The History of Creation, Vol. II (of 2) - Or the Development of the Earth and its Inhabitants by the

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Title: The History of Creation, Vol. II (of 2) - Or the Development of the Earth and its Inhabitants by the - Action of Natural Causes
Author: Haeckel, Ernst, 1834-1919
Language: English
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| Transcriber’s note: |
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| This book was published in two volumes, of which this is the |
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| Numbers enclosed in square brackets, e.g. [1], relate to |
| footnotes, which have been placed at the end of the text. |
| Numbers enclosed in parentheses, e.g. (1), relate to works |
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| In the text versions of these two volumes, words in _italics_ |
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THE HISTORY OF CREATION.

[Illustration: Hypothetical Sketch of the Monophyletic Origin of Man.]

THE
HISTORY OF CREATION:

_OR THE DEVELOPMENT OF THE EARTH AND ITS
INHABITANTS BY THE ACTION OF NATURAL CAUSES._

A POPULAR EXPOSITION OF
THE DOCTRINE OF EVOLUTION IN GENERAL, AND OF THAT OF
DARWIN, GOETHE, AND LAMARCK IN PARTICULAR.

FROM THE GERMAN OF
ERNST HAECKEL,
PROFESSOR IN THE UNIVERSITY OF JENA.

THE TRANSLATION REVISED BY
PROFESSOR E. RAY LANKESTER, M.A., F.R.S.,
FELLOW OF EXETER COLLEGE, OXFORD.

_IN TWO VOLUMES._
VOL. II.

NEW YORK:
D. APPLETON AND COMPANY,
1, 3, AND 5 BOND STREET.
1880.

A sense sublime
Of something far more deeply interfused,
Whose dwelling is the light of setting suns,
And the round ocean, and the living air,
And the blue sky, and in the mind of man;
A motion and a spirit that impels
All thinking things, all objects of all thought,
And rolls through all things.

In all things, in all natures, in the stars
Of azure heaven, the unenduring clouds,
In flower and tree, in every pebbly stone
That paves the brooks, the stationary rocks,
The moving waters and the invisible air.

WORDSWORTH.

CONTENTS OF VOL. II.

CHAPTER XV.
PAGE
PERIODS OF CREATION AND RECORDS OF CREATION.

Reform of Systems by the Theory of Descent.—The Natural System
as a Pedigree.—Palæontological Records of the
Pedigree.—Petrifactions as Records of Creation.—Deposits of the
Neptunic Strata and the Enclosure of Organic Remains.—Division
of the Organic History of the Earth into Five Main Periods:
Period of the Tangle Forests, Fern Forests, Pine Forests,
Foliaceous Forests, and of Cultivation.—The Series of Neptunic
Strata.—Immeasurable Duration of the Periods which have elapsed
during their Formation.—Deposits of Strata only during the
Sinking, not during the Elevation of the Ground.—Other Gaps in
the Records of Creation.—Metamorphic Condition of the most
Ancient Neptunic Strata.—Small Extent of Palæontological
Experience.—Small proportion of Organisms and of Parts of
Organisms Capable of Petrifying.—Rarity of many Petrified
Species.—Want of Fossilised Intermediate Forms.—Records of the
Creation in Ontogeny and in Comparative Anatomy 1

CHAPTER XVI.

PEDIGREE AND HISTORY OF THE KINGDOM OF THE PROTISTA.

Special Mode of Carrying out the Theory of Descent in the
Natural System of Organisms.—Construction of Pedigrees.—Descent
of all Many-celled from Single-celled Organisms.—Descent of
Cells from Monera.—Meaning of Organic Tribes, or Phyla.—Number
of the Tribes in the Animal and Vegetable Kingdoms.—The
Monophyletic Hypothesis of Descent, or the Hypothesis of one
Common Progenitor, and the Polyphyletic Hypothesis of Descent,
or the Hypothesis of many Progenitors.—The Kingdom of Protista,
or Primæval Beings.—Eight Classes of the Protista Kingdom:
Monera, Amœbæ, or Protoplastæ; Whip-swimmers, or Flagellata;
Ciliated-balls, Cili Catallacta; Labyrinth-streamers, or
Labyrinthuleæ; Flint-cells, or Diatomeæ; Mucous-moulds, or
Myxomycetes; Root-footers (Rhizopoda).—Remarks on the General
Natural History of the Protista: Their Vital Phenomena,
Chemical Composition, and Formation (Individuality and
Fundamental Form).—Phylogeny of the Prostista Kingdom 36

CHAPTER XVII.

PEDIGREE AND HISTORY OF THE VEGETABLE KINGDOM.

