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Title: Essays on the Microscope - Containing a Practical Description of the Most Improved - Microscopes, a General History of Insects, etc., etc.
Author: Adams, George Burton
Language: English
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Copyright Status: Not copyrighted in the United States. If you live elsewhere check the laws of your country before downloading this ebook. See comments about copyright issues at end of book.

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  Transcriber’s Notes

  Text printed in italics has been transcribed between _underscores_.
  Small capitals have been replaced with ALL CAPITALS. ^{text}
  represents superscript text.

  More Transcriber’s Notes may be found at the end of this text.



  ESSAYS
  ON THE
  MICROSCOPE.


[Illustration: _T.S. Duché pinxit_

_Truth discovering to Time, Science instructing her Children in the
Improvements on the Microscope._

_London, Published July 1.^{st} 1787, by Geo.^{e} Adams, N.^{o} 60 Fleet
Street._]



  ESSAYS
  ON THE
  MICROSCOPE;

  CONTAINING
  A PRACTICAL DESCRIPTION OF THE MOST IMPROVED
  _MICROSCOPES_;

  A GENERAL HISTORY OF INSECTS,
  THEIR TRANSFORMATIONS, PECULIAR HABITS, AND ŒCONOMY:

  AN ACCOUNT OF THE VARIOUS SPECIES, AND SINGULAR PROPERTIES, OF THE
  HYDRÆ AND VORTICELLÆ: A DESCRIPTION OF THREE HUNDRED
  AND EIGHTY-THREE ANIMALCULA:

  WITH

  A CONCISE CATALOGUE OF INTERESTING OBJECTS: A VIEW OF THE
  ORGANIZATION OF TIMBER, AND THE CONFIGURATION OF SALTS, WHEN
  UNDER THE MICROSCOPE.

  _ILLUSTRATED WITH THIRTY-TWO FOLIO PLATES_

  BY THE LATE
  GEORGE ADAMS,
  MATHEMATICAL INSTRUMENT MAKER TO HIS MAJESTY, &c.

  THE SECOND EDITION,
  WITH CONSIDERABLE ADDITIONS AND IMPROVEMENTS, BY
  FREDERICK KANMACHER, F. L. S.

  LONDON:
  PRINTED BY DILLON AND KEATING,
  FOR THE EDITOR; AND FOR W. AND S. JONES, HOLBORN.

  MDCCXCVIII.

  PRICE 1_l._ 8_s._ IN BOARDS.



  TO
  THE KING.


  SIR,

  Every work that tends to enlarge the boundaries of science has a
  peculiar claim to the protection of Kings. He that diffuses science,
  civilizes man, opens the inlets to his happiness, and co-operates with
  the Fountain and Source of all knowledge. By science truth is
  advanced; and of DIVINE TRUTH Kings are the representatives.

  The work which I have now the honour to present to YOUR MAJESTY, calls
  the attention of the reader to those laws of Divine order by which the
  universe is governed and supported; in it we find that the minutest
  beings share in the protection, and triumph in the bounty of the
  Sovereign of all things: that the infinitely small manifest to the
  astonished eye the same proportion, regularity and design, which are
  conspicuous to the unassisted sight in the larger parts of creation.
  By finding all things formed in beauty, and produced for use, the
  mind is raised from the fleeting and evanescent appearances of matter,
  to contemplate the permanent principles of truth, and acknowledge that
  the whole proceeds from the wisdom that originates in love.

  It was by YOUR MAJESTY’S goodness and gracious patronage that I was
  first induced to undertake a description of mathematical and
  philosophical instruments, that I might thereby facilitate the
  attainment of those sciences that are connected with them, and by
  shewing what was already obtained, excite emulation, and quicken
  invention.

  It is to the same goodness that I am indebted for this opportunity of
  subscribing myself,

  SIR,
  YOUR MAJESTY’S
  Most humble,
  Most obedient,
  and most dutiful
  Subject and Servant,
  GEORGE ADAMS.



PREFACE.


In the preface to my ESSAYS ON ELECTRICITY AND MAGNETISM, I informed the
public that it was my intention to publish, from time to time, essays
describing the construction and explaining the use of mathematical and
philosophical instruments, in their present state of improvement. This
work will, I hope, be considered as a performance of my promise, as far
as relates to the subject here treated of.[1]

  [1] Towards the completion of this design, our author afterwards
  published, 1. Astronomical and Geographical Essays; 2. Geometrical and
  Graphical Essays; 3. An Essay on Vision; 4. Lectures on Natural and
  Experimental Philosophy. He had projected other compilations, and was
  preparing a new edition of this work; but, alas! how uncertain are all
  human projects! constant attention to an extensive business and to
  literature, preyed on a constitution far from robust, and at length
  rapidly accelerated his dissolution, which happened at Southampton, on
  the 14th of August, 1795; aged 45. By this event, the world was
  prematurely deprived of the beneficial effects of his farther labours,
  and his friends of the conversation of a man, whose amiable and
  communicative disposition endeared him to all those who had the
  pleasure of knowing him. His life had been devoted to religious and
  moral duties, to the acquisition of science, and its diffusion for the
  benefit of mankind. To those who had no personal knowledge of Mr.
  ADAMS, his works will continue to display his merits as an author, and
  his virtues as a valuable member of society. EDIT.

The first chapter contains a short history of the invention and
improvements that have been made on the microscope, and Father Di
Torre’s method of making his celebrated glass globules. The second
treats of vision, in which I have endeavoured to explain in a familiar
manner the reason of those advantages which are obtained by the use of
magnifying lenses; but as the reader is supposed to be unacquainted with
the elements of this science, so many intermediate ideas have been
necessarily omitted, as must in some degree lessen the force, and weaken
the perception of the truths intended to be inculcated: to have given
these, would have required a treatise on optics.

In the third chapter, the most improved microscopes, and some others
which are in general use, are particularly described; no pains have been
spared to lessen the difficulty of observation, and remove obscurity
from description; the relative advantages of each instrument are briefly
pointed out, to enable the reader to select that which is best adapted
to his pursuits. The method of preparing different objects for
observation, and the cautions necessary to be observed in the use of the
microscope, are the subjects of the fourth chapter.

When I first undertook the present essays, I had confined myself to a
re-publication of my fathers work, entitled, Micrographia Illustrata;
but I soon found that both his and Mr. Baker’s tracts on the microscope
were very imperfect. Natural history had not been so much cultivated at
the period when they wrote, as it is in the present day. To the want of
that information which is now easily obtained, we may with propriety
impute their errors and imperfections. I have, therefore, in the fifth
chapter, after some general observations on the utility of natural
history, endeavoured to remedy their defects, by arranging the subject
in systematic order, and by introducing the microscopic reader to the
system of Linnæus, as far as relates to insects: by this he will learn
to discriminate one insect from another, to characterize their different
parts, and thus be better enabled to avoid error himself, and to convey
instruction to others.

As the transformations which insects undergo, constitute a principal
branch of their history, and furnish many objects for the microscope, I
have given a very ample description of them; the more so, as many
microscopic writers, by not considering these changes with attention,
have fallen into a variety of mistakes. Here I intended to stop; but the
charms of natural history are so seducing, that I was led on to describe
the peculiar and striking marks in the œconomy of these little
creatures. And should the purchaser of these essays receive as much
pleasure in reading this part as I did in compiling it; should it induce
him to study this part of natural history; nay, should it only lead him
to read the stupendous work of the most excellent Swammerdam, he will
have no reason to regret his purchase, and one of my warmest wishes will
be gratified.

In the next chapter I have endeavoured to give the reader some idea of
the internal parts of insects, principally from M. Lyonet’s Anatomical
and Microscopical Description of the Caterpillar of the Cossus or
Goat-moth. As this book is but little known in our country, I concluded
that a specimen of the indefatigable labour of this patient and humane
anatomist would be acceptable to all lovers of the microscope; and I
have, therefore, appropriated a plate, which, whilst it shews what may
be effected when microscopic observation is accompanied by patience and
industry, displays also the wonderful organization of this insect. This
is followed by a description of several miscellaneous objects, of which
no proper idea could be formed without the assistance of glasses.

To describe the fresh-water polype or hydra; to give a short history of
the discovery of these curious animals, and some account of their
singular properties, is the business of the succeeding chapter. The
properties of these animals are so extraordinary, that they were
considered at first to be as contrary to the common course of nature, as
they really were to the received opinions of animal life. Indeed, who
can even now contemplate without astonishment animals that multiply by
slips and shoots like a plant? that may be grafted together as one tree
to another, that may be turned inside out like a glove, and yet live,
act, and perform all the various functions of their contracted spheres?
As nearly allied to these, the chapter finishes with an account of those
vorticellæ which have been enumerated by Linnæus. It has been my
endeavour to dissipate confusion by the introduction of order, to
dispose into method, and select under proper heads the substance of all
that is known relative to these little creatures, and in the compass of
a few pages to give the reader the information that is dispersed through
volumes.

From the hydræ and vorticellæ, it was natural to proceed to the
animalcula which are to be found in vegetable infusions; microscopic
beings, that seem as it were to border on the infinitely small, that
leave no space destitute of inhabitants, and are of greater importance
in the immense scale of beings than our contracted imagination can
conceive; yet, small as they are, each of them possesses all that beauty
and proportion of organized texture which is necessary to its
well-being, and suited to the happiness it is called forth to enjoy. A
short account of three hundred and seventy-seven[2] of these minute
beings is then given, agreeable to the system of the laborious Müller,
enlarging considerably his description of those animalcula that are most
easily met with, better known, and consequently more interesting to the
generality of readers.

  [2] To these, six more are now added, making the whole three hundred
  and eighty three. EDIT.

The construction of timber, and the disposition of its component parts,
as seen by the microscope, is the subject of the next chapter; a subject
confessedly obscure. With what degree of success this attempt has been
prosecuted, must be left to the judgment of the reader. The best
treatise on this part of vegetation is that of M. Du Hamel du Monceau
sur la Physique des Arbres. If either my time or situation in life would
have permitted it, I should have followed his plan; but being confined
to business and to London, I can only recommend it to those lovers of
the works of the Almighty, who live in the country, to pursue this
important branch of natural history. There is no doubt but that new
views of the operations in nature, and of the wisdom with which all
things are contrived, would amply repay the labour of investigation.
Every part of the vegetable kingdom is rich in microscopic beauties,
from the stateliest tree of the forest, from the cedar of Lebanon, to
the lowliest moss and the hyssop that springeth out of the wall; all
conspiring to say how much is hid from the natural sight of man, how
little can be known till it receives assistance, and is benefited by
adventitious aid.

From the wonderful organization of animals, and the curious texture of
vegetables, we proceed to the mineral kingdom, and take a cursory view
of the configuration of salts and saline substances, exhibiting a few
specimens of the beautiful order in which they arrange themselves under
the eye, after having been separated by dissolution; every species
working as it were upon a different plan, and producing cubes, pyramids,
hexagons, or some other figure peculiar to itself, with a constant
regularity amidst boundless variety.

Though all nature teems with objects for the microscopic observer, yet
such is the indolence of the human mind, or such its inattention to what
is obvious, that among the purchasers of microscopes many have
complained that they knew not what subjects to apply to their
instrument, or where to find objects for examination. To obviate this
complaint, a catalogue is here given, which is interspersed with the
description of a few insects, and other objects, which could not be
conveniently introduced in the foregoing chapters. By this catalogue it
is hoped that the use of the microscope will be extended, and the path
of observation facilitated.

To avoid the formal parade of quotation, and the fastidious charge of
plagiarism, I have subjoined to this preface a list of the authors which
have been consulted. As my extracts were made at very distant periods,
it would have been impossible for me to recollect to whom I was indebted
for every new fact or ingenious observation.

The plates were drawn and engraved with a view to be folded up with the
work; but as it is the opinion of many of my friends that they would, by
this mean, be materially injured, I have been advised to have them
stitched in strong blue paper, and leave it to the purchaser to dispose
of them to his own mind.



  A
  LIST OF THE AUTHORS
  WHICH HAVE BEEN CONSULTED IN THE COMPILATION OF THE FORMER
  AND PRESENT EDITION OF THESE ESSAYS.


  ADAMS.       Micrographia Illustrata, or the Microscope
               Explained.                         London, 1746 and 1781.

  ADDISON.     Spectator.

  BAKER.       An Attempt towards the Natural History of
               the Polype.                                 London, 1743.

  BAKER.       The Microscope made Easy.                   London, 1744.

  BAKER.       Employment for the Microscope.              London, 1753.

  BARBUT.      Genera Insectorum of Linnæus. 4to.          London, 1781.

  BERKENHOUT.  Botanical Lexicon. 8vo.                     London, 1764.

  BERKENHOUT.  Synopsis of Natural History. 2 vols. 8vo.   London, 1789.

  BIRCH.       History of the Royal Society. 4to. 4 vols.  London, 1756.

  BLAIR.       Sermons.                                    London, 1792.

  BONNANI.     Observationes circa Viventia, quæ in Rebus
               non Viventibus reperiuntur, &c. 4to.                1691.

  BONNET.      Oeuvres d’Histoire Naturelle et de
               Philosophie. 9 tom. 4to.                Neufchatel, 1779.

  BORELLUS.    De vero Telescopii Inventore.

  BRAND.       Select Dissertations from the Amœnitates
               Academicæ, &c. 8vo.                         London, 1781.

  CURTIS.      Instructions for Collecting and Preserving
               Insects. 8vo.                               London, 1771.

  CURTIS.      Translation of the Fundamenta Entomologiæ.
               8vo.                                        London, 1772.

  CURTIS.      Flora Londinensis. Folio.               London, 1777, &c.

  CURTIS.      Botanical Magazine. 8vo.                London, 1787, &c.

  CYCLOPÆDIA.  By Dr. Rees. 4 vols. Folio.                 London, 1786.

  DE GEER.     Memoires pour servir a l’Histoire des
               Insectes. 4to. 7 tom.                               1752.

  DELLEBARRE.  Memoires sur les Differences de la
               Construction et des Effects du Microscope.          1777.

  DERHAM.      Physico-Theology. 8vo.                      London, 1732.

  DONOVAN.     History of British Insects. 8vo.        London, 1792, &c.

  DONOVAN.     Treatise on the Management of Insects. 8vo. London, 1794.

  DU HAMEL DU MONCEAU. La Physique des Arbres.              Paris, 1757.

  ELLIS.       Essay towards a Natural History of
               Corallines. 4to.                                    1755.

  ELLIS.       Zoophytes, by Dr. Solander. 4to.            London, 1786.

  ENCYCLOPÆDIA BRITANNICA. 4to. 18 vols.                Edinburgh, 1797.

  EPINUS.      Description des Nouveaux Microscopes.

  FABRICIUS.   Philosophia Entomologica. 8vo.                      1778.

  GEOFFROY.    Histoire Abregee des Insectes. 2 tom. 4to.   Paris, 1764.

  GLEICHEN.    Les plus Nouvelles Deucouverts dans le
               Regne Vegetal, &c. Folio.                           1770.

  GOLDSMITH.   History of the Earth and Animated Nature.
               8vo.                                        London, 1774.

  GREW.        Anatomy of Plants. Folio.                   London, 1682.

  HALLER.      Physiologia.

  HEDWIG.      Theoria Generationis et Fructificationis
               de Plantarum Cryptogamicarum.              Petersb. 1784.

  HILL.        Review of the Royal Society. 4to.           London, 1751.

  HILL.        History of Animals. Folio.                  London, 1752.

  HILL.        Essays in Natural History. 8vo.             London, 1752.

  HILL.        The Construction of Timber explained by
               the Microscope. 8vo.                        London, 1770.

  HILL.        Inspector.

  HOME.        Treatise on Ulcers, &c. 8vo.                London, 1797.

  HOOKE.       Micrographia. Folio.                        London, 1665.

  HOOKE.       Lectures and Collections. 4to.              London, 1678.

  HOOPER.      Economy of Plants. 8vo.                     Oxford, 1797.

  JOBLOT.      Observations d’Histoire Naturelle faites
               avec le Microscope. 4to. 2 tom.                    Paris.

  JOURNAL DE PHYSIQUE, PAR ROZIER, &c.

  JONES.       A Course of Lectures on the Figurative
               Language of the Holy Scriptures. 8vo.               1787.

  KIPPIS.      Biographia Britannica. Folio.                   1778, &c.

  LEDERMULLER. Microscopische Ergötzungen. 4 theile. 4to.

  LEEUWENHOEK. Arcana Naturæ. 4to.                      Lugd. Bat. 1722.

  LEEUWENHOEK. Opera Omnia. 4to.                             Ibid. 1722.

  LETTSOM.     Naturalist’s Companion. 8vo.                London, 1774.

  LINNEAN SOCIETY. Transactions. 3 vols. 4to.          London, 1791, &c.

  LINNÆUS.     Systema Naturæ. 8vo. edit. 12mo.            Holmiæ, 1766.

  LYONET.      Theologie des Insectes de Lesser. 2 tom.
               8vo.                                       La Haye, 1742.

  LYONET.      Traite Anatomique de la Chenille qui ronge
               le Bois de Saule. 4to.

  MACQUER.     Dictionary of Chemistry.                    London, 1777.

  MAGNY.       Journal d’Economie.                                 1753.

  MALPIGHI.    Opera. 4to.                            Lugduni Bat. 1687.

  MARTIN.      Micrographia Nova. 4to.                    Reading, 1742.

  MARTIN.      Optical Essays. 8vo.                              London.

  MULLER.      Animalcula Infusoria Fluviatilia et
               Marina. 4to.                                Hauniæ, 1786.

  NICHOLSON.   Introduction to Natural Philosophy. 2
               vols. 8vo.                                          1787.

  NICHOLSON.   Journal of Natural Philosophy, &c.                  1797.

  NEEDHAM.     New Microscopical Discoveries. 8vo.         London, 1745.

  NEUERE GESCHICHTE DER MISSIONS ANSTALTEN. 4to.            Halle, 1796.

  PALLAS.      Elenchus Zoophytorum. 8vo.              Hagæ Comit. 1766.

  PARSONS.     Microscopic Theatre of Seeds. 4to.          London, 1745.

  POWER.       Microscopical Observations. 4to.                    1664.

  PRIESTLEY.   On Light, Vision, and Colours. 4to.                 1772.

  REAUMUR.     Memoires pour servir a l’Histoire des
               Insectes. 8vo.                           Amsterdam, 1737.

  REDI.        De Insectis.                                        1671.

  REID.        On the Intellectual Powers of Man.    Nürnberg, 1746, &c.

  ROSEL.       Insecten Belustigung. 4 theile. 4to.

  ROYAL SOCIETY. Philosophical Transactions.

  RUTHERFORTH. Natural Philosophy. 2 vols. 4to.         Cambridge, 1748.

  SCHIRACH.    Histoire Naturelle de la Reine des
               Abeilles.                                A la Haye, 1771.

  SHAW.        Naturalist’s Miscellany. 8vo.           London, 1790, &c.

  SMITH, R.    Optics. 2 vols. 4to.                     Cambridge, 1738.

  SMITH, I. E. English Botany. 8vo.                    London, 1790, &c.

  SPALANZANI.  Opuscules de Physiques Animale et
               Vegetale.                                   Geneva, 1777.

  STILLINGFLEET. Miscellaneous Tracts. 8vo.                London, 1762.

  SWAMMERDAM.  The Book of Nature, revised by Hill.
               Folio.                                      London, 1758.

  SWEDENBORG.  Œconomia Regni Animalis, cui accedit
               Introductio ad Psychologiam Rationalem.
               4to.                                     Amsterdam, 1743.

  SWEDENBORG.  Regnum Animale, Anatomice, Physice et
               Philosophice Perlustratum. 4to.         Hagæ Comit. 1744.

  TREMBLEY.    Memoires pour servir a l’Histoire des
               Polypes d’eau douce.                         Paris, 1744.

  VALMONT DE BOMARE. Dictionnaire Raisonne universal
               d’Histoire Naturelle.                         Lyon, 1776.

  WALKER.      A Collection of Minute and Rare Shells.
               4to.                                        London, 1784.

  YEATS.       Institutions of Entomology. 8vo.              Ibid. 1773.



  LONDON, _Dec. 12, 1797_.


  The Public are hereby respectfully informed, that the STOCK and
  COPYRIGHT of the following Works by the same AUTHOR, lately deceased,
  have been purchased by W. and S. JONES, Opticians, &c. and that they
  are now to be had at their Shop in Holborn.


I. GEOMETRICAL AND GRAPHICAL ESSAYS. This Work contains, 1. A select Set
of Geometrical Problems, many of which are new, and not contained in any
other Work. 2. The Description and Use of those Mathematical Instruments
that are usually put into a Case of Drawing Instruments. Besides these,
there are also described several New and Useful Instruments for
Geometrical Purposes. 3. A complete and concise System of SURVEYING,
with an Account of some very essential Improvements in that useful Art.
To which is added, a Description of the most improved THEODOLITES, PLANE
TABLES, and other Instruments used in Surveying; and most accurate
Methods of adjusting them. 4. The Methods of LEVELLING, for the Purpose
of conveying Water from one Place to another; with a Description of the
most improved Spirit Level. 5. A Course of PRACTICAL MILITARY GEOMETRY,
as taught at Woolwich. 6. A short Essay on Perspective. The Second
Edition, corrected, and enlarged with the Descriptions of several
Instruments unnoticed in the former Edition, by W. JONES, Math. Inst.
Maker; illustrated by 35 Copper-plates, in 2 vols. 8vo. Price 14s. in
Boards.


II. AN ESSAY ON ELECTRICITY, explaining clearly and fully the Principles
of that useful Science, describing the various Instruments that have
been contrived, either to illustrate the Theory, or render the Practice
of it entertaining. To which is added, A LETTER to the AUTHOR, from Mr.
JOHN BIRCH, Surgeon, on MEDICAL ELECTRICITY. Fourth Edition, 8vo. Price
6s. illustrated with six Plates.


III. AN ESSAY ON VISION, briefly explaining the Fabric of the Eye, and
the Nature of Vision; intended for the Service of those whose Eyes are
weak and impaired, enabling them to form an accurate Idea of the State
of their Sight, the Means of preserving it, together with proper Rules
for ascertaining when Spectacles are necessary, and how to choose them
without injuring the Sight. 8vo. Second Edition. Illustrated with
Figures. Price 3s. in Boards.


IV. ASTRONOMICAL AND GEOGRAPHICAL ESSAYS, containing, 1. A full and
comprehensive View of the general Principles of Astronomy, with a large
Account of the Discoveries of Dr. Herschel, &c. 2. The Use of the
Globes, exemplified in a greater Variety of Problems than are to be
found in any other Work; arranged under distinct Heads, and interspersed
with much curious but relative Information. 3. The Description and Use
of Orreries and Planetaria, &c. 4. An Introduction to Practical
Astronomy, by a Set of easy and entertaining Problems. Third Edition,
8vo. Price 10s. 6d. in Boards, illustrated with sixteen Plates.


V. AN INTRODUCTION TO PRACTICAL ASTRONOMY, or the Use of the Quadrant
and Equatorial, being extracted from the preceding Work. Sewed, with two
Plates, 2s. 6d.


VI. AN APPENDIX to the GEOMETRICAL AND GRAPHICAL ESSAYS, containing the
following Table by Mr. JOHN GALE, viz. a Table of the Northings,
Southings, Eastings, and Westings to every Degree and fifteenth Minute
of the Quadrant, Radius from 1 to 100, with all the intermediate
Numbers, computed to the three Places of Decimals. Price 2s.


  _In the Press, and speedily will be Published_,
  LECTURES
  ON NATURAL AND EXPERIMENTAL PHILOSOPHY,

In Five Volumes 8vo. The Second Edition, with upwards of Forty large
Plates, considerable Alterations and Improvements; containing more
complete Explanations of the Instruments, Machines, &c. and the
Description of many others not inserted in the former Edition.

BY W. JONES, MATHEMATICAL AND PHILOSOPHICAL INSTRUMENT MAKER.



_ADVERTISEMENT._


_The editor esteems it his indispensable duty, to point out the several
improvements which have been made in this work, in order to render it
still more acceptable to the public._

_The whole has been carefully revised--many typographical errors
corrected--numerous additions and emendations from the author’s own copy
incorporated, and some superfluities rejected. Wherever any ambiguity
occurred, the editor has endeavoured to elucidate the passage, observing
due caution not to misconceive the idea which the author meant to
inculcate. A more regular arrangement has been attempted, and occasional
notes subjoined: in these, and in other parts of the work, it has been
the editor’s primary object to ascertain facts, not to decide
peremptorily. Should he in any instance have erred, he can assure the
candid critic, that he shall experience a most sensible pleasure in
conviction._

  _The principal additions are_,

  Accounts of the latest improvements which have been made in the
  construction of microscopes, particularly the lucernal.

  A description of the glass, pearl, &c. micrometers, as made by Mr.
  Coventry, and others.

  An arrangement and description of minute and rare shells.

  A descriptive list of a variety of vegetable seeds.

  Instructions for collecting and preserving insects, together with
  directions for forming a cabinet.

  A copious list of objects for the microscope.

  A list of Mr. Custance’s fine vegetable cuttings.

  _With respect to the plates, three new engravings are introduced,
  viz._

  PLATE IV. Exhibiting the most improved compound microscopes, with
  their apparatus.

  PLATE XIV. Microscopical figures of minute and rare shells.

  PLATE XV. Microscopical figures of a variety of vegetable seeds.

_Many additional figures have been inserted in other plates, and a
number of errors in the references corrected._

_A complete list of the plates and a more extensive index are also
added._

_It has been generally understood, that the author intended to have
published this edition in octavo; but, the impropriety of adopting that
mode must appear evident, for the very reason assigned by the author
himself in the concluding part of his preface. If the plates are liable
to sustain damage by folding them into a quarto, they would have been
subjected to far greater injury by being doubled into an octavo size,
besides, being extremely incommodious for reference. As the work now
appears, the purchaser may either retain the plates in the separate
volume, or, without much inconvenience, if properly guarded, have them
bound with the letter press._

_It affords the editor a pleasing satisfaction to mention, that
notwithstanding the additional heavy expense incurred in the article of
paper, &c. yet, by somewhat enlarging the page, and other economical
regulations in the mode of printing, this edition is offered to the
public at a trifling advance on the original price, though the
improvements now made occupy considerably more than one-hundred pages._

_Anxious, lest the reputation which the work has already acquired,
should be diminished by any deficiency on his part, the editor has
sedulously applied himself to render it extensively useful to the
serious admirer of the wonders of the creation; whether he has
succeeded, is now submitted to the decision of the intelligent part of
the public. He shall only add, that conscious of the purity of his
intentions, and convinced of the instability of all terrestrial
attainments, he trusts that he is equally secured from the weakness of
being elevated by success, or depressed by disappointment._

  _Apothecaries Hall, London,

  Jan. 1, 1798._



CONTENTS.


  CHAP. I.

  A concise History of the Invention and Improvements which have been
  made upon the Instrument called a Microscope. p. 1.

  CHAP. II.

  Of Vision; of the optical Effects of Microscopes, and of the Manner of
  estimating their magnifying Powers. p. 26.

  CHAP. III.

  A Description of the most improved Microscopes, and the Method of
  using them. p. 64.

  CHAP. IV.

  General Instructions for using the Microscope, and preparing the
  Objects. p. 129.

  CHAP. V.

  The Importance of Natural History; of Insects in general, and of their
  constituent Parts. p. 167.

  CHAP. VI.

  A general View of the internal Parts of Insects, and more particularly
  of the Caterpillar of the Phalæna Cossus. A Description of sundry
  miscellaneous Objects. p. 334.

  CHAP. VII.

  The Natural History of the Hydra, or Fresh Water Polype. p. 357.

  CHAP. VIII.

  Of the Animalcula Infusoria. p. 415.

  CHAP. IX.

  On the Organization or Construction of Timber, as viewed by the
  Microscope. p. 574.

  CHAP. X.

  Of the Crystallization of Salts, as seen by the Microscope; together
  with a concise List of Objects. p. 600.

  CHAP. XI.

  An Arrangement and Description of minute and rare Shells. A
  descriptive List of a Variety of vegetable Seeds, as they appear when
  viewed by the Microscope. By the Editor. p. 629.

  CHAP. XII.

  Instructions for collecting and preserving Insects. A copious List of
  microscopic Objects. By the Editor. p. 665.

  ADDITIONS. p. 713.



ERRATA.


  Page 16, line 22, _for_ lead _read_ led

  Page 20, line 6, _for_ Fig. T _read_ Fig. 1

  Page 49, last line, _for_ usefully _read_ successfully

  Page 62, last but one, _for_ stop _read_ stage

  Page 80, line 22, _after_ microscope _add_ by

  Page 88, three lines from bottom, _for_ improvent _read_ improvement

  Page 95, line 2, _for_ R _read_ K

  Page 111, two lines from bottom, _for_ VK _read_ VX

  Page 115, line 12, _for_ g _read_ q

  Page 125, note, _for_ Fig. 13 _read_ Fig. 13*

  Page 145, line 17, _for_ cast of _read_ cast-off

  Page 153, line 21, _for_ unkown _read_ unknown

  Page 169, eight lines from bottom, _for_ is _read_ are

  Page 188, note line 9, _for_ preventatives _read_ preventives

  Page 195, line 7, _for_ exagon _read_ hexagon

  Page 238, line 16, _for_ scarc _read_ scarce

  Page 319, line 19, _for_ rise _read_ raise

  Page 346, line 18, _for_ bread _read_ bred

  Page 354, three lines from bottom, _for_ Fig. 1 and 2 _read_ Fig. 1
  and 3

  Page 445, line 18, _for_ immediate _read_ intermediate



LIST OF THE PLATES,

WITH REFERENCES TO THE PAGES WHERE THE SEVERAL FIGURES ARE DESCRIBED.


  Plate                                                             Page

       I. Various diagrams illustrative of vision and the optical
          effect of microscopes                                       29

      II. A. Ibid.--Needle micrometer, 54.--Coventry’s pearl, &c.
          micrometers                                                 59

          B. Fig. 1. Wilson’s microscope and apparatus, 115.--Fig.
          2. Ditto with a scroll                                     117

          Fig. 3, 4. Small opake microscope and apparatus            118

     III. Fig. 1, 2, and 4. Adams’s lucernal microscope and
          apparatus                                                   64

          Fig. 3. Argand’s patent lamp                                69

      IV. Fig. 1. Jones’s improved compound microscope and
          apparatus                                                   92

          Fig. 2. Jones’s most improved ditto, ditto                  99

          Fig. 3. Culpeper’s three-pillared microscope and
          apparatus                                                  104

       V. Martin’s improved solar opake and transparent microscope   106

      VI. Fig. I. Withering’s botanical microscope, 123.--Fig. 2.
          Pocket botanical and universal microscope                  124

          Fig. 3. Lyonet’s anatomical microscope                     122

          Fig. 4. Transparent solar microscope and apparatus         113

          Fig. 5. Tooth and pinion microscope                      ibid.

          Fig. 14. Common flower and insect microscope          note 125

     VII. A. Cuff’s double constructed microscope and apparatus       89

          B. Ellis’s aquatic microscope                              119

    VIII. Fig. 1-6. Portable microscope and telescope with
          apparatus                                                  125

          Fig. 7, 8. Botanical magnifiers                          ibid.

      IX. Fig. 1, 2. Engine for cutting sections of wood, and
          appendage                                                  127

          Fig. 3, 4. Jones’s improved lucernal microscope and
          apparatus                                                   80

          Fig. 5, 7. The Rev. Dr. Prince’s and Mr. Hill’s
          improvements on the illuminating lenses and lamp of the
          lucernal microscope                                         84

          Fig. 6. Lanthorn microscope and screen                      88

       X. Fig. 1, 2. Nest of the phalæna neustria.--Fig. 3, 4.
          Vertical section of ditto.

          Fig. 5, 6. Horizontal section                              287

          Fig. 7, 8. Scales of the parrot fish, 355.--Fig. 9, 10.
          Scales of sea perch                                        356

      XI. Fig. 1, 2, 3. Larva of the musca chamæleon                 248

          Fig. 4, 5. Eels in blighted wheat                          469

          Fig. 6, 8, 9, 10, 11. Paste eel                            462

          Fig. 7. Vinegar eel                                        461

     XII. Fig. 1, 2, 3, 4. Dissection of the caterpillar of the
          phalæna cossus                                             336

          Fig. 5, 6, 7. Dissection of the head of the caterpillar    337

    XIII. Fig. 1, 2. Beard of the lepas anatifera                    344

          Fig. 3, 4. Collector of the bee                            182

     XIV. Fig. 1, 2. Wing of the forficula auricularia       143 and 205

          Fig. 2 to 47. Magnified figures of minute and rare
          shells                                                     629

      XV. Fig. 1, 2. Wing of the hemerobius perla                    206

          Fig. 1 to 46. Microscopic views of a variety of
          vegetable seeds                                            645

     XVI. Fig. 1, 2, and B, C, D, E. Proboscis of the tabanus        188

          Fig. 3, 4. Cornea of the libellula                         197

          Fig. 5, 6. Cornea of the lobster                         ibid.

          Fig. 7, 8, E, F, H, I. Feathers of the wings of the
          sphinx stellatarum                                 208 and 627

    XVII. Fig. 1, 2, 3. Leucopsis dorsigera                          347

   XVIII. Fig. 1 and 6. The lobster insect                           348

          Fig. 2 and 7. Skin of the lump-sucker                      352

          Fig. 3, 4, 5. Thrips physapus                              350

     XIX. Fig. 1-4. Feet of the monoculus apus                       354

          Fig. 5 and 6. Skin of the sole fish.--Fig. 7, 8. Scale
          of the haddock.--Fig. 9, 10. Scale of West Indian
          perch.--Fig. 11, 12. Scale of sole fish                    356

      XX. Fig. 1 and A. Cimex striatus, 352.--Fig. 2 and B.
          Chrysomela asparagi                                        353

          Fig. 3 and C. Meloe monoceros                              354

     XXI. Fig. 1-24. Various hydræ and vorticellæ                    364

    XXII. Fig. 26-40. Ditto                                          392

   XXIII. A. Fig. 1-13. Various hydræ, 365. B. Fig. 14-29. Ditto     382

    XXIV. A. Fig. 1-10. and B. Fig. 11-24. Ditto                     376

     XXV. Fig. 1-68. A variety of animalcula infusoria               431

    XXVI. Fig. 1-23. Ditto                                           548

   XXVII. Fig. 1-66. Ditto                                           519

  XXVIII. Fig. 1, 2. Transverse section of chenopodium               599

          Fig. 3, 4. Transverse section of a reed from Portugal    ibid.

    XXIX. Fig. 1, 2. Transverse section of althæa frutex           ibid.

          Fig. 3, 4. Transverse section of hazel                   ibid.

          Fig. 5, 6. Transverse section branch of lime tree        ibid.

     XXX. Fig. 1, 2. Transverse section of sugarcane.              ibid.

          Fig. 3, 4. Transverse section of bamboo cane             ibid.

          Fig. 5, 6. Transverse section of common cane             ibid.

    XXXI. Fig. 1, 2. Crystals of nitre                               606

          Fig. 3, 4. Distilled verdigrise                          ibid.

   XXXII. Fig. 1. Microscopical crystals of salt of wormwood         607

          Fig. 2. Microscopical crystals of salt of amber          ibid.

          Fig. 3. Microscopical crystals of salt of hartshorn      ibid.

          Fig. 4. Microscopical crystals of salt of sal ammoniac   ibid.

  N. B. The reader will find no references to the several letters which
  appear in the bodies of these figures, for reasons assigned by the
  author as above; in order not to deface the plate, they were suffered
  to remain.



  ESSAYS
  ON THE
  MICROSCOPE.



CHAP. I.

A CONCISE HISTORY OF THE INVENTION AND IMPROVEMENTS WHICH HAVE BEEN MADE
UPON THE INSTRUMENT CALLED A MICROSCOPE.


It is generally supposed that microscopes[3] were invented about the
year 1580, a period fruitful in discoveries; a time when the mind began
to emancipate itself from those errors and prejudices by which it had
been too long enslaved, to assert its rights, extend its powers, and
follow the paths which lead to truth. The honor of the invention is
claimed by the Italians and the Dutch; the name of the inventor,
however, is lost; probably the discovery did not at first appear
sufficiently important, to engage the attention of those men, who, by
their reputation in science, were able to establish an opinion of its
merit with the rest of the world, and hand down the name of the inventor
to succeeding ages. Men of great literary abilities are too apt to
despise the first dawnings of invention, not considering that all real
knowledge is progressive, and that what they deem trifling, may be the
first and necessary link to a new branch of science.

  [3] The term microscope is derived from the Greek μικρος little, and
  σκοπεω to view; it is a dioptric instrument, by means of which objects
  invisible to the naked eye, or very minute, are by the assistance of
  lenses, or mirrors, represented exceeding large and very distinct.
  EDIT.

The microscope extends the boundaries of the organs of vision; enables
us to examine the structure of plants and animals; presents to the eye
myriads of beings, of whose existence we had before formed no idea;
opens to the curious an exhaustless source of information and pleasure;
and furnishes the philosopher with an unlimited field of investigation.
“It leads,” to use the words of an ingenious writer, “to the discovery
of a thousand wonders in the works of his hand, who created ourselves,
as well as the objects of our admiration; it improves the faculties,
exalts the comprehension, and multiplies the inlets to happiness; is a
new source of praise to him, to whom all we pay is nothing of what we
owe; and, while it pleases the imagination with the unbounded treasures
it offers to the view, it tends to make the whole life one continued act
of admiration.”

It is not difficult to fix the period when the microscope first began to
be generally known, and was used for the purpose of examining minute
objects; for, though we are ignorant of the name of the first inventor,
we are acquainted with the names of those who introduced it to the
public, and engaged their attention to it, by exhibiting some of its
wonderful effects. Zacharias Jansens and his son had made microscopes
before the year 1619, for in that year the ingenious Cornelius Drebell
brought one, which was made by them, with him into England, and shewed
it to William Borel, and others. It is possible, this instrument of
Drebell’s was not strictly what is now meant by a microscope, but was
rather a kind of microscopic telescope,[4] something similar in
principle to that lately described by Mr. Æpinus, in a letter to the
Academy of Sciences at Petersburgh. It was formed of a copper tube six
feet long and one inch diameter, supported by three brass pillars in the
shape of dolphins; these were fixed to a base of ebony, on which the
objects to be viewed by the microscope were also placed. In
contradiction to this, Fontana, in a work which he published in 1646,
says, that he had made microscopes in the year 1618: this may be also
very true, without derogating from the merit of the Jansens, for we have
many instances in our own times of more than one person having executed
the same contrivance, nearly at the same time, without any communication
from one to the other.[5] In 1685, Stelluti published a description of
the parts of a bee, which he had examined with a microscope.

  [4] Vide Borellum de vero Telescopii Inventore.

  [5] In 1664 Dr. Power published his “Experimental Philosophy,” the
  first part of which consists of a variety of microscopical
  observations; and in the following year Dr. Hooke produced his
  “Micrographia,” illustrated with a number of elegant figures of the
  different objects. EDIT.

If we consider the microscope as an instrument consisting of one lens
only, it is not at all improbable that it was known to the ancients much
sooner than the last century; nay, even in a degree to the Greeks and
Romans: for it is certain, that spectacles were in use long before the
above-mentioned period: now, as the glasses of these were made of
different convexities, and consequently of different magnifying powers,
it is natural to suppose, that smaller and more convex lenses were made,
and applied to the examination of minute objects. In this sense, there
is also some ground for thinking the ancients were not ignorant of the
use of lenses, or at least of what approached nearly to, and might in
some instances be substituted for them. The two principal reasons which
support this opinion are, first, the minuteness of some ancient pieces
of workmanship, which are to be met with in the cabinets of the curious:
the parts of some of these are so small, that it does not appear at
present how they could have been executed without the use of magnifying
glasses, or of what use they could have been when executed, unless they
were in possession of glasses to examine them with. A remarkable piece
of this kind, a seal with very minute work, and which to the naked eye
appears very confused and indistinct, but beautiful when examined with a
proper lense, is described “Dans l’Histoire de l’Academie des
Inscriptions,” tom. 1, p. 333. The second argument is founded on a great
variety of passages, that are to be seen in the works of Jamblichus,
Pliny, Plutarch, Seneca, Agellius, Pisidias, &c. From these passages it
is evident that they were enabled by some instrument, or other means,
not only to view distant objects, but also to magnify small ones; for,
if this is not admitted, the passages appear absurd, and not capable of
having a rational meaning applied to them. I shall only adduce a short
passage from Pisidias, a christian writer of the seventh century, Τα
μελλοντα ως δια διοπτρου συ βλεπεις: “You see things future by a
_dioptrum_:” now we know of nothing but a perspective glass or small
telescope, whereby things at a distance may be seen as if they were near
at hand, the circumstance on which the simile was founded. It is also
clear, that they were acquainted with, and did make use of that kind of
microscope, which is even at this day commonly sold in our streets by
the Italian pedlars, namely, a glass bubble filled with water. Seneca
plainly affirms it, _Literæ, quamvis minutæ et obscuræ, per vitream
pilam aqua plenam majores clarioresque cernuntur_. Nat. Quæst. lib. 1,
cap. 7. “Letters, though minute and obscure, appear larger and clearer
through a glass bubble filled with water.” Those who wish to see further
evidence concerning the knowledge of the ancients in optics, may consult
Smith’s Optics, Dr. Priestley’s History of Light and Colours, the
Appendix to an Essay on the first Principles of Natural Philosophy by
the Rev. Mr. Jones, Dr. Rogers’s Dissertation on the Knowledge of the
Ancients, and the Rev. Mr. Dutens’s Enquiry into the Origin of the
Discoveries attributed to the Moderns.[6]

  [6] A new edition in French of this learned and valuable work, with
  many and useful notes, is just published. EDIT.

The history of the microscope, like that of nations and arts, has had
its brilliant periods, in which it has shone with uncommon splendor, and
been cultivated with extraordinary ardour; these have been succeeded by
intervals marked with no discovery, and in which the science seemed to
fade away, or at least lie dormant, till some favourable circumstance,
the discovery of a new object, or some new improvement in the
instruments of observation, awakened the attention of the curious, and
animated their researches. Thus, soon after the invention of the
microscope, the field it presented to observation was cultivated by men
of the first rank in science, who enriched almost every branch of
natural history by the discoveries they made with this instrument: there
is indeed scarce any object so inconsiderable, that has not something to
invite the curious eye to examine it; nor is there any, which, when
properly examined, will not amply repay the trouble of investigation.

I shall first speak of the SINGLE MICROSCOPE, not only as it is the most
simple, but because, as we have already observed, it was invented and
used long before the double or compound microscope. When the lenses of
the single microscope are very convex, and consequently the magnifying
power very great, the field of view is so small, and it is so difficult
to adjust with accuracy their focal distance, that it requires some
practice to render the use thereof familiar; at the same time, the
smallness of the aperture to these lenses has been found injurious to
the eyes of some observers: notwithstanding, however, these defects,
the great magnifying power, as well as the distinct vision which is
obtained by the use of a deep single lens, more than counterbalances
every difficulty and disadvantage. It was with this instrument that
Leeuwenhoek and Swammerdam, Lyonet and Ellis examined the minima of
nature, laid open some of her hidden recesses, and by their example
stimulated others to the same pursuit.

The construction of the single microscope is so simple, that it is
susceptible of but little improvement, and has therefore undergone but
few alterations; and these have been chiefly confined to the mode of
mounting it, or the additions to its apparatus. The greatest improvement
this instrument has received, was made by Dr. Lieberkühn, about the year
1740; it consisted in placing the small lens in the center of a highly
polished concave speculum of silver, by which means he was enabled to
reflect a strong light upon the upper surface of an object, and thus
examine it with great ease and pleasure. Before this contrivance, it was
almost impossible to examine small opake objects with any degree of
exactness and satisfaction; for the dark side of the object being next
the eye, and also overshadowed by the proximity of the instrument, its
appearance was necessarily obscure and indistinct.

Dr. Lieberkühn adapted a microscope to every object; it consisted of a
short brass tube, at the eye end of which a concave silver speculum was
fixed, and in the center of the speculum a magnifying lens: the object
was placed in the middle of the tube, and had a small adjustment to
regulate it to the focus; at the other end of the tube there was a plano
convex lens, to condense and render more uniform the light which was
reflected from the mirror. But all these pains were not bestowed upon
trifling objects; his were generally the most curious anatomical
preparations, a few of which, with their microscopes, are, I believe,
deposited in the British Museum. It will be proper, in this place, to
give some account of Mr. Leeuwenhoek’s microscopes, which were rendered
famous throughout all Europe, on account of the numerous discoveries he
had made with them, as well as from his afterwards bequeathing a part of
them to the Royal Society. The microscopes he used were all single, and
fitted up in a convenient simple manner; each of them consisted of a
very small double convex lens, let into a socket between two plates
rivetted together, and pierced with a small hole; the object was placed
on a silver point or needle, which, by means of screws adapted for that
purpose, might be turned about, raised or depressed at pleasure, and
thus be brought nearer to, or be removed farther from the glass, as the
eye of the observer, the nature of the object, and the convenient
examination of its parts required. Mr. Leeuwenhoek fixed his objects, if
they were solid, to the foregoing point with glue; if they were fluid,
he fitted them on a little plate of talc, or exceeding thin blown glass,
which he afterwards glued to the needle, in the same manner as his other
objects. The glasses were all exceeding clear, and of different
magnifying powers, which were proportioned to the nature of the object,
and the parts designed to be examined. But none of those, which were
presented to the Royal Society, magnify so much as the glass globules,
which have been used in other microscopes. He had observed, in a letter
of his to the Royal Society, that from upwards of forty years
experience, he found that the most considerable discoveries were to be
made with such glasses, as magnifying but moderately, exhibited the
object with the most perfect brightness and distinctness. Each
instrument was devoted to one or two objects: hence he had always some
hundreds by him.[7] There is some reason for supposing, that Leeuwenhoek
was acquainted with a mode of viewing opake objects, similar to that
invented by Dr. Lieberkühn.[8]

  [7] Philosophical Transactions, No. 980, No. 458.

  [8] Priestley’s History of Optics, p. 220.

About the year 1665, small glass globules began to be occasionally
applied to the single microscope, instead of convex lenses. By these
globules, an immense magnifying power is obtained. The invention of them
has been generally attributed to M. Hartsoeker; it appears, however, to
me, that we are indebted to the celebrated Dr. Hooke for this discovery;
for he described the manner of making them in the preface to his
“Micrographia,” which was published in the year 1665. Now the first
account we have of any microscopical discovery by M. Hartsoeker, was
that of the spermatic animalculæ, made by him when he was eighteen years
old; which brings us down to the year 1674, long after Dr. Hooke’s
publication.

As these glass globules have been very useful in the hands of
experienced observers, I shall lay before my readers the different modes
which have been described for making them, that the reader may be
enabled thereby to ascertain the reality of the discoveries that have
been said to be made with them.

Take a small rod[9] of the clearest and cleanest glass you can procure,
free, if possible from blebs, veins, or sandy particles; then by melting
it in a lamp with spirit of wine, or the purest and clearest sallad oil,
draw it out into exceeding fine and small threads; take a small piece of
these threads, and melt the end thereof in the same flame, till you
perceive it run into a small drop, or globule, of the desired size; let
this globule cool, then fix it upon a thin plate of brass or silver, so
that the middle of it may be directly over the center of a very small
hole made in this plate, turning it till it is fixed by the
before-mentioned thread of glass. When the plate is properly fixed to
your microscope, and the object adjusted to the focal distance of the
globule, you will perceive the object distinctly and immensely
magnified. “By these means,” says Dr. Hooke, “I have been able to
distinguish the particles of bodies not only a million times smaller
than a visible point, but even to make those visible whereof a million
of millions would hardly make up the bulk of the smallest visible grain
of sand; so prodigiously do these exceeding small globules enlarge our
prospect into the more hidden recesses of nature.”

  [9] Lectures and Collections by Dr. Hooke.

Mr. Butterfield, in making of the globules, used a lamp with spirit of
wine; but instead of a cotton wick, he used fine silver wire, doubled up
and down like a skain of thread.[10] He prepared his glass by beating it
to powder, and washing it very clean; he then took a little of this
glass upon the sharp point of a silver needle, wetted with spittle, and
held it in the flame, turning it about till a glass ball was formed;
then taking it from the flame, he afterwards cleaned it with soft
leather, and set it in a brass cell.

  [10] Philos. Trans. No. 141.

No person has carried the use of these globules so far as Father Di
Torre, of Naples, nor been so dexterous in the execution of them; and if
others have not been able to follow him in the same line, it may be
fairly attributed to a want of that delicacy of touch for adjusting the
objects to their focus, and that acuteness of vision which can only be
acquired by long practice. Di Torre has also described, more minutely
than any other author, the mode of executing these globules, which, as
it throws much light upon the preceding description by Dr. Hooke, will
not, it is presumed, be unacceptable to the reader.

Three things are necessary for forming of these globules: 1. A lamp and
bellows, such as are used by the glass-blowers. 2. A piece of perfect
tripoli. 3. A variety of small glass rods. When the flame of the lamp is
blown in an horizontal direction, it will be found to consist of two
parts; from the base to about two thirds of its length, it is of a white
colour; beyond this, it is transparent and colourless. It is this
transparent part which is to be used for melting the glass, because by
this it will not be in the least sullied; but it will be immediately
soiled, if it touch the white part of the flame. The part of the glass
which is presented to the flame, ought to be exceeding clean, and great
care should be taken that it be not touched by the fingers. If the glass
rod has contracted any spots, it must either be thrown away, or the
parts that are spotted must be cut off.

The piece of tripoli which is to be used in forming the globules, should
be flat on one side, and so large that it may be handled conveniently,
and protect the fingers from the flame. A piece four or five inches
long, and three or four inches thick, will answer very well. The best
tripoli for this purpose is of a white colour, with a fine grain, heavy
and compact, and which, after it has been calcined, is of a red colour.
This kind resists the fire best, is not apt to break when calcined, and
the melted glass does not adhere to it. To calcine this tripoli, cover
it well all round with charcoal nearly red hot, leaving it thus till the
charcoal is quite cold; it may then be taken out. Let several
hemispherical cavities be made on the flat side of the tripoli; they
should be of different sizes, nicely polished, and neatly rounded at the
edges, in order to facilitate the entrance of the flame. The large
globules are to be placed in the large cavities, and the minuter ones,
in the small cavities. The holes in the tripoli must never be touched
with the finger. If it be necessary to clean them, it should be done
with white paper; the larger globules may be cleaned with wash leather.
The glass rods should be of various sizes, as of ¹⁄₁₀th, ¹⁄₂₀th, ¹⁄₃₀th
of an inch in diameter, as clean and free from specks and bubbles as
possible.


TO MAKE SMALL GLASS MICROSCOPIC GLOBULES.

Take two rods of glass, one in each hand, place their extremities close
to each other, and in the purest part of the flame; when you perceive
the ends to be fused, separate them from each other; the heated glass
following each rod, will be finer, in proportion to the length it is
drawn to, and the smallness of the rod; in this manner you may procure
threads of glass of any degree of fineness. Direct the flame to the
middle of the thread, and it will be instantly divided into two parts.
When one of the threads is perfectly cool, place it at the extremity of
the flame, by which it will be rendered round; and, if the thread of
glass be very fine, an exceeding small globule will be formed. This
thread may now be broke off from the rod, and a new one may be again
drawn out as before, by the assistance of the other glass rod.

The small ball is now to be separated from the thread of glass; this is
easily effected by the sharp edge of a piece of flint. The ball should
be placed in a groove of paper, and another piece of paper be held over
it, to prevent the ball from flying about and being lost. A quantity of
globules ought to be prepared in this manner; they are then to be
cleaned, and afterwards placed in the cavities of the tripoli, by means
of a delicate pair of nippers. The globules are now to be melted a
second time, in order to render them completely spherical; for this
purpose, bring one of the cavities near the extremity of the flame,
directing this towards the tripoli, which must be first heated; the
cavity is then to be lowered, so that the flame may touch the glass,
which, when it is red hot, will assume a perfect globular form; it must
then be removed from the flame, and laid by; when cold, it should be
cleaned, by rubbing between two pieces of white paper. Let it now be set
in a brass cap, to try whether the figure be perfect. If the object be
not well defined, the globule must be thrown away. Though, if it be
large, it may be exposed two or three times to the flame. When a large
globule is forming, it should be gently agitated by shaking the tripoli,
which will prevent its becoming flat on one side. By attending to these
directions, the greater part of the globules will be round and fit for
use. In damp weather, notwithstanding every precaution, it will often
happen, that out of forty globules, four or five only will be fit for
use.

Mr. Stephen Gray, of the Charter-House, having observed some irregular
particles within a glass globule, and finding that they appeared
distinct and prodigiously magnified when held close to his eye,
concluded, that if he placed a globule of water, in which there were any
particles more opake than the water, near his eye, he should see those
particles distinctly and highly magnified. This idea, when realized, far
exceeded his expectation. His method was, to take on a pin a small
portion of water which he knew had in it some minute animalculæ; this he
laid on the end of a small piece of brass wire, till there was formed
somewhat more than an hemisphere of water; on applying it then to the
eye, he found the animalculæ most enormously magnified; for those which
were scarce discernible with his glass globules, with this appeared as
large as ordinary sized peas. They cannot be seen in day-time, except
the room be darkened, but are seen to the greatest advantage by
candle-light. Montucla observes, that when any objects are inclosed
within this transparent globule, the hinder part of it acts like a
concave mirror, provided they be situated between that surface and the
focus; and that by these means they are magnified three times and an
half more than they would be in the usual way. An extempore microscope
may be formed, by taking up a small drop of water on the point of a pin,
and placing it over a fine hole made in a piece of metal; but as the
refractive power of water is less than that of glass, these globules do
not magnify so much as those of the same size which are made of glass:
this was also contrived by Mr. Gray. The same ingenious author invented
another water microscope, consisting of two drops of water, separated in
part by a thin brass plate, but touching near the center; which were
thus rendered equivalent to a double convex lens of unequal convexities.

Dr. Hooke describes a method of using the single microscope, which seems
to have a great analogy to the foregoing methods of Mr. Gray. “If you
are desirous,” says he, “of obtaining a microscope with one single
refraction, and consequently capable of procuring the greatest clearness
and brightness any one kind of microscope is susceptible of; spread a
little of the fluid you intend to examine, on a glass plate, bring this
under one of your microscopic globules, then move it gently upwards,
till the fluid touch the globule, to which it will soon adhere, and that
so firmly, as to bear being moved a little backwards or forwards. By
looking through the globule, you will then have a perfect view of the
animalculæ in the drop.”[11]

  [11] Hooke’s Lectures and Conjectures, p. 98.

Having laid before the reader the principal improvements that have been
suggested, or made in the single microscope, it remains only to point
out those instruments of this kind, which, from the mode in which they
are fitted up, seem best adapted for general use; the peculiar
advantages of which, as well as the manner of using them, will be
described in the third chapter of this work.

Fig. 1. Plate VI. A botanical microscope, contrived by Dr. Withering.

Fig. 2. Plate VI. A botanical microscope, by Mr. B. Martin, being the
most universal pocket microscope.

Fig. 3. Plate VI, represents that which was used by M. Lyonnet for
dissecting the cossus.

Fig. 5. Plate VI. The tooth and pinion microscope, which is now
generally substituted in the room of Wilson’s. Fig. 1. Plate II. B.

Fig. 1. Plate VII. B. The aquatic microscope used by Mr. Ellis for
investigating the nature of coralline, and recommended to botanists by
Mr. Curtis, in his valuable publication, the “Flora Londinensis.”

Fig. 7. Plate VIII. A botanical magnifier, or hand megalascope, which by
the different combinations of its three lenses produces seven different
magnifying powers; when the three are used together, they are turned in,
and the object viewed through the apertures in the sides.

Fig. 8. Plate VIII. A botanical magnifier, having one large lens and two
small ones, but not admitting of more than three powers.

A COMPOUND MICROSCOPE, as it consists of two, three, or more glasses, is
more easily varied, and is susceptible of greater changes in its
construction, than the single microscope. The number of the lenses, of
which it is formed, may be increased or diminished, their respective
positions may be varied, and the form in which they are mounted be
altered almost ad infinitum. But among these varieties, some will be
found more deserving of attention than others; we shall here treat of
these only.

The three first compound microscopes deserving of notice, are those of
Dr. Hooke, Eustachio Divinis, and Philip Bonnani. Dr. Hooke gives an
account of his in the preface to his Micrographia, which has been
already cited; it was about three inches in diameter, seven long, and
furnished with four draw-out tubes, by which it might be lengthened as
occasion required: it had three glasses--a small object glass, a middle
glass, and a deep eye glass. Dr. Hooke used all the glasses when he
wanted to take in a considerable part of an object at once, as by the
middle glass a number of radiating pencils were conveyed to the eye,
which would otherwise have been lost: but when he wanted to examine with
accuracy the small parts of any substance, he took out the middle glass,
and only made use of the eye and object lenses; for the fewer the
refractions are, the clearer and more bright the object appears.

An account of Eustachio Divinis’s microscope was read at the Royal
Society, in 1668.[12] It consisted of an object lens, a middle glass,
and two eye glasses, which were plano convex lenses, and were placed so
that they touched each other in the center of their convex surfaces; by
which means the glass takes in more of an object, the field is larger,
the extremities of it less curved, and the magnifying power greater. The
tube, in which the glasses were inclosed, was as large as a man’s leg,
and the eye glasses as broad as the palm of the hand. It had four
several lengths; when shut up, it was sixteen inches long, and magnified
the diameter of an object forty-one times; at the second length, ninety
times; at the third length, one hundred and eleven times; at the fourth
length, one hundred and forty-three times. It does not appear that E.
Divinis varied the object lenses.

  [12] Philos. Trans. No. 42.

Philip Bonnani published an account of his two microscopes in 1698;[13]
both were compound; the first was similar to that which Mr. Martin
published as new, in his Micrographia Nova,[14] in 1742. His second was
like the former, composed of three glasses, one for the eye, a middle
glass, and an object lens; they were mounted in a cylindrical tube,
which was placed in an horizontal position; behind the stage was a small
tube, with a convex lens at each end; beyond this was a lamp; the whole
capable of various adjustments, and regulated by a pinion and rack; the
small tube was used to condense the light on the object, and spread it
uniformly over it according to its nature, and the magnifying power that
was used.

  [13] Bonnani Observationes circa Viventia.

  [14] Micrographia Nova, by B. Martin, 4to.

If the reader attentively consider the construction of the foregoing
microscopes, and compare them with more modern ones, he will be led to
think with me, that the compound microscope has received very little
improvement since the time of Bonnani. Taken separately, the foregoing
constructions are equal to some of the most famed modern microscopes. If
their advantages be combined, they are far superior to that of M.
Dellebarre, notwithstanding the pompous eulogium affixed thereto by
Mess. De L’Academie Royale des Sciences.[15]

  [15] Memoires sur les Differences de la Construction et des Effets du
  Microscope, de M. L. F. Dellebarre, 1777.

From this period, to the year 1736, the microscope appears not to have
received any considerable alteration, but the science itself to have
been at a stand. The improvements which were making in the reflecting
telescope, naturally led those who had considered the subject, to expect
a similar advantage would accrue to microscopes on the same principles:
accordingly we find two plans of this kind; the first was that of Dr.
Robert Barker. This instrument is entirely the same as the reflecting
telescope, excepting the distance of the two speculums, which is
lengthened, in order to adapt it to those pencils of rays which enter
the telescope diverging; whereas, from very distant objects, they come
in a direction nearly parallel. But this was soon laid aside, not only
as it was more difficult to manage, but also because it was unfit for
any but very small or transparent objects: for the object being between
the speculum and the image, would, if it were large and opake, prevent a
due reflection of light on the object.

The second was contrived by Dr. Smith.[16] In this there were two
reflecting mirrors, one concave and the other convex; the image was
viewed by a lens. This microscope, though far from being executed in the
best manner, performed, says Dr. Smith, very well, so that he did not
doubt but that it would have excelled others, if it had been properly
finished.

  [16] Dr. Smith’s Optics, Remarks, p. 94.

As some years are more favourable to the fruits of the earth, so also
some periods are more favourable to particular sciences, being rich in
discovery, and cultivated with ardor. Thus, in the year 1738, Dr.
Lieberkühn’s invention of the solar microscope was communicated to the
public: the vast magnifying power which was obtained by this instrument,
the colossal grandeur with which it exhibited the minima of nature, the
pleasure which arose from being able to display the same object to a
number of observers at the same time, by affording a new source of
rational amusement, increased the number of microscopic observers, who
were further stimulated to the same pursuits by Mr. Trembley’s famous
discovery of the polype: the wonderful properties of this little animal,
together with the works of Mr. Trembley, Baker, and my father, revived
the reputation of this instrument.[17]

  [17] Trembley Memoires sur les Polypes. Baker’s Microscope made Easy;
  Attempt towards an History of the Polype; Employment for the
  Microscope. Adams’s Micrographia Illustrata. Joblot’s Observations
  d’Histoire Naturelle.

Every optician now exercised his talents in improving, as he called it,
the microscope; in other words, in varying its construction, and
rendering it different from that sold by his neighbour. Their principal
object seemed to be, only to subdivide the instrument, and make it lie
in as small a compass as possible; by which means, they not only
rendered it complex and troublesome in use, but lost sight also of the
extensive field, great light, and other excellent properties of the more
ancient instruments; and, in some measure, shut themselves out from
further improvements on the microscope. Every mechanical instrument is
susceptible of almost infinite combinations and changes, which are
attended with their relative advantages and disadvantages: thus, what is
gained in power, is lost in time; “he that loves to be confined to a
small house, must lose the benefit of air and exercise.”

The microscope, nearly at the same period, gave rise to M. Buffon’s
famous system of organic molecules, and M. Needham’s incomprehensible
ideas concerning a vegetable force and the vitality of matter. M. Buffon
has dressed up his system with all the charms of eloquence, presenting
it to the mind in the most agreeable and lively colours, exerting the
depths of erudition in the most interesting and seducing manner to
establish his hypothesis, making us almost ready to adopt it against
the dictates of reason, and the evidence of facts. But whether this
great man was misled by the warmth of his imagination, his attachment to
a favourite system, or the use of imperfect instruments, it appears but
too evident, that he was not acquainted with the objects whose nature he
attempted to investigate; and it is probable, that he never saw[18]
those which he supposed he was describing, continually confounding the
animalculæ produced from the putrifying decomposition of animal
substances, with the spermatic animalculæ, although they are two kinds
of beings, differing in form and nature; so that the beautiful fabric
attempted to be raised on his hypothesis, vanishes before the light of
truth and well conducted experiments.

  [18] Porro Buffonius, ut cum illustris viri venia dicam, omnino non
  videtur vermiculos seminales vidisse. Diuturnitas enim vitæ quam suis
  corpusculis tribuit, ostendit non esse nostra animalcula (id est,
  spermatica) quibus brevis et paucarum horarum vita est. Haller
  Physiol. tom. 7.

After this period, the mind, either satisfied with the discoveries
already made, which will be particularly described hereafter, or tired
by its own exertions, sought for repose in other pursuits; so that for
several years this instrument was again, in some measure, laid aside. In
1770, Dr. Hill[19] published a treatise, in which he endeavoured to
explain the construction of timber by the microscope, and shew the
number, the nature, and office of its several parts, their various
arrangements and proportions in the different kinds; and point out a way
of judging, from the structure of trees, the uses they will best serve
in the affairs of life. So important a subject soon revived the ardor
for microscopic pursuits, which seems to have been increasing ever
since. About the same time, my father contrived an instrument for
cutting the transverse sections of wood, in order that the texture
thereof might be rendered more visible in the microscope, and
consequently be better understood; this instrument was afterwards
improved by Mr. Cumming. Another instrument for the same purpose, more
certain in its effects, and more easily managed, is represented in Fig.
1. Plate IX; and will be described in one of the following chapters. Dr.
Hill and Mr. Custance now endeavoured to bring back the microscope
nearer to the old standard, to increase the field by the multiplication
of the eye glasses, and to augment the light on the object, by
condensing lenses; and in this they happily succeeded: Mr. Custance was
unrivalled in his dexterity in preparing, and accuracy in cutting thin
transverse sections of wood.

  [19] Dr. Hill on the Construction of Timber.

In 1771, my father published a fourth edition of his Micrographia, in
which he described the principal inventions then in use; particularly a
contrivance of his own, for applying the solar microscope to the camera
obscura, and illuminating it at night by a lamp, by which means a
picture of microscopic objects might be exhibited in winter evenings.

It appears[20] from the testimony of M. Æpinus, that Dr. Lieberkühn had
considerably improved the solar microscope, by adapting it to view opake
objects. This contrivance was by some means lost. The knowledge,
however, that such an effect had been produced, led Æpinus to attend to
the subject himself, in which he in some measure succeeded, and would,
no doubt, have brought it to perfection, if he had increased the size of
his illuminating mirror. Some further improvements were made on this
instrument by M. Ziehr; but the most perfect instrument of the kind, is
that of Mr. B. Martin, who published an account of it in the year
1774.[21] The common solar microscope does not shew the surface of any
object, whereas the opake solar microscope not only magnifies the
object, but exhibits on a screen an expanded picture of its surface,
with all its colours, in a most beautiful manner.

  [20] Priestley’s Hist. of Optics, p. 743.

  [21] Martin’s Description and Use of an Opake Solar Microscope. The
  merits and ingenuity in constructing and improving microscopes by this
  learned optician, seem to be unnoticed by our late author. The
  following pamphlets by Mr. B. Martin are, among others of his valuable
  publications, instances of his indefatigable industry. Description and
  Use of a Pocket Reflecting Microscope, with a Micrometer; 1739.
  Micrographia Nova, or a New Treatise on the Microscope; 1742.
  Description of a New Universal Microscope; a Postscript to his New
  Elements of Optics; 1759. Description of several Sorts of Microscopes,
  and the Use of the Reflecting Telescope, as an universal Perspective
  for viewing every Sort of Objects. Optical Essays; 1770. A Description
  and Use of a Proportional Camera Obscura, with a Solar Microscope
  adapted thereto, annexed to his Description of the Opake Solar
  Microscope above-mentioned. Description of a New Universal Microscope;
  1776. Description and Use of a Graphical Perspective and Microscope;
  1771. Microscopium Polydynamicum, or a New Construction of a
  Microscope; 1771. An Essay on the genuine Construction of a standard
  Microscope and Telescope; 1776. Microscopium Pantometricum, or a new
  Construction of a Micrometer adapted to the Microscope. The most
  essential articles in the above works will be hereafter described.
  EDIT.

About the year 1774, I invented the improved lucernal microscope; this
instrument does not in the least fatigue the eye: it shews all opake
objects in a most beautiful manner; and transparent objects may be
examined by it in various ways, so that no part of an object is left
unexplored; and the outlines of all may be taken with ease, even by
those who are most unskilled in drawing.

M. L. F. Dellebarre published an account of his microscope in the year
1777. It does not appear from this, that it was superior in any respect
to those that were made in England, but was inferior in others; for
those published by my father in 1771 possessed all the advantages of
Dellebarre’s in a higher degree, except that of changing the eye
glasses.

In 1784, M. Æpinus published a description of what he termed
new-invented microscopes, in a letter to the Academy of Sciences at
Petersburgh;[22] they are nothing more than an application of the
achromatic perspective to microscopic purposes. Now it has been long
known to every one who is the least versed in optics, that any telescope
is easily converted into a microscope, by removing the object glass to a
greater distance from the eye glasses; and that the distance of the
image varies with the distance of the object from the focus, and is
magnified more as its distance from the object is greater: the same
telescope may, therefore be successively turned into a microscope, with
different magnifying powers. Mr. Martin had also shewn, in his
description and use of a polydynamic microscope, how easily the small
achromatic perspective may be applied to this purpose. Botanists might
find some advantage in attending to this instrument; it would assist
them in discovering small plants at a distance, and thus often save them
from the thorns of the hedge, and the dirt of a ditch.

  [22] Description des Nouveaux Microscopes inventes par M. Æpinus.

Fig. 1. Plate III, represents the improved lucernal microscope.

Fig. 1. Plate IV. The improved compound and single microscope.

Fig. 2. Plate IV. The best universal compound microscope.

Fig. 3. Plate IV, is what is usually called Culpeper’s, or the common
three pillared compound microscope.

Fig. 1. Plate V, represents Martin’s solar opake microscope.

Fig. 4. Plate VI, is a picture of the common solar microscope.

Fig. 1. Plate VII. A, is Cuff’s common compound microscope.

Fig. 3. Plate VIII. Martin’s new microscopic telescope, or convenient
portable apparatus for a traveller.

We cannot conclude this chapter better than with the following
observations on the microscope. We are indebted to it for many
discoveries in natural history; but let us not suppose that the Creator
intended to hide these objects from our observation. It is true, this
instrument discovers to us as it were a new creation, new series of
animals, new forests of vegetables; but he who gave being to these, gave
us an understanding capable of inventing means to assist our organs in
the discovery of their hidden beauties. He gave us eyes adapted to
enlarge our ideas, and capable of comprehending a universe at one view,
and consequently incapable of discerning those minute beings, with which
he has peopled every atom of the universe. But then he gave properties
and qualities to matter of a particular kind, by which it would procure
us this advantage, and at the same time elevated the understanding from
one degree of knowledge to another, till it was able to discover these
assistances for our sight.

It is thus we should consider the discoveries made by those instruments,
which have received their birth from an exertion of our faculties. It is
to the same power, who created the objects of our admiration, that we
are ultimately to refer the means of discovering them. Let no one,
therefore, accuse us of prying deeper into the wonders of nature, than
was intended by the great author of the universe. There is nothing we
discover by their assistance, which is not a fresh source of praise; and
it does not appear that our faculties can be better employed, than in
finding means to investigate the works of God.

From a partial consideration of these things, we are very apt to
criticise what we ought to admire; to look upon as useless what perhaps
we should own to be of infinite advantage to us, did we see a little
farther; to be peevish where we ought to give thanks; and at the same
time to ridicule those who employ their time and thoughts in examining
what we were, i. e. some of us most assuredly were created and appointed
to study. In short, we are too apt to treat the Almighty worse than a
rational man would treat a good mechanic, whose works he would either
thoroughly examine, or be ashamed to find any fault with them. This is
the effect of a partial consideration of nature; but he who has candor
of mind, and leisure to look farther, will be inclined to cry out:

  How wond’rous is this scene! where all is form’d
  With number, weight, and measure! all design’d
  For some great end! where not alone the plant
  Of stately growth; the herb of glorious hue,
  Or food-full substance! not the laboring steed,
  The herd, and flock that feed us; not the mine
  That yields us stores for elegance and use;
  The sea that loads our table, and conveys
  The wanderer man from clime to clime, with all
  Those rolling spheres, that from on high shed down
  Their kindly influence; not these alone,
  Which strike ev’n eyes incurious, but each moss,
  Each shell, each crawling insect, holds a rank
  Important in the plan of Him, who fram’d
  This scale of beings; holds a rank, which lost,
  Would break the chain, and leave behind a gap
  Which nature’s self would rue. Almighty Being,
  Cause and support of all things, can I view
  These objects of my wonder; can I feel
  These fine sensations, and not think of thee?
  Thou who dost thro’ th’ eternal round of time,
  Dost thro’ th’ immensity of space exist
  Alone, shalt thou alone excluded be
  From this thy universe? Shall feeble man
  Think it beneath his proud philosophy
  To call for thy assistance, and pretend
  To frame a world, who cannot frame a clod?--
  Not to know thee, is not to know ourselves--
  Is to know nothing--nothing worth the care
  Of man’s exalted spirit:--all becomes,
  Without thy ray divine, one dreary gloom,
  Where lurk the monsters of phantastic brains,
  Order bereft of thought, uncaus’d effects,
  Fate freely acting, and unerring chance.
  Where meanless matter to a chaos sinks,
  Or something lower still, for without thee
  It crumbles into atoms void of force,
  Void of resistance--it eludes our thought.
  Where laws eternal to the varying code
  Of self-love dwindle. Interest, passion, whim,
  Take place of right and wrong, the golden chain
  Of beings melts away, and the mind’s eye
  Sees nothing but the present. All beyond
  Is visionary guess--is dream--is death.[23]

  [23] Stillingfleet’s Miscellaneous Tracts.



CHAP. II.

OF VISION; OF THE OPTICAL EFFECT OF MICROSCOPES, AND OF THE MANNER OF
ESTIMATING THEIR MAGNIFYING POWERS.


The progress that has been made in the science of optics, in the last
and present century, particularly by Sir Isaac Newton, may with
propriety be ranked among the greatest acquisitions of human knowledge.
And Mess. Delaval and Herschel have shewn by their discoveries, that the
boundaries of this science may be considerably enlarged.

The rays of light, which minister to the sense of sight, are the most
wonderful and astonishing part of the inanimate creation; of which we
shall soon be convinced, if we consider their extreme minuteness, their
inconceivable velocity, the regular variety of colours they exhibit, the
invariable laws according to which they are acted upon by other
substances, in their reflections, inflections, and refractions, without
the least change of their original properties; and the facility with
which they pervade bodies of the greatest density and closest texture,
without resistance, without crouding or disturbing each other. These, I
believe, will be deemed sufficient proofs of the wonderful nature of
these rays; without adding, that it is by a peculiar modification of
them, that we are indebted for the advantages obtained by the
microscope.

The science of optics, which explains and treats of many of the
properties of those rays of light, is deduced from experiments, on which
all philosophers are agreed. It is impossible to give an adequate idea
of the nature of vision, without a knowledge of these experiments, and
the mathematical reasoning grounded upon them; but as to do this would
alone fill a large volume, I shall only endeavour to render some of the
more general principles clear, that the reader, who is unacquainted with
the science of optics, may nevertheless be enabled to comprehend the
nature of vision by the microscope. Some of the most important of these
principles may be deduced from the following very interesting
experiment.

Darken a room, and let the light be admitted therein only by a small
hole; then, if the weather be fine, you will see on the wall, which is
facing the hole, a picture of all those exterior objects which are
opposite thereto, with all their colours, though these will be but
faintly seen. The image of the objects that are stationary, as trees,
houses, &c. will appear fixed; while the images of those that are in
motion, will be seen to move. The image of every object will appear
inverted, because the rays cross each other in passing through the small
hole. If the sun shine on the hole, we shall see a luminous ray proceed
in a strait line, and terminate on the wall. If the eye be placed in
this ray, it will be in a right line with the hole and the sun: it is
the same with every other object which is painted on the wall. The
images of the objects exhibited on the same plane, are smaller in
proportion as the objects are further from the hole.

Many and important are the inferences which may be deduced from the
foregoing experiment, among which are the following:

1. That light flows in a right line.

2. That a luminous point may be seen from all those places to which a
strait line can be drawn from the point, without meeting with any
obstacle; and consequently,

3. That a luminous point, by some unknown power, sends forth rays of
light in all directions, and is the center of a sphere of light, which
extends indefinitely on all sides; and if we conceive some of these rays
to be intercepted by a plane, then is the luminous point the summit of a
pyramid, whose body is formed by the rays, and its base by the
intercepting plane. The image of the surface of an object, which is
painted on the wall, is also the base of a pyramid of light, the apex of
which is the hole; the rays which form this pyramid, by crossing at the
hole, form another, similar and opposite to this, of which the hole is
also the summit, and the surface of the object the base.

4. That an object is visible, because all its points are radiant points.

5. That the particles of light are indefinitely small; for the rays,
which proceed from the points of all the objects opposite to the hole,
pass through it, though extremely small, without embarrassing or
confounding each other.

6. That every ray of light carries with it the image of the object from
which it was emitted.

The nature of vision in the eye may be imperfectly illustrated by the
experiment of the darkened room; the pupil of the eye being considered
as the hole through which the rays of light pass, and cross each other,
to paint on the retina, at the bottom of the eye, the inverted images of
all those objects which are exposed to the sight, so that the diameters
of the images of the same object are greater, in proportion to the
angles formed at the pupil, by the crossing rays which proceed from the
extremities of the object; that is, the diameter of the image is
greater, in proportion as the distance is less; or, in other words, the
apparent magnitude of an object is in some degree measured by the angle
under which it is seen, and this angle increases or diminishes,
according as the object is nearer to, or farther from the eye; and
consequently, the less the distance is between the eye and the object,
the larger the latter will appear.

From hence it follows, that the apparent diameter of an object seen by
the naked eye, may be magnified in any proportion we please; for, as the
apparent diameter is increased, in proportion as the distance from the
eye is lessenned, we have only to lessen the distance of the object from
the eye, in order to increase the apparent diameter thereof.[24] Thus,
suppose there is an object, A B, Plate I. Fig. 1, which to an eye at E
subtends or appears under the angle A E B, we may magnify the apparent
diameter in what proportion we please, by bringing our eye nearer to it.
If, for instance, we would magnify it in the proportion of F G to A B;
that is, if we would see the object under an angle as large as F E G, or
would make it appear the same length that an object as long as F G would
appear, it may be done by coming nearer to the object. For the apparent
diameter is as the distance inversely; therefore, if C D is as much less
than C E, as F G is greater than A B, by bringing the eye nearer to the
object in the proportion of C D to E D, the apparent diameter will be
magnified in the proportion of F G to A B; so that the object A B, to
the eye at D, will appear as long as an object F G would appear to the
eye at E. In the same manner we might shew, that the apparent diameter
of an object, when seen by the naked eye, may be infinite. For since
the apparent diameter is reciprocally as the distance of the eye, when
the distance of the eye is nothing or when the eye is close to the
object at C, the apparent diameter will be the reciprocal of nothing, or
infinite.

  [24] Rutherforth’s System of Natural Philosophy, p. 330.

There is, however, one great inconvenience in thus magnifying an object,
without the help of glasses, by placing the eye nearer to it. The
inconvenience is, that we cannot see an object distinctly, unless the
eye is about five or six inches from it; therefore, if we bring it
nearer to our eye than five or six inches, however it may be magnified,
it will be seen confusedly. Upon this account, the greatest apparent
magnitude of an object that we are used to, is the apparent magnitude
when the eye is about five or six inches from it: and we never place an
object much within that distance; because, though it might be magnified
by these means, yet the confusion would prevent our deriving any
advantage from seeing it so large. The size of an object seems
extraordinary, when viewed through a convex lens; not because it is
impossible to make it appear of the same size to the naked eye, but
because at the distance from the eye which would be necessary for this
purpose, it would appear exceedingly confused; for which reason, we
never bring our eye so near to it, and consequently, as we have not been
accustomed to see the object of this size, it appears an extraordinary
one.

On account of the extreme minuteness of the atoms of light, it is clear,
a single ray, or even a small number of rays, cannot make a sensible
impression on the organ of sight, whose fibres are very gross, when
compared to these atoms; it is necessary, therefore, that a great number
should proceed from the surface of an object, to render it visible. But
as the rays of light, which proceed from an object, are continually
diverging, different methods have been contrived, either of uniting them
in a given point, or of separating them at pleasure: the manner of
doing this is the subject of dioptrics and catoptrics.

By the help of glasses, we unite in the same sensible point a great
number or rays, proceeding from one point of an object; and as each ray
carries with it the image of the point from whence it proceeded, all the
rays united must form an image of the object from whence they were
emitted. This image is brighter, in proportion as there are more rays
united; and more distinct, in proportion as the order, in which they
proceeded, is better preserved in their union. This may be rendered
evident; for, if a white and polished plane be placed where the union is
formed, we shall see the image of the object painted in all its colours
on this plane; which image will be brighter, if all adventitious light
be excluded from the plane on which it is received.

The point of union of the rays of light, formed by means of a glass
lens, &c. is called the FOCUS.

Now, as each ray carries with it the image of the object from whence it
proceeded, it follows, that if those rays, after intersecting each
other, and having formed an image at their intersection, are again
united by a refraction or reflection, they will form a new image, and
that repeatedly, as long as their order is not confounded or disturbed.

It follows also, that when the progress of the luminous ray is under
consideration, we may look on the image as the object, and the object as
the image; and consider the second image as if it had been produced by
the first as an object, and so on.

In order to gain a clear idea of the wonderful effects produced by
glasses, we must proceed to say something of the principles of
refraction.

Any body, which is so constituted as to yield a passage to the rays of
light, is called a MEDIUM. Air, water, glass, &c. are mediums of light.
If any medium afford an easy passage to the rays of light, it is called
a RARE MEDIUM; but if it do not afford an easy passage to these rays, it
is called a DENSE MEDIUM.

Let Z, Fig. 2. Plate I. be a rare medium, and Y a dense one; and let
them be separated by the plane surface G H. Let I K be a perpendicular
to it, and cutting it in C.

With the center C, and any distance, let a circle be described. Then let
A C be a ray of light, falling upon the dense medium. This ray, if
nothing prevented, would go forward to L; but because the medium Y is
supposed to be denser than Z, it will be bent downward toward the
perpendicular I K, and describe the line C B.

The ray A C is called the INCIDENT RAY; and the ray C B, the REFRACTED
RAY.

The angle A C I is called the ANGLE OF INCIDENCE, and the angle B C K is
called the ANGLE OF REFRACTION.

If from the point A upon the right line C I, there be let fall the
perpendicular A D, that line is called the sine of the angle of
incidence.

In the same manner, if from the point B, upon the right line I K, there
be let fall the perpendicular B E, that line will be the sine of the
angle of refraction.

The sines of the angles are the measures of the refractions, and this
measure is constant; that is, whatever is the sine of the angle of
incidence, it will be in a constant proportion to the sine of the angle
of refraction, when the mediums continue the same. A general idea of
refraction may be formed from the following experiments.

EXPERIMENT 1. Let A B C D, Fig. 3. Plate I. represent a vessel so
placed, with respect to the candle E, that the shadow of the side A C
may fall at D. Suppose the vessel to be now filled with water, and the
shadow will withdraw to d; the ray of light, instead of proceeding to D,
being refracted or bent to d. And there is no doubt but that an eye,
placed at d, would see the candle at e, in the direction of the
refracted ray d A. This is also confirmed by the following pleasing
experiment.

2. Lay a shilling, or any piece of money, at the bottom of a bason; then
withdraw from the bason, till you lose sight of the shilling; fill the
bason nearly with water, and the shilling will be seen very plainly,
though you are at the same distance from it.

3. Place a stick over a bason which is filled with water; then reflect
the sun’s rays, so that they may fall perpendicularly on the surface of
the water; the shadow of the stick will fall on the same place, whether
the vessel be empty or full.

What has been said of water, may be applied to any transparent medium,
only the power of refraction is greater in some than in others. It is
from this wonderful property, that we derive all the curious effects of
glass, which make it the subject of optics. It is to this we owe the
powers of the microscope and the telescope.

To produce these effects, pieces of glass are formed into given figures,
which, when so formed, are called lenses. The six following figures are
those which are most in use for optical purposes.

1. A PLANE GLASS, one that is flat on each side, and of an equal
thickness throughout. F, Fig. 13. Plate I.

2. A DOUBLE CONVEX GLASS, one that is more elevated towards the middle
than the edge. B, Fig. 13. Plate I.

3. A DOUBLE CONCAVE is hollow on both sides, or thinner in the middle
than at the edges. D, Fig. 13. Plate I.

4. A PLANO CONVEX, flat on one side, and convex on the other. A, Fig.
13. Plate I.

5. A PLANO CONCAVE, flat on one side, and concave on the other. C, Fig.
13. Plate I.

6. A MENISCUS, convex on one side, concave on the other. E, Fig. 13.
Plate I.

It has been already observed, that light proceeds invariably from a
luminous body, in strait lines, without the least deviation; but if it
happen to pass from one medium to another, it always leaves the
direction it had before, and assumes a new one. After having taken this
new direction, it proceeds in a strait line, till it meets with a
different medium, which again turns it out of its course.

A ray of light passing obliquely through a plane glass, will go out in
the same direction it entered, though not precisely in the same line.
The ray C D, Fig.4. Plate I. falling obliquely upon the surface of the
plane glass A B, will be refracted towards the glass in the direction D
E; but when it comes to E, it will be as much refracted the contrary
way. If the ray of light had fallen perpendicularly on the surface of
the plane glass, it would have passed through it in a strait line, and
not have been refracted at all.

If parallel rays of light, as a b c d e f g, Fig. 6. Plate I. fall
directly upon a convex lens A B, they will be so bent, as to unite in a
point C behind it. For the ray d D which falls perpendicularly upon the
middle of the glass, will go through it without suffering any
refraction: but those which go through the sides of the lens, falling
obliquely on its surface, will be so bent, as to meet the central ray at
C. The further the ray a is from the axis of the lens, the more
obliquely it will fall upon it. The rays a b c d e f g will be so
refracted, as to meet or be collected in the point C, called the
principal focus, whose distance, in a double convex lens, is equal to
the radius or semi-diameter of the sphere of the convexity of the lens.
All the rays cross the middle ray at C, and then diverge from it to the
contrary side, in the same manner as they were before converged.

If another lens, of the same convexity, as A B, Fig. 6. Plate I. be
placed in the rays, and at the same distance from the focus, it will
refract them, so that after going out of it, they will all be parallel
again, and go on in the same manner as they came to the first glass A B,
but on the contrary sides of the middle ray.

The rays diverge from any radiant point, as from a principal focus:
therefore, if a candle be placed at C, in the focus of the convex lens A
B, Fig. 6. Plate I. the rays diverging from it will be so refracted by
the lens, that after going out of it, they will become parallel. If the
candle be placed nearer the lens than its focal distance, the rays will
diverge more or less, as the candle is more or less distant from the
focus.

If any object, A B, Fig. 7. Plate I. be placed beyond the focus of the
convex lens E F, some of the rays which flow from every point of the
object, on the side next the glass, will fall upon it, and after passing
through it, they will be converged into as many points on the opposite
side of the glass; for the rays a b, which flow from the point A, will
converge into _a b_, and meet at C. The rays c d, flowing from the point
G, will be converged into _c d_, and meet at g; and the rays which flow
from B, will meet each other again at D; and so of the rays which flow
from any of the intermediate points: for there will be as many focal
points formed, as there are radiant points in the object, and
consequently they will depict on a sheet of paper, or any other
light-coloured body, placed at D g C, an inverted image of the object.
If the object be brought nearer the lens, the picture will be formed
further off. If it be placed at the principal focus, the rays will go
out parallel, and consequently form no picture behind the glass.

To render this still plainer, let us divest what has been said of the
A’s and B’s, and of the references to figures. When objects are viewed
through a flat or plane glass, the rays of light in passing through it,
from the object to the eye, proceed in a strait direction and parallel
to each other, and consequently the object appeared at the same distance
as to the naked eye, neither enlarged or diminished. But if the glass be
of a convex form, the rays of light change their direction in passing
through the glass, and incline from the circumference towards the center
of convexity, in an angle proportional to the convexity, and meet at a
point at a less or greater distance from the glass, as it is more or
less convex. The point where the rays thus meet is called the focus;
when, therefore, the convexity is small, the focus is at a great
distance, but when it is considerable, the focus is near; the magnifying
power is in proportion to the change made in the rays, or the degree of
convexity, by which we are enabled to see an object nearer than we
otherwise could; and the nearer it is brought to the eye, the larger
will be the angle under which it appears, and consequently the more it
will be magnified.

The human eye is so constituted, that it can only have distinct vision,
when the rays which fall on it are parallel, or nearly so; because the
retina, on which the image is painted, is placed in the focus of the
crystalline humor, which performs the office of a lens in collecting
rays, and forming the image in the bottom of the eye.

As an object becomes perceptible to us, by means of the image thereof
which is formed on the retina, it will, therefore, be seen in that
direction, in which the rays enter the eye to form the image, and will
always be found in the line, in which the axis of a pencil of rays
flowing from it enters the eye. We from hence acquire a habit of judging
the object to be situated in that line. Note; as the mind is
unacquainted with the refraction the rays suffer before they enter the
eye, it judges them to be in the line produced back, in which the axis
of a pencil of rays flowing from it is situated, and not in that in
which it was before the refraction.

If the rays, therefore, that proceed from an object, are refracted and
reflected several times before they enter the eye, and these refractions
or reflections change considerably the original direction of the rays
which proceed from the object, it is clear, that it will not be seen in
that line, which would come strait from it to the eye; but it will be
seen in the direction of those rays which enter the eye, and form the
image thereof on it.

We perceive the presence and figure of objects, by the impression each
respective image makes on the retina; the mind, in consequence of these
impressions, forms conclusions concerning the size, position, and motion
of the object. It must however be observed, that these conclusions are
often rectified or changed by the mind, in consequence of the effects of
more habitual impressions. For example, there is a certain distance, at
which, in the general business of life, we are accustomed to see
objects: now, though the measure of the image of these objects changes
considerably when they move from, or approach nearer to us, yet we do
not perceive that their size is much altered; but beyond this distance,
we find the objects appear to be diminished, or increased, in proportion
as they are more or less distant from us.

For instance, if I place my eye successively at two, at four, and at six
feet from the same person, the dimensions of the image on the retina
will be nearly in the proportion of 1, of ¹⁄₂, of ¹⁄₃, and consequently
they should appear to be diminished in the same proportion; but we do
not perceive this diminution, because the mind has rectified the
impression received on the retina. To prove this, we need only consider,
that if we see a person at 120 feet distance, he will not appear so
strikingly small, as if the same person should be viewed from the top of
a tower, or other building 120 feet high, a situation to which we had
not been accustomed.

From hence, also, it is clear, that when we place a glass between the
object and the eye, which from its figure changes the direction of the
rays of light from the object, this object ought not to be judged as if
it were placed at the ordinary reach of the sight, in which case we
judge of its size more by habit than by the dimensions of the images
formed on the retina; but it must be estimated by the size of the image
in the eye, or by the angle formed at the eye, by the two rays which
come from the extremity of the object.

If the image of an object, formed after refraction, be greater or less
than the angle formed at the eye, by the rays proceeding from the
extremities of the object itself, the object will appear also
proportionably enlarged or diminished; so that if the eye approach to or
remove from the last image, the object will appear to increase or
diminish, though the eye should in reality remove from it in one case,
or approach toward it in the other; because the image takes place of the
object, and is considered instead of it.

The apparent distance of an object from the eye, is not measured by the
real distance from the last image; for, as the apparent distance is
estimated principally by the ideas we have of their size, it follows,
that when we see objects, whose images are increased or diminished by
refraction, we naturally judge them to be nearer or further from the
eye, in proportion to the size thereof, when compared to that with which
we are acquainted. The apparent distance of an object is considerably
affected by the brightness, distinctness, and magnitude thereof. Now as
these circumstances are, in a certain degree, altered by the refraction
of the rays, in their passing through different mediums, they will also,
in some measure, affect the estimation of the apparent distance.

In the theory of vision it is necessary to be cautious not to confound
the organs of vision with the being that perceives, or with the
perspective faculty. The eye is not that which sees, it is only the
organ by which we see. A man cannot see the satellites of Jupiter but by
a telescope. Does he conclude from this, that it is the telescope that
sees those stars? By no means; such a conclusion would be absurd. It is
no less absurd to conclude, that it is the eye that sees. The telescope
is an artificial organ of sight, but it sees not. The eye is a natural
organ of sight, by which we see; but the natural organ sees as little as
the artificial.

The eye is a machine, most admirably contrived for refracting the rays
of light, and forming a distinct picture of objects upon the retina; but
it sees neither the object nor the picture. It can form the picture
after it is taken out of the head, but no vision ensues. Even when it is
in its proper place, and perfectly sound, it is well known, that an
obstruction in the optic nerve takes away vision, though the eye has
performed all that belongs to it.[25]

  [25] Reid on the Intellectual Powers of Man, p. 78.


OF THE SINGLE MICROSCOPE.

The single microscope renders minute objects visible, by means of a
small glass globule, or convex lens, of a short focus. Let E Y, Fig. 11.
Plate I. represent the eye; and O B a small object, situated very near
to it; consequently, the angle of its apparent magnitude very large. Let
the convex lens R S be interposed between the eye and the object, so
that the distance between it and the object may be equal to the focal
length; and the rays which diverge from the object, and pass through the
lens, will afterwards proceed, and consequently enter the eye parallel:
after which, they will be converged, and form an inverted picture on the
retina, and the object will be clearly seen; though, if removed to the
distance of six inches, its smallness would render it invisible.

When the lens is not held close to the eye, the object is somewhat more
magnified; because the pencils, which pass at a distance from the
center of the lens, are refracted inward toward the axis, and
consequently seem to come from points more remote from the center of the
object, as may be seen in Fig. 12. Plate I. where the pencils which
proceed from O and B are refracted inwards, and seem to come from the
point i and m.

Fig. 8. Plate I. may, perhaps give the reader a still clearer view, why
a convex lens increases the angle of vision. Without a lens, as F G, the
eye at A would see the dart B C under the angle b A c; but the rays B F
and C G from the extremities of the dart in passing through the lens,
are refracted to the eye in the directions f A and g A, which causes the
dart to be seen under the much larger angle D A E (the same as the angle
f A g.) And therefore the dart B C will appear so much magnified, as to
extend in length from D to E.

The object, when thus seen distinctly, by means of a small lens, appears
to be magnified nearly in the proportion which the focal distance of the
glass bears to the distance of the objects, when viewed by the naked
eye.

To explain this further, place the eye close to the glass, that as much
of the object may be seen at one view as is possible; then remove the
object to and fro, till it appear perfectly distinct, and well defined;
now remove the lens, and substitute in its place a thin plate, with a
very small hole in it, and the object will appear as distinct, and as
much magnified, as with the lens, though not quite so bright; and it
appears as much more magnified in this case, than it does when viewed
with the naked eye, as the distance of the object from the hole, or
lens, is less than the distance at which it may be seen distinctly with
the naked eye.

From hence we see, that the whole effect of the lens is to render the
object distinct, which it does by assisting the eye to increase the
refraction of the rays in each pencil; and that the apparent magnitude
is entirely owing to the object being seen so much nearer the eye than
it could be viewed without it.

Single microscopes magnify the diameter of the object,[26] as we have
already shewn, in the proportion of the focal distance (to the limits of
distinct vision with the naked eye) to eight inches. For example, if the
semi-diameter of a lens, equally convex on both sides, be half an inch,
which is also equal to its focal distance, we shall have as ¹⁄₂ is to 8,
so is 1 to 16; that is, the diameter of the object in the proportion of
sixteen to one. 2. As the distance of eight inches is always the same,
it follows, that by how much the focal distance is smaller, there will
be a greater difference between it and the eight inches; and
consequently, the diameter of the object will be so much the more
magnified, in proportion as the lenses are segments of smaller spheres.
3. If the object be placed in the focus of a glass globule or sphere,
and the eye be behind it in the focus, the object will be seen distinct
in an erect situation, and magnified as to its diameter, in the
proportion of ³⁄₄ of the diameter of the globule to eight inches; thus
suppose the diameter of the sphere to be ¹⁄₁₀ of an inch, then ³⁄₄ of
this will be equal to ³⁄₄₀; consequently, the real diameter of the
object to the apparent one, as ³⁄₄₀ to 8, or as 3 to 320, or as 1 to 106
nearly.

  [26] Cyclopedia, Article Microscope.


OF THE DOUBLE OR COMPOUND MICROSCOPE.

In the compound microscope, the image is viewed instead of the object,
which image is magnified by a single lens, as the object is in a single
microscope. It consists of an object lens N L, Fig. 5. Plate I. and an
eye glass F G. The object B O is placed a little further from the lens
than its principal focal distance, so that the pencils of rays
proceeding from the different points of the object through the lens, may
converge to their respective foci, and form an inverted image of the
object at Q P; which image is viewed by the eye through the eye glass F
G, which is so placed, that the image may be in its focus on one side,
and the eye at the same distance on the other. The rays of each pencil
will be parallel, after passing out of the glass, till they reach the
eye at E, where they will begin to converge by the refractive powers of
the humours; and after having crossed each other in the pupil, and
passed through the crystalline and vitreous humours, they will be
collected in points on the retina, and form a large inverted image
thereon.

It will be easy, from what has been already explained, to understand the
reason of the magnifying power of a compound microscope. The object is
magnified upon two accounts; first, because if we viewed the image with
the naked eye, it would appear as much larger than the object, as the
image is really larger than it, or as the distance f R is greater than
the distance f b; and secondly, because this picture is again magnified
by the eye glass, upon the principle explained in the foregoing article
on vision, by single microscopes.

But it is to be noted, that the image formed in the focus of a lens, as
is the case in the compound microscope, differs from the real object in
a very essential particular; that is to say, the light being emitted
from the object in every direction, renders it visible to an eye placed
in any position; but the points of the image formed by a lens, emitting
no more than a small conical body of rays, which arrives from the glass,
can be visible only when the eye is situate within its confine. Thus,
the pencil, which emanates from o in the object, and is converged by
the lens to D, proceeds afterwards diverging towards H, and, therefore,
never arrives at the lens F G, nor enters the eye at E. But the pencils
which proceed from the points o and b, will be received on the lens F G,
and by it carried parallel to the eye; consequently, the correspondent
points of the image Q P will be visible; and those which are situate
farther out towards H and I, will not be seen. This quantity of the
image Q P, or visible area, is called the field of view.

Hence it appears, that if the image be large, a very small part of it
will be visible; because the pencils of rays will for the most part fall
without the eye glass F G. And it is likewise plain, that a remedy which
would cause the pencils, which proceed from the extremes B and O of the
object, to arrive at the eye, will render a greater part of it visible:
or, in other words, enlarge the field of view. This is effected by the
interposition of a broad lens D E, Fig. 5, of a proper curvature, at a
small distance from the focal image. For, by those means, the pencil D
N, which would otherwise have proceeded towards H, is refracted to the
eye, as delineated in the figure, and the mind conceives from thence the
existence of a radiant point at Q, from which the rays last proceeded.
In like manner, and by a parity of reason, the other extreme of the
image is seen at P, and the intermediate points are also rendered
visible. On these considerations it is, that compound microscopes are
usually made to consist of an object lens N L, by which the image is
formed, enlarged, and inverted; an amplifying lens D E, by which the
field of view is enlarged, and an eye glass or lens, by which the eye is
allowed to approach very near, and consequently to view the image under
a very great angle of apparent magnitude. It is now customary to combine
two or more lenses together at the eye glass, in the manner of Eustachio
Divinis and M. Joblot; by which means the aberration of light from the
figure is in some measure corrected, and the apparent field increased.


OF THE SOLAR MICROSCOPE.

In this instrument, the image of the object is refracted upon a screen
in a darkened room. It may be considered under two distinct heads: 1st,
the mirror and lens, which are intended to reflect and transmit the
light of the sun upon the object; and 2dly, that part which constitutes
the microscope, or which produces the magnified image of the object,
Fig. 10. Plate I. Let N O represent the side of a darkened chamber, G H
a small convex lens, fixed opposite to a perforation in the side N O, A
B a plane mirror or looking glass, placed without the room to reflect
the solar rays on the lens C D, by which they are converged and
concentrated on the object fixed at E F.

2. The object being thus illuminated, the ray which proceeds from E will
be converged by the lens G H to a focus K, on the screen L M; and the
ray which comes from F will be converged to I, and the intermediate
points will be delineated between I and K; thus forming a picture, which
will be as much larger than the object, in proportion as the distance of
the screen exceeds that of the image from the object; a small object,
such as a mite, &c. may be thus magnified to eight or ten feet in
diameter.

From what has been said, it appears plainly, the advantages we gain by
microscopes are derived, first, from their magnifying power, by which
the eye is enabled to view more distinctly the parts of minute objects:
secondly, that by their assistance, more light is thrown into the pupil
of the eye, than is done without them. The advantages procured by the
magnifying power, would be exceedingly circumscribed, if they were not
accompanied by the latter: for if the same quantity of light be
diffused over a much larger surface, its force is proportionably
diminished; and therefore the object, though magnified, will be dark and
obscure. Thus, suppose the diameter of the object to be enlarged ten
times, and consequently the surface one-hundred times, yet, if the focal
distance of the glass were eight inches, provided this were possible,
and its diameter only about the size of the pupil of the eye, the object
would appear one-hundred times more obscure when viewed through the
glass, than when it was seen by the naked eye; and this even on the
supposition that the glass transmitted all the light which fell upon it,
which no glass can do. But if the glass were only four inches focal
distance, and its diameter remained as before, the inconvenience would
be vastly diminished, because the glass could be placed twice as near
the object as before, and would consequently receive four times as many
rays as in the former case, and we should, therefore, see it much
brighter than before. By going on thus, diminishing the focal distance
of the glass, and keeping its diameter as large as possible, we shall
perceive the object proportionably magnified, and yet remain bright and
distinct. Though this is the case in theory, yet there is a limit in
optical instruments, which is soon arrived at, but which cannot be
passed. This arises from the following circumstances.[27]

  [27] Encyclopædia Britannica, last edition, vol. xiii, p. 357.

1. The quantity of light lost in passing through the glass.

2. The diminution in the diameter of the glass or lens itself, by which
it receives only a small quantity of rays.

3. The extreme shortness of the focal distance of great magnifiers,
whereby the free access of the light to the object we wish to view is
impeded, and consequently the reflection of the light from it is
weakened.

4. The aberration of the rays, occasioned by their different
refrangibility.

To make this more clear, let us suppose a lens made of such dull kind of
glass, that it transmits only one half the light that falls upon it. It
is evident, that supposing this lens to be of four inches focus, and to
magnify the diameter of the object twice, and its own breadth equal to
that of the pupil of the eye, the object will be four times magnified in
surface, but only half as bright as if it was seen by the naked eye at
the usual distance; for the light which falls upon the eye from the
object at eight inches distance, and likewise the surface of the object
in its natural size, being both represented by 1, the surface of the
magnified object will be 4, and the light which makes it visible only 2;
because, though the glass receives four times as much light as the naked
eye does at the usual distance of distinct vision, yet one half is lost
in passing through the glass. The inconvenience, in this respect, can
only be removed so far as it is possible to increase the transparency of
the glass, that it may transmit nearly all the rays which fall upon it;
and how far this can be done, has not been yet ascertained.

The second obstacle to the perfection of microscopic glasses, is the
small size of great magnifiers; by which means, notwithstanding their
near approach to the object, they receive a smaller quantity of light
than might be expected. Thus, suppose a glass of only one-tenth of an
inch focal distance, such a glass would increase the visible diameter
eighty times, and the surface 6400 times. If the breadth of the glass
could at the same time be preserved as great as the pupil of the eye,
which we shall suppose one-tenth of an inch, the object would appear
magnified 6400 times, and every part would be as bright as it appears to
the naked eye. But if we suppose the lens to be only ¹⁄₂₀ of an inch
diameter, it will then only receive one-fourth of the light which would
otherwise have fallen upon it; therefore, instead of communicating to
the magnified object a quantity of light equal to 6400, it would
communicate an illumination suited only to 1600, and the magnified
object would appear four times as dim as it does to the naked eye. This
inconvenience can, however, in a great degree be removed, by throwing a
much larger quantity of light on the object. Various methods of
effecting this purpose will be pointed out in the course of this work.

The third obstacle arises from the shortness of the focal distance in
large magnifiers; this inconvenience can, like the former, be remedied
in some degree, by artificial means of accumulating light; but still the
eye is strained, as it must be brought nearer the glass than it can well
bear, which in some measure supersedes the use of very deep lenses, or
such as are capable of magnifying beyond a certain degree.

The fourth obstacle arises from the different refrangibility of the rays
of light, which frequently causes such deviations from truth in the
appearance of things, that many have imagined themselves to have made
surprising discoveries, and have communicated them as such to the world;
when, in fact, they have been only so many optical deceptions, owing to
the unequal refraction of the rays. In telescopes, this error has been
happily corrected by the late Mr. Dollond’s valuable discovery of
achromatic glasses; but how far this invention is applicable to the
improvement of microscopes, has not yet been ascertained; and, indeed,
from some few trials made, there is reason for supposing they cannot be
successfully applied to microscopes with high powers; so that this
improvement is yet a desideratum in the construction of microscopes, and
they may be considered as being yet far from their ultimate degree of
perfection.[28]

  [28] How many useful and ingenious discoveries have arisen from
  accidental circumstances? To adduce one recent instance
  only--Aerostation, a science, which after having baffled the skill and
  ingenuity of philosophers for a series of years, and by many
  illiterate persons deemed an idea bordering on absurdity, has been of
  late discovered, and successfully applied to practice. EDIT.


