæus_, common on our heaths, the anterior of this part
is armed by three horizontal horns, the intermediate one being the
shortest[830]. _Copris lunaris_ also, another of our own beetles,
has three short posterior thoracic horns, two lateral and triangular
ones, and a transverse intermediate elevation, with a notch in the
middle[831]. In _Dynastes Neptunus_ the horns are porrected, the
middle one being very long, and the lateral ones short[832]. In _D.
Geryon_ the point of the lateral horns is towards the anus, and
the base of the intermediate one covers the scutellum[833]. Others
have _four_ of these singular arms: this is the case with one of
our rarest beetles, _Bolbocerus mobilicornis_ K., which has four
dentiform horns, the intermediate pair being the shortest, arranged
in a transverse line on the anterior part of the thorax[834]. In
_B. quadridens_ these are merely teeth. In _Phanæus Faunus_[835] it
has two lateral, elongated, compressed, truncate, horizontal horns,
and two intermediate teeth. _Dynastes Milon_ has a still greater
number of horns on the thorax of the male, there being two lateral
anterior ones and three posterior ones--the intermediate being the
longest[836]; and _Copris Antenor_ Fabricius and Olivier describe as
having a many-toothed thorax; and from the figure of the latter[837],
the male appears to have seven prominences.
But the males of insects are not only occasionally distinguished by
these dorsal arms--in a few instances they are also furnished with
_pectoral_ ones. The illustrious traveller Humboldt found in South
America a species of weevil (_Cryptorhynchus Spiculator_ Humb.), the
breast of which was armed with a pair of long projecting horns; and
I possess both sexes of four species, three at least from Brazil,
that exhibit in one individual the same character. One, concerning
the country of which I am uncertain, recedes somewhat from the type
of form of the rest, and comes very near that of _Rynchænus Strix_
F.[838] In the individual which I take to be _C. Spiculator_, the
pectoral horns are very long, curving upwards at the apex, and
nearly in a horizontal position; while in the three others they are
much shorter, and inclined towards the horizon. The males of some
species of _Rynchites_, as _R. Bacchus_ and _Populi_[839], are also
armed with a pair of lateral horns or spines, which may be termed
pectoral rather than dorsal.
I shall now advert to the sexual characters that are to be found in
the _instruments of motion_ attached to the trunk--beginning with
those for _flight_. In the female of the common glow-worm (_Lampyris
noctiluca_) not the slightest vestige of elytra or wings is visible,
and it resembles a larva rather than a perfect insect; yet its
mate is a true beetle furnished with both. The same circumstance
distinguishes the female cockroach (_Blatta_) and is more universally
prevalent in that genus than in _Lampyris_, in which a large number
of females have both elytra and wings. The males of _Bombyx antiqua_
and _Gonostigma_, and of many other moths, have wings of the usual
ample dimensions, while those of their females are merely rudiments.
This is the case, also, with some of the _Ichneumonidæ_[840]. In the
tribes of Ants, _Termites_, &c. the neuters or workers are without
wings. Amongst the plant-lice (_Aphides_) there are individuals
of both sexes, some of which have wings, and others not[841].
Amongst the _Coleoptera_, the female of _Tenebrio Molitor_, the
common meal-worm, has elytra and no wings; while the male has
both[842].--Sometimes these organs vary in size in the sexes: thus
in _Aradus Betulæ_ F., a kind of bug, the hemelytra and wings are
narrower and shorter in the female than in the male[843]. In the
genus _Blaps_ F., the mucro that arms the apex of each elytrum is
longer in the former sex than in the latter. In _Ateuchus gibbosus_
F., a dung-beetle, the elytra have a basal gibbosity near the suture
in one sex that does not obtain in the other. In the _Orthoptera_
order, the sexes are often to be known, almost at first sight, by
a difference in the veining and areolets of the wings; but upon
this I enlarged so fully when I treated of the sounds produced by
insects, that it is not necessary to repeat what I have said; which
observation also applies to the drums which distinguish the male
_Cicadæ_[844]. The wings of some butterflies, and of most moths and
hawkmoths (_Sphinx_ L.), are furnished with a singular apparatus for
keeping them steady, and the under-wing from passing over the upper
in flight. This appears to have been first noticed by _Moses Harris_,
and was afterwards more fully explained by _M. Esprit Giorna_[845].
From the base of the under-wing proceeds a strong bristle, received
by an annulus or socket, which springing between the two principal
nervures of the upper-wing terminates in the disk of the wing:
in this annulus the bristle moves to and fro, and prevents the
displacement of the under-wing. This apparatus is perfect only in
the males, which alone have occasion for long flights; the females,
though they have often several bristles, having no annulus[846].
The other instruments of motion, the _legs_, also differ in the
sexes. In some instances they are disproportionably long. This is
particularly the case with the _anterior_ pair of some beetles, as
_Macropus longimanus_, _Scarabæus longimanus_ L., in which they are
so long as to make the males of these individuals rather inconvenient
in a cabinet. Amongst British beetles _Clytra longimana_ and
_Curculio longimanus_ Marsh. are also remarkable in this respect. In
some other males the _middle_ pair are the longest; as in _Anthophora
retusa_ Latr., a kind of wild-bee[847]. There are two known instances
of remarkably long _posterior_ legs in the Capricorn tribe, which
I suspect belong to the present head. One is _Saperda hirtipes_
Oliv.[848], in which the hind-legs are longer than the whole body,
and adorned with a singular tuft of hairs; and the other a _Clytus_,
I think, which Mr. MacLeay purchased from the late Mr. Marsham's
collection, in which the hind-legs are not only very long, but have
tarsi convolute, like some antennæ. From analogy I should affirm that
these were the characters of _male_ insects.
To come to the _parts_ of legs. Sometimes the _coxæ_ of the last
mentioned sex are distinguished from those of the female by
being armed by a _mucro_ or spine. Thus the male of _Megachile
Willughbiella_, and others of that tribe, have such a spine on the
inner sides of the anterior coxa[849]. The _Trochanter_ also of some
differs sexually; and you will find that the posterior one of the
male in _Anthidium manicatum_ is of a different shape from what it is
in the female[850]. In _Sphodrus leucopththalmus_, one of the beetles
called _black dors_, in one sex the same trochanter terminates in a
long mucro or spine[851], and in the other it is rounded at the apex.
Peculiar characters in their _thighs_ also often indicate different
sexes. In _Prionus damicornis_ there is a short spine at the apex of
the _anterior_ ones in the female that is not in the male; while in
_Macropus longimanus_, at their base externally the male is armed
with a mucro, which I cannot find in the female[852]. In _Scarabæus
longimanus_ L. this thigh is furnished with two teeth[853].--The
_intermediate_ thighs also sometimes differ. In an _Onitis_ from
China, a variety perhaps of _O. Sphinx,_ those in the male are
dolabriform, and in the other sex of the ordinary shape. In _Odynerus
spinipes_ they have on their lower side two sinuses, so as to give
them the appearance of being toothed. The _posterior_ thighs are
sometimes incrassated in the male, and not in the female. This you
will see in a weevil, not uncommon, _Apoderus Betulæ,_ and also
in many species of _Cimbex_ F., a kind of saw-fly; and the same
circumstance distinguishes the latter sex in many species of _Lygæus_
F., a kind of bug: I discovered this from _L. cruciger_, of which I
have both the sexes; and from Stoll's figure of _L. Pharaonis_[854].
In some of these the female thighs are enormously large. A remarkable
variation in this respect is observable in the coleopterous genus
_Œdemera_ (_Necydalis_ L.). In _Œ. Podagrariæ_ these limbs are
incrassated in one sex and not in the other[855]; in _Œ. cærulea_
they are so in both sexes; and in _Œ. ceramboides_ in neither. In
_Pelecinus Polycerator_ F., one of the Ichneumon tribe, or an insect
very near it from Brazil, these thighs in the female are armed with
two spines underneath, which are not in the male.
The _anterior tibiæ_ in _Scarabæus longimanus_ L. differ remarkably
in the sexes. In the female they are of the ordinary shape, and
serrated externally; but in the male they are very long, incurved,
and without teeth or serratures[856]. In the males of the genus
_Onitis_ F. they are bent like a bow, and acute at the end; but
in the females they are formed on the common type[857]. In _Hispa
spinipes_ F. they are armed internally with a crooked spine[858].
But the most extraordinary sexual variation of this joint of the
leg may be seen in the male of _Crabro cribarius_ F. and several
other species of the same family, in which these tibiæ are dilated
externally into a concavo-convex plate, or rather have one fixed
to them and part of the thigh, of an irregular and somewhat
angular shape[859], with numerous transparent dots, so as not
badly to resemble a sieve: whence the trivial name of the species.
Rolander, who first described it, fancied that this plate was really
perforated, and that by means of it the animal actually sifted the
pollen; but it is most probably for sexual purposes. In another
species, the plate is ornamented with transparent converging streaks.
In the bee-tribes (_Anthophila_ Latr.) the _posterior_ tibia of
the working sex is generally bigger than the corresponding part in
their more idle partners: this is particularly conspicuous in the
genus _Euglossa_, in the females of which this part is triangular,
very broad towards the apex, and fitted for carrying a large mass
of pollen paste. The tibiæ of the _males_ of some _Lepidoptera_ are
remarkable in this respect. That of _Hepialus Humuli_ is much more
hairy; but in _H. Hectus_ it is a dilated mis-shapen mass, without a
tarsus, and with long scales pendent from the disk[860]. Differences
of this kind also occur in the _calcaria_ or spurs that arm the apex
of the tibiæ of a large number of insects. Thus in _Acanthopus_ Klug,
a singular bee, in the male the spur of the intermediate leg is
dilated at the apex, and armed with six strong spines, the inner one
larger than the rest[861].
But the part of the leg in which the sexes most vary is the _tarsus_;
and this variation takes place both in the number of the joints,
and their form and circumstances. The first case has been observed
only with regard to certain species of _Cryptophagus_ Herbst, as _C.
fumatus_, &c. in which the female is _pentamerous_, or having _five_
joints in all the tarsi; and the male _heteromerous_, or having
_five_ joints in the two _anterior_ pairs, and only _four_ in the
_posterior_[862]. With respect to the form of the tarsal joints, the
sexes more frequently differ; and by inspecting this part, especially
in the predaceous and carnivorous _Coleoptera_, you may often,
without further examination, ascertain whether any individual is male
or female. Even in the slender-footed _Cicindelidæ_, the three first
joints of the anterior tarsus of the male are more dilated than the
two last, and covered underneath with a brush of stiffish hair; in
the female all are equally slender, and not so hairy. In _Carabus_,
_Feronia_, &c. Latr. the _four_ first joints of these tarsi in the
males are dilated, and furnished with a brush or cushion: in the
_Silphidæ_, also, the same circumstance takes place. In _Harpalus_
Latr., and _Silpha americana_, the _four_ anterior ones are similarly
formed in this respect. But one of the most remarkable sexual
characters, in this tribe of insects, that distinguish the males,
are those orbicular patellæ, furnished below with suckers of various
sizes, and formed by the three first joints of the tarsus, which are
to be met with in the _Dytiscidæ_, &c.; but as I shall have occasion
to treat of these more fully in another Letter, I shall only allude
to them now. The second pair of tarsi have in these also the three
first joints dilated and cushioned[863]. In _Hydrophilus piceus_,
another water-beetle, the fifth joint of the tarsus is dilated
externally, so as to form nearly an equilateral triangle[864].
Christian, a German writer on the _Hymenoptera_, has described
some very singular appendages which he observed on the first joint
of the four posterior tarsi of _Xylocopa latipes_ F. These were
battledore-shaped membranaceous laminæ, with a reticulated surface,
of a pale colour; which were fixed in pairs by the intervention of
a footstalk to the above joint, on which they sometimes amounted
to more than a hundred: the use of which, he conjectures, is the
collection of pollen[865]. I possess two specimens of this bee;
one has none of these appendages, and on the other I can discover
them only in one of the tarsi--from which circumstance I am led to
conjecture that, like the supposed _Clavariæ_ that were imagined to
grow on some humble-bees, but which are now ascertained to be the
anthers of flowers--these also belong to the kingdom of Flora, and
are spoils which the bee in question has filched from the blossom
of some plant. The individuals that have been thus circumstanced
are males; whether the female is guilty of similar spoliations is
not known. In my specimen there are no traces of them. In many
bees, the first joint of the posterior tarsi is much larger in the
females and workers than in the males; but in the hive-bee this
joint is largest in the latter[866]. In _Beris clavipes_ and _Empis
nigra_, two flies, the joint in question is large and thick in the
male, but slender in the female. The penultimate tarsal joint in the
posterior legs is dilated internally, and terminates in a mucro in
one sex of _Anoplognathus Dytiscoides_ of Mr. W. MacLeay[867]. In
some insects the anterior tarsus of the males has been supposed to
be altogether wanting: I allude to the petalocerous genus _Onitis_
F.; but I have a specimen of _Onitis Apelles_ of this sex, or a
species nearly related to it, in which one of these tarsi is to be
found[868]; which, though very slender, consists of five joints,
and is armed with a double claw: from which circumstance it may, I
think, be concluded, that although, as in _Phanæus_, these tarsi are
very minute, they are not wanting. What renders this more probable
is, a circumstance which every collector of insects, who has many
specimens of Mr. W. MacLeay's _Scarabæidæ_ in his cabinet, must have
noticed: namely, that in all, except _Copris_ and _Onthophagus_, the
anterior tarsi are usually broken off. Out of seventeen individuals
of _Scarabæus_ MacLeay in my own, not a single one has a relic of
an anterior tarsus; and scarcely one in a much greater number of
_Phanæi_. The tarsus in question in the nobler sex in _Crabro_, at
least in _C. cribrarius_ and its affinities, is also very short,
especially the three intermediate joints; but at the same time very
broad and flat. In the species just named, the external claw forms
a kind of hook; and in the rest it is considerably longer than the
other[869]. The _claws_, indeed, occasionally vary in the sexes in
other _Hymenoptera_: thus in _Melecta_ Latr., a kind of bee, in the
female they are intire, but in the male they are furnished with an
internal submembranaceous tooth or process[870]. In _Cœlioxys conica_
and others, those of the latter sex are bifid at the apex, but those
of the former acute[871]. In _Megachile_, the male claw is as in the
instance just mentioned, while the female has a lateral tooth[872];
and a similar character distinguishes the sexes in the hive-bee[873].
3. The _abdomen_. This part affords many external sexual characters,
whether we consider its general shape; the number of segments that
compose it; its base, middle, or extremity.
In general _shape_ it often differs in the sexes. Thus, the abdomen
of female _Tipulæ_ is lanceolate; that of the male cylindrical, and
thickest at the extremity[874]. In _Molorchus_ F. it is convex above
in the former, and flat in the latter,--the female of this beetle not
unaptly representing some female _Ichneumons_ in this respect, and
the male their males[875]. In _Andrena_ it is oblong in the one, and
lanceolate in the other. In the hive-bee the drones have a thick,
obtuse, and rather long abdomen; in the females it is long, and
nearly represents an inverted cone; and in the workers a three-sided
figure, or prism.
The _number of segments_, also, is generally different in the two
sexes--the male having one more than the female; but in _Dytiscus
marginalis_, &c. the reverse of this takes place: the female, if you
reckon the bipartite half-concealed anal segment as one, having seven
ventral segments, and the male only six. She has also eight dorsal, and
the male seven.--In the ant tribes (_Formica_ L.), the little vertical
scale, at the _base_ of the abdomen in one description of them, or the
double knot in another, is less in the male than in the female. In a
very singular male insect belonging to the _Vespidæ_, and related to
_Synagris_, (which I purchased from the late Mr. Drury's cabinet,)
the second ventral segment sends forth from its disk two remarkable
parallel very acute and rather long spines. The same sex of _Chelostoma
maxillosa_ has likewise on the same segment a concave elevation,
opposite to which on the fifth is a cavity which receives it, when the
animal rolls itself up to take its repose[876]. In another species, _C.
Campanularum_, the segment in question has only a tubercle[877].
On the second segment of the abdomen of some specimens, probably
males, of the remarkable African genus _Pneumora_ before alluded
to[878], there are thirteen little elevated ridges, placed rather
obliquely in an oblique series; and gradually, though slightly,
diminishing in size towards the belly: on their upper side they
are flat, forming nearly a horizontal ledge, but on the lower they
slope to the abdomen. The posterior thigh in its natural position
covers the three first of them, and, if moved downwards, would strike
them all[879]. I conjecture, therefore, that these are the animal's
instruments of sound, imitating the harp or violin rather than the
drum; and that the thigh acts the part of the hand or bow. The
abdomen of these insects being blown out like a bladder, and almost
empty[880], must emit a considerable sound when the thigh of the
animal passes briskly over these ridges; and their different length
would produce a modulation in the sound. When struck with a pin, they
emit a grating noise.
In _Staphylinus splendens_, the _penultimate_ ventral segment is very
deeply cleft, and the antepenultimate emarginate in one sex, and intire
in the other. In _S. laminatus_, an allied species, the penultimate
segment is cleft, less deeply, however; but the antepenultimate is
very short and intire; while the fourth is extremely long, and rounded
at the margin, appearing as if it was only an elevated part of the
last-mentioned segment; for which it was mistaken by Gravenhorst[881],
while it is of the usual form in the other sex.
The _extremity_ of the abdomen or its _anal_ segments and organs
furnish a variety of sexual characters. Sometimes the last dorsal
segment is emarginate in the male, and not in the female; as
in _Megachile ligniseca_, one of the leaf-cutter bees, _Cimex
hæmorrhoidalis_, &c.[882] At other times little lateral teeth
are added to this notch, as in another of the same tribe, _M.
Willughbiella_[883]. Again, in other males, both the ventral and dorsal
anal segment are armed each with a pair of teeth or mucros, as in
_Chelostoma maxillosa_[884]. In _Anthidium manicatum_, another bee,
the anus terminates in five spines[885]. In _Cœlioxys conica_ of the
same tribe, in which this part in the female is very acute, that of
the male is armed with six points[886]. In that singular Neuropterous
genus _Panorpa_, while the abdomen of the female is of the ordinary
form, with a pair of biarticulate palpiform organs attached to the
last retractile joint, or ovipositor, that of the male terminates in
a jointed tail, not unlike a scorpion's, at the end of which is an
incrassated joint armed with a forceps[887]. In the common earwig
(_Forficula auricularia_) the two sexes differ considerably in their
anal forceps: in one it is armed with internal teeth at the base, and
suddenly dilated, above which dilatation it is bent like a bow: in the
other it is smaller, without teeth, grows gradually narrower, is very
minutely crenulate from the base to the end, and is straight, except at
the very summit, where it curves inwards. Misled by these and similar
differences, Mr. Marsham has considered them (the sexes both of _F.
auricularia_ and _F. minor_) as distinct species.
The tail of some species of the genus _Ephemera_ is furnished with
three long, jointed, hairy bristles. We learn from Reaumur with
respect to one, that though in the female these are all equal in
length, yet in the male there is only a rudiment of the third. On
the belly near the anus these males have four fleshy appendages, the
posterior ones setaceous and long, and the anterior pair filiform and
shorter. They are supposed to represent the anal forceps of other
insects[888]. In _Ephemera vulgata_, described by De Geer, both sexes
have three bristles, but those of the male are the longest; and he
describes the forceps as consisting of only a pair of jointed pieces,
forming a bow not unlike the forceps of an earwig[889].
v. All the differences I have hitherto noticed between the sexes
of insects occur in their _bodily_ structure; but there are others
of a somewhat higher description observable in their _character_.
You may smile at the idea of character in beings so minute; but if
you recollect what I formerly related to you when treating upon the
societies of insects, you will allow that something of this kind does
take place amongst them. In general the males are more fitted for
locomotion and more locomotive; and the females, on the contrary, are
necessarily more stationary. And this for an obvious reason:--the law
is, that the male shall seek the female, and therefore he is peculiarly
gifted for this purpose, both in his organs of sensation and motion:
while his partner in many cases has very simple antennæ, he has very
complex ones; and while she has either no wings or only rudiments
of them, he is amply provided with them. Again: amongst the insects
that suck the blood of man or beast, such as the gnat (_Culex_) or
horse-flies (_Tabanidæ_), it is the female alone that is bloodthirsty,
the males contenting themselves with the nectar of flowers[890]. But
the difference of character in the sexes is most conspicuous, at least
it has been more noticed, in those that live in societies, and is quite
the reverse of what takes place in the human species. While the females
and workers (which are now generally considered as sterile females, in
which the ovaries are not developed) are laborious and active, diligent
and skilful, wise and prudent, courageous and warlike;--the males, on
the contrary, take no part in promoting the common weal, except merely
a sexual one. Though till a certain period they are supported at the
expense of the community, they take no part in its labours, either in
collecting and forming the public stores, or in feeding and attending
the young. They are idle, cowardly, and inactive; have neither art
nor skill of any kind, and are unprovided with the usual offensive
weapons of their species. These observations in their full force
apply particularly to the hive-bee, and partially to the other social
insects; amongst which, if you consult my former communications, there
are some exceptions to this slothful character in the males[891].
II. _Age._ There is less diversity in the duration of the lives of
insects in their perfect than in their larva or pupa state. Some,
like several species of _Ephemeræ_, live only a few hours; some never
even see the sun[892]: others, as flies, moths, and butterflies,
and indeed the majority of insects, a few days or weeks; and a
comparatively small number, such as some of the larger _Coleoptera_,
_Orthoptera_, &c., six, nine, twelve, or fifteen months--a period
beyond which the life of perfect insects rarely extends. Some,
however, certainly enjoy a longer existence in the perfect state.
Mr. Baker kept one of the darkling beetles (_Blaps Mortisaga_) alive
under a glass upwards of three years. The rose-beetle (_Cetonia
aurata_), Rösel informs us he fed with fruit and moist white bread
for as long a period[893]. Esper kept our most common water-beetle
(_Dytiscus marginalis_) in water in a large glass vessel, feeding
it with meat, for three years and a half[894]. With regard to the
_Arachnida_, from the very slow growth of _Scorpio europæus_,
Rösel suspects that it must live two or three years; and Audebert
is stated to have kept a spider for several[895]. In this respect
insects follow a law very different from that which obtains amongst
vertebrate animals. In these the duration of their life is in
proportion to the term of their growth: those which attain to
maturity the latest, in almost every case living the longest. In
insects, on the contrary, we often meet with the very reverse of this
rule. Thus the larva of the great goat-moth (_Cossus ligniperda_)
is three years, that of the cabbage-butterfly (_Pieris Brassicæ_)
not three months, in attaining maturity; yet the perfect insects
live equally long. _Melolontha vulgaris_, which in its first state
lives four years, as a beetle lives only eight or ten days[896]. And
some _Ephemeræ_, whose larvæ have been two years in acquiring their
full size, live only an hour; while the flesh-fly, whose larva has
attained to maturity in three or four days, will exist several weeks.
There is yet another anomaly in the duration of the life of perfect
insects. This is not, as in larger animals, a fixed period liable
to be shortened only by accident or disease, and incapable of being
prolonged; but an indeterminate one, whose duration is dependent on
the earlier or later fulfilment of a particular animal function--that
of propagation. The general law is, that a few days, or at most weeks,
after the union of the sexes, both perish, the female having first
deposited her eggs. If, therefore, this union takes place immediately
after the disclosure of the insect from the pupa, their existence
in the perfect state will not exceed a few _days_ or _weeks_, or in
some cases _hours_, as in that of the _Ephemera_, and likewise of
the _Phalænæ Attaci_ L. &c., which fall down dead immediately after
oviposition[897]. But if by any means it be put off or prevented, their
life may be protracted to three or four times that period. Gleditsch
asserts, that by keeping apart the sexes of a grasshopper, their lives
were prolonged to eight or nine weeks, instead of two or three, their
ordinary length; and under similar circumstances _Ephemeræ_, which
usually perish in a day, have been kept alive seven or eight. It is
in consequence of this very curious fact, which has not received from
physiologists the attention that it merits, that many butterflies and
other insects, which, when excluded from the pupa in summer, perish in
less than a month, live through the winter, if excluded late in the
autumn, and the union of the sexes does not ensue. It is probable that
the great age to which Baker's _Blaps_, Rösel's _Cetonia_, and Esper's
_Dytiscus_ attained, was owing to their being virgins when taken, and
subsequently kept from any sexual intercourse. A parallel case happens
in the vegetable kingdom:--if annual plants are kept from seeding, they
will become biennial; as, likewise, if they are sown too late in the
year to produce seeds.
In the case, however, of the earlier or later exclusion of the imago,
another agent has probably some influence. Buffon found that, other
circumstances being alike, the silkworm-moths placed in a _northern_,
lived longer than those exposed to a _southern_ aspect: whence it
appears that the stimulus of heat shortens the lives of insects, and
consequently that cold tends to lengthen them.
It must be observed too, that as the death of the female insect does
not take place until all the eggs are excluded, the term of her life,
though usually short in the majority of species, which lay their
whole number at once, is proportionably long in those which, like
the queen-bee, have a longer period assigned them for this important
office. Huber affirms, that he had certain proofs that she was
engaged for two years in laying eggs, all impregnated by a single
sexual union[898]; and in the females of most insects that live in
society, several months are required to mature the last eggs that are
in the ovary. There is one tribe of insects, however, the females
of which are affirmed to survive this operation: I mean _Dorthesia_
Bosc; after which they even moult, though not so often as before[899].
I formerly related to you the singular fact, that the drones in a
beehive at a certain period are without mercy slaughtered by the
workers[900]. A fact the reverse of this is recorded by Morier with
respect to the locusts: he affirms that the female, when she has done
laying her eggs, is surrounded and killed by the males. He says that
he never himself witnessed this extraordinary circumstance; but that
he heard it from such authority that he gave full credit to it[901].
It is a fact, however, that seems to require further evidence to
entitle it to such credit. These are instances in which, by a law of
nature, the life of these insects is shortened by violence. It does
not appear to have been ascertained how long those drones live that,
under particular circumstances, as stated in a former letter[902],
are exempted from the usual slaughter.
I am, &c.
FOOTNOTES:
[683] See above, VOL. II. p. 346.
[684] Reaum. i. _Mem. ult._ De Geer i. 73. Swamm. _Bibl. Nat._ i. 184.
[685] Swamm. _Ibid._
[686] Jurine _Hymenopt._ 16.
[687] iv. 342. Herold also attributes the rapid expansion of the wing
to the flow of an aqueous fluid, which he calls _blood_, into the
nervures, the orifices of which open into the breast. _Entwickelungs.
der Schmetterl._ 101. sect. 106.--M. Chabrier, in his admirable
_Essai sur le Vol des Insectes_ (_Mém. du Mus._ 4ieme, ann. 325),
having observed a fluid in the interior of the nervures of the
wings of insects, thinks it probable that they can introduce it
into them and withdraw it at their pleasure: the object of which,
he conjectures, is either to strengthen them and facilitate their
unfolding, or to vary the centre of gravity in flight, and increase
the intensity of the centrifugal force.
[688] _Ibid._ 340.
[689] Brahm. _Insek._ ii. 423.
[690] Reaum. vi. 505--. _t._ xlvi. _f._ 9. Comp. De Geer ii. 627--.
[691] Reaum. iii. 378.
[692] Ibid. 385.
[693] Insects of the beetle tribe, especially such as undergo their
metamorphosis under ground, in the trunks of trees, &c., are often
a considerable time after quitting the puparium before their organs
acquire the requisite hardness to enable them to make their way to
the surface. Thus, the newly-disclosed imago of _Cetonia aurata_
remains a fortnight under the earth, and that of _Lucanus Cervus_,
according to Rösel, not less than three weeks.
[694] See above, VOL. I. p. 34--.
[695] Jurine _Hymenopt._ 9. Note 1.
[696] Oliv. N. i. _t._ i. _f._ 1. _c. f._ N. 3. _t._ iii. _f._ 22. _a
b c._ _t._ v. _f._ 33. _t._ vi. _f._ 5. _t._ xiii. _f._ 124. _a b._
[697] Reaum. vi. 423.
[698] Kirby Mon. _Ap. Angl._ ii. _t._ xvi. _f._ 12, 13. _t._ xvii.
_f._ 10-12.
[699] Reaum. iv. 393.
[700] See above, VOL. I. 473--.
[701] De Geer vii. 304.
[702] Reaum. iv. 30.
[703] Ibid. _t._ iv. _f._ 15.
[704] See above, VOL. II. 36.
[705] De Geer iii. 25.
[706] _Linn. Trans._ iv. 54--.
[707] ix. 65. _n._ 110.
[708] vi. 423.
[709] _Entomologische_, &c. 224.
[710] De Geer ii. 847. 850. Jurine _Hymenopt._ 100.
[711] Kirby _Mon. Ap. Angl._ ii. 296. 264.
[712] _Ibid._ ii. 142--. 144, 147, 148, &c.
[713] A remarkable anomalous exception to this rule sometimes occurs
in the female of _D. marginalis_, which has smooth elytra like the
male (Gyll. _Ins. Suec._ i. 467-). I have this variety from the Rev.
Mr. Dalton, of Copgrove, Yorkshire.
[714] De Geer i. _t._ vii. _f._ 11.
[715] See above, VOL. II. 125, Note^b.
[716] _Melitta_ ** c. Kirby _Mon. Ap. Angl._ i. 140.
[717] _Ibid._ _t._ iv. _f._ 10. _a. b. f._ 14.
[718] _Ibid._ _t._ xiii. _f._ 20. _a._
[719] Kirby _Mon. Ap. Angl._ i. _t._ xi. Apis **. d. 2. α. β. _f._ 18
_a. b. c. d._
[720] Coquebert _Illustr. Icon._ i. _t._ vi. _f._ 6.
[721] Kirby _Mon. Ap. Angl._ i. _Apis_ **. _c._ 1. α. **. c. 1. β.
**. c. 2. α. **. c. 2. β. **. c. 2. γ. **. c. 2. δ.
[722] _Ibid._ _t._ viii. _f._ 28. _f. g._
[723] Christ. _Hymenopt._ _t._ iv. _f._ 3. _b._
[724] Kirby _Mon. Ap. Angl._ i. _t._ iv. _Melitta_ **. c. _f._ 1. _a._
[725] Scheven _Naturfors._ stk. xx. 65. _t._ ii. _f._ 4. Compare
_Ibid._ x. 101.
[726] Reaum. iii. _t._ xv. _f._ 18, 19.
[727] Oliv. no. 84. _Brentus_, _t._ i. _f._ 1. _b. c. t._ ii. _f._
17. _a. b._
[728] Oliv. no. 3. _Scarabæus_, _t._ xviii. _f._ 169.
[729] Oliv. _Scarabæus_, _t._ xii. _f._ 114. _t._ xv. _f._ 138. _a._
[730] _Ibid._ _t._ v. _f._ 33.
[731] _Ibid._ _t._ xii. _f._ 112.
[732] _Linn. Trans._ vi. _t._ xix. _f._ 12. _t._ xx. _f._ 2.
[733] Oliv. no. 57. _Tenebrio_, _t._ i. _f._ 2.
[734] Oliv. _ubi supr._ No. 3. _t._ i. _f._ 1.
[735] Oliv. no. 3. _t._ iii. _f._ 20. _a._
[736] Ibid. no. 55. _Diaperis_, _t._ i. _f._ 3.
[737] Oliv. _Scarabæus_, _t._ xx. _f._ 185.
[738] As _Dynastes Actæon_, _Elephas_, _Typhon_, &c. differ from _D.
Hercules_, &c., not only in their general habits, horns, &c., but
also in their maxillæ and labium,--the former in _D. Actæon_ being
simple, and in _D. Hercules_ toothed, and the labium of the first
bilobed at the apex, and in the last entire and acute,--according to
the modern system they ought, therefore, to be considered as distinct
genera. I would restrict the name _Dynastes_ to _D. Hercules_ and its
affinities: _D. Actæon_, &c. I would call _Megasoma_.
[739] Oliv. _Scarabæus_, _t._ xvii. _f._ 156.
[740] _Ibid._ _t._ viii. _f._ 63.
[741] This insect is beautifully figured in M. Latreille's _Insectes
sacres des Egyptiens_, _f._ 11. See Luke xi. 15. Heb. בעלןבול
_Dominus stercoris_.
[742] Oliv. no. 83. 160. _t._ vi. _f._ 60. ♂. _t._ v. _f._ 45. ♀?
[743] _Ibid._ no. 36. _t._ ii. _f._ 12.
[744] _Ibid._ no. 6. _t._ vii. _f._ 61.
[745] See above, VOL. II. 224--.
[746] Coquebert _Illustr. Icon._ iii. _t._ xxi. _f._ 2.
[747] Stoll _Cigales_, _t._ xviii. _f._ A B C. _Grillons_ _t._ iv.
_f._ 16-18. This singular animal, which was found by Mr. Patterson
at the Cape of Good Hope, is stated to be an _aquatic_; and affords
the only known instance of an _Orthopterous_ insect inhabiting the
waters. The _Gryllotalpa_ loves the vicinity of water.
[748] _Mon. Ap. Angl._ i. _Melitta_ **. b. 139. _t._ ii. _f._ 4-6.
[749] _Ibid._ **. a. _f._ 4, 5.
[750] _Ibid. Apis_ *. b. 190--. _t._ v. _f._ 18 _b._
[751] By Rösel, by a friend of De Geer's, and by M. Marechal. De Geer
iv. 331--. _Nouv. Dict. d'Hist. Nat._ xviii. 225.
[752] Oliv. no. i. _Lucanus_, _t._ ii. _f._ 3.
[753] _Ibid._ _t._ iii. _f._ 7.
[754] _Linn. Trans._ xii. 410. _t._ xxi. _f._ 12.
[755] _Ibid._ vi. 185. _t._ xx. _f._ 1.
[756] Oliv. _ubi supr._ _t._ ii. _f._ 4.
[757] _Regne Animal_, iii. _t._ xiii. _f._ 3.
[758] See VOL. I. PLATE I. FIG. 3.
[759] Christ. _Hymenopt._ _t._ xviii. _f._ 2.
[760] _Mon. Ap. Angl._ i. _Melitta_ *. a. _t._ i. _f._ 5. ♀. 7. ♂.
[761] _Ibid._ _Melitta_ **. a. _t._ ii. _f._ 6. ♀. 7. ♂. and **. b.
_t._ iii. _f._ 3. ♀. 4. ♂.
[762] _Ibid._ _t._ viii. _f._ 11. ♀. 12. ♂.
[763] _Ibid._ i. _t._ viii. _f._ 9. ♀. 10. ♂.
[764] _Ibid._ _Apis_ **. c. 2. β. _t._ ix. _f._ 6. ♀. 7. ♂.
[765] See above, VOL. II. 125. Note^b.
[766] _Mon. Ap. Angl_. ubi supr. _t._ xiii. _f._ 13. ♀. 14. ♂.
[767] MacLeay _Hor. Entomolog._ 4--.
[768] _N. Dict. d'Hist. Nat._ xxii. 488.
[769] _Linn. Trans._ xii. 425--. _t._ xxii. _f._ 6.
[770] PLATE XXVI. FIG. 2.
[771] _Ibid._ FIG. 3.
[772] Oliv. no. xxv. _Lymexylon_, _t._ 1. _f._ 1.
[773] De Geer vii. 249--. _t._ xiv. _f._ 20, 21. Treviranus
_Arachnid._ 36--. _t._ ii. _f._ 16. _a b c._ _t._ iv. _f._ 35-37.
[774] _Mon. Ap. Angl._ i. Apis **. c. 2. γ. _t._ ix. _f._ 7. ♀. 9. ♂.
[775] _Ibid._ _Melitta_ **. a. _t._ ii. _f._ 8. ♀. 9. ♂. and **. b.
_t._ iii. _f._ 6. ♀. 7. ♂. **. c. _t._ iv. _f._ 11. ♀. 12. ♂.
[776] Jurine _Hymenopt._ _t._ 11. _f._ 2.
[777] _Mon. Ap. Angl._ i. Apis **. d. 1. _t._ x. _f._ 7.
[778] Oliv. no. 80. _Macrocephalus_, _t._ i. _f._ 2.
[779] Latr. _Gen. Crust. et Ins._ iv. 156.
[780] Jurine _Hymenopt._ 61. _t._ vi. _f._ 8.
[781] Ibid. 289.
[782] _Mon. Ap. Angl._ i. _t._ ix. Apis **. c. 2. γ. _f._ 9.
[783] PLATE XI. FIG. 19.
[784] PLATE V. FIG. 3.
[785] PLATE XI. FIG. 18.
[786] Ibid. FIG. 17.
[787] PLATE XXV. FIG. 11. _Linn. Trans._ xii. _t._ xxi. _f._ 4. _a._
[788] _Ibid._ _f._ 3.
[789] PLATE XXV. FIG. 22.
[790] De Geer i. _t._ xix. _f._ 11, 12.
[791] Jurine _Hymenopt._ _t._ vi. _f._ 8.
[792] PLATE XXV. FIG. 25, 26.
[793] Ibid. FIG. 4.
[794] Reaum. iv. _t._ xl. _f._ 2. _a a._ ♂. _t._ xxxix. _f._ 3. ♀. In
the last the hairs are too conspicuous.
[795] PLATE XII. FIG. 24.
[796] Jurine _Hymenopt._ _t._ vi. _f._ 3.
[797] PLATE XII. FIG. 25, 26. XXV. FIG. 17, 32.
[798] Ibid. FIG. 12.
[799] PLATE XI. FIG. 22.
[800] _N. Dict. d'Hist. Nat._ xiv. 395.
[801] PLATE XII. FIG. 7.
[802] PLATE XXV. FIG. 1.
[803] Ibid. FIG. 21.
[804] _Linn. Trans_. xii. _t._ xxii. _f._ 8. _e._ ♂. _f._ ♀.
[805] _Hist. Nat. des Fourmis_, 195--. 270--.
[806] De Geer ii. 1094.
[807] Ibid. 650. _Mon. Ap. Angl._ i. _t._ xi. _Apis_ xx. _c._ 1. _f._
2. ♂. _t._ xii. _f._ 3. ♀.
[808] PLATE XXVI. FIG. 39. De Geer ii. 651. 659.
[809] Voet _Coleopt._ i. _t._ xxxix. _f._ 47, 48. ♂. 46. ♀.
[810] Oliv. no. 3. _t._ vi. _f._ 46. _a._ ♂. _b._ ♀.
[811] Ibid. _t._ i. _f._ 1. iv. x. _f._ 31. xi. _f._ 102. xii. _f._
114.
[812] Ibid. _t._ xxvi. _f._ 219.
[813] Ibid. _t._ i. _f._ 2.
[814] Ibid. _t._ xxiii. _f._ 35.
[815] Ibid. _t._ ii. _f._ 7.
[816] Ibid. _t._ v. _f._ 40.
[817] Ibid. xix. _f._ 175.
[818] Ibid. _t._ xii. _f._ 115.
[819] _Copris floriger_ Kirby in _Linn. Trans._ xii. 396.
[820] Oliv. no. 3. _t._ ii. _f._ 18.
[821] Ibid. _t._ xxii. _f._ 32.
[822] Ibid. _t._ ix. _f._ 85.
[823] Ibid. _t._ iii. _f._ 22.
[824] Ibid. _t._ xiii. _f._ 124. _a._
[825] Ibid. _t._ v. _f._ 38.
[826] Ibid. _t._ xxviii. _f._ 242. _t._ xviii. _f._ 169.
[827] Ibid. _t._ xvi. _f._ 152.
[828] Ibid. _t._ xxviii. _f._ 247.
[829] Ibid. _t._ xv. _f._ 138. _a. t._ v. _f._ 33.
[830] Samouelle's _Compend._ _t._ i. _f._ 1.
[831] Oliv. no. 3. _t._ v. _f._ 36. _a._
[832] _Schon. Synon._ i. _t._ 1.
[833] Oliv. no. 3. _t._ xxiv. _f._ 208.
[834] Ibid _t._ x. _f._ 88.
[835] Ibid. _f._ 87.
[836] Ibid. _t._ xx. _f._ 185.
[837] Ibid. _t._ vi. _f._ 42. _a._
[838] Ibid. n. 83. _Curculio_ _t._ xxii. _f._ 295.
[839] Oliv. no. 81. _Attelabus_ _t._ ii. _f._ 27. _b._ 28.
[840] De Geer ii. _t._ xxxi. _f._ 18-22.
[841] Ibid. iii. 21.
[842] Lesser L. i. 185.
[843] De Geer iii. 308.
[844] See above, VOL. II. 394--.
[845] _Linn. Trans._ i. 145. 135--.
[846] _Ibid._ _t._ xiii. _f._ 1. 2. ♂. 3. ♀.
[847] _Mon. Ap. Angl._ i. _t._ xi. Apis **, a. 2. α. β. _f._ 18.
[848] Oliv. no. 68. _Saperda_ _t._ i. _f._ 8.
[849] _Mon. Ap. Angl._ i. _t._ viii. _f._ 28. _c._
[850] _Ibid._ _t._ ix. Apis **. c. 2. β. _f._ 12.
[851] Clairv. _Ent. Helv._ ii. _t._ xii. _f._ B.
[852] Oliv. _Ins._ no. 66. _t._ iii. iv. _f._ 12.
[853] Ibid. no. 3. _t._ iv. _f._ 27.
[854] _Punaises_, _t._ iii. _f._ 20.
[855] Mr. Marsham has made two species of this from this
circumstance, viz. _Necydalis Podagrariæ_ and _simplex_.
[856] Oliv. n. 3. _t._ xxvii. _f._ 27. ♀. and _t._ iv. _f._ 27. ♂.
[857] Ibid. _t._ vii. _f._ 58. ♂. _f._ 57. ♀.
[858] Ibid. n. 95. _Hispa_ _t._ i. _f._ 4. PLATE XXVII. FIG. 24.
[859] PLATE XV. FIG. 3.
[860] De Geer i. _t._ vii. _f._ 14, 15.
[861] Coquebert _Illust. Icon._ i. _t._ vi. _f._ 6. PLATE XXVII. FIG.
32.
[862] Illig. _Mag._ iv. 214. Gyllenhal. _Insect. Suec._ i. 168.
[863] PLATE XV. FIG. 9.
[864] Ibid. FIG. 8.
[865] Christ. _Hymenopt._ 118. _t._ iv. _f._ 3.
[866] _Mon. Ap. Angl._ i. _t._ xi. _Apis_ **. e. 1. ♂. _f._ 8. _e._
and _t._ xii. **. e. 1. neut. _f._ 19. _c._
[867] _Hor. Entomolog._ 144.
[868] PLATE XXVII. FIG. 45. _a._
[869] De Geer ii. _t._ xxviii. _f._ 2.
[870] _Mon. Ap. Angl._ i. _t._ v. _Apis_ **. a. _f._ 10. ♂. 11. ♀.
[871] _Ibid._ _t._ vii. Apis **. c. 1. α. 17. ♀. 18. ♂.
[872] _Ibid._ _t._ viii. _f._ 30. ♂. 31. ♀.
[873] _Ibid._ _t._ xi. Apis **. e. 1. mas. _f._ 9. _t._ xii. Apis **.
e. 1. fem. _f._ 9. and neut. _f._ 22.
[874] De Geer vi. _t._ xviii. _f._ 12, 13.
[875] De Geer v. 151--.
[876] _Mon. Ap. Angl._ i. 177. _t._ ix. Apis **. c. 2. γ. _f._ 11.
_a_, _d_.
[877] _Ibid._ _f._ 13. _a._
[878] See above, VOL. II. 395.
[879] PLATE XXIX. FIG. 13. Stoll. _Spectres_, &c. _t._ xxv. _f._ 99.
[880] Sparrman. _Voyage_, i. 312--.
[881] _Coleopt. Micropt._ 16.
[882] _Mon. Ap. Angl._ i. _t._ viii. _f._ 25. De Geer iii. 255. _t._
xiv. _f._ 8.
[883] _Mon. Ap. Angl._ i. _t._ viii. _f._ 24.
[884] _Ibid._ _t._ ix. Apis xx. c. 2. γ. _f._ 12.
[885] _Ibid._ Apis **. c. 2. β. _f._ 11.
[886] _Ibid._ _t._ vii. Apis **. c. 1. α. _f._ 11, 12. ♀. 13, 14. ♂.
[887] PLATE XV. FIG. 12. De Geer ii. _t._ xxiv. _f._ 9, 10. ♀. _t._
xxv. _f._ 2, 3. ♂.
[888] Reaum. vi. 494. _t._ xliv. _f._ 3-11.
[889] De Geer ii. _t._ xvii. _f._ 5-7.
[890] _N. Dict. d'Hist. Nat._ xxxii. 443.
[891] See above, VOL. II. 110, 118.
[892] VOL. I. 283.
[893] II. i. 6.
[894] Clairville _Ent. Helvet._ ii. 214--. I have seen it asserted in
some popular work on _Natural History_, (the title of which I do not
recollect,) that _Mantis religiosa_ has been known to live ten years;
and a _flea_, when fed and taken care of, six. But this is so contrary
to experience in other cases, that the statement seems quite incredible.
[895] Rösel III. 379. _N. Dict. d'Hist. Nat._ ii. 285.
[896] Dumeril _Traité Elément._ ii. 87. n. 683.
[897] De Geer ii. 288.
[898] Huber i. 106.
[899] _N. Dict. d'Hist. Nat._ ix. 553.
[900] VOL. II. 173--.
[901] Morier's _Second Journey through Persia_, 100.
[902] VOL. II. 175.
LETTER XXXIII.
_EXTERNAL ANATOMY OF INSECTS._
TERMS, AND THEIR DEFINITION.
Having shown you our little animals in every state, and traced their
progress from the egg to the perfect insect, I must next give you
some account of their _structure_ and _anatomy_. And under this
head I shall introduce you to a microcosm of wonders, in which the
hand of an ALMIGHTY workman is singularly conspicuous. One would
at first think that the giant bulk of the elephant, rhinoceros, or
hippopotamus, must include a machine far more complicated, a skeleton
more multifarious in its composition--covered by muscles infinitely
more numerous--instinct with a nervous system infinitely more
ramified--with a greater variety of organs and vascular systems in
play, than an animal that would scarcely counterpoise a ten-millionth
portion of it. Yet the reverse of this is the fact; for the Creator,
the more to illustrate his wisdom, power, and skill, has decreed that
the minute animals whose history we are recording, shall be much
more complex in all the above respects than these mighty monarchs
of the forest and the flood. Of this in the present and subsequent
letters you will find repeated and scarcely credible instances,
which in every rightly constituted mind are calculated to excite, in
an extraordinary degree, those sensations of reverence and love for
the INVISIBLE AUTHOR of these wonders, and that faith and trust in
his Power and Providence, which an attentive survey of the works of
Creation has a natural tendency to produce. And you will not only be
struck by this circumstance, but equally by the infinite variations
in the structure that will present themselves to your notice; and
that not sudden and _per saltus_, but by approaches made in the most
gradual manner from one form to another. And all along, where the
uses of any particular organ or part have been ascertained, if you
consider its structure with due attention, you will find in it the
nicest adaptation of means to an end: a circumstance this, which
proves most triumphantly, that the POWER who immediately gave being
to all the animal forms, was neither a blind unconscious power,
resulting from a certain order of things, as some philosophists love
to speak[903]; nor a formative appetency in the animals themselves,
produced by their wants, habits, and local circumstances, and giving
birth, in the lapse of ages, to all the animal forms that now people
our globe[904]; but a Power altogether distinct from and above
nature, and its ALMIGHTY AUTHOR[905].
I trust that what I have here advanced will excite your attention
to the subject I am now to enter upon; and I flatter myself, that
although at first sight it may promise nothing more than a dry and
tedious detail of parts and organs, you will find it not without its
peculiar interest and attraction.
This department of the science--the Anatomy of Insects--may
still be regarded as in its infancy; and considering the almost
insuperable difficulties which, from the minuteness of the objects,
oppose themselves to the skill and instruments of the entomological
anatomist, we can scarcely hope that it will ever attain to that
certainty and perfection to which, as far as the larger animals
are concerned, anatomy has arrived. Yet infinitely more has been
accomplished than might have been expected, and new accessions of
light are daily thrown upon it. When we consider what has been done
by Malpighi, Leeuwenhoeck, and especially Swammerdam, we admire the
patience, assiduity, and love of science, that enabled them, in spite
of what seemed insurmountable obstacles, to ascertain, the first with
respect to the silk-worm, and the latter in numerous instances, the
internal organization of these minute creatures, as well as their
external structure. Reaumur, and his disciple De Geer, extending
their researches, have also contributed copiously to our knowledge in
this branch of our science.
But in this field no one has laboured so indefatigably and with so
much success as the celebrated Lyonnet; and though his attention was
confined to one object--the caterpillar of the goat-moth (_Cossus
ligniperda_ F.),--every one who studies his immortal work must admire
the patient and skilful hand, the lyncean eye, and keen intellect,
that discovered, denuded, and traced every organ, muscle, and fibre
of that animal. Much is it to be regretted that his proposed works
on the pupa and imago of the same insect, which, he informs us, were
far advanced[906], were never finished and given to the world. Our
regret, however, is in some degree diminished by the elaborate work of
M. Herold on the butterfly of the cabbage (_Pieris Brassicæ_), before
eulogized[907]; in which he has done much to supply this desideratum.
In more modern times, besides Herold, MM. Latreille, Illiger,
Marcelle de Serres, Savigny, Ramdohr, Treviranus Sprengel, Audoin,
Chabrier, and, above all, M. Cuvier in his celebrated _Lectures on
Comparative Anatomy_, have considerably extended the boundaries of
our knowledge in this department: and much of what I have to say
to you in my letters on this subject, will be derived from these
respectable sources. In the exterior anatomy of insects, I flatter
myself that I shall be enabled to make some material additions to the
discoveries of my predecessors; though few have occurred to me with
respect to their internal organization.
In treating of the anatomy of the _vertebrate animals_, it is usual,
I believe, to consider, first, the skeleton and its integuments,
whether of skin or muscle, and their accessories; and afterwards
the organs of the different vital functions and of the senses. But
in considering the anatomy of _Insects_, the difference before
stated[908], observable between them and the sub-kingdom just
mentioned, as to their structure, renders it advisable to divide
this subject into two parts--the first treating of their _external_
anatomy, and the second of their _internal_.--I shall begin by
drawing up for you a Table of the Nomenclature of the parts of their
_external_ crust; its appendages and processes[909], external or
internal, accompanied by definitions of them; and followed by such
observations respecting them as the subject may seem to require for
its more full elucidation.
Anatomists have divided the human skeleton into _three_ greater
sections--the _Head_, the _Trunk_, and the _Limbs_. That of insects,
likewise, is resolvable into _three_ primary sections, but without
including the limbs (which, as being _appendages_, and therefore
_secondary_, had best be considered under the section of which they
form a part), for the _abdomen_ in insects, as well as the rest
of the body, being covered with a _crust_, and forming a distinct
part, may be properly regarded as a _primary_ section. And in fact
these three parts may be received as primary under another view--the
_head_, as containing the principal organs of _sensation_; the
_trunk_, as containing those of _motion_; and the _abdomen_, as
containing those of _generation_[910]. Under each of these primary
sections, I shall consider its respective organs, members, and parts.
You are not to expect to find every part included in the following
Table in every insect; since it has been my aim to introduce into it,
the most remarkable of those that are peculiar to particular tribes,
genera, &c. With respect to these, I shall generally refer you to the
individuals in which they may be found.
_DEFINITIONS._
CORPUS (the _Body_). The whole crust of the insect; consisting of
the _Exoderma_ or external covering, and the _Esoderma_ or internal
cuticle that lines it[911]. It is divided into three primary parts,
or sections--_Caput_, _Truncus_, _Abdomen_.
INSERT FOLDOUT HERE
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I. CAPUT (The HEAD).
The _Head_ is the anterior section of the body; consisting of a
kind of box without suture or segment, which receives the organs
of sensation and manducation. It includes the _Os_, _Facies_,
_Subfacies_, and _Collum_.
i. OS (the _Mouth_). That part of the head which receives and
prepares the food for passing into the stomach. It includes the
_Trophi_[912].
1. TROPHI (the _Trophi_). The different instruments or organs
contained in the mouth, or closing it, and employed in
manducation or deglutition. They include the _Labrum_, _Labium_,
_Mandibulæ_, _Maxillæ_, _Lingua_, and _Pharynx_.
A LABRUM (the _Upper-lip_). A usually moveable organ; which,
terminating the face anteriorly, covers the mouth from _above_,
and is situate between the _Mandibulæ_[913]. It includes the
_Appendicula_.
a APPENDICULA (the _Appendicle_). A small piece sometimes appended
to the upper-lip[914]. Ex. _Halictus_ ♀ Walck. (_Melitta_ **. b.
K.)
B LABIUM (the _Under-lip_). A moveable organ, often biarticulate,
which terminating the surface anteriorly, covers the mouth from
_beneath_, and is situate between the _Maxillæ_[915]. It includes
the _Mentum_, and _Palpi Labiales_.
a MENTUM (the _Chin_). The lower joint of the _Labium_, where it
is jointed; in other cases its base. It is usually seated between
the base of the _Maxillæ_[916].
b PALPI LABIALES (the _Labial Feelers_). Two jointed sensiferous
organs, the use of which is not clearly ascertained, which
emerge, one on each side, from the _Labium_, mostly near its
summit[917].
C MANDIBULÆ (the _Upper-jaws_). Two transverse lateral organs,
in most insects used for manducation; generally corneous,
moving horizontally, and closing the mouth above, under the
_Labium_[918]. They include the _Prostheca_, _Dentes_, and _Mola_.
a PROSTHECA (the _Prostheca_). A subcartilaginous process attached
to the inner side, near the base, of the _Mandibulæ_ of some
_Staphylinidæ_[919]. Ex. _Ocypus similis_ K., _Creophilus
maxillosus_ K., &c.
b DENTES (the _Teeth_). The terminating points of the _Mandibulæ_.
They include the _Incisores_, _Laniarii_, and _Molares_[920].
_A_ INCISORES (the _Cutting-teeth_). Teeth somewhat wedge-shaped,
externally convex and internally concave[921]. Ex. _Gryllotalpa_
Latr., _Gryllus_ Latr. (_Acheta_ F.), &c. &c.
_B_ LANIARII (the _Canine-teeth_). Very sharp and usually long
conical teeth[922]. Ex. _Forficula_ L., _Mantis_ L., _Libellula_
L.
_C_ MOLARES (the _Grinding-teeth_). Teeth that terminate in a
broad uneven surface, fit for grinding the food[923]. Ex. the
herbivorous _Orthoptera_.
c MOLA (the _Mola_). A broad, flat, subrotund space, transversely
grooved or furrowed, observable on the inner side of some
mandibles that have no grinding-teeth at their apex[924].
Ex. _Euchlora_ MacLeay, _Anoplognathus_ Leach, Larva of
_Lucanus_[925].
D MAXILLÆ (the _Under-jaws_). Two organs moving subhorizontally,
fixed on each side at the base of the _Labium_, and often
parallel with it--which in masticating insects seem primarily
designed to hold the food[926]. They include the _Cardo_,
_Stipes_, _Lobi_, and _Palpi maxillares_.
a CARDO (the _Hinge_). A small, transverse, usually triangular,
corneous piece, upon which the _Maxilla_ commonly sits[927].
b STIPES (the _Stalk_). The corneous base of the _Maxilla_, below
the _Palpus_[928].
c LOBI (the _Lobes_). The parts of the _Maxilla_ above the
_Palpus_[929]. They include the _Lobus superior_, the _Lobus
inferior_, and the _Ungues_.
_A_ LOBUS SUPERIOR (the _Upper-lobe_). The outer lobe of the
_Maxilla_, incumbent on the inner one. In the _Predaceous
Beetles_ this lobe is biarticulate and palpiform[930]; and in
_Staphylinus olens_, &c. it also consists of two joints[931]. It
is called the _Galea_ by Fabricius, in _Orthoptera_, &c.[932]
_B_ LOBUS INFERIOR (the _Lower-lobe_). The inner lobe of the
_Maxilla_, covered by the outer one[933].
_C_ UNGUES (the _Claws_). One or more corneous sharp claws which
arm the lobes of the _Maxilla_[934]. In the _Predaceous
Beetles_ there is only one terminating the lower lobe, with
which, in _Cicindela_, it articulates; in the _Orthoptera_ and
_Libellulina_ there are several.
d PALPI MAXILLARES (the _Maxillary Feelers_). Two jointed
sensiferous organs, the use of which is not clearly ascertained,
emerging from an exterior lateral sinus of the _Maxilla_[935].
E LINGUA (the _Tongue_). The organ situated within the _Labium_ or
emerging from it, by which insects in many cases collect their
food and pass it down to the _Pharynx_, situated at its roots
above. It varies considerably in different orders and tribes.
In the _Orthoptera_, _Libellulina_, &c. it is _linguiform_, and
quite distinct from the _Labium_[936]; it appears also distinct
in the _lamellicorn_ beetles, &c.[937] In many _Hymenoptera_
it emerges from the _Labium_, and is fitted to collect liquids
and pass them downwards[938]. In _Formica_ it appears to be
retractile[939]. In a considerable proportion of insects it
seems connate with the _Labium_, and forming its inner surface?
According to circumstances it might perhaps be denominated
_Lingua_ or _Ligula_. It includes the _Paraglossæ_.
a PARAGLOSSÆ (the _Paraglossæ_). Lateral and often membranous
processes observable on each side of the tongue in some
_Hymenoptera_, &c.[940]
F PHARYNX (the _Pharynx_). The opening into the gullet[941]. It
includes the _Epipharynx_ and _Hypopharynx_.
a EPIPHARYNX (the _Epipharynx_). A small valve under the _Labrum_,
that in many _Hymenoptera_ closes the _Pharynx_, and is an
appendage of its upper margin[942].
b HYPOPHARYNX (the _Hypopharynx_). An appendage of the lower
margin of the _Pharynx_, observable in _Eucera_ F.[943]
_The_ seven _organs of the mouth above defined_, viz. _the_ Labrum,
Labium, _the two_ Mandibulæ, _the two_ Maxillæ, _and the_ Lingua,
_constitute what may be denominated a_ perfect _mouth, peculiar
to those insects that_ masticate _their food_[944]. _In those
that take it by_ suction, _the_ Trophi, _to adapt them for that
purpose, assume a variety of forms, and should be distinguished by
as many appellations. In almost every case, however, the_ rudiments
_or_ representatives _of the above organs have been detected by
the elaborate researches of that learned and able zoologist, M.
Savigny_[945]. _I shall next subjoin definitions of the principal
kinds of suctorious mouths._
2. PROMUSCIS (the _Promuscis_). The oral instrument of _Hemiptera_,
in which the ordinary _Trophi_ are replaced[946] by a jointed
sheath, covered above at the base by the _Labrum_, without
_Labella_ (Liplets) at the end, and containing four long
capillary lancets, and a short tongue[947]. It includes the
_Vagina_, and _Scalpella_.
A VAGINA (the _Vagina_). The jointed sheath of the _Promuscis_,
representing the _Labium_ in a _perfect_ mouth[948].
B SCALPELLA (the _Lancets_). Four pieces adapted for perforating
the food of the insect, which when united form a tube for
suction. The upper pair represent the _Manidibulæ_[949], and the
lower the _Maxillæ_[950].
3. PROBOSCIS (the _Proboscis_). The oral instrument of _Diptera_,
in which the ordinary _Trophi_ are replaced by an exarticulate
sheath, terminated by _Labella_, and containing one or more
lancets covered by a valve[951]. It includes the _Theca_, and
_Haustellum_.
A THECA (the _Theca_). The sheath or case of the _Proboscis_,
representing the _Labium_ in a _perfect_ mouth[952]. It includes
the _Basis_, and _Labella_.
a BASIS (the _Base_). The whole lower part of the _Theca_, from the
mouth of the insect as far as the _Labella_, probably to be
regarded as representing the _Mentum_?
b LABELLA (the _Liplets_). A pair of tumid lobes, often corrugated
and capable of tension and relaxation, which terminate
the _Theca_, and perhaps represent the termination of the
_Labium_[954]?
B HAUSTELLUM (the _Haustellum_). The instrument of suction
contained in the _Theca_[955]. It includes the _Valvula_,
_Cultelli_, and _Scalpella_.
a VALVULA (the _Valvule_). A corneous piece which covers the
instruments of suction above, representing the _Labrum_ in a
perfect mouth[956].
b CULTELLI (the _Knives_). The upper pair of the instruments of
suction, which probably make the first incision in the food
of the insect; they represent the _Mandibulæ_ of the perfect
mouth[957].
c SCALPELLA (the _Lancets_). A pair of instruments, usually more
slender than the _Cultelli_, which probably enter the veins or
sap-vessels, and together with them form a tube for suction[958].
4. ANTLIA (the _Antlia_). The oral instrument of _Lepidoptera_, in
which the ordinary _Trophi_ are replaced by a spiral, bipartite,
tubular machine for suction, with its appendages[959]. It
includes the _Solenaria_, and _Fistula_.
A SOLENARIA (the _Solenaria_). The two lateral subcylindrical
air-tubes of the _Antlia_[960].
B FISTULA (the _Fistula_). The intermediate subquadrangular pipe,
formed by the union of the two branches of the _Antlia_, which
conveys the nectar to the _Pharynx_[961]. These two branches
represent the _Maxillæ_ of the perfect mouth.--N. B. M. Savigny
_discovered the rudiments of the remaining_ Trophi _in this kind
of mouth_[962].
5. ROSTRULUM (the _Rostrulum_). The oral instrument of
_Aphaniptera_ (_Pulex_ L.), in which the ordinary _Trophi_ are
replaced by a bivalve beak, between the valves of which there
appear to be three lancets[963]. It includes the _Laminæ_,
_Scalpella_, and _Ligula_.
A LAMINÆ (the _Laminæ_). Two corneous plates which are laterally
affixed to the mouth of a flea, probably representing the
_Mandibulæ_ of the perfect mouth, which somewhat resemble the
beak of a bird[964].
B SCALPELLA (the _Lancets_). The two upper or outer instruments,
probably for making an incision in the skin; these are flat
and acute, and seem to represent the _Maxillæ_ of the perfect
mouth[965].
C LIGULA (the _Ligula_). A capillary instrument between the
lancets; probably representing the _tongue_ of the perfect
mouth[966].
6. ROSTELLUM (the _Rostellum_). The oral instruments of _Pediculus_
and some other _Aptera_, in which the ordinary _Trophi_ are
replaced by an exarticulate retractile tube, which exerts a
retractile siphuncle. It includes the _Tubulus_ and _Siphunculus_.
A TUBULUS (the _Tubulet_). The tube or retractile base of the
_Rostellum_.
B SIPHUNCULUS (the _Siphuncle_). The real instrument of suction,
which when unemployed is retracted within the tubulet.
_Besides the above variations from the type of what I call a_ Perfect
Mouth, _there are others in which the parts of the_ Trunk _appear to
aid in the conversion of the food, and become a kind of accessory_
Labium, Maxilla, &c. _Thus in the_ Myriapods, _the anterior pair of
legs assume a_ Maxillary _form and office_[967]; _the_ Prosternum
_those of a_ Labium[968]: _in the_ Arachnida, _also, the anterior_
Coxæ _are accessory_ Maxillæ. _In this_ Class, _likewise, as has been
more than once observed_[969], _the representatives of the interior
pair of_ Antennæ _of the_ Crustacea, _are thought to assume the form
and the functions of suctorious_ Mandibles[970].
ii. FACIES (the _Face_). The upper surface of the head[971]. It
includes all the parts that lie between its junction with the
_Prothorax_ and the _Labrum_: viz. _Nasus_, _Postnasus_, _Frons_,
_Vertex_, _Occiput_, _Genæ_, _Tempora_, _Oculi_, _Stemmata_, and
_Antennæ_.
1. NASUS (the _Nose_). That portion of the face, often elevated
and remarkable, situated between the _Labrum_, _Postnasus_,
and _Genæ_, and with which the _Labrum_ articulates; called by
Fabricius the _Clypeus_[972]. It includes the _Rhinarium_.
A RHINARIUM (the _Nostril-piece_). The space between the anterior
margin of the _Nasus_ and the _Labrum_, in which, in vertebrate
animals, the nostrils are often situated[973].--N. B. _This
is remarkable in some Lamellicorn beetles, as_ Anoplognathus
_Leach_. _In_ Necrophorus, _and some others, it is membranous_.
2. POSTNASUS (the _Postnasus_). That part of the _Face_ immediately
contiguous to the _Antennæ_, that lies behind the _Nasus_, when
distinctly marked out.--Ex. _Sagra_, _Prosopis_.
3. FRONS (the _Front_). That part of the _Face_ which lies behind
the _Postnasus_, and usually between the posterior part of the
eyes. This is sometimes the region of the _Stemmata_; or they are
partly in this or partly in the _Vertex_[974].
4. VERTEX (the _Vertex_). The horizontal part of the _Facies_,
next the front, that lies behind the eyes and between the
temples[975]. This also is often the region of the _Stemmata_.
5. OCCIPUT (the _Occiput_). The back part of the head when it is
vertical, or nearly so, to its point of junction with the
trunk[976].--Ex. _Meloe_, _Ripiphorus_, _Hymenoptera_, _Diptera_.
6. GENÆ (the _Cheeks_). Those parts which lie on the outside of the
anterior half of the eyes, and intervene also between them and
the _Mandibulæ_[977].
7. TEMPORA (the _Temples_). Those parts which lie on the outside of
the posterior half of the eyes, between which the _Frons_ and
_Vertex_ intervene[978].
8. OCULI (the _Eyes_). The principal organs of sight, most commonly
two in number, placed in the sides of the head. In the majority
they are compound, consisting of hexagonal lenses. In the
_Arachnida_ they are simple[979].
A CANTHUS (the _Canthus_). A process of the face, which enters the
notch or sinus of the eye[980].--Ex. _Scarabæus_ L., _Cerambyx_ L.
9. STEMMATA (the _Eyelets_). Two, or more commonly three, convex,
crystalline, simple eyes, observable in the _Frons_ or _Vertex_,
or common to both[981].--Ex. _Orthoptera_, _Hemiptera_,
_Hymenoptera_.
10. ANTENNÆ (the _Antennæ_). Two moveable and jointed sensiferous
organs, situated in the space between or before the eyes, but
in no instance behind them[982]. They include the _Torulus_,
_Scapus_, _Pedicellus_, and _Clavola_.
A TORULUS (the _Bed_). The cavity or socket in which the base of
the _Antenna_ is planted[983].
B SCAPUS (the _Scape_). The first and in many cases the most
conspicuous joint of the _Antennæ_[984]. It includes the _Bulbus_.
a BULBUS (the _Bulb_). The base of the _Scapus_, by which it
inosculates in the _Torulus_, often subglobose, and looking like
a distinct joint[985]. It acts the part of a _Rotula_, being the
pivot upon which the _Antenna_ turns.
C PEDICELLUS (the _Pedicel_). The second joint of the
_Antenna_[986]: in some insects acting also the part of a
_Rotula_ in the socket of the _Scapus_, to give separate motion
to the _Clavola_.
D CLAVOLA (the _Clavolet_). The remaining joints of the _Antenna_
taken together[987]. It includes the _Capitulum_.
a CAPITULUM (the _Knob_). The last joints of the _Clavola_ when
suddenly larger than the rest[988].
iii. SUBFACIES (the _Subface_). The lower surface or underside of the
head[989]. It includes the _Lora_ and _Jugulum_.
1. LORA (the _Lora_). A corneous angular machine observable in the
mouth of some insects, upon the intermediate angle of which the
_Mentum_ sits, and on the lateral ones the _Cardines_ of the
_Maxillæ_; and by means of which the _Trophi_ are pushed forth or
retracted[990].--Ex. _Hymenoptera_.
2. JUGULUM (the _Throat_). That part of the subface that lies
between the temples[991].
iv. COLLUM (the _Neck_). The constricted posterior part of a
pedunculate head, by which it inosculates in the trunk[992]. It
includes the _Nucha_, _Gula_, and _Myoglyphides_.
1. NUCHA (the _Nape_). The upper part of the neck[993]. It includes
the _Myoglyphides_.
A MYOGLYPHIDES (the _Muscle-notches_). Notches in the posterior
margin of the neck, usually two in number, observable in
Coleopterous insects, to which the levator muscles are
attached[994].
2. GULA (the _Gula_). The lower part of the neck[995].
v. CEPHALOPHRAGMA (the _Cephalophragm_). A Y-shaped partition
that divides the head internally in _Locusta_ Leach, into two
chambers, an anterior and posterior.
II. TRUNCUS (The TRUNK).
The _Trunk_ is the intermediate section of the body, which lies
between the _Head_ and the _Abdomen_[996]. It includes the
_Manitruncus_, and the _Alitruncus_[997].
/#[6.2] i. MANITRUNCUS (the _Manitrunk_). The anterior segment
of the trunk, in which the head inosculates, or on which it
turns[998]. It includes the _Prothorax_ and _Antepectus_.
1. PROTHORAX (the _Prothorax_). The upper part or the shield of
the manitrunk, in _Coleoptera_, _Orthoptera_, &c. called by
way of eminence the _Thorax_[999]. It includes the _Ora_,
_Patagia_, _Umbones_, and _Phragma_.
A ORA (the _Ora_). The inflexed or inferior lateral margin of the
_Prothorax_, separated in many genera from the _Antepectus_ by
a suture[1000].
B PATAGIA (the _Patagia_). Two corneous scales observable in
_Lepidoptera_, fixed on each side of the trunk, just behind the
head, and covered with a long tuft of hair[1001].
C UMBONES (the _Bosses_). Two moveable bosses surmounted by a
spine, with which the _Prothorax_ of the Coleopterous genus
_Macropus_ is armed.
D PHRAGMA (the _Phragm_). The _Septum_ that closes the posterior
orifice of the _Prothorax_ in _Gryllotalpa_ Latr.
2. ANTEPECTUS (the _Forebreast_). The underside or breastplate of
the manitrunk, and the bed of the _Arms_[1002]. It includes
the _Spiracula Antepectoralia_, _Prosternum_, _Antefurca_, and
_Brachia_.
A SPIRACULA ANTEPECTORALIA (the _Antepectoral Spiracles_). A pair
of breathing-pores fixed in the membrane that connects the
_Antepectus_ with the _Medipectus_[1003].
B PROSTERNUM (the _Forebreast-bone_). A longitudinal or other
elevation of the _Antepectus_ between the _Brachia_[1004].
C ANTEFURCA (the _Antefurca_). An internal vertical process of
the _Antepectus_, consisting usually of two branches, which
afford a point of attachment to muscles of the _Brachia_[1005].
D BRACHIA (the _Arms_). The first pair of legs of _Hexapods_, the
direction of which is usually towards the head; when spoken of
with the other legs, called the _Forelegs_[1006]. They include
the _Clavicula_, _Scapula_, _Humerus_, _Cubitus_, and _Manus_.
a CLAVICULA (the _Clavicle_). The _first_ joint of the
_Brachium_, answering to the _Coxa_ in the legs.
b SCAPULA (the _Scapula_). The _second_ joint of the _Brachium_,
answering to the _Trochanter_ in the legs.
c HUMERUS (the _Humerus_). The _third_ and elongated joint of the
_Brachium_, answering to the _Femur_ in the legs.
d CUBITUS (the _Cubitus_). The _fourth_ and elongated joint,
answering to the _Tibia_ in the legs. It includes the
_Coronula_ and _Calcaria_. . _A_ CORONULA (the _Coronula_). A
coronet or semicoronet of spines, observable at the apex of the
_Cubitus_ or _Tibia_ of some insects.--Ex. _Dilophus_ Latr.,
_Fulgora_ L.
_B_ CALCARIA (the _Spurs_). See the definition under _Pedes
Postici_. They include the _Velum_.
_a_ VELUM (the _Velum_). A membrane attached to the inner side of
the cubital spur in _Apis_ L.[1007]
e MANUS (the _Hand_). The terminal jointed portion of the
_Brachium_, answering to the _Tarsus_ in the legs[1008]. It
includes the _Pulvilli_, _Palma_, and _Digitus_.
f PULVILLI (the _Pulvilli_). See definition under _Pedes Postici_.
g PALMA (the _Palm_). The first joint of the _Manus_, when longer
and broader than the subsequent ones, or otherwise remarkable;
answering to the _Planta_ in the legs[1009].
_A_ DIGITUS (the _Finger_). See definition under _Pedes Postici_.
It includes the _Ungula_.
_a_ UNGULA (the _Claw-joint_). See definition under _Pedes
Postici_. It includes the _Pollex_, _Unguiculi_, and _Palmula_.
α POLLEX (the _Thumb_). A small accessory joint, attached to the
_Ungula_ of the _Manus_ in _Mantis_ F.
β UNGUICULI (the _Claws_). See definition under _Pedes Postici_.
γ PALMULA (the _Palmlet_). A minute accessory joint between the
claws, answering to the _Plantula_ in the legs. It includes the
_Pseudonychia_.
* PSEUDONYCHIA (the _Spurious Claws_). See definition under
_Pedes Postici_.
ii. ALITRUNCUS (the _Alitrunk_). The _posterior_ segment of the
trunk to which the abdomen is affixed, and which bears the legs
and wings[1010]. It includes the _Mesothorax_ and _Medipectus_,
and the _Metathorax_ and _Postpectus_.
1. MESOTHORAX (the _Mesothorax_). That segment of the alitrunk
which bears the _Elytra_, or the anterior pair of wings, and
the intermediate pair of legs[1011]. It includes the _Collare_,
_Prophragma_, _Dorsolum_, _Scutellum_, _Frænum_, and _Pnystega_.
A COLLARE (the _Collar_). The _first_ or anterior piece of
the _Mesothorax_. In most insects that have a conspicuous
_Prothorax_, as the _Coleoptera_, this piece appears scarcely
to have a representative; but in the _Libellulina_ it co-exists
with it, and is more conspicuous[1012]. It is particularly
remarkable in _Hymenoptera_ and _Diptera_.
B PROPHRAGMA (the _Prophragm_). A partition of an elastic
substance, rather horny, connected posteriorly with the
_Dorsolum_, which passes down into the anterior cavity of the
alitrunk, of which it forms the upper separation from that
of the manitrunk. It affords a point of attachment to several
muscles of the wings, &c.[1013]
C DORSOLUM (the _Dorslet_). The piece which lies between the
_Collare_ and _Scutellum_, to which the prophragm is anteriorly
attached, and which bears the upper or anterior organs of
flight[1014]. It includes the _Pteropega_, _Elytra_, _Tegmina_,
_Hemelytra_, _Alæ Superiores_, and _Tegulæ_.
a PTEROPEGA (the _Wing-socket_). The space in which the organs
for flight are planted. That for the secondary or under-wings
is in the _Metathorax_[1015].
b ELYTRA (the _Elytra_). The _upper_ organs for flight, when
they are without nervures, and uniformly of a thicker harder
substance than membrane whether corneous, or coriaceous; lined
by a fine membrane; and when closed, united by the longitudinal
suture[1016]. They include the _Axis_, _Sutura_, _Epipleura_,
_Alula_, and _Hypoderma_, and are peculiar to the _Coleoptera_
and _Dermaptera_.
_A_ AXIS (the _Axis_). A small, prominent, irregular process of
the base of the _Elytrum_, upon which it turns, and by the
intervention of which it is affixed to the _Dorsolum_, in the
anterior wing-socket[1017].
_B_ SUTURA (the _Suture_). The conflux of the sutural or inner
margins of the two _Elytra_, where when closed they unite
longitudinally[1018].
_C_ EPIPLEURA (the _Epipleura_). The inflexed accessory margin
observable underneath in many _Elytra_, which covers the sides
of the alitrunk and abdomen[1019].
_D_ ALULA (the _Winglet_). A small, membranous, wing-like
appendage, attached to the _Elytrum_ on one side and the
_Frænum_ on the other; which probably serves to prevent the
dislocation of the former[1020].--Ex. _Dytiscus_. N. B. _A
similar organ for a similar purpose is to be found in_ Blatta
_and the_ Diptera.
_E_ HYPODERMA (the _Hypoderma_). The skin, in some species
beautifully coloured, that lines the _Elytra_[1021]. N. B.
_This skin is also found in some_ Hemelytra, _but not in_
Tegmina.
c TEGMINA (the _Tegmina_). The upper organs of flight, when
of a uniform coriaceous or pergameneous texture, veined
with nervures, and lapping over each other[1022]. Ex.
_Orthoptera_[1023].
d HEMELYTRA (the _Hemelytra_). The upper organs of flight, when
they are corneous or coriaceous at the base and membranous
at the apex[1024].--Ex. The _heteropterous Hemiptera_. They
include the _Corium_ and _Membrana_.
_A_ CORIUM (the _Corium_). The corneous or coriaceous part of the
_Hemelytrum_[1025].
_B_ MEMBRANA (the _Membrane_). The membranous part of the
same[1026].
e ALÆ SUPERIORES vel PRIMARIÆ (the _Upper_ or _Primary Wings_).
The upper or anterior organs of flight when formed of membrane,
or of the same substance with the under-wings[1027]. They
include the _Axes_, _Areæ_, _Areolæ_, _Neuræ_, _Stigma_,
_Parastigma_, and _Lobuli_.
_A_ AXES (the _Axes_). Several osseous or horny pieces, by which
the wing is connected with the _Dorsolum_[1028]. One usually to
each area.
_B_ AREÆ (the _Areas_). The larger longitudinal spaces into
which the wing may be divided[1029]. They include the _Area
Costalis_, _Intermedia_, and _Analis_.
_a_ AREA COSTALIS (the _Costal Area_). That part of the wing lying
between the anterior margin and the post-costal nervure[1030].
In _Hymenoptera_ and _Diptera_ it includes all the space
bounded by the nervures that spring from the postcostal.
_b_ AREA INTERMEDIA (the _Intermediate Area_). That part of the
wing lying between the costal area and the interno-medial
nervure, in _Diptera_; or the _Anal_ in _Orthoptera_,
_Hemiptera_, _Hymenoptera_, &c.[1031]
_c_ AREA ANALIS (the _Anal Area_). All that part of the wing which
in _Diptera_ lies between the internomedial nervure; or in
_Orthoptera_, &c. between the anal nervure and the posterior
margin[1032].
_C_ AREOLÆ (the _Areolets_). The smaller spaces into which the
wing is divided by the nervures. They include the _Areolæ
Basilares_, _Mediæ_, and _Apicales_.
_a_ AREOLÆ BASILARES (the _Basal Areolets_). The parallel areolets
of the base of the wing[1033].
_b_ AREOLÆ MEDIÆ (the _Middle Areolets_). The areolets of the wing
that lie between the basal areolets and the apical[1034].
_c_ AREOLÆ APICALES (the _Apical Areolets_). Those areolets of the
wing that terminate in or very near the apex[1035].
_D_ NEURÆ (the _Nervures_). Corneous tubes, for expanding
the wing and keeping it tense, and to afford protection
to the air-vessels--commonly called the _Nerves_. They
include the _Neura Costalis_, _Postcostalis_, _Mediastina_,
_Externo-media_, _Interno-media_, _Analis_, _Axillaris_, and
_Spuria_.
_a_ NEURA COSTALIS (the _Costal Nervure_). The first principal
nervure of the wing, close to or forming the anterior margin
in _Lepidoptera_, _Hymenoptera_, and _Diptera_; but sometimes
remote from it in _Tegmina_[1036]. It includes the _Phialum_
and _Hamus_.
α PHIALUM (the _Phial_). A little bag to receive fluid at
the will of the insect, by which the weight of the wing
is increased. It is found also in the under-wings in
_Coleoptera_[1037].
β HAMUS (the _Hook_). A Hook fixed to the _Costal Nervure_, near
its base on the under-side, in the wings of some _Lepidoptera_,
in which the tendon runs[1038].
_b_ NEURA POSTCOSTALIS (the _Postcostal Nervure_). The second
principal, and often strongest, nervure of the wing[1039]. It
includes the _Neuræ Subcostales_.
α NEURÆ SUBCOSTALES (the _Subcostal Nervures_). Nervures
springing from the under-side of the postcostal nervure, or
from each other; called the _first_, _second_, _third_, &c. in
the order of their occurrence[1040].
_c_ NEURA MEDIASTINA (_Mediastinal Nervure_). A usually slender
nervure, springing from near the base of the postcostal;
between which and the costal it intervenes. In the _Lepidoptera
Diurna_, however, it is often a strong nervure[1041].
_d_ NEURA EXTERNO-MEDIA (the _Externo-medial Nervure_). The _third_
principal nervure of the wing[1042]. It includes the _Neura
Subexterno-media_.
α NEURA SUBEXTERNO-MEDIA (the _Subexterno-medial Nervure_).
A nervure that in some cases intervenes between the
externo-medial and interno-medial[1043].
_e_ NEURA INTERNO-MEDIA (_the Interno-medial Nervure_). The
_fourth_ principal nervure[1044]. It includes the _Neura
Subinterno-media_.
α NEURA SUBINTERNO-MEDIA (the _Subinterno-medial Nervure_). A
nervure that sometimes intervenes between the externo-medial
and the anal[1045].
_f_ NEURA ANALIS (the _Anal Nervure_). The principal nervure
nearest the interior or posterior margin, with which it
includes a space often subtriangular, traversed in most
_Diptera_ and many _Hymenoptera_ by another nervure; and in
many _Tegmina_ and _Hemelytra_ by several[1046]. In these kinds
of upper-wing it is in many cases accompanied by a fold; and
the part between it and the interior margin seems often capable
of separate motion.
_g_ NEURA AXILLARIS (the _Axillary Nervure_). The short nervure,
where there is only one, intervening between the anal nervure
and the interior margin; replaced in some _Muscidæ_ by a
spurious nervure[1047].
_h_ NEURÆ SPURIÆ (the _Spurious Nervures_). Very obsolete nervures,
sometimes found in addition to those usually occurring; as in
_Syrphus_[1048].
_E_ STIGMA (the _Stigma_). A corneous spot or plate, supposed to
contain fluid, in the anterior margin of the upper wings;
often produced by the conflux of the costal and postcostal
nervures[1049].
_F_ PARASTIGMA (the _Parastigma_). A corneous spot between the
costal and postcostal nervures, distinct from the _Stigma_
observable in the _Libellulina_.
_G_ LOBULI (_Lobuli_). One or more rounded portions of the base of
the wing, separated from the rest by fissures peculiar to the
_Muscidæ_, and the under-wings of some _Hymenoptera_[1050].
f TEGULÆ (the _Tegulæ_). Small corneous concavo-convex scales,
which in many Orders, particularly _Hymenoptera_, cover and
defend the base of the _Upper-Wings_[1051].
D SCUTELLUM (the _Scutellum_). A piece, usually triangular, which
follows the _Dorsolum_; and in _Coleoptera_ is often only a
continuation of it--placed between the base of the _Elytra_ or
upper-wings[1052].
E FRÆNUM (the _Frænum_). A piece that lies under the lateral
margin of the _Scutellum_ and _Dorsolum_, or is adjacent to it;
and which in many cases connects with the base of the upper
organs of flight, so as to prevent their dislocation, by being
pushed too far outwards[1053].
F PNYSTEGA (the _Pnystega_). A corneous scale or plate, which
covers certain pneumatic vessels, usually supported by the
_Scapularia_, in _Libellulina_, &c. becoming dorsal[1054].
2. MEDIPECTUS (the _Mid-breast_). The underside of the _first_
segment of the alitrunk[1055]. It includes the _Peristethium_,
_Scapularia_, _Mesosternum_, _Medifurca_, and _Pedes
Intermedii_.
A PERISTETHIUM (the _Peristethium_). The anterior piece of the
_Medipectus_, which intervenes between the _Brachia_ and
mid-legs[1056].
B SCAPULARIA (the _Scapulars_). Two pieces, one on each side the
_Medipectus_, which succeed the _Peristethium_, and lie between
the midlegs and the _Pteropega_ or wing-socket[1057]. It
includes the _Spiracula Scapularia_.
a. SPIRACULA SCAPULARIA (the _Scapular Spiracles_). Two spiracles
observable, one in each scapular, in _Acrida laurifolia_, &c.
C MESOSTERNUM (the _Mid-breastbone_). The elevated and central
part of the _Medipectus_, between the midlegs, often
terminating anteriorly in a mucro; sometimes, as in _Elater_,
in a cavity, receiving the mucro of the _Prosternum_[1058].
D MEDIFURCA (the _Medifurca_). A branching vertical process of
the _Endosternum_, which serves as the point of attachment to
the muscles that move the midlegs[1059].
E PEDES INTERMEDII (the _Mid-legs_). The intermediate pair of
legs, consisting of the same parts as the posterior legs[1060].
3. METATHORAX (the _Metathorax_). The posterior segment of
the _Alitruncus_[1061]. It includes the _Mesophragma_,
_Postdorsolum_, _Postscutellum_, _Postfrænum_, _Pleuræ_, and
_Metaphragma_.
a MESOPHRAGMA (the _Mesophragm_). A partition of a firm
consistence, connected by its posterior margin with the
_Postdorsolum_, and passing down vertically into the mid-chest;
serving as a point of attachment to several of the muscles
that move the wings[1062]. This, with the prophragm, forms the
anterior cavity of the alitrunk, and with the metaphragm it
forms the posterior cavity.
b POSTDORSOLUM (the _Postdorsolum_). The middle-piece between the
mesophragm and the _Postscutellum_. In _Coleoptera_ it consists
of a tense elastic membrane, which is quite covered by the
_Mesothorax_[1063].
c POSTSCUTELLUM (the _Postscutellum_). A narrow channel running
from the _Dorsolum_ to the _Abdomen_ in _Coleoptera_, forming
an isosceles triangle reversed. In other orders it is either a
triangular elevation of the middle of the posterior part of the
_Postdorsolum_, or a distinct triangular piece[1064].
d POSTFRÆNUM (the _Postfrænum_). In _Coleoptera_ the part of the
_Metathorax_ in which the _Postscutellum_ lies, at first nearly
horizontal, but posteriorly it takes a vertical direction
towards the abdomen. In general it may be defined, the part
that intervenes between the _Postscutellum_ and the _Abdomen_;
and which in many cases is connected with the posterior basal
margin of the under-wings, and prevents their being pushed too
far forwards[1065].
e PLEURÆ (the _Pleuræ_). The space behind the scapulars, on which
the lower organs of flight are fixed[1066]. They include the
_Alæ Inferiores_.
_A_ ALÆ INFERIORES (the _Under-wings_). The lower or secondary pair
of organs for flight[1067]. They include the _Commissura_,
_Tendo_, _Hamuli_, _Pterygium_, _Alula_, and _Halteres_.
_a_ COMMISSURA (the _Commissura_). A joint in the costal nervure
of the wings of _Coleoptera_, where they bend to take a
transverse fold[1068].
_b_ TENDO (the _Tendon_). A strong bristle, or bristles
observable at the base underneath in the under-wings of
many _Lepidoptera_, which plays in the _Hamus_ of the
upper-wings[1069].
_c_ HAMULI (the _Hooklets_). Very minute hooks in the middle of the
anterior margin, observable in some _Hymenoptera_, by which the
under-wing is fixed to the upper, to cause both to act as one
organ in flight[1070].
_d_ PTERYGIUM (the _Pterygium_). In under-wings this is a small
wing-like appendage, fixed at the base of the wing in some
_Lepidoptera_[1071].
_e_ ALULA (the _Winglet_). A small concavo-convex scarious
appendage, fixed behind the wings at their base, in many
_Diptera_[1072].