The Natural System of the Vegetable Kingdom.—Division of the
Vegetable Kingdom into Six Branches and Eighteen Classes.—The
Flowerless Plants (Cryptogamia).—Sub-kingdom of the Thallus
Plants.—The Tangles, or Algæ (Primary Algæ, Green Algæ, Brown
Algæ, Red Algæ).—The Thread-plants, or Inophytes (Lichens and
Fungi).—Sub-kingdom of the Prothallus Plants.—The Mosses, or
Muscinæ (Water-mosses, Liverworts, Leaf-mosses,
Bog-mosses).—The Ferns, or Filicinæ (Leaf-ferns, Bamboo-ferns,
Water-ferns, Scale-ferns).—Sub kingdom of Flowering Plants
(Phanerogamia).—The Gymnosperms, or Plants with Naked Seeds
(Palm-ferns = Cycadeæ; Pines = Coniferæ).—The Angiosperms, or
Plants with Enclosed Seeds.—Monocotylæ.—Dicotylæ.—Cup-blossoms
(Apetalæ).—Star-blossoms (Diapetalæ).—Bell-blossoms
(Gamopetalæ) 77

CHAPTER XVIII.

PEDIGREE AND HISTORY OF THE ANIMAL KINGDOM.

I. ANIMAL-PLANTS AND WORMS.

The Natural System of the Animal Kingdom.—Linnæus’ and Lamarck’s
Systems.—The Four Types of Bär and Cuvier.—Their Increase to
Seven Types.—Genealogical Importance of the Seven Types as
Independent Tribes of the Animal Kingdom.—Derivation of
Zoophytes and Worms from Primæval Animals.—Monophyletic and
Polyphyletic Hypothesis of the Descent of the Animal
Kingdom.—Common Origin of the Four Higher Animal Tribes out of
the Worm Tribe.—Division of the Seven Animal Tribes into
Sixteen Main Classes, and Thirty-eight Classes.—Primæval
Animals (Monera, Amœbæ, Synamœbæ), Gregarines, Infusoria,
Planæades, and Gastræades (Planula and Gastrula).—Tribe of
Zoophytes.—Spongiæ (Mucous Sponges, Fibrous Sponges, Calcareous
Sponges).—Sea Nettles, or Acalephæ (Corals, Hood-jellies,
Comb-jellies).—Tribe of Worms 117

CHAPTER XIX.

PEDIGREE AND HISTORY OF THE ANIMAL KINGDOM.

II. MOLLUSCA, STAR-FISHES, AND ARTICULATED ANIMALS.

Tribe of Molluscs.—Four Classes of Molluscs: Lamp-shells
(Spirobranchia); Mussels (Lamellibranchia); Snails (Cochlides);
Cuttle-fish (Cephalopoda).—Tribe of Star-fishes, or
Echinoderma.—Their Derivation from Ringed Worms (Mailed Worms,
or Phracthelminthes).—The Alternation of Generation in the
Echinoderma.—Four Classes of Star-fish: Sea-stars (Asteridea);
Sea-lilies (Crinoidea); Sea-urchins (Echinidea); Sea-cucumbers
(Holothuridea).—Tribe of Articulated Animals, or
Arthropoda.—Four Classes of Articulated Animals: Branchiata, or
Crustacea, breathing through gills; Jointed Crabs; Mailed
Crabs; Articulata Tracheata, breathing through Air
Tubes.—Spiders (Long Spiders, Round
Spiders).—Myriopods.—Insects.—Chewing and Sucking
Insects.—Pedigree and History of the Eight Orders of Insects 154

CHAPTER XX.

PEDIGREE AND HISTORY OF THE ANIMAL KINGDOM.

III. VERTEBRATE ANIMALS.

The Records of the Creation of Vertebrate Animals (Comparative
Anatomy, Embryology, and Palæontology).—The Natural System of
Vertebrate Animals.—The Four Classes of Vertebrate Animals,
according to Linnæus and Lamarck.—Their Increase to Nine
Classes.—Main Class of the Tube-hearted, or Skull-less Animals
(the Lancelet).—Blood Relationship between the Skull-less Fish
and the Tunicates.—Agreement in the Embryological Development
of Amphioxus and Ascidiæ.—Origin of the Vertebrate Tribe out of
the Worm Tribe.—Main Class of Single-nostriled, or
Round-mouthed Animals (Hag and Lampreys).—Main Class of
Anamnionate Animals, devoid of Amnion.—Fishes (Primæval Fish,
Cartilaginous Fish, Osseous Fish).—Mud-fish, or Dipneusta.—Sea
Dragons, or Halisauria.—Frogs and Salamanders, or Amphibia
(Mailed Amphibia, Naked Amphibia).—Main Class of Amnionate
Animals, or Amniota.—Reptiles (Primary Reptiles, Lizards,
Serpents, Crocodiles, Tortoises, Flying Reptiles, Dragons,
Beaked Reptiles).—Birds (Feather-tailed, Fan-tailed,
Bush-tailed) 192

CHAPTER XXI.

PEDIGREE AND HISTORY OF THE ANIMAL KINGDOM.