OF THE MAGNIFYING POWERS OF THE MICROSCOPE.

We have already treated of the apparent magnitude of objects, and shewn
that they are measured by the angles under which they are seen, and that
this angle is greater or smaller according as the object is nearer to,
or further from, the eye; and, consequently, the less the distance at
which it can be viewed, the larger it will appear: but from the limits
of natural vision, the naked eye cannot distinguish an object that is
very near to it; yet, when assisted by a convex lens, distinct vision is
obtained, however short the focus of the lens, and, consequently, how
near soever the object is to the eye; and the shorter the focus of the
lens is, the greater will be the magnifying power thereof. From these
considerations, it will not be difficult to estimate the magnifying
power of any lens used as a single microscope; for this will be in the
same proportion that the limits of natural sight bear to the focus of
the lens. If, for instance, the convex lens is of one inch focus, and
the natural sight of eight inches, an object seen through that lens will
have its diameter apparently increased eight times; but, as the object
is increased in every direction, we must square this apparent diameter,
to know how much the object is really magnified; and thus multiplying 8
by 8, we find the superficies is magnified 64 times.

From these principles, the following general rule for ascertaining the
magnifying power of single lenses, is deduced. Place a small thin
transparent object on the stage of the microscope, adjust the lens till
the object appears perfectly distinct, then measure the distance
accurately between the lens and the object, reduce the measure thus
found to the hundredths of an inch, and calculate how many times this
measure is contained in eight inches, first reducing the eight inches
into hundredths, which will give you the number of times the diameter of
the object is magnified; which number multiplied into itself, or
squared, gives the apparent superficial magnitude of the object.

As only one side of an object can be viewed at a time, it is sufficient,
in general, to know how much the surface thereof is magnified: but when
it is necessary to know how many minute objects are contained in a
larger, as for instance, how many given animalculæ are contained in the
bulk of a grain of sand, then we must cube the first number, by which
means we shall obtain the solidity or magnified bulk.

The foregoing rule has been also applied to estimate the magnifying
power of the compound microscope. To this application, Mr. Magny, in the
“Journal d’Economie pour le mois d’Aout 1753,” has made several
objections: one or two of these I shall just mention; the first is the
difficulty of ascertaining with accuracy the precise focus of a small
lens; the second is the want of a fixed or known measure, with which to
compare the focus when ascertained. These considerations, though
apparently trifling, will be found of importance in the calculations
which are relative to deep magnifiers. To this it may be further added,
that the same standard or fixed measure cannot be assumed for a
short-sighted, that is used for a well-constituted eye. To obviate these
difficulties, and some errors in the methods which were recommended by
Mess. Baker and Needham, Mr. Magny offers the following

PROPOSITION. All convex lenses of whatsoever foci, double the apparent
diameter of an object, provided that the object be at the focus of the
glass on one side, and the eye be at the same distance, or on the focus
of the glass, at the opposite side.

EXPERIMENT. Take a double convex lens, of six or eight inches focus, and
fix it as at A, Fig. 1, Plate II. A, into the piece A, which is fixed
perpendicular to the rule F G, and may be slid along it by means of its
socket: the rule is divided into inches and parts. Paste a piece of
white paper, two or three tenths of an inch broad, and three inches
long, on the board D; draw three lines with ink on this piece of paper,
so as to divide it into four equal parts, taking care that the middle of
the paper corresponds with the center of the lens. There is also a
sliding eye-piece, which is represented at e.

Take this apparatus into the darkest part of the room, but opposite to
the window; direct the glass towards any remarkable and distant object
which is out of doors, and move the sliding piece B, until the image of
the object on the paper be sharp and clear. The distance between the
face of the paper and the lens (which is shewn on the side of the rule
by the divisions thereon) is the focus of the glass; now set the
eye-piece e E to the same distance on the other side of the glass, then
with one eye close to the sight at e, look at the magnified image of the
lines, and with the other eye at the lines themselves: the image, seen
by means of the glass, and expressed in the figure by the dotted lines,
will be double the breadth of the same object seen by the natural eye.
This will be found to be true, whatsoever is the focus of the lens with
which the experiment is made.

This experiment is rendered more simple to those who are not accustomed
to observe with both eyes at the same time, by making use of half a
lens, and placing the diameter perpendicular to the rule, as they may
then readily view the magnified image and real object with the same
glance of the eye, and thus compare them together with ease and
accuracy.

Let the angle A F B, Fig. 3. Plate II. A, represent that which is formed
at the naked eye, by the rays of light which pass from the extremities
of the object, and unite at the eye in the point F. The angle D F E is
formed of the two rays, which at first proceeded parallel to each other
from the extremities of the object, but that were afterwards so
refracted, or bent, by passing through the glass, as to unite at its
focal point F. C O is equal to the focal distance of the lens on the
side next the object, C F equal thereto on the side next the eye, F O
the distance of the eye.

From the allowed principles of optics, it is evident, that the object
would appear double the size to the eye at C, than it would to the eye
when placed at F; because the distance F O is double the distance C O.
We have only to prove then, that the angle A C B is equal to the angle I
F K, in order to establish the proposition.

The optical axis is perpendicular to the glass and the surface of the
object. The rays A I, B K, which flow from the points A B are parallel
to each other, and perpendicular to the glass, till they arrive at it;
they are then refracted and proceed to F, where they form the triangle I
F K, resting on the base I K: now as C F is equal to C O, and I K is
equal to A B, the two triangles A C B, I F K are similar, and
consequently the angle at C is equal to the angle F. If the visual rays
are continued to the surface of the object, they will form the triangle
D F E, equiangled to the triangle A B C; and therefore, as C O is to A
B, so is F D to D E; and consequently, the apparent diameter of the
object seen through the lens is double the size that it is when viewed
by the naked eye. No notice is here taken of the double refraction of
the rays, as it does not affect the demonstration.

If you advance towards M, half the focal distance, the apparent diameter
will be only increased one-third. If, on the contrary, the point of
sight is lengthened to double the distance of its focus, then the
magnified diameter will appear to be three times that of the real
object. Mr. Magny concludes from hence, that there is an impropriety in
estimating the magnifying power of the eye glass of compound
microscopes, by seeing how often its focus is contained in eight or ten
inches; and to obviate these defects, he recommends two methods to be
used, which reciprocally confirm each other.

The first and most simple method to find how much any compound
microscope magnifies an object, is the same which is described by Dr.
Hooke in his Micrographia, and is as follows: place an accurate scale,
which is divided into very minute parts of an inch, on the stage of your
microscope; adjust the microscope, till these divisions appear distinct;
then observe with the other eye how many divisions of a rule, similarly
divided and held at the stage, are included in one of the magnified
divisions: for if one division, as seen with one eye through the
microscope, extend to thirty divisions on the rule, which is seen by the
naked eye, it is evident, that the diameter of the object is increased
or magnified thirty times.

For this purpose, we often use a small black ebony rule, (see Fig. 4.
Plate II. A,) three or four tenths of an inch broad, and about seven
inches long; at each inch is fixed a piece of ivory, the first inch is
entirely of ivory, and subdivided into ten equal parts.

2. A piece of glass, Fig. 2, fixed in a brass or ivory slider; on the
diameter of this are drawn two parallel lines, about three-tenths of an
inch long; each tenth being divided, one into three, the second into
four, the third into five parts. To use this, place the glass, Fig. 2,
on the middle of the stage, and the rule, Fig. 4, on one side, but
parallel to it; then look into the microscope with one eye, keeping the
other open, and observe how many parts one-tenth of a line in the
microscope takes in upon the parts of the rule seen by the naked eye.
For instance, suppose with a fourth magnifier that one-tenth of an inch
magnified answers in length to forty-tenths or parts on the rule, when
seen by the naked eye, then this magnifier increases the diameter of the
object forty times.

This mode of actual admeasurement is, without doubt, the most simple
that can be used; by it we comprehend, as it were, at one glance, the
different effects of combined glasses; it saves the trouble, and avoids
the obscurity that attends the usual modes of calculation; but many
persons find it exceedingly difficult to adopt this method, because they
have not been accustomed to observe with both eyes at once. We shall
therefore proceed to describe another method, which has not this
inconvenience.


OF THE NEEDLE MICROMETER.

Fig. 8. Plate II. A, represents this micrometer. The first of this kind
was made by my father, and was described by him in his Micrographia
Illustrata. It consists of a screw, which has fifty threads to an inch;
this screw carries an index, which points to the divisions on a circular
plate, which is fixed at right angles to the axis of the screw. The
revolutions of the screw are counted on a scale, which is an inch
divided into fifty parts; the index to these divisions is a flower de
luce marked upon the slider, which carries the needle point across the
field of the microscope. Every revolution of the micrometer screw
measures ¹⁄₅₀ part of an inch, which is again subdivided by means of the
divisions on the circular plate, as this is divided into twenty equal
parts, over which the index passes at every revolution of the screw; by
which means, we obtain with ease the measure of one-thousandth part of
an inch; for 50, the number of threads on the screw in one inch, being
multiplied by 20, the divisions on the circular plate, are equal to
1000; so that each division on the circular plate shews that the needle
has either advanced or receded one-thousandth part of an inch.

To place this micrometer on the body of the microscope, open the
circular part F K H, Fig. 8. Plate II. A, by taking out the screw G,
throw back the semicircle F K which moves upon a joint at K, then turn
the sliding tube of the body of the microscope, so that the small holes
which are in both tubes may exactly coincide, and let the needle g of
the micrometer have a free passage through them; after this, screw it
fast upon the body by the screw G.

The needle will now traverse the field of the microscope, and measure
the length and breadth of the image of any object that is applied to it.
But further assistance must be had, in order to measure the object
itself, which is a subject of real importance; for though we have
ascertained the power of the microscope, and know that it is so many
thousand times, yet this will be of little assistance towards
ascertaining an accurate idea of its real size; for our ideas of bulk
being formed by the comparison of one object with another, we can only
judge of that of any particular body, by comparing it with another
whose size is known: the same thing is necessary, in order to form an
estimate by the microscope; therefore, to ascertain the real measure of
the object, we must make the point of the needle pass over the image of
a known part of an inch placed on the stage, and write down the
revolutions made by the screw, while the needle passed over the image of
this known measure; by which means we ascertain the number of
revolutions on the screw, which are adequate to a real and known measure
on the stage. As it requires an attentive eye to watch the motion of the
needle point, as it passes over the image of a known part of an inch on
the stage, we ought not to trust to one single measurement of the image,
but ought to repeat it at least six times; then add the six measures
thus obtained together, and divide their sum by six, or the number of
trials; the quotient will be the mean of all the trials. This result is
to be placed in a column of a table, next to that which contains the
number of the magnifiers.

By the assistance of the sectoral scale, we obtain with ease a small
part of an inch. This scale is shewn at Fig. 5, 6, 7. Plate II. A, in
which the two lines c a c b, with the side a b, form an isosceles
triangle; each of the sides is two inches long, and the base one-tenth
of an inch. The longer sides may be of any given length, and the base
still only of one-tenth of an inch. The longer lines may be considered
as the line of lines upon a sector opened to one-tenth of an inch.
Hence, whatever number of equal parts ca cb are divided into, their
transverse measure will be such a part of one-tenth as is expressed by
their divisions. Thus, if it be divided into ten equal parts, this will
divide the inch into one-hundred equal parts; the first division next c
will be equal to one-hundredth part of an inch, because it is the tenth
part of one-tenth of an inch. If these lines be divided into twenty
equal parts, the inch will be by those means divided into two hundred
equal parts. Lastly, if a b c a be made three inches long, and divided
into one-hundred equal parts, we obtain with ease the one-thousandth
part. The scale is represented as solid at Fig. 6, but as perforated at
Fig. 5 and 7; so that the light passes through the aperture, when the
sectoral part is placed on the stage.

To use this scale, first fix the micrometer, Fig. 8. Plate II. A, to the
body of the microscope; then fit the sectoral scale, Fig. 7, in the
stage, and adjust the microscope to its proper focus or distance from
the scale, which is to be moved till the base appears in the middle of
the field of view; then bring the needle point g, Fig. 8, by turning the
screw L, to touch one of the lines c a exactly at the point answering to
20 on the sectoral scale. The index a of the micrometer, Fig. 8, is to
be set to the first division, and that on the dial plate to 20, which is
both the beginning and end of its divisions; we are then prepared to
find the magnifying power of every magnifier in the compound microscope
which we are using.

EXAMPLE. Every thing being prepared agreeable to the foregoing
directions, suppose you are desirous of ascertaining the magnifying
power of the lens marked No. 4; turn the micrometer screw, until the
point of the needle has passed over the magnified image of the tenth
part of one inch; then the division, where the two indices remain, will
shew how many revolutions, and parts of a revolution, the screw has
made, while the needle point traversed the magnified image of the
one-tenth of an inch; suppose the result to be twenty-six revolutions of
the screw, and fourteen parts of another revolution, this is equal to 26
multiplied by 20, added to 14; that is, 534 thousandth parts of an
inch.

The twenty-six divisions found on the strait scale of the micrometer,
while the point of the needle passed over the magnified image of
one-tenth part of an inch, were multiplied by 20, because the circular
plate C D, Fig. 8, is divided into twenty equal parts; this produced
520; then adding the fourteen parts of the next revolution, we obtain
534 thousandth parts of an inch, or 5-tenths and 34-hundredth parts of
another tenth, which is the measure of the magnified image of 1-tenth of
an inch, at the aperture of the eye glasses, or at their foci. Now if we
suppose the focus of the two eye-glasses to be one inch, the double
thereof is two inches; or if we reckon in the thousandth part of an
inch, we have two thousand parts for the distance of the eye from the
needle point of the micrometer. Again, if we take the distance of the
image from the object at the stage at six inches, or six thousandths,
and add thereto two thousand, double the distance of the focus of the
eye glass, we shall have eight thousand parts of an inch for the
distance of the eye from the object; and as from the proposition, page
51, we gather that the glasses double the image, we must double the
number 534 found upon the micrometer, which then makes 1068: then, by
the following analogy, we shall obtain the number of times the
microscope magnifies the diameter of the object; say, as 240, the
distance of the eye from the image of the object, is to 800, the
distance of the eye from the object, so is 1068, double the measure
found on the micrometer, to 3563, or the number of times the microscope
magnifies the diameter of the object. By working in this manner, the
magnifying power of each lens used with the compound microscope may be
easily found, though the result will be different in different compound
microscopes, varying, according to the combination of the lenses, their
distance from the object, and one another, &c.

Having discovered the magnifying power of the microscope, with the
different object lenses that are used therewith, our next subject is to
find out the real size of the objects themselves, and their different
parts; this is easily effected, by finding how many revolutions of the
micrometer-screw answer to a known measure on the sectoral scale, or
other object placed on the stage; from the number thus found, a table
should be constructed, expressing the value of the different revolutions
of the micrometer with that object lens, by which the primary number was
obtained. Similar tables must be constructed for each object lens. By a
set of tables of this kind, the observer may readily find the measure of
any object he is examining; for he has only to make the needle point
traverse over this object, and observe the number of revolutions the
screw has made in its passage, and then look into his table for the real
measure which corresponds to this number of revolutions, which is the
measure required.


ACCOUNT OF GLASS, PEARL, &c. MICROMETERS, BY THE EDITOR.

Having seen some glass, &c. micrometers with exquisite fine divisions,
for the purposes of applying to microscopes and telescopes; and in
accuracy, being equivalent to the micrometer just described by our
author, I judge, some account of their application and uses here will be
very acceptable to the curious and inquisitive reader. A particular
description of these as made by the ingenious Mr. Coventry, has been
already given in the Encyclopædia Britannica, Vol. XI. p. 708.

The singular dexterity which Mr. Coventry and others now possess, of
cutting by an engine fine parallel lines upon glass, pearl, ivory, and
brass, at such minute distances as, by means of a microscope, are proved
to be from the 100th to the 5000dth part of an inch, render this sort of
micrometer the easiest and most accurate means of obtaining the exact
natural size of the object to be magnified, and how many times that
object is magnified. Mr. B. Martin, and other opticians, many years ago
applied divided slips of glass, ivory, and horn to the body, in the
focus of the eye glass of microscopes; but the thickness of the whole
medium of the glass was found to diminish the distinct view of the
object: ivory and horn, from their variable texture, were found to
expand and contract too readily to be commodious. It is therefore to Mr.
Cavallo that we are indebted for the happy thought of adapting slips of
divided pearl to telescopes, to ascertain their power, &c. which
substance the opticians now find to be the best for microscopical
micrometers. It possesses a sufficient degree of transparency, when made
about the thickness of writing paper; is a steady substance; admits very
easily of the finest graduations, and is generally made in breadth about
the 20th part of an inch.

Fig. 9. Plate II. A, is a representation of this scale, with divisions
of the 200ths of an inch, every fifth and tenth division being left
longer than the others, which only go to about the middle. If the eye
glass of the microscope or telescope, to which this micrometer is to be
applied, magnify very much, its divisions may be proportionably minute.

To measure by this micrometer the size of an object in a single
microscope, nothing more is required than to lay it on the micrometer,
and adjust it to the focus of the magnifier, noticing how many
divisions it covers or coincides with. Supposing the parallel lines to
be the 1000dths of an inch, and the object covers two divisions, its
real size is the 500th of an inch; if five, 200th of an inch, &c.

To find how much the object is magnified, is not so easily done by the
single, as by the compound microscope, as has been before explained. The
following simple method has been adopted by Mr. Coventry, and which may
be considered tolerably accurate. Adjust a micrometer under the
microscope, suppose 100th of an inch of divisions, with a small object
on it, if square, the better; notice how many divisions one side of the
object covers, suppose ten; then cut a piece of white paper something
larger than the magnified appearance of the object; fix one eye on the
object through the microscope, and the other at the same time on the
paper, lowering it down till the object and the paper appear level and
distinct: then cut the paper till it appear exactly the size of the
magnified object; the paper being then measured, suppose an inch square:
now, as the object under the magnifier, which appeared to be one inch
square, was in reality only ten hundredths, or the tenth of an inch, the
experiment proves that it is magnified ten times in length, one hundred
times in superficies, and one thousand times in cube, which is the
magnifying power of the glass; and in the same manner a table may be
made of the power of all the other glasses.

In using the compound microscope, the real size of the object is found
by the same method as in the single; but to demonstrate the magnifying
power to greater certainty, adopt the following method. Lay a two-feet
rule on the stage, and a micrometer level with its surface, (an inch
suppose, divided into 100 parts:) with one eye see how many of those
parts are contained in the field of the microscope, suppose 50; and with
the other, at the same time, look for the circle of light in the field
of the microscope, which with a little practice will soon appear
distinct; mark how much of the rule, from the center of the stage, is
intersected by the circle of light, which will be half the diameter of
the field. Suppose eight inches; consequently the whole diameter will be
sixteen. Now, as the real size of the field by the micrometers appeared
to be only 50 hundredths, or half an inch, and as half an inch is only
one 32d part of 16 inches, it shews the magnifying power to be 32 times
in length, 1024 superficies, and 32768 in cube or bulk. For accuracy, as
well as for comparative observations, the rule should always be a
certain distance from the eye; eight inches in general is a proper
distance.

Another way, and the most easy for finding the magnifying power of
compound microscopes, is by using two micrometers of the same divisions;
one adjusted under the magnifier, the other fixed in the body of the
microscope in the focus of the eye glass. Notice how many divisions of
the micrometer in the body are seen in one division of the micrometer
under the magnifier, which again must be multiplied by the power of the
eye glass. Example: Ten divisions of the micrometer in the body are
contained in one division under the magnifier; so far the power is
increased ten times: now, if the eye glass be one inch focus, such glass
will of itself magnify about eight times in length, which, with the ten
times magnified before, will be eight times ten, or 80 times in length,
6400 superficies, and 512000 cube.

Fig. 10. Plate II. A, represents the field of view of the compound
microscope, with the pearl micrometer, as applied to the aperture in the
body, called the eye stop; and a magnified micrometer that is laid on
the stage, shewing that one of the latter contains ten of the former.

A set of ivory and glass micrometers, about six in number, besides one
or two pearl ones for the eye stops, are generally packed up with the
best sort of microscopes made by Messrs. W. and S. Jones, Opticians,
Holborn. They are divided into lines and squares, from the 100th to the
1000dth parts of an inch; and, besides measuring the magnifying powers
of microscopes, are generally found useful in measuring the diameters,
proportions, &c. of opake and transparent objects, even of the minutest
kind. The smallest divisions of the glass micrometer to be useful, are
those divided into the 4000dth part of an inch; and as these may be
crossed again with an equal number of lines in the same manner, they
form squares of the SIXTEEN MILLIONTH part of an inch surface, each
square of which appearing under the microscope true and distinct. And,
even small as this is, animalculæ are found so minute as to be contained
in one of these squares!

Glass micrometers with squares, applied to the solar microscope, divide
the objects into squares on the screen in such a manner, as to render a
drawing from it very easy; and are employed with great advantage in the
lucernal microscope.

The micrometers are constructed with moveable frames or tubes, so as to
be either applied or taken away in the readiest manner.

For the uses of the pearl micrometer as applied to the telescope, see
Mr. Cavallo’s pamphlet descriptive of its use, 8vo. 1793, and the
Philosophical Transactions for 1791.



CHAP. III.

A DESCRIPTION OF THE MOST APPROVED MICROSCOPES, AND THE METHOD OF USING
THEM.


In the preceding chapter I have endeavoured to give a comprehensive view
of the theory of the microscope, and the principles on which the
wonderful effects of this instrument depend. I shall now proceed to
describe the various instruments themselves, their apparatus, and the
most easy and ready mode of applying them to use; selecting for
description those that, from some peculiar advantage in their
construction, or from the reputation of the authors who have recommended
and used them, are in most general use. What is said of these will, I
hope, be sufficient to enable the reader to manage any other kind that
may fall in his way.


DESCRIPTION OF ADAMS’S IMPROVED AND UNIVERSAL LUCERNAL MICROSCOPE. Fig.
1. Plate III.

This microscope was originally thought of, and in part executed by my
father; I have, however, so improved and altered it, both in
construction and form, as to render it altogether a different
instrument. The approbation it has received from the most experienced
microscopic observers, as well as the great demand I have had for them,
has fully repaid my pains and expenses, in bringing it to its present
state of perfection.

As the far greater part of the objects which surround us are opake, and
very few sufficiently transparent to be examined by the common
microscopes, an instrument that could be readily applied to the
examination of opake objects, has always been a desideratum. Even in the
examination of transparent objects, many of the fine and more curious
portions are lost, and drowned as it were in the light which must be
transmitted through them; while different parts of the same object
appear only as dark lines or spots, because they are so opake, as not to
permit any light to pass through them. These difficulties, as well as
many more, are obviated in the lucernal microscope; by which opake
objects of various sizes may be seen with ease and distinctness; the
beautiful colours with which most of them are adorned, are rendered more
brilliant, without in the least changing their natural teints. The
concave and convex parts of an object retain also their proper form.

The facility with which all opake objects are applied to this instrument
is another considerable advantage, and almost peculiar to itself; as the
texture and configuration of the more tender parts are often hurt by
previous preparation, every object may be examined by this instrument,
first as opake, and afterwards, if the texture will admit of it, as
transparent.

The lucernal microscope does not in the least fatigue the eye; the
object appears like nature itself, giving ease to the sight, and
pleasure to the mind: there is also in the use of this instrument, no
occasion to shut that eye which is not directed to the object.

A further advantage peculiar to this microscope is, that by it the
outlines of every object may be taken, even by those who are not
accustomed to draw; while those who can draw well, will receive great
assistance, and execute their work with more accuracy, and in less time
than they would otherwise have been able to have performed it in. Most
of the designs for this work were taken with the lucernal microscope;
and I hope the accuracy with which they are executed, will be deemed a
sufficient testimony in favour of the instrument. In this point of view
it will, I think, be found of great use to the anatomist, the botanist,
the entomologist, &c. as it will enable them not only to investigate the
object of their researches, but to convey to others accurate
delineations of the subject they wish to describe.

By the addition of a tin lanthorn, transparent objects may be shewn on a
screen, as by the solar microscope.

Transparent objects may be examined with this instrument in three or
four different modes; from a blaze of light almost too great for the eye
to bear, to that which is perfectly easy to it.

When this instrument is fitted up in the best way, it is generally
accompanied with a small double and single microscope.

Fig. 1. Plate III. represents the IMPROVED LUCERNAL MICROSCOPE, mounted
to view opake objects; A B C D E is a large mahogany pyramidical box,
about fourteen inches long, and six inches square at its larger end,
which forms the body of the microscope; it is supported firmly on the
brass pillar F G, by means of the socket H, and the curved piece I K.

L M N is a guide for the eye, in order to direct it in the axis of the
lenses; it consists of two brass tubes, one sliding within the other,
and a vertical flat piece, at the top of which is the hole for the eye.
The outer tube is seen at M N, the vertical piece is represented at L M.
The inner tube may be pulled out, or pushed in, to adjust it to the
focus of the glasses. The vertical piece may be raised or depressed,
that the hole, through which the object is to be viewed, may coincide
with the center of the field of view; it is fixed by a milled screw at
M, which could not be shewn in this figure.

At N is a dove-tailed piece of brass, made to receive the dove-tail at
the end of the tubes M N, by which it is affixed to the wooden box A B C
D E. The tubes M N may be removed from this box occasionally, for the
convenience of packing it up in a less compass.

O P a small tube on which the magnifiers are screwed.

O one of the magnifiers; it is screwed into the end of a tube, which
slides within the tube P; the tube P may be unscrewed occasionally from
the wooden body.

Q R S T V X a long square bar, which passes through the sockets Y Z, and
carries the stage or frame that holds the objects; this bar may be moved
backward or forward, in order to adjust it to the focus, by means of the
pinion which is at a.

b e is a handle furnished with an universal joint, for more conveniently
turning the pinion. When the handle is removed, the nut, Fig. 2, may be
used in its stead.

d e is a brass bar, to support the curved piece K I, and keep the body A
B firm and steady.

f g h i is the stage for opake objects; it fits upon the bar Q R S T by
means of the socket h i, and is brought nearer to, or removed farther
from the magnifying lens, by turning the pinion a; the objects are
placed in the front side of the stage, which cannot be seen in this
figure, between four small brass plates; the edges of two of these are
seen at k l. The two upper pieces of brass are moveable; they are fixed
to a plate, which is acted on by a spiral spring that presses them down,
and confines the slider with the objects; this plate, and the two upper
pieces of brass, are lifted up by the small nut m.

At the lower part of the stage, there is a glass semiglobe n, which is
designed to receive the light from the lamp, Fig. 3, and to collect and
convey it to the concave mirror o, from whence it is to be reflected on
the object.

The upper part, f g r S, of the opake stage takes out, that the stage
for transparent objects may be inserted in its place.

Fig. 4. represents the stage for transparent objects; the two legs 5 and
6, fit into the under part r S of the stage for opake objects; 7 is the
part which confines or holds the sliders, and through which they are to
be moved; 9 and 10 a brass tube, which contains the lenses for
condensing the light, and throwing it upon the object; there is a second
tube within that, marked 9 and 10, which may be placed at different
distances from the object by the pin 11.

When this stage is used as a single microscope, without any reference to
the lucernal, the magnifiers or object lenses are to be screwed into the
hole 12, and to be adjusted to a proper focus by the nut 13.

N. B. At the end A B of the wooden body there is a slider, which is
represented as partly drawn out at A; when quite taken out, three
grooves will be perceived, one of which contains a board that forms the
end of the box, the next contains a frame with a greyed glass; the
third, or that farthest from the end A B, two large convex lenses.


OF THE LAMP.

Fig. 3, represents one of Argand’s lamps, which is the most suitable for
microscopic purposes, on account of the clearness, the intensity, and
the steadiness of the light. The following method of managing it, with
other observations, is copied from an account given by Mr. Parker, with
those he sells.

The principle on which the lamp acts, consists in disposing the wick in
thin parts, so that the air may come into contact with all the burning
fuel, by which means, together with an increase of the current of air
occasioned by rarefaction in the glass tube, the whole of the fuel is
converted into flame.

The wicks are circular, and, the more readily to regulate the quantity
of light, are fixed on a brass collar with a wire handle, by means of
which they are raised or depressed at pleasure.

To fix the wick on, a wood mandril is contrived, which is tapered at one
end, and has a groove turned at the other.

The wick has a selvage at one end, which is to be put foremost on the
mandril, and moved up to the groove; then putting the groove into the
collar of the wick-holder, the wick is easily pushed forward upon it.

The wick-holder and wick being put quite down in their place, the spare
part of the wick should, while dry, be set alight, and suffered to burn
to the edge of the tubes; this will leave it more even than by cutting,
and, being black by burning, will be much easier lighted: for this
reason, the black should never be intirely cut off.

The lamp should be filled an hour or two before it is wanted, that the
cotton may imbibe the oil, and draw the better.

The lamps which have a reservoir and valve, need no other direction for
filling, than to do it with a proper trimming pot, carefully observing
when they are full; then pulling up the valve by the point, the
reservoir being turned by the other hand, may be replaced without
spilling a drop.

Those lamps which fill in the front like a bird-fountain, must be
reclined on the back to fill, and this should be done gently, that the
oil in the burner may return into the body when so placed and filled;
if, by being too full, any oil appear above the guard, only move the
lamp a little, and the oil will disappear; the lamp may then be placed
erect, and the oil will flow to its proper level.

The oil must be of the spermaceti kind, commonly called chamber oil,
which may generally be distinguished by its paleness, transparency, and
inoffensive scent; all those oils which are of a red and brown colour,
and of an offensive smell, should be carefully avoided, as their
glutinous parts clog the lamp, and the impurities in such oil not being
inflammable, will accumulate and remain in the form of a crust on the
wick. Seal oil is nearly as pale and sweet as chamber oil, but being of
a heavy sluggish quality, is not proper for lamps with fine wicks.

Whenever bad oil has been used, on changing it, the wick must also be
changed, because, after having imbibed the coarse particles in its
capillary tubes, it will not draw up the fine oil.

To obtain the greatest degree of light, the wick should be trimmed
exactly even, the flame will then be completely equal.

There will be a great advantage in keeping the lamp clean, especially
the burner and air tubes; the neglect of cleanliness in lamps is too
common: a candlestick is generally cleaned every time it is used, so
should a lamp; and if a candlestick is not to be objected to, because it
does not give light after the candle is exhausted, so a lamp should not
be thought ill of, if it does not give light when it wants oil or
cotton; but this last has often happened, because the deficiency is less
visible.

The glass tubes are best cleaned with a piece of wash leather.

If a fountain lamp be left partly filled with oil, it may be liable to
overflow; this happens by the contraction of the air when cold, and its
expansion by the warmth of a room, the rays of the sun, or the heat of
the lamp when re-lighted: this accident may be effectually prevented by
keeping the reservoir filled, the oil not being subject to expansion
like air. On this account, those with a common reservoir are best
adapted for microscopic purposes.


TO EXAMINE OPAKE OBJECTS WITH THE LUCERNAL MICROSCOPE.

The microscope is represented as mounted, and entirely ready for this
purpose, in Fig. 1. Plate III.

To render the use of this instrument easy, it is usually packed with as
many of the parts together as possible; it occupies on this account
rather more room, but is much less embarrassing to the observer, who has
only three parts to put on after it is taken out of its box, namely, the
guide for the eye, the stage, and the tube with its magnifier.

But to be more particular, take out the wooden slide A, then lift out
the cover and the grey glass from their respective grooves under the
slide A.

Put the end N of the guide for the eye L M N into its place, so that it
may stand in the position which is represented in this figure.

Place the socket, which is at the bottom of the opake stage, on the bar
Q X T, so that the concave mirror o may be next the end D E of the
wooden body.

Screw the tubes P O into the end D E. The magnifier you intend to use is
to be screwed on the end o of these tubes.

The handle G b, or milled nut, Fig. 2, must be placed on the square end
of the pinion a.

Place the lamp lighted before the glass lump n, and the object you
intend to examine between the spring plates of the stage, and the
instrument is ready for use.

In all microscopes, there are two circumstances which must be
particularly attended to; the modification of the light, or the proper
quantity to illuminate the object; secondly, the adjustment of the
instrument to the focus of the glasses and the eye of the observer. In
the use of the lucernal microscope there is a third circumstance, which
is the regulation of the guide of the eye, each of which I shall
consider by itself.

1. To throw the light upon the object. The flame of the lamp is to be
placed rather below the center of the glass semiglobe n, and as near it
as possible; the concave mirror o must be so inclined and turned, as to
receive the light from the semiglobe; and reflect it thence upon the
object; the best situation of the concave mirror, and the flame of the
lamp, depends on a combination of circumstances, which a little practice
will best point out.

2. To regulate the guide for the eye, or to place the center of the eye
piece L, so that it may coincide with the focal point of the lenses, and
the axis of vision. Lengthen and shorten the tubes M N by drawing out or
pushing in the inner tube, and raising or depressing the eye-piece M L,
till you find the large lens, which is placed at the end A B of the
wooden body, filled by an uniform field of light, without any prismatic
colours round the edge; for, till this piece be properly fixed, the
circle of light will be very small, and only occupy a part of the lens;
the eye must be kept at the center of the eye-piece L, during the whole
of the operation; which may be rendered somewhat easier to the observer,
on the first use of the instrument, if he hold a piece of white paper
parallel to the large lenses, removing it from or bringing it nearer to
them, till he finds the place where a lucid circle, which he will
perceive on the paper, is brightest and most distinct, then to fix the
center of the eye-piece to coincide with that spot; after which a very
small adjustment will set it perfectly right.

3. To adjust the lenses to their focal distance. This is effected by
turning the pinion a, the eye being at the same time at the eye-piece L.
I often place the grey glass before the large lenses, while I am
regulating the guide for the eye, and adjusting for the focal distance.

If the observer, in the process of his examination of an object, advance
rapidly from a shallow to a deep magnifier, he will save himself some
labour by pulling out the internal tube at O.

The upper part f g r s of the stage, is to be raised or lowered
occasionally, in order to make the center of the object coincide with
the center of the lens at O.

To delineate objects, the grey or rough ground glass must be placed
before the large lenses; the picture of the object will be formed on
this glass, and the outline may be accurately taken, by going over the
picture with a pencil.

The opake part may be used in the day-time without a lamp, provided the
large lenses at A B be screened from the light.


TO USE THE LUCERNAL MICROSCOPE IN THE EXAMINATION OF TRANSPARENT
OBJECTS.

The microscope is to remain as before: the upper part f g r s of the
opake stage must be removed, and the stage for transparent objects,
represented at Fig. 4, put in its place; the end, Fig. 9 and 10, to be
next the lamp.

Place the rough glass in its groove at the end A B, and the objects in
the slider-holder at the front of the stage; then transmit as strong a
light as you are able on the object, which you will easily do, by
raising or lowering the lamp.

The object will be beautifully depicted on the rough glass: it must be
regulated to the focus of the magnifier, by turning the pinion a.

The object may be viewed either with or without the guide for the eye; a
single observer will see an object to the greatest advantage by using
this guide, which is to be adjusted as we have described, page 73. If
two or three wish to examine the object at the same time, the guide for
the eye must be laid aside.

Take the large lens out of the groove, and receive the image on the
rough glass; in this case the guide for the eye is of no use: if the
rough glass be taken away, the image of the object may be represented on
a paper screen.[29]

  [29] A tin cover is sometimes made to go over the glass chimney of the
  lamp, Fig. 3, with only a small square aperture in front, sufficient
  to suffer the rays to pass into the microscope: this, by excluding all
  extraneous rays, adds in many cases most materially to the effect,
  particularly by day, and when objects are to be represented on the
  rough glass or screen only. EDIT.

Take out the rough glass, replace the large lenses, and use the guide
for the eye; attend to the foregoing directions, and adjust the object
to its proper focus. You will then see the object in a blaze of light
almost too great for the eye, a circumstance that will be found very
useful in the examination of particular objects; the edges of the object
in this mode will be somewhat coloured, but as it is only used in this
full light for occasional purposes, it has been thought better to leave
this small imperfection, than by remedying it, to sacrifice greater
advantages; the more so, as this fault is easily corrected, and a new
and interesting view of the object is obtained, by turning the
instrument out of the direct rays of light, and permitting them to pass
through only in an oblique direction, by which the upper surface is in
some degree illuminated, and the object is seen partly as opake, partly
as transparent. It has been already observed, that the transparent
objects might be placed between the slider-holders kl of the stage for
opake objects, and then be examined as if opake.

Some transparent objects appear to the greatest advantage when the lens
at 9 and 10 is taken away; as, by giving too great a quantity of light,
it renders the edges less sharp.

The variety of views which may be taken of every object, by means of the
improved lucernal microscope, will be found to be of great use to an
accurate observer: it will give him an opportunity of correcting or
confirming his discoveries, and investigating those parts in one mode,
which are invisible in another.


TO TRANSMIT THE IMAGE OF TRANSPARENT OBJECTS ON A SCREEN, AS BY THE
SOLAR MICROSCOPE.

It has been long a microscopical desideratum, to have an instrument by
which the image of transparent objects might be shewn on a screen, as by
the common solar microscope; and this not only because the sun is so
uncertain in this climate, and the use of the solar microscope requires
confinement in the finest part of the day, when time seldom hangs heavy
on the rational mind, but as it also affords an increase of pleasure, by
displaying its wonders to several persons at the same instant, without
the least fatigue to the eye.

This purpose is now effectually answered, by affixing the transparent
stage, Fig. 4, of the lucernal to a lanthorn containing one of Argand’s
lamps. The lamp is placed within the lanthorn, and the end 9, 10 of the
transparent stage is screwed into a female screw, which is rivetted in
the sliding part of the front of the lanthorn; the magnifying lenses are
to be screwed into the hole represented at 12; they are adjusted by
turning the milled nut. The quantity of light is to be regulated, by
raising and lowering the sliding plate, or the lamp. N. B. This part,
with its lanthorn and lamp, may be had separate from the lucernal
microscope.[30]

  [30] This effect by the lanthorn and lamp is subject to much
  limitation in the field of view, or circle of light thrown upon the
  screen. A circle of not more than from 12 to about 15 inches can ever
  be obtained with any tolerable strength of light, to shew the most
  transparent sort of objects that can be found, such as the scale of a
  sole fish, a fly’s wing, &c. The great difference between the light of
  the sun and a lamp is a natural obstacle to great performances in this
  way, and renders them far short of the effects of the solar
  microscope. The exhibition, however, is considerable, and much
  deserving of the notice of any observer disposed to this sort of
  apparatus. Probably, subsequent experiments may yet produce more light
  on this instrument. The best sort of apparatus for this purpose
  hitherto made, I shall describe in a following section. EDIT.


APPARATUS WHICH USUALLY ACCOMPANIES THE IMPROVED LUCERNAL MICROSCOPE.

The stage, Fig. 1, f g h i, for opake objects, with its glass semiglobe,
and concave mirror, which is moveable upon the bar Q R S T, and set
readily to any distance by the screw at a. The glasses o and n are also
moveable upon the bar for regulating and adjusting the light upon the
object.

The stage, Fig. 4, for transparent objects, which fits on the upper part
P S of the foregoing stage. When this is to be applied occasionally to a
lanthorn for shewing transparent objects on a screen, &c. it is made of
a much larger diameter, to admit of the illuminating lenses at 9, 10,
and 11, of greater power of condensing the rays from the lamp.

The sliding tube O P, to which the magnifiers are to be affixed; one end
of this is to be screwed on the end B of the wooden body; the magnifier
in use is to be screwed to the other end on the inner tube. This tube
slides inwards or outwards; it is first used to set the magnifier at
nearly the right distance from the object, before the exact adjustment
for the focus is made, by turning the pinion at a with Hook’s joint and
handle b e.

Eight magnifying lenses in brass cells, Fig. 5. Plate III. these are so
constructed that any two of them may be combined together, and thus
produce a very great variety of magnifying powers. The cells unscrew to
admit of the glasses being cleaned.

A fish-pan, such as is represented at Fig. 6, whereon a small fish may
be fastened in order to view the circulation of its blood; its tail is
to be spread across the oblong hole at the smallest end, and tied fast
by means of the attached ribbon. The knob on its back is to be put
through a slit hole on the brass piece, No. 5, of Fig. 4. The tail of
the fish is to be brought then immediately before the magnifier.

A steel wire, Fig. 7, with a pair of nippers at one end, and a steel
point at the other; the wire slides backwards or forwards, in a spring
tube which is affixed to a joint at the bottom, on which is a pin to fit
the hole in the leg, No. 6, Fig. 4. This is used to confine small
objects.

A slider of brass, Fig. 8, containing a flat glass slider and a brass
slider, into which are fitted some small concave glasses. It is for
confining small living objects, and when used is placed between the two
plates, No. 7, Fig. 4.

A pair of forceps, Fig. 9, by which any occasional small object may be
conveniently taken up.

Six large ivory sliders, with transparent objects placed between two
plates of talc, and confined by brass rings, and six small ditto with
ditto. Fig. 10. The larger ones usually contain a set of Custance’s fine
vegetable cuttings.

Fourteen wood sliders, containing on each four opake objects, and two
spare sliders for occasional objects; all fitted to the cheeks kl of the
stage. Fig. 11.

Some capillary tubes, Fig. 12, to receive small fish, and for viewing
small animalcula. They are to be placed between the two plates of the
stage No. 7, Fig. 4.

A small ivory double box, containing spare plates of talc and brass
rings, for replacing any in the small ivory sliders, when necessary.

A single lens mounted in a tortoiseshell case, to examine minute objects
previous to their being applied to the sliders.

Opake objects are easily put on the spare sliders by a wetted wafer;
and, for good security, gum water may be added.

For the prices of the lucernal, as well as all the other sorts of
microscopes, see the list annexed to these Essays.


A DESCRIPTION OF THE SEVERAL IMPROVEMENTS MADE UPON MR. ADAMS’S LUCERNAL
MICROSCOPE. BY THE EDITOR.

The lucernal microscope being unquestionably the only instrument for
exhibiting all sorts of opake objects under a brilliant and magnified
appearance, was, as formerly constructed by the late Mr. G. Adams,
attended with some inconveniences and imperfections. Upon a proper
inquiry into various improvements, and from some observations made by
myself, I can recommend, as a complete instrument, one with the
following emendations, being, in my opinion, the best of any hitherto
made known.

The lucernal microscope, when placed up for use, as represented in Fig.
1. Plate III. is of some considerable length. When the eye at L is
viewing the image of the object upon the glasses, the objects themselves
in the sliders placed at kl at the stage, are without the reach of the
hand; so that the indispensible change of the parts of an object, or of
one object to another, can only be obtained by the observer’s moving
himself from the object to the eye-piece, and vice versa. This
adjustment, therefore, proves uncertain and troublesome. The application
of rack-work motion to the stage has been contrived and applied to the
lucernal microscope by Mr. W. Jones, of Holborn, accompanied with
Hooke’s joint and handle, and a lever rod; so that, without altering his
position, the observer may change both the horizontal and vertical
position of the sliders, and thereby readily investigate all the variety
of the objects, and their parts, and with the same exactness as by other
microscopes.

For persons who may not wish to be at the expense of the lucernal, as
formerly mounted by Mr. Adams, Mr. Jones has altered the manner of its
support; which, as well as the other particulars, and the method of
using it, may be understood from the following description.

Plate IX. Fig. 3, is a representation of the instrument as placed up for
use. AA, the top of a mahogany chest, about two feet long, thirteen
inches and an half high, and eight inches broad, which serves both as a
case to contain the instrument, and to support and preserve it steady
when in use. A groove is cut in the top of the box, and another in the
inside at the bottom, in both of which the base of the instrument is
made to slide. When the instrument is placed inside, a long slip of
mahogany slides in at the top, to secure the groove, and make the top
perfect. Thus the instrument may be most readily slid out of its case,
and then into the groove at top for use, and in much less time than by
the brass frame and jointed stand adopted by Mr. Adams. Fig. 3 B, is the
stage for the objects, with the condensing lens _a_, and concave mirror
_b_, the same as in Mr. Adams’s. C, the brass slider case for opake
objects, with a rack cut into its lower edge, and which is turned by a
pinion. To this pinion is applied an handle, D, with Hooke’s universal
joint; this contrivance gives a certain horizontal motion to the objects
while viewing. The stage at C is also made to slide vertically, and a
lever-rod or handle, E, to apply through the top, to bring the objects
to a just height. Hence, by applying the left hand to the handle, E, and
the right to the rod D, the adjustment or the changing of the objects,
while under exhibition on the large lenses at F, is produced in the most
convenient and accurate manner, and the observer has no occasion, for
one slider, to shift from his seat or position.

Rack-work might be applied to the vertical motion, but it is not
essentially necessary; for when once the center of the slider is
observed, there requires very little change from that position for the
complete exhibition of the objects. The whole of the stage, with the
lense and mirror, is fixed to a brass dove-tailed slider at G, which
slides in another brass piece fixed to the wooden slider or base of the
instrument. A long brass rod, H, with an adjusting screw at its end,
passes through the two brass pillars, K, K, to the stage at _f_, upon
which it acts; and according as it is turned to the right or left hand
while examining the objects, moves the objects nearer to or farther from
the magnifiers screwed on at L, and produces the just distance for
rendering the appearance of the objects the most distinct and brilliant
upon the glasses at F.

The management of the light from the lamp, through the lens, _a_, and
from the concave mirror, _b_, to the objects, is exactly the same as
before directed by Mr. Adams. For the exhibiting of transparent objects,
the stage, C, is to be slid away, and the body, Fig. 4, applied in its
place, in that position, with the large lens outwards next the lamp. The
slider with the objects passes through at _a_, and the focus for the
different magnifiers is adjusted by turning the long rod, D, to the
right or left, as with the opake objects. In this case the lamp is to be
raised to the center of the body of the microscope, or even with the
magnifiers at L. The image of the objects may also, as in Mr. Adams’s,
be best received on the rough glass placed at F, for the simple
reflected light through the body will sometimes be so strong, as to
irritate the eye; the operator must, therefore, both modify that from
the lamp, and place the roughed glass to his own ease and pleasure. The
guide for the eye, N, in this instance is not necessary. Care being
taken that the roughed glass at F be kept in as dark a situation as
possible, there will be a certainty of a clear and well-defined view of
the object.

A tin chimney placed over the glass of the lamp about ten inches long,
with a suitable aperture to admit the light to pass through it to the
glasses, is of material service; it excludes all superfluous light from
the eye of the observer, keeps the room sufficiently darkened, and
enables the observer to view his object with the proper brilliancy. As a
pleasing relief to the eye, the interposition of a small piece of blue
or green glass at the sight hole, N, Mr. Jones has sometimes found
necessary, but it gives rather a false teint to the colour of the
objects.

In the year 1789 the same artist applied a brass screw pillar and arm to
the top of the box at O, on which is occasionally slid the condensing
lens, _a_. The lamp being then applied at the side of the box at O,
instead of the end, and the lens, _a_, moved to such a distance as to
give the strongest possible light upon the opake objects at C; they were
found to be more strongly illuminated by this simple refracted light
than by the refracted and reflected light before used. Light is always
somewhat diminished by reflection, although condensed; therefore, as it
is sometimes best to view the objects from oblique reflected light, and
sometimes from direct refracted, he constructs the apparatus so as to
give the operator the means of easily using either. The dotted lines, O
P, shew the manner that the glass semiglobe, _a_, is occasionally
applied to refract or converge directly the light from the lamp to the
objects on the stage.

It is scarcely necessary to observe to the reader, the propriety of all
the glasses of the apparatus being perfectly clean before the
observations; for if, after being laid aside some time, or by dust, &c.
they should appear soiled, it will be necessary to wipe them previously
with a piece of soft shammy leather usually sent in the box for that
purpose, or a clean soft cloth. The two large lenses at F, Fig. 3, may
be readily separated by turning aside the two brass screws that act upon
a brass ring.

From the various ingenious admirers of this sort of instrument, many
improvements and alterations have been suggested; among several that
have been communicated, those by the two following gentlemen appear to
me the most deserving of notice, and which I shall leave to the reader’s
judgment and experience.

The Rev. John Prince, LL. D. now of Salem, Massachuset’s States, North
America, a valuable correspondent and friend of our late author,
transmitted to him an alteration in the construction; and of which I
here insert the brief account, in nearly the words given by Mr. Adams.

Dr. Prince applies a strong joint similar to that of a telescope at
about the middle of the center part of the pyramidical box, and a sort
of adjusting screw at the large end. The joint is nearly in the center
of gravity, so that a very small motion is sufficient to bring any
object less than an inch in diameter into the field of view. This motion
is effected by two screws at right angles to each other; one screw
raising or levelling the body, the other moving it sidewise, the screw
at the same time forming a double joint to accommodate the parts to the
movement.[31]

  [31] A figure of this, with an explanation, as recommended by Mr. John
  Hill, Wells, in Norfolk, may be seen in the Gentleman’s Magazine, Vol.
  LXVI. 2d part, page 897. In this particular, as well as in the
  deviation from the parallel position of the glasses to the surfaces of
  the objects, I think the construction not so simple and perfect, as
  that by rack-work and pinion applied by Mr. Jones. Probably, Dr.
  Prince had not, at the time of his contriving the joint-work to the
  box, seen or heard of the other method. His subsequent contrivances
  shew real ingenuity; and to the inquisitive in this instrument, will
  afford much useful entertainment and advantage.

To secure the image formed upon the rough glass more completely from the
light, at times essentially necessary, there is a pyramidical mahogany
box, of the same size, to pack, when not used, in the body of the
microscope; when in use, the broad end of this screen box is to be slid
into the groove, from which the exterior cover at the end has been
taken. This method is peculiarly useful in the day-time; as, by
screening the large lenses from the light, it may even then be used with
satisfaction.

One of the large lenses may occasionally be placed on the outer edge of
the screen box, the other lens being taken out; the view on the rough
glass is by these means magnified, and appears to greater advantage.
But, besides the grey glass used in the former construction, there is a
second in this, placed farther within the body, about half way; and,
when the large lens is in the screen box, objects appear better in this
than in the former way. It has a still greater effect upon those who are
unacquainted with the nature of lenses, as it makes them judge the
distance and magnitude much greater than they really are, and is
therefore more pleasing than the grey glass in front. Only one grey
glass can be used at a time; both being removed when opake objects are
viewed.

The stage, F, Fig. 5, is considerably different from that at C, Fig. 3;
it is judged more convenient and commodious than the other, and serves,
with a small alteration, for both transparent and opake objects. A
truncated cone can also be here applied for cutting off superfluous rays
of light occasionally.

The method of illuminating the objects is also different. The mode now
adopted answers better for opake and transparent objects, throws a
stronger light, and is more convenient in application. It consists of
two lenses, 1 and 2, Fig. 5; the larger one is to be placed at the end
of the bar next the lamp. The smaller one to be adjusted so as to give a
strong light. A third is also added, to be used occasionally with opake
objects; it is to be applied close to the large lens. Experience will
shew when it is to be used, or not. By moving the bar, G, on which these
lenses are placed round the stage pillar, M, you bring it so much
fronting the stage as effectually to enlighten opake objects by means of
the lamp. The light thus afforded is received directly, and none lost by
reflection. The objects are fixed on circular wheels of wood, see Fig.
7, the brass centers of which, are fitted to the hole, _b_, of the
stage, Fig. 5; and about this center they are to be turned by the hand
for the changing of the objects.

As some objects, such as sections of wood, are seen to advantage both as
transparent and opake, a frame containing a plane and a concave mirror
is added to this instrument, serving two purposes: by bringing the bar
to the front of the stage, removing the large lens, and putting the
mirror in its place, the object may be viewed either way, without moving
from the seat, by turning the instrument a little round. This experience
will discover. The light of the sun may be thrown by the plane mirror on
the condensing lens, so as to produce a strong full field of light on
the grey glass. This has a grand effect when the large lens is at the
end of the screen box, and could not be applied in this manner in former
constructions. It becomes also an opake solar microscope, by turning the
bar round to enlighten opake objects.

By bringing the concave mirror to a focus that will burn objects, a set
of very curious and entertaining experiments may be made and exhibited
on the grey glass. The object for combustion should be put in the
nippers, and a piece of slate tied as a ground on the stage. The
ebullition of a piece of alum viewed in this manner is very beautiful;
the bubbles, as they rise and pass off rapidly, appear tinged with all
the colours of the rainbow.

There are large-sized magnifiers for the purpose of throwing transparent
objects on a screen, in imitation of the solar microscope. By removing
the large lenses in front and the grey glass, and placing the black tin
cylinder represented in the drawing by dotted marks, over the lamp, they
may be shewn in that manner to several persons; thus, this instrument in
a great degree supersedes the use of a lanthorn. The image may be
contracted occasionally by one of the large lenses.

The following improvement consists in the manner of applying the lamp,
by Mr. Hill. By attaching it to the instrument, it renders the light
more permanent and steady, and reduces considerably the bulk as well as
the trouble of this appendage, and is to be preferred when the lamp is
not wanted separately for other uses or experiments.

H, a brass support to the arm, G, for sustaining the weight of the lamp;
it turns round with the bar on the pillar, M. At about I is a brass cap
soldered to the above support, and which slips over the slider carrying
the larger lens, 2. At K, is a strong joint connected with the said cap,
and by which an horizontal motion of the cap is given, when an oblique
light is required. To the end of this the lamp is fixed, and in such a
manner as to admit of its being easily slid upwards or downwards in a
perpendicular direction, to procure the just height of the flame. L is a
square brass rod to be occasionally screwed into the reservoir of the
lamp, for supporting the tin cylinder screen, when transparent objects
are to be represented on a screen in a darkened room.

The transparent microscope, part of the lucernal, is sometimes adapted
to a large japanned tin lanthorn, such as represented at Fig. 6. A brass
female screw is soldered to the front of the lanthorn, which has a
motion upwards or downwards, fitted to the male screw of the transparent
microscope. A tall chimney is placed at the top of the lanthorn to
conduct the heated air from an Argand’s lamp withinside. The transparent
objects in the sliders are magnified by the lenses screwed on at _a_,
and shewn on the screen A; this screen may be about three feet square,
of white paper, the objects on which, if represented in a field larger
than twelve or eighteen inches, will not be sufficiently vivid.

Mr. Jones has found that a large square glass, from twelve to sixteen
inches in the side, rough ground on one of its surfaces, exhibits the
objects the best of any other contrivance; answers tolerably well for
opake objects, and gives the artist the means of tracing their figure
most correctly on its surface. Such sort of objects he fixes upon slips
of glass for that purpose, or applies them to a pair of nippers shewn at
_b_, sent with the microscope. A concave silver speculum screws on at
_c_, before the magnifiers, which reflects upon the objects the light
that issues from the lamp through the body of the microscope. The least
dimensions of the lanthorn are about ten inches square, and fourteen
inches high.

This microscope and lanthorn, when made as a separate apparatus from the
lucernal, is called the LANTHORN MICROSCOPE. Its effect is considerably
short of what is produced by the solar microscope, and not equal to what
is much wished for in this manner of magnifying minute objects; see
note, page 77.

Partly from the improvements just described, Mr. Jones is now
constructing a lucernal microscope that he conceives will be the most
simple and perfect yet made. It could not be completed in time to be
described in this work; but its improvement and advantages will be quite
evident to any reader who has attended to the description which I have
just given.


DESCRIPTION OF CUFF’S DOUBLE-CONSTRUCTED MICROSCOPE, REPRESENTED AT Fig.
1. Plate VII. A.[32]

  [32] The compound or double microscope is in more general use than any
  other sort. Besides its being less expensive than the lucernal or
  complete solar, it is found commodious and portable in the observer’s
  apartment, when only a confined degree of microscopical pursuit is
  intended, and that chiefly for a few hours amusement; it may be used
  both by day and night. In the most improved of this kind the objects
  appear magnified in a field of view from about 12 to 15 inches in
  diameter. It is better adapted to transparent than to opake objects,
  yet the latter may often be viewed to great advantage by the
  assistance of the sun’s rays or the light of a candle condensed on
  them. The intelligent reader, by attending to the accounts of the
  different microscopes described in this work, will be enabled to
  select that best adapted to the kind of objects he wishes to explore,
  and the manner in which he is desirous of having them exhibited. EDIT.

This instrument was first described by Mr. Baker, and recommended by
him. It was also described by my father in the fourth edition of his
Micrographia Illustrata, page xix.

A B C represents the body of this microscope; it contains an eye-glass
at A, a large lens at B, and a magnifier which is screwed on at C, one
of which is represented at Q.

The body of the microscope is supported by the arm D E, from which it
may be removed at pleasure.

The arm D E is fixed on the sliding bar F, and may be raised or
depressed to any height within its limits.

The main pillar a b is fixed in the box b e, and by means of the brass
foot d is screwed to the mahogany pedestal X Y, in which is a drawer
containing all the apparatus.

O, a milled-headed screw, to tighten the bar F when the adjusting screw
c g is used.

p q is the stage or plate which carries the objects; it has a hole at
the center n.

G, a concave mirror, that may be turned in any direction, to reflect the
light of the candle, or the sky, upon the object.


A LIST OF THE APPARATUS TO CUFF’S DOUBLE-CONSTRUCTED MICROSCOPE.[33]

  [33] This microscope is made oftentimes with a joint at the bottom of
  the main pillar at _e_, to admit placing the instrument into any
  oblique situation, and connected to the bottom of a mahogany chest; on
  which account, it is by some of the instrument makers called the Chest
  Compound Microscope. EDIT.

H, a convex lens, to collect the rays of light from the sun or a candle,
and condense them on the object, or to magnify a flower or other large
object placed upon the stage.

L, a cylindrical tube, open at each side, with a concave silver speculum
screwed to the lower end h.

P, the slider-holder; it consists of a cylindrical tube, in which an
inner tube is forced upwards by a spiral spring, it is used to receive
an ivory slider K, which is to be slid between the plates h and i. The
cylinder P fits the hole n in the stage: the hollow part at k is
designed to receive a glass tube N.

R is a brass cone, to be put under the bottom of the cylinder P, to
intercept occasionally some of the rays of light.

S, a box containing a concave and a flat glass, between which a small
living insect may be confined; it is to be placed over the hole n.

T, a flat glass to lay any occasional object upon; there is also a
concave one u, for fluids.

O, a long steel wire, with a small pair of pliers at one end, and a
point at the other, designed to stick or hold objects; it slips
backwards and forwards in the short tube o; the pin p fits into an hole
m, in the stage for that purpose.

W, a little round ivory box, to hold a supply of talc and rings for the
sliders.

Z, a hair brush, to wipe any dust off the glasses, or to take up by the
other end a drop of any liquid.

V, a small ivory cylinder, that fits on the pointed end of the steel
wire O; it is designed for opake objects. Light-coloured ones are to be
stuck upon the dark side, and vice versa.

Y, a common magnifying glass for any occasional purpose.

M, a fish-pan whereon to fasten a small fish, to view the circulation of
the blood: the tail is to be spread across the oblong hole at the small
end k, and tied fast by means of a ribband fixed thereto; the knob l is
to be put through the slit made in the stage, and the tail may be
brought under the magnifier.

X is a wire to clean the glass tubes by.


TO USE THIS MICROSCOPE.

Screw the magnifier you intend to use to the end C of the body, place
the slider-holder P in the hole n, and the ivory slider K with the
object, between the plates _h i_ of the slider-holder; set the upper
edge of the bar D E to coincide with the division which corresponds to
the magnifier you have in use, and tighten it by the milled nut O; now
reflect a proper quantity of light upon the object, by means of the
concave mirror G, and regulate the body exactly to the eye and the focus
of the glasses by the adjusting screw _c g_, at the same time you are
viewing the object.

To view opake objects, take away the slider-holder P, and place the
object on a flat glass u, under the center of the body, or on one end of
the jointed nippers o. Then screw the silver concave speculum to the end
of the cylinder L, and slide this cylinder on the lower part of the
body, so that the upper edge thereof may coincide with the line which
has the same mark with the magnifier that is then used; reflect the
light from the concave mirror G to the silver speculum, from which it
will be again reflected on the object. The glasses are to be adjusted to
their focal distance as before directed.


THE DESCRIPTION AND USE OF JONES’S IMPROVED COMPOUND OR DOUBLE
MICROSCOPES, REPRESENTED IN Fig. 1 AND 2. Plate IV. BY THE EDITOR.

The chief imperfections of Cuff’s microscope, as well as of others
formerly made, are, their construction rendering them only compound
microscopes, the body of the instrument having but a fixed position over
the object, and the smallness of the field of view by the old
construction of the glasses in the body. To obviate these defects, as
well as for the application of material improvements, the late Messrs.
Martin and Adams, and the present Messrs. W. and S. Jones, have
constructed this kind of microscope in various ways. Two microscopes by
the latter artists, which I am now going to describe, appear to me to be
the best of any hitherto invented.

Fig. 1 is a representation of the second best sort of compound
microscopes. The improvements, though few in number, are essential to
the use thereof. The field of view is considerably larger than in the
former microscope. The stage and the mirrors are both moveable, so that
their respective distances may be easily varied. The magnifiers may be
moved about over the object. There is also a condensing glass, for
increasing the density of the light, when it is reflected by the mirror
from a candle or lamp. It is furnished with two mirrors, one plane and
the other concave, and may likewise be used as a complete single
microscope.

A B, Fig. 1. represents the body of the microscope, containing a double
eye glass, and a body glass; it is here shewn as screwed to the arm C D,
from whence it may be occasionally removed, either for the convenience
of packing, or when the instrument is to be used as a single microscope.

The eye glasses and the body glasses are contained in a tube which fits
into the exterior tube A B; by pulling out a little this tube, when the
microscope is in use, the magnifying power of each lens is increased.

The body A B of the microscope is supported by the arm C D; this arm is
moveable in a square socket cut in the head that is connected to the
main pillar E F, which is screwed firmly to the mahogany pedestal G H;
there is a drawer to this pedestal, which holds the apparatus. This arm
may be slid backwards and forwards in its socket, carrying the
magnifiers and the body of glasses, and also turned horizontally quite
round upon the pillar, giving a general motion all over the object on
the stage below; which is a material improvement and advantage of this
microscope over a similar one described in the former edition of this
work, as any unavoidable motion of the living object to be viewed may be
followed, by the observer’s hand moving the arm C D as the object
changes its place.

N I S is the plate or stage which carries the slider-holder K, this
stage is moved up or down the pillar E F, by turning the milled nut M;
this nut is fixed to a pinion, that works in a toothed rack cut on one
side of the pillar. By means of this pinion the stage may be gradually
raised or depressed, and the object adjusted to the focus of the
different lenses.

K is the slider-holder, which fits into a hole that is in the middle of
the stage N I S; it is used to confine and guide either the motion of
the sliders which contain the objects, or the glass tubes that are
designed to confine small fishes, for viewing the circulation of the
blood. The sliders and tubes are to be passed between the two upper
plates.

L is a brass tube, in the upper part of which is fixed the condensing
lens before spoken of; it screws into the wire arm a, which is placed in
the hole I of the stage, with the glass underneath, and may be set at
different distances from the object, according to its distance from the
mirror or the candle.

O is the frame which holds the two reflecting mirrors, one of which is
plane, the other concave. These mirrors may be moved in various
directions, in order to reflect the light properly, by means of the
pivots on which they move, in the semicircle Q, and the motion of the
semicircle itself on the pin R; the concave mirror generally answers
best in the day-time; the plane mirror combines better with the
condensing lens in L, and a lamp or candle at night.

At S is a hole and slit for receiving either the nippers _b_, or the
fish-pan _c_; when these are used, the slider-holder K must be removed.

T, a hole to receive the pin of the convex lens and illuminator _d_.

There are six magnifying lenses contained in a brass wheel screwed in a
circular brass box P; this wheel is moveable about its center with the
finger, and stops by a click when the magnifiers are each centrally
under the body A B above, or the hole in the arm C D. They are marked
from No. 1, to 6, and the proper number shewn in a small opening made in
the side of the brass box. This wheel P screws into the arm C D, and may
occasionally be taken off to admit of the silver speculum, or a single
magnifier, hereafter to be described.

There is a small line cut on the edge of the arm C D, which must be
brought to the right hand edge of its socket, in order to center the
magnifier to the body and the stage.

By unscrewing the body A B, the single magnifiers in the wheel P being
then only left, the instrument readily forms a single microscope.

A small pocket hand single or opake microscope may easily be extracted
from this apparatus. When the body A B is screwed off, and the arm C D
slipt away from its frame with the wheel of magnifiers, and the forceps,
wire, and joint _b_ applied to it, by a hole made in the arm for that
purpose, as represented at V, it is then ready for the examination of
any small object that may present itself in the garden, &c. and will be
found very convenient whenever the whole instrument is not required.


LIST OF APPARATUS GENERALLY MADE TO THIS MICROSCOPE.

The wheel, with the magnifiers, P. Fig. 1.

The body of the microscope, A B.

The slider-holder, K.

The tube, with the condensing lens L, to be used by candle-light.

The pin and arm _a_, either for the above lens, or for the silver
concave speculum _e_.

The silver concave speculum _e_, fitted to the arm above, and used
common to all the magnifiers in the wheel and body A B, it is to reflect
the light from the concave or plane mirror O below, upon the opake
objects, then called the compound opake microscope.

A silver concave speculum _f_, with a single magnifier; it screws to the
under part of the arm C D in room of the wheel of magnifiers, and forms
then the single opake microscope.

A brass cone _g_, to place under the stage N I S, and serves to diminish
the reflected light when necessary.

The jointed nippers _b_, fitted to the stage, to hold any small insect,
or other opake object.

A cylinder of ivory _h_, to fix on the pointed end of the nippers, black
on one side and white on the other, to make a contrast to the opake
object used.

Six ivory sliders, _i_, each having four holes, and objects contained
between two talcs confined together by brass circular wires. One of the
sliders is usually sent without objects, to be supplied at pleasure.
When used, they are placed between the perforated plates of the
slider-holder K; where also is to be applied the brass frame slider _k_,
containing in one brass piece four small concave glasses fixed; a narrow
slip of glass slides over these, all within the frame; so that any very
small living object, as a mite, &c., may be viewed with the proper
security.

A set of glass tubes, _l_, three in number, to contain tadpoles, water
newts, small frogs, eels, &c. which are curious objects for affording a
fine view of the circulation of the blood, &c. They are also to be
placed in the slider-holder K. There is a small hole at one end to admit
air, the other end is to be stopped with cork, to contain the fluid and
prevent the escape of the animal. A brass twisted wire is sent, to
assist in the cleaning of these tubes.

A small ivory box, _m_, containing talcs and wires to supply the ivory
sliders with, should any be lost or damaged.

A lens set in a brass cell, _n_, of such a focus as to view objects
under a magnifying power sufficient for the applying them to the
instrument for further inspection; hence it has been called the
explorator. It may occasionally be screwed to the arm C D, and is then
well adapted for viewing objects of the larger kind, or the whole of an
insect, &c. before the observing of it in part under the regular
magnifiers.

A concave, or a circular plane glass, _o_, for transparent objects, or
animalcula in fluids, &c. it is fitted to the side, I, of the stage.

It is necessary to describe the lens and frame, _d_, noticed at page 95;
it is either for converging the sun’s rays upon opake objects laid upon
the stage, or for magnifying a flower, or other large objects applied to
the stage, or on the nippers or point, _b_. By its pin and spring socket
it is easily raised to any height, for the sun, candle, or the eye of
the observer.

A brass insect box, _h_, consisting of a concave and plane glass that
screw close together; by means of which a louse, flea, &c. may be
secured, viewed alive, and retained for any time. It is applied to the
hole I, of the stage, Fig. 1.

A pair of small brass forceps, _q_, by which any small object may be
conveniently taken up or moved.

This microscope packs into a mahogany pyramidical shaped case, about
seven inches square at its base, and fourteen inches in height. For its
price, see the general list annexed to this work.


TO USE THIS MICROSCOPE.

It will be obvious to the reader from the preceding description that it
must be put together as represented in the figure; that he has to place
the slider-holder, K, to the stage, N I S, with one slider of objects;
to reflect as strong a light as possible from the concave mirror, O,
below, by turning it into the best position, and moving it upwards or
downwards all the while he is looking down the body, A B. Then, for a
distinct view of the object, to turn the pinion, M, in a slow and gentle
manner. A small degree of practice will render the management very
familiar.

For opake objects, the slider-holder, K, is to be removed; the silver
speculum, _e_, screwed to the arm, _a_, and by its pin placed in the
hole, I, of the stage, with the concave part downward above the stage;
the glass, _o_, or the nippers, _b_, with ivory, _h_, placed at the
stage: then the light reflected from the mirror, O, up to the speculum
above, which will again reflect the light very strongly upon the object.
Practice also in this case can make it easy to the beginner. The use of
the rest of the apparatus has been sufficiently explained.


OF THE MOST IMPROVED COMPOUND MICROSCOPE, BEING UNIVERSAL IN ITS USES,
AND FORMING THE SINGLE, COMPOUND, OPAKE, AND AQUATIC MICROSCOPES.

A person much accustomed to observations by the microscope, will readily
discern the several advantages of this instrument over the preceding
one. Besides its containing an additional quantity of useful apparatus,
it is more commodious and complete for the management while observing,
as it may instantly be placed in a vertical, oblique, or horizontal
situation, turned laterally at the ease of the observer, and the objects
viewed by the primary direct light, or reflected as usual, at pleasure.
These particulars the following description will clearly shew. I shall
not again so fully describe the same apparatus, as the reader must
already understand their uses from the preceding references.

Fig. 2 is a representation of this instrument as placed up for use. A B
is the compound body. The eye-glasses are contained in an inner tube
that slides outwards or inwards, thus altering its distance from a glass
at B, and thereby increasing or diminishing the magnifying power, when
thought necessary. This body may be screwed on or off to the arm C D, as
in the microscope just described; the arm C D may also be moved in any
direction over the object. E F is the square stem or bar, on which is
moved by the rack-work and pinion M, the stage N I S, to adjust a
distinct view to any of the magnifiers, or apparatus used. V is a strong
brass pillar with a joint-piece at top, connected to the stem E F; by
means of this joint the position of the microscope is readily altered
from a vertical to an oblique or horizontal one, as may be desired or
found most easy and convenient to the observer, while sitting or
standing; it will also enable him to view objects by direct unreflected
light; for, when the stem, E F, is put into an horizontal position, the
mirrors, O, R, may be drawn off and laid aside. Against or before the
condensing lens, U, the common day-light or the light of a candle may
then be directed.

At the stage N I S, is a sliding brass spring, N, serving to confine
down slips of glass or large sliders, when objects placed thereon are
intended to be viewed out of the horizontal position of the stage. A
lens, U, called the condensing lens, fixed in a frame connected to a
socket, is for condensing and modifying the rays of light reflected from
the concave or plane mirror, O, below; it may be set to a proper
distance by raising it up by two little screws, one of which is shewn at
_u_. This lens is of considerable use by candle-light, as it serves to
fill the whole body, A B, beautifully with light on the object. It is
turned aside on a joint pin, when not in use. Six magnifiers are
contained in the wheel at P, as in the former microscope. The mirrors,
O, below may also be slid upwards or downwards on the stem, by pushing
against the screws at _r_. Thus the stage, lens U, and mirrors below,
being all in one axis of motion, admit the adjustment of the distinct
view, light, &c. in the most accurate and pleasing manner. When the
instrument is packed into its case, the feet, G G H, may all be folded
together as one, and the body A B, screwed off, for the advantage of
being portable. The body, as screwed off, leaves the instrument a single
microscope.


THE GENERAL APPARATUS TO THIS MICROSCOPE IS AS FOLLOWS.

First, such as accompany the preceding microscope. The brass wheel with
magnifiers, P, Fig. 2. The slider-holder, K. The brass pin and arm, _a_,
for receiving the concave speculum, _e_, which is applied to the upper
side of the stage, and used common to all the magnifiers. The silver
concave speculum, _f_, with a magnifier set therein, used by itself in
the arm C D. These two speculums form the instrument into what is called
an OPAKE MICROSCOPE.

A brass cone, g, fitting the under side of the stage, N I S, to exclude
superfluous light. The illuminator, or convex lens, _d_, Fig. 1, fitted
to T of the stage. The jointed nippers, _b_, fitted to the stage, and
either on the point or nippers to hold any small insect, or other opake
object. An ivory black and white piece, _h_, is also fitted to the point
to contrast the colour of any object laid thereon; the light upon this
is reflected from the silver concaves placed above, which reflect the
light downwards received from the mirrors at O. Six ivory sliders as
shewn at _i_, containing a selection of objects, placed between Muscovy
talc, and fastened by spring wires; and a brass frame slider, _k_: all
for the stage, K, when in use. A set of glass tubes for fish or liquids,
_l_, to be filled with water and stopped with cork, for the
slider-holder K. A pan, _c_, for fish or frogs, fitted to the stage at
S. A small ivory box, _m_, with spare talcs and wires. The explorator,
_n_, a lens set in a brass cell, for viewing the larger sort of objects
either by the hand, or from the arm C D, Fig. 2. A plane glass, _o_, and
a concave ditto, _s_, both fitted to the hole of the stage, N I S, for
viewing fluids, and confining the animalcula, &c. between them, and so
forming what is called the AQUATIC MICROSCOPE.

A brass box, _p_, with a concave and plane glass, for insects and other
objects, fitted to the stage N I S, when they are to be examined by the
instrument. A pair of brass forceps, _q_, to take or hold any object by.
A camel hair brush, _t_.


ADDITIONAL APPARATUS TO THIS BEST MICROSCOPE.

Three large wood sliders, as shewn at X, with talcs and wires, for the
larger sort of wings of flies, and other objects which are too large for
the small ivory sliders, _i_; they are to be placed in the slider-holder
K, when on the stage N I S, and the objects to be magnified either by
the magnifiers in the wheel P, or the lens shewn at _n_, screwed on the
arm C D. A brass cell, _y_, with a very small globule or lens, or an
extraordinary great magnifier, usually about the 30th or 40th of an inch
focus; it is to be screwed into the arm C D, when the wheel, P, is first
unscrewed away. It is for the purpose of viewing extreme minute objects,
which may be so small as to elude the power of the magnifiers in the
wheel, P.

A moveable stage, W, which by the pin, _a_, is applied to the hole, S,
of the stage Fig. 2, and thereby has an horizontal motion under the
whole field of view, without disturbing any other part of the
instrument. To the large hole of this stage are fitted a deep concave
glass, _r_, and the concave and plane glasses, _s_ and _o_; and to the
small holes, _x_ _x_, a black and white piece of ivory, _w_, for opake
objects, and a concave and plane glass similar to _o_ and _s_. An extra
concave silver speculum with a less magnifier than the other, as shewn
at _f_, used for the larger kind of opake objects, like the other,
fitted to the arm C D, and used instead of the magnifiers in the wheel,
P.

Rack-work is sometimes cut in the arm C D, to turn the pinion above, so
as to move the magnifiers in a linear direction over the objects in the
most accurate degree; and also the stage N I S jointed, to turn by a
screw and teeth in an horizontal direction at right angles to the above,
thereby rendering a slow and accurate motion, perfectly suitable to the
various positions of any living animal under examination.

Six or more larger ivory sliders, with cuttings of different woods, &c.
are also frequently added; but as these enhance the expense, and may be
extended to the desire of the purchaser, his choice, and not my
description here, will determine the extent of the apparatus to the
microscope. When packed up into its mahogany, or black shagreen case,
the outside dimensions are about twelve inches and an half long, nine
inches broad, and three inches three-quarters deep.

A microscope from this plan is frequently made of smaller dimensions,
for the convenience of persons who frequently travel, and is contained
in a fish-skin case about seven inches long, four inches and an half
broad, and two inches deep, and is the most complete instrument of the
sort.


TO USE THIS MICROSCOPE.

As in the former one, place the slider-holder K, with a slider of
objects in it, in the stage N I S; move the arm C D, in its socket, so
that a mark on the side is brought to the edge of the socket; then turn
the arm till the magnifier is directly central over the object; look
down the tube A B, and during that time, reflect the light strongly and
clearly up into it from the mirror O below; and then, while you are
looking through the body, gently turn the pinion at M to the right or
left, till you see the object magnified in the most distinct and
well-defined manner. Attending properly to this mode is the only care
necessary to use any microscope whatsoever; and for want of doing which,
many a beginner finds a difficulty in using properly his instrument. For
price, see the list at the end.

For opake objects, you take away the slider-holder, K; place on the
stage either the concave glass, _s_, or the nippers, _b_; screw the
concave speculum, _e_, to the arm, _a_, which place on the stage with
the arm in the hole, I. The light is now to be reflected into this
concave dish from one of the mirrors, O, below, and it will thus be
strongly condensed upon the object. With this concave speculum any of
the magnifiers in the wheel, P, may be used. When the single silver
concave, _f_, is used, it is screwed to the arm C D, and the one, _e_,
and arm, _a_, are not then applied.

For further directions for the management of microscopes, the light, &c.
see Chap. IV. p. 129, and sequel.


A DESCRIPTION OF CULPEPER’S, OR THE COMMON THREE-PILLARED MICROSCOPE.
Plate IV. Fig. 3.

The only recommendations of this original instrument are, its simple
construction and lowness of price. It gives a pleasing view of the
object. It is precluded by its form from some of the advantages of the
two foregoing instruments, because both the stage and the mirror are
confined. This microscope consists of a large exterior brass body, A B,
supported on three brass scrolls, which are fixed to the stage F; the
stage is supported by three larger scrolls that are screwed to the
mahogany pedestal G H. There is a drawer in the pedestal which holds the
apparatus. The concave mirror, I, is fitted to a socket in the center of
the pedestal. The lower part, B, of the body forms an exterior tube,
into which the upper part of the body, C, slides, and may be moved up or
down by the hand, so as to bring the magnifiers which are screwed on at
D, nearer to, or further from the object.


A LIST OF THE APPARATUS TO CULPEPER’S MICROSCOPE.

Five magnifiers, each fitted in a brass cell; one of these is seen
screwed on at D. Six ivory sliders, _k_, five of them with objects; and
a small ivory box, _m_, containing some spare talcs, and wires for them.
A brass tube, N, to hold the concave speculum. A brass box, M, for the
same speculum. A fish-pan, _c_. A set of glass tubes, _b_. A flat and a
concave glass, both fitted to the stage. A brass cone, _g_, to exclude
superfluous light; it applies at the under side of the stage, F. A brass
box, _p_, with plane and concave glasses for living objects. A pair of
forceps, _q_. A steel wire, _b_, with a pair of nippers at one end, a
point at the other, and a small ivory cylinder, _h_, to fit on the
pointed end of the nippers. A convex lens, E, moveable in a brass
semicircle; this is affixed to a long brass pin, which fits into a hole,
F, on the stage. The uses of the above apparatus have been sufficiently
described in the preceding pages.


TO USE THIS MICROSCOPE.

Screw one of the five cells, which contains a magnifying lens, to the
end, D, of the body; place the slider _i_ or _k_, with the objects,
between the plates of the slider-holder, K. Then, to attain distinct
vision and a pleasing view of the object, adjust the sliding body to the
focus of the lens you are using, by moving the upper part, C, gently up
and down while you are looking at the object, and regulate the light by
the concave mirror, I, below. The image of the objects in this
microscope is seen in a field of view of about six inches in diameter;
but, in the improved ones before described, it is from about twelve to
fifteen inches.

For opake objects, two additional pieces must be used; the first is a
cylindrical tube of brass, represented at N, which fits on the
cylindrical snout above D of the body: the second piece is the concave
speculum, L; this is to be screwed to the lower end of the aforesaid
tube. The upper edge of this tube should be made to coincide with the
line which has the same number affixed to it as the magnifier you are
using; that is, if you are making use of the magnifier marked 5, slide
the tube to the circular line on the tube above D, that is marked also
with No. 5.

The slider-holder, K, should be removed when you are going to view opake
objects, and a plane glass should be placed on the stage in its stead to
receive the object; or it may be placed on the nippers, _b_, the pin of
which fits into the hole in the stage.


A DESCRIPTION OF MARTIN’S IMPROVED SOLAR MICROSCOPE, WHICH IS
CONSTRUCTED TO EXHIBIT TRANSPARENT AND OPAKE OBJECTS. Plate V.

The solar microscope is generally supposed to afford the most
entertainment, on account of the wonderful extent of its magnifying
power, and the ease with which several persons may view each single
object at the same time. The use of it was, however, confined for many
years only to transparent objects. About the year 1774, Mr. B. Martin so
far improved this instrument, as to render it applicable to opake, as
well as to transparent objects, exhibiting the magnified image of either
kind on a large screen. Treating of it himself, he says[34], “With this
instrument all opake objects, whether of the animal, vegetable, or
mineral kingdom, may be exhibited in great perfection, in all their
native beauty; the lights and shades, the prominences and cavities, and
all the varieties of different hues, teints, and colours, heightened by
the reflection of the solar rays condensed upon them.” From its enlarged
dimensions, transparent objects are also shewn with greater perfection
than in the common solar microscope.

  [34] Description and Use of an Opake Solar Microscope. 8vo. 1774.

Plate V. Fig. 1, represents the solar opake microscope, placed together
for exhibiting opake objects.

Fig. 2, is that part called the single tooth and pinion microscope,
which is used for shewing transparent objects; the cylindrical tube, Y,
thereof, being made to fit into the tube E F, Fig. 1. It may be
occasionally used as a hand single, or Wilson’s microscope, and for
which purpose, the handle, _c_, is fitted by a screw to the body at _g_,
and the tube, Y, screwed away.

Fig. 3, the slider which contains the six magnifiers; it fits into a
dove-tail under P, Fig. 2, at the upper part of the microscope.

Fig. 4 represents a brass dove-tail slider, containing a small lens: it
is called a condenser. There are three in number, marked 1 and 2, &c.
corresponding to the number of the magnifiers used: they serve to
condense the sun’s rays strongly upon the object, and enlarge the circle
of light. They slide in at _h_, Fig. 2.

A B C D E F, Fig. 1, represents the body of the solar microscope; one
part thereof, A B C D, is conical, the other, C D E F, is cylindrical.
The cylindrical part receives the tube, G, of the opake object box, or
the tube, Y, of the single microscope, Fig. 2. At the large end, A B, of
the conical part there is a convex lens to receive the rays from the
mirror, and refract them convergingly into the box, H I K L.

N O P is a brass frame which is fixed to the moveable circular plate, _a
b c_; in this frame there is a plane mirror, to reflect the solar rays
through the afore-mentioned lens. This mirror may be moved into the
proper positions for reflecting the solar rays, by means of rack-work
turned by the nuts Q and R. By the nut Q, it may be moved from right to
left; it maybe elevated or depressed by the nut, R. _d_ _e_, two screws
to fasten the microscope to a window-shutter, or a board fitted entirely
before the window.

The box for opake objects is represented as open at H I K L; it contains
a plane mirror, M, for reflecting the light that it receives from the
large lens to the object, and thereby illuminating it; S is a screw to
adjust this mirror to its proper angle for reflecting the light. V X,
two tubes of brass, one sliding within the other, the exterior one in
the box, H I K L; these carry two magnifying lenses: the interior tube
is sometimes taken out, and the exterior one is then used by itself.
Part of this tube may be seen in the plate as within the box, H I K L.

At H, is a brass plate, the back part of which is fixed to a tube, _h_,
containing a spiral wire, which keeps the plate always bearing against
the side, H, of the brass box H I K L. The sliders, with the opake
objects, Fig. 5, pass between this plate and the side of the box; to
apply which, the plate is to be drawn back by means of the nut, g. _k
i_, a door to one side of the opake box, to be opened when adjusting the
mirror, M.

The foregoing pieces constitute the several parts necessary for viewing
opake objects. We shall now proceed to describe the single microscope,
which is used for transparent objects; but, in order to examine these,
the box, H I K L, must be first removed, and in its place we must insert
the tube, Y, of the single microscope, Fig. 2, now to be explained.

Fig. 2 represents a large tooth and pinion microscope; at _m_, within
the body of this microscope, are two thin plates that are to be
separated, in order to let the ivory sliders, Fig. 7, pass between them;
they are pressed together by a spiral spring, which bears up the under
plate, and forces it against the upper one. The slider, Fig. 3, that
contains the magnifiers, fits into a hole at _n_; any of the magnifiers
may be placed before the object, by moving the aforesaid slider: when
the magnifier is at the center of the hole P, a small spring falls into
one of the notches which is on the side of the slider, Fig. 3. At _h_,
slides a condenser, Fig. 4, for condensing the sun’s rays, and enlarging
the field of view on the screen: the number must correspond with that of
the magnifier used. This microscope is adjusted to the focus, while
exhibiting the object, by turning the milled nut O.


APPARATUS TO THE OPAKE SOLAR MICROSCOPE.

The mirror O P, Fig. 1, and square plate, and the tubular body of the
microscope, A F. The opake box and its tube, I K G. The tooth and pinion
or single microscope, Fig. 2. The slider of magnifiers, Fig. 3. The
megalascope magnifier, Fig. 6, fitted to P of Fig. 2. Six ivory sliders
with transparent objects, Fig. 7. Twelve wood sliders with opake
objects, and a brass frame to hold them, Fig. 5. A brass square-formed
slider case, Fig. 8, to hold any animal, piece of ore, or other opake
object, and is to be placed like the other slider at H, Fig. 1. A pair
of nippers and point, Fig. 9, the pin, _a_, of which fits into the hole
of the slider, Fig. 4, and holds before the magnifiers at P, Fig. 2, any
small fly or other complete object to be magnified. A four-glass slider
in a brass frame, Fig. 10, for any animalcula, &c. to be placed between
the plates at _m_, Fig. 2. A set of glass fish tubes, Fig. 11. A pair of
forceps, Fig. 12. Two brass nuts for the window-shutter or board, Fig.
13; and the two brass fastening screws, _d e_, Fig. 1, which may be
either used with or without the above two nuts.

The figures on the plate are about half the original size, and the
apparatus now made by Messrs. Jones packs into a case thirteen inches
long, nine inches broad, and four inches deep. For price, see the list
at the end.


TO USE THE SOLAR MICROSCOPE.

Make a round hole in a window-shutter or window-board, that is opposite
to the meridian sun, or as nearly so as possible, a little larger than
the circle _a b c_; pass the mirror, N O P, through this hole, and apply
the square plate to the shutter; then mark with a pencil the places
which correspond to the two holes through which the screws are to pass;
take away the microscope, and bore two holes at the marked places, large
enough to admit the milled screws, _d e_, to pass through them. These
screws are to pass from the outside of the shutter, to go through it,
and being then screwed into their respective holes in the square plate,
they will, when screwed home, hold it fast against the inside of the
shutter, and thus support the microscope.

Another way, and perhaps more convenient, is to previously screw the two
brass nuts, Fig. 13, to the shutter or window-board, at the inside at a
suitable distance, to receive the two milled screws; these nuts will
always be ready for use, and the operator may in a minute, within his
room, fasten the plate, _a b c_, to the shutter by the two milled
screws, being placed contrarywise.

Screw the conical tube, A B C D, to the circle, _a b c_, and then slide
the tube, G, of the opake box into the cylindrical part, C D E F, of
the body, if opake objects are to be examined; but if transparent
objects are intended to be shewn, then place the tube Y, Fig. 2, within
the tube C D E F. The room is to be darkened as much as possible, that
no light may enter but what passes through the body of the microscope;
for, on this circumstance, together with the brightness of the sun, the
perfection and distinctness of the image in a great measure depend.

We shall first consider the microscope as going TO BE USED FOR OPAKE
OBJECTS. Adjust the mirror, N O P, so as to receive the solar rays, by
means of the two finger-screws or nuts, Q, R; the first, Q, turns the
mirror to the right or left; the second, R, raises or depresses it: this
you are to do, till you have reflected the sun’s light through the lens
at A B, strongly upon a white-paper screen or cloth, from four to eight
feet square (about the latter dimensions for transparent objects) placed
from about five to eight feet distance from the window, and formed
thereon a round spot of light: a white wainscot or wall at a suitable
distance answers very well. An unexperienced observer will find it more
convenient to obtain the light by first forming this spot, before he
puts on either the opake box, or the tooth and pinion microscope, Fig.
2.

Now apply the opake box, and place the object between the plates at H;
open the door, _k i_, and adjust the mirror, M, till you see you have
illuminated the object strongly. If you cannot effect this by the screw
S, you must move the screws Q, R, in order to get the light reflected
strongly from the mirror, N O P, on the mirror M; without which the
latter cannot illuminate the object. The object being strongly
illuminated, shut the door, _k i_, and a distinct view of the object
will soon be obtained on your screen, by adjusting the tubes V X, with
the magnifiers, which is effected by moving them backwards or forwards.

A perfectly round spot of light cannot always be procured in northern
latitudes, the altitude of the sun being often too low; neither can it
be obtained when the sun is directly perpendicular to the front of the
room. As the sun is continually changing its place, it will be
necessary, in order to keep his rays full upon the object, to keep them
continually directed through the axis of the instrument, by turning the
two screws Q and R.

To view transparent objects, remove the opake box, and insert the tube,
Y, of Fig. 2, in its place; put the slider, Fig. 3, into its place at
_n_, a condenser, Fig. 4, at _h_, and the slider with the objects
between the plates at _m_; then adjust the mirror, N O P, as before
directed, by the screws, Q, R, so that the light may pass through the
object; regulate the focus of the magnifier by the pinion, O. The most
pleasing magnifiers in use are the fourth and fifth. The size of the
object is generally from four to eight feet, and may be increased or
diminished by altering the distance of the screen from the microscope;
five or six feet is a convenient distance.

The effect by this sort of microscope is stupendous, and never fails to
excite wonder in an observer at the first view, in seeing a flea, &c.
augmented in appearance to SEVEN, EIGHT, or even TEN FEET in length,
with all its colours, motions, and animal functions, distinctly and
beautifully exhibited.

TO EXAMINE TRANSPARENT OBJECTS OF A LARGER SIZE, or to render the
instrument what is usually called a megalascope, take out the slider,
Fig. 3, from its place at _n_; screw the cell and lens, Fig. 6, into the
hole at P, Fig. 2; remove the glass which is placed at _h_, and regulate
the light and focus agreeable to the foregoing directions.

At C D, is placed a lens for increasing the density of the rays, for the
purpose of burning or melting any fusible substance; this lens must be
removed in most cases, lest the objects should be burnt. The intensity
of the light is also varied by moving the tube G, and Fig. 2, Y, inwards
or outwards.


DESCRIPTION OF THE TRANSPARENT SOLAR MICROSCOPE AND APPARATUS. Plate VI.
Fig. 4, to 14.

The foregoing description will, in great part, answer for this
microscope; but, the dimensions, apparatus, &c. varying in a small
degree from the preceding, a distinct description here, may be
acceptable to those, who possess this sort of microscope only.

A B C D, Fig. 4, represents the body of the microscope, consisting of
two brass tubes. E F is the end of the inner moveable tube; _e f_, that
of the single tooth and pinion microscope. Fig. 5, screws into the end
of this inner tube; at the end, A B, of the external tube there is a
convex lens, to receive the sun’s rays from the mirror, K L, and to
condense them on the object; the end, A B, screws into the circular
plate, G H I. This part may also be used as a single microscope, and may
have at _m_ the handle, _c_, screwed to it. K L, a long frame fixed to
the moveable circular plate, with a plane mirror, to reflect the rays of
the sun on the lens at A B. An endless worm or screw, which is cut on
the lower part of the nut, M, works in a small wheel which is fixed to
the frame, K L, so that by turning the nut, the frame, K L, is moved up
or down: the nut, N, moves the mirror to the right or left. O, P, two
screws to fasten the square plate to the window-shutter.

Fig. 5, the single microscope; _e f_, the end which screws on to the
part, E F, Fig. 4, of the internal tube of the body; _q_, the
dove-tailed slit for receiving the slider, Fig. 8; _g_, the hole in
which the megalascope magnifier, Fig. 6, is to be screwed, when the
slider, Fig. 8, is removed. At _h_, are the moveable plates, between
which the object sliders are placed; under the lowermost of these, the
lens represented at Fig. 11 is to be placed, when the magnifiers in the
slider, Fig. 8, are to be used, _a k_ is a small piece of rack-work,
which is moved backwards and forwards by the pinion fixed to the milled
nut, _b_; by the gradual motion of this rack, the objects are adjusted
to the foci of the different lenses. Fig. 8 is a brass slider, with six
lenses, or magnifying glasses; it is to be inserted into the hole at
_q_; either of the magnifiers may be placed before the object, by
sliding it one way or the other: you may perceive when the glass is in
the center of the eye-hole by a small spring acting upon a notch which
is made on the side of the slider opposite to each lens.


APPARATUS BELONGING TO THIS SOLAR MICROSCOPE.

Square plate and mirror. The body, A D, consisting of two tubes, one
within the other. The single microscope, Fig. 5. The megalascope lens,
Fig. 6. The slider, Fig. 8, with six lenses. The two screws O, P. Six
ivory sliders and a talc box, Fig. 7 and 13. Some glass tubes, Fig. 9. A
slider or brass case, Fig. 10, containing a plane piece of glass, and a
brass slider with holes, into which are cemented small concave glasses,
designed for confining minute insects between the plane and concave
glasses, which are thus preserved from being crushed, or from moving out
of the field of view. Three condensing lenses to enlarge the field of
view, such as Fig. 11, that are fitted to the hole, _l_, of Fig. 5.
Their numbers correspond with the numbers used. Fig. 12, two brass nuts
for the window-shutter or board, to receive the two screws, O and P.


TO USE THE TRANSPARENT SOLAR MICROSCOPE. Fasten the square plate against
the inside of a window-shutter, by the two screws O, P, which are to go
from the outside of the window-shutter through it, and then be screwed
into their respective holes in the square plate at G H I. The mirror is
to be on the outside of the shutter, passing through a hole made for
that purpose. Darken the room; then place a screen at about six or eight
feet distance from the window, the farther it is from it the larger is
the image: now move the mirror, K L, by the two nuts M N, till the sun’s
rays come through the instrument in an horizontal direction to the
screen, forming a round spot thereon; screw the microscope, Fig. 5, into
its place E F; put the slider with the lenses, Fig. 8, at _q_, Fig. 5,
and the object slider between the plates at _h_; adjust the object to
the focus of the magnifying lens by the screw _b_, till the object
appears distinct and clear on the screen. By moving the internal tube of
the body, the object may be placed at different distances from the lens
which is fixed at A B, so as to be sufficiently illuminated, and not
burnt by the solar rays. If the screws O, P, are to pass inside the
room, the two nuts, Fig. 12, must be previously fixed.


THE SCREW BARREL, OR WILSON’S SINGLE POCKET MICROSCOPE. Plate II. B.
Fig. 1 and 2.

This microscope of Mr. Wilson’s is an invention of many years standing,
and was in some measure laid aside, till Dr. Lieberkühn introduced the
solar apparatus to which he applied it, there being no other instrument
at that time which would answer his purpose so well; it is much esteemed
in particular cases. The body of the microscope is represented at A B,
Fig. 1, and is made either of silver, brass, or ivory. C C is a long
fine-threaded male screw, that turns into the body of the microscope. D,
a convex glass at the end of the said screw, on which may be placed, as
occasion requires, one of the two concave apertures of thin brass to
cover the said glass, and thereby diminish the aperture when the
greatest magnifiers are used. E, three thin plates of brass within the
body of the microscope, one whereof is bent to an arched cavity for the
reception of a tube of glass. F, a piece of wood or brass, curved in the
manner of the said plate, and fastened thereto. G, the other end of the
microscope, where a female screw is adapted to receive the different
magnifiers. H, a spiral spring of steel, between the said end, G, and
the plates of brass, E, intended to keep the plates in a due position,
and counteract against the long screw, C. I, a small ivory handle. To
this microscope belong seven different magnifying glasses, six of which
are set in cells, as in Fig. K, and are marked from 1, to 6: the lowest
numbers to the greatest magnifiers. L is the seventh magnifier, set in
the manner of a little barrel, to be held in the hand for viewing any
large object. M is an ivory slider with the objects. Six of these, and
one of brass, are usually sold with this microscope. There is also a
brass slider not shewn in the figure, to confine any small object, that
it may be viewed without crashing or destroying it. N, a pair of
forceps, or pliers, for the taking up of insects or other objects, and
applying them to the sliders or glasses. O, a camel hair brush, to take
up and examine a small drop of liquid, brush the dust away, &c. P is a
glass tube to confine living objects, such as frogs, fishes, &c.

When you view an object, push the ivory slider, in which the said object
is placed, between the two flat brass plates, observing always to put
that side of the slider, where the brass rings are, farthest from the
eye; then screw in the magnifying glass you intend to use at the end of
the instrument G, and looking through it against the light, turn the
long screw, C C, till your object is brought to appear distinct, or to
the true focal distance. To examine any object accurately, view it first
through a magnifier that will shew the whole at once, and afterwards
inspect the several parts more particularly with one of the greatest
magnifiers; for thus you will gain a true idea of the whole, and all
its parts: and, though the greatest magnifiers can shew but a minute
portion of any object at once, such as the claw of a flea, the horn of a
louse, &c. yet by gently moving the slider that contains your object,
the eye will gradually see the whole; and if any part should be out of
the focal distance, the screw, C C, will easily bring it to the true
focus. As objects must be brought very near the glass, when the greatest
magnifiers are used, be particularly careful not to rub the slider
against the glasses as you move it in or out. A few turns of the screw,
C C, will easily obviate this.


DESCRIPTION OF A SCROLL FOR FIXING WILSON’S POCKET MICROSCOPE, AND A
MIRROR FOR REFLECTING LIGHT INTO IT.

A B C, Fig. 2, is a brass scroll, which, for the better conveniency of
carriage, is made to unscrew into three parts, and may be put into the
drawer upon which it stands, with its reflecting mirror D, and Wilson’s
pocket microscope, G. The upper part of the scroll is taken off at B, by
unscrewing half a turn of the screw; then, if lifted up, it will come
out of the socket. The lower part unscrews at C, and the base at E. The
mirror lifts out at F, which, with the scroll, lies in one partition of
the box.

To apply this scroll for use, fix the body of the microscope to the top
thereof by the screw, A, as in Fig. 2, by screwing it in the same hole
as the ivory handle was applied to before. The brass or ivory slider
being fixed as before described, and the microscope placed in a
perpendicular position, move the mirror, D, in such a manner as to
reflect the light of the sky, of the sun, or a candle, directly upwards
through the microscope; by which means the object will be most
conveniently viewed. It is further useful for viewing opake objects, by
screwing the arm, Q R, Fig. 1, into the body of the microscope at G;
then screwing into the round hole, R, that magnifier which you think
will best suit your object, and putting the concave speculum, S, on the
outside of the ring, R, you will observe in the body of the microscope,
between the wood or brass, F, and the end of the male screw, C C, a
small hole, _u_, through which slides the long wire, T, which has a
point at one end, and forceps at the other, that may be used
occasionally as your objects require. When you have fixed this, and your
object on it, turn the arm, R, till the magnifier is brought over the
object; it may be then adjusted to the true focus, by turning the screw,
as before. It must also be brought exactly over the speculum, by turning
the upper part of the scroll to one side, till your object and the two
specula are in one line, as will be found by trial; and then fix it by
the screw, B, at which time the upper surface of the object will be
enlightened by the light reflected from the mirror, D, to the concave
speculum.


DESCRIPTION OF A SMALL MICROSCOPE FOR OPAKE OBJECTS. Plate II. B. Fig. 3
and 4.

A, Fig. 3, is a fixed arm, through which passes a screw, B, the other
end is fastened to the moveable arm, C. D, a nut fitted to the said
screw, which, when turned, will either separate or bring together the
two arms, A C. E, a steel spring, that separates the two sides when the
nut is unscrewed. F, a piece of brass turning round in a spring socket,
moving on a rivet, in which moves a steel wire pointed at the end G, and
the other end a pair of pliers, H: these are either to thrust into, or
take up and hold any object, and may be turned round as required. I, a
ring of brass, with a female screw fixed on an upright piece of the same
metal, turning on a rivet, that it may be set at a due distance when the
least magnifiers are used, and is adapted to the screws of all the
magnifiers.

Fig. 4, K, a concave speculum of polished silver, in the center of which
a lens is placed. On the back of this speculum a male screw, L, is made
to fit the brass ring I, Fig. 3. Four of these specula of different
concavities, with four glasses of different magnifying powers, as the
objects may require. The greatest magnifiers have the least apertures.
M, a round object plate, one side white and the other black, intended to
render objects the more visible, by placing them, if black, upon the
white, and if white, on the black side. A steel spring, N, turns down on
each side, to secure any object; from the object plate there is a hollow
pipe, to screw it on the needle’s point G, Fig. 3. O, a small box of
brass, with a glass on each side, to confine any living object in order
to examine it, having a pipe to screw upon the end of the needle at G.
P, an ivory handle. Q, a pair of pliers to take up any object. R, a soft
hair brush.

To view any object, screw the speculum, with the magnifier you intend to
use, into the brass ring, I; place your object either on the needle G,
in the pliers H, on the object plate M, or in the brass hollow box O, as
may be most convenient; then holding up your instrument by the handle P,
look against the light through the magnifying lens, and by means of the
nut, D, together with moving of the needle at its lower end, the object
may be turned about, raised or depressed, brought nearer the glass, or
put farther from it, till you have the true focal distance, and the
light be seen reflected from the speculum strongly upon the object.[35]

  [35] Opake microscopes are now constructed more elegantly and simply.
  The chief merit of Wilson’s microscope appears, in being particularly
  adapted to minute objects, and these principally of the transparent
  kind; the barrel form is useful for excluding adventitious light.
  Excepting these peculiarities, its general utility is considered far
  short of the universal pocket microscope hereafter to be described.
  EDIT.


OF ELLIS’S SINGLE OR AQUATIC MICROSCOPE. Plate VII. B.

This instrument takes its name from Mr. John Ellis, author of “An Essay
towards a Natural History of Corallines,” and of the “Natural History
of many curious and uncommon Zoophytes.” By this instrument he was
enabled to explain many singularities in the œconomy and construction of
these wonderful productions of nature. To the practical botanist this
instrument is recommended by the respectable authority of Mr. Curtis,
author of the Flora Londinensis, a work which does credit to the author
and the nation. This microscope is simple in its construction, easy in
its use, and very portable; these advantages, as well as some others
which it also has over other portable microscopes, have accelerated the
sale thereof, and caused it to be very much adopted.


DESCRIPTION OF THE VARIOUS PARTS OF THE MICROSCOPE.

K, the box which contains the whole apparatus; it is generally made of
fish-skin; on the top of the box there is a female screw, for receiving
the screw which is at the bottom of the brass pillar A, and which is to
be screwed on the top of the box, K. D, a brass pin which fits into the
pillar; on the top of this pin is a hollow socket to receive the arm
which carries the magnifiers; the pin is to be moved up and down, in
order to adjust the lenses to their focal or proper distance from the
object.

In the representation of this microscope, Plate VII. B. Fig. 1, the pin,
D, is delineated as passing through a socket at one side of the pillar,
A; it is now usual to make it pass down a hole bored through the middle
of the pillar.

E, the bar which carries the magnifying lens; it fits into the socket,
X, which is at the top of the pillar, D. This arm may be moved backwards
and forwards in the socket X, and sidewise by the pin, D; so that the
magnifier, which is screwed into the ring at the end, E, of this bar,
may be easily made to traverse over any part of the object lying on the
stage or plate B. F is a polished silver speculum, with a magnifying
lens placed at the center thereof, which is perforated for this
purpose. The silver speculum screws into the arm E, as at F. G, another
speculum of a different concavity from the former, with its lens. H, the
brass semicircle which supports the mirror, I; the pin, R, affixed to
the semicircle, H, passes through the hole which is towards the bottom
of the pillar, A. B, the stage or the plane on which the objects are to
be placed; it fits into a small dove-tailed arm which is at the upper
end of the pillar, A. C, a plane glass, with a small piece of black silk
stuck on it; this glass is fitted to a groove made in the stage, B. M, a
deep concave glass, to be laid occasionally on the stage instead of the
plane glass, C. L, a pair of nippers; these are fixed to the hole of the
stage, _a_, by the pin K; the steel wire of these nippers slides
backwards and forwards in the socket, and this socket is moveable
upwards and downwards by means of the joint, so that the position of the
object may be varied at pleasure. The object may be fixed in the
nippers, stuck on the point, or affixed by a little gum-water, &c. to
the ivory cylinder, N. O, a small pair of brass forceps to take up
minute objects by. P, a brush to clean the glasses.