_f_ HALTERES (the _Poisers_). Small capitate processes or organs,
observable under the wings of _Diptera_, attended by a
spiracle[1073].
_B_ METAPNYSTEGA (the _Metapnystega_). A corneous scale or lamina
that covers the pneumatic organs in the _Metathorax_, situated
sometimes in the _Pleuræ_, as in the _Coleoptera_; at others in
the _Postfrænum_, as in _Tenthredo_ L.; and sometimes, as in
the _Libellulina_, between that part and the abdomen[1074].
_C_ METAPHRAGMA (the _Metaphragm_). A nearly vertical septum or
partition, attached behind to the _Postfrænum_, and usually
deeply cleft at its apex in _Coleoptera_, of a rather horny
consistence, which forms the upper separation of the second
cavity of the Alitrunk from that of the _Abdomen_[1075]. It
affords a point of attachment for many muscles of both alitrunk
and abdomen. It includes the _Septula_.
_a_ SEPTULA (the _Septula_). The lesser ridges and partitions
raised on the surfaces of the metaphragm, and on those of
other parts of the cavities of the trunk, serving as points of
attachment to various muscles[1076].
4. POSTPECTUS (the _Postpectus_). The underside of the _second_
segment of the alitrunk[1077]. It includes the _Mesostethium_,
_Parapleuræ_, _Metasternum_, _Postfurca_, _Opercula_, and
_Pedes Postici_.
A MESOSTETHIUM (the _Mesostethium_). A central piece between the
intermediate and posterior legs, and bounded laterally in
_Coleoptera_ by the _Parapleuræ_--along the middle of which,
where it exists, the _Metasternum_ runs[1078].
B PARAPLEURÆ (the _Parapleuræ_). Two pieces, one on each side
of the _Postpectus_, included between the _Scapularia_,
_Mesostethium_, and _Pleuræ_[1079]. They include the _Spiracula
Parapleuritica_.
a SPIRACULA PARAPLEURITICA (the _Parapleuritic Spiracles_). Two
spiracles, one in each of the _Parapleuræ_ of _Tetyra_[1080].
C METASTERNUM (the _Metasternum_). The central and often
elevated part of the _Mesostethium_. Its anterior mucro,
in _Coleoptera_, often meets the posterior one of the
_Mesosternum_, and sometimes appears to form one piece with it,
as in _Hydrophilus_, and many _Lamellicorn_ beetles. Sometimes,
as in _Cetonia vitticollis_, it even passes between the _arms_,
and covers the _Prosternum_, or supplies its place. Behind,
it often terminates in a bifid mucro. It is not present in
many Orders: as in the _Hymenoptera_, _Diptera_, &c.[1081] It
includes the _Pectines_.
a PECTINES (the _Pectines_). Two moveable processes, fixed one
on each side by its base below the posterior legs to the
_Metasternum_ in _Scorpio_: on the lower side is fixed a series
of parallel biarticulate processes, resembling the teeth of a
comb[1082].
D POSTFURCA (the _Postfurca_). A process of the _Endosternum_,
terminating in three subhorizontal acute branches,
resembling the letter Y, and forming an acute angle with the
_Endosternum_, to which the muscles that move the hind-legs,
&c. are affixed[1083].
E OPERCULA (the _Opercula_). Plates that cover the vocal
spiracles in humming insects; and likewise two large
cartilaginous plates fixed to the posterior part of the
_Postpectus_, which cover the _Tympana_ in male _Tettigonia_
F.[1084] Perhaps these may be regarded as a kind of
_Metapnystega_ in a new situation.
F PEDES POSTICI (the _Hind-legs_). The pair of legs affixed to
the postpectus[1085]. They include, the _Acetabulum_, _Coxa_,
_Trochanter_, _Femur_, _Tibia_, and _Tarsus_.
a ACETABULUM (the _Socket_). The socket in the _Postpectus_ in
which the leg is planted[1086]. It includes the _Pessella_.
_A_ PESSELLA (the _Pessella_). Two little acute processes,
fixed one in each, in the socket of the hind-legs in male
_Tettigoniæ_, which appear designed to keep down the
_Opercula_[1087].
b COXA (the _Hip_). The _first_ joint of the leg which plays in
the socket[1088].
c TROCHANTER (the _Trochanter_). The _second_ joint of the leg,
by which the thigh inosculates in the _Coxa_. It appears to
have no motion separate from that of the thigh. It is sometimes
biarticulate[1089].
d FEMUR (the _Thigh_). The _third_ joint of the leg, long and
usually compressed[1090]. It includes the _Gonytheca_.
_A_ GONYTHECA (the _Knee-pan_). A concavity at the apex of the
thigh, underneath, to receive the base of the _Tibia_[1091].
e TIBIA (the _Shank_). The _fourth_ joint of the leg, very long,
and usually triquetrous[1092]. It includes the _Epicnemis_,
_Molula_, _Talus_, _Calcaria_, and _Coronula_.
_A_ EPICNEMIS (the _Epicnemis_). An accessory joint at the base of
the _Tibia_ in many _Arachnida_, which does not appear to have
separate motion[1093].
_B_ MOLULA (the _Knee-ball_). The convex and sometimes bent head of
the _Tibia_, armed with a horny process on each side, by which
it is attached to the thigh[1094].
_C_ TALUS (the _Ankle_). The apex of the _Tibia_, where it is
united to the _Tarsus_[1095].
_D_ CALCARIA (the _Spurs_). One, two, or more _moveable_ spines,
inserted usually at the apex of the _Tibia_; and in many
_Carabi_ L., _Lepidoptera_ L., and _Trichoptera_ K., in
the middle also. They may be regarded as a kind of fingers
auxiliary to the _Tarsus_, and furnish often an important
character in the discrimination of genera[1096].
_E_ CORONULA (the _Coronula_). A coronet or semicoronet of _fixed_
spines observable at the apex of the posterior _Tibia_ in
_Fulgora candelaria_, &c.
f TARSUS (the _Tarsus_). The _fifth_ principal portion of the
legs; consisting in the majority of insects of 1-5 joints,
but in the _Phalangidæ_ of sometimes as many as 50[1097]. It
includes the _Planta_, _Digitus_, and _Solea_.
_A_ PLANTA (the _Instep_). The first joint of the _Tarsus_ is so
called when it is remarkably long and broad[1098]. It includes
the _Calx_.
_a_ CALX (the _Heel_). The curving part of the _Planta_, by which
it inosculates with the _Tibia_.
_B_ DIGITUS (the _Toe_). The remaining joints of the _Tarsus_ taken
together[1099]. It includes the _Allux_ and _Ungula_.
_a_ ALLUX (the _Toe-ball_). The last joint but one of the _Tarsus_,
when remarkable, as in Rhyncophorous beetles (_Curculio_
L.)[1100].
_b_ UNGULA (the _Claw-joint_). The last joint of the _Tarsus_,
which bears the claws[1101]. It includes the _Arthrium_,
_Unguiculi_, and _Plantula_.
α ARTHRIUM (the _Arthrium_). A very minute joint at the base of
the claw-joint, in most Tetramerous and Trimerous beetles[1102].
β UNGUICULI (the _Claws_). One or two pair of moveable incurved
claws, which usually arm the apex of the _Ungula_[1103].
γ PLANTULA (the _Plantula_). A minute accessory joint, sometimes
attached within the claws to the apex of the _Ungula_[1104].
Ex. The _Lucanidæ_. It includes the _Pseudonychia_.
* PSEUDONYCHIA (the _Spurious Claws_). Two stiff clawlike
bristles, that terminate the _Plantula_[1105].
_C_ SOLEA (the _Sole_). The underside of the _Tarsus_[1106]. It
includes the _Pulvilli_.
_a_ PULVILLI (the _Pulvilli_). Cushions of short hairs very closely
set; or of membrane, capable of being inflated, or very soft;
or concave plates, which cover the underside, or their apex,
of the four first joints of the _Manus_ or _Tarsus_, and
sometimes even of the ends of the _Calcaria_, as in _Cimbex_;
which act so as to produce a vacuum, and enable the animal to
suspend itself, or walk against gravity[1107]. Ex. _Timarcha_,
_Buprestis_, _Priocera_ K., the _Gryllina_, _Muscidæ_, &c.
III. ABDOMEN (the _Abdomen_).
The _Abdomen_ is the _third_ or posterior section of the body which
follows the _Truncus_[1108]. It includes the _Tergum_, _Venter_,
_Petiolus_, _Cauda_, and _Anus_.
i. TERGUM (the _Tergum_). The upper or supine surface of the
abdomen[1109]. It includes the _Segmenta Dorsalia_, and
_Pulmonaria_.
1. SEGMENTA DORSALIA (the _Dorsal Segments_). Transverse segments of
the back, the sides of which often lap over and cover those of
the ventral segments[1110].
2. PULMONARIA (the _Pulmonary Space_). Two longitudinal soft spaces,
capable of tension and relaxation, one on each side of the back
of the abdomen, in which, where they exist, the dorsal spiracles
are planted[1111]. They include the _Spiracula Dorsalia_.
a SPIRACULA DORSALIA (the _Dorsal Spiracles_). Lateral
breathing-pores observable in the dorsal segments, often covered
by the preceding segment[1112].
ii. VENTER (the _Belly_). The lower or prone part of
the abdomen[1113]. It includes the _Hypochondria_,
_Epigastrium_[1114], _Segmenta Ventralia_, and _Elastes_.
1. HYPOCHONDRIA (the _Hypochondria_). Two portions of segments, one
on each side; which in some genera[1115] (_Carabus_ L., &c.)
intervene between the first _intire_ ventral segment and the
posterior part of the _Postpectus_.
2. EPIGASTRIUM (the _Epigastrium_). The first intire ventral
segment[1116]. It includes the _Mucro_ and _Tympana_.
A MUCRO (the _Mucro_). The central posterior point of the
_Epigastrium_ observable in many of the Orders, which reposes
between the posterior legs; and, according to M. Chabrier, is
useful to the insect during flight[1117].
B TYMPANA (the _Drums_). Two deep cavities, containing a complex
machinery on each side of the _Epigastrium_ in male _Tettigoniæ_,
which are the instruments of sound[1118].
3. SEGMENTA VENTRALIA (the _Ventral Segments_). Transverse sections
of the belly[1119]. In Elytrophorous insects they are usually of
a firmer consistence than those of the back. They include the
_Spiracula Ventralia_.
A SPIRACULA VENTRALIA (the _Ventral Spiracles_).--Breathing-pores
observable in some genera in the intermediate ventral segments,
one on each side[1120]. Ex. _Dynastes Aloeus_, &c.
4. ELASTES (the _Elastes_). The elastic organs on the ventral
segments of _Machilis polypoda_ which assist this insect in
leaping.
iii. PETIOLUS (the _Footstalk_). A slender part by which the abdomen
of many _Hymenoptera_ is united to the trunk, in some genera
very long, in others very short, and in others wanting[1121]. It
includes the _Funiculus_, _Foramen_, _Squama_, and _Nodus_.
1. FUNICULUS (the _Funiculus_). A small cartilaginous _cord_,
passing through a minute orifice of the _Postfrænum_, just above
the point where the footstalk is fixed, to an opposite hole above
it, which enables the animal the better to elevate or drop the
abdomen[1122].
2. FORAMEN (the _Foramen_). The orifice in the abdomen, through
which the above cord passes[1123].
3. SQUAMA (the _Scale_). A vertical flat scale, observable on the
footstalk of the genus _Formica_, &c.[1124]
4. NODI (the _Knots_). One or more subrotund protuberances of the
footstalk in the genus _Myrmica_[1125].
iv. CAUDA (the _Tail_). Where the abdomen grows suddenly slenderer,
and terminates in a long jointed tail, as in _Scorpio_ and
_Panorpa_[1126]. It includes the Centris.
1. CENTRIS (the _Centris_). The last inflated joint of the tail,
terminating in the _Sting_.
v. ANUS (the _Anus_). The termination of the abdomen, consisting of
the two last segments. It includes the _Podex_, _Hypopygium_,
_Culus_, _Ovipositor_, and _Appendices_.
1. PODEX (the _Podex_). The last dorsal segment of the abdomen[1127].
2. HYPOPYGIUM (the _Hypopygium_). The last ventral segment of the
abdomen[1128].
3. CULUS (the _Culus_). The orifice at the end of the anus.
4. OVIPOSITOR (the _Ovipositor_). The instrument of oviposition,
by which the insect conducts the eggs to their appropriate
nidus, and often bores a way to it; the same instrument is by
some genera used as a weapon of offence, when it is called the
_Aculeus_[1129]. It includes the _Unci_, _Tubulus_, _Valvæ_,
_Vaginula_, and _Terebellæ_.
A UNCI (the _Unci_). Two pair of robust organs, the upper incurved
and the lower recurved, with which the anus of _Locusta_ Leach is
furnished[1130].
B TUBULUS (the _Tubulus_). A tubular ovipositor, consisting of
several pieces often retractile within each other, like the tubes
of a telescope[1131].
C VALVÆ (the _Valves_). Two lateral laminæ, often coriaceous, by
which the ovipositor when unemployed is covered[1132].
D VAGINULA (the _Sheath_). A corneous case, with two grooves, in
which the _Terebella_ or _Spicula_ play[1133].
E TEREBELLÆ (the _Terebellæ_). Instruments by which the insect
saws or bores a passage for its eggs to the place in which her
instinct directs her to deposit them[1134].
5. ACULEUS (the _Sting_). The above instrument, when fitted for an
offensive weapon[1135]. It includes, besides the _Valvæ_ and
_Vaginula_ before defined, the _Spicula_.
A SPICULA (the _Darts_). The proper stings which inflict the wound:
retractile within the sheath, externally serrulate at the
apex[1136]. They include the _Retinaculum_.
a RETINACULUM (the _Retinaculum_). A minute horny moveable scale or
plate with which the darts are furnished, which prevents their
dislocation by being shot forth too far[1137].
vi. APPENDICES (the _Appendages_). Other instruments and organs, with
which the anus of various insects is furnished. They include--the
_Forceps_, _Forfex_, _Furca_, _Styli_, _Foliola_, _Flosculus_,
_Caudulæ_, _Fila_, _Mammulæ_, _Papillæ_, and _Siphonuli_.
1. FORCEPS (the _Forceps_). A pair of anal organs that open and shut
transversely, and _meet_ at their inner margin, or at the apex.
Ex. _Forficula_.
2. FORFEX (the _Forfex_). A pair of anal organs, which open or shut
transversely, and _cross_ each other[1138]. Ex. Male of _Raphidia
Ophiopsis_.
3. FURCA (the _Fork_). An inflected elastic anal organ, ending in a
fork, by which the animal is enabled to leap[1139]. Ex. _Podura_.
4. STYLI (the _Styles_). Rigid, exarticulate, long and narrow anal
organs[1140]. Ex. _Staphylinus_.
5. FOLIOLA (the _Leaflets_). Rigid, exarticulate, dilated, leaf-like
anal organs[1141]. Ex. _Libellulina_.
6. FLOSCULUS (the _Floret_). A small, tubular, lunulate anal organ,
with a central style[1142]. _Fulgora candelaria_, &c.
7. CERCI (the _Cerci_). Two short, flattish, sublanceolate, jointed,
lateral anal organs[1143]. Ex. _Blatta_.--N.B. Analogous organs
are observable in the _Gryllina_, but usually conical and without
joints[1144]. In _Gryllus_ Latr. they are setiform[1145].
8. CAUDULÆ (the _Caudulæ_). Two or more slender, filiform or
setaceous, _jointed_, flexile anal organs[1146]. Ex. _Lepisma_,
_Machilis_, _Ephemera_.
9. FILA (the _Threads_). Two exarticulate, slender, filiform anal
organs[1147]. Ex. _Machilis_.
10. MAMMULÆ (the _Mammulæ_). Anal protuberances, containing
instruments for spinning web[1148]. Ex. _Araneidæ_. They include
the _Fusi_.
11. FUSI (the _Spinners_). Organs, consisting of two retractile
pieces, issuing from the _Mammulæ_, and rendering the
threads[1149].
12. SIPHONULI (the _Siphonets_). Truncated, fistular, setiform anal
organs, emitting a saccharine fluid[1150]. Ex. _Aphis_.
You will observe, that when the _whole upper-side_ of the _Truncus_
is spoken of, it is called the _Thorax_; and as in _Coleoptera_,
and some other Orders, the whole of the _Mesothorax_ except the
_Scutellum_ is covered by the _Thorax_, and the whole of the
_Metathorax_ by the _Mesothorax_ and _Elytra_--the _Thoracic shield_,
may without danger of mistake be denominated the _Thorax_, as it has
always been. When the _whole under-side_ of the _Trunk_ is spoken of,
it is called the _Pectus_. When the _three Sternums_ are spoken of
together, they may be called the _Sternum_; and the _whole interior
elevation_ of the _Pectus_ may be called the _Endosternum_.
FOOTNOTES:
[903] Lamarck _Hist. Nat. des Anim. sans Vertèbr._ i. 311, 214.
[904] _Ibid._ 162. Compare the _Systême des Anim. sans Vertèbr._ of
the same author, p. 12--.
[905] The doctrine of Epicurus--that the Deity concerns not himself
with the affairs of the world or its inhabitants, which, as Cicero
has judiciously observed (_De Nat. Deor._ 1. 1. ad calcem), while it
acknowledges a God in _words_, denies him in _reality_; has furnished
the original stock upon which most of these bitter fruits of modern
infidelity are grafted. Nature, in the eyes of a large proportion of
the enemies of Revelation, occupies the place and does the work of
its Great Author. Thus Hume, when he writes against miracles, appears
to think that the Deity has delegated some or all of his powers to
nature, and will not interfere with that trust. _Essays_, ii. 75--.
And to name no more, Lamarck, treading in some measure in the steps
of Robinet (who supposes that all the links of the animal kingdom,
in which nature gradually ascends from low to high, were experiments
in her progress towards her great and ultimate aim--the formation of
man. Barclay _On Organization_, &c. 263), thus states his opinion:
"La nature, dans toutes ses opérations, ne pouvant procéder que
graduellement, n'a pu produire tous les animaux à-la-fois: elle n'a
d'abord formé que les plus simples; et passant de ceux-ci jusques
aux plus composés, elle a établi successivement en eux différens
systêmes d'organes particuliers, les a multipliés, en a augmenté de
plus en plus l'énergie, et, les cumulant dans les plus parfaits,
elle a fait exister tous les animaux connus avec l'organisation et
les facultés que nous leur observons." (_Anim. sans Vertèbr._ i.
123.) Thus denying to the Creator the glory of forming those works
of creation, the animal and vegetable kingdom (for he assigns to
both the same origin, _Ibid._ 83), in which his glorious attributes
are most conspicuously manifested; and ascribing them to nature, or
_a certain order of things_, as he defines it (214)--a blind power,
that operates necessarily (311); which he admits, however, to be the
product of the will of the Supreme Being (216). It is remarkable,
that in his earlier works, in which he broaches a similar opinion,
we find no mention of a Supreme Being. (See his _Systême des Animaux
sans Vertèbres_, Discours d'Ouverture.) Thus we may say that, like
his forerunner Epicurus, _Re tollit_, dum _oratione relinquit Deum._
But though he ascribes all to _nature_; yet as the _immediate_ cause
of all the animal forms, he refers to the local circumstances, wants,
and habits of individual animals themselves; these he regards as the
modifiers of their organization and structure (162). To show the
absurd nonplus to which this his favourite theory has reduced him,
it will only be necessary to mention the individual instances which
in different works he adduces to exemplify it. In his _Systême_,
he supposes that the web-footed birds (_Anseres_) acquired their
natatory feet by frequently separating their toes as far as possible
from each other in their efforts to swim. Thus the skin that unites
these toes at their base contracted a habit of stretching itself; and
thus in time the web-foot of the duck and the goose were produced.
The waders (_Grallæ_), which, in order to procure their food, must
_stand_ in the water, but do not love to _swim_, from their constant
efforts to keep their bodies from submersion, were in the habit of
always stretching their legs with this view, till they grew long
enough to save them the trouble!!! (13--). How the poor birds escaped
drowning before they had got their web feet and long legs, the author
does not inform us. In another work, which I have not now by me,
I recollect he attributes the long neck of the camelopard to its
efforts to reach the boughs of the mimosa, which, after the lapse of
a few thousand years, it at length accomplished!!! In his last work,
he selects as an example one of the _Molluscæ_, which, as it moved
along, felt an inclination to explore by means of _touch_ the bodies
in its path: for this purpose it caused the nervous and other fluids
to move in masses successively to certain points of its head, and
thus in process of time it acquired its horns or tentacula!! _Anim.
sans Vertèbr._ i. 188. It is grievous that this eminent zoologist,
who in other respects stands at the head of his science, should
patronize notions so confessedly absurd and childish.
[906] Lyonnet _Traité_, &c. Pref. xxii. Want of due encouragement, it
is to be feared, caused the abortion of these valuable treatises. The
MSS. are, I believe, still in existence. It would probably answer now
to publish them.
[907] See above, p. 52--.
[908] See above, p. 43--.
[909] There are certain processes which are a continuation of the
internal surface of the crust; and serve, as well as the rest of it,
for points of attachment to the muscles: these, though completely
internal, must be considered as parts of the external skeleton.
[910] See above, p. 28--.
[911] The crust which covers the body of insects is lined internally
with a kind of fibrous cuticle. _Query_, Whether in any degree
analogous to the _Periosteum_ of Vertebrate animals?
[912] We employ this term instead of _Instrumenta Cibaria_ F., to
avoid circumlocution.
[913] PLATES VI. VII. &c. a´, and XXVI. FIG. 30-33.
[914] Ibid. FIG. 30. _Mon. Ap. Angl._ i. 139. _Melitta_ **. b. _t._
ii. _f._ 4, 5.
[915] PLATES VI. VII. &c. and XXVI. FIG. 23-29. b´.
[916] PLATES VI. and VII. a´´, and XXVI. FIG. 34, 35.
The part in this work regarded as the _mentum_, does not in all
cases accord with what MM. Latreille, Savigny, &c. have regarded as
entitled to that denomination. Thus in _Hymenoptera_, their _Mentum_
is what we term the _Labium_, while our _Mentum_ is the small piece
upon which that part sits (PLATE VII. FIG. 3. a´´). This is called
the _Fulcrum_ in _Mon. Ap. Angl._ (See i. Explan. of the Plates.) Our
Mentum may generally be known by its situation between the hinges and
base of the _Maxillæ_.
[917] PLATES VI., VII., and XXVI. b´´.
[918] Ibid.
[919] PLATE XIII. FIG. 7. c´´.
[920] Marcel de Serres _Comparaison des Organes de la Mastication des
Orthoptères._ 7. _Ann. du Mus._ 11.
[921] PLATE VI. FIG. 6. c´, a´´´. and XIII. FIG. 5. a´´´.
[922] PLATE VI. FIG. 12. b´´´. and XIII. FIG. 5. b´´´.
[923] PLATE XXVI. FIG. 16. c´´´.
[924] Ibid. FIG. 20. d´´´.
[925] Cuv. _Anat. Comp._ iii. 322--.
[926] PLATES VI. VII. d´. and XXVI. FIG. 9-15.
[927] Ibid. c´´.
[928] Ibid. f´´.
[929] Ibid. and XXVI. FIG. 13-15.
[930] PLATE VI. FIG. 3. d´´´.
[931] PLATE XXVI. FIG. 11. d´´´.
[932] PLATE VI. FIG. 6, 12. d´´´.
[933] Ibid. FIG. 3, 6, 12. and XXVI. FIG. 9, 10. e´´´.
[934] Ibid. VI. FIG. 3, 12. f´´´.
[935] PLATES VI. VII. h´´. XIII. FIG. 1-4, 8. h´´. and XXVI. FIG. 1-8.
[936] PLATE VI. FIG. 6, 12. e´.
[937] PLATE XXVI. FIG. 26, 29. e´.
[938] PLATE VII. FIG. 2, 3, e´.--What is here called the _Lingua_ in
_Hymenoptera_ has been usually regarded as the _Labium_; but surely
that organ which collects, and as it were _laps_ the honey, and passes
it down to the _Pharynx_, is properly to be considered as the tongue.
The _Labium_ itself appears to be represented by what has been called
the _Mentum_, and the true _Mentum_, as was lately observed, is at the
base of the part last mentioned, in the usual situation of that piece.
This, though long since noticed (Kirby _Mon. Ap. Angl._ i. 103--), has
not been much attended to by modern entomologists.
[939] Huber _Fourmis_, 4--.
[940] PLATE VII. FIG. 2, 3. and XXVI. FIG. 28. i´´.
[941] PLATE VII. FIG. 14. f´.
[942] Ibid. FIG. 2. k´´. This is M. Savigny's name for this part. It
has also been called _Epiglossa_. Latreille _Organisation Extérieure
des Insectes_, 185.
[943] Vide Savigny _Mém. sur les Anim. sans Vertèbr._ I. i. 12--.
[944] The majority of Hymenopterous insects, though they have the
ordinary _Trophi_, are not _masticators_, using their _mandibulæ_
only for purposes connected with their economy.
[945] See his _Mémoires sur les Animaux sans Vertèbres_, I. i.
[946] I have used this word here and on a former occasion (see above,
p. 29), perhaps not with strict propriety, in the sense of the French
word _remplacer_, for which we seem to have no single corresponding
word in our language.
[947] PLATE VI. FIG. 7-9.
[948] PLATE VI. FIG. 7, 9. b´.
[949] Ibid. c´.
[950] Ibid. d´.
[951] Ibid. VII. FIG. 5, 6.
[952] Ibid. b´.
[953] Ibid. FIG. 6. b´.
[954] Ibid. _a._ The _Labella_ have been usually thought confined,
or nearly so, to the genus _Musca_ L.; but they may be traced in all
genuine _Diptera_, i. e. excluding _Hippobosca_ L.
[955] PLATE VII. FIG. 5. a´, c´, d´.
[956] PLATE VII. FIG. 5, 6. a´.
[957] Ibid. c´.
[958] Ibid. d´. It has not yet been satisfactorily ascertained,
whether _all_ the ordinary Trophi are represented in every Dipterous
mouth, the number of the lancets seeming in some cases to vary.
[959] PLATE VI. FIG. 13.
[960] Ibid. _a._
[961] Ibid. _b._
[962] Ibid. Labrum a´; Mandibulæ c´; Maxillary Palpus h´´.
[963] PLATE VII. FIG. 8.
[964] Ibid. c´.
[965] Ibid. d´. Maxillary Palpi h´´.
[966] Ibid. e´.
[967] PLATE VII. FIG. 11, 13. _f_´.
[968] Ibid. FIG. 11. _d_´.
[969] See above, p. 18, &c.
[970] PLATE VI. FIG. 10. c´.
[971] PLATE VI. FIG. 1, 4, 10. â.
[972] Ibid. a.
[973] Ibid. g´.
[974] PLATE VI. c.
[975] Ibid. d.
[976] Ibid. e.
[977] Ibid. f.
[978] Ibid. g.
[979] PLATES VI. VII. and XXVI. h.
[980] PLATE VI. FIG. 1. and VII. FIG. 2. h´.
[981] PLATE VI. FIG. 4, 10. VII. FIG. 1, 2, 4. and XXVI. FIG. 39-41. i.
[982] PLATES XI. XII. and XXV.
[983] PLATE VI. FIG. 1, 2. and VII. FIG. 1. i´.
[984] Ibid. XII. FIG. 6. 9. k´.
[985] Ibid. l´´.
[986] Ibid. l.
[987] Ibid. FIG. 6. m´.
[988] Ibid. FIG. 6, 8-10. m´´.
[989] PLATE VI. FIG. 2, 8. ê.
[990] PLATE VII. FIG. 2. l. _Mon. Ap. Angl._ i. _t._ xiii. _f._ 1.
_a_, _e_.
[991] PLATE VI. FIG. 2. m.
[992] Ibid. î.
[993] Ibid. n.
[994] PLATE XXVII. FIG. 1, 3, 4. n.
[995] PLATE VI. FIG. 2. o.
[996] PLATE IX. FIG. 7, 10, 11, &c. and XVI. FIG. 4, 8. B.
[997] M. Chabrier, in his admirable _Mémoires sur le Vol des Insectes_.
uses the term _Tronc Alifère_, which suggested the terms here employed.
[998] PLATE IX. FIG. 3, 12, 16, &c.
[999] Ibid. FIG. 1, 2, 10, 11, &c.
[1000] Ibid. FIG. 2. a´.
[1001] Ibid. IX. FIG. 4.
[1002] Ibid. VIII. FIG. 3, 11.
[1003] PLATE XXIX. FIG. 12. _c´_.
[1004] PLATE VIII. FIG. 2, 11. _d´_.
[1005] PLATE XXII. FIG. 7. _e´_.
[1006] M. Latreille, in his _Organisation Extérieure des Insectes_
(_Mem. du Mus._ viii. 198.) proposes calling the fore-legs of
Hexapods _Propedes_; but having long ago applied this term to the
false legs of caterpillars (see above, VOL. II. p. 288. &c.), we
shall not adopt it.
[1007] PLATE XXVII. FIG. 36. _a´_.
[1008] PLATE XV. FIG. 6-9.
[1009] PLATE XXVII. FIG. 59. a.
[1010] PLATE VIII. FIG. 3, 4, 12-14, 16, 17. IX. FIG. 1, 3, 7, 8,
10-12, 15.
[1011] Ibid. _c._
[1012] PLATE IX. FIG. 7, 11, 12, 15, 19. _g´._ The _Collare_
of _Hymenoptera_ and _Diptera_ has usually been regarded as
representing the _Prothorax_ of _Coleoptera_, _Orthoptera_, &c.
But this difference obtains between them--the latter evidently
belongs to the _Manitrunk_, and its muscles do not appertain at
all to the _Alitrunk_; whereas the _Collare_ as evidently is a
part of the latter, its muscles belong to it, and its functions in
assisting in flight are important. These reasons, and others we
shall state hereafter, induced us long ago to consider this part
as not representing the _Prothorax_; and they seem to have induced
M. Chabrier almost to adopt a similar opinion. _Sur le Vol des
Insectes._ _Ann. du Mus._ 3eme Ann. 414. et 4eme Ann. 54--.
[1013] PLATE XXII. FIG. 8, 11. _h´._
[1014] Ibid. FIG. 8. PLATE VIII. FIG. 3, 12, 14, 16. IX. FIG. 1, 7,
8, 10-12, 15, 19, 21. _i´._
[1015] PLATE VIII. FIG. 14, 20. IX. FIG. 11, 12. and XXII. FIG. 8.
_b´´._
[1016] PLATE X. FIG. 1.; and XXVIII. FIG. 1-8, 10.
[1017] PLATE XXVIII. FIG. 3-5. _b´´´._
[1018] PLATE X. FIG. 1. _c´´´._
[1019] PLATE XXVIII. FIG. 6-8. _d´´´._
[1020] PLATE XXIII. FIG. 6. _e´´´._
[1021] PLATE XXVIII. FIG. 2. _a´´´._
[1022] Ibid. FIG. 19. and PLATE X. FIG. 2.
[1023] The upper organs of flight of many of the _homopterous_
section of the _Hemiptera_ seem altogether membranous, and may almost
be included under the term _Alæ Superiores_.
[1024] PLATE X. FIG. 3.
[1025] Ibid. _f´´´._
[1026] PLATE X. FIG. 3. _g´´´._
[1027] Ibid. FIG. 5-9, 11-15. and PLATE XXVIII. FIG. 18.
[1028] Ibid. _h´´´._
[1029] N.B. In the Plate the _Costal Area_ is _red_, the
_Intermediate white_, and the _Anal yellow_. When the _Hemelytra_
are considered as divided into _Areas_, the _Membrana_ might be
denominated the _Apical Area_.
[1030] PLATE X. FIG. 2, 3, _b^.._
[1031] Ibid. _c^.._
[1032] PLATE X. FIG. 2, 3. _d^.._
[1033] Ibid. FIG. 7-15. _e^.._
[1034] Ibid. _f^.._
[1035] Ibid. _g^.._
[1036] Ibid. _h^.._
[1037] Chabrier _Sur le Vol des Insectes_, _Ann. du Mus._ 3eme ann.
428, 4eme ann. 325--. 3d Cahier 78.
[1038] _Linn. Trans._ i. _t._ xiii. _f._ 2. 3. _d._
[1039] PLATE X. FIG. 5-15. _i^.._
[1040] Ibid. _a*._
[1041] Ibid. FIG. 6. _k^.._
[1042] Ibid. _l^.._
[1043] Ibid. FIG. 5, 6, 13. _b*._
[1044] Ibid. FIG. 5-15. _m^.._
[1045] Ibid. FIG. 5, 6, 13. _c*._
[1046] PLATE X. FIG. 5-15. _n^.._
[1047] Ibid. _o^.._
[1048] Ibid. FIG. 14. _p^.._
[1049] Ibid. FIG. 11. _m´´´._
[1050] Ibid. FIG. 14, 15. _n´´´._
[1051] PLATE IX. FIG. 5, 11. _g´´._
[1052] PLATES VIII. IX. XXVIII. _k´._
[1053] Ibid. _l´._
[1054] PLATE IX. FIG. 7. _m´._
[1055] PLATE VIII. FIG. 4, 13, 17.; and IX. FIG. 3, 8, 12. _d._
[1056] Ibid. _n´._
[1057] PLATES VIII. IX. _o´._
[1058] PLATE VIII. FIG. 4, 8, 13, 17. _p´._
[1059] PLATE XXII. FIG. 6. _q´._
[1060] PLATE XVI. FIG. 4-6. _r´._
[1061] PLATE VIII. FIG. 3, 12.; and IX. FIG. 1, 7, 10, 11, 12, 15. _c._
[1062] PLATE XXII. FIG. 9, 11. _s´._
[1063] PLATE VIII. FIG. 3, 12, 20. and IX. FIG. 7, 10-12, 15, 20. _t´._
[1064] Ibid. _u._
[1065] PLATES VIII. IX. XXVIII. _v´._
[1066] PLATES VIII. and IX. _w´._
[1067] PLATE X. FIG. 4, 10.
[1068] PLATE X. FIG. 4. _o´´´._
[1069] _Linn. Trans._ i. _t._ xiii. _f._ 1. _b._ 3. _a._
[1070] Kirby _Mon. Ap. Angl._ i. _t._ xiii. _f._ 19.
[1071] De Geer ii. _t._ ix. _f._ 9. _d._
[1072] Ibid. vi. _t._ ii. _f._ 23. _a a._
[1073] PLATE IX. FIG. 19. _p´´´._
[1074] Ibid. FIG. 7. and PLATE XXII. FIG. 14. _k´´._
[1075] PLATE XXII. FIG. 10, 11. _x´._
[1076] Ibid. FIG. 9-11. _l´´._
[1077] PLATES VIII. and IX. _f._
[1078] Ibid. _y´._
[1079] Ibid. _z´._
[1080] PLATE XXIX. FIG. 15. _m´´._
[1081] PLATES VIII. IX. _a_†.
[1082] PLATE XXVII. FIG. 50.
[1083] PLATE XXII. FIG. 3. _b_†.
[1084] PLATE VIII. FIG. 18; and XXII. FIG. 13. _c_†.
[1085] PLATE XIV. FIG. 5-8.
[1086] PLATE VIII. FIG. 2, 4, 11, 13, &c. _o´´._
[1087] Ibid. FIG. 18. _q´´´._
[1088] PLATE XIV. FIG. 6-8; and XXVII. FIG. 12. _p´´._
[1089] Ibid. _q´´._
[1090] PLATE XIV. FIG. 5-8; and XXVII. FIG. 6-8. _r´´._
[1091] PLATE XXVII. FIG. 7, 8, 15. _r´´´._
[1092] PLATE XIV. FIG. 5-8. _s´´._
[1093] PLATE XXVII. FIG. 21. _s´´´._
[1094] Ibid. FIG. 9, 10, 16, 17. _t´´´._
[1095] Ibid. FIG. 34-36. _u´´´._
[1096] PLATE XIV. FIG. 6; and XXVII. FIG. 29-36. _v´´´._
[1097] PLATE XIV. FIG. 5-8; and XXVII. FIG. 44, 45, 62, 63. _t´´._
[1098] PLATE XXVII. FIG. 25, 26, 41. _w´´´._
[1099] PLATE XXVII. FIG. 25, 26. _x´´´._
[1100] PLATE XXVI. FIG. 47, 48; and XXVII. FIG. 43. _r^.._
[1101] Ibid. _s^.._
[1102] PLATE XXVI. FIG. 47, 48. _d*._
[1103] PLATE XXVII. FIG. 37-57. _e*._
[1104] Ibid. FIG. 56, 57. _f*._
[1105] Ibid. FIG. 56. _a_ ψ.
[1106] Ibid. FIG. 59. _y´´´._
[1107] PLATE XV. FIG. 9; and XXVII. FIG. 35, 59-61. _t^.._
[1108] PLATE VIII. FIG. 5, 6, 9, 15, 18, 19.
[1109] Ibid. FIG. 5, 15. _A._
[1110] Ibid. _A´._
[1111] Ibid. FIG. 5, 9. _B´._
[1112] Ibid. FIG. 5, 9, 15. _A´´._
[1113] PLATE VIII. FIG. 6, 9, 15. _B._
[1114] The scientific reader must recollect that these terms
are employed, not because these parts are thought to be true
representatives of the _Epigastrium_ and _Hypochondria_ of vertebrate
animals, but merely on account of some analogy between them.
[1115] PLATE VIII. FIG. 6. _C´._
[1116] Ibid. _D´._
[1117] Ibid. _B´´._
[1118] Ibid. FIG. 18, 19. _C´´._
[1119] Ibid. FIG. 6, 9, 15. _E´._
[1120] PLATE VIII. FIG. 9. _D´._
[1121] PLATE IX. FIG. 17, 18. _C._
[1122] Ibid. FIG. 13. _F´._
[1123] Ibid. _G´._
[1124] Ibid. FIG. 17. _H´._
[1125] Ibid. FIG. 18. _I´._
[1126] PLATE XV. FIG. 12. _D._
[1127] PLATE VIII. FIG. 5, 15. _K´._
[1128] Ibid. FIG. 6, 15, 18. _L´._
[1129] PLATE XV. FIG. 18-22; and XVI. FIG. 1-3.
[1130] PLATE XV. FIG. 18. _E´._
[1131] PLATE XV. FIG. 22; and XVI. FIG. 2, 3.
[1132] Ibid. FIG. 20, 21; and XVI. FIG. 1. _F´´._
[1133] PLATE XV. FIG. 20. _G´´._
[1134] Ibid. FIG. 20, 21; and XVI. FIG. 1. _II´´._
[1135] Kirby _Mon. Ap. Angl._ i. _t._ xii. _Apis_ **. e. 1. _neut.
f._ 23-25; and _t._ xiii. _f._ 27, 28.
[1136] _Ibid._ _t._ xiii. _f._ 30, 31.
[1137] _Ibid._ _a._
[1138] PLATE XV. FIG. 12. _L´´._
[1139] PLATE XV. FIG. 14. _M´´._
[1140] Ibid. FIG. 17. _N´´._
[1141] Ibid. FIG. 15. _O´´._
[1142] Ibid. FIG. 13. _P´´._
[1143] Ibid. FIG. 23. _Q´´._
[1144] De Geer iii. _t._ xxii. _f._ 10. _a a._
[1145] Ibid. _t._ xxiv. _f._ 2. _c_; and _f._ 11.
[1146] PLATE XV. FIG. 16. _R´´._
[1147] Ibid. _S´´._
[1148] Ibid. FIG. 10; and PLATE XXIII. FIG. 16, 17. _T^*´´._
[1149] Ibid. FIG. 12. _B´´´._ 15.
[1150] De Geer _ubi supr._ _t._ iii. _f._ 5, 20, 21. _c._
LETTER XXXIV.
EXTERNAL ANATOMY OF INSECTS.
THE HEAD, AND ITS PARTS.
Before I confine my observations to the _head_ of insects, which I
propose to consider separately in the present letter, I must premise
a few words upon their _body_ in general, or rather its _crust_, or
external integument. In this we may notice its _substance_, general
_form_, _sculpture_, _pubescence_, and _composition_.
i. I have already noticed the _substance_ of this integument in
the preparatory states of insects[1151]; I shall not, therefore,
here repeat what I then said, but restrict myself chiefly to the
consideration of it as it is found in their _last_ state, in which
it is usually firmer than in their previous stages of existence. In
this respect, however, it varies much in the different Orders, and
even in the different genera of the same Order. In some Coleopterous
insects, for instance, it is very hard, and difficult to perforate;
while in others it is soft, flexible, and a pin easily passes through
it[1152]. And in general, from a substance in hardness resembling
horn or shell, it passes through the intermediate degrees of that of
leather and parchment, almost to a thin membrane. Yet in all cases
there is enough of rigidity and hardness to answer the principal uses
of a skeleton--to afford, namely, a sufficient point of attachment
for the muscles, and to support and defend the interior organization;
so that the play and action of the vital and secretory systems may
not be interrupted or impeded.
With respect to the principles which enter into the composition
of this integument, very little seems to be known at present; but
few insects having been submitted to a chemical analysis. The
blister-beetle (_Cantharis vesicatoria_), from its importance in
medicine, has, however, been more than once analysed; and though the
products have not been very precisely stated, yet we find amongst
them phosphate of lime, albumen, and some other usual components
of the substance of vertebrate animals[1153]. But which of these
products belong to the integument, and which to its contents, cannot
be ascertained, without a separate process for each; which would
not, I conceive, be very feasible. The substance, however, of the
integument of insects, though we know not its precise contents,
which probably vary in different genera, &c., appears not to be
exactly of the nature of any of those substances after which it
has usually been denominated: it is not properly analogous either
to real _horn_, _shell_, _skin_, or _leather_, &c. This seems to
result from the following circumstance:--Most of the excretions of
vertebrate animals, as horn, skin (at least when tanned), feathers,
wool, hair, &c. when exposed to the action of fire liquify, more or
less, before they incinerate; emitting at the same time a peculiar
and disagreeable scent: but upon applying this test to the parts of
insects of the different Orders, I found, in every instance, that
incineration took place without liquefaction, and was unaccompanied
by that peculiar scent which distinguishes the others. Even the
_claws_, which to the eye appear, as to their substance, exactly
like those of _Mammalia_, birds, &c. burn without melting, and
retain their form after red heat. That the insect integument is
not _calcareous_ like that of the _Crustacea_, and the shells of
_Molluscæ_, you may easily satisfy yourself, by immersing them in
an acid test. I made this experiment upon portions of insects of
several of the Orders, in an equal mixture of muriatic acid and
water, and the result was, not only that all hexapods, but octopods,
_Arachnida_, and even _Scolopendridæ_, upon immersion only emitted
a few air-bubbles; while, when the other myriapods, _Polydesmus_,
_Iulus_, _Glomeris_, &c. and the _Oniscidæ_, were immersed, a
violent effervescence took place; proving the different nature of
their substance. It is remarkable that the two great branches of
the _Myriapods_, the _Scolopendridæ_ and _Iulidæ_ (_Chilopoda_ and
_Chilognatha_ Latr.), should in this respect be so differently
circumstanced--the latter having a calcareous integument, and the
former not.--A further difference distinguishes these two tribes:
_old_ specimens of the _Iulidæ_ usually lose their colour and turn
white, like _Oniscidæ_; while those of the _Scolopendridæ_ retain it.
ii. The _form_ of insects is so variable, that it can be reduced to
no other general rules--than that, for the most part, the length
exceeds the breadth, and the breadth the depth, and that the upper
surface is usually convex. But to these rules there are numerous
exceptions. Thus many _Tetyræ_ F. (_Scutellera_ Latr.), a kind of
bug, are as broad as they are long[1154]; in the genus _Gonyleptes_
K.[1155] amongst the _Aptera_, and _Epeira cancriformis_, a
crab-shaped spider, the breadth exceeds the length; in _Cynips_, and
several other _Hymenoptera_, in _Acrida_ K.[1156] (_Locusta_ F.), and
other Orthopterous insects, the depth exceeds the breadth; and in
that singular beetle, _Eurychora_; the cockroach (_Blatta_), &c. the
upper surface is flat.
iii. The _sculpture_ of the integument of insects is often very
remarkable; but as this will call for attention hereafter, I shall
only here observe in general, that ornament and variety seem not to
be the sole object of those elevations and depressions which form so
prominent a feature of many of the animals in question; for by means
of these, many important purposes, that at first sight do not strike
the observer, may be served: such as giving firmness to the crust
in those places where it is most wanted; diminishing its powers of
resistance in others, so that it may yield somewhat to the action of
the muscles; increasing or deducting from the weight of the body,
so as to produce a proper equipoise during its motions, whether on
the earth, in the air, or in the water. The depressions of the outer
surface of the crust, in many instances, produce an elevation of
it in the interior, and so afford a useful point of attachment to
certain muscles. This observation seems more especially applicable
to those excavations that are common to particular tribes or genera:
thus the dorsal longitudinal channel to be met with on the prothorax
of most of the _Carabi_ of Linné on the inside of the crust have a
corresponding ridge. In _Locusta Dux_, also, (a Brazil locust,) the
same part has _four_ transverse channels, corresponding with which
on the inside are as many _septa_, or ridges, to which muscles are
attached; and those larger impressed puncta denominated _puncta
ordinaria_, which distinguish the same part in _Geotrupes_ and many
of the _Scarabæidæ_, within are elevated, so as to form a kind of
ginglymous articulation with the base of the anterior coxæ. The
other impressed puncta so often to be seen on the different parts
of various insects, which sometimes so intirely cover the surface
that scarcely any interval is discoverable between them, though in
many cases they appear to be mere impressions that attenuate but
do not perforate the crust--yet in others, perhaps equally or more
numerous, they are real _pores_, which pass through the integument.
If, for instance, you take the thoracic shield of the cockchafer
(_Melolontha vulgaris_), and after removing the muscle &c., hold it
against the light, with the inner side towards the eye, you will see
the light through every puncture: or take the elytra of _Geotrupes
stercorarius_, or any common beetle in which these organs have
punctate striæ, and examine them under a lens on the inside, and you
will see distinctly that the punctures pass through the elytrum, and
the membrane that lines it[1157]. It is not improbable that in the
case last mentioned these pores may be of use, as the spiracles are
usually closely covered by the elytra, for the better transmission of
the air to those respiratory organs. Whether the pores in the other
parts of the body are for transpiration, is more than I shall venture
to affirm; but as insects sometimes perspire, at least this has been
ascertained with respect to the hive-bee[1158], this must be by the
means of some pores.
iv. The integument of insects is often clothed, either partially or
generally, with _pubescence_, or hairs of various kinds--a circumstance
which seems to have more than one object. In _Parnus_, _Heterocerus_,
_Gerris_, _Argyroneta aquatica_, and some other aquatic insects, the
end in view seems to be to keep the water from wetting the crust; and
in this case the covering of hairs is dense, silky, and decumbent.
Another object is preventing friction from being injurious: thus
humble-bees, that from their mode of nidification[1159], are usually
more particularly exposed to it, are well clothed with hair; and in
those articulations of insects where much friction takes place, we may
often observe a dense fringe or coating of the same substance. This
you may see in the common stag-beetle (_Lucanus Cervus_), where the
thorax receives the head; and very remarkably at the same point in the
Hercules-beetle (_Dynastes Hercules_ MacLeay): but besides these uses,
there is probably one more universal, which will apply as well to those
thinly scattered bristles and hairs, here and there one, to be noticed
in many insects: but concerning this I can only throw out a conjecture,
as I do not recollect ever to have seen any experiments with regard to
this use of animal hairs. But may they not act as conductors, either to
introduce some invisible fluid into the body in a positive state, or to
convey it out, when received by other means, in a negative state? Every
one knows that the fur of a cat has electric properties, and there may
be an important general use of this kind attached to the fur and hairs
of animals[1160]. But, as I said, I give this as a mere conjecture;
and only wish it may excite your attention to the subject, and put in
exercise your natural tact for experiment.
M. Cuvier regards the hairs of insects as merely a continuation of
the epidermis, with which they fall when the animal changes its
skin[1161]; but this will apply only to the hairs of larvæ: for the
hairs of perfect insects in many cases are implanted in a pore, and
pass through epidermis or crust to the membrane that lines it, in
which they terminate.
v. We are now to consider the _composition_ of the integument; under
which term I would include the different layers of which it consists,
and its articulation.
1. With respect to the _first_ of these circumstances, the
_layers_ of which the integument consists, it seems to exhibit
some, although not an exact, analogy with the _skin_, rather than
the _skeleton_, of the vertebrate animals[1162]. In these last, the
skin is stated to consist of _four_ layers. Of these the exterior
one is the _epidermis_, or scarf-skin: under this is the _rete
mucosum_, or mucous tissue, which gives its colour to the skin; next
follows the _papillary tissue_ formed by the extremities of the
nerves, and in which the sense of _touch_ principally resides; the
last and innermost layer is the _skin proper_, or leather, called
_Dermis_, _Derma_, or _Corium_[1163]. _Two_ of these layers M.
Cuvier assigns to insects. They have, he observes, in every state,
a true _epidermis_[1164]; and in their state of larva he finds
that the infinite variety of colours that so adorn many of them is
produced by a mucous substance observable between the epidermis
and the muscles[1165]: this seems analogous to the _rete mucosum_.
To this, dried and mixed with their horny substance, he attributes
also the colours of the perfect insect: "for," says he, "when the
_Lepidoptera_ are in the chrysalis, the little coloured scales
which are to ornament their wings, are then in a state of mucosity
similar to that which is found under the skin of the caterpillar.
The colours of the _Arachnida_," he goes on, "are also due to this
mucosity: it is discoverable under the skin, and has the appearance
of minute glandular points of which the shades vary considerably.
But in the _Coleoptera_, and many other Orders, the colours of the
skin are mixed in its horny tissue, nearly as those of the _Testacea_
are in their calcareous shells"[1166]. In the perfect insects,
therefore, in most cases, we may consider the _epidermis_ and _rete
mucosum_ as together forming the exterior and coloured integument of
insects--that part which in the table, since it is not properly an
_epidermis_, I have distinguished by the name of _Exoderma_.
The learned author just quoted has observed nothing under the skin
of white-blooded animals that he regards as analogous to _nervous
papillæ_[1167]. In some parts of insects, as in the lamellæ of the
antennæ of the _Petalocera_, and the extremities of the joints,
especially the last, of many palpi, there is however an appearance
of them; and it seems reasonable to suppose that where the sense
of _touch_ resides, there must, even in insects, be something of a
_papillary tissue_.
With regard to the innermost integument of the vertebrate animals,--the
_leather_, or real skin,--this learned comparative anatomist finds
nothing analogous to it in the integuments of insects[1168]; but as he
does not notice it, he appears to have overlooked the substance that
lines the outer crust, or _exoderma_, in the _Coleoptera_ and most
other orders. This is not always easily detected; but it may generally
be discovered by breaking, or rather tearing (not cutting), after
having cleared away the muscles, any part of the body of an insect.
It is always very visible on the under side of _elytra_[1169], but is
not discoverable in _tegmina_. It appears to consist, in many cases,
of several layers of a whitish membrane, and generally breaks into
fibres. In some elytra of the larger _Dynastidæ_, towards the sides
the exterior layer is separated from the rest by a kind of cellular
substance. The fibrous structure of this inner skin (which I call the
_Esoderma_) seems to give it some affinity to the skin of vertebrate
animals[1170]. In many parts of the body, however, it appears to be
merely a thin pellicle. A medical friend, to whom I showed specimens of
it, thinks it a kind of cellular membrane.
2. A few words are next necessary with regard to the _articulation_
of the integument, or the mode by which the several pieces of which
it and its members consist, are united to each other. In some, as
in several of the parts of the head, the occiput, vertex, temples,
cheeks, &c.--the line of distinction is merely imaginary; in others
an impressed line separates a part from its neighbours, as is the
case with the _nose_ in _Vespa_, &c. the head in the _Arachnida_. But
in the majority of instances the parts are separated by a suture, or
form a real joint. The kinds of articulation observed by anatomists
in vertebrate animals do not all occur in insects, and they seem to
have some peculiar to themselves. Thus, for instance, they have no
proper _suture_; for though they exhibit the appearance both of the
_harmonic_ and _squamose_ (_ecailleuse_ Cuv.) sutures[1171], yet
these parts being all limited by the _esoderma_, or skin, above
noticed as lining the integument, and all admitting a degree of
motion more or less intense, rather afford examples, as the case
may be, of other kinds of articulation[1172]. Again, they have no
proper _Enarthrosis_, or ball and socket; though the anterior coxæ
of the Capricorn-beetles (_Cerambyx_ L.) approach very near to this
kind of articulation, as will be shown more fully in another place.
The inosculating segments or rings, which distinguish the abdomen,
and sometimes other parts of insects, are an example of a kind of
articulation not to be met with in the _Vertebrata_. The ginglymous
articulation, in which the prominences of the ends of two joints
are mutually received by their cavities, and which admits only of
flexion and extension, often prevails in the limbs, &c. of insects;
but in many cases the joints are merely suspended to each other by a
ligament or membrane; and, in fact, the integument of insects, with
regard to its articulation, even where the joints ginglymate, may
be said in general to consist of pieces connected by the internal
ligament, membrane, or skin that lines it; for even in the legs,
where the ginglymous articulation is sometimes very remarkable and
complex, as will be shown to you hereafter, the joints are also
connected by this substance, as you may see if you examine the legs
of any Coleopterous insect.
The _number_ of articulations or pieces that form the integument and
its members in these animals, varies greatly in different tribes,
genera, &c. Thus, in the common louse (_Pediculus humanus_) they
scarcely reach fifty, while in some cockroaches (_Blatta_) they
amount to more than eight times that number.
Having premised these observations on the external anatomy of the
body in general, in the remainder of the present letter I shall
confine myself to the consideration of the _head_ and its _parts_.
I. The _Head_ of insects, as the principal seat of the organs of
sensation, must be regarded in them, as well as in the vertebrate
animals, as the _governing_ part of the body. It may be considered with
respect to its _substance_, _figure_, _composition_, _superficies_,
_proportion_, _direction_, _articulation_ with the _trunk_,
_motions_--and more particularly as to its _parts_ and _appendages_.
i. With regard to its _substance_--the head may be said in general
to be the _hardest_ part of the crust: and it is so for very good
reasons. In the first place, as it has to make way for the rest of
the body when the animal moves, it is thereby best fitted to overcome
such resistance as may be opposed by the medium through which it has
to pass; in the next, as it bears the organs of manducation, it was
requisite that it should be sufficiently firm and solid to support
their action, which is often upon very hard substances; and besides
this, as no motion of its parts _inter se_, as in the case of the
trunk, is requisite to facilitate the play of its organs, a thin
integument was not wanted.
ii. The most general law relative to the _figure_ or shape of the
head seems to be, that it should approach to that of an equilateral
triangle, with its angles rounded, and the vertex being the mouth;
and that the vertical diameter should be less than the horizontal,
whether longitudinal or transverse. But the infractions of this
law are numerous and various. Thus, in some insects an isosceles
triangle is represented by the head, the length being greater than
the breadth; in others, instead of being flat it is compressed, so
that the horizontal diameter is less than the vertical; in others,
again, it is orbicular, or round and depressed; in others nearly
spherical: occasionally it is rather cylindrical. In many instances
it is very long; in others the width exceeds the length. Though often
narrowest before, in some cases the reverse takes place. Its anterior
end is often attenuated into a long or short snout or rostrum, and
its posterior into a long or short neck. Its contour, though usually
regular, is sometimes either cut into lobes, or scooped out into
sinuosities. But to enumerate minutely all the variations of form
which take place in the head of insects would be endless; I shall
therefore proceed to the next particular.
iii. The _composition_ of the head is very simple; for, exclusive
of its organs, it consists only of a single piece or box, without
suture or segment, with an aperture at the end below to receive the
instruments of manducation, others for the eyes and stemmata when
present, and also for the antennæ. In the _Arachnida_, &c., in which
the head is not separated from the thorax, it is merely a plate, the
under-side or cavity of which is occupied and filled by the above
instruments.
iv. With regard to its _superficies_, the head of insects is generally
more or less uneven, though in some cases it presents no inequalities.
In many of the Lamellicorn tribes, and a few other individuals, in
one sex at least, as has been before observed[1173], it is armed with
long horns, or prominent tubercles; it is often covered with numerous
puncta, or pores; and some of its parts, as the nose, after-nose, &c.
in particular groups, marked out by an impressed line[1174]. In many
_Hymenoptera_, _Diptera_, &c. its upper surface is convex, and the
lower concave; in others both surfaces are convex.
v. It is the most general rule, as to its _proportion_, that it shall
be smaller than either trunk or abdomen; but in some instances, as in
the S. American ant, _Atta megacephala_, it is much larger than either.
vi. By the _direction_ of the head, I mean its inclination with
respect to the prothorax. The most natural direction, or that
which obtains most generally, is for it to form an angle more or
less obtuse with the part just mentioned. This seems to obtain
particularly in _Coleoptera_; but in some, as _Mylabris_, it is
inflexed, forming an acute angle with it. In the Heteropterous
_Hemiptera_ (_Cimex_ L. &c.) it is generally in the same line with
the body, or horizontal; and in many _Diptera_ it is vertical.
vii. We now come to a circumstance which will detain us longer,
namely, its _articulation with the trunk_, or rather with its anterior
segment, the _prothorax_.--M. Cuvier makes _two_ principal kinds of
articulation of the head upon the prothorax, in one of which the points
of contact are solid, and the movement subordinate to the configuration
of the parts; in the other, the articulation is ligamentous, the head
and the thorax being united and kept together by membranes.
1. The _first_ of these kinds of articulation--that by the contact
of solid parts--takes place, he says, in _four_ different ways.
"In the most common conformation, in the part that corresponds
to the neck, the head bears one or two smooth tubercles, which
receive corresponding cavities of the anterior part of the prothorax
observable in the Lamellicorn and Capricorn beetles. In this case
the head can move backwards, and the mouth forwards and downwards.
The _second_ mode of solid articulation takes place when the
posterior part of the head is rounded, and turns upon its axis in a
corresponding cavity of the anterior part of the prothorax; as may
be seen in _Curculio_, _Reduvius_, &c. The axis of motion is then
at the centre of articulation, and the mouth of the insect moves
equally backwards and forwards, upwards and downwards, to right and
left.--The _third_ sort of articulation, by solid surfaces, takes
place when the head, truncated posteriorly, and presenting a flat
surface, is articulated, sometimes upon a tubercle of the thorax,
and sometimes upon another flat and corresponding surface, as in
almost all the _Hymenoptera_ and the majority of the _Diptera_. The
disposition of the _fourth_ kind of articulation allows the head only
the movement of the angular hinge (_le seul mouvement de charnière
angulaire_). The only examples at present known are in some species
of _Attelabus_ F. The head of these insects terminates behind in a
round tubercle, received in a corresponding cavity of the thorax: the
lower margin of this cavity has a notch, and permits the movement of
the head only in one direction[1175]."
2. The _second_ kind of articulation, the ligamentous, he affirms takes
place only in _orthopterous_ and some _neuropterous_ insects: "The head
in this kind of articulation is only impeded in its movements towards
the back, because it is stopped there by the advance of the prothorax;
but below it is quite free. The membranes or ligaments extend from the
circuit of the occipital cavity to that of the anterior part of the
prothorax, which gives a great extent to the movement[1176]."
When I consider the well-deserved celebrity of the great author whose
words I have here quoted, and the great and useful light that the
genius and learning which conducted his patient labours and researches
have thrown over every department of comparative anatomy,--a science he
may be almost said to have founded,--I feel the most intire reluctance
to differ in any thing from an authority so justly venerable to all
lovers of that interesting study. But, however great my diffidence and
hesitation to express an opinion at all opposed to his, the interests
of truth and science require that I should state those particulars in
which my own observations, made upon a careful examination of various
insects of every Order, have led to results in some respects different
from the above. "_Aliquando bonus dormitat Homerus_;" and if the
Genius of Comparative Anatomy ever nodded, it sometimes happened when
he was examining the structure of insects. An instance of this with
regard to the mouth of the bee has been noticed by Mr. Savigny[1177];
and indeed it is not wonderful that in so extensive an undertaking, in
which the number of examples to be examined upon every branch of his
subject must be immense, that he did not always scrutinize minutely
those that seemed less important. Every writer on every department
of Natural History, especially where the objects of research, as in
the insect world, are so infinite in number, will be liable to such
mistakes; but these will meet with due allowance from every candid
mind--
"Hanc veniam damus, petimusque vicissim:"
and I shall express my trust that you will overlook any errors of
mine; and doubtless I shall not be free from them--
"---------Quas aut incuria fudit,
Aut humana parum cavit natura----"
The two kinds of articulation of the head which our learned author
has stated as the principal ones, will, I think, be found upon
examination not so widely distant as his expressions seem to
indicate; for in fact in all insects, as well as the _Orthoptera_,
this part is _suspended_ by a membrane or ligament which unites
the margins of the occipital cavity with those of the anterior one
of the prothorax: thus forming all round some protection to the
organs that are transmitted from the head through the latter part to
the rest of the body. Though the head in most _Orthoptera_ is not
partly received into the cavity of the prothorax, as is the case in
the Order _Coleoptera_, but is rather suspended to it, yet in some
instances, for example in the mole-cricket (_Gryllotalpa vulgaris_),
it is partially inserted.
Again: when, in his _first_ mode of articulation by contact of solid
parts, he speaks of one or two smooth tubercles of the neck, with
their corresponding cavities in the prothorax, as forming the most
common conformation, you would expect to find examples of this in
very many insects; yet upon a close examination, unless in _Oryctes
nasicornis_[1178], and perhaps in others of the _Dynastidæ_ MacLeay,
you would scarcely meet with any thing that could be called a
tubercle and its corresponding cavity in the neck or prothorax of any
Lamellicorn or Capricorn beetle that you might chance to examine.
You would find, indeed, that the occiput was usually smooth and very
slippery, as if lubricated; that in its margin were one or two notches
(_Myoglyphides_), with muscles attached to them; that in the former of
these tribes, the _Lamellicorns_, it projected on each side so as to
form a more or less prominent angle; and that the throat (_jugulum_)
was very convex, and lodged in a cavity of the lower margin of the
prothorax: but further appearances of tubercles &c. you would in vain
look for even in this tribe; and in the _Capricorns_ you would find
that the general conformation in this respect belonged to our learned
author's _second_ mode of solid articulation, resembling that of the
majority of the weevils (_Curculio_ L.), in which the head has no
projecting angles or tubercles, or other elevation, but is received
usually into the circular cavity of the prothorax.
His _third_ mode of this articulation, that of the _Hymenoptera_
and _Diptera_, is so peculiar, that it ought to be considered as a
_primary_ kind; since in this the head moves _upon_ the prothorax as
upon a pivot, and has a kind of versatile motion.
With regard to his _fourth_ mode, which from his description appears
to be that of _Apoderus_ Oliv., he allows motion to the head only in
_one_ direction, observing that the lower margin of the prothoracic
cavity has a notch. But M. Latreille calls the articulation of the
head in this genus an _Enarthrosis_[1179], which admits motion in
every direction; and if you examine the common species (_A. Coryli_),
you will find that the prothorax has a sinus taken out of its upper
margin, as well as out of its lower one--which at any rate will allow
a motion _upwards_.
I merely mention these little inaccuracies, with due diffidence,
as some apology for giving you a different and at least a more
popular and general view of this part of my subject, which I shall
now proceed to state to you. It seems to me most convenient for the
Entomologist, and most consonant to nature, to divide insects, with
respect to the articulation of the head with the trunk, into three
_primary_ sections, each admitting one or more subdivisions.
1. The _first_ consists of those whose head inosculates more or less in
the anterior cavity of the chest; and whose articulation, therefore,
seems to partake in a greater or less degree of the ball and socket
(_Enarthrosis_). The head, however, is often capable of being protruded
from this cavity. If you take into your hand any common _Harpalus_
that you may find under a stone, you will see, if pressed, that it
can shoot forth its head, so as to be entirely disengaged from the
prothorax: a neck of ligament intervening between them[1180]: of course
this power of protruding the head enables the animal to disengage
it at its will from the restriction imposed upon its motions by the
surrounding margin of the prothoracic cavity. To this section belong
all the _Coleoptera_, the Heteropterous _Hemiptera_ (_Cimex_ L., &c.),
and some of the _Neuroptera_ (_Raphidia_, _Semblis_, &c.).--It may
be further divided into _two_ subsections--those, namely, whose head
inosculates in the prothorax by means of a _neck_: as for instance
Latreille's _Trachelides_, _Apoderus_, and the _Staphylinidæ_, amongst
the beetles; the _Reduviadæ_ amongst the _Heteropterous_ insects, and
_Raphidia_ in the _Neuroptera_; and those whose head inosculates in the
prothorax without the intervention of a neck; as, the _Petalocera_,
the aquatic beetles (_Dytiscus_, _Hydrophilus_, &c.), and most of the
genus _Curculio_ L. in the first of these orders, the great body of the
_Cimicidæ_ in the second, and _Semblis_, _Corydalis_, &c. in the third.
2. The _second_ section consists of those insects whose head does not
inosculate in the chest, but is merely suspended to it by ligament or
membrane. To this belong most of the tribes of the _Orthoptera_ Order,
with the exception of the _Mantidæ_, the _Dermaptera_, the _Homopterous
Hemiptera_, and such of the _Aptera_ as have the head distinct from
the prothorax.--This section admits of a _triple_ subdivision: those,
namely, whose head is _wholly_ covered by the shield of the prothorax,
as in _Blatta_ L.; those whose head is _partly_ covered by it, as
_Gryllotalpa_, and other _Gryllina_; and those whose head is quite
free, not being at all impeded in its motion by the prothorax, as the
_Dermaptera_, _Nirmus_, _Pediculus_, &c.
3. The _third_ section consists of those whose head is truncated
posteriorly, and flat or concave, with a very small occipital
aperture, and is attached to a neck of the prothorax upon which
it turns, or is merely suspended to that part. This includes
the _Lepidoptera_, _Hymenoptera_, _Diptera_, the _Libellulina_,
&c. in the _Neuroptera_, and the _Mantidæ_ in the _Orthoptera_.
_Three_ subsections at least, if not more, present themselves in
this section: the first is, of those whose head is united to the
prothorax, without the latter forming any _neck_. To this belong the
_Lepidoptera_, _Trichoptera_? The _second_ is of those the upper
side of whose thoracic neck is _ligamentous_; and here you may range
most of the _Hymenoptera_. The _third_ is of those in whom it is a
_continuation_ of the ordinary _integument_. In this subsection the
_Diptera_, _Libellulina_ and _Mantidæ_ will find their place. In this
last section the head appears to turn upon the thorax as upon a pivot.
Before I finish what I have to say on the _articulation_ of the
head, I must direct your attention to the _analogies_ that hold in
this respect between the different tribes. Thus the _Coleoptera_
are analogous to the _Heteropterous Hemiptera_; the _Orthoptera_,
with the exception of the _Mantidæ_, to the _Homopterous Hemiptera_;
the _Mantidæ_ to the _Libellulina_; the _Lepidoptera_ to the
_Trichoptera_; the _Hymenoptera_ to the _Diptera_, with a slight
variation, and probably others might be traced.
viii. A word or two upon the _motions_ of which the head of insects
is capable. M. Cuvier, in the extracts lately laid before you,
speaks of different powers of movement as the result of different
configurations of the parts of the head. This probably is correct
with regard to many cases; but a great deal will depend upon the
power the insect has of protruding its head and disengaging its base
from the restriction of the prothorax; for where, like the _Harpali_,
_Staphylini_, &c. it is able to do this, it can probably move its
head in every direction. It is only where the ligaments are less
elastic, or allow of little tension, that its movements are confined;
and few living insects have been sufficiently examined to ascertain
how far this takes place. In those cases belonging to the _third_
section of articulations, in which the head moves _upon_ the thorax
as upon a pivot, as is the case with _Hymenoptera_ and _Diptera_,
the movement is nearly versatile. I have seen a fly turn its head
completely round, so that the mouth became supine and the vertex
prone; and from the form and fixing of the head, it should seem that
those of the _Mantidæ_ were endued with the same faculty.
ix. The _parts_ and _appendages_ of the head are now in the last
place to be considered. I shall begin with the _Mouth_, or rather
the orifice in which the _trophi_ or organs of manducation are
inserted. In some insects, as was before observed, they occupy all
the under-side of the head, as in the _Arachnida_, _Myriapoda_,
&c; but in the great majority they fill an orifice in its anterior
part, which in some instances, as in _Lampyris_, the _Lepidoptera_,
_Cimex_ L., _Truxalis_, appears to be nearly under the head; but in
general it terminates that part, though it extends further below than
above. In _Chermes_, a Homopterous genus, the promuscis is stated
to be in the _Antepectus_, and consequently the _mouth_; but, as I
shall endeavour to prove to you hereafter, this is a fallacy. In the
males of the species of _Coccus_ there is no mouth at all. In that
of the elm (_C. Ulmi_) in lieu there are ten little shining points,
arranged two before and two behind in a line, and three on each side
in a triangle[1181]. It is to be observed that the orifice of which
I am speaking is usually much smaller in those insects which take
their food by suction, the _Hemiptera_, _Lepidoptera_, _Diptera_,
&c., than in the masticating tribes. With regard to the real mouth,
or that through which the food enters, I have nothing at present to
observe, except that it lies between the upper-lip and tongue, is
sometimes covered by a valve, as in _Apis_, _Vespa_[1182], &c., and
is different in the masticators and suckers.
* * * * *
I shall next offer a few observations _seriatim_, as they stand
in the Table, upon the organs of manducation; which, to avoid
circumlocution, instead of _Instrumenta cibaria_, the name Fabricius
gave them, I shall call _trophi_ or _feeders_. It is upon these
parts, you are aware, that the system of the celebrated Entomologist
just mentioned is founded; and could they always, or even for the
most part, be inspected with ease, they would no doubt afford
characters as various and discriminative as those of the vertebrate
animals. Differences in these parts indicate a difference in the
mode in which the animal takes its food, and often in the kind of
food, and sometimes in its general economy and habits,--circumstances
which are powerful and weighty in supporting the claim of any set
of animals to be considered as forming a natural genus or group.
Trifling variations, however, of these parts, unless supported by
other characters and qualities, ought not to have much stress laid
upon them, since, if we insist upon these, in some tribes almost
every species might be made a genus.
With respect to their _trophi_ in general, insects of late have been
divided into two great tribes[1183], _masticators_ and _suckers_;
the _first_ including those that are furnished with instruments to
separate and _masticate_ their food; namely, an upper- and under-lip
(_labrum_ and _labium_), upper- and under-jaws (_mandibulæ_ and
_maxillæ_), labial and maxillary palpi, and a tongue (_lingua_): and
the _second_ those in which these parts are replaced by an articulate
or exarticulate machine, consisting of several parts and pieces
analogous to the above, which pierce the food of the animal, and
form a tube by which it _sucks_ its juices. If, however, the mode in
which insects take their food be strictly considered, it will be
found that in this view they ought rather to be regarded as forming
_three_ tribes; for the great majority of the _Hymenoptera_ order,
and perhaps some others, though furnished with mandibles and maxillæ,
never use them for mastication, but really lap their food with their
tongue: these, therefore, might be denominated _lappers_.
When a mouth is furnished with the _seven_ ordinary organs used in
taking the food and preparing it for deglutition--I mean the upper-lip
and the two upper-jaws; the under-lip and the two under-jaws, including
the labial and maxillary palpi; and the tongue--I denominate it a
_perfect mouth_; but when it is deficient in any of these organs, or
they exist merely as rudiments, or when their place is supplied by
others, (which, though they may be analogous parts, have little or no
connection with them in their use or structure,) I denominate it an
_imperfect mouth_. This last I would further distinguish, according to
the nature of its _trophi_, by other and more distinctive terms, as I
shall presently explain to you.
1. _Labrum_[1184].--I shall first consider the organs present in
a _perfect mouth_, beginning with the _upper-lip_ (_labrum_).
This part, which Fabricius sometimes confounded with the _nose_,
miscalling it _clypeus_, is usually a moveable[1185] piece, attached
by its base to the anterior margin of the part last named, and
covering the mouth, and sometimes the mandibles, from above. In
insects in their last state it is usually of a horny or shelly
_substance_; yet in some cases, as in _Copris_ and _Cetonia_, beetles
that imbibe juices, it is membranous. In _form_ and shape it varies
greatly, being sometimes nearly square, at others almost round; in
some insects representing a parallelogram, in others a triangle, and
in many it is oblong. In some instances it is long and narrow, but
more generally short and wide. It is often large, but occasionally
very minute. In the majority it has an intire _margin_, but it is
not seldom emarginate or bilobed, or even dentate. Its _surface_
is commonly even, but it is sometimes uneven, sometimes flat, at
others convex, and in a few species armed with a short horn or
tubercle[1186]. As to its _pubescence_, it is often naked, but now
and then fringed or clothed with down or hairs, or sprinkled with
bristles. It consists in almost every instance of a single piece;
but an exception to this occurs in _Halictus_, a little bee, in the
females of which it is furnished with a slender appendage[1187].--The
_direction_ of the upper-lip is various. It is rarely horizontal, or
in the same line with the nose, often vertical; it sometimes forms an
obtuse angle with the anterior part of the head, and occasionally an
acute one, when it is more or less inflexed. The _use_ of this part
is ordinarily to close the mouth from above, to assist in retaining
the food while undergoing the process of mastication; but in many
Hymenopterous insects its principal use seems to be, to keep the
_trophi_ properly folded; and in some cases where it is inflexed,
as in the leaf-cutter bees (_Megachile_ Latr.), to defend its base,
while the mandibles are employed, from injury by their action[1188].
2. _Labium_[1189].--On the under-side of the head, and opposed
to the upper-lip, the mouth is closed by another moveable organ,
concerning the nomenclature and analogies of which Entomologists
have differed considerably. At the first view of it, this organ
seems a very complex machine, since the under-jaws or _maxillæ_ are
attached to it on each side, and the tongue is often seen to emerge
from it above, so as to appear merely a part of it; but as the
former answer to the upper-jaws, and the latter is the analogue of
the part bearing the same name in the vertebrate animals, I shall
consider these as distinct and _primary_ organs, and treat of the
under-lip (_labium_) of which I am now speaking, by itself. Linné
takes no notice of this part, but his illustrious compatriot and
cotemporary, De Geer, did not so overlook it: he appears to consider
the whole apparatus, including the _maxillæ_, as the _labium_[1190];
but sometimes he distinguishes the middle piece by that name[1191];
and the tongue, in the case of the stag-beetle, he denominates a
proboscis (_trompe_)[1192]. In the _Hymenoptera_ he calls this part
_tongue_, _under-lip_, and _proboscis_: but seems to prefer the
last term[1193]. Fabricius originally regarded the whole middle
piece as a _labium_[1194]; but afterwards (though his definition
is not accurate, since he assigns the _palpi_ to the _ligula_,
which he affirms is covered by the _labium_--circumstances by no
means universal in _Coleoptera_) he considers this as consisting
of _ligula_ and _labium_[1195]. Latreille at first regarded the
_ligula_ of Fabricius as the _labium_, and called the _labium_ of
that author the _mentum_[1196]; but afterwards he gave the name of
_labium_ to the whole middle piece of the lower apparatus of the
mouth--calling the upper piece, with Fabricius, the _ligula_, and
retaining the denomination of _mentum_ for the lower[1197].
If the circumstances of the case are duly considered, I think you will
be convinced that the term under-lip, or _labium_, should be confined
to that part which the learned Dane so named. For I would ask, Which
is the part on the under side of the head that is the antagonist, if I
may so speak, of the upper-lip or _labrum_? Is it not that organ which,
when the mouth is closed, meets that part, and in conjunction with it
shuts all in? Now in numerous insects, particularly the Lamellicorn
beetles (_Scarabæus_ and _Lucanus_ L.), this is precisely the case. In
the Predaceous beetles, indeed, (_Cicindela_, _Carabus_, _Dytiscus_
L. &c.) the under-lip does not meet the upper, to close the mouth and
shut in the tongue; neither can the tongue be said so to do, but only,
from some circumstances connected with its manner of taking its food,
it is requisite that the last-mentioned organ should not be retractile
or covered; but its miscalled _mentum_ is still the analogue of that
part which helps to close the mouth in the former tribe. Should not
this, therefore, which so often performs the _office_, be distinguished
by the _name_, of a lip? Again, is it not rather incongruous to
consider that organ which confessedly more or less performs the office
of a _tongue_, as a part of the _lip_? Though it often wears that
appearance, yet I believe, if the matter is thoroughly and patiently
investigated, it will be found that on their upper side its roots are
attached to the interior of the upper side of the head, as well as on
their lower side to the _labium_; so that it may be regarded as common
to the two lips, and therefore not properly considered as an appendage
of the under-lip alone.
Having assigned my reasons for preferring the name given to the part
in question by Fabricius, rather than that of Latreille, I shall next
make my observations on the part itself. In many cases the _labium_,
or the middle piece of the lower oral apparatus, appears to consist of
_two_ joints: this you may see in the great water-beetle (_Hydrophilus
piceus_), the burying-beetles (_Necrophorus_), the Orthopterous
tribes[1198], the _Hymenoptera_[1199], and others. In this case the
upper or terminal piece is to be regarded as the _labium_, and the
lower or basal one (which Mr. MacLeay calls the _stipes_) as the
_mentum_ or chin--at other times, as in some Lamellicorn beetles, the
only separation is a transverse elevated line, or an obtuse angle
formed by the meeting of the two parts, and very frequently there is no
separation at all, in which case the whole piece, the _mentum_ merging
in it, may be denominated the _labium_.
With respect to its _substance_, the _labium_ in most Coleopterous
insects is hard and horny, in _Necrophorus_ it is membranous,
and the _mentum_ harder; in _Prionus coriarius_, our largest
Capricorn-beetle, both are membranous; in the bee-tribes, _Apis_
L., the _labium_ rather resembles leather, while the _mentum_ is
hard. Its _surface_ is often convex, sometimes plane, and sometimes
even concave; as for instance in _Melolontha Fullo_, a rare chafer
occasionally found on the coast of Kent. In some it is covered with
excavated points; in others it is quite smooth. In numbers, as in
the Predaceous beetles, both _labium_ and _mentum_ are perfectly
naked; in others, as in the common cockchafer, they are hairy;
in _Geniates barbatus_ Kirby, another chafer in the male insect,
the _labium_ is naked, while the _mentum_, which forms a piece
distinct from that part, is covered with a dense rigid beard[1200].
In _shape_ the whole _labium_ varies considerably, much more than
the _labrum_; for in addition to most of the forms I enumerated
when I described that organ, which I shall not here repeat, you
may meet with examples of many others. Thus, to instance in the
Petalocerous tribes (_Scarabæus_ L.), in some, as in the _Rutelidæ_,
the _labium_ is urceolate, or representing in some degree the shape
of a pitcher[1201]; in others it is deeply concave, and not a little
resembles a basin or a bowl[1202]; this form is peculiar to the
_labium_ of _Cremastocheilus_ Knoch, a scarce North American beetle;
in another related to this, but of an African type (_Genuchus_ Kirby
MS. _Cetonia cruenta_ F.), it is a trapezoid plate, which is elevated
from the head, and hangs over the throat like a chin[1203]. In the
_Hymenoptera_ it is extremely narrow and long, and embraces the sides
of the tongue, as well as covering it from below; so that it wears
the appearance of a kind of tube[1204]. Generally speaking, the
length of the _labium_ exceeds its breadth; but in the Predaceous
beetles the reverse of this takes place, it being very short and
wide, and usually terminating towards the tongue in three lobes or
teeth which form two sinuses varying in depth[1205].
The _mentum_ taken by itself affords no very striking characters
to which I need call your attention: I shall only observe, that
in _Hymenoptera_ it is generally of a triangular shape[1206]; but
before I proceed to consider the labial palpi, it will be proper to
notice the remarkable _labium_ of _Orthopterous_ insects, and of the
_Libellulina_, between which there is no little analogy. At first you
would imagine the terminal part of this organ in the former to be the
analogue of the tongue, or _ligula_ F.; as it is indeed generally
regarded by modern Entomologists[1207]. It seems, like the tongue of
the _Carabi_ L., _Dytisci_, &c., to be a distinct piece, which has
below it both _labium_ and _mentum_; but when you look within the
mouth, you will find a linguiform organ[1208], which evidently acts
the part of a tongue, and therefore ought to have the name; and the
piece just alluded to must either be regarded as the termination of
the lip, or as an external accompaniment of the tongue, analogous,
it may be, to the _paraglossæ_ in bees[1209]. In a specimen of
_Acrida viridissima_ (_Locusta_ F.) which I dissected, the tongue is
as long as the appendage of the under-lip, and by its upper surface
seems to apply closely to it. In the _Libellulina_ a similar organ
is discoverable[1210], which on its upper-side terminates in the
_pharynx_, like that of one of the _Harpalidæ_ before mentioned. In
the _Orthoptera_, therefore, I regard the _labium_ as consisting
of three articulations, the upper one divided into two, three, or
more lobes[1211]; the intermediate one more directly answering to
the _labium_ of other insects, and the basal one or _mentum_. This
organ in the _Libellulina_ is of a different structure: it has only
two articulations representing _labium_ and _mentum_; but the former
consists of three parallel pieces, the two exterior ones rising
higher than the intermediate one, and at their inner angle having an
acute sinus from which the palpi emerge; and the intermediate piece,
which is longitudinally channelled, lapping over the inner side of
the lateral pieces. From the angle of the covered part of these
pieces, a subulate short horizontal horn points inwards towards the
tongue, which it must keep from closing with the _labium_[1212].
3. _Palpi Labiales_[1213].--The last-mentioned organs, the _labial
palpi_, next claim our attention; but before I advert particularly
to them, it will be proper to premise a few words upon _palpi_, or
feelers, in general. These are usually jointed moveable organs,
of a corneous or coriaceous substance, attached by ligaments to
the _labium_ and _maxillæ_, and in the _Crustacea_ even to the
_mandibulæ_. Their joints, which are usually more or less obconical,
articulate also in each other by ligaments, with perhaps some
little mixture of the ball and socket. Their ends, the last joint
especially, seem furnished with nervous _papillæ_ which indicate some
peculiar sense, of which they are the instrument. What that sense is
has not been clearly ascertained, and concerning which I shall enter
more into detail in another place. Their motion seems restrained, at
least in some, to two directions, towards and from the mouth. They
were called _palpi_ or feelers, because the insect has been supposed
to use them in exploring substances. There seem to be no organs in
the vertebrate animals directly analogous to the _palpi_ of insects
and _Crustacea_, unless, perhaps, the _cirri_ that emerge from the
lips of some fishes, as the cod, red mullet, &c. which Linné defines
as used in exploring (_prætentantes_). Whether the _vibrissæ_,
miscalled _smellers_, of some quadrupeds and birds have any reference
to them, I will not venture to affirm; but the feline tribe evidently
use their bristles as explorers, and they are planted chiefly in the
vicinity of the mouth.
Having made these general remarks, I shall now confine myself to the
_labial palpi_. I call them _labial_ palpi, because that term is in
general use, and because in many cases they really do emerge from what
I consider as the _labium_, as in most of the _chafers_; but they
might with equal propriety be denominated _lingual_ palpi, since they
sometimes appear to emerge from the _tongue_ as in the stag-beetle
(_Lucanus Cervus_). In some instances, as in the Predaceous beetles,
they seem to be common to both _labium_ and tongue, being attached
at their base on the upper side to the former, and on the under side
to the latter. As to their _situation_: they emerge from the _base_
of the _labium_ in the locusts (_Locusta_ Leach)[1214]; from its
_middle_ in _Hister maximus_[1215]; from its _summit_ in _Amblyterus_
MacLeay[1216]; and from its lateral margin in _Dynastes_ MacLeay, &c.
They consist of from _one_ to _four_ joints; which, I believe, they
never exceed. They vary in _length_; though generally shorter than the
maxillary palpi, yet in the ferocious tiger-beetles (_Cicindela_ L.)
they equal them in length; and in the hive-bee and humble-bees, and
many other bees, they are considerably longer[1217]. The two first
joints of these palpi, however, in these _bees_ are different in their
structure from the two last, being compressed and flat, or concave;
and the two last joints, instead of articulating with the apex of the
second, emerge from it below the apex: so that these two first joints
seem rather elevators of the palpi than really parts of them[1218].
With respect to the relative _proportions_ of their joints to each
other: in some cases the first joint is the longest and thickest,
the rest growing gradually shorter and smaller[1219]; in others, the
second is the longest[1220]; in others, again, the third[1221], and
sometimes the last[1222]; and often all are nearly of the same size
and length[1223]. They are more commonly _naked_, but sometimes either
generally or partially _hairy_. Thus in _Cicindela_, the last joint
but one is usually planted with long snow-white bristles in a double
series, while the rest of the joints have none; and in _Copris_ Latr.
all of them are extremely hairy. In _shape_ they do not vary so much
as the maxillary palpi, being most frequently filiform or subclavate,
and sometimes setaceous; the last joint varies more in shape than the
rest, and is often remarkably large, triangular, and shaped like the
head of a hatchet[1224]; and at others it resembles the moon in her
first quarter[1225]. In the great dragon-fly, or _demoiselle_ if you
prefer the gentler French name (_Æshna_ F.) the labial palpi, which
are without any visible joints, are terminated by a minute mucro
or point[1226]. With regard to their _direction_ and flexure, they
frequently, as in the instance just mentioned, turn towards each other,
and lie horizontally upon the end of the _labium_. Sometimes, as in the
_Cicindelidæ_, they appear to point towards the tail of the insect, the
last joint rising, and forming an angle with the rest of the feeler.
In other instances they diverge laterally from the _labium_, the last
joint turning again towards it at a very obtuse angle.
4. _Mandibulæ_[1227].--Having considered the analogues of the
_lips_ in our little beings, I must next call your attention to the
representatives of the _jaws_. The vertebrate animals, you know,
are mostly furnished with a single pair of jaws, one above and the
other below, in which the teeth are planted and which have a vertical
motion. But insects are furnished with _two_ pair of jaws, a pair
of upper-jaws and a pair of under-jaws, which have no teeth planted
in them, and the motion of which is horizontal.--I shall begin
with an account of the upper-jaws. These by modern Entomologists,
after Fabricius, are denominated _mandibles_ (_mandibulæ_): a term
appropriated by Linné to the beaks of birds. The upper-jaws of
insects this great naturalist named _maxillæ_--and not improperly,
since the office of mastication is more peculiarly their office than
that of the under-jaws, which Fabricius has distinguished by that
name: as the term _mandible_, however, is generally adopted, I shall
not attempt to disturb it.
The _mandibles_ close the mouth on each side under the _labrum_ or
upper-lip. They are generally powerful organs, of a hard _substance_
like horn; but in the Lamellicorn beetles of Mr. MacLeay's families
of _Scarabæidæ_ and _Cetoniadæ_, they are soft, membranous, and unapt
for mastication. In Coleopterous insects they commonly _articulate_
with the head by means of certain _apophyses_ or processes, of
which in many cases there are _three_ discoverable at the exterior
base of the mandibles; one, namely, at each angle, and one in the
middle. That on the lower side is usually the most prominent, and
wears the appearance of the condyle of a bone: it is received by
a corresponding deep socket (or cotyloid cavity) of the cheek, in
which, being perfectly smooth and lubricous, it moves readily, but
without _synovia_, like a _rotula_ in its _acetabulum_. The upper
one projects from the jaw, forms the segment of a circle, and is
concave also on its inner face. A corresponding more shallow, or,
as anatomists speak, glenoid cavity of the cheek, where it meets
the upper-lip, receives it, and the concave part admits a lubricous
ball projecting from the cheek, upon which it turns[1228].
This structure you will find in the stag-beetle, and some other
timber-devourers. Other _Coleoptera_ have only a process of a
similar structure at each of the dorsal angles of the base of the
mandible, the intermediate one being wanting; and the articulation
does not materially differ, as far as I have examined them, in the
_Hymenoptera_ and _Neuroptera_. In the _Orthoptera_, the structure
approaches more nearly to that of the stag-beetle, since there are
_three_ prominences: it is thus well described by M. Marcel de
Serres: "This articulation," says he, "takes place in _two_ ways.
At first, in the upper surface of the mandible, and at its base,
may be observed two small prominences and a glenoid cavity; these
prominences are received in two glenoid cavities excavated in the
shell of the front, as the cavity of the mandible receives a small
prominence of the same part. Below the mandible, and at its base,
there is a kind of condyle, which has its play in a cotyloid cavity
excavated in the shell of the temple, far below the eye, and at the
extremity of the coriaceous integument of the head[1229]." Within
the head in this order, at least in _Locusta_ Leach, is a vertical
_septum_, which divides the head into two chambers, as it were,
an occipital and a frontal, consisting of a concave triangular
stem, terminating in two narrower concave triangular branches, so
as to resemble the letter Y, and forming three openings, an upper
triangular one, and two lateral subquadrangular ones, which last are
the cavities that receive the base of the mandibles. This partition,
which I would name _Cephalophragma_, doubtless affords a point of
attachment to many of the muscles of the head. It does not appear to
have been noticed, unless it be synonymous with the _intermaxillary
arcade_ of Marcel de Serres[1230]. Probably a corresponding support
to the muscles, &c. may exist, as we have seen it does in _Vespa_
L.[1231], in many other heads of the different Orders, which have
not yet fallen under examination. Many mandibles, as those of the
hornet &c., appear to be suspended to the cavity of the head on
the inside by a marginal ligament sufficiently relaxed to admit
of their play: those of the _Orthoptera_, M. Marcel de Serres
informs us, are united to the head by means of two cartilages, the
outermost being much the shortest, to which their moving muscles
are attached. These he considers as prolongations of the substance
of the mandible[1232]. The bottom of mandibles, when cleared of the
muscles &c., inclines almost universally to a triangular form; but
in some cases, as in the stag-beetle, it is nearly a _trapezium_.
I cannot conclude this subject without noticing the _motions_ of
the mandibles. What the author lately quoted has said with regard
to those of the _Orthoptera_, will, I believe, apply equally well
to all the mandibulate orders. "The articulation of mandibles with
the skull appears to take place by two points solely; and as these
parts only execute movements limited to a certain direction, they
may be referred to _ginglymus_[1233].--The movements of mandibles
are limited to those from within outwards, and from without
inwards[1234]." Whether they are restricted from any degree of
vertical motion, has not yet been proved, as the jaws of vertebrate
animals move horizontally as well as vertically--so those of insects
may have some motion vertically as well as horizontally; and it seems
necessary for some of their operations that they should. I am not
anatomist enough to speak with confidence on the subject, but the
ball and socket articulation at the lower part of the mandible, and
the curving one at the upper, though a kind of _ginglymus_, seems to
imply a degree of _rotatory_ movement, however slight.
I must next say something upon the general shape of these organs.
Almost universally they incline to a triquetrous or three-sided
figure, with their external surface convex, sometimes partially
so, and their internal concave. Most frequently they are arched,
curving inwards; but sometimes, as in _Prionus octangularis_[1235], a
Capricorn beetle, and others of that genus, they are nearly straight;
and in _Rhina barbirostris_[1236], a most remarkable Brazilian
weevil, their curvature is outwards. In _Pholidotus lepidotus_
MacLeay, and _Lucanus Elephas_, two insects of the stag-beetle tribe,
they are bent downwards; and in _Lucanus nebulosus_ K. (_Ryssonotus_
MacLeay) they turn upwards[1237]. They are usually widest at the
base, and grow gradually more slender to the apex, but in the hornet
(_Vespa Crabro_) the reverse takes place, and they increase in width
from the base to the apex; and in the hive-bee, and others of that
tribe, they are dilated both at base and apex, being narrowest in the
middle; others are nearly of the same width every where. In those
insects that use their mandibles principally for purposes connected
with their economy, they are often more broad in proportion to
their thickness, than they are in those which use them principally
for mastication. In the locust tribes (_Locusta_ Leach), they are
extremely thick and powerful organs, and fitted for their work
of devastation; but in the glow-worm (_Lampyris_), they are very
slender and minute. In those brilliant beetles, the _Buprestes_,
they are very short; but in the stag-beetles, and those giants in
the Capricorn tribe, the _Prioni_, they are often very long[1238].
They either meet at the summit, lap over each other, cross each
other, or are protended straight from the head; as you have doubtless
observed in the stag-beetle, whose terrific horns are mandibles
of this description. These organs are usually _symmetrical_, but
in some instances they are not: thus in _Hister lævus_, a kind of
dung-beetle, the left hand mandible is longer than the right; in
_Creophilus maxillosus_ K. (_Staphylinus_ L.), a common rove-beetle,
in the left hand mandible the tooth in the middle is bifid, and in
the right hand one intire; and in _Bolbocerus_ K. the mandible of one
side, in some species the dexter, and in others the sinister, has two
teeth, and the other none.
The next circumstance with respect to these organs which demands our
attention, is the _teeth_ with which they are armed. These are merely
processes of the substance of the mandible, and not planted in it by
_gomphosis_[1239], as anatomists speak, as they are in vertebrate
animals. They have, however, in their interior, at the base at least,
in the _Orthoptera_, a coriaceous _lamina_ that separates them in
some sort from the body of the mandible[1240]. Many insects, however,
have mandibles without teeth; some merely tapering to a sharp point,
others obtuse at the end, and others truncated[1241]. Of those that
have teeth, some have them on the inside at the base, as _Manticora_,
an African tiger-beetle[1242]; others in the middle, as _Staphylinus
olens_, a rove-beetle, _Lethrus cephalotes_, &c.[1243]; others at the
end, as many weevils (_Curculio_ L.)[1244]; others again on the back,
as the _Rutelidæ_, a tribe of chafers[1245], and _Lethrus_, a beetle
just named; others once more on the lower side of the base, in the form
of a tooth or spine, as in _Melitta spinigera_, a species of wild-bee,
and some of its affinities[1246]; and lastly, others on the upper side
of the base in the form of a long tortuous horn, as in that singular
wasp _Synagris cornuta_ F. before noticed as a sexual character[1247].
In the stag-beetle tribes (_Lucanus_ L.) these teeth are often
elongated into short lateral branches, or a terminal fork[1248]. They
are sometimes truncated, sometimes obtuse, and sometimes acute.
But with regard to their _kind_, it will be best to adopt the ideas
of M. Marcel de Serres; for though his remarks are confined to
the _Orthoptera_, they may be applied with advantage to the teeth
that arm the mandibles of insects in general. He perceives an
analogy between those of this Order and the teeth of quadrupeds;
and therefore divides them into _incisive_ or cutting, _laniary_
or canine, and _molary_ or grinding teeth. He denominates those
_incisives_ that are broad, having in some degree the shape of a
wedge, their external surface being convex, and their internal
concave; whence they are evidently formed for cutting. The
_laniaries_ are those which have a conical shape, are often very
acute, and in general the longest of any; and in some insects, as
the carnivorous _Orthoptera_ (and the _Libellulina_), they cross
each other. The _molaries_ are the largest of all, and their purpose
is evidently to grind the food. There is never only a single one to
each mandible, while the number of the incisives and laniaries is
very variable. As the molaries act the principal part in mastication,
they are nearer the inner base of the mandible or point of support:
they serve to grind the food, which has been first divided by the
incisives or torn by the laniaries. The carnivorous tribes are
destitute of them; in the omnivorous ones they are very small, and
in the herbivorous ones they are very large[1249]. So that in some
measure you may conjecture the food of the animal from the teeth
that arm its mandibles. Of _incisive_ teeth you may find an example
in those that arm the end of the mandibles of most grasshoppers
(_Locusta_), and of the leaf-cutter-bees (_Megachile_ Latr.)[1250];
of the _laniary_ or canine teeth, you will find good examples in
the mandibles of the dragon-flies (_Libellulina_); the two external
teeth of the apex of those of the leaf-cutter bees may be regarded
as between the incisives and laniaries; and the pointed mandibles
without teeth may be deemed as terminating in a laniary one[1251].
The lower part of the inner or concave surface of the mandibles of
grasshoppers will supply you with instances of the _molary_ teeth,
and the apex, also, of those of some weevils, as _Curculio Hancocki_
K.[1252] But the most remarkable example of a molary organ is
exhibited by many of the Lamellicorn beetles, especially those that
feed upon vegetables, whether flower or leaf.--Knoch, who indeed
was the first who proposed calling mandibles according to their
teeth, incisive, laniary, or molary, but who does not explain his
system clearly, observed that the mandibles of some _Melolonthæ_
have a projection with transverse, deep furrows, resembling a file,
for the purpose of bruising the leaves they feed upon[1253]: and
M. Cuvier, long after, observed that the larvæ of the stag-beetle
have towards their base a flat, striated, molary surface; though he
does not appear to have noticed it in any perfect insect[1254]. This
structure, with the exception of the _Scarabæidæ_ and _Cetoniadæ_,
seems to extend very generally through the above tribe; since it may
be traced even in _Geotrupes_, the common dung-chafer, in which at
the base of one mandible is a concave molary surface, and in the
other a convex one, but without any furrows: a circumstance that
often distinguishes those that have furrows.--In the _Dynastidæ_ the
affinity of structure with the _Melolonthidæ_ &c. is more pronounced,
the furrows to which ridges in the other mandible correspond being
reduced to one or two wide and deep ones; whereas in some of the
latter tribe they are very numerous. These mandibles, in many cases,
at their apex are furnished with incisive teeth to cut off their
food, and with miniature mill-stones to grind it[1255]. The part here
alluded to I call the _Mola_.
Were I to ask you what your idea is with regard to the use of
the organs we are considering, you would perhaps reply without
hesitation, "Of what possible use can the _jaws_ of insects be but
to _masticate_ their food?" But in this you would in many instances
be much mistaken; as you will own directly if you only look at
the mandibles of the stag-beetle--these protended and formidable
weapons, as well as those of several other beetles, cannot be thus
employed. "Of what other use, then, can they be?" you will say.
In the particular instance here named, their use, independent of
mastication, has not been satisfactorily ascertained; but in many
other cases it has. Recollect, for instance, what I told you in a
former letter, of those larvæ that use their unguiform mandibles
as instruments of _motion_[1256]. Again: amongst the Hymenopterous
tribes, whose industry and varied economy have so often amused and
interested you, many have no other tools to aid them in their
various labours and mechanical arts: to some they supply the place of
trowels, spades, and pick-axes; to others that of saws, scissors, and
knives--with many other uses that might be named. In fact, with the
insects of this intire Order mastication seems merely a _secondary_,
if it is at any time their use. Still comprehending in one view all
the mandibulate Orders, though some use their mandibles especially
for purposes connected with their economy, yet their most general
and _primary_ use is the division, laceration, and mastication of
their food; and this more exclusively than can be affirmed of the
under-jaws (_maxillæ_). This will appear evident to you, when you
consider that insects in their larva state, in which universally
their primary business is _feeding_, with very few exceptions use the
organs in question for the purpose of mastication, even in tribes, as
the _Lepidoptera_, that have only rudiments of them in their perfect
state--while the _maxillæ_ ordinarily are altogether unapt for such
use. The exceptions I have just alluded to are chiefly confined to
the instance of suctorious mandibles; or those which, being furnished
at the end with an orifice, the animal inserting them into its prey,
imbibes their juices through it. This is the case with the larvæ of
some _Dytisci_, _Hemerobius_, and _Myrmeleon_[1257]; and spiders have
a similar opening in the claw of their mandibles, which is supposed
to instil venom into their prey[1258].
Under this head I must not pass without notice an appendage of the
mandibles, to be found in some of the rove-beetles (_Staphylinidæ_),
as in _Ocypus_, _Staphylinus_, and _Creophilus_ Kirby. In the first
of these it is a curved, narrow, white, subdiaphanous, submembranous,
or rather cartilaginous piece, proceeding from the upper side of the
base of the mandible[1259]; in the second it is broader, straighter,
and fringed internally and at the end with hairs; and in this at
first it wears the appearance of being attached laterally to the
mandible under the tooth[1260], but if closely examined, you will
find that it is separate: in _Creophilus maxillosus_ it is broader.
This is the part I have named _prostheca_. It is perhaps useful in
preventing the food from working out upwards during mastication.
5. _Maxillæ_[1261]. The antagonist organs to the mandible in the
lower side of the head, are the under-jaws, or _maxillæ_--so
denominated by the illustrious Entomologist of Kiel. Linné appears
to have overlooked them, except in the case of his genus _Apis_, in
which he regards them, and properly, as the sheath of the tongue.
De Geer looked upon them in general as part of the apparatus of the
under-lip or _labium_; and such in fact they are, as will appear when
we consider them more particularly. Fabricius has founded his system
for the most part upon these organs, the principal diagnostic of
ten out of his thirteen Classes (properly Orders) being taken from
them; and in the modern, which may be termed the _eclectic_, system,
although the Orders are not founded upon them, yet the characters of
genera, and sometimes of large tribes, are derived from them: and as
they appear less liable to variation than almost any other organ, as
Mr. W. S. MacLeay has judiciously observed, there seems good reason
for employing them--it is therefore of importance that you should be
well acquainted with them.
Their _situation_ is usually below each mandible, on each side of the
_labium;_ towards which they are often somewhat inclined, so that
their tips meet when closed. In some cases, as in the Predaceous
beetles (_Carabus_ L. &c.), they exactly correspond with the
mandibles; but in others their direction with respect to the head is
more longitudinal, as in the _Hymenoptera_, &c. In _substance_ they
may be generally stated to be less hard than those organs; yet in
some instances, as in the _Libellulina_, _Anoplognathidæ_, &c. they
vie with them, and in the _Scarabæidæ_ and _Cetoniadæ_ exceed them,
in hardness. In the bees, and many other _Hymenoptera_, they are
soft and leathery. Their _articulation_ is usually by means of the
hinge on which they sit: it appears entirely ligamentous, and they
are probably attached to the _labium_ at the base, or _mentum_--at
least this is evidently the case with the _Hymenoptera_, in which
the opening of the _maxillæ_ pushes forth the _labium_ and its
apparatus. In that remarkable genus related to the glow-worms, now
called _Phengodes_ (_Lampyris plumosa_ F.), and in the case-worm
flies (_Trichoptera_ K.), the _maxillæ_ appear to be connate with
the _labium_, or at least at their base.--As to their _composition_,
these organs consist of several pieces or portions. At their base
they articulate with a piece more or less triangular, which I call
the hinge (_Cardo_)[1262]. This on its inner side is often elongated
towards the interior of the base of the _labium_, to which it is, as
I have just observed, probably attached. This elongate process of the
hinge in _Apis_, _Bombus_, &c. appears a separate articulation; and
the two together form an angle upon which the _mentum_ sits[1263],
and by this the _maxilla_ acts upon the labial apparatus.
The next piece is the _stipes_ or stalk of the _maxilla_. This is the
part that articulates with the hinge, and may be regarded in some
cases, as in the _Orthoptera_ &c., as the whole of the _maxilla_ below
the feeler; and in others, as in the _Geotrupidæ_, _Staphylinidæ_ &c.,
as only the back of it, the inside forming the lower lobe. This piece
is often harder and more corneous than the terminal part, is linear,
often longitudinally angular, and in the bee-tribes (_Apis_ L.) is
remarkable on its inner side for a series of bristles parallel to each
other like the teeth of a comb[1264]. In _Pogonophorus_ Latr., a kind
of dor or clock-beetle, it is armed on the back with four jointed
spines, the intermediate one being forked[1265]. M. Latreille has thus
described the stipes of the _maxillæ_ of _Coleoptera_: "Next comes
the stalk," says he, "which consists of three parts: one occupies the
back and bears the feeler; the second forms the middle of the anterior
face, and its figure is triangular; the third fills the posterior
space comprised between the two preceding; and is that which is of
most consequence in the use of the _maxilla_; the anterior feeler,
where there are two, the _galea_, and the other appendages that are of
service in deglutition, are part of that piece[1266]."
The _third_ and terminal portion of the _maxilla_ is formed by the
lobe, or lobes (_Lobi_). This may be called the most important part
of the organ, since it is that which often acts upon the food, when
preparing for deglutition. When armed with teeth or spines at the
end, its substance is as hard as that of the mandibles; but when not
so circumstanced, it is usually softer, resembling leather, or even
membrane[1267]; and sometimes the middle part is coriaceous, and the
margin membranous. This part is either simple, consisting only of
_one_ lobe, as you will find to be the case with the _Hymenoptera_,
_Dynastidæ_, _Nemognatha_, and several other beetles; or it is
compound, consisting of _two_ lobes. In the former case, the lobe is
sometimes very long, as in the bee tribes, and the singular genus
of beetles mentioned above[1268], _Nemognatha_; and at others very
short, as in _Hister_, &c. The bilobed _maxillæ_ present several
different types of form. Nearest to those with one lobe are those
whose lower lobe is attached longitudinally to the inner side of
the stalk of the organ, above which it scarcely rises. Of this
description is the _maxilla_ in the common dung-beetle (_Geotrupes
stercorarius_), and rove-beetle (_Staphylinus olens_).[1269]
Another kind of formation is where the lower lobe is only a little
shorter than the upper: this occurs in a kind of chafer (_Macraspis
tetradactyla_ MacLeay).[1270] A third is where the upper lobe covers
the lower as a shield; as you will find in the _Orthoptera_ order,
and the _Libellulina_, and almost in _Meloe_[1271]. A fourth form is
where the upper lobe somewhat resembles the galeate _maxilla_ just
named; but consists of two joints. This exists in _Staphylinidæ_,
&c.[1272] The last kind I shall notice is when the upper lobe not
only consists of two joints, but is cylindrical, and assumes the
aspect of a feeler or _palpus_[1273]. This is the common character
of almost all the Predaceous beetles (_Entomophagi_ Latr.). This
lobe, which has been regarded as an additional feeler, is strictly
analogous to the upper lobe in other insects, and therefore should
rather be denominated a palpiform lobe than a _palpus_. Where there
are two lobes, the upper one is most commonly the longest; but in
many species of the tribe last mentioned the lower one equals or
exceeds it in length[1274].
The lobes vary in form, clothing, and appendages. The upper palpiform
lobe in those beetles just mentioned, in general varies scarcely
at all in _form_; but the genus _Cychrus_ (which is remarkable
for a retrocession from the general type of form of the _Carabi_
L. making an approach towards that of those _Heteromera_ which,
from their black body and revolting aspect, Latreille has named
_Melosomes_,) affords an exception, the upper joint being rather
flat, linear-lanceolate, incurved, and covering the lower lobe[1275],
which it somewhat resembles. The lower lobe also in this tribe
varies as little as the upper, being shaped like the last joint of
that lobe in _Cychrus_ just described, except that in _Cicindela_ it
is narrowest in the middle[1276]. In other tribes the upper valve is
sometimes linear and rounded at the apex, and the lower truncated, as
in _Staphylinus olens_[1277]; sometimes the upper one is truncated or
obtuse, and the lower acute, as in _Trogosita_ and _Parnus_[1278]. In
_Ptinus_, another tribe of beetles, before noticed as injurious to
our museums[1279], the reverse of this takes place, the upper-lobe,
which is the smallest and shortest, being acute, and the lower
truncated[1280]. In _Blaps_ both are acute[1281]. In _Rhipiphorus_
and _Scolytus_ the lobes are nearly obsolete. The lower lobe is bifid
in _Languria_, a North American genus of beetles, so as to give the
maxilla the appearance of three lobes[1282]; and in _Erotylus_,
a South American one, the upper is triangular[1283]: it is often
oblong, quadrangular, linear, &c. in others.--In those that have
only one lobe the shape also varies. In _Gyrinus_, the beetle that
whirls round and round on the surface of every pool, which, though
it belongs to the Predaceous tribe, has only one lobe, the lobe
represents a mandible in shape of the laniary kind, being trigonal
and acute[1284]; and in the _Anoplognathidæ_, a New Holland tribe
of chafers, in which it is, as it were, broken, the lobe forming an
angle with the stalk, it is concavo-convex and obtuse, and somewhat
figures a molary tooth[1285]. In the first tribe into which the bees
(_Apis_ L.) have been divided (_Melitta_ Kirby), the lobe is often
linear or strap-shaped, and bifid at the apex; and in the second
(_Apis_ K.) lanceolate and intire[1286]. In _Cerocoma_ it is long and
narrow[1287]. More variations in form might be named, but these are
sufficient to give you a general idea of them in this respect. With
regard to their _clothing_, I have not much to observe--in examining
the Predaceous beetles you will observe, that the interior margin of
the lower incurved lobe is fringed with stiff bristles or slender
spines, and in many other beetles either one or both lobes have a
thick coating or brush of stiffish hairs[1288]; but in several cases
only the apex of the lobe is hairy. In the _Orthoptera_ order, and
many of the _Melolonthidæ_ or chafers, the whole _maxilla_ is without
hairs, or nearly so.
The _appendages_ of the _maxillæ_ are next to be noticed. These are
principally their claws, or laniary teeth; for they are seldom armed
with incisive or molary teeth. The whole tribe of Predaceous beetles,
with few exceptions, have the inner lobe of their _maxilla_ armed
with a terminal claw, which in the _Cicindelidæ_ articulates with the
lobe, and is moveable, but in the rest of the tribe is fixed[1289].
In _Phoberus_ MacLeay the lower lobe has two spines[1290]. In
_Locusta_ this lobe has three or four spines or laniary teeth, and
in _Æshna_ there are six, which, like the claw of _Cicindela_, are
moveable[1291]. In others both lobes terminate in a single spine or
claw: this is the case with _Paxillus_ MacLeay[1292]. In _Passalus_,
nearly related to the last genus, the upper lobe is armed with a
single spine, and the lower one with two[1293]. Those _maxillæ_
that terminate in a single lobe are also often distinguished by the
spines or teeth with which it is armed; thus in a nondescript chafer
belonging to the _Dynastidæ_ (_Archon_ K. MS.) it terminates in _two_
short teeth; in that remarkable Petalocerous genus _Hexodon_ Oliv.
in _three_ truncated _incisive_ ones[1294]; in _Dynastes Hercules_
in three _acute_ spines[1295]. _Four_ similar ones arm the apex of
the _maxilla_ in that tribe of _Rutelidæ_ which have striated elytra;
and _five_ that are stout and triquetrous those of _Melolontha
Stigma_ F. Many others have _six_ spines, sometimes arranged in a
triple series[1296]. Besides teeth or spines, in some cases the
lobes of _maxillæ_ terminate in several long and slender _laciniæ_
or lappets fringed with hairs. At least those of a _Leptura_
(_L. quadrifasciata_ L.) described by De Geer, appear to be thus
circumstanced. He conjectures that this beetle uses its _maxillæ_ to
collect the honey from the flowers[1297].
As the principal use of the mandibles is cutting and masticating, so
that of the organs we are considering seems to be primarily that of
_holding_ the food and preventing it from falling while the former
are employed upon it. I say this is their _primary_ use; for I
would by no means deny that they assist occasionally in comminuting
or lacerating it. In fact, were there no organs appropriated to
this use, and if both mandibles and _maxillæ_ were employed at
the same time in comminuting the food, it seems to me that it
must fall from the mouth. In a large proportion of insects the
lobes of the _maxillæ_ are not at all calculated for laceration or
comminution; and in those tribes--as the _Melolonthidæ_, _Rutelidæ_,
_Dynastidæ_--in which they seem most fitted for that purpose, the
mandibles have _incisive_ teeth at their apex, and at their base a
powerful _mola_ or grinder: circumstances which prove, that even in
this case the business of mastication principally devolves upon them.
6. _Palpi Maxillares_[1298]. There is one circumstance that
particularly distinguishes the _maxillæ_ from the mandibles--they
are _palpigerous_, as well as the under-lip. The feelers, or palpi,
emerge usually from a sinus observable on the back of the _maxillæ_
where the upper lobe and stalk meet. Their articulation does not
materially differ from that of the labial palpi. Each _maxilla_ has
properly only _one_ feeler; but, as was lately observed[1299], in
certain tribes the upper lobe is jointed and palpiform, which has
occasioned it to be considered as a feeler, and these tribes have
been regarded as having six feelers. The most general rule with
regard to the _length_ of the _palpi_ is, that the maxillary shall
be longer than the labial; but the reverse often takes place. In
many _bees_ the maxillary consist only of a _single_ joint, and
are very _short_; while the labial consist of _four_, and are very
_long_[1300]: and in some insects (as in _Pogonophorus_ Latr.)
the four palpi are of equal length[1301]. The antennæ are most
commonly longer than the palpi; but in several aquatic beetles, as
_Elophorus_, _Hydrophilus_, &c., whose antennæ in the water are not
in use, the organs we are considering are the longest.--As to the
_number_ of their articulations, it varies from one to six; which
number they are not known to exceed. In each of the Orders a kind
of law seems to have been observed as to the number of joints both
in the maxillary and labial palpi, but which admits of several
exceptions. Thus in the _Coleoptera_, the _natural_ number may
be set at _four_ joints for the _maxillary_, and _three_ for the
_labial_ palpi: yet sometimes, as in _Stenus_, _Notoxus_, &c., the
_former_ have only _three_ joints, and the _latter_, as in _Stenus_
and _Tillus_, only _two_. In the _Orthoptera_ the law enjoins _five_
for the _maxillary_, and _three_ for the _labial_; and to this I
have hitherto observed no exception. In the _Hymenoptera_, the rule
is _six_ and _four_, but with considerable exceptions, especially
as to the _maxillary_ palpi, which vary from _six_ joints to a
_single_ one: thus in the hive-bee and the humble-bee, the labials,
including the two flat joints or elevators, have four joints, while
the maxillaries are not jointed at all[1302]. In _Chrysis_, in which
the latter consist of _five_, the former are reduced to _three_. The
_Libellulina_ may almost be regarded as having no maxillary palpi,
since they exhibit no organ that is distinctly palpiform. It seems to
me that the upper lobe of their maxilla, which articulates with the
stalk in the same manner as a feeler, may be regarded as an instance
in which that lobe and the feeler coalesce into one; and the mucro
that proceeds from the lobe has the aspect of an emerging feeler, and
corresponds somewhat with the labial one above noticed[1303]. In the
remainder of the _Neuroptera_ and the _Trichoptera_, the prevailing
number is _five_ and _three_. In the latter there are exceptions,
which will furnish good characters for genera. In the _Lepidoptera_
we find _two_, and sometimes _three_, the maxillary being very
minute[1304]. The _Diptera_ Order presents two tribes in this
respect quite distinct from each other. The most natural number of
joints in the maxillary palpi of the _Tipulidæ_, _Culicidæ_, &c. is
_four_ or _five_: the last joint, however, in _Tipula_, _Ctenocera_,
&c. like that of the antennæ in _Tabanus_ L., appears to consist
of a number of very minute joints[1305]; but in the _Asilidæ_ and
_Muscidæ_, &c., the number _two_ seems to be most prevalent[1306].
The _labial_ palpi in this order are obsolete.--As to _shape_, the
maxillary palpi, as well as the labial, are usually filiform; but in
the weevil tribes (_Curculio_ L.) they are most commonly very short
and conical[1307]; in the chafers (_Scarabæus_ L.) they usually are
thickest at the apex[1308]; in _Megachile_ and _Euglossa_, wild bees,
they are setaceous, growing gradually more slender from the base
to the summit[1309]: a tribe of small water-beetles (_Haliplus_),
the saw-flies (_Tenthredo_ L.), and several other _Hymenoptera_,
have them thickest in the middle[1310]. Their most important part,
however, and that which varies most in form, is the _terminal_
joint:--of this I have already related some singular instances[1311],
and shall now describe a few more. This joint is sometimes acute,
at others blunt, at others truncated: in figure it is ovate,
oblong, obtriangular, hatchet-shaped, lunate, transverse, conical,
mammillate, subulate, branched, chelate, laciniate, lamellate, &c.
&c.[1312]: terms which I shall more fully explain to you hereafter,
and which I only mention here to show the numerous variations as to
figure, of which this joint exhibits examples. The palpi in general
at their vertex are often rather concave; and this concavity is
formed by a thin papillose membrane, which it is supposed the animal
has the power of pushing out a little, so as to apply it to surfaces.
The _primary_ use of the palpi of insects will be considered when I
treat of their senses; but they probably answer more purposes than
one. For instance, when I was once examining, under a lens, the
proceedings of a species of _Mordella_, which was busily employed
in the blossom of some umbelliferous plant, it appeared to me to
open the anthers with its maxillary palpi, and they often held the
anther between them: when not so employed, they were kept in intense
vibration, more than even its antennæ; and at the same time, as far
as I could judge, an _Elater_ made the same use of them.
7. _Lingua_[1313].--This name was applied by Linné to the part in
insects representing the _tongue_ in vertebrate animals; and as it
performs most of the common offices of a tongue, and the _pharynx_
is situated with respect to it, as we shall presently see, nearly
as it is in those animals, there seems no more reason for giving
it a new name, than there is for giving a new name to the head or
legs of insects, because in some respects they differ from those of
the higher animals. I shall not therefore call it _Ligula_, with
Fabricius and Latreille, nor _Labium_, with Cuvier and others, but
adhere to the original term, which every one understands.
The _tongue_ lies between the two _lips_--the _labrum_ and _labium_.
On its upper side, at the base, it meets the palate or roof of the
mouth, below which it is attached, it may be presumed, by its roots
to the crust of the head, on each side the _pharynx_ or swallow; and
on its lower side, in many cases, it is attached to the _labium_, and
that very closely, so as to appear to be merely a part of it, and
to form its extremity: but in the _Orthoptera_ and _Libellulina_,
it is more free, and in form somewhat resembling the tongue of the
quadrupeds[1314].--In _substance_ the tongue varies. In general it
seems something between membrane and cartilage; but in the Predaceous
beetles, in which it is not covered by the _labium_, it approaches
nearer to the substance of the general integument, and in _Anthia_ F.
it is quite hard and horny:--that just mentioned of the _Orthoptera_
and _Libellulina_ is more fleshy[1315]. With regard to its _station_,
in many cases, as in the instance just named, in the Lamellicorn
tribe (_Scarabæus_ L.) and others, it is, when unemployed, concealed
within the mouth; the lips, mandibles, and maxillæ all closing over
it. The tongue of some _Hymenoptera_ also is retractile within the
mouth. "When _ants_ are disposed to drink," says M. P. Huber, "there
comes out from between their lower jaws, which are much shorter
than the upper, a minute, conical, fleshy, yellowish process, which
performs the office of a tongue, being pushed out and drawn in
alternately: it appears to proceed from the lower-lip.--This lip has
the power of moving itself forwards in conjunction with the lower
jaws: and when the insect wishes to lap, all this apparatus moves
forward; so that the tongue, which is very short, does not require to
lengthen itself much to reach the liquid[1316]." M. Lamarck thinks
that the _labium_ of insects has a _vertical_ motion (_de haut en bas
ou de bas en haut_)[1317]. This it certainly has in some degree; but
it has also, as in the above case, a more powerful _horizontal_ one,
which is produced, in _Hymenoptera_ at least, by the opening of the
maxillæ--as I have already observed[1318].
I have little to say with respect to the _structure_ of the tongue:
it generally seems to be without articulations; but in many bees it
articulates with the _labium_ where it enters it, so as when unemployed
to form a fold with it. In the hive-bee it terminates in a kind of
knob or button, which has been falsely supposed to be perforated
for imbibing the honey by suction. The upper part of this tongue
is cartilaginous, and remarkable for a number of transverse rings:
below the middle, it consists of a membrane, longitudinally folded in
inaction, but capable of being inflated to a considerable size: this
membranous bag receives the honey which the tongue, as it were, laps
from the flowers, and conveys it to the _pharynx_[1319]. In _Stenus_
this organ is retractile, and consists of two joints[1320].
The _shape_ of the tongue of insects probably varies as much as
any other part; but as it is apt to shrink when dried[1321],
and is not easy to come at, we know but little of its various
configurations:--in the bees it is very long, in most other insects
very short. Though frequently simple and undivided, in many cases
it presents a different conformation. Thus in the saw-flies
(_Tenthredo_ L.) it terminates in three equal lobes[1322]; in
_Stomis_ and _Geotrupes_ in three unequal ones, the intermediate
being very short[1323]; in _Carabus_, in three short teeth[1324];
in _Pogonophorus_ it represents a trident[1325]; in the wasp it is
bifid, each lobe being tipped with a callosity[1326]; in _Melolontha
Stigma_ it is bipartite[1327]; in _Elaphrus_, the analogue of the
tiger-beetles, it terminates in a single tooth or point; in the
aquatic beetles, _Dytiscus_ L., it is quadrangular and without
teeth[1328]; in some _Ichneumonidæ_ it is concavo-convex, and forms a
demitube; and in others it is nearly cylindrical[1329].
In many insects it has no _hairs_, but in the Predaceous beetles it
generally terminates in a couple of bristles[1330]. In the hive-
humble- and other bees, it is extremely hairy[1331]; a circumstance
which probably enables it more effectually to despoil the flowers of
their nectar. In _Geotrupes stercorarius_, the common dungchafer, and
_Melolontha Stigma_ lately mentioned, the lobes of the tongue are
fringed with incurved hairs[1332]; and in _Æshna_ it is hairy on the
upper side, each hair or bristle crowning a minute tubercle. In many
cases the tongue is attended, and sometimes sheathed at the base,
by two usually membranous appendages:--these the learned Illiger
has denominated _paraglossæ_; and I shall adopt his term. You
will find them frequently attached to the tongue of the Predaceous
beetles[1333], and to that of many _Hymenoptera_. In the hive-bee and
humble-bee they are short, and take their origin within the _labial_
feelers[1334]: in _Euglossa_, another bee, they are long, involute at
the tips, and, what is not usual with them, very hairy[1335]: in the
wasp, like the lobes of the tongue, they are tipped with a callosity.
Under this head I may observe to you, that the insects whose oral
organs we are considering besides a _tongue_ appear likewise to be
furnished with a _palate_ (_Palatum_). This, though a part of the
roof of the mouth, is not precisely in the situation of the palate
of vertebrate animals, since it seems rather the internal lining of
the _labrum_. If you take the common dragon-fly (_Æshna viatica_),
you will find that the under side of this part and of the _rhinarium_
is lined with a quadrangular fleshy cushion, beset, like the upper
surface of the tongue, with minute black tubercles, crowned with
a bristle. This cushion is divided transversely into two parts by
a depression; the anterior or outer piece being attached to the
_labrum_, and the other piece to the _rhinarium_. The former has a
central longitudinal cavity, black at the bottom, on the sides of
which the tubercles are flat and without a bristle. From its base on
each side a spiniform process emerges, forming a right angle with it.
These processes seem the antagonists of those mentioned above[1336],
that emerge from the _labium_. The posterior or inner piece has on
each side a roundish space, attached to the under surface of the two
sides of the _rhinarium_, beset also with bristle-bearing tubercles.
You will find something similar lining the _labrum_ and _nasus_ of
some _Coleoptera_,--say _Geotrupes_, _Necrophorus_, and _Dytiscus_.
The first piece I regard as the analogue of the palate, and the
second as connected with the sense of _smelling_. In _Necrophorus_
the circular pieces are covered with a finely striated membrane, and
in _Dytiscus_ each has a little nipple.
8. _Pharynx_[1337].--On the upper side of the tongue, usually at its
base or root, is the _pharynx_, or aperture by which the food passes
from the mouth to the _œsophagus_. This orifice, which is situated
with respect to the tongue of the _Orthoptera_ and _Libellulina_
nearly as in those insects (at least as far as I have been able to
examine them), whose tongue is called a _ligula_ or _labium_,--of
course exists in all the mandibulate Orders whose mouth we are now
considering. In the _Hymenoptera_ it is covered by a valve, the
_Epipharynx_ of Savigny; and it appeared to me to be so likewise in
one of the _Harpalidæ_ that I examined. The formation seems different
in _Geotrupes_, as far as I can get an idea of it; but it is so
difficult to examine the interior of the mouth without laceration of
some of the parts, that I can only tell you what the appearances were
in one instance, upon removing the _labrum_ from the _mandibles_; and
in another, separating the whole apparatus of the _labium_, including
the _maxillæ_, from the _mandibles_ and _labrum_. In the former case,
the mandibles coincided at the base, the two molary plates (_molæ_),
which in this genus are narrow, transverse and not furrowed, are
so applied as evidently to have an action upon each other, as the
mandible opens and shuts, proper for trituration. Within these is
the base of the tongue, under the form of a ventricose sack. The
upper part of this last organ, which forms the internal covering
of the labium, appears to consist of three (in the recent insect
_fleshy_) lobes, the middle one being bent downwards internally, so
as to form a kind of sloping cover to an orifice in the part I call
the base. After two or three days, the tongue shrinks and dries to
a hard substance;--between the mandibles and the base of the tongue
I could not discover the _pharynx_. The above apparent opening
covered by the tongue was the only one I could perceive. In the
latter case, the form and structure of the base of the tongue is more
visible: it is an oblong ventricose tubular sack, projecting above
anteriorly into an acute angle formed by a fine white membrane, most
beautifully and delicately striated with oblique striæ, to be seen
only under a powerful lens: on the anterior side of this sack are
two parallel cartilaginous ridges close to each other, fringed with
short hairs, which take their origin from the angle. I could not be
certain whether the orifice covered by the intermediate lobe was only
apparent, or real; but I did not succeed in my endeavour to find any
other _pharynx_, though from the molary structure of the base of the
mandibles one may conjecture that there must be one situated at the
base of this sack to receive the food they render after trituration.
The excrement of this animal is not fluid. In the _Libellulina_
the _pharynx_ seems closed by two valves meeting. This part in
_Hymenoptera_, and probably in other Orders, has the aspect of being
cartilaginous and fitted to sustain the action of the substances that
have to pass through it[1338].
The _Epipharynx_ is a valve, called by M. Latreille _sublabrum_
(_sous labre_[1339]), attached by its base to the upper margin of
the _pharynx_, or that next the _labrum_. In the bees it is said by
Reaumur to be of a fleshy substance, and capable of changing its
figure. He seems to think it the real _tongue_ of the bee[1340]; but
as it does not appear to have any of the uses of a tongue, and merely
closes the orifice of the mouth, it surely does not merit that name.
M. Savigny calls it a membranous appendage which exactly closes the
_pharynx_[1341]. De Geer has examined the _epipharynx_ of the wasp,
which he describes as of a scaly substance, and regards merely as the
cover of the part just named[1342].
With regard to the _Hypopharynx_, which Latreille considers as a
support and appendage of the _epipharynx_, I have little to add to
the definition I have given of it above. In the _Libellulina_ the
base of the tongue terminates towards the _pharynx_ in a fleshy
cushion, armed at each angle next to that part with a short hard
horn or tooth of a black colour. This cushion, I suppose, may be
analogous to the _hypopharynx_ of M. Savigny[1343]. On the opposite
side the pharynx is closed by another fleshy cushion (_epipharynx?_),
which appears to line the nose, behind those two mammillæ before
described[1344], which form the internal covering of the _rhinarium_.
Before I call your attention to what I would denominate an
_imperfect mouth_, in which some one or more of the seven organs
above enumerated exist under another form, or only as rudiments,--I
must say something upon the mouth of the _Myriapods_ and _Arachnida_,
in which there seem to be _redundant_ organs of manducation.--M.
Latreille, in the Essay lately quoted, in which, though some of
his notions seem fanciful, he has shown a vast depth and range of
thought and research, has asserted,--from the admirable and curious
observations of M. Savigny, and those which since their publication
he has made himself,--that the masticating organs of _annulose_
animals (called by him _condylopes_) are a kind of _legs_[1345].
And M. Savigny, whose indefatigable labours and unparalleled
acuteness have opened the door to a new and vast field in what may
be denominated analogical anatomy,--has observed, that with certain
_Apiropods_[1346] the organs that serve for manducation do not differ
essentially from those which, with the other _Apiropods_ and the
_Hexapods_, serve for _locomotion_[1347]: and the unguiform mandibles
of the larvæ of certain _Diptera_, you have before been told, are
used not only in manducation, but also as legs[1348]. These remarks
will satisfactorily prove to you, that organs which at first sight
possess no visible affinity or analogy--as for instance, jaws and
legs--may, if traced through a long series of beings, exhibit a very
great one;--and will lessen your surprise when you find, that in
certain tribes such commutations of organs and their use take place.
The following is the structure, as to its organs, of the mouth of
the myriapods, as exhibited by the centipedes (_Scolopendridæ_). The
part which appears to perform the office of the upper lip (but which
M. Savigny regards as the nose, calling it the _chaperon_,) is a
transverse piece with a deep anterior sinus, in the centre of which is
a minute tooth[1349]. This piece is separated from the forepart of the
head by a suture; but it probably is not moveable: however, it covers
the mouth, and may be regarded rather as analogous to the _labrum_.
Below this are two mandibles, armed at their end with five sharp
triangular teeth[1350], under which are the _maxillæ_, terminating
in a moveable concavo-convex lobe, resembling the valve of a bivalve
shell[1351]; and between them is the _labium_, of a rhomboidal shape,
divisible into two lobes, attached laterally to the maxillæ: these
lobes M. Savigny terms the _second maxillæ_, forming with the others,
according to him, the _labium_[1352]. Affixed to the base of this
labium, or covering it on the outside, are a pair of pediform palpi,
which he considers as the first auxiliary _labium_, and representative
of the first pair of legs of hexapods and _Iuli_[1353]. I imagine them
to be also the analogues, in some degree, of the labial palpi of a
perfect mouth. The last of the organs in question is a large rhomboidal
plate affixed to the first apparent segment of the trunk, crowned at
its vertex with two truncated denticulated teeth, and from the upper
sides of which emerge a pair of moveable organs terminating in a
powerful incurved claw, and which entirely covers all the other parts
of the mouth[1354]. This, M. Savigny deems as a _second_ auxiliary
_labium_, and the lateral organs of prehension,--which may be regarded
each as a kind of maxillary hand, and as the only representatives in
this tribe of the maxillary palpi, though widely different,--he looks
upon as really analogous to the _second_ pair of legs in _Iulus_
and the hexapods[1355]. These two pairs of pedipalpes (to use an
expressive French term) show their relation to legs by their general
structure, and their analogy with palpi by their use as _oral_ organs,
though belonging to the _trunk_: so that here we see the _legs_ and
their appendages assume a material function in _manducation_, forming
a singular contrast to what we had observed before with regard to
_mandibles_ becoming instruments of _locomotion_. The mouth of the
_Iulidæ_, with little variation, is upon the same plan[1356] with those
here described.
The next type of form with regard to the oral organs is that of the
_Arachnida_. In these, as you know, the head is confounded with the
trunk; so that they are a kind of Blemmyes in the insect world. Their
organs of manducation, amongst which there is no _labrum_ or upper lip,
are, in the first place, a pair of mandibles planted close and parallel
to each other in the anterior part of the head, which they terminate.
In the spiders they consist of two tubular joints, of which the first
is much the largest, more or less conical or cylindrical, and armed
underneath with a double row of stout teeth; and the terminal one is
more solid and harder, in the form of a very sharp crooked claw, which
in inaction is folded on the first joint between the teeth. Under its
extremity on the outside is a minute orifice, destined to transmit a
venomous fluid, which is conducted there by an internal canal from
the base of the first joint, where is the poison-bag[1357]. In the
scorpion and harvest-man (_Phalangium_) the mandible consists of two
joints terminated by a _chela_ or double claw, the exterior one being
moveable[1358].--M. Latreille, as has been before observed, regards
these not as representatives of the mandibles of hexapods, but as
replacing the interior pair of antennæ, in the situation of which they
are precisely placed, of the _Crustacea_[1359]: and M. Savigny is of
opinion that the _Arachnida_ may in some sort be defined as _Crustacea_
without a head, and with twelve legs, of which the two first pair are
converted into _mandibles_ and _maxillæ_[1360]. From the _situation_ of
the organs in question, the first of these opinions seems preferable;
but the conversion of the legs in other cases, at least the _coxæ_,
into organs of manducation, gives some weight to the last. With regard
to their _use_, it is said to be to retain the insect which the animal
has seized, and to facilitate the compression which the maxillæ
exercise upon it for the extraction of the nutritive matter[1361].
If this be correct, _in this respect_ the mandibles may be said to
represent the _maxillæ_ of the mandibulate hexapods; and, _vice versa_,
the _sciatic_ maxillæ, as they have been denominated[1362], of the
_Arachnida_, their mandibles. The palpi are pediform, and the first
joint of the _coxa_, or hip, acts the part of a _maxilla_:--this is
composed of a single piece or plate, more or less oval or triangular,
sometimes straight and sometimes inclined to the _labium_, with
the interior extremity very hairy. The _labium_ consists also of a
single piece, and is only an appendage of the anterior extremity of
the breast. The interior of the mouth, or palate, presents a fleshy,
hairy, linguiform piece, which is usually applied to the internal face
of the _labium_. An opening is supposed to exist in its sides, for
the transmission of the alimentary juices[1363]. If you examine the
under side of the body of a scorpion, you will find that not only the
palpi, but the two anterior pair of legs, by means of their _coxæ_, are
concerned in manducation: so that these insects have in fact _three_
pairs of maxillæ--a circumstance that M. Savigny has observed to take
place also in the harvest-men (_Phalangium_ L.)[1364]. The _palpi_ of
the scorpion, which may be called its _hands_, like the anterior legs
of the lobster and crab, terminate in a tremendous _chela_ or forceps,
consisting of a large triangular joint, armed at the end with a double
claw internally toothed; the _exterior_ one of which, contrary to
what takes place in the animals just named, is moveable, and not the
_interior_[1365].
* * * * *
Having given you this full account of the _trophi_ of those animals
that have all the organs of manducation developed, I must next advert
to those in which one part receives an increment at the expense of
others, and the whole oral machine is fitted for _suction_; or where
some parts appear to be deficient, so that this may be called an
_imperfect_ mouth. At first sight one would regard the trophi of a
_bee_ as of this description; but this is not the case, since it has
all the ordinary organs, though the tongue is unusually long, and
looks as if it was made for suction; which, however, as you have been
informed, is not the case.
There are _five_ kinds of _imperfect_ mouth to be met with in insects
that take their food by suction, each of which I shall distinguish
by a separate denomination. The first is that of the _Hemiptera_
Order:--this I term the _Promuscis_; the second is that of the
_Diptera_, which with Linné I call _Proboscis_; the third, peculiar
to the _Lepidoptera_, is with me an _Antlia_; the fourth, which I
name _Rostrulum_, is confined to the _Aphaniptera_ order, or genus
_Pulex_ L.; and the last is _Rostellum_, which I employ to denote the
suctory organs of the louse tribe (_Pediculidæ_).
i. _Promuscis_[1366].--The organ we are first to consider has usually
been denominated _Rostrum_: but since that term is likewise in
general use for the snout of insects of the weevil tribes (_Curculio_
L.), I think you will concur with me in adopting the one here
proposed, for the very different oral instruments of the _Hemiptera_.
Illiger has employed _promuscis_ to denote those of _bees_[1367]:
but since, as I have just observed, they consist of all the ordinary
organs, they seem to require no separate denomination: the term,
therefore, may be applied to represent a different set of _trophi_,
without any risk of producing confusion. This part consists of
_five_ pieces: viz. a minute, long, conical piece, commonly very
slender, which covers the base of the _promuscis_, and represents the
_labrum_[1368]; a jointed sheath (_vagina_), consisting of either
three or four joints, the analogue of the _labium_, and four slender
rigid lancets (_scalpella_), the two exterior ones, according to M.
Savigny, representing the _mandibles_, and the intermediate pair
the _maxillæ_[1369]. By the union of these four pieces a suctorious
tube is formed, which the animal inserts into the substance, whether
animal or vegetable, the juices of which form its nutriment. These
pieces are dilated at their base, and serrated at their apex; and the
two central ones, though at their origin they are asunder, form one
tube, which has often been mistaken for a single piece. A _pharynx_
and _tongue_ have been discovered by M. Savigny in this apparatus;
who thinks that in _Nepa_ there are also rudiments, but very
indistinct, of _labial palpi_: so that the _maxillary palpi_ seem to
be the only part absolutely wanting[1370].
The _Promuscis_ when at rest is usually laid between the legs; but
when employed, in most cases its direction is outward. In the genus
_Chermes_ L. (_Psylla_ Latr.) the origin of the _promuscis_ has
been supposed to be in the _breast_; but if closely examined, this
anomaly in nature will be found not to exist. If you take one of
these insects, the first thing that strikes you upon inspecting the
head, is a pair of remarkable conical processes into which the front
appears to be divided. Look below these, and you will there discover
the upper-lip: and from this you may follow the _promuscis_ till it
gets beyond the forelegs, when it takes a direction perpendicular
to the body[1371]; a circumstance which has given rise to the above
false notion. Though in _Coccus_, _Chermes_, &c. this instrument is
short, in some _Aphides_ it is longer in proportion than in any other
insect. In _A. Quercus_ it is three times the length of the body; so
that when folded, it stretches out beyond it, and looks like a long
tail[1372]; and in _A. Abietis_ it even exceeds that length[1373].
ii. _Proboscis_[1374].--Linné long since, and after him Fabricius,
has employed this term to designate the oral instruments, or rather
their sheath, in the _Muscidæ_ and some others, calling the same
organ, when without fleshy lips, _rostrum_ and _haustellum_: but
as the parts of the mouth in all true _Diptera_ (for _Hippobosca_
and its affinities can scarcely be deemed as co-ordinate with the
rest), are analogous to each other; although in some they are stiff
and rigid, in others flexile and soft, and in _Œstrus_ (except the
palpi) mere rudiments,--the same appellation ought to designate them
all. I am happy to find that M. Latreille agrees with me in this
opinion; and to his sensible observations on this head, if you wish
for further information, I refer you[1375]. The mouth of Dipterous
insects appears to vary in the number of pieces that it presents;
but in all, the _theca_ or sheath is present, which represents the
_labium_ (including the _mentum_) of the mandibulate Orders[1376].
It consists of _three_ joints, the last of which is formed by the
liplets (_Labella_). Those in the _Muscidæ_ are large, turgid,
vesiculose, and capable of dilatation; in the _Bombylidæ_ and other
tribes they are small, slender, long and leathery, and sometimes
recurved. The second joint or stalk, which may be said to represent
the _mentum_, the liplets being properly in a restricted sense
the analogue of the _labium_, its sides being turned up, forms a
longitudinal cavity, which contains the _haustellum_. The upper piece
of this, the _valvula_, is long, rigid, and very sharp, representing
the _labrum_[1377]. Beneath this cover, in the above cavity, are the
lancets; which, as far as they are at present known, vary in number
and form: sometimes there are _five_ of them, sometimes _four_,
sometimes _two_, and sometimes, it should seem, only _one_[1378]. In
the gnat (_Culex_) they are finer than a hair, very sharp, and barbed
occasionally on one side[1379]; in the horse-fly (_Tabanus_ L.) they
are flat and sharp like the blade of a knife or lancet[1380]. In
this tribe the upper pair, or the knives (_Cultelli_), represent the
_mandibles_; the lower pair, or the lancets (_Scalpella_), usually
palpigerous, the _maxillæ_; and the central one the _tongue_. In the
horse-fly Reaumur has figured only _four_, exclusive of the _labrum_
and _labium_; but in a specimen I have preserved there appear to be
_five_, one of which, as slender as a hair, I regard as the analogue
of the tongue[1381].--When the lancets are reduced to two, they
probably represent the _maxillæ_, the mandibles being absorbed in the
_labrum_; and where there is only one, the maxillæ also are absorbed
by the _labium_, which then bears the palpi, the lancet representing
the tongue[1382]. The lancets are so constructed in many cases, as
to be able by their union to form a tube proper for suction, or
rather for forcing the fluid by the pressure of the lower parts to
the _pharynx_[1383]. _Labial palpi_ appear not usually present in the
_proboscis_; but M. Savigny thinks he has discovered vestiges of them
in _Tabanus_[1384]. In this genus the maxillary ones are large, and
consist of _two_ joints[1385]. The proboscis is often so folded, as
to form two elbows; the base forming an angle with the stalk, and the
latter with the lips, so as in shape to represent the letter Z, only
that the upper angle points to the breast, and the lower one to the
mouth: this is the case with the flesh-fly and many others. In other
flies, as _Conops_ and _Stomoxys_, whose punctures on our legs so
torment us[1386], there is only a single fold, with its angle to the
breast. The _proboscis_ is received in a large oblong cavity of the
underside of the anterior part of the head.
It may here be observed, that in the _promuscis_ the elongation
of the organs seems to be made chiefly at the expense of _all_ the
palpi, but in the _proboscis_ at that of the _labial_ only; and in
some cases at that also of the _mandibles_ or _maxillæ_;--the former
merging in the _labrum_ and the latter in the _labium_.
iii. _Antlia_[1387].--The _third_ kind of imperfect mouth is that
of the _Lepidoptera_, which I have called _Antlia_. Fabricius
denominates it _lingua_: but as this organ has no analogy with the
real tongue of insects, this is confessedly improper, and it appeared
necessary therefore to exchange it for another denomination: I
have endeavoured to apply a term to it that indicates its use--to
pump up, namely, the nectar of the flowers into the mouth of the
insect. On a former occasion I described to you the structure of
this instrument[1388]; but further discoveries with regard to it
having since been made by MM. Savigny and Latreille, I shall here
give you the result of their observations. The former of these
able physiologists has detected in the mouth of the _Lepidoptera_
rudiments of almost all the parts of a perfect mouth. Of the
correctness of this assertion you may satisfy yourself, if you
consult his admirable elucidatory plates, and compare them with the
insects. Just above the origin of the spiral tongue or pump, the head
is a little prominent and rounded; and immediately below the middle
of this prominence there is a very minute, membranous, triangular or
semicircular piece; which from its position, as covering the base of
the _antlia_, may be regarded as the rudiment of the _upper-lip_
(_labrum_)[1389]. On each side of the outer base of the _antlia_ is
another small immoveable piece, resembling a flattened tubercle,
the end of which is internally hairy or scaly: these pieces appear
to represent the _mandibles_[1390]. Near the base of each half
of the _antlia_, just below a sinus, may be distinctly seen the
minute, usually biarticulate rudiment of a _maxillary palpus_[1391];
demonstrating to a certainty that these spiral organs, at least their
lateral tubes or _Solenaria_, are real maxillæ[1392]. The rudiment
of the _under-lip_ (_Labium_) is the almost horny triangular piece
united by membrane to the two stalks of the maxillæ, and supporting
at its base the recurved labial palpi; which are so well known
that I need not enlarge upon them[1393]. Amongst these parts there
seems at first sight no representative of the _tongue_; but M.
Latreille has advanced some very ingenious, and I think satisfactory
arguments[1394], which go to prove that this part, at least the
tongue of _Hymenoptera_, has its analogue in the intermediate tube or
_Fistula_ formed by the union of the two maxillæ, and which conveys
the fluid aliment of this Order to the _pharynx_. As in _Diptera_
the _maxillæ_ sometimes merge in the _labium_, so here the _tongue_
(as it were divided longitudinally) merges in the _maxillæ_. He
further observes, that in a transverse section of the maxilla of the
death's-head hawk-moth (_Sphinx Atropos_), the lateral tube appeared
to be divided into two by a membranous partition, and to contain
in the upper cavity a small cylindrical tube, which seemed to be a
_trachea_[1395]. To animals that are without lungs, and breathe by
_tracheæ_, suction must be performed in a very different way from
what it is by those that breathe by the _mouth_: and as in the very
extended organs in question the fluid has a long space to pass before
it reaches the _pharynx_, in some way or other these lateral tubes
may have the power of producing a vacuum in the middle tube, and so
facilitate its passage thither. We see, in the _antlia_, that the
maxillæ receive their vast elongation at the expense of all the other
organs, except the _labial palpi_.
iv. _Rostrulum_[1396].--An animal very annoying to us affords the
type of the next kind of imperfect mouth--I mean the _flea_. Its oral
apparatus, which I would name _rostrulum_, appears to consist of
_seven_ pieces. First are a pair of triangular organs, the _laminæ_,
which together somewhat resemble the beak of a bird, and are affixed,
one on each side of the mouth, under the antennæ: these represent
the _mandibles_ of a perfect mouth[1397]. Next, a pair of long sharp
lancets (_Scalpella_), which emerge from the head below the laminæ:
these are analogous to _maxillæ_[1398]: a pair of palpi, consisting
of four joints, are attached to these near their base[1399], which
of course are _maxillary palpi_. And lastly, in the midst of all is
a slender setiform organ (_ligula_), which is the counterpart of
the _tongue_[1400]. Rösel, and after him Latreille, seem to have
overlooked this last piece, since they reckon only _six_ pieces
in the flea's mouth[1401]: but the hand and eye of our friend
Curtis have detected a _seventh_, as you see in his figure. From
this account it appears, that the elongation of the organs of the
_Aphaniptera_ Order is at the expense of the _labium_ and its _palpi_.
v. _Rostellum._--So little is known of the composition of the next
kind of imperfect mouth, that I need not enlarge upon it. It is
peculiar to the louse tribe (_Pediculidæ_), and it consists of the
tubulet (_Tubulus_), and siphuncle (_Siphunculus_). The former is
slenderer in the middle than at the base and apex, the latter being
turgid, rather spherical, and armed with claws which probably lay
hold of the skin while the animal is engaged in suction. When not
used, the whole machine is withdrawn within the head; the siphuncle,
which is the suctorious part, being first retracted within the
tubulet, in the same way as a snail retracts its _tentacula_[1402].
This apparatus seems formed at the expense of all the other organs.
There are some other kinds of imperfect mouth, which, though they
seem not to merit each a distinct denomination, should not be passed
altogether without notice. The first I shall mention is that of the
family of _Pupipara_ Latr. (_Hippobosca_ L.). It consists of a pair
of hairy coriaceous valves, which include a very slender rigid tube
or siphuncle, the instrument of suction, which Latreille describes as
formed by the union of two setiform pieces[1403]. In _Melophagus_,
the sheep-louse, the union of the valves of the sheath is so short,
that they appear like a tube; but if cut off they will separate,
and show the siphuncle, as fine as a hair, between them. This organ
is of a type so dissimilar, as was before observed, to that of the
_Diptera_ in general, and approaches so near to that of the dog-tick
(_Ixodes_), that they may be deemed rather apterous insects with two
wings, than to belong to that Order; and the circumstance that some
of the family are apterous confirms this idea. In fact they are a
_transition_ family that connects the two Orders, but are nearest to
the _Aptera_. In _Nycteribia_ the oral organs differ from those of
the other _Pupipara_ in having _palpi_. This also is the case with
those of the genus _Ixodes_, the palpi of which are placed upon the
same base with the instrument of suction, than which they are longer:
they appear to consist of _two_ joints, the last very long and flat.
The instrument of suction itself is formed by three hard rigid
laminæ; two shorter parallel ones above, that cover the third, which
is longer and broader, and armed on each side with several teeth
like a saw, having their points towards the base[1404]. Many of the
other _Acari_ L. have mandibles, and several have not: but their oral
organs have not yet been sufficiently examined; and from the extreme
minuteness of most of them, this is no easy task; nor to ascertain in
what points they differ or agree.
If you consider the general plan of the organs of manducation in the
vertebrate animals, how few are the variations that it admits! An
upper and a lower jaw planted with teeth, or a beak consisting of an
upper or a lower mandible with a central tongue, form its principal
features. But in the little world of insects, how wonderful and
infinite is the diversity which, as you see, in this respect they
exhibit! Consider the number of the organs, the varying forms of
each in the different tribes, adjusted for nice variations in their
uses:--how gradual, too, the transition from one to another! how one
set of instruments is adapted to prepare the food for deglutition by
mastication; another merely to lacerate it, so that its juices can
be expressed; a third to lap a fluid aliment; a fourth to imbibe it
by suction--and you will see and acknowledge in all the hand of an
almighty and all-bountiful CREATOR, and glorify his wisdom, power,
and goodness, so conspicuously manifested in the structure of the
meanest of his creatures. You will see also, that all things are
created after a pre-conceived plan; in which there is a regular and
measured transition from one form to another, not only with respect
to beings themselves, but also to their organs--no new organ being
produced without a gradual approach to it; so that scarcely any
change takes place that is violent and unexpected, and for which the
way is not prepared by intermediate gradations. And when you further
consider, that every being, with its every organ, is exactly fitted
for its functions; and that every being has an office assigned, upon
the due execution of which the welfare, in certain respects, of this
whole system depends, you will clearly perceive that this whole plan,
intire in all its parts, must have been coeval with the Creation; and
that all the species,--subject to those variations only that climate
and different food produce,--have remained essentially the same, or
they would not have answered the end for which they were made, from
that time to this.
* * * * *
Having given you this particular account of the _trophi_ or organs
of the mouth of insects, I must now make some observations upon the
_other_ parts of the head. I have divided it, as you see in the
Table, into _face_ and _subface_; the former including its _upper_
and the latter its _lower_ surface. Strictly speaking, some parts of
the face, as the temples and cheeks, are common to both surfaces; but
I do not therefore reckon them as belonging to the subface, which,
exclusive of the mouth and its organs, consists only of the _throat_,
and where there is a neck, the _gula_.
i. _Nasus_[1405].--I shall consider the parts of the face in the
order in which they stand in the Table, beginning with the _nasus_
or nose. Fabricius has denominated this part the _clypeus_, in which
he has been followed by most modern Entomologists. You may therefore
think, perhaps, that I have here unnecessarily altered a term so
generally adopted, and expect that I assign some sufficient reasons
for such a change. I have before hinted that there is good ground
for thinking that the sense of _smell_ in insects resides somewhere
in the vicinity of this part; and when I come to treat of their
senses, I shall produce at large those arguments that have induced
me to adopt this opinion: and if I can make out this satisfactorily,
you will readily allow the propriety of the denomination. I shall
here only state those _secondary_ reasons for the term, which, in
my idea, prove that it is much more to the purpose than _clypeus_.
This last word was originally applied by Linné in a metaphorical
sense to the ample covering of the head of the _Scarabæidæ_, and the
thoracic shield of _Silpha_, _Cassida_, _Lampyris_, and _Blatta_: in
all which cases there was a propriety in the figurative use of it,
because of the resemblance of the parts so illustrated to a _shield_.
But when _Fabricius_ (though he sometimes employs the term, as Linné
did, merely for illustration,) admitted it into his orismological
table, as a term to represent universally the anterior part of the
face of insects to which the labrum is attached (though in some
cases he designates the _labrum_ itself by this name), it became
extremely inappropriate; since in every case, except that of the
_Scarabæidæ_, the part has no pretension to be called a _shield_;--so
that the term is rather calculated to mislead than illustrate. This
impropriety seems at length to have struck M. Latreille, since in a
late essay[1406] he has changed the name of this part to _Epistomis_,
a term signifying _the part above the mouth_. But there are reasons,
exclusive of those hereafter to be produced concerning the sense of
smell, which seem to me to prove that _nasus_ is a preferable term;
not to mention its claim of priority, as having been used to signify
this part a century ago[1407]. When we come to consider the terms for
the other parts of the head, as _lips_, _jaws_, _tongue_, _eyes_,
_temples_, _cheeks_, _forehead_, &c. the concinnity, if I may so
speak, and harmony of our technical language, seem to require that
the part analogous in point of situation to the _nose_ of vertebrate
animals should bear the same name. And any person who had never
examined an insect before, if asked to point out the _nose_ of the
animal, would immediately cast his eye upon this part: so that one
of the principal uses of imposing names upon parts--that they might
be more readily known--would be attained. If it is objected, that
calling a part a _nose_ that has not the sense of smell, supposing it
to be so, might lead to mistakes--I would answer, that this objection
is not regarded as valid in other cases: for instance, the _maxillæ_
are not generally used as _jaws_, and yet no one objects to the term;
because, from their situation, they evidently have an analogy to the
organs whose name they bear. But enough on this subject--we will now
consider the part itself.
To enable you to distinguish the nose of insects when it is not
separated from the rest of the face by an impressed line, you must
observe that it is the terminal middle part that sometimes overhangs
the upper-lip, and at others is nearly in the same line with it; that
on each side of it are the cheeks, which run from the anterior half
of the eyes to the base of the mandibles. Just below the antennæ is
sometimes another part distinct from the nose, which I shall soon have
to mention; so that the nose must not be regarded as reaching always
nearly to the base or insertion of the antennæ, since it sometimes
occupies only half the space between them and the upper-lip, which
space is marked out by an impressed line. But you will not always be
left at such uncertainty when you want to ascertain the limits of
the nose; for it is in many cases a distinct piece, separated by an
elevated or impressed line from the rest of the face. This separation
is either partial or universal. Take any species of the genera
_Copris_, _Onitis_, or _Ateuchus_, and you will see the nose marked
out in the centre of the anterior part of the face by two _elevated_
lines, forming nearly a triangle and bounded by the horn[1408]. Or
take a common wasp or hornet, and you will find a similar space,
though approaching to a quadrangular figure, marked out by _impressed_
lines[1409]. In _Rhagio_ and _Sciara_, two Dipterous genera, this
impression is so deep as to look like a suture. Between these lines,
in those cases, is included what I call the _nose_. As to _substance_,
in general it does not differ from the rest of the head; but in the
_Cleridæ_ it is almost membranous. You must observe, that in all these,
what at first sight appears to be the termination of the front, is not
the nose, but the narrow depressed piece that intervenes between it
and the lip. With regard to its _clothing_, it is most commonly naked,
but in some genera it is covered with hair; in _Crabro_ F. often with
golden or silver pile, which imparts a singular brilliance to the mouth
of the insects of that genus: M. Latreille supposes that the brilliant
colours of the golden-wasp (_Chrysis_ L.) may dazzle their enemies,
and so _promote_ their escape[1410]; the brilliance of the mouth of
the _Crabro_ may on the contrary at first dazzle their prey for a
moment, so as to _prevent_ their escape. The _form_ of the nose, where
distinct from the rest of the face, admits of several variations: thus
in the _Staphylinidæ_ and _Cleridæ_ it is transverse and linear; in
_Copris_ it is triangular, with the vertex of the triangle truncated;
in _Vespa Crabro_ it is subquadrate and sinuated. In many Heteromerous
beetles[1411] it is rounded posteriorly: in _Pelecotoma_, a new genus
in this tribe, related to _Asida_, there is a deep anterior sinus; in
_Blaps_ the anterior margin is concave; in _Cetonia_[1412] _Brownii_,
and _atropunctata_ (forming a distinct subgenus), it is bifid: it
varies in the _Scarabæidæ_, in some being bidentate, in others
quadridentate, and in others again sexdentate, including the cheeks:
in _Mylabris_, a kind of blister-beetle, it is transverse and nearly
oval; in _Lamia_, a capricorn-beetle, it represents a parallelogram;
and in most _Orthoptera_ it is subtriangular: in _Tettigonia_ F. it
is prominent, transversely furrowed, and divided by a longitudinal
channel: in _Otiocerus_ K. it presents the longitudinal section of
a cone[1413]: in the _Diptera_ Order, with the exception of the
_Tipulidæ_ and some others, in which it unites with the cheeks, &c. to
form a rostrum, the nose in general, as to _form_, answers to its name,
resembling that of many of the _Mammalia_: in some of the _Asilidæ_
it is very tumid at the end, and terminates in a sinus, to permit
the passage of the proboscis to and fro: in many of the _Syrphidæ_,
&c. it is first flat and depressed, and then is suddenly elevated,
so as to give the animal's head the air of that of a monkey: in some
tribes, as _Rhingia_, _Nemotelus_, _Eristalis_, &c., in conjunction
with the cheeks it forms a conical rostrum: in _Tabanus bovinus_, and
other horse-flies, it terminates in three angles or teeth. Many more
forms might be mentioned, but these will suffice to give you a general
idea of them. In _size_ and _proportions_ the nose also varies. It
is frequently, as in _Tettigonia_, the most conspicuous part of the
face, both for size and characters; but in the _Staphylinidæ_ it is
very small, and often scarcely discernible, being overshadowed by its
ample front: and it may be observed in general, that when the antennæ
approximate the mouth, as in this genus and many others, the _front_
becomes _ample_, and the _nose_ is reduced to its _minimum_: but when
they are distant from the mouth, the reverse takes place; and the
nose is at its _maximum_ and the front at its _minimum_. _Mutilla_,
_Myrmecodes_, _Scolia_, &c. in the _Hymenoptera_, are an example of
the former; and the _Pompilidæ_, _Sphecidæ_, _Vespidæ_, &c. of the
latter. In _Myopa buccata_, &c. its length exceeds its width; but more
commonly the reverse takes place. The _circumscription_ of the _nose_
also deserves attention. It is usually terminated behind by the front
(_frons_), or, where it exists, by the _postnasus_, in the sides by the
cheeks, and anteriorly by the _labrum_. But this is not invariably the
case; for in the _Cimicidæ_, in which the cheeks form the bed of the
_Promuscis_, the front embraces it on each side by means of two lateral
processes, that sometimes meet or lap over each other anteriorly, which
gives the nose the appearance of being insulated; but it really dips
below these lobes to join the _labrum_. This structure you may see in
_Edessa_ F., and many other bugs. This part sometimes has its _arms_.
Thus in _Copris_, and many _Dynastidæ_, the horns of the head seem, in
part at least, to belong to this portion of it; in _Tipula oleracea_
(the crane-fly), &c. it terminates before in a horizontal mucro. In
_Osmia cornuta_, a kind of wild-bee, each side of the nose is armed
with a vertical horn. The _margin_ of the nose in most Lamellicorn
insects, though mostly level, curves upwards.
I am next to mention a part of the nose which merits a distinct
name and notice, which I conceive in some sort to be analogous to
the _nostrils_ of quadrupeds, and which I have therefore named the
_Rhinarium_ or nostril-piece. I had originally distinguished it by
the plural term _nares_, nostrils; but as it is usually a single
piece, I thought it best to denote it by one in the singular. When
I treat of the senses of insects, I shall give you my reasons, as I
have before said, for considering this part as the organ of scent,
or connected with it, which you will then be able to appreciate.
I shall only here observe, that the piece in question is in the
usual situation of the nostrils--between the nose and the lip.
In a large number of insects this part may be regarded as nearly
obsolete; or at least it is merely represented by the very narrow
membranous line that intervenes between the nose and the lip and
connects them; which, as in the case of the head of _Harpali_
before noticed, may be capable of tension and relaxation, and so
present a greater surface to the action of the atmosphere. But I
offer this as mere conjecture. In the lady-bird (_Coccinella_) this
line is a little wider, and becomes a distinct _Rhinarium_; as it
does also in _Geotrupes_. With respect to its _insertion_, the
_rhinarium_ is a piece that either entirely separates the nose from
the lip, or only partially: the former is the most common structure.
It is particularly remarkable in a New Holland genus of chafers
(_Anoplognathus_ Leach). In _A. viridiæncus_ it is very ample, and
forms the under side of the recurved nose, so that a large space
intervenes between the margin of the latter and the base of the
_labrum_. In _Macropus_ Thunb., of the Capricorn tribe (_Cerambyx_
L.), the nostril-piece, which forms a distinct segment, is narrower
than the nose, and the upper-lip than the nostril-piece, forming as
it were a triple gradation from the front to the mouth. Again, in
others the part in question is received into a sinus of the nose.
This is the case with the dragon-flies (_Libellulina_), in which this
sinus is very wide; in the burying-beetle (_Necrophorus_)[1414], in
some species of which it is deep but narrow; and in a species of
_Tenebrio_ from New Holland, which perhaps would make a subgenus.
If you examine with a common glass any of the larger rove-beetles
(_Staphylinidæ_), you will find that the nose itself seems lost in
the nostril-piece, both together forming a very narrow line across
the head above the _labrum_, without any apparent distinction between
them; but if you have recourse to a higher magnifier, you will find
this divided into an upper and lower part, the former of the hard
substance of the rest of the head, and the latter membranous. I once
was of opinion that the prominent transversely furrowed part, so
conspicuous in the face of _Tettigonia_ F.[1415], was the _front_:
but upon considering the situation of this, chiefly below the eyes
and antennæ, and comparing it with the analogous piece in _Fulgora
laternaria_ and other insects of the Homopterous section of the
_Hemiptera_, I incline to think that it represents the _nose_, and
that the longitudinal ridge below it is the nostril-piece[1416].
In the Heteropterous section it is merely the vertical termination
of their narrow nose. In other insects again, this part approaches
in some measure to the common idea of nostrils; there being _two_,
either one on each side the nose, or two approximated ones. If you
catch the first humble-bee that you see busy upon a flower, you will
discover a minute membranous protuberance under each angle of the
nose. Something similar may be observed in some species of _Asilus_
L. In the _Orthoptera_, especially in _Blatta_, _Phasma_, and some
_Locustæ_, two roundish or square pieces, close to each other on the
lower part of the nose, represent the nostrils[1417].--With regard to
_substance_, in the chafer-tribes, at least those that feed on leaves
or living vegetable matter, as the _Melolonthidæ_, _Anoplognathidæ_,
and in many other insects, the _rhinarium_ is of the same substance
with the rest of the head; but in _Macropus_ Thunb., _Staphylinus_,
_Necrophorus_, &c., it consists of membrane.
ii. _Postnasus_[1418].--This is a part that appears to have been
confounded by Entomologists with the front of insects; in general,
indeed, it may be regarded as included in the nose, and does not
require separate notice: but there are many cases in which it is
distinctly marked out and set by itself, and in which it forms a
useful diagnostic of genera or subgenera. There is a very splendid and
beautiful Chinese beetle, to be seen in most collections of foreign
insects (_Sagra purpurea_), in which this part forms a striking
feature, and helps to distinguish the genus from its near neighbour
_Donacia_. If you examine its face, you will discover a triangular
piece, below the antennæ and above the _nasus_, separated from the
latter and from the front by a deeply-impressed line: this is the
_postnasus_ or _after-nose_. Again: if you examine any specimens of a
Hymenopterous genus called by Fabricius _Prosopis_ (_Hylæus_ Latr.),
remarkable for its scent of baum, you will find a similar triangle
marked out in a similar situation[1419]. In many Coleopterous
insects, besides _Sagra_, you will discover traces of the part we are
considering: as in _Anthia_, _Dytiscus_, and several others of the
Predaceous beetles. In _Cistela_ it is larger than the nose itself;
but it is more conspicuous in the _Orthoptera_, particularly in
_Locusta_ (_Gryllus_ F.), in which it is the space below the antennæ,
distinguished by two or four rather diverging ridges[1420]. In the
_Libellulina_, _Myrmeleonina_, &c. it is a distinct transverse piece.
In _Dasyga_ Latr., a kind of bee, it is armed with a transverse ridge
or horn--But enough has been said to render you acquainted with it; I
shall therefore proceed to the next piece.
iii. _Frons_[1421].--The _Front_ of insects may be denominated the
_middle_ part of the face between the eyes, bounded anteriorly by the
nose, or after-nose, where it exists, and the cheeks; laterally by
the eyes; and posteriorly by the vertex. Speaking properly, it is the
region of the _antennæ_; though when these organs are placed before
the eyes, under the margin of the nose, as in many Lamellicorn and
Heteromerous beetles, they seem to be rather _nasal_ than _frontal_.
This part is often elevated, as in the elastic beetles (_Elater_),
whose faculty of jumping, by means of a pectoral spring, has been
related to you[1422]. In _Anthia_, a Predaceous beetle, it has
often three longitudinal ridges. In many of the Capricorn beetles
(_Cerambyx_ L.), it is nearly in the shape of a Calvary cross, with
the arms forming an obtuse angle, and then terminating at the sinus
of the eyes in an elevation for the site of the antennæ. In the
ants also (_Formicidæ_), the front is often elevated between those
organs. In _Ponera_, one tribe of them, this elevation is bilobed,
and receives between its lobes the vertex of the _postnasus_. In
the hornet (_Vespa Crabro_) the elevation is a triangle, with its
vertex towards the mouth. In _Sagra_ it is marked out into three
triangles, the _postnasus_ making a fourth, with the vertexes
meeting in the centre. In the _Dynastidæ_ and _Scarabæidæ_ the
horns are often _frontal_ appendages, as is that of _Empusa_ Latr.,
a leaf-insect, and probably those of _Sphinx Iatrophæ_ F., which
affords a singular instance of a horned Lepidopterous one. Sometimes
it is an ample space, reducing the nose to a very narrow line, as in
the _Staphylinidæ_, or sending forth a lobe on each side, as before
mentioned, which embraces the nose. In a species of bug from Brazil,
related to _Aradus_ F., these lobes are dilated, foliaceous, and
meet before the nose, so as to form a remarkable extended frontlet
to the head. In others this part is extremely minute: thus in many
_male_ flies and other insects, as the _Libellulina_, where the
eyes touch each other, the front is cut off from the vertex and
reduced to a small angle. In the female flies the communication
with the vertex is kept open, and the front consequently longer.
In the horse-flies (_Tabanidæ_), in _Hæmatopota_, and _Heptatoma_,
the frontal space is wider than in the rest of that tribe. Many
of these are distinguished by a levigated area behind the antennæ
in the part we are treating of. In the _Libellulina_, and in the
drone-bee, whose eyes are confluent, the stemmata are in the front.
In many _Orthoptera_ also, as _Locusta_ Leach, one of them is below
the antennæ; and in the lanthorn-fly tribe (_Fulgoridæ_), both these
organs, which are situate between them and the eyes, as they do also
in _Truxalis_, appear to be in it[1423]. In this tribe the rostrum is
an elongation of the part in question; and perhaps you would think
at first that what I have considered as the _nose_ in _Tettigonia_
F. was also a tendency to this kind of rostrum; but if you examine
the great lanthorn-fly (_Fulgora laternaria_), you will find besides,
at the lower base of the lanthorn, a triangular piece analogous to
the nose of _Tettigonia_, and below it another representing its
nostril-piece:--the horizontal part of the nose in that genus may
perhaps be regarded as part of the front. In _Truxalis_ F. the face
consists of a supine and prone surface, and the latter is composed
of the front, after-nose, nose, and organs of the mouth. I may
notice here a most remarkable and singular tribe of bugs, of which
two species have been figured by Stoll[1424]: in these the head,
or rather those parts of it that we have now been describing, the
nose, namely, the after-nose, and front, are absolutely divided
longitudinally in two, each half having an eye and antenna planted in
it; or perhaps, as it is stated to be divided in one instance to the
commencement of the _promuscis_, the nose is left intire, and dips
down, as in cases before alluded to: so that in this the nose appears
to leave the lobes of the front, which in others embrace its sides.
iv. _Vertex_[1425].--We now come to the _vertex_, or crown of the head;
which is situated behind the front, and, except where the communication
is intercepted by confluent eyes, adjoins it. It is laterally bounded
by the hind part of the eyes and the temples; and _posteriorly_, where
that part exists, by the _occiput_. The vertex may be denominated the
ordinary region of the _stemmata_: for though in several cases, as
we have just seen, one or more of them are planted in the front; yet
this in the great majority, especially in the _Hymenoptera_, is their
natural station. In _Blatta_ and some other _Orthoptera_ the posterior
angle of the head is the vertex. In many dung-chafers of Latreille's
genus _Onthophagus_, which are said to have _occipital_ horns, as _O.
nutans_, _nuchicornis_, _Xiphias_, &c., the horn really arms the part
I regard as the vertex. In _Locusta_ Leach, this part is very ample,
and in _Truxalis_ very long; but more generally it is small, and not
requiring particular notice.
v. _Occiput_[1426].--The _occiput_, or _hind-head_, is that part of
the face that either forms an angle with the vertex posteriorly,
or slopes downwards from it. It has for its lateral boundaries the
temples, and behind it is either terminated by the orifice of the
head, or in many cases by the neck. In those beetles that have no
neck, as the Lamellicorn and Capricorn, the hind-head is merely a
declivity from the vertex, usually concealed by the shield of the
thorax, very lubricous, to facilitate its motion in the cavity of
that part, and at its posterior margin distinguished by one or two
notches, which I shall notice hereafter, for the attachment of the
levator muscles: but in those beetles or other insects that have
a neck, or a versatile head, the occiput forms an angle with the
vertex, often rounded, and sometimes acute. This structure may be
seen in Latreille's _Trachelides_, and several other beetles. In the
_Hymenoptera_, _Diptera_, and others with a versatile head, the part
now under consideration curves inwards from the vertical line, so
as with the temples and under parts of the head to form a concavity
adapted to its movement upon the trunk.
vi. _Genæ_[1427].--The _cheeks_ of insects (_Genæ_) usually surround
the anterior part of the eyes, and lie between them and the mandibles
or their representatives. Where they approach the latter, as in the
Predaceous beetles (_Cicindela_, _Carabus_ L. &c.), they are very
short, and of course longer where the eyes are further removed from
the mouth; as in the Rhyncophorous beetles (_Curculio_ L.), where
they form the sides of the rostrum, and often contain a channel which
receives the first joint of the antennæ, when they are unemployed.
In the _Scarabæidæ_ and many other Lamellicorn beetles, their
separation on each side from the nose is marked by a ridge[1428];
and in the wasps (_Vespa_) by an impressed line or channel. In an
African tribe at present arranged with _Cetonia_ F., to which _C.
bicornis_ Latr.[1429] and another, which he has named, I believe, _C.
vitticollis_, belong, the cheeks are porrected on each side of the
mouth into a horizontal horn. These horns have at first the aspect
of a pair of open mandibles. In the magnificent _Goliathi_ Lam.,
the horns of the male are rather a process of the _cheek_ than of
the _nose_. In _Alurnus_, _Hispa_, and other beetles, these parts,
by their elevation and conjunction with the lower side of the head,
form a kind of fence which surrounds and protects the oral organs;
in many _Cimicidæ_, by a similar elevation of the cheeks, the bed
of the _promuscis_ is formed. In the Homopterous _Hemiptera_ they
run parallel nearly with the _rhinarium_ or nostril-piece. In the
_Hymenoptera_ they are almost always ample, but they are confined
to the lower side of the eye. In _Sirex grandis_, and others of
that genus, the cheek at the base of the mandible is dilated so
as to form a rounded tooth below it. In the Capricorn-beetles it
is considerable, and sometimes terminates, at the base of the
mandible, in two or three notches. In _Scaurus_ and _Eurychora_,
darkling-beetles, the cheek below projects into a lobe that covers
the base of the _maxilla_. But the animal distinguished by the
most remarkable cheeks is a species of _Phryganea_ L. (_Phryganea
personata_ Spence); for from this part projects a spoon-shaped
process, which curves upwards, and uniting with that of the other
cheek, forms an ample mask before the face, the anterior and upper
margin of which, in the insect's natural state, are closely united;
and the posterior part being applied to the anterior part of the
eye, causes the face to appear much swoln. It looks as if it was a
single piece; but upon pressing the thorax it opens, both above and
in front, into two parts, each convex without and hollow within, and
each having attached to its inside a yellow tuft of hair resembling a
feather. The use of this machinery at present remains a mystery[1430].
vii. _Tempora_[1431].--The temples (_Tempora_) are merely a
continuation of the cheeks to the posterior limit of the head,
forming its sides and posterior angles, and including the hinder part
of the eyes, the vertex, and the occiput. They seldom exhibit any
tangible character, except in certain ants (_Atta_ Latr.), in which
their angle terminates in one or two strong spines, giving the animal
a most ferocious aspect; and in that remarkable genus _Corydalis_
they are armed below with a tooth or point, which was not overlooked
by De Geer[1432].
viii. _Oculi_[1433].--I must now call your attention to organs of more
importance and interest, and which indeed include a world of wonders: I
mean the eyes (_Oculi_) of insects. These differ widely from those of
vertebrate animals, being incapable of motion. They may be regarded as
of _three_ descriptions--_simple_, _conglomerate_, and _compound_.
1. _Simple Eyes_[1434]. We will consider them as to their _number_,
_structure_, _shape_, _colour_, _magnitude_, _situation_, and
_arrangement_.
As to their _number_, they vary from two to sixteen. In the flea,
the louse, the harvest-man (_Phalangium_), there are only _a pair_;
in the bird-louse of the goose (_Nirmus Anseris_), and probably in
others of the same genus, there are _four_[1435]; in some spiders
(_Scytodes_, _Dysdera_, and _Segestria_ Latr.[1436]), and some
scorpions[1437], there are _six_. In the majority of spiders and
_Scolopendra morsitans_, _Scorpio maurus_, &c. there are _eight_;
and in _Podura_ and _Sminthurus_ Latr. there are sixteen[1438].
As to their _structure_, nothing seems to have been ascertained;
probably their organization does not materially differ from that of one
of the lenses of a compound eye; which I shall soon explain to you.
Their _colour_ in the many is black and shining, but in the
bird-louse of the goose they are quite white and transparent.
In spiders they are often of a sapphirine colour, and clear as
crystal. In _Scolopendra morsitans_ and many spiders, scorpions,
and _phalangia_[1439], they appear to consist of iris and pupil,
which gives them a fierce glare, the centre of the eye being dark
and the circumference paler. In the celebrated _Tarantula_ (_Lycosa
Tarantula_), the pupil is transparent, and red as a ruby; and the
iris more opaque, paler, and nearly the colour of amber.
Where there are more than two, they vary in _magnitude_. In the
enormous bird-spider (_Mygale avicularia_) the four external eyes
are larger than the four internal[1440]; but in the Tarantula
and _Sphasus_, the _two_ or _four_ internal are the largest. In
_Clubiona_ and _Drassus_ they are all nearly of the same size[1441];
and in the _Micrommata_ family they are very small[1442].
They vary also in _shape_. In _Scolopendra morsitans_ the three
anterior ones are round, and the posterior one transverse, and
somewhat triangular. In _Mygale calpeiana_, a spider, the two
smallest are round and the rest oval[1443]. In the trapdoor or
mason spider (_Mygale cæmentaria_), the four small internal ones are
round, and the large external ones oval[1444]; and those that are
circumscribed posteriorly with an impressed semicircle, are shaped
like the moon when gibbous[1445].
The _situation_ and _arrangement_ of simple eyes are also various.
In many they are imbedded, as usual, in the head; but in the little
scarlet mite, formerly noticed[1446], (_Trombidium holosericeum_),
they stand upon a small foot-stalk[1447]: the hairiness of this
animal might otherwise have impeded its sight. In spiders they
are planted on the back of the part that represents the head,
sometimes four on a central elevation or tubercle, and the remaining
four below it--as in _Lycosa_; sometimes the whole eight are
on a tubercle, as in _Mygale_; and sometimes, as in the common
garden-spider (_Epeira Diadema_), upon three tubercles, four on the
central one and two on each of the lateral ones. Other variations
in this respect might be named in this tribe. In the scorpions a
pair are placed one on each side, on a dorsal tubercle, and the
other four or six on two lateral ones of the anterior part of the
head[1448]. In the _Phalangidæ_ the _frontal_ eyes of the scorpion
cease, and only a pair of _dorsal_ ones are inserted vertically
in the sides of a horn or tubercle, either bifid or simple, often
itself standing upon an elevation which emerges from the back of
the animal[1449]. If their eyes were not in a vertical and elevated
position, the sight of these insects would be very limited; but by
means of the structure just stated, they get a considerable range of
surrounding objects, as well as of those above them. With regard to
the _arrangement_ of the eyes we are considering, it varies much.