To use this microscope; begin by screwing the pillar, A, to the cover
thereof; pass the pin, R, of the semicircle which carries the mirror
through the hole that is near the bottom of the pillar, A; push the
stage into the dove-tail at B; slide the pin into the pillar, then pass
the bar, E, through the socket, X, which is at the top of the pin D, and
screw one of the magnifying lenses into the ring at F.

Now place the object either on the stage, or in the nippers L, and in
such a manner, that it may be as nearly as possible over the center of
the stage; bring the speculum, F, over the part you mean to observe;
then get as much light on the speculum as you can, by means of the
mirror, I; the light received on the speculum is reflected by it on the
object. The distance of the lens, F, from the object is regulated by
moving the pin, D, up and down, until a distinct view of it is obtained.
The rule usually observed is, to place the lens beyond its focal
distance from the object, and then gradually slide it down, till the
object appears sharp and well defined. The adjustment of the lenses to
their foci, and the distribution of the light on the object, are what
require the most attention.

These microscopes are sometimes fitted up with a rack and pinion to the
pillar A, and pin D, for the more ready adjustment of the glasses to
their proper foci.


DESCRIPTION OF LYONET’S ANATOMICAL MICROSCOPE. Plate VI. Fig. 3.

Fig. 3 represents the instrument with which M. Lyonet made his
microscopical and wonderful dissection of the chenille de saule or
caterpillar of the goat moth,[36] of which a specimen is given in Plate
XII. Fig. 1, &c. of this work. This portable instrument needs no further
recommendation. By it, other observers may be enabled to dissect insects
in general with the same accuracy as M. Lyonet, and thus advance the
knowledge of comparative anatomy, by which alone the characteristic,
nature, and rank of animals, can be truly ascertained.

  [36] Phalæna cossus. Linn. 63.

A B is the anatomical table, which is supported by the pillar O N; this
is screwed on the mahogany foot, D C. The table A B, is prevented from
turning round by means of two steady pins; in this table or board there
is a hole, G, which is exactly over the center of the mirror, F E, that
is to reflect the light on the object; the hole, G, is, designed to
receive a flat or a concave glass, on which the objects are to be placed
that you design to examine or dissect. R X Z is an arm formed of several
balls and sockets, by which means it may be moved in every possible
position; it is fixed to the board by means of the screw, H; the last
arm, I Z, has a female screw, into which a magnifier may be screwed, as
at Z. By means of the screw, H, a small motion may be occasionally given
to the arm I Z, for adjusting the lens with accuracy to its focal
distance from the object. Another chain of balls is sometimes used,
carrying a lens to throw light upon the object; the mirror is also so
mounted, as to be taken from its place at K, and fitted on a clamp, by
which it may be fixed to any part of the table, A B.


TO USE THE DISSECTING TABLE. Let the operator sit with his left side
near a light window; the instrument being placed on a firm table, the
side, D L, towards his breast, the observations should be made with the
left eye: this position is well adapted for observing, drawing, or
writing. In dissecting, the two elbows are to be supported by the table
on which the instrument rests, the hands resting against the board, A B,
in order to give it greater stability, as a small shake, though
imperceptible to the naked eye, is very visible in the microscope; the
dissecting instruments are to be held one in each hand, between the
thumb and two fore-fingers. Farther directions are given on the mode of
dissecting small objects in the following chapter.


DR. WITHERING’S BOTANICAL MICROSCOPE. Plate VI. Fig. 1.

This small instrument consists of three brass parallel plates, A, B, C;
two wires, D and E, are rivetted into the upper and lower plate; the
middle plate or stage is moveable on the aforesaid wires, by two little
sockets which are fixed to it. The two upper plates each contain a
magnifying lens, but of different powers; one of these confines and
keeps in their places the fine point F, the forceps G, and the small
knife H.

To use this instrument, unscrew the upper lens, and take out the point,
the knife, and the forceps; then screw the lens on again, place the
object on the stage, and then move it up or down till you have gained a
distinct view of the object, as one lens is made of a shorter focus than
the other; and spare lenses of a still deeper focus are sometimes added.
The principal merit of this microscope is its simplicity.


THE POCKET BOTANICAL AND UNIVERSAL MICROSCOPE.

This pocket instrument is represented at Plate VI. Fig. 2. It is by most
naturalists deemed preferable to Dr. Withering’s, being equally simple,
more extensive in its application, and the stage unincumbered; though
that of M. Lyonet seems better adapted than either to the purposes of
dissection only.

A B, a small arm, carrying three magnifiers, two fixed to the upper
part, as at B, the other to the lower part of the arm, at C; these may
be used separately or combined together, by which you have seven powers.
The arm, A B, is supported by the square pillar I K, the lower end of
which fits into the socket, E, of the foot, F G; the stage, D L, is made
to slide up and down the square pillar. H, a mirror for reflecting light
on the object.

To use this microscope, place the object on the stage, L, reflect the
light on it from the mirror H, and regulate it to the focus, by moving
the stage nearer to or further from the lenses at B C. The ivory sliders
pass under the stage, L; other objects may be fixed in the nippers, M N,
and then brought under the magnifiers; or they may be laid on one of the
glasses fitted to the stage. The apparatus to this instrument consists
of three ivory sliders, a pair of nippers, a pair of forceps, a flat
glass, and a concave ditto, all fitted to the stage, L. By taking out
the pin, M, the pillar, I K, may be turned half round, and the foot, F
G, made to answer as an handle.[37]

  [37] An adjusting screw, Fig. 13*, to move the stage, with other
  additions, are made by Messrs. Jones; and which then, in my opinion,
  constitute the most complete pocket microscope hitherto made; for the
  particulars of which, I refer the reader to their printed description.
  Fig. 14, represents the common flower or insect microscope. There are
  two lenses, _a_ and _b_, that are used separately or conjointly. EDIT.


BOTANICAL MAGNIFIERS.

Since botany has been cultivated with so much ardor, it has been found
necessary to contrive some very portable instrument, by which the
botanist might investigate the object of his pursuits as it rises before
him. Plate VIII. Fig. 7 and 8, represent two of the most convenient
sort.

In the tortoiseshell case, Fig. 7, three lenses are contained, _d_, _e_,
_f_, of different foci, which are all made to turn into the case, and
may be used combined or separately. The three lenses in themselves
afford three different magnifying powers; by combining two and two, we
make three more; and the three together make, a seventh magnifying
power. When the three lenses are used together, it is best to turn them
into the case, and look through the hole, for more distinctness, and the
exclusion of superfluous light. In the case, Fig. 8, are also three
lenses, _g_, _h_, _i_, of different magnifying powers, that all turn up,
and shut into the case; but these are not capable of combination.


DESCRIPTION OF A PORTABLE MICROSCOPE AND TELESCOPE. Plate VIII. Fig. 1,
to 6.

The telescope is one of those which are composed of several sliding
drawers or tubes, for the convenience of being put into the pocket; the
sliding tubes are made of thin brass, the outside tube of mahogany. The
sliding tubes are contrived to stop, when drawn out to a proper length,
so that by applying one hand to the outside tube, and the other hand to
the end of the smallest tube, the telescope may at one pull be drawn out
to its full length; then any of the tubes (that next the eye is most
generally used) may be pushed in gradually, while you are looking
through it, till the object is rendered distinct to the eye. To make the
tubes slide properly, they all pass through short springs or tubes;
these springs may be unscrewed from the ends of the sliding tubes, by
means of the milled edges which project above the tubes, and the tubes
taken from each other if required, and the springs set closer if at any
time they be too weak.

Fig. 5 represents the exterior tube of the telescope, which is to be
unscrewed from the rest, at _m l_, as it does not make any part of the
microscope; the cover, _k_, which protects the object-glass, serves also
as a box to contain two ivory wheels, Fig. 1 and 2, with the objects,
and a small mirror, Fig. 6.

Fig. 4 is a view of this cover when taken off: unscrew the top part of
it, and the mirror, Fig. 6, may be taken out; unscrew the cover of the
lower part, and you will find therein the two circular object-wheels
above mentioned.

Fig. 3 represents the three internal tubes of the telescope, which
constitute the microscopic part thereof. Draw the tubes out in the
manner as shewn in the figure; then at the inside, but at the lower end
of the exterior tube, a, you will find a short tube, which serves as a
stage to hold the object and support the mirror; pull this tube partly
out, and turn it, so that a circular hole which is pierced in it may
coincide with a similar hole in the exterior tube. This tube is
represented as drawn out at Fig. 3, the mirror, Fig. 6, placed therein
at _b c_, and the transparent object-wheel fixed at a.

Fig. 1 represents the slider with transparent objects.

Fig. 2, that with the opake. They are made of ivory, and turn on a pin
at the center; the slit end of this pin fits on the edge of the tube,
which is then to be pushed up, so that the lower end of the exterior
tube may bear lightly on the upper side of the slider, agreeable to the
view which is given at a, Fig. 3. Now push down the second tube till the
milled part falls on the milled edge of the extreme tube, being careful
of the circular hole in the exterior one. Nothing now remains to be done
but to adjust for the focus, which is effected by pushing in the tube R,
and moving only the first, _n_.

The instrument may be used in two ways for transparent objects: first,
in a vertical position, when the light is to be thrown on the object by
the mirror, _b c_; or it may be examined by looking up directly at the
light; in the latter case the mirror must be taken away. In viewing
opake objects the mirror is not used; as much light as possible must be
admitted on them through the circular holes of the tubes. Any object may
be viewed by first pushing in the tube, R, and then bringing the tube,
_n_, to its focal distance from the object. The telescope, when shut up,
is about eight inches in length, and when drawn out, is about twenty
inches. It is of the achromatic construction.


DESCRIPTION OF AN INSTRUMENT FOR CUTTING THIN TRANSVERSE SECTIONS OF
WOOD, Plate IX. Fig. 1.

It consists of a wooden base, which supports four brass pillars; on the
top of the pillars is placed a flat piece of brass, near the middle of
which there is a triangular hole. A sharp knife which moves in a
diagonal direction, is fixed on the upper side of the afore-mentioned
plate, and in such a manner, that the edge always coincides with the
surface thereof. The knife is moved backwards and forwards by means of
the handle, _a_. The piece of wood is placed in the triangular trough,
which is under the brass plate, and is to be kept steady therein by a
milled screw which is fitted to the trough; the wood is to be pressed
forward for cutting, by the micrometer screw, _b_. The pieces of wood
should be applied to this instrument immediately on being taken out of
the ground, or else they should be soaked for some time in water, to
soften them, so that they may not hurt the edge of the knife. When the
edge of the knife is brought in contact with the piece of wood, a small
quantity of spirit of wine should be poured on the surface of the wood,
to prevent its curling up; it will also make it adhere to the knife,
from which it may be removed by pressing a piece of blotting paper on
it.

Fig. 2, is an appendage to the cutting engine, which may be used instead
of the micrometer screw, being by some practitioners preferred to it. It
is placed over the triangular hole, and kept flat down upon the surface
of the brass plate, while the piece of wood is pressed against a
circular piece of brass which is on the under side of it. This circular
piece of brass is fixed to a screw, by which its distance from the flat
plate on which the knife moves may be regulated.[38]

  [38] Many other kinds of cutting engines have been constructed, but
  the specimens from them have not yet appeared with that perfection
  which is requisite to this sort of objects; whether it lies in the
  preparation of the woods, or engine, I do not take upon me to
  determine. Mr. Custance has certainly produced the most exquisite.
  EDIT.



CHAP. IV.

GENERAL INSTRUCTIONS FOR USING THE MICROSCOPE AND PREPARING THE OBJECTS.


As the advantages which are obtained from any instrument are
considerably increased, if it be used by a person who is master of its
properties, attentive to its adjustments, and habituated by practice to
the minutiæ of management, it is the design of this chapter to point out
those circumstances which more peculiarly require the attention of the
observer, and to give such plain directions, as may enable him to
examine any object with ease; to shew how he may place it in the best
point of view, and if necessary, prepare it for observation.

A small degree of diligence will render the observer master of every
necessary rule, and a little practice will make them familiar and
habitual: the pains he takes to acquire these habits will be rewarded by
an increasing attachment to his instrument, and the wonders it displays.
Let him only persevere till he has overcome the natural indolence that
opposes the advancement of every kind of knowledge, and he will most
assuredly find himself very amply recompensed, by the gratification
arising from the acquisition of a science that has the unlimited
treasures of INFINITE WISDOM for the object of its researches: and his
mind being strengthened by the victory it has gained, will be more keen
in perceiving, and more patient in the investigation of truth.

It has long been a complaint,[39] that many of those who purchase
microscopes are so little acquainted with their general and extensive
usefulness, and so much at a loss for objects to examine by them, that
after diverting themselves and their friends some few times with what
they find in the sliders, which generally accompany the instrument, or
perhaps two or three common objects, the microscope is laid aside as of
little further value: whereas no instrument has yet appeared in the
world capable of affording so constant, various, and satisfactory an
entertainment to the mind. This complaint will, I hope, be obviated by
these Essays, in which I have endeavoured to make the use of the
microscope easy, point out an immense variety of objects, and direct the
observer how to prepare them for examination.

  [39] Baker’s Microscope made Easy, p. 51.

The subject treated of in this chapter naturally divides itself into
three heads: the first describes the necessary preparation and
adjustment of the microscope; the second treats of the proper quantity
of the light, and the best method of adapting it to the objects under
examination; and the third shews how to prepare and preserve the various
objects, that their nature, organization, and texture, may be properly
understood.


OF THE NECESSARY PREPARATION OF THE MICROSCOPE FOR OBSERVATION.

We have in the last chapter explained those particulars that constitute
the difference of one microscope from another, and shewn the manner of
using each instrument, and how the several parts are to be applied to
it. We shall now proceed to give some general directions applicable to
every microscope. The observer is therefore supposed to have made
himself master of his instrument, and to know how to adapt the different
parts of the apparatus to their proper places.

The first circumstance necessary to be examined into, is, whether the
different glasses belonging to the microscope are perfectly clean or
not; if they be not clean, they must be taken out and wiped with a piece
of wash leather, taking care at the same time not to soil the surface of
the glass with the fingers: in replacing the glasses, you must also be
careful not to lay them in an oblique situation, to place the convex
sides as before, and if one glass be taken out, wiped, and replaced
before the next, it may prevent the misplacing of them by an unskilful
hand.

The object should be brought as near the center of the field of view as
possible, for there only will it be exhibited in the greatest
perfection.

The eye should be moved up and down from the eye-glass of a compound
microscope, till you find that situation where the largest field, and
most distinct view of the object is obtained; and as the sight differs
very much in different persons, and even in the same person, we
frequently find each eye to have a different sight from the other,
particularly in those called myopes, or short-sighted, every one ought
to adjust the microscope to his own eye, and not depend upon the
situation in which it was placed by another.

Care must be taken not to let the breath fall upon the eye-glass, nor to
hold that part of the body of the microscope where the glasses are
placed with a warm hand, because the damp that is expelled from the
metal by the heat will be attracted and condensed by the glasses, and
obstruct the sight of the object.

The observer should always begin with a small magnifying power; with
this he will gain an accurate idea of the situation and connection of
the whole, and will therefore be less liable to form any erroneous
opinion, when the parts are viewed separately by a deeper lens. By a
shallow magnifier he will also discover those parts which merit a
further investigation. Objects that are transparent will bear a much
greater magnifying power than those that are opake.

Every object should, if possible, be examined first in that position
which is most natural to it: if this circumstance be neglected, very
inadequate ideas of the structure of the whole, as well as of the
connection and use of the parts, will be formed. If it be a living
animal, care must be taken not to squeeze, hurt, or discompose it.

There is a great difference between merely viewing an object by the
microscope, and investigating its nature: in the first, we only consider
the magnified representation thereof; in the second, we endeavour to
analyse and discover its nature and relation to other objects. In the
first case, we receive the impression of an image formed by the action
of the glasses; in the second, we form our judgment by investigating
this image. It is easy to view the image which is offered to the eye,
but not so easy to form a judgment of the things that are seen; an
extensive knowledge of the subject, great patience, and many
experiments, will be found necessary for this purpose: for there are
many circumstances where the images seen may be very similar, though
originating from substances totally different; it is here the
penetration of the observer will be exercised, to discover the
difference, and avoid error.[40]

  [40] Fontana sur les Poisons, vol. ii, p. 245.

Hence Mr. Baker cautions us against forming too suddenly an opinion of
any microscopic object, and not to draw our inferences till after
repeated experiments and examinations of the objects, in all lights and
various positions; to pass no judgment upon things extended by force, or
contracted by dryness, or in any manner out of a natural state, without
making suitable allowances.

The true colour of objects cannot be properly determined when viewed
through the deepest magnifiers; for, as the pores and interstices of an
object are enlarged, according to the magnifying power of the glasses
made use of, the component parts of its substance will appear separated
many thousand times farther asunder than they do to the naked eye; it
is, therefore, very probable, that the reflection of the light from
these particles will be very different, and exhibit different colours.

Some consideration is also necessary in forming a judgment of the motion
of living creatures, or even of fluids, when seen through the
microscope; for as the moving body, and the space wherein it moves, are
magnified, the motion will also be increased.

If an object be so opake as not to suffer any light to pass through it,
as much as possible must be thrown on its upper surface, by that part of
the apparatus which is peculiarly adapted to opake objects. As the
apertures of deep magnifiers are but small, and consequently admit but
little light, they are not proper for the examination of opake objects:
this, however, naturally leads us to our second head.


OF THE MANAGEMENT OF THE LIGHT.

The pleasure arising from a just view of a microscopic object, the
distinctness of vision, &c. depend on a due management of the light, and
adapting the quantity of it to the nature of the object, and the focus
of the magnifier; therefore, an object should always be viewed in
various degrees of light. It is difficult to distinguish in some objects
between a prominency and a depression, between a shadow and a black
stain; and in colour, between a reflection and a whiteness; a truth
which the reader will find fully exemplified in the examination of the
eye of the libellula, and other flies, which will be found to appear
exceedingly different in one position of the light from what they do in
another.

The brightness of an object depends on the quantity of light; the
distinctness of vision, on regulating the quantity to the object; for
some will be lost and drowned, as it were, in a quantity of light that
is scarce sufficient to render another visible, as a different portion
of light under the same apparatus will often exhibit in perfection, or
totally conceal an object in the substance to be examined. This is more
particularly the case with the animalculæ infusoriæ, whose thin and
transparent form blend as it were with the water in which they swim; the
degree of light must therefore be suited to the object, which, if dark,
will be seen best in a strong and full light, but if very transparent,
it should be examined in a fainter.

A strong light may be thrown on an object various ways: first, by means
of the sun and a convex lens; for this purpose, place the microscope
about three feet from a southern window; take a deep convex lens, that
is mounted in a semicircle and fixed on a stand, so that its position
may be easily varied; place this lens between the object and the window,
so that it may collect a considerable number of the solar rays, and
refract them on the object, or the mirror of the microscope. If the
light thus collected from the sun be too powerful, it may be tempered by
placing a piece of oil paper, or a glass lightly greyed, between the
object and the lens: by these means, a convenient degree of light may be
obtained, and diffused in an equal manner over the whole surface of an
object, a circumstance that should be particularly attended to; for if
the light be thrown in an irregular manner, that is, larger portions of
it on some parts than on others, it will not be distinctly exhibited.

Where the solar light is preferred, it will be found very convenient to
darken the room, and to reflect the rays of the sun on the above
mentioned lens, by means of the mirror of a solar microscope fitted to
the window-shutter; for, by this apparatus, the observer will be enabled
to preserve the light on his object, notwithstanding the motion of the
sun.

Cutting off the adventitious light as much as possible, by darkening the
room where you are using the microscope, and admitting the light only
through a hole in the window-shutter, or at most, keeping one window
only open, will also be found very conducive towards producing a
distinct view of the object.

As the motion of the sun, and the variable state of our atmosphere,
render solar observations both tedious and inconvenient, it will be
proper for the observer to be furnished with a large tin lanthorn, made
something like the common magic lanthorn, fit to contain one of
Argand’s lamps.[41] The lanthorn should have an aperture in front, that
may be moved up and down, and capable of holding a lens; by this a
pleasing uniform dense light may be easily procured. The lamp should
move on a rod, that it may be readily elevated or depressed. The
lanthorn may be used for many other purposes, as for viewing of
pictures, exhibiting microscopic objects on a screen, &c.

  [41] The lamp should not be of the fountain kind, because the
  rarefaction of the air in the lanthorn will often force the oil over.

Many transparent objects are seen best in a weak light; among these we
may place the prepared eyes of flies and animalculæ in fluids; the
quantity of light from a lamp or candle may be lessened by removing the
microscope to a greater distance from them, or it may be more
effectually lessened by cutting off a part of the cone of rays that fall
on the object, either by placing the cone, as already described with the
apparatus to different microscopes, under the stage, or by forming
circular apertures of black paper of different sizes, and placing either
a large or small one on the reflecting mirror, as occasion may require.

There is an oblique position of the mirrors, and consequently of the
light, which is easily acquired by practice, but for which no general
rule can be given, that will exhibit an object more beautifully and more
distinctly than any other situation, shewing the surface, as well as
those parts through which the light is transmitted.

A better view of most objects is obtained by a candle or lamp than by
day-light; it is more easy to modify the former than the latter, and to
throw it on the object with different degrees of density. From what has
been said, the reader will have observed the importance of being able to
examine the object in the greatest variety of positions and appearances,
which cannot be effected with equal convenience by any microscope, but
the improved lucernal.


OF THE PREPARATION OF OBJECTS FOR THE MICROSCOPE.

In the preparation of objects, no man was more successful or more
indefatigable than Swammerdam. In minutely anatomizing, in patiently
investigating, and in curiously exhibiting the minute wonders of the
creation, he stands unrivalled, far exceeding all those that preceded,
as well as those which have succeeded him. Deeply impressed and warmly
animated by the amazing scenes that he continually discovered, his zeal
in pursuit of truth was not to be abated by disappointment, or alarmed
by difficulty; and he was never satisfied till he had attained a
rational and clear idea of the organization of the object, whose
structure he wished to explore; his “Book of Nature,” of which a
translation was published by Dr. Hill, is a work of such vast extent of
knowledge, and so excellent in execution, as to raise the highest
admiration in even a superficial observer.

It is much to be regretted, that we are ignorant of the methods he
employed in his investigations. To discover these, the great Boerhaave
examined with a scrupulous attention all the letters and manuscripts of
Swammerdam, and has communicated the result of his researches, which,
though but small, may enable us to form some idea of his immense labours
in the field of science.

For dissecting of small insects he had a brass table, which was made by
that excellent artist, S. Musschenbroeck; to this table were affixed
two brass arms, moveable at pleasure to any part of it. The upper
portion of these arms was constructed so as to have a slow vertical
motion, by which means the operator could readily alter their height, as
he saw most convenient to his purpose; the office of one of these arms
was to hold the minute bodies, and that of the other to apply the lens
or microscope.

His microscopes or lenses were of various foci, diameters, and sizes,
from the least to the greatest, and the best that could be procured in
regard to the exactness of the workmanship, and transparency of the
substance. His mode was, to begin his observations with the smallest
magnifiers, and from thence proceed by degrees to the greatest. Formed
by nature, and habituated by experience, he was so incomparably
dexterous in the management of these instruments, that he made every
observation subservient to the next, and all tend to confirm each other,
and complete the description.

His chief art seems to have been in constructing very fine scissars, and
giving them an extreme sharpness: these he made use of to cut very
minute objects, because they dissected them equally; whereas knives and
lancets, let them be ever so fine and sharp, are apt to disorder
delicate substances, as in going through them, they generally draw after
and displace some of the filaments. His knives, lancets and styles, were
so very fine, that he could not see to sharpen them without the
assistance of a magnifying glass; but with them he could dissect the
intestines of bees with the same accuracy and distinctness that the most
celebrated anatomist does those of large animals. He was particularly
expert in the management of small glass tubes, which were no thicker
than a bristle, and drawn to a very fine point at one end, but thicker
at the other. These he made use of to shew and blow up the smallest
vessels discovered by the microscope, to trace, distinguish, and
separate their courses and communications, or to inject them with very
subtil coloured liquors.

He used to suffocate the insects in spirit of wine, in water, or spirit
of turpentine, and likewise preserved them for some time in these
liquids; by which means he kept the parts from putrefaction, and
consequently from collapsing and mixing together; and added to them
besides such strength and firmness, as rendered the dissections more
easy and agreeable. When he had divided transversely with his fine
scissars the little creature he intended to examine, and had carefully
noted every thing that appeared without further dissection, he then
proceeded to extract the viscera in a very cautious and deliberate
manner, with other instruments of great fineness; first taking care to
wash away and separate with very fine pencils, the fat with which
insects are very plentifully supplied, and which always prejudices the
internal parts before it can be extracted. This operation is best
performed upon insects while in the nympha state.

Sometimes he put into water the delicate viscera of the insects he had
suffocated; and then shaking them gently he procured himself an
opportunity of examining them, especially the air vessels, which by
these means he could separate from all the other parts whole and intire,
to the great admiration of all those who beheld them; as these vessels
are not to be distinctly seen in any other manner, or indeed seen at all
without damaging them, he often made use of water, injected by a
syringe, to cleanse thoroughly the internal parts, then blew them up
with air and dried them, and thus rendered them durable, and fit for
examination at a proper opportunity. Sometimes he has examined with the
greatest success, and made the most important discoveries in insects
that he had preserved in balsam, and kept for years together in that
condition. Again, he has frequently made punctures in other insects with
a very fine needle, and after squeezing out all their moisture through
the holes made in this manner, he filled them with air, by means of very
slender glass tubes, then dried them in the shade, and last of all
anointed them with oil of spike, in which a little rosin had been
dissolved; by which process they retained their proper forms a long
time. He had a singular secret, whereby he could so preserve the nerves
of insects, that they used to continue as limber and perspicuous as ever
they had been.

He used to make a small puncture or incision in the tail of worms, and
after having gently and with great patience squeezed out all their
humours, and great part of their viscera, he then injected them with
wax, so as to give and continue to them all the appearance of healthy
vigorous living creatures. He discovered that the fat of all insects was
perfectly dissoluble in oil of turpentine; thus he was enabled to shew
the viscera plainly; only after this dissolution he used to cleanse and
wash them well and often in clean water. He frequently spent whole days
in thus cleansing a single caterpillar of its fat, in order to discover
the true construction of this insect’s heart. His singular sagacity in
stripping off the skin of caterpillars that were upon the point of
spinning their cones, deserves particular notice. This he effected by
letting them drop by their threads into scalding water, and suddenly
withdrawing them; for, by these means the epidermis peeled off very
easily; and when this was done, he put them into distilled vinegar and
spirit of wine, mixed together in equal portions, which, by giving a
proper firmness to the parts, gave him an opportunity of separating them
with very little trouble from the exuviæ, or skins, without any danger
to the parts; so that by this contrivance, the nymph could be shewn to
be wrapped up in the caterpillar and the butterfly in the nymph. Those
who look into the works of Swammerdam, will be abundantly gratified,
whether they consider his astonishing labour and unremitted ardour in
these pursuits, or his wonderful devotion and piety. On one hand, his
genius urged him to examine the miracles of the great Creator in his
natural, productions; whilst, on the other, the love of that same
all-perfect Being rooted in his mind struggled hard to persuade him that
God alone, and not the creatures, were worthy of his researches, love,
and attention.

M. Lyonet always drowned first those insects he intended to anatomize,
as by these means he was enabled to preserve both the softness and
transparency of the parts. If the insect, &c. be very small, for
instance one-tenth of an inch, or a little more in length, it should be
dissected in water, on a glass which is a little concave; if, after a
few days, there be any fear that the insect will putrefy, it should be
placed in weak spirit of wine, instead of water. In order to fix the
little creature, it must be suffered to dry, and then be fastened by a
piece of soft wax; after which it may be again covered with water.

Larger objects require a different process; they should be placed in a
small trough of thin wood; the bottom of a common chip box will answer
very well, by surrounding the edge of it with soft wax, to keep in the
water or spirit of wine. The insect is then to be opened, and if the
parts be soft, like those of a caterpillar, they should be turned back
and fixed to the trough by small pins; the pins are to be set by a pair
of small nippers, the skin being stretched at the same instant by
another pair of finer forceps; the insect must then be placed in water,
and dissected therein, and after two or three days it should be covered
with spirit of wine, which should be renewed occasionally; by these
means the subject is preserved in perfection, and its parts may be
gradually unfolded, without any other change being perceived than that
the soft elastic parts become stiff and opake, and some others lose
their colour.

M. Lyonet used the following instruments in his curious dissection of
the caterpillar of the cossus. As small a pair of scissars as could be
made, the arms long and fine; a small and sharp knife, the end brought
to a point; a pair of forceps, the ends of which had been so adjusted,
that they would easily lay hold of a spider’s thread or a grain of sand.
But the most useful instruments were two fine steel needles, fixed in
small wooden handles, about 2³⁄₄ of an inch in length.

An observation of Dr. Hooke’s may be very useful if attended to, for
fixing objects intended to be delineated by the microscope. He found no
creature more troublesome to draw than the ant or pismire, not being
able to get the body quite in a natural posture. If, when alive, its
feet were fettered with wax or glue, it would so twist and twine its
body, that it was impossible any way to get a good view of it; if it was
killed, the body was so small, that the shape was often spoiled before
it could be examined. It is the nature of many minute bodies, when their
life is destroyed, for the parts to shrivel up immediately; this is very
observable in many small plants, as well as in insects; the surface of
these small bodies, if porous, being affected by almost every change of
the air, and this is particularly the case with the ant. But if the
little creature be dropped in well rectified spirit or wine, it is
immediately killed; and when taken out, the spirit of wine evaporates,
leaving the animal dry and in its natural posture, or at least so
constituted, that you may easily place it with a pin in what posture you
please.[42]

  [42] Hooke’s Micrographia, p. 203.

Having thus given a general account of the methods used by Swammerdam
and Lyonet, in their examination and dissection of insects, we shall
proceed to shew how to prepare several of their parts for the
microscope, beginning with the WINGS. Many of these are so transparent
and clear, as to require no previous preparation; but the under wings of
those that are covered with elytra, or crustaceous cases, being
constantly folded up when at rest, they must be unfolded before they can
be examined by the microscope; for this purpose a considerable share of
dexterity and some patience is necessary, for the natural spring of the
wings is so strong, that they immediately fold themselves again, except
they are carefully prevented.

One of the most curious and beautiful wings of this kind, is that of the
FORFICULA AURICULARIA, or EARWIG, of which we have given a drawing,
Plate XIV. Fig. 1, represents it considerably magnified, and Fig. 2, the
same object of its natural size. When expanded, it is a tolerably large
wing, yet folds up under a case not one-eighth part of its size. It is
very difficult to unfold these wings, on account of their curious
texture. They are best opened immediately after the insect is killed.
Hold the earwig by the thorax, between the finger and thumb; then with a
blunt-pointed pin endeavour gently to open the wing by spreading it over
the fore-finger, gradually sliding at the same time the thumb over it.
When fully expanded, separate it from the insect by a sharp knife, or a
pair of scissars. The wing should be pressed for some time between the
thumb and finger before it be removed; it may then be placed between two
pieces of paper, and again pressed for at least an hour; after which it
may be put between the talcs without any danger of folding up again.

The wings of the NOTONECTA, or BOAT-FLY, and other water insects, as
well as most species of the grylli, require equal care and delicacy
with that of the earwig to display them properly.

The wings of BUTTERFLIES and MOTHS are covered with very minute scales
or feathers, that afford a beautiful object for the microscope; near the
shoulder, the thorax, the middle of the wing, and the fringes of the
wings, they are generally intermixed with hair. The scales of one part,
also, often differ in shape from those of another; they may be first
scraped off or loosened from the wing with a knife, and then brushed
into a piece of paper with a camel’s hair pencil; the scales may be
separated from the hairs with the assistance of a common magnifying
glass.

The proboscis of insects, as of the CULEX or GNAT, the TABANUS or
BREEZE-FLY, &c. requires much attention and considerable care to be
dissected properly for the microscope; and many must be prepared before
the observer desides upon the situation and shape of the parts; he will
often also be able to unfold in one specimen some parts that he can
scarce discover in another. It is well known that the COLLECTOR OF THE
BEE forms a most beautiful object; a figure of it is given in plate
XIII. Fig. 3, shews it greatly magnified, and Fig. 4, of the natural
size. In it is displayed a most wonderful mechanism, admirably adapted
to collect and extract the various sweets from flowers, &c. To prepare
this, it should first be carefully washed with spirit of turpentine, by
which means it will be freed from the unctuous and melliferous particles
which usually adhere to it; when dry, it must be again washed with a
camel’s hair pencil, to disengage and bring forward the small hairs
which form one part of its microscopic beauty.

The case which encloses THE STING OF THE BEE, the wasp, and the hornet,
are so hard, that it is very difficult to extract them without breaking
or otherwise injuring them. It will be found, perhaps, the best way to
soak the case, and the rest of the apparatus for some time in spirit of
wine or turpentine, then lay it on a piece of clean paper, and with a
blunt knife draw out the sting, holding the sheath by the nail of the
finger, or by any blunt instrument; great care is requisite to preserve
the feelers, which when cleaned add much to the beauty of the object.

The EYES OF THE LIBELLULA or DRAGON-FLY, and different flies, of the
LOBSTER, &c. are first to be cleaned from the blood and other extraneous
matter; they should then be soaked in water for some days, after which
you may separate one or two skins from the eye, which, if they remain,
render it too opake and confused; some care is, however requisite in
this separation, otherwise the skin may be made too thin, so as not to
enable you to form an accurate idea of its organization.

The EXUVIÆ or CAST-OFF OF SKINS of insects are in general very pleasing
objects, and require but little preparation. If they be curled or bent
up, keep them in a moist atmosphere for a few hours, and they will soon
become so relaxed that you may extend them with ease to their natural
positions. The steam of warm water answers the purpose very well.

The BEARD OF THE LEPAS ANATIFERA or BARNACLE is to be soaked in clean
soft water, and frequently brushed, while wet, with a camel’s hair
pencil; it may then be left to dry; after which it must be again brushed
with a dry pencil, to disengage and separate the hairs, which are apt to
adhere together. A picture of this object is represented in plate XIII.
Fig. 1, magnified; Fig. 2, natural size.

To view the MUSCULAR FIBRES, take a very thin piece of dried flesh, lay
it upon a slip of glass, and moisten it with warm water; when this is
evaporated, the vessels will appear plain and more visible, and by
repeated macerations the parts may be further disengaged.

To examine FAT, BRAINS, and other similar substances, we are advised by
Dr. Hooke to render the surface smooth, by pressing it between two thin
plates of flat glass, by which the substance will be made much thinner
and more transparent; otherwise, the parts lying thick one upon the
other, it appears confused and indistinct.

Some substances are, however, so organized, that if their peculiar form
be altered, the parts we wish to discover are destroyed; such as nerves,
tendons, muscular fibres, pith of wood, &c. Many of these are best to be
examined while floating in some convenient transparent fluid. For
instance, very few of the fibres of any of the muscles can be discovered
when they are viewed in the open air; but if placed in water or oil,
great part of their wonderful fabric may be discovered. If the thread of
a ligament be viewed in this manner, it will be seen to consist of an
indefinite number of smooth round threads lying close together.

Objects of an elastic nature should be pulled or stretched out while
they are under the microscope, that the texture and nature of those
parts, whose figure is altered by being thus pulled out, may be more
fully discovered.

To examine BONES with the microscope. These should first be viewed as
opake objects; afterwards, by procuring thin sections, they should be
looked at as if transparent. The sections should be cut in all
directions, and be well washed and cleaned; a degree of maceration will
be useful in some cases. Or the bones may be put in a clear fire till
they are red hot, and then taken out; by these means the bony cells will
appear more conspicuous and visible, being freed from extraneous matter.

To examine the PORES OF THE SKIN. First, cut or pare off with a razor as
thin a slice as possible of the upper skin; then cut a second from the
same place; apply the last to the microscope.

The SCALES OF FISH should be soaked in water for a few days, and then be
carefully rubbed, to clean them from the skin and dirt which may adhere
to them.

To procure the scales of the eel, which are a great curiosity, and the
more so, as the eel was not known to have any, till they were discovered
by the microscope, take a piece of the skin of the eel that grows on the
side, and while it is moist spread it on a piece of glass, that it may
dry very smooth; when thus dried, the surface will appear all over
dimpled or pitted by the scales, which lie under a sort of cuticle or
thin skin; this skin may be raised with the sharp point of a penknife,
together with the scales which will then easily slip out, and thus you
may procure as many as you please.[43]

  [43] Martin’s Micrographia Nova, p. 29.

On the lizard, the guana, &c. are two skins; one of these is very
transparent, the other is thicker and more opake; by separating these we
procure two beautiful objects.

The LEAVES of many trees, and some plants, when dissected, form a very
pleasing object. To dissect them, take a few of the most perfect leaves
you can find, and place them in a pan with clean water; let them remain
three weeks or a month without changing the water, then take them up,
and try if they feel very soft, and appear almost rotten; if so, they
are sufficiently soaked. You are then to lay them on a flat board, and
holding them by the stalk, draw the edge of the knife over the upper
side of the leaf, which will take off most of the skin; turn the leaf,
and do the same with the under side. When the skin is taken off on both
sides, wash out the pulpy matter, and the fibres will be exhibited in a
beautiful manner. By slitting the stalk you may separate the anatomized
leaf into two parts. The skins that are peeled from the fibres will also
make a very good object. The autumn is the best season for the foregoing
operation, as the fibres of the leaves are much stronger at that season,
and less liable to break.

ORES and MINERALS should all be carefully washed and cleansed with a
small brush, to remove any extraneous matter that may adhere to them.
SHELLS may be ground down on a hone, by which their internal structure
will be displayed.

TO VIEW THE CIRCULATION AND EXAMINE THE PARTICLES OF THE BLOOD. The
principal part the observer must aim at, in order to view the
circulation of the blood, is to procure those small animals or insects
that are most transparent, that by seeing through them he may be enabled
to discover the internal motion. The particular kinds best adapted for
the purpose will be enumerated in the descriptive catalogue at the end
of this work.

If a small eel be used for this purpose, it must be cleansed from the
slime which covers it; after which it maybe put either in the fish-pan,
or a glass tube filled with water, and then placed under the microscope.
If the eel be small enough, the circulation may be viewed in the most
satisfactory manner. Leeuwenhoeck has given, in his 112th Epistle, an
accurate description of the blood vessels in part of the tail of an eel.
The same figure may also be seen in my father’s Micrographia Illustrata,
fourth edition, Plate XVII. The tail of any other small fish may be
applied in the same manner, or tied on a slip of flat glass, and be thus
laid before the microscope. Flounders, eels, and gudgeons, are to be had
at almost any time in London. N. B. By filling the tube with water, when
an eel is used, it will in a great measure prevent the sliminess of the
eel from soiling the glass.

To view the particles of the blood, take a small drop of it when warm,
and spread it as thin as possible upon a flat piece of glass. By
diluting it a little with warm water, some of the larger particles will
divide from the smaller, and many of them will be subdivided into still
smaller; or a little drop of blood may be put into a capillary tube of
glass, and be then presented before the microscope. Mr. Baker advises
the mixing the blood with a little warm milk, which he says, will cause
the unbroken particles to be very distinctly seen. But the most accurate
observer of these particles was Mr. Hewson, and he says they have been
termed globules with great impropriety, being in reality flat bodies.
When we consider how many ingenious persons have been employed in
examining the blood with the best microscopes, it appears surprizing
that the figure of the particles should be mistaken; but the wonder is
lessened when we reflect how many obvious things are overlooked, till
our attention is particularly directed towards them; and besides, the
blood in the human subject, and in quadrupeds, is so full of these
particles, that it is with great difficulty they can be seen separate,
until the blood is diluted. It was by discovering a proper method to
effect this, that Mr. Hewson was indebted for his success. He diluted
the particles with serum, in which they would remain undissolved, and as
he could dilute them to any degree with the serum, he could easily
examine the particles distinct from each other; for example, take a
small quantity of the serum of the human blood, and shake a piece of
crassamentum in it, till it be coloured a little with the red particles;
then with a soft hair pencil spread a little of it on a piece of thin
glass, and place this glass under the microscope, in such a manner as
not to be quite horizontal, but rather higher at one end than the other;
by which means the serum will flow from the higher to the lower
extremity, and as it flows, some of the particles will be found to swim
on their flat sides, and will appear to have a dark spot in the middle;
others will turn over from one side to the other, as they roll down the
glass.

Several authors have described an apparatus for viewing the circulation
of the blood in the mesentery of a frog; but as the cruelty attendant on
these kinds of investigations would deprive the humane reader of a great
part of the gratification which might otherwise result from them, he
will probably rest satisfied with the accounts of such experiments to be
met with in authors; especially as there is an abundant variety of
objects on which he may exercise his ingenuity without sacrificing the
nicer feelings of humanity.[44]

  [44] Whatever right mankind may claim over the lives of every creature
  that is placed in a subordinate rank of being to themselves, in
  respect of food and self-defence, as well as for the improvement of
  science, and their judicious and ingenious application to the various
  purposes of use and ornament in human life, we certainly cannot, on
  the principles of reason and justice, assert a privilege to gratify a
  wanton curiosity, or the sports of an inordinate fancy, by the
  exercise of an unnecessary cruelty over them. The immortal SHAKSPEARE,
  in a passage which has often been quoted, says,

  ------- the poor beetle that we tread upon
  In corporal sufferance finds a pang as great
  As when a giant dies.

  It may, however, be doubted whether this particular instance is
  strictly conformable to fact; different animals certainly possess
  different degrees of sensibility, and some are consequently more
  susceptible of pain than others. It is a remarkable circumstance that
  the Hippobosca equina, or Horse-fly, will live, run, nay even
  copulate, after being deprived of its head; most flies will survive
  that loss for some time, and the loss of a leg or two does not prevent
  their appearing as lively and alert as if they had sustained no
  injury. Many insects, on being caught, will freely and voluntarily
  part with their limbs to escape; and it is well known that lobsters
  shed their claws. Numbers of other instances might be adduced, but on
  this subject it may be prudent not to enlarge.

  Montaigne remarks, that there is a certain claim of kindness and
  benevolence which every species of creatures has a right to, from us.
  It is to be regretted, that this general maxim is not more attended to
  in the affairs of education, and pressed home upon tender minds in its
  full extent and latitude; the early delight which children discover in
  tormenting different animals should by all possible means be
  discouraged, as, by being unrestrained in such sports, they may at
  least acquire a habit of confirmed inattention to every kind of
  suffering but their own, if not progressively be led to the
  perpetration of more atrocious acts of cruelty. The supreme court of
  judicature at Athens thought an instance of this sort not below its
  cognizance, and punished a boy for putting out the eyes of a poor bird
  that had unhappily fallen into his hands; and the inimitable HOGARTH,
  “the great painter of mankind,” has in his “Five Stages of Cruelty,”
  admirably depicted the consequences which may result from an early
  indulgence of a propensity towards cruelty.

  In order to awaken as early as possible in the minds of children an
  extensive sense of humanity, it might be prudent to indulge them with
  a view of several sorts of insects as magnified by the microscope, and
  to explain to them that the same marks of divine wisdom prevail in the
  formation of the minutest insect, as in the most enormous leviathan;
  that they are equally furnished with whatever is necessary, not only
  for the preservation, but the happiness of their beings, in that class
  of existence which Providence has assigned them: in a word, that the
  whole construction of their respective organs distinctly and
  decisively, proclaims them the objects of divine benevolence, and
  therefore they justly ought to be so of ours. EDIT.


OF ANIMALCULA IN INFUSIONS, &C.

These require little or no preparation. The first object is to procure
them, the second, to render them visible by the microscope. A few
observations, however, may be of use. Many drops of water may be
examined before any can be found; so that if the observer be too hasty,
he may be easily disappointed, though other parts of the same water may
be fully peopled by them.

The surface of infused liquors is generally covered with a thin
pellicle, which is easily broken, but acquires thickness by standing;
the greatest number of animalcula are generally to be found in this
superficial film.

In some cases it is necessary to dilute the infusions; but this is
always to be done with distilled water, and that water should be
examined in the microscope before it is made use of: the neglect of this
precaution has been a source of many errors.

Animalcula are in general better observed when the water is a little
evaporated, as the eye is not confused, nor the attention diverted by a
few objects. To separate one or two animalcula from the rest, place a
small drop of water on the glass near that of the infusion; make a small
neck or gutter between the two drops with a pin, which will join them
together; then the instant you perceive that an animalculum has
traversed the neck or gutter, and entered the drop, cut off the
communication between the two drops.

To procure the eels in paste, boil a little flower and water, till it
becomes of a moderate consistence; expose it to the air in an open
vessel, and beat it together from time to time, to prevent the surface
thereof from growing hard or mouldy; after a few days, especially in
summer time, it will turn sower, then if it be examined with attention,
you will find myriads of eels on the surface.

To preserve these eels all the year, you must keep the surface of the
paste moist, by putting a little water or fresh paste from time to time
to the other. Mr. Baker advises a drop or two of vinegar to be put into
the paste now and then. The continual motion of the eels, while the
surface is moist, will prevent the paste getting mouldy. Apply them to
the microscope upon a slip of flat glass, first putting on it a drop of
water, taken up by the head of a pin, for them to swim in.

To make an infusion of pepper. Bruise as much common black pepper as
will cover the bottom of an open jar, and lay it thereon about half an
inch thick; pour as much soft water in the vessel as will rise about an
inch above the pepper. The pepper and water are then to be well shaken
together; after which they must not be stirred, but be left exposed to
the air for a few days, when a thin pellicle will be formed on the
surface of the water, containing millions of animalcula.

The observer should be careful not to form a judgment of the nature, the
use, and the operations of small animalcula, from ideas which he has
acquired by considering the properties of larger animals: for, by the
assistance of glasses, we are introduced as it were into a new world,
and become acquainted not only with a few unknown animals, but with
numerous species thereof, which are so singular in their formation and
habits, that without the clearest proofs even their existence would not
be credited; and while they afford fresh instances of the Creator’s
power, they also give further proofs of the limits and weakness of the
human understanding.


DIRECTIONS FOR FINDING, FEEDING, AND PRESERVING THE POLYPES.

These little animals are to be found upon all sorts of aquatic plants,
upon branches of trees, pieces of board, rotten leaves, stones, and
other substances that lie in the water; they are also to be met with
upon the bodies of several aquatic animals, as on the water-snail, on
several species of the monoculus, &c. they generally fix themselves to
these by their tail, so that it is a very good method when you are in
search of the polypes, to take up a great many of these substances, and
put them in a glass full of water. If there be any polypes adhering to
these, you will soon perceive them stretching out their arms, especially
if the glass be suffered to be at rest for a while; for the polypes,
which contract themselves on being first taken out of the water, will
soon extend again when they are at rest.

They are to be sought for in the corners of ditches, puddles, and ponds,
being frequently driven into these with the pieces of wood or leaves to
which they have attached themselves. You may, therefore, search for them
in vain at one period, in a place where at another they will be found in
abundance. They are more easily perceived in a ditch when the sun shines
on the bottom, than at another time. In winter they are seldom to be met
with; about the month of May they begin to appear and increase.

They are generally to be found in waters which move gently; for neither
a rapid stream, nor stagnant waters ever abound with them. As they are
always fixed to some substance by their tails, and are very rarely loose
in the water, taking up water only can signify but little; a
circumstance which has probably been the cause of much disappointment to
those who have searched for them.

The green polypes are usually about half an inch long when stretched
out; those of the second and third sort are between three quarters of an
inch and an inch in length, though some are to be found at times which
are an inch and a half long.

Heat and cold has the same effect upon these little creatures, that it
has upon those of a larger size. They are animated and enlivened by
heat, whereas cold renders them faint and languid; they should therefore
be kept in such a degree of heat, that the water may not be below
temperate.

It is convenient for many experiments to suspend a polype from the
surface of the water. To effect this, take a hair pencil in one hand,
and hold a pointed quill in the other; with the pencil loosen the polype
from the receiver in which it is kept, and gradually raise it near the
top of the water, so that the anterior end may be next the point of the
pencil; then lift it out of the water, and keep it so for a minute;
after which, thrust the point of the pencil, together with the anterior
end, by little and little under water, until no more than about the
twentieth part of an inch of the polype’s tail remains above its
surface; at this instant, with the pointed quill remove that part of the
polype from the pencil which is already in the water, at the same time
blowing against the polype, by which it will be loosened, and remain out
of the water.

When the polypes were first discovered, Mr. Trembley had some difficulty
to find out the food which was proper for them; but he soon discovered,
that a small species of the millepede answered the purpose very well:
the pulices aquatices have also been recommended. The small red worms,
which are to be found on the mud-banks of the Thames, particularly near
the shores, answer the purpose also, they are easily found when the tide
is out, when they rise in such swarms on the surface of the mud, that it
appears of a red colour. These worms are an excellent food for the
polype. If a sufficient quantity be gathered in November, and put into a
large glass full of water, with three or four inches of earth at the
bottom, you will have a supply for the polypes all the winter. They may
also be fed with common worms, with the larva of gnats and other
insects, and even with butcher’s meat, &c. if it be cut small enough.

River, or any soft water, agrees with them; but that which is hard and
sharp prevents their thriving, and generally kills them in a few days.
The worms with which they are fed should be always cleansed before you
feed the polypes with them.

The polypes are commonly infested with little lice; from these it is
necessary to free them, in order to preserve your polypes in a good
state of health. They may be cleansed from the lice by rubbing them with
a hair pencil; this cannot be easily done, unless they adhere to some
substance: so that if they are suspended from the surface of the water,
you must endeavour to get them to fix themselves to a piece of
packthread; when they are fastened thereto, you may then rub them with a
hair pencil, without loosening them from the thread.

The lice which torment the polype are not only very numerous, but they
are also very large proportionably to its size: they may be said to be
nearly as large with respect to them, as a common beetle is to us. If
not rubbed off, they soon cover their bodies, and in a little time
totally destroy them.

To preserve the polypes in health, it is also necessary often to change
the water they are kept in, and particularly after they have done
eating; it is not sufficient to pour the water off, all the polypes
should be taken out, and the bottom and sides of the vessel rubbed from
the slimy sediment adhering thereto; this is caused by their fæces, and
is fatal to them if not cleaned away. The fæces often occasion a species
of mortification, which daily increases; its progress may be stopped by
cutting off the diseased part. To take them out, first loosen their
tails from the sides or bottom of the glass; then take them up one by
one, with a quill cut in the shape of a scoop, and place them in another
glass with clean water; if they cling to the quill, let it remain a
minute or two in the water, and they will soon disengage themselves.

They are preserved best in large glasses that hold three or four quarts
of water; for in a glass of this size the water need not be renewed so
often, particularly, if the fæces are taken out from time to time with
the feathered end of a pen, to which they readily adhere; and further,
the trouble of feeding each individual is in some measure saved, as you
need only throw in a parcel of worms, and let the polypes divide them
for themselves.

To observe with accuracy the various habitudes, positions, &c. of this
little animal, it will be necessary to place some of them in narrow
cylindrical glasses; then, by means of the microscope, Fig. 3. Plate VI.
you may observe them exerting all their actions of life with ease and
convenience; the facility with which the lens of the fore-mentioned
microscope may be moved and placed in any direction, renders it a most
convenient instrument for examining any object that requires to be
viewed in water.

It is also very proper to dry some of them, and place them between talcs
in a slider; this, however requires some dexterity and a little
practice; though, when executed with success, it fully rewards the pains
of the observer. Choose a proper polype, and put it into a small concave
lens, with a drop of water; when it is extended, and the tail fixed,
pour off a little of the water, and then plunge it with the concave into
some spirit of wine contained in the bowl of a large spoon; by this it
is instantly killed, the arms and body contracting more or less; rub it
gently while in the spirit with a small hair pencil, to cleanse it from
the lice.

The difficulty now begins; for the parts of the polype, on being taken
out of the spirit, immediately cling together, so that it is not
practicable to extend the body, and separate the arms on the talc,
without tearing them to pieces; therefore the only method is, to adjust
them upon the talc while in the spirit: this may be done by slipping the
talc under the body of the polype, while it lies in the spirit, and
displaying its arms thereon by the small hair pencil and a pair of
nippers; then lift the talc, with the polype upon it, out of the spirit;
take hold of it with the nippers in the left hand, dip the pencil in the
spirit with the right hand, and therewith dispose of the several parts,
that they may lie in a convenient manner, at the same time brushing away
any lice that may be seen upon the talc; now let it dry, which it does
in a little time, and place the talc carefully in the hole of the
slider. To prevent the upper talc and ring pressing on the polype, you
must cut three pieces of cork, about the bigness of a pin’s head, and
the depth of the polype, and fix them by gum in a triangular position,
partly on the edges of the said talc, and partly to the sides of the
ivory hole itself; the upper talc may then be laid on these corks, and
pressed down by the ring as usual.[45]

  [45] Baker on the Polypes.


OF VEGETABLES.

It were to be wished a satisfactory account could here be given of all
the preparations which are requisite to fit for the microscope the
objects of the vegetable kingdom. Dr. Hill is the only writer who has
handled this subject. I shall, therefore, extract from his “Treatise on
the Construction of Timber,” what he has said; this, together with the
improvements I have made on the cutting engine, will enable the reader
to pursue the subject and extend it further, both for his own pleasure,
and the advantage of the public.


THE MANNER OF OBTAINING THE PARTS OF A SHOOT SEPARATE.

In the beginning of April, take a quantity of young branches from the
scarlet oak, and other trees. These are first cut into lengths, of the
growth of different seasons; and then part is left entire, part split,
and the rest quartered. In this state they are put into a wicker basket,
with large openings, or of loose work, and a heavy stone is put in with
them; a rope is tied to the handle of the basket, and it is thrown into
a brook of running water: at times it is taken up, and exposed a little
to the air; it is frequently shook about under water, to wash off filth;
and once in ten days the sticks are examined.

By degrees the parts loosen from one another, and by gentle rubbing in a
bason of water just warmed, they will be so far separated, that a pencil
brush will perfect the business, and afford pieces of various sizes,
pure, distinct, and clean. One part will in this way separate at one
time, and another, at another; but by turning the sticks to the water,
and repeating the operation, in the course of four or five weeks every
part may be obtained distinct. They are best examined immediately; but
if any one wish to preserve them for repeated inquiries, it may be done
in this manner: dissolve half an ounce of alum in two quarts of water;
drop the pieces thus separated, for a few moments, into this solution,
then dry them upon paper, and put them up in vials of spirit of wine, no
other fluid being so well adapted to preserve these tender bodies.


TO PREPARE THE RIND FOR OBSERVATION.

As the vessels of the rind are of different diameters in various trees,
though their construction and that of the blebs is perfectly the same in
all, it will be best to choose for this purpose the rind of a tree
wherein they are largest. The rind of the ash-leaved maple is finely
suited. A piece of this may be obtained of two inches long, and will
very successfully answer the intention. Such a piece being prepared
without alum or spirit, but dried from the water in which it had been
macerated, it is to be impregnated with lead in the following manner, to
shew the apertures by their colour.

Dissolve one drachm of sugar of lead in an ounce and an half of water;
filter this through paper, and pour it into a tea-cup. Clip off a thin
slice of what was the lower end of the piece of rind as it grew on the
tree, and plunge it near an inch deep into the liquor; keep it upright
between two pieces of stick, so that one half or more may be above the
water; whelm a wine-and-water glass over the tea-cup, and set the whole
in a warm place. When it has stood two days, take it out, clip off all
that part which was in the liquor, and throw it away.

The circumstances here mentioned, trivial as they may seem, must be
attended to: the operation will not succeed, even if the covering-glass
be omitted; it keeps a moist atmosphere about the rind, and makes its
vessels supple.

While this is standing, put into a bason two ounces of quick lime, and
an ounce of orpiment; pour upon them a pint and an half of boiling
water; stir the whole together, and when it has stood a day and a night,
it will be fit for use. This is the “liquor probatorius vini” of some
of the German chymists; it discovers lead when wines are adulterated
with it, and will shew it any where.

Put a little of this liquor in a tea-cup, and plunge the piece of rind
half way into it.

In the former part of this experiment, the vessels of the rind have been
filled with a solution of lead, that makes of itself no visible
alteration in them; but this colourless impregnation, when the orpiment
lixivium gets to it, becomes of a deep brown; the vessels themselves
appear somewhat the darker for it; but these dots, which are real
openings, are now plainly seen to be such, the colour being perfectly
visible in them, and much darker than in the vessels. This object must
be always viewed dry.

If a piece of the rind, thus impregnated, be gently rubbed between the
fingers, till the parts are separated, we shall be able in one place or
other, to get a view of the vessels all round, and of the films which
form the blebs between them.

Every part of the rind, and every coat of it, even the interstitial
place between its innermost coat and bark, are filled with a fine fluid.
The very course and progress of the fluid may be shewn in this part,
even by an easy preparation; only that different rinds must be sought
for this purpose, the vessels in some being larger than in others.
Repeated trials have shewn me that the whole progress may be easily
marked in the three following kinds, with only a tincture of cochineal.

Put half an ounce of cochineal, in powder, into half a pint of spirit of
wine; set it in a warm place, and shake it often for four days; then
filter off the clear tincture. Put an inch depth of this into a cup,
and set upright in it pieces of the rind of ash, white willow, and
ozier, prepared as has been directed, by maceration in water; for in
that way one trouble serves for an hundred kinds. Let an inch of the
rinds also stand up out of the tincture. After twenty-four hours take
them out, clip off the part which was immersed in the fluid, and save
the rest for observation.


TO PREPARE THE BLEA.

Cut the pieces in a fit season, either just before the first leaves of
Spring, or in the Midsummer shooting time. Then we see all the wonders
of the structure; the thousands of mouths which open throughout the
course of these innumerable vessels, to pour their fluid into the
interstitial matter.

These vessels, which are in nature cisterns of sap for the feeding the
growth of the whole tree, are so large, that they are capable of being
filled with coloured wax, in the manner of the vessels in anatomical
injections; and this way they present pleasing objects for the
microscope, and afford excellent opportunities of tracing their course
and structure.


A METHOD OF FILLING THE SAP VESSELS OF PLANTS.

A great many shoots of the scarlet and other oaks are to be taken off in
the Spring; they must be cut into pieces of about two inches in length,
and immediately from the cutting they must drop into some warm rain
water: in this they are to stand twenty-four hours, and then be boiled a
little. When taken out, they are to be tied on strings, and hung up in a
place where the air passes freely, but the sun does not shine. When they
are perfectly dry, a large quantity of green wax, such as is used for
the seals of law deeds, is to be gently melted in an earthen pipkin set
in water; the water to be heated and kept boiling. As soon as the wax
runs, the sticks are to be put in, and they are frequently to be stirred
about. They must be kept in this state about an hour, and then the
pipkin is to be taken out of the water, and set upon a naked fire, where
it is to be kept with the wax boiling for two or three hours; fresh
supplies of the same wax being added from time to time.

After this it is to be removed from the fire, and the sticks immediately
taken out with a pair of nippers; when they are cold, the rough wax
about them is to be broken off. Both ends of each stick are to be cut
off half an inch long, and thrown away, and the middle pieces saved.
These are then to be cut in smaller lengths, smoothed at the ends with a
fine chissel, and many of them split in various thicknesses.

Thus are obtained preparations, not only of great use, but of wonderful
beauty. Many trees this way afford handsome objects as well as the oak;
and in some, where the sap vessels are few, large, and distinct, the
split pieces resemble striped satins, in a way scarce to be credited. It
is in such that the outer coats of these vessels are most happily of all
to be examined.


THE METHOD OF PREPARING SALTS AND SALINE SUBSTANCES, FOR THE VIEWING
THEIR CONFIGURATIONS.

Dissolve the subject to be examined in no larger a quantity of river or
rain water than is sufficient to saturate it; if it be a body easily
dissoluble, make use of cold water, otherwise make the water warm or
hot, or even boiling, according as you find it necessary. After it is
perfectly dissolved, let it rest for some hours, till, if over-charged,
the redundant saline particles are precipitated, and settle at the
bottom, or shoot into crystals; by which means you are most likely to
have a solution of the same strength at one time as at another; that is,
a solution fully charged with as much as it can hold up, and no more;
and by these precautions the configurations appear alike, how often
soever tried: whereas, if the water be less saturated, the proportions,
at different times, will be subject to more uncertainty; and if it be
examined before such separation and precipitation of the redundant
salts, little more will be seen than a confused mass of crystals.

The solution being thus prepared, take up a drop of it with a goose
quill, cut in fashion of a scoop, and place it on a flat slip of glass,
of about three quarters of an inch in width, and between three and four
inches long, spreading it on the glass with the quill, in either a round
or oval figure, till it appears a quarter of an inch or more in
diameter, and so shallow as to rise very little above the surface of the
glass. When it is so disposed, hold it as level as you can over the
clear part of a fire that is not too fierce, or over the flame of a
candle, at a distance proportionable to the degree of heat it requires,
which experience only can direct, and watch it very carefully till you
discover the saline particles beginning to gather and look white, or of
some other colour, at the extremities of the edges; then having adjusted
the microscope before-hand for its reception, armed with the fourth
glass, which is the fittest for most of these experiments, place it
under your eye, and bring it exactly to the focus of the magnifier; and
after running over the whole drop, fix your attention on that side where
you observe any increase or pushing forwards of crystalline matter from
the circumference towards the center.

This motion is extremely slow at the beginning, unless the drop has been
over-heated, but quickens as the water evaporates, and in many kinds,
towards the conclusion, produces configurations with a swiftness
inconceivable, composed of an infinity of parts, which are adjusted to
each other with an elegance, regularity, and order, beyond what the
exactest pencil in the world, guided by the ruler and compass, can ever
equal, or the most luxurious imagination fancy.

When action once begins, the eye cannot be taken off, even for a moment,
without losing something worth observation; for the figures alter every
instant, till the whole process is over; and in many sorts, after all
seems at an end, new forms arise, different entirely from any that
appeared before, and which probably are owing to some small quantity of
salt of another kind, which the other separates from, and leaves to act
after itself has done; and in some subjects three or four different
sorts are observable, few or none being simple and homogeneous.

When the configurations are fully formed, and all the water evaporated,
most kinds of them are soon destroyed again by the moisture or action of
the air upon them; their points and angles lose their sharpness, become
uneven and defaced, and moulder as it were away; but some few are
permanent, and by being inclosed between glasses, they may be preserved
months or even years.

It happens oftentimes that a drop of a saline solution can hardly be
spread on the slip of glass, by reason of the glass’s smoothness, but
breaks into little globules, as it would do were the surface greasy: the
way to prevent this is, by rubbing the broken drop with your finger over
the glass, so as to leave the glass smeared with it; on which smeared
place, when dry, another drop of the solution may be spread very easily
in whatever form is agreeable.

It sometimes happens, that when a heated drop is placed properly for
examination, the observer finds such a cloudiness that he can
distinguish nothing of the object; which is owing to saline steams that
arise from the drop, covering and obscuring the object glass, and
therefore must immediately be wiped away with a soft cloth or leather.

In all examinations of saline solutions by the microscope, even though
made in the day-time, you must use a candle; for the configurations,
being exceedingly transparent, are rendered much more distinguishable by
the brown light a candle affords, than by the more white and transparent
day-light; and besides, either by moving the candle, or turning the
microscope, such light may be varied or directed just as the subject
requires.

It may be also proper to take notice, that no kinds of microscopes are
fit for these observations, but such as have an open stage, whereon the
slips of glass, with the liquor upon them, may be placed readily, and in
a perfect horizontal position; and moreover, where they can be turned
about freely, and without disordering the fluid.



CHAP. V.

THE IMPORTANCE OF NATURAL HISTORY; OF INSECTS IN GENERAL, AND OF THEIR
CONSTITUENT PARTS.


There is no human science which to a rational mind exhibits a greater
variety of attractions, or which is more deserving of general esteem,
than that of NATURAL HISTORY; accordingly we find, that from the
earliest times in which the sciences have been promulgated, it has never
been entirely destitute of its votaries; but, on the contrary, has for
ages employed the lives of many learned men, as being, in fact, the
study of DIVINE WISDOM displayed in the creation: the farther our
researches are carried, the more striking proofs of it every where
abound. In the present century, an æra particularly devoted to
investigation, and propitious to discovery and improvement in various
branches of science, Natural History, so far from being neglected, has
been more generally cultivated, and pursued with an ardor unprecedented
at any former period. Men of the first rank in literature have become
indefatigable labourers in the vast and unbounded field which it
presents to the eyes of an accurate and attentive observer. The animal,
the vegetable, and the mineral kingdoms, have been examined with the
utmost care; that confusion and perplexity which seemed unavoidably to
result from a view of the immense variety of articles contained in each
of those departments, and which frequently deterred persons from
engaging in the pursuit, have been in a great measure removed by the
introduction of systematic arrangement; by these means, the various
subjects are distributed into classes and genera, enabling us to form
distinct and comprehensive ideas of them. To the same methodical plan,
and the nicety of discrimination thence arising, we must attribute the
discovery and description of many new species; this has excited an
emulation still farther to pursue the inquiry, nor need any apprehension
be entertained that the subject will be exhausted, as, no doubt, an
infinite variety still remains unexplored to engage the utmost attention
of the philosophic mind, and fully to compensate the pains bestowed on
so interesting a branch of knowledge.

Of the abundance of articles enumerated in books of Natural History,
there are comparatively few, whose uses are as yet known, or their
properties fully understood. The true naturalist should always bear in
mind that there is a vast difference between retaining the names, and
investigating the nature and peculiar qualities of the creatures to
which they belong. It is highly proper, indeed necessary, that the
multifarious objects of Natural History should be well ascertained and
distinguished with nicety in all their varieties; the science and
admirers of it are, therefore, unquestionably indebted to the able
naturalists who have devoted their time, and exercised their ingenuity
in devising commodious methods of arrangement, and invented systems for
identifying the several subjects with accuracy, and less danger of
fallacy or mistake: but all who are, or would wish to be thought
naturalists, ought to consider, that the best possible mode of
classification is, after all, but an introduction to Natural History.
The ingenious and indefatigable LINNÆUS, who spent his life in
fabricating the curious system now generally adopted, intended it
certainly for the improvement of the science, as a basis for the service
of knowledge and the benefit of mankind; let us be cautious not to
mistake the means for the end, but in the prosecution of the science,
think of the true ends of knowledge, and endeavour to promote our own
instruction, and the advancement of others, with a view to the adoration
of that DIVINE BEING to whom all creation is indebted for existence, and
their application to the occasions and uses of life, all along
conducting and perfecting the study in the spirit of benevolence.

The study of nature, or in other words, a serious contemplation of the
works of GOD, is indeed a great and proper object for the exercise of
our rational faculties; nor can we perhaps employ them better, than in
endeavouring to make ourselves acquainted with the works of that
glorious Being from whom they were received.

Though there is a great deal of pleasure in contemplating the material
world, or that system of bodies into which the DIVINE ARCHITECT has so
admirably wrought the mass of dead matter, with the several relations
which those bodies bear to one another; there is still something more
wonderful and surprizing arising from the contemplation of the animated
world; by which is to be understood all those animals with which every
part of the universe is furnished. The material world is only the shell
of the universe; the animated world are its inhabitants.

Existence is a blessing to those beings only which are endowed with
perception, and appears useless when bestowed upon dead matter, any
farther than as it is subservient to beings which are conscious of their
existence. Thus we find, from the bodies which lie under our
observation, that matter is only made as the basis and support of
animals, and that there is no more of the one than what is necessary for
the exigence of the other.

There are some living creatures which are raised but just above dead
matter; there are many others, but one remove from these, which have no
other senses but those of feeling and taste; others have still an
additional sense of hearing; others of smell, and again others of sight.
It is wonderful to observe, by what a gradual progress life advances
through a prodigious variety of species, before a creature is formed
that possesses all these senses; and even among these, there is such a
different degree of perfection in the senses which one animal enjoys
beyond what appears in another, that, though the sense in different
animals be distinguished by the same common denomination, it seems
almost of a different nature. If, after this, we look into the several
inward qualities of sagacity, or what is generally called instinct, we
find them rising after the same manner imperceptibly one above another,
and receiving additional improvements, according to the species in which
they are implanted. This progress in nature is so very gradual, that
what appears to us the most perfect of an inferior species, comes very
near to the most imperfect, as we are accustomed to call it, of that
which is immediately above it.

The exuberant and overflowing goodness of the SUPREME BEING, whose mercy
extends to all his works, is plainly seen, as before observed, from his
having made so very little matter, at least what falls within our
knowledge, that does not swarm with life; nor is his goodness less
visible in the diversity than in the multitude of living creatures. Had
he only made one species of animals, none else could have enjoyed the
happiness of existence; he has, therefore, included in his creation,
every degree of life, every capacity of being. The whole chasm of
nature, from a plant to a man, is filled up with diverse kinds of
creatures, rising one above another, by such a gentle and easy ascent,
that the little transitions and deviations from one species to the other
are almost insensible. This intermediate space is so prudently managed,
that there is scarce a degree of perception which does not appear in
some one part of the animated world. Is the goodness or the wisdom of
the DIVINE BEING more manifest in this his proceeding?

In this system of creation there is no creature so wonderful in its
nature, and which so much merits our particular attention, as man, who
fills up the middle space between the animal and intellectual nature,
the visible and invisible world; and is that link, in the chain of
beings, which has been often termed the “nexus utriusque mundi.” So that
he, who in one respect being associated with angels and arch-angels, may
look upon a BEING of infinite perfection as his father, and the highest
order of spirits as his brethren, may, in another respect, say to
corruption, “Thou art my father, and to the worm, thou art my mother and
my sister.”[46]

  [46] Spectator, Vol. vii. Numb. 519.

There are, however, many who form their judgments of the works of nature
from external appearance only; hence they imagine, that the greatest and
most magnificent are the only perfect parts of creation, and worthy of
our regard. Hence they confine their attention to the more splendid and
shining branches of philosophy, and are too apt to treat the other parts
with coolness and indifference, not to say contempt.

But surely a true philosopher is one who diligently pursues the study of
nature in all its branches; who can behold with admiration her noblest
productions, yet view with pleasure the smallest of her works: in short,
one who thinks every thing excellent that owes its formation to the GOD
of nature; and we need only take a transient view of the smaller
creatures with which the earth is peopled, to discover that they are
perfect in their kind, and carry about them as strong marks of infinite
wisdom, power, and beneficence as the greatest. It has been justly said,
“that there is not a vegetable that grows, nor an insect that moves, but
what is sufficient to confound the Atheist, and to afford the candid
observer endless materials for devout adoration and praise.”

If we examine insects with attention, we shall soon be convinced of
their divine origin, and survey with admiration the wonderful art and
mechanism of their structure, wherein such a number of vessels, parts,
and movements are collected in a single point; yet are they furnished
with weapons to seize their prey, dexterity to escape their foes, every
thing requisite to perform the business of their stations, and enjoy the
pleasures of their conditions. What a profusion of the richest ornaments
and the gayest colours are often bestowed on one little insect! and yet
there are thousands of others that are as beautiful and wonderful in
their kind; some are covered with shining coats of mail, others are
adorned with plumes of feathers, all of them furnished with every thing
that is proper to make them answer the purposes for which they were
designed.

“After an attentive examination of the nature and fabric of both the
least and largest animals, I cannot,” says the great and excellent
Swammerdam, “but allow the less an equal, perhaps a superior degree of
dignity; whoever duly considers the conduct and instinct of the one,
with the manners and actions of the other, must acknowledge, that they
are all under the direction and controul of a supreme and particular
intelligence; which, as in the largest it extends beyond the limits of
our comprehension, escapes our researches in the smallest. If, while we
dissect with care the larger animals, we are filled with wonder at the
elegant disposition of their limbs, the inimitable order of their
muscles, and the regular direction of their veins, arteries, and
nerves, to what an height is our astonishment raised, when we discover
all the parts arranged in the least, and in the same regular manner! How
is it possible but we must stand amazed when we reflect, that those
little animals, whose bodies are smaller than the point of the
dissecting knife, have muscles, veins, arteries, and every other part
common to the larger animals? Creatures so very diminutive, that our
hands are not delicate enough to manage, or our eyes sufficiently acute
to see them.”

The subserviency of the several beings in the visible creation to one
another; the order in which each of them appears in that appointed
season, when only it can be conducive to the purposes of the rest; and
the preservation of a sufficient number of every species, amidst the
immense havoc that reigns throughout, are, among other things, proofs of
the amazing and incomprehensible wisdom by which they were all formed.
With what pleasure does the mind, accustomed to look up from effects to
their causes, from created beings to the GREAT SOURCE OF BEING, view
that unbounded beneficence, which leaves not the smallest space, capable
of supporting existence of any kind, unplanted with them. There is
hardly any portion of matter, or the least drop of fluid naturally found
on the surface of the earth, that is not inhabited by multitudes of
animals; the subterraneous regions are peopled with their minute
inhabitants, and the abyss of the sea, where no human eye can penetrate,
abounds with animated beings.

The air is usually considered as the great source of destruction to
bodies, whether animal or vegetable; but we do not always understand by
what means or in what manner it is performed. What we term destruction
and decay of one substance, occasions the production and ripening a
multitude of others; wherever the air is admitted, with it a thousand
different things find their way; and what is usually attributed to the
effects of that fluid, is in general occasioned by the multitudes of
bodies with which it is fraught. Redi observed, that flesh preserved
from the access of flies, would bread no maggots; and it is as constant
an observation, that vegetable substances will keep a long time in
whatever state they are, if the air be excluded; but as soon as it is
admitted, they also produce or afford their several kinds either of
animal, or minuter vegetable inhabitants. In the first of these cases,
the parent flies make their way to the exposed flesh, and there deposit
their eggs for the production of a new offspring; in the other,
multitudes of the seeds of minute plants and ovula of animals are
floating in the air, and accompany it wherever it enters; if they be
thus deposited in a place proper for vegetation and accretion, they
burst their inclosures, and attain their growth as regularly as the
seeds of plants deposited in the earth, or the eggs of larger animals in
the nest.

The same wisdom which placed the sun in the center of the system, and
arranged the several planets around him in their order, has no less
shewn itself in the provision made for the food and dwelling of every
bird that roams in the air, and every beast that wanders in the desert;
equally great in the smallest and in the most magnificent objects; in
the star and in the insect; in the elephant and in the fly; in the beam
that shines from heaven and in the grass that cloathes the ground.
Nothing is overlooked, nothing is carelessly performed: every thing that
exists is adapted with perfect symmetry to the end for which it was
designed. This wisdom displayed by the Almighty in the creation, was not
intended merely to gratify curiosity and to raise wonder; it ought to
beget profound submission, and pious trust in every heart.

Histories of the providence and caution, the care and foresight of the
most inconsiderable among animal beings, must surely ever be read with
pleasure and attention, as conveying a most beautiful lesson to a
reflecting mind; it is impossible for any one thus instructed to think
that the Great Being, who has been so careful of those inferior
creatures, can be regardless of him whom he has placed in a station
infinitely more exalted. Throughout the whole system of things, we
behold a manifest tendency to promote the benefit either of the rational
or the animal creation. In some parts of nature, this tendency may be
less obvious than in others. Objects, which to us seem useless or
hurtful, may sometimes occur; and strange it were, if in so vast and
complicated a system, difficulties of this kind should not occasionally
present themselves to beings, whose views are so narrow and limited as
ours. It is well known, that in proportion as the knowledge of nature
has increased among men, these difficulties have diminished.
Satisfactory accounts have been given of many perplexing appearances;
useful and proper purposes have been found to be promoted by objects
which were at first thought to be unprofitable or noxious.[47]

  [47] The great beauty of the dye produced by the cochineal insect, and
  the medical virtues of the cantharis, have occasioned them to be
  considered as very extensive and valuable articles of commerce. The
  benefits derived from the bee and the silk-worm are universally known;
  and spiders, could a method be devised to induce them to live in
  harmony, might also be productive of very essential advantages to the
  human race. EDIT.

Malignant must be the mind of that person; with a distorted eye he must
have contemplated creation, who can suspect that it is not the
production of infinite benignity and goodness. How many clear marks of
benevolent intention appear every where around us? What a profusion of
beauty and ornament is poured forth on the face of nature? What a
magnificent spectacle presented to the view of man? What a supply
contrived for his wants? What a variety of objects set before him, to
gratify his senses, to employ his understanding, to entertain his
imagination, to cheer and gladden his heart? Indeed the very existence
of the universe is a standing memorial of the goodness of the Creator;
for nothing except goodness could originally prompt creation. No new
accession of felicity or glory was to result to him from creatures whom
he made: it was goodness communicating and pouring itself forth,
goodness delighting to impart happiness in all its forms, which in the
beginning created the heaven and the earth. Hence those innumerable
orders of living creatures with which the earth is peopled, from the
lowest class of sensitive being to the highest rank of reason and
intelligence. Wherever there is life, there is some degree of happiness;
there are enjoyments suited to the different powers of feeling; and
earth, air, and water, are with magnificent liberality made to teem with
life.[48]

  [48] Blair’s Sermons.

Let us not then slight, or deem that unworthy our notice, in which
immensity is so conspicuous; or that trivial, in which there is such a
manifestation of infinite beneficence; but rather let those striking
displays of creating goodness call forth, on our part, responsive love,
gratitude, and veneration. To this Great Father of all existence and
life, to Him who hath raised us up to behold the light of day, and to
enjoy all the comforts which his world presents, let our hearts send
forth a perpetual hymn of praise. Evening and morning let us celebrate
Him who maketh the morning and the evening to rejoice over our heads;
who “openeth his hand and satisfieth the desire of every living thing.”
Let us rejoice that we are brought into a world, which is the production
of infinite goodness; over which a supreme intelligence presides; and
where nothing happens but by his divine permission for the wisest
purposes. Convinced that he hateth not the works which he hath made, nor
hath brought creatures into existence merely to suffer unnecessary pain,
let us even in the midst of sorrow, receive with calm submission
whatever he is pleased to send; thankful for what he bestows; and
satisfied that, without good reason, he takes nothing away.

Such, in general, are the effects which meditation on the works of the
creation ought to produce. It presents such an astonishing conjunction
of power, wisdom, and goodness, as we cannot behold without religious
veneration.

In short, the world around us is the mighty volume wherein god hath
declared himself; a picture wherein his perfections are displayed. The
book of nature is written in a character that every one may read; it
consists not of words, but things; it is a school where GOD is the
teacher. All the objects of sense are as the letters of an universal
language, in which all people and nations have a common interest; the
Creator himself has made this use of it, revealing his will by it, and
referring man to it for instruction. Hence the universal agreement
between nature and revelation; hence, also, he that can understand GOD
as the Fountain of truth and the Saviour of men in the holy scriptures,
will be better enabled to understand and adore him as the fountain of
power and goodness in the natural creation. Thus will philosophy and
divinity go hand in hand, and shew that the world was made, as the
scriptures were written, for our instruction; and that the creation of
GOD is a school for Christians, if they use it aright.[49]

  [49] It is a curious, though melancholy subject of contemplation, to
  observe how different have been the sentiments of learned and
  reputedly pious men in times less enlightened; a period when attention
  to, or compassion for, the animal creation could find no place in a
  breast that withheld and denied the mercy of God unto men; when mercy
  itself was deemed heresy! Even in prior and purer times it was
  affirmed that “It is absurd, and a disparagement to the majesty of GOD
  to suppose him to know how many insects there are in the world, or how
  many fishes in the sea; yea, that such an idea of the Omniscience of
  GOD would be foolish flattery to Him, and an injury to ourselves.” For
  the satisfaction of the learned reader, I shall here quote the
  original. “Absurdum est ad hoc Dei deducere Majestatem, ut sciat per
  momenta singula quot nascantur culices, quotve moriantur; quæ cimicum
  et pulicum et muscarum sit in terra multitudo; quanti pisces in aqua
  natent, et qui de minoribus majorum prædæ cedere debeant. Non simus
  tam fatui Adulatores Dei, ut dum potentiam ejus ad ima detrahimus in
  nos ipsos injuriosi simus.” HIERONYMI Comment. in Abac. Lib. 1. Edit.
  Basil. Tom. vi. p. 187. EDIT.


A GENERAL DESCRIPTION OF INSECTS.

The subjects of that part of the creation we are now going to survey,
merit our attention as exceeding the rest of animated nature in their
numbers, the singularity of their appearance, and the variety of their
forms. Earth, air, and water are filled with hosts of them. Being for
the major part very small, and myriads so diminutive, as even to be
imperceptible to the unassisted eye, our knowledge of them, and their
component parts would be extremely circumscribed and imperfect, were it
not for the advantages derived from the use of the microscope; but
happily possessed of this valuable instrument, an inexhaustible source
of entertainment and instruction is afforded to the curious inquirer
into the wonders of nature. The beauties of the minuter parts of
creation are not more hidden from our unassisted sight, than the ends
and purposes of their œconomy from slight and superficial observation;
the microscope does not more amaze and charm as with a discovery of the
first, than the application of our faculties in investigating the
latter.

The name of INSECT has been appropriated to these small animals on
account of the sections or divisions that are observable in the bodies
of the greatest part of them; though, perhaps, it is impossible to find
any precise term that shall embrace the whole genera, as many
particulars must be described before we can attain an exact notion of
these animals and their structure.

An insect is now generally defined to be, an animated being whose head
is furnished with antennæ; that is destitute of bones, but which,
instead thereof, is covered with a very hard skin; that has six or more
feet; and that breathes through spiracula, or pores placed in the side
of the body.

To be more particular, quadrupeds, birds, and fishes have an internal
skeleton of bones, to which the muscles are affixed; but the whole
interior body of insects is composed of soft flesh, and the muscles are
attached to an external skeleton, serving the double purpose of skin and
bone.

Insects are by most writers considered as divided into four principal
parts: the caput, or head; the thorax, or trunk; the abdomen, or belly;
and artus, or limbs. A perfect knowledge of these parts, and their
several subdivisions, is requisite for those who are desirous of forming
accurate ideas of these minute animals, or who wish to arrange them in
their proper classes.

The head is affixed to the thorax by a species of articulation or joint;
it is the principal seat of the senses, and contains the rudiments of
the brain;[50] it is furnished with a mouth, eyes, antennæ, a forehead,
a throat, and stemmata. In the greater part of insects the head is
distinctly divided from the thorax, but in others it coalesces with it.
The head of some insects is very large compared with the size of their
bodies; the proportion between the head of the same insect is not always
similar; in the caterpillars with horny heads it is generally small,
before they moult or change their skin, but much larger after each
moulting. The hardness of the exterior part of the head prevents its
growth before the change; it is, consequently, in proportion to the body
very small; but when the insect is disposing itself for the change, the
internal substance of the head retires inwards to the first ring of the
neck, where it has room to expand itself; so that when the animal quits
the skin, we are surprized with a head twice the former size; and, as
the insect neither eats nor grows while the head is forming, there is
this further circumstance to be remarked, that the body and the head
have each their particular time of growth: while the head expands and
grows, the body does not grow at all; when the body increases, the head
remains of the same size, without any change. The heads of all kinds of
insects, and their several parts, form very pleasing, as well as most
diversified objects for the opake microscope.

  [50] Fabricius Philos. Entomolog. p. 18.

Os, the mouth, is a part of the insect to which the naturalist will find
it necessary to pay a very particular attention; Fabricius goes so far
as to assert that, without a thorough knowledge of the mouth, its form,
and various appendages, it will be impossible ever to discriminate with
accuracy one insect from another. In the structure of the mouth
considerable art and wisdom is displayed; the diversity of the figure is
almost as great as the variety of species. It is usually placed in the
forepart of the head, extending somewhat downwards; in the chermes,
coccus, and some other insects, it is placed under the breast. In some
insects, the mouth is forcipated, to catch, hold, and tear the prey; in
others, aculeated, to pierce and wound animals, and suck their blood; in
others, strongly ridged with jaws and teeth, to gnaw and scrape out
their food, carry burdens, perforate the earth, nay the hardest wood,
and even stones themselves, for habitations and nests for their young.
Others are furnished with a kind of tube or tongue, at one time
moveable, at another fixed; with this they suck the juices of the
flowers: in some again the tongue is so short, as to appear to us
incapable of answering the purpose for which it was formed, and the
oestri appear to have no mouth.

Maxillæ, the jaws, are generally two in number; in some, four; in
others, more. They are sometimes placed in an horizontal, sometimes in a
transverse direction; the inner edge is serrated, or furnished with
small teeth, as in the cicada, nepa, notonecta, cimex, (bug,) aphis, and
remarkably so in some curculeones.

The rostrum, or proboscis, is in general a very curious and complicated
organ; it is the mouth drawn out to a rigid point. In many insects of
the hemiptera class, it is bent down towards the breast and belly. It
has by some writers been considered as serving at once the different
purposes of mouth, nose, and windpipe, enabling the insect to extract
the juices of plants, communicate the sensation of smelling, and convey
air to the body.

Lingua, the tongue, is a taper and compact instrument, by which the
insect obtains the juices of plants. Some can contract or expand it,
others roll it up with dexterity; in some it is inclosed within a
sheath. It is taper and spiral in the butterfly, tubular and fleshy in
the fly; in all affording agreeable amusement for the microscope. To
exemplify which in one or two instances, while it relieves the reader
from the tediousness of narration, will, it is hoped, animate him to
farther researches on the subject.


OF THE PROBOSCIS OF THE BEE.

Every day’s experience shews that the more we penetrate into the hidden
recesses and internal parts of natural bodies, the more we find them
marked with perfection in form and design; of the truth of which
observation the minute apparatus now to be described will, no doubt,
ensure conviction. Swammerdam, when speaking thereof, breaks out into
this pious and humble confession: “I cannot refrain,” says he, “from
confessing to the glory of the Immense and Incomprehensible Architect,
that I have but imperfectly described and represented this small organ;
for, to represent it to the life in its full perfection, as truly most
perfect it is, far exceeds the utmost efforts of human knowledge.”

From what has here been said, it will be easy to perceive, that the
limits of these Essays will not permit our entering largely into a
description of the minute parts of the proboscis of the bee; for an
ample account of which recourse must be had to the works of Swammerdam
and Reaumur. The last writer, like a skilful workman who takes to pieces
a watch which he himself has made, exhibits to you the several parts of
which it is composed, and explains their fitness, their adjustments,
their uses, the play of the pivots, springs, and pillars; for all these
parts, and many more, are to be found in the proboscis of a bee.

It is by this small instrument that the bee procures the food necessary
for its subsistence. In a general view, it may be considered as
consisting of seven pieces; one of these, i i, b c, Fig. 3. Plate XIII.
is placed in the middle; this is supposed to be pervious, and to
constitute what may be properly called the tongue; the other six smaller
parts or sheaths, disposed in three pairs, are placed on each side of
the former: they not only assist in extracting and gathering the honey
from the flowers, but they also protect and strengthen the part. The
proboscis itself is very curiously divided; the divisions are elegant
and regular, and are beset all round with shaggy triangular fibres or
villi, distributed in beautiful order: these divisions, though very
numerous, appear at first sight as a number of different articulations.
The tongue, considered with respect to its length, may be said to have
three articulations; one with the head, then a kind of cylindrical horny
substance, which forms as it were a base for the true tongue, which is
not horny, but soft, fleshy, and pliable.[51]

  [51] Philos. Trans. for 1792, Part I.

The two pieces a a of the exterior sheath are of a substance partly
between bone and horn, and partly membranaceous; they are set round with
fibres, and are furnished with air vessels, which are distributed
through their whole texture; the upper ends f f of this sheath appear to
be a little bent, but can be straitened by the bee when they are applied
to the proboscis. At d d are two articulations, by means of which the
pieces a a may be occasionally bent. The joints contribute towards
bending the proboscis downwards, or rather underneath, against the head.
These sheaths, together with two interior ones e e, assist in defending,
covering, and protecting it from injuries; it is also probable that they
promote the descent of the honey, by pressing the proboscis. The parts k
k of this sheath have been called by some writers the root.

The two parts e e of the interior sheath are placed higher than those of
the exterior one; they originate at g g on the proboscis itself, and
near that part or articulation, by which the bee can upon occasion bend
the proboscis; this sheath, therefore, always moves with the middle part
i i, and is carried forward by it, the exterior sheath being left
behind, because its attachments and origin are below that of the
proboscis. The pieces e e are very similar in structure to those of a a,
only that each of them has on the upper part three joints, the lower one
is much longer than the other two; they are all of them surrounded with
short fibres. The smaller articulated pieces never lie close to the
proboscis, nor cover it, but are only placed near it, the two upper
joints projecting outwards, as in this figure, even when the whole
apparatus is shut up as much as possible. Swammerdam thinks these joints
are of essential use to the bee, acting as it were in the manner of
fingers, and assisting the proboscis, by opening the leaves of the
flowers, and removing other obstructions from it; or like the two fore
feet of the mole, by the help of which it pushes the earth from the
sides both ways, that it may be able with its sharp trunk to search for
its food more conveniently. There are two smaller pieces or sheaths, m
m, near the bottom of the proboscis; these cannot be well seen without
removing the sheath e e.

The proboscis is partly membranaceous, and partly of a gristly nature;
the lower part is formed in such a manner, that it will swell out
considerably, by which means the internal cavity may be prodigiously
enlarged, and rendered capable of receiving a very large quantity of
native and undigested honey, and larger than might be expected from its
size. When the proboscis is shut up and inactive, it is very much
flattened, and is three or four times broader than it is thick. The
edges are always round; it grows tapering, though very gradually,
towards the extremity. The lower and membranaceous part of the trunk has
no fibres or villi on it, but is covered with little protuberant
transparent pimples, that are placed in regular order, and at equal
distances from each other, resembling the little risings observable on
the skin of birds when the feathers have been plucked off. They are
probably glandules, and may have a considerable share in changing or
preparing the honey that is swallowed or taken up by the proboscis. Down
the middle of the proboscis there is a tube of a much harder nature than
the sides, it grows gradually smaller towards the top; at this place the
tongue itself is extremely villous, having some very long villi at the
point; whether they are open tubes, or whether they only serve as so
many claws, to keep it in its proper place while in action, has not been
determined; Mr. John Hunter conceives them to act somewhat like
capillary tubes.

The proboscis terminates in a small cylinder c, at the top of which
there is a little globule or nipple; the bee can contract this
cylindrical part, and the little membrane in which the villi are fixed,
into a much smaller compass, and draw it inwards. The exterior sheaths
lap over each other on the upper part, so that the outside of the
proboscis is protected by a very strong double case, a covering that was
unnecessary for the under part; because when this instrument is in use
the sheaths are opened, but when it is inactive, it is so folded that
the under part is protected by the body of the bee. Withinside the
exterior sheath, and near the bottom q, are two levers, which are fixed
to the end of the proboscis, and by which it is raised and lowered.

Swammerdam thinks that the honey is, as it were, pumped or sucked up by
the bee through the hole at the end b of the tongue; he does not seem to
have discovered the apertures which are on the cylindrical part, near
the end b. But Reaumur is of opinion that it is used to lap up the
fluid, which is then conveyed down between the sheath to the mouth of
the bee. To ascertain this, he placed a bee in a glass tube, the inside
of which was rubbed over with honey, and little pieces thereof placed in
different parts; the bee placed the tongue on the honey; stretching the
end beyond the piece thereof, she bent it into the form of a bow, and
inserted the most convex part of the bow into the honey; by rubbing the
glass backwards and forwards with this part, she soon cleaned that
portion to which it was applied, conveying the honey afterwards to the
throat by the vermicular motion of the tongue.

If you attentively observe a bee, when it has placed itself on a
full-blown flower, the activity and address with which it uses this
apparatus will be very conspicuous. It lengthens the end, and applies it
to the bottom of the petals or leaves of the flower, moving it
continually in a vast variety of different directions; lengthening and
shortening, bending and turning it in every possible way, to adapt it to
the form, &c. of the leaves of the flower. These various movements are
executed with a promptitude that surpasses all description.

The whole of this curious apparatus can be folded up into a very small
compass under the head and neck. The larynx, or that part next to the
head, falls back into the neck, which brings the extreme end of the
first portion of the proboscis within the upper lip, or behind the two
teeth; then the whole of the second part is bent down upon and under the
first part, and the two last sheaths or scales are also bent down over
the whole; so that the true tongue is inclosed laterally by the two
second horny sheaths, and over the whole lie the two first.


OF THE PROBOSCIS OF THE BUTTERFLY.

From the tongue of the bee, let us now direct our attention to that of
the butterfly. This is a spiral substance, somewhat resembling the
spring of a watch when wound up, consisting of eight rounds; by means of
a pin you may gently pull it out to its full length; it grows gradually
tapering from the base, at the end it divides or separates into two
tubes, each furnished with little organs of suction; probably, it is by
these that it extracts the juices on which it feeds, and not by the
extreme ends of the tongue. As the butterfly has no mouth, the proboscis
is the only alimentary organ; when separated from the insect, it will
often unroll itself, then wind and coil itself up again, continuing
these motions at intervals for a considerable time.


OF THE PROBOSCIS OF THE CULEX OR GNAT.

The proboscis of the gnat consists of a great number of extremely
delicate pieces, all concurring to one purpose; this is the instrument
with which it strikes the flesh, and sucks the blood of animal bodies.
The only part exhibited to the naked eye is the sheath, which contains
all the other pieces. This sheath is a cylindrical tube, which is slit
in such a manner, that the insect can separate it from the dart, and
bend it more or less in proportion as the dart is plunged into the
wound. From this tube the sting is darted, which consists of five or six
blades or lancets of exquisite minuteness, lying one over the other;
some of these are sharpened like a two-edged sword, while others are
dentated and barbed at their extremities like the head of an arrow. The
instant the gnat lances this bundle of darts into the flesh, and
penetrates a vein, a drop or two of fluid is by it insinuated into the
wound, by which the blood is attenuated, and the blades acting as so
many capillary tubes, the blood ascends in them, and is conveyed into
the body of the gnat. The injected fluid also by its fermentation causes
that disagreeable and teazing sensation of itching, to which most
persons are subjected, after having sustained an attack from one or more
of these little animals.[52]

  [52] To some persons the gnat (culex pipiens) is so truly formidable,
  that, during the Summer season, they constantly dread the approach of
  evening, that being the time when these blood-thirsty marauders sally
  forth in great numbers, pursue them wherever they go, and exempt no
  part of the face, hands, or even the legs from their depredations; the
  consequences of which are, violent, though happily only local and
  temporary inflammation, attended with insupportable itching, succeeded
  by tumors very similar to those occasioned by a scald; when these have
  discharged the pellucid fluid they contain, the symptoms subside.
  Instances have been known in the vicinity of London, where for several
  days the eyes of the sufferers have been closed, the nose and lips
  violently swelled, the fingers of both hands so affected as to prevent
  their motion, and the legs equally affected. It is remarkable, that in
  general those who thus suffer are not conscious of the moment when
  they receive the injury, but are soon made sensible of it by the
  effect it produces. The approach of the enemy is, however, always
  known by the singing or humming noise they make; the peculiar note of
  which, though rendered very familiar by daily repetition, is never
  esteemed sufficiently musical to render it pleasant or agreeable to
  the destined victims. Amongst the variety of remedies which have been
  recommended for the cure of this temporary evil, Barbut mentions the
  immediate application of volatile alkali, or scratching the part newly
  stung, and washing it with cold water; he likewise asserts, that
  rubbing the part at night with fuller’s earth and water abates the
  inflammation. As preventives are certainly more acceptable than
  curatives, I wish I were enabled to recommend such in the present
  case: in one instance, the application of vinegar every evening before
  sun-set produced a happy effect; possibly washing the parts exposed
  with extract of saturn properly diluted might prove effectual.

  In the Philosophical Transactions for the year 1767, is an account of
  uncommonly numerous swarms of gnats which made their appearance at
  Oxford, during the months of July, August, and September of the
  preceding year. So many myriads sometimes occupied the same part of
  the atmosphere in contiguous bodies, that they resembled a very black
  cloud, greatly darkened the air, and almost totally interrupted the
  solar rays. The repeated bites of these malignant insects were so
  severe, that the legs, arms, heads, and other parts of many persons
  were swelled to an enormous size. The colour of the parts was red and
  fiery, perfectly similar to that of some of the most alarming
  inflammations. Some of these gnats had their bodies greatly distended
  by the uncommon quantities of blood which they had imbibed.

  In short, there is no species of insects more troublesome to mankind
  than the gnat; others give more pain with their stings, but it is only
  when they are attacked, or by accident, that we are stung by them; but
  the gnats thirst for our blood, and follow us in whole companies to
  attack us. In marshy places of this country the limbs of the
  inhabitants are kept swelled during the whole season. In warmer
  climates, particularly the West Indies, they are, under the
  denomination of musquetoes, still more formidable.

  Hooke, in his Micrographia, pleads in justification of these terrible
  little insects, that they do not wound the skin and suck the blood out
  of enmity or revenge, but through mere necessity, and to satisfy their
  hunger:--it may be so; and on this account we cannot annex the
  criminality to them which appertains to such of the highest rank in
  the scale of the animal creation, who, though not urged by the same
  powerful motive, pursue a somewhat similar conduct; but those who have
  experienced their assaults, will scarcely admit this plea as a
  sufficient apology, or feel themselves amicably disposed towards them;
  as, from whatever cause their attacks may proceed, the effect is so
  very unpleasant, as almost to justify the sufferers in addressing them
  in the language of the frogs in the fable to the boys, “Consider, I
  beseech ye, that though this may be sport to you, it is death to us,”
  and ejaculating a wish, that they might be enabled to gratify their
  rapacious appetites by some other means. EDIT.


OF THE PROBOSCIS OF THE TABANUS OR OX-FLY.

Plate XVI. Fig. 1. is a microscopic view of the proboscis of a tabanus,
with which it pierces the skins of horses and oxen, and nourishes itself
with their blood; Fig. 2. the same of the natural size. The singular and
compound structure, together with the wonderful form and exquisite
beauty of this apparatus, discovers such a view of the wisdom, power,
and greatness of its infinite composer, as must strike with admiration
every contemplative observer, and lead him to reflect on the weakness,
impotence, and nothingness of all human mechanism, when compared with
the immense skill and inimitable finishing displayed in the subject
before us. The whole of this formidable apparatus is composed of six
parts, exclusive of the two guards or feelers a a, all of which are
inclosed in a fleshy case, which in the figure is totally removed, as it
contained nothing remarkably different from that of other insects with
two wings. The guards or feelers a a, are of a spungy or fleshy
substance, and are grey, covered with short hairs or villi; they are
united to the head by a little joint of the same texture, which in this
view of the object could not be shewn. These guards are a defence to the
other parts of the apparatus, as they are laid upon it side by side,
whenever the animal stings, and by that means preserve it from external
injury. The two lancets b b and B, evidently open the wound, and are of
a delicate and tender structure, formed like the dissecting knife of the
anatomist, with a sharp point and slender edge, but gradually increasing
to the back. The two instruments, c c and C, appear as if intended to
enlarge the wound, by irritating the parts round it; to accomplish
which, they are jagged or serrated; they may also serve, from their hard
and horny texture, to defend the tube e E, which is of a softer nature
and tubular to admit the blood, and convey it to the stomach; this
delicate part is inclosed in a case d D, which entirely covers it.
These parts are drawn separately at B, C, D, E. De Geer observes, that
it is only the female that sucks the blood of animals; and Reaumur
declares, that having made one disgorge itself, the blood it threw up,
appeared to him to be more than the whole body of the insect could have
contained.

Many other instances of the variety and curious fabrication of this
little organ in different insects, may be found in the works of Reaumur
and De Geer; enough has been said to shew that its mechanism not only
eludes the human eye, but far surpasses every work of man; I shall
therefore proceed, in the next place, to notice


THE ANTENNÆ OF INSECTS.

The antennæ are fine slender horns consisting of several articulations,
moveable in various directions, and constituting one of the
discriminating characteristics of insects. They are beautiful in form,
and of a very delicate structure, so finely articulated, and so minutely
jointed, as to be instantaneously moveable in every direction. They are
situated on the fore part of the head.

The shape, the length, the number, and kind of articulations, not only
vary in different species, but the antennæ of the male generally differ
from those of the female. The greater number of insects have only two
antennæ, but the oniscus, the pagurus, and astacus have four. Regular
rows of minute holes are said to have been discovered in the antennæ.
Several insects cover their eyes with them while they sleep.

We are far from being certain of the use of this organ; some writers
have conjectured that they were the organs of smell and hearing, others
have supposed them appropriated to a delicate species of feeling,
sensible to the least motion or disturbance in the circumambient fluid
in which they move.[53] The following observations throw some light on
this obscure subject. When a wingless insect is placed at the end of a
twig, or in any other situation where it meets with a vacuity, it moves
the antennæ backward and forward, elevates and depresses them from side
to side, and will not advance further lest it should fall. Place a stick
or any other substance near the antennæ, and the insect immediately
applies them to this new object, seems to examine whether it be
sufficient to support its weight, and then proceeds on its journey. From
these observations it would appear that the antennæ assist the insect in
judging of the vicinity of objects, and probably enable them to walk
with safety in the dark.

  [53] Some have thought them intended to defend the eyes, but though
  this might seem probable in regard to the short plumose ones, it can
  never hold good in those that are slender and smooth, which can be of
  no such service. Others have thought them made for wiping and cleaning
  the eyes, but for this purpose they are totally unfit; the fore legs
  of the insect are much better calculated for this use by the hairs or
  fibrilla with which they are covered. Possibly they may be the organs
  of smelling, since we evidently find that many insects possess this
  sense in a very exquisite degree, and yet we see no external organs
  except these to serve that purpose. EDIT.

That these observations are not, however conclusive, appears from an
experiment of a very ingenious naturalist: being desirous of
ascertaining the nature and use of the antennæ and proboscis of a
butterfly, he gently approached one that was flying about in search of
food; he observed that it turned the antennæ about every way, till
coming within scent of a flower, it kept them fixedly bent toward that
object, directing its course by their guidance, till it arrived at the
flower; there they appeared to act as an organ of smell, and that the
minute holes with which it is furnished assisted in promoting this
operation. When the creature had reached the flower, it hovered over it
as with rapture, poising itself quietly upon its wing, like a kite or
hawk in the air; it then dropped suddenly, till it was on a level with
the flower, when it began to agitate its wings briskly and to unroll its
spiral trunk, thrusting it to the bottom of the flower; in a little time
the trunk was rolled up, and again in a moment unrolled; these
operations it repeated till the flower yielded no more juices, the
butterfly then sought for and alighted on another.[54]

  [54] After all, this subject must for the present remain undecided.
  Indeed, the bodies of insects are throughout formed of parts so
  different from ours, that we can probably conceive no more idea of the
  use of some of their organs, than a man born blind or deaf can of the
  senses of vision or hearing. They may have senses different from ours,
  and these may be the organs of them. EDIT.

The differences in the form, &c. of the antennæ are characterized by
naturalists under the following names:

Setaceæ; are those that, like a bristle, grow gradually taper towards
the point or extremity, as in many of the phalenæ. Filiformes;
thread-shaped, and of an uniform thickness. Moniliformes; these are
filiform like the preceding, and of a regular thickness, but consist of
a series of round knobs, like a necklace of beads, as in the chrysomela.
Clavatæ; formed like a club, increasing gradually from the base to the
extremity, as in the papilio, butterfly. Capitatæ; these are also formed
like a club, but the last articulation is larger than the rest,
finishing with a kind of capital or head. Fissiles; these are like the
former, only that the capitulum or head is divided longitudinally into
three or four parts or laminæ, as in the scarabæi. Perfoliatæ; are also
capitated, but have the capitulum divided horizontally, and the laminæ
connected by a kind of thread passing through their center, as in the
dermestes and dytiscus. Pectinatæ; so called from their similitude to a
comb, though they more properly resemble a feather, as in the phalenæ
and elateres; this is most obvious in the male. Aristatæ; such as have
a lateral hair, which is either naked, or furnished with smaller hairs,
as in the fly.