Sometimes they are placed nearly in the segment of a circle, as
in those spiders that have _six_ eyes only, before noticed[1450];
sometimes in two straight lines[1451]; at others in two segments of
a circle[1452]; at others, in _three_ lines[1453], and at others
in _four_[1454]. Again, in some instances they form a cross, or
two triangles[1455]; in others, two squares[1456]; in others, a
smaller square included in a large one[1457]; in others, a posterior
square and two anterior triangles[1458]; sometimes a square and two
lines. Though generally separate from each other, in several cases
two of the eyes touch[1459]; and in one instance three coalesce
into a triangle[1460]. But it would be endless to mention all the
variations, as to arrangement, in the eyes of spiders.
2. _Conglomerate Eyes_[1461] differ in nothing from simple eyes, except
that instead of being dispersed they are collected into a body, so
as at first sight to exhibit the appearance of a compound eye:--they
are, however, not hexagonal, and are generally convex. They occur
in _Lepisma_, the _Iulidæ_, and several of the _Scolopendridæ_. In
_Scolopendra forficata_ the eye consists of about twenty contiguous,
circular, pellucid lenses, arranged in five lines, with another larger
behind them, as a sentinel or scout, placed at some little distance
from the main body. In the common millepede (_Iulus terrestris_) there
are twenty-eight of these eyes, placed in seven rows, and forming a
triangle, thus [Illustration: triangular eye shape]--the posterior row
containing seven lenses, the next six, and so on, gradually losing one,
till the last terminates in unity. Each of these lenses is umbilicated,
or marked with a central depression. In _Craspedosoma_ Leach, you will
find a similar formation. In _Glomeris zonata_, a kind of wood-louse
that rolls itself into a ball, the lenses are arranged in a line curved
at the lower end, with a single one by itself at the posterior end on
the outside; they are oblong and set transversely, and their white
hue and transparency give them the appearance of so many minute gems,
especially as contrasted with the black colour of the animal[1462].
Between these eyes and the antennæ is another transverse linear white
body, but opaque, seemingly set in a socket, and surrounded by a white
elevated line, like the bezel of a ring. Whether it is an eye, or what
organ, I cannot conjecture[1463]. Its aspect is that of a spiracle.
3. _Compound Eyes_[1464].--These are the most common kind of eye
in hexapod insects, when arrived at their perfect state; in their
larva state, as we have seen, their eyes being usually simple[1465];
except, indeed, those whose metamorphosis is _semicomplete_, which
have compound eyes in every state.--In considering compound eyes, I
shall advert to their _structure_, _number_, _situation_, _figure_,
_clothing_, _colour_, and _size_.
As to their _structure_,--when seen under the microscope they appear
to consist usually of an infinite number of convex _hexagonal_
pieces. If you examine with a good glass the eye of any fly, you
will find it traversed by numberless parallel lines, with others
equally numerous cutting them at right angles, so as apparently to
form myriads of little squares, with each a lens of the above figure
set in it. The same structure, though often not so easily seen,
obtains in the eyes of _Coleoptera_ and other insects. When the eye
is separated and made clean, these hexagons are as clear as crystal.
Reaumur fitted one eye to a lens, and could see through it well, but
objects were greatly multiplied[1466]. In Coleopterous insects they
are of a hard and horny substance; but in _Diptera_, &c. more soft
and membranous. The number of lenses in an eye varies in different
insects. Hooke computed those in the eye of a horse-fly to amount
to nearly 7,000[1467]; Leeuwenhoeck found more than 12,000 in that
of a dragon-fly[1468]; and 17,325 have been counted in that of a
butterfly[1469]. But of all insects they seem to be most numerous in
the beetles of Mr. W. S. MacLeay's genus _Dynastes_. In the eyes of
these the lenses are so small as not to be easily discoverable even
under a pocket microscope, except the eye has turned white[1470]: it
is not, therefore, wonderful, that Fabricius should call these eyes
_simple_[1471]. In some insects, however, as in the _Strepsiptera_
Kirby, the lenses are not numerous: in _Xenos_ they do not exceed
fifty, and are distinctly visible to the naked eye[1472]. These
lenses vary in magnitude, not only in different, but sometimes in
the same eyes. This is the case in those of male horse-flies and
flies, those of the upper part of the eye being much larger than
those of the lower[1473]. The partitions that separate the lenses,
or rather bezels, in which they are set, are very visible in the
eyes just mentioned, and those of _Xenos_; but in many insects they
are only discernible at the intersecting lines of separation between
the lenses. In hairy eyes, such as those of the hive-bee, the hairs
emerge from these _septa_. Every single lens of a compound eye may be
considered as a _cornea_, or a _crystalline humour_, it being convex
without and concave within, but thicker in the middle than at the
margin: it is the only transparent part to be found in these most
remarkable eyes. Immediately under the _cornea_ is an opaque varnish,
varying according to the species, which produces sometimes in one
and the same eye spots or bands of different colours. These spots
and bands form a distinguishing ornament of many of the _Tabani_ and
other flies. And to this varnish the lace-winged flies (_Hemerobius_,
&c.) are indebted for the beautiful metallic hues that often adorn
them. When insects are dead, this varnish frequently loses its
colour, and the eye turns white: hence many species are described
as having _white_ eyes which when alive had _black_ ones. The
consistence of this covering is the same with that of the varnish
of the _choroid_ in the eyes of vertebrate animals; but it entirely
covers the underside of the lens, without leaving any passage for the
light. Below this varnish there are numbers of short white hexagonal
prisms[1474], every one of which enters the concavity of one of the
lenses of the cornea, and is only separated from it by the varnish
just described: this may be considered as the _retina_ of the lens
to which it is attached; but at present it has not been clearly
explained how the light can act upon a _retina_ of this description
through an opaque varnish. Below this multitude of threads (for such
the bodies appear), perpendicular to the _cornea_, is a _membrane_
which serves them all for a base, and which consequently is nearly
parallel with that part. It is very thin, of a black colour, not
produced by a varnish; and in it may be seen very fine white
_tracheæ_, which send forth branches still finer, that penetrate
between the prisms of the _cornea_: this membrane may be called
the _choroid_. Behind this is a thin expansion of the optic nerve,
which is a true nervous membrane, precisely similar to the _retina_
of red-blooded animals. It appears that the white pyramidal threads
which form the _retina_ of each lens are sent forth by this general
_retina_, and pierce the choroid by a number of almost imperceptible
holes[1475]. From this description it appears that the eyes of
insects have nothing corresponding with the _uvea_ or _humours_ of
those of vertebrate animals, but are of a type peculiar to themselves.
Having explained to you the wonderful and complex structure with
which it has pleased the CREATOR to distinguish the organs of vision
of these minute beings, proving, what I have so often asserted,
that when animals seem approaching to nonentity, where one would
expect them to be most _simple_, we find them in many cases most
_complex_, I shall now call your attention to the next thing I am
to consider--the _number_ of the eyes in question. Most insects
have only _two_; but there are several exceptions to this rule.
Those that have occasion to see both above and below the head,
the eyes of all being immovable, must have them so placed as to
enable them to do this. This end is accomplished in many beetles,
for instance _Scarabæus_ L., _Helæus_ Latr., &c., by having these
organs fixed in the _side_ of the head, so that part looks upward
and part downward; but in others _four_ are given for this purpose.
If you examine the common whirlwig (_Gyrinus Natator_) that I have
so often mentioned[1476], which has occasion, at the same time,
to observe objects in the air and in the water, you will find it
is gifted with this number of eyes. _Lamia Tornator_ (_Cerambyx
tetrophthalmus_ Forst.) and some others, of which I make a genus,
under the appellation of _Tetrops_, are also so distinguished. In
these insects, one eye is above and the other below the base of
the antennæ; in fact, in these the _canthus_, instead of dividing
the eye partially, as in the other Capricorn-beetles, runs quite
through it at considerable width[1477]. In _Ryssonotus_ MacLeay
(_Lucanus nebulosus_ K.) the eye appears also to be divided in two
by the _canthus_. In the _Neuroptera_ Order there is more than one
instance of the same kind. In _Ascalaphus_ there are two considerable
eyes on each side of the head, which, though clearly distinct, meet
like those of many male flies and the drone. The male, likewise,
of more than one species of _Ephemera_, besides the common lateral
eyes and the _stemmata_ on the back of the head, have a pair of
compound eyes on the top of a short columnar process[1478]. In the
_Hemiptera_ Order, also, an instance occurs of four eyes in the
genus _Aleyrodes_[1479]. Amongst the vertebrate animals, there
is an example of eyes with two pupils in _Anableps_, a genus of
fishes[1480], but no vertebrate animal has _four_ of these organs.
That many insects should have more than _two_ eyes, will not seem
to you so extraordinary as that any should be found that, like the
Cyclops of old, have only _one_. There is, however, an insect,
before celebrated for its agility[1481] (_Machilis polypoda_ Latr.),
which has a single eye in its forehead; or we may say, its eyes
are confluent, without any line of distinction between them except
a small notch behind. Now that I am treating of the _number_ of
eyes, I must not forget to observe to you, that in some insects no
eyes at all have been discovered. In _Polydesmus complanatus_, on
each side of the head there is an eye-shaped portion separated by a
suture, in which under a powerful lens I cannot satisfy myself that
I can discern any thing like the facets that usually distinguish
compound eyes. In _Geophilus electricus_, another myriapod, they
certainly do not exist[1482]. Whence we may conclude, as was before
observed[1483], that the faculty of emitting light is rather given it
as a means of defence than to guide it in its path.
The _situation_ of compound eyes differs in different tribes. In
some, as in the _Staphylinidæ_, they are planted laterally in the
_anterior_ part of the head; in others, the _Carabi_ &c., in the
_middle_; in others again, _Locusta_ Leach &c., in the _posterior_
part. In some, their station is more in the upper surface, either
before or behind; so that a very narrow space separates them, or
perhaps none at all. Instances of this position of the eyes occur
in a minute weevil (_Ramphus_ Clairv.[1484]), and many _Diptera_,
&c. Of those that form an union on the top of the head, some are
placed obliquely, so as to leave a diverging space below them,
as in many _Libellulina_[1485], the drone[1486], &c. Others, as
_Atractocerus_, in which the eyes occupy nearly the whole head,
and unite anteriorly, have this diverging space _above_ their
conflux. In _Rhina barbirostris_ Latr., another kind of weevil,
they are confluent _below_ the head, at the base of the rostrum,
and a very narrow interval separates them above. In a large number
of the _Heteromerous_ beetles, they are set _transversely_, in the
_Capricorn_ ones _longitudinally_. Their surface, when they are
lateral, has usually two aspects, one _prone_ to see below, the other
_supine_ to see above. In general the eyes are situated behind the
antennæ, so that their position, whether it shall be anterior or
posterior, depends upon that of those organs. Often, indeed, as in
the last-named beetles, part of the eye is behind and part before the
antennæ; but except where there are _four_ eyes, as in _Tetrops_,
they are never placed before or below them.
Though the eyes of insects are generally _sessile_, yet to give them
a wider range they are sometimes, but it rarely occurs, placed, like
those of many _Crustacea_, on a _footstalk_, but not a _moveable_
one. An instance of this in certain male _Ephemeræ_ has already been
mentioned. In the _Hemiptera_ De Geer has figured two species of bugs
(_Cimicidæ_) that are so circumstanced[1487]; as are also all the known
_Strepsiptera_ K., though in these the footstalk is very short[1488]:
but the most remarkable example of columnar eyes is afforded by that
curious _Dipterous_ genus _Diopsis_, in which both eyes and antennæ
stand upon a pair of branches, vastly longer than the head, which
diverge at a very obtuse angle from its posterior part[1489].
In their _figure_ eyes vary much. Sometimes they are so prominent as
to be nearly _spherical_: this is the case with some aquatic bugs,
as _Ranatra_, _Hydrometra_, and several male _Ephemeræ_[1490]. Very
often they are _hemispherical_, as in the tiger-beetles (_Cicindela_
L.), and the clocks or dors (_Carabus_ L.); but in a large number
of insects they are flat, and do not rise above the surface of the
head.--With regard to their _outline_, they are often perfectly
_round_, as in many weevils; _oval_, as in various bees; _ovate_, as
in other bees (_Andrena_ F.); _triangular_, as in the water-boatman
(_Notonecta_). They are also often _oblong_, and occasionally narrow
and _linear_; as in that singular beetle _Helæus_. In many of the
_Muscidæ_ they form nearly a _semicircle_, or rather, perhaps, the
quadrant of a sphere. The eyes of the Capricorn-beetles (_Cerambyx_
L.) have a sinus on their inner side, as it were, taken out of them;
so that they more than half surround the antennæ, before which is the
longest portion of them. An approach to this shape is more or less
observed in the darkling-beetles (_Tenebrio_ L.); but in these the
sinus is not so deep. I may under this head observe, that in those
_Mantidæ_ that represent dry leaves, and some others, these organs
usually terminate in a spine[1491].
Though not distinguished by the beauty and animation that give such
interest to the eye of vertebrate animals, and exhibiting no trace of
iris or pupil, yet from the variety of their _colours_ the compound
eyes of insects, though most commonly black or brown, are often very
striking. Look at those of one of the lace-winged flies that commit
such havoc amongst the _Aphides_[1492], and it will dazzle you with
the splendour of the purest gold, sometimes softened with a lovely
green. The lenses of those of _Xenos_ blaze like diamonds set in
jet[1493]. You have often noticed the fiery eyes of many horse-flies
(_Tabanus_ L.) with vivid bands of purple and green[1494]. Others
are spotted[1495]; and Schellenberg has figured one (_Thereva
hemiptera_)[1496], that exhibits the figure of a flower painted in
red on a black ground. These colours and markings are all most vivid
and brilliant in the _living_ insect, and often impart that fire
and animation to the eyes for which those of the higher animals are
remarkable. Take one of the large dragon-flies that you see hawking
about the hedges in search of prey, examine its eyes under a lens, and
you will be astonished at the brilliance and crystalline transparency
which its large eyes exhibit, and by the remarkable vision of larger
hexagons which appear in motion under the _cornea_, being reflected by
the _retina_--all which give it the appearance of a living eye. This
moving reflexion of the hexagonal lenses in living insects was noticed
long since in some bees (_Nomada_ F., _Cœlioxys_ Latr.)[1497]
Compound eyes differ greatly in their _size_. In some insects,
as _Atractocerus_, the drone-bee, many male _Muscidæ_, &c., they
occupy nearly the whole of the head; while in others, as numerous
_Staphylinidæ_, _Locusta_ Leach, &c., they are so small as to be
scarcely larger than some simple eyes of spiders: and they exhibit
every intermediate difference of magnitude in different tribes,
genera, and species.
Under this head I must say something of the _Canthus_ of the eye;
by which I mean an elevated process of the cheek, which in almost
all the genera of the Lamellicorn beetles enters the eye more or
less, dividing the upper portion from the lower. Though usually
only a _process_ of the cheek, yet in the _Scarabæidæ_ the whole
of that part forms the _canthus_[1498]. It only _enters_ the eye
in the _Rutelidæ_, _Cetonidæ_, &c.; it extends through _half_ of
it in _Copris_; it goes _beyond_ the half in _Ateuchus_; and in
_Ryssonotus_ MacLeay (_Lucanus nebulosus_ K.) it quite divides the
eye into two[1499], as I before observed. In _Lucanus_, _Passalus_
&c. it projects before the eye into an angle; in _Lucanus femoralis_
nearly into a spine; but in _Lamprima_ and _Œsalus_ it does not
exist. The part, also, that enters the eye in the Capricorn-beetles
may be regarded as a kind of _canthus_, though it is merely a
dilatation of the _front_.
4. _Stemmata_[1500].--Having given so full an account of the kinds
and structure of the ordinary eyes of insects, you may perhaps expect
that I should now dismiss the subject: you would, however, have great
cause to blame me, did I not make you acquainted with a kind of
auxiliary eyes with which a large portion of them are gifted; I mean
those pellucid spots often to be found on the posterior part of the
front of these animals, or upon the vertex, frequently arranged in a
triangle. These, Linné, from his regarding them as a kind of coronet,
called _Stemmata_. They have been of late denominated _Ocelli_; but as
this latter term is also in general use for the eyelets on the wings
of _Lepidoptera_, I have adhered to that of the illustrious Swede.
Neither he nor Fabricius has expressed any opinion as to the _use_ of
these organs; but Swammerdam and Reaumur were aware that they were
real _eyes_. The former found that there are nerves that diverge to
them though not easily traced, and that they have a _cornea_, and
what he takes for the _uvea_[1501]; and the latter has supposed that
the compound eyes and these simple ones have, the one the power of
magnifying objects much, and the other but little, so that the former
are for surveying those that are distant, and the latter those that
are near[1502]. The same author relates some experiments that he tried
with the common hive bee, by which he ascertained that the _stemmata_,
as well as the compound eyes, were organs of vision. He first smeared
the _latter_ over with paint, and the animals, instead of making for
their hive, rose in the air till he lost sight of them. He next did the
same with the _former_, and placing the bees whose _stemmata_ he had
painted within a few paces of their hive, they flew about on all sides
among the neighbouring plants, but never far: he did not observe that
these ever rose in the air like the others[1503]. From this experiment
it seems as if the compound eyes were for _horizontal_ sight, and the
_stemmata_ for _vertical_.
The definition of them by Linné and Fabricius as smooth, shining,
elevated or hemispheric puncta, conveys a very inadequate idea of
them; for, except in a very few instances, they are perfectly clear
and transparent, and their appearance is precisely the same as that
of the simple eyes of _Arachnida_ &c., under which head they might
very well have been arranged; but as the last are _primary_ eyes, and
the stemmata _secondary_, it seemed to me best that they should stand
by themselves. The structure of both is probably the same, and their
internal organization that of one of the lenses of a compound eye,
and both are set in a socket of the head.
Though a large number of insects have them, they are by no means
universal, since some Orders, as the _Strepsiptera_, _Dermaptera_, and
_Aptera_, are altogether without them. The _Coleoptera_, also, have
been supposed to afford no instance of species furnished with them;
but in the last number of Germar and Zincken Sommer's _Magasin_, it is
affirmed that they are discoverable in Gravenhorst's genus _Omalium_,
but not in the kindred genera _Micropeplus_ and _Anthophagus_[1504].
Upon examining the former genus, I find, that although _Omalium
planum_ and affinities, _O. striatulum_, and some others, appear
not to have them, yet with the aid of a good magnifier they may be
discovered in most species of that genus; as likewise in _Evœsthetus_
Grav. I find them also very conspicuous in _A. Caraboides_ and other
_Anthophagi_, but some species appear to want them. In these insects
they are two in number, situated in the vertex a little behind the
eyes but within them, and either at each end of a transverse furrow,
or at the posterior termination of two longitudinal ones. Nor are they
found in all the genera of the other Orders. In the _Orthoptera_, the
_Blattidæ_, unless a white smooth spot on the inner and upper side of
the eyes may be regarded as representing them, have them not; but in
all the other genera of that Order they are to be found[1505]. In the
_Hemiptera_ all the _Cicadiadæ_ are gifted with them; as are likewise
_Tetyra_, _Pentatoma_, with many other _Cimicidæ_, and the _Reduviadæ_
very remarkably; but many others in both sections of this order, as
_Thrips_, _Coccus_, _Aphis_, _Capsus_, _Miris_, _Naucoris_, _Nepa_, and
_Notonecta_, &c. are deprived of them[1506]. Of the _Neuroptera_ the
_Libellulina_ add _stemmata_ to their large eyes, in the anterior angle
of which they are stationed[1507]; but many other genera of that Order
are without them; as _Myrmeleon_, _Ascalaphus_, _Hemerobius_, &c. The
_Trichoptera_ and _Lepidoptera_ universally have them; though in the
latter, except in _Castnia_ and the _Sphingidæ_, they are not easily
seen. In the _Hymenoptera_ they are usually very conspicuous, but in
_Larra_ and _Lyrops_, two genera of this order, the posterior pair are
scarcely discernible; and in the neuter ants they are quite obsolete.
In the _Diptera_, though many genera are furnished with them, yet many
also want them; amongst the rest Latreille's _Tipulariæ_, and all the
horse-flies (_Tabanus_ L.). The _Pupiparæ_ (_Hippobosca_ L.) usually
have none; but in _Ornithomyia avicularia_, one of that tribe, though
extremely minute they are visible, arranged in a triangle, in the
polished space of their vertex.
As to the _Number_ of the _stemmata_, _three_ appears to be most
universal. Reaumur mentions an instance in which he counted _four_ in
a fly with two threads at its tail; but great doubt rests upon this
statement[1508]. Some Orthopterous genera, as _Gryllotalpa_, and many
Hemipterous, as _Tetyra_, _Pentatoma_, _Reduvius_[1509], _Cercopis_,
_Fulgora_[1510], &c., have no more than _two_; and in _Larra_ and its
affinities, as just observed, the posterior ones are obsolete, so as
to leave only _one_ discernible.
Where there are _three_ of these organs, they are usually arranged in
an obverse _triangle_ in the space behind the antennæ, at a greater
or less distance from them. In those male flies (_Muscidæ_) whose
eyes are confluent, the _stemmata_ are in a little area _behind_
their conflux; but, as before observed, in the drone-bee and the
_Libellulina_ they are _before_ it. This triangle is in some cases
nearly _equilateral_, as in _Perla_ related to the may-flies, and
many _Hymenoptera_; in others it is _acutangular_, as in _Locusta_
&c., in which the _stemma_ forming the vertex of the triangle is
before the antenna[1511]: in others, again, it is _obtusangular_,
as you will see in _Pepsis_ and various _Hymenoptera_. In the
humble-bees (_Bombus_), a line drawn through them would form a slight
curve. Their _situation_ also varies. In insects that have only
_two_, they are sometimes placed a little _behind_ the eyes, or in
the back part of the space between them: this is the case with most
of the bugs (_Cimex_ L.) that have them.--They are often _distant_,
as in _Tetyra_ F., _Edessa_ F.; and sometimes _approximated_, as
in _Reduvius_ F.[1512] In many of the Homopterous _Hemiptera_, as
_Cercopis_, _Ledra_, &c. they are planted in the _upper_ part of
the head[1513], but in _Iassus_ their situation is on the _under_
part; and in a North American subgenus, as yet without a name, they
are exactly _between_ the two, being placed in the frontal angle.
In _Fulgora_ their station is between the eyes and antennæ[1514].
They are most commonly _sessile_, and as it were _set_ in the head;
but in some, as _Fulgora candelaria_, they stand on a _footstalk_.
The _stemmata_ are set in the side of a frontal tubercle in that
four-winged fly of threatening aspect, _Corydalis_, which in its
_perfect state_ has mandibles, but longer and more tremendous,
like those that distinguish the _larva_ only of the kindred genus
_Hemerobius_[1515]. These organs differ little in _shape_, being
usually perfectly _round_ and somewhat _convex_; but occasionally
they vary in this respect. In _Fulgora serrata_ they are _oblong_,
with a longitudinal depression; in _F. Diadema_ they are also
umbilicated, but the _umbilicus_ is circular; in _Corydalis_ they are
_oval_; in other insects they are _ovate_; in some _semicircular_,
and in a few _triangular_. They vary much in _size_: in some of
these animals being so minute as to be scarcely visible, while in
others, as _Corydalis_, _Dorylus_, _Vespa pallida_ F., _Reduvius_,
&c.[1515], they are as large as some compound eyes. They differ also
in _colour_, though often _black_: in _Fulgora laternaria_ they
are of a beautiful _yellow_; in F. _candelaria_ they are _white_;
in many _Hymenoptera_ they are _crystalline_, in others _red_: the
fierce look of _Reduvius personatus_ is rendered more hateful by its
_stemmata_ having a pale iris round a dark pupil[1516].
Let us here stop and adore the goodness of a beneficent CREATOR, who,
though he has deprived these little beings of the _moveable_ eyes
with which he has gifted the higher animals, has made it up to them
by the variety and complex structure of their organs of vision, where
_we_ have only _two_ points of sight, giving _them_ more than as many
_myriads_.
5. _Antennæ._--But of all the organs of insects, none appear to be
of more importance to them than their _Antennæ_, and none certainly
are more wonderful and more various in their structure, and probably
uses. Upon this last particular I shall enlarge hereafter. Their
structure, as far as it differs in the sexes, I fully discussed in
a former letter[1517]; and the most remarkable kinds of them will
be included in a set of definitions which I shall draw up for you
before our correspondence on this part of my subject closes: I shall
therefore now confine myself to the following particulars--namely,
their _number_, _insertion_, _substance_, _situation_, _proportion_,
_general form_ and _structure_, _clothing_, _expansion_, _motions_,
and _station of repose_.
As to their _Number_, in the majority of _crustaceous_ animals the
antennæ amount to _four_, but no _insect_ has more than _two_. A
genus recently established (_Otiocerus_ Kirby[1518]) seems to afford
an exception to this rule, since the species composing it at first
sight appear to have _four_, and in some instances even _six_ antennæ;
but as only _two_ of them terminate in a bristle, the other, though
proceeding from the same bed of membrane, may perhaps be regarded
as merely appendages. Germar, who has described a species of this
genus[1519] under the name of _Cobax Wintheri_, considers these
appendages as analogous to _palpi_: but as they do not proceed from
the _oral_ organs, but from the bed of the _antennæ_ at the base of the
nose[1520], they ought certainly to be regarded rather as accessories
to the latter, than as representing the former. In the _Aptera_ order
the mites (_Acacus_ L.) appear to be without these organs. In the
pupiparous tribe _Hippobosca_ they seem about to disappear; and in
the _Arachnida_ &c., as has been more than once observed[1521], the
_mandibulæ_ have been thought to represent, not indeed the antennæ of
_insects_, but the _inner_ pair of those of the _Crustacea_.
In considering the _insertion_ of antennæ, by which I mean their
articulation with the head, we must advert first to the orifice
(_Torulus_) that receives them[1522]. This is a perforation of the
crust of the head; commonly, though not invariably, circular: in
Coleopterous insects often with concave lubricous sides, forming
an acetabulum, with processes usual in ginglymous articulations,
larger than the bulb or root of the antennæ; and which is commonly
covered, except the central space occupied by the bulb, with a
tense membrane. Though not in general remarkable, in some cases
it merits attention. In the genus _Rhipicera_ Latr., the elegant
antennæ of whose males I have described in a former letter[1523],
particularly the Brazilian species, it is a long process on each side
of the nose, and might be mistaken for the first joint: in another
Coleopterous genus, _Priocera_ K.[1524], it has somewhat of the
shape of a trumpet: in _Cupes_ a tubercle rises just above the base
of the antenna: a circular process forms the torulus in _Fulgora_
and others. It is also often placed in a cavity of the front, as in
several wild-bees, _Melitta_ K., and in _Locusta_ Leach on the sides
of an elevation of that part[1525]. In a large majority of insects
the bulb (_Bulbus_) or ball which is received by the bed, wears the
appearance, especially in the _Hymenoptera_, of a distinct joint; but
if you carefully examine it, you will clearly see that it is merely
the base of the _scape_ swelled out into a spherical or other kindred
form[1526]; and often marked, as in the _Cicindelidæ_, with impressed
points: as it is the piece by which the antenna moves in its socket,
this form of a _rotula_ was doubtless given for its more ready motion
in all directions. This structure is principally conspicuous in the
_Coleoptera_ and _Hymenoptera_ Orders: in the others the base is not
so distinguished from the rest of the scape. If you carefully extract
the antennæ of a beetle, say a _Copris_ or _Lamia_, and examine its
base or bottom, you will find that it is open for the transmission
of muscles and nerves; that in its upper margin it has a deep notch
or sinus, on each side of which is a smaller notch; and that all
round the margin, which is very lubricous, a membranous ligament is
attached, by which it was affixed in the torulus. Its articulation,
therefore, seems of a mixed kind, like that of most other organs and
parts of insects, partaking of the ligamentous, ginglymous, and ball
and socket. In the _Orthoptera_, _Hemiptera_, &c. the articulation
seems more purely ligamentous.
With regard to their _substance_--these organs are regulated, in some
degree, by the nature of the integument of the animal of which they
are appendages; in the softer insects being of a softer substance than
they are in hard ones. The vertex of the joints, where they receive the
succeeding one, appears in many cases to be softer than the rest of
it, and especially towards the apex, often papillose. The antennæ are
generally opaque; but in _Nebria complanata_, a beetle common on the
sea-coast in Wales and Lincolnshire, they are semitransparent.
The _situation_ of antennæ must next be considered. In this respect
it seems necessary that they should be so situated as to be under
the direction of the eyes: for if you examine ten thousand insects
(except, as was before observed[1527], where there are _four_ eyes),
you will not find one in which these organs are situated either above
or immediately behind them; their station being always either somewhere
in the space between the eyes or that below them. In _Ptinus_ F. they
are placed near the vertex; but in _Gibbium_, which is so nearly
related to that destructive genus[1528], they are beneath them. In many
_Melittæ_ K. they are in the middle of the space between the eyes; and
in many other _Hymenoptera_ and _Coleoptera_ (_Staphylinus_ &c.), in
the anterior part of it. In many Lamellicorn genera (except in some
_Acridæ_, as _A. viridissima_) as _Melolontha_, _Cetonia_, _Lucanus_,
&c. they may be regarded as planted in the lower surface of the cheek
before the eyes; but in _Copris_ &c., in which they are inserted
further under the shield of the head, they are properly in the _prone_
surface of the _front_. In the Capricorn-beetles (_Cerambyx_ L.) and
_Cnodalon_ F. they may be termed _inocular_, or placed in a sinus of
the eye; in the former tribe in its _interior_, and in the latter its
_anterior_ side. In the Rhynchophorous or rostrum-bearing beetles
(_Curculio_ L.) they vary in their situation. Thus in _Macrocephalus_
Oliv. they are inserted at its apex; in _Anthribus_ in its middle,
and in _Calandra_ at its base[1529]. In the water-scorpions (_Nepa_,
_Belostoma_, &c.) they may be called _extraocular_, being placed
under the head in its prone part, outside the eyes[1530]. In _Nirmus
Fringillæ_, a kind of bird-louse, they appear to be _oral_, being
situated, according to De Geer, under the head near the mouth, at a
great distance from the eyes[1531].
In their _proportions_, both as to length and thickness, antennæ vary
extremely. Thus sometimes they are very short--much shorter than
the head; as in the aquatic beetles _Gyrinus_, _Parnus_, and the
water-scorpion; and some land-beetles, as _Anthrenus_, &c. At other
times they far exceed the length of the insect: the males of many
Capricorn-beetles are so distinguished. In that of _Lamia ædilis_
they are more than _four_ times as long as the body; and every
intermediate length between these two may be found amongst them.
They vary also greatly in _thickness_: in _Paussus_, whose antennæ
emit light in the night[1532], and _Cerapterus_, they are nearly as
thick,--at least their knob, which forms the chief part of them,--as
the body of the insect[1533]; while in _Mantis_, _Acrida_ K. and
_Psocus_, they are as slender as a hair. The antennæ in many of the
_Prioni_, especially in _P. imbricornis_, are thick from base to tip;
while in other Capricorn-beetles they are quite the reverse.
It will not be necessary to enlarge here upon the general _form_
of these organs: I shall therefore only notice the two principal
divisions of them in this respect.--Antennæ, regard being had to
one of their uses, may be divided into two sections, distinguished
by forms extremely different: those, namely, that are employed by
insects as _tactors_ to explore their way, and those that cannot be so
employed. The great majority are of the former kind; but those that
may be denominated _setigerous_,--as the antennæ of the _Libellulina_,
_Ephemerina_, of the Homopterous _Hemiptera_, and of many _Diptera_,
the last joint of which terminates in a bristle, or is furnished
with a lateral one, and of some gnats that have short feathered
antennæ,--appear not fitted to be used as tactors to explore by touch,
and form the latter description. This difference in these organs, as
I shall have occasion to prove more at large hereafter, furnishes a
strong presumption that their _primary_ function is not _touch_. Were
this the case, it would be common to them all.
As to their _structure_, antennæ consist in general of a number
of tubular joints; each of which having separate motion, the
animal is thereby enabled to give them every flexure necessary for
its purposes. The _scape_, or first joint, by means of the bulb
inosculates in the _torulus_, or is suspended to it; and the others,
sometimes by a similar, though less pronounced knob at their base,
inosculate in the preceding one; but in some cases the inosculation
seems not so perfect, the joints being simply suspended by ligament.
In pectinated or lamellated antennæ, the branch is usually a lateral
process of the joint from which it issues; but in _Phengodes_
(_Lampyris plumosa_ L.) its involute plumose branches appear to
articulate with the apex of each joint[1534]. I have a specimen of
one of the _Cleridæ_, of a genus undescribed, in which each branch
is forked. In some tribes of the Capricorn-beetles (_Stenocorus_,
&c.) the antennæ are often armed at their apex with spines, sometimes
on the upper side and sometimes below. In some aquatic beetles
(_Gyrinus_, _Parnus_) they are furnished with an auricle at their
base, which, like the lid of a box, shuts them in when unemployed,
and protects them from the water[1535].
The portions into which antennæ may in general be considered as
divided, have been sufficiently explained to you above; but it may
not be amiss to add here a few words on the principal variations in
their structure that I have had an opportunity of observing. The
_scapus_[1536] or first joint, which includes the _bulbus_, is usually
the most conspicuous joint in the antenna (exclusive, I mean, of the
_capitulum_, in those in which that organ terminates in a knob),
it being thicker and often longer than the succeeding ones. In the
Capricorn and Darkling beetles, indeed (_Cerambyx_ and _Tenebrio_ L.),
the third joint is the longest, but the scape is still the thickest;
and in the stag-beetles (_Lucanus_ L.), many of the weevil tribes
(_Curculio_ L.), and those of the bees (_Apis_ L.), except in the
males, it is as long nearly as the remainder of the antennæ, which
forms an angle with it. In shape it is generally somewhat curved and
subclavate, or increasing in size from the base to the summit; but
it is sometimes straight and filiform, at others oblong or square,
at others again triangular, in several instances three-sided: in one
(_Cetonia cruenta_ F. _Genuchus_ K.) it is, as it were, broken, the
upper part forming nearly a right angle with the lower; in _Cerocoma
Schæfferi_ it is foliaceous; and it is occasionally suborbicular: and
probably many other forms might be enumerated.
The _Pedicellus_[1537] is the _second_, and may be deemed the _least
conspicuous_ joint of the antennæ. Though more slender than the scape,
it is generally thicker than that which immediately follows it. In
broken antennæ it is the hinge or pivot on which the _clavola_ or upper
member turns: it is usually very short, campanulate or bell-shaped, or
obconical; but in a species of bug (_Tetyra_, from New Holland--_T.
pedicellata_ Kirb. MS.) it is nearly as long as all the rest of
the joints taken together. In those species of _Lycus_, a genus of
beetles related to the glow-worm, that have flattened antennæ (as _L.
reticulatus_, _fasciatus_, &c.), this joint is almost received into the
socket of the scape, so that their antennæ appear at first to have only
_ten_ joints, but in those which have those organs filiform (as _L.
minutus_, _Aurora_, &c.) it is more conspicuous.
The _Clavola_[1538], or remaining joints of the antennæ taken
together, constitutes the principal part of the organ, which,
especially at its extremity, exercises its functions of touch, or
any other sense. The principal variations, as to form and structure,
that occur in this part will be mentioned in another place. I shall
only here observe, that in many instances the first joint of this
part is longer than the rest; but in _Tetyra pedicellata_ just
mentioned, it is by far the shortest, and shaped like the pedicel
of most insects. In the _Libellulina_, the Homopterous _Hemiptera_,
and those flies whose antennæ terminate in a bristle, the clavolet
is represented by the bristle. But in the flies which have a lateral
bristle, on the last joint, and those with triarticulate antennæ that
have no bristle, the terminal joint represents it. The clavolet often
terminates in a knob, or in several joints thicker than that which
precedes them. This varies greatly, not only in its form, but also
in the number of joints of which it is composed. Thus in _Paussus_,
_Platypus_, and many _Calandræ_, it consists of only a _single_
joint[1539]; in _Anthrenus_, _Ditoma_, &c. of _two_; in _Nitidula_,
_Geotrupes_, &c. of _three_[1540]; in _Tetratoma_, the _Silphidæ_,
of _four_[1541]; of _five_ in _Scaphidium_[1542]; of _six_ in
one species of _Languria_, of _seven_ in the common cockchafer
(_Melolontha vulgaris_[1543]); of _eight_ in _Diaperis Boleti_, in
which the whole clavolet forms the club[1544]; of _nine_ in _Oenas_;
and _ten_ in _Cerapterus_[1545]. All the above, you will observe,
are _beetles_. In the other orders there are _eleven_ joints in the
knob of some butterflies; _twelve_ in that of _Ascalaphus_[1546] and
_Myrmeleon_; and lastly, _fourteen_ in _Trachelus_[1547].
Under _structure_ also, the _number_ of joints of which antennæ in
general consist, should be considered. If you examine the insects
belonging to the different orders, you will find remarkable variations
in this respect. Let us run through them:--In the _Coleoptera_ the
natural number of joints is _eleven_; but this rule is not without
many exceptions. Thus, many have _fewer_ than the prescribed number:
_Paussus_ has only _two_[1548], _Claviger_ and _Platypus_ five,
_Dorcatoma_ and _Calandra_ eight[1549], _Geniates_ K. and _Phanæus_
MacLeay nine[1550], and lastly _Melolontha ten_[1551]. Others, again,
have _more_ than eleven joints: _Cebrio grandis_, _Chrysomela stolida_,
some _Saperdæ_, and several others, have _twelve_. In _Prionus
imbricornis_ the female has _nineteen_, and the male _twenty_[1552].
_Rhipicera marginata_ has _thirty-two_; and in a New Holland species
of this genus I counted _thirty-eight_. In the _Orthoptera_ I can
trace no general law in this respect. In _Locusta_ Leach in some
species you may count _fourteen_ joints, in others _sixteen_, and in
others _twenty-five_. In one, which appears to be a pupa, I found
only _thirteen_. In _Mantis_ they exceed _thirty_; but in _Blatta_,
from between _thirty_ and _forty_, they reach nearly _one hundred
and fifty_; often varying in number in different individuals of the
same species. The order _Hemiptera_ exhibits two peculiar types of
antennæ, which, with some exceptions, distinguish the two natural
sections into which M. Latreille has judiciously divided it. In the
_Heteropterous_ section they are _without_ a bristle at their end; and
in the _Homopterous_ one, with the exception of _Aphis_, _Thrips_,
&c. they _have_ one. In the genera of both these tribes, the number
of joints varies in these organs. Thus, exclusive of the seta, in
_Flata_ and _Cixius_ there are only _two_ joints; in _Galgulus_,
_Fulgora_, and _Cercopis_, there are _three_; in _Lygæus_, _Coreus_,
&c. there are _four_; in _Tetyra_, _Pentatoma_, _Tettigonia_, there
are _five_[1554]; in _Aleyrodes_ there are _six_; in _Aphis seven_; in
_Thrips eight_; in _Psylla ten_, the last of which is terminated by
two bristles[1555]; and in _Coccus eleven_. The _Neuroptera_ order,
as it stands at present, is regulated by no general rule with regard
to the number of joints in the antennæ of the insects that compose
it. Several types of form in these organs distinguish its discordant
tribes. The _first_ is that of the _Ephemeræ_, in which the antennæ
consist of two short joints, crowned by a short, tapering, _unjointed_
bristle. The _second_ is that of the _Libellulina_, similar to the
above, but with a _jointed_ bristle. The _third_ is that of _Psocus_,
in which the antenna has two short thick joints at the base, terminated
by a long filiform bristle, consisting of seven or eight joints, and
finer than a hair. Perhaps these three may be regarded as belonging to
a common type. The _fourth_ type is presented by the short filiform
antennæ of _Termes_; the _fifth_ by the setaceous ones of _Corydalis_,
_Hemerobius_, &c.; and the _sixth_ and last by the clavate and
capitate ones of _Myrmeleon_ and _Ascalaphus_. In the _Lepidoptera_
and _Trichoptera_ orders the antennæ, though varying in their general
form in the three tribes of which Linné formed his genera _Papilio_,
_Sphinx_, and _Phalæna_, with the exception of _Hepialus_, in which
the joints are few, are always _multiarticulate_:--we will therefore,
without further delay, proceed to the _Hymenoptera_. In Latreille's
tribe _Aculeata_ the general rule is, that the females shall have
_twelve_ joints and the males _thirteen_. In his _Ichneumonides_
the law seems to be, that the antennæ shall be multiarticulate
and setaceous; but in most of the other tribes of the order, even
those that in other respects are most nearly related,--as in his
_Tenthredinetæ_,--the number of joints of these organs varies without
end. Thus in _Hylotoma_ there are only _three_ joints[1556]; in _Cimbex
læta_[1557] _five_; in _C. axillaris_ and _Perga_ Leach[1558], six:
and so on to twenty-five or more[1559]. The same fluctuation in this
respect runs throughout the rest of the order. In the _Diptera_ there
are two general types of antennæ:--those of the _Tipulariæ_ Latr.,
consisting usually of from _fourteen_ to _sixteen_ joints, in the
males often resembling beautiful plumes; and those of the remainder of
the order, in which they do not exceed _three_ joints[1560]: though
the last, or _patella_, is often further divided into obsolete or
indistinct ones[1561]. These antennæ may be further subdivided into
_filatæ_ and _aristatæ_, or those without and those with a bristle,
either lateral or terminal.
The _clothing_ of antennæ also merits attention, since it is often
not a little remarkable. By clothing I understand the _down_ or
_hairs_ of every kind with which they are either generally or
partially covered. A great number of filiform and setaceous antennæ
of Predaceous beetles (_Cicindela_ L., _Carabus_ L.) have the first
two, three, or four joints naked, and the rest covered with a fine
down. In insects that have a knob at the end of these organs, whether
lamellated or perfoliate, this down is often confined to it, or to its
intermediate joints, and seems intermixed with nervous papillæ. These
are particularly visible in the flabellate antennæ of _Rhipicera_,
_Lampyris Latreillii_[1562], _Elater flabellicornis_[1563], &c.
covering both surfaces of the processes of the joints. In some male
bees these papillæ are inclosed in hexagonal spaces into which the
antennæ are marked out[1564]. It is to be observed, that in many
antennæ the joints of the clavolet have one or two bristles or more
at their apex, one above perhaps, and one below; the lower angle in
those of the serrated antennæ of _Elater_ is usually so furnished, and
sometimes the upper. In many Capricorn-beetles and various insects the
antennæ are clothed, instead of down, with stiffish hairs or short
bristles. Other insects have these organs, at least the clavolet,
beset with longer hairs standing out from them on all sides: of this
kind are those of a singular beetle (_Sarrotrium muticum_) sometimes
found in this country[1565]. Again, there are some that have only
their underside bearded with longer hairs; as _Lamia curculionoides_,
_speculifera_ K., and other Capricorns[1566]. In another of this tribe,
_Saperda hirsuticornis_, the three intermediate joints are ornamented
with branches of long black hairs, which give them an elegant and
feathery appearance[1567]. In _Callichroma alpina_ the apex of the
slate-coloured joints of its antennæ is bearded with black hairs. In
_Lamia reticulata_, and _Saperda fasciculata_ and _plumigera_, all
also Capricorns, a single bunch of hairs, resembling the brush of a
bottle-cleaner, signalizes the middle of the antenna[1568]: in _Saperda
scopulicornis_ K. this is star-shaped[1569]. Sometimes the _scape_ is
externally bearded, as in _Trox_, a beetle found in horns and bones;
and in many other Lamellicorns[1570]. In this last tribe the two
exterior leaves of the knob of the antennæ are often set with short
bristles[1571]; and in a minute beetle called by De Geer _Dermestes
atomarius_, the hairs of this part are said to form a brush[1572].
When insects, I mean more particularly _Coleoptera_, are about to
move from any station where they have been at rest, the first thing
they usually do, before they set a step, is to bring forward and
_expand_ their antennæ, which have either been carefully laid up
in a cavity fitted to receive them, or back upon the body: if they
terminate in a lamellated knob, they separate the lamellæ as far as
possible from each other; or if it is perfoliate, the joints of it
mutually recede. The object of this is evidently to collect notices
from the atmosphere, since the papillose part of these joints cannot
be applied to surfaces. When the animal begins to move, in many cases
the antennæ do the same, and continue their _motion_ till it stops
and returns to a state of repose. In the parasitic tribes of the
_Hymenoptera_ (_Ichneumon_ L.) they are kept in an almost constant
vibration. Many other insects move them in all directions without
any order or regularity; and others, when they elevate one depress
the other, and so proceed as if balancing themselves by means of
these organs like a rope-dancer. I have before stated to you how by
motions of their antennæ, ants and bees communicate their wants or
discoveries to each other, or make inquiry concerning any thing they
wish to know[1573]. But as I shall have occasion to make some further
remarks upon this subject, when the senses of insects are under
discussion, I shall for the present take my leave of it.
I shall conclude what I have to communicate to you relative to
the organs of which we are treating, with a few observations with
respect to their _station_ when the insect _reposes_. In the
Capricorn-beetles, _Eucera_ and other insects with _long_ antennæ,
they are merely turned back or on one side with no particular cavity
for their reception when unemployed, but probably the apex passes
under the body. In the Predaceous and Darkling beetles (_Carabus_
L., _Tenebrio_ L.) their station is usually under the sides of
the _prothorax_, and in the Tortoise beetles (_Cassida_), under
its anterior margin. In the Elastic beetles (_Elater_) they are
received into a groove between the under margin of that part and
the fore-breast (_antepectus_). In _Anthrenus_, when the animal
reposes or counterfeits death, the antennæ are concealed in a cavity
of the underside of the _prothorax_, at right angles with the
throat[1574]. In the kindred genus _Byrrhus_, another simulator of
death, a large cavity is excavated under the same part, to receive
both the forelegs and antennæ, a narrow space being left between
the angle of the _prothorax_ and fore-breast exactly admitting the
base of the latter, which are quite concealed under the former. In
_Cryptocephalus_ and _Chlamys_, kindred beetles, when at rest they
are withdrawn, except their scape and pedicel, with the head within
the cavity of the _prothorax_. In others they are turned under the
head, without any particular cavity for their reception; as in
many moths, _Apion_, &c. In most of the Lamellicorn beetles their
station is in the cavity formed by the eye and the throat, the knob
forming an angle with the rest of the antenna. In _Heterocerus_
they follow the contour of the eye[1575]. In _Brentus_, a genus
of weevils remarkably long and slender, they are turned back and
received by a slight longitudinal cavity of the rostrum; but in those
of this tribe (_Curculio_ L.) in which the clavolet forms an angle
with the long scape, this latter part, bending back, is laid up in
an oblique channel of that part; and the former, pointing in the
contrary direction, is folded upon it. In many flies (_Muscidæ_) a
vertical frontal cavity receives the antennæ, which point downwards
during repose[1576]. _Cryptocerus_, a very remarkable ant, has on
its head a singular square plate, the sides of which form a deep
longitudinal cavity: in this cavity the antennæ, quite concealed,
repose in safety. A cavity equally remarkable is exhibited by the
water-scorpions, particularly _Belostoma_, in which is a _very_ deep
kidney-shaped box, between the eye and throat, to receive and defend
its singular antennæ[1577]; which, when they are reposing, is closed
by the exterior harder joints, and from which it seems as if they
turned out, like a sentinel out of his box. In some aquatic genera
of beetles, as _Gyrinus_, _Parnus_, &c. they are withdrawn within
a lateral cavity of the same part, and are defended from the water
externally by the auricle at their base[1578]. The flabellated and
lamellated antennæ, previous to their being folded for repose, close
all their plates; which in action are as widely expanded as possible,
so as to form a knob; and in some the middle piece is entirely
concealed, as if in a box. In broken antennæ, or those in which the
clavolet forms an angle with the scape, the former is folded upon the
latter, with its point downwards.
II. _Subfacies._--Having dispatched the _Facies_, or _upper_ side of
the head, I am next to consider the _Subfacies_, or _under_ side:
but as the principal parts that occupy this side have been already
considered, I shall have no occasion to detain you long.
i. _Jugulum_[1579].--This part, which may be regarded as analogous to
the throat in vertebrate animals, lies between the cheeks; from which
it may usually be distinguished by being more lubricous and tumid, and
often separated by an impressed line. It is particularly conspicuous
and elevated in the Lamellicorn beetles, and calculated by its
lubricity for easy motion in the lower side of the cavity of the chest.
Its apex is the base in which the _mentum_ sits. It is not necessary to
enlarge further upon it, as it seldom exhibits striking characters.
III. _Collum_[1580].--In a large proportion of insects the head
inosculates in the trunk without the intervention of a neck, or
a constriction of the head behind. In the Orders _Orthoptera_,
_Trichoptera_, _Lepidoptera_, _Hymenoptera_, and _Diptera_, no
instance of it that I recollect occurs: in the _Coleoptera_ there
are many. In the Predaceous beetles, though several have no distinct
neck, yet others, as _Anthia_, &c. have a short and thick one;
and some few, as _Colliuris_, _Agra_, &c. one more pronounced.
Latreille has named a tribe in this Order _Trachelides_, from the
circumstance of their having a neck: in this tribe you will find the
blister-beetles (_Cantharis_ and _Mylabris_) both of the moderns and
the ancients. In the _Hemiptera_ order the water-scorpions _Nepa_,
&c. have a thick short neck; and _Zelus_, (a kind of bug,) one
longer and more slender; and, like _Raphidia_, the snake's-head fly,
which is similarly circumstanced, has the air of a serpent. Other
_Neuroptera_, likewise, have a neck; as _Hemerobius_, _Corydalis_,
&c. This part presents no other features that merit notice.
IV. _Myoglyphides_[1581].--The _Myoglyphides_, or muscle-notches, are
sinuses, some shallow and some deeper, in the posterior margin of the
upper side of the head, to which the levator muscles are affixed.
They seem principally confined to the _Coleoptera_; though, in some
cases at least, they may be traced in the Heteropterous _Hemiptera_.
These notches vary in number and depth in different insects. Thus
in _Buprestis_ there is only _one_ deep one[1582]: in _Copris_
there are _two_ shallow ones, in a deep sinus separated by a small
prominence[1583]: in _Elater_ and _Lamia_ there are also two not in a
sinus; and in _Calandra Palmarum_ there are four, two on each side,
with a prominent lobe between them[1584]. To each of these notches,
at its under margin, below the ligament that unites the occiput to
the trunk, a muscle to raise the head is usually attached.
FOOTNOTES:
[1151] See above, p. 86, 110, 243--.
[1152] Many species of _Hister_, _Curculio_ L., _Doryphora_ Illig.
are extremely hard, while _Cantharis_ Geoffr., _Meloe_ F., and
_Telephorus_ Geoffr., are very soft.
[1153] Thenard _Traité de Chimie Elémentaire_, iii. 637. n. 2005.
The other products he mentions are--a green oil, a yellow substance,
a black ditto, acetic acid, uric acid, phosphate of magnesia. The
vesicant matter consists of little micaceous laminæ soluble in
boiling alcohol and oil, but insoluble in water.
[1154] Coquebert _Illustr. Icon._ ii. _t._ xviii. _f._ 14, 15.
[1155] _Linn. Trans._ xii. _t._ xxii. _f._ 16.
[1156] This name I would give to _Locusta_ F., reserving, with Dr.
Leach, the latter name to the true _locust_ (_Gryllus_ F.). The name
_Conocephalus_, by which _Locusta_ F. has been distinguished, is
better restricted to those with a conical head.
[1157] PLATE XXVIII. FIG. 1, 2.
[1158] Huber _Nouv. Obs._ ii. 317.
[1159] VOL. I. p. 502--.
[1160] Hair, in the Holy Scriptures, is used as the symbol of
_strength_ or _power_. Judges xvi. 17--. 1 Cor. xi. 10.
[1161] _Anat. Compar._ ii. 624.
[1162] _Anat. Compar._ i. 119.
[1163] _Ibid._ ii. 540.
[1164] _Ibid._ 547.
[1165] _Ibid._ 553.
[1166] _Anat. Compar._ ii. 553.
[1167] _Ibid._ 557.
[1168] _Ibid._ 560.
[1169] PLATE XXVIII. FIG. 2. _a´´´._
[1170] _Anat. Compar._ ii. 557.
[1171] A _harmonic suture_ is when the margins of two flat bones
simply touch each other, without any intermediate substance; and a
_squamose_, when the thin margin of one covers that of the other.
_Anat. Compar._ i. 124. With regard to the flat portions of the
integument of insects, they have some motion; whereas a suture is an
articulation without movement. _Ibid._
[1172] Their connexion by means of a ligament classes them under
_Synneurosis_ (Monro _On the Bones_, Dr. Kirby's edit. 29), but even
this not strictly, since a common ligament connects them all. Those
of the trunk, as admitting a slight degree of motion, belong to
_Amphiarthrosis_ (_Anat. Compar._ i. 126), and those of the abdomen,
which are capable of larger movements, to _Diarthrosis_ (_Ibid._ 127).
[1173] See above, p. 309--.
[1174] In the _hornet_ and other wasps, this line on the inside of the
head furnishes a foundation for a septum, which in the sides of the
nose is very high, and connects also with the hind part of the head.
[1175] _Anat. Compar._ i. 445--.
[1176] _Ibid._ 447.
[1177] _Mém. sur les Anim. sans Vertèbr._ I. i, 11--. Comp. _Anat.
Compar._ iii. 314--.
[1178] It is probable that M. Cuvier took his idea of this first kind
of articulation, by contact of solid parts, from this individual
insect; since, besides its very prominent throat, there is on each
side of the _lower_ part of the occiput a small elevation, or
approach to a tubercle.
[1179] _Gen. des Crustac. et Ins._ ii. 246. _Regne Anim._ iii. 325.
[1180] This was written directly after the experiment recommended in
the text had been tried, with the result there stated.
[1181] Reaum. iv. 40. Latreille _Fourmis_, 328--.
[1182] PLATE VII. FIG. 2. k´´.
[1183] Clairville (_Ent. Helvet._ i. 44) appears to have been the first
who classed insects according to their mode of taking their food.
[1184] PLATE VI. VII. XXVI. a´.
[1185] In _Lucanus_, _Lamprina_, &c. the labrum seems to form the
under-side of the nose, and to be connate with it.
[1186] Kirby _Mon. Ap. Angl._ i. _t._ v. _Apis_ *. b. _f._ 18. _b._
[1187] _Ibid. t._ ii. _Melitta_ **. b. _f._ 4, 5. PLATE XXVI. FIG. 30.
[1188] PLATE XXVI. FIG. 31. _Mon. Ap. Angl._ i. _t._ x. _Apis_ **. c.
2. δ. _f._ 13. _c._
[1189] PLATES VI. VII. and XXVI. b.
[1190] De Geer iv. 124. _t._ iv. _f._ 12. iii. 415. _t._ xxi. _f._ 4.
[1191] Ibid. iv. 281--. _t._ xi. _f._ 7.
[1192] Ibid. 329. _t._ xii. _f._ 3.
[1193] Ibid. ii. 775--. _t._ xxvi. _f._ 10. b c, b c.
[1194] _Philos. Entom._ 18.
[1195] _Syst. Eleuth._ i. Præf. iv.
[1196] _Gen. Crustac. et Ins._ i. 180.
[1197] _N. Dict. d'Hist. Nat._ iv. 246.
[1198] PLATE VI. FIG. 6. b´. a´´.
[1199] PLATE VII. FIG. 3. b´. a´´.
[1200] Kirby _Linn. Trans._ xii. _t._ xxi. _f._ 8. _f_.
[1201] Ibid. _t._ xxi. _f._ 10. _d_. MacLeay _Hor. Entomol._ i. _t._
iii. _f._ 26, 27.
[1202] PLATE XXVI. FIG. 35.
[1203] Ibid. FIG. 34.
[1204] PLATE VII. FIG. 3. b´.
[1205] PLATE XXVI. FIG. 24. b´.
[1206] PLATE VII. FIG. 3. a´´.
[1207] _N. Dict. d'Hist. Nat._ xxiv. 171.
[1208] PLATE VI. FIG. 6. e´.
[1209] PLATE VII. FIG. 3. i´´.
[1210] PLATE VI. FIG. 12. e´.
[1211] PLATE VI. FIG. 6. b´.
[1212] Ibid. FIG. 12. b´.
[1213] PLATES VI. VII. XXVI. b´´.
[1214] PLATE VI. FIG. 6. b´´.
[1215] _Hor. Entomolog._ i. _t._ i. _f._ 1. _g_.
[1216] _Ibid. t._ ii. _f._ 18. _g._
[1217] Kirby _Mon. Ap. Angl._ i. _t._ xii. _neut._ _f._ 1. _g._ _c._
[1218] _Ibid._ 93. 103--. _t._ vi. Apis **. b. _f._ 3. _b._ _c._
[1219] _Ibid._ _t._ i. *. a. _f._ 3. _b._
[1220] _Ibid._ _t._ ix. _Apis_ **. c. 2. γ. _f._ 3. _b._
[1221] _Clairv. Ent. Helvet._ ii. _t._ xxiv. _f._ 1. _c._
[1222] PLATE XXVI. FIG. 24, 28. b´´.
[1223] _Mon. Ap. Angl._ i. _t._ ii. _Melitta_ **. b. _f._ 2. _c._
[1224] PLATE XIII. FIG. 2. _Linn. Trans._ xii. _t._ xxi. _f._ 6. _b._
[1225] This is the case with _Oxyporus_ F. PLATE XIII. FIG. 4.
[1226] PLATE VI. FIG. 12. b´´. Latreille, _N. Dict. d'Hist. Nat._
xvii. 545, seems not to regard these as palpi; but from their tubular
form, and insertion in the socket of the labium, it is clear that
they ought to be so considered.
[1227] PLATES VI. VII. XXVI. c´.
[1228] A corresponding articulation takes place between the tibia and
thigh of some of the _Scarabæidæ_, which will be hereafter described.
See PLATE XXVII. FIG. 8-11.
[1229] _Comparaison des Organes de la Mastication des_ Orthoptères, 2.
[1230] _Comparaison des Organes de la Mastication des_ Orthoptères, 2.
[1231] See above, p. 407. note b.
[1232] _Ubi supra_, 4.
[1233] _Ibid._
[1234] _Ibid._ 5.
[1235] Oliv. _Ins._ no. 66. _Prionus. t._ xiii. _f._ 54.
[1236] _Ibid._ no. 83. _Curculio. t._ iv. _f._ 37.
[1237] _Linn. Trans._ xii. _t._ xxi. _f._ 12.
[1238] For Mandibles of _Locusta_ see PLATE VI. FIG. 6. c´. of
_Lampyris_ Oliv. _Ins._ no. 28. _t._ i. _f._ 1. of _Buprestis_,
_Ibid._ no. 32. _t._ iii. _f._ 17. of _Lucanus_, _Ibid._ no. 1. _t._
i-v. and of _Prionus_, _Ibid._ no. 66. _t._ ii. _f._ 8.
[1239] _Gomphosis_ is, when one bone is immoveably fixed in another
as a nail in a board.
[1240] Marcel de Serres _ubi supra._ 7.
[1241] See PLATE XIII. FIG. 7. Kirby _Mon. Ap. Angl._ i. _t._ xiii.
_f._ 13. and _t._ xii. _neut. f._ 10.
[1242] PLATE XXVI. FIG. 19.
[1243] Oliv. _Ins._ no. 42. _t._ i. _f._ 1. and no. 2. _t._ i. _f._
1. b.
[1244] PLATE XXVI. FIG. 16, 18.
[1245] Ibid. FIG. 21.
[1246] _Mon. Ap. Angl._ i. _t._ iv. _Melitta. f._ 5-8.
[1247] Drury _Ins._ ii. _t._ xlviii. _f._ 3. See above, p. 315.
[1248] Oliv. no. 1. _t._ v. _f._ 16. &c. _t._ iii. _f._ 7.
[1249] _Comparaison des Organes_, &c. 7--.
[1250] PLATE VI. FIG. 6. and XIII. FIG. 5. a´´´.
[1251] PLATE VI. FIG. 12. and XIII. FIG. 5. b´´´.
[1252] PLATE XXVI. FIG. 16.
[1253] I was not aware that Knoch had observed this part, till some
time after the publication of my paper _On Mr. William MacLeay's
Doctrine of Affinity and Analogy_ (see _Linn. Trans._ xiv. 105--),
when I happened to meet with it in a letter from a friend, received
more than thirteen years ago; but without any reference to the work
of Knoch, in which it was stated. It was doubtless taken from his
_Beiträge zur Insektengeschichte_.
[1254] _Anat. Comp._ iii. 321--.
[1255] One of those mandibles is represented in PLATE XXVI. FIG. 20.
a´´´. incisive teeth d´´´. molary plate. Comp. _Linn. Trans._ ubi
supr. _t._ iii. _f._ 4. _c a b._
[1256] VOL. II. p. 275--.
[1257] In the _Myrmeleon_, or ant-lion, the suction is promoted by
the action of a piston, that pumps up the juices. Reaum. vi. 369.
[1258] De Geer iv. 386--. _t._ xv. _f._ 10. See above, p. 121.
[1259] PLATE XIII. FIG. 7. _c´´._
[1260] Oliv. _Ins._ no. 42. _Staphylinus._ _t._ i. _f._ 1. b.
[1261] PLATES VI. VII. XXVI. d´.
[1262] PLATE VI. FIG. 3, 6, 12. VII. FIG. 3. c´´.
[1263] PLATE VII. FIG. 3. a´´. e´´. _Mon. Ap. Angl._ i. _t._ xiii.
_f._ 1. _e._
[1264] _Ibid._ _f._ 3. _a._
[1265] Clairv. _Ent. Helvet._ ii. 146. _t._ xxiii. _f._ super. _b._
[1266] _N. Dict. d'Hist. Nat._ iv. 243.
[1267] In _Anoplognathus_, however, though it has neither teeth nor
spines, it is as hard as the mandibles.
[1268] See above, p. 317.
[1269] PLATE XXVI. FIG. 10, 11. d´´´. e´´´.
[1270] Ibid. FIG. 9. d´´´. e´´´.
[1271] PLATE VI. FIG. 6, 12. d´´´. e´´´. Oliv. _Ins._ no. 45.
_Meloe._ _t._ i. _f._ 1. c. These are what Fabricius calls _galeate_
maxillæ, on which he founded his class _Ulonata_.
[1272] PLATE XXVI. FIG. 11. d´´´. e´´´.
[1273] PLATE VI. FIG. 3. d´´´.
[1274] Clairv. _Ent. Helvet._ _t._ i. _t._ xviii. _f._ super. _b._
[1275] Ibid. _t._ xix. _b._ This genus may be the analogue of some
heteromerous one yet undiscovered, as _Calosoma_ is of _Adelium_
(Kirby _Linn. Trans_. xii. _t._ xxii. _f._ 2.)
[1276] Clairv. _Ent. Helvet._ ii. _t._ xxiv. _f._ super. _b._
[1277] PLATE XXVI. FIG. 11.
[1278] Oliv. _Ins._ no. 19. _Trogosita._ _t._ 1. _f._ d. no. 41 bis.
_Dryops. t._ i. _f._ 1. c.
[1279] See above, VOL. I. p. 238.
[1280] Oliv. _Ins_. no. 17. _Ptinus._ _t._ i. _f._ 1. c.
[1281] _Ibid._ no. 60. _Blaps t._ i. _f._ 2. c.
[1282] _Ibid._ no. 88. _Languria. t._ i. _f._ 2. c.
[1283] _Ibid._ no. 89. _Erotylus. t._ ii. _f._ 12. c.
[1284] Oliv. _Ins._ no. 41. _Gyrinus._ _t._ i. _f._ 1. e.
[1285] PLATE XXVI. FIG. 13. _Hor. Entomolog._ i. _t._ iii. _f._ 29,
30. E.
[1286] _Mon. Ap. Angl._ i. _t._ ii. _Melitta_. **. a. _f._ 2. _t._ v.
_Apis_. *. b. _f._ 4. &c.
[1287] Oliv. _Ins._ no. 48. _Cerocoma_. _t._ i. _f._ 1. c.
[1288] PLATE XXVI. FIG. 10-12.
[1289] Clairv. _Ent. Helvet._ ii. _Cicindela_. _t._ xxiv. _f._ super.
_b._ for _Carabidæ_, _Dytiscidæ_, his other plates.
[1290] _Hor. Entomolog._ i. _t._ ii. _f._ 13. E.
[1291] PLATE VI. FIG. 6, 12. f´´´.
[1292] _Hor. Entomolog._ _t._ i. _f._ 3. E.
[1293] _Ibid._ _f._ 4. E.
[1294] Oliv. _Ins._ no. 7. _Hexodon_. _t._ i. _f._ 1. e.
[1295] _Ibid._ no. 3. _Scarabæus_. _t._ l. _f._ 1. f.
[1296] Kirby in _Linn. Trans._ xiv. 102. _t._ iii. _f._ 4. d.
[1297] De Geer v. 417. _t._ iv. _f._ 12.
[1298] PLATES VI. VII. h´´.
[1299] See above, p. 443.
[1300] _Mon. Ap. Angl._ i. _t._ ix. 2. c. 2. β. _f._ 2. _d. g._ 4.
_t._ xii. _neut. f._ 6. _d._ _t._ xiii. _f._ 3. _b._
[1301] Clairv. _Ent. Helv._ ii. _t._ xxiii. _f._ 1.
[1302] PLATE VII. FIG. 3. b´´. h´´.
[1303] PLATE VI. FIG. 12. b´´. f´´´.
[1304] Ibid. FIG. 13. h´´. Savigny _Anim. sans Vertèbr._ l. i. 29--.
_t._ i.-iii. ȯ.
[1305] De Geer vi. _t._ xix. _f._ 4. _d._
[1306] Ibid. _t._ ix. _f._ 8. _b b._ t. xii. _f._ 20. _b._ _t._ xiv.
_f._ 15. _i i._
[1307] PLATE XXVI. FIG. 6.
[1308] Ibid. FIG. 5.
[1309] Kirby _Mon. Ap. Angl._ i. _t._ x. _Apis._ **. c. 2. δ. _f._ 3.
_a._ and **. d. 1. _f._ 1. _d._
[1310] Clairv. _Ent. Helvet._ ii. _t._ xxxi. _f. super. b. Mon. Ap.
Angl._ i. _t._ xiv. _f._ 1. _h. f._ 3, 5. _c._
[1311] See above, p. 317.
[1312] PLATE XXVI. FIG. 1. As the very remarkable maxillary palpi of
that extraordinary Coleopterous genus _Atractocerus_ seem not to have
been so fully described as they deserve, I shall give here a minute
detail of their composition. They consist of _four_ joints: the first
is wide and short, and somewhat platter-shaped; the second is much
smaller and shorter: the third is concavo-convex, or shaped like a
shallow bowl: towards the breast this joint is elevated, and on the
elevated edge sits the last joint, which is longer than all the rest
taken together. In my specimen it points towards the breast; its
under side is entire and slightly curved, but in the upper side are
two rows of lamellæ (_b_), placed alternately _nine_ on each side,
with an odd one at the end: these lamellæ are full of minute papillæ,
and furrowed on the side next the mouth. From between the first pair
a slender exarticulate hairy branch or appendage emerges (_a_), which
forms nearly a right angle with the main stem. The _labial palpi_
appear to consist of _three_ joints; the two first very short, and
the last large, ovate, and acute. This description is not taken from
_A. necydaloides_, but from a Brazilian species more than five times
its size, which I have named _A. grandis_.
[1313] PLATE VI. VII. XXVI. e´.
[1314] PLATE VI. FIG. 6, 12. e´. Cuvier _Anat. Compar._ iii. 347.
[1315] Cuvier _Ibid._
[1316] Huber _Fourmis_, 4--.
[1317] _Anim. sans Vertèbr._ iii. 304.
[1318] See above, p. 440.
[1319] Reaum. v. 309--.
[1320] PLATE XXVI. FIG. 23.
[1321] Clairv. _Ent. Helvet._ ii. Pref. xxii.
[1322] Kirby _Mon. Ap. Angl._ i. _t._ xiv. (1) 2. _b._
[1323] PLATE XXVI. FIG. 24. e´.
[1324] Clairv. _ubi supr._ _t._ xx. _c._
[1325] PLATE XXVI. FIG. 28. e´.
[1326] Kirby _ubi supr._ fig. (8) 1. _c c._ The lateral pieces in the
tongue in _Vespa_ (_Ibid. c c._) have been regarded as lobes of it,
but they are rather _Paraglossæ_.
[1327] PLATE XXVI. FIG. 29. e´.
[1328] Clairv. _ubi supr. t_. xxx. _c._
[1329] Kirby _ubi supr._ no. 2. _f._ 1, 3.
[1330] PLATE XXVI. FIG. 24. _b._
[1331] Kirby _ubi supr. t._ x. _Apis_. c. 2. δ. _f._ 5. _t._ xii.
_neut. f._ 2, 3. _t._ xiii. _f._ 1. _h._
[1332] PLATE XXVI. FIG. 26, 29.
[1333] PLATE XXVI. FIG. 28. i´´.
[1334] Kirby _Mon. Ap. Angl._ i. _t._ xii. _neut._ _f._ 1. _h h._
_t._ xiii. _f._ 1. _f f._
[1335] _Ibid._ _t._ x. **. d, 1. _f._ 2. _b b._
[1336] See above, p. 425.
[1337] PLATE VII. FIG. 14. f´.
[1338] Reaum. v. 317.
[1339] _Organisation exterieur des Ins._ 184.
[1340] _Ubi supra._
[1341] _Anim. sans Vertèbr._ I. i. 12.
[1342] De Geer ii. 778--. _t._ xxvi. _f._ 11. _m._ PLATE VII. FIG. 2.
k´´.
[1343] _Ubi supra._
[1344] See above, p. 455.
[1345] _Organisation_ &c. 182.
[1346] Under this name M. Savigny includes the _Myriapoda_,
_Arachnida_, and _Crustacea_. _Anim. sans Vertèbr._ I. i. 40.
[1347] _Ibid._ 43.
[1348] VOL. II. p. 275--. Also see above, p. 121--.
[1349] _Anim. sans Vertèbr._ I. i. _t._ ii. _f._ 2. a. a´.
[1350] PLATE VII. FIG. 13. c´.
[1351] Ibid. d´.
[1352] _Anim. sans Vertèbr._ I. i. 106. PLATE VII. FIG. 13. b´.
[1353] _Ubi supr._ 45--.
[1354] PLATE VII. FIG. 11. _f´_, _a´´_.
[1355] _Ubi supra_, 45.
[1356] Ibid. 44--.
[1357] _N. Dict. d'Hist. Nat._ ii. 275--. PLATE VII. FIG. 10. c´.
[1358] De Geer _t._ xl. _f._ 4. _t._ x. _f._ 7, 8.
[1359] See above, p. 18, 30.
[1360] Savigny _Anim. sans Vertèbr._ I. i. 62.
[1361] _N. Dict. d'Hist. Nat._ ii. 277.
[1362] _N. Dict. d'Hist. Nat._ ii. 276.
[1363] _Ibid._
[1364] _Ubi supr._ 58.
[1365] PLATE XV. FIG. 7.
[1366] PLATE VI. FIG. 7-9. a´, b´, c´, d´.
[1367] _Magaz._ 1806.
[1368] PLATE VI. FIG. 7. a´.
[1369] Ibid. Labium b´. Mandibulæ c´. Maxillæ d´.
[1370] Savigny _Anim. sans Vertèbr._ I. i. 37.
[1371] De Geer iii. 137--. _t._ ix. _f._ 4.
[1372] Reaum. iii. 335. _t._ xxviii. _f._ 8-14.
[1373] De Geer iii. 117. _t._ viii. _f._ 22. _b._
[1374] PLATE VII. FIG. 5, 6. a´, b´, c´, d´.
[1375] _N. Dict. d'Hist. Nat._ iv. 253.
[1376] PLATE VII. FIG. 5, 6. a´.
[1377] Ibid.
[1378] Reaum. iv. _t._ XVI. FIG. 13. z.
[1379] Authors are not agreed as to the precise number of lancets
contained in a gnat's proboscis. Swammerdam affirms there are _six_,
including the labrum. i. 156. b. _t._ xxxii. _f._ 3. Reaumur could
find only _five_. iv. 597--. _t._ xlii. _f._ 10. And Leeuwenhoeck
only _four_.
[1380] PLATE VII. FIG. 5.
[1381] PLATE VII. FIG. 5. This figure is copied from Reaumur, and was
engraved before this discovery was made.
[1382] M. Savigny is of opinion that the central lancet or lancets
represent the _Epipharynx_ and _Hypopharynx_; for which he does not
state his reasons: but as these are properly covers of the pharynx,
the idea seems incorrect. _Ubi supr._ 15.
[1383] _N. Dict. d'Hist. Nat._ ix. 489. and iv. 253--.
[1384] _Ubi supr._ 36.
[1385] Ibid. _t._ iv. _f._ 1. o. _o._
[1386] VOL. I. p. 48, 110--.
[1387] PLATE VI. FIG. 13. a´, b´, c´, d´.
[1388] VOL. I. p. 394--.
[1389] PLATE VI. FIG. 13. a´. Savigny _Anim. sans Vertèbr._ I. i.
3--. _t._ i.-iii. a.
[1390] _Ibid._ i. PLATE VI. FIG. 13. c´.
[1391] Ibid. FIG. 13. h´´. Savigny _ubi supr. o._
[1392] PLATE VI. FIG. 13. d´. Savigny _ubi supr. t._ 1-3. _o._
[1393] Ibid. _ö._ PLATE VI. FIG. 13. b´.
[1394] _N. Dict. d'Hist. Nat._ xvii. 467.
[1395] _N. Dict. d'Hist. Nat._ iv. 253.
[1396] PLATE VII. FIG. 8. c´, d´, e´, h´´.
[1397] Ibid, c´.
[1398] Ibid, d´.
[1399] Ibid, h´´.
[1400] Ibid. e´.
[1401] Rösel. ii. _t._ iii. _f._ 15. Latreille _Gen. Crust. et Ins._
iv. 365.
[1402] Swammerdam _Bibl. Nat. t._ ii. _f._ 4.
[1403] _N. Dict. d'Hist. Nat._ xxviii. 266.
[1404] _Ibid._ xvi. 432. De Geer vii. _t._ vi. _f._ 4. Not quite
accurate.
[1405] PLATES VI. VII. XXVII. a.
[1406] _Organisat. Extér. des Ins._ 196.
[1407] In the _Transactions of the Royal Society_, this part in
_Anobium tessellatum_ is so called. xxxiii. 159--.
[1408] PLATE XXVII. FIG. 4. a.
[1409] PLATE VII. FIG. 2. a.
[1410] _Observ. Nouv. sur les Hyménoptères_ (_Ann. du Mus._) 5.
[1411] Those beetles whose posterior pair of tarsi have only _four_
joints, and the two anterior _five_, are so called.
[1412] Kirby in _Linn. Trans._ xii. 464. _t._ xxiii. _f._ 6.
[1413] Ibid. xiii. _t._ i. _f._ 1. _b._
[1414] PLATE VI. FIG. 10. g´.
[1415] Ibid. FIG. 7. a.
[1416] Ibid. g´.
[1417] PLATE VI. FIG. 4. g´.
[1418] PLATES VI. VII. b.
[1419] Kirby _Mon. Ap. Angl._ i. _t._ i. _Melitta._ *. b. _f._ 3.
[1420] PLATE VI. FIG. 4. b.
[1421] PLATES VI. VII. c.
[1422] VOL. II. p. 317--.
[1423] PLATE XXVI. FIG. 41. i.
[1424] Stoll _Punaises_, _t._ xxxix. _f._ 279, 280.
[1425] PLATES VI. VII. XXVI. d.
[1426] PLATES VI. VII. e.
[1427] PLATES VI. VII. f.
[1428] PLATE XXVII. FIG. 4. f.
[1429] Cuv. _Regne Animal._ iii. _t._ xiii. _f._ 4.
[1430] This insect was taken both at Matlock and Exmouth. The body
and thighs are of a light-brown, wings testaceous, legs pale; antennæ
between setaceous and filiform, two-thirds the length of the body;
first joint not much thicker than the rest.
[1431] PLATE VI. VII. g.
[1432] De Geer iii. 561. _t._ xxvii. _f._ 1.
[1433] PLATES VI. VII. XXVI. h.
[1434] PLATE VII. FIG. 8, 9. XXVI. FIG. 43. h.
[1435] Viz. one on each side above, and one below.
[1436] Walckenaer _Aranéïdes_, _t._ v. _f._ 50, 52. _t._ viii. _f._ 82.
[1437] Treviranus (_Arachnid_. 4.) says that _Scorpio Europæus_
has only _two_ eyes. He appears to have overlooked the two on the
anterior side of a tubercle at each angle of the head, where they are
large, but not conspicuous, at least in my specimen.
[1438] De Geer vii. _t._ iii. _f._ 8, 9, 12.
[1439] PLATE XXVI. FIG. 43., h.
[1440] Walck. _Aran._ _t._ i. _f._ 3.
[1441] _Ibid._ _t._ v. _f._ 42-48.
[1442] _Ibid._ _t._ iv. _f._ 41.
[1443] Walck. _Aran._ _t._ i. _f._ 2.
[1444] _Ibid._ _t._ i. _f._ 7.
[1445] _Ibid._ _t._ ii. _f._ 18, 20.
[1446] VOL. I. p. 323.
[1447] De Geer vii. 138. _t._ viii. _f._ 15. _y y_.
[1448] Ibid. _t._ xl. _f._ 3. _o o_, _y y_.
[1449] PLATE XXVI. FIG. 43. h.
[1450] _Segestria perfida_, Walck. _Aran._ _t._ v. _f._ 52. &c.
[1451] _Tetragnatha_ and _Latrodectes_, _Ibid._ _t._ vii. _f._ 64.
and _t._ ix. _f._. 84.
[1452] _Nyssus coloripes_, _Ibid._ _t._ vi. _f._ 58.
[1453] _Dolomeda_, _Ibid._ _t._ ii. _f._ 18, 20.
[1454] _Sphasus_, _Ibid._ _t._ iii. _f._ 24.
[1455] _Mygale avicularia_, _Ibid._ _t._ i. _f._ 3.
[1456] _Sparasus_, _Ibid._ _t._ iv. _f._ 41. PLATE XXVI. FIG. 37.
[1457] _Eresus_, _Ibid._ _t._ iii. _f._ 26.
[1458] _Storena_, _Ibid._ _t._ ix. _f._ 86.
[1459] _Argyroneta_, _Ibid._ _f._ 88.
[1460] _Pholeus_, _Ibid._ _t._ viii. _f._ 80.
[1461] PLATE XIII. FIG. 11.
[1462] PLATE XXIX. FIG. 11. h.
[1463] Ibid. _a._
[1464] PLATE XIII. FIG. 10.
[1465] See above, p. 117--.
[1466] Reaum. iv. 245.
[1467] _Microgr._ 176.
[1468] _Epist._ Mar. 6. 1717.
[1469] _Amœn. Academ._ vii. 141.
[1470] I possess a specimen in which the eye is partly black and
partly white: the lenses are invisible in the _black_ part, but very
visible in the white.
[1471] _Philos. Entomolog._ 19.
[1472] PLATE XXVI. FIG. 38.
[1473] Hooke _Microgr._ schem. xxiv.
[1474] PLATE XXIII. FIG. 3.
[1475] Cuvier _Anat. Compar._ ii. 442--. Compare Swammerdam _Bibl.
Nat._ i. 211. _t._ xx. _f._ 45.
[1476] VOL. II. p. 4, 364, &c.
[1477] PLATE XXVI. FIG. 36. h. Fabricius, and after him Olivier,
though both quote Forster, regard one of these eyes in _Lamia
Tornator_ as a spot; but they could not have examined it attentively.
_Saperda præusta_ F. has also four eyes.
[1478] PLATE XXVI. FIG. 39. h.
[1479] Latreille _Gen. Crust. et Ins._ iii. 73.
[1480] _N. Dict. d'Hist. Nat._ i. 479.
[1481] VOL. II. 320.
[1482] De Geer vii. 562.
[1483] VOL. II. p. 228.
[1484] _Ent. Helvet._ i. _t._ xii.
[1485] PLATE VI. FIG. 10.
[1486] Kirby _Mon. Ap. Angl._ i. _t._ xi. _Apis._ **. e. 1. _f._ 2.
[1487] De Geer iii. _t._ xxxiv. _f._ 17, 18, 24. _o o._
[1488] _Mon. Ap. Angl._ i. _t._ xiv. no. 11. _f._ 1. _f._ _Linn.
Trans._ xi. _t._ ix. _f._ 10. d.
[1489] PLATE XIII. FIG. 9. Fuessly _Archiv._ _t._ vi.
[1490] Schellenberg _Cimices_ _t._ xiii. ix. _f._ 1. _a._ De Geer ii.
_t._ xviii. _f._ 10.
[1491] Stoll _Spectres_, &c. _t._ iv. _f._ 14. _t._ x. _f._ 38, &c.
[1492] VOL. I. p. 261--.
[1493] _Linn. Trans. ubi supr._
[1494] Schellenberg _Mouches_, _t._ xxvii. _f._ 1, 2. _a, d._
[1495] _Ibid._ _t._ ix. _f._ 3. _a._
[1496] _Ibid._ _t._ ii. _f._ 2. _a._
[1497] _Mon. Ap. Angl._ i. 148.
[1498] PLATE XXVII. FIG. 4. h´.
[1499] This circumstance proves that Mr. W. S. MacLeay is correct in
considering this as a subgenus; but it militates against its being
connected with _Lamprima_.
[1500] PLATE VI. FIG. 4, 10. VII. FIG. 1, 2, 4. XXVI. FIG. 39-42. i.
[1501] _Bibl. Nat._ i. 214.
[1502] Reaum. iv. 245.
[1503] Ibid. v. 287--.
[1504] _Magas. der Entomolog._ iv. 410.
[1505] Latreille speaks of _Phasma_ as having no stemmata; but it
should seem that he examined only the _apterous_ ones, all the
_winged_ individuals, at least so far as I have examined them,
having three very visible ones. It may, I think, be laid down as a
rule, that the larvæ and pupæ of _Orthoptera_ have not these organs.
Probably their use is principally in flying?
[1506] _Flata phalænoides_ F. and affinities have no stemmata, while
_Flata reticulata_ and affinities have them: a proof that these
tribes are distinct genera.
[1507] PLATE VI. FIG. 10. i.
[1508] Reaum. iv. 243. He refers for this insect to plate xiv. without
adding any number for the figure; but no such is in that plate.
[1509] PLATE XXVI. FIG. 40. i.
[1510] _Cercopis_, Ibid. FIG. 42; and _Fulgora_, FIG. 41. i.
[1511] PLATE VI. FIG. 4. i.
[1512] PLATE XXVI. FIG. 40. i.
[1513] Ibid. FIG. 42. i.
[1514] PLATE XXVI. FIG. 41. i.
[1515] De Geer iii. _t._ xxvii. _f._ 1. Reaum. iii. _t._ xxxii. _f._
3, 9.
[1516] PLATE XXVI. FIG. 40. i.
[1517] See above, p. 318--.
[1518] _Linn. Trans._ xiii.
[1519] _Mag. der Entomolog._ iv. 5.
[1520] Palpi quatuor, subæquales, cylindrici, _ad basin clypei. Germ._
[1521] See above, p. 18, &c.
[1522] PLATE VI. FIG. 1, 4. i´.
[1523] See above, p. 321. _Linn. Trans._ xii. _t._ xxi. _f._ 3.
[1524] Ibid. _f._ 7.
[1525] PLATE VI. FIG. 4. c. i´.
[1526] PLATE XII. FIG. 9. l´´. This circumstance was very recently
discovered; which will account for this plate not being quite correct
in this respect, the bulb being represented as a distinct joint in
FIG. 6, 10, 26.
[1527] See above, p. 498.
[1528] VOL. I. p. 231, 238.
[1529] Oliv. _Ins._ no. 80. _Macrocephalus t._ i. _f._ 1-4.;
_Anthribus f._ 5-12; and no. 83. _Curculio t._ ii. _Calandra f._ 16.
[1530] Schellenberg _Cimices t._ xiv. _f._ 1. _b._
[1531] De Geer vii. _t._ iv. _f._ 7. _a a._
[1532] VOL. II. p. 421.
[1533] PLATES XII. FIG. 28; and XXV. FIG. 9, 24.
[1534] PLATE XXV. FIG. 4.
[1535] PLATES XII. FIG. 29; and XXV. FIG. 28. _a._
[1536] PLATES XI. XII. XXV. k´´.
[1537] PLATES XI. XII. XXV. l´.
[1538] Ibid. m´.
[1539] PLATES XII. FIG. 28; and XXV. FIG. 13. m´´.
[1540] PLATE XXV. FIG. 2, 5, 21. m´´.
[1541] PLATE XII. FIG. 10. m´´.
[1542] Ibid. FIG. 4. m´´.
[1543] PLATE XXV. FIG. 1. m´´.
[1544] PLATE XI. FIG. 23.
[1545] PLATE XXV. FIG. 24.
[1546] Ibid. FIG. 30.
[1547] Jurine _Hymenopt._ _t._ vii. _f._ 3.
[1548] PLATE XXV. FIG. 28.
[1549] Ibid. FIG. 13.
[1550] Ibid. FIG. 5.
[1551] Ibid. FIG. 1.
[1552] PLATE XI. FIG. 12.
[1553] _Linn. Trans._ xii. _t._ xxi. _f._ 3.
[1554] Latreille says _six_, but only _five_ are discernible; the
three last form a kind of bristle.
[1555] Latr. _Fourmis_, 323.
[1556] Jurine _Hymenopt._ _t._ vi. _f._ 3.
[1557] _Ibid._ _f._ 2.
[1558] _Ibid._ _f._ 1. PLATE XXV. FIG. 7.
[1559] PLATE XXV. FIG. 25, 26.
[1560] PLATE XII. FIG. 16-22.
[1561] Ibid. FIG. 19. _a_.
[1562] _Linn. Trans._ xxii. _t._ xxi. _f._ 3, 4. PLATE XXV. FIG. 11.
[1563] PLATE XI. FIG. 17.
[1564] Kirby _Mon. Ap. Angl._ i. 184. _t._ x. **. d. 1. f. 8.
[1565] PLATE XXV. FIG. 27.
[1566] PLATE XII. FIG. 26.
[1567] PLATE XXV. FIG. 32.
[1568] PLATE XII. FIG. 25.
[1569] PLATE XXV. FIG. 17.
[1570] _Linn. Trans_. xii. _t._ xxiii. _f._ 5. _f._
[1571] _Ibid. t._ xxi. _f._ 8 _g._ 9, 10. _c._
[1572] De Geer iv. 219. _t._ viii. _f._ 20.
[1573] See VOL. II. p. 65, 201--.
[1574] De Geer iv. _t._ vii. _f._ 22.
[1575] PLATE XXV. FIG. 35.
[1576] De Geer vi. _t._ i. _f._ 5.
[1577] PLATE XI. FIG. 21.
[1578] PLATE XII. FIG. 29. _a._
[1579] PLATE VI. m.
[1580] Ibid.
[1581] PLATE XXVII. FIG. 1, 3-5. n´.
[1582] Ibid. FIG. 3.
[1583] Ibid. FIG. 4.
[1584] PLATE XXVII. FIG. 1.
LETTER XXXV.
_EXTERNAL ANATOMY OF INSECTS_,
CONTINUED.
THE TRUNK, AND ITS PARTS AND ORGANS.
As the _head_ of insects is the principal seat of the organs of
_sensation_, so is the _trunk_ of those of _motion_; and in it are
contained the muscles by which they are moved: it may therefore be
regarded as the great centre of motion, and as the main support and
prop of the two other primary sections of the body--the head and
abdomen, between which it is situated--it may be deemed the most
important part of the insect, the key-stone of the whole structure.
In treating upon it, for the greater clearness, I shall consider its
_substance_, _general form_, _proportions_, _composition_, _internal
processes_, and _members_. It will first, however, be necessary to
assign my reasons for the nomenclature of its parts that I have adopted.
Had the entomological world been universally agreed upon this
subject, and there was an established system of Orismology[1585],
I should have proposed no alteration without great reluctance, and
the fullest conviction of the absolute necessity of some change;
but as the standard of language in our science is still unsettled,
and different terms are used by different writers, there seems full
liberty left to me to select those that appear upon the whole most
appropriate; and where proper and significant terms seem wanting, to
invent new ones. M. Latreille, in a late Essay[1586], has proposed
many changes of this kind, and seems to hesitate concerning the
adoption of some of those recently coined in France for the parts of
the trunk[1587]; it may therefore, I think, be permitted me to labour
a little in this hitherto imperfectly cultured field, and to suggest
such improvements as the subject may seem to require or admit.
Linné called the part we are now considering the _trunk_, its
upper-side he usually denominated the _thorax_, and its under-side
the _breast_: he notices also the _scutellum_ and _sternum_[1588].
As the _prothorax_ and _scutellum_ are the only _apparent_ parts of
the back of the trunk in his first Orders (_Coleoptera_, _Hemiptera_
L.), the rest being covered, in noticing these he puts the part for
the whole, calling the _prothorax_ the _thorax_, but which strictly
was not synonymous with what he called by the same name in the other
Orders. Linné's phraseology with regard to the trunk of insects was
adopted by Fabricius and other Entomologists, till Illiger employed
the term _thorax_ to designate the whole of the trunk[1589], calling
the upper part _thorax superior_ and the lower _thorax inferior_.
M. De Blainville, M. Latreille, and other French writers, improved
upon this, naming the upper part the back (_dorsum_), and the lower
the breast (_pectus_); and dividing the trunk, or according to
them _thorax_, into three sections, each bearing a pair of legs.
But I see no sufficient reason for this alteration--the terms
_trunk_, _thorax_, and _breast_, in the common acceptation are well
understood, and lead to no confusion or glaring impropriety; I
shall therefore adhere to the old phraseology, especially as French
Entomologists in popular language still do the same.
As to the division of the trunk into segments by M. Latreille and
others, it has been regarded as consisting of _three_ primary ones,
which have been called in the order of their occurrence, reckoning
from the head--_prothorax_, _mesothorax_, _metathorax_. The first
of these segments, however--and the learned Entomologist just named
seems to hint as much[1590]--is usually more distinct from the other
two, than they are from each other. If this idea be correct, the
trunk is properly resolvable into _two_ primary segments, the first
bearing the arms or fore-legs, and the other the proper legs and
the organs of flight. M. Chabrier calls the latter _tronc alifère_,
or wing-trunk;--a happy term, which I have adopted and latinized,
calling it the alitrunk (_alitruncus_): the first segment, because
it bears the fore-legs, I have named manitrunk (_manitruncus_). I
adopt likewise the terms above mentioned, _prothorax_, _mesothorax_,
_metathorax_, to signify the three segments into which the thorax of
Linné, or the _upper_ side of the trunk, is resolvable; and those of
the breast I denominate _antepectus_, _medipectus_, and _postpectus_.
If terms be thought necessary to designate the two intire segments
into which the alitrunk is resolvable, the first may be the meditrunk
(_meditruncus_), and the other the potrunk (_potruncus_).
I. _Substance._--With regard to its _substance_, the trunk in general
is softer than the head, and harder than the abdomen, especially as
to its upper surface; but in some cases, where it is not protected by
the elytra, as in the rove-beetles (_Staphylinus_ L.), the abdomen
appears as hard as the trunk. Though usually not very different from
the elytra in this respect, in _Meloe_, _Lytta_, and other vesicatory
beetles, it is of a firmer consistence.
II. _General Form._--In the _Coleoptera_ Order the only part of
the trunk that is visible on its upper-side is the _prothorax_:
the _mesothorax_, with the exception of the _scutellum_, and the
_metathorax_, being entirely concealed by it and the elytra; so that,
with regard to _shape_, it may nearly be considered as merging in the
_prothorax_. Below it is more visible, and may be stated as more or
less quadrangular; in oblong beetles inclining to a parallelogram,
and in shorter or hemispherical ones to a square. In the majority
it is more convex below than above, except in the case of the
hemispherical or gibbous beetles (_Coccinella_, _Erotylus_, &c.), in
which the under-side is flat and the upper-side very convex. In the
_Diurnal Lepidoptera_ the trunk approaches to a cubical shape, in the
_Nocturnal_ it is more spherical. A similar difference obtains in
the _Hymenoptera_ and _Diptera_: in the bees, wasps and flies, the
trunk approaching to the figure of a sphere; in the ants, _Scoliæ_,
crane-flies, &c. to that of a cube. The upper part of it in many
_Ichneumonidæ_, female ants, &c. is very elevated, forming an arch,
and sloping towards the abdomen. In general it may be observed with
respect to the remaining Orders, that the form of the trunk merges
in that of the whole body, the tendency of which is often to a
three-sided figure.
III. _Proportions._--The trunk is usually longer and larger than
the head and longer than the abdomen, but not wider: but there are
exceptions to both these rules. In _Colliuris_, _Mantis_, &c.,
it is more _slender_; and in _Atta megacephala_ and some neuter
ants, it is _shorter_ than the _head_; in _Atractocerus_, many
_Staphylinidæ_, _Phasma_, the _Libellulina_, the _Lepidoptera_, and
various _Hymenoptera_, it is shorter, and in the _Mantidæ_ more
_slender_ than the _abdomen_. The greatest disproportion between it
and the last part is exhibited by the genus _Evania_, parasitic upon
the _Blattæ_, in which the abdomen appears merely as a minute and
insignificant appendage of the trunk. The vertical diameter of this
part, almost without exception, is greater than that of either head
or abdomen. When we consider that it contains the muscles that move
both the organs of flight and the legs, we see clearly the reason why
the CREATOR gave it greater volume.
IV. _Composition._--I lately intimated to you that the trunk, though
resolvable into _three_ segments, in most cases properly consists
of only _two_ primary ones. Whoever examines the perfect insects of
every Order, except the _Aptera_[1591], will find this distinction
strongly pointed out, not only by the different direction of the
first pair of legs from that of the two last, but also in a large
proportion by a deep incisure; and in all it is further manifested
by the anterior segment having a motion distinct from that of the
rest of the trunk, and separating readily from it; and this not only
where it is large, as in insects that have a thoracic shield, but
also in those in which the _prothorax_ is less apparent: whereas the
other two pedigerous segments have little or no distinct motion,
will not readily separate from each other, and in some cases exhibit
no pectoral suture between them. Sometimes, however, these two last
segments are more prominently distinguished: in _Lytta_, _Mylabris_,
and other vesicatory beetles, they are separated below by an
incisure, or rather the first or mid-leg segment, is not nearly so
elevated as that of the hind-legs. In some ants (_Atta_ Latr.), in
the neuters, there is no distinction of segments in the trunk; but
in others (_Formica_ Latr.) it follows the general law, and consists
of three. In the _Arachnida_, with the exception of _Galeodes_, in
which the head is distinct, and the three segments of the trunk may
be traced, these parts together form only a single segment. Induced
by these reasons, I consider the trunk as consisting in general of
two _primary_ segments, the _manitrunk_ and _alitrunk_: the latter
resolvable into two _secondary_ ones.
* _Manitruncus_[1592].--The manitrunk, then, is the anterior section
of the trunk, which bears the arms and contains the muscles that move
them. This part has free motion, or a motion independent of that of
the rest of the trunk. This indeed seems a necessary result of the
direction and uses of the arms. It consists of an upper and lower
part--the _prothorax_ and _antepectus_.
i. _Prothorax_[1593].--The upper part of the manitrunk in the
_Coleoptera_, _Orthoptera_, and _Hemiptera_, is by far the most
conspicuous part of the trunk, but in the other Orders it is less so.
With respect to it, insects may be divided into two classes--those
that have and those that have not a _prothorax_. In the _Coleoptera_
Order it is remarkable both for size and variations in its shape and
sculpture. In the _Orthoptera_, though less various, it is almost
equally conspicuous, especially in _Blatta_. In the _Homopterous_
section of the _Hemiptera_, in many genera it has become extremely
short; while in the _Heteropterous_ section its dimensions are not
much reduced. In the majority of the _Neuroptera_, likewise, it is
comparatively large; in the _Libellulina_ much shorter, and in the
_Trichoptera_ and _Lepidoptera_ nearly evanescent[1594].--In the
_Hymenoptera_ and _Diptera_, with very few exceptions, the thoracic
shield altogether disappears, at least if I am correct in an idea,
which I shall hereafter explain, that the _collar_ usually regarded
as the analogue of the _prothorax_, is really a part of the alitrunk.
In these last Orders, though there is no true _prothorax_, the
manitrunk still remains under the form of an _antepectus_, bearing
the fore-legs, and containing the muscles that move them.
The prothorax of insects may in general be considered with respect
to its _parts_, _margin_, _appendages_, _shape_, _sculpture_,
_clothing_, and _proportions_.
1. The _prothorax_, regarded as a whole, distinct from the
_antepectus_ or fore-breast, consists commonly of _two_ pieces--the
_shield_, or upper part[1595], and the _ora_, or under part[1596].
In the shield you are to observe its _apex_[1597], _base_[1598],
_sides_[1599], _limb_[1600], and _disk_[1601]. The _apex_ is the
part next the _head_; the _base_ that next the _abdomen_; the
_limb_ the _circumference_, and the _disk_ the _central_ part. In
many _Orthoptera_ and Heteropterous _Hemiptera_, the shield appears
further to consist of two pieces, an anterior and posterior one.
The _ora_ is a continuation of the shield below the lateral margin,
turned downwards and inwards towards the fore-breast and the legs,
but separated from the former in most cases by a suture, as in
_Carabus_ L.; and in others merely by an impressed line, as in
_Blaps_ F.; but in _Curculio_ and _Cerambyx_ L., &c. there is no ora,
the shield being without a lateral margin, and forming one piece with
the _antepectus_. The part we are now considering varies in different
genera. Sometimes it is very _narrow_, as in _Scarites_; at others
very _broad_, as in _Buprestis_, _Nepa_, &c. In _Lampyris_, except
_L. italica_, and affinities, it projects posteriorly into a _lobe_
or tooth, which forms a right angle with the rest of the _ora_, and
becomes the lower part of the cavity that receives the head; and in
_Dermestes_ this part is excavated into an anterior and posterior one
which admits the antennæ and arms when folded for repose.
2. The _margin_ of the _prothorax_ is a ridge, either defining its
sides or whole circumference. In many cases this margin is broad and
dilated, but in others it is merely a thread or bead that separates
the shield from the _ora_. Though generally terminating the upper
surface, it sometimes, as in _Staphylinus_, dips below it. In many
insects, however, as I just observed, the thoracic shield has no
lateral margin whatever.
3. Various and singular are the _appendages_ with which the
_prothorax_ of numerous insects is furnished. Many of these are
_sexual_ distinctions, and have been before described to you[1602];
but there are others common to both sexes, the most remarkable of
which I shall notice.--Some are distinguished by a long _horn_ which
overhangs the head, as _Membracis cultrata_, _ensata_, &c.[1603];
in others it stands upright, as in _Centrotus spinosus_[1604];
_C. Taurus_ has a pair of thoracic horns like those of a bull,
only dorsal[1605]; in _Ledra aurita_ they are flat, and represent
ears[1606]; in some species of _Tingis_ (_T. Echii_, _Pyri_, &c.)
a kind of reticulated hood, resembling lace, is elevated from the
anterior part of the _prothorax_, which receives and shelters the
head[1607]. In _Centrotus globularis_ and _clavatus_ F., especially
the former, the part in question is armed by a most singular and
wonderful apparatus of balls and spines,--in one case standing
erect[1608], and in the other being horizontal[1609],--which gives
these animals a most extraordinary appearance. In many of the species
here quoted the _prothorax_ is producted posteriorly into a long
scutelliform horizontal horn, which more or less covers the wings and
abdomen; a circumstance which also distinguishes the genus _Acrydium_
F. (_Tetrix_ Latr.). This horn seems to have been sometimes regarded
by Linné and Fabricius as a real _scutellum_, and sometimes only as
a process of the prothorax: but that it is merely the latter will be
evident to you, if you examine carefully any insect furnished with
this appendage; for if you remove that part, you will discover the
true scutellum and other parts of the trunk concealed beneath it. A
very remarkable prothoracic appendage is exhibited by some species
of _Mantis_. In general the part we are treating of in this tribe is
very slender; but in _M. strumaria_, _gongyloides_, &c., it appears
dilated to a vast width, and assumes, either partially or generally,
a subrhomboidal form; but if it is more closely examined, it will be
found that the form of the _prothorax_ is really similar to that of
the rest of the tribe, but that this part is furnished on each side,
either on its whole length or anteriorly, with a large membranous
flat subtriangular appendage resembling parchment[1610]. Perhaps
this kind of sail may be useful to the animal in flight. In _Prionus
coriarius_ &c. its sides are armed with teeth, and in many _Lamiæ_,
_Cerambyces_, and other Capricorn beetles, and often in various bugs
(_Pentatoma_ Latr.) with sharp fixed spines. But the _prothorax_
has _moveable_ as well as _fixed_ appendages; of this kind are
those spines (_umbones_), whose base is a spherical boss moving in
an _acetabulum_ of the thoracic shield of the Capricorn subgenus
_Macropus_ Thunb. If I might hazard a conjecture, I should say that
these organs were given to this animal by an all-provident CREATOR,
to enable it to push itself forward, when in the heart of some tree
it emerges from the pupa, that it may escape from its confinement.
Another kind of moveable appendages are attached to the thorax of
_Lepidoptera_, usually in the form of a pair of concavo-convex scales
covered externally with a tuft of hairs[1611]. M. Chabrier, who
examined these scales in recent insects, describes them as vesicles,
which appeared to him full of a liquid and of air, and capable of
being alternately inflated and rendered flaccid; he regards them
as accessories to a pair of spiracles, which he looks upon as
vocal[1612], opening into the manitrunk just above the insertion of
the arms. These organs are quite distinct from the _tegulæ_ that
cover the base of the primary wings of insects of this Order[1613],
and are what, borrowing a term from Mouffet[1614], I have called in
the table _patagia_, or tippets. Under this head I may include the
_caruncles_ at the anterior angles of the _prothorax_ of a genus
of beetles with soft elytra, named by Fabricius _Malachius_. When
pressed, says De Geer of these insects, a red inflated soft vesicle,
of an irregular shape, and consisting of three lobes, emerges from
the thorax and from each side of the anterior part of the abdomen,
which re-enters the body when the pressure is removed[1615]. M.
Latreille seems to think that these vesicles have some analogy with
the poisers of _Diptera_ and the pectens of scorpions; and that they
are connected with the respiration[1616].
4. We are next to say something upon the _shape_ of the _prothorax_.
The forms of the thoracic shield, especially in the _Coleoptera_,
are so various, that it would be endless to aim at particularizing
all; but it may be useful to notice a few of the most remarkable. The
prothorax of _Moluris_, a darkling-beetle, approaches the nearest
of that of any insect to a spherical form, from its remarkable
convexity; in the wheel-bug (_Reduvius serratus_) it is compressed,
and longitudinally elevated into a semicircular serrated crest: it
is crested, also, in many _Locustæ_ and _Acridæ_, in some having
two parallel ridges; but, generally speaking, its surface is
more depressed. In _Necrodes_ it is nearly circular, in _Blatta
petiveriana_ semicircular, in _Nilion_ and some _Coccinellidæ_
crescent-shaped, in _Carabus_ obcordate, in _Cantharis_ and _Sagra_
approaching to a square, in _Languria_ to a parallelogram; in many
_Cimicidæ_, _Belostoma_, &c., it is triangular, with the vertex
truncated; it is trapezoidal in _Elater_, in _Ateuchus_ rather
pentagonal, and exhibiting an approach to six angles in some
other beetles[1617]: but the prothorax most singular in form is
that of some species of M. Latreille's genus _Helæus_[1618], as
_H. perforatus_, _Brownii_, &c.: in these its anterior angles are
producted, and curving inwards, lap at the end one over the other,
so as to form a circular orifice for the head, which otherwise would
be quite covered by the shield. Thus the upper portion of the eyes
can see objects above, as well as their lower portion those below. I
might enumerate many other forms, but these are sufficient to give
you some notion of the variations of this part.
5. The _prothorax_ is equally various in its _sculpture_; but since
in the Orismological table almost every instance of it has its place,
I shall here only notice it as far as it is common to the whole
tribes, genera, or subgenera. The _Scarabæidæ_ of Mr. W. S. MacLeay
are distinguished by a small _excavation_ on each side of this part,
which, as has been before remarked[1619], furnishes an elevated base
for an internal process with which the anterior _coxæ_ ginglymate. In
_Onitis_ and _Phanæus_, to these excavations are superadded a pair
impressed in the base of the _prothorax_, just above the scutellum;
in _Carabus_ L. a longitudinal channel divides the thoracic shield
into two equal portions; and many genera of that great tribe have
in addition, at the base on each side, one or two excavations or
short furrows. _Elophorus_ F. has on this part several longitudinal
channels, alternately straight and undulated. Generally speaking,
in _Carabus_ L. the _prothorax_ has no impressed points; but in
one or two subgenera of _Harpalidæ_ (_Chlænia_ &c.) it is thickly
covered with them. In numbers of _Locusta_ Leach, the part we are
considering is what Linné terms _cruciate_, being divided into four
longitudinal portions by three elevated lines, the intermediate one
being straight, and the lateral ones diverging from it both at their
base and apex, so as to form a sinus or angle[1620]. In certain
_Acridæ_ K. (_Locusta_ F.) there are only two of these lines or
ridges, but notched or toothed; and in some of the genus first named
only one[1621]; in _Locusta Dux_ and affinities the _prothorax_ has
several transverse channels or rather folds[1622], with corresponding
ridges on its internal surface.
6. With respect to the _clothing_ of the _prothorax_, I have not
much to say: in Coleopterous insects this part is commonly naked;
but in some genera, as _Byrrhus_, _Anthrenus_, _Dermestes_, and many
weevils (_Curculio_ L.) it is partially or totally covered with hairs
or scales. In the other thoracic Orders it is usually naked, but in
some _Neuroptera_, the _Myrmeleonina_, &c., it is hairy; and in the
_Libellulina_ it is fringed posteriorly with hairs.
7. As to its relative _proportions_, the _prothorax_ is sometimes
rather wider than the rest of the trunk and the head, as in _Onitis_,
_Pasimachus_, &c.; it is considerably narrower in _Collyuris_
and _Odacantha_; and of the same width in those _Scaritidæ_ with
_striated_ elytra[1623]. Again, it is sometimes of the same width
with the elytra, but wider than the head, as in _Hydrophilus_,
_Dytiscus_, &c.; in some instances it is of the same width with the
head, and narrower than the elytra, for instance in _Anthia_ and
_Brachinus_. In most _Coleoptera_ it is longer than the head and
shorter than the elytra; but in _Manticora_, the vesicatory beetles,
&c., it is shorter than either. In _Gnoma longicollis_[1624],
it is nearly as long as the elytra; in many _Staphylinidæ_,
_Atractocerus_, &c., longer; in _Phanæus carnifex_, _bellicosus_,
&c., it is longer than the elytra and the rest of the body. With
regard to itself, it is sometimes very wide in proportion to its
length--_Dytiscus_, _Helæus_; at others very long in proportion to
its width--_Colliuris_, _Brentus_, _Mantis_, &c. In _Flata_, and
many other Homopterous _Hemiptera_, it is extremely short; extremely
long in _Gnoma_; in _Sagra_ and _Donacia_ its width about equals its
length; in _Elater_, _Dytiscus_, and many Heteropterous _Hemiptera_,
it is narrowest before; in _Languria_ it is every where of equal
width; in _Anthia_, _Carabus_, &c., it is widest before; and, lastly,
in the _Scarabæidæ_ MacLeay it is usually widest in the middle.
ii. _Antepectus_[1625].--The _antepectus_, as was before
observed[1626], in some tribes forms one piece, without any kind of
separation, with the _prothorax_; but very often this is not the
case. In _Carabus_ L. it occupies almost the whole under-side of
the manitrunk; but in _Elater_, in which the _ora_ is very wide,
the _antepectus_ is merely the _middle_ portion of that part. In
_Carabus_ F. &c. between the _ora_ and the base of the arms is
a convex triangular piece, distinguished from the rest of the
_antepectus_ by a spurious suture; and in _Pentatoma_ and other
Heteropterous _Hemiptera_ a similar piece is observable, which
terminates in a convex bilobed subtriangular sheath, receiving the
base of the clavicle[1627]. This piece seems a prop to that part,
and analogous to the _scapula_ of the _medipectus_ and _parapleura_
of the postpectus. I shall say no more upon the _antepectus_, as it
is seldom remarkable. In the mole-cricket, however, one peculiarity
distinguishes it: it is in this of an elastic leathery substance,
while the _prosternum_ is hard, resembling a bone. In other instances
these parts are both of the same substance.
1. The _sternum_ or breast-bone of insects consists mostly of
_three_ distinct pieces; in this resembling the human _sternum_,
which is described by anatomists as composed originally of _three_
bones[1628]. Each of these pieces is appropriated to a pair of legs,
and each of them at times has been called the _sternum_: thus in
_Elater_ the _prosternum_, in the _Cetoniadæ_ the _mesosternum_,
and in _Hydrophilus_ the _metasternum_, have been distinguished by
this name. Our business is now with the first of these pieces, the
_sternum_ of the _antepectus_ or _prosternum_[1629]: this is the
middle longitudinal ridge of the _fore-breast_, which passes between
the arms, when elevated, extended, or otherwise remarkable. It is
most important in the _Coleoptera_ Order, to which my remarks upon it
will be chiefly confined. In these it is sometimes an _elevation_,
and sometimes a _horizontal_ process of the fore-breast. If you
examine the great _Hydrophilus_ (_H. piceus_), at first you will
think that there is only a single _sternum_ common to all the legs;
but if you look more closely, you will perceive between the head
and the arms a triangular vertical process, with a longitudinal
cavity on its posterior face, which receives the point of the
_mesosternum_ that passes between the arms[1630]: this vertical piece
is the real _prosternum_, and not the other, which really belongs
to the alitrunk. In this case the elevation of the _prosternum_
is _before_ the arms; in others it is _between_ them, as you may
see in a Chinese chafer (_Mimela_ K.), which imitates the external
appearance of a quite different tribe[1631]; in others again it is
_behind_ them, as in most of the Lamellicorn beetles. In the common
dung-chafer (_Geotrupes stercorarius_), it is a hairy process, which,
when the head is bent downwards, is received by a deep cavity of
the _mesosternum_. The _Dynastidæ_ MacLeay may always be known by
a columnar _prosternum_ rising vertically between the arms and the
_medipectus_. Lastly, in other tribes there is a prosternal elevation
both _before_ and _behind_ the arms, as in _Cerambyx thoracicus_,
_dimidiatus_, and affinities. Of the _second_ description, those that
have a less elevated horizontal _prosternum_, the point in most is
to the _anus_, but in some to the _head_: thus in _Carabus_ L. it
is generally a subspathulate flat piece, the point of which slides
over the _mesosternum_, or covers it; but in _Harpalus megacephalus_
Latr.[1632], one of this tribe, though similarly shaped, its point
is to the _head_. These horizontal _prosterna_ vary in their
termination. In that of _Carabus_ L. the apex is obtuse; in that
of _Elater_, above described[1633], and _Dytiscus_ it is _acute_;
in _Prionus lineatus_, _Spencii_ K., &c., it is _bilobed_; and in
_Buprestis variabilis_, _attenuata_, &c., obsoletely _trilobed_.
With regard to the other Orders no striking features of this part
are observable, except in some _Orthoptera_. In _Acrida viridissima_
K. (_Locusta_ F.) it is represented by two long filiform vertical
processes; and in _Locusta_ Leach by a single conical horn[1634],
mistaken by Lichtenstein for a process of the throat[1635]. In
one instance, _Gryllotalpa_, this part is a long piece between
the arms, shaped like the human thighbone or _tibia_, being more
slender in the middle and widest at the ends, and which is of a much
harder substance than the rest of the _antepectus_, and forms the
lower termination of a singular machine which will before long be
noticed. In many bugs (_Cimicidæ_), instead of being elevated, the
three portions of the _sternum_ are hollowed out into a longitudinal
groove, in which the _promuscis_ when unemployed reposes.
The most conspicuous and remarkable appendages of the manitrunk,
are the _brachia_ or arms. I shall not, however, enter into the
full consideration of these, as they consist numerically of the
same parts, till I treat of the legs in general. Here it will
only be necessary to assign my reasons for calling them by a
distinct denomination. In this I think I am authorized, not only
by the example of Linné, who occasionally found it necessary to do
this[1636], and more particularly by the ancient notion that this
pair of organs in insects were not to be reckoned as _legs_[1637],
but likewise from their different position and functions. They are
so inserted in the _antepectus_ as to point towards the _head_,
whereas the other two pair point to the _anus_. With regard to their
_functions_, besides being _ambulatory_, and supporting the manitrunk
in walking, they are applied to many other purposes independent of
that office,--thus they are eminently the _scansory_ or climbing legs
in almost all insects; in most _Carabi_ L., by means of the notch
and calcar[1638], they are _prehensory_ legs; in _Scarites_ belonging
to that tribe, the Lamellicorn beetles, and the mole-cricket, they
are _fossorious_ legs, or proper for digging[1639]; in _Mantis_,
_Nepa_, and some _Diptera_, they are _raptorious_, or fitted to seize
and dispatch their prey[1640]: they are used also by many insects to
clean their head, eyes, and antennæ, &c. For many of these purposes
they cannot be fit without a structure different from that of the
other legs, which renders it a matter of as great convenience in
descriptions to speak of them and their parts under different names
from those of the legs, as it is of the arms of man; on this account
it is that I propose to give to the fore-leg and its part the names
by which the analogous parts, or what are so esteemed, in the human
species are distinguished;--when spoken of in common with the other
legs, they may still be called the forelegs.
* * * * *
** _Alitruncus._ The alitrunk is the posterior segment of the trunk,
which below bears the four true legs, and above the organs for flight
or their representatives. In treating of this part we may consider
its _insertion_ or _articulation_, its _shape_, _composition_,
_substance_, _motions_, and _organs_.
i. With regard to its _insertion_, or articulation with the manitrunk
and abdomen, it may be observed that it is attached to both by its
whole circumference by means of ligament; in the _Coleoptera_,
_Orthoptera_, and Heteropterous _Hemiptera_ being received by the
posterior cavity of the _prothorax_, the shield of which in these
Orders, especially the last, almost covers and conceals it; but in
the remaining ones it is merely suspended to it. In the former also,
especially in the _Coleoptera_, it seems more separate and distinct
from the manitrunk than from the abdomen, and more independent of its
motions than of those of the latter part: but in the _Hymenoptera_
and _Diptera_ its greatest separation is from the abdomen in both
respects. In many insects, as in the Lamellicorn beetles, the
mole-cricket, &c., the _manitrunk_ terminates posteriorly, drawing
a line from the base of the _prothorax_ to the _antepectus_, in
an oblique section; in other tribes, as in the _Cerambyx_ L., the
Predaceous beetles, &c., the section here is _often_ vertical, but
in the _alitrunk_ the anterior one is _always_ vertical, while the
posterior, by which it articulates with the abdomen, in the Orders
with an ample thoracic shield, is oblique, so that the _pectoral_
portion is more ample than the _dorsal_.
ii. As to its _composition_, the alitrunk is usually much more
complex than the manitrunk; for, besides the instruments of motion,
it consists of numerous pieces. It may be regarded as formed of _two_
greater segments, the first bearing the elytra, or the primary wings,
and the intermediate legs; and the second, the secondary wings and
the hind legs.
1. _Collare_[1641]. The first segment of the alitrunk is the middle
piece of the whole trunk, and therefore, when spoken of _per se_, may
be called the _meditruncus_. It consists primarily of an upper and
lower part, which in the table are denominated the _mesothorax_ and
the _medipectus_. The first piece in the former that requires notice
is the _collar_. I formerly regarded this piece, which is peculiar to
the _Hymenoptera_, _Diptera_, and one tribe of the _Neuroptera_, as the
representative of the _prothorax_ in the other Orders, and this opinion
seems at this time very generally adopted, but subsequent observations
have caused me to entertain considerable doubts of its correctness.
Many other Entomologists have thought it improper to distinguish these
parts by the same name[1642]. Much, however, may be said on both
sides of this question, and I shall now lay before you the principal
arguments that may be adduced in defence of each opinion, beginning
with those that seem to prove that the collar _is_ the analogue of
the _prothorax_. First, then, the collar, like the _prothorax_, is
placed precisely over the _antepectus_, and being placed in the _same_
situation, on that account seems entitled to the _same_ denomination;
especially as in some genera, for instance _Chlorion_ F., it assumes
the very semblance and magnitude of a thoracic shield, and is separated
from the _mesothorax_ by a considerable incisure. Again, in some cases
that have fallen under my own observation, the collar is endued with
some degree of motion distinct from that of the alitrunk, since in
_Pompilus_ and _Chrysis_ the animal can make the former slide over
the latter in a small degree. A third and last argument is, that no
_prophragm_ is formed from the collar: insects that have a thoracic
shield are generally distinguished by having the anterior margin of
the _dorsolum_ deflexed so as to form a _septum_, called in the table
the _prophragm_, which enters the chest and separates the cavity of
the _mesothorax_ from that of the _prothorax_; now in _Hymenoptera_
this septum is a process of the piece behind the collar, and excludes
it from having any share in that cavity. These arguments at first
sight seem to prove satisfactorily the _identity_ of the collar and
_prothorax_. But _audi alteram partem_, and I think you will allow
that the scale containing the claims of the collar to be considered
as a piece _sui generis_, dips much the lowest. And, first, I must
observe, that though in _Hymenoptera_ the collar seems to replace
the _prothorax_ by its situation, yet it is in fact a part of the
alitrunk; for, if the _manitrunk_ be separated from the latter,
the collar remains, in most cases, attached to it[1643], while the
_antepectus_ and arm, with the ligament that covers its cavity above,
the real representative of the prothorax, are easily removed, and this
in recent individuals: as a further proof of this, I must request you
will examine a neuter _Mutilla_; you will see that in this the collar
is not separated from the alitrunk in any respect, but forms one piece
with it, while the _antepectus_ is distinct and capable of separate
motion: further, the action of the collar is upon the alitrunk, it
being of essential importance in flight, whereas the _prothorax_ is
of no other importance than as a counterpoise to that part[1644]. A
further argument to prove the distinction of these parts may be drawn
from the case of _Xylocopa_, a kind of bee. In this genus the collar
forms a complete _annulus_ or segment of the body: now, if it really
represented the prothorax, the under side of the segment, as in those
_Coleoptera_ in which no suture separates the upper from the lower part
of the manitrunk[1645], should represent the _antepectus_, and have
the arms inserted in it; but in the case before us there is a distinct
_antepectus_ bearing the arms received by the socket formed by this
annulus. But the most powerful argument is the fact that some insects
have both the _prothorax_ and _collar_, a circumstance that completely
does away every idea of their identity. If you examine the common
hornet (_Vespa Crabro_), or any saw-fly (_Tenthredo_ L.), you will
find, as was before intimated, that the real covering of the cavity of
the manitrunk is a ligamentous membrane, which properly represents the
_prothorax_. In another genus of the same order (_Xiphydria_ Latr.),
the sides of the _antepectus_ turn upwards and nearly form a horny
covering distinct from the collar[1646], the ligamentous part being
reduced to a very narrow line, and in _Fœnus_ the dorsal fissure is
quite filled up, so that in this the manitrunk is perfectly distinct,
and exhibits both _prothorax_ and _antepectus_ of the usual substance.
In _Nomada_ likewise, _N. Goodeniana_ K. was the species I examined,
there is a short minute _prothorax_ besides the collar. Next let
us turn our attention to the _Diptera_; if you examine the common
crane-fly (_Tipula oleracea_), you will find, first, a regular short
_prothorax_, to which the _antepectus_, with the arms, is attached; and
behind this also is a short collar embracing the alitrunk anteriorly.
The next insects that I shall mention, as exhibiting both _prothorax_
and collar, are the _Libellulina_. These are generally admitted to
have the former of these parts[1647], but besides this they have
also the latter, which is the most ample and conspicuous piece in
the whole trunk[1648]; intervening, as the collar should do, between
the _prothorax_ and those parts of the trunk to which the wings are
attached. There is one circumstance connected with the subject which
should not be overlooked. In the _Hymenoptera_, usually under a
lateral process of the posterior part of the collar, is a spiracle or
respiratory apparatus; in the _Diptera_ there is also one, though not
covered by the part in question, in the same situation; now this you
will find precisely so situated with respect to the second piece in
the thorax of _Tipula oleracea_, proving that this piece is the real
representative of the collar. Enough, I think, has been said to satisfy
you that I have not changed my sentiments on this subject upon slight
grounds. Probably traces of the part in question might be detected
in the thoracic Orders in general, in connexion with some vocal or
respiratory organ[1649]; but having had no opportunity, by an extended
examination of living subjects, to verify or disprove this suspicion,
I shall merely mention it, and conclude this head by observing, that
the collar varies most in the _Hymenoptera_ order, and that its most
remarkable form is in _Vespa_, _Cimbex_, _Dorylus_, &c., in which it
bends into an ample sinus that receives the dorsolum[1650].
2. _Dorsolum_[1651]. Where there is no apparent collar, the
_dorsolum_ (dorslet) is the _first_ piece of the _mesothorax_, and
where there is one, the _second_; it bears the elytra or other
primary organs of flight. It varies in the different Orders,
particularly with respect to its exposure. In Coleopterous insects
it is most commonly, but not invariably[1652], covered entirely by
the shield of the _prothorax_, the _scutellum_ alone being visible;
as it is also in the _Orthoptera_ (with the exception of _Mantis_
and _Phasma_, in the first of which it is partially, and in the
latter intirely exposed), and the Heteropterous, and most of the
Homopterous section of the _Hemiptera_. The scutellum is likewise
covered in _Gerris_, _Hydrometra_, and _Velia_, and the whole of the
back of the alitrunk by a process of the _prothorax_ in _Acrydium_
F., _Centrotus_, &c. But in the remaining Orders, and the tribe of
_Tettigonia_ in the Homopterous _Hemiptera_, the _dorsolum_ is not
hidden by the thoracic shield. It is usually less elevated than the
_scutellum_; in _Necrophorus_, and some other beetles, however,
the latter is most depressed. With regard to its _substance_, it
is generally not so hard and rigid as the _scutellum_, but in
most _Coleoptera_ harder than in the other Orders in which it is
covered; in the _Hemiptera_, except in _Tettigonia_, it approaches
to membrane. As to shape and other circumstances, it varies in the
different Orders. In the beetle tribes it has generally a sinus
taken out of its anterior margin, and it approaches more or less
to a trapezium; in _Blatta_ it is transverse and somewhat arched;
in _Gryllotalpa_ it is nearly square, and distinguished besides on
each side by a minute aperture, fitted with a tense membrane, which
perhaps covers a respiratory apparatus. In the locusts it is more
or less triangular, and in _Mantis_ and _Phasma_ long and slender.
In the _Hemiptera_ the _dorsolum_ appears to consist of several
pieces, variously circumstanced, separated by sutures, corresponding
with which are as many ridges on the inside of the crust[1653].
In the _Libellulina_ it is rhomboidal[1654]; in _Panorpa_ nearly
hexagonal; in the _Ephemerina_ it is ample and oblong; in _Sialis_
and the _Trichoptera_ this part is represented by three subtriangular
pieces, the _scutellum_ constituting a fourth, with the vertices
of the triangles meeting in the centre[1655]; in the _Lepidoptera_
the part in question is large, and receives the _scutellum_ into
its posterior sinus[1656]. The _Hymenoptera_ usually exhibit a very
ample _dorsolum_, mostly subtriangular with the vertex rounded or
truncated, and pointing in some (_Vespa_ L.) to the head[1657], and
in others (_Apis_) to the anus; in the _Diptera_, except in _Tipula_,
the parts of the _mesothorax_ are not separated by any suture, but
only indicated by impressed lines or channels; in the genus last
mentioned, however, the _dorsolum_ is distinct, subrhomboidal, and
received by an angular sinus of the _scutellum_, which last, I think,
is not the part that has usually been regarded as entitled to that
denomination; for this opinion I shall soon assign my reasons.
3. _Scutellum_[1658]. Some writers on the anatomy of insects,
looking, it should seem, only at the _Coleoptera_ and _Orthoptera_,
have regarded the _dorsolum_ and _scutellum_ as forming only one
piece[1659], and others have affirmed that the _Lepidoptera_ and
subsequent Orders have no _scutellum_[1660]. But as we proceed in
considering the _scutellum_ in all the Orders, we shall see that
both these opinions are founded on partial views of the subject, and
that all winged insects have a _scutellum_, more or less distinctly
marked out or separated from the _dorsolum_. In the _Coleoptera_
the _scutellum_ is usually the _visible_, mostly triangular,
piece that intervenes between the elytra at their base[1661], and
which terminates the _dorsolum_. Some Lamellicorn beetles, &c.
(_Scarabæidæ_ MacLeay) are stated not to have the part in question
(_exscutellati_): but this is not strictly correct, for in these
cases the _scutellum_ exists as the point of the _dorsolum_ covered
by the _prothorax_, though it does not intervene between the elytra:
in others of this tribe, as _Cetonia chinensis_, _bajula_, &c.,
it separates these organs at their base, though it is covered by
the posterior lobe of the _prothorax_: in _Meloe_ F., the elytra
of which are immoveable, there seems really to be no _scutellum_.
Generally speaking, as was lately observed, but not always, it is
distinguished from the _dorsolum_ by being more elevated: this is
particularly conspicuous in the genus _Elater_, in which it is a
flat plate elevated from the _dorsolum_ by a pedicle; in _Sagra_ the
latter part is horizontal, while the _scutellum_ is vertical: and
even in cases where the distinction is not so striking, these parts
are separated either by a line, or some difference in their sculpture
and substance. In this Order this part varies greatly, and often in
the same tribe or genus, both in size and shape; being sometimes very
large[1662], and sometimes very minute; sometimes very long, and
sometimes very short; sometimes nearly round, at others square; now
oval or ovate, heart-shaped, triangular, acuminate, intire, bifid,
&c. In the _Orthoptera_, though less conspicuous, it still is present
as a triangular elevation of the middle of the posterior part of
the dorsolum, with the vertex either pointing towards the head, as
in _Blatta_, or towards the tail, as in _Locusta_ Leach[1663]. In
the Heteropterous section of the _Hemiptera_ (which, in columns of
_Mandibulata_ and _Haustellata_, appear to bear the same reference
to the _Coleoptera_, that the _Hymenoptera_ do to the _Diptera_,
and the Homopterous _Hemiptera_ to the _Orthoptera_[1664]) the part
we are considering is mostly very large and conspicuous, quite
distinct from the _dorsolum_, and in some (_Tetyra_ F.) covering
the whole abdomen, as well as the _Hemelytra_ and the wings; it is
most commonly, as in the _Coleoptera_, obtriangular[1665], but in
the last-mentioned genus it often approaches to a pentagonal shape.
Though usually so striking a feature in this tribe, in the aquatic
bugs (_Gerris_ &c.) it is covered by the _prothorax_. In some
species of _Reduvius_ F. (_R. biguttatus_, _mutillarius_, _lugens_,
&c.) it is armed with one or more dorsal or terminal spines. In the
Homopterous section, where the _dorsolum_, as in _Tettigonia_ F., is
not covered by the _prothorax_, the _scutellum_, which is merely a
continuation of that part, bears some resemblance to a St. Andrew's
cross, and terminates in a fork[1666]; in _Fulgora_, in which it is
partly covered, it is merely the triangular point of the _dorsolum_:
in the _Cercopidæ_, &c., whose _dorsolum_ is wholly covered, the
triangular scutellum is distinct from it; in _Centrotus_, _Darnis_,
and _Membracis_, in which the _prothorax_ is producted, and covers
the abdomen more or less, the _scutellum_ is a short transverse
distinct piece. In the _Lepidoptera_, from the difficulty of abrading
sufficiently the scales and hairs without injury, it is difficult
to obtain a correct idea of the part in question; in the cabbage
butterfly (_Pieris Brassicæ_) it appears to be triangular: in the
humming-bird hawk-moth (_Macro-glossum Stellatarum_) it approaches
to a rhomboidal shape[1667]; and in the eggar-moth (_Lasiocampa
Quercus_) it is completely rhomboidal. In the _Libellulina_, in the
_Neuroptera_ Order, it seems to be represented by the posterior
point of the _dorsolum_, which terminates in something like a St.
Andrew's cross[1668]. In most of the other tribes of this Order the
_scutellum_ is a triangular piece, with the vertex to the head,
received between two pieces of the dorsolum; in _Psocus_ it is nearly
like that of _Tettigonia_ before described. In the _Hymenoptera_
the _scutellum_ is separated from the _dorsolum_, which it often
embraces posteriorly, as the collar does in front, by a suture; it
varies occasionally in shape in the different tribes, most commonly
it is crescent-shaped, but in many _Ichneumonidæ_ and others it is
triangular[1669]; in the hive bee, &c., it overhangs the succeeding
piece of the alitrunk; in _Melecta_, _Crocisa_, &c., it is armed
with a pair of sharp teeth[1670]; in others (_Oxybelus uniglumis_,
&c.) with one or more spines, and in some with a pair of long
horns[1671]. Before I describe this part in the _Diptera_, it will
be proper to assign my reasons for considering a different piece as
its representative, from what has usually been regarded as such, and
which at first sight seems the analogue of what I admit to be the
_scutellum_ in the _Hymenoptera_. The _dorsolum_, and its concomitant
the _scutellum_, belong to the first pair of the organs of flight,
which are planted usually under the sides of the former, and in the
case of _wings_, by their Anal Area, connected either mediately or
immediately with the latter. Now, if you trace the sides of the piece
that I have considered as the part in question in _Hymenoptera_,
you will find that they lead you not to the base of the _lower_
but to that of the upper _wings_[1672], and in the saw-flies
(_Tenthredo_ L.) you will see clearly that the Anal Area of these
wings is attached to a process of it, a proof that it belongs to
the _mesothorax_, or region of that pair. But in the _Diptera_, the
part that has been usually called the _scutellum_ is not at all
connected, either by situation or as a point of attachment, with
the wing itself, but with the lower valve of the _alula_, which is
with reason thought to be the representative of the secondary wing
of the tetrapterous Orders. You may see this even in the common
crane-fly (_Tipula_), in which there is a real _alula_, connected
by means of a lateral process, terminating in ligament, with this
supposed _scutellum_. If you examine further the same insect, you
will easily find what I regard as the true one in the bilobed piece
which receives the _dorsolum_, situated between the wings, and to
the sides of which they are attached. In _Asilus_, _Tabanus_, &c.,
this part is transverse, and only distinguished on each side by an
oblique impressed line; in the _Muscidæ_ it is square, and marked by
a straight transverse one.
4. _Frænum_[1673]. This appendage to the _scutellum_ and _dorsolum_
varies considerably in the different Orders, and in many cases, as
you will see, is a very important part, being the process by which
the former is mostly connected with the elytra or upper wings. In the
_Coleoptera_, the elytra of which are nearly stationary in flight, and
therefore less require any counteraction to prevent their dislocation,
this part is commonly merely a process or incrassation of the under
margin of the scutellum, which towards the base of the _dorsolum_ is
dilated to form the socket for the elytra. Its use as a countercheck
in this Order is best exemplified in the common water-beetle (_Dytiscus
marginalis_). This at the inner base of the elytra has a membranous
fringed _alula_ resembling those of _Diptera_; to the lower fold of
this the extremity of the _frænum_ is attached, which forms a right
angle with the scutellum, and the upper fold is attached to the base
of the elytrum[1674]. The object of this appendage is probably to
prevent the dislocation of these organs, which seems to indicate that
they are used more in flight than those of other beetles. The _Blattæ_
also, in the next Order, have a winglet attached to the anal area of
the _tegmina_. The _frænum_, as in the preceding Order, lies under the
margin of the _scutellum_ and _dorsolum_, but which here forms one
uninterrupted transverse line; it is nearly vertical, and is attached
to the _alula_. The structure is not very different in the other
_Orthoptera_[1675], but the _frænum_ is surmounted or strengthened
by one or two ridges; in _Mantis_ it runs from the scutellum in an
angular or zigzag direction--but in all it is attached immediately to
the _tegmen_. In the Heteropterous _Hemiptera_ it is represented by the
narrow bead adjacent to the scutellum on each side[1676], which dilates
into a flat plate as it approaches the _Hemelytrum_, with the Anal Area
of which it is connected. But the Homopterous section of the Order in
question furnishes examples of the most remarkable structure of this
countercheck, which proves that it is really, what its name imports, a
_bridle_. If you examine the great lanthorn-fly (_Fulgora laternaria_),
or any species of _Tettigonia_, &c., you will find adjacent to the
scutellum or parallel with it, on each side a flat plate; and
from the angle of that part in the first case, and from one of its
processes in the last, you will further perceive a ridge or nervure
which runs along this plate, in one forming an angle, and in the other
being nearly straight, to the base of the _tegmen_, where it becomes
a marginal nervure to a membrane that is attached to the posterior
part of the base of the Anal and Costal Areas; and that this marginal
nervure, like a _trachea_, consists of a spiral thread, or rather of
a number of cartilaginous rings connected by elastic membrane[1677],
and consequently is capable of considerable tension and relaxation,
as the _tegmen_ rises and falls in flight. In the _Lepidoptera_ it
appears to be a short piece overhung by the scutellum, which as it
approaches the base of the wing is dilated. In the _Libellulina_,
to go to the _Neuroptera_, it has the same kind of elastic nervure
connected with the Anal Area of the wing which I have just described
in the Homopterous _Hemiptera_; another nervure, in _Æshna_ at least,
appears to diverge upwards from the scutellar angle to the Intermediate
Area[1678]: a structure little different distinguishes the rest of the
_Neuroptera_, and even the _Trichoptera_. In the _Hymenoptera_ this
part varies somewhat; in the majority perhaps of the Order, as well
as in the _Diptera_, it appears to be merely the lateral termination
of the scutellum where it joins the wing; but in some tribes, as
in _Tenthredo_ L. (especially _Perga_ Leach), _Sirex_ L., and the
_Ichneumonidæ_, a ridge, and sometimes two, runs from the scutellum to
the wing; the upper one, where there are two, as in _Perga_, being the
stoutest, and connecting with the _Costal_ Area, and the lower one with
the _Anal_.
5. _Pnystega_[1679]. We learn from M. Chabrier, that in the common
dragon-fly, a space, consisting of three triangles, which immediately
succeeds the _frænum_, affords attachment to no muscles, but merely
covers aërial vesicles[1680]. This is the part I have called the
_pnystega_[1681]. An analogous piece may be discovered in _Phasma_
and _Mantis_ in a similar situation; but I cannot trace it in
_Locusta_ Leach, or in the other Orders.
* * * * *
Having considered the parts that constitute the _mesothorax_, we will
next say something upon those, as far as they require notice, that
compose the _medipectus_ or mid-breast. But first I must observe,
in general of the _medipectus_ and _postpectus_ taken together, or
the whole underside of the _alitrunk_, that though usually they
are in the same level with the _antepectus_ or under side of the
_manitrunk_, yet in several instances, as the _Scarabæidæ_ MacLeay,
the _Staphylinidæ_, &c. they are much more elevated than that part;
they are also usually longer, very remarkably so in _Atractocerus_,
but in _Elater sulcatus_ and many others they are shorter. These
parts are also commonly rather more elevated than the abdomen,--much
so in some, as _Molorchus_; but scarcely at all in others, as
_Buprestis_, the Heteropterous _Hemiptera_, &c. In some of the
latter (_Tetyra_ F.) the abdomen seems the most prominent. Another
observation relating to this part must not be omitted, namely, that
though in many cases the _medipectus_ and _postpectus_ are perfectly
distinct and may be separated, yet in others, as for instance the
Lamellicorn beetles, the _Hymenoptera_ and _Diptera_, &c., no suture
separates them; so that though the upper parts, the _mesothorax_ and
_metathorax_, are separable, the lower ones just named are not so.
6. _Peristethium_[1682]. The first piece of the _medipectus_ is
what I have called, after Knoch, the _peristethium_[1683]. This
immediately follows the _antepectus_; on each side it is limited by
the scapulars, and behind by the mid-legs and _mesosternum_. Its
antagonist above is usually the _dorsolum_. In the _Coleoptera_ Order
it varies occasionally, both in form and magnitude, but not so as
to merit particular notice, except that both are regulated by the
scapulars--if these are small, the _peristethium_ is ample; and,
_vice versa_, if they are large it is small. In all the following
Orders, except the _Hymenoptera_, it is equally inconspicuous, but
in them it is often more remarkable. I have a Brazilian species of
_Cimbex_ (_C. mammifera_ K. MS.) which appears undescribed, in which
this part swells into two breast-like protuberances, terminating
posteriorly in membrane, as if it had separate motion: in the
golden-wasps (_Chrysis_ L.) it is anteriorly concave to receive the
_coxæ_ of the mid-legs; and in _Stilbum_, of the same tribe, it is
armed with one or more conical obtuse teeth.
7. _Scapularia_[1684]. The scapulars are situated between the _coxæ_
of the mid-legs and the base or axis of the upper organs of flight,
and they seem to act as a fulcrum to each. In the _Coleoptera_ Order
they are most commonly quadrangular or subquadrangular, often divided
diagonally, and sometimes transversely, by an impressed line; the
posterior part, which is usually the most elevated and often has an
uneven angular surface, is that which intervenes between the coxæ and
elytra: where the former are short, as in the Capricorn beetles, the
scapulars are long; and where they are long, as in the Petalocerous
ones, the latter are short. The anterior part is that which forms
the lateral limit of the _peristethium_, upon which it often
encroaches: this part, in conjunction with the _dorsolum_ above, and
the last-named part below, forms the kind of _rotula_ that plays in
the posterior _acetabulum_ of the manitrunk, as the head does in the
anterior one. In the flower-chafers (_Cetonia_ F.) the scapulars are
very thick and elevated, and interpose between the posterior angles
of the _prothorax_ and the shoulders of the _elytra_, which is one
of the distinguishing characters of that tribe: in this case the
lower angle of the scapular connects with the _coxa_ of the mid-leg,
and the upper angle with the axis of the _elytra_; and the most
elevated and thickest part of the scapular is about midway between
the two. This robust structure seems to indicate that the scapular
has to counteract a powerful action both of the leg and elytrum.
In the _Orthoptera_ the scapulars are usually divided into two
parallel pieces, corresponding probably, though more distinct, with
the two parts lately noticed of those of the _Coleoptera_: the upper
side of the socket of the mid-leg is common to the base of _both_
these pieces, but the articulation of the _tegmen_ is chiefly with
the _anterior_ one. In the grasshoppers, locusts, &c. (_Gryllus_
L.) in which tribe this leg is nearly _opposite_ to that part,
the scapular inclines but little from a vertical position[1685];
but in the praying-insects (_Mantis_), spectres (_Phasma_), and
cockroaches (_Blatta_), in which the insertion of the mid-legs is
_behind_ that of the _tegmina_, it is nearly horizontal. In the
Heteropterous _Hemiptera_ the anterior part of the scapular is
covered by the _antepectus_, and separated by a ridge, more or
less pronounced, from the open part; the whole is of an irregular
shape, and nearly parallel with the _parapleura_. In the Homopterous
section it likewise consists of two pieces, and sometimes of more.
Thus in _Tettigonia_ F. it is bilobed, and between it and the coxa
two small pieces are inserted[1686]. In some others, _Iassus Lanio_
F., &c., it is not very unlike the scapular in _Coleoptera_, being
subquadrangular and divided diagonally. In the _Neuroptera_ this
part and the _parapleura_ are parallel, and placed obliquely[1687].
In the common dragon-fly (_Æshna viatica_) the former forms nearly a
parallelogram[1688], which is not divided by any ridge or channel,
but its lower half is separated into two unequal parts by a black
longitudinal line, opposed to which on the inside is a ridge. The
mid-leg in these is connected with the scapular by the intervention
of a triangular transverse anterior piece, which in fact seems
only marked by a black channel, to which also interiorly a ridge is
opposed[1689]. In the rest of the Order it is divided longitudinally
into _two_ parallel pieces. In _Panorpa_ the posterior piece is
longer than the anterior and props the coxa behind; in _Myrmeleon_
and _Perla_, &c., it appears to consist of _three_ pieces. I have
not been able to obtain a clear idea of them in the _Lepidoptera_,
except that they have more than one piece. _Hymenopterous_ and
_Dipterous_ insects for the most part have no scapular distinct from
the _peristethium_; but in _Cimbex_, _Perga_, and other saw-flies, it
seems represented by its posterior depressed and sometimes membranous
part: in _Vespa_, &c. a small subtriangular piece, just below the
base of the upper wing, is probably its analogue[1690].
8. _Mesosternum_[1691]. The central part of the _medipectus_, or
that which passes between the mid-legs when elevated, protended, or
otherwise remarkable, is called the _mesosternum_ or mid-breast-bone.
In the _Coleoptera_ Order it exhibits the most numerous variations, and
is usually the most strongly marked of any of the three portions of the
_sternum_, affording often important characters for the discrimination
of genera and subgenera. It may be said to be formed upon three
principal types--the first is, where it is a process of the posterior
part of the _peristethium_, and points towards the anus or the
head;--the second, where it is a process of the anterior part of the
_mesostethium_, and points only towards the head: in this case there
is no suture to separate the _medipectus_ from the _postpectus_;--the
last type is where it is a ridge formed by a process both of the
_peristethium_ and _mesostethium_ meeting between the legs; an example
of this you will see in the common dung-chafer (_Geotrupes_ Latr.).
Upon the two first of these cases I shall offer a few remarks;--the
last affording no variation need only be mentioned.
If you examine the terrestrial Predaceous beetles (_Cicindela_ and
_Carabus_ L.) you will find that the _peristethium_ is usually flat,
terminating towards the _postpectus_ in a kind of fork, the sinus
of which receives the anterior point of the _mesostethium_--this
is the _mesosternum_; but in the aquatic insects of this tribe, at
least in _Dytiscus marginalis_, &c. the structure at first sight
seems different, for _apparently_ the _prosternum_ is received by the
anterior fork of the _mesostethium_; but if you proceed to separate the
manitrunk from the alitrunk, you will find that the true _mesosternum_
of the usual form is quite covered by this point, which curves towards
the breast, is longitudinally concave to receive the point of the
_prosternum_, and permit its motion in the groove. In some Heteromerous
beetles, as the _Helopidæ_, &c. this part is anteriorly bilobed, so
as to form a cavity which receives the point of the _prosternum_ when
the head is bent down: in _Helops nitens_ (_Tenebrio_ Oliv.) this
sinus represents a crescent; in _Cistela Ceramboides_ it is shaped
like the Greek letter γ; in the Lady-bird (_Coccinella_ L.) it assumes
nearly the shape of a Saint Andrew's cross; in _Spheniscus_ K.[1692]
the _mesosternum_ is wide, concave and wrinkled, with an anterior and
posterior sinus; while in the analogous genus _Erotylus_[1693] it is
convex anteriorly, and posteriorly more or less rounded; in _Doryphora_
it is a long, robust, subconical horn, often standing at an angle of
about 45°, overhanging the _prosternum_.
In the genus last named, though its _mesosternum_ in its direction
and appearance resembles that of many Petalocerous beetles, yet it is
separated by an evident suture from the _mesostethium_; but in the
last-mentioned tribe its representative is a process of the latter
part: yet as the _peristethium_ and _mesostethium_ are separated by
no suture, though in some cases a transverse channel, and in others
merely a coloured line, marks the point where they may be considered
as soldered together, in these cases the _mesosternum_ may perhaps
be said to be common to both. In this great family, which includes
within its limits some of the most singular and wonderful in their
structure and armour, as well as some of the most brilliant and
beautiful of the beetle tribes,--the part in question, in a vast
number of cases, will enable the Entomologist satisfactorily to
trace its numerous groups, not only where it rises or stretches
out into a horn or ridge, but even often where it is merely a flat
space between the mid-legs. I shall notice some of its most striking
variations in this tribe. In _Phanæus festivus_, and in _Macraspis_
and _Chasmodia_ MacLeay, it is elongated horizontally, with the apex
curving upwards; in _Anoplognathus_ it is horizontal, straight, and
figures an isosceles triangle; in _Cetonia suturalis_, _vitticollis_,
&c. it is very long, passing between the arms and nearly reaching
the head; in _C. marmorea_, _Lanius_, &c. it is a lofty, robust,
conical prominence; and in many _Rutelidæ_, especially those with
striated elytra, it is pyramidal or four-sided; it varies also in its
_termination_, particularly in the _Cetoniadæ_; and even where there
is little or no elevation of it, as in the _Scarabæidæ_ MacLeay, it
is often terminated anteriorly by lines that vary in their angle or
curvature. The genus _Copris_, as restricted by Mr. W. S. MacLeay,
may from an inspection of this circumstance be divided into several
families. Thus in _C. Molossus_ and affinities its _termination_
represents the letter ⅄ reversed, or a triangle surmounted by a
mucro; in _C. orientalis_, &c., it ends in an acute-angled triangle;
in _C. lunaris_, &c. in an obtuse-angled one; and in _C. Iacchus_,
&c., in the segment of a circle.
The part we are considering is not so important in the other Orders.
In the _Orthoptera_, however, it is occasionally remarkable. In
_Acrida viridissima_ (_Locusta_ F.) attached to the anterior margin
of the _peristethium_ are two long triangular pieces which appear to
represent this part; in the kindred subgenus, _Conocephalus_[1694],
it is a single piece bifid at the apex; in _Gryllotalpa_ it is a very
elevated hairy ridge; and in _Locusta_ Leach, it is a flat anterior
process of the _mesostethium_. In the Heteropterous _Hemiptera_ this
part is often merely a portion of the channel in which the _promuscis_
reposes; but sometimes, as in _Edessa_ F., it is an elevated piece
varying in its termination. In the remaining Orders, as far as I have
had an opportunity to examine them, it can scarcely be said to exist
separately from the _medipectus_, except that in _Tipula_ Latr. a
bipartite subtriangular membranous piece seems to be its analogue.
* * * * *
We are now to consider the last segment of the alitrunk, which, as a
whole, may be denominated the _potruncus_; it bears the second pair
of the organs of flight, and the last pair of legs. The upper side of
this is the _metathorax_, and its lower side the _postpectus_.
9. _Postdorsolum_[1695]. The first external piece of the _metathorax_
is the _postdorsolum_, which presents itself under very different forms
and circumstances in the different Orders. In the _Coleoptera_ it is
intirely covered by the _dorsolum_ and _scutellum_; it is generally
more or less of a membranous substance, or partly membranous and partly
corneous, which enables it to yield more to the action of the wings in
flight; it is usually an ample transverse piece with tumid sides[1696];
but in the _Scarabæidæ_ MacLeay, it is short though very wide; and
in _Cychrus_, and probably other _apterous_ beetles, it is extremely
minute and almost obsolete. In the _Orthoptera_ Order, I observe once
for all, the part in question, as well as the _postscutellum_ and
_postfrænum_ are mere counterparts of the _dorsolum_, _scutellum_,
and _frænum_, except that in some cases they are larger[1697]. In the
Heteropterous _Hemiptera_ at first sight it would appear that all
the parts of the _metathorax_ were altogether wanting or absorbed
in the ample _scutellum_; but if you remove this with care, you
will find _under_ it their representatives, its lower surface being
hollowed out to receive them. The _postdorsolum_ appears in these as
a transverse obtusangular band; in the _Nepidæ_, _Notonectidæ_, &c.
the three parts of the _metathorax_ seem united into a single plate,
emerging laterally from under the _scutellum_ below the _frænum_;
in which, however, some traces of a distinction between them may be
discovered. In the Homopterous section the _Fulgoridæ_ exhibit these
pieces very distinctly, covered only at the base by the _mesothorax_:
but in _Tettigonia_ they are not so easily detected; they exist
however as a narrow strip or band, almost concealed by that part.
As to the _Lepidoptera_ Order, in _Pieris Brassicæ_ at least, the
_postdorsolum_ is represented by a pair of nearly equilateral triangles
whose vertexes meet in the centre of the _metathorax_, and between
which and the _scutellum_ is a deep cavity; but in _Macroglossum
Stellatarum_ and _Lasiocampa Quercus_, there appears to be also a
central transverse piece between them. In the _Neuroptera_ there is no
material or striking difference between the parts of the _mesothorax_
and _metathorax_[1698]. In the _Hymenoptera_ more variety occurs in
this part. In the saw-flies, &c. (_Tenthredo_ L.) the _postdorsolum_ is
a transverse piece covered by the _scutellum_; in the _Ichneumonidæ_
it is smaller, but not covered; in the _Vespidæ_ it is apparent,
transverse, and with the _postscutellum_ obtusangular[1699]; in
_Apis_ it is overhung by the _scutellum_. The _Diptera_ exhibit some
variations in this part. In _Tipula_ it consists of three pieces placed
transversely, the central one quadrangular, and the lateral ones
roundish; in the _Asilidæ_ and most others of this Order, with the
_postscutellum_, it forms a segment of a circle[1700], sometimes armed
with a pair of spines, as in _Stratyomis_ F., and is what has been
usually regarded as the real _scutellum_, though, as I have endeavoured
to show, not correctly[1701].
10. _Postscutellum_[1702]. The _postscutellum_ bears the same relation
to the _postdorsolum_ that the _scutellum_ does to the _dorsolum_,
but it is seldom, if ever, a distinct piece. In the _Coleoptera_ it
is represented by the longitudinal narrow channel that terminates
the _postdorsolum_ towards the anus[1703]: this usually figures an
isosceles triangle with the vertex truncated or open; but in _Copris_
the triangle is equilateral. In the other Orders it is little more than
the central posterior point of the _postdorsolum_[1704].
11. _Postfrænum_[1705]. The part now mentioned is much more important
than the preceding one, and must not be passed over so cursorily. In
the _Coleoptera_ it usually presents itself under the form of two
large and usually rather square panels, the disk of which is convex,
but the rest of their surface unequal, which are situated one on each
side of the postscutellum[1706]; under the anterior outer angle of
these is the socket or principal attachment of the secondary wings,
and their basal margin is attached to their outer side; posteriorly
behind the vertex of the _postscutellum_ the _postfrænum_ is crowned
with a ridge or bead, below which it descends vertically or obliquely
to the abdomen; this ridge often turns upwards, and proceeds towards
the middle of the basal margin of the wing. In the Petalocerous
beetles the part in question is usually more or less hairy; but in
many others, as the rose-scented Capricorn (_Callichroma moschatum_),
&c. it is naked. At its side you will commonly observe several plates
and tendons (_osselets_ Chabr.) connected _inter se_ and with the base
of the wing by elastic ligaments, which are calculated to facilitate
the play of those organs. In the _Orthoptera_, _Neuroptera_, and
Homopterous _Hemiptera_, the _postfrænum_ does not differ materially
from the _frænum_[1707]. In the Heteropterous section of the last Order
it is usually a transverse ridge terminating the _postdorsolum_, with
a bifurcation where it unites with the wing; but in _Tetyra_ F. (at
least so it is in _Tetyra signata_,) it is a nearly vertical piece,
marked in the centre with an infinity of very minute folds, which
probably by their alternate tension and relaxation let out and pull
in the wings. Amongst the _Lepidoptera_ it is not remarkable. In the
_Hymenoptera_ Order it is mostly represented, I think, by a double
ridge or fork, sometimes however obsolete, but very conspicuous in the
saw-flies, which laterally terminates the _postdorsolum_; the upper
branch, usually the thickest, going to the anterior part of the base
of the underwing, and the lower one to the posterior. You may observe
something similar in the crane-flies (_Tipula_ Latr.) and _Asilidæ_. A
tendon proceeding from the point of the _postscutellum_ forms a fork
near its end, the upper branch of which connects with the anterior and
the lower with the posterior valve of the winglet; the structure is a
little, but not essentially, different in other _Diptera_.
12. _Pleura_[1708]. By this name I would distinguish the part which
laterally connects the _metathorax_ and _postpectus_. It includes in
it the socket of the secondary wings. In the _Coleoptera_ this is a
two-sided piece lying between the _postfrænum_ and the _parapleura_,
with the upper side horizontal and the lower vertical[1709]--a tendon
usually proceeds from its anterior extremity to the base of the wing.
In the _Orthoptera_, _Neuroptera_, and other Orders, it is merely
the longitudinal line of attachment of that part; but in the genus
_Belostoma_ Latreille, related to the water-scorpion, it presents a
peculiar structure, being a deep channel or demitube, filled at its
posterior extremity by a spiracle and its appendages[1710].
13. _Metapnystega_[1711]. This part, although in the table I have
placed it as an appendage of the _pleuræ_, is not always confined
to them, as you will soon see. It either covers aërial vesicles, or
is the seat of a spiracle. In the Order _Coleoptera_ it is of the
former description. If you examine the _metathorax_ of the common
dung-chafer (_Geotrupes stercorarius_), in the horizontal part of
the _pleura_ you will see a sublanceolate or subelliptical rather
membranous silky tense plate, with its point towards the head,--this
is the part we are considering; something similar you will find in
most beetles; but in some, as _Callichroma moschatum_, it is less
conspicuous. This part, as far as I have observed, is not so situated
in any other Order, except in some Heteropterous _Hemiptera_: in
_Belostoma_ the channel lately mentioned is filled up at its posterior
end by a red organ with an anterior vertical fissure, terminating
behind in a conical bag: in _Notonecta_ the _pleura_ has something of
a plate like that of _Coleoptera_, but of a horny substance. In the
_Orthoptera_ and _Neuroptera_ this part changes its situation, if it
be indeed synonymous; and as the _pnystega_ follows the _frænum_, so
the _metapnystega_ succeeds the _postfrænum_. In the _Libellulina_
M. Chabrier found that this as well as the other covered aërial
vesicles[1712], and it probably does the same in the other cases in
which it occurs. In _Mantis_ and _Phasma_ in the _Orthoptera_ it is
very minute; but in _Locusta_ Leach, it is more conspicuous under the
form of a tense membrane, the surface of which is depressed below that
of the abdomen: in _Acrida viridissima_ K. it fills the sinus of the
_postfrænum_, and is vertical, as it is in _Æshna_. It is worthy of
remark that this piece bears some analogy to that below the ridge of
the part just named in _Coleoptera_, which descends either vertically
or obliquely to the abdomen[1713]. A similar space, though often nearly
obsolete, may be seen in the _Hemiptera_ and _Lepidoptera_. But the
Orders in which this part is most conspicuous are the _Hymenoptera_
and _Diptera_, and in these its aërial vessels are connected with
a spiracle. In _Tenthredo_ L. and _Sirex_ L., what Linné named
_grana_, from their situation, should be regarded as belonging to
the _pnystega_, and whether there is any part representing the
_metapnystega_ I am not quite satisfied; perhaps the membrane at the
base of the abdomen in _Tenthredo_, and the bipartite piece, apparently
its first segment, in _Sirex_[1714], may be its analogues: but in the
great majority of the Order, the convex or flat piece that intervenes
between the _postdorsolum_ and its adjuncts and the abdomen, and which
bears a spiracle on each side, is the _metapnystega_[1715]. This part
is often remarkable, not only for its size, but for the elevated ridges
that traverse it, as in _Ichneumon_, _Chlorion_, &c. In the last genus
it is of a pyramidal shape, with the anterior part horizontal and the
posterior vertical; it is altogether vertical in _Vespa_, _Apis_,
&c. Amongst the _Diptera_, in _Tipula_ it is nearly horizontal, and
shaped like a cushion; but in general in this Order it is vertical, and
concealed under the _postdorsolum_[1716].
* * * * *
We are now to consider the parts that constitute the _postpectus_ or
under-side of the _metathorax_, and which bears the posterior pair of
legs.
14. _Mesostethium_[1717]. This part in _Coleoptera_ is terminated
anteriorly by the _peristethium_, _scapulars_, and _mesosternum_,
laterally by the _parapleuræ_[1718], and behind by the coxæ of the
posterior legs[1719], which generally are inserted transversely between
it and the abdomen. It is commonly very wide; but in _Dytiscus_ L.,
_Carabus_ L., &c., in which the _coxæ_ and _parapleuræ_ are dilated, it
is proportionally reduced: its length is regulated by the distance of
the intermediate and posterior legs; where these are far asunder, as in
the rose-scented Capricorn (_Callichroma moschatum_), &c. it is long:
but where they are near each other, as in the _Scarabæidæ_ MacLeay, it
is short; its width, however, generally exceeds its length. In shape
it is generally subquadrangular[1720], though sometimes rhomboidal,
and other forms of it occur. Between the hind-legs it generally
terminates in a notch or bifurcation distinct from the _metasternum_,
as in _Hydrophilus_, &c.; in _Hister_ there is no notch, and in
many _Scarabæidæ_ it projects between the hind-legs in a truncated
or rounded mucro; in the Vesicatory beetles, _Meloe_ L., it is more
elevated than the _medipectus_, towards which it descends almost
vertically; in _Dytiscus_ L., _Carabus_ L., &c., this part is usually
divided into two by a _transverse_ sinuous channel, and in _Elater_
by a _longitudinal_ straight one. In many _Orthopterous_ genera,
_Gryllotalpa_, _Acrida_ K., _Locusta_ Leach, &c., the _mesostethium_
consists of _two_ pieces[1721]. It is remarkable that in many of these
genera, in this part, as likewise in the _medipectus_ and _antepectus_,
are one or more perforations which appear to enter the chest, the use
of which I shall explain hereafter. In the _Libellulina_, as I shall
soon have occasion to shew, there is a peculiar arrangement of the
legs and wings, in consequence of which this part is placed behind the
posterior ones. In the remaining Orders, the _mesostethium_, though it
exists, exhibits no peculiarities worthy of particular notice, except
in some _Aptera_ and _Arachnida_: thus, in _Nirmus Anseris_ it is
terminated posteriorly by a pair of transverse membranous appendages
which cover the base of the posterior _coxæ_; in _Scorpio_ it consists
of two pieces, the _pectines_[1722] being attached to the sides of the
posterior one.
15. _Parapleura_[1723]. The _parapleura_, speaking generally, is
that piece of the _postpectus_ which, intervening between the
_pleura_, _mesostethium_, and _scapulars_, is attached by its
posterior extremity to the _coxæ_ of the hind-legs; by means of
the _pleura_, from which it does not appear to be separated by any
suture, it connects the secondary or under-wings with the hind-legs,
as the scapular does the primary ones with the mid-legs; so that the
direction of the _parapleura_ depends upon the relative situation
of the legs and wings. In Coleopterous insects its direction is
_horizontal_, it being generally a narrow subquadrangular piece that
runs straight from the posterior coxæ to the scapular[1724], and
usually divided into two unequal portions by an elevated or impressed
line. In the palm-weevil (_Calandra Palmarum_) this part is wider
than usual; in _Dytiscus marginalis_,--in which genus, as likewise
in _Carabus_ L., the _coxæ_ are incapable of separate motion,--it is
nearly a right-angled triangle, and is divided longitudinally into
two _unequal_ portions. In the _Orthoptera_ Order this part usually
consists of two _equal_ portions, and its direction is sometimes
nearly horizontal, as in _Mantis_ and _Phasma_; sometimes forming
an angle with the horizon, as in _Blatta_; and sometimes nearly
vertical, as in _Locusta_ Leach. In the two first cases the wings
are _before_ the legs, and in the last their position is _over_
them. In the Heteropterous _Hemiptera_ it is parallel with the
scapular, is divided into two unequal portions, and its direction is
more or less inclined to the horizon[1725]. As to the _Homopterous_
section--in _Fulgora_ it is of a very irregular shape with an
angular surface, and its direction from the leg to the wing is first
nearly vertical and then horizontal: in _Tettigonia_ it is almost
vertical, and consists of two nearly equal portions. To come to the
_Neuroptera_--in the _Libellulina_ it consists of two pieces, like
those of the scapulars, but smaller[1726], and its inclination is
towards the head: in _Panorpa_ also it resembles the scapulars both
in form and other circumstances[1727]. In the remaining Orders it
exhibits no very remarkable features.
16. _Metasternum_[1727]. The central part of the _mesostethium_
when elevated or porrected, or otherwise remarkable, is called the
_metasternum_. In the _Coleoptera_, in those cases, as we have seen
above[1728], in which the _medipectus_ and _postpectus_ form one piece,
its anterior point becomes the _mesosternum_; but in others, as the
Predaceous and Capricorn-beetles, &c., it is received in a sinus or
fork of that part, or meets it. It is usually neither so remarkable nor
important as the _mesosternum_. In _Bolbocerus_ K. it is a rhomboidal
elevation: in _Gyrinus_ a ridge; as also in many _Hydrophili_, in
which it passes between the hind-legs to the abdomen, and terminates
in a sharp point[1729]; and in _Dytiscus_ its two diverging lobes
cover the base of the posterior trochanters[1730]. In the _Orthoptera_
Order this part is not remarkable; but in _Acrida viridissima_ K. it
consists of three triangular pieces, the lateral ones being erect,
and the intermediate one horizontal: in _Locusta_ Leach it resembles
the _mesosternum_[1731]. In the Heteropterous _Hemiptera_ the whole
_mesostethium_ is elevated, and terminates at both ends in a fork,
the anterior one receiving the point of the _promuscis_, and the
posterior one that of the _epigastrium_: in the Homopterous section,
the _Tettigoniæ_ F. have usually a distinct metasternal point between
their hind-legs. In the remaining Orders there is no _metasternum_,
or no remarkable one, except in one singular Hymenopterous genus,
_Evania_, the parasite of the _Blattæ_[1732], in which there is a
forked posterior process of the _mesostethium_ with recurved points.
17. _Opercula_[1733]. By this term I distinguish those plates, before
largely described[1734], which cover the drums of male _Tettigoniæ_ F.;
and likewise those called also by the same name by M. Chabrier[1735],
which cover, in many cases, the _vocal apparatus_ of the trunk of
insects: those of _Melolontha vulgaris_ he describes as situated below
the wings, and between the two segments of the _alitrunk_[1736]; and
if you take this insect and remove the elytra, the _mesothorax_ and
scapulars, under the latter and below the wing you will find an oval
convex plate, which is probably the part he is speaking of;--but it is
better exemplified, I think, in the common _Dytiscus marginalis_, in
which it is very distinct as a convex subtriangular plate connected
with the _metathorax_ by membranous ligament, covering a kind of pouch,
and appearing to open and shut at the vertex[1737].
* * * * *
I must here observe, with regard to the _Aptera_ and _Arachnida_,
that the trunk in them is much more simple than in those insects that
are furnished with _wings_. In the hexapods, in the former Orders,
though there are usually three pedigerous segments, there is no
distinction of _dorsolum_, _scutellum_, &c. In the _Scolopendridæ_
and _Scutigera_ amongst the Myriapods, according to the acute
observations of M. Savigny[1738],--on which, however, some doubt at
present rests,--there is a remarkable formation, the whole thorax
being represented by the single plate that follows the head, to
the under-side of which are attached the first and second pair of
_palpi_ or _pedipalpi_, and the first pair of legs, representing the
three pairs of legs of hexapods. In the _Iulidæ_ the three segments
that follow the head, each bear a _single_ pair of legs, while
all the rest bear a _double_ one: from whence it should seem to
follow, that these segments and their legs represent the trunk and
legs of Hexapods. In the Octopod _Aptera_ and the _Arachnida_ the
trunk consists of a single piece, not separated from the head, and
sometimes not distinct from the abdomen.
V. _Internal processes_[1739]. Perhaps you will think that this head
would be better considered when I treat of the _Internal Anatomy of
Insects_; but as the parts included under it are really processes of
the _external integument_ of the trunk, it seemed to me best to treat
of them under that head. They are of two descriptions; processes
of the _thorax_ or upper part of the trunk, and processes of the
_breast_ or its under part.
i. _Processes of the thorax_[1740]. These are the _phragma_,
_prophragma_, _mesophragma_, and _metaphragma_. The first belongs to
the _prothorax_, the second to the _mesothorax_, and the two last to
the _metathorax_; each forming a kind of chamber of the under-side of
each segment of the thorax.
1. _Phragma_. The _phragm_, or _septum_ of the _prothorax_, is most
conspicuous in the mole-cricket (_Gryllotalpa_), in which it is a hairy
ligament attached to the inside of the upper and lateral margins of
the base of that part: inclining inwards, it forms the cavity which
receives the _mesothorax_. It is not, however, without a representative
in many _Coleoptera_, though in these it is less striking, from its
being smaller and taking a horizontal direction. In _Elater_, by means
of some prominent points received by corresponding cavities of the
vertical part of the base of the elytrum, it forms a kind of ginglymous
articulation, which probably keeps them from dislocation in repose,
and, by the sudden disengagement of these points from the cavities,
assists the animal in jumping[1741].
2. _Prophragma_[1742]. This is a piece usually almost vertical,
but in _Elater_ horizontal; of a substance between membrane and
cartilage, descending anteriorly from the _dorsolum_, and forming
the first partition of the chest of the _mesothorax_; it is
generally much shorter than the mesophragm. Though very visible in
_Coleoptera_ and the Heteropterous _Hemiptera_, in the other Orders
it is less easily detected, and is sometimes obsolete. It may be
observed here, that in the _Hymenoptera_, at least in the wasp, the
hive-bee, the humble-bee, and the _Diptera_ mostly, the interior of
the upper-side of the alitrunk, instead of _two_, seems at first
to be divided into _four_ chambers, formed by _septula_: but as
these ridges merely mark out the internal limits of the _dorsolum_,
_scutellum_, _postdorsolum_, and _metapnystega_, the last but one
of these being usually less distinct, they seem not analogous to the
three partitions of the alitrunk in other Orders; so that in these
the mesophragm at least seems to have no representative, and the
prophragm and metaphragm include between them only one ample chamber.
In the _Diptera_, wherever there is an external _depression_ or
_suture_ there is a corresponding internal _ridge_ or seam, so that
the parts seem more distinctly marked out on the _inside_ than on the
_outside_ of the crust.
3. _Mesophragma_[1743]. This piece also, which forms the middle
partition of the upper part of the cavity of the alitrunk, dividing it
into two chambers, is most conspicuous in _Coleoptera_. It is usually
in them a vertical piece, resembling the prophragm in substance, but
twice its height, of a quadrangular shape with a notch in the middle;
it fills the sinus of the _postdorsolum_, the sides of which sometimes
descend below it[1744]. In this Order the chamber that it forms with
the prophragm is very small[1745], the motions of the elytra requiring
no powerful apparatus of muscles; but that which it forms with the
metaphragm, which is appropriated to the muscles moving the wings, is
very large[1746]. In the _Orthoptera_ the anterior chamber is larger
than in the preceding Order, which proves that _tegmina_ are more
moved in flight than _elytra_. In the Heteropterous _Hemiptera_ a
remarkable variation takes place--the anterior being larger than the
posterior chamber; which last, in fact, consists of two, one for each
wing: in these the mesophragm towards the abdomen forms an angle, which
in _Pentatoma_, &c., is acute; in _Belostoma_ a right angle, and in
_Notonecta_ an obtuse one. In the two first the angle of the mesophragm
sends two short diverging ridges to the metaphragm; and in the last
only a single one: in this also the posterior chambers together are
nearly as large as the anterior. From this structure it should seem
that in flight the _Hemelytra_ are more important than the wings. In
the Homopterous section the anterior chamber is the smallest, at least
in _Fulgora candelaria_; and the mesophragm is lofty and bipartite. In
the _Lepidoptera_ the anterior chamber is the largest, and the part in
question conspicuous[1747]. In the _Libellulina_ and _Hymenoptera_ it
is merely represented by a low ridge, and in the _Diptera_ it seems
evanescent.
4. _Metaphragma_[1748]. This, in many cases, is the largest and
most remarkable of the three partitions of the upper portion of
the cavity of the alitrunk, which separates it from that of the
abdomen; it is attached to the posterior margin of the _metathorax_,
and is nearly vertical: in substance it may be stated as rather
firmer than the two preceding partitions. In the _Coleoptera_ it
is commonly of the width of the posterior orifice of the alitrunk;
and its centre is cleft so as to form a deep sinus[1749] for the
transmission of the intestines,--a circumstance which also, though
less conspicuously, distinguishes the mesophragm[1750]: from this
sinus it slopes gradually towards the sides, and is sometimes armed
with an intermediate process on each side[1751]. This structure you
will find exemplified in the common cock-chafer and many others of
the Order. I have not, however, discovered traces of it either in
the _Silphidæ_, _Staphylinidæ_, or the vesicatory beetles (_Meloe_
L.); or even in such species of _Carabus_ L. and _Cicindela_ L.
that I have examined; while in _Dytiscus_ it is very visible. In
the _Orthoptera_ it is nearly obsolete; but in _Locusta_ Leach,
under the _metapnystega_, one on each side, is a pair of seemingly
_pneumatic_ pouches which may be mistaken for it. It is almost
equally inconspicuous in both sections of the _Hemiptera_. As to the
_Lepidoptera_,--in _Pieris Brassicæ_, it resembles in some degree,
though in miniature, the metaphragm of the _Coleoptera_; but in
_Sphinx Stellatarum_ and _Lasiocampa Quercus_ it has a sinus on each
side, but no middle one. In _Panorpa_ it nearly closes the posterior
orifice of the trunk, but in the _Libellulina_ it is a mere ridge. In
some _Hymenoptera_, as _Cimbex sericea_, the drone-bee at least, &c.,
it is a large convex bifid piece. In the wasps, under the spiracle of
the _metapnystega_ on each side, as in the _Locusta_, is what I also
take to be a pneumatic pouch, which might easily be mistaken for a
metaphragm. In the _Diptera_ Order this part is very conspicuous. If
you remove the abdomen of any common _Tipula_, you will find that the
posterior orifice of the trunk is closed above by a pair of oblong,
vertical, convex, diverging plates;--do the same by any fly (_Musca_
L.), and you will detect in the same situation a very large convex or
gibbous one notched below, which occupies almost the whole orifice:
this is the metaphragm.
5. _Septula_[1752]. These are the _smaller_ ridges of the interior of
the alitrunk, which afford a point of attachment to many muscles,
and run in various directions both on the interior of the crust
and of the metaphragm. These little seams are not to be found so
generally in the other Orders; but very frequently, as has been
before observed, where there is an exterior impression of the crust,
or a suture, one of these forms its internal base.
ii. _Processes of the pectus_[1753]. We are next to consider the
internal processes of the _breast_ of insects: these consist for
the most part of the _endosternum_, or _internal_ sternum, and its
branches. As the principal feature of this are the processes which
rising from it serve as points of attachment to the muscles that
move the legs, &c., I shall confine myself to them--they are, the
_antefurca_, the _medifurca_, and the _postfurca_.
1. _Antefurca_[1754]. The first portion of the _endosternum_, or
the internal _prosternum_, branches into the _antefurca_. In the
_Coleoptera_ a plate varying in shape and direction[1755] sends
forth a pair of mostly vertical processes of a cartilaginous
substance[1756], differing in height in different genera. In
_Carabus_ L. there is neither this plate nor its processes; but in
_Dytiscus_ the latter are very visible. A very singular and complex
machine represents the part we are considering in that extraordinary
insect the mole-cricket (_Gryllotalpa_ Latr.). When we look at its
prodigious arms and consider their office[1757], we may imagine
that the requisite apparatus for moving them must be very powerful
and peculiar. Their CREATOR has accordingly provided them with a
machine for this purpose more than usually complex, extending from
the _prothorax_ to the _prosternum_; the former being its _base_,
and the latter its _vertex_. The cavity of the manitrunk is divided
longitudinally by a double cartilaginous partition surmounted by
a bony frame, with an anterior condyle or tuberosity, with which
the inner part of the base of the clavicle of the arm appears to
ginglymate; and the manitrunk is preserved from the injury the
powerful action of the arm might occasion, by the counteraction of
this machine, to describe which fully, would demand more space than I
can afford[1758]. I mentioned under the _mesostethium_, the apertures
visible in the breast of _Locusta_ Leach and _Acrida_ K. Each of
these apertures opens into an internal, tubular, horny, process,
which arching off is attached at the other extremity to the sides
of the trunk--a pair being appropriated to each segment; the first
analogous to the _antefurca_, the second to the _medifurca_, and the
last to the _postfurca_. In the _medipectus_ and _postpectus_ of
_Acrida viridissima_ there is only a single aperture, terminating in
a single tube, which after rising vertically a little way sends off
a branch on either hand to the sides of the trunk. Where there are
_three_ of these holes, as in the _antepectus_ and _medipectus_ of
_Locusta Dux_, there are _three_ of these processes, the intermediate
one being vertical. In the subsequent Orders the processes of the
_endosternum_ are not sufficiently remarkable to require particular
notice: my further observations upon them will therefore be confined
to the _Coleoptera_ Order.
2. _Medifurca_[1759]. This part, which belongs to the mid-legs, is
in many cases more conspicuous than the _antefurca_. In _Copris
Molossus_ the _endosternum_ of the _medipectus_ is represented by a
transverse zigzag ridge[1760] between the sockets of the mid-coxæ,
from which proceeds a pair of branches wide at the base and growing
gradually more slender to the extremity[1761], which is attached to
the sides of the trunk; in _Dytiscus marginalis_ a pair of slender,
vertical, straight processes, fitted with a broad cartilaginous
plate at their apex, rises from the _endosternum_, and sends forth a
lateral one to the side of the _medipectus:_ and lastly, in _Carabus_
the _medifurca_ is represented by a pair of subtriangular _laminæ_
attached to the sides of the trunk.
3. _Postfurca_[1762]. This, which belongs to the hind-legs, is the most
remarkable of the pectoral processes, and has been noticed by more than
one writer[1763]. It is a kind of trident, the branches[1764] of which
are acute, and on their upper surface longitudinally concave, elevated
on a footstalk[1765] inclined towards the _medifurca_, consisting
of two plates, a posterior one supporting the lateral branches, and
an anterior or interior one forming a right angle with the other,
supporting the intermediate one. This footstalk rises from between the
posterior _coxæ_, which appear in the Lamellicorns to ginglymate with
it at its base. The middle branch of the trident dips to the sinus
of the _medifurca_. In _Dytiscus marginalis_ the form is different;
for the intermediate branch consists of two parallel pieces, and the
lateral ones are dilated into broad vertical plates: the stalk of this
is triquetrous, and a triple cartilaginous partition appears to go from
its base anteriorly, the lateral ones diverging to the sides of the
trunk, and the intermediate one running straight to the base of the
_medifurca_.