Besides the foregoing terms, the antennæ are called breviores, or short,
when they are shorter than the body; mediocres, or middling, when they
are of the same length; and longiores, when they are longer.

Near the mouth there is also a species of small filiform articulated
antennæ, called the palpi, or feelers; they are generally four in
number, sometimes six; they are placed under and at the sides of the
mouth, which situation, together with their size, sufficiently
distinguish them from the antennæ; they are in continual motion, the
animal thrusting them in every matter, as a hog would its nose, when in
search of food. Some have supposed them to be a kind of hand to assist
in holding the food when it is near the mouth.


OF THE EYES OF INSECTS.

The structure of the eye has always been considered as a wonderful piece
of mechanism; the admirable manner in which those of the human species
are formed, and the nature of vision, are speculations which cannot but
excite the attention of every inquisitive mind. The eyes of insects,
though they differ considerably in their construction from those of
other animals, are no less objects of our admiration. Indeed, among the
exterior parts of insects, none are more worthy of minute investigation,
and very few persons are to be found, who can be insensible to the
beauties of this organ when exhibited under the microscope, as that
instrument alone points out to us the prodigious art employed in their
organization, and evidently shews how many wonders escape the unassisted
sight.

The construction of the eye in insects is not only distinct from that of
other animals, but also differs in different species. They vary in
number, situation, connection, and figure. In other creatures the eyes
are moveable, and two in number, one on each side of the head: in
insects, the genus of cancri excepted, the eyes are fixed; they have no
eye-brows, but the outer coating is hard and transparent.

The greater part of insects have two eyes; in the monoculus they
approach so near to each other, as to appear like one; the gyrinus has
four eyes, the scorpion six, the spider eight, and the scolopendra
three.

Of the eyes of insects, some have them single, that is, placed at a
small distance from each other; while others are furnished with an
indefinite number, all placed in one common case or socket; the latter
are generally termed the reticulated eyes.


OF THE RETICULATED EYES OF INSECTS.

The microscope does not disclose greater wonders, when it exhibits to us
millions of animals invisible to the naked eye, where we should suppose
nothing living existed, than when it discovers to us hidden beauties in
those, which, though they are large enough to be seen by our natural
eye, yet in their several minute parts are no ways discernible, but by
the assistance of glasses.

Thus we readily discern those protuberances on the heads of insects,
which are formed by a congeries of eyes; we can even perceive that they
consist of a number of lines crossing each other with great regularity
and exactness at some little distance, like the meshes of a net. By this
we know that they are reticulated substances; but in what manner they
are so, can only be shewn by the microscope.

The eyes of the libellula, on account of their size, are peculiarly well
adapted for microscopical examination; and, by the assistance of the
instrument, you will find that they are divided into a number of
hexagonal cells, each of which forms a complete eye. The external parts
of these eyes are so perfectly smooth, and so well polished, that, when
viewed as opake objects, they will, like so many mirrors, reflect the
images of all the surrounding objects. The figure of a candle may be
seen on their surface multiplied almost to infinity, shifting its beam
to each eye, according to the motion given to it by the hands of the
observer. Other creatures are obliged to turn their eyes towards the
object, but insects have eyes directed thereto, on whatsoever side it
may appear: they more than realize the wonderful accounts of fabulous
history: poets gave to Argus an hundred eyes; insects are furnished with
thousands, having the benefit of vision on every side with the utmost
ease and speed, though without any motion of the eye or flexion of the
neck.

Each of these protuberances, in its natural state, is a body cut into a
number of faces; like an artificial multiplying glass; but with this
superiority in the workmanship, that as there, every face is plane,
here, every one is convex, immensely more numerous, and contained in a
much smaller space. If one of these protuberant substances be nicely
taken from the head of the insect, washed clean, and placed before the
microscope, its structure is elegantly seen, and it becomes an object
worthy of the highest admiration. You will find that each of the eyes is
an hexagon, varying in its size according to its situation in the head,
and that each of them is a distinct convex lens, and has the same effect
in forming the image of an object placed before it. Of this you will be
convinced, by turning the mirror of the microscope so as to bring the
picture of some well-defined object under the eye; thus, turn it towards
a house, and in the eye of the insect you will perceive the house
diminished to a box, but multiplied into a city; turn it towards a
soldier, and you will have an army of pigmies performing every motion at
the same instant of time; again, turn the mirror towards a candle, and
you will have a beautiful and resplendent blaze from multitudes of
regular flames.

Hooke, Catalan, &c. have shewn that these small eyes are furnished with
every requisite of vision, and that each of them has the use, the power,
and properties of an eye. But we must have recourse to the works of
Swammerdam for a full account of the astonishing organization of the
eyes of insects. Among other things, he has shewn, that under each facet
there is a pyramid of fibres broad at the base, and growing smaller as
it proceeds inwards; the pyramid has the same number of sides as the
eye, and there are as many hexagonal pyramids, as there are small facets
or eyes in the insect. An innumerable number of pulmonary tubes ascend
these fibres, terminating in a white fibrous convex membrane; under
these membranes there is another, still more delicate and transparent;
beneath this, a second species of fibres is transversely applied, like
so many beams to support the pyramids that are laid upon them. Still we
cannot determine with certainty, how these numerous inlets to sight
operate for the service of the animal; they may increase the field of
view, augment the intensity of light, and be productive of advantages of
which we can have no conception.

Hooke computed 14000 of these facets in the two eyes of a drone;
Leeuwenhoek reckoned 6036 in the two eyes of a silkworm, when in its fly
state; in the eyes of the libellula he reckoned 12544 hexangular
lenses.

Swammerdam covered the reticulated eyes of certain insects with black
paint; in this state they flew at random, and seemed to be deprived of
their strength; when they settled, they did not avoid the hand that was
going to take hold of them. Reaumur made similar experiments on the eyes
of bees, which concurred with those of Swammerdam.

Some ephemera flies have four reticulated eyes, two of which are placed
as in the common fly; the other two are placed, one beside the other,
upon the upper part of the head, and have the appearance of a kind of
mushroom, the head extended somewhat beyond the stalk. The first pair
are of a brown colour, those of the mushroom form are of a very
beautiful citron colour.

In some of the fly class, these reticulated eyes are little inferior in
colour and brilliance to the brightest gem. The colour varies in
different species; in some you find it green, in others red, &c. some
have a most elegant changeable colour thrown over them, partly purple,
partly green, and partly of that brassy hue, which is seen on the backs
of some of our beetles, and which is not equalled by any other
production of art or nature.

Fig. 3. Plate XVI. is a representation of a small part of the cornea of
a libellula, as seen by the microscope; the sides of the hexagons in
some positions of the light, appear of a fine gold colour, and divided
into three parallel borders. Fig. 4. the same object of its natural
size.

Fig. 5. Plate XVI. represents a small portion of the cornea of a
lobster; here each of the eyes are small squares, not hexagons; a
conformation which admits a smaller number in the same surface; so great
a number was not necessary in this instance, as the eyes of the lobster
are moveable. Fig. 6. the same of its natural size.


OF THE EYES OF THE MONOCULUS POLYPHEMUS.

The monoculus polyphemus, or king crab, has four eyes, two large and two
small ones; the large eyes are formed of a great number of transparent
amber-like cones, the small ones of a single cone,

“The internal surface of the large eyes, examined with the microscope,
is found to be thick set with a great number of small transparent cones,
of an amber colour, the bases of which stand downward, and their points
upward next the eye of the observer. The cones in general have an
oblique direction, except some in the middle of the cornea, about thirty
in number, the direction of which is perpendicular. The center of every
cone being the most transparent part, and that through which the light
passes, on that account the perpendicular or central cones always appear
beautifully illuminated at their points. In a word, they are all so
disposed, as that a certain number of them receive the light from
whatever point it may issue, and transmit it to the immediate organ of
sight, which we may reasonably suppose is placed underneath them. The
cones are not all of the same length; those on the edges of the cornea
are the longest, from whence they gradually diminish as they approach
the center, where they are not above half the length of those on the
edges.

“The structure of the small eyes being less elaborate, their internal
appearance, when placed in the microscope, will be described in a few
words. They consist of an oval transparent horny plate, of an amber
colour, in the center of which stands a single cone, through which and
the oval plate the light passes.”[55]

  [55] See Mr. André’s paper with a plate, in the Phil. Trans. for 1782,
  page 440.


OF THE EYES OF A SPIDER.

Though the form of this insect is naturally disgusting, yet the eyes
make a beautiful object for the microscope. They have generally eight;
two on the top of the head, that look directly upwards; two in the
front, a little below the foregoing, to discover what passes before it;
on each side a couple more, whereof one points sideways forward, the
other sideways backward; so that the spider can nearly see all around.
These eyes are immoveable, and seem to be formed of a hard transparent
horny substance. A portion of each sphere projects externally beyond the
socket, the largest part is sunk within it. There is round each eye a
circular transparent membrane. Mr. Baker placed the eye of a spider over
a pin-hole made through a piece of card, and then applied it as a lens
to examine objects; he found it magnified the objects greatly, but that
it did not exhibit them distinctly; this he however attributed to the
length of time the spider had been dead whose eye he used. The number of
eyes is not the same in all species of the spider.


OF THE STEMMATA.

It might be imagined, that as every fly has two reticulated eyes, they
could not have occasion for more; but so it has not appeared to that
GREAT BEING who formed them, for many are furnished besides with other
eyes, differing in form and construction from those that are
reticulated.

These were first noticed by M. de la Hire; they are three lucid
protuberances placed on the back part of the head of many insects: their
surface is glossy, of an hemispheric figure, and a coal black colour.
They are transparent, and disposed in a triangular form; by modern
naturalists they are termed stemmata.

Reaumur made experiments on these eyes, similar to those he had made on
the reticulated ones, and found that when the stemmata were covered with
dark varnish, the insects flew but to a small distance, and always at
random.

No insect is, I believe, found with both kind of eyes, unless in its
perfect state: there are many species which are not furnished with
stemmata, gnats and tipulæ are without them.

We are apt to suppose that nature has lavished all her bounty upon her
larger creatures, and left her minims of existence, as Shakspeare
phrases it, unfinished; with what different ideas must those be
impressed, who find the apparatus for vision in these small creatures so
various and so wonderful in their structure, and who must perceive so
much design and order manifested in the position, construction, and
number of these delicate and useful organs.


OF THE BODY OF INSECTS.

The trunk or body of the insect is situated between the head and
abdomen. Naturalists divide it into three parts; the thorax, scutellum,
and sternum.

The thorax is the upper part of the body, it is of various shapes and
proportions; the sides and back of it are often armed with points.

The scutellum, or escutcheon, is the lower part of the body, and is
generally of a triangular form; though it adheres to the thorax, it is
easily distinguished therefrom by its figure, and often by an
intervening suture. It seems intended to assist in expanding the wings.

The sternum is situated on the under part of the thorax; in some species
it is pointed behind, as in the elateres; in others, bifid, as in some
of the dytisci.


OF THE ABDOMEN OF INSECTS.

The abdomen, or under part of the body, contains the stomach, the
intestines, the air vessels, &c. It is composed of several rings or
segments, so that it may be moved in various directions, or lengthened
and shortened at pleasure; in some it is formed of one piece only. It is
perforated with spiracula, or breathing holes, and is terminated by the
tail.

The spiracula are small oblong holes or pores placed singly one on each
side of every ring of the abdomen; these are the means or instruments of
respiration, supply the want of lungs, and form a peculiar
characteristic of insects.


OF THE LIMBS OF INSECTS.

By the limbs are here meant the instruments used by the insect both for
motion and defence. They are, alæ, the wings; halteres, the poisers;
pedes, the legs; cauda, the tail; and aculeus, the sting.


OF THE WINGS OF INSECTS.

The wings are those organs by which the insect is enabled to fly; some
have only two, others are furnished with four, two on each side; these
are, in some, of the same size; in others, the superior ones are much
larger than the inferior: Linnæus has made them the foundation of the
order into which he has divided this numerous class of beings. The
variety in the form and structure of the wings is almost infinite; the
beauty of their colouring, the art with which they are connected to the
body, the curious manner in which some are folded up, the fine
articulations provided for this purpose, by which they are laid up in
their cases when out of use, and yet are ready to be extended in a
moment for flight; together with the various ramifications, by which the
nourishing juices are circulated, and the wing strengthened, afford a
fund of rational investigation highly entertaining; exhibiting,
particularly when examined by the microscope, a most wonderful display
of divine wisdom and power. The more delicate and transparent wings are
covered and protected by elytra, or cases, which are generally hard and
opake. The wings of moths and butterflies are mostly farinaceous,
covered with a fine dust; by the assistance of the microscope, we
discover that this dust is a regular assemblage of organized scales,
which will be more particularly noticed hereafter.

The following names are made use of to describe the different kinds of
wings. They are first distinguished, with respect to their surfaces,
into superior and inferior. The part next the head is called the
anterior part; that nearer the tail, the posterior part. The interior
part is that next the abdomen; the exterior part is the outermost edge.

Those wings are termed plicatiles, which are folded when the insect is
at rest, as in the wasp. Planæ; those which are incapable of being
folded. Erectæ; whose superior surfaces are brought in contact when the
insect is at rest, as in the ephemera, papiliones, &c. Patentes; if they
are extended horizontally when the insect is at rest, as in the phalænæ
geometræ. Incumbentes; those insects which, when they are not in motion,
cover horizontally with their wings the superior part of the abdomen.
Deflexæ; those are also incumbentes, but not horizontally, the outer
edges declining towards the sides, Reversæ, are also deflexæ, with this
addition, that the edges of the inferior wings project from under the
anterior part of the superior ones. Dentatæ; with serrated or scolloped
edges. Caudatæ; in these some of the fibres of the wings are extended
beyond the margin into a kind of tail. Reticulatæ; when the veins or
membranes of the wings put on the appearance of net-work.

The wings are further distinguished by their ornaments, being painted
with spots, maculæ; bands, fasciæ; streaks, strigæ: when these are
extended lengthways, they are called lines, linæ; and if with dots,
punctæ; one or more rings are termed eyes, ocelli; if the spots are
shaped like a kidney, they are termed stigmata.

The elytra, or crustaceous cases of the wings are extended when the
insect flies, and shut when it rests, forming a longitudinal suture down
the middle of the back; they are of various shapes, and distinguished by
the following names:

Abbreviata; when they are shorter than the abdomen. Truncata; when their
extremities terminate in a transverse direct line. Fastigiata; when of
equal or greater length than the abdomen, and terminating in a
transverse line. Serrata; having their external margins edged with teeth
or notches. Spinosa; when their exterior surfaces are covered with small
sharp points. Scabra; when they are very rough. Striata; marked with
slender longitudinal furrows. Porcata; having sharp longitudinal ridges.
Sulcata; with deep furrows. They are likewise distinguished by the
denomination of Hemelytra, when their cases are neither so hard as the
elytra, nor so delicate as the transparent wings.


OF THE HALTERES OR POISERS OF INSECTS.

Under the wings of most insects which have only two, there is a small
head placed on a stalk, frequently under a little arched scale; these
are called halteres, poisers; they appear to be rudiments of the hinder
wings: it has been supposed that they serve to keep the body in
equilibrio when the insect is flying.


OF THE ELYTRA, AND WINGS UNDER THE ELYTRA.

I have already observed, that the delicate and transparent wings of many
insects are covered and protected by elytra, or cases, which also in
some measure act as wings.

These exterior cases are harder and more opake than the wings under
them; they are generally highly polished, and often enriched with
various colours, adorned with ornamental flutings, and studded with
brilliants, whose beauties are beyond description. All these ornaments
are united in the curculio imperialis,[56] or diamond beetle, one of the
richest and most magnificent creatures in nature; the head, the wings,
the legs, &c. are curiously beset with scales of a most splendid
appearance, outvying the ruby, saphire, and emerald, forming in
miniature one of the most noble phenomena that the colours of light can
exhibit. It is said, that in the Brazils, from whence they come, it is
almost impossible to look at them on a sunny day, when they are flying
in little swarms, so great is the glowing splendor of their heightened
colours.

  [56] Fabriciús Spec. Ins. 184. 129.--Drury. Ins. 2 Tab. 33, Fig. 1.

The strength and hardness of the elytra are admirably adapted to the
various purposes of the insects to which they are appropriated; at the
same time that they protect the tender wings beneath them, they serve
as a shield to the body; while the ribs, and other prominences,
contribute to lessen the friction and diminish the pressure to which
they are often exposed. In most of these insects, the under wing is
longer and larger than the exterior one, so that it is obliged to be
bent and folded up, in order to lye under the elytra; for this purpose
they are furnished with strong muscles, and proper articulations to
display or conceal them at pleasure.


OF THE WINGS OF THE FORFICULA AURICULARIA, OR EARWIG.

Fig. 1. Plate XIV. is a magnified view of the wing of an earwig. Fig. 2.
the natural size. Though the insect is so very common, yet few people
know that it has wings, and fewer yet have seen them; they are of a
curious and elegant texture, and wonderful structure. The upper part is
crustaceous and opake, while the other part is beautifully transparent.
They fold up into a very small compass, and lie neatly concealed under
the elytra, which are not more than a sixth part of the wing in size.
They first fold back the parts A B, and then shut up the ribs like a
fan; the strong muscles used for this purpose are seen at the upper part
of the figure. The ribs are extended from the center to the outer edge,
others are extended only from the edge about half-way; but they are all
united by a kind of band, at a small, but equal distance from the edge;
the whole evidently contrived to strengthen the wing, and facilitate the
various motions thereof; so that, in these wings you find all the
motions that are in the most elaborate and portable umbrellas, executed
with a neatness and elegance surpassing description. The earwig is a
very destructive animal, doing considerable injury to most kinds of wall
fruit, to carnations, and other fine flowers, &c. and as they only feed
in the night, they escape the search of the gardener. Reeds open at both
ends, and placed among fruit trees, are a good trap for them, as they
croud into these open channels, and may be blown out into a tub of
water. As they conceal themselves in the day-time, those that are
curious in flowers place tobacco pipes, lobster claws, &c. on the top of
their garden sticks, in order to catch them. This insect differs very
little in appearance in its three different states. De Geer asserts,
that the female sits on her eggs, and broods over the young ones, as a
hen does over her chickens.


OF THE WINGS OF THE HEMEROBIUS PERLA.

So infinite is the variety displayed in the disposition, structure, and
ornaments of the wings of insects, that only to enumerate them would
fill many pages; I must leave this subject to be further pursued by the
reader, contenting myself with presenting him with the view of a wing of
the hemerobius perla, as it appears under the microscope. The insect to
which it belongs, has acquired the name of hemerobius, from the
shortness of its life, as it seldom lives more than two or three days in
the fly state. Linnæus has placed it in his fourth class, among those
insects which have four transparent wings and no sting. The body of the
insect is of a fine green colour; the eyes appear like two delicate
beads of burnished gold, whence it is by many called the golden eye. The
wings are delicate and elegant, nearly of a length, and exactly similar;
they are composed of a beautiful thin transparent membrane, furnished
with slender fine ribs, regularly and elegantly disposed, adorned with
hairs, and slightly tinged with green. Fig. 1. Plate XV. exhibits its
magnified appearance; Fig. 2. the natural size.


OF THE WINGS OF MOTHS AND BUTTERFLIES.

The wings of these insects are mostly farinaceous, being covered with a
fine dust, which renders them opake, and produces those beautiful and
variegated colours by which they are so richly adorned, and so profusely
decked. If this be wiped off, you find the remaining part, or naked
wing, to consist of a number of ribs, like those in the leaves of
plants; but of a crustaceous or talcy nature; the largest rib runs along
and fortifies the exterior edge of the wing; the interior edge is
strengthened by a smaller vessel or rib. The ribs are all hollow, by
which means the wing, though comparatively large, is very light. The
substance between the ribs, and which constitutes the body of the wing,
resembles talc,[57] surprizingly thin and transparent; as this is
extremely tender, one use of the scales may be to protect it from
injuries. When the moth emerges from the chrysalis, the wings are soft
and thick, and if they be examined in that state, will be found to
consist of two membranes, that may be raised up and separated, by
blowing between them with a small tube: the ribs lie between these
membranes. You may with the assistance of glasses discover certain
strait and circular rows of extremely minute holes, running from rib to
rib, or forming figures in the intermediate spaces, which seem to answer
to the figures and variegations on the complete wing, and are probably
the sockets for the stalks or stems of the small scales.

  [57] As the author’s idea of this substance being of the nature of
  talc, does not appear correct, and I cannot find that entomologists
  are agreed in the definition of it, I shall just give the following
  extract on the subject from the Cyclopœdia by Rees, and submit the
  decision to the reader.

  “The substance which connects and fills up the spaces between these
  ribs, is of so peculiar a nature, that it is not easy to find any name
  to design it by, at least there is no substance that enters the
  composition of the bodies of the larger animals, that is at all
  analogous to it. It is a white substance, transparent and friable, and
  seems indeed to differ in nothing from that of the large and thick
  ribs, but in that it is extended into thin plates; but this is saying
  little toward the determining what it really is, since we are as much
  at a loss to know by what name to call the substance they are composed
  of. Malpighi indeed calls them bones; but though they do serve in the
  place of bones, rendering the wing firm and strong, &c. yet, when
  strictly examined, they do not appear to have any thing of the
  structure of bones, but appear rather of the substance of scales, or
  of that sort of imperfect scales, of which, the covering of
  crustaceous insects is composed.” EDIT.

Ever since the microscope was invented, the dust that covers these wings
has engaged the attention of microscopic observers; as by this
instrument it is found to be a regular collection of organized scales of
various shapes, and in whose construction there is as much symmetry, as
there is beauty in their colours. A view of some of these scales, as
they appear in the microscope, is exhibited at F E H I, in Fig. 7. Plate
XVI. and in Fig. 8. of the natural size. Their shapes are not only very
different in moths of various species, but those on the same moth are
also found to differ. Of the scales, some are so long and slender that
they resemble hairs, except that they are a little flattened and divided
at the ends; some are short and broad; some are notched at the edges,
others smooth; some are nearly oval, while others are triangular: they
are mostly furnished with a short stalk or stem to fix them to the wing.
With the microscope, a variety of large stripes or ribs are to be
discovered; between these larger lines, minuter ones may be seen with a
deep magnifier. The larger stripes rise in general from the exterior
notches; some have a rib running down the middle, through their whole
length. The upper and under parts of the wing are equally supplied with
them.

The regular arrangement of these plates, one beside and partly covering
the other, as in the tiling of an house, is best seen by examining a
wing in the opake microscope. The prodigious number of small scales
which cover the wings of these beautiful insects, is a sure proof of
their utility to them, because they are given by HIM who makes nothing
in vain.

That the lively and variegated colours, which adorn the wings of the
moth and butterfly, arise from the small scales or plates that are
planted therein, is very evident from this, that if they be brushed off
from it, the wing is perfectly transparent: but whence this profusion
and difference of colour on the same wing? is a question as difficult to
resolve, as that of Prior, when he asks.

  “Why does one climate and one soil endue              }
  The blushing poppy with a crimson hue,                }
  Yet leave the lilly pale, and tinge the violet blue?” }

As the wings of the moths and butterflies are very light, they can
support themselves for a long time in the air; their manner of flying is
ungraceful, generally moving in a zigzag line, to the right and to the
left, alternately ascending and descending; this undulating motion
however has its uses, as it disappoints the birds who chase them in
taking aim; by which means they frequently elude their pursuit, though
continued for a considerable time.

Dr. Hooke[58] endeavoured to investigate the nature of the motions of
the wings of insects; and, although he was not able, from the
experiments he made, to give a satisfactory account of them, yet as they
may be useful to some future inquirer, and lead him more readily into
the path of truth, I hope an extract therefrom will not prove
unacceptable to the reader. To investigate the mode or manner of moving
their wings, he considered with attention those spinning insects that
suspend, or as it were poise themselves in one place in the air,
without rising or falling, or even moving backwards or forwards; by
looking down on these, he could, by a kind of faint shadow, perceive the
utmost extremes of the vibratory motion of their wings; the shadow,
while they were thus suspended, was not very long, but was lengthened
when they endeavoured to fly forwards. He next tried by fixing the legs
of a fly upon the top of the stalk of a feather with glue, wax, &c. and
then making it endeavour to fly away; he was thereby able to view it in
any posture. From hence he collected, that the extreme limits of the
vibrations were usually somewhat about the length of the body distant
from each other, often shorter, and sometimes longer. The foremost limit
was generally a little above the back, and the hinder one somewhat
beneath the belly; between these, to judge by the sound, they seemed to
move with an equal velocity. The manner of their moving them, if a just
idea can be formed by the shadow of the wing, and a consideration of its
nature and structure, seemed to be this: the wing being supposed to be
in the extreme limit, it is then nearly horizontal, the forepart only
being a little depressed; in this situation the wing moves to the lower
limit; before it arrives at this, the hinder part begins to move
fastest; the area of the wing begins to dip behind, and in that posture
it seems to be moved to the upper limit back again. These vibrations,
judging by the sound, and comparing them with a string tuned in unison
thereto, consist of many hundreds, if not thousands, in a second of
time. The powers of the governing faculty of the insect, and the
vivacity of its sensations, whereby every organ is stimulated to act
with so much velocity and regularity, surpass our present comprehension.

  [58] Hooke’s Micrographia, p. 172.


PEDES THE FEET, AND LEGS OF INSECTS.

These are admirably adapted for their intended service, to give the most
convenient and proper motion, and, from the variety in their
construction, their various articulations, &c. furnish the microscopic
observer with an abundance of curious and interesting objects: the most
general number is six; many of the class aptera have eight, as the
spider; the crab has ten; the oniscus fourteen; the julus has from
seventy to one-hundred and twenty on each side. The legs of those
insects that have not more than ten, are affixed to the trunk; while
those that exceed that number, have part fixed to the trunk, the rest to
the abdomen.

The legs of insects are generally divided into four parts. The first,
which is usually the largest, is called the femur; the second, or tibia,
is joined to the former, and is commonly of the same size throughout,
and longer than the femur; this is followed by the third part, which is
distinguished by the name of tarsus, or foot; it is composed of several
joints, the one articulated to the other, the number of rings varying in
different insects; the tarsus is terminated by the unguis, or claw.

The writers on natural history, in order to render their descriptions
clear and accurate, have given several names to the legs of insects,
from the nature of the motions produced by them. Thus cursorii, from
that of running; these are the most numerous. The saltatorii, those that
are used for leaping; the thighs of these are remarkably large, by which
means they possess considerable strength and power to leap to great
distances. The natatorii, those that serve as oars for swimming; the
feet of these are flat and edged with hairs, possessing a proper surface
to strike against the water, as in the dytiscus, notonecta, &c. Such
feet as have no claws are termed mutici. The chelæ, or claws, are an
enlargement of the extremity of the fore feet, each of which is
furnished with two lesser claws, which act like a thumb and finger, as
in the crab. The under part of the feet in some insects is covered with
a kind of brush or sponge, by which they are enabled to walk with ease,
on the most polished substances, and in situations from which it would
seem they must necessarily fall.

Motion is one of the principal phenomena of nature; it is as it were the
soul of our system, and is as admirable in the smallest animal, as in
the universe at large. It is the principal agent in producing all that
diversity and change which perpetually affect every object in the
creation. The motions of animals are proportioned to their weight and
structure, a flea can leap to the distance of at least two hundred times
its own length; were an elephant, a camel, or an horse to leap in the
same proportion, their weight would crush them to atoms. The same remark
is applicable to spiders, worms, and other insects; the softness of
their texture, and the comparative smallness of their specific gravity,
enable them to fall without injury from heights that would prove fatal
to larger and heavier animals.[59]

  [59] The parts of some of the larger animals are, however, so
  admirably constructed for swiftness, as to enable them to perform
  surprizing acts of agility; for instance, the Siberian jerboa, mus
  saliens, Pennant; this animal springs forward by successive leaping so
  very nimbly, that it is said to be very difficult for a man well
  mounted to overtake it; it is about the size of a large rat. The
  kanguroo, opossum of Pennant, macropus giganteus, Shaw, leaps to so
  uncommon a height, and to so great a distance, as to outstrip the
  swiftest greyhound; its size is that of a full-grown sheep. Accurate
  coloured figures of both these extraordinary animals are given in that
  elegant work, the Naturalist’s Miscellany. EDIT.

Many insects can only move the thigh in a vertical direction, while
others can move it in a variety of ways. The progressive motion of
insects, and the various methods employed to effect it, will be found a
very curious and important subject, and well worthy the attention of the
naturalist. The intelligent mechanic will not find it lost labour if he
bestow some time on the same subject. Very little has been done on this
head, and that principally by Reaumur, in his excellent Memoires; and
by M. Weiss, in a Memoir published in the Journal de Physique for 1771.
The reader may also consult Borelli de Motu Animalium.


OF THE TAIL AND STING OF INSECTS.

Cauda, the tail, terminates the abdomen, and is constructed in a
wonderful manner for answering the purposes for which it is formed,
namely, to direct the motion of the insect, to serve as an instrument of
defence, or for depositing the eggs; the figure and size thereof varying
in each genus and its families. In most insects it is simple, simplex,
and yet capable of being extended or drawn back at pleasure; in others,
elongata, elongated, as in the crab and scorpion; setacea, shaped like a
bristle, as in the raphidia; triseta, with three appendages like
bristles, as in the ephemera; in some it is forked, furcata, as in the
podura; and in others it is furnished with a pair of forceps, forcipata,
as in the forficula; in the blatta, grylli, and others, it is foliosa,
or like a leaf; in the scorpion and panorpa it is telifera, furnished
with a dart or sting. Further particulars may be obtained from the
Philosophia Entomologica of Fabricius.

Aculeus, or the sting, is an instrument with which insects wound and
instil a poison; the sting generally proceeds from the under part of the
last ring of the belly: in some it is sharp and pointed, in others
serrated or formed like a saw. It is used by many insects both as an
offensive and defensive weapon; by others it is only used to pierce the
substances where they mean to deposit their eggs. This instrument cannot
be properly seen or known, but with the assistance of a microscope.


OF THE STING OF A BEE.

Of bees, it is only the labourers and the queen that have stings. The
apparatus is of a very curious construction, fitted for inflicting a
wound, and at the same time conveying poison into that wound.

The apparatus consists of two piercers conducted in a sheath, groove, or
director.

This groove is rather large at the base, but terminates in a point; it
is affixed to the last scale of the upper side of the abdomen by
thirteen thin scales, six on each side, and one behind the rectum. These
scales inclose the rectum all round, and are attached to each other by
thin membranes which allow of a variety of motions; three of them are
however attached more closely to a round and curved process, which comes
from the basis of the groove in which the sting lies, as also to the
curved arms of the sting which spread out externally. The two stings may
be said to begin by those two curved processes at their union with the
scales, and converging towards the groove at its base, which they enter,
and then pass along to its point.

The two stings are serrated or notched towards the points; they can be
thrust out a little way, and drawn within it. These parts are all moved
by very strong muscles, which give motions in almost all directions, but
most particularly outwards. It is wonderful how deep they will pierce
solid bodies with this sting.

To perform this by mere force, two things are necessary, power of
muscles, and strength of sting; neither of which they seem to possess in
a sufficient degree. Mr. J. Hunter thinks that it cannot be by simple
force, because the least pressure bends the sting in any direction. It
is probable that the serrated edges may assist, by cutting their way
like a saw.

The apparatus for the poison consists of two small ducts, which are the
glands that secrete the poison; these lie in the abdomen among the air
cells, they soon however unite into one oblong bag; at the opposite end
of which a duct passes out, which runs towards the angle where the two
stings meet, and, entering between them, forms a canal by the union of
the two stings at this point. From the serrated construction of the
stings the bee can seldom disengage them, and hence, when they pass into
materials of too strong a nature, the bee generally leaves them behind,
and often a part of the bowels therewith.[60]

  [60] Phil. Trans. for 1792, page 189.


DISTINGUISHING CRITERIA OF INSECTS.

It has already been observed, that the bodies of insects are covered
with a hard skin, answering the purpose of an internal skeleton, and
forming one of the characters by which they are distinguished from other
animals. This external covering is very strong in those insects which,
from their manner of life, are particularly liable to great friction, or
violent compression; but is more tender and delicate in such as are not
so exposed. The skin of insects, like that of larger animals, is porous;
the pores in some species are very large; many insects often change or
cast off their skin; this exuvia forms an excellent object for the
microscope.

Another distinguishing criterion of insects is the colour of their
circulating fluid or blood, which is never red; this, at first sight,
seems liable to some objections, on account of the drop of red liquor
which is often procured from small insects when squeezed or pressed to
pieces. It does not appear, however, that this is the blood of the
little animal; when it existed as a worm there was no such appearance,
and when transformed to the perfect, or fly state, it is only found in
the eye, and not in the body, which would be the case if it circulated
in the veins of the insect. It is probable there is a circulation of
some fluid analogous to the blood in most insects: with the assistance
of the microscope this circulation may be perceived in many; but the
circulating liquor is not red.

To these discriminating characteristics we may also add the following
particulars:

1. That the body of insects is divided by incisuræ, or transversal
divisions, from whence they take their name.

2. That they are furnished with antennæ, which are placed upon the fore
part of the head; these are jointed and moveable in various directions.

3. That no insect in its perfect state, or after it has gone through all
its transformations, has less than six legs, though many have more.
There are some moths, whose two fore feet are so small, as scarcely to
entitle them to that name.

4. That insects have neither the organs of smell nor hearing; at least
they have not as yet been discovered, though it is reported that
Fabricius has lately found and described the organs of hearing in a
lobster.[61]

  [61] That many insects are susceptible of a shrill or loud noise, is a
  fact so well ascertained, as to be indisputable; but in what manner,
  or by what organs the sensation is conveyed, is not so evident;
  Barbut, however, supposes them to possess the sense of hearing in a
  very distinct manner. Many insects, he observes, are well known to be
  endued with the power of uttering sounds, viz. large beetles, bees,
  wasps, common flies, gnats, &c. The sphinx atropos squeaks, when hurt,
  nearly as loud as a mouse: this faculty certainly must be intended for
  some purpose, and as they vary their cry occasionally, it appears
  designed to give notice of pleasure or pain, or some affection in the
  creature which possesses it. “The knowledge of their sounds,” says he,
  “is undoubtedly confined to their tribe, and is a language
  intelligible to them only; saving when violence obliges the animal to
  exert the voice of nature in distress, craving compassion; then all
  animals understand the doleful cry; for instance, attack a bee or wasp
  near the hive or nest, or a few of them; the consequence will be, the
  animal or animals, by a different tone of voice will express his or
  their disapprobation or pain; that sound is known to the hive to be
  plaintive, and that their brother or brethren require their
  assistance, and the offending party seldom escapes with impunity. Now,
  if they had not the sense of hearing, they could not have known the
  danger their brother or brethren were in, by the alteration of their
  tone.” Another proof, which he reckons still more decisive, was taken
  from his observation on a spider, which had made a very large web on a
  wooden railing, and was at the time in a cavity behind one of the
  rails, at a considerable distance from the part where a fly had
  entangled himself; the spider became immediately sensible of it,
  though, from the situation of the rail, he could not possibly have
  seen the fly. This observation, however, cannot be considered as
  conclusive, as it is very probable that the spider was alarmed by the
  tremulous motion of the threads of the web occasioned by the
  fluttering of the fly, which he might well know how to distinguish
  from their vibration by the wind. It is this author’s opinion, that
  the organ of hearing is situated in the antennæ; he likewise supposes
  that the organs of smell reside in the palpi or feelers. For his
  reasoning on these subjects, see the Genera Insectorum, Preface, p.
  vii. & seq. EDIT.

5. That they do not respire air by the mouth, but that they inspire and
exhale it by means of organs which are placed on the body.

6. That they move the jaws from right to left, not up and down.

7. That they have neither eye-lid nor pupil.

To these we may also add, that the mechanism resulting from the LIFE of
insects is not of so compound a nature as in animals of a larger size.
They have less variety of organs, though some of them are more
multiplied; and it is by the number and situation of these that their
rank in the great scale of beings is to be determined.

These characters are often united in the same insect; there are,
however, some species in which one or two of them are wanting.

The student in entomology, who wishes to attain a proper knowledge of
the science, and indeed every microscopic observer, desirous of
availing himself of the discoveries of others, and of communicating
intelligibly his own, will find it necessary to make himself conversant
with the various classes, genera, &c. into which insects have been
divided by Linnæus. Every system has its defects, and probably some may
be found in that of this truly celebrated naturalist, but the purpose of
science is answered by using those discriminations which are generally
adopted.

The following general idea of the Linnæan classes may serve as a
foundation for this knowledge: a more particular account may be obtained
by consulting the under-mentioned works.

Institutions of Entomology, a translation of Linnæus’s Ordines et Genera
Insectorum, or systematic arrangement of insects, &c. by Thomas
Pattinson Yeats.

Fundamenta Entomologiæ, or an Introduction to the Knowledge of Insects,
translated from Linnæus by W. Curtis, the ingenious author of Flora
Londinensis, the Botanical Magazine, &c.

The Genera Insectorum of Linnæus, exemplified by various Specimens of
English Insects, drawn from Nature, by James Barbut.[62]

  [62] This work contains two excellent plates, illustrative of the
  Distinctions of the Ordines and Genera Insectorum, by their antennæ,
  tarsi of the feet, &c. EDIT.

Class the first. COLEOPTERA. The insects of this class have four wings;
the upper ones, called the elytra, are crustaceous, being of a hard
horny substance; these, when shut, form a longitudinal suture down the
back, as in the scarabæus, melolontha, or cockchaffer, &c.

2. HEMIPTERA. These have also four wings; but the elytra are different,
being half crustaceous, half membranaceous: the wings do not form a
longitudinal suture, but extend the one over the other, as in the
gryllus, grasshopper, &c.

3. LEPIDOPTERA. Those which have four membranaceous wings covered with
fine scales, appearing to the naked eye like powder or meal, as in the
butterfly and moth.

4. NEUROPTERA. These have four membranaceous transparent wings, which
are generally reticulated, the tail without a sting, as in the
libellula, or dragon fly.

5. HYMENOPTERA. These, like the preceding class, have four membranaceous
naked wings; but the abdomen is furnished with a sting, as in the bee,
wasp, ichneumon, &c.

6. DIPTERA. These have only two wings, and are furnished with halteres,
or poisers, instead of under wings, as in the common house fly, gnat,
&c.

7. APTERA. These are distinguished by having no wings, as in the spider,
louse, acarus, &c.


OF THE TRANSFORMATION OF INSECTS.

Insects are farther distinguished from other animals by the wonderful
changes that all those of the winged species without exception, and some
which are destitute of wings, must pass through, before they arrive at
the perfection of their nature. Most animals retain, during their whole
life, the same form which they receive at their birth; but insects go
through wonderful exterior and interior changes, insomuch that the same
individual, at its birth and middle state, differs essentially from that
under which it appears when arrived at a state of maturity; and this
difference is not confined to marks, colour, or texture, but is extended
to their form, proportion, motion, organs, and habits of life.

The ancient writers on natural history were not unacquainted with these
transformations, but the ideas they entertained of them were very
imperfect and often erroneous. The changes are produced in so sudden a
manner, that they seem like the metamorphoses recorded in the fables of
the ancients, and it is not improbable that those fables owe their
origin to the transformation of insects. It was not till towards the
latter end of the last century that any just conception of this subject
was formed; the mystery was then unveiled by those two great anatomists
Malpighi and Swammerdam, who observed these insects under every
appearance, and traced them through all their forms; by dissecting them
at the time just preceding their changes, they were enabled to prove
that the moth and butterfly grow and strengthen themselves, that their
members are formed and unfolded under the figure of the insect we call
a caterpillar, and that the growth was effected by a developement of
parts; they also shewed that it is not difficult to exhibit in these all
the parts of the future moth, as its wings, legs, antennæ, &c. and
consequently that the changes which are apparently sudden to our eyes,
are gradually formed under the skin of the animal, and only appear
sudden to us, because the insect then gets rid of a case which had
before concealed its real members. By this case it is preserved from
injuries, till its wings, and every other part of its delicate frame are
in a condition to bear the impulse of the sun, and the action of the air
naked; when all the parts are grown firm, and ready to perform their
several offices, the perfect animal appears in the form of its parent.
Though these discoveries dissipated the false wonders of the
metamorphoses that the world before believed, they created a fund of
real admiration by the discovery of the truth. These transformations
clearly prove, that without experience every thing in nature would
appear a mystery; so much so, that a person unacquainted with the
transformation of the caterpillar to the chrysalis, and of this to the
fly, would consider them as three distinct species; for who, by the mere
light of nature, or the powers of reason unaided by experience, could
believe that a butterfly, adorned with four beautiful wings, furnished
with a long spiral proboscis or tongue, instead of a mouth, and with six
legs, proceeded from a disgusting hairy caterpillar, provided with jaws
and teeth, and fourteen feet? Without experience, who could imagine that
a long white smooth soft worm hid under the earth, should be transformed
into a black crustaceous beetle? Nor could any one, from considering
them in their perfect state, have discovered the relation which they
bear to the several changes of state, and their corresponding forms,
through which they have passed, and which are to appearance as distinct
as difference can make them.

The life of those insects which pass through these various changes, may
be divided into four principal parts, each of which will be found truly
worthy of the utmost attention of the microscopic observer.

The first change is from the EGG into the LARVA, or, as it is more
generally called, into the worm or caterpillar. From the LARVA, it
passes into the PUPA, or chrysalis state. From the PUPA, into the IMAGO,
or fly state.

Few subjects can be found that are more expressive of the extensive
goodness of Divine Providence, than these transformations, in which we
find the occasional and temporary parts and organs of these little
animals suited and adapted with the most minute exactness to the
immediate manner and convenience of their existence; which again are
shifted and changed, upon the insects commencing a new scene and state
of action. In its larva state the insect appears groveling, heavy, and
voracious, in the form of a worm, with a long body composed of
successive rings; crawling along by the assistance of these, or small
little hooks, which are placed on the side of the body. Its head is
armed with strong jaws, its eyes smooth, entirely deprived of sex, the
blood circulating from the hind part towards the head. It breathes
through small apertures, which are situated on each side of the body, or
through one or more tubes placed in the hinder part thereof. While it is
in the larva state, the insect is as it were masked, and its true
appearance concealed; for under this mask the more perfect form is
hidden from the human eye. In the pupa, or chrysalis state, the insect
may be compared to a child in swaddling cloathes; its members are all
folded together under the breast, and inclosed within one or more
coverings, remaining there without motion. While in this state, no
insects but those of the hemiptera class, take any nourishment. The
change is effected various ways; in some insects the skin of the larva
opens, and leaves a passage, with all its integuments; in others, the
skin hardens and becomes a species of cone, which entirely conceals the
insect; others form or spin cones for themselves, and in this state they
remain till the parts have acquired sufficient firmness, and are ready
to perform their several offices.

The insect then casts off the spoils of its former state, wakes from a
death-like inactivity, breaks as it were the inclosures of the tomb,
throws off the dusky shroud, and appears in its imago or perfect form;
for it has now attained the state of organical perfection, which answers
to the rank it is to hold in the corporeal world: the structure of the
body, the alimentary organs, and those of motion, are materially
changed. It is now furnished with wings magnificently adorned, soars
above and despises its former pursuits, wafts the soft air, chooses its
mate, and transmits its nature to a succeeding race. Those members,
which in the preceding state were wrapped up, soft, and motionless, now
display themselves, grow strong, and are put in exercise. The interior
changes are as considerable as those of the exterior form, and that in
proportion as the first state differs from the last; some organs acquire
greater strength and firmness, others are rendered more delicate; some
are suppressed, and some unfolded, which did not seem to exist in the
former stages of its life.


OF THE LARVA STATE OF INSECTS.

As the larvæ or caterpillars of the moth and butterfly[63] form the most
numerous family among the tribe of insects, I shall first describe
them, and their various changes from this state to their last and
perfect form, and then proceed to those insects which differ most from
the caterpillar in one or all of their various changes.

  [63] Butterflies are distinguished from moths by the time of their
  flying abroad, and by their antennæ; the butterflies appear by day,
  their antennæ are generally terminated by a little knob; the moths fly
  mostly in the evening, and their antennæ are either setaceous or
  pectinated.

The greater part of those insects which come forth in spring or summer,
perish or disappear at the approach of winter; there are very few, the
period of whose life exceeds that of a year; some survive the rigours of
winter, being concealed and buried under ground; many are hid in the
bark of trees, and others in the chinks of old walls; some, like the
caterpillar of the brown-tailed moth,[64] at the approach of winter not
only secure and strengthen the web in which the society inhabit, and
thus protect themselves from impertinent intruders, but each individual
also spins a case for itself, where it rests in torpid security,
notwithstanding the inclemency of the season, till the spring animates
it afresh, and informs it, that the all-bountiful Author of nature has
provided food convenient for it. Many that are hatched in the autumn
retire and live under the earth during the winter months, but in the
spring come out, feed, and proceed onward to their several changes;
while no small part pass the colder months in their chrysalis or pupa
state: but the greater number of the caterpillar race remain in the egg,
being carefully deposited by the parent fly in those places where they
will be hatched with the greatest safety and success; in this state the
latent principle of life is preserved till the genial influences of the
spring call it into action, and bring forth the young insect to share
the banquet that nature has provided.

  [64] This moth was uncommonly numerous and destructive near London in
  the year 1782, and, aided by the predictions of an empirical imposter,
  occasioned a considerable alarm in the minds of the ignorant and
  superstitious. The judicious publication of a short history of the
  insect, by Mr. Curtis, in some measure contributed to dissipate their
  fears. EDIT.

All caterpillars are hatched from the egg, and when they first proceed
from it are generally small and feeble, but grow in strength as they
increase in size. The body is divided into twelve rings; the head is
connected with the first, and is hard and crustaceous. No caterpillar of
the moth or butterfly has less than eight, or more than sixteen feet;
the six first are crustaceous, pointed, and fixed to the three first
rings of the body; these feet are the covering to the six future feet of
the moth; the other six feet are soft and flexible or membranaceous;
they vary both in figure and number, and are proper only to the larva
state; with respect to their external figure, they are either smooth or
hairy, soft to the touch, or hard like shagreen, beautifully adorned
with a great variety of the most lively teints; on each side of the body
nine little oval holes are placed, which are generally considered as the
organs of respiration. There are on each side of the head of the
caterpillar five or six little black spots, which are supposed to be its
eyes. These creatures vary in size, from half an inch long to four and
five inches.

The caterpillar, whose life is one continued succession of changes,
often moults its skin before it attains its full growth; not one of them
arrives at perfection, without having cast its skin at least once or
twice. These changes are the more remarkable, because when the
caterpillar moults, it is not simply the skin that is changed; for we
find in the exuvia, the skull, the jaws, and all the exterior parts,
both scaly and membranaceous, which compose its upper and under lip, its
antennæ, palpi, and even those crustaceous pieces within the head, which
serve as a fixed basis to a number of muscles; we further find in the
exuvia, the spiracula, the claws, and sheaths of the anterior limbs, and
in general all that is visible of the caterpillar.

The new organs were under the old ones as in a sheath, so that the
caterpillar effects the changes by withdrawing itself from the old skin,
when it finds itself lodged in too narrow a compass. But to produce this
change, to push off the old covering, and bring forward the new, is a
work of labour and time. Those caterpillars who live in society, and
have a kind of nest or habitation, retire there to change their skins,
fixing the hooks of the feet, during the operation, firmly in the web of
their nest. Some of the solitary species spin at this time a slender
web, to which they affix themselves. A day or two before the critical
moment approaches, the insect ceases to eat, and loses its usual
activity; in proportion as the time of change advances, the colour of
the caterpillar becomes more feeble, the skin hardens and withers, and
is soon incapable of receiving those juices by which it was heretofore
nourished and supported. The insect may now be seen, at distant
intervals, to elevate its back, and stretch itself to its utmost extent;
sometimes to lift up the head, move it a little from side to side, and
then let it fall again; near the change, the second and third rings are
seen to swell considerably; by these internal efforts the old parts are
stretched and distended as much as possible, an operation which is
attended with great difficulty, as the new parts are all weak and
tender. However, by repeated exertions, all the vessels which conveyed
the nourishment to the exterior skin are disengaged, and cease to act,
and a slit is made on the back, generally beginning at the second or
third ring; the new skin may now be just perceived, being distinguished
by the freshness and brightness of its colour; the caterpillar then
presses the body like a wedge into this slit, by which means it is soon
opened from the first down to the fourth ring; this renders it large
enough to afford the insect a passage, which it soon effects in a very
curious manner. The caterpillar generally fasts a whole day after each
moulting, for it is necessary that the parts should acquire a certain
degree of consistency, before it can live and act in its usual manner;
many also perish under the operation. The body having grown under the
old skin, till the insect was become too large for it, it always appears
much larger after it has quitted the exuvia: now as the growth was
gradual, and the parts soft, the skin pressed them together, so that
they lay in a small space; but as soon as the skin is cast off, they are
as it were liberated from their bonds, and distend themselves
considerably. Some caterpillars, in changing their skin, from smooth,
become covered with fine hair; while others, that were covered with this
fine hair, have the last skin smooth.[65] The silk-worm, previous to its
chrysalis or pupa state, casts its skin four times; the first is cast on
the tenth, eleventh, or twelfth day, according to the nature of the
season; the second, in five or six days after; the third in five or six
days more, and the fourth and last in six or seven days after the third.

  [65] Valmont de Bomare Dictionnaire Universel d’Histoire Naturelle,
  vol. ii. 2d edit. 12mo. p. 394.

Before we describe the change of the larva into the pupa state, it will
be necessary to give the reader an account of those names by which
entomologists distinguish the different appearances of the insect in its
pupa state. It is called Coarctata, when it is straitened or confined to
a case of a globular form, without the smallest resemblance to the
structure of the insect it contains, as in the diptera. It is called
Obtecta, disguised or shrouded, when the insect is inveloped in a
crustaceous covering, consisting of two parts, one of which surrounds
the head and thorax, the other the abdomen. It is termed Incompleta,
when the pupa has perceptible wings and feet, but cannot move them, as
in most of the hymenoptera. Semicompleta; these can walk or run, but
have only the rudiments of wings. The difference between the pupa and
the larva of this class is very inconsiderable, as they eat, walk, and
act, just as they did in their primitive state; the only remarkable
difference is a kind of case which contains the wings that are to be
developed in their fly state. Completa; those designed by this name take
their perfect form at their birth, and do not pass, like other insects,
through a variety of states, though they often change their skin.

It is a general rule, that all winged insects pass through the larva and
pupa state, before they assume their perfect form: there are also
insects which have no wings, and yet undergo similar transformations, as
the bed bug, the flea, &c. Other insects, which have no wings, and which
always remain without them, never pass through the pupa state, but are
subject to considerable changes, as well with respect to the number, as
the figure of their parts; thus mites have four pair of feet, and two
smaller ones at the fore part of the body, near the head; yet some of
these are born with only three pair of feet, the fourth is not perceived
till some time after their birth.[66] The figure of the monoculus
quadricornis of Linnæus (Fauna Suecica, edit. Stockholm, 1761, No. 2049)
changes considerably after its birth.[67] The julus is an insect with a
great number of feet, some species having an hundred pair and upwards.
M. De Geer has given a description of one with more than two-hundred
pair,[68] and yet these at their birth have only three pair, the rest
are not perceived till some time after.

  [66] De Geer Memoires pour servir a l’Histoire des Insectes, tom. 1.
  p. 154.

  [67] Ibid.

  [68] Memoires des Scavans etrangers, tom. 3, p. 61.


OF THE CHANGE FROM THE LARVA TO THE PUPA STATE.

I shall now return to the caterpillar, and take notice of the care and
provision it makes to pass from the larva state into that of the pupa or
chrysalis; which is, in general, a state of imperfection, inactivity,
and weakness, through which the insect, when it has obtained a proper
size, must pass; and in which it remains often for months, sometimes for
a whole year, exposed, without any means of escaping, to every event;
and in which it receives the necessary preparations for its perfect
state, and is enabled once more to appear upon the transitory scene of
time. During its passage from one state to the other, as well as when it
is in the pupa form, the microscopical observer will find many
opportunities of exercising his instrument.

The transitions of the caterpillar from one state to another, are to it
a subject of the most interesting nature; for in passing through them,
it often runs the risk of losing its life, that precious boon of heaven,
which is ever accompanied with a degree of delight, proportioned to the
state in which the creature exists, and the use it makes of the gift it
has received. If the caterpillar could therefore foresee the efforts and
exertions it must make to put off its present form, and the state of
weakness and impotence under which it must exist while in the pupa
state, it would undoubtedly choose the most convenient place, and the
most advantageous situation, for the performance of this arduous
operation; one where it would be the least exposed to danger, at a time
when it had neither strength to resist, nor swiftness to avoid the
attack of an enemy. All these necessary instructions the caterpillar
receives from the influence of an all-regulating Providence, which
conveys the proper information to it by its own sensations: hence, when
the critical period approaches, it proceeds as if it knew what would be
the result of its operations. Different species prepare themselves for
the change different ways, suited to their nature and the length of time
they are to remain in this state.

When the caterpillar has attained to its full growth, and the parts of
the future butterfly are sufficiently formed beneath its skin, it
prepares for its change into the pupa state; it seeks for a proper place
in which to perform the important business: the different methods
employed by these little animals to secure this state of rest, may be
reduced to four: 1. Some spin webs or cones, in which they inclose
themselves. 2. Others conceal themselves in little cells, which they
form under ground. 3. Some suspend themselves by their posterior
extremity; 4. While others are suspended by a girdle that goes round
their body. I shall describe the variety in these, as well as the
industry used in constructing them, after we have gone through the
manner in which the caterpillar prepares itself for, and passes through
the pupa state.

Preparatory to the change, it ceases to take any food, empties itself of
all the excrementitious matter that is contained in the intestines,
voiding at the same time the membrane which served as a lining to these
and the stomach. The intestinal canal is composed of two principal
tubes, the one inserted into the other; the external tube is compact and
fleshy, the internal one is thin and transparent; it is the inner tube,
which lines the stomach and intestines, that is voided with the
excrement before the change. It generally perseveres in a state of rest
and inactivity for several days, which affords the external and internal
organs that are under the skin an opportunity of gradually unfolding
themselves. In proportion as the change into the pupa form approaches,
the body is observed often to extend and contract itself; the hinder
part is that which is first disengaged from the caterpillar skin; when
this part of the body is free, the animal contracts and draws it up
towards the head; it then liberates itself in the same manner from the
two succeeding rings, consequently the insect is now lodged in the fore
part of its caterpillar covering; the half which is abandoned remains
flaccid and empty, while the fore part is swoln and distended. The
animal, by strong efforts, still forcing itself against the fore part of
the skin, bursts the skull into three pieces, and forms a longitudinal
opening in the three first rings of the body; through this it proceeds,
drawing one part after the other, by alternately lengthening and
shortening, swelling and contracting the body and different rings; or
else, by pushing back the exuvia, gets rid of its odious reptile form.

The caterpillar, thus stripped from its skin, is what we call the pupa,
chrysalis, or aurelia, in which the parts of the future moth are
inclosed in a crustaceous covering, but are so soft, that the slightest
touch will discompose them. The exterior part of the chrysalis is at
first exceedingly tender, soft, and partly transparent, being covered
with a viscous fluid; this soon dries up, thickens, and forms a new
covering for the animal, capable of resisting external injuries; a case,
which is at the same time the sepulchre of the caterpillar, and the
cradle of the moth; where, as under a veil, this wonderful
transformation is carried on.

The pupa has been called a chrysalis, or creature made of gold, from the
resplendent yellow colour with which some kinds are adorned. Reaumur has
shewn us whence they derive this rich colour; that it proceeds from two
skins, the upper one a beautiful brown, which lies upon or covers a
highly polished and smooth white skin: the light reflected from the
last, in passing through, gives it the golden yellow, in the same manner
as this colour is often given to leather; so that the whole appears
gilt, although no gold enters into the tincture. The chrysalis of the
common white butterfly furnishes a most beautiful object for the
lucernal opake microscope.

Those who are desirous to discover distinctly the various members of the
moth in the pupa, should examine it before the fore-mentioned fluid is
dried up, when it will be found to be only the moth with the members
glued together; these, by degrees, acquire sufficient force to break
their covering, and disengage themselves from the bands which confine
them. While in this state, all the parts of the moth may be traced out,
though so folded and laid together, that it cannot make any use of them;
nor is it expedient that it should, as they are too soft and tender to
be used, and pass through this state merely to be hardened and
strengthened.

To examine the moth concealed under the skin of a caterpillar, one of
them should be taken at the last change; when the skin begins to open,
it should be drowned in spirit of wine, or some strong liquor, and be
left therein for some days, that it may take more consistency and harden
itself; the skin of the caterpillar may then be easily removed: the
chrysalis, or feeble moth, will be first discovered, after which the
tender moth may be traced out, and its wings, legs, antennæ, &c. may be
opened and displayed by an accurate observer.

The parts of the moth or butterfly are not disposed exactly in the same
manner in the body of the caterpillar, as when left naked in the
chrysalis. The wings are longer and narrower, being wound up into the
form of a cord, and the antennæ are rolled up on the head; the tongue is
also twisted up and laid upon the head, but in a very different manner
from what it is in the perfect animal, and different from that which it
lies in within the chrysalis; so that it is by a progressive and gradual
change, that the interior parts are prepared for the pupa and moth
state. The eggs, hereafter to be deposited by the moth, are also to be
found, not only in the chrysalis, but in the caterpillar itself,
arranged in their natural and regular order.

While in this state, the creature generally remains immoveable, and
seems to have no other business but patiently to attend the time of its
change, which depends on the parts becoming hard and firm, and the
transpiration of that humidity which keeps them soft; the powers of life
are as it were absorbed in a deep sleep; the organs of sensation seem
obliterated, being imprisoned by coverings more or less strong, the
greater part remains fixed in those situations which the caterpillar had
selected for them till their final metamorphosis; some, however, are
capable of changing place, but their movements are slow and painful.

The time, therefore, which the moth or butterfly remains in the pupa
state is not always the same, varying in different species, and
depending also upon the warmth of the weather, and other adventitious
circumstances; some remain in that situation for a few weeks; others do
not attain their perfect form for eight, nine, or eleven months: this
often depends on the season in which they assume the pupa form, or
rather on the time of their birth. Some irregularities are also
occasioned by the different temperature of the air, by which they are
retarded or accelerated, so as to be brought forward in the season best
suited to their nature and the ends of their existence. I have heard of
an instance, where the pupa, produced from caterpillars of the same
eggs, nourished in the same manner, and which all spun up within a few
days of each other in the autumn, came into the fly state at three
different and distant periods; viz. one-third of them the spring
following their change, one-third more the succeeding spring, and the
remainder the spring after, making three years from their first
hatching; a further and manifest proof of the beauty and wisdom of the
laws of Divine order, which are continually operating for the best
interests of all created beings. As the transformation of insects is
retarded by cold, and accelerated by heat, the ordinary period of these
changes may sometimes be altered, by placing them in different degrees
of heat or cold; by these they may be awakened sooner to a new state of
existence, or kept in one of profound sleep.[69]

  [69] Reaumur Memoires sur les Insectes, tom. 2, mem. 1.

There are some caterpillars which remain in their cone eight or nine
months before they acquire the complete pupa state; so that their
duration in that form is much shorter than it naturally appears to be.


OF THE PREPARATION OF THE CATERPILLAR FOR THE METAMORPHOSES.

The industry of the caterpillar, in securing itself for its change into
the chrysalis, must not be passed by; not only because it naturally
leads the reader to consider and admire that divine agency, by which the
insect is informed, but because the different modes it makes use of
cannot be properly investigated, without the assistance of glasses, it
therefore consequently becomes a proper subject for the microscope; we
shall select from a great variety, a few instances, to animate the
reader in these researches.

Some caterpillars, towards the time of their change, suspend themselves
from the branch of a tree, with the head downwards; in this position
they assume the pupa form, and from thence immerge a butterfly or moth.
In order to secure itself in this position, the insect covers with
threads that part of the branch from which it means to suspend itself;
it places these in different directions, and then covers them with other
threads, laying on several successive thicknesses, each new layer being
smaller in size than that which preceded it; forming, when finished, a
little cone or hillock of silk, as will be found when examined by the
microscope. The caterpillar hooks itself by the hinder feet to this
hillock, and when it has found by several trials that it is strongly
fixed thereto, throws itself forward, letting the body fall with the
head downwards. Soon after it is thus suspended, it bends the fore part
of the body, keeping this bent posture for some time, then straitening
the body, again in a little time bending it, and so on, repeating this
operation till it has formed a slit in the skin upon the back; part of
the pupa soon forces itself through this, and extends the slit as far as
the last crustaceous feet; the pupa then forces upwards the skin, as we
would push down a stocking, by means of its little hooks and the motion
of the body, till it has slipped it off to that part from which the
caterpillar had suspended itself. But the pupa has still to disengage
itself from this small packet, to which the exuvia is now reduced: here
the observer will find himself interested for the little animal, anxious
to learn how the pupa will quit this skin, and how it will be enabled to
fix itself to the hillock, as it has neither arms nor legs. A little
attention soon explains the operation, and extricates the observer from
his embarrassment. It seizes the exuvia by the rings of the body, and
thus holds itself as it were by a pair of pincers; then, by bending the
tail, it frees itself from the old skin, and by the same method soon
suspends itself to the silken mount; it lengthens out the hinder part of
the body, and clasps, by means of its rings, the various foldings of the
exuvia, one after another; thus creeping backward on the spoils, till it
can reach the hillock with the tail; which, when examined by the
microscope, will be found to be furnished with hooks to fix itself by.
It is surprizing to see with what exactness and ease these insects
perform an operation so delicate and dangerous, which is only executed
once in their lives; and nought else can account for it, but the
consideration that HE, who designed that the caterpillar should pass
through these changes, had provided means for that end, regularly
connecting the greater steps by intermediate ones, the desire of
extending their species forming and acting upon the organization, till
the purposes of their life are completed. Different kinds of these
insects require variety in the mode of suspension; some fix themselves
in an horizontal position, by a girdle which they tie round their body;
this girdle appears to the naked eye as a single thread; when examined
with the microscope, it will be found to be an assemblage of fine
threads, lying close to each other, so fixed as to support the
caterpillar, and yet leave it in full freedom to effect the changes.
Like the preceding kind, it fixes the girdle to the branch of a tree; in
this situation it remains for some time motionless, and then begins to
bend, move, and agitate its body in a very singular manner, till it has
opened the exterior covering, which it pushes off and removes much in
the same manner as we have described in the preceding article, and yet
with such dexterity, that the pupa remains suspended by the same girdle.


OF THE IMAGO OR FLY STATE OF INSECTS.

As soon as the moth acquires sufficient strength to break the bonds
which surround it, and of which it is informed by its internal
sensations, it makes a powerful effort to escape from its prison, and
view the world with new-formed eyes. The moth frees itself from the pupa
with much greater ease than the pupa from the caterpillar; for the case
of the pupa becomes so dry, when the moth is near the time of throwing
off its covering, that it will break to pieces if it be only gently
pressed between the fingers; and very few of the parts will be found, on
examination, to adhere to the body. Hence, when the insect has acquired
a proper degree of solidity, it does not require any great exertion to
split the membrane which covers it. A small degree of motion, or a
little inflation of the body, is sufficient for this purpose; these
motions reiterated a few times, enlarge the hole, and afford the moth
room to escape from its confinement. The opening through which they pass
is always at the same part of the skin, a little above the trunk,
between the wings, and a small piece which covers the head; the
different fissures are generally made in the same direction. If the
outer case be opened, it is easy to discover the efforts the insect
makes to emancipate itself from its shell; when the operation begins,
there seems to be a violent agitation in the humours contained in the
little animal; the fluids seem to be driven with rapidity through all
the vessels, and it is seen to agitate its legs, &c. as it were
struggling to get free; these efforts soon break its brittle skin. The
loosening the exterior bands of the pupa is not the only difficulty many
moths have to encounter with; it has often also to pierce the cone or
case in which it has been inclosed, and that at a time when its members
are very feeble, when it is no longer furnished with strong jaws to
pierce and cut its way through; but by the regular laws of divine order,
means are furnished to every creature of attaining the end for which it
was produced: thus, in the present case, some of these insects are
provided with a liquor with which they soften and weaken the end of the
cone; some leave one end feeble, and close it only with a few threads,
so that a slight effort of the head enables the moth to burst the prison
doors, and immerge into day.

When the moth first sees the day, it is humid and moist; but this
humidity soon evaporates, the interior parts dry and harden as well as
the exterior; the wings, which are wrinkled, being thick and small, then
extend themselves, strengthen and harden insensibly, and the fibres
which were at first flexible, become hard and stiff; so much so, that
Malpighi considered them as bones: in proportion as these fibres harden,
the fluid which circulates within them, and extends the wings, loses its
force; so that if any extraneous circumstance prevent the motion of this
fluid, at the first instant of the moth’s escape from its former state,
the wings will then become ill-shaped; often expanding with such
rapidity, that the naked eye cannot trace their unfolding. The wings,
which were scarce half the length of the body, acquire in a few minutes
their full size, so as to be nearly five times as large as they were
before: nor is it the wings only which are thus increased; all their
spots and colours, heretofore so minute as to be scarce discernible, are
proportionably extended, so that what before appeared as only so many
unmeaning and confused points, become distinct and beautiful ornaments;
and those that are furnished with a tongue or trunk, curl and coil it
up. When the wings are unfolded, the tongue rolled up, the moth
sufficiently dried, and the different members strengthened, it takes its
flight. Most of them, soon after they have attained their perfect state,
void an excrementitious substance; Reaumur thinks that they eject very
little, if any, during the rest of their lives.

In the progress of these insects, such changes take place, as we could
have formed no conception of, if the great Author of these wonders had
not been pleased to reward the industrious naturalist with the
discovery.

If the moth be opened down the belly, and the unctuous parts which fill
it, be removed, the gross artery, which has been called the heart, will
be visible, and the contractions and dilatations, by which it pushes
forward the liquor it contains, may be easily observed. One of the most
remarkable circumstances is, that the circulation of this fluid in the
moth is directly contrary to that which took place in the caterpillar;
in this, the liquor moved from the tail to the head, whereas in the
moth, it moves from the head to the tail; so that the fluid which
answers the purposes of the blood in the moth, goes from the superior,
towards the inferior parts, but in the voracious sensual caterpillar,
the order is inverted, it proceeds from the inferior towards the
superior parts; all its members, formerly soft, inactive, and folded up
under an envelope, are expanded, strengthened, and exposed to
observation.

The food of the caterpillar is gross and solid, and even this it is
obliged to earn with much labour and danger; but, when freed as it were
from the jaws of death, and arrived at its perfect form, the purest
nectar is its potion, and the air its element. It was supplied with
coarse food, in the first state, by the painful operation of its teeth,
which was afterwards digested by a violent trituration of the stomach.
The intestines are now formed in a more delicate manner, and suited to a
more pure and elegant aliment, which nature has prepared for its use
from the most fragrant and beautiful flowers. Many internal parts of the
caterpillar disappear in the chrysalis, and many that could not be
perceived before, are now rendered visible: the interior changes are not
less surprizing than those of the exterior form, and are, properly
speaking, creative of them; for it is from these the exterior form
originates, and with these it always corresponds. In a word, the
creature that heretofore crept upon the earth, now flies freely through
the air; and far from creating our aversion by its frightful prickles
and foul appearance, it attracts our notice by the most elegant shape
and apparel, and, from being scarce able to move from one shrub to
another, acquires strength and agility to tower far above the tallest
inhabitant of the forest.


OF THE SILK-WORM.

The industry of those that spin cones or cases, in which they inclose
themselves, in order to prepare for their transformation in security, is
more generally known, as it is from one species of these that we derive
so many benefits, namely from the silk-worm, whose works afford an
ornament for greatness, and add magnificence to royalty. All
caterpillars undergo similar changes with it, and many in the butterfly
state greatly exceed it in beauty: but the golden tissue, in which the
silk-worm wraps itself, far surpasses the silky threads of all the other
kinds; they may indeed come forth with a variety of colours, and wings
bedecked with gold and scarlet, yet they are but the beings of a
summer’s day; both their life and beauty quickly vanish, and leave no
remembrance after them; but the silk-worm leaves behind it such
beneficial monuments, as at once record the wisdom of its Creator, and
his bounty to man.[70]

  [70] Pullein on the Culture of Silk.

The substance of which the silk is formed, is a fine yellow transparent
gum, contained in two reservoirs that wind about the intestines, and
which, when they are unfolded, are about ten inches long; they terminate
in two exceeding small orifices near the mouth, through which the silk
is drawn, or spun to the degree of fineness which its occasions may
require. This apparatus has been compared to the instrument used by
wire-drawers, and by which gold and silver is drawn to any degree of
minuteness. From each of these reservoirs proceeds a thread, which are
united afterwards; so that if it be examined by the microscope, it will
be found to consist of two cylinders or threads glued together, with a
groove in the middle; a separation may sometimes be perceived.

When the silk-worm has found a convenient situation, it sets to work,
first spinning some random threads, which serve to support the future
superstructure; upon these it forms an oval of a loose texture,
consisting of what is called the floss-silk; within this it forms a firm
and more consistent ball of silk, remaining during the whole business
within the circumference of the spheroid that it is forming, resting on
its hinder parts, and with its mouth and fore legs directing and
fastening the threads. These threads are not directed in a regular
circular form, but are spun in different spots, in an infinite number of
zig-zag lines; so that when it is wound off, it proceeds in a very
irregular manner, sometimes from one side of the cone, then from the
other. This thread, when measured, has been found to be about
three-hundred yards long, and so fine, that eight or ten are generally
rolled off into one by the manufacturers. The silk-worm usually employs
about three days in finishing this cone; the inside is generally smeared
with a kind of gum, that is designed to keep out the rain: in this cone
it assumes the pupa form, and remains therein from fifteen to thirty
days, according to the warmth of the climate. When the moth is formed,
it moistens the end of this cone, and by frequent motions of the head
loosens the texture of the silk, so as to form a hole without breaking
it.

When the silk-worm has acquired its perfect growth, the reservoirs of
silk are full, and it is pressed by its sensations to get rid of this
incumbrance, and accordingly spins a cone, the altitude and size of
which are proportioned to its wants: by traversing backwards and
forwards, it is relieved, and attains by an innate desire the end for
which it was formed; and thus a caterpillar, whose form is rather
disgusting to the human unphilosophic eye, becomes a considerable object
of manufacture and trade, a source of wealth, and, from the extensive
employment it affords, a blessing to thousands. The size of the cone is
not always proportioned to that of the caterpillar; some that are small
construct larger cones than others which exceed them in bulk.

There is a caterpillar which forms its silken cone in the shape of a
boat turned bottom upwards, whence it is called by Reaumur the “coque en
batteau;” the construction is complicated, and seems to require more art
than is usually attributed to this insect. It consists of two principal
parts, shaped like shells, which are united with considerable skill and
propriety; each shell or side is framed by itself, and formed of an
innumerable quantity of minute silk rings; in the fore part there is a
projection, in which a small crevice may be perceived, which serves,
when opened, for the escape of the moth; the sides are connected with so
much art, that they open and shut as if framed with springs; so that the
cone, from which the butterfly has escaped, appears as close as that
which is still inhabited.

Those caterpillars which are not furnished with a silky cone, supply
that want with various materials, which they possess sufficient skill to
form into a proper habitation, to secure them while preparing for the
perfect state; some construct theirs with leaves and branches, tying
them fast together, and then strengthening the connection; others
connect these leaves with great regularity; many strip themselves of
their hairs, and form a mixture of hair and silk; others construct a
cone of sand, or earth, cementing the particles with a kind of glue;
some gnaw the wood into a kind of saw-dust, and glue it together; with
an innumerable variety of modes suited to their present and future
state.


OF THE BEETLE.

To make the reader more fully acquainted with a subject which affords
such abundant matter for the exercise of his microscope, I shall
proceed to describe, in as concise a manner as I am able, the changes of
a few insects of different classes, beginning with the beetle.

The beetle is of the first or coleopterous class, having four wings. The
two upper ones are crustaceous, and form a case to the lower ones; when
they are shut, there is a longitudinal suture down the back: this
formation of the wings is necessary, as the beetle often lives under the
surface of the earth, in holes which it digs by its own industry and
strength. These cases save the real wings from the damage which they
might otherwise sustain, by rubbing or crushing against the sides of its
abode; they serve also to keep the wings clean, and produce a buzzing
noise when the animal rises in the air. The strength of this insect is
astonishing; it has been estimated that, bulk for bulk, their muscles
are a thousand times stronger than those of a man!

The beetle is only an insect disengaged from the pupa form; the pupa is
a transformation in like manner from the worm or larva, and this
proceeds from the egg; so that here, as in the foregoing instances, one
insect is exhibited in four different states of life, after passing
through three of which, and the various inconveniences attendant on
them, it is advanced to a more perfect state. When a larva, it trains a
miserable existence under the earth; in the pupa form it is deprived of
motion, and as it were dead; but the beetle itself lives at pleasure
above and under ground, and also in the air, enjoying a higher degree of
life, which it has attained by slow progression, after passing through
difficulties, affliction, and death.

If we judge of the rank which the beetle holds in the scale of
animation, from the places where they are generally found, from the food
which nourishes them, from the disgusting and odious forms of many,
from their antipathy to light, and their delight in darkness, we shall
not form great ideas of the dignity of their situation. But as all
things are rendered subservient to the laws of divine order, it is
sufficient for us to contemplate the wonders that are displayed in this
and every other organ of life, for the reception of which, from the
FOUNTAIN AND SOURCE OF ALL LIFE, each individual is adapted, and that in
a manner corresponding to the state of existence it is to enjoy, and the
energies it is called forth to represent.

The egg of the rhinoceros beetle[71] is of an oblong round figure, of a
white colour; the shell thin, tender, and flexible; the teeth of the
worm that is within the shell come to perfection before the other parts;
so that as soon as it is hatched, it is capable of devouring, and
nourishing itself with the wood among which it is placed. The larva or
worm is curiously folded in the egg, the tail resting between the teeth,
which are disposed on each side the belly; the worm in proper time
breaks the shell, in the same manner as a chicken, and crawls from
thence to the next substance suitable for its food. The worm, when it is
hatched, is very white, has six legs, and a wrinkled naked body, but the
other parts are all covered with hair; the head is then also bigger than
the whole body, a circumstance which may be observed in larger animals,
and which is founded on wise reasons.[72] If the egg be observed from
time to time while the insect is within it, the beating of the heart may
be perceived.

  [71] Scarabæus Acteon, Lin. Syst. Nat. p. 541-3.

  [72] Swammerdam’s Book of Nature, pt. 1, p. 33.

The eggs of the earth-worm, the snail, and the beetle, will afford many
subjects for the microscope, and will be found to deserve a very
attentive examination. Swammerdam was accustomed to hatch them in a
dish, covered with white paper, which he always kept in a moist state.
To preserve these and similar eggs, they must be pierced with a fine
needle; the contained liquors must be pressed out, after which they
should be blown up by means of a small glass tube, and then filled with
a little resin dissolved in oil of spike.

The worm of the rhinoceros beetle, like other insects in the larva
state, changes its skin; in order to effect which, it discharges all its
excrement, and forms a convenient hole in the earth, in which it may
perform the wonderful operation; for it does not, like the serpent, cast
off merely an external covering, but the throat, a part of the stomach,
and the inward surface of the great gut, change at the same time their
skin: as if it were to increase the wonder, and to call forth our
attention to these representative changes, some hundreds of pulmonary
pipes cast also each its delicate skin, a transparent membrane is taken
from the eyes, and the skull remains fixed to the exuvia. After the
operation, the head and teeth are white and tender, though at other
times as hard as bone; so that the larva, when provoked, will attempt to
gnaw iron. For an accurate anatomical description of this worm, I must
refer the reader to Swammerdam; he will find it, like the rest of this
author’s works, well worthy of his attentive perusal. To dissect it, he
first killed it in spirit of wine, or suffocated it in rain water rather
more than lukewarm, not taking it out from thence for some hours. This
preparation prevents an improper contraction of the muscular fibres.

When the time approaches for the worm to assume the pupa form, it
generally penetrates deeper into the ground,[73] or those places where
it inhabits, to find a situation that it can more easily suit to its
subsequent process. Having found a proper place, it forms with the
hinder feet a polished cavity, in this it lies for sometime immoveable;
after which, by voiding excrementitious substances, and by the
evaporation of humidity, it becomes thinner and shorter, the skin more
furrowed and wrinkled, so that it soon appears as if it were starved by
degrees. If it be dissected about this period, the head, the belly, and
the thorax may be clearly distinguished. While some external and
internal parts are changing by a slow accretion, others are gently
distended by the force of the blood and impelled humours. The body
contracting itself, while the blood is propelled towards the head,
forces the skull open in three parts, and the skin in the middle of the
back is separated, by means of an undulating motion of the incisions of
the back; at the same time the eyes, the horns, the lips, &c. cast their
exuvia. During this operation, a thin watery humour is diffused between
the old and new skin, which renders the separation easier. The process
going on gradually, the worm is at last disengaged from its skin, and
the limbs and parts are, by a continual unfolding, transformed into the
pupa state; after which, it twists and compresses the exuvia by the
fundament, and throws it towards the hinder part under the belly. The
pupa is at this time very delicate, tender, and flexible; and affords a
most astonishing appearance to an attentive observer. Swammerdam thinks
it is scarce to be equalled among the wonders which are displayed in the
insect part of the creation; in it the future parts of the beetle are
finely exhibited, so disposed and formed, as soon to be able to serve
the creature in a more perfect state of life, and to put on a more
elegant form.

  [73] The larvæ of those beetles which live under ground are in general
  heavy, idle, and voracious; on the contrary, the larvæ which inhabit
  the waters are exceedingly active.

The pupa[74] of this insect weighs, a little after its change, much
heavier than it does in its beetle state; this is also the case with
the pupa of the bee and hornet. The latter has been found to weigh ten
times as much as the hornet itself; this is probably occasioned by a
superabundant degree of moisture, by which these insects are kept in a
state of inactivity, which may be compared to a kind of preternatural
dropsy, till it is in some measure dissipated; in proportion as this
moisture is evaporated, the skin hardens and dries: some days are
required to exhale this superfluous moisture. If the skin be taken off
at this time, many curious circumstances may be noted; but what claims
our attention most is, that the horn, which is so hard in the male
beetle when in a state of maturity, that it will bear to be sharpened
against a grindstone,[75] in the pupa state is quite soft, and more like
a fluid than a solid substance. How long the scene of mutation continues
is not known; some remain during the whole winter, more particularly
those which quit the larva state in autumn, when a sudden cold checks
their further operations, and consequently they remain in a torpid
state, without any food, for several months. Some species of the beetle
tribe go through all the stages of their existence in a season, while
others employ near four years in the process, and live as winged insects
a year.

  [74] Swammerdam’s Book of Nature, p. 144.

  [75] Mouffet, p. 152.

When the proper time for the final change arrives, all the muscular
parts grow strong, and are thus more able to shake off their last
integuments, which is performed exactly in the same manner as in the
passage of the insect from the larva to the pupa state; so that in this
last skin, which is extremely delicate, the traces of the pulmonary
tubes, that have been pulled off and turned out, again become visible.
All parts of the insect, and more particularly the wings and their
cases, are at this period swelled and extended by the air and fluids
which are driven into them through the arteries and pulmonary tubes; the
wings are now soft as wet paper, and the blood issues from them on the
least wound; but when they have acquired their proper consistency, which
in the elytra is very considerable, they do not exhibit the least sign
of any fluid within them, though cut or torn almost asunder. The pupa
being disengaged from its skin, assumes a different form, in which it is
dignified with the name of a beetle, and acquires a distinction of sex,
being either male or female. The insect now begins to enjoy a life far
preferable to its former state of existence; from living in dirt and
filth, under briars and thorns, it raises itself towards the skies,
plays in the sun-beam, rejoices in its existence, and is nourished with
the oozing liquors of flowers.


OF THE MUSCA CHAMÆLEON.

I shall now proceed to illustrate the nature of the different
transformations in insects, by giving an account of the musca chamæleon.
In the worm or larva condition it lives in the water, breathes by the
tail, and carries its legs within a little snout near its mouth. When
the time arrives for its pupa state, it goes through the change without
casting off the skin of the larva. Lastly, in the imago, or fly state,
it would infallibly perish in the water, that element which had hitherto
supplied it with life and motion, was not the larva by nature instructed
where to choose a suitable situation for its approaching transformation.

This insect is characterized by Linnæus as “Musca chamæleon. Habitat
larva in aquis dulcibus; musca supra aquam obambulare solet.” In a
former edition of the Fauna Suecica he called it oestrus aquæ; but on a
more minute examination, he found it was a musca; besides, the larvæ of
all known oestri are nourished in the bodies of animals. The larva of
this insect appears to consist of twelve annular divisions, see Plate
XI. Fig. 1. by these it is separated into a head, thorax, and abdomen;
but as the stomach and intestines lie equally in the thorax and
abdomen, it is not easy to distinguish their limits until the insect
approaches the pupa state. The parts most worthy of notice are the tail
and snout. The tail is furnished with an elegant crown or circle of hair
b, disposed quite round it in an annular form; by means of this the tail
is supported on the surface of the water, while the worm or larva is
moving therein, the body in the mean while hanging towards the bottom;
it will sometimes remain in this situation for a considerable time,
without the least sensible motion. When it is disposed to sink to the
bottom by means of its tail, it generally bends the hairs of that part
towards each other in the middle, but much closer towards the extremity;
by these means a hollow space is formed, and the bladder of air pent up
in it looks like a pearl, Fig. 2. Plate XI. It is by the assistance of
this bubble, or little balloon, that the insect raises itself again to
the surface of the water. If this bubble escape, it can replace it from
the pulmonary tubes; sometimes large quantities of air may be seen to
arise in bubbles from the tail of the worm to the surface of the water,
and there mix with the incumbent atmosphere. This operation may be
easily seen by placing the worm in a glass full of water, where it will
afford a very entertaining spectacle. The snout is divided into three
parts, of which that in the middle is immoveable; the two other parts
grow from the sides of the former; these are moveable, vibrating in a
very singular manner, like the tongues of lizards and serpents. The
greatest strength of the creature is fixed in these lateral parts of the
snout; it is on these that it walks when it is out of the water,
appearing, as it were to walk on its mouth, using it to assist motion,
as a parrot does its beak to climb, with greater advantage.

We shall now consider the external figure of this worm, as it appears
with the microscope. It is small toward the head, larger about those
parts which may be considered as the thorax; it then again diminishes,
converging at the abdomen, and terminates in a sharp tail, surrounded
with hairs in the form of the rays of a star.

This worm, the head and tail included, has twelve annular divisions, 1,
2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, Fig. 3. Plate XI. Its skin resembles
the covering of those animals that are provided with a crustaceous
habit, more than it does that of naked worms or caterpillars; it is
moderately hard, and like the rough skin called shagreen, being thick
set with a number of grains, evenly distributed. The substance of the
skin is firm and hard, and yet very flexible. On each side of the body
are nine spiracula or holes, for the purpose of respiration; there are
no such holes visible on the tail ring _a_, nor on the third ring
counting from the head; for at the extremity of the tail there is an
opening for the admission and expulsion of air; in the third ring the
spiracula are very small, and appear only under the skin, near the place
where the embryo wings of the future fly are concealed. It is remarkable
that caterpillars, in general, have two rings without these spiracula;
perhaps, because they change into flies with four wings, whereas this
worm produces a fly that has only two. The skin has three different
shades of colour; it is adorned with oblong black furrows, with spots of
a light colour, and orbicular rings, from which there generally springs
a hair, as in the figure before us, only the hair that grows on the
insect’s side is represented; besides this, there are here and there
some other larger hairs, c c. The difference of colour in this worm
arises from the quantity of grains in the same space; for in proportion
as there is a greater or lesser quantity of these, the furrows and rings
are of a deeper or paler colour. The head _d_ is divided into three
parts, and covered with a skin, the grains on which are hardly
discernible. The eyes are rather protuberant, and lie forwards near the
snout. It has also two small horns i i, on the fore part of the head.
The snout is crooked, and ends in a sharp point as at f; but what is
altogether singular and surprizing, though no doubt wisely contrived by
the great and almighty Architect, is, that this insect’s legs are placed
near the snout, between the sinuses, in which the eyes are fixed. Each
of these legs consists of three joints, the outermost of which is
covered with hard and stiff hairs like bristles. From the next joint
there springs a horny bone h h, which the insect uses as a kind of
thumb; the joint is also of a black substance, between bone and horn in
hardness; the third joint is of the same nature. To distinguish these
particulars, the parts that form the upper sides of the mouth and the
eyes must be separated by means of a small fine knife; you may then, by
the assistance of the microscope, perceive that the leg is articulated,
by means of some particular ligaments, with that portion of the insect’s
mouth which answers to the lower jaw in the human frame. We may then
also discern the muscles which serve to move the legs, and draw them up
into a cavity that lies between the snout and those parts of the mouth
which are near the horns i i.

This insect not only walks with these legs at the bottom of the water,
but even moves itself on land by means of them; it likewise makes use of
them to swim, while it keeps its tail on the surface contiguous to the
air, and hangs downward with the rest of the body in the water: in this
situation no motion is perceived in it, but what arises from its legs,
which it moves in a most elegant manner. It is reasonable to conclude
from what has been said, that the principal part of the creature’s
strength lies in these legs; nor will it be difficult for those who are
acquainted with the nature of the ancient hieroglyphics, which are now
opening so clearly, to fix the rank of this insect in animated life, and
point out those orders of being, and the moral state through which it
receives its form and habits of life.

The snout is black and hard, the back part is quite solid, and somewhat
of a globular form, whereas the front f, is sharp and hollow; on the
back part three membranaceous divisions may be observed, by means of
which, and the muscles contained in the snout, the insect can at
pleasure expand or contract it.

The tail is constructed and planned with great skill and wisdom. The
extreme verge or border, is surrounded by thirty hairs, and the sides
adorned with others that are smaller; here and there the large hairs
branch out into smaller ones, which may be reckoned as single hairs.
These hairs are all rooted in the outer skin, which in this place is
covered with rough grains, as may be seen by cutting it off, and holding
it up, when dry, against the light, upon a thin plate of glass. By the
same mode you will find, that at the extremities of the hairs there are
also grains like those of the skin; in the middle of the tail there is a
small opening, within it are minute holes, by which the insect inhales
and expels the air it breathes. The hairs are very seldom disposed in so
regular a manner as they are represented in Fig. 3. Plate XI. except
when the insect floats with the body in the water, and the tail with its
hairs a little lower than the surface, for they are then displayed
exactly as delineated in the plate. The least motion downward of the
tail produces a concavity in the water, and it then assumes the figure
of a wine-glass, wide at the top, narrow at the bottom. The tail serves
the larva both for the purposes of swimming and breathing, and it
receives through the tail that which is the universal principle of life
and motion in animals. By means of the hairs it can stop itself at
pleasure when swimming, or remain suspended quietly in the water for any
length of time. The motion of the insect in swimming is very beautiful,
especially when it advances with its whole body floating on the surface
of the water; after filling itself with air by the tail. To set out, it
first bends the body to the right or left, and then contracts it in the
form of the letter S, and again stretches it out in a strait line: by
thus alternately contracting and then extending the body, it moves along
on the surface of the water. It is of a very quiet disposition, and not
to be disturbed by handling.

These larvæ are generally to be found in shallow standing waters, about
the beginning of June, sooner or later, as the summer is more or less
favourable; in some seasons they are to be found in great numbers, while
in others, it is no easy matter to meet with them. They love to crawl on
the plants and grass which grow in the water, and are often to be met
with in ditches, floating on the surface of the water by means of their
tail, the head and thorax at the same time hanging down; and in this
situation they will turn over the clay and dirt with their snout and
feet in search of food, which is generally a viscous matter that is
common in small ponds and about the sides of ditches. This worm is very
harmless, contrary to the opinion one might form at first sight, from
the surprizing vibratory motion of the legs, which resembles the
brandishing of an envenomed tongue or sting. They are most easily killed
for dissection in spirit of turpentine.

After a certain period they pass into the pupa form; when they are about
to change, they betake themselves to the herbs that float on the surface
of the water, and creep gently thereon, till at length they lie partly
on the dry surface, and partly on the water; when in the larva or pupa
state, they can live in water, but can by no means inhabit there when
changed into flies: indeed, man also, whilst in the uterus, lives in
water, which he cannot do afterwards. When these worms have found a
proper situation, they by degrees contract themselves, and in a manner
scarce perceptible lose all power of motion. The inward parts of the
worm’s tail now separate from the outmost skin, and become greatly
contracted; this probably gives the insect considerable pain: by this
contraction, an empty space is left in the exterior skin, into which the
air soon penetrates.

Thus this insect passes into the pupa state under its own skin, entirely
different from that of the caterpillar, which casts off the exterior
skin at this time; this change may often be observed to take place in
the space of ten or twelve hours, but in what manner it is performed we
are ignorant, as it is effected in a hidden unknown way, inwardly within
the skin, which conceals it from our view.

Whilst the larva is changing under the skin, the body, head, and tail,
separate insensibly from their outward vesture. The legs at this time,
and their cartilaginous bones, are, on account of the parts which are
withdrawn from them, left empty; the worm loses also now the former
skull, the beak, together with the horny bones belonging thereto, which
remain in the skin of the exuvia. It is worthy of notice, that the optic
nerves separate also from the eyes, and no more perform their office.
The muscles of the rings in like manner, and a great part of the
pulmonary points of respiration, are separated from the external skin.
Thus the whole body contracts itself by degrees into a small compact
mass. At this time the gullet and the pulmonary tubes cast a coat within
the skin. To make this evident, it is necessary to open the abdomen,
when the pupa, its parts, together with the cast off pulmonary pipes,
may be clearly seen.

An exact account of all the changes of the interior parts is to be found
in Swammerdam’s Book of Nature. These changes are best examined by
taking the pupa out of the skin, or outside case, when it begins to
harden; for as it has not then quite attained the pupa form, and the
members are somewhat different from what they will be when in that
state, it is more easy to observe their respective situation, than when
the pupa is some days older, and has lost the greatest part of the
superfluous humours. The pupa is inclosed in a double garment; the
interior one is a thin membrane, which invests it very closely; the
other, or exterior one, is formed of the outermost hard skin of the
larva, within which it performs its changes in an invisible manner: it
is this skin which gives it the appearance of the larva while in the
pupa state.

When the time approaches that the hidden insect, now in the pupa form
within its old covering, is to attain the imago, fly, or perfect state,
which generally happens in about eleven days after the preceding change,
the superfluous humours are evaporated by insensible perspiration. The
little pupa is contracted into the fifth ring of the skin, and the four
last rings of the abdomen are filled with air, through the aperture in
the respiratory orifice of the tail. This may be seen by exposing the
pupa for a short space to the rays of the sun, and then putting its tail
in water, when you will find it breathe stronger than it did before,
and, by expressing an air bubble out of its tail, and then sucking it in
again, will manifestly perform the action of inspiration and expiration.
The anterior part of the pupa is drawn back from the skin, and having
partly deserted it, with the beak, head, and first ring of the breast,
the little creature lies still, until its exhaling members have acquired
strength to burst the two membranes which surround it.

If the exterior case be opened near this period, a wonderful variety of
colour may be perceived through the thin skin which invests the pupa.
The colours of many of the different parts are now changed; some parts
from aqueous become membranaceous, some fleshy, and others crustaceous.
The whole body becomes insensibly shaggy, the feet and claws begin to
move: the variations may be accurately observed by opening a pupa every
day until the time of change. For this purpose they should be laid on
white paper in an earthen dish; they should also be made somewhat moist,
and be kept under a glass: the paper serves the pupa to fix its claw to,
when they come forth in the form of a fly. A little water should be
poured into the dish, to keep the pupa from drying and suffocation.

When the fly begins to appear, the exterior skin is seen to move about
the third and fourth anterior ring; the insect then uses all its efforts
to promote its escape, and to quit the interior and exterior skin at one
and the same time. The exterior skin is divided into four parts; the
insect immediately afterwards breaks open its inner coat, and casting it
off, escapes from the prison in which it was entombed, in the form of a
beautiful fly. It is to be observed here, that there is nothing
accidental in the breaking of the outermost skin, being perfectly
conformable to the rule ordained, always happening in the same manner in
all these changes: the skin also is, in those places where it is broke
open, so constructed by the Author of nature, as if joined together by
sutures. Having now acquired its perfect state, the little creature
which lived before in water and mud, enters into a new scene of life,
visits the fields and meadows, is transported through the air on its
elegant wings, and sports in the wide expanse with unrestrained jollity
and freedom.

The larva a queue de rat,[76] musca pendula, Lin. is also transformed
under the skin, which hardens, and forms a case or general covering to
the pupa: two horns are pushed out, while it is in this state, from the
interior parts; they serve the purpose of respiration: this larva will
be more particularly described in a subsequent part of this chapter.

  [76] Reaum. 8vo. edit. tom. 4, pt. 2, 11 mem. p. 199, plate 30 and 31.

According to Reaumur, the insects in this class, that is, those that
pass into the pupa state under the skin of the larva, go through a
change more than the caterpillar, a transformation taking place while
under their skin, before they assume the pupa form.

The aquatic larva of the musca chamæleon retains its form to the last;
but there are many insects that are transformed under their skin, which
forms a cone or case for the pupa. In these the larva loses first its
length; the body becoming shorter, assumes the figure of an egg; and the
skin forms a hard and crustaceous case or solid lodging for the embryo
insect.


OF THE LIBELLULA OR DRAGON FLY.

In the libellula we have an instance of those insects which are termed
in the pupa state, semicompleta, that is, such as proceed from the egg
in the figure which they preserve till the time arrives for assuming
their wings; and who walk, act, and eat as well before that period as
afterwards.

Of all the flies which adorn or diversify the face of nature, there are
few, if any, more beautiful than the libellulæ: they are almost of all
colours, green, blue, crimson, scarlet, and white; some unite a variety
of the most vivid teints, and exhibit in one animal more different
shades than are to be found in the rainbow. It is not to colour alone
that their beauty is confined, it is heightened by the brilliancy of
their eyes, and the delicate texture and wide expansion of their wings.
The larva of the libellula is an inhabitant of the water, the fly itself
is generally found hovering on the borders thereof.

These insects are produced from an egg, which is deposited in the water
by the parent; the egg sinks to the bottom, and remains there till the
young insect finds strength to break the shell. The larva is hexapode,
and is not quite so long as the fly; on the trunk are four prominences
or little bunches, which become more apparent, in proportion as the
larva increases in size and changes its skin. These bunches contain the
rudiments of the wings, which adorn the insect when in its perfect
state.

The head of the larva is exceedingly singular, the whole fore part of it
being covered with a mask, which fits it more exactly than the common
mask does the human face, having proper cavities within to suit the
different prominences of the face; it is of a triangular form, growing
smaller towards the bottom; at this part there is a knuckle which fits a
cavity near the neck, on this it turns as on a pivot. The upper part of
this mask is divided into two pieces or shutters, which the insect can
open or close at pleasure; it can also let down the whole mask whenever
it pleases. The edges of the shutters are jagged like a saw. It makes
use of the mask to seize and hold its prey. There is a considerable
difference in the shape of these masks in different species of the
libellula, some having two claws near the top of it, which they can
thrust out or draw in, as most convenient; these render it a very
formidable instrument to the insects on which they feed.

These animals generally live and feed at the bottom of the water,
swimming only occasionally: their manner of swimming, or rather moving
in the water, is curious, being by sudden jerks given at intervals; but
this motion is not occasioned by their legs, which at this time are kept
immoveable and close to the body; it is by forcing out a stream of water
from the tail that the body is carried forward; this may be easily
perceived, by placing them in a flat vessel, in which there is only
just water enough to cover the bottom. Here the action of the water
squirted from their tail will be very visible; it will occasion a small
current, and give a sensible motion to any light bodies that are lying
on the surface thereof. This action can only be effected at intervals,
because after each expulsion the insect is obliged to inhale a fresh
supply of water. The larva will sometimes turn its tail above the
surface of the water, and eject a small stream from it as from a little
fountain, and that with considerable force.

The pupa differs but very little from the larva, the bunches containing
the wings grow large, and begin to appear like four short thick wings.
It is full as lively as the larva, seeking and enjoying its food in the
same manner: when it is arrived at its full growth, and is nearly ready
to go through its last change, it approaches the edge of the water, or
comes entirely out of it, fixing itself firmly to some piece of wood or
other substance, by its acute claws. It remains for some time
immoveable; the skin then opens down the back, and on the head; through
this opening is exhibited the real head and eyes, and at length the
legs; it then creeps gradually forward, drawing its wings, and then the
body out of the skin. The wings, which are moist and folded, now expand
themselves to their real size; the body is also extended till it has
gained its proper dimensions, which extension is accomplished by the
propelling force of the circulating fluids. When the wings and limbs are
dry, it enters on a more noble state of life: in this new scene it
enjoys itself to the fullest extent, feasts on the living fragrance
issuing from innumerable openings, sports and revels in delight, and,
having laid the foundation for its future progeny, sinks into an easy
dissolution.

The dragon fly is of a ferocious and warlike disposition, hovering in
the air like a bird of prey, in order to feed on and destroy every
species of fly; its appetite is gross and voracious, not confining
itself to small flies only, but the large flesh-fly, moths, and
butterflies, are equally subjected to its tyranny. It frequents marshy
grounds, where insects mostly abound.

The female of the CYNIPS or GALL INSECT, which has no wings, passes
through no transformation; while the male, which has four wings, passes
through the pupa state before it becomes a fly. The only change, though
a considerable one, which takes place in the female gall insect, is
this, that after a certain time it fixes itself to the branch of a tree,
without being able to detach itself; it afterwards increases much in
size, and becomes like a true gall; the female, by remaining thus fixed
for the greater part of her life, to the place where she was first seen,
has very little the appearance of an animal; it is in this period of
their life that they grow most and produce their young, while they
appear a portion of the branch they adhere to; and what is more
singular, the larger they grow, the less they appear like animals, and
whilst they are employed in laying thousands of eggs, seem to be nothing
but mere galls. The genera of gall insects are very extensive; they are
to be found on almost every shrub and tree.

The APHIDES or PLANT LICE, to arrive at their respective state, pass
through that of the semicomplete pupa, and their wings do not appear
till they have quitted their pupa state; but as in all the families of
the pucerons there are many which never become winged, we must not
forget to observe, that these undergo no transformation, remaining
always the same, without changing their figure, though they increase in
size and change their skin. It is remarkable, that amongst insects of
the same kind, some individuals should be transformed, while others are
not at all changed. These insects will be considered more fully in
another part of this chapter.

Reaumur[77] has shewn that the SPIDER FLY, hyppobosca equina, Lin. lays
so large an egg, that the fly which proceeds from it is as big as the
mother, though the egg does not increase the least in size from the time
it is first laid. The insect proceeds also from the egg in the imago or
fly state; it is probably transformed in the egg, for Reaumur has found
it in the pupa state therein, and having boiled some of their eggs which
had been laid for some days, he found the insect in the form of an oval
ball, similar to that in which the pupa of flies with two wings are
generally found. De Geer is of opinion that the egg itself is a true
larva, which, when it is born, has only to disengage its limbs, &c. from
the shell which covers it; and he thinks this the more probable, because
there is no embryo seen in this egg, but it is entirely filled with the
insect; he has also perceived a contracting and dilating motion in the
egg, while it was in the belly of the mother, and immediately after it
was laid; circumstances which do not agree with a simple egg.

  [77] Reaumur, tom. 6, mem. 14.

As M. Bonnet[78] has attempted to give a theory of these various
changes, the following extract from it will, I hope, prove agreeable to
the reader; it will at least tend to render his ideas of this wonderful
subject clearer, and will probably open to his mind many new sources of
contemplation.

  [78] Bonnet Considerations sur les Corps organises. Contemplation of
  Nature, &c.

An insect that must cast off its exuvia, or moult five times before it
attains the pupa state, may be considered as composed of five organized
bodies, inclosed within each other, and nourished by common viscera,
placed in the center: what the bud of the tree is to the invisible buds
it contains, such is the exterior part of the caterpillar to the
interior bodies it conceals in its bosom. Four of these bodies have the
same essential structure, namely, that which is peculiar to the insect
in its larva or caterpillar state: the fifth body is that of the pupa.
The respective state of these bodies is in proportion to their distance
from the center of the animal; those that are farthest off have most
consistence, or unfold themselves soonest. When the exterior body has
attained its full growth, that interior one which is next in order is
considerably unfolded; it is then lodged in too narrow a compass,
therefore it stretches on all sides the sheath which covers it; the
vessels which nourish the external covering, are broken by this violent
distension, and ceasing to act, the skin wrinkles and dries up; at
length it opens, and the insect is cloathed with a new skin, and new
organs. The insect generally fasts for a day or two preceding each
change; this is probably occasioned by the violent state in which it
then is, or it may be necessary to prevent obstructions, &c. let this be
as it may, the insect is always very weak after it has changed its skin,
the parts being as yet affected by the exertions they have gone through.
The scaly parts, as the head and legs, are almost entirely
membranaceous, and imbrued with a fluid that insinuates itself between
the two skins, and thus facilitates their separation; this moisture
evaporates by degrees, all the parts acquire a consistence, and the
insect is then in a condition to act.

The first use that some caterpillars which live on leaves make of their
new form, is to devour greedily their exuvia: sometimes they do not wait
till their jaws have acquired their full strength; some have been seen
to gnaw the shell from which they proceeded, and even the eggs of such
caterpillars as have not been hatched.

When we have once formed the idea that all the exterior parts are
inlaid, or included one within the other, the production of new organs
does not appear so embarrassing, being nothing more than a simple
developement; but it is more difficult to form any conception of the
changes that happen in the viscera before and after the transformation,
the various modifications they undergo eluding our researches. We have
already observed, that a little before the change the caterpillar
rejects the membrane that lines the intestinal bag: this bowel has
hitherto digested only gross food, whereas it must hereafter digest that
which is very delicate: a fluid that circulates in the caterpillar from
the hind part towards the head, circulates a contrary way after
transformation. Now if this inversion is as real as observation seems to
indicate, how amazing the change the interior parts of the animal must
have undergone? When the caterpillar moults, small clusters of the
tracheal vessels are cast off with the exuvia, and new ones are
substituted in their room; but how is this effected, and how are the
lungs replaced by other lungs? The more we endeavour to investigate this
subject, the more we find it is enveloped in darkness.

Whilst the powers of life are employed conformable to the laws of Divine
Providence, to change the viscera, and give them a new form, they are
also unfolding divers other organs, which were useless to the insect
while in the larva state, but which are necessary to that which
succeeds. That these interior operations of life may be carried on with
greater energy, the animal is thrown into a kind of sleep; during this
period, the corpus crassum is distributed into all the parts, in order
to bring them to perfection, while the evaporation of the superfluous
humours makes way for the elements of the fibres to approach each other,
and unite more closely. The little wounds in the inside, which have been
occasioned by the rupture of the vessels, are gradually consolidated;
those parts which had been violently exercised, recover their tone, and
the circulating fluids insensibly find their new channel. Lastly, many
vessels are effaced, and turned into a liquid sediment, which is
rejected by the perfect insect.

When these various changes are considered, we are surprized at the
singularity of the means the AUTHOR OF NATURE has made choice of, in
order to bring the different species of animals to perfection; and are
apt to ask, why the caterpillar was not born a moth? why it passes
through the larva and pupa state? why all insects that are transformed
do not undergo the same change? These, and a variety of questions that
may be started concerning the constituent substances of those existences
which appear before us, derive their solution from the general system
which is unknown to us. If all were to arrive at perfection at once, the
chain would be broken, the creature unhappy, and man most of all. Let us
also consider what riches we should have been deprived of, if the
silk-worm had been born in its perfect state.