It may not be without interest to state here some of the several
objects and uses of this structure of the trunk. When our Saviour
says to his disciples, "But even the very hairs of your head are all
numbered"[1766]--he taught them that the attention and care of the
DEITY were not confined to the mighty and the vast, but directed to
every atom of his creation--that he not only decreed the number and
magnitude of the planets and planetary systems, and of their various
inhabitants, but that the most minute and apparently insignificant
part of each individual, both as to its number and form, was
according to the law by him laid down; and whoever studies them with
attention will find that insects furnish a very interesting homily
upon this text; since in various instances I think I have made it
clear, that parts seemingly of the least importance--as a hair, a
pore, or a slight impression--have their appropriate use[1767].
At first, it would seem that the various pieces of which we have
seen the second primary segment of the trunk of these animals to be
composed, would be of little importance; but when we reflect that
this multiplicity of parts is usually not to be found in those that
have no wings, whether they be apterous sexes or tribes[1768], a
suspicion arises in the mind that they must be of more consequence
than their _prima facie_ appearance seems to warrant:--and this is
really the case. The _manitrunk_, which is destined principally to
incase the muscles that move the _arms_, did not require to be so
complex as the part that had to support the action of _wings_ as
well as _legs_. In those that have a large _prothorax_, as the
_Coleoptera_, it may, indeed, be useful in flight as a counterpoise
to the abdomen; and since when the wings descend it rises, and
_vice versa_, it may be of some service by its vibrations[1769];
but for this it required no complexity of structure. But not so
the _alitrunk_: it consists of parts much more numerous, and this
number of parts is of great importance to the animal in its flight.
All of them are so put together, being lined by a common elastic
ligament[1770], as to be capable of a certain degree of tension and
relaxation, which enables the animal to compress or dilate the trunk
as its necessities require. To cause the elevation of the wings, it
must be _compressed_ or have its _longitudinal_ diameter _increased_,
and its _vertical_ and _transverse diminished_: this compression is
produced by the _condensation_ of the internal air, which parts with
some of its caloric, and by the action of the _levator_ muscles. To
cause the _depression_ of the wings, it must be _dilated_, or have
its _longitudinal_ diameter _diminished_, and its _vertical_ and
_transverse increased_, which is effected by the _rarefaction_ of
the internal air, and the action of the _depressor_ muscles[1771].
In some Orders, the _Coleoptera_, &c., this effect is promoted by
the segments of the trunk, which are attached by loose ligamentous
membranes, and received, one or more of them, into each other, which
facilitates the above action[1772]. Thus much for the general use
of these parts. I shall further here mention a partial one of two
of them which seems indicated by a particular circumstance, and
upon which a theory may be built. In some insects the primary and
secondary wings or their analogues are placed _before_ the legs, in
others _over_ the legs, and in others _behind_ the legs: but whatever
their position, the pieces which I have named the _scapularia_
and _parapleuræ_ invariably connect the one with the other; the
former, the _primary_ wings with the _mid-legs_, and the latter,
the _secondary_ wings with the _hind-legs_. This circumstance seems
to prove that the wings by the intervention of these pieces have
an action upon the legs, and the legs upon the wings; and this is
further proved in one case by an observation of M. Chabrier with
regard to _Melolontha vulgaris_,--that the levator muscles of the
wings, by means of a long tendon, are attached to the lower part
of the posterior coxæ[1773]. Now, more than one medical friend
has suggested to me, that what are called the _coxæ_ in insects
are really analogous to the _thighs_ of vertebrate animals[1774]:
consequently these parts must represent the _coxæ_; whence it would
seem that the wings are really appendages of the legs. It must,
however, be observed, that were this opinion admitted, in the
_Aptera_, _Hymenoptera_, and _Diptera_, or even in the _prothorax_
of other insects, there would scarcely be any analogue of the _coxæ_
at all distinct from the trunk itself, of which even in the other
Orders these pieces are component parts. An instance occurs in the
_Strepsiptera_ K., and in which the arms are furnished with an alary
appendage, and the _metathorax_ has none[1775].
VI. _Organs of Motion._ We are next to consider those organs attached
to the trunk of insects which are instruments of _motion_. These are
principally those by which they are transported through the _air_,
and those by which they move on the _earth_ or in the _water_--their
_wings_ and their _legs_. I shall begin with the first, the
_wings_[1776]. These are not formed precisely after any type at present
discovered in vertebrate animals: in some respects they have an analogy
to those of birds[1777]; in others, to the dorsal fins of fishes: but,
perhaps, altogether they approach the nearest to those of the dragon or
flying-lizard (_Draco volans_ L.), which do not, as in birds, replace
the fore-legs, are kept expanded by diverging bony rays, and are
connected with the hind-legs[1778]. As the Divine Creator appears in
his works to proceed gradually from one type of structure to another,
it has been supposed by a learned physiologist of our own country,
that in winged insects, _four_ of the legs of the Decapod _Crustacea_
are represented by the four wings[1779]: this opinion, however, is not
yet fully proved; a remark which may also be applied to a more recent
one of a celebrated French writer, who seems to think their origin and
structure aërostatic, that they are auxiliary to the legs, and borrowed
in part from the respiratory organs[1780]. Were I disposed to enter
into these subtile speculations, I might here recall your attention to
the analogy that, in their metamorphoses, exists between the _Saurian
Reptiles_ or lizard tribe and insects, and conjecture that the wings
of the _Draco_ are really representatives of the mid-legs of Hexapods,
thus preparing to disappear altogether; but I shall content myself with
throwing out this hint, which you are welcome to pursue. The organs of
flight in general may be considered as to their _number_, _kinds_, and
_composition_.
i. _Number._ The most natural number is _four_, for this obtains in
the majority. In almost every Order, indeed, there occur instances of
insects that have solely a single pair or none[1781].
These, however, are only exceptions to the rule; but in the
_Diptera_, unless we consider the _alulæ_, the representatives of
the secondary wings[1782], as a distinct pair, there are never more
than _two_ wings, and one instance is known in which an insect
of this Order has _none_[1783]. Certain genera or individuals of
the Tetrapterous Orders are also furnished with _alulæ_: besides
_Dytiscus_, _Blatta_, _Phalæna hexaptera_, which have been before
noticed[1784], they may be detected in miniature in _Ammophila_ K.
and affinities; these all may be regarded in some slight degree as
insects with _six wings_.
ii. _Kinds._ Under this head we may consider the organs of flight
as to their _situation_ and as to their _substance_. As to their
_situation_, usually the first pair are attached to the _mesothorax_,
and the second to the _metathorax_; but in one instance, as has been
before observed[1785], in the _Strepsiptera_ K., the anterior pair
belong to the _manitrunk_, and the posterior to the _mesothorax_. As
to their substance, they take the several denominations of _elytra_,
_tegmina_, _hemelytra_, and _wings_, for the most part according to its
variations, as will be seen more at large hereafter. Under this head I
shall only further observe, that in many instances the organs of flight
appear to be mere _abortions_ or _rudiments_, which serve to exemplify
what has been more than once stated, that the CREATOR has seen it good
to approach to new organs gradually as well as to new forms. Thus
_elytra_ are mere rudiments that do not serve to protect the wings in
_Atractocerus_; _tegmina_ in some species of _Phasma_, _Acrydium_,
&c.; _hemelytra_ in the bed-bug[1786]; _wings_ in many female moths, in
_Cryptus hemipterus_ a _Hymenopterous_ insect, &c.
iii. _Composition._ The structure of wings has been before explained
to you[1787], and I shall again have occasion to allude to it; but
here I wish to call your attention to a circumstance that has not
hitherto, that I recollect, been adverted to; I mean that all kinds
of organs of flight, and it may be traced as we shall soon see even
in elytra, are divided longitudinally into three _areas_ or folds;
the first or external one I call the _Costal Area_[1788] from its
beginning with the costal nervure; the second is the _Intermediate
Area_[1789]; and the third is the _Anal Area_[1790].
Having made these observations with respect to the organs of flight
in general, I shall now proceed to consider more at large the
_elytra_, _tegmina_, _hemelytra_, and _wings_.
i. _Elytra._ These are the wing-covers of the _Coleoptera_ Order,
distinguished from _tegmina_ by the absence of _nervures_, from
_hemelytra_ by the want of the membrane at the apex, and from both
by their uniting in almost every instance at the suture. I shall
consider them as to their _substance_; _articulation_ with the
_trunk_; _expansion_; _parts_; _shape_; _appendages_; _sculpture_;
_clothing_; _colours_, and _uses_.
1. _Substance._ The firmness of the substance of elytra is usually
regulated by that of the crust of the insect to which they belong;
in hard insects they are hard, and in soft ones they also are soft.
The most impenetrable ones that occur to my recollection are those of
Illiger's genus _Doryphora_, and the softest and most flexile those
of _Telephorus_, _Meloe_ and affinities. With regard to individuals,
they are mostly as hard as the _prothorax_, and harder than the
_back_ of the abdomen. Elytra also, as far as my observation goes,
are never diaphanous.
2. _Articulation with the trunk._ This is by means of a process of the
base of the elytrum which I call the _axis_[1791] or pivot, attached
by elastic ligaments, and certain little bony pieces (_osselets_
Chabr.) in the socket under the side of the anterior angle of the
_dorsolum_[1792]. You may easily remove the elytra attached to the
_mesothorax_ from _Geotrupes stercorarius_, which will enable you to
see the mode of articulation with little trouble[1793].
3. _Expansion._ It is by means of the bony pieces just mentioned that
the organs in question are opened and shut[1794] under the action
of the antagonist muscles. In opening for flight the two elytra
recede from each other, and are elevated so as not to retain their
horizontal position, which would interfere probably with the play of
the wings, but form an angle with the body. When they return to a
state of rest, the sutures usually meet and coincide longitudinally;
but in some cases when closed, as in _Necydalis_, &c., they diverge
from each other at the apex; and in _Meloe_, like the _Orthoptera_,
to which that genus approaches, one laps over the other.
4. _Parts._ The parts to be considered in an elytrum are the
_areas_, the _axis_, the _suture_, the _margin_, the _epipleura_,
the _base_ and _apex_, the _angles_, and the _hypoderma_. At first
it should seem as if an _elytrum_ was not like other wings divided
into areas; but I think upon examination it will be found that,
though often nearly obsolete, these are represented in it; for the
_epipleura_[1795] with the recurved part of the external margin
seems to me analogous to the _Costal_ Area; the inflexed part
adjoining the scutellum and often going beyond it to the _Anal_,
and the rest of the organ to the Intermediate. All this you may see
in the dung-chafer, _Geotrupes stercorarius_. The _axis_[1796] or
pivot by which the elytrum articulates with the trunk is generally
placed about the middle of its base, but nearer the scutellar than
the humeral angle, and varies in length and shape in the different
tribes, but not so as to merit particular notice; it may be regarded
as composed of _three_ parallel pieces, one belonging to each area,
that of the _costal_ being the longest. In many these pieces are
marked by no line of distinction, but in _Macropus_, &c., they may
be readily traced[1797]. The _suture_[1798] is the _internal_ margin
of the elytrum from the point of the scutellum to the end. In many
beetles the right hand suture, looking from the anus to the head, has
a lower ledge or margin, and the other, one more elevated, which when
they are closed lies upon the former; in some _Dynastidæ_ there seems
a kind of ginglymous structure in this part, each suture being fitted
with a kind of ridge which is received by a channel of the other;
in these the suture is generally marked out by an adjacent channel:
but the most remarkable structure of this part distinguishes the
genuine species of the genus _Chlamys_, in which both the sutures,
except at their base, are armed with little teeth, alternating
with each other like the cogs of a mill-wheel. In apterous beetles
the elytra are often _connate_, or have both sutures as it were
soldered together. The margin[1799] or external edge of the elytra
is generally formed by a bead or ridge, which, except in the case
of the truncated ones, in which it is straight, curves more or less
from the base to the apex; this ridge is often recurved so as to form
a kind of channel between it and the disk of the elytrum, as may
be seen in the _Dynastidæ_; in some there are two parallel ridges,
as in _Copris_; in _Silpha_ the margin is dilated; in _Helæus_ and
_Cossyphus_ it is remarkably so and recurved, so that, in conjunction
with those of the _prothorax_ which are similarly circumstanced, they
give the animal some resemblance to a small model of a barge. Though
the margin of elytra is most commonly intire, yet in some beetles,
as _Gymnopleurus_ Illig., a sinus is taken out of it; in _Cetonia_
it often projects at the _base_, and in _Cryptocephalus_ in the
_middle_, into a lobe; in _Phoberus_ MacLeay it is denticulated, and
in many _Buprestes_ more or less serrulated; sometimes it terminates
before it reaches the apex of the elytrum in a tooth, as in many
_Carabi_ Latr. The _epipleura_[1800] or side-cover is that part of
the organ in question, below the margin, with which it usually forms
an angle, being more or less inflexed, that covers the sides of the
body. It varies in different tribes, being sometimes obsolete, as
in the weevils (_Curculio_ L.); in the Capricorn beetles it is very
narrow; in _Carabus_, &c., dilated at the base; in many Heteromerous
beetles, as _Blaps_, _Pimelia_, &c., it is very wide and conspicuous;
in _Cossyphus_ it stands out a little from the abdomen, so as to
form a kind of fence round it. Its _shape_ generally approaches
that of a scythe, being incurved and growing more slender towards
the apex[1801]; but it is sometimes straighter and shorter. In
_Geotrupes_ and many other Lamellicorns, the _base_ of the elytrum
is nearly vertical, forming a right angle with the rest of it; it is
usually transverse and straight; but in _Calandra Palmarum_ and many
_Cassidæ_ it slants to the scutellum; in _Chlamys_ it is sinuate,
and in _Elater_ it has a deep cavity above the axis which receives
the points of the _phragma_ mentioned before[1802]. The _apex_ of
elytra is usually acute, the angle being formed by the confluence
of a curving and straight line: but there are many exceptions; for
instance, in _Mylabris_ it is rounded; in _Hister_ obliquely, and
in _Necrophorus_ transversely, truncated; in many Capricorns it is
emarginate; in others, as _Macropus longimanus_, it is bidentate; in
some _Prioni_, _P. cinnamomeus_, &c., it terminates in a mucro at
the internal angle; and in _Cerambyx Batus_, _horridus_, &c., at the
_external_; and, to name no more, in some species of _Necydalis_ it
ends in a long acumen. The _scutellar angle_ in insects that have a
large scutellum, as _Macruspis_ MacLeay, is obliquely truncated to
admit it, but where it is small it is generally rectangular, with
the angle rounded; in _Buprestis vittata_ it is obtusangular; and in
_Dytiscus marginalis_, &c., it is emarginate. In _Cassida spinifex_,
_perforata_, &c., the _humeral_ angle is producted into an acute lobe
that stretches beyond the head, and in _C. bicornis_ and _Taurus_
it forms a horn at right angles with the elytrum. In general it
is either rectangular or rounded, with a prominence of the elytrum
within it. The _sutural_ and _anal angles_ exist only where the
elytra are truncated at the apex. In this case the _sutural_ is
generally rectangular, and the _anal_ rather obtusangular or rounded.
The _Hypoderma_ is the fine soft membrane before noticed[1803] that
lines the underside of the elytra, the use of which is probably to
prevent injury to the wings from friction with their usually hard
substance; this membrane is commonly of either a pallid or brownish
colour; but in some insects, as _Staphylinus hybridus_, _murinus_,
&c., _Buprestis grandis_, it is of a beautiful green or blue; and
it exhibits the _puncta_, _striæ_, and other modes of sculpture of
the elytra very distinctly, the pores of which usually perforate
this membrane[1804]. Just under the shoulders of these organs you
may observe an oblong and sometimes roundish spot, occasioned by the
_hypoderma_ in that part being particularly tense, and covering a
cavity or pocket which appears to be connected with the axis by the
hollow part, which I regard as representing the Costal Area; this
pocket is evidently the analogue of a part in the _wings_ noticed by
M. Chabrier[1805], and named by me the _phialum_: from its connexion
with the axis by a channel, this part in elytra should also seem
destined to receive a fluid to add to the weight of the margin and
its means of resistance.
5. _Shape._ The shape of elytra is various; taken together, in which
case, in describing insects, they are denominated _coleoptra_, their
most common form is more or less oblong, or forming more or less a
considerable portion of an ellipse; taken separately, it inclines to
that of an isosceles triangle, with the exterior side curvilinear:
truncated elytra are generally quadrangular, sometimes presenting a
trapezium, at others nearly a parallelogram, and at others a square.
With regard to their proportions they vary considerably, but the most
general law seems to be that the length shall exceed _twice_ the
width; in some, as _Buprestis grandis_, it is more than _thrice_; in
many _Staphylinidæ_ they are as wide as they are long and sometimes
wider; they are generally narrower at the apex than at the base, but
in some species of _Lycus_, as _L. fasciatus_, &c., the reverse takes
place; in _Telephorus_ they are nearly of the same width every where:
with regard to their surface they are sometimes very convex, as in
_Moluris_; at others very flat, as in _Eurychora_, _Akis_, &c.
6. _Appendages._ These, though not so remarkable as those of the
head and prothorax of beetles, ought not to be overlooked. In many
Capricorns, as _Lamia Tribulus_, _speculifera_, &c., the disk and
sides are armed with short sharp spines; in others (_Stenocorus_,
&c.) the sutural and anal angles or one of them terminate in a spine
or tooth; sometimes the whole surface, as in _Hispa atra_, &c., is
covered, like a porcupine, with a host of slender spines, or its
sides defended by spinose lobes, as in _H. erinacea_: the humeral
prominence is armed with a spine pointing to the head in _Macropus
longimanus_, and forming a right angle with the elytrum in some
_Curculionidæ_, as _Rhynchites spinifex_; but the most remarkable
appendage of this kind is exhibited by _Cassida bidens_ and its
affinities,--from the centre of the sutures of the elytrum rise
perpendicularly a pair of long, slender, sharp processes internally
concave, which both apply exactly to each other, so as together to
form a single horn which rises, like a mast from a ship, from the
body of the animal[1806]. Besides the appendages here mentioned, the
elytra exhibit a variety of tubercles and other elevations of various
form and size, which it would be endless to particularize.
7. _Sculpture._ The _sculpture_ of the organs in question is very
various and often very ornamental: but as almost every kind of
it will be noticed in the _orismological_ tables, it will not
be necessary to enlarge upon it here, especially since I have
endeavoured upon a former occasion to explain how it may be useful
and important as well as ornamental to the animal[1807]. I shall
therefore only notice a few instances, amongst many, in which a
particular kind of sculpture distinguishes particular tribes. Amongst
those that are Predaceous the _Cicindelidæ_ have elytra without
striæ or furrows, while the majority of the subsequent terrestrial
tribes of this section are distinguished by them: the _Dynastidæ_ in
the Lamellicorn section are remarkable for a single crenated furrow
next the suture; in the weevil tribes the numerous species of the
genus _Apion_ are ornamented by furrowed elytra with pores in the
furrows, which give them the appearance of neat stitching; in many of
those beetles that have soft elytra, as the glow-worms (_Lampyris_),
the blister-beetles (_Cantharis_, _Mylabris_), and still more in
_Œdemera_, two or three slight ridges generally run longitudinally
from the base to the apex, and are visible also on the under-side;
as the _furrows_ probably lighten a _hard_ elytrum, these ridges
may serve to strengthen a _soft_ one, and it is by these that the
first approach is made to the reticular structure of _tegmina_ or the
wing-covers of _Orthoptera_: _Lycus palliatus_, &c., in its elytra
exhibits a direct resemblance of the reticulations of nervures.
8. _Clothing._ To what I have before said on this subject in
general[1808] I shall here add a few remarks, which, though they
more properly belong to _elytra_, may in many cases be extended to
the whole body of a beetle. In various instances it happens that the
beautiful markings of these organs, as in _Macropus longimanus_,
whose elytra when denuded are black, are produced by short decumbent
hairs; in some these variegations are the effect of scales resembling
those of _Lepidoptera_, often of a metallic lustre; from these
scales is derived all the brilliancy of the diamond-beetle (_Entimus
imperialis_, Germ.); in some the scales are so minute as to resemble
the pollen of flowers, as the white marks observable on the green
elytra of the rose-chafer (_Cetonia aurata_).
9. _Colour._ The organs of flight in the majority of the Orders
with respect to _colour_ are usually the most gaily decorated part
of insects; I therefore deferred the notice of that subject till I
came to treat of them. In general the colour of insects is either
inherent in the substance of their crust, or produced by the hairs
or scales that either partially or totally cover it. To confine
myself to the _Coleoptera_, of whose elytra we are treating, it may
be observed, I think, in general, that the majority of those that
feed upon _putrescent_ substances, the _saprophagous_ tribes of Mr.
W. S. MacLeay, are commonly of a more dark and dismal aspect and
colour than those which feed upon such as are living and fresh,
denominated _thalerophagous_ by the same learned author; this you may
see exemplified in his _Scarabæidæ_ and _Cetoniadæ_. Again, in the
Predaceous beetles a similar contrast of colours is often observable.
How brilliant and gay are the fierce _Cicindelæ_! those tigers of
insects, as Linné calls them; how black as to colour, how horrible
in aspect is their near relation the _Manticora_: what difference
exists in the economy of these animals is not known, except, as I
learn from Mr. Burchell, that the latter is subterraneous, whereas
the former seek the sunbeam and fly rapidly. I shall now point out
a few instances in which the colours of their _elytra_ distinguish
tribes or families. Amongst the Predaceous beetles a large family of
the _Cicindelidæ_ are distinguished by a middle angular white band,
and several white dots on their green or brown elytra, as in _C.
sylvatica_; a family of _Brachinus_, and the majority of _Mylabris_,
_Lamia capensis_ and _fasciatus_, &c., by black elytra, with yellow
or red bands; _Carabus violacea_ and affinities by the violet margin
of these organs; _Calliochroma_ Latreille by their _sericeous_, and
_Eumolpus_ by their _metallic_, lustre. These instances will be
sufficient to turn your attention to this subject, which though not
of _primary_ importance in discriminating genera &c., is not without
its use in a _secondary_ view.
10. _Uses._ I must not quit this subject without saying something
upon the ends which elytra seem designed to serve. Their first and
most obvious use is the protection of the wings when unemployed, that
they may not be lacerated or soiled, and rendered unfit for flight in
the various retreats to which these animals betake themselves either
for food, repose, or to lay their eggs; to promote this purpose more
effectually, the wings are usually curiously folded and laid up under
them; and where the elytra are very short, as in the _Staphylinidæ_,
these folds are very numerous and complex. In some instances,
however, as in _Molorchus_ F., _Atractocerus_, &c., the wings are
only partially protected by the elytra and not folded under them;
probably they are less in danger of laceration from their peculiar
habits than the generality. Another use is to protect the upper-side
of the alitrunk, which for reasons before assigned is usually softer
than the under-side, and also of the abdomen, often above nearly
membranous, from the injury to which they would otherwise be exposed;
in the latter part also the spiracles in _Coleoptera_ are not covered
by the inosculations of the segments, as is the case in most other
Orders, and therefore probably require some covering when the insect
is not flying. In the Apterous beetles this appears to be their
principal use; where these organs are connate, or as it were soldered
together, the back of the abdomen is a thin membrane; the appearance
of _two_ elytra in these cases is given, doubtless, for the sake of
symmetry and beauty, a subordinate attention to which may be traced
in all the works of creation. If we consider the bulk and weight of
many flying beetles, we may imagine that they want some assistance,
more than the extent and dimension of their wings seem to promise,
to support them in the air, and to enable them to move more readily
in it; and although it seems clear from the state of their muscular
apparatus that elytra do not move much in flight, yet by giving a
broad and concave surface to the air, for then they are usually
nearly vertical, they may assist in some measure as sails, and help
them in flying traversely and before the wind[1809].
ii. _Tegmina_[1810]. By this name the learned Illiger has
distinguished the upper organs of flight of the _Orthoptera_ and
Homopterous _Hemiptera_[1811]. They may be considered under the same
heads nearly as elytra.
1. _Substance._ _Tegmina_ differ very materially from _elytra_
in their _substance_, being generally more or less diaphanous,
though in _Blatta Petiveriana_ the dark parts are as opaque as
elytra, and those of the _Mantes_ that resemble dry leaves are only
semidiaphanous. These organs are also of a less dense substance
than elytra, something between coriaceous and membranous, which I
shall express by the term _pergameneous_, as somewhat resembling
parchment or vellum. Another circumstance relative to this head
also distinguishes them,--they are not lined with membrane. In some
instances, as in _B. Petiveriana_ just named, they approach nearly
to the substance of elytra, and in _B. viridis_, some _Mantes_, and
_Tettigonia_, &c., they are little different from wings in their
substance; but this does not diminish their right to be considered as
_tegmina_, since their structure is altogether the same.
2. _Articulation with the trunk._ I observed above that the axis of
elytra may be regarded as formed of _three_ parts, one appertaining
to each of the areas or their representatives[1812]; in _tegmina_,
and indeed in wings in general, these parts are separate and may
be more distinctly traced, the _axis_ of the _Costal_ Area being
generally the longest, and that of the _Intermediate_ often the
shortest; these _axes_ are suspended in the wing-socket by elastic
ligaments, intermixed with hard bony plates, the principal one of
which, called by M. Chabrier the _humerus_[1813], is connected both
with the _tegmen_ and the trunk, and in some a little resembles the
head and neck of a swan. This structure permits the animal to move
the lateral areas in some degree separately, so that each, especially
the _anal_, shall form an angle with the intermediate; as the motion
of the latter is not wanted, its _axis_ often falls short of the
base, or is obsolete, as in _Blatta_.
3. _Composition._ The three areas, traces of which we had discovered
in _elytra_, are particularly visible in _tegmina_. If you take any
cockroach (_Blatta_), you will at first sight see that in it they are
divided into three larger portions by stronger nervures or folds;
and if you also take a _Mantis_, or _Locusta_ Leach, a _Fulgora_ or
_Tettigonia_, the same circumstance will strike you, only you will
see that in these the intermediate portion terminates also in an
axis; these are what I call the three _areas_. The external one or
Costal is usually the longest and narrowest[1814]; the Intermediate
one is commonly triangular, with its inner side curvilinear[1815];
and the interior one, or _Anal_ area, in the _Orthoptera_ is rather
oblong; in _Fulgora_ angular, and in _Tettigonia_ it presents an
isosceles triangle; with its vertex to the apex of the wing[1816].
The first of these may be defined as that portion of the wing that
lies between the _costal_ and _postcostal_ nervures; and perhaps, in
some cases, as in _Mantis_, for there is the fold of the _tegmen_,
the _mediastinal_ may be regarded as its limit; the Intermediate
Area is that which lies between the _postcostal_ or _mediastinal_
nervure and the _anal_ fold of the wing; and the Anal Area is the
remainder. These areas may perhaps best be made out by tracing each
to its axis. To study them carefully in _tegmina_ and _hemelytra_ is
of considerable importance; for in them we find the first outline of
the general plan upon which the wings of insects are constructed,
and which, as we shall see hereafter, more or less enters into the
composition of them all.
4. _Position, and folding in repose._ With regard to their position
when not expanded, _tegmina_ vary somewhat in the different tribes.
In the _Coleoptera_ we have seen that, except in a few instances,
the elytra unite at their suture. Something like this takes place in
_Fulgora_, _Cercopis_ and affinities, in the Homopterous _Hemiptera_;
in these, though the union is not near so exact, yet the _tegmina_ do
not lap over each other; they are usually more or less deflexed, with
scarcely any portion in a horizontal position: in _Tettigonia_ F.,
_Chermes_, _Aphis_, &c., the middle part only of these organs meets,
from which point they diverge both towards their base and apex[1817].
In the _Orthoptera_ the position is quite different, for one tegmen
more or less lies over the other. In _Blatta_, in which the _tegmina_
are nearly horizontal, the left hand one covers almost half the
other[1818]: in the other tribes of the Order, with little variation,
the Anal Area of the _tegmen_ is horizontal, and covers the back of
the animal, and the Intermediate and Costal are vertical and cover
its sides; the former, however, in some cases, only forms the angle
between them. Sometimes in these the right-hand one is laid upon the
left, as in _Acheta_; and sometimes the reverse of this takes place,
as in _Acrida_ K. With regard to the folding of the _tegmina_, the
most remarkable instance that occurs is that of _Acheta monstrosa_,
in which the ends of both these organs and the wings, in repose, are
folded like a fan, and then rolled up like a serpent[1819].
5. _Shape._ The shape of _tegmina_ is various. In the _Blattæ_
and some _Mantes_ they are more or less _oblong_; in _Mantis
precaria_, _strumaria_[1820], and others, they incline to
_elliptical_; in _Phasma grandis_ and _Acheta monstrosa_ they
are rather _panduriform_[1821]; in _M. gongyloides_ they are
_semi-cordate_[1822]; in _Pterophylla trapeziformis_ they are
_rhomboidal_[1823]; in _Conocephalus erosus_ they are _sinuated_; in
_Locusta_ Leach they are usually _linear_ or linear-oblong[1824]; in
_Pterophylla_ K. they generally terminate in a short mucro[1825]; and
in some of those _Mantidæ_ whose _tegmina_ simulate arid leaves, in a
recurved one[1826]. In the Homopterous _Hemiptera_ the shape of these
organs is less various. In the _Fulgorellæ_ Latr. they incline to a
trapezium, sometimes to a pentagon[1827]; in the _Tettigoniæ_ F. they
approach to an obtuse-angled triangle; and in others of the tribe
they are nearly wedge-shaped[1828].
6. _Neuration._ The circumstance that most strikingly distinguishes
_tegmina_ from _elytra_ is their _neuration_ or veining; which adds
much to their strength, without increasing their weight so much as
to render them unapt for flight. To look at these organs in _Blatta
Petiveriana_, you would imagine them at first to be deprived of
this distinction; but if you observe them attentively, particularly
their white spots, you will soon detect their nervures; and if
you further examine their lower surface, you will find them very
visible. The gibbous _Blattæ_ also, _Blatta picta_ and affinities,
the analogues of _Erotylus_ amongst the _Coleoptera_, have _tegmina_
which, except at their apex, exhibit but faint traces of the nervures
of their tribe, and approach to elytra besides by the innumerable
minute impressed points that cover them. In the _Orthoptera_ and
some Homopterous _Hemiptera_ the nervures may be divided into
_longitudinal_ ones more or less ramified, and _traversing_ ones.
In the _Blattæ_ the traversing nervures cut the longitudinal ones
nearly at right angles, but not at regular intervals, so as to cover
the tegmen with quadrangular areolets; in _Mantis precaria_ and
affinities the longitudinal nervures of the Anal Area diverge from
the base, and are traversed nearly as in _Blatta_, while those of
the Costal diverge from the mediastinal nervure, but the traversing
ones form innumerable irregular reticulations; in _Mantis sinuata_
K.[1829] the whole tegmen has such reticulations but less numerous;
in _Locusta_ Leach it is regularly reticulated at the base, but the
areolets of the apex are quadrangular; in the _Mantes_, with oblong
wings, all are quadrangular; in _Pterophylla_ K. the longitudinal
diverging nervures are not numerous, and the traversing ones cut
them into quadrangular and triangular areolets, besides which they
are covered by innumerable impressed points, so as altogether to
exhibit a most exact resemblance of the leaf of some evergreen: in
_Gryllotalpa_ the longitudinal nervures of the Anal Area rather
converge towards the apex, are traversed by few transverse nervures,
and those of the Costal Area which diverge from the mediastinal
nervure by still fewer; the neuration of _Acheta_ F. has been before
described[1830]; I shall only observe here, that the constructors of
_stringed_ instruments of music might, perhaps, from the _tegmina_
of the male, the nervures of which probably modulate the sounds
which it produces, take a hint for giving the strings in them a
serpentine or convolute direction, and so might produce something new
in that department, corresponding with the serpents and French-horns
in _wind_ instruments. Of the Homopterous _Hemiptera_ in the
_Fulgorellæ_ Latr., which are most analogous to the _Orthoptera_
of all that tribe, the longitudinal nervures are more numerous and
branching, more especially toward the apex of the _tegmen_, and are
traversed as much by transverse ones, sometimes reticulating the wing
with roundish areolets, as in _F. laternaria_, and at others with
quadrangular ones, as in _F. candelaria_; in some of these however,
as _Otiocerus_ K., _Flata_ F., &c.[1831], there are no traversing
nervures; and these lead to the _Cercopidæ_ and others in which the
longitudinal nervures become few, and some are without any[1832],
and these terminate those of this section of the Order in which the
nervures in question are continued to the margin of the wing. We next
come to those, _Darnis_, _Centrotus_, _Membracis_, &c., in which they
are circumscribed a little within the apex by a traversing nervure,
so that the tegmen ends in a margin of pure membrane, and thus some
approach seems to be made to the _Hemelytra_, from _Tettigonia_, the
most conspicuous genus of this tribe, in which the _areolets_, few
in number, like those of _Lepidoptera_, are not formed, except the
terminal ones, by traversing nervures, but by the ramifications of
the longitudinal ones; in _Chermes_ the Intermediate Area, which is
connected with the base of the wing by a single nervure, is the only
part that has any areolets[1833].
7. _Colour._ Orthopterous insects are seldom remarkable for _tegmina_
of brilliant _colours_; there is in them none of that gilding or
metallic lustre which so often distinguishes elytra: they are also
frequently less ornamented in this respect than the wings, with which
they usually form an agreeable contrast. Their reticulations and
nervures, which are sometimes of a different colour from the rest of
the tegmen, decorate them considerably: a remarkable circumstance
belonging to this head attends the black tegmina of _Blatta
Petiveriana_; one has _four_ white spots, and the other only _three_;
but as one laps over the other, the symmetry of the arrangement is
preserved: the Homopterous _Hemiptera_ are more distinguished in
this respect, and some of the _Fulgoridæ_ imitate the _Lepidoptera_
both by their ocelli and spots: _Fulgora laternaria_, _Candelaria_,
_serrata_, and _Diadema_, sufficiently exemplify this remark, as do
several _Flatæ_ likewise[1834].
We may observe here--that _tegmina_ are more calculated for flight
than _elytra_, both from their thinner substance, and from the angle
that their Anal Area, and often the Costal, forms with the rest of
the _tegmen_; a circumstance which, in wings, M. Chabrier thinks
presents some facilities in that kind of motion.
iii. _Hemelytra_[1835]. The next species of wing-covers, which
though varying in the substance of their base, terminate in a part
distinct from the three areas, consisting in almost every case of
mere membrane, peculiar to the Heteropterous _Hemiptera_, are called
_hemelytra_, or half-elytra:--this term was also formerly employed,
but certainly incorrectly, to denote _tegmina_. I shall consider them
with respect to such of the particulars noticed under the former
heads as apply to them, but without repeating them formally.
1. As to their _substance_, they must be separately considered with
regard to their base and apex. In various instances the _base_,
or part consisting of the three areas, is almost corneous, as
in _Cydnus Morio_ and _bicolor_, bugs not uncommon with us, and
many others[1836]; in these cases it is lined with a _hypoderma_
like elytra; and in many the points, which are impressed upon it,
also perforate the _hemelytrum_, and seem to act as pores: but in
_Lygæus_, _Reduvius_, _Capsus_, _Miris_, and the majority of the
Heteropterous _Hemiptera_, the organs in question being soft and
flexible, may be stated as rather resembling leather than horn;--on
this account this part of a _hemelytrum_ is denominated the _corium_.
In _Scutellera_ the portion covered by the scutellum is membranous;
and in _Acanthia paradoxa_, and the cucullated species of _Tingis_,
the wing-covers are entirely so. The apex of these organs is almost
universally either membranous or coriaceo-membranous, on which
account it is called the _membrana_. I say _almost_, because in
_Aradus_ and the _Hydrocorisæ_ Latr., this part, though rather
thinner than the rest of the _Hemelytrum_, is also coriaceous; in
the latter tribe usually with a very narrow membranous edge; and in
many _Reduvii_ and _Zeli_ there is scarcely any difference in the
substance of the base and apex.
2. As to the _articulation_ of _Hemelytra_ with the trunk, it seems
not strikingly different from that of _tegmina_: the point or base
of the Intermediate Area, which falls short of that of the lateral
areas, seems connected by a slender ligamentous piece, with its axis,
which is thick; and I do not discern Chabrier's _humerus_ shaped like
a swan's head and neck[1837].
3. The _composition_ of these organs differs from that of _tegmina_
in more respects than one: in the first place, they consist, as
was lately observed, of _four_ instead of _three_ areas; in the
next, they appear to have, at least several of them, a part, which
I suspect to be analogous to that above described in _Coleoptera_,
supposed to represent the _phialum_ of wings[1838]. I shall first
speak of the _areas_. In some apterous species related to the
bed-bug, _Lygæus brevicollis_ Latr.[1839], &c., there is no trace
of the usual areas, and the _membrana_ is a very narrow strip; in
_L. apterus_ the former are very faintly traced out, but they are
present in all those that are furnished with wings; whence we may
conjecture that they are of the same importance in flight with the
folds observable in those organs[1840]. The three basal areas may be
said most commonly to present three isosceles triangles, the Costal
one being narrow and curvilinear[1841], the Intermediate the most
ample[1842], and the Anal one the narrowest and shortest[1843], with
its vertex towards the apex of the _Hemelytrum_, while in the two
former it is at its base. In _Lygæus compressipes_ (_Rhinuchus_ K.
MS.) the Anal Area is cultriform; and in most of the _Hydrocorisæ_ it
has an angle in the middle of its posterior margin. The proportion
that the _membrana_ or _apical area_ bears to the rest of the wing
varies in the different tribes. In some, as before stated, it is
obsolete, in others nearly so; in the majority, perhaps, it occupies
about a _third_ of the _hemelytrum_; in _Lygæus compressipes_,
_cruciatus_, &c., full _half_; in _Alydus calcaratus_, _two-thirds_;
in _Reduvius_, nearly _three-quarters_[1844]; and in _Aradus
depressus_ the corium,--divided, however, though indistinctly, into
the three areas,--is driven to the _base_ of the wing: two ends are
answered by this structure--as this insect lives under bark, its
thin _hemelytra_ take less room; and as it flies, though it has only
rudiments of wings, they are more fit to supply their place: the part
we are speaking of usually runs obliquely from the vertex of the
Anal Area to the base of the Costal.
4. As to their _position and folding in repose_, _Hemelytra_ are
usually nearly or altogether _horizontal_; but in _Notonecta_ and
_Plea_ they are _deflexed_ and cover the sides of the body; and the
apical area of one wing precisely covers that of the other; where
the scutellum does not intervene, as in _Scutellera_, _Pentatoma_,
&c., the vertical angles of the Anal Area meet in the middle of the
back, so as to exhibit the appearance of a cross. In _Notonecta_, in
which the _hemelytra_ are deflexed, at the apex of the _membrana_
is a fissure which permits the two sides to form an angle with each
other, and to apply exactly to the body. In _Plea_, in which there
is no apical area, the posterior margins of the _tegmina_, as they
ought rather to be termed, unite, but do not lap over each other.
With regard to the appearance of something like a _phialum_, if you
examine the _hemelytra_ of most species of bugs on the underside, you
will see that the costal nervure at the base is inflexed and covers a
kind of channel; if you next take one of _Belostoma grandis_, where
the structure is most conspicuous, or even the common _Nepa cinerea_,
you will find in the same situation, adjacent to the inflexed costal
nervure, a hollow tube running from the base of the wing, and
terminating, after proceeding about one-fourth of its length, in a
hollow cavity, which, as it is covered by a membrane, appears to me
to be a collapsed pouch. This circumstance is worthy of further and
more general investigation.
5. In their _shape_, with few exceptions, _hemelytra_ more or less
represent a wedge, being wider at their apex, where they are usually
obliquely truncated, than at the base; but in _Plea_ Leach they are
obtusangular, with the angle in the sutural margin; in _Notonecta_,
on the contrary, an obtusangular sinus distinguishes that part; in
_Naucoris_ they are curvilinear and every where of equal width;
in _Ranatra_ they are linear and straight; in _Aradus_ they are
oblong, usually with an external lobe or dilatation at their base:
a remarkable instance of the intention of this is observable in a
nondescript Brazilian species, in which the head, prothorax, and
abdomen, are edged with a number of broad foliaceous appendages; if
the base of the _hemelytrum_ had not been furnished with a similar
appendage, the symmetry of the whole body would have been destroyed
by the hiatus between the prothorax and abdomen, as may be seen by
removing the _hemelytra_; but by this compensating contrivance of
Providence, the gap is filled, the above lobe fitting exactly into it.
6. The _neuration_ of these organs will not occupy us long, since
the _corium_ or harder part, though in some species there are traces
of nervures, is often without them. Those of the cucullated species
of _Tingis_ resemble many _tegmina_ in being ornamented by them with
a kind of network, which looks like the finest lace; in several
_Lygæi_, _Edessa_, and some _Reduvii_, there are a few diverging
longitudinal nervures which occasionally by a ramification here and
there form an areolet[1845], but there are seldom any traversing
nervures. The Apical Area is usually most distinguished by nervures,
in some forming several areolets, as in _Aradus_, in others running
parallel to each other, nearly to the end of this area, as in
_Belostoma grandis_, where they are met by a traversing nervure; the
object of this is doubtless to strengthen the membrane.
7. Both _tegmina_ and _hemelytra_ are most commonly naked, yet very
short _hairs_ are found on those of some species of _Cercopis_, and
in many more instances in those of the latter description, as in
_Notonecta_, several _Lygæi_ and _Reduvii_, &c.
8. _Colours_ in _hemelytra_ are very various, and in many instances
are peculiar to families; in certain _Lygæi_ (_L. Hyoscyami_, &c.)
black and red; in _Lygæus compressipes_ and affinities a dingy black;
in some _Reduvii_ black with a large white spot;--but it is needless
to enlarge further on this subject.
9. That _hemelytra_ are used in flight is evident not only from
the large space allowed for their muscles[1846], but likewise from
a circumstance noticed by M. Chabrier, that in flight, in the
_Pentatomæ_ Latr., the corium of the _hemelytrum_ is fixed to the
wing[1846]; in which case both must describe the same arc.
iv. _Wings._ We are next to consider organs which are exclusively
appropriated to _flight_, and therefore are properly denominated
_wings_. These in the Orders that have _elytra_, _tegmina_, or
_hemelytra_, are the pair that correspond with the secondary wings of
the other Orders. It may be said, indeed, that in several instances
both _tegmina_ and _hemelytra_ do not differ at all in substance
or use from the wings that they cover. This is true; but as their
structure in other respects is the same with that of those that are
more solid and less apt for flight, it was convenient to consider
them under the same name.
1. To begin with the _articulation of these organs with the trunk_; in
general it may be stated that this, as in _tegmina_ and _hemelytra_,
is usually by the intervention of three axes, formed by the conflux
of the nervures of the three areas at the base of the wing, which
either immediately or by other pieces are implanted in the trunk, so
as to receive from it the aërial and other fluids, necessary for its
expansion and motions[1847]. Having given this general statement, I
shall next apply it to the wings in some of the different Orders. If
you carefully extract one from the stag-beetle (_Lucanus Cervus_)
or any large species of the _Dynastidæ_, in the _Coleoptera_; the
first thing that will strike you, upon examining the base, will be
the plate before mentioned called by Chabrier the _humerus_, which
is a stout transverse corneous piece, with a deep sinus towards
the wing, filled with ligament: if you again follow the costal,
mediastinal, and postcostal nervures, you will find them unite to
form an axis, consisting of three parallel pieces, which connects
by its intermediate internal piece with one end of this plate. The
nervures of the Intermediate Area terminate also in a corneous axis at
a greater distance from the base than the other two, which connects
with Chabrier's _humerus_ by means of the ligament of the sinus just
named. Those of the Anal Area are received by a ligament attached to
a transverse plate, widest at its anterior end, which connects with
the posterior part of the said _humerus_; and at its posterior end is
united to the _postfrænum_[1848], with which it forms a right angle.
In the _Orthoptera_ Order the structure is not very different, but the
axes and other plates of the base of the wing are less distinct and
rather cartilaginous; the nervures of the Anal Area often terminate
in a transverse one that there forms the segment of a circle[1849];
the inner base of this circle is ligament connected with the
_postfrænum_[1850]. In the Homopterous _Hemiptera_ the three axes may
be readily traced, but the _humeral_ plate, with which they all are
connected, is more irregular in shape, and in _Fulgora_ longitudinal,
with an angular surface; in this Order the nervure, in some cases
consisting of cartilaginous rings[1851], in which the _frænum_ and
_postfrænum_ terminate in the _tegmina_ and wings, is attached
posteriorly to the ligament of the Anal Area. In the Heteropterous
section the three axes are evident, but the _humeral_ plate is not
easily made out. In the _Libellulina_ the axes of the Costal and
Intermediate Areas are the coloured broad plates at their base, formed
by the dilatation of their nervures; that, however, of the Anal is not
dilated, but forms one nervure, in the primary wing, with the _frænum_,
and in the secondary with the _postfrænum_. Having given you this clue
to trace the axes in those tribes in which they are most conspicuous,
it will assist you in searching for them in the remaining Orders,
in all of which they may be traced, except perhaps in those minute
_Hymenoptera_ whose wings have solely the costal nervures; probably in
these there is only _one_ axis. In the _Lepidoptera_ and _Hymenoptera_
a circumstance connected with the present head is observable, which is
not to be discovered in the other Orders: these are the _tegulæ_ or
base-covers, which appear intended to defend the base of the anterior
wings. They are concavo-convex scales, which in the _Lepidoptera_ are
large and of an irregular shape[1852], but in the _Hymenoptera_ are
smaller and semicircular[1853].
2. Wings, with regard to their _substance_, may generally be termed
_membranous_; but they vary in this respect, some being much thicker
than others, either _partially_ or _totally_: in spotted wings,
as in those of many _Libellulina_, _Tettigoniæ_ F., &c., the dark
opaque parts are denser than those that are transparent: in several
_Orthopterous_ insects, as in _Phasma_, some _Mantes_, &c., the
Costal Area or covering part of the wing is of a substance equally
firm with that of the _tegmen_. This is a compensating contrivance,
that where the latter is shorter and smaller than the former,
its membranous part, when folded, may be protected from injury.
Another similar contrivance of DIVINE WISDOM is exhibited by those
_Pterophyllæ_ K. (_Locusta_ F.) whose _tegmina_ resemble the leaves
of plants (_Pt. laurifolia_, &c.); in these the tip of the wings when
folded being longer, is not covered by the _tegmina_, and therefore
exposed to injury; to prevent which this small piece, while the
whole wing, as far as covered by those organs, is membranous, is of
the same substance with them[1854]. The wings of most _Coleoptera_,
_Orthoptera_, _Hemiptera_, and _Thereva coleoptrata_, in the
_Diptera_, &c., are of a firmer substance than those of the other
Orders; in many _Locustæ_ Leach, _Fulgoræ_, &c., they are nearly as
firm as the _tegmina_; and in _Ascalaphus italicus_, except at their
base, the _secondary_ wings are less membranous than the _primary_.
M. Chabrier has observed[1855] that the wings of insects in general
diminish in thickness from their base to their apex, and from their
anterior to their posterior margin.
3. I should have had, it is probable, but little original matter
to communicate under the head of the _composition_ and _neuration_
of wings, had M. Jurine, who has written so ably on those of
_Hymenoptera_, undertaken a survey of the organs of flight in every
Order of insects: but as his views were confined to only _two_ of
the Linnean Orders, it is not wonderful that his system and set
of terms should fail where a generalization is necessary; and I
may stand acquitted of presumption and conceit if I attempt to
substitute a system and body of terms more universally applicable.
Had the plan of this able Entomologist led him to pay attention to
_tegmina_ and _hemelytra_, their division into three longitudinal
areas would have immediately struck him; and having acquired this
outline of the greater natural divisions, he would have applied it
to the Orders that have _wings_ only, and having discovered that it
is to be traced in all, the result would have probably superseded
my labors. Had his life been longer spared, perhaps something of
this kind would have been effected by him; but as he, alas! is gone,
and no abler hand seems to have undertaken the task, I will do what
I can to give you satisfaction on this subject[1856]. You have
already got a tolerably good idea of these areas from what has been
said upon the subject under _tegmina_ and _hemelytra_; but I shall
now more particularly state to you how they are circumstanced in
_wings_. I shall first explain the general law as to their limits.
The _Costal Area_[1857] is all that longitudinal portion of the wing
that lies between the anterior margin and the postcostal nervure;
the _Intermediate Area_[1858] is all that longitudinal portion of
the wing that lies between the postcostal and the anal nervures;
and the _Anal Area_[1859] is all that longitudinal portion of the
wing that lies between the anal nervure and the posterior margin.
But there are other helps to enable you to distinguish the areas
in the different Orders. The Anal Area in all Orders forms the
posterior _fold_ of the wing; in _Coleoptera_ turned under when in
repose; in _Orthoptera_ folded like a fan; in _Lepidoptera_, in some
_Papilionidæ_, forming an arch over the abdomen. Again, in _Blatta_,
the Costal Area is distinguished chiefly by _longitudinal_ nervures;
the Intermediate by _oblique_ ones; and the Anal by _radiating_ ones;
and in both this tribe and the _Mantidæ_ this last Area is marked
out from the Intermediate by a marginal notch, which is not present
in _Phasma_, but is found in both sections of the _Hemiptera_. In
_Locusta_ Leach the notch is between the Costal and Intermediate
Areas: in _Phasma_ the nervures of the Intermediate Area are branches
of the externo-medial, while those of the Anal, as they do in all
the _Orthoptera_, diverge from the base of the wing: in many, as
in _Pterophylla_ K., the part of the wing lately alluded to, that
is longer than the _tegmen_, and of the same substance, points out
the limit of the Costal Area; and in others this part terminates
in a segment of a circle and is differently reticulated at the
apex from the Intermediate: in the Homopterous _Hemiptera_ and the
_Libellulina_, in which the areas at first seem indistinct, they
may generally be easily traced by following them from the axes. The
separation of the Costal from the Intermediate in the remaining
Orders seems less easy on account of the branching of the nervures:
in the rest of the _Neuroptera_ and the _Lepidoptera_, if the
posterior branches of the postcostal nervure are not included, you
will have a narrow Postcostal Area, which in most cases forms an
angle more or less prominent, in _Corydalis_ almost a right angle,
with the Intermediate: in _Hemerobius_ and affinities this part is
distinguished by areolets formed by _transverse_ nervures, while
those of the rest of the wing are _longitudinal_[1860]: but if the
posterior branches are included, the Costal Area will be more ample:
a similar observation applies to the _Hymenoptera_ and _Diptera_;
in these, in all cases, the areolets adjoining the anterior margin,
which follow the _stigma_, should be regarded as belonging to the
Area in question[1861]. In those tribes of the former Order, whose
wings are without _nervures_, the areas are often marked by _folds_.
M. Chabrier has observed that in _Coleoptera_ the specific weight of
the margin of the wing, and its means of resistance, are augmented
by a liquid which is introduced, at the will of the animal, into
a long pocket under the _brachial_, here called the _costal_ and
_mediastinal_ nervures, covered by a supple membrane, which in a
state of repose becomes flaccid[1862]: it is easily detected, being
of a paler colour than the nervures between which it lies; this is
what I call the _Phialum_; we have before seen that it exists also in
_Elytra_ and some _Hemelytra_[1863]; but I have not detected it in
any other _wings_.
I have before given you a sufficiently full account of the _alulæ_
or winglets of _Diptera_[1864]; and shall here only observe that
they are not confined to _one_ particular tribe, as has been usually
imagined; but though sometimes extremely minute, simple, and not
easily detected, are an _universal_ distinction of the Order.
Having thus endeavoured to elucidate the _larger_ Areas into
which wings appear to be divided; I shall next say something on
the _smaller_ ones produced by the intersection or ramification
of the nervures; these had been named areolets (_areolæ_) several
years before M. Jurine's work, in which he calls them, I think
_improperly_, cellules (_cellulæ_), was published; I therefore
retain the _prior_ term. The general structure of the nervures of
the wings of insects having been before explained[1865], I shall not
here repeat what I then said; but there is a curious circumstance
connected with it, particularly visible in the wings of certain
_Hymenoptera_, that I must not pass without notice. If you examine
attentively with a microscope against the light the wing of any
_Nomada_ or _Andrena_, you will discover little transparent points
in some of the smaller transverse nervures that form the middle
areolets, in which the nervure becomes white and looks as if it
was interrupted, though in substance it seems continued: these
little points, somewhat resembling minute air bubbles detained in
the tubes, are what M. Jurine, who first discovered them, has, on
that account, named _bullæ_, which he thus further describes:--"When
the tube (of the nervure) arrives at the spot where a _bulla_ is to
be formed, it extends itself on all sides in minute threads in the
upper membrane of the wing, losing its colour and tubular structure,
which it resumes immediately after the formation of the bulla[1866]."
But if you look closely at them you will find that there is always
a slight _fold_ of the wing that cuts the nervure exactly at the
_bullæ_, and if the fold changes its direction they accompany it;
their object, therefore, is clearly to relax the tension so as to
admit a little motion where the fold is; consequently, rather than
_bullæ_ (bubbles), they should be denominated _articulations_. A
similar construction, but on a larger scale, may be observed in the
wings of _Coleoptera_[1867] and some others, as _Psocus_, where the
folds traverse the nervures. I shall next make a few observations
on the principal nervures; and first a word upon their _names_. M.
Jurine, being of opinion that a striking analogy exists between the
wings of _insects_ and those of _birds_, in which M. Chabrier seems
to agree with him, has named the nervures in the anterior margin of
the wings of the former, _radius_ and _cubitus_, as corresponding
with the bones so named in the fore-arm of the latter, and the plate
which often terminates these nervures in _Hymenoptera_, he names
the _carpus_; it may look like presumption to differ from two such
weighty authorities, but as their observations seem to have been
too limited, in one case to the _Hymenoptera_ and _Diptera_ only;
and in various Orders there is nothing analogous to the _stigma_ or
_carpus_, and all the other nervures of an insect's wing have no
analogue in that of a bird, but more especially as M. Latreille seems
to think with me on this subject[1868], I have retained Linné's term
for the marginal nervure, and for most of the others have adopted
those of the great French Entomologist just mentioned. I shall here
only further observe,--and it seems to me an observation of prime
importance, in the determination of the question of the analogy of
the wings of insects,--that they are not, as in birds, the _fore-leg_
converted into an organ of flight, but, like the wing of the _Draco_,
an organ _superadded_ to the legs; and, further, that the connection
is not with the fore-legs, but, as has been before observed[1869],
with the two posterior pairs.
The _Costa_[1870] is usually the strongest of the nervures, and
that upon which the wing seems to be built; but in some cases, as
in _Blatta_, _Scutellera_, _Cynips_, &c., it is represented by
the mere membrane of the anterior margin; in some _Coleoptera_,
as in _Geotrupes_, _Dytiscus_, &c., its structure, except at the
base, appears to be annular or nearly so, at least a vast number
of corrugations, running transversely, are observable on its upper
and lower surfaces; it is thus capable of greater tension and
relaxation, and more flexile. The _stigma_ or _carpus_[1871], though
most conspicuous in the _Hymenoptera_ Order, may be traced in some
_Coleoptera_, Heteropterous _Hemiptera_, the _Libellulina_, &c.;
but it has no representative in the _Orthoptera_, _Lepidoptera_,
_Trichoptera_, &c. The _mediastinal_ is usually a very slender
nervure, placed between the _costa_ and _postcosta_, sometimes
terminating in the former[1872], and at others in the latter[1873]: in
the _Orthoptera_, _Lepidoptera_, &c., however, and some others, it is
a very conspicuous and principal one[1873]; in the _Hymenoptera_ it
is obsolete, merging in those nervures[1874]. The _Postcosta_ is the
principal nervure of the wing in _Scutellera_, but in _Staphylinus_
it is wanting; in _Chalcis sispes_ it is the only true nervure of
that organ, the others being represented by spurious ones[1875]. The
_externomedial_ and _internomedial_ are sometimes distinct at their
origin, but more frequently are branches from a common stem.
Having made these _general_ remarks, I shall now consider
_particularly_ the _neuration_ of the wings in the different Orders,
beginning with the _Coleoptera_. The first thing that strikes the
physiologist in surveying a wing belonging to an insect of this
Order, is the general arrangement of the nervures[1876]; which are
so placed that the required degree of tension may be given to every
part of this organ: thus some are nearly straight[1877]; others
run in a serpentine direction[1878]; others are forked with one
branch recurrent and another proceeding onwards[1879]; others again
are insulated, or do not originate from the base of the wing, or
from other nervures, but are merely placed to strengthen an open
space of it[1880]: these nervures are also usually broader and more
substantial than those of the wings of the subsequent Orders. Another
striking circumstance with regard to them is that the nervures form
few or no closed areolets, except in the Costal Area, where they
are inconspicuous; in _Dytiscus marginalis_, indeed, and _Tenebrio
Molitor_ one or two may be found, but in general there are none. In
many of this tribe the _postcosta_, which terminates at the joint
of the wing, becomes recurrent, so as to form a hook, which perhaps
represents the _stigma_, as in _Dynastes_[1881]; in _Creophilus_
K., a rove-beetle, there is no hook but a broad plate adjacent to
the _costa_. In the _Strepsiptera_ Order the neuration is extremely
simple, the nervures, except one insulated one, diverging from the
base of the wing[1882]: in this respect, as well as in the form
of that organ, an approach is made to the _Orthoptera_. In the
_Dermaptera_ this approach is still more evident; in the common
earwig[1883], the diverging nervures become numerous; between each is
an insulated one, taking its origin in the middle of the wing, and
running to the margin; a little nearer to the latter all the nervures
are dilated into a plate; those of the anal area are angular[1884],
and the exposed part of the costal is as hard as the elytra. The
neuration in the _Orthoptera_ Order may be called _radiate_, the
longitudinal nervures for the most part diverging from the base of
the wing like _rays_: in some few instances[1885], but not often, I
believe, an insulated nervure intervenes between each; traversing
or connecting nervures, cutting the longitudinal ones in various
directions, ornament these wings with an infinity of areolets,
causing them to resemble fine gauze or beautiful lace or net-work;
very often these areolets are quadrangular, sometimes rhomboidal,
frequently nearly circular, and differing occasionally, as has been
before observed[1886], in the different areas: it sometimes occurs
that there are no traversing nervures[1887], when the wing of course
is without areolets. In the Heteropterous _Hemiptera_ the type of
neuration, as to the wing, seems borrowed from the _Coleoptera_, a
further proof that these are the analogues of that Order amongst
the _Haustellata_ Clairv. In these the nervures usually are few and
dispersed, and seldom form any closed areolets. If you examine any
_Scutellera_, _Pentatoma_, or _Lygæus_, you may trace the uncinated,
forked, serpentine, and insulated nervures of Coleopterous insects;
in _Gerris_ and _Velia_ there is an approach to the neuration of
some _Homopterous_ species, and in _Belostoma_ &c. the wing is
reticulated by _spurious_ nervures. In the Homopterous section
there are several types of neuration; thus the _Fulgoræ_ resemble
the _Orthoptera_ in this respect; while the _Tettigoniæ_ F., &c.,
approach nearer to the _Hymenoptera_ and _Diptera_, and have their
apical areolets circumscribed _within_ the margin by a traversing
nervure; in _Flata_, &c., the areolets are mostly formed, not by
traversing nervures, but by the branching of the longitudinal ones;
in this respect they are not unlike the _Lepidoptera_. In this
last-named Order there are some variations with regard to their
neuration--thus, amongst the _butterflies_ in _Urania_, &c., there is
no closed areolet in any of the wings, and almost all the nervures
diverge from the base[1888]; in _Morpho_, &c., there is only one in
the primary wing[1889]; in _Heliconia_, &c., there is one in both
wings; amongst the _moths_, in the _Bombyces_ L., this is divided
into _two_, and in _Cossus labyrinthicus_ Don. into _three_ areolets:
in some butterflies (_Lycæna_) there is one insulated nervure[1890],
and in others (_Hesperia_) there are two[1891]; in these two last,
and _Heliconia_, _Urania_, &c., the end of the Costal Area is
divided into several areolets by oblique nervures[1892], which
gives them some analogy to the wings of many _Neuroptera_; and at
the base of this Area, in _Morpho_, is a roundish areolet[1893]. In
this Order the externo-medial and interno-medial nervures coalesce
into one, and are only represented separately by their first and
third branches[1894]. In the _Neuroptera_ Order the general type
of neuration is borrowed from the _Orthoptera_; but in _Osmylus_,
_Termes_, &c., there is an approach to that of _Flata_ in the
Homopterous _Hemiptera_, and in _Psocus_ to others of that section;
in the second of these genera the nervures, except those of the
costal margin, are spurious.
I now come to the Order in which M. Jurine has laboured with so
much success, I mean the _Hymenoptera_; and I only regret that his
labours were directed to so small a portion of the Class _Insecta_,
and in that portion only to a part of the upper wing; I say only
a _part_, because all those areolets of the posterior part of the
wing, in some cases amounting to _five_[1895], that lie behind his
_cubital cellules_, are not employed by him as diagnostics, and are
left without a name. By dividing the areolets of the Intermediate
Area of these wings into _three_ portions, the _basal_, _medial_,
and _apical_[1896], I have endeavoured to remedy this defect, and by
naming each set of areolets in the middle portion, as you will see in
the Orismological Definitions, under the term _Areolets_, you will
find it easy to describe any given areolet and its place in the wing;
those of the base may be called the _anterior_, _intermediate_, and
_posterior_, where _three_ occur; and the first and last of these
terms will suffice where there are only _two_; the apical areolets,
or those that are open to the margin, may be called, _first_,
_second_, and _third_ in the order of their occurrence, reckoning
from the anterior or costal margin.
In this Order it is curious to trace the progress of neuration in
the wings of different genera. Thus in _Psilus_ only the _costal_
nervure and the _stigma_ are to be traced[1897]; in _Chalcis_ the
_postcostal_ and _stigma_[1898]; in _Codrus_ and _Leucospis_ the
_costal_, _postcostal_, _stigma_, and a nervure representing the
_externo-medial_ and _interno-medial_ coalescing into one[1899];
in _Omalus_ the _basilar_ areolets appear[1900]; in _Crabro_ both
_basilar_ and _medial_[1901]; in _Cynips basilar_, _medial_, and
_apical_[1902]; and in _Hylotoma_ the wing is filled with its
greatest complement of areolets[1903]. The medial areolets of
the Intermediate Area, as you will see in the definitions, form
_three_ distinct series; these may be called the _protomesal_,
_deuteromesal_, and _tritomesal_, reckoning from the postcostal
areolets; the first of these corresponds with the cubital cellules of
Jurine. These series may be expressed, according to the number of
their areolets; by figures, the protomesal standing first. They vary
much in this respect in the different genera. Thus in _Cyclostoma_
K.[1904], reckoning the didymous areolet as two, the numbers
will stand 4:2:1; in _Hylotoma_, &c., 3:2:1[1905]; in _Aulacus_,
&c., 2:2:1[1906]; in _Bracon_, &c., 2:1:1[1907]; in _Chelonus_,
2:0:1[1908]; in _Cynips erythrocephalus_ Jur., 2:0:0[1909]; in
_Formica_, 1:1:1[1910]; in _Oxybelus_, 1:0:1[1911]; in _Chrysis_,
0:1:1[1912]; and in _Cynips Rubi_ K., 1:0:0[1913]. The most natural
number is 3:2:1. The next in importance to the medial areolets of the
Intermediate Area are the _apical_, or those open to the margin; the
most usual number of them, excluding the postcostal areolets which
belong to the Costal Area, is _three_; but in _Sirex_ there is an
approach to _four_[1914]; in _Evania_ there are only _two_[1915];
and in _Philanthus_ there are none[1916]; in many, as _Prosopis_,
_Nomada_, _Andrena_[1917], though there is the usual number, they
are incomplete and do not reach the margin. The _basal_ areas are
of little importance in assisting to determine genera; they are
most commonly _two_ in number, but in _Cynips_, &c., there is only
_one_[1918]. The shape and other circumstances of the areolets vary
considerably in different genera and species: upon these however
I shall not enlarge further, but proceed in the next place to
consider very briefly the wings of the _Diptera_ Order as to their
neuration. These are not so easily made subservient to a general
plan. The _basilar_ areolets are now reduced considerably in length,
occupying merely the base of the wing[1919]; the _medial_ are become
less numerous and important[1920]; and the _apical_, in a variety
of instances, are the most conspicuous[1921]; in some wings, as in
those of _Penthetria_, the Intermediate Area has no nervures or
areolets, or only spurious ones; in _Psychoda_ the nervures diverge
from the base almost without branching, so as to form no closed
areolets[1922]; in many, the lower medial areolets are very long,
resembling the basilar in _Hymenoptera_[1923]; these are often
crowned by a single small one, as in the _Stratyomidæ_, _Tipula_,
&c., from which numerous branches proceed to the margin[1924]; but in
_Musca_ two large ones approach the margin, the anterior one having
an angle open to it[1925]; in the _Hippoboscidæ_ almost the whole of
the wing is occupied by the apical areolets[1926]; though in some
cases they are incomplete[1927].
4. I am next to consider the _position_ of wings in _repose_ and
their _folding_. The most important object of this is that when
unemployed they may occupy less space, be less in the way of the
insect, and be most effectually protected from injury. Another end is
also served by this structure,--that wings can thus be very ample,
and present a large surface to the action of the atmosphere without
incommoding the insect when it has not occasion to use them.
With respect to this head, insects may be divided into _two_
classes--namely, those whose wings in repose are covered by
wing-cases harder than the wings themselves, and those that have
no such protection. In the former the wings, though the rule
admits several exceptions, have more folds than in the latter. As
the different mode of folding the wings has been assumed for a
characteristic of the earlier Orders, I shall explain to you with as
much brevity as possible how each is circumstanced in this respect,
beginning as usual with the _Coleoptera_.
There are _two_ principal folds of the wing in this Order, which
may be named the _anal_ and the _apical_: the _former_ is when
the Anal Area or part of it is folded on the under surface of the
base of the wing; this fold is always more or less _longitudinal_:
the _latter_, the apical fold, is by means of the _commissura_
or joint of the _postcosta_ lately mentioned: which in _Hister_,
_Staphylinus_, &c., for obvious reasons[1928] is nearer the base
of the wing; in _Necrophorus_ in the middle; in _Dynastes Aloeus_
beyond the middle[1929]; in _Tenebrio Molitor_ near the apex; and
in _Dytiscus marginalis_ there appears to be no joint at all; but
the fact is, that in this insect the _postcosta_,--the termination
of which really forms the joint, the _costa_ itself being only
flexible at that point,--stands at a greater distance from the latter
at its end. Well, at this joint the above fold is made, the apex
of the wing, being first folded longitudinally, turning under and
inwards, and forming an angle, more or less acute, with the joint or
costal margin, so that the fold is not quite but nearly transverse:
this at least is the case in _Geotrupes stercorarius_ and other
Lamellicorns: in _Staphylinus_, &c., there are several transverse and
longitudinal folds, and thus the wing is more easily packed under
the short elytra; in _Molorchus_, _Necydalis_, &c., in which it is
left uncovered, except at its base, the anal fold takes place, and
the apical in some degree; a short portion near the apex forming an
obtuse angle with the margin; in _Atractocerus_ the wing appears to
be only _longitudinally_ folded; and in _Buprestis vittata_ only
the _anal_ fold is to be detected. Besides these transverse and
longitudinal folds these organs, in many beetles, have an infinity of
fine corrugations, which ramify like the nervures of the _tegmina_
of _Flata_[1930], &c., proceeding from the Costal Area or the disk
of the wing to the posterior margin; the object of these plicatures
is doubtless to present a more ample surface to the action of the
atmosphere in flight[1931]. When all these folds have been made in
a Coleopterous wing, the apex of the one at its posterior margin
crosses or rests upon that of the other[1932].
In the _Dermaptera_[1933], at least the common earwig, there is a
triple transverse fold of the wing, and besides this it has numerous
longitudinal ones like those of a fan, each of the diverging nervures
representing one of the sticks. In the _Strepsiptera_ the folds
are only longitudinal; a circumstance which, besides the form and
neuration of the wing, sufficiently attests that its station is
more near the _Orthoptera_ and _Coleoptera_ than the _Diptera_. We
next come to the _Orthoptera_[1934]; in these the folds in general
are longitudinal; and those of the Anal Area in particular, either
in whole or in part, exact counterparts of a fan: wherever there
is a straight nervure, there is usually a fold or a tendency to
it; this is the case even with the short oblique ones observable
in the Intermediate Area of _Blatta_: in this tribe the Anal Area,
or a considerable portion of it, is folded under the rest of the
wing, and the whole lies on the back of the animal, so that in this
wing there are only two primary folds; but in those with a narrower
body, as _Phasma_, &c., there are more, and the Anal Area, folded
like a fan, lies horizontally on the back; the Costal is vertically
applied to the sides, and the Intermediate is between both, as in the
_tegmina_[1935]. In _Gryllus_ Latr., _Gryllotalpa_, &c., when the
wings are folded, the end of the Anal Area projects so as to present
the appearance of two tails[1936]; and in that remarkable Chinese
animal _Gryllus monstrosus_, in which these tails are very long,
they are convolute like those of some quadrupeds[1937]. It is to be
observed that in the secondary folds of these wings the angles of the
folds are surmounted by a nervure.
In both sections of the _Hemiptera_ Order, as in the _Coleoptera_,
the Anal Area is turned under the wing and lies over the back of
the insect; this is the only _primary_ fold, but besides there are
several longitudinal semifolds or _secondary_ ones, in which one
part of the surface forms an obtuse angle with another; and in
_Tettigonia_, &c., these folds ramify in the wings as well as in
the _tegmina_ at the margin: a number of semifolds also, sometimes
transverse and sometimes oblique, run in pairs from each side of
every nervure of the disk of both _tegmina_ and wings in the genus
last named, the use of which has been before mentioned[1938].
We now come to those Orders that have _four_ membranous wings: first,
I shall consider the _Lepidoptera_. With respect to the position of
their wings in repose some variations take place. In the majority
of the _day-fliers_ (_Papilio_ L.), when the animal reposes the
wings are applied to each other by their upper surface so as to be
_vertical_; but in the skippers (_Hesperia_), the secondary wings
assume a _horizontal_ position, while the primary are _vertical_ but
applied to each other. In the _Crepuscular_ tribes (_Sphinx_ L.)
the upper wings are incumbent on the lower, and deflexed. In the
_night-fliers_ (_Phalæna_ L.) the types of position are various.
In some _Attacus_, _Saturnia_, _Noctua_, &c., the wings cover each
other, and are a little inclined from a horizontal position; in
_Gastropacha_, _Odenesis_, and some other _Bombycidæ_, they are
deflexed, and the anterior margin of the under wing projects beyond
that of the upper: in some of the _Tineæ_ L., as _Crambus_, the wings
are convoluted, and in others, _Galleria_, they are applied close to
the sides of the body, and being elevated at the apex, terminate, to
use a French term--_en queue de coq_: in _Noctua_, _Geometra_, &c.,
the wings usually cover the abdomen, and are nearly horizontal. With
regard to the _folds_ of their wings, the Anal Area of the secondary
is the only part that has any striking one; in _Papilio Hector_
and affinities it turns up so as to defend the sides and part of
the back of the abdomen; in _Morpho Teucer_ it turns down, and
meeting that of the opposite wing, forms a semitube which receives
and shelters that part below. In the _Crepuscular_ and _Nocturnal_
Lepidoptera this fold, especially in the former, is very slight. With
respect to semifolds in the _Diurnal_, there is one originating in
the disk, between each of the nervures, that goes to the margin of
the wing; likewise the under wings, particularly of many _Noctuæ_,
_Arctiæ_, &c., have many longitudinal semifolds.
In the _Neuroptera_ Order several variations take place with regard
to the _position_ of these organs in repose: thus, in _Æshna_,
_Libellula_, &c., they continue expanded; in _Argion_ they are
applied to the body; in _Myrmeleon_ the upper are horizontally
incumbent on the lower; in _Hemerobius_ they incline to the horizon.
With regard to their _folds_ in _Æshna_, &c., the longitudinal
nervures alternately form the summit or the bottom of a semifold, as
do those branches that terminate in the posterior margin; this kind
of plicature may be observed, but in a less degree, in _Ascalaphus_,
_Myrmeleon_, &c.; in _Panorpa_ every nervure is the ridge of a
slight fold; in _Termes_, on the contrary, it forms its bottom. In
the _Trichoptera_, the under wing being much more ample than the
upper, the Anal Area forms a fold under the wing, and there seem
longitudinal secondary folds besides.
We now come to the _Hymenoptera_. In this Order the wings, as to
their position in repose, are usually incumbent upon each other,
and cover the abdomen; in the _Vespidæ_, however, they are placed
parallel to the body, but do not cover it. Before I notice the
plicature of these wings, I must recall your attention to what I
lately observed[1939] with regard to Jurine's _bullæ_ (bubbles),
but which are really the _joints_ of the nervures, as they are to
be found only where the folds pass; and where they exist they are
an index by which the folds, or rather semifolds, may be traced. I
counted eleven of these little joints in the upper wing of _Andrena
cineraria_; sometimes, however, instead of a _bulla_, a nervure
stops short to admit the fold. Wings in this Order have often three
longitudinal semifolds more or less conspicuous; these you may
trace in the saw-flies (_Tenthredo_ L.), whose wings Linné terms
_tumidæ_, by which term he would indicate the elevation of the
whole surface produced by this structure; in the under wings of
these, and _Scolia_, _Bembex_, &c., the Anal Area is turned under
the wing, as in many preceding tribes[1940]: in _Sirex_, &c., that
Area of the upper wing turns upwards, forming an acute angle with
the rest of the organ; the same circumstance distinguishes the under
wing in the _Ichneumonidæ_. Several apical semifolds, marked by a
pellucid streak, distinguish _Tiphia_ F., and in _Bombus_, _Bembex_,
&c., an infinity of branching ones, like those before described in
_Coleoptera_, corrugate the apical margin. In the _Vespidæ_ the
_upper_ wings are folded longitudinally into _three_ nearly equal
portions, but in the _under_ ones the Anal Area only forms the fold.
In the _Diptera_ Order, as to their _position_ when at rest, the
wings are mostly incumbent one on the other; but in _Psychoda_
they are deflexed, so as to form a kind of penthouse. With regard
to their _plication_, in some, _Tipula oleracea_, &c., a slight
oblique semifold runs from the _stigma_ to the apical margin, and
the Anal Area has two, as it has in many _Muscidæ_, itself forming
nearly a right angle with the rest of the wing; besides these it is
corrugated with minute transverse semifolds, which are observable
also in several other Dipterous insects; in many _Stratyomidæ_ they
are oblique, and run from the disk to the posterior margin; and in
_Asilus_, _Bombylius_, &c., they are wavy.
5. We are next to say something upon the _shape_ of wings: this,
though apparently extremely various in the different Orders and
tribes, may I think be traced in every wing to one original
prototype, a _triangle_ with the largest angle rounded and subtended
by the anterior or costal margin: in some, as the _Coleoptera_,
_Orthoptera_, &c., this type of formation is a _right-angled_
triangle[1941]; and in others, as in the _Hymenoptera_, _Diptera_,
&c., the majority of the _Neuroptera_, &c., it is an _obtusangled_
one[1942]; it may be further observed, that in receding from these
forms wings very often assume that of the half or quadrant of
some regular figure, as we shall see when we consider those of
the different Orders. Another general observation I shall first
mention,--that these organs are universally narrowest at their
base and widest at the apex, provided we consider as the apex the
termination outwards of the three Areas; otherwise we might say
that wings in the _Coleoptera_, _Orthoptera_, &c., were wider at
the base than at the apex[1943]. The wings in the former Order, and
in several of the Heteropterous _Hemiptera_, as _Gerris_, _Velia_,
&c., may in general, as to their _shape_, be termed semicordate
or semiovate[1944]; in the _Dermaptera_ they incline to an oval
figure[1945]: in the _Strepsiptera_, _Orthoptera_, most Homopterous
and many Heteropterous _Hemiptera_, they approach to the quadrant
of a circle; in a considerable portion of the _Lepidoptera_ the two
under wings, if united at their posterior margin, approach a circular
form; the upper ones vary a little from the prototype of the under
ones, forming an obtusangled triangle[1946]; in many _Neuroptera_
the _primary_ wings may be called oblong or linear-oblong, while the
_secondary_ betray more evidently the _right-angled_ or _obtusangled_
triangle; in the _Hymenoptera_ this latter form is every where
conspicuous, with little deviation, except in the rounding of the
angles[1947]; and, finally, in the _Diptera_ this form shades off
again into an oblong, ovate, or linear shape, the wing being most
commonly attenuated at the base into a kind of footstalk[1948]. Some
singular variations with respect to the termination or marginal
processes of the wings are exhibited by many _Lepidoptera_; thus in
_Attacus Atlas_, &c., the primary wings are falcated or hooked at
their apex[1949]; and in great numbers both wings are there scolloped
into alternate bays and capes, if I may so speak, varying in depth
and length[1950]. There is usually a sinus between every pair of
nervures, each of which terminates in the adjoining prominence, as
a fold does in the sinus[1951]. Where present, in the _primary_
wings there are _eight_ of these sinuses, and in the _secondary_,
where they are most usual, _seven_; some are remarkable for the long
_tails_ which distinguish their secondary wings; those in _Papilio_
are usually an elongation of the fifth, from the anterior margin, of
the prominences before mentioned, into a spathula-shaped diverging
process, varying in length and width[1952]: but in _P. Ulysses_ it
does not diverge; and in _P. Podalirius_ it is linear. They are
found also in other subgenera; thus in _Urania Patroclus_ there are
_two_; in _U. Riphæus_ _three_; in _Erycina Cupido_ _five_; and in
_E. Endymion_ _six_ of these tails; in some, as in _E. Dorylas_, the
whole wing seems to form the tail; in others again, as in _Hesperia
Proteus_ and _Bombyx Luna_, it is an elongation of the anal angle.
Other wings in this Order are divided into lobes resembling feathers,
as you may see in _Pterophorus hexadactylus_, &c.[1953]
6. We are next to consider the _clothing_ of wings: these, in the
Orders in which they are covered by elytra, tegmina, or hemelytra,
are generally naked, except that the spots in those of _Fulgora
laternaria_, _serrata_, &c., and the whole wing in _Flata_,
_Aleyrodes_, and others, are covered with a kind of farinaceous
powder; but in all the remaining Orders, hairs or scales are more
or less implanted in these organs: as the _Lepidoptera_ are the
most remarkable for the clothing of their wings, I shall leave them
till the last, and begin with the _Neuroptera_. If you lightly
pass your finger over the wing of any dragon-fly (_Libellula_ F.,
_Æshna_ F.), from the apex towards the base, you will find that the
longitudinal nervures are, as it were, serrulated with very minute
bristles, which point towards the extremity; if you next move the
finger across the wing, from the posterior to the anterior margin, a
similar circumstance will strike you. M. Chabrier conjectures that,
amongst other uses[1954], these hairs may contribute to fix the
atmospheric fluid when the wings are depressed in flight, while it
glides over them as they rise[1955]; in _Ascalaphus_, _Myrmeleon_,
_Nemoptera_, _Hemerobius_, &c., the nervures are more visibly
bristled; the bristles diverging on each side from the longitudinal
ones, but all pointing towards the apex from the connecting or
transverse ones; in _Panorpa_, besides these bristles, short hairs,
pointing the same way, are thickly planted in the membrane of the
wing; and in _Hemerobius_ the margins of the wing are fringed; in
the _Ephemerina_, _Corydalis_, &c., the wings are naked. In the
_Trichoptera_ Order, as their name imports, they are covered with
minute decumbent hairs, less easily seen but still existing in the
secondary pair. In the _Hymenoptera_ in general the wings are covered
with minute hairs or bristles; but in _Tiphia_, _Scolia_--with the
exception of _S. Radula_ and affinities in which they are hairy--and
others, the wings are nearly naked; in _Pompilus_, _Pepsis_, &c.,
the hairs are infinitely numerous and very short; in the _Sphecidæ_,
_Mutilla_, &c., they are more distinct, longer, and less numerous;
in the humble-bee (_Bombus_) and many others the apex of the wing is
darkened by a large number of more conspicuous hairs, each of which
seems to spring from a minute tubercle: as these tubercles are in
a part of the wing that is strengthened by few nervures, they may
probably be intended to supply their place, in giving firmness and
tension to this part. The wings of _Diptera_, under the present head,
may be viewed with regard to the hairs that are implanted in the
_membrane_ of the wing, in its _nervures_, and in its _margin_. In
the first view, in _Stratyomis_ and immediate affinities the wing is
nearly naked; but in _Xylophagus_, _Beris_, and the great majority
of the Order, the membrane of the wings is thickly planted with
innumerable very minute bristles, not to be seen but under a powerful
lens, often black, and seemingly crowning a little prominence, and
giving the wing an appearance of the finest net-work. As to the
clothing of the nervures, the costal, in _Anthrax_, _Bombylius_,
&c., is often remarkably bristly at the base, with hairs intermixed;
in _Œstrus Ovis_, in the inner margin or edge of this nervure, is
a single series of bristles, or rather short spines, like so many
black points; in _Œ. Equi_ the whole _costa_ is covered with short
decumbent hairs or bristles; in _Musca pagana_ F., just at the apex
of the costal areolet, that nervure is armed with a spur or diverging
bristle larger than the rest, which is also to be found in many
others of the _Muscidæ_, some of which have two and others more of
these spurs. The little moth-like midges (_Psychoda_ Latr., _Hirtæa_
F.) at first appear to have the whole surface of their wings covered
with hairs; but upon a closer examination it will be seen that they
are planted in the nervures, from each of which they diverge, so
as under a lens to give it a very elegant appearance[1956]. This
fly has its wings beautifully fringed with fine hairs, the _third_
circumstance to be attended to under this head; in the Tipulidans,
and many others of this Order, the apex and posterior margin are
also finely fringed with short hairs. Some Dipterous insects make a
near approach to the _Lepidoptera_ in the _covering_ of their wings:
in the common gnat, when the wings are not rubbed, the nervures are
adorned by a double series of _scales_, and the marginal fringe also
consists of them[1957]; and in a Georgian genus, which appears in
some degree to connect _Culex_ with _Anthrax_ &c., there are scales
scattered upon the membrane as well as upon the nervures; besides,
its antennæ[1958] and abdomen are also covered with them.
The Order, the clothing of whose organs of flight excites the
admiration of the most incurious beholder, is that to which the
excursive butterfly belongs, the _Lepidoptera_. The gorgeous wings of
these universal favourites, as well as those of the hawk-moths and
moths, owe all their beauty, not to the _substance_ of which they are
composed, but to an infinite number of little _plumes_ or _scales_
so thickly planted in their upper and under surface, as in the great
majority entirely to conceal that substance. Whether these are really
most analogous to plumes or scales has been thought doubtful. De
Geer is inclined to think, from their terminating at their lower
end in little quills and other circumstances, that they resemble
_feathers_ as much as scales[1959]; Reaumur on the contrary suspects
that they come nearer to _scales_[1960]. Their substance, approaching
to membrane, seems to make further for the former opinion, and their
shape and the indentations that often occur in their extremity,
furnish an additional argument for the latter. Their numbers are
infinite; Leeuwenhoek found more than 400,000 on the wings of the
silk-worm moth (_Bombyx Mori_)[1961]; and in those of some of the
larger moths and butterflies the number must greatly exceed this.
You will observe however that in many _Lepidoptera_ the wings are
_partially_, and in some instances _generally_, transparent: thus in
_Hesperia Proteus_, a butterfly before noticed for the long tail that
distinguishes its secondary wings, there are many transparent spots;
in _Attacus Atlas_, one of the largest of moths, and its affinities,
there is as it were a _window_ in each wing formed by a transparent
triangular space; in _A. Polyphemus_, _Paphia_, &c., the pupil of
the ocellus is transparent, which in the former is divided by a
nervure. In several of the Heliconian butterflies, and in _Zygæna_
F., &c., the greater part of both wings is transparent, with scales
only upon their nervures, round their margin, or forming certain
bands or spots upon them; in _Parnassius Apollo_, _Mnemosyne_, &c.,
the scales are so arranged as not wholly to cover the wings, which
renders them semidiaphanous; and in some (_Nudaria_) the wings are
intirely denuded. With regard to _size_, the scales vary often
considerably in different tribes; in _Heliconia_ they appear to be
more minute than in the rest; and in _Castnia_ they are the largest
and coarsest; the extremity of the wings of Lepidopterous insects in
general is fringed with longer scales than their surfaces, and even
those of the last in the same wing; sometimes vary in magnitude.
The little seeming tooth that projects from the middle of the
posterior margin in the upper wings of _Notodonta_, a subgenus of
_Bombyx_ L., is merely produced by some longer diverging hairs. The
_shape_ and _figure_ also of scales are very various--some being
long and slender; others short and broad; some nearly round; others
oval, ovate, or oblong; others spathulate; others panduriform or
parabolical; some again almost square or rhomboidal; many triangular;
some representing an isosceles triangle, and others an equilateral
one; lastly, some are lanceolate and others linear; again, some have
a very short pedicle and others a very long one: with regard to their
_extremity_; some are intire, without projecting points or incisions,
while others are furnished with them: of these some terminate in a
single long mucro, others have several shorter ones; some are armed
with teeth, varying in number from two to thirteen in different
species[1962]. Many other forms might be enumerated, but these are
sufficient to give you a general notion of the infinite variety of
this part of the works of the CREATOR. I must next say a word or two
upon their _arrangement_ on the wing. In most instances this is in
transverse lines, which sometimes vary a little from a rectilinear
course, and the extremity of the scales of one row reposes on the
base of those of the succeeding one, so that in this respect their
arrangement is like that of tiles in a roof: in some cases it is
not so regular: thus the minute scales on the wings of _Parnassius
Apollo_, and others with subdiaphanous wings, are arranged without
order; in _Pieris_ and other Diurnal _Lepidoptera_, and many of the
Crepuscular and Nocturnal, there appears to be a _double_ layer of
scales on both sides of the wing; the under layer usually consisting
of _white_ ones. If you denude the wings of any butterfly, which you
may easily do by scraping it lightly on both sides with a penknife,
you will be amused to trace the lines in which the scales were
planted, consisting of innumerable minute dots: the lines of the
under side, in some cases, so cut those of the upper side, as by
their intersection to form lozenges. With regard to the position of
the scales on the wing, they usually lie flat, but sometimes their
extremity is incurved: in the beautiful _Argynnis Vanillæ_ a very
singular appearance of numerous transverse ridges is produced by the
extremity of those scales that cover the longitudinal nervures of the
primary wings, except at the base, being recurved.
But though the general clothing of the wings of _Lepidoptera_ consists
of these little scales, yet in some cases they are either replaced by
_hairs_ or mixed with them. Thus, in the _clear_ parts of the wings of
Heliconians, _Attaci_, &c., short inconspicuous hairs are planted; in
a large number of the Orders the _upper_ side of the Anal Area of the
secondary wings is hairy; in several Crepusculars (_Sphinx Phœnix_,
&c.), where there is a double layer as before mentioned, the upper
one consists of dense hairs, except at the apex, and the lower one
of scales; and in most of them the scales of the primary wings are
piliform, and the secondary are covered by what approach very near to
real hairs; many of the _Attaci_ are similarly circumstanced: the four
wings of _A. Cytherea_ are also covered externally with hair.
7. Before I conclude this long diatribe on the organs of flight of
insects, I must not omit some notice of the infinite diversity of
_colours_ with which their wings are often variegated and adorned
by the CREATOR, who loves to delight us by the beauty, as well as
to astonish and awe us by the immensity and grandeur of his works.
Though the wings in every Order exhibit instances of brilliant and
beautiful colouring, yet those of the _Lepidoptera_ in this respect
infinitely excel them all, and to these, under this head, after
noticing a few in the less privileged Orders, my observations will
be confined. Although in the _Coleoptera_ the wings are seldom
distinguished by their splendour; yet those of some _Cetoniadæ_,
as _Cetonia africana_, are extremely brilliant, and resemble those
of many _Xylocopæ_ in the lovely violet hue that adorns them:
amongst the _Orthoptera_ some _Pterophyllæ_, and in the Homopterous
_Hemiptera_ some _Fulgoræ_, emulate the _Lepidoptera_ in the _ocelli_
that give a kind of life to these organs[1963]; and a vast number of
the destructive tribe of locusts (_Locusta_ Leach) are remarkable for
the fine colours and gaiety of their wings[1964]; in the _Neuroptera_
numerous _Libellulinæ_ emulate the Heliconian butterflies by their
maculation; and in the genus _Ascalaphus_, which represents the
_Lepidoptera_ by its clubbed antennæ[1965], many also have the
resemblance increased by the painting of their wings, so that some
Entomologists have actually considered some of them as belonging to
that Order[1966]; the wings of the _Xylocopæ_, before alluded to,
sometimes add to the deep tints of the violet--which also prevail
in the wings of several _Diptera_--towards their extremity the most
brilliant metallic green or copper varying,
"As the site varies in the gazer's hand,"
and even those wings that consist of clear colourless membrane
are often rendered extremely beautiful from the reflection of the
prismatic colours. I should undertake an endless task did I attempt
to specify all the modes of marking, clouding, and spotting, that
variegate a wing, and all the shades of colour that paint it, amongst
the Lepidopterous tribes; I shall therefore confine myself to a
few of the principal, especially those that distinguish particular
tribes and families. Of whole coloured wings--I know none that dazzle
the eye of the beholder so much as the upper surface of those of
_Morpho Menelaus_ and _Telemachus_: Linné justly observes that there
is scarcely any thing in nature that for brightness and splendour
can be paralleled with this colour; it is a kind of rich ultramarine
that vies with the deepest and purest azure of the sky; and what
must cause a striking contrast in flight, the prone surface of the
wings is as dull and dark as the supine is brilliant, so that one
can conceive this animal to appear like a planet in full radiance,
and under eclipse, as its wings open and shut in the blaze of a
tropical sun: another butterfly, _Papilio Ulysses_, by its radiating
cerulean disk, surrounded on every side by a margin intensely black,
gives the idea of light first emerging from primeval obscurity; it
was probably this idea of light shining in darkness that induced
Linné to give it the name of the wisest of the Greeks in a dark and
barbarous age. I know no insect upon which the sight rests with
such untired pleasure, as upon the lovely butterfly that bears the
name of the unhappy Trojan king (_P. Priamus_); the contrast of the
rich green and black of the velvet of its wings with each other,
and with the orange of its abdomen, is beyond expression regal and
magnificent. But peculiar beauties of colour sometimes distinguish
whole _tribes_ as well as _individuals_. What can be more lovely
than that tribe of little butterflies that flit around us every
where in our summer rambles, which are called _blues_, and which
exhibit the various tints of the sky? _Lycæna Adonis_ of this tribe
scarcely yields to any exotic butterfly in the celestial purity of
its azure wings: our native _coppers_ also, _Lycæna dispar_[1967],
_Virgaureæ_, &c., are remarkable for the fulgid colour of these
organs; in _Argynnis_ the upper side of their wings is tawny,
spotted with black, while the under side of the secondary ones is
very often adorned by the appearance of _silver_ spots. How this
remarkable effect of metallic lustre, so often reflected by spots in
the wings of butterflies, is produced, seems not to have occupied
the attention of Entomologists. M. Audebert is of opinion that the
similar lustre of the plumes of the humming birds (_Trochilus_) is
owing to their density, to the polish of their surface, and to the
great number of little minute concave mirrors which are observable
on their little beards[1968]. But these observations will not apply
to the scales of the wings of butterflies, which are always very
thin and generally very flat: in some instances, as in _Morpho
Menelaus_, there appears more than one very slight channel upon a
scale; but this takes place also in others that reflect no lustre.
Their metallic hues must therefore principally be occasioned by
the high polish of their surface and the richness of their tints.
It is the purity of the white, in conjunction with their shining
surface, contrasted with the dull opaque colour of the under side
of the secondary wings, that causes the spots that decorate those
of the Fritillaries (_Argynnis_) to emulate the lustre of silver.
In _Papilio_ the Trojans are distinguished by the black wings with
sanguine spots, and the Greeks by the same with yellow spots; but
these have proved in some instances only sexual distinctions[1969].
In the _Danai candidi_ L. the colour of the tribe may be described
as sacred to the _day_, since every shade, from white or the palest
yellow to full orange, is exhibited by them. The yellows prevail also
in those _Noctuæ_, the trivial names of which Linné made to end in
_ago_, as _N. Fulvago_, _Citrago_, &c. I must not conclude this part
of my subject without noticing one of the most striking ornaments of
the wings of _Lepidoptera_, the many-coloured _eyes_ which decorate
so large a number of them. Some few birds, as the Peacock and Argus
Pheasant, have been decked by their CREATOR very conspicuously with
this almost dazzling glory; but in the insects just named it meets us
every where. Some, as one of our most beautiful butterflies, _Vanessa
Io_[1970], have them both on the primary and secondary wings;
others, as _Noctua Bubo_[1971], only on the primary; others again,
as _Smerinthus ocellata_[1972], only on the secondary: in some also
they are on both sides of the wing, as in _Hipparchia Ægeria_[1973],
and in others only on the upper side, as in _Vanessa Io_; in others
again only on the under side, as in _Morpho Teucer_[1974]: in some
likewise they are very large, as in the secondary wings of the same
butterfly: and in others very small, as in those in the wings of the
blues (_Lycæna_). Once more, in some they consist only of _iris_ and
_pupil_, as in _Hipparchia Semele_, and in others of many concentric
circles besides, as in _Morpho Teucer_, &c.
v. _Legs_[1975]. We are next to consider those organs of motion
affixed to the trunk, by which insects transport themselves
from one place to another on the earth or in the water, and by
which also they perform various operations connected with their
economy[1976]. In treating of them we should consider their _number_;
_kind_; _substance_; _articulation_ with the _trunk_; _position_;
_proportions_; _clothing_; _composition_; _folding_; and _motions_.
1. _Number._ Having before very fully explained to you the number
and kind of the legs of insects in their _preparatory_ states[1977],
I shall now confine myself to the consideration of these organs
in their _perfect_ or last state; beginning with their _number_.
Insects, properly so called, as I formerly observed[1978], in this
state, including the anterior pair or arms, have only _six_ legs,
none exceeding or falling short of this number; but in several of
the Diurnal _Lepidoptera_ (_Vanessa_, &c.) the anterior pair are
_spurious_, or at least not used as legs, the tarsi having neither
joints nor claws[1979]; this in some cases is said to be only a
_sexual_ distinction[1980]. In _Onitis_, _Phanæus_, and some other
_Scarabæidæ_ M^cL., the arm has either none or a spurious tarsus or
_manus_[1981]; which in the first of these genera is also a sexual
character. From both these instances we see that walking is only a
_secondary_ use of forelegs in the insect tribes. Besides insects
proper, a whole tribe of mites (_Caris_ Latr., _Leptus_ Latr., _Astoma_
Latr., _Ocypete_ Leach) have only _six_ legs; the rest, and the
_Arachnida_ in general, have _eight_; in the _Myriapods_, _Pollyxenus_
has _twelve pairs_; _Scutigera_ has _fifteen_; the terrestrial
_Glomerides_ (_G. Armadillo_, &c.) _sixteen_; and the oceanic (_G.
ovalis_) _twenty_; the oriental _Scolopendræ_ Leach, _twenty-one_;
_Polydesmus_ has usually about _thirty pairs_; _Craspedosoma_,
_fifty_; _Geophilus electricus_ at least _sixty_; in _Iulus terrestris_
there are more than _seventy_; in _I. sabulosus_ nearly _one hundred_;
in _I. fuscus_, 124; and in _I. maximus_ 134 pairs or 268 single legs.
But with respect to the _Geophili_, _Iuli_, &c., it is to be observed,
that the number of pairs varies in different individuals; and the
circumstance that has been before mentioned[1982], that these animals
keep acquiring legs in their progress to the perfect state, instead
of losing them, renders it difficult to ascertain what is the natural
number of pairs in any species.
2. _Kinds._ Upon a former occasion I gave you a sufficiently full
account of the _kinds_ of legs[1982], and I have also assigned my
reasons for giving a different denomination to the _anterior_ legs
under certain circumstances[1983]; I shall not therefore enlarge
further upon this head.
3. _Substance._ The _substance_ of the legs is generally regulated
more or less by that of the rest of the body, only in soft-bodied
insects they seem usually more firm and unbending. Each joint is a
tube, including the moving muscles, nerves, and air vessels.
4. _Articulation with the Trunk._ M. Cuvier has observed that the
hip (_coxa_), which is the joint that unites the leg with the body,
rather inosculates, in its acetabulum, than articulates in any
precise manner[1984]; but this observation, though true of a great
many, will not apply universally, for the legs of _Orthopterous_
insects, and of most of the subsequent Orders, are _suspended_
rather than inosculating. Even in many _Coleoptera_ a difference
is observable in this respect. I have before mentioned that what
are called the _puncta ordinaria_, which distinguish the sides of
the _prothorax_ of many _Scarabæidæ_ and _Geotrupidæ_, form a base
for an elevation of the interior surface with which the extremity
of the base of the clavicle, which plunges deep into the breast,
ginglymates[1985]; this structure may also be found in other
Lamellicorns, as the stag-beetle (_Lucanus_) and _Dynastes_, that
have not those excavations; in these last it is an elevated ridge
forming a segment of a circle with, it should seem, a posterior
channel, receiving a corresponding cavity and protuberance of the
clavicle. With regard to the mid-leg, in _Copris_, the _coxa_ is
emboxed in a nearly longitudinal cavity of the _medipectus_, and the
_coxa_ of the hind-leg anteriorly is suspended to a transverse cavity
of the _postpectus_, but posteriorly it is received by a cavity of
the first segment of the abdomen; so that it may be regarded as
suspended anteriorly, and inosculating posteriorly.
In some tribes of this Order, as the Weevils (_Curculio_ L.) and
Capricorns (_Cerambyx_), the coxæ of the four anterior legs are
subglobose[1986] and extremely lubricous, and are received each by
a socket that fits it, and is equally lubricous. In the bottom of
this externally, and in the head of the coxa, is an orifice for
the transmission of muscles, nerves, and bronchiæ; but the coxa
is suspended by ligament in the socket. This structure approaches
as near the ball and socket as the nature of the insect skeleton
will permit; the high polish of the articulations acts the part of
_synovia_, and the motion is in some degree rotatory or versatile,
whereas in _Copris_, &c., lately mentioned, it seems to be more
limited, and is probably, at least in the mid- and hind-legs, only
in two directions; in the middle pair, probably, from the _coxæ_
being in a position parallel with the breast, opposite to that of the
hind pair. In _Dytiscus_ L., _Carabus_ L., and some other beetles,
the coxæ, especially the posterior pair, appear to be fixed and
incapable of motion. In many insects these coxæ seem to belong as
much to the abdomen as to the trunk. We have just seen this to be the
case in _Copris_, &c.; and in the _Lepidoptera_, if the former be
separated from the latter, the legs will be detached with it.
4. _Location._ We are now to consider the _location_ and _position_
of the legs, both in general and with respect to each other. And
first, as has been before stated, we may observe that, in the
hexapods with wings, the _arms_ belong to the _manitrunk_, and are
attached to the _antepectus_ on each side the _prosternum_; and the
two pair of _legs_ to the _alitrunk_, the _mid-legs_ being attached
to the _medipectus_, between the _scapularia_ and _mesosternum_; and
the _hind-legs_ to the _postpectus_, between the _parapleura_ and
the _posternum_; and further, that the _arms_ are opposed to the
_prothorax_: the _mid-legs_ to the _mesothorax_ and the _primary_
organs of flight; and the _hind-legs_ to the _metathorax_ and the
_secondary_ organs of flight; though in some cases the wings appear
to be _behind_ the legs and in others _before_ them: thus, in
_Panorpa_, the former are nearer the head than the latter; but in
the _Libellulina_ the reverse of this takes place, the legs being
much nearer the head than the wings: in both cases, however, the
_scapularia_ and _parapleuræ_ run from the legs to the wings, but
in an oblique direction; and in _Panorpa_ these pieces assume the
appearance of articulations of the legs. In most of the _apterous_
hexapods they appear to be attached laterally between the _thorax_
and the _pectus_[1987]; but in the flea (_Pulex_) they are _ventral_.
In this tribe the arms are usually stated to be inserted in the
_head_[1988]: but I once succeeded in separating the head of a
flea from the trunk, and these organs remained attached to the
latter[1989]. As to the _Octopods_ and _Arachnidæ_, in the mites
(_Acarus_ L.) they are lateral, and in their analogues, the spiders
(_Aranea_ L.), they emerge between the thorax and the breast,
which last they nearly surround; in the _Phalangidæ_ the bases of
the coxæ approach near to each other, being separated only by a
narrow _sternum_; in their antagonists, _Chelifer_ and _Scorpio_,
they apply to each other, the anterior ones acting as _maxillæ_.
In the _myriapods_ the legs of the _Chilopoda_ Latr., and some
_Chilognatha_, as _Glomeris_, are inserted laterally, a single pair
in a segment; but in _Iulus_ L. their attachment is ventral, the coxæ
seem to spring from a common base, and there are two pair to each
segment[1990], except the three first, which bear each a single pair.
I shall next consider how the legs are located with respect to each
other. To render this clear to you I shall represent each of the
variations, which amount in all to twelve in the hexapods that have
fallen under my notice, by six dots.
1. [Illustration: dots] In this arrangement the legs are all planted
near to each other, there being little or no interval between the
pairs, and between the legs of each pair. It is exemplified in the
_Lepidoptera_, _Blatta_, and many _Diptera_.
2. [Illustration: dots] Similar to the preceding, but the anterior pair
are distant from the two posterior; exemplified in the bees (_Apis_)
and most _Hymenoptera_; _Chironomus_; _Scutellera_; _Pachysoma_ K.[1991]
3. [Illustration: dots] Like the last, but the posterior pair is
distant from the two anterior. _Examples_: _Silpha_, _Necrophorus_,
_Telephorus_, &c.
4. [Illustration: dots] Similar to the last, but the legs of the
posterior pair are more distant from each other than the four
anterior. _Ex. Curculio_ L.
5. [Illustration: dots] The legs of each pair near each other, but
the pairs distant. _Ex. Gibbium._
6. [Illustration: dots] Both the legs of each pair and the pairs
distant. _Ex. Blaps_, &c.
7. [Illustration: dots] Anterior pair distant from the two posterior,
and the legs of the middle pair rather more distant from each other
than those of the other pairs. _Ex. Scarabæus_ M^cL.
8. [Illustration: dots] Like the preceding, only the legs of the middle
pair are at a much greater distance from each other. _Ex. Copris_ M^cL.
9. [Illustration: dots] Legs of the two posterior pairs distant. _Ex.
Hister_, _Scaphidium_.
10. [Illustration: dots] Like the preceding, but the posterior legs
more distant than those of the middle pair. _Ex. Lygæus._
11. [Illustration: see previous] Like the last, but the legs of the
anterior pair also distant. _Ex. Velia._
12. [Illustration: see previous] The arms distant, intermediate legs
more distant, posterior legs close together. _Ex. Byrrhus_ L.
5. _Proportions._ In general the legs of some insects are
disproportionally _long_ and _slender_, as in _Phalangium Opilio_
and some species of _Gonyleptes_[1992]: those of others are
disproportionally _short_, as in _Elater_, &c. With regard to their
relative proportions, the most general rule is, in Hexapods, that
the anterior pair shall be the shortest and most slender, and the
posterior the longest and thickest; but there are many exceptions:
thus, in _Macropus longimanus_, _Clytra longimana_, &c., in the male
the _arms_ are the longest; again, a thing that very rarely occurs,
in the same sex of _Podalirius retusa_ the _intermediate legs_ are
the longest[1993]; but in _Rhina barbirostris_ and many weevils they
are the shortest: in _Saperda hirtipes_ Oliv.[1994] the _hind-legs_
are disproportionally long: with regard to _thickness_, they are in
general extremely slender in _Cicindela_, and in the _Scarabæidæ_ very
_thick_. In _Goliathus Cacicus_ the arms are more robust than the four
legs[1995]; in _Gyrinus_ the latter are more dilated than the former;
in many _Rutelidæ_, and particularly in the celebrated Kanguroo beetle
(_Scarabæus Macropus_ Franc.) the hind-legs are much the thickest; in
a new genus of weevils from Brazil (_Plectropus_ K.), the intermediate
pair are more slender than either the arms or the posterior pair.
6. _Clothing._ The _hairs_ on the legs of insects, though at first
sight they may seem unimportant, in many cases are of great use to
them, both in their ordinary avocations and motions: but as most
of these were sufficiently noticed when I treated of the sexes of
insects[1996], I shall not here repeat my observations, but confine
myself to cases not then adverted to. Some insects have all their
legs very hairy, as many spiders, the diamond beetle (_Entimus
imperialis_), or at least a species very near it and common in
Brazil[1997], &c.: in others they are nearly naked, as in the
stag-beetle. In the Crepuscular _Lepidoptera_ (_Sphinx_ L.) and
some of the Nocturnal ones (_Bombyx_ L.) the thighs are much more
hairy than the rest of the legs: and in _Lucanus_, _Geotrupes_,
and many other Lamellicorns, &c., the anterior ones have a yellow
or golden spot at their base, composed of decumbent hairs, which
prevent them from suffering by the violent friction to which they
are exposed in burrowing. In most Petalocerous beetles the tibiæ are
set with scattered bristles, and sometimes the thighs. The Tiger
beetles (_Cicindela_) are similarly circumstanced: but the bristles,
which are white, are generally arranged in rows. In _Dytiscus_,
_Hydrophilus_, &c., the four posterior tarsi; and in _Notonecta_
the posterior pair, and also the tibiæ--are fringed on each side
with a dense series of hairs, which structure assists them in
swimming[1998]. The tarsi, especially the anterior pair, in a certain
family of _Lamia_ F. (_L. papulosa_, &c.[1999]), are similarly
fringed, only the hairs curl inwards; and the _hand_ in _Sphex_
and _Ammophila_, but not in _Pelopæus_ and _Chlorion_, is fringed
externally with long bristles.
7. _Composition._ With regard to their _composition_, both arms and
legs generally consist of _five_ pieces, which Entomologists have
denominated--the _coxa_ or _hip_--the _trochanter_--the _femur_ or
thigh--the _tibia_ or shank--and the _tarsus_ or foot. Where the
structure and use of the fore-leg is different from that of the four
hind-legs, I propose calling these pieces by names corresponding
with those which anatomists have appropriated to the _arm_ in the
higher vertebrate animals: thus, as you will see in the table, I call
the whole fore-leg the _brachium_ or arm; and the _coxa_ becomes
the _clavicula_ or collar-bone; the _trochanter_, the _scapula_ or
shoulder-blade; the _femur_, the _humerus_ or shoulder; the _tibia_,
the _cubitus_ or arm; the _tarsus_, the _manus_ or hand. But let me
not lead you to suppose that the pieces, either in the arms or legs
of insects, which are there named after certain others in vertebrate
animals, precisely correspond with them--by no means--since that
is a very doubtful point; and some of them, as the _trochanter_,
clearly do not. Many gentlemen skilled in anatomy, as I have before
observed[2000], have thought that what is regarded as the _coxa_ in
insects really represents the _femur_: but there are considerable
difficulties in the way of this supposition, several of which I then
stated. I shall not however enter further into the subject, and take
the above names; since this application of them is so general and so
well understood, except with regard to the fore-leg, under certain
circumstances, as I find them. I shall now consider them in the order
in which I have named them.
a. _Coxa_ or _Clavicula_[2001]. The _coxa_ is the joint that connects
the leg with the trunk of the insect. With regard to their _shape_,
the most general form of the four anterior is more or less that
of a truncated cone: in the _Staphylinidæ_, however, they tend
to a pyramidal or four-sided figure; as do the whole six in the
_Trichoptera_: in numbers of the weevils and capricorns they are
subglobose; in the Lamellicorns they are mostly oblong, and not
prominent: the posterior pair in the _Coleoptera_ are generally flat
and placed in a transverse position, and more or less oblong and
quadrangular: in _Elater_, &c., they are cuneiform: in _Haliplus_
Latr. they are dilated, and cover the thigh[2002]: in _Buprestis_,
_Copris_, &c., they have a cavity that partly receives it: the
corresponding part, the _clavicle_, in the _arm_ of _Gryllotalpa_,
is very large and remarkable; viewed underneath it is triangular,
and trifid where the trochanter articulates with it: in that of
_Megachile Willughbiella_ the clavicle is armed with a spine[2003].
As to their _proportions_, the most general law seems to be, that the
anterior pair shall be the shortest and smallest, and the posterior
the longest and largest. In some instances, as in _Buprestis_, the
two anterior pair are nearly equal; in others (_Mantis_, _Eurhinus_
K.), the anterior are the longest, in the former as long as the
thigh, and the four posterior the shortest: in the _Trichoptera_,
_Lepidoptera_, &c., all are nearly equal; in _Mantis_ the two
_posterior_, and in _Phengodes_ the _intermediate_ pair are the
largest; but in _Necrophorus_ they are the smallest:--though almost
universally without articulations, in _Galeodes_ the clavicle
consists of _two_ and the coxa of _three_[2004].
b. _Trochanter_ or _Scapula_[2005]. This is the _second_ joint of the
leg: and if the _coxa_ is regarded as the analogue of the _thigh_
in vertebrate animals, this should seem to represent the _patella_
or _rotula_, vulgarly called the knee-pan. Latreille and Dr. Virey
consider this articulation as merely a joint of the _coxa_[2006]; but
if closely examined, especially in Coleopterous insects, you will
find it so fixed to the thigh as scarcely to have separate motion
from it, and in many cases it seems to be merely its fulcrum; but
I am not aware that any instance occurs in which it has not motion
separate from that of the former joint.
As to its _articulation_ with the _coxa_,--in the _Coleoptera_ it
appears to be of a mixed kind; for it inosculates in that joint,
is suspended by ligament to its orifice, and its protuberances are
received by corresponding cavities in it; and its cavities receive
protuberances, which belongs to a ginglymous articulation. I have
observed two variations in this Order, in one of which the motion
of the thigh and trochanter is only in _two_ directions, and in the
other it is nearly _versatile_ or rotatory. The _Lamellicorns_ afford
an example of the first, and the _Rhyncophorous_ beetles or weevils
of the second. If you extract from the _coxa_ the thigh with the
trochanter of the larger species of _Dynastes_ M^cL., you will find
that the head of the latter is divided into two obtuse incurving
lobes or condyles: that on the inner side being the smallest and
shortest, and constricted just below its apex: and that under
this is a shallow or glenoid cavity, terminating posteriorly in a
lubricous flat curvilinear ridge. If you next examine the trochanter
in articulation with the coxa, you will perceive that the head of
the former inosculates in it, that the lower condyle is received
by a sinus of the coxa, which also has a lubricous _very_ shallow
cavity corresponding with the ridge, in which it turns; and in the
head of the coxa, on the lower side, is an external condyle, which
is received by a sinus common to both, of the head of the thigh and
of the exterior side of the trochanter[2007], in which it likewise
turns: this last condyle has also an internal protuberance, which
appears to ginglymate with a cavity of the trochanter: from this
structure the leg is limited chiefly to a motion up and down upon two
pivots, or to fold and extend itself. You will find an articulation
very near this, but on a smaller scale, in the stag-beetle. In the
other kind of articulation, which admits of freer motion, the head
of the trochanter is prolonged, and the process terminates in a
short interior condyle, which appears to work in a corresponding
cavity of the interior of the coxa; and the base of the process is
encompassed by a ridge with a cavity behind it, which is received by
another of the lower part of that piece, and admits a corresponding
ridge--a structure that allows a rotatory motion. In the hind-legs of
this tribe the motion is chiefly limited to folding and extending;
in _Carabus_, &c., also the head of the trochanter is nearly
hemispherical, and the articulation approaches ball and socket.
In most of the other Orders, the _Hymenoptera_ excepted, there is
little or no inosculation, the trochanter being simply suspended by
ligament to the _coxa_ as well as to the _thigh_; its connection
with the latter is similar in _Coleoptera_; but in _Cicindela_, &c.,
it inosculates in it. The part we are considering varies in its
position with respect to the thigh: in the hind-legs of _Carabus_,
&c., it forms a lateral fulcrum on the inner side of that part, and
does not intervene between its base and the coxa; the muscles from
the latter entering the former, not at the bottom of the base, but
at its side: but in the four anterior legs it forms their base, as
it does in all the legs in _Apion_, and in all the Orders except the
_Coleoptera_, cutting them entirely off from contact with the coxa:
in the _Lamellicorns_ they cut off part of the base obliquely, but so
as to permit their coming in contact with the condyle of the coxa, as
before mentioned. In the _Ichneumonidæ_ and some other _Hymenoptera_
the _trochanter_ appears to consist of _two_ joints particularly
visible in the posterior legs[2008].
As to _size_ in general,--the part in question is smaller than the
coxa; but in _Notonecta_ it is larger, and in the dog-tick (_Ixodes
Ricinus_) longer than that joint. It exhibits few variations in its
_shape_ or _appendages_ worthy of particular notice. In general,
in the _Coleoptera_ it is triangular or trigonal; but in _Carabus_
L., in the hind-leg it is oblong or rather kidney-shaped; in that
of _Necrophorus_[2009] it terminates in one or two teeth or spines,
varying in length in the different species: in the other Orders it is
not remarkable in this respect.
c. _Femur_ or _Humerus_[2010]. The _femur_ or thigh is the _third_,
and usually the largest and most conspicuous joint of the leg. In
the hypothesis before alluded to[2011] it is considered as the
analogue of the _tibia_ of vertebrate animals. With regard to
the _articulation_ of this part with the trochanter, it has been
sufficiently explained under that head, and that with the _tibia_
I shall treat of when I come to that joint. As to the _size_ of
the thighs, and their relative _proportions_ to each other and to
the remaining joints of the leg, the most general law is, that
the _anterior_ pair shall be the _shortest_ and _smallest_, and
the _posterior_ the _longest_ and _largest_. With respect to the
remaining articulations, most commonly the _thigh_ is longer and
larger than the _tibia_, and the _tibia_ than the _tarsus_. But there
are numerous exceptions to both these rules. With respect to the
_first_, we may begin by observing that the increase of the magnitude
of the thigh, from the anterior to the posterior pair, is usually
_gradual_: but in many jumping insects, and likewise many that do
not jump, the posterior pair are _suddenly_ and disproportionally
thicker than the rest[2012]. Again, in many insects the _anterior_
pair are the _longest_ and _thickest_, as in _Macropus longimanus_,
_Bibio_, _Nabis_, &c.: in others, the _intermediate_ exceed the rest
in _magnitude_, as in _Onitis Aygulus_, _cupreus_; _Sicus flavipes_,
&c.; in many Lamellicorns _all_ the thighs are incrassated and nearly
equal in size: but in some, as _Ryssonotus nebulosus_ M^cL.[2013],
the _intermediate_ pair are rather smaller than the rest. With
respect to the _second_ rule--in some, as in the male of _Macropus
longimanus_, the _anterior tibia_, though more slender, is longer
than the _thigh_; in _Hololepta maxillosa_ it is longer and more
dilated; in _Lamia marmorata_, or one related to it from Brazil, the
_intermediate_ pair are longer; in _Ateuchus gibbus_ and others of
that tribe the _posterior thighs_ are smaller than the _tibiæ_: and,
to mention no more; in _Callichroma latipes_ the _posterior_ tibia
is wider than the part last named. Again, the _tarsi_ are as long
as either _tibia_ or _thigh_ in many of the larger _Dynastidæ_, as
_Megasoma Actæon_, &c.; longer than either in _Melolontha subspinosa_
F.; and in _Tiphia_, _Scolia_ and affinities, often as long, or
longer than both together.
As to _shape_,--the _thigh_, especially in the fore-leg, varies
considerably: most generally it is flat, linear, and a little thicker
where it is united to the _tibia_, on the outer side convex, and
concave next the body; but in many it is gradually thicker from the
base to the apex: in some _Cerambyces_ (_C. thoracicus_) it is clavate;
in others of this genus and _Molorchus_ they may be called capitate;
in _Pterostichus_ they are rather lanceolate; in _Onitis Sphinx_
the humerus is triangular, and the intermediate thigh rhomboidal;
in _Bruchus Bactris_ it is bent like a bow; and in some Brazilian
_Halticæ_ it is nearly semicircular. The _humerus_ in _Phasma_ is
attenuated at the base; in _Empusa gongyloides_ it is at first
ovato-lanceolate, and terminates below in a kind of footstalk[2014];
in _Phasma flabelliforme_ it is dolabriform[2015]; in _Mantis_ often
semioval or semielliptical, and thickest at the inner edge, which
affords space for two rows of spines with which it is planted. In
_Phyllium siccifolium_ all the thighs are furnished on both sides
with a foliaceous appendage nearly from base to apex[2016]: in a
species of _Empusa_ (_E. macroptera_), the four posterior ones are so
distinguished only on their posterior side[2017]: others of this last
genus, as _E. gongyloides_, have an alary appendage on _both_ sides at
the apex of these thighs[2018]; and another family, as _E. pauperata_,
have only one on the _posterior_ side[2019]. The thighs of no insect
are more remarkable for their elegant shape,--tapering gradually from
the base to the apex, where they swell again into a kind of knee,--than
the posterior ones of the locusts (_Locusta_ Leach); each side of
these thighs is strengthened with three longitudinal nearly parallel
ridges, and the upper and under sides are adorned by a double series,
in some coalescing as they approach the tibia, of oblique quadrangular
elevations resembling scales[2020].
I shall next say a few words upon the _spines_ and other _processes_
which arm the thigh. Those moveable ones of _Mantis_ which help to
form a fearful instrument of destruction, have just been mentioned,
and similar ones, but less conspicuous, arm the intermediate thighs
of _Sicus flavipes_: other appendages of this kind are for a less
destructive purpose--to keep the tibia when folded in its place. This
seems to be the use of the serratures and spine that arm the thigh of
_Bruchus Bactris_, or the Hymenopterous genera _Leucospis_, _Chalcis_,
&c.; in _Onitis Aygulus_ a short filiform horn arms the humerus, and
a longer crooked one that of many species of _Scaurus_[2021]. In many
_Stenocori_ the thighs terminate in two spines, and in _Gonyleptes_
K. the posterior ones are armed internally with very strong ones;
with which, as the legs converge at their knee[2022], they may
probably detain their prey. The knee-pan (_Gonytheca_) of the thigh,
or the cavity at its end, which receives the head of the _tibia_,
is very conspicuous in the weevils; but in no insects more than in
_Locusta_[2023], in which tribe it deserves your particular attention.
d. _Tibia_ or _Cubitus_[2024]. The _tibia_ or shank is the _fourth_
joint of the leg, which according to the hypothesis lately alluded
to is the analogue, in the _anterior_ leg of the _carpus_ or carpal
bones, and in the _four posterior_ ones of the _tarsus_ or tarsal
bones of vertebrate animals. This may be called the most conspicuous
of the articulations of the leg; for though it is generally more
slender and often shorter than the thigh, it falls more under the eye
of the observer, that joint being more or less concealed by the body:
it consists in general of a single joint; but in the _Araneidæ_ and
_Phalangidæ_ it has an accessory one, often incrassated at its base,
which I have named the _Epicnemis_[2025].
With respect to the _articulation_ of the _tibia_ with the thigh--we
may observe that in general it is by means of _three_ processes or
condyles, two lateral and one intermediate, of the head of the former
joint[2026]: the lateral ones are usually received by a cavity or
sinus of the _gonytheca_ of the thigh[2027]; and upon these the
_tibia_ turns, with a semirotatory motion up and down as upon a
pair of pivots: at the same time the _mola_ or head of the latter
joint, which has often a flexure so as to form an elbow with the
rest of it, inosculates in the _gonytheca_, and is also suspended
by ligament to the orifice through which the muscles, nerves, and
bronchiæ are transmitted: so that in fact the articulation, strictly
speaking, belongs exclusively to none of the kinds observable in
vertebrate animals, but partakes of several, and may properly be
denominated a _mixed_ articulation,--a term applicable in numerous
instances also to the other articulations of the legs of insects.
In the different Orders some variations in this respect take
place,--I will notice some of the most remarkable. In no Coleopterous
insects is the structure more distinctly visible than in the larger
Lamellicorns. In _Copris bucephalus_, for instance, if you divide
the thigh longitudinally, you will find on each side, at the head,
that it is furnished with a nearly hemispherical protuberance,
perforated in the centre for the transmission of muscles, and
surrounded externally by a ridge, leaving a semicircular cavity
between them[2028]: if you next examine the _tibia_, after having
extracted it, you will find on each side, at the base, a cavity
corresponding with the protuberance of the thigh which it receives,
having likewise a central orifice, and surrounded by a semicircular
ridge corresponding with the cavity in the thigh in which it acts:
below this ridge another cavity, forming a small segment of a
circle, receives the ridge of the thigh[2029]. You will observe that
the ridge of the _tibia_ represents the lateral condyle lately
noticed: in the _Dynastidæ_ this is more prominent, and often forms
a smaller segment of a circle. In these also the protuberance of
the thigh is more minute, and its ridge is received by a cavity of
the _tibia_ nearly semicircular[2030]; in _Geotrupes_ Latr. the
articulation is not very different, though on a reduced scale; in
_Calandra Palmarum_ the lateral condyles of the _tibiæ_ are flatter
and broader[2031]; and the articulation not being quite so complex,
this joint is kept steady by an intermediate process observable in
the _gonytheca_[2032]. From the above description it appears that
the dislocation of the _tibia_ is effectually prevented in the
Lamellicorns by the protuberance and ridge of the thigh working
in their corresponding cavities, while the condyle of that part
turns with a rotatory motion in the cavity of the thigh. In the
_Orthoptera_ Order the _tibia_ is suspended by a ligament, in the
_gonytheca_ the lateral condyles, which are very prominent, working
in a sinus of that part[2033]. The subsequent Orders exhibit no
very striking variations from these types of articulation, I shall
therefore not detain you longer upon this head.
With regard to the _proportions_ and _magnitude_ of the joint we
are considering,--the most general law is, that the _anterior_ pair
should be shorter and more slender than the _intermediate_; and
the _intermediate_ than the _posterior_; and that all the _tibiæ_
should be shorter and more slender than the _thighs_, and longer
and thicker than the _tarsi_. Various exceptions, however, to this
rule in all these cases might be produced; but I shall only observe
that in all those insects in which the fore-legs are calculated for
digging or seizing their prey, as in the _Petalocerous_ beetles, the
_Gryllotalpa_, _Mantis_, &c., this joint of the leg is usually much
enlarged and more conspicuous than the others.
As to its _figure_ and _shape_--most commonly the _tibia_
grows thicker from the base to the apex, as in the majority of
_Coleoptera_, _Hymenoptera_, &c.; in the _Orthoptera_, _Neuroptera_,
&c., it is generally equally thick every where. Another peculiarity
relating to this head observable in it, is its tendency to a trigonal
figure: this, however, though very general, is not universal;--thus,
in some _Orthoptera_, as _Pterophylla_ K., its horizontal section is
quadrangular; in others, as _Locusta_ Leach and many other insects,
it is nearly a circle; in some scorpions it is almost a hexagon. The
superficial shape also of this joint in numerous instances is more or
less triangular, but it sometimes recedes from this form:--thus, in
_Callichroma latipes_ it is a segment of a circle; in some _Empides_
it is clavate; in _Onitis Sphinx_, dolabriform; in the _Orthoptera_,
_Neuroptera_, &c., it is usually linear; in some _Lygæi_ it is
angular[2034]: but the most remarkable _tibiæ_ in this respect are
those of such species of this last genus as have the posterior
ones winged or foliaceous, so that they resemble the leaf of some
plant--the _tibia_ being the _rachis_, and the _wing_ (which in some
species is veined) representing the _leaf_ itself. This structure
is exemplified in _Lygæus compressipes_, _phyllopus_, _foliaceus_,
&c.[2035] Under this head I must say a few words upon the _flexure_
of this joint, which in some cases merits notice. I have before
mentioned its bend at the knee[2036] or base: the apex also is
sometimes incurved--in the anterior one of the male of _Macropus
longimanus_ so as almost to form a hook[2037]: in _Lygæus Pharaonis_
the posterior pair are flexuose[2038]; in _Bruchus Bactris_,
_Leucospis_, and several species of _Chalcis_, these _tibiæ_ curve
so as to adapt themselves to the bend of the thigh when folded. The
notch on the inside of the anterior pair, in a large majority of
_Carabus_ L., armed above by a spur[2039], a structure which probably
assists them in seizing and detaining their prey, may also here be
introduced: in the generality it is a little removed from the apex of
the joint in question; but in _Pamborus_ it is very near to it, and
in _Cychrus_, _Carabus_, &c., it becomes obsolete. I may mention here
also a singular character which distinguishes the cubit of both sexes
of _Gryllus campestris_, _domesticus_, &c. At the base there is an
aperture which passes through the joint--anteriorly it is oval, and
posteriorly elliptical and much larger, and on both sides is closed
by a tense membrane.
The most striking peculiarities as to the _clothing_ of his joint have
been chiefly noticed under the sexual characters of insects[2040],
but some appear not to be of that description. In _Sphæridium_ Leach,
while the thighs and _tarsi_ are naked, the posterior _tibiæ_ are
remarkably beset with stiff bristles; in _Empis pennipes_ they are
thickly fringed on both sides; in _Scarabæus_ M^cL. only externally,
and in _Dytiscus serricornis_ internally; in _Necydalis barpipes_ K.
this fringe is longer at the apex; and in _Saperda hirtipes_ Ol. the
same _tibiæ_ at that part are adorned with a large brush, like that
observable in the antennæ of some _Lamiæ_[2041].
I must next call your attention to the _teeth_, _spines_, and _spurs_
with which the _tibiæ_ of insects are sometimes armed. With regard
to _teeth_, you have doubtless often observed those that distinguish
the _cubitus_ of the arm of most Lamellicorn beetles: these vary
in number from _one_, as in _Trox suberosus_, to _seven_, as in
_Geotrupes autumnalis_; but the most universal number is _three_:
in some species of _Geotrupes_, as _G. stercorarius_, &c., the
_third_ tooth from the apex, and those that follow it, may be called
_double_. These teeth, in their cubit or anterior shank, doubtless
assist these insects in burrowing. The four posterior _tibiæ_ in
this tribe are also distinguished by a kind of teeth which occupy
their whole diameter, and resemble so many steps. I have before
noticed the remarkable cubit of the _Gryllotalpa_, and likewise that
of _Scarites_, _Pasimachus_, &c., in which some of the teeth are
prolonged into _spines_[2042], which are the next description of
tibial arms that I mentioned. Spines are of _two_ kinds--those which
are merely _processes_ of the crust of the _tibia_, and those that
are _implanted_ in it, and seem to have a _gomphosis_ or perhaps an
_amphiarthrosis_ articulation[2043]. An instance of the _first_ kind
may be seen in the hind-legs of some grasshoppers[2044] (_Locusta_
Leach), the _Rutelidæ_, &c. though in others they are implanted:--of
the _second_, in the _cubitus_ of the _Mantidæ_, and of _all_ the
_tibiæ_ of the dragon-flies (_Libellulina_ M^cL.)[2045];--and of
_both_ kinds in the hind-legs of _Acrida_ K., those which arm the
upper angles of the tibiæ being _processes_, and those of the lower
being _implanted_. The term _spine_ I think ought to be restricted
to the first kind; the _second_ ought rather to be denominated
_spurs_ (_calcaria_), and may perhaps be regarded as in some degree
synonymous with those most important appendages of the joint in
question, that are implanted in or near their apex, which have been
hitherto distinguished by this last denomination, and which I am
next to consider. But though I have not altered a term generally
adopted, I must here express my opinion that they ought rather to be
considered as minute _toes_ or _fingers_, and that the denomination
best agreeing with their functions, as accessories to the main toe,
would be _digituli_: this is proved particularly by a character
peculiar to those of many species of the genus _Cimbex_ amongst the
saw-flies, in which these organs are furnished with a _sucker_ or
_pulvillus_ (as they are also in _Œnas_ a kind of blister beetle),
as well as the joints of the tarsi[2046]; which makes it evident
that they are applied by the animal to surfaces, and assist it in
walking or climbing; and in general it may be observed that in most
insects their principal use is connected with these motions, and with
burrowing. This circumstance tends to prove that the generality of
insects (for all have not these organs) have really a didactyle or
tridactyle hand or foot; and the hypothesis so often alluded to--that
the _cubitus_ or _tibia_, &c., is really analogous to the _carpus_
or _tarsus_ in vertebrate animals[2047]--seems to receive no small
confirmation from it; since, if the _spurs_ be really analogous to
_fingers_ or _toes_, the part they articulate with cannot be the
_tibia_, &c. Though the parts in question did not escape the notice
of Reaumur, Linné, De Geer, Latreille, &c., yet they have not been
employed in the determination of tribes, genera, &c., except by the
author last named, but perhaps adopted from Bonelli[2048], in the
subgenera _Zabrus_ and _Pelorus_: in many instances, however, they
afford excellent subsidiary characters, sometimes common to a whole
Order, and at others distinguishing its various subdivisions. With
regard to their _number_--I have noticed many variations which I
will now state to you, first observing that I shall express them by
_three_ figures, the _first_ representing the number of spurs on the
_anterior_ leg, the _second_ that of those on the _intermediate_,
and the _third_ on the _posterior_; and where there are spurs, as in
the _Trichoptera_ and _Lepidoptera_, on the _middle_ as well as at
the _end_ of the _tibia_, I shall express it by one figure _over_
another, the upper one representing the number of the _middle_ spurs.
If you make an examination yourself, it will be proper to remind
you that these little organs are extremely liable to be broken off,
but the socket in which they were planted is usually very visible.
The most _natural_ number is represented by 2:2:2; this you will
find very prevalent in the _Coleoptera_ Order, as in the Predaceous
and numerous other beetles: in the _Orthoptera_ and _Hemiptera_
Orders, however, I have not discovered an instance of it; but in
all the rest it more or less occurs: next to this number--_tibiæ_
with obsolete or no spurs seem most prevalent, particularly in the
_Hemiptera_; not a single instance of an insect furnished with them
occurring to me in the _Heteropterous_ section; and it is doubtful
whether there are any in the _Homopterous_.--Having stated the most
universal structure in this respect, I will next consider the Orders
seriatim. Amongst the _Coleoptera_ though the numbers 2:2:2 are most
frequent in occurrence, yet there are numerous exceptions. Thus, in
the Lamellicorns, 1:1:1 represents the _calcaria_ of one tribe of
the _Scarabæidæ_ M^cL. formed of the genus _Scarabæus_ M^cL.; 1:2:1
represents those of another tribe of that family, including the
subgenera _Ateuchus_, _Copris_, _Phanæus_, &c.; 1:2:2 again forms
the character in this respect of _Aphodius_ and the great majority
of the Lamellicorns; while 2:2:2 is confined in this section to
_Æsalus_ F. and _Melolontha chrysomeloides_ Schranck (_Psephus_
M^cL. MS.). In the other tribes of _Coleoptera_ other numbers occur.
Thus, 0:1:1 characterizes _Hylœcetus_; 0:1:2 _Mordella_; 0:2:2
_Macropus_; 1/1:2:2 _Harpalus_, and all those _Carabi_ L., except
_Zabrus_, that have a _notch_ in their anterior _tibiæ_; 1/2:2:2
_Zabrus_. In the _Orthoptera_ Order it is not easy to distinguish
the real _spurs_ from the implanted _spines_ that frequently arm
the legs: these in _Blatta_ are extremely numerous, even at the
apex of the _tibiæ_; but I cannot distinguish any that can be
regarded as true analogues of the former: the most natural number
of spurs in this Order is represented by 0:0:4; this you will see
in all the Locusts; in _Acrida_, _Conocephala_, _Pterophylla_; and
in _Truxalis_, _Pneumora_, &c.; in _Phasma_ there are none. In
_Mantis_, if the terminal process of the _cubitus_ is excluded,
it will be 0:2:2; in _Gryllotalpa_, admitting the terminal teeth
of that part[2049] as analogues of spurs, the number is 4:4:4;
in _Tridactylus_ Latr. 0:0:5[2050]; in _Gryllus_ Latr. 3:3:5; in
_Gryllus monstrosus_, 4:4:6. In the whole _Hemiptera_ Order I have
discovered no instance of an insect furnished with the real spurs:
for though in _Tettigonia_ F., _Cercopis_, &c., there are implanted
spines in the posterior _tibia_, and several at the apex, there are
none of them clearly analogous to real spurs. In the _Lepidoptera_
the most general arrangement appears to be 1/0:2:2/2; and next to
this, 1/0:2:2. In this Order most commonly there is no spur at the
end of the cubit, but one resembling a thumb[2051] arms its middle;
in _Pieris_, &c., this thumb is not present, so that the number is
0:2:2; in _Agarista_ Leach, _Erebus_, &c., you will find 1/0:2:4,
the posterior _calcaria_ being all terminal; and in _Attacus Atlas_,
all these organs are obsolete except the thumb. In the _Neuroptera_
the most general arrangement is 2:2:2; but in the _Libellulina_,
although the legs are very spinose, there are no spurs. In the
_Trichoptera_ K., in _Phryganea rhombica_ and affinities, the number
of them is expressed by 1/2:1/2:1/2; and in those with long antennæ,
_P. atra_, &c., by 2/2:2/2:2/2. In the _Hymenoptera_ the number 1:2:2
is most prevalent; and next to this, as in _Apis_ L., 1:1:2. In the
_Ichneumones minuti_ L. the spurs are 1:1:1; in _Atta_ Latreille, a
kind of ant[2052], 1:0:0. In the _Diptera_ it is often difficult to
distinguish the spurs from the spines; but the number most universal
is, I think, 2:2:2; in _Tipula_ it is 1:2:2; in the _Tabanidæ_ 0:2:0;
and in _Culex_, _Limonia_, &c., there are none. Amongst the insects
with more than six legs, most commonly the tibiæ have no spurs; but
in the _Araneidæ_ each is armed with _two_, a circumstance which also
distinguishes the corresponding joint of the _pedipalpi_.
These little organs inosculate each in an appropriate socket of the
end, or in many cases of the middle of the _tibia_; and that part
of their head or base that is received by it, is often constricted
for the purpose: from hence it follows that they are capable of some
degree of motion, but in some insects, as those on the four posterior
legs of _Scarabæus sacer_ and its more immediate affinities, and
those at the end of the cubit of _Gryllotalpa_, they are immoveable,
and appear almost processes of the joint to which they belong. They
are commonly sharp, of a subtriquetrous figure, with the lower side
flat: where there are two, the outer one is usually the longest; and
in general the spurs on the hind legs are longer than those on the
four anterior: but there are exceptions--thus, in _Acanthopus_ Latr.
the _intermediate_ spurs are the longest; and in _Cicindela_ the
_anterior_ are longer than the former; in _Blaps mortisaga_ those
on all the legs are nearly equal in length. They vary sometimes in
_shape_--those on the middle of the cubit of many _Lepidoptera_,
which may be regarded as a kind of thumb[2053], are of a lanceolate
shape; in _Meloe_ the external posterior one is flat and obtuse;
in _Œnas_ Latr. it is obconical, concave at the extremity, and
apparently furnished with a sucker; in _Ateuchus smaragdulus_ the
_anterior_, and in _Copris Carolina_ the _posterior_ is forked and
emarginate; in _Sirex_ the former is hooked and winged; in _Lamprima_
it is triangular and dilated; in _Aphodius analis_ it is dolabriform;
in _Dynastes retusus_ and _Juvencus_ the spurs are bent like a bow.
In many _Hymenoptera_, as the _Sphecidæ_, they are pectinated[2054],
with a series of minute parallel spines--a structure which assists
the animal in burrowing[2055]; in _Acanthopus_ Latr. they are armed
with little teeth or spines[2056]; in the hive bee the spur of the
cubit is furnished with a membranous appendage which I have called
the velum[2057]; and in a subgenus related to _Saropoda_ Latr.
(_Ctenoplectra_ K. MS.), the interior spur of the posterior leg is
crescent-shaped, fixed transversely, and fitted on the inner side
with a membrane, the edge of which is finally pectinated.
e. _Tarsus_ or _Manus_[2058]. This is the _last_ portion of the leg,
usually supposed to be analogous to the hand or foot of vertebrate
animals; but, according to the hypothesis so often alluded to, rather
the representative of their jointed finger or toe. In treating of
this part I shall consider its _articulation_ with the _tibia_,
and of its joints _inter se_; the _number_ of those joints; their
_proportion_ and _shape_; their _parts_ and _appendages_.
I seem to have observed _three_ kinds of tarsal _articulation_. The
_first_ is a species of _enarthrosis_ or ball and socket, the joints
terminating in a globular head, perforated indeed for the transmission
of muscles, &c., and which is received by a corresponding cavity of the
_tibia_ or preceding joint, as may be seen in many weevils (_Curculio_
L.[2059]). This admits of some rotatory motion.--The _second_ is a
_mixed_ articulation between _enarthrosis_ and _ginglymus_, when at the
base of the ball a deep transverse channel receives a corresponding
ridge of the _tibiæ_ or preceding joint: this may be found in _Rutela_
and probably many other Lamellicorn beetles; and something very similar
in the Predaceous ones.--The _third_ kind is where there is little or
no inosculation, and the joints are scarcely more than _suspended_:
this takes place in the _Orthoptera_, _Neuroptera_, &c.; but in
_Blatta_ and the hind legs of _Mantis_ there is some approach to the
foregoing kinds.
We are now to consider the _number_ of joints of the _tarsus_, which
varies considerably in the different Orders, and in one has been
assumed as a clue for a subdivision of it into sections[2060], which,
though not perfectly natural, is very convenient, and has been adopted
by most modern Entomologists. In treating of this head, I shall use
those denominations that have been employed by M. Latreille and others
to express the variations of the number of the tarsal joints in the
_Coleoptera_, but shall apply them to insects in general. Insects in
this view, therefore, may be called _pentamerous_; _heteromerous_;
_tetramerous_; _trimerous_; _dimerous_; or _monomerous_.
_Pentamerous_ insects are those which have _five_ joints in _all_
their _tarsi_. This is the most universal, and may be called the
_natural_ number of these joints. More than half the _Coleoptera_
belong to this section; in the _Orthoptera_--the _Blattidæ_, _Mantidæ_,
and _Phasmidæ_; all the _Lepidoptera_ except those butterflies called
_tetrapi_ (_Vanessa_, &c.); all the _Trichoptera_, _Hymenoptera_,
and _Diptera_; in the _Neuroptera_--_Ascalaphus_, _Myrmeleon_,
_Hemerobius_, _Corydalis_, &c.; and in the _Aptera_--_Pulex_[2061].
_Heteromerous_ insects are those in which the number of these joints
varies in the different pairs of legs[2062]. These variations, like
the spurs, may be expressed by three figures, the first representing
the _anterior tarsus_, the second the _intermediate_, and the third
the _posterior_. I begin with 5:5:4. This number represents those
beetles that have been _exclusively_ regarded as _heteromerous_ by
modern Entomologists--of this description is the Linnean _Tenebrio_,
_Meloe_, &c., now subdivided into numerous genera; they have _five_
joints in the two anterior pair, and _four_ in the posterior. The
tarsal joints of the aquatic genus _Hydroporus_ (a singular anomaly
in the Order to which they belong) are expressed by 4:4:5, thus
reversing the number in the preceding tribe: other Heteromerous
genera are to be found amongst the _Hemiptera_. Thus, in _Ranatra_
the numbers are 2:1:1; in _Sigara_ and _Nauceris_ 1:2:2; in a new
subgenus between _Belostoma_ and _Naucoris_ (_Xiphostoma_ K. MS.),
brought by Dr. Bigsby from Canada, 3:2:2; in the _Lepidoptera_ the
butterflies called _tetrapi_ (_Vanessa_, &c.) may be expressed
by 1:5:5. Amongst the _Aptera_ and _Arachnida_ there are three
remarkable genera, which if their pedipalps are included may
be deemed Heteromerous. I mean _Phrynus_, _Thelyphena_, and
_Galeodes_;--in the former the numbers will be *:4:4:4, the asterisk
denoting more than ten; in the second, 8:4:4:4.; and in _Galeodes_
(in which the first pair of pedipalps are not chelate, the mandibles
performing their office) the numbers are 1:1:3:3:3.[2063]
_Tetramerous_ insects are those in which all the _tarsi_ consist of
_four_ joints; these in the _Coleoptera_ are next in number to the
_pentamerous_--indeed a very large proportion of them strictly speaking
are really of the latter description, since in Linné's four great
genera, _Curculio_, _Cerambyx_, _Chrysomela_, and _Cassida_ and some
others, the _claw-joint_ (_ungula_) consists of _two_ articulations,
one very short, forming merely the ball at its base[2064], which
inosculates in the socket of the preceding joint, and the other
constituting the remainder: if you carefully separate these two pieces,
you will find that the last inosculates in the summit of the ball, and
is moved by appropriate muscles[2065]. This structure probably permits
the readier elevation and depression of this joint. In the _Orthoptera_
the tetramerous genera are those which Linné called _Tettigonia_
amongst his _Grylli_ (_Locusta_ F.); _Acheta monstrosa_ also, and in
the _Neuroptera_, _Raphidia_ belong to this section.
_Trimerous_ insects are those whose _tarsi_ consist of only _three_
joints. Amongst beetles the Lady-birds (_Coccinella_ L.) are
remarkable for this structure, but in them the claw-joint is also
_biarticulate_, so that strictly speaking they are _tetramerous_;
in the _Orthopterous_ Order the migratory locusts (_Locusta_ Leach)
belong to this section, as likewise _Gryllus_ Latr. and _Gryllotalpa_
Latr.: in the first of these genera is an appearance of there being
more joints in the _tarsus_, because there is more than one cushion
below the first[2066]. To this section also belong the great majority
of the _Hemiptera_, excluding only those tribes that connect the two
sections of the Order constituting the two Linnean genera _Nepa_ and
_Notonecta_; the _Libellulina_ likewise belong here, as do also the
_Scorpionidæ_ and _Scolopendridæ_.
_Dimerous_ insects are those that have _two_ joints in all their
_tarsi_. Such are the _Pselaphidæ_ in the Coleoptera Order[2067];
in the _Hemiptera_--_Belostoma_ and _Notonecta_; in the hexapod
_Aptera_--_Pediculus_; in the octopod--the _Acari_ of Linné; in the
myriapod--_Iulus_; and in the _Arachnida_--the _Araneidæ_.
_Monomerous_ insects are those which have only a single tarsal
joint. Only one Coleopterous and also one Hemipterous genus is so
distinguished: the first is _Dermestes Armadillus_ De Geer[2068], and
the second the common water-scorpion, _Nepa_ Latr. Among the _Aptera_
we find _Nirmus_, _Podura_, _Sminthurus_, &c., that belong to this
section.
To the above sections another may be added for those insects whose
_tarsi_ have more than _five_ joints, which may be denominated
_Polymerous_. Here belong the genera _Gonyleptes_ K., _Phalangium_
and _Scutigera_ Latr. In the first the number of joints varies from
_six_ to _eleven_, and in the two last they far exceed that number,
amounting in some species of _Phalangium_ to more than _fifty_, and
becoming convolute like the antennæ of Ichneumons[2069].
I am next to notice the _proportions_ and _shape_ of the _tarsus_ and
its joints. The most general law is, that it shall be shorter and more
slender than the _tibia_; but it admits of several exceptions--thus,
in _Megasoma_ K.[2070], in _all_ the legs; in _Agrostiphila_ M^cL.
MS.[2071] in the _intermediate_, and in _Amphicoma lineata_ in the
_posterior_ pair the _tarsi_ are the longest; in _Trichius Delta_
these last are longer than the thigh and _tibia_ together. In some
insects the _tarsi_ are disproportionally short, as in _Cassida_,
the _Pselaphidæ_, _Locusta_ Leach, &c. Though generally more slender
than the _tibia_, in several instances they are as thick or thicker,
or more dilated, as in most of the tetramerous beetles, which being
climbers require a dilated _tarsus_. Again, comparing the three pairs
of this joint with each other, the most general rule is, that the
_anterior_ should be the _shortest_, and the _posterior_ the _longest_:
but in some, as the Capricorn beetles, &c., they are nearly equal in
length; in others, as _Lytta marginata_, the _anterior_ pair, and in
_Rhipiphorus_ the _intermediate_, are the longest; in _Trichius Delta_
these last are the shortest. With respect to _thickness_, the anterior
_tarsi_, except in many males[2072], are not very strikingly different
from the rest.
With regard to the proportion of the joints of the _tarsus_ to each
other,--according to the most general law, the first is the longest,
the last next in length, then the second and third, and the fourth is
the shortest. In _Gonyleptes_ K. and other _Phalangidæ_ the first is
almost thrice the length of all the rest taken together; but there
are numerous exceptions to the rule. In the female _Carabi_ the first
joint is not longer than the last, and in the males not so long; and
in _Hydrophilus_, &c., it is the shortest of all. Again, the second
joint is longer than the three following ones in _Dasytes ater_[2073];
and than the last in _Cicindela sylvatica_: the _third_ joint is
shorter than the fourth in _Lampyris ignita_: it is longer than the
first in _Donacia_, many _Melolonthidæ_, &c. Once more, the _fourth_
joint, usually the shortest of all, is longer than the second and
third in _Anthia_, &c. Lastly, the claw-joint, usually the second in
length, in the _Eproboscidea_ Latr. (_Hippobosca_ L.) is very long and
large, while the four first joints are so extremely short as to be
scarcely distinguishable from each other: it is the shortest of all in
_Colymbetes_, &c.; it is of the length of the _third_ in _Cicindela
sylvatica_, of the _fourth_ in _C. sexguttata_. Though commonly the
slenderest joint of all, particularly so in _Raphidia_, in many
Heteromerous and Lamellicorn beetles it is the largest, conspicuously
so in _Mellinus tricinctus_. Sometimes, as in _Buprestis chrysis_, &c.,
all the tarsal joints are nearly equal in length and thickness.
We are next to say something upon the _shape_ of the _tarsi_ and
their joints. In general we may first observe that their upper
surface is commonly more or less convex, and the lower flat or
concave: in insects that are swift _runners_, as the terrestrial
Predaceous beetles, they are usually slender and filiform[2074]; in
those that swim, as _Dytiscus_, the two posterior pair taper nearly
to a point from the base to the apex[2075]; in some that climb,
as _Buprestis_, they are rather flat and linear; and in others
(the Weevils, _Curculio_ L.) they grow gradually wider towards
the claw-joint[2076]; sometimes, as in _Mordella_ Latr., the four
anterior _tarsi_ are of this shape, and the posterior pair setaceous.
In _Gyrinus_ the four posterior are flat and triangular; and in that
extraordinary insect _Gryllus monstrosus_ the _tarsi_ are foliaceous
and lobed[2077]. In many males and some others the _anterior_ pair or
_hands_ are of a different shape from the two _posterior_: thus, in
several _Carabi_ they are lanceolate; in _Staphylinus_, _Creophilus_,
&c. in both sexes they are often nearly circular, like those of male
_Dytisci_[2078]. With regard to the _shape_ of individual joints
it may be said in general that they are rather triangular, with
an anterior sinus for the reception of the succeeding joint: the
first joint usually departs most from this form; in the bees it is
commonly much larger than the rest, especially in the last pair of
legs, and nearly forming a parallelogram[2079]; in _Euglossa_ it is
trapezoidal; in the majority nearly linear or filiform. With regard
to their _termination_--in _Brachycerus_ and some ants (_Ponera_,
_Myrmica_, &c., Latr.) the _three first_ joints; in _Dascillus_,
_Lycus reticulatus_ and affinities, the _third_ and _fourth_; and
in the great majority of the Tetramerous insects the _penultimate_
joint is bilobed; although in most Predaceous beetles this joint is
entire or simply emarginate, yet in _Colliuris_ it terminates in a
single oblique lobe; and in _Lebia_, _Drypta_, &c., it is nearly
bipartite. I must now advert to the _Ungula_ or claw-joint: it
is usually clavate or thickest at the end and curved; but in the
_Asilidæ_ it is shaped like a vase or cup; in _Phanæus_, in the four
posterior _tarsi_, in which the claws are obsolete, it is thickest
at the base and sharpest at the extremity[2080]; it usually forms an
angle with the rest of the _tarsus_, rising upwards, which enables
the insect to move more easily without hindrance from the claws,
and also more readily to lay hold of any object it meets with; but
in the Lamellicorn beetles and many other insects it is in the same
line with it. As in the beetles last mentioned this joint is often
inserted in the extremity of the preceding one; but in _Œdemera_ it
articulates with the middle of its upper surface; and in _Lycus_ and
a numerous host of _Tetramerous_ beetles it springs from its base,
just behind where it diverges into two lobes.
I shall next call your attention to the different kinds of
_appendages_ with which the _tarsi_ are furnished. They are
seldom armed, like the _tibiæ_, with teeth, or spines, or horns;
but something of the kind occasionally distinguishes them. In
_Phileurus_, _Oryctes_, and several other _Dynastidæ_, the first
joint is armed at the apex externally with a considerable mucro; in
the fore-leg of _Dasytes ater_ a similar process is prolonged into a
crooked horn[2081]. But the most important appendages of the _tarsi_
are the _claws_ which almost universally arm their extremity, and
which appear clearly analogous to those of _birds_, _quadrupeds_,
&c., though probably differing as to their substance[2082]. Some
few, however, are without them; this, as I lately observed, is the
case with _Phanæus_ with respect to the four _posterior_ legs; the
_anterior_ ones of _Vanessa_ amongst the _Lepidoptera_, and all those
of _Stylops_ and many _Acari_ L., are also without them: this is
likewise the case with the first pair of legs, or the second of the
pedipalps of _Galeodes_. In this genus these organs consist of two
joints[2083]. With respect to _number_ they vary in different tribes,
but not so much as the _calcaria_: these variations may likewise be
represented by three numbers. The most natural is _two_ in all the
_tarsi_, exhibited by the Predaceous beetles and the great majority;
2.2.1. are to be found in _Hoplia_, _Anisonyx_, &c.[2084]; 1.2.2.
in _Belostoma_; three in all the legs in the _Araneidæ_[2085]; in
_Meloe_[2086], _Elater_, &c., each claw is double or consisting of
two, which makes _four_ in each leg; and in many _Hippoboscidæ_ there
are _six_[2087]; in _Nepa_ and the Myriapods there is only _one_.
In most insects, perhaps, the claws are simple or undivided[2088];
but in _Galeruca_, _Melolontha subspinosa_[2089], &c., they are
bifid at the apex; as is the exterior claw of the four posterior
legs in _Chasmodia_ and _Macraspis_[2090] M^cL., and of _all_ in
_Melolontha horticola_; in _Serica brunnea_ M^cL. the claws are all
cleft at the extremity, but the internal tooth is broad, flat, and
obtuse[2091]; in _Melolontha vulgaris_ and _Pelidnota punctata_
M^cL.[2092], the claws are armed with an internal tooth near the
base[2093]. In the _Araneidæ_, which have three claws, the two
external ones are furnished with several parallel teeth, which the
animal uses to keep separate the threads of its web, and probably for
other purposes[2094]; and some Predaceous beetles, as _Lebia_ and
_Cymindis_, have both their claws similarly furnished[2095]. These
organs vary in their relative _proportions_: thus, in _Anoplognathus_
the inner claw is much smaller than the other[2096]; and in _Elater
sulcatus_, _fuscipes_, &c., it is represented by a mere bristle; in
_Hoplia_, in the anterior _tarsus_ it is not half the length of the
outer one[2097]; in _Areoda_ and _Pelidnota_ M^cL. this last is the
smallest. They vary also in length--in _Rynchænus_, _Ascalaphus_,
&c., they are very short; in the Lamellicorns, _Galeodes_, &c., very
long; and in _Myrmeleon_ longer than the claw-joint. With regard to
their _curvature_ they generally form the segment of a circle; in
many _Asilidæ_ they are crooked like the claws of the eagle[2098],
and the posterior one of the _Hopliæ_ is bent like a hook[2099];
they most commonly diverge from each other; but in the _Rutelidæ_,
_Anoplognathidæ_, &c., they are perfectly parallel, and in the
former often inflexed[2100]. With regard to _other_ appendages of
the part we are treating of, if you examine the stag-beetle and many
other Lamellicorns, you will find between the claws a minute but
conspicuous joint terminated by two bristles which seem to mimic
the _ungula_ and its claws; these parts are what are denominated
in the table the _palmula_, _plantula_, and _pseudonychia_: in the
stag-beetle these are long[2101]; in the _Melolonthidæ_ short[2102];
and in many _Cetoniadæ_ they resemble an intermediate claw.
The most remarkable of the _appendages_ of the _tarsi_ are to be
looked for on their under side or sole (_solea_), and are the means
by which numbers of insects can overcome atmospheric pressure and
walk against gravity. Many of these have been fully described in a
former letter[2103]; but much that relates to them was there omitted,
which I shall now detail to you. _Four_ kinds of _pulvilli_, as I
would call these appendages, are found in the sole of insects, upon
each of which I shall make a few remarks.
The _first_ is a _cushion_ or brush composed of very thickly set hairs
or short bristles: examples of this you will find in the majority of
_Tetramerous_ and _Trimerous_ beetles. In _Chrysomela_, _Timarcha_,
&c., there is _one_ of these cushions on each of the _three_ first
joints; in _Prionus_, _Liparus_, &c., there is a pair; and in
_Coccinella_ on the _two_ first; in others (_Balaninus Nucum_, &c.)
a pair only on the penultimate joint; in _Calandra Palmarum_, _Rhina
barbirostris_, &c., that joint has an intire cushion; in _Eurynotus
muricatus_ K.[2104] the three first joints of the four anterior tarsi
are similarly circumstanced, but the cushions resemble sponge[2105].
The _second_ kind of cushion is a vesicular _membrane_ capable of
being inflated. This distinguishes the tarsi of _Thrips_[2106], and
many _Acari_ L.[2107]; likewise those of _Xenos_[2108]; and also of
many _Orthoptera_ fully described on a former occasion[2109], though
the fact of their capacity of inflation has not been ascertained,
belong to this section.
The _third_ kind of covering of the sole is when the three or
four first joints of the _tarsus_ each terminate in _one_ or
_two_ membranous lobes or appendages: of the first description is
_Priocera_ K., in which the lobes are involute[2110]; and of the
second _Rhipicera_ Latr.[2111], in which there is a pair on each
joint, in the Brazil species set with very fine hairs.
The _fourth_ and last kind are what may with the utmost propriety be
denominated _suckers_, since their use as such is clearly ascertained.
These are not only to be found in a large proportion of the _Diptera_,
in some of which there are _two_ of them, as in the _Asilidæ_[2112];
and in others _three_, as the _Tabanidæ_[2113]; but also in many of
the subsequent Orders: thus, in the Heteropterous _Hemiptera_, in
_Scutellera_ and _Pentatoma_, but not the _Reduviadæ_, and in the
Neuropterous genus _Nymphes_ Leach there is a minute one under each
claw. It is discoverable between the claws in many _Hymenoptera_, as
_Apis_[2114], _Vespa_, &c. But the genus that exhibits to the curious
Entomologist the most singular and elaborate apparatus of this kind is
_Dytiscus_ Latr.; and the examination of the under side of the _hand_
of any _male_ of this genus will almost compel the most inattentive
observer to glorify the wisdom and skill of the ALLFATHER so
conspicuously manifested in the structure of these complex organs. For
this part in these, instead of two or three pedunculate cups as in the
insects just mentioned, is composed of a vast number, some large and
some small. If you take a male specimen of the common _D. marginalis_,
you will find that the three first joints of the hand are very much
dilated, so as to form a plate or shield nearly circular, fringed all
round with stiffish hairs; if you next examine the under side of this
plate with a good magnifier, you will discover at the base, where it
is united to the cubit, two circular cups, the external one more than
three times the size of the other, with an umbilicated centre[2115];
besides these two larger cups the rest of the shield is covered by a
vast number of minute ones of a similar construction[2116]: the larger
cups are nearly sessile, but the smaller are elevated upon a tubular
footstalk[2117]; the three first joints of the intermediate _tarsi_
are also dilated, but not into an orbicular shield, and thickly set
with minute pedunculated suckers[2118]. The structure varies however
in different species. Thus in _D. limbatus_ the shield is triangular
with the smaller suckers at the base, and two rows of larger oblong
ones, concave but not umbilicated, at the apex; in another Brazilian
undescribed species (_D. obovatus_ K. MS.) the shield is oblong and
quite covered with suckers like those last mentioned; in _D. sulcatus_
(_Acilius_ Leach) almost the whole plate is occupied by a very large
sucker, above which, at some distance in the inner side, are two
smaller ones, while the extremity of the shield is covered by minute
ones elevated on long footstalks: the central umbilicated elevation
of the large one, which nearly fills its cavity, is in this species
beautifully radiated. The male of _Colymbetes transversalis_ has also
an orbicular shield, but the suckers are much less strongly marked. The
use of this organ has been before sufficiently explained[2119].
A few words will be necessary upon the _folding_ of the legs in
_repose_. When insects _walk_, the thigh is usually in an _ascending_
position, rising _above_ the horizontal line, the _tibia_ forming with
it rather an obtuse angle, and the _tarsus_ nearly a right one with
the _tibia_; but in the Myriapods, as far as I can unravel their swift
many-footed motions, these angles in walking do not take place; in
repose however, in many insects, the _coxa_ forms an angle with the
thigh _below_ the horizontal line and with the _tibia_ above it, and
the _tibia_ and _tarsus_ continue in the same line, and point downwards
nearly vertically; in others, as in the _Tetramerous_ beetles, the
last-mentioned joints form an angle with each other and turn upwards,
the _tibia_ having an external oblique cavity to permit this; but
the insects most remarkable for packing close their legs are those
carnivorous genera _Dermestes_, _Anthrenus_, _Byrrhus_, &c. In the
last-mentioned genus there are cavities in the under side of the trunk,
in each division of the breast, and at the base of the abdomen, to
receive the legs when folded; the _coxæ_ have also a cavity to receive
the _base_ of the thigh. In the _anterior_ legs this last part has a
longitudinal one on its _upper_ side, and in the four _posterior_ on
the _under_, which receives the _tibiæ_, which at the inner edge are
straight, and at the outer curvilinear, and the _tarsi_ are turned up
and received by the concave part, on the _anterior_ side of the _first_
pair and the _posterior_ side of the two _last_ of the _tibiæ_, so
as to lie between it and the body: when the legs are close packed,
the animal looks almost as if it had none. I have observed that when
_Dytisci_ repose on the water, the posterior legs are turned up and
laid over the elytra, and curved towards the head.
vi. _Pectines._ I must next say a few words upon a remarkable organ,
which seems in some degree supplementary to the _legs_, by which
the CREATOR has distinguished the genus _Scorpio_, called from
its parallel teeth, set in a back, their _pecten_ or comb[2120].
This back consists of two or more articulations, is attached by
its anterior extremity to the sides of the posterior piece of the
_mesostethium_, and is marked by a longitudinal furrow or channel.
The teeth, which vary in number in the different species, and in
the same species at different periods of its growth, are usually
ovato-lanceolate, or obtusangular, furnished on their exterior edge
with what appears to be a longitudinal sucker, and supported between
their bases, or at the base, both within and without, by triangular,
conical, or subglobose props. With regard to the _use_ of these
organs, it has not been clearly ascertained. Amouroux states that
he has seen the animals use them as feet, and he conjectures that
by them they may fix themselves and turn upon them as on a pivot,
when they have to make a retrograde movement[2121]. M. Latreille,
from their having branchial pouches immediately under them, seems to
think that they are connected with respiration[2122]. This may be
true; but from the suckers just described, I am inclined to think
with Amouroux, that they are useful to the animal in its _motions_,
and that like the suckers of the Gecko, flies, &c., they enable it to
support itself against gravity and to climb perpendicular surfaces.
Whether the five obtriangular plates, elevated on a pedicle, which are
found arranged in a series on the under side of each of the jointed
_coxæ_ of the posterior legs in _Galeodes_, are at all analogous to the
pectens of scorpions, has not been ascertained[2123]. M. Leon Dufour
watched them very attentively in one species (G. _intrepidus_), but he
could observe no motion in them[2124].
FOOTNOTES:
[1585] For the reason which induced the authors to use this word
instead of _Terminology_, before employed, see VOL. I. _Pref._ p.
xii--. They are gratified to see that M. Latreille has adopted this
term in the work quoted on the other side, p. 194.
[1586] _Organisation Extérieure des Insectes_, Mém. du Mus. _t._ viii.
[1587] _Ibid._ 199--. I have never been able to procure M. Audoin's
_Mémoire_ on this subject.
[1588] _Fundament. Entomolog._ in _Amœn. Acad._ vii. 143.
[1589] _Terminologie_, 1578, &c. He afterwards called the trunk
_Stethidium_: _Terminologie der Insekten_ Magaz. 1806. 14.
[1590] _Organisation_, &c. 198.
[1591] In _Nirmus Anseris_, &c. however, in this Order, the same
distinction is observable.
[1592] PLATES VIII. & IX. _á_.
[1593] PLATE VIII. _a._
[1594] If the head of any individual of these two Orders be carefully
taken off, it will be found that above there is a very short piece
representing the _prothorax_, and quite unlike the collar of
_Hymenoptera_.
[1595] PLATE VIII. FIG. 1.
[1596] Ibid. FIG. 2. _a´_.
[1597] Ibid. FIG. 1, 10. a.
[1598] Ibid. b.
[1599] Ibid. c.
[1600] Ibid. _b_.
[1601] Ibid. _a_.
[1602] See above, p. 327--.
[1603] Coquebert _Illustr. Ic._ ii. _t._ xviii. _f._ 2, 4.
[1604] Stoll _Cigales_ _t._ xxi. _f._ 116.
[1605] _Ibid. t._ xi. _f._ 53.
[1606] PLATE II. FIG. 4.
[1607] PLATE XIII. FIG. 18. _a_.
[1608] Stoll _Cigales t._ xxviii. _f._ 163.
[1609] _Ibid._ _t._ xxi. _f._ 115. Coquebert _Illust. Ic._ ii. _t._
xviii. _f._ 5.
[1610] Stoll _Spectres_ _t._ xi. _f._ 42. _t._ xii. _f._ 45. _t._
xvi. _f._ 58, 59.
[1611] PLATE IX. FIG. 4.
[1612] _Sur le Vol des Ins._ c. vii. 374. _t._ xviii. _f._ 9. _i i._
[1613] PLATE IX. FIG. 5.
[1614] _Theatr. Ins._ 98.
[1615] De Geer iv. 74.
[1616] _Organisation Extérieure des Ins._ 177.
[1617] A subgenus, related to _Lebia_ (_Hexagonia_ K. MS.) and some
_Cimicidæ_, are so circumstanced.
[1618] _Regne Animal_ iii. _t._ xiii. _f._ 6.
[1619] See above, p. 398.
[1620] PLATE XIII. FIG. 17.
[1621] PLATE VIII. FIG. 10.
[1622] Ibid.
[1623] _Linn. Trans._ vi. _t._ xxi. _f._ 10.
[1624] _Ibid._ _f._ 8.
[1625] PLATE VIII. _b._
[1626] See above, p. 536.
[1627] Something of the kind is observable at the base of the other
legs in this tribe.
[1628] Monro _On the Bones_, 160.
[1629] PLATE VIII. _d´._
[1630] Ibid. FIG. 7. _d´._
[1631] Kirby in _Linn. Trans._ xiv. _t._ iii. _f._ 4. i.
[1632] It is doubtful whether M. Latreille's _Harpalus megacephalus_
is synonymous with _Carabus megacephalus_ Fab. Comp. _Gen. Crust. et
Ins._ i. 206. with _Syst. Eleuth._ i. 187. 95.
[1633] VOL. II. p. 317--.
[1634] PLATE VIII. FIG. 11. _b._
[1635] _Linn. Trans._ iv. 53.
[1636] _Syst. Nat._ i. Cancer. Scorpio.
[1637] Moses, when he describes insects as going upon _four_ legs,
evidently considers the anterior pair as _arms_; Bochart does the
same. _Levit._ xi. 20--. _Hierozoic._ ii. 497.
[1638] PLATE XXVII. FIG. 31.
[1639] PLATE XV. FIG. 5, 6.
[1640] Samouelle _t._ v. _f._ 4.
[1641] PLATE IX. _g._
[1642] Latreille _Organization_ &c., 199. Chabrier _Sur le Vol des
Ins._ c. i. 412. c. iv. 54, &c.
[1643] In _Chlorion_, _Ammophila_, &c., this part separates more
readily from the alitrunk.
[1644] Chabrier _Sur le Vol des Ins._ c. i. 413--. c. iv. 54.
This author seems to regard the _collar_ as something peculiar to
_Hymenoptera_.
[1645] See above, p. 536.
[1646] PLATE IX. FIG. 11.
[1647] PLATE IX. FIG. 6. a.
[1648] Ibid. FIG. 7. _g´_.
[1649] M. Chabrier (_Vol. des Ins._) supposes that the _humming_ of
insects is produced by the exit of the superfluous air from their
thoracic spiracles, &c.; in _Melolontha_ he thinks they are in the
_metathorax_ under the wings (c. i. 457--. PLATE XXII. FIG. 13. c. †.
represents the _operculum_ of one of those of _Dytiscus marginalis_):
in the _Hymenoptera_, in the _mesothorax_, near the posterior lobes
of the collar (Ibid. 459. c. iv. 50.); and in the _Diptera_, in the
_metathorax_, near the poiser (c. i. 457). I observed myself lately,
that _Elophilus tenax_, if held by the anterior part of the body,
when it hummed, alternately opened and shut this spiracle. The wings
during the sound vibrated intensely. The hum ceased and was renewed,
as they were restrained from this motion or released from restraint;
when the wing was moved towards the head, a different sound was
emitted from that produced when it merely vibrated.
[1650] PLATE IX. FIG. 11. _g´._
[1651] PLATES VIII. IX. _i´._
[1652] When the _prothorax_ is separated from the elytra by a kind of
isthmus, as in _Scarites_, _Passalus_, &c., the _dorsolum_ is more or
less uncovered.
[1653] PLATE VIII. FIG. 16. 20. _i´._
[1654] PLATE IX. FIG. 7. _i´._
[1655] Ibid. FIG. 10. _i´._ _k´._
[1656] Ibid. FIG. 1. _i´._ _k´._
[1657] Ibid. FIG. 11. i´.
[1658] PLATES VIII. IX. XXVIII. _k´._
[1659] Audoin, Chabrier, &c.
[1660] Olivier. He seems also to have thought that neither the
_Orthoptera_ nor Homopterous _Hemiptera_ have this part. _N. Dict.
d'Hist. Nat._ x. 112.
[1661] PLATE VIII. FIG. 3. _k´._
[1662] In _Macraspis_ MacLeay it is often half as big as an elytrum.
[1663] PLATE VIII. FIG. 12. _k´._
[1664] Mr. W. S. MacLeay opposes the _Hemiptera_ to the _Orthoptera_,
the _Homoptera_ to the _Neuroptera_, and the _Aptera_ to the
_Coleoptera_: but if analogous structure be made the guide, I think
my arrangement will be found most correct. _Hor. Entomolog. 367._
[1665] PLATE VIII. FIG. 20. _k´._
[1666] Ibid. FIG. 16. _k´._
[1667] PLATE IX. FIG. 1. _k´._ N. B. This is from _Cossus_ F.
[1668] PLATE IX. FIG. 7. _k´._
[1669] Ibid. FIG. 11, 15. _k´._
[1670] _Mon. Ap. Angl._ i. _t._ vi. _Apis._ ** a. _f._ 2. _a a._
[1671] Stoll _Cigales_ _t._ xxviii. _f._ 164.
[1672] PLATE IX. FIG. 12. _k´._
[1673] PLATES VIII. IX. XXVIII. _l'._
[1674] PLATE XXIII. FIG. 6. _e´´´._
[1675] PLATE VIII. FIG. 12. _l´._
[1676] Ibid. FIG. 20. _l´._
[1677] PLATE XXVIII. FIG. 11. _l´._
[1678] Chabrier _Sur le Vol des Ins._ c. iii. _t._ viii-v. B. _i._
[1679] PLATE IX. FIG. 7. _m´._
[1680] Chabrier _Sur le Vol des Ins._ c. iii. 354.
[1681] From πνυμι to breathe and σέγω to cover.
[1682] PLATES VIII. IX. _n_´.
[1683] At first I had named this piece the _antecosta_, and the
_mesostethium_ the _postcosta_; and there is certainly some analogy
between the thorax of insects, consisting of several pieces that follow
each other, and the vertebral column; between their three _sternums_
and the _sternum_, and between their other pieces and the _ribs_ of
vertebrate animals. Comp. Chabrier, _ubi supr._ c. iv. 49. note 1.
[1684] PLATES VIII. IX. _o´._
[1685] PLATE VIII. FIG. 12. 13. _o´._ _z´._
[1686] Ibid. FIG. 17. _o´._
[1687] PLATE IX. FIG. 8. _o´._ _z´._
[1688] Ibid. _o´._
[1689] PLATE IX. FIG. 8. a.
[1690] Ibid. FIG. 12. _o´._
[1691] PLATE VIII. FIG. 3, 13. _p´._
[1692] _Linn. Trans._ xii. _t._ xxii. _f._ 4.
[1693] A remarkable instance of analogy is afforded by this genus. In
_Erotylus_ there are two groups; one distinguished by gibbous elytra,
and the other by flatter ones. The same distinction is observable in
_Spheniscus_; for to this genus belongs _Helops fasciatus_ Oliv.,
which represents the flat _Erotylí_, and even individually _Erotylus
trifasciatus_ Oliv., _E. fasciatus F._
[1694] I would restrict this name to the conical-headed _Locustæ_ F.
[1695] PLATE VIII. IX. _t´._ _Linn. Trans._ xi. _t._ ix. _f._ 16. c.
[1696] PLATE VIII. FIG. 3. _t´._
[1697] Ibid. FIG. 12. Comp. _i´_, _k´_, _l´_, with _t´_, _u´_, _v´_.
[1698] PLATE IX. FIG. 7. _t´._
[1699] Ibid. FIG. 11. _t´._
[1700] PLATE IX. FIG. 19, 20. _t´._
[1701] See above, p. 558--.
[1702] PLATES VIII. IX. _u´._
[1703] PLATE VIII. FIG. 3. _u´._
[1704] Ibid. VIII. FIG. 12. _u´_. PLATE IX. 7. _u´._
[1705] PLATES VIII. IX. _v´._
[1706] PLATE VIII. FIG. 3. _v´._
[1707] PLATE VIII. FIG. 12, 16.; and PLATE IX. FIG. 7. _v´._
[1708] PLATE VIII. FIG. 3. _w´._
[1709] PLATE XXII. FIG. 14. _w´._
[1710] PLATE XXIX. FIG. 25. _w´._
[1711] Ibid. and PLATE VIII. FIG. 12.; and PLATE IX. FIG. 7. _k´´._
[1712] _Sur le Vol des Ins._ c. iii. 354.
[1713] See above, p. 572.
[1714] PLATE IX. FIG. 15. _k´´._
[1715] PLATE IX. FIG. 11. _k´´._
[1716] Ibid. FIG. 20. _k´´._
[1717] PLATES VIII. IX. _y´._
[1718] PLATE VIII. FIG. 4. _z´._
[1719] Ibid. _p´´._
[1720] Ibid. _y´._
[1721] PLATE VIII. FIG. 13. _y´._ _a´_ †.
[1722] PLATE XXVII. FIG. 50.
[1723] PLATES VIII. IX. _z´._
[1724] PLATE VIII. FIG. 4. _z´._
[1725] PLATE XXIX. FIG. 15. _z´._
[1726] PLATE IX. FIG. 8. z´.
[1727] PLATES VIII. IX. _a_ †.
[1728] See above, p. 565.
[1729] PLATE VIII. FIG. 8. _a_ †.
[1730] De Geer iv. _t._ iv. _f._ 3. _d d._ _c c._
[1731] PLATE VIII. FIG. 13. _a_ †.
[1732] The history of this parasite has been traced by Dr. Reid; but
alas! this learned and acute observer of nature did not live to give
his discoveries to the world: it is hoped, however, they will not be
lost, being in most able hands.
[1733] PLATE VIII. FIG. 18. and XXII. FIG. 13. _c_ †.
[1734] VOL. II. p. 405.
[1735] _Sur le Vol des Ins._ c. i. 459.
[1736] Ibid. 457--.
[1737] PLATE XXII. FIG. 13. _c_ †.
[1738] _Mem. sur les Anim. sans Vertèbr._ 45--. _Hor. Entomolog._ 411--.
[1739] PLATE VIII. FIG. 3. _x´_. IX. FIG. 2. _s´_. and XXII. FIG. 5-14.
[1740] PLATE XXII. FIG. 8-11.
[1741] VOL. II. p. 318.
[1742] PLATE XXII. FIG. 8, 11. _h´_.
[1743] PLATE XXII. FIG. 9, 11. _s´_.
[1744] Ibid. FIG. 9. a a.
[1745] Ibid. FIG. 11. a.
[1746] Ibid. b.
[1747] PLATE IX. FIG. 2. _s´._
[1748] PLATE XXII. FIG. 10, 11. _x´._ Comp. _Linn. Trans._ xi. _t._
ix. _f._ 16. g.
[1749] PLATE XXII. FIG. 10, 11. d.
[1750] Ibid. FIG. 9. c.
[1751] Ibid. FIG. 10. a.
[1752] Ibid. FIG. 9-11. _l´´._
[1753] PLATE XXII. FIG. 5-7.
[1754] Ibid. FIG. 7.
[1755] Ibid. a.
[1756] Ibid. _e´._
[1757] See above, VOL. I. p. 191. and II. p. 257, 366.
[1758] This machine is described by Dr. Eschscholtz, _Beiträge zur
Naturkunde_, &c. Heft. i. 24--. _t._ i. ii.
[1759] PLATE XXII. FIG. 6.
[1760] PLATE XXII. FIG. 6. a.
[1761] Ibid. b.
[1762] Ibid. FIG. 5. _b_ †.
[1763] MacLeay, _Horæ Entomolog._ 9. Chabrier, _Sur le Vol des Ins._
c. i. 417.
[1764] PLATE XXII. FIG. 5. b b b.
[1765] Ibid. c.