Amongst insects, some are produced in the state in which they will
remain during their whole lives; others come forth inclosed in an egg,
and are hatched from this into a form that admits of no variation; many
come into the world under a form which differs but little from that
which they have when arrived at an age of maturity; some again assume
various forms, more or less remote from that which constitutes their
perfect state; lastly, some go through part of these transformations in
the body of the parent, and are born of an equal size with them. By
these various changes, a single individual unites within itself two or
three different species, and becomes successively the inhabitant of two
or three worlds: and how great is the diversity of its operation in
these various abodes!

Since it has been shewn that the larva or caterpillar is really the
moth, crawling, eating, and spinning, under the form of the worm, and
that the pupa is only the moth swathed up, it is clear that they are not
three beings, but that the same individual feels, tastes, sees, and acts
by different organs, at different periods of its life, having sensations
and wants at one time, which it has not at another; these always bearing
a relation to the organs which excite them.


OF THE RESPIRATION OF INSECTS.

As respiration is one of the most important actions in the life of every
animal, great pains have been taken by many naturalists to investigate
the nature of this action in insects; to prove its existence, and
explain in what manner it is carried on. Malpighi, Swammerdam, Reaumur,
and Lyonet have discovered in the caterpillar two air-vessels placed the
whole length of the insect, these they have called the tracheæ; they
have also shewn that an infinite number of ramifications proceed from
these, and are dispersed through the whole body; that the tracheal
vessels communicate with particular openings on the skin of the
caterpillar, termed spiracula; there are nine of these on each side of
the body. These vessels seem calculated for the reception of air; they
contain no fluids, are of a cartilaginous nature, and when cut preserve
their figure, and exhibit a well-terminated opening. Notwithstanding
this discovery, respiration has not been proved to exist in many species
of insects, and the mechanism thereof is very obscure in all; nor is the
absence of it more surprising in the caterpillar or embryo state of
insects, than in that of other animals, where we find that respiration
is by no means necessary to existence previous to their birth, though
indispensably so afterwards.

Reaumur thought that the air entered by the spiracula into the trachea,
but was not expelled by the same orifice, and consequently that the
respiration of insects was carried on in a manner totally different from
that of other animals; that the air was expired through a number of
small holes or pores which are to be found in the skin of the
caterpillar, after having been conducted to them through the extremities
of the finer ramifications of the tracheal vessels; whereas Bonnet, in
consequence of a great variety of experiments, supposed that the
inspiration and expiration of the air was through the spiracula, and
that there was no expiration of air through the pores of the skin. These
experiments were made either by plunging the caterpillars into water, or
anointing them with fat and greasy substances, some all over, others
only partially. The number of small bubbles which are observed to cover
the surface of their bodies, when they are immerged in water, does not
arise from the air which is included within, and then proceeding from
them, but they are formed by the air which is lodged near the surface of
their bodies, in the same manner that it is about all other substances.
To render the experiments more accurate, and prevent the air from
adhering to the skin, before he plunged the caterpillars in water he
always brushed them over with an hair pencil; after this, very few air
bubbles were found on their bodies when immerged in water. Caterpillars
will remain a considerable time under water, without destroying the
principle of life; and they also recover, in general, soon after they
are taken out. To know whether a few only of the spiracula might not be
sufficient for the purposes of respiration, he plunged some partially in
water, so that only two or more spiracula remained in the open air: in
these cases the caterpillar did not become torpid as it did when they
were all immerged in water. One caterpillar, upon which Bonnet made his
experiments, lived eight days suspended in water, with only two of its
anterior spiracula in the air; during this time he observed, that when
the insect moved itself, little streams of bubbles issued from the
anterior spiracula on the left side; from this, and many other
experiments, it appeared to him, that amongst all the eighteen
spiracula, the two anterior and the two posterior are of the greatest
use in respiration.[79] Sometimes when the apertures of these have been
stopped with oil, the caterpillar has fallen into convulsions. If the
posterior part had been oiled, that part became paralytic.
Notwithstanding these experiments, and many more which have been made,
the subject is far from being decided, and many still doubt whether
there is any respiration in insects similar to ours, at least at certain
periods of their life. This opinion seems to be further confirmed by the
experiments of M. Lyonet. He confined several large musk beetles under a
glass for more than half an hour, exposed to the fumes of burning
sulphur; and, though during their continuance there the vapour was so
thick that he could not see them, yet on their being liberated, they did
not seem at all effected thereby.[80]

  [79] Philos. Trans. vol. xlv. p. 300.

  [80] Lesser Theologie des Insectes, tom. 1, p. 124. Ibid. p. 126.

Supposing respiration to be absolutely necessary to the existence of the
pupæ of different insects, when we reflect on the great solidity of
their cases or cones, it is not easy to conceive how they can live
several months under the earth, in spaces so confined, and almost
impervious to the air: and indeed if they did respire, the same
situation seems to preclude a continuance of the operation, as the air
would soon be corrupted, and unfit for the offices of life. As the
tracheæ are divided and subdivided to a prodigious degree of minuteness,
it has been conjectured by some writers, that they may act as so many
sieves, which, by separations properly contrived, filtrate the air, and
so furnish it to the body of different degrees of purity and subtilty,
agreeable to the purposes and nature of the various parts. The
experiments that have been made with the air-pump are by no means
conclusive; the injury which the insect sustains when the atmospheric
pressure is taken from the body, does not prove that it inspired and
expired the air that we have removed; it only shews that an incumbent
pressure is necessary to their comfortable existence, as it prevents the
fluids from disengaging themselves in an aerial form, and as it
counterbalances and re-acts on the principle of life, and, by keeping
the action thereof in proper tone and order, confines and regulates its
energies.

Though it is difficult to ascertain whether some insects respire, at
least at certain periods of their existence, yet there are others to
whom the inspiration and expiration of air seems absolutely necessary:
there are many aquatic insects which are obliged to keep their tails
suspended on the surface of the water for this purpose. To prove this,
keep the tail under water, and you will perceive the insect to be
agitated and uneasy, and to seek for some opening to expose this part to
the air; if it find none, it soon goes to the bottom and dies. Some
aquatic beetles resist the trial for a considerable time, while their
larvæ can only support it for a few minutes. There is a circumstance
which renders all experiments on this subject with insects doubtful and
difficult, namely, the vast tenaciousness of the life principle in the
lower orders of animated nature, and its dissemination through their
whole frame.

Musschenbroeck inclosed the pupa of a moth in a glass tube, very little
larger than the moth itself, and of the following figure.

[Illustration]

The end A of the tube was drawn out in a capillary form, the other end
was covered with a piece of wet bladder to exclude the air; the
capillary end B was then plunged in water, which rose to D. He placed
the capillary part of the tube before a microscope, on a small
micrometer, in order to observe any motion or change in the situation of
the water; as it is evident the expiration or inspiration of air by the
insect would make it rise or fall alternately. In the first experiment
he observed a small degree of motion at distant intervals, not above two
or three times in an hour; in a second experiment on another subject, he
could observe no motion at all. He then placed some pupæ under the
receiver of an air-pump, in water which he had previously purged of its
air; on exhausting the air from the receiver, he observed one bubble to
arise in a part near the tail, and a few near the wings. The pupæ did
not swell under the operation; on the contrary, on letting in the air,
it was found to be diminished in a small degree, but in less than a
quarter of an hour it recovered its former figure. M. Martinet published
at Leyden, in 1753, a dissertation, in which, it is said, he has clearly
proved by a number of experiments that the pupæ of caterpillars and some
other insects do not respire.


OF RESPIRATION IN THE LARVA OF THE MUSCA PENDULA.

Among the insects in which respiration seems to be most clearly proved,
are the larvæ of the musca pendula, Lin. These, while in the worm state,
live under water in the mud, to which they affix themselves; the
respiration of fresh air in this situation is necessary to their
existence; for this purpose they are furnished with a tail, which often
appears of an excessive length comparatively with the body, as this is
seldom more than three quarters of an inch in length, while the tail is
frequently more than four inches; it is composed of two tubes, which run
one into the other, something similar to the tubes of a refracting
telescope. Besides this, the materials of which the tubes are composed
are capable of a great degree of extension. When the tail is at its full
length, it is exceeding small, not being larger near the extremity than
a horse-hair; there is a little knob at the end, which is furnished with
small hairs, to extend on the water, in some measure resembling those at
the tail of the musca chamæleon.

In the body of the larva are two large tracheal vessels; these
air-vessels extend from the head to the tail, terminate in the respiring
tubes, and receive the air from them. The larva quits the water when the
time of its transformation approaches, and enters into the earth, where
the skin hardens and forms a case in which the pupa is formed; soon
after the change, four tubes or horns are seen projecting from the case:
these Reaumur supposes to be organs for communicating air to the
interior parts of the insect; they are connected with little bladders
which are found filled with air, and by which it is conveyed to the
spiracula of the pupa. The larvæ of gnats, and other small aquatic
insects of the same kind, are furnished with small tubes, that play on
the surface of the water, and convey the air from thence to the insect.
Many other singularities are to be found amongst the aquatic larvæ.


OF THE GENERATION OF INSECTS.

One of the greatest mysteries in nature is generation, or that power by
which the various species of animals, &c. are propagated, enabling one
single individual to give birth to thousands, or even millions of
individuals like itself; all formed agreeable to proportions which are
only known to that ADORABLE WISDOM which has established them. We shall
never be able to form any adequate conception of this power, till we are
acquainted with the principles of life, and can trace their various
gradations in different orders of beings. Many ancient philosophers,
from a misconception and perversion of the sentiments of the more
ancient sages, imagined that insects were produced from corrupt and
putrefied substances; that organized bodies, animated with life, and
framed in a most wonderful manner, owed their origin to mere chance! Not
so the most ancient sages; they taught that every degree of life must
proceed from the fountain and source of all life, and that therefore,
when manifested, it must be replete with infinite wonders; but then they
also shewed, that if in its descent through the higher orders of being
it was perverted, it would be manifested in loathsome forms, and with
filthy propensities; and that according to the degree of reception of
the Divine Goodness and Truth, or the perversion thereof, new forms of
life would be occasionally manifested. The gloom of night still wraps
this subject in obscurity; will the dawn of day ere long gild the
horizon of the scientific world? or is the time of its breaking forth
yet far from us? Be this as it may, insects will be found to conform to
that general law of order which runs through the whole of animated
nature, namely, that the conjunction of the male and female is necessary
for the production of their offspring. Where we cannot ascertain causes,
we must be content with facts.

Though insects are, like larger animals, distinguished into male and
female, yet in some classes there is a kind of mules, partaking of
neither sex, though themselves originating from the conjunction of both:
many other particularities relative to the sexes can only be touched
upon here. In many insects the male and female are with difficulty
distinguished, and in some they differ so widely, that an unskilful
person might easily take the male and female of the same insect for
different species; as for instance, in the phalæna humuli, piniaria,
russula. The dissimilarity is still greater in those insects in which
the male has wings and the female none, as in the coccus lampyris,
phalæna antiqua, &c. In general the male is smaller than the female. The
antennæ of the male are, for the most part, larger than those of the
female. In some moths, and other insects which are furnished with
feathered antennæ, the feathers of the male fly are large and beautiful,
while those of the female are small, and hardly perceptible. Some male
beetles are furnished with a horn, which is wanting in the female.

“Pleraque insectorum genitalia sua intra anum habent abscondita, et
penes solitarios, sed nonnulla penem habent bifidum: cancri autem et
aranei geminos, quemadmodum nonnulla amphibia, et quod mirandum in loco
alieno, ut cancer, sub basi caudæ. Araneus mas palpos habet clavatos,
qui penes sunt, juxta os utrinque unicum, quæ clavæ sexum nec speciem
distinguunt; et fœmina vulvas suas habet in abdomine juxta pectus; heic
vero si unquam vere dixeris: res plena timoris amor, si enim procus
inauspicato accesserit, fœmina ipsum devorat, quod etiam fit, si non
statim se retraxerit. Libellula fœmina genitale suum sub apice gerit
caudæ, et mas sub pectore, adeo ut cum mas collum fœmina forcipe caudæ
arripit, illa caudam suam pectori ejus adplicet, sicque peculiari
ratione connexæ volitent.”

Insects are either oviparous or viviparous; or, in other words, the
species is perpetuated either by their laying of eggs, or bringing forth
their young alive. The former is the more general case; there are but
few instances of the latter. Those insects which pass through the
different transformations already described, cannot propagate till they
arrive at their imago or perfect state; and we believe there is seldom
any conjunction of the sexes in other classes till they have moulted, or
put off their last skin, the cancri and monoculi excepted.

To form a just idea of the ovaries of insects, I could wish the reader
to consult the description that Swammerdam has given of that of the
queen bee, and to take a view of the elegant figure that accompanies it,
a figure that speaks to the eyes, and by them to the imagination.
Malpighi has given a description of the ovaries of the silk-worm moth.

Reaumur mentions six or seven species of two-winged flies that are
viviparous, bringing forth worms, which are afterwards transformed into
flies. The womb of one of these is singularly curious; it is formed of a
band rolled up in a spiral form, and about two inches and an half in
length; so that it is seven or eight times longer than the body of the
fly, and composed of worms placed one on the side of the other with
wonderful art: they are many thousands in number.[81]

  [81] Reaumur Mem. des Insectes, tom. 4, p. 415.


OF THE APHIDES OR PUCERONS.

These are a species of insects that have opened new views of the œconomy
of animated beings; they belong to the hemiptera class. The rostrum is
inflected, the antennæ are longer than the thorax; some have four erect
wings, others are entirety without them. Towards the end of the abdomen
there are two tubes ejecting that most delicate juice called honey-dew.
Various names have been applied to them, the proper one is aphis, that
by which they are most generally known, is puceron; they are also
frequently called vine-fretters or plant-lice: many among the genera are
both oviparous and viviparous, bringing forth their young alive in
summer, but in autumn depositing their eggs upon the branches and bark
of trees. The different aphides are very curious objects for the
microscope: they are a very numerous genus, Linnæus has enumerated
thirty-three different species, whose trivial names are taken from the
plant which they inhabit, though it is probable the number is much
larger, as the same plant is often found to support two or three
different sorts of them. Their habits are very singular: an aphis or
puceron, brought up in the most perfect solitude from the very moment of
its birth, in a few days will be found in the midst of a numerous
family; repeat the experiment on one of the individuals of this family,
and you will find this second generation will multiply like its parent;
and this you may pursue through many generations.

M. Bonnet had repeated experiments of this kind, as far as the sixth
generation, which all uniformly presented the observer with fruitful
virgins, when he was engaged in a series of new and tedious experiments,
from a suspicion imparted by M. Trembley in a letter to him, who thus
expresses himself: “I have formed the design of rearing several
generations of solitary pucerons, in order to see if they would all
equally bring forth young. In cases so remote from usual circumstances,
it is allowed to try all sorts of means; and I argued with myself, Who
knows but that one copulation might serve for several generations?” This
“WHO KNOWS” persuaded M. Bonnet that he had not sufficiently pursued his
investigations. He therefore now reared to the tenth generation his
solitary aphides, having the patience to keep an exact account of the
days and hours of the birth of each generation. The result of this
pursuit was, his discovering both males and females among them, whose
amours were not in the least equivocal; the males are produced only in
the tenth generation, and are but few in number; these soon arriving at
their full growth, copulate with the females, and the virtue of this
copulation serves for ten successive generations; all these generations,
except the first from fecundated eggs, are produced viviparous, and all
the individuals are females, except those of the last generation, among
whom some males appear, to lay the foundation of a fresh series.

In order to give a further insight into the nature of these insects, I
shall insert an extract of a description of their different generations,
by Dr. Richardson, as published in the Philosophical Transactions for
the year 1771.

The great variety of species which occur in the insects now under
consideration, may make an inquiry into their particular natures seem
not a little perplexing, but by reducing them under their proper genera,
the difficulty is considerably diminished. We may reasonably suppose all
the insects, comprehended under any distinct genus, to partake of one
general nature; and, by diligently examining any particular species, may
thence gain some insight into the nature of all the rest. With this view
Dr. Richardson chose out of the various sorts of aphides the largest of
those found on the rose-tree, not only as its size makes it the more
conspicuous, but as there are few others of so long a duration. This
sort appears early in the spring, and continues late in the autumn;
while several are limited to a much shorter term, in conformity to the
different trees and plants from whence they draw their nourishment.

If at the beginning of February the weather happen to be so warm, as to
make the buds of the rose-tree swell and appear green, small aphides are
frequently to be found on them, though not larger than the young ones
in summer, when first produced. It will be found, that those aphides
which appear only in spring, proceed from small black oval eggs, which
were deposited on the last year’s shoots; though when it happens that
the insects make too early an appearance, the greater part suffers from
the sharp weather that usually succeeds; by which means the rose-trees
are some years in a manner freed from them. The same kind of animal is
then at one time of the year viviparous, and at another, oviparous.
Those aphides which withstand the severity of the weather seldom come to
their full growth before the month of April, at which time they usually
begin to breed, after twice casting off their exuvia, or outward
covering. It appears that they are all females, which produce each of
them a numerous progeny, and that without having intercourse with any
male insect; they are viviparous, and what is equally singular, the
young ones all come into the world backwards. When they first come from
the parent, they are enveloped by a thin membrane, having in this
situation the appearance of an oval egg; these egg-like appearances
adhere by one extremity to the mother, while the young ones contained in
them extend the other, by that means gradually drawing the ruptured
membrane over the head and body to the hind feet. During this operation,
and for some time after, the fore part of the head adheres, by means of
something glutinous, to the vent of the parent. Being thus suspended in
the air, it soon frees itself from the membrane in which it was
confined; and after its limbs are a little strengthened, is set down on
some tender shoots, and left to provide for itself.

In the spring months there appear on the rose-trees but two generations
of aphides, including those which proceed immediately from the last
year’s eggs; the warmth of the summer adds so much to their fertility,
that no less than five generations succeed one another in the interval.
One is produced in May, which casts off its covering; while the months
of June and July each supply two more, which cast off their coverings
three or four times, according to the different warmth of the season.
This frequent change of their outward coat is the more extraordinary,
because it is repeated more often when the insects come the soonest to
their growth, which sometimes happens in ten days, where warmth and
plenty of nourishment conspired.

Early in the month of June, some of the third generation, which were
produced about the middle of May, after casting off their last covering,
discover four erect wings, much longer than their bodies; and the same
is observable in all the succeeding generations which are produced
during the summer months, but still without any diversity of sex; for
some time before the aphides come to their full growth, it is easy to
distinguish which will have wings, by a remarkable fullness of the
breast, which in the others is hardly to be distinguished from the body.
When the last covering is rejected, the wings, which were before folded
up in a very narrow compass, are gradually extended in a surprizing
manner, till their dimensions are at last very considerable.

The increase of these insects in the summer time is so very great, that
by wounding and exhausting the tender shoots, they would frequently
suppress all vegetation, had they not many enemies to restrain them.
Notwithstanding these insects have a numerous tribe of enemies, they are
not without friends, if those may be considered as such, who are
officious in their attendance for the good things they expect to reap
thereby. The ant and the bee are of this kind, collecting the honey in
which the aphides abound, but with this difference, that the ants are
constant visitors, the bee only when flowers are scarce; the ants will
suck in the honey while the aphides are in the act of discharging it,
the bees only collect it from the leaves on which it has fallen.

In the autumn three more generations of aphides are produced, two of
which generally make their appearance in the month of August, and the
third before the middle of September. The two first differ in no respect
from those which are found in summer; but the third differs greatly from
all the rest. Though all the aphides which have hitherto appeared were
females, in this tenth generation several male insects are found, but
not by any means so numerous as the females.

The females have at first the same appearance with those of the former
generations, but in a few days their colour changes from a green to a
yellow, which is gradually converted into an orange before they come to
their full growth; they differ also in another respect from those which
occur in summer, for all these yellow females are without wings. The
male insects are, however, still more remarkable, their outward
appearance readily distinguishing them from this and all other
generations. When first produced, they are not of a green colour like
the rest, but of a reddish brown, and have afterwards a dark line along
the back; they come to their full growth in about three weeks, and then
cast off their last covering, the whole insect being after this of a
bright yellow colour, the wings only excepted; but after this change to
a deeper yellow, and in a very few hours to a dark brown, if we except
the body, which is something lighter coloured, and has a reddish cast.
The males no sooner come to maturity than they copulate with the
females, who in a day or two after their intercourse with the males lay
their eggs, generally near the buds. Where there are a number crowded
together, they of course interfere with each other, in which case they
will frequently deposit their eggs on other parts of the branches. It is
highly probable that the aphides derive considerable advantages by
living in society; the reiterated punctures of a great number of them
may attract a larger quantity of nutritious juices to that part of the
tree or plant where they have taken up their abode.

The aphides are very injurious to trees and vegetables of almost every
kind; the species is so numerous, and all endued with so much fertility,
that if they were not destroyed by a numerous host of enemies, the
leaves, the branches, and the stem of every plant would be covered with
them. On almost every leaf inhabited by aphides, a small worm is to be
found, that feeds not upon the leaves, but upon these insects, devouring
them with incredible rapacity: Reaumur supplied a single worm with above
one-hundred aphides, every one of which it devoured in less than three
hours. Indeed myriads of insects seem to be produced for no other
purpose than to destroy them.


OF THE APIS OR BEE.

The bee belongs to the hymenoptera order, the mouth is furnished with
two jaws, and a proboscis protected by a double sheath, see Fig. 3.
Plate XIII. They have four wings; when these are at rest, the two
foremost cover those behind. There is a sting in the tail of the working
and female bee. Of the bee kind fifty-five species are enumerated by
Linnæus. Our present observations are confined to the common or domestic
bee.

In the natural history of insects new objects of surprize are
continually rising before the observer: however singular the preceding
account of the production of the aphides may appear, that of bees is not
less so. This little republic has at all times gained universal esteem
and admiration; and, though they have attracted the attention of the
most ingenious and laborious inquirers into nature, yet the mode of
propagating their species seems to have baffled the ingenuity of ages,
and rendered all attempts to discover it abortive; even the labours and
scrupulous attention of Swammerdam were unsuccessful. He spent one month
entirely in examining, describing, and representing their intestines;
and many months on other parts; employing whole days in making
observations, and whole nights in registering them, till at last he
brought his treatise of bees to the wished for perfection; a work which,
from the commencement of natural history to our own times, has not its
equal. Reaumur, however, thought he had in some measure removed the
veil, and explained their manner of generating: he supposes the queen
bee to be the only female in the hive, and the mother of the next
generation; that the drones are the males, by which she is fecundated,
and that the working bees, or those that collect wax on the flowers,
that knead it, and form from it the combs and cells, which they
afterwards fill with honey, are of neither sex. The queen bee is known
by its size, being generally much larger than the working bee or the
drone.

M. Schirach, a German naturalist, affirms that all the common bees are
females in disguise, in which the organs that distinguish the sex, and
particularly the ovaria, are obliterated, or at least from their extreme
minuteness have escaped the observer’s eye; that every one of these
bees, in the earlier period of its existence, is capable of becoming a
queen bee, if the whole community should think it proper to nurse it in
a particular manner, and raise it to that rank: in short, that the queen
bee lays only two kinds of eggs, those that are to produce the drones,
and those from which the working bees are to proceed. Schirach made his
experiments not only in the early spring months, but even as late as
November. He cut off from an old hive a piece of the brood-comb, taking
care that it contained worms which had been hatched about three days. He
fixed this in an empty hive, together with a piece of honey-comb, for
food to his bees, and then introduced a number of common bees into the
hive. As soon as these found themselves deprived of their queen and
their liberty, a dreadful uproar took place, which lasted for the space
of twenty-four hours. On the cessation of this tumult, they betook
themselves to work, first proceeding to the construction of a royal
cell, and then taking the proper methods for feeding and hatching the
brood inclosed with them; sometimes even on the second day the
foundation of one or more royal cells were to be perceived; the view of
which furnished certain indications that they had elected one of the
inclosed worms to the sovereignty. The bees may now be left at liberty.
The final result of these experiments is, that the colony of working
bees being thus shut up with a morsel of brood-comb, not only hatch, but
at the end of eighteen or twenty days produce from thence one or two
queens, to all appearance proceeding from worms of the common sort,
converted by them into a queen merely because they wanted one.[82] From
experiments of the same kind, varied and often repeated, Schirach
concludes that all the common working bees were originally of the female
sex; but that if they are not fed, lodged, and brought up in a
particular manner while they are in the larva state, their organs are
not developed; and that it is to this circumstance attending the
bringing up the queen, that the extension of the female organs is
effected, and the difference in her form and size produced.

  [82] Schirach Histoire Naturelle des Abeilles.

Mr. Debraw has carried the subject further, by discovering the
impregnation of the eggs by the males, and the difference of the size
among the drones or males; though indeed this last circumstance was not
unknown to Mess. Maraldi and Reaumur. Mr. Debraw watched the glass hives
with indefatigable attention, from the moment the bees, among which he
took care there should be a large number of drones, were put into them,
to the time of the queen’s laying her eggs, which generally happens on
the fourth or fifth day; he observed, that on the first or second day,
always before the third from the time the eggs are placed in the cells,
a great number of bees, fastening themselves to one another, hung down
in the form of a curtain, from the top to the bottom of the hive; they
had done the same at the time the queen deposited her eggs, an operation
which seems contrived on purpose to conceal what is transacting;
however, through some parts of this veil he was enabled to see some of
the bees inserting the posterior part of their bodies each into a cell,
and sinking into it, but continuing there only a little while. When they
had retired, it was easy to discover a whitish liquor left in the angle
of the basis of each cell, which contained an egg. In a day or two this
liquor was absorbed into the embryo, which on the fourth day assumes its
worm or larva state, to which the working bees bring a little honey for
nourishment, during the first eight or ten days after its birth. When
the bees find the worm has attained its full growth, they leave off
bringing it food, they know it has no more need of it; they have still,
however, another service to pay it, in which they never fail; it is that
of shutting it up in its cell, where the larva is inclosed for eight or
ten days: here a further change takes place; the larva, which was
heretofore idle, now begins to work, and lines its cell with fine silk,
while the working bee incloses it exteriorly with a wax covering. The
concealed larva then voids its excrement, quits its skin, and assumes
the pupa; at the end of some days the young bee acquires sufficient
strength to quit the slender covering of the pupa, tears the wax
covering of its cell, and proceeds a perfect insect.

To prove further that the eggs are fecundated by the males, and that
their presence is necessary at the time of breeding, Mr. Debraw made the
following experiments. They consist in leaving in a hive the queen, with
only the common or working bees, without any drones, to see whether the
eggs she laid would be prolific. To this end he took a swarm, and shook
all the bees into a tub of water, leaving them there till they were
quite senseless; by which means he could distinguish the drones without
any danger of being stung: he then restored the queen and working bees
to their former state, by spreading them on a brown paper in the sun;
after this he replaced them in a glass hive, where they soon began to
work as usual. The queen laid eggs, which, to his great surprize, were
impregnated, for he imagined he had separated all the drones or males,
and therefore omitted watching them; at the end of twenty days he found
several of his eggs had, in the usual course of changes, produced bees,
while some had withered away, and others were covered with honey. Hence
he inferred, that some of the males had escaped his notice, and
impregnated part of the eggs. To convince himself of this, he took away
all the brood-comb that was in the hive, in order to oblige the bees to
provide a fresh quantity, being determined to watch narrowly their
motions after new eggs should be laid in the cells. On the second day
after the eggs were deposited, he perceived the same operation that was
mentioned before, namely, that of the bees hanging down in the form of a
curtain, while others thrust the posterior part of their bodies into the
cells. He then introduced his hand into the hive, broke off a piece of
the comb, in which there were two of these insects; he found in neither
of them any sting, a circumstance peculiar to the drones; upon
dissection, with the assistance of a microscope, he discovered the four
cylindrical bodies which contain the glutinous liquor of a whitish
colour, as observed by Maraldi in the large drones. He was therefore now
under the necessity of repeating his experiments, in destroying the
males, and even those that might be suspected to be such. He once more
immersed the same bees in water, and when they appeared in a senseless
state, he gently pressed every one, in order to distinguish those armed
with stings from those which had none, and which of course he supposed
to be males: of these last he found fifty-seven, and replaced the swarm
in a glass hive, where they immediately applied again to the work of
making cells, and on the fourth or fifth day, very early in the morning,
he had the pleasure to see the queen bee deposit her eggs in those
cells: he continued watching most part of the ensuing days, but could
discover nothing of what he had seen before.

The eggs, after the fourth day, instead of changing in the manner of
caterpillars, were found in the same state they were in the first day,
except that some were covered with honey. A singular event happened the
next day, about noon; all the bees left their own hive, and were seen
attempting to get into a neighbouring one, on the stool of which the
queen was found dead, being no doubt slain in the engagement. This event
seems to have arisen from the great desire of perpetuating their
species, and to which end the concurrence of the males seems so
absolutely necessary; it made them desert their habitations, where no
males were left, in order to fix a residence in a new one, in which
there was a good stock of them. To be further satisfied, Mr. Debraw took
the brood-comb, which had not been impregnated, and divided it into two
parts; one he placed under a glass bell, No. 1, with honey-comb for the
bees food, taking care to leave a queen, but no drones, among the bees
confined in it; the other piece of the brood-comb he placed under
another glass bell, No. 2, with a few drones, a queen, and a
proportionable number of common bees. The result was, that in the glass,
No. 1, there was no impregnation, the eggs remaining in the same state
they were in when put into the glass; and on giving the bees their
liberty on the seventh day, they all flew away as was found to be the
case in the former experiment; whereas in the glass, No. 2, the very day
after the bees had been put into it, the eggs were impregnated by the
drones, and the bees did not leave their hive on receiving their
liberty.

The editor of the Cyclopædia says, that the small drones are all dead
before the end of May, when the larger species appear, and supersede
their use; and that it is not without reason that a modern author
suggests, that a small number of drones are reserved to supply the
necessities of the ensuing year; but that they are very little, if any,
larger than the common bee.

It does not enter into our plan to notice further in this place the
wonders of this little society. A bee-hive is certainly one of the
finest objects that can offer itself to the eyes of the beholder. It is
not easy to be weary of contemplating those workshops, where thousands
of labourers are constantly engaged in different employments.[83]

  [83] The remarks made by the late Mr. Hunter on the experiments of
  Messrs. Schirach and Debraw, in my opinion, merit the attention of the
  reader; they are contained in his “Observations on Bees,” comprizing a
  variety of information respecting the history and œconomy of those
  curious insects. This ingenious and interesting account is inserted in
  the Philosophical Transactions for the year 1792, page 128-195. I
  cannot altogether subscribe to his opinion relative to the minuteness
  and prolixity of Swammerdam. EDIT.


OF THE EGGS OF INSECTS.

The eggs are contained and arranged in the body of the insect, in
vessels which vary in number and figure in different species; the same
variety is found in the eggs themselves: some are round, others oval,
some cylindrical, and others nearly square; the shells of some are hard
and smooth, while others are soft and flexible. It is a general rule,
that eggs do not increase in size after they are laid; among insects, we
find however an exception to this; the eggs of the tenthredo of Linnæus
increase after they are laid, but their shell is soft and membranaceous.
The eggs of insects differ in their colours; some may be found of almost
every shade, of yellow, green, brown, and even black. The eggs of the
lion puceron,[84] hemerobius, Lin. are very singular objects, and cannot
have escaped the eye of any person who is conversant among the insects
which live on trees; though of the many who have seen them, few, if any,
have found what they really were. It is common to see on the leaves and
pedicles of the leaves of the plumb-tree, and several other trees, as
also on their young branches, a number of long and slender filaments,
running out to about an inch in length; ten or twelve of these are
usually seen placed near one another, and a vast number of these
clusters are found on the same tree; each of these filaments is
terminated by a sort of swelling or tubercle of the shape of an egg.
They have generally been supposed to be of vegetable origin, and that
they were a sort of parasitical plant growing out of others. There is a
time when these egg-like balls are found open at the ends; in this state
they very much resemble flowers, and have been figured as such by some
authors, though they are only the shells of the eggs out of which the
young animals have escaped after being hatched. If these eggs be
examined by a microscope, a worm may be discovered in them; or they may
be put into a box, in which, in due time, they will produce an insect,
which, when viewed with a microscope, will be found to be the true lion
puceron.

  [84] Reaumur Hist. de Insectes, vol. xi. p. 142.

Divine Providence instructs the insects, by a lower species of
perception, to deposit their eggs not only in safety from their numerous
enemies, but also in situations where a sufficient quantity of food is
on the spot to support and nourish the larva immediately on breaking the
shell. Some deposit their eggs in the oak leaf, producing there the red
gall; others choose the leaf of the poplar, which swells into a red node
or bladder; to a similar cause we must attribute the red knob which is
often seen on the willow leaf, and the three pointed protuberances upon
the termination of the juniper branches. The leaves of the veronica and
cerastium are drawn into a globular head by the eggs of an insect lodged
therein. The phalæna neustria glues its eggs with great symmetry and
propriety round the smaller branches of trees. Fig. 1. Plate X.
represents a magnified view of the nest of eggs taken off the tree after
the caterpillar had eaten its way through them; the strong ground-work
of gum, by which they are connected and bound together, is very visible
in many places; they strengthen this connection further, by filling up
all the intervening space between the eggs with a very tenacious
substance. These eggs are crustaceous, and similar to those of the hen;
Fig. 2 represents the natural size. Fig. 3 is a magnified vertical
section of the eggs, shewing their oval shape; Fig. 4 the natural size.
Fig. 5 is an horizontal section through the middle of the egg, and Fig.
6 the same not magnified. It is not easy to describe the beauty of these
objects, when viewed in the lucernal microscope; the regularity with
which they are placed, the delicacy of their texture, the beautiful and
ever-varying colours which they present to the eye, give the spectator a
high degree of rational delight.

In the Lapland Alps there is a fly covered with a downy hair, called the
rhen-deer gad-fly, oestrus tarandi, Linn. it hovers all day over these
animals, whose legs tremble under them; they prick up their ears, and
flee to the mountains covered with ice and snow to escape from a little
hovering fly, but generally in vain, for the insect but too soon finds
an opportunity to lodge its egg in the back of the deer; the worm
hatched from this egg perforates the skin, and remains under it during
the whole winter: in the following year it becomes a fly. The oestrus
bovis is an equal terror to oxen; the hippobosca equina, to horses;
oestrus ovis,[85] to the sheep, &c.

  [85] Oestrus ovis in naso sive sinu frontis animalium rumenantium.
  Linn.

The gnat, the ephemera, the phryganea, the libellula, hover over the
water all day to drop their eggs, which are hatched in the water, and
continue there all the time they are in the larva form. The mass formed
by the gnat resembles a little vessel set afloat by the insect; each egg
is in the form of a keel, these are curiously connected together. The
gnat lays but one egg at a time, which she deposits on the water in a
very ingenious and simple manner; she stretches her legs out, and
crosses them, thus forming an angle to receive and hold the first egg; a
second egg is soon placed next the first; then a third, and so on, till
the base is capable of supporting itself; these, as they come to
maturity, sink deeper. The spawn of this insect is sometimes above an
inch long, and one-eighth of an inch in diameter, and tied by a little
stem or stalk to some stick or stone. Sometimes they are laid in a
single, sometimes in a double spiral line; sometimes transversely. Many
moths cover their offspring with a thick bed of hair, which they gather
from their own body; while others cover them with a glutinous
composition, which, when hard, protects them from moisture, rain, and
cold. The gall-flies, it has been observed, know how to open the nerves
of the leaves, to deposit thus their eggs in a place which afterwards
serves them for a lodging and a magazine of food. The solitary bees and
wasps prepare an habitation for their little ones in the earth, placing
there a proper quantity of food for them, when they proceed from the
egg. The voracious and cruel spider is attentive and careful of its
eggs; the wolf spider carries them on its back in a little bag formed of
its silk, it cannot be separated from them but by violence, and exhibits
the most marked signs of uneasiness when deprived of them: a
circumstance the more remarkable, as they love to destroy each other,
and even carry on their courtships with a diffidence and caution unknown
in any other species of animals. The history of bees and wasps, and
their care and attention to their offspring, is so well known, that I
may with propriety pass it over here, and proceed just to notice the
industrious ant, whose paternal affection and care is not so well known.
They are not satisfied with placing their eggs in situations made on
purpose, and to raise or rear them till they come to the nymph or pupa
state, but they even extend their care to the pupæ themselves, removing
them from their nest to the surface of the earth, whenever the weather
is fine, that they may receive the benignant influence of the sun,
carrying them back again as soon as the air begins to grow cold. If any
accident disturb their nest, and disperse the pupæ, they manifest the
greatest signs of distress, seeking those which are lost and scattered,
placing them in some sheltered place while they repair the nest, when
they again transport them to it.[86] Many other curious particulars
might be related relative to this industrious insect; as their uniting
together in scooping out earth, the conveyance of materials for the
construction of their nests, and the curious structure of the nest
itself, which, though it appears piled up at random, will be found, on
stricter examination, to be a work of art and design, with other
circumstances which are too long to be enumerated here.

  [86] Lessers Theologie des Insectes, tom. 1, p. 143.

The fecundity of insects exceeds in an astonishing degree that of all
the productions of nature; the vegetables which cover the surface of the
earth bear no proportion to their multitudes, every plant supporting a
number often of scarce perceptible creatures: of the fatal effects of
their prodigious multiplication, our fruit trees, &c. are too frequently
a deplorable testimony. On the continent whole provinces sometimes
languish in consequence of the dreadful havoc made by them.

Reaumur calculated the fecundity of the queen bee as follows: he found
that she laid in the two months of March and April 12,000 eggs, so that
the swarm which left the hive in May consisted of near 12,000 bees, all
produced from one mother: but this calculation falls short of that which
was made by Leeuwenhoek on a fly, whose larva feeds on flesh, putrid
carcases, &c. which multiply prodigiously, and that in a short space of
time. One of these laid 144 eggs, from which he got as many flies in the
first month; so that, supposing one-half of these to be females, in the
third month we shall have 746,496, all produced in three months from one
fly.

The following is an experiment of M. Lyonet on the generation of a moth
which comes from the chenille a brosse: out of a brood of 350 eggs,
produced by a single moth of this kind, he took 80, from which he
obtained, when they were arrived at their perfect state, 15 females;
from whence he deduces the following consequence: if 80 eggs give 15
females, the whole brood of 350 would have produced 65; these 65,
supposing them as fertile as their mother, would have produced 22,750
caterpillars, among which there would have been at least 4265 females,
who would have produced for the third generation 1,492,750 caterpillars.
This number would have been much larger, if the number of females among
those which were selected by M. Lyonet had been greater. M. de Geer
counted in the belly of a moth 480 eggs; reducing these to 400, if
supposing one-fourth only of these to be females and as fruitful as
their mother, they will give birth to 40,000 caterpillars for the second
generation; and for the third, supposing all things equal, four millions
of caterpillars. It is not surprizing, therefore, that they are found so
numerous in years that are favourable to their propagation. But the
Creator of all things has for our sakes limited this abundant
multiplication, and wisely ordained, that those species which are the
most numerous shall have the greatest number of enemies, who, though
constantly employed on the destruction of individuals, are unable to
effect that of the species; by which means an equilibrium is preserved,
and no one species preponderates. Few insects live long after their last
transformation, but their species are continued by their amazing
fecundity; their growth is completed, and their parts hardened sooner
than those of larger animals, and the duration of their existence is
proportionably limited. There are, however some species of flies which
lie in a torpid state during the winter, and revive with the returning
warmth of spring.


OF THE FOOD OF INSECTS.

There are few, if any, productions either of the animal or vegetable
kingdoms, which do not supply some kind of insect with food. They may,
therefore, be considered under two heads, those which live on
vegetables, and those which are supported by animal food; each insect
knows that which is proper to sustain its life, where to seek it, and
how to procure it. I have already observed, that several insects, when
arrived at a state of perfection, feed after their transformation upon
food totally different from that which nourished them in their larva
state.

Among those which feed on vegetables, some sink themselves in the earth,
and by destroying the roots of the plants, do considerable injuries to
our gardens. The food of others is dry and hard; they pierce the wood,
reduce it to powder, and then feed on it; some, as the cossus, attack
and destroy the trees, while the food of others more delicate is the
leaves. The leaf is eaten in a different manner by different insects;
some eat the whole substance, while others feed only on the parenchymous
parts, which are contained between its superficial membranes, forming
withinside the leaf paths and galleries. These insects are not always
content with the leaf, but attack the flower also: even this food is too
gross for many; the bee, the butterfly, the moth, as well as several
species of flies, feed only on the honey, or finer juices, which they
collect from flowers. We are continually finding the larva of some
insect in pears, plumbs, peaches, and other fruit; these unwelcome
intruders on the produce of human industry divide fruits, grain, and
corn with us, often depriving us of large quantities. There is, indeed,
no part of a plant which does not serve as food to different insects;
some have one kind of plant marked out for them to inhabit and feed on,
others have another assigned to them, on which, and no other, they will
feed; each has its appropriate food, and though the parent animal eats
not at all, or lives upon food entirely different, yet she is guided, as
has before been observed, to deposit her eggs on that peculiar shrub or
plant that will be food for her young; while some, more voracious than
the rest, feed upon all with equal avidity; but in countries less
cultivated than our own, their annoyance and devastations are terrible.
The gryllus migratorius, a few years since, poured out of Tartary in
such quantities, as to lay waste a great part of Europe, producing
almost unequalled calamities, swarming in such multitudes as to cloud
the air and cover the ground, mocking human power and craft; wherever
they settled, all verdure disappeared, and the summer fruitfulness was
turned into winter desolation; in Sweden the cattle perished with
hunger, and the men were forced to abandon their country, and fly to the
neighbouring regions.[87] The far greater part feed only, however, on
one species of plant, or at most on those which are similar to it, and
the same species may always be found on the same plant. Reaumur says,
that the caterpillar which infests and feeds upon the cabbage, destroys
in twenty-four hours more than twice its weight. If larger animals
required a proportionable quantity, the earth would not afford
sufficient nourishment for its inhabitants.

  [87] Select Dissertations from the Amœnitates Academicæ, vol. I, p.
  398.

A great number of insects reject vegetable, and live on animal food;
some seeking that which is beginning to putrefy, while others delight in
food entirely putrid; others again are nourished by the most filthy
puddles, and disgusting excrements; some attack and feed on man himself,
while others are nourished by his provision, his cloaths, his furniture:
some prey upon insects of another species; others, again, attack their
own, and harrass each other with perpetual carnage. Reaumur informs us,
that those insects which feed upon dead carcases never attack living
animals; the flesh-fly deposits her eggs in the bodies of dead animals,
where her progeny receive that nourishment best adapted for them; but
this fly never attempts to lay her eggs in the flesh of sound and living
animals.

Every animal has its appropriate lice, which feed on and infest it. M.
Rhedi has given an accurate account of a great number of these little
noxious creatures accompanied with figures; but, as if it were not
sufficient that these creatures should dwell and live on the external
part of the body, and suck the blood of the animal that they infest, we
find another species of insects seeking their food in the more vital
parts, and feeding on the flesh of the animal, while full of life and
health. Reaumur has given an history of a fly, oestrus bovis, the larva
of which lives upon the backs, and feeds on the flesh of young oxen and
cows, where it produces a kind of tumor. The fly lodges its eggs in the
flesh, by making a number of little wounds, in each of which it deposits
eggs, so that every wound becomes a nest, the eggs of which are hatched
by the heat of the animal. Here the larvæ find abundant food, at the
same time that they are protected from the changes of the weather; and
here they stay till they are fit for transformation. The parts they
inhabit are often easy to be discovered by a kind of lump or tumor,
which they form by their ravages; this tumor suppurates, and is filled
with matter; on this disgusting substance the larvæ feed, and their
heads are always found plunged in it.[88]

  [88] The obscure and singular habitations of the British oestri are
  the stomach and intestines of the horse, the frontal and maxillary
  sinuses of sheep, and beneath the skin of the backs of horned cattle.
  In other parts of the world they inhabit various other animals.

  The larva of the oestrus bovis lives beneath the skin of horned
  cattle, between it and the cellular membrane, in a proper sack or
  abcess, which is rather larger than the insect, and by narrowing
  upwards opens externally to the air by a small aperture. When arrived
  at its full growth, it effects its escape from the abcess by pressing
  against the external opening; when the opening has thus obtained the
  size of a small pea, the larva writhes itself through, and falls from
  the back of the animal to the ground; and, seeking a convenient
  retreat, becomes a chrysalis, in which state it continues from about
  the latter end of June to about the middle of August; the perfect
  insect, on leaving the chrysalis, forces open a very remarkable
  marginated triangular lid or operculum. The oestrus in its perfect or
  fly state is the largest of the European species of this genus, and is
  very beautiful. Although its effects on the cattle have been so often
  remarked, yet the fly itself is rarely seen or taken, as the attempt
  would be attended with considerable danger. The pain it inflicts in
  depositing its egg is much more severe than in any of the other
  species: when one of the cattle is attacked by this fly, it is easily
  known by the extreme terror and agitation of the whole herd; the
  unfortunate object of the attack runs bellowing from among them to
  some distant part of the heath, or the nearest water, while the tail,
  from the severity of the pain, is held with a tremulous motion
  straight from the body, in the direction of the spine, and the head
  and neck are also stretched out to the utmost. The rest, from fear,
  generally follow to the water, and disperse to different parts of the
  field. The larvæ of this insect are mostly known among the country
  people by the name of wornuls, wormuls, or warbles, or more properly
  bots.

  The larva of the oestrus equi is very commonly found in the stomach of
  horses. These larvæ attach themselves to every part of the stomach,
  but are generally most numerous about the pylorus; and are sometimes
  found in the intestines. They hang most commonly in clusters, being
  fixed by the small end to the inner membrane of the stomach, to which
  they adhere by two small hooks or tentacula. The larvæ having attained
  their full growth in about a month, on dropping to the ground find
  some convenient retreat, change to the chrysalis, and in about six or
  seven weeks the fly appears.

  The larva of the oestrus hæmorrhoidalis resembles in almost every
  respect that of the oestrus equi, and occupies the same situation in
  the stomach of the horse. When it is ripe, and has passed through the
  intestines and the sphincter ani it assumes the chrysalis state in
  about two days, and in about two months the fly appears.

  The generally received opinion has been that the female fly enters the
  anus of the horse to deposit its eggs, and Reaumur relates this
  circumstance on the authority of Dr. Gaspari; from the account of its
  getting beneath the tail, it is probable that the fly he saw was the
  hippobosca equina, which frequently does this: its getting within the
  rectum appears to have been additional. That a fly might deposit its
  eggs on the verge of the anus is not impossible, but we know no
  instance of it: the fact is, that the part chosen by the oestrus
  hæmorrhoidalis for this purpose is the lips of the horse, which is
  very distressing to the animal from the excessive titillation it
  occasions; for he immediately after rubs his mouth against the ground,
  his fore legs, or sometimes against a tree, or if two are standing
  together, they often rub themselves against each other. At the sight
  of this fly, the horse appears much agitated, and moves its head
  backward and forward in the air to baulk its touch, and prevent its
  darting on the lips; but the fly, watching for a favourable
  opportunity, continues to repeat the operation; till at length, the
  enraged animal endeavours to avoid it by galloping away to a distant
  part of the field. If still pursued, its last resource is in the
  water, where the oestrus is never observed to follow him.

  The oestrus veterinus is by Linnæus called nasalis, from an idea of
  its entering the nostrils of the horse to deposit its eggs, which it
  could not well do without destroying its wings, and is therefore
  probably as much a fable as the “mire per anum intrans” of the oestrus
  hæmorrhoidalis.

  The oestrus ovis is mostly found in the horns and frontal sinuses of
  the sheep, though it has been remarked that the membranes lining these
  cavities were hardly at all inflamed, while those of the maxillary
  sinuses were highly so; from which it is suspected that they inhabit
  the maxillary sinuses, and crawl, on the death of the animal, into
  these situations in the horns and frontal sinuses. When the larvæ are
  full-grown they fall through the nostrils, and change to the pupa
  state, lying on the earth, or adhering by the side to a blade of
  grass. The fly bursts the shell of the pupa in about two months.

  The above concise account of the different oestri is extracted from
  the excellent paper on the subject by Mr. B. Clark, F. L. S. For his
  more ample description, accompanied with coloured figures of the
  several British species, see Transactions of the Linnean Society, vol.
  iii. page 283-329, just published. EDIT.

Neither the larva, pupa, or even the egg-state of some insects are
exempt from the attacks of others, who deposit their eggs in them;
these, after having passed through the usual transformations, become
what is termed the ichneumon fly. The following are the curious
observations of an ingenious naturalist on this fly. “As I was
observing,” says he, “one day some caterpillars which were feeding
voluptuously on a cabbage leaf, my attention was attracted to part of
the plant, about which a little fly was buzzing on its wing, as if
deliberating where to settle: I was surprized to see the herd of
caterpillars, creatures of twenty times its size, endeavouring in an
uncouth manner, by various contortions of the body to get out of its
way, and more so whenever the fly poised on the wing as if going to
drop; at length the creature made its choice, and seated itself on the
back of one of the largest and fairest of the cluster; it was in vain
the unhappy reptile endeavoured to dislodge the enemy. If the
caterpillar had shewn terror on the approach of the fly, its anguish at
intervals now seemed intolerable, and I soon found that it was in
consequence of the strokes or wounds given by the fly. At every wound
the poor caterpillar wreathed and twisted its whole frame, endeavouring
to disengage itself, by shaking off the enemy, sometimes aiming its
mouth towards the place; but it was all in vain; its little, but cruel
tormentor kept its place. When it had inflicted thirty or forty of these
wounds, it took its flight with a visible triumph; in each of these
wounds the little fly had deposited an egg. I took the caterpillar home
with me, to observe the progress of the eggs which were thus placed in
its body, taking care to give it a fresh supply of leaves from time to
time; it recovered to all appearance in a few hours from the wounds it
had received, and from that time, for the space of four or five days,
seemed to feed with its usual avidity. The eggs were all hatched into
small oblong voracious worms, which fed from the moment of their
appearance on the flesh of the caterpillar, in whose body they were
inclosed, and seemingly without wounding the organs of respiration or
digestion; and when they had arrived at their full growth, they eat
their way out of the sides of the animal, at the same time destroying
it. The caterpillar thus attacked by the larva of the ichneumon never
escapes, its destruction is infallible; but then its life is not taken
away at once; the larva, while it is feeding thereon, knows how to spare
the parts which are essential to its life, because its own is at that
time tied up in that of the caterpillar. No butterfly is produced from
it; the worms that feed on the wretched creature, are no sooner out of
its body, than every one spins its own web, and under this they pass the
state of rest necessary to introduce them to their winged form.”[89] To
treat of each species of the ichneumon would alone fill a volume;
Linnæus enumerates no less than seventy-seven of them.[90]

  [89] Inspector, No. 64.

  [90] “The genus of insects called ichneumon derive their support and
  nourishment from other insects, some depositing their eggs in the
  larva, others again in the pupa, and some even in the ovum or egg
  itself, the contents of which, minute as they are, are sufficient to
  support the young larvæ until their change into their pupa state. Some
  deposit only one egg in a place, as the ichneumon ovulorum, and others
  again a great number, as ichneumon puparum, &c. but whether the egg be
  placed in the pupa, larva, or ovum, the destruction of the foster
  parent is inevitable. The larvæ of large moths or butterflies that
  have been wounded by an ichneumon, live and feed, though with evident
  marks of disease, until those parasites are full fed, and able to
  change into their second or pupa state.” See Observations on the
  Œconomy of the Ichneumon Manifestator, in the Transactions of the
  Linnean Society, vol. 3, p. 23 & seq. by T. Marsham, Esq. Sec. L. S.
  EDIT.

Of this strange scene it is difficult for us to form a proper judgment;
we are unacquainted with the organs of the caterpillar, ignorant of the
nature of its sensations, and therefore we cannot be assured what may be
the effects of that which we see it suffer. “It is wisdom to suppose we
are ignorant, while we know the Creator cannot be cruel.” From
revelation we learn, that man is the mean through which life is conveyed
to the creatures of this lower world; that by sinking into error, and
fostering evil, he perverts his own life, and corrupts all that which
proceeds from him: so that the effects are the same on the orders
beneath him, as would arise to the world if a continual cloud was placed
between us and the sun, depriving us at once of the salutary effects of
its invigorating heat and cheering light. Hence there is in this
degraded world an obscure and melancholy shade cast over all the
beauties of creation.

Lastly, the number of insects which feed upon others, nay, some even
upon their own species, is very great: it is among these that we find
the traces of the greatest art and cunning, as well in attack as
defence; some indeed use main force alone. Most persons are acquainted
with the dexterous arts of the spider, the curious construction of the
web he spins, and the central position he takes, in order to watch more
effectually the least motion that may be communicated to its tender net.
Those who wish to pursue this subject further, will find ample
satisfaction by consulting the works of Reaumur and De Geer.


OF THE HABITATION OF INSECTS.

Insects may be divided, with respect to their habitations, into two
classes, aquatic and terrestrial.

Stagnant waters are generally filled with insects, who live therein in
different manners. These are, 1. Aquatic insects which remain always on
the superficies of the water, or which at least plunge themselves
therein but rarely. 2. Others that live only in the water, and cannot
subsist out of it. 3. Many, after having lived in the water while in the
larva and pupa state, quit it afterwards with wings, and become entirely
terrestrial. 4. Some undergo all their transformations in the water, and
then become amphibious. 5. Others again are born and grow in the water,
but undergo their pupa state on dry land, and after they are arrived at
their perfect state, live equally in air and water; and 6. There are
some who live at the same time part in the water and part on land, but
after their transformation cease to be aquatic.

Among the insects which remain on the superficies of the water, are some
spiders, which run with great address and agility, without moistening
their feet or their body; when they repose themselves, they extend their
feet as much as possible. There are also aquatic bugs, which swim, or
rather run on the water with great velocity, and by troops; another bug
walks very slowly on the water; the gyrinus moves very swiftly, and in
circles. There is a species of podura[91] which live in society, and are
often accumulated together in little black lumps. Those insects which
always live in the water are generally born with the figure which they
retain during their whole lives, as the monoculi, crabs, several kinds
of water mites, &c.

  [91] De Geer Discours sur les Insectes, tom. 2, p. 103.

Those insects which, after having lived in the water, leave it when in a
winged state, are very numerous: among these we may reckon the
libellula, the ephemera, the phryganea, culices, tipulæ, and some
species of muscæ. All these, when in the larva and pupa state, live in
the water; but when they have assumed their perfect form, are entirely
terrestrial, and would perish in their former element.

The notonecta, the nepa or aquatic scorpion, &c. never quit the water
till they have passed through all their transformations, when they
become amphibious, generally quitting it in the evening.

The water-beetles, of which there are many species, remain in the water
all day, but toward evening come upon the ground and fly about, then
plunge themselves again in the water at the approach of the rising sun.
The larvæ of these insects are entirely aquatic, but when the time of
their pupa state arrives, they take to the earth, where they make a
spherical case; so that these insects are aquatic in the larva,
terrestrial in the pupa, and amphibious in the imago state.

We find an instance of an insect that lives at the same time in the
water and the air, in the singular larva described by Reaumur, Memoires
de l’Acad. in 1714, p. 203. It has the head and tail in the water, while
the rest of the body is continually kept above the surface. In order to
support itself in this singular position, it bends the body, bringing
the head near the tail, raising the rest above the water, and supporting
itself against some fixed object, as a plant, or against the borders of
the pond; or, if it be placed in a glass vessel, against the sides of
the vessel; and if the glass be inclined gently, so that the water may
nearly cover the larva, it immediately changes its position, in order
that part of the body may be kept dry.

At the baths of Abano, a small town in the Venetian state, there is a
multitude of springs, strongly impregnated with sulphur, and of a
boiling heat. In the midst of these boiling springs, within three feet
of four or five of them, there is a tepid one about blood-warm. In this
water, not only the common potamogetons and confervas, or pond-weeds and
water-mosses are found growing in an healthy state, but numbers of small
black water beetles are seen swimming about, which die on being taken
out and plunged suddenly into cold water.[92]

  [92] Jones’s Physiological Disquisitions, p. 171.

Many insects that live under the surface of the earth crawl out on
certain occasions, as the julus, scolopendra, and the oniscus; they are
often also to be found under stones, or pieces of rotten wood. Some
insects remain under ground part of their life, but quit that situation
after their change; as do some caterpillars, many of the coleoptera
class, &c. There are some species of spiders, which form habitations in
sand; one of which makes a hole in the sand, lining it with a kind of
silk, to prevent its crumbling away; this spider generally keeps on the
watch near the mouth of the hole, and, if a fly approach, runs at it
with such velocity, as seldom to fail in its attempt of seizing the
little animal, which is immediately conveyed to the den of the spider.
The formica-leo, or ant-lion, also inhabits sand.[93]

  [93] The art and dexterity with which the formica-leo entraps ants, as
  well as other insects, merits notice; he makes a pit in fine dry sand,
  shaped like a funnel or an inverted cone, at the point or reverted
  apex of which he takes his station, concealing every part of his body
  except the tips of his two horns; these are expanded to the two sides
  of the pit. When an insect treads on the edge of this precipice, it
  perhaps slides into it; if not, its steps remove a little of the sand,
  which of course descends down the sides, and gives the enemy notice of
  his prey. He then throws up the sand with which his head is covered,
  to involve the insect, and bring it to the bottom with the returning
  force of the sand: this, by repeated efforts he is sure to effect, as
  all the attempts of the unfortunate victim to escape, when once within
  the verge of the pit, are in vain. One species of the formica-leo
  forms no pit to entrap its prey, but seizes it by main force. EDIT.

Another spider, discovered by M. l’Abbe Sauvage,[94] burrows in the
earth like a rabbit, making a hole one or two feet deep, of a regular
diameter, and sufficiently large to move itself with ease. It lines the
whole of it, either to keep the ground from tumbling in, or in order to
perceive more regularly at the bottom what happens at the mouth, at
which it forms a kind of door, made of different layers of earth,
connected together by threads and covered with a strong web of a close
texture; the threads are prolonged on one side, and fixed to the ground,
so as to form a strong joint; the door is hung in such a manner, as
always to fall by its own gravity. One of these cases or nests is in her
Majesty’s cabinet at Kew.

  [94] Histoire de l’Acad. 1758, p. 26.

The several parts of trees and plants afford a variety of habitations
for insects, where they find an abundance of food. They dwell, l. in the
roots; 2. in the wood; 3. in the leaves, and in the galls which grow
upon them and the branches; 4. in the flowers; 5. in the fruits and
grains. To enumerate the various species of these inhabitants would be
endless; many particulars have been already noticed; it has also
appeared that some inhabit the most fœtid substances they can find,
while others dwell with and live on the larger animals; so that it only
remains just to mention some of those in whom industry and art is more
strongly marked to our eyes than in others.

Among the solitary bees there are so many curious circumstances to be
described, that a single volume would not suffice to contain the
particulars; we shall here only relate such as concern their
habitations. One of these forms its nest under ground, which is composed
of several cells artfully let into each other, but not covered with a
common inclosure; each cell consists of two or three membranes,
inexpressibly fine, and placed over each other. The cavity, in which the
nest is placed, is smeared over with a layer of matter, like that of
which the cells are formed, and apparently similar to the viscous humour
which snails spread in their passage from one place to another, and it
is probable that they are formed of the same materials; this substance,
though of so delicate a nature, gives them such a degree of consistency,
that they may be handled without altering their form. An egg is
deposited at the bottom of each cell, where, after it is hatched, the
worm finds itself in the midst of a plentiful stock of provision; for in
each cell there is placed a quantity of paste, or a kind of wax, which
is to serve as food for the worm, and support the wall of the cell. The
worm is also instructed so to conduct itself, and eat this food, as to
leave sufficient props for supporting the walls of its apartment. Many
species of these bees content themselves with penetrating into the
earth, scooping out hollow cavities therein, polishing the walls, then
depositing an egg and a sufficient quantity of provisions.

There is another species, that forms its nest under ground with
remarkable industry; this bee generally makes a perpendicular hole in
the earth about three inches deep, and cylindrical, till within about
three-fourths of an inch of the bottom, when it begins to enlarge; as
soon as the bee has given it the suitable proportions, it proceeds to
line not only the whole inside of its dwelling, but round the entrance;
the substance with which it is lined is of a crimson colour, and looks
like satin. From this circumstance Reaumur[95] terms it the tapestry
bee. This tapestry or lining is formed of fragments of the flowers of
the wild poppy, which she cuts out curiously, and then seizing them with
her legs, conveys them to her nest. If the pieces are wrinkled, she
first straightens and then affixes them to her walls with wonderous art;
she generally applies two layers of these fragments one over the other.
If the piece she has cut and transported be too large for the place she
intends it for, she clips off the superfluous parts and conveys the
shreds out of the apartment. After the bee has lined her cell, she fills
it nearly half an inch deep with a paste proper to nourish the larva
when hatched from the egg; when the bee has amassed a sufficient
quantity of paste, she then takes her tapestry, and folds it over the
paste and egg, which are by these means inclosed as it were in a bag of
paste; this done, she fills up with earth the empty space that is above
the bag. There is another bee which does the same with rose-leaves, and
in the substance of a thick post. A friend of mine had a piece of wood
cut from a strong post that supported the roof of a cart-house, full of
these cells or round holes, three-eighths of an inch in diameter, and
about three-fourths deep, each of which was filled with these rose-leaf
cases finely covered in at top and bottom.

  [95] Reaumur Memoires pour l’Histoire des Insectes, edit. 8vo. tom. 6,
  partie 1, p. 170.

The mason bee is so called by Reaumur from the manner of its building
its nest. These bees collect with their jaws small parcels of earth and
sand, which they glue together with a strong cement furnished from the
proboscis; and of this they form a simple but commodious habitation,
which is generally placed along walls that are exposed to the south.
Each nest resembles a lump of rude earth, of about six or seven inches
diameter, thrown against the wall; the labour of constructing so large
an edifice must be very great, as the bee can only carry a few grains at
a time. The exterior form is rude and irregular, but the construction
and art exhibited in the interior parts make up for this seeming defect;
it is generally divided into twelve or fifteen cells, separated from
each other by a thick wall; in each of these an egg is deposited by the
parent bee. The cells are not constructed all at once, for when one is
finished, she places an egg therein, with a sufficient quantity of honey
to nourish the larva; she then builds another. When the insect is
arrived at a proper state, it penetrates through its inclosures by means
of its strong jaws. When all the bees have quitted the nest, there are
as many holes on the surface thereof as there are cells within. We find
no neutral bees among this species, or at least we do not know of any
being yet discovered.

Another species of the solitary bee (apis centuncularis, Linn.)
constructs her nest in pieces of rotten wood, and has therefore been
called the carpenter bee.[96] She divides it into stages, disposing them
sometimes in three rows, with partitions curiously left between each; in
these she deposits her eggs, with the food necessary for the young ones
when hatched. They separate the wood in a very expeditious manner, by
dividing its ligneous fibres or threads, till they have made a proper
sized hole.

  [96] Geoffroy Hist. abregee des Insectes, tom. 2, p. 401.

The art and sagacity displayed by another bee,[97] whose nest is
constructed of single pieces of leaves, is truly wonderful. The nest
itself is cylindrical, formed of several cells, placed one within the
other, as thimbles are in a hard-ware shop. The cells consist of several
pieces cut from one leaf, of forms and proportions proper to coincide
with the place each is intended to occupy. The outer case or cover is
formed with equal care and exactness. In a word, says Bonnet, there is
so much exactness, symmetry, uniformity, and skill, in this little
master-piece, that we should not believe it to be the work of a fly, if
we did not know at what school she learnt the art of constructing it. In
each cell the mother deposits an almost liquid substance, and yet so
nicely are the cells formed, as not to suffer any of this substance to
be lost. But for a minute account of the works of this bee, and the
curious mechanism of its cells, we must refer the reader to Reaumur’s
admirable history of insects.

  [97] Reaumur Memoires pour l’Histoire des Insectes, tom. 6, par. 1, p.
  122.

The proceedings of the mason ichneumon wasp,[98] sphex, Linn. are
totally different from those of the common wasp, though equally curious.
It generally begins its work in May, and continues it for the greatest
part of June. The true object of her labour seems to be the digging of a
hole a few inches deep in the ground; yet in the constructing of this,
she forms a hollow tube above ground, the base of which is the aperture
of the hole, and which is raised as high above ground as the hole is
deep below; it is formed with a great deal of care, resembling a gross
kind of fillagree work, consisting of the sand drawn from the hole. The
sand out of which she excavates her cell, is nearly as hard as a common
stone; this it readily softens with a penetrating liquor with which she
is well provided; a drop or two of it is imbibed immediately by the sand
on which it falls, which is instantly rendered so soft, that she can
separate and knead it with her teeth and fore feet, forming it into a
small ball, which she places on the edge of the hole as the foundation
stone of the pillar she is going to erect; the whole of it is formed of
such balls, ranged circularly, and then placed one above the other. She
leaves her work at intervals, probably in order to renew her stock of
that liquor which is so necessary for her operations. These intervals
are of short duration; she soon returns, and labours with so much
activity and ardour, that in a few hours she will dig a hole two or
three inches deep, and raise a hollow pillar two inches high. After the
column has been raised a certain height perpendicular from the ground,
it begins to curve a little, which curvature increases till it is
finished, though the cylindrical form is maintained: she constructs
several of these holes all of the same form, and for the same purpose.
It is easy to see why the hole was dug in the ground; that it was
destined to receive an egg; but it is not so easy to perceive why the
tube of sand was formed. By attending to the labours of the wasp, one
end, however, may be discovered; it will be found to serve the purpose
of a scaffold, and that the balls are as useful to the wasp, as
materials, &c. to the mason; and are therefore placed as much within her
reach as possible. She uses them to stop and fill up the hole after she
has deposited an egg therein, so that the pillar is then destroyed, and
not the least remains left in the nest. The parent wasp generally leaves
ten or twelve worms as provision necessary and proper for the growth of
the young larva: no purveyor could take better precautions than our
wasp, for she has received her instructions from HIM who provides for
the necessities of all his creatures. In selecting the worms, she
chooses those of a proper size, that they may be sufficient in quantity,
and of an age that will not be in danger of perishing with hunger, in
which case they would have been corrupted; she therefore selects them
when they have their full growth. It is also observed, that if she
choose a larger sort, she gives a less number of them, and so
reciprocally.

  [98] Reaumur Mem. pour l’Histoire des Insectes, tom. xi. par. 2, p. 9.

From a retrospect view of this chapter, we may observe a striking
difference between man and the lower orders of animal creation. Man is
born totally ignorant; so much so, that he has no knowledge even of the
mother’s breast, till he has been brought acquainted with it by repeated
trials; he has no innate ideas, is unable to choose what is proper for
his food; he cannot form his voice to any articulate pronunciation, or
to express the affections of love; whereas the quadruped, the bird, and
the insect, are born to all that knowledge which is necessary for the
gratification of those desires or that love which forms their life; and,
consequently, in the knowledge of every thing relating to their
well-being, their food, their habitations, the commerce of the sexes,
their provision for their young, &c. from the impulse of the pleasure
arising from these innate desires and affections, the larva is also
prompted to seek and aspire after a change of its earthly state. If it
were not foreign to the subject in hand, it might be easy to shew, by a
variety of reasons, that this imperfection of man at his nativity
constitutes his real perfection, and places him infinitely, if I may so
speak, above the brute creation; for man is not created relatively
perfect, but formed a recipient of all perfection.


OF THE TERMITES, GENERALLY CALLED WHITE ANTS.

As no insects exceed the termites in their wonderful œconomy, wise
contrivances, and stupendous buildings, it will be proper to give the
reader some account of them; which I am enabled to do from the excellent
paper written by the late Mr. Smeathman, and published in the
Philosophical Transactions for the year 1781, part 1.

The termites are represented by Linnæus as the greatest plagues of both
Indies, and are indeed justly deemed so every where between the
tropics, on account of the vast damages sustained through them in
consequence of their eating and perforating wooden buildings, utensils,
furniture, &c. which are totally destroyed by them if not timely
prevented; for no substance less hard than metal or stone can escape
their most destructive jaws.

These insects have been noticed by various travellers in different parts
of the torrid zone; where numerous, as is the case with all equinoctial
continents, and islands not fully cultivated, many persons have been
excited by curiosity to observe them; and, indeed, those devoid of that
disposition must have been very fortunate, if, after a short residence,
they were not compelled to pay them attention for the preservation of
their property. They make their approaches chiefly under ground,
descending below the foundations of houses and stores, at several feet
from the surface, and rising again either in the floors, or entering at
the bottoms of the posts of which the sides of the buildings are
composed, boring quite through them, following the course of the fibres
to the top, or making lateral perforations and cavities here and there
as they proceed.

While some are employed in gutting the posts, others ascend from them,
entering a rafter, or some other part of the roof. If they once find the
thatch, which seems to be a favourite food, they soon bring up wet clay,
and build their pipes or galleries through the roof in various
directions, as long as it will support them; sometimes eating the
palm-tree leaves and branches of which it is composed, and perhaps, for
variety seems very pleasing to them, the rattan, or other running plant,
which is used as a cord to tie the various parts of the roof together,
and that to the posts which support it. Thus, with the assistance of the
rats, who during the rainy season are apt to shelter themselves there,
and to burrow through it, they very soon ruin the house, by weakening
the fastenings, and exposing it to the wet. In the mean time the posts
will be perforated in every direction as full of holes as that timber in
the bottoms of ships, which has been bored by the worms; the fibrous and
knotty parts, which are the hardest, being left to the last.

These insects are not less expeditious in destroying the shelves,
wainscotting, and other fixtures of an house, than the house itself.
They are continually piercing and boring in all directions, and
sometimes go out of the broadside of one post into that of another
adjoining to it; but they prefer and always destroy the softer
substances the first, and are particularly fond of pine and fir boards,
which they excavate and carry away with wonderful dispatch and
astonishing cunning; for, except a shelf has something standing upon it,
as a book, or any thing else which may tempt them, they will not
perforate the surface, but artfully preserve it quite whole, and eat
away all the inside, except a few fibres which barely keep the two sides
connected together; so that a piece of an inch-board, which appears
solid to the eye, will not weigh much more than two sheets of pasteboard
of equal dimensions, after these animals have been a little while in
possession of it. In short, the termites are so insidious in their
attacks, that we cannot be too much upon our guard against them: they
will sometimes begin and raise their works, especially in new houses,
through the floor. If you destroy the work so begun, and make a fire
upon the spot, the next night they will attempt to rise through another
part; and if they happen to emerge under a chest or trunk, early in the
night will pierce the bottom, and destroy or spoil every thing in it
before the morning. On these accounts the inhabitants set all their
chests or boxes upon stones or bricks, so as to leave the bottoms of
such furniture some inches above the ground, which not only prevents
these insects finding them out so readily, but preserves the bottoms
from a corrosive damp, which would strike from the earth through, and
rot every thing therein: a vast deal of vermin also would harbour under,
such as cockroaches, centipedes, millepedes, scorpions, ants, and
various other noisome insects.

It may be presumed that they have obtained the name of ants from the
similarity in their manner of living with those insects, which is in
large communities, that erect very extraordinary nests, for the most
part on the surface of the ground; from whence their excursions are made
through subterraneous passages or covered galleries, which they build
whenever necessity obliges, or plunder induces them to march above
ground, and at a great distance from their habitations, carry on a
business of depredation and destruction scarce credible but to those who
have seen it; but, notwithstanding they live in communities, and are,
like the ants, omnivorous; though, like them, at a certain period they
are furnished with four wings, and emigrate or colonize at the same
season, they are by no means the same kind of insects, nor does their
form correspond with that of ants in any one state of their existence.

The termites resemble the ants, indeed, in their provident and diligent
labour, but surpass them, as well as the bees, wasps, beavers, and all
other animals, in the art of building, as much as Europeans excel the
most uncultivated savages. They shew more substantial instances of
ingenuity and industry than any other animals; and do, in fact, lay up
vast magazines of provisions and other stores; a degree of prudence
which has of late years been denied, perhaps without reason, to the
ants.

The communities consist of one male and one female, which are generally
the common parents of the whole or greater part of the rest, and of
three orders of insects, apparently very different species, but really
the same, which together compose great commonwealths or rather
monarchies.

The great Linnæus having seen or heard of but two of these orders, has
classed the genus erroneously, for he has placed it among the aptera, or
insects without wings; whereas the insect in its perfect state, having
four wings without any sting, belongs to the neuroptera; in which class
it will constitute a new genus of many species.

The different species of this genus resemble each other in form, in
their manner of living, and in their good and bad qualities, but differ
as much as birds in the manner of building their habitations or nests,
and in the choice of the materials of which they compose them.

There are some species which build upon the surface of the ground, or
part above and part beneath; and one or two species, perhaps more, that
build on the stem or branches of trees.

There are of every species of termites three orders: 1. The working
insects, which for brevity we shall call labourers. 2. The fighters or
soldiers, which do not labour; and 3. The winged or perfect insects,
which are male and female, and capable of propagation. From these the
kings and queens are chosen, and nature has so ordered it, that they
emigrate within a few weeks after their elevation to this state, and
either establish new kingdoms, or perish within a day or two. Of these,
the working insects or labourers are always the most numerous; among
that species emphatically called termes bellicosus, which is the
largest, there seem to be at the least one-hundred labourers to one of
the fighting insects or soldiers. They are in this state about
one-fourth of an inch long, and twenty-five of them weigh about a grain,
so that they are not so large as some of our ants; from their external
habits and fondness for wood, they have been very expressively called
wood-lice by some people, and the whole genus has been known by that
name, particularly among the French. They resemble them, it is true,
very much at a distance; they run as fast or faster than any other
insect of their size, and are incessantly in a bustle.

The second order, or soldiers, have a very different appearance from the
labourers, and have been by some authors supposed to be the males, and
the former neuters; but they are, in fact, the same insects as the
foregoing, only they have undergone a change of form, and approached one
degree nearer to the perfect state. They are much larger, being half an
inch long, and equal in size to fifteen of the labourers. There is now,
likewise, a most remarkable circumstance in the form of the head and
mouth; for in the former state the mouth is evidently calculated for
gnawing and holding bodies; but in this state, the jaws being shaped
like two very sharp awls a little jagged, they are incapable of any
thing but piercing or wounding, for which purposes they are well
calculated, being as hard as a crab’s claw and placed in a strong horny
head larger than all the rest of the body together.

The insect in its perfect state is varied still more in its form; the
head, thorax, and abdomen, differ almost entirely from the same parts in
the labourers and soldiers; and, besides this, the animal is now
furnished with four fine large brownish transparent wings, with which it
is, at the time of emigration, to wing its way in search of a new
settlement; in short, it differs so much from its form and appearance in
the two other states, that it has never been supposed to be the same
animal, but by those who have seen it in the same nest; and some of
these have distrusted the evidence of their senses. It was so long
before Mr. Smeathman met with them in the nests, that he doubted the
information which was given him by the natives, that they belonged to
the same family: indeed, twenty nests may be opened without finding one
winged one; for those are to be found only just before the commencement
of the rainy season, when they undergo the last change, which is
preparative to their colonization. Add to this, they sometimes abandon
an outward part of their building, the community being diminished by
some accident that is unknown; sometimes different species of the real
ant, formica, possess themselves by force of a lodgment, and so are
frequently dislodged from the same nest, and taken for the same kind of
insects. This is often the case with the nests of the smaller species,
which are frequently totally abandoned by the termites, and completely
inhabited by different species of ants, cockroaches, scolopendræ,
scorpions, and other vermin fond of obscure retreats, that occupy
different parts of their roomy buildings.

In the winged state, their size as well as form is altered. Their bodies
in this state measure between six and seven-tenths of an inch in length,
their wings above two inches and an half from tip to tip, and they are
equal in bulk to about thirty labourers, or two soldiers. They are
furnished with two large eyes placed on each side of the head; if they
had any before, they are not easily to be distinguished. In this form
the animal comes abroad during or soon after the first tornado, which at
the latter end of the dry season proclaims the approach of the ensuing
rains, and seldom waits for a second or third shower; if the first, as
is generally the case, happen in the night, and bring much wet after it,
the quantities that are to be found the next morning all over the
surface of the earth, but particularly on the waters, is astonishing;
for their wings are only calculated to carry them a few hours; and after
the rising of the sun, not one in a thousand is to be found with four
wings, unless the morning continues rainy, when here and there a
solitary being is seen winging its way from one place to another, as if
solicitous to avoid its numerous enemies, particularly various species
of ants, which are hunting on every spray, on every leaf, and in every
possible place for this unhappy race, of which probably not one pair in
many millions are preserved to fulfil the first law of nature, and lay
the foundation of a new community. Not only all kinds of ants, and other
insects, but birds, and carnivorous reptiles, are upon the hunt for
them, and the inhabitants of many countries eat them.

From one of the most active, industrious, and rapacious; from one of the
most fierce and implacable little animals in the world, they are in this
state changed into an innocent helpless insect, incapable of making the
least resistance to the smallest ant. The ants are to be seen on every
side in infinite numbers, of various species and sizes, dragging these
annual victims to their different nests. Some are however so fortunate
as to escape, and be discovered by the labouring insects that are
continually running about the surface of the ground under their covered
galleries, the little industrious creatures immediately inclose them in
a small chamber of clay, suitable to their size, into which at first
they leave but one small entrance, only large enough for themselves and
the soldiers to go in and out, but necessity obliges them to make more
entrances. The voluntary subjects charge themselves with the task of
providing for the offspring of their sovereigns, as well as to work and
to fight for them, until they shall have raised a progeny capable at
least of dividing the task with them.

The business of propagation soon commences; and the labourers having
constructed a small wooden nursery, hereafter to be described, carry the
eggs and lodge them there as fast as they can obtain them from the
queen.

About this time a most extraordinary change begins to take place in the
queen, to which we know nothing similar, except in the pulex penetrans
of Linnæus, the jigger of the West-Indies, and in the different species
of coccus cochineal. The abdomen of this female begins gradually to
extend and enlarge to such an enormous size, that an old queen will have
it increased so as to be fifteen hundred or two thousand times the bulk
of the rest of her body, and twenty or thirty thousand times the bulk of
a labourer; the skin between the segments of the abdomen extends in
every direction, and at last the segments are removed to half an inch
distance from each other, though at first the length of the whole
abdomen was not above half an inch. They preserve their dark-brown
colour, and the upper part of the abdomen is marked with a regular
series of brown bars, from the thorax to the posterior part of the
abdomen, while the intervals between them are covered with a thin,
delicate, transparent skin, and appear of a fine cream colour, a little
shaded by the dark colour of the intestines and watery fluid seen here
and there beneath. It is supposed that the animal is upwards of two
years old when the abdomen is increased to three inches in length: they
have sometimes been found of near twice that size. The abdomen is then
of an irregular oblong shape, being contracted by the muscles of every
segment, and is become one vast matrix full of eggs, which make long
circumvolutions through an innumerable quantity of very minute vessels,
that circulate round the inside in a serpentine manner, which would
exercise the ingenuity of a skilful anatomist to dissect and develope.
This singular matrix is not more remarkable for its amazing extension
and size, than for its peristaltic motion, which resembles the
undulation of waves, and continues incessantly without any apparent
effort of the animal; so that one part or other is alternately rising
and sinking in perpetual succession. The matrix seems never at rest, but
to be always protruding eggs to the amount, in old queens, of sixty in
a minute, or eighty thousand and upwards in one day of twenty-four
hours.

These eggs are instantly taken from her body by her attendants, and
carried to the nurseries, which in a great nest may some of them be four
or five feet distant in a straight line, and consequently much farther
by their winding galleries. Here the young, when they are hatched, are
attended and provided with every thing necessary, until they are able to
shift for themselves, and take their share of the labours of the
community.

The termes bellicosus being the largest species, is most remarkable, and
best known on the coast of Africa. It erects immense buildings of
well-tempered clay or earth, which are contrived and finished with such
art and ingenuity, that we are at a loss to say whether they are most to
be admired on that account, or for their enormous magnitude and
solidity. The reason that the larger termites have been most remarked is
obvious; they not only build larger and more curious nests, but are also
more numerous and do infinitely more mischief to mankind.[99]

  [99] It may appear surprizing, that a Being perfectly good should have
  created animals which seem to serve no other end but to spread
  destruction and desolation wherever they go. But let us be cautious in
  suspecting any imperfection in the Father of the universe: what, on a
  superficial view may seem only productive of mischief, will upon
  mature deliberation be found worthy of that wisdom which pervades
  every part of the creation. Many poisons prove valuable medicines;
  storms are beneficial; and diseases often preserve life, and are
  conducive to its future enjoyments. The termites, it must be allowed,
  are frequently pernicious to mankind, but they are also very useful,
  and even necessary; one valuable purpose which they serve, is, to
  destroy decayed trees and other substances, which, if left on the
  surface of the ground in hot climates, would in a short time pollute
  the air. In this respect, they resemble very much the common flies,
  which are regarded by the generality of mankind as noxious, and at
  best, as useless beings in the creation; but this is certainly for
  want of due consideration. There are not probably in all nature
  animals of more importance; and it would not be difficult to prove,
  that we should feel the want of one or two species of large quadrupeds
  much less than of one or two species of these despicable looking
  insects. Nothing is more disagreeable or more pestiferous than putrid
  substances; and it is apparent to all who have made the observation,
  that these little insects contribute more to the quick dissolution and
  dispersion of putrescent matter than any other. They are so necessary
  in all hot climates, that even in the open fields a dead animal or
  small putrid substance cannot be laid on the ground two minutes,
  before it will be covered with flies and their maggots, which
  instantly entering, quickly devour one part, and, perforating the rest
  in various directions, expose the whole to be much sooner dissipated
  by the elements. Thus it is with the termites; the rapid vegetation in
  hot climates, of which no idea can be formed by any thing to be seen
  in this, is equalled by as great a degree of destruction from natural
  as well as accidental causes. When trees and even woods are in part
  destroyed by tornados or fire, it is wonderful to observe how many
  agents are employed in hastening the total dissolution of the rest; in
  this business none are so expert or so expeditious and effectual as
  the termites, who in a few weeks destroy and carry away the bodies of
  large trees without leaving a particle behind; thus clearing the place
  for other vegetables, which soon fill up every vacancy. See Encycl.
  Brit. art. Termes. EDIT.

The nests of this species are so numerous all over the island of
Bananas, and the adjacent continent of Africa, that it is scarcely
possible to stand upon any open place, such as a rice plantation, or
other clear spot, where one of these buildings is not to be seen almost
close to each other. In some parts near Senegal, as mentioned by M.
Adanson, their number, magnitude, and closeness of situation, make them
appear like the villages of the natives. These buildings are usually
termed hills, by the inhabitants as well as strangers, from their
outward appearance, which is that of little hills more or less conical,
generally very much in the form of sugar-loaves, and about ten or twelve
feet in perpendicular height above the common surface of the ground.

These hills continue quite bare until they are six or eight feet high;
but, in time, the dead barren clay of which they are composed becomes
fertilized by the genial power of the elements in these prolific
climates, and the addition of vegetable salts and other matters brought
by the wind; and in the second or third year the hillock, if not
overshaded by trees, becomes like the rest of the earth, almost covered
with grass and other plants; and in the dry season, when the herbage is
burnt up by the rays of the sun, it is not much unlike a very large
hay-cock.

Every one of these buildings consists of two distinct parts, the
exterior and interior. The exterior cover is one large clay shell, in
the form of a dome, capacious and strong enough to inclose and shelter
the interior building from the vicissitudes of the weather, and the
inhabitants from the attacks of natural or accidental enemies. The
external cover is always, therefore, much stronger than the interior
building, which is the habitable part, divided with wonderful regularity
and contrivance into an amazing number of apartments for the residence
of the king and queen, for the nursing of their numerous progeny, and
for magazines, which are always found well filled with stores and
provisions.

These hills make their first appearance above ground by a little turret
or two in the shape of sugar-loaves, which are run a foot high or more;
soon after, at some little distance, while the former are increasing in
height and size, they rise others, and so go on increasing the number,
and widening them at the base, till their works below are covered with
these turrets, which the insects always raise highest and largest
towards the middle of the hill, and by filling up the intervals between
each turret, collect them as it were into one dome. They are not very
curious or exact about these turrets, except in making them very solid
and strong; and when, by the junction of them, the dome is completed,
for which purpose the turrets serve as scaffolds, they take away the
middle ones entirely, except the tops, which joined together make the
crown of the cupola, and apply the clay to the building of the works
within, or to erecting fresh turrets for the purpose of raising the
hillock still higher; so that no doubt some part of the clay is used
several times, like the boards and posts of a mason’s scaffold.

The royal chamber, which, on account of its being adapted for, and
occupied by the king and queen, appears to be in the opinion of this
little people, of the most consequence, is always situated as near the
center of the interior building as possible, and generally about the
height of the common surface of the ground, at a pace or two from the
hillock; it is always nearly in the shape of half an egg or an obtuse
oval within, and may be supposed to represent a long oven. In the infant
state of the colony, it is not above an inch, or thereabouts, in length;
but in time will be increased to six or eight inches or more in the
clear, being always in proportion to the size of the queen, who,
increasing in bulk as in age, at length requires a chamber of such
dimensions. The floor is horizontal, sometimes an inch thick and upward
of solid clay; the roof also, which is one solid and well-turned oval
arch, is generally of about the same solidity, but in some places it is
not a quarter of an inch thick; this is on the sides where it joins the
floor, and where the doors or entrances are made. These entrances will
not admit any animal larger than the soldiers or labourers; so that the
king, and the queen, who is when full grown a thousand times the weight
of a king, can never possibly go out. The royal chamber, if in a large
hillock, is surrounded by an innumerable quantity of others, of
different sizes, shapes, and dimensions; but all of them arched,
sometimes of a circular, sometimes of an elliptical form. These chambers
either open into each other, or have communicating passages, and being
always empty, are evidently made for the soldiers and attendants; of
whom, it will soon appear, great numbers are necessary, and of course
always in waiting.

These apartments are joined by the magazines and nurseries; the former
are chambers of clay, and are always well filled with provisions, which
to the naked eye seem to consist of the raspings of wood and plants,
which the termites destroy, but are found by the microscope to be
chiefly composed of the gums or inspissated juices of plants, thrown
together in little masses, some of which are finer than others, and
resemble the sugar about preserved fruits; others are like drops of gum.
The magazines are intermixed with the nurseries, buildings totally
different from the rest of the apartments, being composed entirely of
wooden materials, seemingly joined together with gums. They are called
nurseries because they are invariably occupied by the eggs and young
ones, which appear at first in the shape of labourers, but as white as
snow. These buildings are exceedingly compact, and divided into many
very small irregular-shaped chambers, placed all round the royal
apartments, and as near as possible to them.

When the nest is in the infant state, the nurseries are close to the
royal chamber; but as in process of time the queen increases in size, it
is necessary to enlarge the chamber for her accommodation; and as she
then lays a greater number of eggs, and requires a more numerous train
of attendants, so it is necessary to enlarge and increase the number of
the adjacent apartments; for which purpose, the small nurseries which
are first built, are taken to pieces, rebuilt a little further off, a
size larger, and the number of them increased at the same time. Thus
they continually enlarge their apartments, pull down, repair, or
rebuild, according to their wants, with a degree of sagacity,
regularity, and foresight, not even imitated by any other kind of
animals or insects. The nurseries are inclosed in chambers of clay, like
those which contain the provisions, but much more extensive. In the
early state of the nest they are not larger than an hazel nut, but in
great hills are often as large as a child’s head of a year old.

The royal chamber is situated nearly on a level with the surface of the
ground, at an equal distance from all the sides of the building, and
directly under the apex of the hill. It is, on all sides, both above and
below, surrounded by what may be called the royal apartments, which have
only labourers and soldiers in them, and can be intended for no other
purpose than for these to wait in, either to guard or serve their common
father and mother, on whose safety depends the happiness, and, according
to the account of the negroes, even the existence of the whole
community.

These apartments form an intricate labyrinth, which extends a foot or
more in diameter from the royal chamber on every side. Here the
nurseries and magazines of provisions begin, and being separated by
small empty chambers and galleries, which go round them, or communicate
from one to the other, are continued on all sides to the outward shell,
and reach up within it two-thirds or three-fourths of its height, having
an open area in the middle under the dome, resembling the nave of an old
cathedral. This area is surrounded by large gothic arches, which are
sometimes two or three feet high next the front of the area, but
diminish very rapidly as they recede from thence, like the arches of
aisles in perspective, and are soon lost among the innumerable chambers
and nurseries behind them. All these chambers, and the passages leading
to and from them, being arched, contribute to support one another; and
while the interior large arches prevent their falling into the center,
and keep the area open, the exterior building supports them on the
outside.

The interior building, or assemblage of nurseries, chambers, &c. has a
flattish top or roof without any perforation; by this contrivance, if
any water should penetrate the external dome, the apartments below are
preserved from injury. It is never exactly flat and uniform, because
they are always adding to it by building more chambers and nurseries: so
that the divisions or columns between the future arched apartments
resemble the pinnacles upon the fronts of some old buildings, and demand
particular notice, as affording one proof that for the most part the
insects project their arches, and do not make them by excavation. The
area is likewise water-proof, and contrived so as to let the water off,
if it should get in and run over, by some short way, into the
subterraneous passages, which run under the lowest apartments in the
hill in various directions, and are of an astonishing size, being wider
than the bore of a great cannon. There is an account of one that was
measured, which was perfectly cylindrical, and thirteen inches in
diameter.

These subterraneous passages or galleries are lined very thick with the
same kind of clay of which the hill is composed, and ascend the inside
of the outward shell in a spiral manner; winding round the whole
building up to the top, they intersect each other at different heights,
opening either immediately into the dome in various places, and into the
interior building, the new turrets, &c. or communicating thereto by
other galleries of different bores or diameters, either circular or
oval.

From every part of these large galleries are various small pipes or
galleries, leading to different parts of the building; under ground
there are a great many which lead downward, by sloping descents three
and four feet perpendicular among the gravel, from whence the labouring
termites cull the finer parts, which being worked up in their mouths to
the consistence of mortar, becomes that solid clay or stone, of which
their hills and all their buildings, except the nurseries, are composed.
Other galleries again ascend and lead out horizontally on every side,
and are carried under ground near to the surface, a vast distance.

There is a kind of necessity for the galleries under the hills being
thus large, as they are the great thoroughfares for all the labourers
and soldiers going forth or returning upon any business whatever,
whether fetching clay, wood, water, or provisions; and they are
certainly well calculated for the purposes to which they are applied, by
the spiral slope which is given them.

Those species which build either the roofed turrets, or the nests in the
trees, seem in most instances to have a strong resemblance to the
preceding, both in their form and œconomy, going through the same
changes from the egg to the winged state. The queens also increase to a
great size when compared with the labourers, but very short of those
queens before described. The largest are from about an inch to an inch
and an half long, and not much thicker than a common quill. There is the
same kind of peristaltic motion in the abdomen, but in a much smaller
degree; and as the animal is incapable of moving from her place, the
eggs, no doubt are carried to the different cells by the labourers, and
reared with a care similar to that which is practised in the larger
nests.

It is remarkable of all these different species, that the working and
the fighting insects never expose themselves to the open air, but either
travel under ground, or within such trees and substances as they
destroy; except, indeed, when they cannot proceed by their latent
passages, and find it convenient or necessary to search for plunder
above ground: in that case they make pipes of that material with which
they build their nests. The larger sort use the red clay; the turret
builders use the black clay; and those which build in the trees employ
the same ligneous substance of which their nests are composed.

The termites, except their heads, are exceedingly soft, and covered with
a very thin and delicate skin; being blind, they are no match on open
ground for the ants, who can see, and are all of them covered with a
strong horny shell not easily pierced, and are of dispositions bold,
active, and rapacious.

Whenever the termites are dislodged from their covered ways, the various
species of formicæ or ants, who probably are as numerous above ground,
as the latter are in their subterraneous passages, instantly seize and
drag them away to their nests, to feed the young brood. The termites
are, therefore, exceedingly solicitous about the preserving their
covered ways in good repair; and if you demolish one of them for a few
inches in length, it is wonderful how soon they re-build it. At first in
their hurry they get into the open part an inch or two, but stop so
suddenly, that it is very apparent they are surprized; for, though some
run straight on, and get under the arch as speedily as possible in the
further part, most of them run as fast back, and very few will venture
through that part of the track which is left uncovered. In a few minutes
you will perceive them re-building the arch, and by the next morning
they will have restored their gallery for three or four yards in length,
if so much has been ruined; and upon opening it again, will be found as
numerous as ever under it, passing both ways. If you continue to destroy
it several times, they will at length seem to give up the point, and
build another in a different direction; but, if the old one should lead
to some favourite plunder, in a few days will re-build it again, and,
unless you destroy their nest, never totally abandon their, gallery.


OF THE HABITATIONS OF CATERPILLARS.

Though the view which has already been given of the various proceedings
of insects in forming their habitations, has extended to some length, I
cannot with propriety omit noticing the wonderful art and industry
which is manifested in these respects by the caterpillar; and more
particularly so, as from the larva state the foundation of all our
present knowledge of the natural history of insects has been obtained.

Some species of caterpillars form a kind of hammock, in which they eat
and go through their various changes; while others erect a silken tent,
under which they live until they have consumed the surrounding herbs.
They then leave their abodes, and pitch their tents in a more fruitful
spot.

Many associate together all their lives; these proceed from the same
moth, who deposited her eggs near each other, or rather laid them in a
heap, forming as it were a kind of nest. They are generally hatched on
the same day, and, living together, constitute a new species of
republic, in which all are brethren. They often amount to near six
hundred in a family, though they are frequently to be found with only
about two hundred. Of these social caterpillars there are some species
which not only continue with the society while they are in a larva
state, but even place their pupæ close together. There are other kinds
who associate only for a short period.

Among the vast variety of insects which inhabit the oak, there is a
species of caterpillar which live separate till they arrive at a certain
age; they then assemble together, and do not quit each other till they
attain their perfect state. As the number thus assembled is
considerable, the nest is also very large. They remain in-doors during
the day, not leaving their habitation till sun-set. When they go out,
one of the body precedes the rest as a chief, whom they regularly
follow; when the leader stops, the rest do the same, and wait till it
goes on again, before they recommence their march. The first file
generally consists of a single caterpillar, which is succeeded by a
double file; these, by three in a row, which are then followed by files
of five, and so on. They keep exceeding close to each other, not leaving
any interval either between the ranks, or those in each rank; all of
them following their captain in every direction, whether straight or
crooked. After they have taken their repast, which is done on the march,
they return to their nest in the same order in which they set out.

This mode is followed till they are full grown, when each forms a cone,
in which it is changed into a chrysalis. M. Bonnet has shewn, that
though these caterpillars proceed often very far from their nest, it is
by no means difficult for them to get back again, because they spin over
all the places in their rout. The first leads the way, the second
follows spinning, the third spins after the first and second, and so on
with the rest. All these threads form by degrees a small shining track,
a little path; and all these paths meet at the nest. To be fully
convinced of the use of these threads, let any one but break the
continuation of them in some particular part, and he will see the little
caterpillars turn back, as if they were at a loss, till one more daring
than the rest restores the communication by spinning new threads.

The reader who is desirous of a fuller information concerning the habits
of these, as well as many other insects, must be referred to the
laborious and interesting memoirs of Reaumur. Happy if he should, like
De Geer, be induced thereby to follow the steps of so great a master; he
will derive from thence a continual source of new pleasures and
increasing delights; and the more he extends the boundaries of his
observations, the more he will be convinced that INFINITY is, as it
were, impressed on all the works of the CREATOR.

Different species of caterpillars are often to be found in great numbers
on the same tree or plant; but then as they seem to have no connection
with each other, and the actions of the one have no influence on the
rest, they may be considered as solitary; but there are others who seem
still more independent of each other, and greater friends to solitude,
constructing a lodging formed of leaves tied together with considerable
ingenuity, in which they live as in a hermitage. The operation by which
these tie the leaves together, is far surpassed by another kind, who
fold and bend one part of the leaf till it meets the other. These are
again exceeded by those who roll the leaves which they inhabit. For this
purpose the caterpillar chooses a part of a leaf which it finds in some
degree bent; here it establishes its abode, and begins its work, moving
the head with great velocity in a curved line, or rather vibrating it
like a pendulum, the middle of the body being the center on which it
moves. At each motion of the head a thread is spun, and fixed to that
part to which the head seems to be applied. The threads are extended
from the bent to the flat part of the leaf, being always adjusted both
in length and strength to the nature of the leaf, and the curvature
which is to be given to it.

De Geer attending to the operations of a species of this kind of
caterpillar, observed that at each new thread it spun, the edges of the
leaf insensibly approached to each other, and were bent more and more,
in proportion as the caterpillar spun new threads; when the last thread
that was spun was tight, that which preceded it was loose and floating
in the air. To effect this, the caterpillar, after it has fixed a thread
to the two edges of the leaf, and before it spins another, draws it
towards itself by the hooks of its feet, and by these means bends the
leaf; it then spins another thread, to maintain the leaf in this
position, which it again pulls towards itself, and repeats the
operation, till it has bent the leaf in its whole direction. It now
begins again, placing the threads further back upon the bent part of the
leaf, and by proceeding in this manner, it is rolled up; when it has
finished this business, it strengthens the work, by fastening the ends
of the leaf together. The habitation thus formed is a kind of hollow
cylinder, open to the light at both ends, the sides of it affording the
insect food and protection, for within it the creature feeds in safety.
In the same case they are also transformed; at the approach of the
change the caterpillar lines the rolled leaf with silk, that the rough
parts of it may not injure the chrysalis.

A great number of the smaller larvæ require an artificial covering, to
protect them from the open air. Among these, some inhabit the interior
parts of leaves, making their way between the superior and inferior
membranes, living upon the parenchymous parts of the leaf; and as they
are exceedingly small, a leaf affords them a spacious habitation. If the
distance between the membranes be not large enough for them, they
enlarge the space by forming different folds in one of them, in which
they can move with ease: from these circumstances they have been named
by Reaumur miners of leaves. This illustrious author has described these
larvæ, the flies into which they are changed, and all the Various
methods made use of by them in performing this work. Some mine a large
oval or circular space; others form a kind of gallery, which is
sometimes straight, sometimes crooked. They only leave a thin membrane
on the upper side of the leaf; but they leave the under side more
substantial. One species of moth which proceeds from these larvæ is very
small but exceedingly beautiful.

The larvæ of the phryganea mostly live in little cases of their own
building, which are formed of a variety of materials, that they train
after them in the water wherever they go. These cases are generally
cylindrical, and open at both ends; the inside is lined with silk spun
by the larva, the outside formed of different substances, as bits of
reed, stone, gravel, and some entirely of small shells, &c. which they
arrange and manage with singular dexterity: they never quit this case.
When they walk, they put out the head, and a few of the first rings of
the body, training the case after them.

Having lived in the water for some time, they become inhabitants of the
air. They assume the pupa form in the water, closing up the two ends of
the case with bars of silk, by which it is secured from the attacks of
its enemies; and at the same time there is a free passage for the water,
which is still necessary for its existence. At a proper period the pupa
forces its way through the case, and makes for the land, where its
further change instantly commences, and is soon completed.

We shall close these specimens of the industry of insects with an
account of that which is displayed by the larvæ of the tineæ. The
greatest part of the body of these little creatures, except the head and
six fore feet, is covered over with a thin tender skin; the body of the
insect is cylindrical, and lodged in a tube which is open at both ends.
Soon after they are born, they begin to cover themselves, and are,
therefore, seldom to be found but in these tubes or cases. They are in
general so small, that it is not easy to distinguish the cases without a
magnifier; but as the body lengthens, the case becomes too short; it is,
therefore, part of its daily employ to lengthen it. For this purpose it
extends the head beyond the tube, and having found the materials which
answer its purpose, it tears it off, and brings it to the end of the
tube, and fixes it there, repeating this manoeuvre till it has
sufficiently lengthened it. After it has finished one end, it turns
itself round within the case, and performs the same operation at the
other.

This does not terminate their labours, for the tube must also be
increased in diameter, as it soon becomes too small for the body; the
means they make use of to enlarge it, is precisely the same as we
ourselves should adopt under similar circumstances. The insect slits the
tube at the two opposite sides, at the same end, and inserts in the slit
two pieces of the required size; it then performs the same at the other
end. By these means they soon enlarge it sufficiently, without exposing
themselves to the air during the operation. The outside of these cases
is made of silk, hair, &c. the inside is of silk only. Their covering
always partakes of the colour of the cloth or tree, &c. from whence it
was taken; if it pass over a red piece, the colour will be red. When
they are come to their perfect growth, they abandon the cloth, and seek
for a proper place wherein they may pass from their present to a more
perfect state.

I cannot conclude this long chapter better than in the words of Mr.
Stillingfleet. “Many are apt to treat with contempt any man whom they
see employed in poring over a moss, or examining an insect, from day to
day, thinking that he spends his time and his life in unimportant and
barren speculations; yet were the whole scene of nature laid open to our
views, were we admitted to behold the connections and dependences of
every thing on every other, and to trace the œconomy of nature through
the smaller, as well as greater parts of this globe, we might, perhaps,
be obliged to own that we were mistaken; that the Supreme Architect had
contrived his works in such a manner, that we cannot properly be said to
be unconcerned in any one of them; and, therefore, that studies, which
seem upon a slight view to be quite useless, may in the end appear of no
small importance to mankind. Nay, were we only to look back into the
history of arts and sciences, we must be convinced that we are apt to
judge over hastily of things of this nature. We should there find many
proofs that he who gave this instinctive curiosity to some of his
creatures, gave it for good and great purposes, and that he rewards with
useful discoveries all these minute researches.

“It is true, this does not always happen to the searcher, or his
contemporaries, nor even sometimes to the immediate succeeding
generation; but I am apt to think, that advantages of one kind or other
always accrue to mankind from such pursuits; some men are born to
observe and record what perhaps by itself is perfectly useless, but yet
of great importance to another who follows and goes a step further,
still as useless; to him another succeeds, and thus by degrees, till at
last one of a superior genius comes, who laying all that has been done
before this time together, brings on a new face of things, improves,
adorns, exalts human society.

“All those speculations concerning lines and numbers, so ardently
pursued, and so exquisitely conducted by the Grecians, what did they aim
at? or what did they produce for ages? a little arithmetic, and the
first elements of geometry, were all they had need of. This Plato
asserts; and though, as being himself an able mathematician, and
remarkably fond of these sciences, he recommends the study of them; yet
he makes use of motives that have no relation to the common purposes of
life.

“When Kepler, from a blind and strong impulse, merely to find analogies
in nature, discovered that famous one between the distance of the
several planets from the sun, and the periods in which they complete
their revolutions, of what importance was it to him or the world?

“Again; when Galileo, pushed on by the same irresistible curiosity,
found out the law by which bodies fall to the earth, did he, or could he
foresee that any good would come from his ingenious theorems; or was any
immediate use made of them?

“Yet had not the Greeks pushed their abstract speculations so far, had
not Kepler and Galileo made the above-mentioned discoveries, we never
could have seen the greatest work that ever came from the hands of man,
Sir Isaac Newton’s Principia.

“Some obscure person, whose name is not so much as known, diverting
himself idly, as a stander-by would have thought, with trying
experiments on a seemingly contemptible piece of stone, found out a
guide for mariners on the ocean, and such a guide as no science, however
subtil and sublime its speculations may be, however wonderful its
conclusions, would ever have arrived at. It was mere curiosity that put
Sir Thomas Millington upon examining the minute parts of flowers; but
his discoveries have produced the most perfect and most useful system of
botany that the world has yet seen.

“Other instances might be produced to prove, that bare curiosity in one
age, is the source of the greatest utility in another; and what has
frequently been said of chemists, may be applied to every other kind of
vertuosi. They hunt, perhaps, after chimeras and impossibilities; they
find something really valuable by the bye. We are but instruments under
the Supreme Director, and do not so much as know, in many cases, what is
of most importance for us to search after; but we may be sure of one
thing, viz. that if we study and follow nature, whatever paths we are
led into, we shall at last arrive at something valuable to ourselves and
others, but of what kind we must be content to remain ignorant.”



CHAP. VI.

A GENERAL VIEW OF THE INTERNAL PARTS OF INSECTS, AND MORE PARTICULARLY
OF THE CATERPILLAR OF THE PHALÆNA COSSUS---A DESCRIPTION OF SUNDRY
MISCELLANEOUS OBJECTS.


The interior part of insects includes four principal viscera; the spinal
marrow, the intestinal bag, the heart, and tracheal vessels.

The spinal marrow, or principal trunk of the nerves of insects, is a
whitish thread, extended the whole length from the head to the
hindermost part, furnished at intervals with small knots or ganglions.
From these knots proceed the nervous threads that are supposed to be the
instruments of sensation and motion.

On the medullary thread is placed the intestinal bag, which is equal to
it in length; it is a long gut, in which are contained the oesophagus,
the stomach, and intestines.

Along the back, and parallel to the intestinal bag, runs a long thin
vessel, in which may be perceived through the skin of the insect
alternate contractions and dilatations; this part is supposed to perform
the functions of the heart.

The tracheal vessels of insects are very similar to those of plants; are
of the same structure, colour, and elasticity, and are, like them,
dispersed through the whole body.

A clearer idea of these parts will be obtained by the short extract I
shall give of M. Lyonet’s work; which, at the same time that it displays
the wonderful organization of insects, shews how worthy it is of the
attention of a rational being; and, though this description is confined
to a particular species, it will be found to accord in general with a
great number.

Of all the modifications of which matter is susceptible, the most noble
is undoubtedly the organization thereof. In the structure of animals,
the Sovereign Wisdom is exhibited to our view in the most striking
manner. The body of an animal is a little particular system more or less
complicated, and which, like the system of the universe at large, is the
result of the combination and connection of a multitude of different
parts, which all conspire to produce one general effect, the
manifestation of the principle which we term life. So wonderful are
these combinations that we are incapable of comprehending, or even of
admiring sufficiently the astonishing apparatus of springs, levers,
counter-weights, tubes of different diameters, &c. which constitute
these organical machines. The interior parts of the insect, the most
despicable in appearance, would absorb all the powers of the most able
anatomist. He would be lost in the labyrinth as soon as he attempted to
explore all its windings. A truth that will be evident to every one who
considers only the small portion here introduced of the anatomy of the
caterpillar inhabiting the trunk of the willow-tree. This caterpillar
produces the phalæna cossus, or goat-moth. M. Lyonet in his admirable
work entitled, “Traite Anatomique de la Chenille qui ronge le Bois de
Saule,” has given an ample and minute description of this insect. In the
following concise abstract enough will appear to convince the reader of
the utility of microscopic glasses, in displaying the wonders of the
creation, and to afford additional proof that the attention of the
Almighty is not confined merely to objects of magnitude.

In a former edition of this work, I entered into a more minute detail of
the several parts contained in the figures exhibited in plate XII. This
account I have now omitted, as after all it could not convey a clear
idea of the muscles alone, much less of the different parts of the
caterpillar, without a reference to other plates of M. Lyonet’s work. I
therefore concluded it would be better to let the figures speak for
themselves, and then give a general description of the interior parts of
the caterpillar; referring the reader for full particulars to the
original.

Figures 1 and 2 represent the muscles of the caterpillar, when it is
opened at the belly. Fig. 3 and 4 exhibit a view of the muscles when it
is opened at the back. Fig. 5 and 6, an anatomical delineation of the
head; so complex is this organ, that in order to give an adequate idea
of its structure, M. Lyonet has employed no less than twenty figures.
Fig. 7 is an out-line of the head more magnified than in the last
figures. In order to obtain the views here exhibited, the muscles were
freed as well from fat, as from the nerves and other vessels.

The BODY of the caterpillar in the Plate Fig. 2 and 3, is divided into
twelve parts, corresponding to its rings marked by the numbers 1 to 12;
to the first number the word RING is affixed. Each of these rings is
distinguished from that which follows, and that preceding it, by a kind
of neck or small hollow part. By conceiving a line to pass through these
necks, and forming boundaries to the rings, we acquire twelve more
divisions, Fig. 1 and 4; these are also marked with the numbers 1 to 12;
to the first the word DIVISION is annexed. The several parts exhibited
in the divisions, Fig. 1, are the muscles; those in Fig. 2, under the
word ring, are also muscles, which appear when those in Fig. 1 are
removed, lying under them.

The anatomical delineation of the muscles of the head, Fig. 5 and 6,
should be considered as consisting of two figures, which join in the
middle, being terminated by the superior and inferior lines. The head,
as here represented, is magnified about three-hundred times. H H are the
two palpi: the truncated muscles d, belong to the lower lip, and form a
part of those which give it motion: K, the two ganglions of the neck
united: I I, the two silk vessels: L, the oesophagus: M, the two
dissolving vessels: the Hebrew letters denote the continuation of the
cephalic arteries: S T U W and X are the ten abductor muscles of the
jaw: under e e and f f are seen four occipital muscles: a a, a nerve of
the first pair, belonging to the ganglion of the neck; b, a branch of
this nerve.

Fig. 7 is an outline of the head magnified considerably more than in the
last figure, exhibiting the nerves as seen from the under part.
Excepting in two or three instances, only one nerve of each pair is
shewn, as a greater number would have occasioned confusion. The nerves
of the first ganglion of the neck are designed by capital letters; those
of the ganglion a, are distinguished by Roman letters; those of the
small ganglion, by Greek characters; and those of the frontal ganglion,
except one, by numbers.


A GENERAL VIEW OF THE INTERIOR PARTS OF THE CATERPILLAR.

The MUSCLES have neither the exterior form, nor the colour of those of
larger animals. In their natural state they are soft, and have the
appearance of a jelly; they are of a greyish blue, and the
silver-coloured appearance of the aerial or pulmonary vessels, which
creep over and penetrate their substance, exhibits under the microscope
a most beautiful spectacle. When the caterpillar has been soaked for
some time in spirit of wine, they lose their elasticity and
transparency, and become firm, opake, and white; the aerial vessels
disappear. At first sight they might be taken for tendons, as they are
of the same colour and possess almost the same lustre. They are
generally flat, and of an equal size throughout; the middle seldom
differs either in colour, substance, or size, from the extremities. The
ends are fixed to the skin; the rest of the muscle is generally free and
floating; several of them branch out considerably; the branches extend
sometimes so far, that it is not always easy to discover whether they
are distinct and separate muscles, or parts of another. They are of a
moderate strength; those that have been soaked in spirit of wine, when
examined by the microscope, will be found to be covered with a membrane
which may be separated from them; they then appear to consist of several
parallel bands, disposed according to the length of the muscle. These,
when divided by the assistance of very fine needles, appear to be
composed of still smaller bundles of fibres, in the same direction;
which, when examined by a very deep magnifier, and in a favourable
light, appear twisted like a small cord. The muscular fibres of the
spider, which are much larger than those of the caterpillar, are found
on examination to consist of two substances, one soft, and the other
hard; the last is twisted round the former spirally, and thus gives to
it the afore-mentioned cord-like appearance. If the muscles are
separated by means of very fine needles, in a drop of some fluid, we
find that they are not only composed of fibres, membranes, and aerial
vessels, but also of nerves; and, from the drops of oil that may be seen
floating on the fluid, that they are also furnished with many unctuous
particles. The muscles in a caterpillar are very numerous, exceeding by
much those of the human body; the reader may form some idea of their
number by inspecting Fig. 1 2 3 and 4 of Plate XII. They occupy the
greatest part of the head; there is an amazing number at the oesophagus,
the intestines, &c. the skin is as it were lined by different beds of
them, placed one under the other, and ranged with very great symmetry.
The number of muscles that our observer has been able to distinguish is
truly astonishing; he found 228 in the head, 1647 in the body, and 2066
in the intestinal tube, making in all 3941!

The SPINAL MARROW, and the brain of the caterpillar, if it can be said
to have any, seem to have very little relation to those of man; in the
last, the brain is inclosed in a bony cavity; it occupies the greatest
part of the head, and is anfractuose, and divided into lobes. There is
nothing similar to this in the caterpillar; we find indeed in the head
of that which we are describing, a part which seems to answer the
purpose of the brain, because the nerves that are disseminated through
the head are derived from it; but then this part is unprotected, and so
small, that it does not occupy one-fifth part of the head; the surface
is smooth, and has neither lobes nor anfractuousness; and if we must
call this a brain, the caterpillar may be said to have thirteen, as
there are twelve more such parts following each other in a line; they
are nearly of the same size with that in the head, and of the same
substance, and it is from them that the nerves are distributed through
the whole body. Lest the idea of thirteen brains might be disagreeable
to his readers, Lyonet has called these parts ganglions. The spinal
marrow in the human species descends down the back, inclosed in a bony
case; is large with respect to its length, and not divided into
branches, diminishing in thickness in proportion as it is removed
further from the brain. In the caterpillar, the spinal marrow goes along
the belly, is not inclosed in any tube, is very small, forks out at
intervals, and is nearly of the same thickness throughout, except at the
ganglions. For a description of the numerous vessels, and curious
texture of these parts, reference must be had to the original work of
Lyonet. The substance of the spinal marrow, and of the ganglions, is not
near so tender and easily separated as in man; it has a very great
degree of tenacity, and does not break without considerable tension. The
substance of the ganglions differs from that of the spinal marrow, as no
vessels can be discovered in the latter, whereas the former are full of
very delicate ones. The patient anatomist of the caterpillar has counted
forty-five pair of nerves, and two single ones; so that there are
ninety-two principal nerves, whose ramifications are innumerable.

The TRACHEAL ARTERIES of the caterpillar are two large aerial elastic
vessels, which with their numerous ramifications may be pressed close
together, and drawn out considerably, but return immediately to their
usual size when the tension ceases; they creep under the skin close to
the spiracula, one at the right side of the insect, the other at the
left, each of them communicating with the air, by means of nine
spiracula; they are nearly as long as the body, beginning at the first
spiraculum, and going a little farther than the last, terminating in
some branches which extend to the extremities of the body. Round about
each spiraculum the tracheal artery pushes forth a great number of
branches, which are again divided into smaller ones; these further
subdivide, and spread through the whole body of the caterpillar. This
vessel and its principal branches are composed of three coats, which may
be separated one from the other. The exterior covering is a thick
membrane, furnished with a great number of fibres, which describe a vast
variety of circles round it, communicating with each other by numerous
shoots. The second is very thin and transparent; no particular vessel is
distinguished in it. The third is composed of scaly threads, which are
generally turned in a spiral form, and come so near each other, as
scarce to leave any interval; these threads are curiously united with
the membrane which occupies the intervals, and form a tube which is
always open, notwithstanding the flexure of the vessel. There are also
many other peculiarities in its structure, which cannot be well
explained without more plates. The principal tracheal vessels branch out
into 236 smaller ones, from which there spring 1326 different
ramifications.

The part of the caterpillar which naturalists call the HEART, without
being certain that it performs the functions thereof, is of a nature
very different from that of larger animals. It is almost as long as the
caterpillar itself, lies immediately under the skin at the top of the
back, entering into the head, and terminating near the mouth. It is
large and spacious towards the last rings of the body, and diminishes
very much as it approaches the head, from the fourth to the twelfth
division; it has on both sides, at each division, an appendage, which
partly covers the muscles of the back; but, growing narrower as it
approaches the lateral line, forms a number of irregular lozenge-shaped
bodies. This muscular tube has been called the heart of the caterpillar;
first, because it is generally filled with a kind of lymph, which has
been supposed to be the blood of the caterpillar; secondly, because in
all caterpillars, whose skin is in some degree transparent, continual,
regular, and alternate dilatations and contractions may be perceived
along the superior line, beginning at the eleventh ring, and going on
from ring to ring to the fourth, whence this vessel has been considered
as a file of hearts; but still this viscera seems to have very little
relation to the heart of larger animals; we find no vessel opening into
it, to answer to the aorta, vena cava, &c. &c. Near the eighth division
are two white oblong masses, that join the tube of the heart; they have
been called reniform bodies, because they are something similar to a
kidney in their shape.

The CORPUS CRASSUM is, with respect to volume, the most considerable
part of the whole caterpillar; it is the first and only substance that
is seen on opening it, forming a kind of sheath, which envelopes and
covers all the entrails, and introducing itself into the head, enters
all the muscles of the body, filling the greatest part of the empty
spaces in the caterpillar. It is of a milk-white colour. In its
configuration it is very similar to the human brain. When the different
masses of the corpus crassum which covers the entrails are removed, the
largest parts are the oesophagus, the ventricle, and the large
intestines.

The OESOPHAGUS descends from the bottom of the mouth to about the fourth
division. The anterior part which is in the head is fleshy, narrow, and
fixed by different muscles to the crustaceous parts thereof; the lower
part which passes into the body is wider, and forms a kind of
membranaceous bag, which is covered with very small muscles; near the
stomach it is again narrower, and is as it were bridled by a strong
nerve, which is fixed to it at distant intervals.

The VENTRICLE begins a little above the fourth division, where the
oesophagus finishes, and terminates at the tenth division; it is about
seven times longer than it is broad; the anterior part, which is the
broadest, is generally folded. The folds diminish with the bulk, in
proportion as it approaches the intestines. An assemblage of nerves
cover the surface, it is surrounded by a number of aerial vessels, and
opens into a tube, which Lyonet calls the large intestine.

There are three of these large tubes or INTESTINES, each of which
differs from the other so much, both in structure and character as to
require a particular name to distinguish them; though this is not the
place to enumerate these characteristic differences. As most
caterpillars are endued with a power or faculty of spinning, they are
provided with two vessels where the substance is prepared, which, when
drawn out, and extended in the air, becomes a silken thread; these two
vessels are termed the silk-vessels or tubes; in the caterpillar of the
cossus, they are often above three inches long, and are distinguished
into three parts, the anterior, the intermediate, and posterior. It has
also two other vessels, which are supposed to prepare and contain the
liquor by which it dissolves the wood on which it feeds.

Thus have we endeavoured to give the reader some idea of the wonderful
organization of this apparently imperfect animal. Assuredly the
four-thousand[100] muscles employed in the construction of the
caterpillar of the cossus cannot be considered without the deepest
astonishment: their admirable co-ordination and junction with other
parts equally numerous, yet all harmonizing and acting together as if
they were essentially one, naturally lead the mind to consider the
nature and perfection of creation, and to perceive that it is an
exhibition of the highest wisdom; and that this wisdom, which in the
minutest things gives evidence of such an immense attention to order and
use, has, no doubt, framed the whole for some great purpose; but what
that purpose is, exceeds the present limits of the human understanding
to discover.

  [100] Lyonet sur la Chenille de Saule, p. 584.


  A DESCRIPTION
  OF
  SUNDRY MISCELLANEOUS OBJECTS,
  EXHIBITED
  IN SEVERAL PLATES OF THIS WORK.


OF THE LEPAS ANATIFERA OR BARNACLE.[101]

Plate XIII. Fig. 1 and 2.

This is a tender and brittle shell-fish of a very peculiar species; its
length is about an inch, and its diameter about three quarters of an
inch. The shell is not composed of two pieces or valves, as in others,
but of five; two of these are larger than the rest, to which are affixed
two smaller ones; the fifth piece is long, slender, and crooked, running
down length-ways, and covering the joinings of the other pieces. The
shell part is of a pale red, variegated with white; it adheres to a neck
or pedicle of an inch long, and about a fifth of an inch in diameter; by
which means it affixes itself to old wood, to stones, to sea-plants, or
any other solid substance that lies under water. It can shorten or
extend this neck at pleasure, which resembles a small gut, and is
usually full of a glareous liquor; it is composed of two membranes, an
external one, hard and brown, an internal one, soft and of an orange
colour. The large portions of the shell open and shut in the manner of
the bivalves; the others, being moveable by means of their membranaceous
attachments, give way to the opening of these, and to the motions of the
body of the fish in any direction. It is furnished with a cluster of
filaments or tentacida, placed in a row on each side, usually twelve,
sometimes fourteen in number. They are a kind of arms appropriated for
catching its prey, and therefore placed so as to surround the mouth of
the animal, which is situated between them, and consequently easily
receives what they thrust towards it. By the motion of these arms, which
may be exerted in such a manner as to play either within or without the
cavity of the shell, it forms a current of water, which brings with it
the prey it feeds upon. Fig. 1 represents two of these arms as magnified
by the microscope; Fig. 2, the natural size of those from which these
drawings were made. Each arm consists of several joints, and each joint
is furnished on the concave side of the arm with a brush of fibrillæ or
long hairs. The arms, when viewed in the microscope, seem rather opake;
but they maybe rendered transparent, and form a most beautiful object,
by extracting out of the interior cavity a bundle of longitudinal
fibres, which runs the whole length of the arm. Mr. Needham[102] thinks
the motion and use of these arms illustrates the nature of that rotatory
motion which some writers have thought they discovered in the wheel
animal.

  [101] This animal is classed by Linnæus among the Vermes Testaceæ. Its
  generic character is: Animal, resembling a triton; Shell, consisting
  of several unequal valves; affixed by its base. Specific character:
  Pedunculated Barnacle, with compressed shell consisting of five
  valves. Syst. Nat. p. 1107, 1109. EDIT.

  [102] Needham’s Microscopical Observations.

In the midst of the arms is a hollow trunk, consisting of a jointed
fibrous or hairy tube, which incloses a long round tongue or proboscis,
that the animal can push occasionally out of the tube or sheath, and
retract at pleasure. The mouth of this animal is singular in its kind,
consisting of six laminæ, which go off with a bend, indented like a saw
on the convex edge, and by their circular disposition are so ranged,
that the teeth in the alternate elevation and depression of each plate,
act against whatever intervenes between them. The plates are placed
together in such a manner, that to the naked eye they form an aperture
not much unlike the mouth of a contracted purse.

The western isles of Scotland, and some other parts of the British
dominions, are abundantly stored, at certain times of the year, with a
bird of the goose kind, commonly known in those places by the name of
the brent goose or barnacle. These birds rarely breed with us, but seek,
for their sitting season, islands less frequented than those where we
find them in common. The seeing the birds so frequent, and yet never
finding any of their nests, induced ignorant people to believe they
never had any, and that they were not bred like other birds.

About the very shores where these birds are most common, the lepas
anatifera is also found in great abundance. The fishermen, who observed
vast quantities of these shells affixed to rotten wood, or dead trees
that were floating in the water, or lodged by it on the shore, were soon
led to imagine that the fibrous substances that hung out of them
resembled feathers, and persuaded themselves that the geese, whose
origin they could before by no means make out, were bred from them,
instead of being hatched, like other birds, from eggs.[103] It was
afterwards affirmed, that the shells themselves originally grew on the
trees, in the manner of their fruit; and that the young bird, having in
the shell obtained its plumage, dropt from thence into the water. From
this arose the opinion that the barnacle or brent goose was the produce
of a tree.[104]

  [103] Hill’s Natural History of Animals.

  [104] The absurd idea, that the brent goose or barnacle derived its
  origin from this shell, was not confined to the illiterate; men of
  science, incautiously confiding in the bold assertions of the
  ignorant, appear to have given full credit to this truly curious
  hypothesis, and disseminated the knowledge of it in their writings.
  Even Gerard, the author of the Herbal, caught the infection: so
  confident was he of the fact, that he invited the credulous to apply
  to him for full satisfaction; his words are, “For the truth hereof, if
  any do doubt, may it please them to repaire unto me, and I shall
  satisfie them by the testimonie of good witnesses.” See his Herbal,
  page 1587.

  Barbut says, “This fabulous account originated from the sea-fowls,
  when ready to lay their eggs, depositing them on the marine plants;
  and, pecking sometimes these anatiferous shells, oblige the fish to
  come out, which having devoured, they lay eggs in their place. The
  young when hatched break through their prison, and fly away.” Genera
  Vermium, Pars ii. page 13. EDIT.


OF THE LEUCOPSIS DORSIGERA.

Plate XVII. Fig. 1, 2, and 3.

This very beautiful and singular insect was first pointed out to me by
T. Marsham, Esq. Sec. L. S. who had seen it in the cabinet of insects
belonging to the Queen, in the royal observatory at Richmond. Her
Majesty was pleased to permit me to have the drawing taken from it, from
which this plate was engraved. When Mr. Marsham first saw it at
Richmond, he considered it as a non-descript insect, and an unique in
this country. But he has since found that it is mentioned by Fabricius,
in his Systema Entomologiæ, as a new genus under the name of leucospis
dorsigera. There is one of the insects in the cabinet of the celebrated
Linnæus, now in the possession of J. E. Smith, M. D. F. R. S. & Pr. L.
S. Sulz, and other writers, have also described it.

It appears at first sight like a wasp, to which genus the folded wings
would have given it a place, had not the remarkable sting or tube on the
back removed it from thence. It is probably a species between, and
uniting the sphex and wasp, in some degree partaking of the characters
of both. The antennæ are black and cylindrical, increasing in thickness
towards the extremity; the joint nearest the head is yellow, the head is
black, the thorax is also black, encompassed round with a yellow line,
and furnished with a cross one of the same colour near the head. The
scutellum is yellow, the abdomen black, with two yellow bands, and a
spot of the same colour on each side between the bands. A deep black
polished groove extends down the back, from the thorax to the anus, into
which the sting turns and is deposited, leaving the anus very circular;
a yellow line runs on each side the sting. The anus and the whole body,
when viewed with a shallow magnifier, appear punctuated; these points,
when examined in the microscope, appear hexagonal, as in the plate; and
in the center of each hexagon a small hair is to be seen; the feet are
yellow, the hinder thighs very thick and dentated, forming also a groove
for the next joint; they are yellow with black spots. This insect is
found in Italy, Switzerland, France, and Germany. Fig. 1 shews it very
much magnified; Fig. 2 is a side view of it less magnified; Fig. 3 is
the object of its real size.


OF THE LOBSTER INSECT.

Plate XVIII. Fig. 1 and 6.

This extraordinary little creature was found by my ingenious friend, Mr.
John Adams, of Edmonton; he was at the New Inn, Waltham Abbey, where it
was spied by some labouring men who were drinking their porter. The man
who first perceived it, thought it was of an uncommon form; on a more
minute inspection, it was supposed to be a louse with unusual long
horns; others thought it was a mite. This produced a debate, which
attracted the attention of my friend, who obtained the insect from them
for further observation. Mr. Martin has given some account of it in the
third volume of “The Young Gentleman and Lady’s Philosophy.” Mr. Adams
favoured me with the insect, that an accurate drawing might be taken
from it, which I thought would be highly pleasing not only to the lovers
of microscopic observations, but also to the entomologist. It appears to
be quite a distinct species from the phalangium cancroides of Linnæus,
of which a good drawing has been given by Hooke, Rösel, Schæffer, &c.;
it has also been described by Scopoli, Geoffroy, and other naturalists;
not one, however, of these descriptions agrees with the animal under
consideration. The abdomen of this is more extended, the claws are
larger and much more obtuse; the body of the other being nearly
orbicular, the claws slender, and finishing almost in a point, more
transparent, and of a paler colour. It is very probable, that there are
several species nearly similar. Mr. Marsham has two in his possession,
one like the drawings of Reaumur, the other not to be distinguished from
that which is represented in the plate, except that it wants the break
or dent in the claws, so conspicuous in this. The latter he caught on a
flower in Essex, the first week in August, firmly affixed by its claws
to the thigh of a large fly, and could not disengage it from thence
without considerable difficulty; to accomplish which, he was obliged to
tear off the fly’s leg, and was much surprized to see the bold little
creature spring forward full a quarter of an inch, and once more seize
its prey, from which he again found it very difficult to disengage it.
Fig. 1 represents the insect considerably magnified, Fig. 6 the natural
size.[105]

  [105] According to Aldrovandus, this insect was not unknown to
  Aristotle, who mentions it as being found in books and paper.
  Wolphius, on the authority of Gesner, says that a few are to be met
  with in some parts of Switzerland. Scaliger also notices it, having
  found two of them in his books. It has been by various systematic
  writers referred to different genera; De Geer has instituted a new
  genus for it under the name of chelifer; Fabricius has remanded it to
  that of scorpio, to which perhaps it is more nearly allied than any
  other.

  Amongst the number of naturalists who have observed and described the
  insect, it appears rather extraordinary that none have met with one
  similar to that in the plate, in respect to the break in the claws. In
  a cabinet of curious microscopic objects which I purchased several
  years since, and which originally came from Holland, there were four
  of them in the most perfect condition. A botanical friend, Mr. Young,
  also favoured me with a living one which he found among some plants
  collected by him in one of his excursions; but, as his box contained a
  variety of plants, and he did not discover the insect till his return,
  it was impossible to ascertain the particular one on which it was
  taken. All these resembled the one here exhibited, excepting the claws
  being longer and more slender, and being deficient in the
  distinguishing characteristic; I have lately seen another, in which
  the two fangs that are shewn highly magnified in Plate 85 of the
  Naturalist’s Miscellany, are very apparent, being so large, as to
  exceed in diameter the thickest part of the claws.

  My respectable friend, Matthew Yatman, Esq. informs me, that some
  years since one was found on a bottle of wine packed in saw-dust, at
  the house in which he then resided in Percy street; on putting the
  point of a pin towards it to remove it from the bottle, it ran
  backward, put itself into an attitude of defence, and opened its claws
  as meditating vengeance. In the same cellar one had many years
  previous been discovered, sufficiently large to admit its being
  fastened to a card with thread by a young gentleman, being at least
  four times the usual size.

  Rösel says it dwells among paper, in old books and their bindings, in
  chests of drawers, and in the crevices of old buildings. In order to
  discover whether the insect possessed a sting, he often by various
  means endeavoured to irritate it; but it never shewed the smallest
  inclination to defend itself, on the contrary, it always endeavoured
  to avoid a contest; if so, it evidently appears that those few met
  with in this country are of a more bold and warlike disposition.

  Seba asserts that these insects resemble the large scorpions, the tail
  excepted, which is small, and usually concealed by being drawn close
  to the under part of the abdomen; but in this respect he must probably
  have been mistaken, as it does not appear that this circumstance has
  been noticed by any other person. EDIT.


OF THE THRIPS PHYSAPUS.

Plate XVIII. Fig. 3, 4, and 5.

The insect, which is represented very considerably magnified at Fig. 3,
is of the hemiptera class. It was first described and figured by De Geer
in the Swedish Transactions for 1744, under the name of physapus ater,
alis albis; Linnæus afterwards introduced it in a subsequent edition of
the Systema Naturæ distinguished by the name thrips physapus.

These insects live upon plants, and particularly in flowers. The one
figured here is the black thrips, with white wings; the antennæ have six
articulations; the body is black; the wings whitish, long, and hairy;
the head small, with two large reticular eyes. The antennæ are of an
equal size throughout, and divided into six oval pieces which are
articulated together. The extremities of the feet are furnished with a
membranaceous and flexible bladder, which it can throw out and draw in
at pleasure. It places and presses this bladder against the substances
on which it is walking, and seems to fix itself thereby to them; the
bladder sometimes appears concave towards the bottom, the concavity
increasing or diminishing in proportion to the degree of pressure.

They have four wings, two upper and two under ones; these last are with
great difficulty perceived, they are fixed to the upper part of the
breast, lying horizontally; both of them are rather pointed towards the
edges, and have a strong nerve running round them, which is set with a
fringe of fibrillæ, tufted at the extremity. The wings are represented
by themselves at Fig. 4; the insect of the real size at Fig. 5. They are
to be found in great plenty in the spring and summer, in the flowers of
the dandelion, and various other plants.


OF THE SKIN OF THE LUMP SUCKER.

Plate XVIII. Fig. 2 and 7.

For a full description of this singular fish, I must refer the reader to
Pennant’s British Zoology, vol. iii. p. 117. The Linnean name is
cyclopterus lumpus. Fig. 2 is a piece of the skin highly magnified:
there are no scales on the body, but a great number of tubercles, which
are here exhibited. Fig. 7 is the natural size of the object.

These fishes being extremely fat, renders them an agreeable diet to the
natives of Greenland, in which seas they abound in the months of April
and May; they also resort in multitudes during spring to the coast of
Sutherland, near the Ord of Caithness in North Britain, where the seals
prey greatly upon them, leaving the skins; numbers of which thus emptied
float at that season ashore. When a good specimen is procured, it forms
a most beautiful object for the opake microscope.


OF THE CIMEX STRIATUS.

Plate XX. Fig. 1 and A.

This is a beautiful insect of the hemiptera class, or that kind where
the elytra are only in part crustaceous, and which do not form a
longitudinal suture down the back, but fold over about one-third of
their length toward the bottom, where it is also partly transparent. It
is of the genus cimex, and called striatus by Linnæus. Its colours are
bright and elegantly disposed: the head, proboscis, and thorax are
black. The thorax is ornamented with yellow spots, the middle one
large, and occupying almost one-third of the posterior part; the other
two are on each side, and triangular. The scutellum has two yellow
oblong spots, pointed at each end; the ground of the elytra is a bright
yellow, spotted and striped with black. The nerves are yellow, and there
is a brilliant triangular spot of orange, which unites the crustaceous
and membranaceous parts; the latter is brown and clouded. The feet are
of a fine red, and the rings of the abdomen are black, edged with white.
This pretty insect is to be found in June, upon the elm-tree. It is
represented at A of the natural size.


OF THE CHRYSOMELA ASPARAGI.

Plate XX. Fig. 2 and B.

A very common, though elegant insect of the coleoptera class, is
represented at Fig. 2, as seen in the lucernal microscope, and of its
natural size at B; it is called by Linnæus chrysomela asparagi, from the
larva feeding on the leaves of that plant. Its shape is oblong, the
antennæ black, composed of many joints nearly oval. The head is of a
bright, but deep blue; the thorax red and cylindrical; the elytra blue,
with a yellow margin, and three spots of the same colour on each, one at
the base of an oblong form, and two united with the margin; the legs are
black, but the under side of the belly is of the same blue colour with
the elytra and head. This little animal, when viewed by the naked eye,
scarcely appears to deserve any notice; but when examined by the
microscope, is one of the most pleasing opake objects we have. It is
found in June, on the asparagus after it has run to seed. De Geer says,
that it is very scarce in Sweden.


OF THE MELOE MONOCEROS.

Plate XX. Fig. 3 and C.

The insect which comes at present under our inspection is particularly
adapted to shew the advantages of the microscope, which alone will
discover the peculiarities of its figure; this is so remarkable, that
entomologists appear undetermined as to its genus. Geoffroy formed a new
one for it, under the title of notoxus, in which he has been followed by
Fabricius; even Linnæus himself could not determine at first where to
place it, for in the Fauna Suecica he makes it an attelabus, but in the
last edition of the Systema Naturæ he has fixed it as a meloe, calling
it the meloe monoceros; but still he adds, “genus difficile terminatur
forte huic proximum.” Both Geoffroy and Schæffer have given figures of
it, but as they had not that kind of microscope which would assist them,
their figures are imperfect.

The head is black, and appears to be hid or buried under the thorax,
which projects forwards like a horn; the antennæ are composed of many
articulations, and with the feet are of a dingy yellow. The hinder part
of the thorax is reddish, the fore part black. The elytra are yellow,
with a black longitudinal line down the suture; there is a band of the
same colour near the apex, and also a black point near the base; the
whole animal is curiously covered with hair. Geoffroy says it is found
on umbelliferous plants: the one here described was found in May; the
natural size is seen at C.

Plate XIX. Fig. 1 and 3,

Represent two magnified views of the feet of the monoculus apus of
Linnæus. They are curiously contrived to assist the animal in swimming,
and form very agreeable objects for the microscope. Fig. 2 and 4 are the
same objects of the natural size.


OF THE SCALES OF FISH.

The outside covering or scales of fish afford an immense variety of
beautiful objects for the microscope. They are formed in the most
admirable manner, and arranged with inconceivable regularity and
symmetry: some are long, others nearly round, others again square;
varying in shape, not only in different species, but even considerably
on the same fish; those which are taken from one part not being entirely
similar to those which are taken from another.

Leeuwenhoeck supposed each scale to consist of an infinity of scales
laid one over the other; or, more simply, of an infinity of strata, of
which those next to the body of the fish are the largest.

These strata, when viewed with the microscope, exhibit specimens of
wonderful mechanism and exquisite workmanship. In some scales we
discover a prodigious number of concentric flutings, too fine, as well
as too near each other, to be easily enumerated; they are probably
formed by the edges of each stratum, denoting the limits thereof, and
the different stages of the growth of the scale. These flutings are
often traversed by others diverging from the center of the scale, and
generally proceeding from thence in a straight line to the
circumference.

Plate X. Fig. 7, exhibits a scale from a species of the parrot fish of
the West-Indies, considerably magnified. Fig. 8, the real size of the
scale.

Plate X. Fig. 9, is a magnified scale of the sea-perch, which is found
on the English coast. Fig. 10, the same scale of the natural size.

Plate XIX. Fig. 7, a scale from the haddock, as seen in the microscope.
Fig. 8, the same of the natural size.

Plate XIX. Fig. 9, a scale from a species of perch from the West-Indies,
magnified. Fig. 10, the scale of its real size.

Plate XIX. Fig. 11, a scale from the sole-fish, delineated as it appears
in the microscope; the pointed part is that which stands without the
skin, as may be seen in Fig. 5, which represents a piece of the skin of
a sole, as viewed by the opake microscope. Fig. 6 and 12, the same
objects of their real size.



CHAP. VII.

THE NATURAL HISTORY OF THE HYDRA, OR FRESH-WATER POLYPE.


Having in the two preceding chapters given the reader such a general
idea of the history and œconomy of a great variety of those minute
animated bodies, called insects, as I am inclined to hope has not only
afforded him entertainment and instruction, but tended to excite an
emulation for further researches; I shall endeavour to gratify so
laudable a disposition, by introducing him to a class of beings whose
œconomy and singular properties equally engage the attention of the
philosopher and the natural historian; a scene which opposes our general
system of vitality, and which presents to the eye of the mind, as well
as that of the body, a series of astonishing wonders. It is among the
minutiæ of nature that we find her models most diversified, and
displaying the marvellous fecundity of its powers.

The polypes described in this chapter are fresh-water insects, of the
genus of hydra, of the order of zoophytes, and class of vermes. The body
consists of a single tube, furnished at one end with long arms, by these
it seizes small worms, and conveys them to its mouth. It has, according
to our general notions, neither head, heart, stomach, nor intestines of
any kind; and is without the distinction of sexes, yet extremely
prolific. From the simplicity of its structure those of its œconomy and
functions are probably derived. When they are cut or divided into a
number of pieces, the separated parts in a very little time become so
many perfect and distinct animals; each piece having a power of
producing a head, a tail, and the other organs necessary for its
existence.

They are generally known by the name of polype; but as this was thought
by many to be improper, because that, strictly speaking, they have no
feet, Linnæus called the genus hydra, probably from their property of
re-producing the parts which are cut off, a circumstance that naturally
brings to mind the fabulous story of the Lernean hydra. Dr. Hill called
them biota, on account of the strong principle of life with which every
part is endued.

Leeuwenhoeck, whose indefatigable industry in his researches after small
insects permitted very few things to escape his notice, discovered these
animals, and gave some account of them in the Philosophical Transactions
for the year 1703. There is also in the same volume a letter from an
anonymous hand on this subject. We had, however, no regular account of
them, their various habits, their different species, or of their
wonderful properties, till the year 1740, when they first engaged the
attention of M. Trembley, to whose assiduity and observations we are
indebted for the display of their nature and œconomy.

Previous to the successful experiments of this gentleman, Leibnitz and
Boerhaave, as well as some of the ancient philosophers, reflecting on
the various gradations in the scale of animated nature, had endeavoured
to prove that there might be degrees of life between the animal and the
plant, and that animals might be found which would propagate by slips,
like plants. These conjectures were verified by Trembley, but not in
consequence of any pre-conceived ideas in favour of such a supposition;
on the contrary, it was only by repeated observations that he could
destroy his own prejudices, and join these wonderful beings to the
animal kingdom.[106]

  [106] A great part of the knowledge of the ancients consisted in an
  extensive variety of ingenious hypotheses, the result of intense study
  and application; and it need not excite surprize, if, amongst a number
  of suppositions, some of them have since been found conformable to
  truth.

  The moderns, animated by the example of the great Bacon, by an
  abundance of experiments frequently repeated, and the assistance of
  good instruments, have introduced unquestionable demonstration in the
  place of speculation; this renders the present philosophy very far
  superior to that of the ancients.

  Thus it is with respect to the subject now under consideration; many
  of the ancients conjectured that animated beings might exist possessed
  of the wonderful properties of the hydra; that some of them, however,
  were even witnesses of the fact, cannot well be disputed; though it
  may be fairly presumed, that their knowledge of this animal,
  comparatively with that we are now in possession of, was very
  circumscribed and imperfect.

  St. Augustine relates that one of his friends performed the experiment
  before him, of cutting a polype in two, and that immediately the two
  parts thus separated betook themselves to flight, moving with
  precipitation different ways. The original passage is too long to be
  here inserted, but may be found in his work “De Quantitate Animæ,” c.
  62, p. 431, col. 1.

  Aristotle, speaking of insects with many feet, expresses himself
  nearly in the same manner; without naming the particular creatures to
  which he alludes, he observes, that there are of these animals or
  insects, as well as of plants and trees, some that propagate
  themselves by shoots; and, as what were but the parts of a tree
  before, become thus distinct and separate trees; so, in cutting one of
  these animals, the pieces which before composed altogether but one
  animal, become suddenly so many distinct individuals. And he adds,
  that the soul in these insects is in effect but one, though multiplied
  in its powers, as it is in plants. Aristot. de Histor. Animal. tom. 1,
  lib. 4, cap. 7, pag. 824, & de Part. Animal. lib. 4, tom. 1, cap. 6,
  pag. 1029. &c. This will suffice to shew that the ancients were not
  entirely unacquainted with the subject before us; though it does not
  derogate from the merit of Leeuwenhoeck, Trembley, and other ingenious
  naturalists, by whose assiduous and patient investigations we have
  obtained a more perfect knowledge of this astonishing class of
  animated beings. EDIT.

Though natural history is so fruitful in extraordinary facts, it has
hitherto produced none so singular as the various properties of the
different species of the hydra.

I shall endeavour, first, to trace the progress of this discovery, in
which we shall see with what sage caution and accuracy Trembley, and
other naturalists examined this wonderful phænomenon, and what
accumulated evidence was judged necessary to establish the fact.

We find M. Trembley writing in January, 1741, to M. Bonnet, that he did
not know whether he should call the object which then engaged his
attention, a plant or an animal. “I have studied it,” says he, “ever
since June last, and have found in it striking characteristics of both
plant and animal. It is a little aquatic being. At first sight, every
one imagines it to be a plant; but if it be a plant, it is sensitive and
ambulant; if it be an animal, it may be propagated by slips or cuttings,
like many plants.” It was not till the month of March, in the same year,
that he could satisfy himself as to their nature.

When Reaumur saw, for the first time, two polypes formed from one that
he had divided into two parts, he could hardly believe his eyes; and
even after having repeated the operation an hundred times, and again
examined it an hundred more, he says that the sight was not become
familiar to him.

The first account the Royal Society received of the surprizing
properties of the hydra, was in a letter from M. Buffon, dated the 18th
of July, 1741, to Martin Folkes, Esq. their president, acquainting them
with the discovery of a small insect called a polypus, which is found
sticking about the common duck weed, and which, being cut in two, puts
forth from the upper part a tail, and from the lower end a head, so as
to become two animals instead of one. If it be cut into three parts,
the middlemost puts out from one end a head, and from the other a tail,
so as to become three distinct animals, all living like the first, and
performing the various offices of their species: which observations are,
adds Buffon, well averred.

There is no phænomenon in all natural history more astonishing than
this, that man, at pleasure, should have a kind of creative power,
and out of one life make two, each completely formed with all its
apparatus and functions, its perceptions and powers of motion and
self-preservation; and as complete in all respects as that from which
they derived their existence, and equally enjoying the humble
gratifications of their nature.[107]

  [107] Goldsmith’s History of the Earth and Animated Nature.

Mr. Folkes, in confirmation of the foregoing article, communicated to
the Society a letter from the Hon. W. Bentinck, Esq. at the Hague, dated
September, describing the insects discovered by Trembley, adding, that
he himself had seen them. In November, a letter was read from Dr.
Gronovius, of Leyden, giving an account of a water insect not yet known
to, or described by any author; after describing it, he adds, “but what
is more surprizing, if this animal is cut into five or six pieces, in a
few hours there will be as many animals, exactly similar to their
parent.” The accounts of this animal were so extraordinary, that they
were not credited until Professors Albinus and Musschenbroeck were
provided with some specimens, and found all that had been related
thereof to be exactly true.

November 25, a letter from Cambridge was read to the Royal Society, in
which the author endeavours to lessen, by reason, the prejudices which
then combated the belief of these facts. “Some of our friends,” says
the author, “who are firmly attached to the general metaphysical notions
they have formerly learned, reason strongly against the possibility of
such a fact: but I have myself owned on other occasions, my distrust of
the truth, or certainty at least, of some of those principles, and I
shall make no scruple of acknowledging, that I have already seen so many
strange things in nature, that I am become very diffident of all general
assertions, and very cautious in affirming what may or may not possibly
be. The most common operations both of the animal and vegetable world,
are all in themselves astonishing, and nothing but daily experience and
constant observation can make us see without amazement an animal bring
forth another of the same kind, or a tree blossom and bear leaves and
fruit.

“The same observation and experience make it also familiar to us, that,
besides the first way of propagating vegetables from their respective
fruit and seed, they are also propagated from cuttings, and every one
knows that a twig of a willow particularly, cut off and only stuck into
the ground, does presently take root and grow, and become as real and
perfect a tree as the original one from which it was taken. Here then we
find in the vegetable kingdom quite common, the very thing of which we
have an example before us in the animal kingdom, in this new-discovered
insect. The best philosophers have long observed strong analogies
between these two classes of beings; and the more they have penetrated
into nature, the more they have extended this analogy: now in such a
scale, who is the man that will be bold to say, just here animal life
entirely ends, and here vegetable life begins? or, just so far, and no
farther, one sort of operation goes; and just here another sort, quite
different, takes its place? or again, who will venture to say, life in
every animal is a thing absolutely different from that which we dignify
by the same name in every vegetable?” Thus does the author endeavour to
persuade the prejudiced, and lead them to pay attention to the facts
which were now laid open to their view, and which were further confirmed
by a letter from M. Trembley, in January 1740; which letter was
strengthened by an extract from the preface to the sixth volume of
Reaumur’s history of insects. In March, 1742, Mr. Folkes gave an account
of them to the Royal Society, from observations made on several polypes
which had been sent by M. Trembley from Holland to him. The insects now
began to be known, and were soon found in England, and the experiments
that had been made on them abroad were published by Mr. Folkes,[108] my
father,[109] and Mr. Baker:[110] conviction now became too strong for
argument, and metaphysical objections gave way to facts. The animal is
described in the following manner:


HYDRA.[111]

Flos: os terminale, cinctum cirris setaceis. Stirps vaga, gelatinosa,
uniflora, basi se affigens.[112]

  [108] Philosophical Transactions.

  [109] Micrographia Illustrata.

  [110] Natural History of the Polype.

  [111] The hydræ or polypes have generally been denominated Insects: is
  there not a manifest impropriety in the application of this term to
  them? If we admit of the systematic arrangement of LINNÆUS, we find
  that he has divided the animal kingdom into six classes: 1. Mammalia.
  2. Aves. 3. Amphibia. 4. Pisces. 5. _Insecta_; and 6. _Vermes_. Of the
  last or _Vermes_, the Zoophytes (from ζωοφυτον, or animal plant)
  constitute the fifth order. He defines it as Animalia composita,
  efflorescentia more vegetabilium: amongst these he includes the
  various species of Vorticellæ and Hydræ.

  The term animalculæ, or small animals, is certainly not inapplicable
  to them, but they differ materially in the peculiar characteristics by
  which insects are distinguished, see page 179, and pages 215-220. They
  do not undergo those transformations to which insects are subject, and
  which have been so fully described in the preceding part of this work:
  their figure, habits, and œconomy are also very different. In short,
  they seem to be in every respect, except their minuteness, quite a
  distinct race of animated beings, as will be more fully exemplified in
  the following pages. EDIT.

  [112] Lin. Syst. Nat. p. 1320.

This animal fixes itself by its base, it is gelatinous, linear, naked,
can contract itself, and change its place. Its mouth, which is at one
end, is surrounded by hair, like feelers. It sends forth its young ones
from its sides, which drop off.

1. Hydra viridis, tentaculis subdenis brevioribus.

Green polype, generally with about ten short arms; it is represented in
Plate XXI. Fig. 5.

2. Hydra fusca, tentaculis suboctonis longissimis.

This polype has very long arms, often eight in number; it is represented
at Plate XXI. Fig. 7. The arms are several times longer than the body.

3. Hydra grisea, tentaculis subseptenis longioribus.

This polype has also generally long arms, in number about seven; it is
of a yellowish colour, small towards the bottom; it is represented at
Plate XXI. Fig. 6.

4. Hydra pallens, tentaculis subsenis mediocribus.

The arms of this polype are generally about six in number, and of a
moderate length.

5. Hydra hydatula, tentaculis quaternis obsoletis corpore vesicario.
Plate XXI. Fig. 1, 2, 3, 4.

This polype has a vesicular body, and four obsolete arms; is found in
the abdomen of sheep, swine, &c.

6. Hydra stentorea, tentaculis ciliaribus corpore infundibuliformi.

This polype has been called tunnel-shaped; the mouth is surrounded with
a row of hairs; it is represented at Plate XXII. Fig. 27 and 28.

7. Hydra socialis, mutica torosa rugosa.

Bearded, thick, and wrinkled. Plate XXI. Fig. 11.


OF THE HYDRA VIRIDIS, HYDRA FUSCA, AND HYDRA GRISEA.

Plate XXI. and XXIII.

These three species of the hydra having been those on which the greatest
number of experiments have been made, and of which we have the best
information, it is of these only I shall speak in the following account,
unless it is particularly mentioned otherwise.

There are few animals more difficult to describe than the hydra, as it
has scarce any thing constant in its form, varying continually in its
figure: they are often so beset with young, as to appear ramose and
divaricated, the young ones constituting as it were a part of the
parent’s body.

Whoever has looked with care at the bottom of a wet shallow ditch, when
the water is stagnant, and the sun has been powerful, may remember to
have seen many little transparent lumps, of a jelly-like appearance,
about the size of a pea, and flatted on one side; the same appearances
are also often to be seen on the under side of the leaves of those weeds
or plants that grow on the surface of the water; these are the hydræ
gathered up into a quiescent state, and seemingly inanimate, because
either undisturbed or not excited by the calls of appetite to action.
They are generally fixed by one end to some solid substance, at the
other end there is a large opening, round about which the arms are
placed as so many rays round a center, which center is the mouth.

They are slender and pellucid, formed of a tender kind of substance, in
consistence something like the horns of a snail, and can contract the
body into a very small compass, or extend it to a considerable length.
They can do the same with the arms; with these they seize minute worms
and various kinds of aquatic insects, bring them to the mouth, and
swallow them. After the food is digested, and the nutritive parts which
are employed in sustaining its life are separated from the rest, they
reject the remainder by the mouth.

The first polype which Trembley discovered was one of the hydra viridis,
represented in Plate XXI. Fig. 5. These are generally of a fine green
colour. The indications of spontaneous motion were first perceived in
the arms of these little creatures; they can extend or contract, bend
and wind them divers ways. Upon the slightest touch they contract
themselves so much, as to appear little more than a grain of a green
substance, the arms disappearing entirely. He soon after found the hydra
grisea, Fig. 6, and saw it eat, swallow, and digest worms much larger
than itself. This discovery was soon followed by that of the hydra
fusca, Fig. 7.

The most general attitudes of these hydræ are those which are
represented in Fig. 5 and 6 of the same plate. They fix the posterior
extremity _b_ against a plant or other substance, as _e f_; the body _a
b_; and the arms _a c_, being extended in the water. There is a small
difference in the attitudes of the three kinds which we are now
describing.

The bodies of the hydra viridis, Fig. 5, and of the hydra grisea, Fig.
6, diminish from the anterior to the posterior extremity by an almost
insensible gradation. The hydra fusca does not diminish in the same
gradual manner, but from the anterior extremity _a_, to the part _d_,
which is often two-thirds of the length of their body, it is nearly of
an equal size; from this part it becomes abruptly smaller, and goes on
from thence of a regular size to the end. The number of arms in these
three kinds are at least six, and at most twelve or thirteen, though
eighteen may sometimes be found on the hydra grisea. They can contract
their bodies till they are not above one-tenth of an inch in length;
they can also stop at any intermediate degree, either of contraction or
extension, from the greatest to the least. The species represented at
Fig. 5, are generally about half an inch long when stretched out. Those
exhibited at Fig. 6 and 7, are about three-fourths of an inch, or one
inch in length, though some are to be found at times about an inch and
half long. The arms of the hydra viridis, Fig. 5, are seldom longer than
their bodies; those of Fig. 6 are commonly one inch long, while those of
Fig. 7 are generally about eight inches; whence Trembley has called it
the long-armed polype.

The bulk of the hydræ decreases, in proportion as they extend
themselves, and vice versa. They may be made to contract themselves,
either by touching them, or agitating the water in which they are
contained. They all contract themselves so much when, taken out of the
water, as to appear only like a little lump of jelly. They can contract
or extend their arms without extending or contracting the body, or the
body, without making any alteration in the arms; or they can contract or
dilate only some of the arms, independent of the rest: they can also
bend their body and arms in all possible directions. Those represented
at Fig. 7 let their arms in general hang down, making different turns
and returns, often directing some of them back again to the top of the
water. They can also dilate the body at different places, sometimes at
one part, and then again at another; sometimes they are thick set with
folds, which, if carelessly viewed, might be taken for rings.

They have a progressive motion, which is performed by that power by
which they stretch out, contract, and turn themselves every way. For
suppose the hydra or polype, _a b_, Fig. 16, to be fixed by the tail
_b_, having the body and the arms _a_ extended in the water; in order to
advance, it draws itself together, by bending itself so as to bring the
head and arms down to the substance on which it is to move; to do this,
it fixes the head or the arms as in Fig. 17; when these are well fixed,
it loosens the tail, and draws it towards the head, as in Fig. 18, which
it again loosens, and resting on the tail, stretches it out, as in Fig.
19. It is easy to see from this account, that their manner of walking is
very analogous to that of various terrestrial and aquatic animals. They
walk very slow, often stopping in the middle of a step, turning and
winding their body and arms every way. Their step is sometimes very
singular, as in the following instance: suppose the polype _a b_, Fig.
20, to be fixed by the tail _b_, the body and arms being extended in the
water, it first bends the fore-part towards the substance on which it is
moving, and fixes it thereto, as at _a_, Fig. 21; it then loosens the
lower end, and raises it up perpendicular, as in Fig. 22; now bending
the body to the other side, it fixes the tail, as in Fig. 23; then
loosening the anterior end, it rises up, as in Fig. 24.

They descend at pleasure to the bottom of the water, and ascend again,
either by the sides, or upon some aquatic plants; they often hang from
the surface of the water, resting as it were upon the tail; or, at other
times they are suspended by one arm from it. They walk also with ease
upon the surface of the water. If the extremity of the tail _b_, Fig. 7,
be examined with a magnifying glass, a small part of it will be found to
be dry, and above the surface of the water, and as it were in a little
concave space, of which the tail forms the bottom, so that it seems to
be suspended on the surface of the water, on the same principle that a
small pin or needle is made to swim.

Hence, when a polype means to pass from the sides of the glass to the
surface of the water, it has only to put that part out of the water by
which it means to be supported, and give it time to dry, which it always
does upon these occasions. They attach themselves so firmly by the tail
to aquatic plants, stones, &c. as not to be easily driven from the place
where they have fixed themselves; they often further strengthen these
attachments by means of one or two of their arms, which they throw out
and fix to adjacent substances, as so many anchors.

The mouth of the polype or hydra is situated at the fore-part of the
body, in the middle between the shooting forth of the arms. The mouth
assumes different appearances, according to the different purposes of
the insect; sometimes it is lengthened out, and forms a little conical
nipple, as in Plate XXIII. A. Fig. 13; sometimes it appears truncated,
as in Plate XXI. Fig. 8; at other times the interval between the arms
appears closed, as in Plate XXIII. A. Fig. 2 and 12; or hollow, as in
Fig. 11 of the same plate. If it be observed with a deep magnifier in
either of the two last cases, a small aperture may be discovered.

The mouth of the polype opens into the stomach, which is a kind of bag
or gut that goes from head to tail; this may be perceived by the naked
eye, when the animal is exposed to a strong light, or a candle placed on
the opposite side to the eye; for the colour of the polype does not
destroy the transparency thereof. The stomach will, however, be better
seen, if the eye be assisted by a deep magnifier; one of them is
represented as highly magnified in Plate XXI. Fig. 8. To be fully
satisfied whether they were perforated throughout, Trembley cut one
transversely into three parts; each piece immediately contracted itself,
and became very short; being then placed in a shallow glass full of
water, and viewed through the microscope, they were found to be visibly
perforated. Their microscopic appearance is represented in Plate XXIII.
A. Fig. 6, 7, 8; its mouth was at the anterior end _a_, Fig. 8, of one
of these parts. The tail was at the end _b_ of the third part, Fig. 6;
as this piece was also perforated, it plainly appears that the tail of
the hydra is open. The perforation, which is thus continued from one end
to the other, is called the stomach, because it contains and digests the
aliments. The skin which incloses the bag, and forms the stomach, is the
skin of the polype itself; so that the animal may be said to consist of
but one skin, disposed in the form of a tube or gut open at both ends.
On opening the polype, no vessels are to be distinguished; and whatever
be the nature of its organization, it must reside in the skin.

The skin must be so far organized, as to perform all the operations
necessary for the nutrition and growth of the animal, without
considering those that are necessary for its various motions. Whatever
are the means the Author of Nature has employed for these purposes, we
are ignorant of them. If their skin be examined by a microscope, it
appears like shagreen, or as if it were covered with little grains;
these are more or less separated from each other, according to the
degree in which the body is extended or contracted.

If the lips of a polype be cut transversely, and placed so that the cut
part of the skin may lie directly before the microscope, the skin
throughout its whole thickness will be found to consist of an infinite
number of these grains. To know whether the inside of the stomach was
formed of similar grains, several of them have been laid open and
examined by the microscope; the interior surface was then found to
consist of an immense number of them, being as it were more shagreened
than the exterior one, and less transparent. The grains are not strongly
united to each other, but may be separated without much trouble. Plate
XXIII. A. Fig. 10, represents a piece of skin thus laid open. To examine
these particulars further, a piece of skin a, Fig. 9, was laid in a few
drops of water, on a piece of glass before the microscope, and some of
the grains were separated from it, as at b c d, by pressing them with
the point of a pin; in endeavouring to open them, they spread themselves
into all parts of the water, and at last remained in heaps, as at e and
f.

If a polype be carefully placed before the microscope, without wounding
it, you will seldom be disappointed in seeing some of these grains
detach themselves from the superficies thereof, and that even in the
most healthy.

But if the grains separate themselves in large quantities, it is the
symptom of a very dangerous disorder; the surface of the polype thus
attacked becomes more and more irregular, and is no longer well
terminated and defined as before. The grains fall off on all sides, the
body and arms contract and dilate, it becomes of a white shining colour,
loses its form as at a, Fig. 4, and then dissolves into a heap of
grains, as at b, Fig. 5. The progress of this disorder is most easily
observed in the hydra viridis.

A very attentive and accurate examination shews that the skin is formed
of a kind of glareous substance, a species of gum, which fills up the
intervals between the grains, in which they are lodged, and by which
they are attached, though weakly, together. It has been already
observed, that it is to these grains that it owes its shagreen-like
appearance; it is from them also that it derives its colour; for, when
they are separated from the polype, they are the same colour with it,
whereas the glareous matter is without any distinguishing colour. The
construction of the polype seems then to be confined to these glandular
grains, to the viscous matter, and the invisible fibres which act upon
the glareous substance.

The structure of the arms of the polypes is very analogous to that of
their body. When they are examined by the microscope, either in a
contracted or dilated state, their surface is shagreened; if the arm be
much contracted, it appears more so than the body; on the contrary, it
appears less so in proportion as they are more extended; almost quite
smooth when at their full extension; so that in the hydra viridis the
appearance of the arms is continually varying, and these variations are
more sensible towards the extremity of the arm than at its origin, as,
in Plate XXI. Fig. 10; but more thinly scattered, or farther asunder, in
the parts further on, as at Fig. 9. The hairs which are exhibited in
this figure cannot be seen without a very deep magnifier, however they
indicate a further degree of organization in this little animal. The
extremity is often terminated by a knob.

All animals of this kind have a remarkable attachment to turn towards
the light, and this might naturally induce the inquirer to look for
their eyes; but how carefully soever this search has been pursued, and
however excellent the microscope with which every part has been
examined, yet no appearance of this organ has been found.
Notwithstanding this, they constantly turn themselves toward the light;
so that if that part of the glass in which we placed them be turned from
it, they will be found the next day to have removed themselves to the
side that is next the light, and the dark side will be quite
depopulated.


OF THE FOOD OF THE HYDRÆ, AND THEIR METHOD OF SEIZING AND SWALLOWING
THEIR PREY.

As the hydra fusca, Plate XXI. Fig. 7, has the longest arms, its manner
of feeding, and the different manœuvres it makes use of to seize and
manage its prey, are more remarkable than those of the two other
species; it will be, therefore, this kind only which will be principally
spoken of under the present head. To obtain a proper view, it should be
placed in a glass seven or eight inches deep. If the polype be fixed
near the top of the glass, the arms for the most part hang down toward
the bottom. This is a very convenient situation for feeding it, and
observing its management of the food.

The polypes are in general very voracious: an hungry one extends its
arms as a fisherman his nets; it spreads them every way, so that they
form a circle of considerable extent, every part of which is entirely
within the reach of one of them. In this expanded posture it lies in
expectation of its food; whatever comes within the verge of this circle
is seized by one or other of its arms: the arms are then contracted till
the prey is brought to the mouth, when it is soon devoured. While the
arms are contracting and exerting themselves vigorously to counteract
the efforts of the animal, which it has seized, to escape, they may be
observed to swell like the muscles of the human body when they are in a
state of exertion.

Though in general all ideas are derived from the senses, there are
certainly some that seem infused into us independently of the exertions
of any sense. This may be confirmed by many instances of animal
instinct; among others, it may be illustrated by the polype. Who taught
it, when just separated from the parent stock, to expand its arms, that
it might catch its prey? That its native element abounded with insects?
or that these were its proper food? No sense that we are acquainted with
could first give the information.

The polype does not always wait for its prey, it feels for it, and in a
manner follows it. It may be asked how can it perform this if destitute
of vision? or do the glandular grains answer the purpose of eyes? Who
can answer the question? what are our own eyes but glandular grains of a
larger size? If this should be the case, our hydra, like the libellulæ
and other insects, would realize, nay, exceed the fables of the
ancients, being an Argus entirely composed of eyes. Be this as it may,
they are certainly in possession of some sensation by which they are
informed of the approach of their prey, and which renders them attentive
to all that may confirm or destroy this perception.

When the arms of a polype are extended within a glass, put a centipe or
any kind of worm into it, see Plate XXIV. A. Fig. 1, and with the point
of a pin push it towards one of the arms; as soon as it touches this it
is seized; the worm or centipe endeavours by quick and strong efforts to
disengage itself, often swimming and dragging the arm from one side of
the glass to the other. This violent motion of the prey obliges the
polype to contract strongly the arm; in doing which, it often twists it
in the form of a cork-screw, as at o i, by which means it shortens it
more rapidly. The struggles of the devoted animal soon bring it in
contact with another arm; these contracting further, the little creature
is presently engaged with all the arms, and by degrees conveyed to the
mouth, against which it is held and subdued.

When a polype has nothing to eat, its mouth is generally open, but so
small, that it can scarce be perceived without the assistance of a
magnifying glass; but as soon as the arms have conveyed the prey to the
mouth, it opens itself wider, and this in proportion to the size of the
animal that is to be devoured; the lips gradually dilate, and adjust
themselves accurately to the figure of the prey. The greatest part of
the animals on which the polype feeds, are to its mouth, what an apple
the size of our heads would be to the mouth of a man.

The worms or other minute animals which are seized by the polype, are
not always brought to the mouth in the same situation; if they be
presented to it by one of their extremities, it is not requisite that
the polype should open its mouth considerably, and in effect it only
opens it so wide, as precisely to give entrance to the worm, Fig. 5. If
it be not too long for the stomach, it remains there extended; but if it
be longer, the end which first enters is bent, so that when the worm is
entirely swallowed, it may be seen lying folded in the stomach, Plate
XXIV. B. Fig. 12.

If the middle, or any other part of the worm, be presented to the mouth
of the polype, it seizes this part with the lips, extending them on both
sides, and applying them against the worm, so that the mouth assumes the
form of a boat, pointed at each end, Plate XXIV. A. Fig. 2; the polype
gradually closes the two points of its boat-like lips, and by this
motion and suction swallows the worm, Fig. 4.

The polypes kill worms so speedily, that Fontana thinks they must
contain the most active and powerful venom; for the lips of a polype
scarce touch the worm, but it expires, so great is the energy of the
poison it conveys into it, though no wound can be observed in the dead
animal.

As soon as the stomach is filled, its capacity is enlarged, the body is
shortened, Plate XXIV. A. Fig. 6, the arms are for the most part
contracted, the polype hangs down without motion, and appears to be in a
kind of stupor, and very different from its shape when extended; but in
proportion as the food is digested, and it has voided the
excrementitious parts, the body lengthens, and gradually recovers its
usual form.

The transparency of the polype permits us to see distinctly the worm it
has swallowed, Plate XXIV. B. Fig. 12, which gradually loses its form.
It is at first macerated in the stomach of the polype, and when the
nutritious juices are separated from it, the remainder is discharged by
the mouth, Fig. 13. It is with these, as with other voracious animals,
as they devour a great quantity of food at once, so also they can fast
for a long time. The history of insects furnishes many examples of this
kind.

One circumstance is observable, which probably contributes much to the
digestion of their food, namely, that the aliments are continually
pushed backward from one extremity of the stomach to the other; this
motion may be easily observed with a microscope, in a polype which is
not too full, and in which the food has been already divided into little
fragments. For these observations, it is best to feed the polype with
such food as will give a lively-coloured juice; as for example, those
worms whose intestines are filled with red substances: for by these
means we shall see that the nutritious juices are conveyed not only to
the extremity of the body, but also into the arms; from whence it is
probable that each of the arms form also a kind of gut, which
communicates with that of the body. Some bits of a small black snail
that is frequently to be found in our ditches, was given to a polype.
The substance of this skin was soon reduced into a pulp, consisting of
little black fragments; on examining the polype with the microscope,
these particles were perceived to be driven about the stomach, and to
pass from head to tail, and into their arms, even where these were as
fine as a thread; they were afterwards forced into the stomach, and from
thence to the tail, from whence they were again driven into the arms,
and so on.

The grains take their tinge from the food which nourishes the polypes;
these grains become red or black, if the polype be fed with juices that
are either red or black; and they are more or less tinged with these
different colours, in proportion to the strength and quantity of the
nutritive juices. It is also observable, that they lose their colour if
fed with aliments that are not of the same colour with themselves.

The polypes feed on the greater part of those insects that are to be
found in fresh water. They may be nourished with worms, the larvæ of
gnats, &c. they will also eat larger animals if they are cut into small
pieces, as snails, large aquatic insects, small fish, butcher’s meat,
&c. Sometimes two polypes seize the same worm, and each begins to
swallow its own end, continuing so to do till their mouths meet, Plate
XXIV. A. Fig. 8; in this position they remain for some time, at last the
worm breaks, and each has its share; sometimes the combat does not end
here, for each continuing to dispute the prize, one of the polypes
opens its mouth advantageously, and swallows the other with its portion
of the worm, Plate XXIV. B. Fig. 14; this combat ends more fortunately
for the devoured polype than might be at first expected, for the other
often gets the prey out of its stomach, but lets it out again sound and
safe, after having imprisoned it above an hour. From hence we learn,
that the stomach of the polype, which so soon dissolves the animal
substances which are conveyed into it, is not capable of digesting that
of another polype.

Plate XXIV. A. Fig. 5, represents a polype with one half a centipe in
its mouth, as at a; the other part without, as at m. Fig. 1 represents
one suspended in water by a piece of packthread; c n, a centipe seized
by it, and drawn partly towards the mouth; i o, the bendings in the arm;
p, an arm in search of a small aquatic insect. Fig. 2, a polype
stretching itself into a boat-like form, to take or swallow a worm lying
sideways. Fig. 4, the same polype with the worm swallowed and bent
within it. Fig. 6, is a polype in the situation they generally assume
when they have satisfied their voracious appetite. Fig. 7, one that has
swallowed a small monoculus. Fig. 9, a, one whose arms are loaded with
monoculi. Fig. 10, a polype full of them from head to tail. Fig. 3, one
that has only swallowed a few of them. Fig. 8, represents two polypes
engaged in combat for a worm, of which both of them have swallowed a
part.

Plate XXIV. B. Fig. 11, represents a polype engaged with a very large
worm. Fig. 12, a worm seen within the skin of a polype. Fig. 13, a
polype disgorging the excrementitious parts of a worm.

Plate XXI. Fig. 12, a polype that has swallowed a small fish, and taken
the shape thereof.


OF THE GENERATION OF THE HYDRÆ.

As the hydra fusca and the hydra grisea are considerably larger than the
hydra viridis, it is more easy to observe the manner of their producing
their young. It is upon these, therefore, that most of the observations
here recited have been made. If one of them be examined in summer, when
the animals are most active, and more particularly prepared for
propagation, it will be found to shoot forth from its side several
little tubercles, or knobs, which grow larger and larger every day;
after two or three days inspection, what at first appeared but a small
excrescence, takes the figure of a small animal, entirely resembling its
parent. It does not inclose a young polype, but is the real animal in
miniature, united to the parent, as a sucker to the tree.

When a young polype first begins to shoot, the excrescence terminates in
a point, as at e, Plate XXIV. B. Fig. 24; so that it is rather of a
conical figure, and of a deeper colour than that of the body. This cone
soon becomes truncated, and in a little time appears cylindrical. The
arms then begin to shoot from the anterior end c i. The tail adheres to
the body of the parent, but grows gradually smaller, till at last it
only adheres by a point b, Fig. 23, it is then ready to be separated;
for this purpose the mother and young ones fix themselves to the glass,
or other substance upon which they may be situated. They have then only
to give a sudden jerk, and they are divided from each other. There are
some trifling differences to be observed now and then in their
performing this operation, which it would be too tedious to enumerate
here. A polype, a b, Fig. 20, with a young one, c d, places its body in
an arch of a circle a d b, against the sides of the glass, the young one
being fixed at the top d of the arch, with its head also fixed against
the glass; so that the mother, by contracting the body, and thus
becoming straight, loosens herself from the young one.

The young ones shoot in proportion to the warmth of the weather, and the
nature of the food eaten by the mother; some have been observed to be
perfectly formed in twenty-four hours, while others have required
fifteen days for the same purpose; the first were produced in the midst
of summer, the latter in a cold season.

The tail of the young polype communicates with, and partakes of the food
from the parent in the same manner as its own arms do, and the food lies
in the same manner as in the arms. When this fœtus is furnished with
arms, it catches its prey, swallows, digests, and distributes the juices
thereof even to the parent body; every good is common to each. Here then
we have evident communication between the fœtus and the mother; this
communication was further proved by the following experiment. A large
polype, one of the hydra fusca, was placed on a slip of paper, in a
little water; the middle of the body of the young one was cut, and the
superior part of that end which remained fixed to the parent was found
to be open. The parent polype was then cut on each side of the shoot.
Thus a short cylinder was obtained, which was open at both ends. This
being viewed through a microscope, the light was seen to come through
the side slip, or young one, into the stomach of the old one. For
further conviction, the cylindrical portion was cut lengthways; on
observing these parts, not only the hole t of the communication, Plate
XXIV. B. Fig. 17, was distinctly seen, but one might see through the end
o of the young one. On changing the situation of these two pieces of
prepared polypes, and looking through the opening e, Fig. 18, the
day-light was seen through the hole of communication i.

This communication, between the parent polype and its young ones may be
seen on feeding them; for, after the parent a b, Plate XXIV. B. Fig. 22,
has eaten, the bodies of the young ones swell, being filled with the
aliments as if they themselves had been eating. In the hydra fusca the
young ones do not proceed from the tail part b c, Plate XXIII. B. Fig.
16, but only from the part a c, with this exception, there is no
particular part of the body before the rest, on which they produce their
young. Some of them have been so closely observed, and have so greatly
multiplied, that there would be scarce any impropriety in saying they
produced their young ones from all the exterior parts of their body. A
polype puts forth frequently five or six young ones at the same time.
Trembley has had some that have produced nine or ten at the same time,
and when one dropped off another came in its place.

Though this gentleman had for two years thousands of them under his eye,
and considered them with the most scrupulous attention, he never
observed any thing like copulation. To be more certain on this head, he
took two young ones the instant they came from their parent, and placed
them in separate glasses; they both multiplied, not only themselves, but
their offspring, which were separated and watched in the same manner to
the seventh generation; nay, they have even the faculty of multiplying
while they adhere to the parent. The arms of the young ones do not
sprout till the body has attained some length.

Several excrescences or buds often appear at the same time on a polype,
which are so many polypes growing from one trunk; whilst these are
developing, they also bud, which buds again put forth little ones, the
parent and the young ones forming a singular kind of animal society, in
which all participate of the same life, and the same wants. In this
state, the parent appears like a shrub thick set with branches. Several
generations are often thus attached to one another, and all to the
parent polype; after a time, this tree of polypes or hydræ is
decomposed, and gives birth to new generations, or fresh genealogical
trees. Here we see a surprizing chain of existence continued, and
numbers of animals naturally produced, without any union of sexes; every
polype raising a numerous posterity by a kind of animal vegetation.

From Fig. 16, Plate XXIII. B. the reader may form an idea of the
promptitude with which these creatures increase and multiply; the whole
group formed by the parent and its young was about an inch and an half
long, and one inch broad, the arms of the mother and her nineteen little
ones hanging down towards the bottom of the vessel; the animal would eat
about twelve monoculi per day, and the little ones about twenty among
them, or rather more than thirty for the group.


OF THE RE-PRODUCTION OF THE HYDRÆ.

So strange is the nature of this creature’s life, that the method by
which other animals are killed and destroyed becomes a means of
propagating these. When divided and cut to pieces in every direction
that fancy can suggest, it not only continues to exist, but each section
becomes an animal of the same kind.

A polype cut transversely or longitudinally, in two or three parts, is
not destroyed; each part in a little time becomes a perfect polype. This
species of fecundity is so great in these animals, that even a small
portion of their skin will become a little polype, a new animal rising
as it were from the ruins of the old, each small fragment yielding a
polype. If the young ones be mutilated while they grow upon the parent,
the mutilated parts are re-produced; the same changes succeed also in
the parent. A truncated portion will put forth young before it is
perfectly formed itself, or has acquired its new head and tail;
sometimes the head of the young one supplies the place of that which
would grow out of the anterior part of the trunk.

If a polype be slit, beginning at the head, and proceeding to the middle
of the body, a polype will be formed with two heads, and will eat at the
same time with both. If the polype be slit into six or seven parts, it
becomes a hydra with six or seven heads. If these be again divided, we
shall have one with fourteen; cut off these, and as many new ones will
spring up in their place, and the heads thus cut off will become new
polypes, of which so many new hydræ may again be formed; so that in
every respect it exceeds the fabulous relation of the Lernean hydra.

As if the wonders already related of the polype were not sufficient to
engage our attention to these singular animals, new circumstances, as
surprizing as the foregoing, present themselves to convince us of the
imperfection of our ideas of animality, and of the greatness of the
power of our LORD and SAVIOUR, who is the source and origin of every
degree of life, in all its immense gradations, as unity is the origin of
number in all its varied series, multiplied proportions and
combinations; and as numbers may be considered as recipient of unity, in
order to make manifest the wonderful powers thereof, so the universe and
its parts are adapted to receive life from the source of all life, and
thus become representatives of his immensity and eternity.

The polypes may be as it were grafted together. If the truncated
portions of a polype be placed end to end, and then pushed together with
a gentle force, they will unite, and form a single one. The union is at
first made by a fine thread, and the portions are distinguished by a
narrow neck, which gradually fills up and disappears, the food passing
from one portion to another. Portions not only of the same, but pieces
of different polypes may be thus united together. You may fix the head
of one polype to the trunk of another; and that which is thus produced,
will grow, eat, and multiply like another.

There is still another method of uniting these animals together, more
wonderful in its nature, and less analogous to any known principles of
animation, and more difficult to perform. It is effected by introducing
one within the other, forcing the body of one into the mouth of the
other, and pushing it down so that their heads may be brought together:
in this state it must be kept for some time; the two individuals are at
last united, and grafted into each other; and the polype, which was at
first double, is converted into one, with a great number of arms, and
performs all its functions like another.

The hydra fusca furnishes us with another prodigy, to which we know
nothing that is similar either in the animal or vegetable kingdom. They
may be turned inside out like a glove, and, notwithstanding the apparent
improbability of the circumstance, they live and act as before. The
lining or coating of the stomach now forms the epidermis, and the former
epidermis now constitutes the coating of the stomach. A polype thus
turned, may often have young ones attached to its side. If this be the
case, after the operation they are of course inclosed in the stomach.
Those which have acquired a certain size extend themselves towards the
mouth, that they may get out when separated from the body; those which
are but little grown, turn themselves inside out, and by these means
place themselves again on the outside of the parent polype.

The polype thus turned combines itself a thousand different ways. The
fore-part often closes itself, and becomes a supernumerary tail. The
polype which was at first straight, now bends itself, so that the two
tails resemble the legs of a pair of compasses, which it can open and
shut. The old mouth is at the joint as it were of the compasses; it
cannot, however, act as one, so that a new one is formed near it, and in
a little time a new species of hydra is formed with several mouths.

Plate XXIII. B. Fig. 18, represents the upper part of a polype that has
been divided into two parts; a, the upper, c, the lower part, the end c
being something larger than that of a common polype, and is sensibly
perforated; in the summer time this part often walks and eats the same
day it is cut. Fig. 17, the other part of the same polype; the anterior
end is very open, and the edges of it turned a little outwards, which
afterwards folding inwards, close the aperture. This end now appears
swelled, as at c, Fig. 21; the arms shoot out from this end: at first
three or four points only begin to shoot, as at c, Fig. 20, and while
these increase in size, others appear between them; they can seize their
prey and eat before their arms have done growing. In the height of
summer the arms will often begin to shoot in twenty-four hours; but in
cold weather it will be fifteen or twenty days before the head is
formed. Fig. 22, represents a polype that was cut close under the arms;
this became also a complete animal in a little time.

The sides of a polype that has been cut longitudinally, roll themselves
up in different ways, generally beginning at one of the extremities,
rolling itself up in a heap, as in Plate XXIII. B. Fig. 19, with the
outside of the skin inwards; it soon unrolls itself, and the cut sides
form themselves into a tube, whereof the edges a b and e i, Fig. 15, on
both sides meet each other and unite. Sometimes they begin to join at
the tail end, at other times the whole sides gradually approach each
other. The sides join so close, that from the first moment of their
junction no scar can be discovered. Fig. 14, represents a polype partly
joined, as at i b, the part c a e not yet closed. Fig. 29, represents a
polype, the heads of which have been repeatedly divided, by which means
it becomes literally a hydra. Fig. 24, represents a polype that has been
turned, endeavouring to turn itself back again, the skin of the anterior
part lying back upon the other; the arms varying in their direction,
being sometimes turned towards the head, see Fig. 24 and 26, at others,
towards the tail. The anterior extremity c, formed by the edges of the
reversed part a, remained open for some days, and then began to close;
new arms shot out near the old ones, and several mouths were formed at
those parts where the arms joined the body. Fig. 23, 25, 27, 28,
represent the different changes that took place in another polype that
had been turned inside out, and the different revolutions it went
through before it acquired a fixed state; a c always shews the part the
polype had turned back, and a b the part it could not turn back.

A polype, which has been partly turned back, remains but a little time
in that situation. Fig. 28, a, the part where the portion it had turned
back joined to the body a b; this became straight, and formed a right
angle with a b; the same day another head appeared at e, and several
arms, a o, a n, began to shoot from the mouth a; at the other side of
this mouth there were the old arms a d. The next day the portion a c was
drawn near the body, and formed an acute angle with it, as at Fig. 25.
Fig. 27, represents the same swelled, after having swallowed a worm.
Four days afterwards its form had varied considerably, as may be seen by
comparing Fig. 25 and 28, having now one common mouth, and two small
polypes growing on it.

We may now be permitted to make a few reflections on this singular
animal. On considering the various properties that have been already
described, many particulars will be found in them that are very
analogous to others that are continually carrying on around us; we
perceive that there is a successive unfolding of new parts. In every
organized frame there is a continual effort to extend its sphere of
action, and enlarge the operation of that portion of life which is
communicated to it. This gradual evolution requires a secret and curious
mechanism, to regulate and modify by re-action the continued conatus of
the forming principle within it. The polype is an organized whole, of
which each part, each molecule, each atom, tends to produce another; it
is, if we may so speak, one entire ovary, a compound of germ, or seed.
In cutting a polype to pieces, the nourishing juices, which would have
been employed in supporting the whole, are made to act upon each
portion.

When a polype is divided longitudinally, it forms two half tubes; the
opposite edges of these approach, and in a very short time form a
perfect tube. The sides are made to touch each other by certain motions
and contractions of the piece; but as soon as the edges come in contact,
a slight adhesion takes place, the corresponding vessels unite, and new
ones are unfolded, as in a vegetable graft; by these means the points of
connection and cohesion are multiplied, the motion of the fluids is
re-established, and with them the vital œconomy. This is performed with
more rapidity than in vegetables, because the polype is nearly
gelatinous, and its parts are extremely ductile; this ductility is
supported and preserved by the element which it inhabits. The same
reasoning applies equally to explain the formation of so many heads to a
polype, as constitute it a real hydra.

A new polype is formed out of small portions or fragments, in a very
different manner, the operations in nature being always varied,
according as the circumstances differ; each fragment is puffed up, the
skin separated, and an empty space is formed within it; this part is to
become the stomach of the rising polype, which soon sends forth arms,
and is formed to the perfection proper to its kind. We learn from this
instance that the skin of the polype is not so simple as was at first
imagined; for we find it dividing itself into two membranes, and forming
thereby a cavity fit to perform all the functions of a stomach; but why
these membranes are separated in the small portions, and not in the
larger, we cannot tell; but though we are ignorant of this, and many
more circumstances relative to the re-production of these little
animals, yet the foregoing facts enable us to understand better the
nature of the existence of these polypes which have been turned inside
out.

For as that part which formed the interior skin of the stomach in the
little fragments before-mentioned, became the exterior part of the
animal, the inside of the polype is consequently so similar to the
exterior skin, that one may be substituted for the other, without
injuring the vital functions; from hence we might, in some measure, have
inferred the possibility of the polypes living, after they have been
turned inside out, independent of the fact itself.

The viscera of the animal are situated in the thickness of the skin, and
absorbing pores are placed both on the inside and outside, so that the
animal can live whether the skin be turned one way or the other. The
Author of nature did not create the polype to be turned as we turn a
glove; but he formed an animal whose viscera were lodged in the
thickness of the skin, and with powers to resist the various accidents
to which it was unavoidably exposed by the nature of its life; and the
organization necessary for this purpose was so constructed, that the
skin might be turned without destroying life.

Every portion of a divided polype has, like the vegetable bud, all the
viscera necessary to its existence; it can, therefore, live by itself,
and push forth a head and tail, when placed end to end against another
piece. The vegetation consists in uniting the portions, the vessels of
each part increase in length, and a communication is soon formed between
them, which unites the whole. The ease with which the parts unite, is as
has been observed before, probably owing to their gelatinous nature; for
we find many similar instances in tender substances. The solid parts of
the embryo, as the fingers, unite in the womb; tender fruit and leaves
may be also thus united.

A portion of these creatures is capable of devouring its prey almost as
soon as it is divided from the rest. In the structure of those animals
which are most familiar to us, a particular place is appropriated for
the developement and passage of the embryo. But on the body of an
animal, which, like a tree, is covered with prolific gems, it is not
surprizing that the young ones should proceed from its sides, like
branches from a tree. The mother and her young ones form but one whole;
she nourishes them, and they contribute to her existence, as a tree
supports, and is reciprocally supported by its branches and leaves.


OF THE HYDRA PALLENS.

The hydra pallens has been fully described only by M. Rösel;[113] it is
very seldom to be met with, is of a pale yellow colour, and grows
smaller gradually from the bottom, the tail is somewhat round or
knobbed, the arms are about the length of the body, of a white colour,
and generally seven in number, apparently composed of a chain of
globules; it brings forth the young from all parts of its body. Linnæus
defines it as, hydra pallens tentaculis subsenis mediocribus;[114]
Pallas as, hydra attenuata corpore flavescente, sursum attenuato.[115]

  [113] Insecten Belustigung, 3. Theil. pag. 465. Tab. LXXVI. LXXVII.

  [114] System. Nat. p. 1320, No. 4.

  [115] Zoophyt. 4.


OF THE HYDRA HYDATULA.

Plate XXI. Fig. 1, 2, 3, and 4.

The next in order is the hydra hydatula, which we have already defined
from Linnæus as a hydra with four obsolete arms, and a vesicular body:
it is spoken of by several medical writers, who are enumerated in the
Systema Naturæ, p. 1321. It is described also by Hartman, Misc. Nat.
Cur. Dec. I. An. 7, Obs. 206, Dec. II. An. 4, Obs. 73, as hydatis
animata; also in the Dissert. de Inf. Viv. p. 50; n. 6, tænia
hydatoidea. Pallas defines it as tænia hydatigena rugis imbricata
corpore postice bulla lymphaticæ terminato. The following description is
extracted from that in the Philosophical Transactions, No. 193, by Dr.
Tyson, who names it lumbricus hydropicus.

In the dissection of a gazella or antelope, Dr. Tyson observed several
hydatides or films filled with water, about the size of a pigeon’s egg,
and of an oval form, fastened to the omentum, and some in the pelvis,
between the bladder of urine and the rectum; and he then suspected them
to be a particular sort of insect, bred in animal bodies, or at least
the embryos or eggs of them: 1. Because he observed them included in a
membrane, like a matrix, so loosely, that by opening it with a finger or
knife, the internal bladder, containing the serum or lympha, seemed no
where to have any connection with it, but would very readily drop out,
still retaining its liquor, without spilling any of it. 2. He observed
that this internal bladder had a neck or white body, more opake than the
rest of the bladder, and protuberant from it, with an orifice at its
extremity, by which, as with a mouth, it exhausted the serum from the
external membrane, and so supplied its bladder or stomach. 3. Upon
bringing this neck near the candle, it moved and shortened itself. Fig.
1, represents one of these watery bladders inclosed in its external
membrane, its shape was nearly round, being only a little depressed or
flatted, as a drop of quicksilver will be by lying on a plane. In Fig.
2, the neck is better seen; the external membrane being taken off, an
open orifice is found at its extremity; it consists of circular rings or
incisures, which are more visible when magnified, as in Fig. 3; it then
appears granulated with a number of little eminences all over the
surface; the orifice at the extremity seems to be formed by retracting
itself inwards, and upon trial it was found to be so; for in Fig. 4, the
neck of this polype is represented magnified and drawn out its whole
length; on opening it there were found within the two strings a, a,
which probably convey into the stomach the moisture and nourishment,
which the animal, by protruding its neck, extracts from the external
membrane.[116]

  [116] Hydra hydatula habitat in abdomine mammalium, ovium, suum,
  murium, &c. inter peritoneum et intestina. Vesica lymphatica,
  pellucida, magnitudine pruni, petiolata corpore cylindrico, in cujus
  apice os, quod, corpore compresso, movet tentacula vix manifesta.
  Linn. Syst. Nat. p. 1321, No.5.


OF THE HYDRA STENTOREA.

Plate XXII. Fig. 27 and 28.

Hydra tentaculis ciliaribus corpore infundibuliformi.

The arms of this hydra are rows of short hairs, the body trumpet-shaped.

This species of hydra is very common, and has been described by almost
every writer on these subjects; it is placed by Müller among the
vorticellæ.

Vorticella stentorea caudata, elongata, tubæformis limbo ciliato. Müller
animalcula infusoria.

Mr. Baker originally named it the funnel-like polype, which Messrs.
Trembley and Reaumur changed to the tunnel-like polype, under which name
it appears in the Philosophical Transactions, No. 474.

There are three kinds of them, which are of different colours, green,
blue, and white. The white ones are the most common. It is necessary to
observe them often, and in various attitudes, in order to obtain a
tolerable idea of their structure. They do not form clusters, but adhere
singly by their tail to whatever comes in their way; their anterior end
is wider than the posterior, and being round, gives the animal somewhat
of a funnel form, though it is not completely circular, having a sort of
slit or gap that interrupts the circle. The edge of this opening is
furnished with a great number of fibrillæ, which by their brisk and
continual motions excite a current of water; the small bodies that float
or swim near this current, are forced by it into the mouth of the
little animal. Trembley says, that he has often seen a number of very
small animalcula fall one after another into the mouth, some of which
were afterwards let out again at another opening, which he was not able
to describe.

They can fashion their mouths into several different forms. If any thing
touch them, they shrink back and contract themselves. They live
independent of each other, swimming freely through the water in search
of their prey, and fix to any thing they meet with.

These animals multiply by dividing themselves, not longitudinally, nor
transversely, but sloping and diagonal wise; the proceedings in nature
continually varying in every new form of life. Of the two polypes
produced by the division of one, the first has the old head and a new
tail; the other, the old tail and a new head.

To make the description more clear, Trembley called that with the old
head the superior polype, that with the new head the inferior one. The
first particular that is observable in these polypes, when they are
going to divide, is the lips of the inferior one; a transverse and
oblique stripe indicates the part where it is going to divide; the new
lips are formed at about two-thirds of the length of the polype,
reckoning from the head; the division is made in a sloping line, that
goes about half way round the parent animal; these lips are at first
discerned by a slow motion, which engages the attention of the observer.
They then insensibly approach each other and close, whereby a swelling
is formed on the side of the polype, which is soon found to be a new
head. When the swelling is considerably increased, the two polypes may
be plainly distinguished. The superior one being now connected with the
inferior one only by its lower extremity, is soon detached from it, and
swims away to fix itself on some convenient substance; the inferior one
remains fastened to the place where the original polype was fixed before
the division.

From the various modes by which different species of polypes are
multiplied, we are led to form more exalted ideas of nature, and to see
that the little we discover is but an exceeding small part of her
contents; we learn also to be more cautious in reasoning from analogy,
and laying down the known for a model to the unknown, because we find
that the operations in nature are varied ad infinitum.

The growth of the hydra fusca is very quick, but that of the hydra
stentorea is much more so. The progress of the fœtus is always more
rapid than that of the infant and adult animal; but in these organized
atoms the evolution is so rapid, as to appear almost like an immediate
creation.

Fig. 28 represents the hydræ stentoreæ, or funnel-polypes, fixed to the
under side of a piece of some vegetable substance; they are in this
figure of their natural size.

Fig. 27, the same polypes magnified; the different forms they assume are
also seen here, sometimes short and thick, as at m m; long, as at n;
nearly globular, as at o; extended to the full size, as at k; seen as
contracted at i. The fibrillæ or little hairs may be seen in most of the
attitudes except those of l.


OF THE HYDRA SOCIALIS.

Plate XXI. Fig. 11.

Hydra socialis mutica torosa rugosa.[117]

  [117] Linn. Syst. Nat. p. 1321. No. 7.

Social hydra, bearded thick and wrinkled.

This species of hydra has been described by many writers. It is the
vorticella socialis of Müller, who defines it as vort cella caudata,
aggregata, clavata; disco obliquo. Müller Animalcula Infusoria, p. 304.
Pallas makes it a brachionus, Pall. Zooph. 53.

In Fig. 11, these animals are represented as considerably magnified;
they appear like a circle, surrounded with crowns, or ciliated heads,
tied by small thin tails to a common center, from whence they advance
towards the circumference, where they turn like a wheel, with a great
deal of vivacity and swiftness, till they occasion a kind of whirlpool,
which brings into its sphere the proper food for the polype. When one of
them has been in motion for a time, it stops, and another begins;
sometimes two or three may be perceived in motion together. They are
often to be found separate, with the tail sticking in the mud. The body
contracts and dilates very much, so as sometimes to have the appearance
of a cudgel; at others, to assume almost a globular form. The young
polypes of this species have been sometimes taken for the hydra
stentorea.


OF THE VORTICELLÆ.

We now come to another division of these animals, to which later writers
have given the name of vorticellæ; this term I shall therefore adopt,
being of opinion that it behoves every man to maintain that order in
scientific arrangement which is not inconsistent with truth, except he
can produce another arrangement more expressive of the nature of the
objects it is designed to discriminate; a process requiring no small
degree of attention.

The variety that may be observed in these minute animals confirms a
principle, which, the more it is inquired into, the more it will be
found to accord with the general operations in nature, namely, that
there is always a pre-existent principle of life necessary to the
organization both of animals and vegetables; that the alimentary and
other particles which are added to, or apparently belong to them,
produce nothing of themselves; they are incapable of forming the least
fibre, but they are able to become constituent parts of one organical
whole, together with the instruments whereby the forming principle is
manifested, and rendered capable of acting upon certain orders of
creatures.


VORTICELLA.

Animal calyce vasculoso; ore contractili ciliato, terminali. Stirps
fixa.

A small animal, with a vascular cup; the mouth is at one end ciliated,
and capable of being contracted, the stem fixed.


VORTICELLA ANASTATICA.

Plate XXI. Fig. 13, 14, 15, and 16*.

Vorticella anastatica, composita, floribus campanulatis, stirpe
multiflora rigescente.

Vorticella anastatica, compound, with bell-shaped flowers, and a rigid
stem.

Cluster polype, second species. Trembley, Philos. Trans. vol. xliv.
part. 2. p. 643.

These polypes form a group resembling a cluster, or more properly an
open flower; this flower or cluster is supported by a stem, which is
fixed by its lower extremity to some of the aquatic plants or extraneous
bodies that are found in the water; the upper extremity forms itself
into eight or nine lateral branches, perfectly similar to each other;
these have also subordinate branches, whose collective form much
resembles that of a leaf. Every one of these assemblages is composed of
one principal branch or nerve, which makes with the main stem of the
cluster an angle somewhat greater than a right one; from both sides of
this nerve the smaller lateral branches proceed; these are shorter the
nearer their origin is to the principal branch.

At the extremity of the principal branch, and also of all the lateral
ones, there is a polype or vorticella. There are others on both sides of
the lateral twigs, but at different distances from their extremity.
These polypes are all exceeding small, and of a bell-like figure; near
their mouth a quick motion may be discerned, though not with sufficient
distinctness to convey an adequate idea of its cause; upon the branches
of these clusters are round bodies, which will be more particularly
described presently.

Every cluster has eight or nine of these branches or leaves; they do not
all proceed from the same point, but the points from whence they set out
are not far asunder; each of these branches is bent a little inwards, so
that all of them taken together form a kind of shallow cup. If the eye
be placed right over the base of this cup, the appearance of the whole
eight or nine branches is like unto that of a star, with so many rays
proceeding from the center. If the cluster be slightly touched, all the
branches instantly fold up, and form a small round mass. The stem which
supports the cluster contracts also at the same time, folding up like a
workman’s measuring rule, that consists of three or four joints. This
extraordinary assemblage constitutes one organized whole, formed of a
multitude of similar and particular ones. A new species of society, in
which all the individuals are members of each other in the strictest
sense, and all participate of the same life.

A few days after one of these clusters is formed, small round bodies or
bulbs may be perceived to protrude in several places from the body of
the branch; these grow very fast, and arrive at their greatest growth in
two or three days. The bulbs detach themselves from the branches out of
which they spring, and go away, swimming till they can settle upon some
substance which they meet with in the water, and to which they fix
themselves by a short pedicle; the bulbs are then round, only a little
flatted on the under side, the pedicle continues to lengthen gradually
for about twenty-four hours, during the same time the bulbs also change
their figure, and become nearly oval. There are in a cluster but few of
these bulbs, compared with the number of the vorticellæ, neither do all
the bulbs come out at the same time. The bulb then divides lengthways
into two smaller ones, but which are still much larger than the
vorticellæ themselves. It is not long before these are separated like
the first, and thus form four bulbs on the same stalk; these again
divide themselves, and form eight; which again subdivide, and
consequently make sixteen. They are all connected with the stalk by a
proper pedicle, but they are not all of an equal size; the largest
continue to divide, and the smallest begin to open, and take the
bell-formed shape. Trembley observed from one round bulb, in about
twenty-four hours, by repeated divisions, one-hundred and ten vorticellæ
to be formed.

It has been asked with propriety, what plant or what animal could have
led us to expect an existence and mode of propagation similar to that of
the vorticella anastatica?

Fig. 13 represents one branch of the vorticella anastatica; on this
branch, besides the vorticellæ which are of a bell-like form, some of
those round bodies from which they first spring, and by which they are
so remarkably distinguished from any other species, may be seen.

Fig. 14 represents one of the globular bodies after it has parted from
the cluster, and has fixed itself to some other body, and after the
globule itself and its pedicle have begun to lengthen.

Fig. 15 represents the two bodies that were formed by the parting of
that which is shewn at Fig. 14.

Fig. 16* represents four that were formed by the separation of the two
bulbs, exhibited in the foregoing figure.


VORTICELLA PYRARIA.

Plate XXII. Fig. 25, 26.

Vorticella composita, floribus muticis obovatis; tentaculis bigeminis,
stirpe ramosa. Compound, with beardless oval florets, two double arms,
the stem branched.

It is somewhat of a pear shape, the base is pellucid, the top truncated,
the lateral arms, which are a pair on each side, cannot be distinguished
without some attention; they are sometimes to be seen disengaged from
the pedicle, and rolling swiftly in a kind of circle.


VORTICELLA CRATÆGARIA.

Plate XXII. Fig. 40.

Vorticella composita, floribus muticis globosis; tentaculis binis,
stirpe ramosa. Compound, with globous naked florets, two tentacules, and
a branched stem.

These vorticellæ are to be found in the month of April, both in the mud,
and upon the tail of the monoculus quadricornis; they are generally
heaped together in the manner in which they are represented in the
figure; they are of a spherical form, and united to one common stalk.
They are also often to be found without any pedicle. The body is rather
contracted; the aperture is circular, and surrounded with a marked
margin; it has two small arms. With a deep magnifier, a vehement
rotatory motion may be seen. They sometimes separate from the community,
and go forwards in a kind of spiral line, and then in a little time
come back again to the rest.

The figure represents a parcel of these vorticellæ united together.

Among the other authorities for this animal, Linnæus refers to Baker’s
description of the mulberry insect, “Employment for the Microscope,” p.
348, which, as it differs a little from the preceding account, we shall
insert here. That from which his drawing was made, and which he has
described, was found in a ditch near Norwich; he called it the mulberry
insect, from the resemblance it bore to that fruit; though the
protuberances that stand out round it are more globular than those of a
mulberry. It is to be seen rolling about from one place to another, and
is probably a congeries of animalcula; they are to be met with in
different numbers of knobs or protuberances, some having fifty or sixty,
others more or less, down to four or five. The manner of moving is the
same in all. They are generally of a pale yellow.


VORTICELLA OPERCULARIA.

Plate XXII. Fig. 29.

Vorticella composita floribus muticis ovalibus, stirpe ramosa. Compound,
with naked oval florets, and a branched stem.

These vorticellæ are of a lemon shape, and are generally found in
clusters, branching out from a stem, which mostly adheres to some
convenient substance.

That species of them which is described by Baker had a very short
pedicle, and the animals were much longer than those which are
represented at Fig. 29. There was no main stem, but all the pedicles
were joined in one center, round which the animals extended themselves
as so many radii, forming a very pleasing figure.

The mouths of these animalcula are not ciliated, but they are furnished
with a round operculum or cover, connected by a long ligament or muscle,
which extends downwards through the body, and is affixed withinside of
it, near the tail. This ligament may be contracted or dilated, so that
the cover can be removed to some distance from the mouth; in this
situation several short hairs maybe found to radiate from it; these have
a vibratory motion, by which they excite a current of water, most
probably to draw in the proper nourishment, after which they shut or
pull down the cover, which they again extend at pleasure: when the cover
is pulled close down, the mouth contracts, and no hairs are to be seen.

Fig. 29 represents the vorticella opercularia; ſ, the operculum removed
at some distance from the mouth, at t; it is nearly close at r, the
mouth contracted, the cover drawn in, and no hairs to be seen; u, a part
of the stalk, from which some of the animalcula are separated.


VORTICELLA UMBELLARIA.

Plate XXII. Fig. 30.

Vorticella composita, floribus ciliatis globosis muticis, stirpe
umbellata. Compound, with ciliated globous naked florets and an
umbellated stem.

Vorticella acinosa, simplex, globosa, granis nigricantibus, pedunculo
rigido. Müller Animal. Infus. p. 319.

We frequently find in divers places, upon water-plants, and other bodies
in the water, a whitish substance that looks like mould; plants, pieces
of wood, snail shells, &c. are often entirely covered over with this
substance. If we examine any of these minute bodies by the microscope,
we shall find such motions as will induce us to think them an assemblage
of living animals, severally fixed to the extremities of small stems or
pedicles, many of which are often so united as to form together a sort
of branches or clusters, from whence they have been termed clustering
polypes, or des polypes en bouquet.

These clusters are larger or smaller, according to the species of the
vorticellæ which form them, as well as owing to the concurrence of many
other circumstances. To obtain a clear idea of the figure of these
animals, it is best to observe the smaller clusters, as in the larger
they are often rendered less distinct on account of the number.

The length of those which are represented at Fig. 30, is about the 240th
of an inch; they are of a bell-shape. The anterior part a c generally
appears open, the posterior part is fixed to a stem or pedicle, b e; it
is by the extremity of this pedicle that the vorticella fastens itself
to any substance. It appears in the microscope of a brownish colour,
excepting at the smaller end b, where it is transparent, as well as the
whole pedicle b e. When the anterior part a c is open, a very lively
motion may be perceived about its edges; and when it presents itself in
a particular manner, something very much resembling the little wheels of
a mill, moving with great velocity, may be discovered on both sides of
the edges of this anterior part.

These vorticellæ are able to contract themselves suddenly. They may be
made to do this, either by touching them, or moving the substance to
which they are fixed. When they contract, the edges of the anterior
parts are drawn quite into the body; on resuming their former posture,
the edges may be seen to come forth, and put themselves in motion as
before. Minute substances that float in the water are often forced down
into these openings, and sometimes are thrown out again.

They are capable of swimming about singly, but their form is in that
case considerably different from that which they have when they are
fixed. To see regularly in what manner the clusters are formed, and in
what way these little creatures multiply, it is best to observe one that
is fixed by itself.

The pedicle of a single vorticella is at first short, but it soon grows
longer, and then begins to multiply, that is, to divide or split itself
into two lengthways. To effect this, the lips are first drawn into the
body, the anterior part closes and becomes round, and loses its bell
shape, the motion about the lips ceases, though a small degree of motion
may be perceived within the body. The anterior end flattens gradually,
and spreads wider in proportion as it grows smaller. It then gradually
splits down the middle, that is, from the middle of the head to the
pedicle, so that in a little time two separate round bodies appear to be
joined to the end of the pedicle that before supported but one.

The mouth or anterior part of each of these bodies now opens by degrees;
and in proportion as they open, the lips of the new vorticella begin to
display themselves. The motion before spoken of may then also be
perceived. Indeed it is the best time of observing it; it is at first
slow, but more rapid in proportion as the mouth opens, when it is as
swift as that of the vorticella before it began to divide, and we may
now look upon it as completely formed. A vorticella is generally about
one hour in dividing itself.

The lower of the three drawings, Fig. 30, represents two vorticellæ
joined by their posterior extremity to one pedicle; soon after the
division, each vorticella begins to shew a pedicle of its own.

Fig. 30 represents a cluster of eight vorticellæ; by this figure we may
form some idea in what manner the pedicles are disposed as their number
increases. There were at first only two at b, whose branches lengthened
to d, and then each of them was divided into two, now forming four;
these again lengthened and reached i; when they were again subdivided,
as in the figure.

The reader will join with Bonnet in admiring the group of wonders
afforded by a single spot of mouldiness. What unforeseen, varied, and
interesting scenes are presented within so small a compass! what a
theatre is exhibited to a thinking mind! But our abode is so recluse,
that we have but a glimmering view of it: how great would our
astonishment be, if the whole spectacle was disclosed to us at once, and
we were enabled to penetrate into the interior structure of this
wonderful assemblage of living atoms! Our eyes see only the gross parts
of the decorations, whilst the machines that execute them remain in
impenetrable darkness! Who shall enlighten this profound obscurity, or
dive into an abyss where reason is lost; or draw from thence the
treasures of wisdom concealed within it? Let us learn to be content with
the small portion that is communicated to us, and contemplate with
gratitude the first traces of human understanding that are imparted to
us in these discoveries.


VORTICELLA BERBERINA.

Vorticella composita, floribus ovalibus muticis, stirpe ramosa.
Compound, with oval beardless florets.

This is a species of the vorticellæ, which resembles the preceding one
in many respects, particularly in being multiplied in the same manner,
that is, by dividing or splitting, according to its length.

They are more slender than the vorticella umbellaria; the branches of
the clusters are transparent. When many of them are together, they
appear of a changeable violet colour; the clusters are not unlike a
sprig of spun glass. The motion of the lips is not so easily
distinguished as in the foregoing species, though it may be observed in
these whilst they are opening and completing their formation. For at
these times the motion is but slow, whereas it becomes afterwards very
quick in those that are arrived at a state of perfection.

All the cluster vorticellæ detach themselves from time to time from the
stem, and from these they swim about till they fix again upon some
convenient substance; the branches, when deserted, bear no more
vorticellæ.


VORTICELLA DIGITALIS.

Plate XXII. Fig. 31.

Vorticella composita, floribus cylindricis, unisulcatis semiclausis,
stirpe ramosa. Compound, with cylindrical florets.

Vorticella composita, cylindrica, crystallina, apice truncata et fissa,
pedunculo fistuloso ramosa. Müller Animal. Infus. p. 327.

This species of the vorticella is very scarce, it seems only to have
been seen by Rösel, who found it on the monoculus quadricornis, till it
was discovered in the year 1784 by Müller, who had sought for it several
years before, but in vain.

The body is cylindrical, crystalline, and appears almost empty; it has
three pellucid points disposed lengthways, the apex is truncated in an
oblique direction, the margin bent back. The upper part contracts
itself, and the margin then assumes a conical shape, with a convex
surface; there are in general but few branches from the principal stem,
and these are short and thick. It excites an undulatory motion, but no
hairs, nor any rotatory motion, have been discovered. Fig. 31, o and n,
represents the vorticella adhering to the monoculus quadricornis.


VORTICELLA CONVALLARIA.

Plate XXII. Fig. 39.

Vorticella simplex, gregaria, flore campanulata mutico; tentaculis
bigeminis, stirpe fixa. Simple, but gregarious, the florets bell-shaped,
with two pair of little arms, and a fixed stem.

Vorticella simplex, campanulata, pedunculo rotortili. Müller Animal.
Infus.

These vorticellæ, or bell-animals, as they are termed by Baker, are
generally found adhering to some substance in the water; they are
represented here as found by Rösel, fixed to a curious cornu ammonis,
with points projecting from the back. To the naked eye they appear only
as so many little white points, but under the microscope, as little
bells, agitating the water to a considerable distance. The stems of
these have a particular motion, they draw themselves up and shorten all
at once, taking the form of a spiral wire or screw; in a moment after
they again resume their former shape, stretching themselves out straight
as before. Many of them may be seen at times adhering to each other by
their tails; the cilia, which are two on each side of the mouths, are
very seldom to be perceived.