[1766] Luke xii. 7.
[1767] See above, p. 397--.
[1768] See above, p. 580.
[1769] Chabrier _Sur le Vol des Ins._ c. i. 413--.
[1770] See above, p. 402.
[1771] Chabrier _Sur le Vol des Ins._ c. i. 446, 448, 451--.
[1772] Ibid. 412.
[1773] Ubi supr. c. ii. 333.
[1774] According to M. Chabrier, who agrees with him, M. Latreille
also is of opinion, that the _parapleura_ is the analogue of the
posterior _coxæ_. _Ubi supra_, c. ii. 312. Note 2.
[1775] M. Latreille has changed the denomination of this Order to
_Rhiphiptera_, because at first he thought that these organs were
not at all analogous to elytra or wings; but since, upon further
investigation, he appears to admit that they assist in flight (_Annales
Génér. des Scienc. Phys._ VI. xviii. 8. Compare MacLeay, _Hor. Entom._
423. Note *), in common justice he is bound to restore the name
originally given to the Order. In the same place of the work here
quoted, M. Latreille also speaks of these _pseudelytra_, as I would
call them, as appendages of the _mesothorax_: but whoever consults
Mr. Bauer's admirable figures of _Xenos Peckii_ (_Linn. Trans._ xi.
_t._ ix.), and is aware of the unimpeached and minute accuracy of that
admirable microscopic artist, will be convinced that they belong to the
_anterior_ legs, and consequently to the _prothorax_.
[1776] PLATE X. and PLATE XXVIII. FIG. 18-23.
[1777] Chabrier, _Analyse_, &c. 27.
[1778] _N. Dict. d'Hist. Nat._ ix. 568. We have seen above (p. 578.)
that the wings of insects are connected with their legs by the
_scapula_ and _parapleura_.
[1779] MacLeay, _Hor. Entomolog._ 413--. Mr. MacLeay's opinion seems
to receive some confirmation from a circumstance overlooked when the
_larvæ_ of insects were treated of above (p. 130--), and to which
he alludes (411); namely, that in _that_ state they consist of two
segments more than in the _imago_; these follow the three pedigerous
segments, have no pro-legs, and are supposed to belong to the trunk
rather than to the abdomen. To make this circumstance bear upon the
question, it must be proved that in the perfect insect these segments
in some manner become the back of the trunk and bear the wings. This
would not be more wonderful than many changes that are known to occur
in insects.
[1780] Latreille, _Organization extérieure des Ins._ 173--.
[1781] For instance _Meloe_, the female glow-worm, _Lygæus
brevipennis_, _Ephemera diptera_, _Cynips aptera_, neuter ants, &c. &c.
[1782] See above, p. 559.
[1783] _Chionea araneoïdes_ Dolm.
[1784] See above, p. 560, and VOL. II. 348, 352--.
[1785] See above, p. 591, Note c.
[1786] De Geer, iii. _t._ xvii. _f._ 10, 11. _f f_. M. Savigny has
noticed a part in some _Annelides_, which he regards as analogous to
_elytra_. _Système des Annelides_, 4, 9, 11.
[1787] VOL. II. p. 346--.
[1788] PLATES X. and XXVIII. _b^.._
[1789] Ibid. _c^.._
[1790] Ibid. _d^.._
[1791] PLATE XXVIII. FIG. 3-5. _b´´´._
[1792] Chabrier _Sur le Vol des Ins._ c. i. 439.
[1793] PLATE XXVIII. FIG. 10.
[1794] Chabrier _ubi supr._
[1795] PLATE XXVIII. FIG. 6-8. _d´´´._
[1796] Ibid. FIG. 3-5. _b´´´._
[1797] PLATE XXVIII. FIG. 3.
[1798] PLATE X. FIG. 1. _c´´´._
[1799] PLATE X. FIG. 1. c.
[1800] PLATE XXVIII. FIG. 6-8. _d´´´._
[1801] PLATE XXVIII. FIG. 8.
[1802] See above, p. 582.
[1803] See above, p. 402--.
[1804] Ibid. 399.
[1805] _Sur le Vol des Ins._ i. c. 428--. c. ii. 325.
[1806] Oliv. _Ins._ No. 97. _Cassida_, _t._ i. _f._ 10.
[1807] See above, p. 397--.
[1808] See above, p. 399--.
[1809] M. Chabrier says that the arc described by the _wings_ of
_Melolontha vulgaris_ to that of the _elytra_, is as 200 to less than
50. _Sur le Vol des Ins._ c. i. 440.
[1810] PLATE X. FIG. 2. and XXVIII. FIG. 18-20.
[1811] _Magas._ 1806. _Terminologie der Insekt._ 18. 1675.
[1812] PLATE X. FIG. 2. is the tegmen of a _Blatta_ divided into areas.
[1813] _Sur le Vol des Ins._ c. ii. 327--.
[1814] PLATE X. FIG. 2. _b^.._
[1815] Ibid. _c^.._
[1816] Ibid. _d^.._
[1817] Stoll, _Cigales_, _t._ viii. _f._ 39.
[1818] PLATE X. FIG. 2.
[1819] Stoll _Grillons_ _t._ i. c. _f._ 2.
[1820] Ibid. _Spectres_ _t._ xxv. _f._ 95. and xi. _f._ 42.
[1821] Ibid. _t._ ii. _f._ 5. _Grillons_ _t._ i. c. _f._ 1.
[1822] Ibid. _Spectres_ _t._ xvi. _f._ 58.
[1823] Ibid. _Sauterelles à Sabr._ _t._ iii. _f._ 7. By this name
(_Pterophylla_) I distinguish those _Locustæ_ F. without a conical
head that are veined like leaves.
[1824] Stoll _Ibid._ _t._ vi. a. _f._ 18. and PLATE XXVIII. FIG. 19.
[1825] Stoll _Sauterel. à Sabr._ _t._ i-iii.
[1826] Ibid. _Spectres_ _t._ iv. _f._ 14.
[1827] Ibid. _Cigales_ _t._ i. _f._ 1, 3-5. and _t._ vi. _f._ 31.
[1828] Stoll _Cigales_ _t._ iii. _f._ 12-15. and _t._ xvii. _f._ 92.
[1829] _Linn. Trans._ xii. 449, no. 96.
[1830] VOL. I. p. 395--.
[1831] _Linn. Trans._ xiii. _t._ i. _f._ 14. _Flata_ should come
before this genus.
[1832] Of this kind is one of Stoll's _Cigales_, _t._ xxv. _f._ 141.
[1833] PLATE XXVIII. FIG. 18.
[1834] Stoll _Cigales_ _t._ i. _f._ 1. _t._ x. _f._ 46. _t._ xxix.
_f._ 170. _t._ v. _f._ 22. _t._ iv. _f._ 19. &c.
[1835] PLATE X. FIG. 3.
[1836] In Latreille's whole genus _Pentatoma_, including several
Fabrician genera, the _Hemelytra_ are more substantial than in the
subsequent tribes.
[1837] See above, p. 607.
[1838] Ibid. p. 600.
[1839] My insect, which nearly resembles the Coleopterous genus
_Cerylon_ Latr., agrees with Latreille's description in all respects,
except that it cannot be said to be _membrana nulla apicali_.
[1840] Chabrier _Analyse_, &c. 24.
[1841] PLATE X. FIG. 3. _b^.._
[1842] Ibid. _c^.._
[1843] Ibid. _d^.._
[1844] PLATE XXVIII. FIG. 23. _f´´´_ is the _corium_ and _g´´´_ the
_membrana_ of a species of _Reduvius_ F.
[1845] PLATE XXVIII. FIG. 23.
[1846] Chabrier _Analyse_, &c. 23.
[1847] Chabrier _Sur le Vol des Ins._ c. ii. 325--. and 326. Note 1.
[1848] See above, p. 572--.
[1849] PLATE XXVIII. FIG. 9. a.
[1850] See above, p. 572.
[1851] Ibid. p. 560. and PLATE XXVIII. FIG. 11. a.
[1852] PLATE IX. FIG. 5.
[1853] Ibid. FIG. 11. 12. _g´´._
[1854] Stoll _Sauterelles à Sabr. t._ iv. _f._ 12. _t._ vi. _f._ 21. &c.
[1855] _Sur le Vol. des Ins._ c. i. 424.
[1856] The idea of dividing the wing of an insect into larger areas
seems first to have been acted upon in _Monogr. Apum Angl._ (1801), in
which those of _Hymenoptera_ were stated to consist of three portions,
viz. _Basis_, _Medium_, _Apex_ (i. 211.); which mode of dividing them
was at first adopted by M. Latreille (_Gen. Crust. et Ins_. iii.
226. Note 1.) The same learned author (Ibid. iv. 239.), with regard
to the _Diptera_, made a near approximation to the plan of dividing
wings into longitudinal areas, but by the addition of a _basal_ area,
which interrupts the attention to the communication of the areas with
their _axes_, he has rendered his system less perfect. Two of his
terms--_Costal Area_ and _Intermediate Area_, are here adopted; but
his _Internal_ is changed to the _Anal_ Area, for the term _internal_
belongs rather to the base of the wing. M. Latreille afterwards
relinquished both these plans, _N. Dict. d'Hist. Nat._ i. 248--.
[1857] PLATE X. and XXVIII. _b^.._ _i^.._ is the Postcostal Nervure.
[1858] Ibid. _c^.._ _n^.._ is the Anal Nervure.
[1859] Ibid. _d^.._
[1860] PLATE X. FIG. 7. _h^.._ _i^.._ _k^.._
[1861] Ibid. FIG. 8. 9. 12. _a_ *.
[1862] _Sur le Vol. des Ins._ c. i. 428.
[1863] See above, p. 600. 616.
[1864] VOL. II. p. 358--. See above, p. 559.
[1865] VOL. II. p. 346--.
[1866] Jurine _Hymenopt._ 19. and _t._ v.
[1867] PLATE X. FIG. 4.
[1868] _N. Dict. d'Hist. Nat._ i. 251.
[1869] See above, p. 564, 578, 591.
[1870] PLATE X. _h^.._
[1871] Ibid. FIG. 4, 11. _m´´´._
[1872] PLATE X. FIG. 14. _k^.._
[1873] Ibid. FIG. 12. _k^.._
[1874] Ibid. FIG. 8. 9.
[1875] Jurine _Hymenopt._ _t._ v. Gen. 47.
[1876] PLATE X. FIG. 4.
[1877] Ibid. a. _n^._, _o^.._
[1878] Ibid. _m^.._
[1879] Ibid. _l^.._
[1880] Ibid. a.
[1881] Ibid. _o´´´._
[1882] PLATE II. FIG. 1. Comp. _Linn. Trans._ xi. _t._ ix. _f._ 1.
[1883] PLATE X. FIG. 5.
[1884] Ibid. _n^._, _o^._, _p^.._
[1885] Stoll _Spectres_, _t._ xviii. _f._ 65.
[1886] See above, p. 624.
[1887] Stoll figures _Empusa_ as without them, _t._ ix. _f._ 35. but?
I have a nondesc. _Phasma?_ without them.
[1888] Jones in _Linn. Trans._ ii. _t._ viii. _f._ 2.
[1889] _Ibid. f._ 5.
[1890] Jones in _Linn. Trans._ ii. _t._ viii. _f._ 7.
[1891] _Ibid._ _f._ 9.
[1892] _Ibid._ _f._ 2, 3, 6-9.
[1893] I wonder Mr. Jones's plan of ascertaining the divisions
or subgenera of butterflies by the neuration of their wings has
never been followed up; it would I think furnish an easy clue for
the extrication of the tribes of all the _Lepidoptera_. I mean as
subsidiary to more important characters.
[1894] PLATE X. FIG. 6. _l^._, _m^.._
[1895] Ibid. FIG. 8.
[1896] PLATE X. FIG. 8. basal _e^._, medial _f^._, apical _g^.._
[1897] Jurine _Hymenopt._ _t._ v. Gen. 48.
[1898] _Ibid._ Gen. 47.
[1899] _Ibid._ Gen. 45, 46. Comp. PLATE X. FIG. 11.
[1900] Jurine _Ibid._ Gen. 43.
[1901] _Ibid._ _t._ iv. Gen. 47.
[1902] _Ibid._ _t._ v. Gen. 40.
[1903] _Ibid._ _t._ ii. Gen. 2.
[1904] This is a remarkable insect belonging to _Vespa_ L., related
to the hornets (_V. Crabro_), distinguished by having a semicircular
piece taken out of the internal margin of each mandible, so that when
these organs are closed there is a circular orifice,--whence the name
_Cyclostoma_.
[1905] Jurine _Hymenopt._ _t._ ii. Gen. 2.
[1906] _Ibid._ Ord. ii. Gen. 2.
[1907] _Ibid._ _t._ iii. Gen. 3.
[1908] _Ibid._ _t._ v. Gen. 41.
[1909] _Ibid._ _t._ xii. Gen. 40.
[1910] _Ibid._ _t._ v. Gen. 39.
[1911] _Ibid._ _t._ iv. Gen. 29.
[1912] _Ibid._ _t._ v. Gen. 42.
[1913] This _Cynips_ inhabits a long polythalamous gall of the bramble.
[1914] Jurine _Ibid._ _t._ ii. Gen. 11.
[1915] _Ibid._ Ord. ii. Gen. 1.
[1916] _Ibid._ _t._ iv. Gen. 23.
[1917] _Ibid._ Gen. 30-32.
[1918] _Ibid._ _t._ v. Gen. 40.
[1919] PLATE X. FIG. 12, 15. _c^.._
[1920] Ibid. FIG. 15. _f^.._
[1921] Ibid. FIG. 12. _g^.._
[1922] Ibid. FIG. 13.
[1923] Ibid. FIG. 15. c.
[1924] Ibid. d.
[1925] Ibid. FIG. 14. e.
[1926] Leach on _Eproboscideous Insects_, _Mem. Wern. Soc._ 1817.
_t._ xxv. _f._ 3, 5, 8, &c.
[1927] _Ibid. t._ xxvi. _f._ 7, 10, 13.
[1928] Insects with _short_ elytra of course must fold their wings
nearer the base than those with _long_ ones.
[1929] PLATE X. FIG. 4. _o´´´._
[1930] See above, p. 611.
[1931] See above, p. 613, and Chabrier _Analyse_, &c. 24.
[1932] PLATE XXIII. FIG. 5.
[1933] PLATE X. FIG. 5.
[1934] PLATE XXVIII. FIG. 22.
[1935] See above, p. 608--.
[1936] Stoll _Grillons_, _t._ iii. c. _f._ 11-13.
[1937] _Ibid._ _t._ i. c. _f._ 1, 2.
[1938] See above, p. 636.
[1939] See above, p. 625.
[1940] Ibid. p. 635, 637. &c.
[1941] PLATE X. FIG. 4, 5. and XXVIII. FIG. 21, 22.
[1942] PLATE X. FIG. 6-14.
[1943] Ibid. FIG. 4, 5. and XXVIII. FIG. 21, 22.
[1944] PLATE X. FIG. 4.
[1945] Ibid. FIG. 5.
[1946] PLATE X. FIG. 6.
[1947] Ibid. FIG. 8-11.
[1948] Ibid. FIG. 12-15.
[1949] PLATE XIV. FIG. 4.
[1950] Ibid. FIG. 2.
[1951] In _Gastropacha quercifolia_, &c., amongst the _Nocturnal
Lepidoptera_, these sinuses exist, in the upper wing _ten_, and in
the lower _nine_, but without the folds.
[1952] PLATE XIV. FIG. 1. _s._
[1953] Ibid. FIG. 3.
[1954] For some uses of hairs, see above. p. 399--.
[1955] _Analyse_, 24. He seems to think that certain crooked hairs,
in some wings, supply the place of folds. _Ibid._
[1956] PLATE X. FIG. 13.
[1957] Reaum. iv. _t._ xxxix. _f._ 4-11.
[1958] A portion of the antenna of the insect here mentioned is
figured PLATE XII. FIG. 23.
[1959] De Geer i. 63--.
[1960] Reaum. i. 200.
[1961] Hoole's _Leeuwenhoek_. i. 63--.
[1962] De Geer has given 34 figures of different scales (i. _t._ iii.
_f._ 28); and in PLATE XXII. FIG. 6. a-w. 22 others, collected from
Reaumur, are given.
[1963] Stoll _Sauterelles à Sabre_. _Pterophylla ocellata t._ i. ii.,
_Cigales_, _Fulgora laternaria t._ i. _f._ i., and _F. serrata t._
xxix. _f._ 170.
[1964] _Ibid._ _Sauter. de Passage_, _Locusta Dux t._ i. 5. _L.
carinata t._ v. b. _f._ 16. _L. cristata_ _t._ ix. b. _f._ 30. &c. &c.
[1965] PLATE XXV. FIG. 30.
[1966] Scopoli, Hubner.
[1967] PLATE III. FIG. 1.
[1968] _N. Dict. d'Hist. Nat._ viii. 257.
[1969] See above, p. 303.
[1970] Sepp. I. i. _t._ vii. _f._ 6.
[1971] Rœmer _Genera t._ xxii. _f._ 2.
[1972] Sepp I. iii. _t._ ii. _f._ 7.
[1973] Ibid. i. _t._ vi. _f._ 7.
[1974] Rœmer _ubi supr. t._ xiv. _f._ 1.
[1975] PLATES _f^._, _r^._, _d_†.
[1976] See above, p. 546--.
[1977] Ibid. 131--.
[1978] VOL. II. p. 307.
[1979] De Geer i. _t._ xx. _f._ 11.
[1980] _Règne Animal._ iii. 546.
[1981] PLATE XXVII. FIG. 44, 45.
[1982] VOL. II. p. 312, 363, 365.
[1983] See above, p. 546--.
[1984] _Anatom. Compar._ i. 453.
[1985] See above, p. 308.
[1986] PLATE XXVII. FIG. 18, 19.
[1987] Mr. Montague describes the legs of _Nycteribia_, as _dorsal_
(_Linn. Trans._ xi. 13); but Dr. Leach calls them _lateral_
(Samouelle, 303).
[1988] _N. Dict. d'Hist. Nat._ xxviii. 247.
[1989] PLATE XXIII. FIG. 4.
[1990] PLATE XXVII. FIG. 58. M. Savigny affirms that these insects
cannot have, and really have not, but one pair to each segment; only
that the segments are alternately membranous and shelly, and that
the former are concealed under the latter (_Anim. sans Vertebr._ I.
i. 44.): but, _pace tanti viri_, I cannot discover that any _suture_
separates these portions from each other: so that, admitting his
theory, they must be regarded as two segments soldered together.
[1991] It is by this arrangement of the legs that _Pachysoma_ is
principally distinguished, as a subgenus, from _Scarabæus_ M^cL.
[1992] See above, p. 37.
[1993] _Monogr. Ap. Angl._ i. _t._ xi. _Apis_ **. d. 2. α. _f._ 18.
ii. 296--.
[1994] Oliv. _Ins._ 68. _t._ i. _f._ 8.
[1995] _Ibid._ n. 6. _t._ iv. _f._ 22.
[1996] See above, p. 305--.
[1997] This variety appears to differ very little from the _Curculio
imperialis_ of Fabricius and Olivier, except in the remarkable
hairiness of its legs.
[1998] VOL. II. p. 563.
[1999] Oliv. _Ins._ n. 67. _t._ xx. _f._ 156.
[2000] See above, p. 591. Some physiologists have been of opinion,
that in _birds_, what is called the _thigh_ should properly be
denominated the _tibia_, and that this last is really the _tarsus_.
Illiger, _Terminologie_, 184. § 185. n. 1246.
[2001] PLATES XIV. XV. XXVII. _p._
[2002] PLATE XV. FIG. 1. _p´´_, _r´´_.
[2003] PLATE XXVII. FIG. 27.
[2004] L. Dufour, _Descr. des six Arachn._ &c.: _Annales Generales_,
&c. 1820. 19. _t._ lxix. _f._ 7. _d_.
[2005] PLATE XIV. XV. XXVII. _q´´_.
[2006] _N. Dict. d'Hist. Nat._ xvi. 195. xxvi. 157.
[2007] PLATE XXVII. FIG. 12. b.
[2008] PLATE XXVII. FIG. 20. _q´´_.
[2009] Ibid. FIG. 28.
[2010] PLATE XIV. XV. XXVII. _r´´_.
[2011] See above, p. 591, 662.
[2012] VOL. II. p. 314--.
[2013] _Linn. Trans._ xii. _t._ xxi. _f._ 12.
[2014] Stoll _Spectres t._ xvi. _f._ 58, 59.
[2015] Ibid. _t._ xviii. _f._ 65.
[2016] Stoll _Spectres t._ vii. _f._ 25.
[2017] _Ibid. t._ viii. _f._ 30.
[2018] _Ibid. ubi supr_.
[2019] _Ibid. t._ x. _f._ 40.
[2020] PLATE XIV. FIG. 5. This appearance of scales on the thighs is
principally confined to this tribe.
[2021] PLATE XXVII. FIG. 23.
[2022] _Linn. Trans._ xii. _t._ xxii. _f._ 16.
[2023] PLATE XIV. FIG. 5, and XXVII. FIG. 15. _r´´´._
[2024] PLATES XIV. XV. XXVII. _s´´._
[2025] PLATE XXVII. FIG. 21. _s´´´._ M. Savigny (_Anim. sans
Vertèbr._ 1. i. 46. Note _b._) seems to think that this structure
obtains in all his _Apiropods_; viz. the Octopod _Aptera_,
_Arachnida_, and _Myriapoda_: but it seems to me _evident_ only in
the two tribes mentioned in the text.
[2026] PLATE XXVII. FIG. 6, 16, 17. _t´´´._
[2027] PLATE XXVII. FIG. 15. _r´´´._
[2028] Ibid. FIG. 11. _r´´´._
[2029] Ibid. FIG. 10. _t´´´._
[2030] PLATE XXVII. FIG. 8. _Thigh._ a. Protuberance. b. Semicircular
cavity, c. Ridge. FIG. 9. _Tibia._ a. Central cavity. b. Ridge. c.
Exterior cavity.
[2031] Ibid. FIG. 6. a.
[2032] Ibid. FIG. 7. a.
[2033] Ibid. FIG. 15. Thigh of _Locusta_ Leach, a. Sinus in which
the condyle of the tibia works. FIG. 16. Tibia of Do. aa. Lateral
condyles. b. Intermediate one.
[2034] Stoll _Punaises_, _t._ x. _f._ 67. _t._ xvi. _f._ 114.
[2035] Stoll _Punaises, t._ ii. _f._ 14. _t._ viii. _f._ 54. _t._
xxviii. _f._ 201. PLATE XV. FIG. 2.
[2036] See above, p. 671.
[2037] Oliv. _Ins._ n. 66. _t._ iii. _f._ 12. Compare _Scarabæus
longimanus_, _Ibid_ n. 3. _t._ iv. _f._ 27.
[2038] Stoll _Punaises_, _t._ iii. _f._ 20.
[2039] PLATE XXVII. FIG. 31.
[2040] See above, p. 306--.
[2041] Oliv. _Ins._ n. 68. _t._ i. _f._ 8. comp. n. 67. _t._ xii.
_f._ 83. and PLATE XII. FIG. 25. _a._
[2042] VOL. II. p. 365. and PLATE XV. FIG. 5. 6.
[2043] See above, p. 433, Note b. and 404, Note a.
[2044] PLATE XIV. FIG. 5.
[2045] It is remarkable that in this tribe _all_ the legs may be
called _raptorious_, though the thighs are not incrassated, for they
are armed with a double series or more of fine long spurs, which
enable them to catch and retain their prey.
[2046] PLATE XXVII. FIG. 35. _v´´´._ _Philos. Trans._ 1816. _t._ xix.
_f._ 8, 9. See above, VOL. II. p. 331.
[2047] See above, p. 591, 667, &c.
[2048] _Règne Animal_, iii. 191. I have never had an opportunity to
consult Bonelli's _Observ. Entomolog._ on the genus _Carabus_ L. in
the Memoirs of the Turin Academy.
[2049] PLATE XV. FIG. 6. _v´´´._
[2050] Coquebert _Illustr. Ic._ iii. _t._ xxi. _f._ 3. D.
[2051] PLATE XXVII. FIG. 29. _v´´´._
[2052] Most of Latreille's genera of ants are confirmed by
differences in their spurs. Thus _Formica_ is 1:1:1; _Ponera_ 1:2:2
with the internal intermediate one pectinated: _Myrmica_ 1:2:2 with
all symmetrical, &c.
[2053] PLATE XXVII. FIG. 29. _v´´´._
[2054] Ibid. FIG. 33. _v´´´._
[2055] _Linn. Trans._ iv. 200. Note _a_.
[2056] PLATE XXVII. FIG. 32. _v´´´._
[2057] Ibid. FIG. 36. _a^.._
[2058] PLATES XIV. XV. XXVI. XXVII. _a´´_, _t´´._
[2059] PLATE XXVI. FIG. 44, 46, 47. a.
[2060] By Geoffroy--_Hist. Ins._ i. 58.
[2061] The _Cleridæ_, which M. Latreille has placed in the
_pentamerous_ section, vary considerably in the number of their tarsal
joints. Thus in general in _Thanasimus_ the _tarsi_ are _pentamerous_;
but in _T. formicarius_ they appear to be _heteromerous_; and in
_Enoplium_, _Opilo_, _Clerus_ and _Necrobia_ they are _tetramerous_. M.
Latreille's expression, (_N. Dict. d'Hist. Nat._ vii. 172.) "le premier
article etant fort court et caché sous le second," seems to indicate
that there is a _fifth_ joint in some of these, the first being
concealed under the second; but I have never been able to discover it.
Perhaps he reckoned the _pulvillus_ as a joint?
[2062] The term _heteromerous_ properly belongs to _all_ insects in
which the different pairs of tarsi vary _inter se_ in the number of
their joints, and it is here used in that large sense.
[2063] These three genera appear _really_ to have only _six_ legs,
since the pedipalps or maxillary legs are not armed with claws, while
the real representatives of the legs, or three last pair, are so
distinguished. In _Phrynus_ and _Thelyphona_ the anterior pair are
chelate; but in _Galeodes_ they are pediform, as in the _Araneidæ_,
and the great chelæ are the mandibles.
[2064] PLATE XXVI. FIG. 47, 48. _d_ *.
[2065] PLATE XXVI. FIG. 49. _s^.._ a.
[2066] VOL. II. p. 330.
[2067] Dr. Leach says there are _three_ joints in this tribe. _Nat.
Misc._ iii. 80.
[2068] From De Geer's description this insect seems related to
_Agathidium_ (iv. 221--. _t._ viii. _f._ 21-23). M. Leclerck de Laval
discovered it to be _monomerous_. _Règne Animal_, iii. 365.
[2069] PLATE XXVII. FIG. 22.
[2070] See above, p. 311. Note a.
[2071] _Melolontha sericea_ and _aurulenta_. _Linn. Trans._ xii. 463.
400. belong to this subgenus.
[2072] See above, p. 335--.
[2073] PLATE XXVII. FIG. 25.
[2074] PLATE XIV. FIG. 7. _t´´._
[2075] Ibid. FIG. 6. _t´´._
[2076] PLATE XXVI. FIG. 47.
[2077] PLATE XXVII. FIG. 41.
[2078] PLATE XV. FIG. 9.
[2079] _Mon. Ap. Angl._ i. _t._ xii. _neut._ _f._ 20.
[2080] PLATE XXVII. FIG. 44. _s^.._
[2081] PLATE XXVII. FIG. 26. _w´´´._
[2082] See above, p. 396.
[2083] L. Dufour _Descr. de six Arachnides_. Annales, &c. 1820. 19.
[2084] PLATE XXVII. FIG. 51. is the posterior claw of _Hoplia_.
[2085] PLATE XXIII. FIG. 14.
[2086] PLATE XXVII. FIG. 52.
[2087] Ibid. FIG. 46.
[2088] Ibid. FIG. 53, 54.
[2089] Ibid. FIG. 49.
[2090] Ibid. FIG. 38.
[2091] Ibid. FIG. 39.
[2092] This structure is not general in this genus.
[2093] PLATE XXVII. FIG. 40.
[2094] PLATE XXIII. FIG. 14.
[2095] PLATE XXVII. FIG. 43.
[2096] Ibid. FIG. 47.
[2097] Ibid. FIG. 48.
[2098] PLATE XXVII. FIG. 53.
[2099] Ibid. FIG. 51.
[2100] Ibid. FIG. 47.
[2101] Ibid. FIG. 56. _a_ψ, _f_*.
[2102] Ibid. FIG. 49. _a_ψ, _f_*.
[2103] VOL. II. p. 326--.
[2104] _Linn. Trans._ xii. _t._ xxii. _f._ 1.
[2105] For other instances of this structure, see above, p. 336.
[2106] De Geer, iii. 7.
[2107] Ibid. vii. 84. PLATE XXVII. FIG. 60, 63.
[2108] Ibid. FIG. 61.
[2109] VOL. II. p. 327--.
[2110] PLATE XXVII. FIG. 59.
[2111] _Linn. Trans._ xii. _t._ xxi. _f._ 3.
[2112] PLATE XXVII. FIG. 53.
[2113] PLATE XXVII. FIG. 54. _Philos. Trans._ 1816. _t._ xviii. _f._
9-11.
[2114] PLATE XXVII. FIG. 55. _t._
[2115] PLATE XV. FIG. 9. a.
[2116] Ibid. b.
[2117] _Philos. Trans._ 1816. _t._ xx. _f._ 9, 12-15.
[2118] _Philos. Trans._ 1816. _t._ xx. _f._ 4, 11.
[2119] See above, p. 305--.
[2120] PLATE XXVII. FIG. 50.
[2121] Amouroux _Insectes Venimeux_, 44.
[2122] _Observations Nouvelles_, &c. Mém. du Mus. viii. 177.
[2123] _N. Dict. d'Hist. Nat._ xii. 370.
[2124] _Descr. de six Arachnides_, &c. Annales Gen. des Scienc. Phys.
1820. 19. _t._ lxix. _f._ 7. _d._
LETTER XXXVI.
EXTERNAL ANATOMY OF INSECTS
CONTINUED.
THE ABDOMEN, AND ITS PARTS.
The _abdomen_ of insects, which we are next to consider, is the
_third_ great section of the body, and is the seat of the organs of
generation, as well as of a principal part of those connected with
respiration. My remarks upon it will be under the following heads:
Its _substance_; _articulation with the trunk_; _composition_; _shape
and proportions_; its _appendages_; and its _clothing_.
i. _Substance._ Under this head I may observe in general, that where
the abdomen is protected by _hard_ elytra or tegmina, as in most
_Coleoptera_, and many Heteropterous _Hemiptera_, the _upper_ side is
generally of a softer and more flexible substance than the _under_,
which from its exposure requires a greater degree of hardness and
firmness to prevent its being injured. In some,--as the _Dynastidæ_
and those beetles whose elytra are connate, or as it were soldered
together, the former is scarcely more than _membrane_. In others of
the above tribes, nearly the _whole_ of the back of whose abdomen, as
in _Staphylinus_; or only its anal _extremity_, as in _Melolontha_;
or its _sides_, as in _Lygæus_, &c., is not covered by the elytra or
tegmina, that part, as was requisite for its protection, is harder
than the covered portion.
ii. _Articulation with the trunk._ Two distinct modes of this
articulation take place:--in the first the abdomen is united to the
trunk by the _whole_ diameter of its base, without any appearance of
incision; in the other only a _small part_ of that diameter, with
a very visible incision. All the Orders, except the majority of
the _Hymenoptera_ and _Diptera_, and the _Araneidæ_, belong to the
_first_ of these sections; for in all these the aperture by which the
abdomen is suspended to the trunk, occupies the whole of the base;
I say _suspended_, because, though in many cases it inosculates in
the posterior cavity of the latter part, it does not in all, and the
margins of the orifice are united by ligament to those of that cavity.
Indeed, in the _Coleoptera_ and others that have a somewhat prominent
metaphragm[2125], the trunk may with more propriety be said to
inosculate in the abdomen. With regard to the _second_ section,--those
in which the orifice is of less diameter than the base, occupying
only a portion of it,--it may be further subdivided into those whose
abdomen is _sessile_, and those in which it is united to the trunk
by the intervention of a long or short _pedicle_ or footstalk: to
the first of these subdivisions belong all those _Diptera_ that have
an incision between the trunk and abdomen--for many tribes of this
Order, as the _Tipulidæ_, _Asilidæ_, &c., belong rather to the _first_
section--and the _Araneidæ_; the abdomen, however, in _all_ is merely
suspended, without any inosculation. To the _second_ subdivision belong
all the _Hymenoptera_, except the _Tenthredinidæ_ and _Siricidæ_,
the abdomen of which is united to the trunk by the whole diameter
of its base; these may be further subdivided into those that have a
very _short_ pedicle and those that have a _long_ one; but as the
mode of articulation in both these is the same, there will be no
necessity to consider them separately. M. Cuvier has included the
_Diptera_ and _Araneidæ_ in the same tribe with such _Hymenoptera_
as have a petiolate abdomen[2126]; but as the manner in which the
latter articulates with the trunk is widely different from that of
the _Diptera_ &c., I thought it best to consider them as distinct;
especially as in the _Diptera_ there is no tendency to a pedicle,
while only the above two tribes of _Hymenoptera_ are wholly without
it. This learned author thus describes the articulation where the
abdomen is connected by a pedicle. "They have," says he, "a real solid
articulation, a kind of hinge in which the first segment is emarginate
above, and receives a saliant portion of the trunk upon which it moves;
this articulation is rendered solid by elastic and powerful ligaments;
muscles which have their attachment in the interior of the trunk
are inserted in this first segment, and determine the extent of its
movement[2126]." But this passage by no means conveys an adequate idea
of the singular mechanism by which the _Divine Artificer_ has enabled
these little creatures to impart the necessary movements to an organ
so bulky compared with its very diminutive point of attachment. As
no author that has fallen in my way has examined the articulation of
the abdomen with the trunk in these _Hymenoptera_ with the attention
which it merits[2127], I shall enlarge a little upon it. You would
be surprised, and not without reason incredulous, were I seriously
to assert that these insects lift their weighty posteriors by means
of a _rope_ and _pulley_; yet something like this really does take
place, though not with all in a manner equally striking. The point of
articulation in the insects in question, except in _Evania_, is at the
base of the metathorax just above the posterior pair of legs: here
you see a small orifice, either insulated or connected by a narrow
opening with the larger one, when the abdomen is removed, which in
many instances, as in the common wasp, is surmounted by another still
smaller, through which, if you examine it attentively, you will find
there is transmitted a flat and sometimes broadish ligament or rather
_tendon_, in which the levator muscles of the abdomen, attached by
their other end to the metaphragm[2128], terminate: another minute
orifice above the base of the pedicle affords a point of attachment to
the tendon, so as to give it prize upon the abdomen. Here the upper
orifice in the trunk is the _pulley_ (_trochlea_)[2129], the tendon is
the _rope_ (_funiculus_)[2129], and the abdomen is the weight to be
lifted. When the muscles contract, the tendon, running over the edge of
the aperture, is pulled in, and the part just named is elevated; and
when they are relaxed the tendon is let out, and it falls. Some little
variation in the structure takes place in different tribes: thus, in
the _Formicidæ_, _Scoliadæ_, &c., instead of a separate orifice, the
part I call the pulley is merely an upper sinus of the large orifice
that receives the pedicle of the abdomen. The shape of these orifices,
both of the trunk and abdomen, varies in different genera: thus, in the
bee it is triangular, with the vertex reversed; and in the wasp the
upper one is circular, and the lower one transversely oblong; but in
all, the apertures of the trunk correspond with those of the abdomen.
In _Evania_, in which the minute abdomen is inserted in the upper side
of the metathorax, there is scarcely any trace of this structure.
With regard to the articulation of the pedicle itself with the lower
orifice of the trunk, it appears simply suspended, with little or no
inosculation. I may observe under this head, that though the abdomen in
almost all insects is wholly clear of the cavity of the trunk, yet in
some _Phalangidæ_ (_Gonyleptes_ K.) it appears almost retracted within
it[2130].
iii. _Composition._ I shall next consider the _segments_ into which
the abdomen is usually divided, their number, and other circumstances
connected with them. In the _Hippoboscidæ_, _Acaridæ_, _Phalangidæ_,
and _Araneidæ_, the part we are considering is not divided into
segments, though in some instances, as in _Gonyleptes_ and the
cancriform _Epeiræ_[2131], they are represented by _folds_; but in the
great majority of insects it consists of several dorsal and ventral
pieces or segments, forming by their union the _annuli_ or rings into
which it appears divided. The _number_ of these abdominal segments
varies in different insects; I have noticed more than _twenty_ such
variations, and probably there are many more. Before I give you them
in detail, I must first observe that the dorsal and ventral segments,
though sometimes they correspond in number, yet very often do not,
the dorsal most commonly exceeding the ventral by a segment; in a few
cases however the reverse takes place. In the sexes also there is
frequently a difference in the number of segments, as has been before
observed[2132]. I shall express the variations in question by two
figures, the _first_ representing the number of _dorsal_ segments, and
the _second_ the _ventral_--they usually only express the _apparent_
segments: perhaps a very general examination and dissection might bring
many of them nearer to a common type.
1:1. _Chelonus._
3:3. _Chrysidæ_[2133].
4:2. _Leucospis_[2134].
5:5. _Syrphus_.
5:6. _Halictus_ ♀.
6:5. _Nepa._
6:6. { _Halictus_ ♂.
{ _Belostoma._
7:5. { _Curculio_ L.
{ _Cerambyx_ L.
7:6. _Dytiscus_ ♀.
7:7. _Ammophila_, &c.
8:6. { _Dytiscus_ ♂.
{ _Lucanus_, &c.
8:7. _Geotrupes_ Latr.
8:8. _Pimpla._
8:10. _Euchlora_ M^cL.[2135]?
8:13. _Scutigera._
9:5. _Carabus_ Latr.
9:6. _Gymnopleurus_ Ill.
9:7. _Perga_ Leach ♀.
9:8. _Perga_ ♂.
10:7. _Locusta_ Leach ♀.
10:8. --------------- ♂.
10:10. _Æshna._
11:7. _Phasma._
11:9. _Chelifer._
12:11. _Thelyphonus._
Many: _Myriapoda._
I shall next explain the articulation of the segments with each other,
both that of the rings formed by the union of the dorsal and ventral
pieces, and that of those pieces themselves. In general it may be
stated with respect to the former, that each ring is suspended by
ligament to that which precedes it; but this takes place in _three_
ways--in some the margins of the suspended rings _touch_ each other
only, with little or no _inosculation_; in others the _dorsal_ segments
only touch, and the base of each _ventral_ is covered more or less by
the apex of the preceding one; and in others again the base of the
whole ring, both above and below, is so covered, or inosculates. The
first kind here mentioned you will find exemplified in _Melolontha_,
_Geotrupes_, _Musca_, &c.; the second in _Scorpio_; and the third in
_Staphylinus_, the _Hymenoptera_, and many others. In the _Coleoptera_,
says M. Cuvier, speaking of the movements of the abdomen, the rings
only touch each other at the margin, and the movement is very limited;
whilst in the _Hymenoptera_ they are so many little hoops, which
inosculate in each other as the tubes of a telescope, one third only of
their extent often appearing uncovered[2136]. We see the reason of this
structure when we consider the calls they have for greater powers of
movement in this part in laying their eggs, and annoying their enemies
and assailants; and also in the _Staphylinidæ_ to enable them to turn
up their abdomen like a scorpion, both as a posture of attack, and to
fold their wings: in all cases, however, as far as my observation goes,
these animals, when they want to lengthen this part, can disengage the
rings from almost all inosculation, so that no impediment remains to
any movement.
The articulation of the dorsal and ventral segments with each
other is next to be considered. In _Iulus_ and some _Centroti_ the
ring appears to be formed of a single piece, with scarcely any
trace of the existence of any such division; it is however almost
universal, and is of _three_ descriptions; in the first the dorsal
segments are united to the ventral _at_ the lateral margin or edge
of the abdomen; in the second it is _above_ this margin, and in
the third _below_ it. You will find that in _Fulgora_ and many
other Homopterous _Hemiptera_ these segments unite at the margin,
as they do likewise in _Cimex lectularius_ belonging to the other
Hemipterous section; but in the rest of the Heteropterous tribes,
the ventral segments turn upwards, and their union with the dorsal
is in the back of the abdomen; in these the _Hemelytra_ and wings
only cover the dorsal segments, leaving the edge, formed of the
ends of the ventral, uncovered. The Lamellicorn beetles also, and
many other _Coleoptera_, exhibit the same structure. To the last
description, in which the dorsal segments turn down to meet the
ventral, belong the _Lepidoptera_, _Locusta_ Leach; likewise _Sirex_,
_Chrysis_, and many other _Hymenoptera_. The articulation between
these segments is by means of an elastic membranous ligament, which
usually is not externally visible; but in many instances, in which
the connecting ligament is of a firmer substance, as in _Scorpio_,
_Thelyphonus_, and _Phrynus_, it is very conspicuous, and in the
latter genus exhibits many longitudinal folds, as it does likewise in
_Gryllotalpa_, which must permit a vast extension of the abdomen. In
this membrane, in some cases, as in _Dynastes_ M^cL., _Melolontha_,
&c., the two or three first spiracles are fixed[2137]. In the
_Hymenoptera_ and many other insects the dorsal segments do not unite
by their _margin_ with the ventral, but the _end_ of each dorsal laps
over that of the corresponding ventral.
_Dorsal segments_[2138]. I shall next notice the segments _seriatim_,
in the order of their occurrence, beginning with the _dorsal_ ones.
The most remarkable circumstance with respect to these that occurs
to my recollection takes place in the Cancroid spiders (_Epeira
cancriformis_, _aculeata_, &c.), in which the back of the abdomen is
formed by a plate, in some extended in a transverse direction (_E.
cancriformis_), in others in a longitudinal one (_E. aculeata_),
of a much harder substance than the under side and quite flat, set
with strong sharp spines, in the former species apparently moveable,
and terminating behind in a piece resembling in some measure the
scutellum of the _Stratyomidæ_ and similarly armed with a pair of
spines[2139]: in _E. aculeata_ the sides of the abdomen, under the
plate, have a number of longitudinal folds like those of _Phrynus_.
In _Cryptocerus_, a genus of ants peculiar to South America, the
_first_ segment, not reckoning the pedicle, forms almost the whole
back of the abdomen, and the three last are so minute as scarcely
to be distinguishable. Nothing very remarkable is exhibited by the
other segments, except that in _Trichius_ the _penultimate_ is the
largest; in some _Staphylinidæ_ (_S. splendens_) and _Brachini_ (_B.
melanocephalus_) it is emarginate, and in the former tribe also often
terminating in a white membrane. The _dorsal_ segment most worthy
of notice is the last, which is called the _podex_; for though in
general it is a minute piece, often retracted within the abdomen
and invisible, as in many _Diptera_, yet sometimes it is the most
conspicuous of the dorsal segments. It is most commonly triangular,
and usually deflexed and forming an angle with a horizontal line;
but in _Clytra_, _Chlamys_, and _Oryctes_, it is inflexed; in many
Lamellicorns it is nearly vertical. In _Tettigonia_ F., many other
Homopterous _Hemiptera_, and some _Hymenoptera_ (_Cimbex_), its sides
turn down and become ventral; on its lower side it has in these a
longitudinal cavity which receives the ovipositor in repose[2140].
In many other insects it unites with the last ventral segment, the
_hypopygium_, to form a tube for that organ, as you will find in
_Callidium violaceum_[2141], many _Muscidæ_, and _Thelyphonus_. As to
its _termination_ the podex is sometimes bifid, _Blatta_; bipartite,
_Ranatra_; mucronate, _Sirex_; acuminate, _Melolontha vulgaris_,
_Trichius hemipterus_. Generally this part is flat; but the disk is
elevated or gibbous in _Oryctes_ and some other Lamellicorns. In the
majority of the _Coleoptera_ Order it is quite covered by the wings
and elytra; but in many of the last-mentioned tribe, and sometimes
the penultimate segment also, it is not covered by them[2142]. In
some insects the piece we are considering appears to consist of
_two_ segments; in the male of _Locusta morbillosa_ the whole podex
is rhomboidal, but it is formed by two triangular pieces which
articulate with each other; this structure permits the more easy
elevation of the terminal one for the extrusion of the feces.
_Ventral Segments_[2143]. We are now to turn our attention to the
_ventral_ segments of the abdomen. The first of them is what is
called the _epigastrium_[2144] in the table. This part, according
to M. Chabrier, is of considerable importance to the animal in
flight, as, by its pressure against the trunk, not only regulating
the movements of the abdomen, but as, in his opinion, contributing
to push forward the trunk[2145] in the descent of the animal. It is
remarkable only in the _Coleoptera_ and Heteropterous _Hemiptera_,
to which my observations upon it will be confined. It may be stated
as usually consisting of two articulations, that nearest the trunk
being narrow, and in the Predaceous beetles[2146], as also in
_Scutellera_, _Pentatoma_, &c., interrupted in the middle[2147].
In many _Lamellicorns_ this joint is concealed under the posterior
_coxæ_, and with the anterior part of the second forms a hollow
cavity for their reception; this last joint is what is properly
the _Epigastrium_, the former, especially when distinct, being
called in the table the _Hypochondria_. In _Sagra_ and _Brentus_
the _epigastrium_ is particularly conspicuous for its size, in the
former occupying half, and in the latter nearly two-thirds of the
under side of the abdomen; but in general it is distinguished from
the remaining segments only by the central mucro or point that
terminates it towards the trunk[2148], and which is received by
a sinus of the _metasternum_; this point is generally minute and
triangular, but in _Sagra_ it is large and rounded at the extremity,
and in _Calandra_ it terminates nearly in a transverse line somewhat
waving. It is most remarkable, however, in some species of the
Heteropterous genus _Edessa_ F.; for in _E. nigripes_ and affinities
it is a sharp _sterniform_ conical horn, which passing between the
four posterior legs covers the end of the _promuscis_. In fact, this
part appears a kind of abdominal _sternum_. In the _Cetoniadæ_,
&c., the _Hypochondria_ unite before this mucro, and form a ridge
which articulates with it, and dips towards the abdominal cavity;
in _Scolytus_ the _epigastrium_ is much elevated from the rest of
the ventral segments, so that the under side of the abdomen appears
as if it were suddenly cut off, whence Herbst's awkward though not
inexpressive name, _Ekkoptogaster_; this part in this genus has
something of a posterior mucro.
The intermediate ventral segments exhibiting no very remarkable
peculiarities, I shall pass them without further notice, and call
your attention to the last, which is opposed to the _podex_,
and which I have named the _hypopygium_[2149]. Though usually a
_single_ small piece, in _Edessa_ and many _Pentatomæ_ it consists
of _several_ plates; and in _Trichius_ it is very large: it is
mostly _intire_, but in the male _Dytisci_ it is _cleft_; in _Lamia
ocellata_ trilobed; in _Edessa_ tripartite; in _Centrotus Taurus_
it is boat-shaped and hollowed out to receive the stalk of the
ovipositor. It is also generally in the same line with the body, but
in _Xenos_ it is turned up and bent inwards[2150].
iv. _Shape._ With regard to _shape_, in some Orders the abdomen
varies considerably; but the most general form is one that approaches
to trigonal, so that a transverse section will be a triangle, with
the vertex more or less obtuse, and the base more or less convex;
some tendency to this form will often be found even in those insects
whose abdomen appears almost as flat as a leaf, as in many _Aradi_.
In the hive-bee the transverse section is almost an equilateral
triangle; in _Belostoma grandis_ the disk of the under side of the
part in question is longitudinally elevated into a trigonal ridge,
the section of which is an equilateral triangle, the sides being
quite flat. In general, in the vertical section of an abdomen, the
vertex of the triangle points _downwards_, but in _Libellula_ F. it
points _upwards_. In _Blatta_ this section is nearly lanceolate; in
_Staphylinus olens_ it is a segment of a circle with the convex side
downwards; in _Æshna_ F. with that side upwards; and in _Agrion_
the section is circular. In _Copris_, _Ateuchus_, &c., the abdomen
is very short and thick; in _Staphylinus_ slender and long; in
_Aradus_, _Nepa_, &c., depressed and flat; compressed in _Ophion_
and _Evania_; conical in _Cœlyoxis_; rhomboidal in many _Mantes_;
boat-shaped in many _Lygæi_; fusiform in various _Papilionidæ_;
lanceolate in some _Ichneumonidæ_, falcate in others; nearly
round in _Diapria pupurascens_; ovate in _Lyrops_; elliptical in
_Andrena_; oblong in many _Xylocopæ_; heart-shaped in the naked
_Euglossæ_; triangular in _Dytiscus_; gibbous in _Flata_; and
vaulted in _Chrysis_. At its base it is truncated in _Sirex_; retuse
in most _bees_; forming the segment of a circle in _Andrena_; in
general sessile, but in the majority of _Hymenoptera_, as has been
already observed, terminating in a pedicle. The pedicle is very
short in the _Andrenidæ_ and _Apidæ_; long in the _Sphecidæ_; thick
in the _Formicidæ_; slender in _Evania_; fusiform in _Pelecinus_;
clavate in _Ammophila_; campanulate in many _Vespidæ_; nodose in
_Myrmica_[2151]; squamigerous in _Formica_[2152]: it sometimes also
consists of _two_ joints, as in _Ammophila_ and many _Vespidæ_.
As to _margin_, some have none, as _Centrotus_; in others, as
_Dytiscus_, it is very narrow; in others again, wide and flat, as in
the _Nepidæ_; in _Staphylinus_, &c., it is distinguishable only on
the upper side of the abdomen; in _Locusta_ Leach only on the under
side, though mostly intire; it is serrated in _Blatta_, sinuated in
_Acanthia paradoxa_, and crenated in _Cerceris_.
v. _Proportions._ These vary greatly in the different tribes; in some
the abdomen is long and slender, as in _Locusta_, and _Staphylinus_;
disproportionably so in a remarkable degree in some _Agrionidæ_ from
South America, as _A. lineare_, &c.[2153]; in others it is extremely
short and thick, as in _Copris_, &c.; a mere appendage in _Evania_;
it is shorter than the elytra in _Trox_; of the same length in most
beetles; longer in _Melolontha_, _Hister_, &c.; disproportionably so
in _Staphylinus_: though usually of the same width with the trunk,
in many _Mantidæ_ it is much wider[2154]; and more slender in the
_Libellulina_, _Myrmeleon_, &c.
vi. _Arms and Appendages_[2155]. These are various; and may be
considered under the following heads: _processes_; _organs_ of
_respiration_, _motion_ and _prehension_; _weapons_; and other _anal
appendages_ the use of which is unknown.
1. _Processes._ Under this term I include all prominences of whatever
kind, whether _tubercles_, _teeth_, _spines_, or _horns_, that arm
any part of the abdomen. Many of these are _sexual_ characters, and
have been sufficiently described in a former letter[2156]; I need
not therefore detain you long on this head. Of the first kind is a
remarkable elevation that distinguishes the second ventral segment of
_Scolytus Destructor_ (_Ips Scolytus_ Marsh.) or of a species allied
to it[2157]; in _S. pygmæus_ (_I. multistriatus_ Marsh.) the same
segment is armed by a flat horizontal _tooth_ or horn; in an _Aradus_
from Brazil, before alluded to[2158] (_A. laminatus_ K. MS.), the
margin of the abdomen is surrounded by eight flat subquadrangular
laminæ; in another species figured by Stoll[2159], it is cut out into
bays by a number of denticulated teeth; and in _Acanthia paradoxa_
by long spinose lobes[2160]. In _Edessa_ F., another genus of bugs,
the abdomen usually terminates in four strong sharp dentiform spines,
the intermediate ones being the shortest, and in some the _margin_ is
also armed with spines[2161]; occasionally the anal spines are very
long[2162]. In addition to the ventral horns before mentioned that
distinguish the sexes of some insects[2163]; the males of the genus
_Conops_, a two-winged fly, have, on the antepenultimate ventral
segment, a singular process, varying in length and shape in the
different species, standing nearly at right angles with the belly,
convex towards the trunk, and concave towards the anus. De Geer
supposes that with the anal extremity this forms a forceps with which
this fly seizes the other sex[2164].
2. _Organs of respiration_[2165]. I shall defer my account of the
_spiracles_, and other external respiratory organs, till I come
to treat of the system of _respiration_ in insects, when every
thing connected with that subject will be most properly discussed;
but there are certain appearances in some insects, which at first
sight seem to partake of the same character, but which being really
independent of that vital function, may here have their place. If you
examine the abdomen of the mole-cricket (_Gryllotalpa vulgaris_),
you will easily discover the true spiracles in the folds of the
_pulmonarium_, which separates the back of that part from the belly;
if you next inspect the five intermediate segments of the latter,
you will discover on each nearer the base a pair of oblique little
channels, which precisely resemble closed spiracles. These may be
denominated false or blind spiracles. Again, if you examine the
pupa of any _Scutellera_ or _Pentatoma_, in which tribe the true
spiracles are _ventral_, you will discover, placed in a square on the
two or three intermediate _dorsal_ segments, four or six elevated
points resembling spiracles, but not perforated, connected often
by corrugations in the skin or crust[2166]; in the larvæ also of
some _Reduvii_ the first minute dorsal segment, at each lateral
extremity, has a similar elevation with a central umbilicus precisely
resembling a spiracle, but still not perforated: another instance of
false spiracles in this section of the _Hemiptera_, is furnished by
_Aradus laminatus_ before mentioned, in the perfect insect; between
the spiracle and the margin of each ventral segment is a white round
callus, with a dark point resembling a perforation on its exterior
side, and terminating internally in a channel covered by membrane
leading to the disk of the segment, so that the whole in shape
resembles a tobacco-pipe[2167]. A number of similar callosities with
a central impression, but without any channel, variously disposed,
are also to be found in another bug, _Rhinuchus compressipes_
K.[2168] In the Homopterous section of this Order, a series of
impressed points, which may be easily mistaken for spiracles, are
to be discovered on both sides of the abdomen, at the margin in
_Centrotus_, in which the real spiracles are quite concealed.
In spiders, as we learn from Treviranus, the open _ventral_ spiracles
of the scorpion are replaced by pseudo-spiracles; these in _Epeira
Diadema_ are three pair of small black points: on the back of the
abdomen also are _four_ pair, but in some species there are only
_two_[2169]: the most remarkable, however, are exhibited by the
cancriform spiders before noticed[2170]: in _Epeira cancriformis_, in
the plate which covers the abdomen, they are dark red spots with an
elevated rim and centre[2171] exactly resembling spiracles, except
that they are not perforated; there are twenty-four of them, twenty
arranged round the margin, and four in a square in the disk.
3. _Organs of motion._ In a former letter you were told that several
insects are enabled to leap by means of _organs_ in their abdomen;
I shall now describe such of them as require further elucidation. I
then said that _Podura_ and _Sminthurus_, two apterous genera, take
their leaps by means of an anal _fork_[2172]. In the former genus the
fork consists of a single piece attached to the under side of the
anus, and terminating in a pair of long slender sharp processes which
articulate with it and form the fork or saltatorious instrument[2173].
In _Sminthurus_ the _tines_, as they may be called, of the fork do not
articulate with the base, but are of the same piece and consist of two
joints, the terminal one being flat and obtuse[2174]. _Machilis_ to
the anal fork adds eight pair of ventral linear springs (_Elastes_),
which are covered with hair or scales, and terminate in a bristle or
two. I have on a former occasion mentioned the natatorious laminæ with
which the anus of the larva of _Agrion_ and of some _Diptera_ is
furnished[2175]; the same part in that of _Dytiscus_ ends in a pair
of tapering organs, fringed on each side like the hind-legs of the
imago[2176], which doubtless assist it in swimming; those respiratory
foliaceous laminæ which so singularly distinguish the abdomen of the
larvæ of _Ephemera_, like the legs of the Branchiopod _Crustacea_, are
probably used in some degree as fins, and aid their motions in the
water[2177]. Under this head may also be mentioned the many-jointed
bristles that form the long tails[2178] of the fly that proceeds from
these larvæ, whose interesting history I long since enlarged upon; for
when they fly the two lateral ones diverge from the central one, and
perhaps perform the same office as the tail feathers (_rectrices_) of
birds. These bristles are also to be found in _Machilis_[2179], and
probably, as its _leaps_ are almost as long as _flights_, for a similar
purpose, to steady their motion. I may here lastly state that I once
saw a _Cryptophagus_ (_Corticaria_ Marsh.), but I forgot to note the
species, walking upon my window, which when it wanted to turn fixed
itself to the glass by an inflated anal vesicle, and so accomplished
its purpose.
4. _Organs of Prehension_[2180]. The abdominal organs of _prehension_
are various; but as the great body of them are connected with the
sexual intercourse of insects, I shall not consider them till I come
to treat on that subject. The only remarkable one that is common to
both sexes is that of the earwig, which is too well known to every
child to call for any long description. The external organs of
_oviposition_ I shall also describe hereafter, and likewise those of
_secretion_ that have not already been noticed.
5. _Weapons._ As the _stings_ of some _Hymenoptera_ are analogous to
the _ovipositors_ of the majority of that Order, I shall consider
them both together when I treat of the sexual organs of insects;
but there is one, and that a tremendous one, not connected with
those organs, which may be noticed here. I mean the sting of the
_scorpion_. There appears to be some analogy between the poisonous
fangs of one tribe of the Ophidian reptiles[2181], the mandibulæ
of spiders[2182], the second pair of pedipalps, or the fangs of
the _Scolopendridæ_[2183], and the organ in question[2184]; but
the last possesses this peculiarity, that it is placed at the
opposite extremity of the body, where it is preceded by a long
jointed tail, which properly speaking is merely a continuation of
the abdomen, since the spinal marrow, the intestinal canal, and the
_pseudocardia_, are extended into it[2185]. Providence might have a
double view in thus contracting the dimensions of this part of the
abdomen; in the first place, the animal is by this enabled to turn
its tail over its back preparatory to its inflicting a wound, and
in the second, perhaps, this formation favours the sublimation of
the venom, the long tail acting as an alembic for that purpose. This
machine consists of six angular joints including the sting, the last
but one being the longest, and the last inflated, as it were, at the
base, and terminating in a sharp subulato-conical point which curves
downwards, and has an orifice in a channel at the end on each side.
Treviranus could not discover these orifices in the sting of _Scorpio
europæus_[2186]; they may however be readily seen if viewed with a
sufficiently high power, though not under a common pocket microscope.
Whether the very slender, many-jointed, _real_ tail of the remarkable
genus _Thelyphonus_ is used in any respect as a _weapon_, has not
been ascertained: it is a filiform hairy organ consisting in some
specimens of more than _twenty_ joints, the first being very much
larger than the rest[2187].
6. _Appendages_[2188]. We are lastly to advert to those _appendages_
of the abdomen of which the use is not at present discovered.
These are the styles (_styli_) of the _Staphylinidæ_; the leaflets
(_foliola_) of the _Libellulina_; the floret (_flosculus_) of the
_Fulgoræ_; the _cerci_ of the _Blattidæ_ and _Gryllina_; and the
threads (_fila_) of _Machilis_: but having nothing important to add
concerning them, the definitions of those terms will give you a
sufficiently clear idea of them[2189]. As they are common to both
sexes, if their use is connected with the sexual intercourse, it
must be similar to that which Treviranus ascribes to the pectens of
scorpions, they must be instruments of excitement.
* * * * *
And now, after this long discourse on the External Anatomy and
structure of these little beings, you may think perhaps at first
that the subject is exhausted; and that I must have discovered and
described every part and every variation of every part of the crust
of an insect. But when you go on to reflect what a comparatively
small number of these creatures have fallen under my examination,
and in those, after all my laborious and painful researches, from
my limited faculties and other imperfections of our common nature,
how much will probably have eluded my notice, you may conclude that
thousands of facts still remain concealed to reward the patient
assiduity of future investigators. Such are the immensity and variety
of the works of the CREATOR in this department, that it would require
a long life, and fill volumes upon volumes, to discover and give a
description of all the peculiarities of structure of the insects that
are already known; and could all that exist[2190] be so studied and
explained in full detail, the library that the Calif Omar ordered to
be burned at Alexandria could scarcely have contained more books than
would be required to receive the results. But "who is sufficient for
these things[2191]?" This is a question that the most able and most
experienced physiologist must often feel disposed to put to himself
when, lost in the intricate labyrinth of the works of his Maker, he
sees all things arranged, "wheel within wheel," in an order that
he can only _partially_ unravel, instead of tracing the "regular
confusion" through all its windings. But glimpses of light, and
points of irradiation, here and there discover to _fragments_ of the
truth of things, and such vestiges of the grand system of the DEITY,
as enable him in some degree to appreciate, and dispose him humbly to
adore that WISDOM, POWER, and GOODNESS, that at first created and now
sustains in its full beauty and harmony the WONDROUS WHOLE.
I am, &c.
END OF THE THIRD VOLUME.
Printed by Richard Taylor,
Shoe-Lane, London.
[Illustration: _Plate VI._]
[Illustration: _Plate VII._]
FOOTNOTES:
[2125] _Anatom. Compar._ i. 450.
[2126] _Anatom. Compar._ i. 451.
[2127] De Geer notices something of the kind in _Cimbex femorata_.
ii. 947.
[2128] It was omitted to be observed, when the supposed pneumatic
pouches in the genus _Vespa_ were mentioned (see above, p. 585), that
they have also a very conspicuous metaphragm, as probably have most
_Hymenoptera_, to which the muscles that move the wings are attached.
[2129] PLATE IX. FIG. 13. _F´_ is the tendon, G´ the aperture in the
abdomen C, and a, the aperture in the trunk B.
[2130] PLATE XV. FIG. 11. _Linn. Trans._ xii. _t._ xxii. _f._ 16.
[2131] Surely these _Epeiræ_, of so different a habit from the rest,
form a distinct genus?
[2132] See above, p. 339.
[2133] There is reason to suppose that in _Chelonus_ and the _Chrysidæ_
several segments are retracted within the abdomen, and if the cavity of
its under side in the latter be examined, it will be discovered that
the _epigastrium_ is divided in the middle into two pieces, and that
both the sides of this and the following segments are covered by three
narrow accessory plates, one to each, the last being the shortest. De
Geer (ii. 833.) describes _Chrysis ignita_ as having _four_ abdominal
rings; but this is only in _appearance_, there being really only
_three_. This appearance is produced by the apex of the last dorsal
segment being more depressed and marked with several deep little
excavations that look like holes. In some species of _Stilbum_ this
segment consists as it were of three ridges or steps.
[2134] In this genus the ventral segments are replaced by a long
narrow central plate, succeeded by a minute one.
[2135] In this genus the bed of the posterior coxæ appears to consist
of two segments, which are beautifully fringed with parallel short
bristles.
[2136] _Anatom. Compar._ i. 451.
[2137] PLATE VIII. FIG. 9. _A´´_, _B´_.
[2138] Ibid. FIG. 5. _A´´._
[2139] PLATE XV. FIG. 10.
[2140] Reaum. v. _t._ xvii. _f._ 14. _a. a._
[2141] _Linn. Trans._ v. _t._ xii. _f._ 15.
[2142] Daldorf (_Asiatic Society's Trans._ vii.) has divided
_Geotrupes_ into two families, one with the podex _covered_ (_G.
vernalis_, &c.) which he calls _modesti_, the other with it
_uncovered_ (_G. stercorarius_, &c.) which he calls _obscæni_.
[2143] PLATE VIII. _E´._
[2144] Ibid. _D´._
[2145] _Sur le Vol des Ins._ c. i. Addend. 299.
[2146] In _Dytiscus marginalis_ the upper side of the margin of the
_Hypochondria_ is curiously cut into transverse corrugations.
[2147] PLATE VIII. FIG. 6. _C´._
[2148] Ibid. _B´´._
[2149] PLATE VIII. _L´._
[2150] _Linn. Trans._ xi. _t._ ix. _f._ 15. _b._
[2151] PLATE IX. FIG. 18. _I´._
[2152] Ibid. FIG. 17. _H´._
[2153] Rœmer. _Genera_, &c. _t._ xxiv. _f._ 4.
[2154] Stoll _Spectr._ _t._ vii.
[2155] PLATE XV. FIG. 10-23.
[2156] See above, p. 339--.
[2157] This tubercle I find only in a specimen from Sweden, sent
to me by Major Gyllenhal, but not in any British one I possess. In
this specimen the declivity before mentioned (see above, p. 709.) is
observable in the _first_ segment, but in the others it is formed by
the _second_.
[2158] See above, p. 617.
[2159] _Punaises_, _t._ xiii. _f._ 84.
[2160] Stoll _Punaises_, _t._ xiii. _f._ 101.
[2161] _Ibid._ _t._ xvii. _f._ 117.
[2162] _Ibid._ _t._ xxxvi. _f._ 253.
[2163] See above, p. 339--.
[2164] De Geer, vi. 260. _t._ xv. _f._ 8. _d._
[2165] PLATE XXIX.
[2166] PLATE XXIX. FIG. 22. is part of the back of the abdomen of the
pupa of a _Pentatoma_. _a_ the pseudo-spiracle, _b_ the connecting
corrugations.
[2167] Ibid. FIG. 24. _a._
[2168] Ibid. FIG. 27. _a._
[2169] Treviranus. _Arachnid._ 23--.
[2170] See above, p. 702, 706.
[2171] PLATE XXIX. FIG. 26. represents one of them.
[2172] VOL. II. p. 319--.
[2173] PLATE XV. FIG. 14. _M´´._ De Geer, vii. _t._ ii. _f._ 5, 10, 21.
[2174] Ibid. _t._ iii. _f._ 4, 14.
[2175] See above, p. 154.
[2176] PLATE XVIII. FIG. 5. _a._
[2177] PLATE XXIX. FIG. 3, 4. De Geer, ii. _t._ xvii. _f._ 12. and
_t._ xviii. _f._ 2.
[2178] Ibid. _t._ xvi. _f._ 8-13.
[2179] PLATE XV. FIG. 16. _S´´._
[2180] Ibid. FIG. 12. _L´´._
[2181] _Philos. Trans._ 1818. _t._ xxii.
[2182] _N. Dict. d'Hist. Nat._ ii. 275--. Hoole's _Leeuwenh._ i. _t._
ii. _f._ 19. I.
[2183] Leeuwenh. _Epist._ 17. Octobr. 1687. _f._ 10. C.
[2184] Hoole's _Leeuwenh_. i. _t._ v. _f._ 12, 13.
[2185] Treviranus, _Arach._ 4.
[2186] Treviranus, _ubi supr._ 14.
[2187] In my specimen including the first joint there are _twenty_,
and some seem to have been broken off. In Rœmer's figure (_Genera_,
_t._ xxix. _f._ 11.) there are only _ten_. Perhaps they vary in
number according to the age of the animal.
[2188] PLATE XV. FIG. 13, 16, 17.
[2189] See above, p. 391--.
[2190] I have heard it stated upon good authority that 40,000 species
of insects are already known, as preserved in collections. How great,
then, must be the number existing in this whole globe!
[2191] 2 Cor. ii. 16.
EXPLANATION OF THE PLATES[2192].
PLATE VI.[2193]
FIG.
1. Head of _Mylabris_. Upper side, or _face_.
2. ------------------- Under side, or _subface_.
3. Trophi of _Dytiscus_. _Six_ pieces.
4. Head of _Locusta_. Face.
5. ------------------ Front view, to exhibit the mouth.
6. Trophi of ditto. _Seven_ pieces.
7. Head of _Cicada_. Face.
8. ------- _Scutellera_. Subface.
9. Trophi, or _promuscis_ of _Hemiptera_. _Three_ pieces.
10. Head of _Æshna_. Face.
11. ---------------- Front view.
12. Trophi of ditto. _Seven_ pieces.
13. ------ or _antlia_ of _Lepidoptera_. _Four_ pieces.
14. ------ of _Panorpa_. _Three_ pieces.
PLATE VII.[2194]
FIG.
1. Head and trophi of _Phryganea_ L. Face.
2. ------------------ _Vespa Crabro_. Ditto.
3. Trophi of _Bombus_.
4. Head of _Tabanus_ L. Face.
5. Trophi or _proboscis_ of ditto. (Reaum.)
6. ------------------------ _Bombylius_[2195].
7. Head of _Oxypterum_. Face.
8. Head of _Pulex_, with its antennæ and trophi, or _rostrulum_.
Side view.
9. ------- _Araneidæ_, with the trunk.
10. Trophi of ditto.
11. Head of _Scolopendra morsitans_. Subface.
12. ---------------- --------------- Front view, to show the mouth.
13. Trophi of ditto.
14. Pharynx of _Pentatoma_. (Savigny.)
[Illustration: _Plate VIII._]
PLATE VIII.[2196]
FIG.
1. Prothorax of _Lucanus_. a. Apex. b. Base. c d. Sides. _a._ Disk.
2. Antepectus of ditto.
3. Alitrunk of ditto. Upper side. a. A piece between the
metathorax and metaphragm.
4. ------------------ Under side.
5. Abdomen. Upper side, or _tergum_.
6. -------- Under side, or _venter_.
7. Antepectus of _Hydrophilus piceus_.
8. Alitrunk of ditto. Under side, to show the metasternum.
9. Abdomen of _Dynastes Aloeus_, to show the dorsal and ventral
spiracles.
10. Prothorax of _Locusta_. a. Apex. b. Base, c c. Sides.
11. Antepectus of ditto, to show the prosternum.
12. Alitrunk of ditto. Upper side.
13. ------------------ Under side.
14. ------------------ Lateral view. VOL. III. p. 48.
15. Abdomen of ditto. Lateral view.
16. Alitrunk of _Cicada_ Latr. Upper side.
17. -------------------------- Under side. a. The piece in the ♀
corresponding to the drum-covers of the ♂.
18. Abdomen, and part of postpectus of ♂ ditto. Under side, to show
the drums. VOL. II. p. 405--.
19. Abdomen, and part of postpectus of ♂. Lateral view, with the
covers removed to show the machinery.
20. Alitrunk. Upper side. _Pentatoma_.
[Illustration: _Plate IX._]
PLATE IX.[2197]
FIG.
1. Alitrunk of _Cossus ligniperda_. Upper side.
2. Part of ditto, to show the mesophragm.
3. ------------- Under side.
4. Patagia of _Lepidoptera_. Upper and under sides. VOL. III. p.
368, 539.
5. Tegulæ of ditto. _Two_ species. VOL. III. p. 378.
6. Prothorax of _Æshna_. a. The base elevated and forming an
obtuse angle with the rest.
7. Alitrunk of ditto. Upper side. a. Two elevated areas of the
posterior parts of the collar, strengthened by a marginal ridge
and denticles, internally connected by an elastic ligament,
apparently to aid and sustain the powerful action of the
wing-muscles.
8. ------------------ Lateral view. a. A piece by which the
mid-leg is connected with the scapular. VOL. III. p. 48, 565.
9. Part of the abdomen of _Libellula_.
10. Trunk of _Semblis_ F. Upper side.
11. Alitrunk of _Vespa Crabro_. Upper side. a. Aperture in the
trunk for the passage of the ligament that elevates the abdomen.
12. Lateral view of ditto.
13. --------------- posterior part of ditto, and of the base of the
abdomen, to show the above apparatus. a. The aperture. VOL.
III. p. 701.
14. Head and part of the manitrunk of _Tenthredo_ L. to show the
membrane _a._ representing the prothorax. VOL. III. p. 550--.
15. Alitrunk of _Xiphydria_. Upper side.
16. ------------------------ Lateral view.
17. Part of trunk and abdomen of _Formica_, to show the _squama_.
VOL. III. p. 389. 3.
18. ------------------------- of _Myrmica_, to show the _nodus_.
VOL. III. p. 389. 4.
19. Alitrunk of _Musca_. Upper side. a. _Alula_ or winglet.
20. Metathorax of ditto.
21. Alitrunk of ditto. Lateral view.
22. Abdomen of ditto. Venter.
[Illustration: Plate X.]
PLATE. X.[2198]
N.B. In this plate the _red_ points out the _costal_, and
the _yellow_ the _anal_ areas, the _intermediate_ being
_uncoloured_.
FIG.
1. Elytra, a. Base. b. Shoulder. c. Lateral margin. d. Apex.
2. Tegmina. _Blatta_.
3. Hemelytra. _Pentatoma_.
4. Wing. _Coleoptera._ a. An insulated nervure. VOL. III. p. 625.
5. ----- _Dermaptera._
6. ----- _Lepidoptera._
7. ----- _Neuroptera._
8. ----- _Hymenoptera. Tenthredo_ L.
9. ------------------- _Bombus._
10. Under wing. _Hymenoptera._
11. --------------------------- _Proctotrupes._
12. ----------- _Diptera. Tipula._
13. --------------------- _Psychoda._ VOL. III. p. 645.
14. --------------------- _Musca._ a b. Two areolets between
the costal and mediastinal nervures. c. Areolet between the
mediastinal and postcostal nervures. d. Areolet between
the postcostal and subcostal nervures, e. Open areolet. VOL.
III. p. 634.
15. Under wing. _Diptera._ _Stratyomis._ a b. The two areolets
between the costal and postcostal nervures; the mediastinal
being nearly obsolete. c. Middle areolets crowned by a small
one, d.
[Illustration: Plate XI.]
[Illustration: Plate XII.]
PLATE XI.[2199] _Antennæ._
FIG.
1. Setaceous.
2. Capillary.
3. Filiform.
4. Incrassate.
5. Fusiform.
6. Prismatic.
7. Ensiform.
8. Falciform.
9. Moniliform.
10. Dentate.
11. Serrate.
12. Imbricate.
13. Distichous.
14. Pectinate.
15. Duplicato-pectinate.
16. Ciliate.
17. Flabellate.
18. Ramose.
19. Furcate.
20. Auriculate. _a._ The _auricle_.
21. Palmate.
22. Irregular.
23. Perfoliate.
PLATE XII. _Antennæ._
FIG.
1. Capillaceous.
2. Mucronate.
3. Uncinate.
4. Clavate.
5. Nodose, or Biclavate.
6. Convolute.
7. Geniculate.
8. Capitate with a tunicate knob.
9. Capitate with a solid knob.
10. Capitate with a perfoliate knob.
11. Filiform.
12. Globiferous.
13. Connate.
14. }
15. } Setigerous.
16. Subulate.
17. }
18. } Filate, simple.
19. Filate, compound. _a._ Joints.
20. Filate.
21. Aristate. Setarious _a._ Bristle.
22. Aristate. Plumate _a._ Bristle.
23. Stupeous. VOL. III. p. 646.
24. Plumose.
25. Scopiferous. _a._ Brush.
26. Barbate.
27. Verticillate.
28. Inflated.
29. Auriculate. _a._ Auricle.
PLATE XIII.[2200]
1. Unguiculate feeler. _Gonyleptes._ _a._ Claw.
2. Securiform ditto. _Cychrus._ _a._ Terminal joint.
3. Inflated ditto. _Araneidæ_ ♂. _a._ ditto.
4. Lunulate ditto. _Oxyporus._ _a._ ditto.
5. Dentate mandible. _Megachile._
6. Suctorious ditto. Larva of _Dytiscus_. _a._ Aperture.
7. Prosthecate ditto. _Staphylinus._ VOL. III. pp. 356, 439.
8. Trophi of _Curculio_ L.
9. Pedunculate eyes. _Diopsis._ _a._ Footstalk.
10. Compound ditto. _Muscidæ._ VOL. III. p. 494. 3.
11. Conglomerate ditto. _Iulus._ Ibid. p. 494. 2.
12. Rostrate head. _Balaninus._
13. Capistrate ditto. _Nitidula._
14. Clypeate ditto. _Copris._
15. Lychnidiate ditto. _Fulgora._
16. Buccate ditto. _Myops._ _a._ The inflated part.
17. Cruciate prothorax. _Locusta._
18. Cucullate and alate ditto. _Tingis._
19. Subulate elytra. _Sitaris._
20. Ampliate ditto. _Lycus._ #/
[Illustration: _Plate XIII._]
[Illustration: _Plate XIV._]
[Illustration: _Plate XV._]
PLATE XIV.[2201]
FIG.
1. Ideal wing, to exemplify painting. VOL. IV. p. 286--. a.
Anterior or exterior margin. b. Interior ditto. c. Posterior
ditto. d. Humeral angle. e. Scutellar ditto. f. Posterior
ditto. g. Anal ditto. _a._ Articulate _fascia_, or band.
_b._ Macular ditto. _c d._ Sesquialterous ditto. _d e._
Sesquitertious ditto. _f._ Dimidiate ditto. _g._ Abbreviate
ditto. _h._ Pyramidate ditto. _i._ Supercilium. _k._ Hastate
pupil. _l._ Compound eyelet or _ocellus_. _m._ Nictitant ditto.
_n._ Simple ditto. _o._ Annulet. _p._ Bipupillate eyelet. _q._
Sesquialterous ditto. _r._ Double ditto. _s._ Caudate wing.
_t._ Pupil. _u._ Iris. _v._ Atmosphere.
2. Reversed wings. _Gastrophaca._
3. Digitate ditto. _Pterodactylus._
4. Falcate ditto. _Attacus._
5. Saltatorious leg, with loricate thigh. _Locusta._
6. Natatorious ditto. _Dytiscus._
7. Ambulatorious ditto. _Lucanus._
8. Prehensorious ditto. _Gonyleptes._
PLATE XV.[2202]
FIG.
1. Laminate coxa. _Haliplus._
2. Alate tibia. _Lygæus phyllopus_, a. The appendage.
3. Clypeate ditto. _Crabro_ ♂. a. The clypeus. VOL. III. p. 334.
4. Dolabriform ditto. _Curculio maritimus_ E.B.
5. Fossorious leg, with palmate tibia. _Clivina._ VOL. II. p. 365.
6. --------------- with digitate ditto. _Gryllotalpa._ Ibid. p.
366.
7. Chelate feeler. _Scorpio._
8. Scutate tarsus. _Hydrophilus piceus_ ♂. VOL. III. p. 336.
9. Patellate ditto. _Dytiscus marginalis_ ♂. a. Cups. Ibid. p.
336, 694--.
10. Obumbrate _abdomen_. _Epeira cancriformis._
11. Retracted ditto. _Gonyleptes._
12. Cheliferous tail. _Panorpa_ ♂.
13. Flosculiferous ditto. _Fulgora._
14. Saltatorious ditto. _Podura._
15. Folioliferous ditto. _Æshna._
16. Cauduliferous, and filiferous ditto. _Machilis._
17. Styliferous ditto. _Staphylinus._
18. Unciferous ovipositor. _Locusta._
19. Ensate ditto. _Acrida._
20. Navicular ditto. _Cicada._
21. Serrulate ditto. _Tenthredo_ L.
22. Telescopiform ditto. _Chrysis._
23. Anal apparatus of _Blatta_.
[Illustration: _Plate XVI._]
PLATE XVI.[2203]
FIG.
1. Extricated ovipositor. _Pimpla._ _Two_ pieces.
2. Telescopiform ditto. _Stomoxys calcitrans?_ (Reaum.)
3. -------------------- _Œstrus._ (Ibid.) VOL. I. p. 150.
4. Semicomplete pupa. _Cicada._
5. Subsemicomplete ditto. _Libellula._ _a._ Mask. VOL. III. p.
125--.
6. Incomplete ditto. _Hydrophilus._ (Lyonnet.)
7. ----------------- _Myrmeleon_ emerging from its cocoon. (Reaum.)
8. ----------------- _Vespa vulgaris._
9. ----------------- _Chironomus plumosus._ (Reaum.) _a b._
Respiratory plumes.
10. Obtected pupa. _Apatura Iris._
11. -------------- _Vanessa Urticæ._ _a._ Head-case with _two_
points.
12. -------------- _Gonepteryx Rhamni._ _a._ Head-case with _one_
point.
13. Obtected pupa. _Sphinx Ligustri._ _a._ The tongue-case. _b._
The eye-case. _c._ The trunk-case. _d._ First segment of the
abdomen. _e._ The adminicula. _f._ The mucro, or point of the
tail. VOL. III. p. 249--.
14. Hairy obtected pupa of _Laria fascelina_.
[Illustration: _Plate XVII._]
[Illustration: _Plate XVIII._]
PLATE XVII.[2204]
FIG.
1. Coarctate pupa. _Œstrus hæmorrhoidalis._ (Reaum.)
2. --------------- _Stratyomis chamæleon._ (Ibid.) _a._ The pupa
as formed within the skin of the larva.
4. Oviform body which many pupæ of _Diptera_ at first assume under
the skin of the larva. (Ibid.). VOL. III. p. 235.
3. The same when the parts begin to show themselves. (Ibid.)
5. Cocoon of _Saturnia pavonia_. _a._ Pupa. _b._ Threads that
close the orifice. VOL. III. p. 217, 279.
6. Loose and irregular ditto, of _Arctia villica_. Ibid. p. 220.
7. Boatshaped ditto, of _Tortrix prasinana_. Ibid. p. 221.
8. Network ditto, attached to the stalk of a plant.
9. Ditto, imitating the scales of fish. (Reaum.) VOL. I. p. 462.
10. Spiral case of _Trichopterous_ larva, formed of pieces of leaf.
(De Geer.)
11. Grate spun by these larvæ to prevent ingress. (Ibid.) VOL. II.
p. 264.
12. Chilopodimorphous larva of _Melolontha vulgaris_. VOL. III. p.
163.
13. Araneidiform? ditto of _Cicindela campestris_. Ibid. 152, 163.
PLATE XVIII.[2205]
FIG.
1. Anoplurimorphous larva. _Chrysomela Populi._ _a._ _Osmateria_,
or scent organs. VOL. II. p. 245. III. p. 163, 166.
2. Anoplurimorphous larva. _Cassida_. _a_. The fecifork covered
with excrement. VOL. IV. p. 353. 5.
3. Helminthimorphous or vermiform ditto of _Balaninus Nucum_. VOL.
III. p. 163.
4. Chilognathimorphous ditto of _Elater Segetum_. _a. a._
Spiracles.
5. Decapodimorphous ditto of _Dytiscus marginalis_. VOL. III. p.
165.
6. Chilopodimorphous ditto of _Staphylinus_? _a._ Anal proleg.
7. Amphipodimorphous ditto of _Acrida_. VOL. III. p. 165.
8. Larva of _Zelus_.
9. Helminthimorphous ditto. _Apis mellifica_. (Reaum.)
10. Larva of _Sirex_.
11. -------- _Tenthredo_ L. (Reaum.) _a._ 6 legs. _b._ 16 prolegs.
12. -------- _Sphinx._ _a._ 6 legs. _b._ 10 prolegs. _c._ Anal horn.
13. Spinose ditto of _Vanessa Io_.
[Illustration: _Plate XIX._]
PLATE XIX.[2206]
FIG.
1. Larva of _Papilio Machaon_, _a._ Its retractile osmaterium
emerging from its neck. VOL. II. p. 244--. III. p. 148.
2. Larva of _Cerura Vinula_. _a._ Its anal mastigia. VOL. III. p.
151.
3. Onisciform ditto of _Thecla Rubi_.
4. Larva of _Stauropus Fagi_. (Rösel.) VOL. III. p. 133. note^d.
5. -------- _Notodonta ziczac._ (Reaum.)
6. -------- _Laria fascelina._ _a._ Pencil of hairs, _b._
Verricules of ditto. _c._ Fascicule of ditto. VOL. IV. p. 277.
3, 5, 7.
7. -------- of one of the Geometers in their attitude of
surveying.
8. Araneidiform larva of _Myrmeleon_. (Reaum.)
9. Larva of _Culex pipiens_. (Reaum.) _a._ Tail. _b._ Respiratory
apparatus.
10. ----- of _Chironomus plumosus_. (Reaum.) _a._ Respiratory
organs.
11. ----- of a _Volucella_ inhabiting the nests of humble-bees.
(Reaum.) _a._ Anal radii.
12. ----- of _Elophilus pendulus_. (Reaum.) _a._ Respiratory tubes.
13. ----- of _Stratyomis Chamæleon_. (Swamm.) _a._ Plumes of
respiratory orifice.
[Illustration: _Plate XX._]
PLATE XX.[2207]
FIG.
1. Larva of a _Musca_.
2. -------- an _Œstrus_.
3. Egg of _Vanessa Urticæ_. (Sepp.)
4. ------ _Hipparchia Pilosellæ_. (Ibid.)
5. ------------------ _Hyperanthus_. (Ibid.)
6. ------ _Geometra Cratægata_. (Ibid.)
7. ------ _Pieris Brassicæ_. (Ibid.)
8. ------ _Hipparchia Ægeria_. (Ibid.)
9. ------ _Ourapteryx Sambucaria_. (Ibid.)
10. ------ _Noctua nupta_. (Ibid.)
11. -------------- _Fraxini_. (Ibid.)
12. ------ _Geometra prunaria_. (Ibid.)
13. ---------------- _armillata_. (Ibid.)
14. ------ _Lasiocampa neustria_. (Reaum.)
15. ------ _Hipparchia Jurtina_. (Sepp.)
16. ------ _Pentatoma_. _a._ Bow-shaped spring, by which the
operculum is thrown off. VOL. III. p. 104.
17. ------ _Apis mellifica_. (Reaum.)
18. ------ _Culex pipiens_. (Ibid.) _a._ Summit.
19. ------ _Scatophaga_. (Ibid.) _a a._ Auricles.
20. Necklace of eggs. VOL. III. p. 67.
21. Egg of _Tipula oleracea_. (Reaum.)
22. ------ _Ophion luteum_. (De Geer.) VOL. IV. p. 213--.
23. ------ _Nepa cinerea_. (Swamm.)
24. Jelly, with a necklace of eggs running in a spiral direction
from end to end, taken out of the water.
25. Jelly of more consistence, enveloping the eggs of _Phryganea
atrata_. VOL. III. p. 68.
Printed by Richard Taylor,
Shoe-Lane, London.
FOOTNOTES:
[2192] Recourse must be had to the synoptical table of the
nomenclature of the parts of the external crust of Insects (VOL. III.
p. 354) for the explanation of the reference letters not here given.
[2193] VOL. I. p. 394--. III. p. 355--, 394--. IV. p. 305--.
[2194] Ibid.
[2195] Probably e´ is resolvable into two pieces.
[2196] VOL. III. p. 367--, 529--. IV. p. 326--.
[2197] VOL. III. p. 367--, 529--. IV. p. 326--.
[2198] VOL. II. p. 347--. III. p. 372--, 595--.
[2199] VOL. III. p. 366, 510--. IV. p. 316--.
[2200] VOL. IV. p. 307. iii, iv. 309. b. 310. d. 313. viii. 328, 334.
[2201] VOL. IV. p. 286--, 338, 345--.
[2202] Ibid. p. 345--, 350--.
[2203] VOL. IV. p. 351. ii. III. LETTER XXXII. VOL. I. p. 65--.
[2204] _Ubi supr._
[2205] VOL. III. LETTER XXXI.
[2206] VOL. III. LETTER XXXI.
[2207] _Ubi supr._ and LETTER XXX.
Tanscriber's Notes:
Obvious punctuation and spelling errors have been fixed throughout.
Inconsistent hyphenation is as in the original.
The Errata mentioned on Page vi for this volume and Page viii for
Volumes I and II have been made to the appropriate volumes.
Elements in the Figures that have an asterisk above them are referred
in the text as a superscipt asterisk, since most fonts won't display
the asterisk above.
Footnote 953: There is no anchor for this in the original, left as is.
Footnote 1553: There is no anchor for this in the original, left as is.
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