VORTICELLA URCEOLARIS.

Plate XXII. Fig. 33, 34, 35, 36, 37, 38.

Vorticella simplex, pedunculata, ore dentato. Single, with a short tail,
and toothed mouth.

Brachionus capsularis testa ovata apice sexdentata basi incisa, cauda
longa bicuspi. Müller Animal. Infus. p. 356.

To the naked eye it appears as a white moveable point; but when examined
by the microscope, a tail projecting from the lower part is discovered,
and a double rotatory instrument is seen, which it can conceal or expose
at pleasure. It has been seen and described by most microscopical
writers; but as Baker’s seems to be the most perfect description, I
shall principally follow his account of it.

He discovered three species of them, two of which are included under the
vorticella urceolaris. Fig. 33, 34, 35, are of the first species; Fig.
36, 37, 38, are of the second kind. The first sort, when extended, is
about twice as long as it is broad. It is contained in a shell; the fore
part of this is armed with four sharp teeth or points; the opposite side
has no teeth, but is waved or bent in two places, like the form of a
Turkish bow. At the bottom there is a hole, through which it pushes the
tail. It fastens itself by this tail to any convenient substance when it
intends to use its rotatory organs; but when it is floating in the
water, and at all other times when not adhering to any body, it wags the
tail backwards and forwards something like a dog.

We may consider it as divided into a head, thorax, and abdomen; each of
which may be extended and contracted considerably: it can, by dilating
all three, protrude the head beyond the shell, or by contracting them,
draw the whole body within the same.

The head, when extended, divides itself into two branches, between
which, another part, a kind of proboscis, is pushed out; at the end of
this are two fibrils, that appear when they are at rest like a broad
point, but which can be moved to and from each other very briskly with a
vibratory motion, see Fig. 33.

The form and situation of the two branches are sometimes changed, the
ends thereof becoming more round, and the vibratory motion is altered to
a rotatory one: this alteration is represented at Fig. 34: the head also
appears in this figure. The thorax is annexed to the lower part of the
head; it is muscular: within it there is a moving intestine, which has
been supposed to be either the lungs or the heart of the little
creature, see b, Fig. 33 and 34.

A communication is formed between the thorax and the abdomen by means of
a short vessel c, whose alternate contractions and dilatations occasion
the abdomen to rise and fall alternately, having at the same time a sort
of peristaltic motion. The food is conveyed through this vessel into the
abdomen, where it is digested; it is then discharged by the anus, which
is placed near the tail.

The tail has three joints, and is cleft or divided at the extremity, by
which means it can better fasten itself to suitable objects. It is in
general projected from the lower end of the shell, moving nimbly to and
fro, serving the animal as a rudder when it is swimming, to direct its
course.

When the water in which the little animal is placed is nearly dried
away, or when it has a mind to compose itself to rest, it contracts the
head and fore-part of the body, brings them down into the shell, and
pulls the tail upwards, so that the whole of this minute creature is
contained within the shell, see Fig. 35. The shell is so transparent
that the terminations cannot be easily distinguished when the animal is
extended; but whatever is transacted within the shell, is as plain as if
there was no substance between the eye and the interior parts.

Fig. 36, 37, 38, exhibit the appearance of another species of these
animals, which differs from the foregoing kind. This has also a head, a
thorax, and abdomen, but then they are not separated by a gut or
intermediate vessel, as in the former, but are joined immediately
together, and at the place where in the first kind a moveable intestine
was seen; in this a muscle, most probably the heart, may be discovered;
it has a regular systole and diastole: this part is intended to be shewn
at a, Fig. 36, 37, 38. Like the other, it draws the head and tail within
the shell, which then appears to have six teeth or spikes on one side,
and two on the other. It very seldom protrudes its head so far out as
the other; sometimes the fibrillæ may be seen within the margin of the
shell.

Both species carry their young in an oval integument or bag, fastened
externally to the lower part of the shell, somewhere about the tail;
these bags are sometimes opake at one end, and seemingly empty at the
other, see d, Fig. 34: sometimes the middle is opake, with a transparent
margin, see b, Fig. 36.

It is highly entertaining to see a young one burst its integument, and
gradually force its way out; in performing this operation, it is much
assisted by the motion of the tail of the parent. The head part comes
out first, it then sets its rotatory organ in motion, by which it is
completely disengaged, leaving the integument behind, which the
vorticella freed itself from by repeated strokes with its tail. A young
one almost disengaged is seen at b, Fig. 38; another embryo, c, was left
adhering to the shell.

There are four more species of the vorticellæ mentioned by Linnæus,
which are, the vorticella encrinus, the vorticella polypina, the
vorticella stellata, and the vorticella ovifera; which, being marine
animals, do not come properly within our plan. The vorticella polypina
will be described hereafter.


TUBULARIA CAMPANULATA.

Plate XXII. Fig. 32.

Tubularia reptans, tubis campanulatis. Creeping, with campanulated
tubes.

It is called by Baker the bell-flowered, or plumed animal.

These little creatures dwell in colonies together, from ten to fifteen
in number, living in a kind of slimy mucilaginous case, which, when
expanded in the water, has some resemblance to a bell with its mouth
upwards. These bells or colonies are to be found adhering to the large
leaves of duck-weed and other aquatic plants.

The bell or case which these animals inhabit, being very transparent,
all the motions of its inhabitants may be discerned distinctly through
it. There are several ramifications or smaller bells proceeding from the
larger one; in each of these there is an inhabitant. The opening at the
top of these bells is just large enough for the creature’s head, and a
small part of its body to be thrust out from it, the rest remaining in
the case, into which it also draws the head on the least alarm.

Besides the particular and separate motions which each of these
creatures is able to exert within its case, and independent of the rest,
the whole colony has a power of altering the position of the bell, and
removing it from one place to another. These animalcula seem not to like
to dwell in societies, whose number exceeds fifteen; when the colony
happens to increase in number, the bell may be observed to split
gradually, beginning from about the middle of the upper extremity, and
proceeding downwards towards the bottom, till they at last separate and
become two colonies, independent of each other.

The arms are very near each other; sixty may often be counted in one
plume, having each the figure of an Italic _ʃ_, one of whose hooked ends
is fastened to the head; and altogether, when expanded, compose a figure
somewhat like a horseshoe, convex on the side next the body, but
gradually opening and turning outwards, so as to leave a considerable
distance within the outer extremities of the arms.

The plumed polype is of a very voracious disposition, devouring a great
number of small animals. If the arms, when extended, be observed
attentively with the microscope, they will be found to have a constant
vibratory motion; alternately bending withinside of the plume, and then
rising up again. When one arm ceases its motion, the same is performed
by another; thus by the perpetual agitation of the several arms, such a
strong current is produced in the water, as brings the animalcula, and
other minute bodies, that are floating near the polype, into its mouth,
which is situated between the arms. The food, if agreeable to the
creature, is swallowed; if otherwise, it is rejected by a contrary
motion.

The animal may be seen very plain when it has retired within the tube.
The body is about one-eighth of an inch long, without reckoning the
plume, which is about the same length. It is cylindrical, and the skin
is very transparent. The plume is only a continuation of this
transparent skin, it is very broad in proportion to the body, and of a
remarkable figure; the base is of the shape of a horseshoe; from this
base the arms project, they bend rather outwards. The plume which they
form, gives them a resemblance to some flowers. The arms may be
compared, from their fineness and transparency, to very fine threads of
glass. The base of the plume is grooved, and is fixed to the animal by
the middle of the horseshoe which it forms, and it is here that there is
an opening which serves as a mouth to the animal. The intestines are
easily distinguished through its transparent skin; when it has just been
eating, they are of a deep brown colour. Three principal parts are very
visible, the oesophagus, the stomach, and the rectum.

In the inside of these animals a small oblong whitish body is formed,
which is carried to the outside, and remains fixed in a perpendicular
direction to the body; many of these are formed daily, and of these
oval bodies new animals are produced, exactly similar to the parent.

If these minute bodies be eggs, they are of a singular kind, being
destitute of any covering, and are neither membranaceous nor
crustaceous; we cannot with propriety say the young ones are hatched
from them; we can, however, perceive these oviform bodies to unfold
themselves gradually. The developement is accomplished in a few minutes,
and an animalculum appears like the parent.

Trembley amassed a great number of these eggs, and carried them from
England with him, keeping them quite dry; on putting them into water,
they gradually developed, and became as perfect as the tubularia from
which they proceeded.

There is a very great similarity in the construction of this little
creature and many of the marine polypes, who, like it, exist in tubes of
the same growth with themselves.

Fig. 32 represents three tubulariæ campanulatæ or plumed polypes very
much magnified, namely, one, b f a c d d e h g i, which is out of its
cell; e h, the oesophagus; f g, the stomach; a f, the rectum; a c d d e,
the plume, consisting of the base a e, which is but little seen, and the
arms c d d, which proceed from the edges of this base; a second polype,
_A B I_, which is within its cell, and in which the skin containing the
plume is reversed. The third polype, s t u u, is a young one exhibited
out of its cell; g o o, threads which are fixed at one end to the
intestines of the animal, by the other to the bottom of the cell, l k.



CHAP. VIII.

OF THE ANIMALCULA INFUSORIA.


Our knowledge of the microscopic world is at present very contracted,
but we know enough to give us high conceptions of its concealed wonders,
and to fill us with profound astonishment at the infinite variety of
forms that are made recipient of life. A few of the inhabitants of this
minute world have been discovered. The figure and apparent habits of
life of these, resemble so little those with which we are more
acquainted, that it is often difficult to find terms to express what is
represented to the eye.

Animalculum signifies a little animal, and therefore the term might be
applied to every animal which is considerably inferior in size to
ourselves. It has been customary, however, to distinguish by the name of
animalcula only such animals as are of a size so diminutive, that their
true figure cannot be discerned without the assistance of glasses; and
more especially it is applied to such as are altogether invisible to the
naked eye, and cannot even be perceived to exist, but by the aid of
microscopes.

By the help of magnifying glasses we are brought into a kind of new
world; and numberless animals are discovered, which, from their
minuteness, must otherwise for ever have escaped our observation: and
how many kinds of these invisibles there may be, is yet unknown; as they
are observed of all sizes, from those which are barely invisible to the
naked eye, to such as resist the action of the microscope, as the fixed
stars do that of the telescope, and with the best magnifiers hitherto
invented, appear only as so many moving points.

The smallest living creatures our instruments can shew, are those that
inhabit the waters; for, though possibly animalcula equally minute, or
perhaps more so, may fly in the air, or creep upon the earth, it is
scarce possible to obtain a view of them; whereas, water being
transparent, and confining the creatures within it, we are enabled, by
applying a drop of it to our glasses, to discover with ease a great part
of its contents, and in a space barely visible to the naked eye, often
perceive a thousand little creatures, all full of life and vigour.

By the animalcula infusoria are meant, not the larvæ of those insects
which in their first state are inhabitants of water, and afterwards
become winged insects, as the gnat, &c. Baker, and many other writers on
the subject, have often confounded these, and hence entered into a train
of reasoning contrary to fact and experience. The animalcula infusoria
take their name from their being found in all kinds either of vegetable
or animal infusions; if seeds, herbs, or other vegetable substances, be
infused in water, it will soon be filled with an indefinite number of
these minute beings. There is a prodigious variety in their forms; some
perfectly resemble the bell-polype; others are round or oblong, without
any, at least apparent, members; some resemble a bulb with a long taper
tail; some are nearly spherical; the greater part are vesicular and
transparent. Those most generally found in every drop of ditch water are
mere inflated bladders, with a small trace of intestines in the center;
the next are a flat kind, with a number of legs under the belly.

Motion seems to be their great delight; they pervade with equal ease and
rapidity, and in all forms and directions, the whole dimensions of the
drop, in which they find ample space for their various progressions,
sometimes darting straight forward, at other times moving obliquely,
then again circularly: they know how to avoid with dexterity any
obstacles that might obstruct their progress. Hundreds may be seen in a
drop of water in constant action, yet never striking against each other.
If at any time the clusters prove so thick as to impede any of their
motions, they roll and tumble themselves over head, creep under the
whole range, force their way through the midst, or wheel round the
cluster, with surprizing swiftness; sometimes they will suddenly change
the direction in which they are moving, and take one diametrically
opposite thereto. By inclining the glass on which the drop of water is
laid, it may be made to move in any direction; the animalcula in the
drop will swim as easily against the stream as with it.

If the water begin to evaporate, and the drop to grow smaller, they
flock impetuously towards the remaining part of the fluid; an anxious
desire of attaining this momentary respite of life is very visible, as
well as an uncommon agitation of the organs by which they imbibe the
water. These motions grow more languid as the water fails, till at last
they entirely cease.

Animalcula and insects will support a great degree of cold, but both one
and the other perish when it is carried beyond a certain point. The same
degree of heat that destroys the existence of insects, is fatal to
animalcula; as there are animalcula produced in water at the freezing
point, so there are insects which live in snow.

If the smallest drop of urine be put into a drop of water where these
animalcula are roving about, apparently happy and easy, they instantly
fly to the other side, but the acid soon communicating itself to this
part, their struggles to escape are increased, but the evil also
increasing, they are thrown into convulsions, and soon expire.

Among animalcula, as in every other part of nature, there is constantly
a certain proportion preserved between the size of the individuals and
their number. There are always fewest amongst the larger kinds, but they
increase in number as they diminish in size, till of the last, or lowest
to which our powers of magnifying will reach, there are myriads to one
of the larger. Like other animals, they increase in size from their
birth till they have attained their full growth. When deprived of food,
they grow thin and perish; and different degrees of organization are to
be discovered in their structure.

The birth and propagation of these microscopic beings is as regular as
that of the largest animals of our globe; for though their extreme
minuteness prevents us, in most cases, from seeing the germ from which
they spring, yet we are well assured, from numerous observations, that
the manner in which they multiply is regulated by constant and
invariable laws.

It has been shewn that different species of the hydræ and vorticellæ
multiply and increase by natural divisions and subdivisions of the
parent’s body; this manner of propagation is very common among the
animalcula in infusions, though with many remarkable varieties. Some
multiply by a transverse division, a contraction takes place in the
middle, forming a kind of neck that becomes smaller every instant, till
they are enabled by a slight degree of motion to separate from each
other. These animalcula in general studiously avoid each other; but when
they are in the labour of multiplication, and the division is in great
forwardness, it is not uncommon to see one of them precipitate itself on
the neck of the dividing animalculum, and thus accelerate the
separation.

Another species, when it is on the point of multiplying, fixes itself to
the bottom of the infusion; it then forms an oblong figure, afterwards
becomes round, and begins to turn rapidly, as if upon an internal
center, continually changing the direction of its rotatory motion; after
some time, we may perceive two lines on the spherule, forming a kind of
cross; soon after which the animalculum divides into four distinct
beings, which grow, and are again subdivided.

Some multiply by a longitudinal division, which in one kind begins in
the fore-part, and others in the hind-part; from another kind a small
fragment is seen to detach itself, which very soon acquires the form of
the parent animalculum. Lastly, some propagate in the same manner as
those we deem more perfect animals.

From what has been said, it appears clearly that their motions are not
purely mechanical, but are produced by an internal spontaneous
principle, and that they must therefore be placed among the class of
living animals, for they possess the strongest marks, and the most
decided characters of animation; and consequently, that there is no
foundation for the supposition of a chaotic and neutral kingdom, which
can only have derived its origin from a very transient and superficial
view of these animalcula.

It may also be further observed, that as we see the motions of the
limbs, &c. of the more noble animals, viz. the human species, are
produced by the mechanical construction of the body and the action of
the soul thereon, and are forced by the ocular demonstration arising
from anatomical dissection, to acknowledge this mechanism which is
adapted to produce the various motions necessary to the animal; and as
when we have recourse to the microscope, we find those pieces which had
appeared to the naked eye as the primary mechanical causes of the
particular motions, to consist themselves of lesser parts, which are the
causes of motion, extension, &c. in the larger; when the structure can
therefore be traced no further by the eye or glasses, we have no right
to conclude, that the parts which are invisible, are not equally the
subject of mechanism: for this would be only to assert in other words,
that a thing may exist because we see and feel it, and has no existence
when it is not the object of our senses.

The same train of reasoning may be applied to microscopic insects and
animalcula; we see them move, but because the muscles and members which
occasion these motions are invisible, shall we infer that they have not
muscles, with organs appropriated to the motion of the whole and its
parts? To say that they exist not, because we cannot perceive them,
would surely not be a rational conclusion. Our senses are indeed given
us, that we may comprehend some effects; but then we have also a mind
with reason bestowed upon us, that from the things which we do perceive
with our senses, we may deduce the nature of those causes and effects
which are imperceptible to the corporeal eye.

Messrs. Buffon, Needham, and Baron Münchhausen, have considered this
part of animated nature in so different a light from other writers, that
we cannot with propriety entirely pass them over. Needham imagined that
there was a vegetative force in every microscopical point of water, and
every visible filament of which the whole vegetable contexture consists;
that the several species of microscopic animals may subside, resolve
again into gelatinous filaments, and again give lesser animals, and so
on, till they can be no further pursued by glasses. That agreeable to
this idea, every animal or vegetable substance advances as fast as it
can in its revolution, to return by a slow descent to one common
principle, whence its atoms may return again, and ascend to a new life.
That notwithstanding this, the specific seed of one animal can never
give another of a different species, on account of the preparation it
must receive to constitute it this specific seed.

Buffon asserts, that what have been called spermatic animals, are not
creatures really possessing life, but something proper to compose a
living creature, distinguishing them by the name of organic particles,
and that the moving bodies which are to be found in the infusions either
of animal or vegetable substances, are of the same nature.

Baron Münchhausen supposed that the seeds of mushrooms were first
animals, and then vegetables; and this, because he had observed some of
the globules in the infusions of mushrooms, after moving some time, to
begin to vegetate.

It might be sufficient in the first instance to observe, that Messrs.
Needham, and Buffon, by having recourse to a vegetative force and
organic particles, to account for the existence and explain the nature
of animalcula, and the difficulties of generation, have substituted
words in the place of things; and that we are no gainers by the
substitution, unless they explain the nature of these powers. But to
this we may add, that all those who have examined the subject with
accuracy and attention, as Bonnet, De Saussure, Baker, Wrisberg,
Spalanzani, Haller, Ellis, Müller, Ledermüller, Corti, Rofredi, &c.
disagree with the foregoing gentlemen, proving that they had deceived
themselves by inaccurate experiments, and that one of them, Buffon, had
not seen the spermatic animals he supposed himself to be describing,
insomuch that Needham was at last induced to give up his favourite
hypothesis.

Though we can by no means pretend to account for the appearance of most
animalcula, yet we cannot help observing, that our ignorance of the
cause of any phænomenon is no argument against its existence. Though we
are not, for instance, able to account in a satisfactory manner for the
origin of the native Americans, yet we suppose Buffon himself would
reckon it absurd to maintain, that the Spaniards on their arrival there
found only ORGANIC PARTICLES moving about in disorder. The case is the
very same with the eels in paste, to whose animation he objects. They
are exceedingly small in comparison with us; but, with the solar
microscope, Baker has made them assume a more respectable appearance, so
as to have a diameter of an inch and an half, and a proportionable
length. They swam up and down very briskly; the motion of their
intestines was very visible; when the water dried up they died with
apparent agonies, and their mouths opened very wide. Now, were we to
find a creature of the size of this magnified eel gasping in a place
where water had lately been, we certainly should never conclude it to be
merely an ORGANIC PARTICLE, or fortuitous assemblage of them, but a
fish. Why then should we conclude otherwise with regard to the eel in
its natural state, than that it is a little fish? In reasoning on this
subject, we ought ever to remember, that however essential the
distinction of bodies into great and small may appear to us, they are
not so to the Deity, with whom, as Baker well expresses himself, “an
atom is a world, and a world but as an atom.” Were the Deity to exert
his power a little, and give a natural philosopher a view of a quantity
of paste filled with eels, from each of whose bodies the light was
reflected as in the solar microscope; our philosopher, instead of
imagining them to be mere organic particles, as the paste would appear
like a little mountain, he would probably look upon the whole as an
assemblage of serpents, and be afraid to come near them. Whenever,
therefore, we discover beings to appearance endued with a principle of
self-preservation, or whatever we make the characteristic of animals,
neither the smallness of their size, nor the impossibility of our
knowing how they came there, ought to cause us to doubt of their being
animated.

I shall here insert some extracts of the experiments made by Ellis at
the desire of Linnæus, and which are a full refutation of those made by
Needham and Münchhausen. By those he made on the infusions of mushrooms
in water, it appeared evidently that the seeds were put in motion by
minute animals, which arose on the decomposition of the mushroom; these,
by pecking at the seeds, which are little round reddish bodies, moved
them about with great agility in a variety of directions, while the
little animals themselves were scarce visible till the food they had
eaten discovered them.

The ramified filaments, and jointed or coralloid bodies, which the
microscope discovers to us on the surface of most vegetable and animal
infusions, when they become putrid, and which were supposed by Needham
to be zoophytes, were found by Ellis to be of that genus of fungi called
mucor, many of which have been figured by Michelius, and described by
Linnæus. Their vegetation is so quick, that they may be seen to grow and
seed under the eye of the observer. Other instances of similar mistakes
in Needham’s experiments may be seen in Ellis’s paper, Philos. Trans.
vol. lix. p. 138.

A species of mucor arises also from the bodies of insects putrefying in
water; this species sends forth a mass of transparent filamentous roots,
from whence arise hollow seed vessels; on the top there is a hole, from
which minute globules often issue in abundance, and with considerable
elastic force, which move about in the water. It will however be found,
with a little attention, that the water is full of very minute
animalcula, which attack these seeds, and thus prolong their motion; but
after a small space of time they rise to the surface, and remain there
without any motion; a fresh quantity rises up, and floating to the edge
of the water, remains there inactive; but no appearance can be observed
of detached and separated parts becoming what are called microscopic
animalcula. Indeed, it is surprizing that Needham should ever take the
filaments of the moistened grains for any thing else than a vegetable
production, a true species of mouldiness.

On the 25th of May, Fahrenheit’s thermometer 70°, Ellis boiled a potatoe
in the New River water, till it was reduced to a mealy consistence. He
put part of it, with an equal proportion of the boiling liquor, into a
cylindrical glass vessel, that held something less than half a wine
pint, and covered it close immediately with a glass cover. At the same
time he sliced an unboiled potatoe, and, as near as he could judge, put
the same quantity into a glass vessel of the same kind, with the same
proportion of New River water not boiled, and covering it with a glass
cover, placed both vessels close to each other. On the 26th of May,
twenty-four hours afterwards, he examined a small drop of each by the
first magnifier of Wilson’s microscope, whose focal distance is reckoned
at ¹⁄₅₀ part of an inch; and, to his amazement, they were both full of
animalcula of a linear shape, very distinguishable, moving to and fro
with great celerity; so that there appeared to be more particles of
animal than vegetable life in each drop. This experiment he repeatedly
tried, and always found it to succeed in proportion to the heat of the
circumambient air; so that even in winter, if the liquors be kept
properly warm, at least in two or three days the experiment will
succeed.

The animalcula are infinitely smaller than spermatic animals, and of a
very different shape; the truth of which every accurate observer will
soon be convinced of, whose curiosity may lead him to compare them, and
he is persuaded they will find they are no way akin. Having learnt from
M. De Saussure, of Geneva, that he found one kind of these animalcula
infusoria that increases by dividing across into nearly two equal parts,
and that the infusion was made from hemp-seed, he procured a quantity of
this seed, some of it he put into New River water, some into distilled
water, and some into very hard pump water; the result was, that in
proportion to the heat of the weather, or the warmth in which they were
kept, there was an appearance of millions of minute animalcula in all
the infusions; and some time after some oval ones made their appearance;
these were much larger than the first, which still continued. These
wriggled to and fro in an undulatory motion, turning themselves round
very quick all the time that they moved forwards.

Ellis found out by mere accident a method to make their fins appear very
distinctly, especially in the larger kind of animalcula, which are
common to most vegetable infusions, such as the terebella. This has a
longish body, with a cavity or groove at one end, like a gimblet. By
applying a small stalk of the horseshoe geranium, the geranium zonale of
Linnæus, fresh broken, to a drop of water in which these animalcula are
swimming, we shall find that they will become instantly torpid,
contracting themselves into an oblong oval shape, with their fins
extended like so many bristles all round their bodies. The fins are in
length about half the diameter of the middle of their bodies. After
lying in this state of torpitude for two or three minutes, if a drop of
clean water be applied to them, they will recover their shape, and swim
about immediately, rendering their fins again invisible. Before he
discovered this expedient, he tried to kill them by different kinds of
salts and spirits; but though they were destroyed by these means, their
fins were so contracted, that he could not distinguish them in the
least.[118]

  [118] The preceding recital of the hypothesis of Messrs. Buffon,
  Needham, and Baron Münchhausen, may appear superfluous, having been so
  ably refuted by Mr. Ellis; the consideration, however, that it may
  afford entertainment to some of my readers, and prove beneficial to
  others, by cautioning them against too precipitately adopting
  plausible suppositions, induced me to retain the account. EDIT.

It is one of the wonders of the modern philosophy to have invented means
for bringing creatures so imperceptible as the various animalcula under
our cognizance and inspection. One might well have deemed an object that
was a thousand times too little to be able to affect our sense, as
perfectly removed from human discovery; yet we have extended our sight
over animals to whom these would be mountains. The naked eye takes in
animal beings from the elephant to the mite; but below this, commences a
new order, reserved only for the microscope, which comprehends all those
from the mite, to those many millions of times smaller; and this order
cannot be said to be exhausted, if the microscope be not arrived at its
ultimate state of perfection. In reality, the greater number of
microscopic animalcula are of so small a magnitude, that through a lens,
whose focal distance is the tenth part of an inch, they only appear as
so many points; that is, their parts cannot be distinguished, so that
they appear from the vertex of that lens under an angle not exceeding
the minute of a degree. If we investigate the magnitude of such an
object, it will be found nearly equal to ³⁄₁₀₀₀₀₀ of an inch long.
Supposing, therefore, these animalcula to be of a cubic figure, that is,
of the same length, breadth, and thickness, their magnitude would be
expressed by the cube of the fraction ³⁄₁₀₀₀₀₀, that is, by the number
²⁷⁄₁₀₀₀₀₀₀₀₀₀₀₀₀₀₀₀, that is, each animalculum is equal to so many parts
of a square inch. This contemplation of animalcula has rendered the idea
of indefinitely small bodies very familiar to us; a mite was formerly
thought the limit of littleness, but we are not now surprized to be told
of animals many millions of times smaller than a mite; for, “there are
in some liquors animalcules so small, as, upon calculation, the whole
magnitude of the earth is not found large enough to be a third
proportional to these minute floating animals and the whales in the
ocean.”[119] These considerations are still further heightened, by
reflecting on the internal structure of animalcula, for each must have
all the proportion, symmetry and adjustment of that organized texture,
which is indispensably necessary for the several functions of life, and
each must be furnished with proper organs, tubes, &c. for secreting the
fluids, digesting its food, and propagating its species.[120]

  [119] Chambers’s Cyclopedia by Rees, Art. Animalcule.

  [120] Minute animals proportionably exceed the larger kinds in
  strength, activity, and vivacity. It has been already observed, p.
  212, that the spring of a flea vastly outstrips any thing animals of a
  greater magnitude are capable of; the motion of a mite is much quicker
  than that of the swiftest race-horse. M. De L’Isle, Hist. Acad.
  Scienc. 1711. p. 23, has given the computation of the velocity of a
  little creature, so small as to be scarcely visible, which he found to
  run three inches in a second; supposing now its feet to be the
  fifteenth part of a line, it must make five-hundred steps in the space
  of three inches, that is, it must shift its legs five-hundred times in
  a second, or in the time of the ordinary pulsation of an artery. The
  rapidity with which many of the water insects skim the surface of the
  fluid, and others swim in it, is astonishing, nor is the celerity of
  the various species of animalcula infusoria less deserving of
  admiration. EDIT.

Having thus given a general idea of the properties of animalcula, I now
proceed to describe the various individuals, following the arrangements
of O. F. Müller,[121] and giving the discriminating characters by which
he has distinguished them; abridging, enlarging, or altering the
descriptions, to render them in some instances more exact, in others
less tedious, and upon the whole, I hope, more interesting to the
reader.

  [121] Müller Animalcula Infusoria, Fluviatilia, et Marina.


  A
  METHODICAL DIVISION
  OF THE
  ANIMALCULA INFUSORIA.

I. THOSE THAT HAVE NO EXTERNAL ORGANS.

1. MONAS: punctiforme. A mere point.

2. PROTEUS: mutabile. Mutable, or changeable.

3. VOLVOX: sphæricum. Spherical.

4. ENCHELIS: cylindraceum. Cylindrical.

5. VIBRIO: elongatum. Long.

Membranaceous.

6. CYCLIDIUM: ovale. Oval.

7. PARAMÆCIUM: oblongum. Oblong.

8. KOLPODA: sinuatum. Crooked, or bent.

9. GONIUM: angulatum. With angles.

10. BURSARIA. Hollow like a purse.

II. THOSE THAT HAVE EXTERNAL ORGANS.

Naked, or not inclosed in a shell.

11. CERCARIA: caudatum. With a tail.

12. LEUCOPHRA: ciliatum undique. Every part ciliated.

13. TRICHODA: crinitum. Hairy.

14. KERONA: corniculatum. With horns.

15. HIMANTOPUS: cirratum. Cirrated, or curled.

16. VORTICELLA: ciliatum apice. The apex ciliated.

Covered with a shell.

17. BRACHIONUS: ciliatum apice. The apex ciliated.


I. MONAS.

Vermis inconspicuus, simplissimus, pellucidus, punctiformis. An
invisible,[122] pellucid, simple, punctiform worm.

  [122] By invisible, we only mean that they are too small to be
  discerned by the naked eye.


1. MONAS TERMO. M. gelatinosa. Gelatinous mona.

Animalcules semblable a des points. Spallanzani Opusc. Phys. I. Bullæ
continuo motu. Bonanni Obs. p. 174.

Among the various animalcula which are discovered by the microscope,
this is the most minute, and the most simple; a small jelly-like point,
eluding the powers of the compound microscope, and being but imperfectly
seen by the single; these, and some others of the mona kind, are so
delicate and slender, that it is no wonder they often escape the sight
of many who have examined infusions with attention; in a full light they
totally disappear, their thin and transparent forms blending as it were
with the water in which they swim.

Small drops of infused water are often so full of these, that it is not
easy to discover the least empty space, so that the water itself appears
changed into another substance less transparent, but consisting of
innumerable globular points, thick sown together; which, though full of
life, seem only a kind of inflated bladders. In this a motion may be
perceived, something similar to that which is observed when the sun’s
rays shine on the water, the animalcula being violently agitated, or in
a commotion like unto a hive of bees. They are very common in ditch
water, and in almost all infusions, both of animal and vegetable
substances.


2. MONAS ATOMUS. M. albida puncto, variabili instructa, Plate XXV. Fig.
1. White mona, with a variable point.

This animalculum appears as a white point, which, when it is highly
magnified, is somewhat of an egg-shape; the smaller end is generally
marked with a black point; the situation of this is sometimes varied,
and found at the other end of the animalculum: sometimes two black
points are to be seen crossing the middle of the body. It was found in
sea water that had been kept the whole winter; it was not, however, very
fetid; there were no other animalcula in the same water.


3. MONAS PUNCTUM. M. nigra. A black mona.

A very minute point, solid, opake and black, round and long. They are
dispersed in the infusion, and move with a slow wavering motion; were
found in a fetid infusion of pears.


4. MONAS OCELLUS. M. hyalina puncto centrali notata. Transparent like
talc, with a point in the middle.

The margin black, and a black point in the middle; it moves
irregularly, is found in ditches covered with conferva, and frequently
with the cyclidium milium, see No. 84.


5. MONAS LENS. M. hyalina. Transparent mona of the appearance of talc.

This is among the number of the smaller animalcula, nearly of a round
figure, and so pellucid, that it is not possible to discover the least
vestige of intestines. Though they may often be seen separate, yet they
are more generally collected together, forming a kind of vesicular or
membranaceous mass. Contrary to the custom of other animalcula, they
seek the edges of the evaporating water, the consequence of which is
almost immediate death. When the water is nearly evaporated, a few dark
shades are perceived, probably occasioned by the wrinkling of the body.
A slow tremulous motion, confined to one spot, may be perceived at
intervals; this in a little time becomes more lively, and soon pervades
the whole drop. Its motions are in general very quick: two united
together may sometimes be seen swimming among the rest; while in this
situation, they have been mistaken by some writers for a different
species, whereas it is the same generating another by division. It is to
be found in all water, though but seldom in that which is pure; they are
in great plenty in the summer in ditch water, also in infusions of
animal or vegetable substances, made either of fresh or salt water,
myriads being contained in a drop; numbers of various sizes are to be
found in the filth of the teeth.[123]

  [123] The circumstance of animalcula being found in the teeth is
  mentioned with confidence by various authors; some doubts may,
  however, still remain of the fact. Mr. Willughby detected a woman, who
  pretended to take worms out of the teeth with a quill, having forced
  the quill, from her just as she was putting it into his mouth, and
  found small worms in it; see Birch’s History of the Royal Society,
  vol. iv. p. 387. I am inclined to think that the accounts usually met
  with in authors have no better foundation. It has also repeatedly
  happened, that ingenious men, from their anxiety for discovery, have
  imagined that objects have appeared to their view, which, having
  related as facts, themselves or others have afterwards found to be
  nothing more than a deceptio visus; and thus they have been, at least
  for a time, the unintentional promulgators of error; considerable
  caution is therefore necessary on these occasions, see p. 132, 133.

  Some authors, in support of a favourite system, have made bold
  assertions on the subject of animalcula; the small-pox, the measles,
  the epilepsy, &c. have been attributed to them: Langius reduces all
  diseases in general to the same principle. A writer at Paris, who
  assumed the title of an English physician, has proceeded still
  farther; he not only accounts for all diseases, but for the operation
  of all medicines, from the hypothesis of animalcula. He has peculiar
  animals for every disorder; scorbutic animalcula, podagrical
  animalcula, variolous animalcula, &c. all at his service. Journ. des
  Scav. tom. lxxxvii. p. 535, &c.

  It is not at all surprising that the wonderful discoveries relating to
  animalcula should have been applied, however improperly, to support
  the most whimsical and chymerical systems. Most of the discoveries in
  natural philosophy have been subjected to similar abuses, and laid the
  foundation for the warm imaginations of some men to fabricate
  visionary theories; these have been of great prejudice to real
  science, the primary object and ultimate reward of which is the
  acquisition of truth. EDIT.

The animalcula of this, and the first species are so numerous as to
exceed all calculation, though they are contained in a very confined
space.


6. MONAS MICA. M. circulo notata. Mona, marked with a circle.

This lucid little point may be discovered with the third lens of the
common single microscope; when the magnifying power is increased, it
appears either of an oval or spherical figure, for it assumes each of
these at pleasure. It is transparent, and has a small ellipse inscribed
as it were within its circumference; this ellipse is moveable, being
sometimes in the middle, sometimes a little towards the fore-part, at
others, nearer the hind-part. There is a considerable variety in its
motions; it often turns round for a long time in the same place; an
appearance like two kidneys may sometimes be perceived in the middle of
the body, and the animalculum is beautifully encompassed with a kind of
halo, arising most probably from invisible and vibrating fibrillæ. They
are to be found in the purest waters.


7. MONAS TRANQUILLA. M. ovata, hyalina, margine nigro. Egg-shaped,
transparent mona, with a black margin.

These animated points seem to be nearly fixed to one spot, where they
have a fluctuating or reeling motion. They are frequently surrounded
with a halo, and differ in their figure, being sometimes rather
spherical, at others quadrangular. The black margin is not always to be
found, and sometimes one would almost be tempted to think it had a tail.
They are found in urine which has been kept for a time. The urine is
covered, after it has remained in the vessel, with a dark-coloured
pellicle or film, in which these animals live: although the urine was
preserved for several months, no new animalcula were observed therein.
It has been already shewn, that a drop of urine is in general fatal to
other animalcula, yet we find in this instance, that there are animated
beings of a peculiar kind, appropriated to, and living in it.


8. MONAS LAMELLULA. M. hyalina compressa. Flat transparent mona.

This is mostly found in salt water. It is of a whitish colour, more than
twice as long as it is broad, transparent, with a dark margin, the
motion vacillatory; it often appears as if double.


9. MONAS PULVISCULUS. M. hyalina, margini virente. Transparent mona,
with a green margin.

Little spherical pellucid grains of different sizes, the circumference
green, a green bent line passes through the middle of some, probably
indicating that they are near separating or dividing into two distinct
animalcula; sometimes three or four, at others, six, seven, or even
more, are collected together. They rove about with a wavering motion;
and are mostly found in the month of March in marshy grounds.


10. MONAS UVA. M. hyalina gregaria. Transparent gregarious mona.

It is not easy to decide on the nature of these little assemblages of
corpuscles, which sometimes consist of four, at others of five, and
frequently of many more: the corpuscles are of different sizes,
according to the number assembled in one group. When collected in a
heap, the only motion they have is a kind of revolution or rotatory one.
The smaller particles separate from the larger, often dividing into as
many portions as there are constituent particles in the group; when
separated, they revolve with incredible swiftness. To try whether this
was a group of animalcula collected together by chance, or whether this
was their natural state, the following experiment was made. A single
corpuscle was taken the moment it was separated from the heap, and
placed in a glass by itself; it soon increased in size, and when it had
attained nearly the same bulk as the group from which it was separated,
the surface began to assume a wrinkled appearance, which gradually
changed till it became exactly similar to the parent group. This
new-formed group was again decomposed, like the preceding one, and in a
little time the separated particles became as large as that from which
they proceeded. It is found in a variety of infusions.


II. PROTEUS.

Vermis inconspicuus, simplicissimus, pellucidus, mutabilis. An
invisible, very simple, pellucid worm, of a variable form.


11. PROTEUS DIFFLUENS. P. in ramulos diffluens, Plate XXV. Fig. 2 and 3.
Proteus, branching itself out in a variety of directions.

A very singular animalculum, appearing only as a grey mucous mass; it is
filled with a number of black globules of different sizes, and is
continually changing its figure. Being formed of a gelatinous pellucid
substance, the shape is easily altered, and it pushes out branches of
different lengths and breadths. The globules which are within divide and
pass immediately into the new formed parts, always following the various
changes of form in the animalcula. The changes that are observed in the
form of this little creature, do not arise from any extraneous cause,
but are entirely dependent on its internal powers. It is to be met with
but very seldom; the indefatigable Müller only saw it twice, although he
examined such an immense variety of infusions. It is to be found in
fenny situations.


12. PROTEUS TENAX. P. in spiculum diffluens, Plate XXV. Fig. 4 and 5.
Proteus, running out into a fine point.

A gelatinous pellucid body, stored with black molecules; it changes its
form like the preceding, but always in a regular order, first extending
itself out in a straight line, Fig. 5, the lower part terminating in an
acute bright point, a, without any intestines; and the globules being
all collected in the upper part, c, it next draws the pointed end up
towards the middle of the body, swelling it into a round form. The
contraction goes on for some time, after which the lower part is swelled
out as it is represented in Fig. 4, d; the point a, is afterwards
projected from this ventricose part. It passes through five different
forms before it arrives at that which is seen, at Fig. 4. It scarcely
moves from one spot, only bending about sideways. It is to be found in
river water.


III. VOLVOX.

Volvox inconspicuus, simplicissimus, pellucidus, sphæricus. An
invisible, very simple, pellucid, spherical worm.


13. VOLVOX PUNCTUM. V. sphæricus, nigricans, puncto lucido. Spherical,
of a black colour, with a lucid point.

A small globule; one hemisphere is opake and black, the other has a
pellucid crystalline appearance; a vehement motion is observable in the
dark part. It moves in a tremulous manner, and often passes through the
drop, turning round as if upon an axis. Many may be often seen joined
together in their passage through, the water; they sometimes move as in
a little whirlpool, and then separate. They are found in great numbers
on the surface of fetid sea water.


14. VOLVOX GRANULUM. V. sphæricus, viridis, peripheria hyalina.
Spherical and green, the circumference of a bright colour.

There seems to be a kind of green opake nucleus in this animalculum; the
circumference is transparent. It is to be found generally in the month
of June, in marshy places; it moves but slowly.


15. VOLVOX GLOBULUS. V. globosus; postice subobscurus. Globular volvox,
the hind-part somewhat obscure.

This globular animalculum is ten times larger than the monas lens; it
verges sometimes a little towards the oval in its form. The intestines
are just visible, and make the hinder part of the body appear opake; it
has commonly a slow fluttering kind of motion, but if it be disturbed,
the motion is more rapid. It is found in most infusions of vegetables.


16. VOLVOX PILULA. V. sphæricus, interaneis immobilibus virescentibus.
Small round volvox, with immoveable green intestines.

This is a small transparent animalculum; its intestines are immoveable,
of a green colour, and are placed near the middle of the body, the edges
often yellow; a small obtuse incision may be discovered on the edge,
which is, perhaps the mouth of the animalculum. This little creature
appears to be encompassed with a kind of halo or circle. If this be
occasioned by the vibratory motion of any fringe of hairs, they are
invisible to the eye, even when assisted by the microscope. It seems to
have a kind of rotatory motion, at one time slow, at another quick; and
is to be found in water where the lemna minor, or least ducks-meat,
grows, sometimes as late as the month of December.


17. VOLVOX GRANDINELLA. V. sphæricus, opacus, interaneis immobilibus.
Spherical and opake, with immoveable intestines.

This is much smaller than the preceding, and is marked with several
circular lines; no motion is to be perceived among the interior
molecules. It sometimes moves about in a straight line, sometimes its
course is irregular, at others it keeps in the same spot with a
tremulous motion.


18. VOLVOX SOCIALIS. V. sphæricus, moleculis crystallinis, æqualibus
distantibus. Spherical volvox, with crystalline molecules, placed at
equal distances from one another.

When very much magnified this animalculum seems to have some relation to
the vorticella socialis, as seen with the naked eye. It consists of
crystalline molecules, disposed in a sphere, and filling up the whole
circumference; they are all of an equal size. Whether they are included
in a common membrane, or whether they are united by one common stalk, as
in the vorticella socialis, has not been discovered. We are also
ignorant of the exact figure of the little particles of which it is
composed; when a very large magnifying power is used, some black points
may be discerned in the center of the crystalline molecules. The motion
is sometimes rotatory, sometimes from right to left, and the contrary.
It is found where the chara vulgaris has been kept.


19. VOLVOX SPHÆRICULA. V. sphæricus, moleculis similaribus rotundis. Pl.
XXV. Fig. 6. Spherical volvox, with round molecules.

This spherule is formed of pellucid homogeneous points of different
sizes. It moves slowly about a quarter of a circle from right to left,
and then back again from left to right.


20. VOLVOX LUNULA. V. hemisphæricus, moleculis similaribus lunatis.
Plate XXV. Fig. 7. An hemispherical volvox, with lunular molecules.

Is a small roundish transparent body, composed of innumerable molecules,
homogeneous, pellucid, and of the shape of the moon in its first
quarter, without any common margin. It is in a continual two-fold
motion; the one, of the whole mass turning slowly round; the other, of
the molecules one among the other. They are found in marshy places in
the beginning of spring.


21. VOLVOX GLOBATOR. V. sphæricus membranaceus. Spherical membranaceous
volvox.

This is a transparent globule, of a greenish colour; the fœtus is
composed of smaller greenish globules. It becomes whiter and brighter
with age, moves slowly round its axis, and may be perceived by the naked
eye. But to the microscope the superficies of this pellucid membrane
appears covered with molecules, as if it were granulated, which has
occasioned some observers to imagine it to be hairy; the round pellucid
molecules that are fixed in the center are generally largest in those
that are young. The exterior molecules may be wiped off, leaving the
membrane naked. When the young ones are of a proper size, the membrane
opens, and they pass through the fissure; after this the mother melts
away. They sometimes change their spherical figure, the superficies
being flattened in different places. Most authors speak of finding eight
lesser globules within the larger; but Müller says, that he has counted
thirty or forty of different sizes. This wonderful capsulate situation
of its progeny is well known; indeed it often exhibits itself big with
children and grand-children.

Leeuwenhoeck was the first who noticed this curious animalculum, and
depicted it; a circumstance which has not been mentioned by Baker and
other microscopic writers, who have described it. It may be found in
great plenty in stagnant waters in spring and summer, and in infusions
of hemp-seed and tremella. Baker describes it as follows: This singular
minute water animal, seen before the microscope, appears to be exactly
globular, without either head, tail, or fins. It moves in all
directions, forwards or backwards, up or down, rolling over and over
like a bowl, spinning horizontally like a top, or gliding along smoothly
without turning itself at all. Sometimes its motions are very slow, at
other times very swift; and when it pleases, it can turn round as upon
an axis very nimbly, without moving out of its place. The body is
transparent, except where the circular spots are placed, which are
probably its young. The surface of the body in some is as it were dotted
all over with little points, and in others, as if granulated like
shagreen. Baker thought also that in general it appeared as if it was
set round with short moveable hairs. By another writer they are thus
described: These animalcula are at first very small, but grow so large
as to be discerned with the naked eye; they are of a yellowish green
colour, globular figure, and in substance membranaceous and transparent.
In the midst of this substance several small globes may be perceived;
each of these are smaller animalcula, which have also their diaphanous
membrane, and contain within themselves still smaller generations, which
may be distinguished by the assistance of very powerful glasses. The
larger globules may be seen to escape from the parent, and then increase
in size, as has been already observed.


22. VOLVOX MORUM. V. membranaceus orbicularis, centro moleculis
sphæricis viridibus. Membranaceous orbicular, with spherical green
molecules in the center.

This animalculum has some resemblance to the volvox uva, but is
sufficiently distinguished by the surrounding bright orbicular membrane:
the middle part is full of clear green globules. The globules seldom
move, though a quivering motion may sometimes be perceived at the
center. It has a slow rotatory motion, and is found amongst the lemna,
in the months of October and December.


23. VOLVOX UVA. V. globosus, moleculis sphæricis virescentibus nudis.
Globular volvox, composed of green spherical globules, which are not
inclosed in a common membrane.

This animalculum seems to be a kind of medium between the volvox pilula,
No. 16, and the gonium pectorale, No. 114, being, like the one, composed
of green spherules, and in form, resembling the other. It consists of a
congeries of equal globules of a greenish colour, with a bright spot in
the middle; the whole mass is sometimes of a spherical form, sometimes
oval, without any common membrane; a kind of halo may be perceived round
it, but whether this is occasioned by the motion of any invisible hairs
has not been discovered. The mass generally moves from right to left,
and from left to right; scarce any motion can be discovered in the
globules themselves. It was found in the month of August, in water where
the lemna polyrrhiza was growing. Two masses of these globules have been
seen joined together. They contain from four to fifty of the globules,
of which a solitary one may now and then be found.


24. VOLVOX VEGETANS. V. ramulis simplicibus et dichitomis, rosula
globulari terminatis. A volvox with simple dichitomous branches,
terminating in a little bunch of globules.

It consists of a number of floccose opake branches, which are invisible
to the naked eye; at the apex of these there is a little congeries of
very minute oval pellucid corpuscles. Müller at first thought it to be a
species of microscopic and river sertularia; but afterwards he found
the bunches quitting the branches, and swimming about in the water with
a proper spontaneous motion. Many old branches were found deserted of
their globules, while the younger branches were furnished with them. It
was found in river water in November 1779 and 1780.


IV. ENCHELIS.

Vermis inconspicuus, simplicissimus, cylindraceus. An invisible, simple,
cylindric worm.


25. ENCHELIS VIRIDIS. E. subcylindrica, antice oblique truncata. Green
enchelis, of a subcylindric figure, the fore-part truncated.

This is an opake green, subcylindric animalculum, with an obtuse tail,
the fore-part terminating in an acute truncated angle; the intestines
obscure and indistinct. It is continually varying in its motion, turning
from right to left.


26. ENCHELIS PUNCTIFERA. E. viridis, subcylindracea, antice obtusa,
postice acuminata, Plate XXV. Fig. 8. Green enchelis, subcylindric, the
fore-part obtuse, the hinder part pointed.

It is an opake animalculum, of a green colour; there is a small pellucid
spot in the fore-part _a_, in which two black points may be seen; a kind
of double band, _c c_, crosses the middle of the body. The hinder part
is pellucid and pointed; an incision is discovered at the apex of the
fore-part, which seems to be the mouth. When in motion, the whole of it
appears opake and green. It is found in marshes.


27. ENCHELIS DESES. E. viridis, cylindrica, subacuminata gelatinosa.
Green, cylindrical, gelatinous, the end somewhat pointed.

The body is round, the colour a very dark green, so that it is quite
opake; the fore-part is bluntly rounded off, the hinder-part is somewhat
tapering, but finishes with a rounded end. From its opacity, no internal
parts can be discovered; there is a degree of transparency near the
ends. It is exceeding idle, moving very slowly; to be found, though
rarely, in an infusion of lemnæ.


28. ENCHELIS SIMILIS. E. obovato opaca, interaneis mobilibus. Enchelis,
of an egg-shape, opake with moveable intestines.

It is an opake body, with a pellucid margin; both extremities are
obtuse, but the upper one much more so than the under one; it is filled
with moveable spherules. Its motion is generally quick, either to the
right or the left; it is probably furnished with hairs, because, when
moving rapidly, the margin appears striated. It is found in water that
has been kept for months.


29. ENCHELIS SEROTINA. E. ovato cylindracea, interaneis immobilibus.
Enchelis partly oval, partly cylindrical, the interior parts immoveable.

An oval animalculum, round the fore-part smaller than the hind-part, the
margin of a black colour; it is replete with grey vesicular molecules,
and moves slowly.


30. ENCHELIS NEBULOSA. E. ovato-cylindracea, interaneis manifestis
mobilibus. Oval and cylindric enchelis, with visible moveable
intestines.

The body is shaped like an egg, the fore-part narrow, and often filled
with opake confused intestines; in moving, it elevates the fore-part of
the body. It is found in the same water as the cyclidium glaucoma, No.
86, but is three times its size, and considerably more scarce.


31. ENCHELIS SEMINULUM. E. cylindracea æqualis. Enchelis equally
cylindric.

It is a cylindrical animalculum, twice as long as it is broad, the fore
and hind-part of the same size; the intestines in the fore-part are
pellucid, those in the hinder-part obscure. It moves by ascending and
descending alternately. It may be seen sometimes swimming about with the
extremities joined together. Found in water that has been kept for some
days.


32. ENCHELIS INTERMEDIA. E. cylindracea, hyalina, margine nigricante.
Cylindrical enchelis, transparent, with a blackish margin.

This animalculum forms an intermediate kind between the monas punctum,
the enchelis seminulum, and the cyclidium milium. It is one of the
smallest among the animalcula. The body is transparent, it has no
visible intestines, the fore and hind-part are of an equal size, the
edge of a deeper colour than the rest of the body; a point is to be seen
in the middle of some of them; in others, it is as if a line passed
through the middle.


33. ENCHELIS OVULUM. E. cylindrico-ovato hyalina. Egg-shaped transparent
enchelis.

A transparent, round, egg-shaped animalculum; nothing is discovered
withinside, even by the third magnifier; but, with an increased power,
some long foldings may be seen on the superficies, and here and there a
few bright molecules.


34. ENCHELIS PIRUM. E. inverse conica, postice hyalina. Pear-form
enchelis, the hinder-part transparent.

This enchelis is lively and pellucid, the fore-part is protuberant, and
filled with molecules, the hinder-part smaller and empty; it has
moveable molecular intestines. Its motion is rapid, passing backwards
and forwards through the diameter of the drop. When at rest, it seems to
have a little swelling, or tubercle, on the middle of the body.


35. ENCHELIS TREMULA. E. ovato-cylindracea, gelatina. Oval enchelis,
cylindrical, gelatinous.

This is also to be placed amongst the most minute animalcula; the end of
it is rather pointed, and has a tremulous motion; it almost induces one
to think it has a tail. Two of these little creatures may at times be
perceived to adhere together. It was found in an infusion with the
paramæcia aurelia, No. 93, and many other animalcula.


36. ENCHELIS CONSTRICTA. E. obovata, crystallina, medio coarctata.
Sub-oval enchelis, crystalline, with a stricture in the middle.

An animalculum of an oval shape, the middle part drawn in, as if a
string was tied round it. It is of a very small size, and is found in
salt water.


37. ENCHELIS PULVISCULUS. E. elliptica, interaneorum congerie viridi. Of
an elliptic shape, with a congeries of green intestines.

It is a round animalculum, pellucid, the fore-part obtuse, the hind-part
rather sharp, marked with green spots; myriads may sometimes be seen
wandering about in one drop; it is found among the green matter on the
sides of the vessels in which water has been kept for some time.


38. ENCHELIS FUSUS. E. cylindracea, utraque extremitate angustiore
truncata. Cylindrical enchelis, both ends truncated.

The body is round and transparent, the fore and hind-part smaller than
the rest of the body, and equally so, the ends a little truncated. In
the inside a long and somewhat winding intestine, a sky-coloured bright
fluid, and some black molecules transversely situated, may be discerned.
The motions of this animalculum are languid; it was found in pure water.


39. ENCHELIS FRITILLUS. A cylindric enchelis, the fore-part truncated.

This is one of the most transparent animalcula; the hinder-part of an
obtuse convexity, the fore-part truncated. Müller suspects that there is
a rotatory organ in the fore-part. No intestines can be seen. It runs
backwards and forwards through the drop in a diametrical line, with a
wavering motion; sometimes turns round for a moment, but presently
enters on its usual course. Is found in an infusion of grass and hay.


40. ENCHELIS CAUDATA. E. elongata, antice obtusa, postice in caudam
hyalinam attenuata, Plate XXV. Fig. 9. Enchelis with a long body, the
fore-part obtuse, the hinder-part diminishing into a kind of tail.

The body is of a grey colour, pellucid, with globular molecules divided
from each other, and dispersed through the whole body; the fore-part a,
thick and obtuse, the hind-part b, crystalline and small, the end
truncated. It is but seldom met with.


41. ENCHELIS EPISTOMIUM. E. cylindrico-elongata, apice gracili
subgloboso. Enchelis with a long cylindric body, the fore-part slender
and roundish.

It is among the smaller animalcula, the body is cylindrical and bright,
the hinder-part obtuse, the fore-part smaller, and terminating in a
globule; a black line may now and then be perceived down the middle of
it.


42. ENCHELIS GEMMATA. E. cylindracea, serie globulorum duplici, in
collum hyalinum producta. Enchelis with a cylindrical body, the upper
part prolonged into a transparent neck, a double series of globules
running down the body. Its motion is slow, and generally in a straight
line; it is found in ditch-water where the lemna thrives.


43. ENCHELIS RETROGRADA. E. hyalina, antice angustata, apice globulari.
Plate XXV. Fig. 11 and 12. Transparent enchelis, the fore-part rather
smaller, and terminating in a small globule.

It has a gelatinous transparent body; no visible intestines, though a
pellucid globule is discoverable near the hinder-part; the body is
thickest in the middle, and grows smaller towards each end. It generally
moves side-ways, sometimes in a retrograde manner; and if it be
obstructed in its motion, draws itself up, as it is represented at Fig.
11.


44. ENCHELIS FESTINANS. E. cylindrica oblonga, obtusa, antice hyalina.
Oblong cylindrical enchelis; the ends obtuse, the fore-part
transparent.

The body is round, of an equal size throughout, and both ends obtuse;
more than half the length is without any visible intestines, the lower
end full of vesicular, pellucid, minute globules; a large globular
vesicle is also to be found in the fore-part; it moves quickly from one
side to the other, in a reeling or staggering manner. It was found in
sea water.


45. ENCHELIS FARCIMEN. E. cylindracea curvata utrinque truncata. A
cylindric enchelis, crooked and truncated at both ends.

The body of this is cylindrical, about four times as long as broad,
even, truncated at both ends, the intestines opake, and not to be
distinguished from one another; it turns the extremities opposite ways,
so as to form the figure of an S. It is to be found in water that has
stood for some time, though but seldom. Joblot found it in an infusion
of corn centaury or blue-bottle; it moves in an undulatory manner, but
very slowly.


46. ENCHELIS INDEX. E. inverse conica, apicis altero angulo producto.
Enchelis in the form of an inverted cone, one edge of the apex produced
out so as to form an angle with the other part.

The body rather opake, of a grey colour, and of a long conical figure;
the lower end obtuse, the fore-part thick, one side of this part
projecting like a finger from the edge; two very small projections
proceed also sometimes from the lower end. This animalculum has the
power of retracting these projections, and making both ends appear
obtuse. It moves about but slowly, and was found in water with the lemna
minor, or least ducks-meat.


47. ENCHELIS TRUNCUS. E. cylindrica, subcapitata. Plate XXV. Fig. 10.
Cylindrical enchelis with a kind of head.

This is the largest of this kind of animalcula; the body is cylindrical,
mucose, grey, long and rather opake, the fore-part globular, the
hind-part obtuse. Something like three-teeth, c, may be sometimes seen
to proceed from one of the sides; it can alter its shape considerably.
Globules of different sizes may be seen within the body. It rolls about
slowly from right to left.


48. ENCHELIS LARVA. E. elongata, medio papillula utrinque notata. A long
enchelis, with two little nipples projecting from the middle of the
body, one on each side.

It is long, round, and filled with grey molecules; the fore-part is
obtuse and pellucid; a kind of neck or small contraction is formed at
some little distance from this end. The lower part pointed; about the
middle of the body there are two small projections.


49. ENCHELIS SPATULA. E. cylindrica striata, apice hyalino spatulata. A
cylindrical striated enchelis, the fore-part transparent, and of the
shape of a spatula.

This animalculum is perfectly cylindrical, very pellucid, of a
crystalline appearance; it is marked with very fine longitudinal
furrows, and has generally two transparent globules, one placed below
the middle, the other near the extremity of the body; on the other side
are five smaller ones, which are oval. The top is dilated, with the
corners rounded like the spatula, or instrument for spreading plaisters.
It has a wavering kind of motion, folding the spatula variously, yet
retaining its general form. Müller mentions his seeing it once draw the
spatula into the body, and keep it there for two hours, when it again
appeared.


50. EXCHELIS PUPULA. A cylindric enchelis, the fore-part papillary.

The fore-part is protuberantly round, and rather opake, the hind-part
pellucid, both extremities obtuse, furnished with a papillary
finger-shaped head, the hinder part marked with a transparent circle, or
circular aperture. The fore-part filled up with moveable molecules,
which are more scarce in the hinder-part. It has a rotatory motion on a
longitudinal axis, and moves through the water in an oblique direction.
It is to be found in dunghill water in November and December.


51. ENCHELIS PUPA. E. ventricoso cylindrica, apice in papillam producta.
Enchelis forming a kind of ventricose cylinder, with a small nipple
proceeding from the apex.

It is not unlike the preceding animalculum, but is much larger; the
anterior end not so obtuse, the nipple gradually formed from the
fore-part, all but this end is opake, and filled with obscure particles:
it has no transparent circle, as was observed in the enchelis pupula.
Its motion is exceeding slow.


V. VIBRIO.

Vermis inconspicuus, simplicissimus, teres, elongatus. An invisible
worm, very simple, round, and rather long.


52. VIBRIO LINEOLA. V. linearis minutissimus. Very small linear vibrio.

This is one of the most minute animalcula, surpassing in slenderness the
monas termo, No. 1. The greatest magnifier exhibits little more than a
tremulous motion of myriads of little oblong obscure points. In a few
days it almost fills the whole substance of the water in vegetable
infusions.


53. VIBRIO RUGULA. V. linearis flexuosus. Vibrio like a bent line.

Myriads of this species may be found; it is between the vibrio lineola,
just described, and the vibrio undula, No. 55. It appears as a little
line, which is sometimes drawn up in an undulated shape, and moves
backwards and forwards in a straight line, often without bending the
body at all.


54. VIBRIO BACILLUS. V. linearis, æqualis utrinque truncata. Linear
vibrio, equally truncated at both ends.

This is an exceeding small creature, but visible with the third lens; in
a certain position of the light, transparent. It is gelatinous, and not
half so large as the monas lens, No. 5, though six, and sometimes ten
times longer; it is everywhere of an equal size, and has no visible
intestines; its action is languid, the serpentine flexures of the body
are with great difficulty perceived. Müller made two infusions of hay in
the same water, and at the same time, in the one he put the hay whole,
in the other it was cut in small pieces; in the first there were none of
the vibrio bacillus, but many of the monas lens and kolpoda cucullus,
No. 108; in the latter, many of the vibrio bacillus, and few of the
monæ.


55. VIBRIO UNDULA. V. filiformis flexuosus. A filiform flexuous vibrio.

A perfect undulating little line, round, gelatinous, without any visible
intestines. It is never straight; when at rest it resembles the letter
V, when in motion the letter M, or a bending line like that which geese
form in their flight through the air; its motions are so rapid, that the
eye can scarce follow them. It generally rests upon the top of the
water, sometimes it fixes itself obliquely by one extremity, and whirls
itself round. This is the little creature that Leeuwenhoeck says exceeds
in slenderness the tail of the animalculum seminale, which he has
described in Fig. 5, Epis. Phys. 41, being an hundred times less than a
mustard-seed, and on which he makes the following very just observation:
That as these very small animalcula can contract and variously fold
their little tails, we must conclude that tendons and muscles are as
necessary to them as to other animals; if to these we add the organs of
sensation, and those of the intestines, the mind is lost in the
astonishment which arises from the impression of infinite, in the
indefinitely small.


56. VIBRIO SERPENS. V. filiformis, ambagibus in angulum obtusum
productis. A filiform vibrio, the windings or flexures obtuse.

A slender gelatinous little animal, in the form of a long serpentine
line, all the bendings being nearly equal in size, and at equal
distances; it generally moves in a straight line; an intestine may be
discovered down the middle. It is to be found in river water, but is not
commonly to be met with.


57. VIBRIO SPIRILLUM. V. filiformis, ambagibus in angulum acutum
tornatis. Filiform vibrio, twisted something like a spiral wire or
cork-screw, the bending acute.

It is an exceeding minute, singular creature, twisted in a spiral form;
the shape of these bendings remains the same even when the animal is in
motion, not occasioned by any internal force, but are its natural shape.
It moves generally in a straight line, vibrating the hind and
fore-parts. It was found in 1782, in an infusion of the sonchus
arvensis, or corn sow-thistle.


58. VIBRIO VERMICULUS. V. tortuosus gelatinus. This little vibrio is
twisted and gelatinous.

The body is white, or rather of a milky appearance, cylindric, long, the
apex obtuse, rather growing smaller, and twisted towards the hind-part.
Its motion is languid and undulatory, like that of the common worm; it
sometimes moves quicker, but with seeming labour. When it bends itself
alternately from one side to the other, a black long line may be
discovered, sometimes whole, sometimes broken: when at rest, it
occasionally twists into various folds. It may be observed easily with
the first lens of the single microscope, and is probably the same
animalculum mentioned by Leeuwenhoeck in all his works, as found in the
dung of frogs, and in the spawn of the male libellula. It is to be found
in marshy water in November, though but seldom.


59. VIBRIO INTESTINUM. V. gelatinosus, teres, antice angustatus. This
vibrio is gelatinous, round, the fore-part small.

It is cylindric, milk-coloured, and slender towards the top, both ends
obtuse; no traces of intestines to be discovered, though four or five
spherical eggs are perceived at the extremity of the hind-part. It can
draw the fore-part so much inwards as to give it a truncated and dilated
appearance, something like a spatula. Its motion is slow and
progressive. It is found in marshy waters.


60. VIBRIO BIPUNCTATUS. V. linearis, æqualis, utraque extremitate
truncata, globulis binis mediis. Linear vibrio, of an equal size
throughout, both ends truncated, and two small globules in the middle of
the body.

It is of a small size, and rather less than the following animalculum;
the body is of a pellucid talc-like appearance, the fore and hind-part
truncated; in the middle are two (sometimes there is only one) pellucid
globules, placed lengthwise. It most commonly moves forward in a
straight line; its movements are slow. It was found in fetid salt water.


61. VIBRIO TRIPUNCTATUS. V. linearis, utrinque attenuatus, globulis
tribus, extremis minoribus. Linear vibrio, both the ends smaller than
the middle, furnished with three globular points, the two which are at
the extremities being smaller than that at the middle.

The body is pellucid, talky, each of the ends rather tapering, furnished
with three pellucid globules, the middle one is the largest; the space
between these globules is generally filled with a green matter; in some
there is nothing of the green substance near the extremities, but only
about the middle. It seldom moves far, and then its motion is
rectilinear, backwards and forwards.


62. VIBRIO PAXILIFER. V. flavescens paleis gregariis multifariam
ordinatis. Plate XXV. Fig. 13, 14, 15. Yellow, gregarious, straw-like
vibrio.

This is a wonderful animalculum, or rather a congeries of animalcula. It
is invisible to the naked eye, and consists of a transparent membrane,
with yellow intestines, and two or three visible points; they are
generally found collected together in different parcels, from seven to
forty in number, and ranged in a variety of forms, sometimes in a
straight line, as in Fig. 14, then forming the concave Figure 13, at
others, moving in a zig-zag direction, as in Fig. 15; when at rest they
are generally in a quadrangular form, and found in great plenty with the
ulva latissima, or brown laver.

As this animalculum seems to have some affinity with the hair-like
animal of Baker, I think the reader will be better pleased to see his
description of it introduced in this place, than to have it raised into
a new and distinct species.

This little animal is extremely slender, and not uncommonly one-hundred
and fifty times longer than broad. Its resemblance to an hair induced
Baker to call it the hair-like insect. The body or middle part, which is
nearly straight, appears in some composed of such parallel rings as the
windpipe of land animals consists of, but seems in others scaled, or
rather made up of rings that obliquely cross each other. Its two ends
are bent or hooked, pretty nearly in the same degree, but in a direction
contrary each to the other; and as no eyes can be discerned, it is
difficult to judge which is the head or tail. Its progressive motion
differs from that of all animals hitherto described; for,
notwithstanding the body is composed of many rings and joints, it seems
unable to bend them, or move directly forwards; but when it is
inclinable to change its quarters, it can move from right to left, or
left to right, and proceed at the same time backwards or forwards
obliquely; and this it performs by turning upon one end as a center, and
describing with the other the quarter of a circle; then it does the same
with the other end, and so alternately; whereby its progression is in a
diagonal line, or from corner to corner. Of this any one may immediately
be satisfied, who will take the trouble of shifting the points of a
pair of compasses in that manner. All its motions are extremely slow,
and require much patience and attention in the observer. It has neither
feet, fins, nor hairs, but appears perfectly smooth and transparent,
with the head bending one way, and the tail another, so as to be like a
long Italic S; nor is any internal motion, or particularly opake part,
to be perceived, which may determine one to suppose it either the
stomach, or the intestines.

These creatures are so small, that millions of millions might be
contained in an inch square. When viewed singly, or separated from one
another, they are exceedingly transparent, and of a lovely green; but,
like all other transparent bodies, when numbers of them are brought
together they become opake, and lose their green colour in proportion as
the quantity increases, till at last they appear entirely black.

Notwithstanding the extreme minuteness of these animalcula, they seem to
be fond of society; for, on viewing for some time a parcel of them taken
up at random, they will be seen to disperse themselves in a kind of
regular order. If a multitude of them be put into a jar of water, they
will form themselves into a regular body, and ascend slowly to the top,
where, after they have remained some time exposed to the air, their
green colour changes to a beautiful sky-blue. When they are weary of
this situation, they form themselves into a kind of rope, which slowly
descends as low as they intend.

A small quantity of the substance containing these creatures having been
put into a jar of water, it so happened, that one part descended
immediately to the bottom, the other continuing to float on the surface.
After some time, each of these swarms of animalcula exhibited a
disposition to change its quarters. Both armies, therefore, set out at
the same time, the one proceeding upwards, and the other downwards; so
that after some hours journey they met in the middle. A desire of
knowing how they would conduct themselves on this occasion, engaged the
observer to watch them carefully; and to his surprize, he saw the army
that was marching upwards open to the right and left, to make room for
those that were descending. Thus without confusion or intermixture each
held on its way, the ascending army marching in two columns to the top,
and the other proceeding in one column to the bottom, as if each had
been under the direction of wise leaders.


63. VIBRIO LUNULA. V. arcuatus, utraque extremitate æquali. Plate XXV.
Fig. 16. Bow-shaped vibrio, both ends of an equal size.

The body resembles much the shape of the moon at the first quarter; it
is of a green colour, and has generally from seven to ten globules
disposed lengthwise; the smaller ones are of a very pale colour, a pale
green vacuity may sometimes be seen in the middle: some little varieties
may be observed amongst them, which are not easily to be described; it
will be enough to have given the reader their general and distinguishing
characteristics.


64. VIBRIO VERMINUS. V. linearis compressus, antice quam postice
angustior. Linear compressed vibrio, the fore-part narrower than the
hind-part.

A round transparent animalculum, or rather a long crystalline membrane,
the hind-part broader than the fore-part, the apex subtruncated, the
base obtuse, no perceptible intestines; in the middle are two spherical
vesicules, and a third towards the lower edge. It moves quickly
backwards and forwards with an undulatory motion; they seem to be
joined in a very singular manner, and were found in great plenty in salt
water that had been kept several days, till it became fetid.


65. VIBRIO MALLÆUS. V. linearis basi globuli, apice linea transversa. A
linear vibrio, with a globule at the base, and transverse line at the
apex.

This is a white pellucid animalculum, resembling the letter T, with a
globule affixed to the base. It is in motion and at rest every moment
alternately; in the former case, it resembles the letter V; in the
latter, the letter T. They are found plentifully in spring water.


66. VIBRIO ACUS. V. linearis, colli, apice obtuso, cauda setacea. Linear
vibrio, with a neck, the upper extremity obtuse, the lower one
terminating in a setaceous tail.

This vibrio is of the shape of a sewing needle; the neck round, partly
transparent, and marked in the middle with a red point; the trunk
cylindrical, the edges obscure, the middle bright, and nearly of a
triangular appearance, the tail resembling a fine bristle. A motion may
be observed in the inside of this little creature. It does not bend the
body when in motion.


67. VIBRIO SAGITTA. V. sublinearis, colli, apice truncato atro, cauda
setacea. Somewhat linear in its appearance, a well-marked neck, the apex
truncated and open, the tail setaceous.

The body is very long and flexible, broadest towards the middle, which
is also filled with grey molecules; the fore-part is drawn out into a
straight transparent neck, the upper end of it thick and black. The
motion of this animalculum seems to be produced by the contraction and
extension of the neck. It is found in salt water.


68. VIBRIO GORDIUS. V. æqualis, caudæ apice tuberculato. Vibrio of an
equal size throughout, the tail terminated by a little tubercle.

A round animalculum; the fore-part for about one-sixth of the whole
length is transparent, and furnished with a sky-coloured alimentary
tube; the lower part is bright and pointed, the middle full of small
globules; a small knob terminates the tail. Found in an infusion made
with salt water.


69. VIBRIO SERPENTULUS. V. æqualis utrinque subacuminatus. This vibrio
is of an equal size, rather pointed at both ends.

It is very similar to the vibrio anguillula, No. 71, differing
principally in the shape of the ends, which in this are furnished with a
long row of the most minute points. It does not adhere to objects by the
pointed tail. The body is of a whitish colour, frequently convoluted,
and drawn into different figures. Its motion is serpentine, sometimes to
be met with perfectly straight and still, and is found in infusions of
vegetables after some weeks standing.


70. VIBRIO COLUBER. V. filiformis, seta caudali geneculata. Filiform
vibrio, the tail setaceous, and bending up nearly to form a right angle
with the body.

In this vibrio, the mouth, the oesophagus, the molecules in the
intestines, and the twisting of them, are very conspicuous. The tail is
exceeding small, and bent so as to form a considerable angle with the
body. It is found in river water.


71. VIBRIO ANGUILLULA. V. æqualis, subrigidus. Vibrio of an equal size
throughout, and somewhat hard.

This animalculum may be divided into four varieties, if not distinct
species: namely, 1. Anguillula aceti. 2. Anguillula glutinis farinosi.
3. Anguillula aquæ dulcis; and 4. Anguillula aquæ marinæ. These
varieties I shall first describe, together with the eels in blighted
wheat, and then proceed with the rest of the vibrio.


1. ANGUILLULA ACETI, OR VINEGAR EEL.

Plate XI. Fig. 7.

Chaos redivivum, Linn. Syst. Nat. 1326.[124] Leeuwenhoeck Opera Omn. p.
3, n. 1, f, l, o. Joblot Observ. Micros. 1, p. 2, pl. 2. Hooke’s
Micrograph, p. 216, pl. 25, fig. 3. Borelli Observ. Micros. 1, p. 7.
Power’s Micros. Observ. p. 32. Adams Micrograph. Illustr. 4th edition,
p. 125, pl. 38, fig. 197, A, B, C, D. Rozier Journal Physique, Mars
1775, Janv. & Mars 1776. Spallanzani Opusc. Phys. part 1, p. 83.

  [124] Linnæus includes this and the paste eel under the same
  title:--Habitat in aceto et glutine bibliopegorum. He
  adds,--Reviviscit ex aqua per annos exsiccatum. EDIT.

This eel is both oviparous and viviparous; it is filiform, but in other
respects differs considerably from the paste eel. It is longer, not near
so large, the tail is smaller and more tapering; it moves with much
greater ease, and is more lively. In the tail of this eel we may observe
in miniature, what may be seen on a much larger scale in that of the
viper, viz. a small projection somewhat resembling a tongue, which
occasionally appears as delineated in the figure at _a b_, and at other
times adheres close to the body. An alimentary duct may be easily
discovered, but no other intestines can be discerned, without deranging
altogether the organization of the animalculum. The pungent taste of
vinegar was formerly attributed to these animalcula, an opinion which
was soon exploded.


2. ANGUILLULA GLUTINIS FARINOSI, OR PASTE EEL.

Plate XI. Fig. 6, 8, 9, and 10.

Chaos redivivum, Linn. Syst. Nat. 1326. Ledermüller Micros. Ergötzungen,
p. 33, tab. 17. Baker Micros. made easy, p. 81. Ibid. Empl. for the
Micros. p. 244, pl. 10, no. 8 and 9. Rozier Journal Physique, Mars 1775,
Mars 1776. Adams Micrograph. Illustr. 4th edition, p. 125, pl. 38, fig.
179.

The eels in paste have been more distinguished than most other
animalcula, as well on account of their many curious properties, as the
various speculations and theories to which they have given rise. Four
different species of eels may be found in paste; of the first, I shall
now give a particular description. The body is filiform or like a
thread, round, pellucid, replete with little grains in the middle, both
extremities very pellucid and empty, the fore-part a little truncated,
the hind-part terminating in a very short bristly point. It is the same
of every age and size. To be certain of procuring this species of eels,
boil some flower in water, to which you have added a few drops of
vinegar; provide an earthen pot which has an hole at the bottom, and
fill it with earth; then put the paste in a piece of coarse cloth, and
bury it in this earth; the pot is to be exposed to the sun in the
summer, or kept in a warm place in the winter; by these means in ten or
twelve days you will very seldom fail of finding a large quantity of
eels in the paste.

This eel, when at its full growth, is about one-tenth of an inch long,
and rather less than one-hundredth of an inch in diameter. Fig. 6
represents one of these eels magnified about one-hundred and twenty
times, only compressed so much between two plates, by means of an
adjusting screw, as not only to prevent it from moving, but to lengthen
and flatten it in a small degree. At the upper part there are two little
moveable pieces or nipples, _a a_, between which an empty space _b_ is
formed, that terminates in the mouth; the hinder-part is round, but
there projects from it a short setaceous tail _w_; in the young eels the
termination of the tail is not so abrupt as in the present specimen, but
it finishes by a gradual diminution. There is probably a vent near _z_,
for the passage of the excrements; because when that part has been
gently pressed, two or three jets of a very subtile substance have been
observed to issue from it. If the pressure be increased, a small bladder
will be forced out, a further compression bursts the bladder, and the
intestines are forced through the opening.

A greater degree of magnifying power is necessary to obtain an exact
idea of the viscera of these eels. Fig. 10 represents the alimentary
duct further magnified, from its origin to the belly. It is shewn here
as separated from the animal, which is easily effected; for nature,
assisted by very little art, performs the operation. The oesophagus, _b
c_; Fig. 6 and 10, at its origin _a a_, is very small, but soon grows
larger, as at _c_, and forms a kind of oblong bag, _c d_; the diameter
of this increases till it comes to _d_, where it swells out as at _d e
f_; it then grows smaller till it comes to _g_, when it again swells out
at _g k l_. The part _k l_ is the stomach. M. Becli has shewn, that the
alimentary duct of many species of worms is formed of two bags, one of
which is inclosed within the other. It is the same with this
animalculum; the little vessel _b c_, that we have called the
oesophagus, which is the origin of the bag _c d_, enters into the same
bag, and preserves its form within it till it comes to _m_, from whence
it is prolonged in the form of a black line _m n_, which passes by the
axis of the duct _e_, and apparently terminates itself at the beginning
of the abdomen _l_. To this tube, near the center of the swelling _g k
l_, are fixed two small transparent bodies; that end of these which is
connected with the tube is round, the other end is pointed; these small
pieces cannot be discerned in every position of the eel.

I shall now shew how this duct is to be forced out of the eel. The body,
when compressed, generally bursts either at the head or tail, and always
at that part which is least pressed; hence when the mass of fluids
contained in the body is forced towards the anterior part, they meet
with a resistance in passing from the abdomen to the duct already
described; the abdomen, being forced by the fluids which are made to act
against it, bursts at the upper end, and the fluids, striking against
the neck, force it, with all its contents, out of the body, through an
opening at the anterior part; on lessening the pressure, the intestine
thus discharged will float in the water between the two plates of glass.

Not to enter into a detail of those parts which have been supposed by
some writers to constitute the heart, &c. of these minute animalcula, it
will be sufficient here to describe those in which motion may be
discovered, and to leave the rest to future observations on the subject.
The parts which may be seen in motion within these minute creatures are,
1. the small tube or duct, from its origin at _m_, to the two
appendages; 2. these appendages themselves, _h_; 3. the remainder of the
tube, from the appendages to the insertion at the ventricle _k_; 4. in
the swelling _g k l_. The rest of this duct, from the beginning by the
oesophagus _b c_, to the second swelling, has no motion. There is a
variety in the motions of the first part of this duct, sometimes it
dilates and contracts, at other times it has an oscillatory motion. It
is difficult to gain a good view of the appendages; but when the
position of the little creature is favourable, they seem to have a
two-fold motion, by which the pointed ends approach to, and then
separate from, each other, and another by which they move up and down.
The part _g k l_ moves backwards and forwards alternately; the motion of
each of these parts is independent of the rest. These are the principal
parts, whose motion is connected with the life of the animal.

The other viscera that are contained in the body of the eel, and which
may be observed by the aid of the microscope, are, the vessels which
contain the food, those which are filled with a transparent substance,
and the womb or ovary. The first form the abdomen and intestines; these
are filled with a black substance, which prevents their being properly
and clearly distinguished; these vessels, in their passage through the
posterior part of the body, form an empty space, in which we may
perceive that one side of the animalculum is occupied by the ovary _q q
q_, which runs from _j_ to _u x_; it is at these two extremities of the
ovaries that the eggs begin to be formed, for the largest eggs are
always to be found in the middle, and the smallest at the ends, as may
be seen at _j f_ and _u x_.

All the eels which bear eggs have two protuberances, _y y_, formed on
the exterior part near the center of the ovary; it appears like a
transparent semicircular membrane, but is really a kind of hernia or
bag, in which one or two eggs may be sometimes seen; all the larger eels
have this appendage, which also bears the marks of having been burst.
Now, as the younger eels have not this appendage, nor any marks of a
rupture, we may reasonably conclude that it is from hence that the
little eels issue from the parent.

In the latter part of the year, and during the winter, these eels are
oviparous, and the young eels may be seen to proceed from the egg; at
other times they are viviparous; six live eels have been seen at one
time in the belly of the parent, twenty-two eggs have been counted in
the ovary. Müller suspected that there was a difference of sex in some
of these animalcula, but it was left to M. Roffredi to afford the proof,
and it was only from a variety of repeated observations that he could
allow himself to be convinced of this truth. He continued his researches
upon the same subject on other microscopic eels, and has since been able
to distinguish the sexual parts of the vinegar eels.

The second species of paste eel is oviparous. It is easily distinguished
from the first kind by being much smaller; in Fig. 8, is exhibited a
magnified view of this eel. The conformation of the alimentary duct and
the intestines are in general nearly the same, though an intelligent
observer will find out some specific differences. By the flexion of the
intestines _c c c_, a void space is left a little beyond the middle of
the body, where the ovary, _d d_, is situated. There is no exterior
protuberance near this ovary, as in the preceding one.

We meet with another eel in paste, which may with propriety be called
the common eel. It is often to be found in grains placed in the earth,
in which the germ is destroyed, in the roots and stems of farinaceous
plants, in the tremella of Adanson, and in several species of conferva,
as well as in several infusions. This eel, when at its full growth is
rather longer than the common eel of blighted wheat; one of them is
represented at Fig. 11. They are easily distinguished from the eels of
blighted wheat, because they have no ranges of globules like it, by the
two little protuberances which are near the middle of the body, and by
the regular diminution of the tail. It is oviparous.

A very small species, represented at Fig. 9, may also be found in paste;
they may be distinguished from the young eels of the larger sort by
their vivacity and slenderness.

As the eels in paste are objects which are so often exhibited in the
microscope, it will be proper, before we leave this subject, to inform
the reader how he may procure the young eels from the parent animalcula;
a discovery which was originally made by Mr. Sherwood, but more
particularly pursued and described by Baker. Take up a very small
quantity of paste where these eels abound on the point of a pin, or with
a sharpened quill; lay it on a slip of glass, and dilute it well with
water; by these means, many of them will become visible to the naked
eye; then with the nib of a pen cut to a very fine point, and shaved so
thin as to be extremely pliable, single out one of the largest eels, and
insinuate the point of the pen underneath it; remove it into a very
small drop of water, which you must have ready prepared on another slip
of glass. When thus confined, it may easily be cut asunder transversely,
by the help of a good eye and steady hand, with a lancet or sharp
penknife; or if the eye be deficient, a hand-magnifier will enable
almost any person to perform the operation. As soon as the parts are
separated, apply your object to the microscope, and if the division has
been made about the middle of the animal, several oval bodies of
different sizes will be seen to issue forth. These are young anguillulæ
of different degrees of maturity, each of which is coiled up, and
included in its proper membrane, of so exquisite a fineness, as to be
scarce discernible by the greatest magnifier while it incloses the
embryo animal. The largest and most forward break immediately through
this delicate integument, unfold themselves, and wriggle about nimbly in
the water; others get out, uncoil, and move about more slowly; and the
least mature continue entirely without motion. The uterus or vessel that
contains all these oval bodies is composed of many annula or ringlets,
not unlike the aspera arteria of land animals, and it seems to be
considerably elastic; for as soon as the operation is performed, the
oval bodies are thrust out with some degree of violence by the spring or
action of this bowel. An hundred or upwards of young ones have been seen
to issue from one single eel, whereby the prodigious increase of them
may be accounted for, as probably several such numerous generations are
produced in a short time. Hereby we also learn that these creatures are
not only like eels in shape, but are likewise viviparous, as eels are
generally supposed to be.

Few experiments are to be found more entertaining, or in which there is
so little risk of being disappointed; for they seem, like earth-worms,
to be all prolific, and you may be sure of success, unless by accident
you cut one that has already brought forth all its young, or make your
trials when the paste has been kept a very long time, in which cases
they have been found unfruitful.


3. ANGUILLULA AQUÆ DULCIS, OR FRESH WATER EEL.

Corculum vermiculo simile, Linn. Amæn. (Mund. Invis.) Anguille Vulgaire,
Rozier Journal Physique, 1775. Mars, Nov. 1776. Ibid. Anguille du Bled
Rachitique. Ibid. Anguille du Faux Ergot. Spallanz. Opusc. Phys. part 2,
p. 354, pl. 5, fig. 10.

The body of this is exceedingly transparent, with no visible entrails,
though a few transverse lines may be discovered on the body. It is
sometimes, though rarely, furnished with a long row of little globules,
and often with two small oval ones; the tail terminates in a point.
Müller says he found these eels in the sediment which is formed by
vegetables on the sides of vessels in which water had been kept for some
time.


4. ANGUILLULA AQUÆ MARINÆ, OR SALT WATER EEL.

This, when pressed between two plates of glass, appears to be little
more than a crystalline skin, with a kind of clay-coloured intestines.
The fore-part of the body is truncated, the lower part drawn out to a
fine point, the rest of the body is of an equal size throughout. The
younger ones are filled with pellucid molecular intestines.


OF THE EELS IN BLIGHTED WHEAT.

Plate XI. Fig. 4 and 5.

These animalcula were discovered by Needham, and described by him in a
work entitled, New Microscopical Discoveries, and afterwards more fully
treated upon by Baker. They are not lodged in those blighted, grains
which are covered externally with a soot-like dust, whose inside is
often also little more than a black powder; but abundance of ears may be
observed in some fields of corn, which have grains that appear blackish,
as if scorched: these, when opened, are found to contain a soft white
substance, that when attentively examined looks like a congeries of
threads or fibres lying as close as possible to each other in a parallel
direction, and much resembling the unripe down of some thistles. This
fibrous matter does not discover any signs of life or motion, unless
water be applied to it; the fibres then separate, and prove themselves
to be living creatures.

These eels are in general of a large size, and may be seen with a common
magnifying glass, being about one-thirtieth of an inch in length, and
one-hundred and fortieth broad. Fig. 5 represents one of them magnified
about one-hundred and twenty times; they are in general of a bright
chesnut colour, the extremity _a b_ is whiter and more transparent than
the rest of the body. The end _a_ is rather round, the end _c_ is
pointed. A distinguishing mark of these little creatures is a row of
transparent globules, which are placed at intervals through the whole
length of the body, beginning at _b_, where the transparency of the
fore-part ceases, and going on towards the extremity _c_. They are in
diameter rather less than one-third of the body. Another peculiar mark
is a small lunular space _d_, near the middle of the body. This part is
transparent, and is free from the coloured matter of the intestines;
there is a neck in the intestines near this space, which confines them
to one part of the body.

Great care should be taken by the observer, not to burst the skin of the
eels in disengaging them from the grain, for they never break or burst
of themselves; but if broke, visible intestines, filled with a black
matter, rush out of the body, from which little black globules are
disengaged; if the observation be made immediately after these globules
proceed from the eel, they swim slowly about the water, though divested
of any principle of internal motion; but if the eels that are broke be
left long in the water, the same phænomena will take place, as in other
animal and vegetable infusions. The want of due attention to these
circumstances has been productive of many of the fanciful positions of
Needham, which were deduced from ill-conducted experiments; and,
consequently, when properly examined, are found to be in a great measure
false.

M. Roffredi sowed some of the grains of this wheat, which sprang up; but
the ear was either wholly or in a great measure spoiled, being filled
with these eels. He also found them in other parts of the plant; in
order to disengage them, the plant must be soaked in water, and then
compressed a little. At first sight these eels seem to resemble the
foregoing, but a more accurate inspection shews that they have neither
the same curious disposition of the internal globules, nor the
transparent place in the middle of the body. The intestinal bag leaves
indeed in these an empty space, but it is of an undetermined form. The
animalcula from the plant are much more lively than those which are
procured from the dried grains.

The principal phænomena in this kind of blighted wheat is probably owing
to these animalcula, who prevent the regular circulation of the sap.
They increase in size in a certain proportion to the plant, so that at
last they may be observed with great ease by the naked eye, being
two-tenths of an inch long, and nearly one-tenth in diameter. Fig. 4
represents one of these magnified nearly in the same proportion as Fig.
5; _a a a a_, the ovary, which may be traced almost from the lower
extremity to the middle of the body, where the body becomes so opake as
to prevent its being seen any further. The eggs, when arrived at their
full growth, are nearly of a cylindric shape, both ends rounded; towards
the extremity _b_ there are two little protuberances _d d_, through
which the eggs are most probably extruded; these protuberances are not
always visible. The eggs are formed of a fine transparent membrane; it
covers the young eel, which is folded curiously therein; these eggs may
be frequently found in the plant.

A most satisfactory view of these eels is obtained by examining them
with the solar microscope; it affords one of the most surprizing and
magnificent spectacles; two generations may be often seen, one, which
draws near the allotted period of its existence, and another which only
begins to enjoy the blessings of life: some arrived at their full
growth, and others quite small. In some we may perceive the young
animalcula in motion in the eggs, in others, no such motion can be
observed; with a variety of other circumstances too tedious to
enumerate, though they afford great pleasure to the spectator.

One of the most remarkable circumstances in these animalcula is the
faculty they have of receiving again the powers of life, after having
lost them for a considerable time; for instance, when some of these
blighted grains, that have been preserved for many years, have been
soaked in water for ten or twelve hours, living eels of this species
have been found in it; if the water evaporate, or begin to fail, they
cease to move, but, on a fresh application, will be again revived.[125]

  [125] The property of revivification is not confined to this species,
  being common to other kinds of worms, and it is not improbable that
  the hydræ may possess the same faculty. EDIT.

It may be proper to notice here, that according to the observations of
Roffredi, those eels which have done laying of eggs are incapable of
being resuscitated upon being moistened; the same seems to be also the
case with those that are very young; it is probable they must attain a
certain age and degree of strength before they are endowed with this
wonderful faculty.

In the month of August, 1743, a small parcel of blighted wheat was sent
by Mr. Needham to Martin Folkes, Esq. President of the Royal Society,
with an account of his then new discovery; which parcel the president
was pleased to give to Mr. Baker, desiring him to examine it carefully.
In order so to do, he cut open some of the grains that were become dry,
took out the fibrous matter, and applied water to it on a slip of glass,
but could discern no other motion than a separation of the fibres or
threads, which separation he imputed wholly to an elasticity in the
fibres; and perceiving no token of life, after watching them with due
care, and repeating the experiment till he was weary, an account thereof
was written to Needham, who, having by trials of his own, found out the
cause of this bad success, advised him to steep the grains before he
attempted to open them; on doing which he was very soon convinced of his
veracity, and entertained with the pleasing sight of this wonderful
phænomenon. At different times after this, Baker made experiments with
grains of the same parcel, without being once disappointed. He soaked a
couple of grains in water for the space of thirty-six hours, when,
believing them sufficiently moistened, he cut one open, and applying
some of the fibrous substance to the microscope in a drop of water, it
separated immediately, and presented multitudes of the anguillulæ
without the least motion or sign of life; but being taught by experience
that they might notwithstanding possibly revive, he left them for about
four hours, and then examining them again, found much the greatest
number moving their extremities pretty briskly, and in an hour or two
after they appeared as lively as these creatures usually are. Mr. Folkes
and some other friends were witnesses of this experiment. We find an
instance here that life may be suspended and seemingly destroyed; that
by an exhalation of the fluids necessary to a living animal, the
circulations may cease, all the organs and vessels of the body may be
shrunk up, dried, and hardened; and yet, after a long while, life may
begin anew to actuate the same body, and all the animal motions and
faculties may be restored, merely by replenishing the organs and vessels
with a fresh supply of fluid. Here is a proof that the animalcula in the
grains of blighted wheat can endure having their bodies quite dried up
for the space of four years together, without being thereby deprived of
the property of resuscitation.

It appears plainly from the foregoing experiments, that when the
blighted grains of wheat have been kept a long time, and the bodies of
these animalcula are consequently become extremely dry, the rigidity of
their minute vessels requires to be relaxed very gently, and by
exceeding slow degrees; for we find that, on the application of water
immediately to the bodies of these animalcula, when taken from the dry
grains, they do not so certainly revive, as they do if the grains
themselves be either buried in earth, or steeped in water for some time
before they are taken out: the reason of which most probably is, that
too sudden a relaxation bursts their delicate and tender organs, and
thereby renders them incapable of being any more employed to perform the
actions of life; and, indeed, there are always some dead ones amongst
the living, whose bodies appear bursten, or lacerated, as well as others
that lie extended and never come to life.

Some discretion is needful to adapt the time of continuing the grains in
water or earth to the age and dryness of them; for if they be not opened
before they have been too much or too long softened, the animalculum
will not only seem dead, but will really be so. Of the two grains
mentioned to have been four years old when put to soak, one was opened
after it had lain thirty-six hours, and the event proved as already
related; the other was suffered to lie for above a week, on opening
which, all the anguillulæ near the husk were found dead, and seemingly
in a decayed condition; but great numbers issued alive from the middle,
and moved themselves briskly. Unless the husks be opened to let these
creatures out after being steeped, they all inevitably perish; and when
taken out and preserved in water, if the husks be left with them, they
will die in a few days; but otherwise, continue alive in water for
several months together; and, should the water evaporate, may be revived
again by giving them a fresh supply.


72. VIBRIO LINTER. V. ventricoso-ovatus, collo brevissimo. Ventricose
oval vibrio, with a short neck.

This is one of the larger animalcula, of an egg-shape, pellucid,
inflated, somewhat depressed at top; the apex is prolonged into a
moveable crystalline neck, the belly is replete with pellucid molecules.
It is not very common, though occasionally to be found among the lemnæ.


73. VIBRIO UTRICULUS. V. teres, antice angustatus truncatus, postice
ventricosus. Round vibrio, the fore-part narrow and truncated, the lower
ventricose.

It does not ill resemble a bottle in shape; the belly is replete with
molecular intestines, the neck bright and clear, the top truncated; in
some a pellucid point is visible at the bottom of the belly. It is in an
unceasing, vehement, and vacillatory motion, the neck moving from one
side to the other as fast as possible.


74. VIBRIO FASCIOLA. V. antice attenuatus, medio latiusculus, postice
acutus. Vibrio with a small fore-part, the middle a little bigger, the
hind-part acute.

This is a pellucid animalculum, in the middle are the intestines in the
form of points; an alimentary pipe, which lessens gradually in size, is
also perceptible. The motion of it is quick, darting itself up and down
in the water with great velocity. It is found in water just loosened
from the frost, and seldom elsewhere.


75. VIBRIO COLYMBUS. V. crassus, postice acuminatus, collo subfalcato.
Thick vibrio, sharpened at the end, the neck a little bent.

It is larger than most of the vibrios, and not unlike a bird in shape.
The neck is round, shorter than the trunk, of an equal size throughout,
and of a bright appearance, the apex obtuse. The trunk is thick,
somewhat triangular, full of yellow molecules; the fore-part broad, the
hinder-part acute, the motion slow.


76. VIBRIO STRICTUS. V. elongatus linearis, anticem versus attenuatus,
apice obtuso. Vibrio lengthened out almost to a line, small towards the
fore-part, the apex obtuse.

The body linear, being a bright membranaceous thread, without any
flexure; the hind-part somewhat thicker, round, and filled with
molecules, excepting just at the end, where there is a small pellucid
empty space. The apex is obtuse, and rather globose; it has a power of
contracting and drawing in the filiform part.


77. VIBRIO ANAS. V. oblongus, utroque fine attenuatus, collo cauda
longiore. Oblong vibrio, both ends attenuated, the neck longer than the
tail.

The trunk is oblong, opake, and filled with molecules. Both the fore and
the hind-part is prolonged into a pellucid talky membrane, which the
animalculum has a power of retracting at pleasure. The tail is more
acute than the neck. It is most generally found in salt water; a species
of them have been found in river water, with a longer neck.


78. VIBRIO CYGNUS. V. ventricosus, collo adunco. Corpulent vibrio, with
a crooked neck.

This animalculum is little more than a most pellucid line, crooked at
top, prominent in the middle, and sharp at the end; the fore-part, or
neck, is equal in length to the rest of the body, and three times longer
than the hind-part or tail; the intermediate part swelling out, is full
of dark-coloured molecules and pellucid intestines. It is very small,
and the most slothful of all those which move and advance their necks.


79. VIBRIO ANSER. V. ellipticus, collo longo, tuberculo dorsali. Plate
XXV. Fig. 27 and 29. Elliptical vibrio, with a long neck, and a little
lump on the back.

It is between the vibrio proteus and vibrio falx, and is distinguished
by the lump _b_, Fig. 29, on the back, placed behind the neck; from this
an even long neck, _a_, proceeds. The trunk, _d_, is elliptic, round,
and without any lateral inequality; full of molecules, the hind-part,
_e_, sharp and bright, the fore-part produced into a bending neck that
is longer than the body; the apex even and whole, with blue canals
passing between the marginal edges, occupying the whole length of the
neck; in one of them a vehement descent of water to the beginning of the
trunk is perceivable. The motion of the body is slow, that of the neck
is more lively and flexuous, sometimes spiral. It is found in water
where duck-weed grows.


80. VIBRIO OLOR. V. ellipticus, collo longissimo, apice nodoso. Plate
XXV. Fig. 28. Elliptical, with a very long neck, and a knob on the apex.

The form of the body is elliptical and ventricose, the hind-part
somewhat sharp. It is membranaceous, dilatable, winding variously; the
hind-part is sometimes replete with darkish molecules. The neck, _d_, is
three or four times longer than the body, of an equal size throughout,
except a small degree of thickness at the apex, _f_, very pellucid. The
motion of its neck is very lively, that of the body slow. It is found in
water that has been kept for a long time, and which has acquired a
vegetable greenness.


81. VIBRIO FALX. V. gibbosus, postice obtusus, collo falcato. A gibbous
vibrio, the hind-part obtuse, the neck crooked.

The body is pellucid, elliptical, the fore-part lessening into a little
round bright neck, nearly of the same length as the trunk, the hind-part
obtuse. The trunk itself is rather rounding or tending to the gibbous,
and filled with very small molecules; there are also two bright
globules, one within the hind extremity, the other in the middle of the
body. The neck being immoveable, the motions of the animalculum somewhat
resemble those of a scythe.


82. VIBRIO INTERMEDIUS. V. membranaceus, antice attenuatus, postice
subacutus. Membranaceous vibrio, the fore-part small, the hinder part
somewhat acute.

It seems to be an intermediate species between the preceding vibrio and
the fasciola, No. 74; it is a thin membrane, constantly folded. The
whole of it has a crystalline talky appearance, the middle replete with
grey particles of different sizes; it has all round a distinct bright
margin; the apex of the neck is truncated, the tail obtuse.


VI. CYCLIDIUM.

Vermis inconspicuus, simplicissimus, pellucidus, complanatus,
orbicularis vel ovatus. A simple, invisible, flat, pellucid, orbicular
or oval worm.


83. CYCLIDIUM BULLA. C. orbiculare hyalinum. Orbicular bright cyclidium.

A very pellucid white animalculum, or orbicular skin, the edges a little
darker than the rest. By the assistance of the compound microscope, some
globular intestines of a very crystalline appearance are just
perceptible. Its motion is slow and semicircular. It is found
occasionally in an infusion of hay.


84. CYCLIDIUM MILIUM. C. ellipticum crystallinum. Elliptic and
crystalline cyclidium.

It is very pellucid, of a crystalline splendour, membranaceous and
elliptical; a line may be perceived through the whole length of it, a
point in the fore-part, the hinder-part getting darker. Its motion is
swift, fluttering, and interrupted; probably both extremities are
ciliated.


85. CYCLIDIUM FLUITANS. C. ovale crystallinum. Oval crystalline
cyclidium.

This is one of the smallest animalcula. The body of an oval, or rather
suborbicular shape, depressed, crystalline; two small blue spaces may
be discovered by the assistance of the microscope at the sides of this
little creature.


86. CYCLIDIUM GLAUCOMA. C. ovatum, interaneis ægre conspicuis. Oval
cyclidium, the intestines perceived with difficulty.

A pellucid oval body, with both ends plain, or an oval membrane, with a
distinct well-defined edge; the intestines are so transparent that they
can scarce be discerned, when it is empty; when full, they are of a
green colour, and there are dark globules discoverable in the middle.

In plenty of water it moves swiftly in a circular and diagonal
direction; whenever it moves slowly it seems to be taking in water, the
intestines are then also in a violent commotion. Two of the smaller ones
may often be perceived cohering to each other, and drawing one another
by turns; nor are they separated by death, for they remain united even
when the water is evaporated. Those who are not familiar with these
kinds of observations, may easily mistake the shade in a single one for
a junction of two, or the junction of two for a copulation, for they
generate by division.


87. CYCLIDIUM NIGRICANS. C. oblongiusculum, margine nigricans. Oblong
cyclidium, with a black margin.

It is very small, pellucid, and flat. With a small magnifier, it may be
mistaken for an enchelis.


88. CYCLIDIUM ROSTRATIUM. C. ovale, antice mucronatum. An oval
cyclidium, the fore-part pointed.

This is an oval, smooth, and very pellucid animalculum, with the
fore-part running out into an obtuse point; with this it seems to feel
and examine the bodies which it approaches. It is probably ciliated,
though the hairs have not been discovered.

The intestines are filled with a blue liquor, forming in a tube, which,
from the aperture to the middle of the body, is divided into two legs or
branches; beyond the middle there are two little transverse blue lines.
This colour sometimes vanishes, and then they seem to be composed of
vesicles.


89. CYCLIDIUM NUCLEUS. C. ovale, postice acuminatum. An oval cyclidium,
the hind-part pointed.

The body is pellucid, depressed, the fore-part obtusely convex, the
hind-part acute, the intestines vesicular, the fore and hind-part on
each side dark. It resembles a grape-seed.


90. CYCLIDIUM HYALINUM. C. ovatum, postice acutum. Oval cyclidium, the
hind-part acute.

This cyclidium is oval, flat, and bright, without any visible
intestines, the hinder-part somewhat smaller than the fore-part; it has
a tremulous kind of motion.


91. CYCLIDIUM PEDICULUS. C. ovale convexum, subtus planum. An oval
convex cyclidium, the bottom even. Trembley Polyp. 1, p. 282.

This is a gelatinous white animalculum, the bottom gibbous over the
back, the extremities depressed and truncated, with one end sometimes
apparently cloven into two; perhaps this is the aperture of the mouth.
It is scarce ever seen but on the arms and the body of the hydra
pallida, upon which it runs as if it had feet.


92. CYCLIDIUM DUBIUM. C. ovale, supra convexum, subtus cavum. Oval
cyclidium, the upper part convex, the under part concave.

This is one of the larger species, the margin is pellucid, and the inner
part contains a great number of black molecules.


VII. PARAMÆCIUM.

Vermis inconspicuus, simplex, pellucidus, membranaceus, oblongus. An
invisible, simple, membranaceous, flat, and pellucid worm.


93. PARAMÆCIUM AURELIA. VOLVOX TEREBELLA. ELLIS. P. compressum, versus
anticem plicatum, postice acutum. Compressed paramæcium, oblong, folded
towards the fore-part, the hinder-part acute.

This is rather a large animalculum, membranaceous, pellucid, and four
times longer than it is broad; the fore-part obtuse, transparent,
without intestines; the hind-part replete with molecules of various
sizes; the fold, which goes from the middle to the apex is a striking
characteristic of the species, forming a kind of triangular aperture,
and giving it somewhat the appearance of a gimblet. Its motion is
rectilinear, reeling or staggering, and generally vehement.

They are frequently found cohering lengthwise; the lateral edges of both
bodies appear bright. They may also sometimes be seen lying on one
another alternately, at others, adhering by the middle. They will live
many months in the same water without its being renewed. They are to be
found in June in ditches where there is plenty of duck-weed.


94. PARAMÆCIUM CHRYSALIS. P. cylindraceum, versus anticam plicatum,
postice obtusum. Plate XXV. Fig. 26. Cylindrical paramæcium, folded
towards the fore-part, the hinder-part obtuse.

It differs very little from the preceding, only the ends, _a b_, are
more obtuse, and the margins filled with black globules. It is an
inhabitant of salt water.


95. PARAMÆCIUM VERSUTUM. P. cylindraceum, postice incrassatum, utraque
extremitate obtusum. Cylindrical paramæcium, the lower part thick, and
both ends very obtuse.

An oblong, green, and gelatinous body, filled with molecules; the
lower-part thick, the fore-part smaller, both ends obtuse, and may be
seen to propagate by division. It is found in ditches.


96. PARAMÆCIUM OVIFERUM. P. depressum, intus bullis ovalibus. Plate XXV.
Fig. 25. Depressed paramæcium, with large oval molecules withinside.

A membranaceous, oval, oblong animalculum, grey and pellucid, having
many oval very pellucid corpuscles, _a_, dispersed about the body, and
many black grains towards _b_.


97. PARAMÆCIUM MARGINATUM. P. depressum, griseum, margine duplici. Plate
XXV. Fig. 24. Depressed paramæcium, grey, with a double margin.

This is one of the largest of the class, flat, elliptical, every part
filled with molecules, except in the lower end, _b_, where there is a
pellucid vesicle; this animalculum is surrounded by a broad double
margin; when expiring, a bright spiral intestine is observable. _a_, the
apex; _b_, the vesicle; _c_, the spiral intestine.


VIII. KOLPODA.

Vermis inconspicuus, simplicissimus, pellucidus, complanatus, sinuatus.
An invisible, very simple, pellucid, flat and crooked worm.


98. KOLPODA LAMELLA. K. elongata, membranacea, antice curvata.

This animalculum resembles a long, narrow, and pellucid membrane, the
hind-part obtuse, narrower, and curved towards the top; no intestines
discoverable, only a ridge or fold going through the middle. Its motion
is reeling or staggering, and very singular, moving to and fro on its
edge, not on the flat side, as is usual with most microscopic animals.
It is found in water, but is very seldom to be met with.


99. KOLPODA GALLINULA. K. oblonga, dorso antico membranaceo hyalino.
Oblong kolpoda, the back towards the fore-part bright and membranaceous.

The apex rather bent; the belly oval, convex and striated. It is found
in fetid salt water.


100. KOLPODA ROSTRUM. K. oblonga, antice uncinata. Oblong, the fore-part
hooked.

The fore-part is bent into a kind of hook; the hind-part is obtuse, and
everywhere filled with black molecules. One of the edges from the
fore-part to the middle, is often so blunted and dilated, that the rest
of the body appears quite smooth, and that part thick and triangular. It
has a slow and horizontal motion. It is to be found, though but seldom,
in water where the lemnæ grow.


101. KOLPODA OCHREA. K. elongata, membranacea, apice attenuato, basi in
angulum rectum producta. Long kolpoda, membranaceous, the apex
attenuated, the base bent in a right angle to the body.

A large animalculum, long, and of a singular figure, depressed,
membranaceous, flexible; one edge nearly straight, the other somewhat
bent, filled with obscure molecules, and a few little bladders dispersed
here and there; the apex bright and small, the base projecting like the
human foot from the leg.


102. KOLPODA MUCRONATA. K. membranacea dilatata, antice angustata,
altero margine incisa. Membranaceous, dilated kolpoda, the fore-part
smaller than the hind-part, with a small incision at one side.

This animalculum is a dilated bright membrane; the apex an obtuse point,
with a broad marked border running entirely round it; within the margin
it is filled with grey molecules, a fleshy disc on one side, which
terminates in a splendid little point on the other side the disc. It has
a truncated appearance.


103. KOLPODA TRIQUETRA. K. obovata depressa, altero margine retuso.
Kolpoda nearly of an egg-shape, one edge turned back.

This animalculum appears to consist of two membranes; the upper side
flattened, the lower convex; the apex is bent so as to form a kind of
shoulder. It was found in salt water.


104. KOLPODA STRIATA. K. oblonga, subarcuata depressa, candida, antice
acuminata, postice rotundata. Oblong, somewhat of a pear-shape, white,
the fore-part pointed, the hind-part round.

It is very pellucid and white, the upper part rather bent, and
terminating in a point, the lower part obtusely round; at the apex or
mouth there is a little black pellucid vesicle; when a very great
magnifying power is used, the body appears covered with long streaks;
the lower extremity is furnished, like many other animalcula, with very
small globules. It is to be found in salt water.


105. KOLPODA NUCLEUS. K. ovata, vertice acuto. Egg-shaped kolpoda, with
an acute vertex.

It is of an oval shape, the vertex pointed, of a brilliant transparency,
which renders the viscera visible; they consist of a number of round
diaphanous vesicles.


106. KOLPODA MELEAGRIS. K. mutabilis, antice uncinata, postice
complicata. Plate XXV. Fig. 22. Changeable, with the fore-part like a
hook, the hind-part folded up.

A most singular animalculum of the larger species; it has a dilated
membrane, with the finest folds, which it varies and bends in a moment;
the fore-part of the body to the middle is clear and bright, the
hind-part variously folded in transverse elevated plaits, and full of
molecules; the apex turned into a hook, the margin sinuous, and beneath
the apex denticulated with three or four teeth; but in some which are
more beautifully wrought, the edge is obtusely notched, and set with
still smaller notches; in the hind-part there are twelve or more equal
pellucid globules. It moves sometimes in a straight, at other times in a
crooked line, _a_, the hooked apex; _b_, the denticulated margin; _c_,
the series of globules; _d_, the folded part at bottom.


107. KOLPODA ASSIMILIS. K. depressa, non plicatilis apice uncinato,
margine antico ad medium, usque crenulato postice, dilatato acutiusculo.
Depressed kolpoda, the apex turned in the form of a small hook; the
margin of the fore-part notched from the top to the middle, the lower
part swells out, then diminishes again into a short point. It has an
elliptic mass in the middle, but is never folded like the preceding. It
was found on the sea coast.


108. KOLPODA CUCULLUS. K. ovata, ventricosa, infra apicem incisa. Plate
XXV. Fig. 23. Egg-shaped, ventricose, with an incision in the fore-part.

It is very pellucid, with a well-defined margin, filled with little
bright vesicles, differing in size, and of no certain number. Its figure
is commonly oval, the top bent into a kind of beak, seldom an acute one,
sometimes oblong, but most usually obtuse. Its intestines are formed of
from eight to twenty-four bright little vesicles, not conspicuous in
such as are young. Some have supposed these to be animalcula which the
kolpoda had swallowed, but Müller is of opinion that they are its
offspring. In some only one crystalline vesicle occupies the middle of
the body. It moves in general with great vivacity, and in all
directions. When this creature is near death in consequence of the
evaporation of the water, it protrudes its offspring with violence. It
is found in infusions of vegetables, and in fetid hay. In some few a
transparent membranaceous substance may be perceived projecting beyond
the beak, and resembling an exuvia; the same may also be observed in the
enchelis and vibrio: it is, therefore, possible that these animalcula
cast their skin, as is the case with many of the class of insects. _a_
shews the cap or hood, _b_ the incision.


109. KOLPODA CUCULLULUS. K. oblonga, infra apicem oblique incisa. Oblong
kolpoda, with an oblique incision a little below the apex.

A very pellucid crystalline animalculum; it is furnished with several
pellucid globules; there is a bending a little beneath the top, which in
some positions is very distinctly seen, in others not. It was observed
in an infusion of the sonchus arvensis.


110. KOLPODA CUCULLIO. K. ovalis depressa, infra apicem tantillum
sinuata. Flat oval kolpoda, with a small degree of bending beneath the
apex.

This is an oval, or rather an elliptical kolpoda, membranaceous and
bright; flat on the upper side, and convex on the under; the fore-part
is clear, and from the middle to the hinder-part it is filled with
silver-like globules. It frequently stretches out the fore-part, and
folds it in different positions.


111. KOLPODA REN. K. crassa medio sinuata. This kolpoda is thick, and
carved in the middle.

The body is yellow, thick, and rather opake; curved a little, in the
middle, so as to have the appearance of a kidney; the whole body is
filled with molecules. Its motion is quick, fluctuating, and
interrupted. When the water in which it swims is about to fail, it
assumes an oval form, is compressed, and at last bursts. It is found in
an infusion of hay, generally about thirteen hours after the infusion is
made.


112. KOLPODA PIRUM. K. convexa, ovalis, apice in rostrum producta. Plate
XXV. Fig. 20 and 21. Convex kolpoda, oval, the apex formed into a kind
of beak.

The body is uniform and transparent, without any sensible inequality;
the neck rather long and a little bent; it is of a pale colour, and
furnished with obscure little globules. It propagates by division. Fig.
20 represents this animalculum; Fig. 21, the same dividing to form
another; _a_, the fore-part; _b_, the hind-part; _c_, where it is
dividing.


113. KOLPODA CUNEUS. K. clavata, teres, apice dentata. Clavated kolpoda,
round, the apex dentated.

This is a large animalculum, the body white, gelatinous, without any
distinct viscera. It has a pellucid, bright, striated pustule on one
side of the fore-part; the apex is distinguished by three or four teeth,
the hinder-part is smaller than the fore-part, with an obtuse
termination, which it can bend into a spiral form.


IX. GONIUM.

Vermis inconspicuus, simplicissimus, complanatus, angulatus. An
invisible, simple, smooth, angular worm.


114. GONIUM PECTORALE. G. quadrangulare, pellucidum moleculis sedecim
sphæricis. Plate XXV. Fig. 17. This gonium is quadrangular, pellucid,
with sixteen spherical molecules.

These sixteen little oval bodies are nearly equal in size, of a greenish
colour, pellucid, and set in a quadrangular membrane, like the jewels in
the breast-plate of the high-priest, reflecting light on both sides. Its
animality is evinced by its spontaneous motion, advancing alternately
towards the right and left; these little bodies seem oval when in
motion, round when at rest; the four interior ones are a little larger
than the rest. It is found in pure water.


115. GONIUM PULVINATUM. G. quadrangulare, opacum pulvillis quatuor.
Quadrangular, opake, with four little pillows.

This appears like a little quadrangular membrane, plain on both sides;
with a large magnifier it looks like a bolster, formed of three or four
cylindric pillows, flattened or sunk here and there. Thus it appeared to
Müller on the first examination; some days after all the sides were
plain, without any convexity, and divided into little square spaces by
lines crossing each other. It is found upon dunghills.


116. GONIUM CORRUGATUM. G. quadrangulare, albidum, medio correptum.
Quadrangular gonium, white, sunk a little in the middle.

It is somewhat of a square shape, very minute, without any visible
viscera, a little depressed in the middle. It is found in various
infusions; in some positions it appears streaked.


117. GONIUM RECTANGULUM. G. rectangulum, dorso arcuato. This gonium is
rectangular, the hind-part arched.

This differs but little from the preceding; the angle at the base is a
right one, the larger vesicle is transparent, the rest green.


118. GONIUM TRUNCATUM. G. obtusangulum, postice arcuatum. Gonium with
obtuse corners, the hind-part arched.

Much larger than the foregoing, the fore-part is a straight line, with
which the sides form obtuse angles, the ends of the sides being united
by a curved line; the internal molecules are of a dark green, there are
two little bright vesicles in the middle; its motion is languid. It is
found chiefly in pure water, and that but seldom.


X. BURSARIA.

Vermis simplicissimus, membranaceus, cavus. A very simple, hollow,
membranaceous worm.


119. BURSARIA TRUNCATELLA. B. ventricosa, apice truncata. Ventricose
bursaria, the top truncated.

An animalculum that is visible to the naked eye, white, oval, and
truncated at the top, where there is a large aperture descending towards
the base; most of them have four or five yellow eggs at the bottom. It
moves itself at pleasure from right to left, and from left to right,
ascending to the surface of the water in a right line, and sometimes
rolling about while descending.


120. BURSARIA BULLINA. B. cymbæformis, antice labrata. Boat-shaped
bursaria, the fore-part formed into a lip.

A pellucid crystalline animalculum, furnished with splendid globules of
different sizes swimming about within it; the under-side convex, the
upper side hollow, the fore-part forming a kind of lip.


121. BURSARIA HIRUNDINELLA. B. utrinque laciniata, extremitatibus
productis. Plate XXV. Fig. 19.

Bursaria with two small projecting wings, which give it somewhat of the
appearance of a bird, and it moves something like a swallow. It is
invisible to the naked eye, but by the microscope appears to be a
pellucid hollow membrane; no intestines are visible. _a_, the head; _b_,
the tail; _c_, one of the wings.


122. BURSARIA DUPLELLA. B. elliptica, marginibus inflexis. Plate XXV.
Fig. 18. Elliptic bursaria with the edge bent in and out.

A crystalline membrane folded up, without any visible intestines, if we
except a little congeries of points under one of the folds. It was found
among duck-weed.


123. BURSARIA GLOBINA. B. sphærica, medio pellucentissima. Spherical
bursaria, very pellucid in the middle.

A subspheric hollow animalculum, the lower end furnished with black
molecules of various sizes, the fore-part with obscure points, the rest
entirely empty, and the middle very pellucid; it moves slowly from right
to left.


XI. CERCARIA.

Vermis inconspicuus, pellucidus, caudatus. An invisible pellucid worm
with a tail.


124. CERCARIA GYRINUS. C. rotundata, cauda acuminata. Round cercaria,
with a sharp tail.

It has a white gelatinous body, without any traces of intestines; the
fore-part somewhat globular, the hind-part round, long, and pointed;
sometimes it appears a little compressed on each side. When swimming,
the tail is in a continual vibration, like that of a tadpole. It seems
very similar to the spermatic animalcula.


125. CERCARIA GIBBA. C. subovata, convexa, antice subacuta, cauda
tereti. Somewhat of an oval shape, convex, the fore-part rather acute,
the tail round.

It is a small animalculum, gelatinous, white, opake, and without any
visible intestines; the upper part convex or gibbous; many of them were
found in infusions of hay, as well as of other vegetables.


126. CERCARIA INQUIETA. C. mutabilis, convexa, cauda lævi. Plate XXV.
Fig. 31 and 32. Changeable convex cercaria, with a smooth tail.

This animalculum so often changes the form of its body, that it is not
easy to describe it; it is sometimes spherical, sometimes like a long
cylinder, at other times of an oval figure, white and gelatinous; the
tail is filiform and flexible, the upper part vibrating vehemently; no
visible viscera; a pellucid globule may be observed at the base, and two
very small black points placed near the top at _d_, Fig. 32; whether
they be eyes to the animalculum is not known. It was found in salt
water. _a_, Fig. 31, the body; _b_, the tail.


127. CERCARIA LEMNA. C. mutabilis, subdepressa, cauda annulata. Plate
XXV. Fig. 33, 34, and 35. Mutable cercaria, somewhat flattened, with an
annulated tail.

This animalculum varies its form so much, that it might be mistaken for
the proteus of Baker, though, in fact, it is totally different. The body
sometimes appears of an oblong, sometimes of a triangular, and sometimes
of a kidney shape. The tail is generally short, thick, and annulated,
but sometimes long, flexible, cylindric, and without rings; vibrating,
when stretched out, with so much velocity, that it appears as it were
double. The intestines are not very distinct; a small pellucid globule,
which Müller supposes to be its mouth, is observable at the apex; and
two black points not easily discovered, he thinks are its eyes;
sometimes it draws the tail entirely into the body. It walks slowly
after taking three or four steps, and extends the tail, erecting it
perpendicularly, shaking and bending it; in which state it very much
resembles a leaf of the lemna. Fig. 33, _a_, the body rather spherical;
_b_, the tail. Fig. 34, _c_, the triangular body; _b_, the tail. Fig.
35, the body extended; _e e_, the eyes; _f f_, the intestines; _g_, a
large vesicle; _h_, a smaller one.


128. CERCARIA TURBO. C. globulosa, medio coarctata, cauda uniseta. Plate
XXV. Fig. 30. Globular cercaria, the middle contracted, with a tail like
a bristle.

Partly of an oval, and partly of a spherical shape, pellucid, and of a
talky appearance. It seems to be composed of two globular bodies, the
lowermost of which is the smallest; this figure is occasioned by the
contraction at the middle. There are two black points, like eyes, even
with a transverse line which crosses the upper part of this little
creature; several large globules may also be discerned; the tail is
sometimes quite straight, sometimes turned back on the body. It is to be
found among duck-weed.


129. CERCARIA PODURIA. C. cylindracea, postice acuminata subfissa. Plate
XXV. Fig. 36 and 37. Cylindric cercaria, the hind-part sharp and
somewhat cloven.

It resembles the young ones of the podura[126] which live among the
lemnæ, is pellucid, and appears to consist of a head, trunk, and tail;
the head resembles that of a herring; the trunk is cylindric, replete
with black spiral intestines, and appears more or less extended, at the
will of the animal; nothing is to be discovered in the hinder-part. The
tail most commonly appears to be divided into two bristles. The
intestines are in a continual motion when the body moves, and by reason
of their various shades give it a very rough appearance; some lateral
hairs or cilia are likewise to be perceived. When it moves, it revolves
at the same time as upon an axis. It is to be found in November and
December, in marshy places that are covered with the lemna. Fig. 36,
_a_, the head; _b_, the trunk; _c_, the tail; _d_, with one point; it is
seen at _e_, Fig. 37, with two points; _f_, the hairs on the side.

  [126] A genus of insects of the order of aptera. Linn. Syst. Nat. p.
  1013.


130. CERCARIA VIRIDIS. C. cylindracea mutabilis, postice accuminata
fissa. Cylindrical cercaria, mutable, the lower end sharp, and divided
into two parts.

This animalculum in some of its states considerably resembles the last,
but has a much greater power of changing its shape. It is naturally
cylindrical, the lower end sharp, and divided into two parts; but it
sometimes contracts the head and tail so as to assume a spherical
figure, at other times it projects outwards. It is found in the spring,
in ditches of standing water.


131. CERCARIA SETIFERA. C. cylindracea, antice angustior, postice
acuminata. Cylindric cercaria, the fore-part smallest, the hind-part
pointed.

This is a small cercaria, the body rather opake, and of a round figure.
The upper part is bright, and smaller than the rest; the trunk is more
opake; the tail sharp, and near it a little row of short hairs. It has a
slow rotatory motion. It is found in salt water, though but seldom.


132. CERCARIA HIRTA. C. cylindrica, antice subtruncata, postice obtusa,
bimucronata. Cylindrical cercaria, the fore-part somewhat truncated, the
lower part obtuse, finishing with two small points.

A cylindrical opake animalculum, with two small points at the lower end,
moveable, yet rigid, and placed at some distance; when in motion, the
body appears to be surrounded with rows of small hairs separated a
little from each other. It was observed in salt water.


133. CERCARIA CRUMENA. C. cylindraceo-ventricosa, antice oblique
truncata, cauda lineari bicuspidata. Cylindrical, ventricose cercaria,
the fore-part obliquely truncated, the tail linear, terminating with two
diverging points.

The body is ventricose, cylindrical, thick, and wrinkled; the lower part
small, the upper part terminates in a small, straight neck, like that of
a pitcher; the tail terminates in two diverging points.


134. CERCARIA CATELLUS. C. tripartita, cauda bisecta. Three-parted
cercaria, the tail divided into two parts.

This animalculum is more complex in its form than many others; it has a
moveable head, which is affixed to the body only by a point; an abdomen,
which is not so wide, but twice as long as the head, replete with
intestines; and a tail which is shorter than the head, narrower than the
belly, and terminating in two bristles, which it can unite and separate
at pleasure. It moves with vivacity, though without going far from its
own place.


135. CERCARIA CATELINA. C. tripartita, cauda bicuspidata. Cercaria
distinguished into three parts, with a short forked tail.

It differs from the preceding in several respects, being larger, the
body thicker, and more cylindrical; the lower part truncated, with two
short diverging points projecting from the middle. It was found in a
ditch containing plenty of duck-weed.


136. CERCARIA LUPUS. C. cylindrica, elongata, torosa cauda spinis
duabus. Plate XXV. Fig. 39. Cylindric cercaria, long, the tail furnished
with two spines.

This animalculum is larger than most of the cercarias, and in some
particulars resembles the vorticella. It is full of muscles, capable of
being contracted or extended; cylindric, composed of a head, a trunk,
and a tail; the head is larger than the body, the apex turned down into
a little hook; the tail is like the body, but narrower, terminating in
two very bright spines, which it extends in different directions;
sometimes it contracts itself into one half its common size; and again
extends itself as before. It was found in water among duck-weed. _a_ the
head, _b_ the trunk, _c_ the tail, _d d_ the spines thereof.


137. CERCARIA VERMICULARIS. C. cylindrica annulata, proboscide
exsertili, cauda spina duplici. Plate XXV. Fig. 40. Cylindrical,
annulated, with a projecting proboscis, two small spines for the tail.

It is a long, cylindrical, fleshy, mutable animalculum, divided into
eight or nine rings, or folding plaits; the apex either obtuse or
notched into two points; the hind-part rather acute, and terminating in
two pellucid thorns, between which a swelling is sometimes perceived. It
often projects a kind of cloven proboscis. It is found in water where
duck-weed grows. _d d_ the points of the fore-part, _e_ the proboscis.


138. CERCARIA FORCIPATA. C. cylindrica, rugosa, proboscide forcipata
exsertili, cauda bicuspidata.

Cylindrical cercaria, wrinkled, with a forked proboscis, which it can
extend, or retract. It is found in marshy situations.


139. CERCARIA PLEURONECTES. C. orbicularis, cauda uniseta. Orbicular,
the tail consisting of one bristle.

It is membranaceous, rather round, and white. In the fore-part are two
blackish points; the hind-part is furnished with a slender sharp tail;
it has orbicular intestines of different sizes in the middle; the
largest of them are bright. Its motion is staggering or wavering; in
swimming it keeps one edge of the lateral membrane upwards; the other
folded down. It is found in water which has been kept for several
months.


140. CERCARIA TRIPOS. C. subtriangularis, brachiis deflexis, cauda
recta. Plate XXV. Fig. 38. Cercaria somewhat of a triangular form, two
bent arms, and a straight tail.

The body is flat, pellucid, and triangular, having each angle of the
base or fore-part bent down into two linear arms; the apex of the
triangle is prolonged into a tail. It was found in salt water; _b_, the
tail; _a a_, the bent arms.


141. CERCARIA CYCLIDIUM. C. ovalis, postice subemarginata, cauda
extersili. This is oval, the hind-part somewhat notched, with a tail
that it thrusts out at pleasure.

It has an oval, smooth, membranaceous, and pellucid body, with a black
margin. The tail is not fixed to the edge, but concealed under it, and
comes out from it at every motion, but in such a manner, as to project
but little from the edge. There is also a kind of border to the
hinder-part. Its intestines are very pellucid vesicles. It is frequently
found in pure water.


142. CERCARIA TENAX. C. membranacea, antice crassiuscula, truncata,
cauda triplo breviore. Membranaceous, the fore-part rather thick,
truncated, the tail three times shorter.

It is an oval, pellucid membrane, something larger than the monas lens.
The fore-edge is thick and truncated, the hinder-part acute, and
terminating in a short tail. It whirls about in various directions with
great velocity.


143. CERCARIA DISCUS. C. orbicularis, cauda curvata. A small orbicular
animalculum, with a bent tail.


144. CERCARIA ORBIS. C. orbicularis, seta caudali duplici longissima.
Orbicular cercaria, with a tail consisting of two very long bristles.


145. CERCARIA LUNA. C. orbicularis, cauda lineari duplici brevi. This is
likewise orbicular, with two short spines for a tail; the fore-part
hollowed, so as to form a kind of crescent.


XII. LEUCOPHRA.

Vermis inconspicuus, pellucidus, undique ciliatus. An invisible worm,
pellucid, and everywhere ciliated.


146. LEUCOPHRA CONFLICTOR. L. sphærica, subopaca, interaneis mobilibus.
Spherical opake leucophra, with moveable intestines.

This animalculum, or rather a heap of animalcula, is larger than most
species of the vorticella; it is perfectly spherical, and
semi-transparent, of a yellow colour, the edges dark. It rolls at
intervals from right to left, but seldom removes from the spot where it
is first found. It is filled with a number of the most minute molecules,
which move as if they were in a violent conflict. In proportion to the
number of these little combatants, which are accumulated either on one
side or the other, the whole mass rolls either to the right or left, the
molecules going in the same direction; it is then tranquil for a short
time, but the conflict soon becomes more violent, and the sphere moves
the contrary way in a spiral line. When the water begins to fail, they
assume an oblong, oval, or cylindric figure; the hind-part of some being
compressed into a triangular shape, and the transparent part escaping as
it were from the intestines, which continue to move with the same
violence till the water wholly fails, when the molecules are spread into
a shapeless mass, which also soon vanishes, and the whole shoot into a
form, having the appearance of crystals of sal ammoniac, as figured by
Baker. Empl. for the Micros. Plate III. No. 3.


147. LEUCOPHRA MAMILLA. L. sphærica, opaca, papilla exsertili. Sphærical
opake leucophra, with a small papillary projection.

It is of a dark colour, and filled with globular molecules, the short
hairs are curved inwards; and it occasionally projects and retracts a
little white protuberance. It is not uncommon in marshy water.


148. LEUCOPHRA VIRESCENS. L. cylindracea, opaca, postice crassiore.
Cylindrical, opake, leucophra, the lower part much thicker than the
upper part.

This is a large, pear-shaped, greenish coloured animalculum, filled with
opake molecules, and covered with short hairs; generally moving in a
straight line. It is found in salt water.


149. LEUCOPHRA VIRIDIS. L. ovalis opaca. Oval, opake leucophra.

Though at first sight it may be taken for a variety of the leucophra
virescens; yet, on a further examination, it differs in many
particulars; it cannot lengthen and shorten itself as that does. It is
also much smaller. Sometimes it appears contracted in the middle, as if
it were about to be divided in two.


150. LEUCOPHRA BURSATA. L. viridis, ovalis, antice truncata. Green oval
leucophra, the fore-part truncated.

This is similar in many respects to the foregoing leucophra; it is of a
long oval shape, bulging in the middle, and filled with green
molecules; every where ciliated, except at the apex, which is truncated,
and shaped somewhat like a purse; the hairs larger, and sometimes
collected in minute fasciculi. It is to be found in salt water.


151. LEUCOPHRA POSTHUMA. L. globularis, opaca, reticulo pellucenti. This
is globular and opake, covered as it were with a pellucid net. It was
found in fetid salt water.


152. LEUCOPHRA AUREA. L. ovalis, fulva, utraque extremitate æquali
obtusus. Oval yellow leucophra, both ends of it equally obtuse.

The little hairs are discovered with difficulty; it has, in general, a
vehement rotatory motion.


153. LEUCOPHRA PERTUSA. L. ovalis, gelatinosa, apice truncato obtusa
altera latera suffossa. Oval gelatinous leucophra, the apex obtusely
truncated, one side sunk down.

Gelatinous, yellow, and small, without any molecules; the forepart is
truncated, the hind-part brought nearly to a point, with a kind of oval
hole on one side. It was found in salt water.


154. LEUCOPHRA FRACTA. L. elongata, sinuato angulata subdepressa.
Leucophra long, with sinuated angles, rather flat.

The body is white, gelatinous, and granulated; it changes its form
considerably.


155. LEUCOPHRA DILATATA. L. complanata, mutabilis, marginibus sinuatis.
Smooth changeable leucophra, with a sinuated edge.

A gelatinous membrane, with a few grey molecules in the forepart, and a
great number in the hinder-part; it is sometimes dilated into a
triangular form, with sinuated sides; at other times the shape is more
irregular and oblong.


156. LEUCOPHRA SCINTILLANS. L. ovalis, teres, opaca, viridis. Oval,
round, opake, green leucophra.

This animalculum is supposed to be ciliated, from its bright twinkling
appearance, which probably arises from the motion it gives the water; it
is nearly of an egg-shape. It was found in December among the lemna
minor.


157. LEUCOPHRA VESICULIFERA. L. ovata, interaneis vesicularibus. Plate
XXV. Fig. 41. Oval leucophra, with vesicular intestines.

An animalculum that is a kind of mean between the orbicular and oval,
very pellucid, with a defined dark edge and inside, containing some very
bright vesicles, or bladders. The middle frequently appears blue, and
the vesicles seem as if set in a ground of that colour. Müller could
never perceive any of those rays which are mentioned by Spallanzani; he
confesses, however, that he once saw an individual like this environed
with very small unequal shining rays.


158. LEUCOPHRA GLOBULIFERA. L. crystallina, ovato-oblonga. Crystalline
leucophra, of an oblong oval shape.

The body is round, very pellucid, without molecular intestines, though
at one edge it has three little pellucid globules; it is everywhere set
with short hairs. It was found in a ditch where the lemna minor grew.


159. LEUCOPHRA PUSTULATA. L. ovato oblonga, postice oblique truncata. An
oblong oval leucophra, the lower end obliquely truncated.

The body is white, gelatinous, and somewhat granulated; the lower part
truncated, as if an oblique section were made in an egg near the bottom.
It is covered with little erect shining hairs; at the lower extremities
a few bright pustules may be discovered. It is found in marshy waters.


160. LEUCOPHRA TURBINATA. L. inverse conica, subopaca. Leucophra in
shape like an inverted cone, and rather opake.

It is a round pellucid body, somewhat of the shape of an acorn, with a
pellucid globule at the lower end. It was found in fetid salt water.


161. LEUCOPHRA ACUTA. L. ovata, teres, apice acuto, mutabilis,
flaviscans. Oval leucophra, round, with the apex acute, mutable, yellow.

This is gelatinous, thick, and capable of assuming different shapes; the
apex bright, and the rest of the body filled with innumerable little
spherules; sometimes it draws itself up into an orbicular shape, at
other times one edge is sinuated. It was found in salt water.


162. LEUCOPHRA NOTATA. L. ovata, teres, puncto marginali atro. Oval
leucophra, round, with a black point at the edge.


163. LEUCOPHRA CANDIDA. L. hyalina, oblonga, altera extremitate
attenuata, curvata. Leucophra of a talky appearance, oblong, one end
smaller than the other, and bent back.

The body membranaceous, flat, very white, with no visible intestines,
except two oval bodies which are with difficulty perceptible; the whole
edge is ciliated. Found in an infusion with salt water.


164. LEUCOPHRA NODULATA. L. ovato-oblonga, depressa, serie nodulorum
duplici. An oblong oval species of leucophra, with a double row of
little nodules.


165. LEUCOPHRA SIGNATA. L. oblonga, subdepressa. Oblong, subdepressed
leucophra, with a black margin, filled with little molecular globules,
but more particularly distinguished by a curved line in the middle,
something in the shape of a long S; one end of which is at times bent
into the form of a small spiral. It is common in salt water, in the
months of November and December.


166. LEUCOPHRA TRIGONA. L. crassa, obtusa, angulata, flava. Thick,
obtuse, angular, and yellow leucophra.

A yellow, triangular mass, filled with unequal pellucid vesicles, one of
which is much larger than the rest, and the edge surrounded with short
fluctuating hairs. It was found in a marshy situation, but is not
common.


167. LEUCOPHRA FLUIDA. L. subreniformis, ventricosa. Leucophra somewhat
of a kidney shape, but ventricose.


168. LEUCOPHRA FLUXA. L. sinuata reniformis. Reniform, sinuated
leucophra.


169. LEUCOPHRA ARMILLA. L. teres annularis. Round annular leucophra.


170. LEUCOPHRA CORNUTA. L. inverse conica, viridis opaca. Plate XXV.
Fig. 42 and 43. An inverted cone, green, opake.

It bears some resemblance to the vorticella polymorpha, No. 290, and the
vorticella viridis, No. 283, and requires to be observed for some time
before its peculiar characters can be ascertained; the body is composed
of molecular vesicles, of a dark green colour; for the most part it is
like an inverted cone, the fore-part being wide and truncated, with a
little prominent horn or hook on both sides; the hind-part conical,
everywhere ciliated, the hairs exceedingly minute; those in the
fore-part are three times longer than the latter, and move in a circular
direction. The hinder-part is pellucid, and sometimes terminates in two
or three obtuse pellucid projections. The animalculum will at one moment
appear oval, at another reniform, and ciliated at the fore-part; but at
another time the hairs are concealed. When the water evaporates, it
breaks or dissolves into molecular vesicles. It is found late in the
year in marshy grounds. Fig. 42, _a_, the hinder-part pointed; _g_, the
cilia; _h h_, the sides. Fig. 43, _b_, the hinder-part obtuse; _e_, the
fore-part; _f_, the horns.


171. LEUCOPHRA HETEROCLITA. L. cylindrica, antice obtusa, postice organo
cristato duplici exsertili. Plate XXV. Fig. 44 and 45. Cylindrical
leucophra, the fore-part obtuse, the hind-part furnished with a
double-tufted organ, which it can thrust in or out at pleasure. To the
naked eye it appears like a white point; in the microscope, as a
cylindrical body, the fore-part obtusely round, the middle rather drawn
in, the lower-part round, but much smaller than the upper-part. With a
large magnifying power the whole body is found to be ciliated. The
intestines are very visible. It is represented in Fig. 44 as it
generally appears; _a_, the fore-part; _b_, the hind-part; _d_, the
hooked intestines; in Fig. 45, with the plumed organs; _i i_, the
plumes; _g g_, the sheaths from which they are projected.


XIII. TRICHODA.

Vermis inconspicuus, pellucidus, crinitus. An invisible, pellucid, hairy
worm.


172. TRICHODA GRANDINELLA. T. sphærica, pellucida, superne crinata.
Spherical, pellucid, the upper-part hairy.

A most minute pellucid globule, the intestines scarce visible, the top
of its surface furnished with several short bristles, which are not
easily distinguished, as the animalculum has a power of extending and
withdrawing them in an instant. It is found in pure water, and in
infusions of vegetables.


173. TRICHODA COMETA. T. sphærica, antice crinita, globulo appendente.
Plate XXV. Fig. 46 and 47. Spherical, the fore-part hairy, with an
appendant globule.

It is a pellucid globule, replete with bright intestines, the fore-part
furnished with hairs, the hind-part with a pellucid appendant globule.


174. TRICHODA GRANATA. T. sphærica, centro opaco peripheria crinita.
Plate XXV. Fig. 48. Spherical, with an opake center, the periphery
hairy.

It resembles the trichoda grandinella and trichoda cometa just
described. It has a darkish nucleus in the center; its intestines are
imperceptible; short hairs on the edge.


175. TRICHODA TROCHUS. T. subpiriformis, pellucida, antice utrinque
crinita. Trichoda somewhat of a pear-shape, pellucid, each side of the
fore-part distinguished by a little bunch of hairs.


176. TRICHODA GYRINUS. T. ovalis, teres, crystallina, antice crinita.
Oval, round, crystalline trichoda, the front hairy.

It is one of the smallest among the trichoda, the body smooth and free
from hairs, except at the fore-part, where there are a few. It is found
in salt water.


177. TRICHODA SOL. T. globularis, undique radiata. Plate XXV. Fig. 65
and 66. Globular trichoda, everywhere radiated.

This splendid creature constitutes a new genus, but as we know of no
more of the same kind, it is introduced here. It is a little crystalline
round corpuscle, the upper part convex; it is beset with innumerable
diverging rays, which are longer than the diameter of the body,
proceeding from every part of its surface: the inside is full of
molecules. The body contracts and dilates, but the animalculum remains
confined to the same spot. It was found with other animalcula in water
which had been kept for three weeks. It propagates by division, and is
represented as dividing in Fig. 66.


178. TRICHODA SOLARIS. T. sphæroidea, peripheria crinita. Spheroidal
trichoda, with a few hairs round the circumference.

The body is orbicular, bright, and filled with globular intestines; in
many, a moveable substance, something like the letter S, may be
discovered; it has hairs, seldom exceeding seventeen in number, which
are disposed round the circumference, each of them nearly equal in
length to the diameter of the animalculum.


179. TRICHODA BOMBA. T. mutabilis, antice pilis sparsis. Plate XXV. Fig.
67 and 68. Changeable, with a few hairs dispersed on the fore-part.

It is a thick animalculum, larger than the trichoda granata, No. 174,
and of a yellow colour; pellucid, and replete with clay-like molecules;
it is very lively, moving about with so much velocity, as to elude the
sharpest sight and most pertinacious observer, and assuming various
shapes, sometimes appearing spherical, sometimes reniform, or
kidney-shaped, sometimes as at Fig. 67.


180. TRICHODA ORBIS. T. orbicularis, antice emarginata crinita.
Orbicular, the fore-part notched and hairy.

It in some, respects resembles the former, but is larger. It is composed
of vesicular molecules; is of a spherical figure, smooth, pellucid, and
a little notched in the fore-part. The notched part is filled with long
hairs, but there are none on the rest of the body.


181. TRICHODA URNULA. T. urceolaris, antice crinita. Plate XXV. Fig. 64.
This trichoda is in the form of a water pitcher, the fore-part hairy.

A membranaceous pellucid animalculum, the hind-part obtuse, the middle
something broader, the fore-part truncated, filled with vesicular black
molecules; the hairs in the fore-part are even and short. Its motion is
slow.


182. TRICHODA DIOTA. T. urceolaris, antice angustata, ora apicis
utrinque crinita. Pitcher-shaped trichoda, the fore-part smallest; the
upper part of the mouth hairy at the edges.

The body is of a clay-colour, and filled with molecules; the upper-part
cylindrical and truncated, the lower part spherical.


183. TRICHODA HORRIDA. T. subconica antice latiuscula, truncata postice
obtusa, setis radiantibus cincta. Trichoda somewhat of a conical form,
the fore-part rather broad and truncated, the lower-part obtuse, and the
whole covered with radiating bristles.


184. TRICHODA URINARIUM. T. ovata, rostro brevissimo crinito.
Egg-shaped, with a short hairy beak.


185. TRICHODA SEMILUNA. T. Semiorbicularis, antice subtus crinita.
Semiorbicular, the fore-part hairy underneath.

A smooth pellucid animalculum, and shaped like a crescent.


186. TRICHODA TRIGONA. T. convexa, antice ciliata, postice erosa. Plate
XXV. Fig. 63. Convex, the fore-part ciliated, the hind-part as it were
gnawed off.

This is a triangular animalculum, a little convex on both sides, the
fore-part acute, the hind-part a little broader. A notch is seen at _a_,
in the hind-part; _b_, the ciliated fore-part; _c_, a tube.


187. TRICHODA TINEA. T. clavata, antice crinita, postice grossa. This is
clubbed, the fore-part hairy, the hind-part large.

This animalculum is round, not very pellucid, narrow in the fore-part,
and resembling an inverted club; it is also like some of the tinea.


188. TRICHODA NIGRA. T. ovalis compressa, antice latior crinita. Oval,
compressed trichoda, the fore-part broader and hairy.

The body is opake, when in violent motion it is black, when at rest one
side is pellucid; the middle of the fore-part is furnished with little
moveable hairs. It was found in salt water.


189. TRICHODA PUBES. T. ovato-oblonga gibba, antice depressa. Plate XXV.
Fig. 61 and 62. An egg-shaped oblong bunch, the fore-part depressed.

An animalculum with a bunch above the hind-part, marked with black
spots, depressed towards the top, a little folded, and somewhat convex
underneath; at least this is its appearance when in motion. Very minute
hairs occupy the apex, but they are seldom visible till the creature is
in the agonies of death, when it extends and moves them vehemently from
an arched chink at top, apparently endeavouring to draw in the last drop
of water. It is found in water where the duck-weed grows, chiefly in
December. _b_, the hairs; _c_, the black globules; _a_, the projecting
bunch.


190. TRICHODA FLOCCUS. T. membranacea, antice subconica, papillis tribus
crinitis. Membranaceous trichoda, the fore-part rather conical; three
small papillæ project from the base, which are set with hairs.


191. TRICHODA SINUATA. T. oblonga depressa, altero margine sinuato
crinita, postice obtusa. An oblong depressed trichoda, one margin hollow
and hairy, the lower end obtuse.

The intestines seem to be more lymphatic than molecular; it is of a
yellow colour, and the hollow edge ciliated. It was found in river
water.


192. TRICHODA PRÆCEPS. T. membranacea, sublunata, medio protuberante,
extorsum crinita. Membranaceous trichoda, somewhat lunated, protuberant
in the middle, a row of hairs on the outside.

A pellucid membrane, the fore-part formed into a kind of neck, one edge
rising into a protuberance like a hump-back, the other edge convex.


193. TRICHODA PROTEUS. T. ovalis, postice obtusa, collo elongata
retractile, apice crinito. Plate XXV. Fig. 56, 57, 58, 59, 60. Oval
trichoda, the lower-part obtuse, with a long neck, which it has a power
of contracting or extending.

Baker in his Employment for the Microscope, p. 260-266, dignifies this
animalculum with the name of proteus, on account of its assuming a great
number of different shapes, so as scarce to be known for the same animal
in its various transformations; and, indeed, unless it be carefully
watched while passing from one shape to another, it will often become
suddenly invisible.

When water, wherein any kinds of vegetables have been infused, or
animals preserved, has stood quietly for some days or weeks in a glass
or other vessel, a slimy substance will be collected about the sides,
some of which being taken up with the point of a penknife, placed on a
slip of glass in a drop of water, and viewed through the microscope,
will, be found to harbour several kinds of little animals that are
seldom seen swimming about at large. The insect we are treating of is
one of these, and was discovered in such slime-like matter taken from
the side of a glass jar, in which small fishes, water-snails, and other
creatures had been kept. Its body in substance and colour resembled that
of a snail; the shape thereof was somewhat elliptical, but pointed at
one end, whilst from the other proceeded a long, slender, and finely
proportioned neck, terminated with a head, of a size perfectly suitable
to the other parts of the animal.


194. TRICHODA VERSATILIS. T. oblonga, postice acuminata, collo
retractili, infra apicem crinito. Oblong trichoda, the hind-part acute,
with a neck that it can extend or contract at pleasure, the under-part
of the extremity of the neck hairy.

It resembles in some measure the trichoda proteus just described, but
the neck is shorter, the apex less spherical, and the hinder part of the
trunk acute. It lives in the sea.


195. TRICHODA GIBBA. T. oblonga, dorso gibbera, ventre excavata, antice
ciliata, extremitatibus obtusis. Plate XXV. Fig. 55. Oblong trichoda,
with a bunch on the back, the belly hollowed out, the fore-part
ciliated, both ends obtuse.

The body is pellucid, the upper part swelled out, within it are numerous
obscure molecules, and three large globules, the ends rather incline
downwards; when the water begins to fail, a few minute hairs may be
discovered about the head and at the abdomen; the body then becomes
striated longitudinally.


196. TRICHODA FOETA. T. oblonga, dorso protuberante, antice ciliata,
extremitatibus obtusis. Oblong trichoda, with the back protuberant, the
fore-part ciliated, both ends obtuse.

The body is round and long, and when extended somewhat resembles a
rolling-pin in shape; both ends are obtuse, and one shorter than the
other; it can draw in the ends and swell out the sides, so as to appear
almost spherical.


197. TRICHODA PATENS. T. elongata, teres, antice foveata, fovæ
marginibus ciliata. Plate XXV. Fig. 54. This trichoda is long, round, in
the fore-part it has a long hole, the edges of which are ciliated.

It is a long cylindrical animalculum, filled with molecules; the
fore-part bright and clear, with a long opening, _a_, near the top,
which tapers to a point, and is beset with hairs. It is found of
different lengths in salt water.


198. TRICHODA PATULA. T. ventricosa, subovata, antice canaliculata,
apice et caniculo crinito. Big-bellied, rather inclining towards an oval
figure, with a small tube at the fore-part, the upper-end of which is
covered with hairs.


199. TRICHODA FOVEATA. T. oblonga, latiuscula, antice corniculis
micantibus, postice mutica. Oblong trichoda, rather broad, three little
horns on the fore-part, the hinder-part beardless.


200. TRICHODA STRIATA. T. oblonga, altero margine cursum, sinuata et
ciliata, utraque extremitate obtusa. Oblong trichoda, one edge rather
curved, and also furnished with a row of hairs; both extremities
obtuse.

It is a splendid animalculum, of a fox colour, and at first sight might
be taken for a kolpoda. The body is oblong, the lower end somewhat
larger than the other, the body becoming smaller at that part where the
hairs commence; it has a set of streaks which run from one end to the
other, and at the abdomen a double row of little eggs, lying in a
transverse direction. It was found in river water in December.


201. TRICHODA UVULA. T. planiuscula elongata, æqualis, antice crinita.
Plate XXV. Fig. 53. Rather flat and long, of an equal size throughout,
the fore-part hairy.

This animalculum is six times longer than broad, round, flexuous, and of
an equal size; the greater part filled with obscure molecules; the
fore-part, _a_, rather empty, distinguished by an alimentary canal, and
lucid globules near the middle, _c_; short hairs occupy the margin of
the fore-part, some are dispersed into a chink near the canal. It is
found in an infusion of hay and other vegetables.


202. TRICHODA AURANTIA. T. subsinuata, ovata, antice patula, apice ad
medium crinita. Trichoda somewhat sinuated, oval, the fore-part broad,
the apex hairy to the middle.

It is of a gold colour, pellucid, and filled with a variety of vesicles.


203. TRICHODA IGNITA. T. ovata, apice acuminata, subtus fulcata, fulco
crinito. Oval trichoda, the apex rather acute, the under-part furrowed,
the furrows hairy.

It is of a fine purple gold colour, somewhat of a reddish cast,
pellucid, splendid, with a number of globules of different sizes; the
fore-part small, the hind-part obtuse, and having a very large opening,
which appears to run through the body.


204. TRICHODA PRISMA. T. ovata, subtus convexa, supra in carinam
compressa, antice angustior. Oval trichoda, the under part convex, the
upper part compressed into a kind of keel, the fore-part small.

It is very small, and so transparent that it cannot easily be
delineated; its form is singular, and no hairs can be observed.


205. TRICHODA FORCEPS. T. ovalis, antice forcipata, cruribus inæqualibus
crinitis. Oval trichoda, with a pair of forceps at the fore-part, with
unequal hairy legs.

A large animalculum, somewhat depressed, of a pellucid yellow colour,
and filled with molecules; in the lower part there is a black opake
globule, the fore-part is divided into long lobes, one of which is
falciform and acute, the other dilated, and obliquely truncated; both
the apex and the edge of these are furnished with hairs of different
lengths; it can open, shut, or cross these lobes at pleasure; by this
motion of them it appears to suck in the water. It was found about the
winter solstice in water, covered with lemnæ.


206. TRICHODA FORFEX. T. ventrosa, antice forcipata, postice papilla
duplici instructa. Round and prominent trichoda, the fore-part formed
into a kind of forceps, and two small protuberances.

One of the forceps of this animalculum is twice as long as the other,
hooked, and ciliated. It was found in river water.


207. TRICHODA INDEX. T. obovata, margine antico subtus crinito,
alteroque apicis in degitum producto. Obovated trichoda, the under part
of the front of the margin hairy, the apex is formed by the fore-part,
projecting like the finger on a direction-post. It was found in salt
water.


208. TRICHODA S. T. striata, antice ciliata, extremitatibus in oppositum
flexis. Striated trichoda, the fore part ciliated, the extremities bent
in opposite directions.

A yellow animalculum, formed of two pellucid membranes, striated
longitudinally; the lower end is obliquely truncated.


209. TRICHODA NAVICULA. T. triquetra, antice truncata ciliata, postice
acuta prominula. Three-cornered trichoda, the fore-part truncated and
ciliated, the hind-part acute, and bent a little upwards.

It has a crystalline appearance, rather broad, the under side towards
the hinder-part convex, the fore-part broad, the apex nearly a straight
line, the bent end pointed and turned upwards; and a kind of
longitudinal keel running down the middle.


210. TRICHODA SUCCISA. T. ovalis depressa, margine crinito, postice in
crura inæqualia erosa. Flattened oval trichoda, the edge hairy, the
hinder part hollowed out so as to form two unequal legs.


211. TRICHODA SULCATA. T. ovato-ventricosa, apice acuminata, fulco
ventrali, utrinque crinito. Ovated ventricose trichoda, the apex acute,
with a furrow at the abdomen, and both sides of it ciliated.


212. TRICHODA ANAS. T. elongata, apice colli subtus crinito. Plate XXV.
Fig. 49. Long, the apex of the neck underneath hairy.

A smooth animalculum, five times broader than it is long, filled with
darkish molecules; it has a bright neck, _b c_; under the top of the
neck at _d_ a few unequal hairs are perceptible. Its motions are
languid. It is found in pure water.


213. TRICHODA BARBATA. T. elongata, teres, subtus ab apice ad medium
crinita. Long trichoda, round, the under part from the apex to the
middle hairy.

This animalculum is round, somewhat linear, with both ends obtuse; the
fore-part narrower, forming as it were a kind of neck, under which is a
row of fluctuating hairs. The trunk is full of grey molecules.


214. TRICHODA FARCIMEN. T. elongata, torulosa, setulis cincta. Plate
XXV. Fig. 50 and 52. Long and thick trichoda, surrounded with small
bristles.

The body is long, round, pellucid, and covered with very minute hairs;
it has also a great number of mucid vesicles about the body.


215. TRICHODA CRINITA. T. elongata, teres, undique ciliata, subtus ad
medium usque crinita. Long trichoda, round, everywhere ciliated on the
upper part, and the under part likewise hairy as far as the middle.


216. TRICHODA ANGULUS. T. angulata, apice crinita. Angular, the apex
hairy.

This animalculum is long, more convex than most of the genus, divided by
a kind of articulation into two parts equal in breadth, but of different
lengths, the fore-part being shorter than the hind-part; the apex
furnished with short waving hair, indistinct molecules withinside, no
hair on the hind-part.


217. TRICHODA LINTER. T. ovato oblonga, utraque extremitate prominula.
Plate XXV. Fig. 51. The shape of an oblong egg, with prominences at both
extremities.

Both extremities of the body are raised, so that the bottom becomes
convex, and the upper part depressed like a boat. It varies in shape at
different ages, and sometimes has a rotatory motion. It is found in an
infusion of old grass.


218. TRICHODA PAXILLUS. T. linearis depressa, antice truncata
crinitaque, postice obtusa. Linear flat trichoda, the fore-part
truncated and hairy, the hinder-part obtuse.

A long animalculum, full of grey molecules; the fore-part rather smaller
than the hind-part, and furnished with minute hairs. It was found in
salt water.


219. TRICHODA VERMICULARIS. T. elongata, cylindracea, collo brevi, apice
crinito. Plate XXVII. Fig. 1. Long cylindrical trichoda, with a short
neck, the apex hairy.

Gelatinous, the fore-part pellucid, the hind-part full of molecules. It
was found in river water. It is represented in different appearances in
the figure; _a_, the neck; _b_, the hairs; _c_, a little vesicle in the
hinder-part.


220. TRICHODA MELITŒA. T. oblonga, ciliata, colli dilatabilis, apice
globoso, pilifero. Plate XXVII. Fig. 3. Oblong ciliated trichoda, with a
dilatable neck, the apex globular, and surrounded with hairs, the edge
is ciliated, and a kind of peristaltic motion perceivable in it. It is
found, in salt water, though but very rarely. _a_, the neck; _b_, the
globular apex; _c_, the body ciliated.


221. TRICHODA FIMBRIATA. T. obovata, apice crinita, postice oblique
truncata, serrata. Plate XXVII. Fig. 2. Obovated trichoda, the apex
hairy, the hinder-part obliquely truncated and serrated.


222. TRICHODA CAMELUS. T. antice crinita, crassiuscula medio utrinque
emarginata. Thick, and the fore-part hairy, with notches on the middle
and each side.

The fore-part of the body is ventricose; the back divided by an incision
in the middle into two tubercles; the lower part of the belly sinuated;
its motions are languid. It is found, though not often, in vegetable
infusions.


223. TRICHODA AUGUR. T. oblonga, vertice truncata, antico corporis
margine, superne pedata, inferne setosa. The body is oblong, depressed,
pellucid, and filled with molecules; the vertex truncated, the fore-part
forming a small beak; underneath are three feet; beyond these, towards
the hinder-part, it is furnished with bristles.


224. TRICHODA PUPA. T. cucullata, fronte crinita, cauda inflexa, This
trichoda is hooded, the front hairy, the tail inflected.

The body is rather round, pellucid and consists of three parts; the
head, which is broad, appears to be hooded, the top being furnished with
very small hairs; a transparent vesicle occupies the lower region of the
head; and over the breast from the base of the head is suspended a
production resembling the sheath of the feet in the pupa of the gnat.


225. TRICHODA LUNARIS. T. arcuata, teres, apice crinita, cirro, caudali
inflexo. Arched trichoda, round, the apex hairy, the tail bent.

This animalculum is round and crystalline; the hind-part somewhat
smaller than the fore-part; the intestines are with difficulty
distinguished. The edge of the back and the part near the tail are
bright and clear. It bends itself into the form of an arch.


226. TRICHODA BILUNIS. T. arcuata, depressa, apice crinita, cauda
biseta. Arched flattened trichoda, the apex hairy, and two little
bristles proceeding from the tail.


227. TRICHODA RATTUS. T. oblonga, carinata, antice crinita, postice seta
longissima. Plate XXVII. Fig. 4. Oblong trichoda, with a kind of keel;
the fore-part hairy, and a very long bristle proceeding from the
hinder-part. _a_, the mouth; _b_, a small knob at the bending of the
tail; _c_, the tail.


228. TRICHODA TIGRIS. T. subcylindrica, elongata, apice crinita, cauda
setis duabus longis. This trichoda is long, and somewhat cylindrical,
the apex hairy, the tail divided into two long bristles.

It resembles the former, but differs in the form of the tail, which
consists of two bristles, and likewise in having a kind of incision in
the body, at some little distance from the apex.


229. TRICHODA POCILLUM. T. oblonga, antice truncata, crinita, cauda
articulata, biseta. Plate XXVII. Fig. 5 and 6. Oblong trichoda, the
fore-part truncated and hairy, the tail articulated, and divided into
two bristles.

The body is cylindrical, pellucid, muscular, and capable of being folded
up; it appears double; the interior part is full of molecules, with an
orbicular muscular appendage which it can open and shut, and this forms
the mouth. The external part is membranaceous, pellucid, dilated, and
marked with transverse streaks; the animalculum can protrude or withdraw
the orbicular membrane at pleasure. Some have four articulations in the
tail, others five; and it has two pair of bristles, or projecting parts,
one placed at the second joint, the other at the last. It has been
frequently found in marshes. In Fig. 6 it is seen with the mouth open;
in Fig. 5, with it shut, _a a_, the jaws; _b b_, the first bristles; _c
c_, the second pair; _d_, the spine at the tail.


230. TRICHODA CLAVUS. T. antice rotundata, crinita, postice
acuminato-caudata. The fore-part round and hairy, the hind-part
furnished with a sharp tail. This animalculum has a considerable
resemblance to a common nail.


231. TRICHODA CORNUTA. T. supra convexa, subtus plana, apice crinita,
cauda lineari simplici. Trichoda with the upper part convex, the under
side plain, the apex hairy, the tail linear and simple.

To these characters we may add, that the body is membranaceous,
elliptical, closely filled with molecules; the fore-part lunated, the
hinder-part round, and terminating in a tail as long as the body.


232. TRICHODA GALLINA. T. elongata, antice sinuata, fronte crinita,
cauda pilosa. Long trichoda, the fore-part sinuated, the front hairy,
the tail formed of small hairs.

It is of a grey colour, flat, with seven large molecules and globules
within it, the front obtuse, and set with hairs; the hinder-part
terminating in a tail formed of very fine hairs. It was found in river
water.


233. TRICHODA MUSCULUS. T. ovalis, antice crinita, postice subtus
caudata. Plate XXVII. Fig. 7. Egg-shaped, the fore-part hairy, the tail
projecting from the under part.

A smooth egg-shaped animalculum, with a double margin or line drawn
underneath it; the fore-part narrow, and furnished with short hairs,
which are continually playing about; underneath the hind-part is a small
tail. It has molecular intestines, and moves slowly. It is found in
infusions of hay which have been kept for some months, _a_, the head;
_b_, the tail.


234. TRICHODA DELPHIS. T. clavata, fronte crinita, cauda acuminata,
subreflexa. Clubbed trichoda, the front hairy, the tail small and rather
bent upwards.

It is smooth and pellucid, having the fore-part dilated into a
semicircle, gradually decreasing in breadth towards the tail; the front
is hairy, the hairs standing as rays from the semicircular edge; one of
these edges is sometimes contracted. It is to be found in river water.


235. TRICHODA DELPHINUS. T. oblonga, antice crinita, postice cauda
reflexa truncata. Plate XXVII. Fig. 8. Oblong, the fore-part hairy; in
the hind-part is the tail, which is turned back, the end of it
truncated.

A pellucid, smooth, egg-shaped animalculum; the hind-part terminating in
a tail about half the length of the body, dilated at the upper end,
truncated, and always bent upwards.

In the inside are vesicles of an unequal size; it moves sometimes on its
belly, sometimes on its side; the tail seldom varies its position. It
was found in hay which had been infused for some months, _a_, the hairs
on the fore-part; _b_, the tail.


236. TRICHODA CLAVA. T. clavata, fronte crinita, cauda reflexili. Club
trichoda, the fore-part hairy, the tail turned back.

The fore-part is thick, the hind-part narrow; both extremities obtuse,
pellucid, and replete with molecules; the hind-part bent down towards
the middle.


237. TRICHODA CUNICULUS. T. oblonga, antice crinita, postice
subacuminata. Oblong, the fore-part hairy, the hind-part rather acute,
filled with molecules and black vesicles.


238. TRICHODA FELIS. T. curvata, grossa, antice angustior, postice in
caudam attenuata, subtus longitudinaliter crinita. Plate XXVII. Fig. 9.
Curved trichoda, large, the fore-part small, the hinder-part gradually
diminishing into a tail; the under part set longitudinally with hairs.
_a_, the head; _b_, the tail; _c_, the hairs.


239. TRICHODA PISCIS. T. oblongata, antice crinita, postice in caudam
exquisitam attenuata. Plate XXVII. Fig. 13 and 14. Oblong, the fore-part
is hairy, the hind-part terminating in a very slender tail. It is
smooth, pellucid, much longer than broad, but of nearly an equal breadth
throughout, and filled with yellow molecules; the fore-part obtuse, the
hind-part exquisitely slender and transparent; the upper side is convex.
_a_, the fore-part; _b_, the tail.


240. TRICHODA LARUS. T. elongata, teres, crinita, cuspidi caudali
duplici. Long, round trichoda, surrounded with hairs, the tail divided
into two points. See Zoologia Danica.


241. TRICHODA LONGICAUDA. T. cylindracea, antice truncata et crinita,
cauda elongata, biarticulata et biseta. Plate XXVII. Fig. 10.
Cylindrical trichoda, the fore-part truncated and surrounded with hairs,
the tail long, furnished with two bristles, and having two joints. _a_,
the hairs at the mouth; _d_, the oesophagus; _e_, the articulation of
the tail; _f_, the bristles.


242. TRICHODA FIXA. T. sphærica, peripheria crinita, pedicello
solitario. Spherical trichoda; this has the circumference set with
hairs, and a little solitary pedicle projecting from the body.


243. TRICHODA INQUILINUS. T. vaginata, folliculo cylindrico hyalino,
pedicello intra folliculum retortili. Sheathed trichoda, in a
cylindrical transparent bag, having a little pedicle bent back within
the bag. See Zool. Dan. prodr. addend. p. 281.


244. TRICHODA INGENITA. T. vaginata, folliculo depressa, basi latiore
sessilis. Sheathed trichoda, the bag depressed, the base broadest.

The animalculum that is contained in this sheath is funnel-shaped, with
one or more hairs, proceeding from each side of the mouth of the funnel.
It can extend or contract itself freely in the bag, fixing its tail to
the base, without touching the sides. It was found in salt water.


245. TRICHODA INNATA. T. vaginata, folliculo cylindrico, pedicello extra
folliculum. Plate XXVII. Fig. 11. Trichoda sheathed in a cylindrical
bag, with a pedicle passing through and projecting beyond it. These
characters distinguish it sufficiently from the preceding one. _b_, the
animalculum in the sheath; _d_, the tail.


246. TRICHODA TRANSFUGA. T. latiuscula, antice crinita, postice setosa,
altero latere sinuata, altero mucronata. Broad trichoda, the fore-part
hairy, the hinder-part full of bristles; one side sinuated, and the
other pointed. See Zool. Dan. prod. addend. p. 281.


247. TRICHODA CILIATA. T. ventricosa, postice crinibus pectinata.
Ventricose, the hinder-part covered with hair. See Zool. Dan. Icon. Tab.
73, Fig. 13, 15.


248. TRICHODA BULLA. T. membranacea, lateribus inflexis, antice et
postice crinita. Membranaceous trichoda, the sides bent inwards; the
fore and hind-part are both furnished with hairs.


249. TRICHODA PELLIONELLA. T. cylindracea, antice crinita, postice
setosa. Cylindrical, the fore-part hairy, the hinder-part furnished with
bristles.

This trichoda is rather thick in the middle, and pellucid, with a few
molecules here and there, the sides obtuse, the fore-part ciliated with
very fine hairs, the hind part terminating in a kind of bristles.


250. TRICHODA CYLLIDIUM. T. ovata, apice hiante, basique crinita. Plate
XXVII. Fig. 15. Egg-shaped, the apex gaping, the base hairy.

Pellucid, the hinder extremity filled with globules of various sizes,
the fore-part narrower, without any appearance of an external organ. It
vacillates upon the edge, commonly advancing on its flat side, and
continually drawing in water; it then gapes, and opens into a very acute
angle, almost to the middle of the body; but this is done so
instantaneously, that it is scarcely perceptible. _a_, the mouth; _b_,
the hairs or bristles, which it extends when nearly expiring.


251. TRICHODA CURSOR. T. ovata, antice crinita, postice duplici pilorum
strictorum et curvorum fasciculo. Oval trichoda, the fore-part hairy,
and the hinder-part also furnished with some straight and curved hairs
in two fascicles.

The body is flat and filled with molecules; in the fore-part is an
oblong empty space, into which we may sometimes see the water sucked in.


252. TRICHODA PULEX. T. ovata, antice incisa, fronte et basi crinita.
Plate XXVII. Fig. 12. Egg-shaped, with an incision in the fore-part;
the front and base hairy. _a_, the anterior part; _b_, the posterior
part; _c_, the incision.


253. TRICHODA LYNCEUS. T. subquadrata, rostro adunco, ore crinito. Plate
XXVII. Fig. 16. Nearly square, with a crooked beak, the mouth hairy.

At first sight it does not seem very dissimilar to some of the monoculi.
The body is membranaceous, and appears compressed, stretched out into a
beak above, the lower part truncated; under the beak is a little bundle
of hairs; the lower edge bends in and out, and is surrounded with a few
bristles. The intestines are beautifully visible, and a small bent tube
goes from the mouth to them in the middle of the body; these, as well as
the tube, are in frequent agitation. There is likewise another tube
between the fore and hind edge filled with a blue liquor. _a_, the beak;
_b_, the mouth; _c_, the base.


254. TRICHODA EROSA. T. orbicularis, antice emarginata, altero latere
crinita, postice setosa. Orbicular trichoda, the fore-part notched; one
side furnished with hairs, the hinder-part with bristles.


255. TRICHODA ROSTRATA. T. depressa, mutabilis, flavescens, ciliis
longis setisque pediformibus. Depressed trichoda, mutable, yellow, with
long ciliated hairs, and feet tapering to a point.

The figure of the body is generally triangular; the apex formed into an
obtuse beak, which the animalculum sometimes draws in, so that it
appears quite round; the feet are four in number, one of them is longer
than the rest; both feet and hairs are within the margin. It is found in
water where duck-weed has been kept.


256. TRICHODA LAGENA. T. teres, ventricosa, rostro producta, postice
setosa. Round ventricose trichoda, with a long neck, and the lower end
set with bristles.


257. TRICHODA CHARON. T. cymbiformis fulcata, antice et postice crinita.
Plate XXVII. Fig. 17 and 18. Boat-shaped trichoda with furrows, the fore
and hind-parts both hairy.

The body is oval; it resembles a boat as well in its motion as shape;
the upper part is hollowed, the under part furrowed and convex; the
stern round, with several hairs proceeding from it. It was found in salt
water. Fig. 17, _a_, the head; _b_, the tail. Fig. 18, _d_, a pellucid
bubble that is sometimes to be perceived.


258. TRICHODA CIMEX. T. ovalis, marginibus lucidis, antice et postice
crinita. Plate XXVII. Fig. 19. Oval trichoda, with a lucid margin, both
the fore and hind-part hairy.

It is about the size of the trichoda lynceus, No. 253, has an oval body,
with a convex back, flat belly, and an incision in the margin of the
fore-part, the edges of which incision appear to be in motion. Its
intestines are pellucid and ill-defined. When it meets with any
obstacles in swimming, it makes use of four small bristles, which are
fixed to the under side, as feet. _a_, the hairs in the fore-part; _b_,
the bristles at the hind-part; _d_, the back; _e_, two small projecting
hairs; _f_, the substance to which the animalculum has affixed itself.


259. TRICHODA CICADA. T. ovalis, marginibus obscuris, antice et subtus
crinita, postice mutica. Oval trichoda, with an obscure margin, the
fore-part covered with hairs on the under side, and the hinder-part
beardless.

It does not differ considerably from the preceding, though Müller has
pointed out some shades by which they may be discriminated.


XIV. KERONA.

Vermis inconspicuus corniculatus. An invisible worm with horns.


260. KERONA RASTELLUM. K. orbicularis membranacea, nasuta, corniculis in
tota pagina. Membranaceous, orbicular kerona, with one projecting point,
the upper surface covered with small horns. There are three rows of
horns on the back, which nearly occupy the whole of it. It was found in
river water.


261. KERONA LYNCASTER. K. subquadrata, rostro obtuso, disco corniculis
micantibus. This species of kerona is rather square, and its disc
furnished with shining horns. See Zool. Dan. prod. add. p. 281.


262. KERONA HISTRIO. K. oblonga, antice punctis mucronatis nigris,
postice pinnulis longitudinalibus instructa. Plate XXVII. Fig. 20.

It is an oblong membrane, pellucid, with four or five black points in
the fore-part, which are continually changing their situation, thick set
with small globules in the middle, among which four larger ones are
sometimes perceived, these are probably eggs; in the middle space of the
hind-part are some longitudinal strokes resembling bristles, which,
however, do not seem to project beyond the body. _b_, the horns; _c_,
some hairs; _d_, a solitary horn; _e_, a large globule; _f_, some
bristles.


263. KERONA CYPRIS. K. obovata, versus postica superne sinuata, antice
crinita. Plate XXVII. Fig. 21. Egg-shaped, towards the hind-part
sinuated, the fore-part hairy.

This animalculum is compressed, and somewhat of a pear-shape; the
fore-part broad and blunt; the front is furnished with short hairs or
little vibrating points inserted under the edge _a_, shorter in the
hind-part _e_, partly extended straight, and partly bent down, having a
retrograde motion. It is found in water which is covered with lemna.


264. KERONA HAUSTRUM. K. orbiculata, corniculis mediis, antice
membranacea ciliata, postice setosa. Orbicular kerona, with the horns in
the middle, the fore-part membranaceous and ciliated, and several
bristles at the hinder-part.


265. KERONA HAUSTELLUM. Differs from the preceding only in having the
hinder-part without any bristles.


266. KERONA PATELLA. K. univalvis, antice emarginata corniculata,
postice setis flexilibus pendulis. Plate XXVII. Fig. 22 and 23. Kerona
with a univalved shell, orbicular, crystalline; the fore-part somewhat
notched; the fleshy body lies in the middle of the shell; above and
below are hairs or horns of different lengths jutting out beyond the
shell, and acting instead of feet and oars, some of which are bent; the
superior ones constitute a double transverse row. _a_, the fore-part;
_b_, the horns; _d_, a lunated figure in the shell; _c_, a pulpous body;
_f_, bristles at the hinder-part.


267. KERONA VANNUS. K. ovalis subdepressa, margine altero flexo,
opposito ciliato, corniculis anticis, setisque posticis. Oval and rather
flat kerona, with one edge bent, the opposite one ciliated, the front
furnished with horns, and the hind-part with bristles.


268. KERONA PULLASTER. K. ovata, antice sinuata, fronte crestata, basi
crinita. Plate XXVII. Fig. 24 and 25. Oval, the fore-part sinuated, a
crest on the front, the base hairy.

It agrees in many respects with the trichoda pulex, No. 252; but the
upper part is pellucid, without any black molecules; the front
truncated, the whole surface of the head covered with hair, and the
fore-part sinuous. _a_, the horns; _b_, the hairs at the hinder-part;
_c_, the cilia of the front.


269. KERONA MYTILLUS. K. subclavata, utraque extremitate latiori,
hyalina ciliata. Plate XXVII. Fig. 29. Rather clubbed, broad at both
extremities, clear and ciliated.

A large animalculum, the fore and hind-part rounded, very pellucid and
white, dark in the middle, with black intestines, intermixed with a few
pellucid vesicles; both extremities appear as if composed of two thin
plates. The fore-part is ciliated, the hairs short, lying within the
margin; it is also ornamented with two small horns, erected from an
obscure mass; with these it agitates the water, forming a little
whirlpool. The hind-part is likewise ciliated, and furnished with two
bristles, extending beyond the margin. _a_, the horns; _b_, the
fore-part ciliated; _c_, the hind-part; _d_, projecting bristles.


270. KERONA LEPUS. K. ovata, apice crinito, basi setosa. Egg-shaped, the
fore-part hairy, the base furnished with bristles.

The body is egg-shaped, compressed, pellucid, and crowned with short
waving hairs, the base terminating with bristles.


271. KERONA SILURUS. K. oblonga, antice et postice crinita, dorso
ciliato. Oblong, the fore and hind-part hairy, the back ciliated.

An oval smooth animalculum, somewhat crooked and opake, with a fascicle
of vibrating hair on the fore-part; it has a sharp tail, furnished with
unequal rows of moveable hairs, producing a rotatory motion; in the
inside are some partly lucid, and partly opake points. The figure varies
from oval to oblong, the filaments of the conferva are often entangled
in the tail.


272. KERONA CALVITIUM. R. latiuscula, oblonga, antice corniculis
micantibus. Rather broad, oblong, with glittering horns on the
fore-part.

The body is rather broad and flat, both sides obtuse, filled with black
molecules, and there is a dark spot near the hinder-part, where there
are likewise a few short bristles. The interjacent vesicles are
pellucid; no hairs on the fore-part, but instead thereof two little
moveable horns, and from three to five moveable black points. It is
found in the infusions of vegetables.


273. KERONA PUSTULATA. K. ovalis convexa, postice altero margine
sinuata, utraque extremitate crinita, corniculisque anticis. Oval,
convex, kerona, one edge of the hinder-part sinuated, both ends set with
hairs, and some horns placed on the fore-part. This animalculum was
found in salt water.


XV. HIMANTOPUS.

Vermis inconspicuus, pellucidus, cirratus. A pellucid, invisible,
cirrated[127] worm.

  [127] That is, furnished with a tuft or lock of hair.


274. HIMANTOPUS ACARUS. H. ventrosus, postice cirratus, antice
acuminatus. Plate XXVII. Fig. 27. Round and prominent himantopus, the
hinder-part cirrated, the fore-part sharp.

It is a lively, conical, ventricose animalculum, full of black
molecules, the fore-part bright and transparent. The apex, which has
long hairs on the under part set like rays, is more or less attenuated,
at the will of the little creature; four locks of long and crooked hair,
or feet, proceed from the belly; and it is continually moving these and
the other hairs in various directions. It is found, though seldom, where
the lemna grows. _a_, the apex; _b_, the ciliated part; _c_, the feet.


275. HIMANTOPUS LUDIO. H. cirrata, supra crinita, cauda sursum extensa.
Plate XXVII. Fig. 26. Curled himantopus, the upper part hairy, the tail
extended upwards.

This is a lively and diverting animalculum, smooth, pellucid, full of
small points, the fore-part clubbed and a little bent, the hind-part
narrow; the base obliquely truncated, and terminating in a tail
stretched out transversely. The top of the head, and the middle of the
back _b_, are furnished with long vibrating hairs; three moveable and
flexible curls _a_, are suspended from the side of the head, at a
distance from each other. When the animalculum is at rest, its tail is
curled; but when in motion, it is drawn tight, and extended upwards,
frequently appearing as if it were cleft, as at _f_.


276. HIMANTOPUS SANNIO. H. incurvata, supra ciliata, infra crinita.
Crooked himantopus, the upper part ciliated, the under part hairy.

This very much resembles the himantopus ludio, the cilia are longer than
the hairs, and are continually vibrating; it has two moveable curls
hanging on the side of the head. Is found, though seldom, in water where
the lemna grows.


277. HIMANTOPUS VOLUTATOR. H. lunatus, antice cirratus. Lunated
himantopus, the fore-part hairy.

A very lively animalculum, often turning round in a circular direction.
Its shape is that of a crescent, with some crystalline points; the
convex part is furnished with a row of hairs, which are longest towards
the tail, and underneath are four feet.


278. HIMANTOPUS LARVA. H. elongatus, medio cirratus. Long himantopus,
cirrated in the middle.

The body is rather depressed and long; the hinder-parts acute, and
generally curved, pellucid, and filled with granular molecules. Its
motion resembles that of the himantopus ludio, No. 275, but its figure,
and the situation of its parts are different.


279. HIMANTOPUS CHARON. H. cymbæformis fulcata, in fovea ventrali
cirrata. Boat-shaped furrowed himantopus, the hollow part of the belly
cirrated.

An oval pellucid membrane, the fore-part hairy, furrowed longitudinally,
each side bent up, so as to form an intermediate hollow place, or belly,
filled with grey molecules; beneath the middle it has several bent
diverging rows of hairs; no hairs on the hinder-part. It is found in sea
water, but rarely.


280. HIMANTOPUS CORONA. H. semiorbiculata, depressa, in utraque pagina
cirrata. Semiorbicular himantopus, flattened, both sides cirrated.

A membranaceous lamina, very thin, pellucid, crystalline, and semilunar;
the edge of the base is thick set with molecular intestines; the
fore-part furnished with short hairs, or a kind of mane; towards the
hind-part are three equal curved hairs, or spines.


XVI. VORTICELLA.

Vermis contractilis, nudus, ciliis rotatoriis. A naked worm, with
rotatory cilia, capable of contracting and extending itself.


281. VORTICELLA CINCTA. V. trapeziformis, nigro-viridis, opaca. Plate
XXVII. Fig. 30. This vorticella is in the form of a trapezium, of a
blackish green colour, and opake.

It is of an irregular shape, sometimes assuming an oval figure, and
appearing as if girt round with a transverse keel, _a_. It is invisible
to the naked eye, ciliated on every side; the hairs all moveable, and
longer on one side than the other.


282. VORTICELLA SPHÆROIDA. V. cylindrico-globosa, uniformis, opaca. A
globous cylinder, uniform and opake.

To the naked eye this appears also little more than a point, but the
microscope exhibits it as a globular mass of a dark green colour. It
occasions a vehement motion in the surrounding water, which is probably
effected by some very short hairs, which are perceptible.


283. VORTICELLA VIRIDIS. V. cylindracea, uniformis, viridis opaca. Plate
XXVII. Fig. 31. Cylindrical, uniform, green, and opake.

This vorticella is visible to the naked eye, appearing like a minute
green point; but the microscope discovers it to be nearly cylindrical,
of a dark green colour, a little thicker at the fore-part _a_, than the
hinder-part _b_, and both extremities obtuse. It appears to be totally
destitute of limbs; notwithstanding which, it keeps the water in
constant motion; so that it has probably some invisible rotatory
instrument. It does not change its figure. Its motion is sometimes
circular, at others, in a straight line. At _c_, some short hairs are
visible.


284. VORTICELLA LUNIFERA. V. viridis, postice lunata, medio margine
mucronato. Green vorticella, the hinder part lunated, with a point in
the middle projecting from the edge.

The fore-part obtuse, the base broad, and hollowed away like a crescent,
with a protuberance in the middle of the concave part shorter than the
horns or points of the crescent; the fore-part is ciliated. It is found
in salt water.


285. VORTICELLA BURSATA. V. viridis, apertura truncata, papillaque
centrali. Plate XXVII. Fig. 32. Green vorticella, the aperture
truncated, with a central papillary projection.

Round and prominent, filled with molecules; the fore-part truncated, and
both sides of it pellucid; in the center of the aperture there is a
prominent papilla or nipple, which when the animalculum is at rest,
appears notched; the edge of the aperture is surrounded with cilia;
these are sometimes all erect, shining, and in motion, or part bent back
and quiescent, and part in motion; sometimes a few of them are collected
together, and turned back like little hooks, one on each side. It is
found in salt water. _a_, the cilia; _b_, the projecting papilla; _c_,
the pellucid space at the fore-part.


286. VORTICELLA VARIA. V. cylindrica, truncata, opaca, nigricans.
Cylindrical, truncated, opake, blackish-coloured vorticella, the
fore-part ciliated.


287. VORTICELLA SPUTARIUM. V. ventrosa, apertura orbiculari, ciliis
longis raris excentricis. Round and prominent, with an orbicular
aperture, and long hairs radiating as from a center.

This is one of the most singular of the microscopic animalcula; when
viewed sidewise, it is sometimes nearly cylindrical, but somewhat
tapering towards the hinder-part, and having a broad pellucid edge;
viewed from the top, it has sometimes a broad face or disc furnished
with radiating hairs, the under part contracted into a globular shape,
of a dark green colour, and filled with small grains. It was found in
October with the lesser lemna.


288. VORTICELLA NIGRA. V. trochiformis nigra. Plate XXVII. Fig. 36 and
37. Top-shaped black vorticella.

This may be seen with the naked eye, appearing like a black point
swimming on the surface of the water; the microscope exhibits it as a
minute conical body, opake, obtuse, and ventricose at one extremity, and
acute at the other. When it extends the extremities, two small white
hooks become visible; by the assistance of these it moves in the water,
and it is probable from some circumstances that they inclose a rotatory
organ. It moves continually in a vacillating manner on the top of the
water. It is found in August, in meadows that are covered with water.
_a_, the rotatory organ; _b_, the two small hooks; _c_, the acute end.


289. VORTICELLA MULTIFORMIS. V. viridis, opaca, varia, vesiculis
sparsis. Green, opake, variable vorticella, with vesicles scattered
about the body.

The vesicles of this vorticella are larger; in other respects it so much
resembles the preceding one, that a further description is unnecessary.
It is found in salt water.


290. VORTICELLA POLYMORPHA. V. multiformis, viridis, opaca. Plate XXVII.
Fig. 33, 34, 35. Many-shaped vorticella, green, opake.

To the naked eye it appears like a green point, moving with great
agility; but, when viewed through a microscope, it assumes such a
variety of forms, that they can neither be exhibited to the eye by
drawings, nor described by words; it is truly one of the wonders of
nature, astonishing the mind, fatiguing the eye, and continually
exciting the beholder to ask,

  “Quo teneam vultus mutantem protea nodo?”

The body is granulous, and a series of pellucid points is sometimes to
be observed, as at _b b_.

Fig. 33, 34, 35, represent this vorticella in three different forms;
_a_, the fore-part; _g_, the hind-part; _c_, the fore-part simple; _d_,
the fore-part turned in or doubled.


291. VORTICELLA CUCULLUS. V. elongata, teres, apertura oblique truncata.
This vorticella is long, round, the aperture or mouth obliquely
truncated.

This being visible to the naked eye, may likewise be ranked among the
larger vorticellæ. The body is somewhat conical, of a dingy red colour;
its shape has been compared to that of a grenadier’s cap.


292. VORTICELLA UTRICULATA. V. Viridis, ventricosa, productilis, antice
truncata. Green vorticella, the belly round and prominent, capable of
being lengthened or shortened; the fore-part truncated, much in the
shape of a common water-bottle; the neck is sometimes very long, at
others, very short, and filled with green molecules.


293. VORTICELLA OCREATA. V. subcubica, infra in angulum obtusum
producta. This vorticella is somewhat of a cubical figure, the under
part bent in an obtuse angle.

It is a very singular animalculum, in shape somewhat resembling the
lower part of a boot; the apex of the upper part or leg is truncated and
ciliated, the heel pointed, and the foot round. It is to be found in
rivers, though very rarely.


294. VORTICELLA VALGA. V. cubica, infra divaricata. Cubical vorticella,
the lower part divaricated.

This is as broad as long, and filled with grey molecules, the apex
truncated and ciliated; both angles of the base projecting outwards, one
somewhat like a wart, the other like a finger. It is found in marshy
waters.


295. VORTICELLA PAPILLARIS. V. ventricosa, antice truncata, papilla
caudali et laterali hyalina. Big-belled vorticella, the fore-part
truncated, with a papillary tail, and a splendid papillary excrescence
on the side. It is found in marshes where the conferva nitida grows.


296. VORTICELLA SACCULUS. V. cylindracea, apertura repanda, margine
reflexo. Cylindrical vorticella, the aperture broad and flat, the edge
turned down.

A thick animalculum, of an equal diameter everywhere, and filled with
molecules; the edge of the mouth is bent back, the hinder-part obtuse,
sometimes notched and contracted, with cilia on both sides of the mouth.


297. VORTICELLA CIRRATA. V. ventrosa, apertura sinuata, cirro utrinque
ventrali. Big-bellied vorticella, the aperture sinuated, two tufts of
hair on each side of the belly. It is found in ditch water.


298. VORTICELLA NASUTA. V. cylindracea, crateris medio mucrone
prominente. Plate XXVII. Fig. 38, 39. Cylindrical, with a prominent
point in the middle of the cup.

An animalculum that is invisible to the naked eye; but the microscope
discovers it to be furnished with a rotatory organ, which encompasses
the middle of the body.

It is pellucid, cylindrical, of an unequal size; the fore-part, _a_,
truncated and ciliated, and a triangular prominence, _e_, in the middle
of the aperture; the hind-part is obtuse, with a point on each side of
the middle of the body. This is the appearance of the little creature
when in motion; but when the water is nearly exhaled, some further parts
of its structure are rendered visible; two rotatory organs are now
observable; one on the fore-part, and the other encompassing the middle
of the body, _h h_; the hairs of the latter are in vehement motion.
Other fascicles of moving hair may likewise be observed, and the
variegated and quick motion of this apparatus is very surprizing,
especially if the animalculum be big with young, moving at the same
time within the mother.


299. VORTICELLA STELLINA. V. orbicularis, disco moleculari, peripheria
ciliata. Orbicular vorticella, with a molecular disc, and ciliated
margin.


300. VORTICELLA DISCINA. V. orbicularis, margine ciliato, subtus
convexo-ansata. Plate XXVI. Fig. 8, 9, 10. Orbicular vorticella, the
edge ciliated, with a kind of convex handle on the under-side.


301. VORTICELLA SCYPHINA. V. craterformis, crystallina, medio spærula
opaca. Bowl-shaped vorticella, crystalline, with an opake spherule in
the middle.


302. VORTICELLA ALBINA. V. cylindrica, postice acuminata. The fore-part
cylindrical, the hinder-part tapering, and ending nearly in a point.


303. VORTICELLA FRITILLINA. V. cylindrica vacua, apice truncata, ciliis
prælongis. Empty cylindrical vorticella, the apex truncated.


304. VORTICELLA TRUNCATELLA. V. cylindrica, differta, apice truncata,
cyliis breviusculis. Cylindrical vorticella, stuffed or filled, the apex
truncated, with very short cilia.

This is one of the larger kind of animalcula; the body is crystalline,
and replete with black molecules; the skin is perfectly smooth and
colourless, the hinder extremity rounded, and the anterior truncated; at
this extremity there is a large opening thickly ciliated, which serves
as a mouth.


305. VORTICELLA LIMACINA. V. cylindrica, truncata, ciliis bigeminis.
Plate XXVII. Fig. 60. Cylindrical truncated vorticella, with two pair of
cilia.


306. VORTICELLA FRAXININA. V. gregaria, cylindracea, oblique truncata,
ciliis bigeminis, apice margine fissa. Gregarious cylindrical
vorticella, obliquely truncated, with two pair of cilia, and a fissure
or notch at the upper edge.

The greater part of the body is cylindrical; the hinder-part rather
tapering, and filled with opake molecules; towards the upper end it is
transparent; within the edge, at the top are two small tubercles, from
each side of which proceed a pair of small hairs.


307. VORTICELLA CRATEGARIA. V. composita, floribus muticis globosis;
tentaculis binis, stirpe ramosa, Plate XXII. Fig. 40. Compound, with
globous naked florets, two tentacules, and a branched stem. For an ample
description of this animalculum, see page 400.


308. VORTICELLA HAMATA. V. bursæformis, margine aperturæ aculeis
rigidis. Plate XXVII. Fig. 40. Purse-formed; the edge of its aperture or
mouth set with rigid points.

It is not ciliated, nor have any hairs been discovered upon it; the body
is granulated, the fore-part broad and truncated, the hinder-part
obtuse, and capable of being contracted or extended. _a_, the rigid
points.


309. VORTICELLA CRATERIFORMIS. V. subquadrata, ciliorum fasciculis etiam
postice. Plate XXVII. Fig. 40, 41. Approaching somewhat to a square
figure, with fascicles of cilia even at the hinder-part.

A lively animalculum, pellucid, round, longer than it is broad, with
convex sides; the head is situated at the large end, the skin smooth,
and some traces of intestines may be discovered with difficulty. There
is a considerable opening surrounded with hair at the larger end, and
the filaments composing it are in continual motion. Two of them are
sometimes seen joined together, as at Fig. 41, and full of small
spherules; in this state they draw each other alternately different
ways, the surface is smooth and the hairs invisible. _e_, moveable
cilia.


310. VORTICELLA CANALICULATA. V. dilatata, pellucida, latere inciso.
Dilated, pellucid, with an incision in the side.

To the naked eye it appears as so many white points adhering to the
sides of the glass; when magnified, the anterior part is narrower than
the hind one; in the side a kind of incision may be perceived, and the
hind-part is a little notched towards the middle; it is furnished with a
rotatory organ, with which it excites a continual whirling motion in the
water.


311. VORTICELLA VERSATILIS. V. elongata spiculiformis, mox urceolaris.
Long spear-formed vorticella, but which often changes its shape into a
pitcher-like form.

A pellucid, gelatinous animalculum, of a greenish colour, furnished with
small radii, particularly about the circumference, which gives it the
appearance of a minute water hedge-hog.


312. VORTICELLA AMPULLA. V. folliculo ampulaceo, pellucido, capite
bilobo. Plate XXVI. Fig. 4 and 5. This vorticella is contained in a
pellucid bottle-shaped bag, the head divided into two lobes.

Little more need be said to enable the reader to know this animalculum,
if he should meet with it, than to observe that the bag is nearly in the
shape of the common water-bottle, and that the animalculum is sometimes
to be observed at the bottom of it, sometimes nearly filling it.


313. VORTICELLA FOLLICULATA. V. oblonga, folliculo cylindraceo hyalino.
Oblong vorticella, in a bright cylindrical bag.

This animalculum is gelatinous and cylindrical; when at its greatest
extension, the base appears attenuated, and the apex truncated.


314. VORTICELLA LARVA. V. cylindrica, apertura lunata, spinis caudalibus
binis. Cylindrical, the aperture somewhat in the shape of a crescent,
two small thorny points projecting from the hinder-part.

The head, the trunk, and the tail, may be easily distinguished from each
other. It is of a clay-colour, the aperture ciliated; with a globular
projection at times appearing to proceed from it.


315. VORTICELLA SACCULATA. V. inverse conica, apertura lunata, trunco
postice bidentato, cauda elongata biphylla. Plate XXVII. Fig. 42 and 43.
This vorticella is in the shape of an inverted cone, with an aperture
the figure of a crescent; the lower part of the trunk is notched,
forming as it were two teeth; the tail biphyllous. Each of these parts
is surrounded with a loose bright skin, the head is divided from the
trunk by a deep incision. _a a a_, small points projecting from the
head; _b_, the cilia; _c_ and _d d_, the interior parts; Fig. 42, _l_,
the little horn at the bottom of the trunk.


316. VORTICELLA AURITA. V. cylindrico-ventrosa, apertura mutica, ciliis
utrinque rotantibus cauda, articulata biphylla. Cylindrical and
big-bellied, the aperture destitute of hairs, both sides of it are
furnished with rotatory cilia, the tail biphyllous.


317. VORTICELLA TREMULA. V. inverse conica, apertura lobata spinulosa,
cauda brevi unicuspi. Somewhat of a conical shape; the mouth being
divided into two parts which are set with small spines, and a point
projects from the tail.

It is a pellucid crystalline ventricose animalculum, within the body on
one side, there is a large clay-coloured oval mass, and a pellucid oval
substance adjacent to it; the tail is articulated and very short.


318. VORTICELLA SERITA. V. inverse conica, apertura spinosa integra,
cauda brevi bicuspi. Somewhat of the shape of a cone, the aperture set
with spines, the tail short and divided into two points.

The body is muscular, pellucid, folding variously; the fore-part
truncated; round the margin of the aperture are rows of hairs, but it
has also stiffer hairs or spines continually vibrating, with which it
draws in both animate and inanimate substances. It has some resemblance
to the larger vorticella rotatoria, but is easily distinguished from it
by its horned spiny aperture, and simple rotatory organ.


319. VORTICELLA LACINULATA. V. inverse conica, apertura lobata, setis
binis caudalibus. Plate XXVII. Fig. 45. Shaped like an inverted cone,
the aperture lobated, the tail small and furnished with two bristles,
_d_.

The body is pellucid, cylindrical, and muscular; the apex about a third
part down, drawn into a little neck; in the middle is a little lamina or
triangular point; another of these is discovered when the aperture faces
the observer, which makes it appear like a small flower. The hind-part,
when in motion, is a little bent; it terminates in two minute bristles,
which are seen sometimes united, at other times diverging. When the
animalculum is swimming, its rotatory organ, _a_, may be seen; molecular
intestines are visible; it moves with velocity in an oblique direction.
It is found in pure water.


320. VORTICELLA CONSTRICTA. V. elliptico-ventricosa, apertura integra,
cauda annulata biphylla. Elliptical ventricose vorticella, the aperture
or mouth undivided, the tail annulated and forked.

There are two kinds of this vorticella; viz. one of a pale yellow, the
other of a white colour; the head, the tail, and the trunk, are fully
distinguished; a substance in motion has been perceived, which has been
supposed to be the heart; they move by fixing their tail to the glass
upon the stage of the microscope, and extending their body as much as
possible; they then fix the fore-part to the place where they intend to
move, and draw the hinder-part to it, proceeding thus alternately. They
sometimes turn round about upon one of the points of their tail, at
other times they spring forwards with a jerk. When at rest they open
their mouths very wide; the lips are ciliated, in some of them two black
globules are discovered.


321. VORTICELLA TOGATA. V. subquadrata, apertura integra, spinis
caudalibus binis, plerumque unitis. Square vorticella, the aperture not
divided, the tail consisting of two long spines, which are sometimes so
united as to appear as one.

The body is convex, of a dark colour, and filled with molecules; the
middle part is pellucid, the hinder-part rather broader than the
fore-part; the latter is ciliated, and the tail formed of two very thin
pellucid spines, which are somewhat curved and much longer than the
body.


322. VORTICELLA LONGISETA. V. elongata, compressa, setis caudalibus
binis longissimis. Long vorticella, flat, the tail formed of two very
long bristles.

The fore-part sinuated, and set with minute cilia; the two bristles
which constitute the tail are long, but one is longer than the other.


323. VORTICELLA ROTATORIA. V. cylindrica, pedicello collari, cauda longa
quadracuspi. Plate XXVI. Fig. 1, 2, 3, 6, 7, 11, 12, 14, 15, 16, 17, 18,
19, 20, 21, 22, 23, and Plate XXVII. Fig. 46, 47, 48, and 49.
Cylindrical vorticella, with a little foot projecting from the neck, a
long tail furnished with four points.

Brachionus corpore conico subæquali. Hill Hist. Anim. Brachionus corpore
conico toruloso. Ibid. Brachionus. Pallas Zooph. 50. Joblot Micros, part
2, p. 77, pl. 10, fig. 18; and p. 96, pl. 5, A B C D E K. Adams’s
Microgr. Illustr. p. 148, pl. 40, fig. 255. Leeuwenhoeck Contin. Arc.
Nat. p. 386, fig. 1, 2. Baker’s Micros. made easy, p. 91-93, pl. 8, fig.
6, 7, 8. Ibid. Empl. for the Micr. p. 267-294, pl. 11, fig. 1 to 13.
Spallanz. Opusc. Phys. 2, p. 301, 315, pl. 4, fig. 3, 4, and 5. Rozier
Journal Physique, 1775, p. 220.

This animalculum has long been known by the name of the wheel animal; in
the description of which no person appears to have succeeded so well as
Baker; and to him every writer has since referred for an ample account
of this curious little being. What I shall now say on the subject will
be chiefly extracted from the same source of information, with such
alterations and additions as appear to be necessary to render his
account more complete.

I shall begin with observing, that Müller’s wheel animal differs in some
respects from that of Baker’s; first, with regard to the rotatory organs
which are extended on the back like ears; secondly, the two little
splendid substances within the body; and thirdly, the two black points
near the top of the head, which are probably the creature’s eyes.

This little animal is found in rain water that has stood for some days
in leaden gutters; in the hollows of lead on the tops of houses; or in
the slime and sediment left in rain water; they are also sometimes to be
met with in ditches and amongst duck-weed.

It has been called the wheel animal, because it is furnished with a pair
of instruments, which in figure and motion resemble wheels. It appears
only as a living creature when immersed in water; notwithstanding which,
it may be kept for many months out of water, and in a state of perfect
dryness, without losing the principle of life. When dry, it is of a
globular form, about the size of a grain of sand, and without any
apparent signs of life. If it be put into water, in the space of half
an hour a languid motion begins, the globule turns itself about,
lengthens itself by slow degrees, and becomes very lively; in a short
time it protrudes its wheels, and swims about in search of food; or
else, fixing itself by its tail, brings the food to it by its rotatory
organs, which throw the whole circumjacent fluid into a violent
commotion; when its hunger is satisfied, it generally becomes quiescent,
and sometimes resumes its globular form.

If the water that is found standing in gutters of lead, or the sediment
it has left behind, has any appearance of a red or a dark brown colour,
little doubt need be entertained of its containing these animalcula. In
the summer season, if a small quantity of this dust be put into water,
and placed under a microscope, it seldom fails of discovering a great
number of minute reddish globules, which are, in fact, the animals
themselves. It will be best to view them first with the third or fourth
magnifiers, and afterward apply those possessing greater powers.

The motions of this little creature somewhat resemble those of a
caterpillar; like many of those insects, removing itself from place to
place by first fixing the tail to some substance, then extending the
whole body, fixing the head, and afterward drawing the tail to it; by
these alternate actions it moves with some degree of swiftness.

This animal frequently changes its appearance, and assumes a very
different form; for, the snout being drawn inwards, the fore-part
becomes clubbed, and immediately dividing, exhibits to our view two
circular instruments set with minute hairs, that move very briskly,
sometimes in a rotatory, at other times in a kind of trembling or
vibratory manner. An aperture or mouth is also perceived between the
two semicircles; whilst in this state, the animal may often be perceived
swimming about in pursuit of food.

The most distinguishing parts of this animalculum are, the head, the
thorax, and the abdomen. It differs from any other creature hitherto
described in the wonderful form and structure of its head; the sudden
changes of which from one form to another are equally surprizing and
singular; from being of a very taper form, it becomes almost
instantaneously as broad as any part of its body, and protrudes an
amazingly curious machinery formed to procure its food.

The circular bodies which project from the animal have much the
resemblance of wheels, appearing to turn round with considerable
velocity, by which means a very rapid current of water is brought from a
great distance to its mouth. As these wheels are very transparent, the
edges excepted, which are set with fibrillæ, as cogs to a wheel, it is
difficult to determine how the rotatory motions are performed, or
whether their figure be flat, concave, or conical; be this as it may,
they are protruded from a couple of tubular cases, into which they can
be again withdrawn, at the will and pleasure of the animal. They do not
always turn the same way, nor with the same degree of velocity,
sometimes moving in opposite directions, at other times both one way.
The figure varies according to the degree of their protrusion, as well
as from other circumstances. They appear occasionally like minute oblong
squares, rising from the periphery of a circle; at other times they
terminate in sharp points, and sometimes they are curved, bending the
same way like so many hooks; now and then the ends appear clubbed, or in
resemblance like a number of small mallets.

When the fore-part of this creature is first seen to open or divide, the
parts, which when fully protruded resemble wheels, seem only like a
couple of semicircles, the edges of which are set with little spiculæ,
having a nimble, and continually vibrating motion upwards and downwards,
for the purpose of agitating the water, each wheel being in this case
doubled, or like a round piece of paper folded in the middle.

When the wheels are in motion, the head appears very large in proportion
to the size of the animal; and though it is then everywhere transparent,
yet a ring or circle, more particularly distinguished by its brightness,
may be perceived about the middle of the forehead, from whence many
vessels are seen to originate.

The thorax or breast is united to the head by a short annular circle or
neck; the size of the thorax is nearly one-sixth part of the whole
animalculum. In it the heart is distinctly seen; being placed nearly in
the center, the diastole and systole cannot fail to attract the eye of
every attentive observer; the alternate dilatation and contraction is
very perceptible through the back of the animal, being performed with
great strength and vigour. It appears to be composed of two semilunar
parts, which in the time of contraction approach each other laterally,
and form between them a figure somewhat like a horse-shoe, whose upper
side is flat, the under one convex. In the diastole, these two parts
separate; the separation begins exactly in the middle of the lower part
next the tail. In each of the semilunar parts there is a cavity, which
closes when they come together; and opens when they separate.

The motion of the heart is communicated to all the other parts of the
thorax, and indeed through the whole animal. It is necessary however to
remark, that this motion is sometimes suspended, or at least quite
imperceptible, for two or three minutes, after which it re-commences,
and goes on with the same vigour and regularity as before. From the
under part of the thorax a small transparent horn proceeds, which cannot
be seen unless the insect turns on its back or side.

Below the thorax there is an annular circle that joins the thorax to the
abdomen; this is considerably the largest part of the animal, and
contains the stomach and viscera. When full of food, the intestines are
opake, and of a crimson colour, extending from the thorax quite through
the abdomen and a great part of the tail, exhibiting a fine view of the
peristaltic motion, or those gradual contractions and dilatations of the
intestines, which propel their contents downwards. Numerous
ramifications of vessels, both longitudinal and transverse, surround the
intestines. The abdomen is not only capable of contraction, but also
admits of such a degree of extension, as to form a case for all the
other parts of the body. The tail extends from a joint at the lower part
of the belly to the posterior extremity; it is of a tapering form, and
consists generally of three joints; when the animal is inclined to fix
itself to any thing by the tail, it thrusts out four, sometimes six,
little hooks from the extreme part; these are placed in pairs, one at
the very extremity itself, the other two a little way up the sides; the
three pair are seldom seen at the same time. The wheels appear to be the
organs used by the animal to assist it in swimming.

All the actions of this creature seem to imply sagacity and quickness of
sensation; at the least touch or motion in the water, they instantly
draw in their wheels. Baker conjectures that they have eyes lodged near
the wheels, because while they are in the globular or maggot state,
their motions are slow and stumbling; but after the wheels are
protruded, they are performed with great regularity, swiftness, and
steadiness. Can we sufficiently admire the wonderful contrivance in the
apparatus of this animal? a being so diminutive, as not to exceed in
size a grain of sand!

Plate XXVI. Fig. 17, represents the wheel animal in what Baker calls the
maggot state; while in this form small spiculæ are seen to dart out near
the anterior part; the snout is sometimes more, at other times less
acute than in this delineation. _a_, a small horn near the thorax.

Fig. 15 represents its manner of moving from place to place, while in
the maggot state. _a_, the projecting horn.

Fig. 12 exhibits it with the two semicircular parts, _a a_, protruded,
and in the posture in which it places itself, when preparing to swim
about, or going to set its wheels in motion.

Fig. 1 shews the head at its full extent, and a couple of small bodies,
_a a_, on the top of it, armed with small teeth, _b_, like those of the
balance-wheel of a watch.

At Fig. 18 the interior parts are more particularly exhibited. _a_, the
circle from which many vessels originate; _b_, the thorax or breast,
joined to the head by the neck, _c_; the part which is supposed to be
the heart is plainly seen at _d_; the abdomen, _f_, is separated from
the breast by a ring, _e_; _g_, the tail.

Fig. 19 exhibits the animal not fully extended, though with its wheels
in motion.

Fig. 20 shews it with its side towards the eye; in this position one of
the wheels, _a_, appears to lie considerably below the other.

Fig. 6 and 16 represent two of these creatures in the postures in which
they are frequently seen when the wheels are not protruded, but with the
fibrillæ, _a b_, vibrating quickly.

Fig. 2 exhibits the animal with the body nearly drawn into the abdomen;
at Fig. 21, the body still further drawn in; at Fig. 22, as it appears
with the tail partly drawn in; at Fig. 23, in a globular form, but still
adhering by the tail.

Sometimes, when in the maggot form, it rolls its head and tail together,
without drawing them into the body; as represented at Fig. 14.

Baker has also described three other species, one of which, differing
only from the preceding in having a very long tail, is represented at
Fig. 7.

Fig. 11 is another kind, with crustaceous spiculæ, _b_, at the
fore-part; within this, at _c_, an opake oval body may be seen, which
has been taken for an egg.

Fig. 3 is another kind; it has two projecting points, _a a_, from the
tail, and the head furnished with a number of fibrillæ, _b b_.

Fig. 13 represents another species, described by Spallanzani.

Plate XXVII. Fig. 46, 47, 48, 49, represent the wheel animals seen and
delineated by Müller. _a_, the head; _b_, the eyes; _c_, a small horn;
_d_, the rotatory organ; _e_, the tail; _f_, the points of the tail.


324. VORTICELLA FURCATA. V. cylindrica, apertura integra, cauda
longiuscula bifida. Cylindrical vorticella, the aperture undivided, the
tail rather long, and divided into two parts.

A cylindric body with a rotatory organ, consisting of a row of hairs at
the apex; the tail is divided into two parts turning a little inwards.
When at rest, it joins the segments of the tail; but opens them when in
motion. It is generally found in common water.


325. VORTICELLA CATULUS. V. cylindracea, apertura mutica, cauda
perbrevi, reflexa, bicuspi. Plate XXVII. Fig. 50. Cylindrical
vorticella, the aperture plain, the tail short, bent back, and divided
into two points.

It is a little thick muscular animalculum, folding itself up; of an
equal breadth throughout, the body disfigured by longitudinal folds
winding in various directions; the anterior part or head is connected to
the body by a little neck, and it occasionally exhibits a very minute
rotatory organ. The tail, _e_, is short, terminating in two very small
bristles, _d_, which are exposed or concealed at pleasure; the
intestines ill-defined. Its motion is rotatory, but in different
directions. It is commonly found in marshy waters.


326. VORTICELLA CANICULA. V. cylindracea, apertura mutica, cauda brevi,
articulata, bicuspi. Cylindrical vorticella, the aperture plain, with a
short articulated tail divided into two pointed parts.


327. VORTICELLA FELIS. V. caudata, cylindracea, mutica, cauda spinis
duabus longis terminata. With a tail, cylindrical, beardless, the tail
terminating in two long spines.

The body is large, the apex of an equal thickness, obtuse, with rotatory
filaments; the tail acute, with two pellucid spines, in length about
one-third part of the body, alternately separating from and approaching
each other.


328. VORTICELLA STENTOREA. V. caudata, elongata, tubæformis limbo
ciliato. Long-tailed vorticella, trumpet-shaped, the arms furnished with
rows of short hairs. See this fully described by the name of hydra
stentorea, in page 392.


329. VORTICELLA SOCIALIS. V. caudata, aggregata, clavata; disco obliquo.
A description of this vorticella has also been given, as hydra socialis,
in page 395.


330. VORTICELLA FLOSCULOSA. V. caudata, aggregata, oblongo-ovata, disco
dilatato pellucido. Plate XXVII. Fig. 51 and 52. With a tail aggregated,
of an oblong oval shape, with a dilated