IV. MAMMALS.

The System of Mammals according to Linnæus and
Blainville.—Three Sub-classes of Mammals (Ornithodelphia,
Didelphia, Monodelphia).—Ornithodelphia, or Monotrema.—Beaked
Animals (Ornithostoma).—Didelphia, or Marsupials.—Herbivorous
and Carnivorous Marsupials.—Monodelphia, or Placentalia
(Placental Animals).—Meaning of the Placenta.—Tuft
Placentalia.—Girdle Placentalia.—Disc
Placentalia.—Non-deciduates, or Indeciduata.—Hoofed
Animals.—Single and Double-hoofed Animals.—Whales.—Toothless
Animals.—Deciduates, or Animals with
Decidua.—Semi-apes.—Gnawing Animals.—Pseudo-hoofed
Animals.—Insectivora.—Beasts of Prey.—Bats.—Apes 231

CHAPTER XXII.

ORIGIN AND PEDIGREE OF MAN.

The Application of the Theory of Descent to Man.—Its Immense
Importance and Logical Necessity.—Man’s Position in the Natural
System of Animals, among Disco-placental Animals.—Incorrect
Separation of the Bimana and Quadrumana.—Correct Separation of
Semi-apes from Apes.—Man’s Position in the Order of
Apes.—Narrow-nosed Apes (of the Old World) and Flat-nosed Apes
(of America).—Difference of the two Groups.—Origin of Man from
Narrow-nosed Apes.—Human Apes, or Anthropoides.—African
Human-apes (Gorilla and Chimpanzee).—Asiatic Human-apes (Orang
and Gibbon).—Comparison between the different Human Apes and
the different Races of Men.—Survey of the Series of the
Progenitors of Man.—Invertebrate Progenitors (Prochordata) and
Vertebrate Progenitors 263

CHAPTER XXIII.

MIGRATION AND DISTRIBUTION OF MANKIND. HUMAN SPECIES AND HUMAN
RACES.

Age of the Human Race.—Causes of its Origin.—The Origin of
Human Language.—Monophyletic or Single, Polyphyletic or
Multiple Origin of the Human Race.—Derivation of Man from many
Pairs.—Classification of the Human Races.—System of Twelve
Species of Men.—Woolly-Haired Men, or Ulotrichis.—Bushy-Haired
(Papuans, Hottentots).—Fleecy-haired (Caffres,
Negroes).—Straight-haired Men, or Lissotrichi.—Stiff-haired
(Australians, Malays, Mongols, Arctic, and American
Tribes).—Curly-haired (Dravidas, Nubians, Midlanders).—Number
of Population.—Primæval Home of Man (South Asia, or
Lemuria).—Nature of Primæval Men.—Number of Primæval Languages
(Monoglottists and Polyglottists).—Divergence and Migration of
the Human Race.—Geographical Distribution of the Human Species 296

CHAPTER XXIV.

OBJECTIONS AGAINST, AND PROOFS OF THE TRUTH OF, THE THEORY OF
DESCENT.

Objections to the Doctrine of Filiation.—Objections of Faith
and Reason.—Immeasurable Length of the Geological
Periods.—Transition Forms between Kindred Species.—Dependence
of Stability of Form on Inheritance, and of the Variability of
Form on Adaptation.—Origin of very Complicated Arrangement of
Organisation.—Gradual Development of Instincts and Mental
Activities.—Origin of à priori Knowledge from Knowledge a
posteriori.—The Knowledge requisite for the Correct
Understanding of the Doctrine of Filiation.—Necessary
Interaction between Empiricism and Philosophy.—Proofs of the
Theory of Descent.—Inner Causal-Connection between all the
Biological Series of Phenomena.—The Direct Proof of the Theory
of Selection.—Relation of the Theory of Descent to
Anthropology.—Proofs of the Animal Origin of Man.—The Pithecoid
Theory as an Inseparable Part of the Theory of
Descent.—Induction and Deduction.—Gradual Development of the
Human Mind.—Body and Mind.—Human Soul and Animal Soul.—A Glance
at the Future 334

LIST OF WORKS REFERRED TO IN THE TEXT 371

APPENDIX (Explanation of the Plates) 379

INDEX 402

LIST OF ILLUSTRATIONS.

PLATES.

XV.—Hypothetical Sketch of the Monophyletic Origin
of Man _Frontispiece_

IV.—Hand of Nine different Mammals _To face page_ 34

V.—Single-Stemmed, or Monophyletic, Pedigree of the
Vegetable Kingdom ” 112

VI.—Historical Growth of the Six Great Stems of Animals ” 122

VII.—Animal Plants, or Zoophytes ” 140

VIII.—Star Fishes—First Generation _Between pp._ 170, 171

IX.—Star Fishes—Second Generation ” ” ”

X.—Nauplius-Youth-Form of Six Crab Fish ” 174, 175

XI.—Adult-Form of the same Six Crab Fish ” ” ”

XII.—Ascidia and Amphioxus ” 201, 202

XIII.—Ascidia and Amphioxus ” ” ”

XIV.—Single, or Monophyletic, Pedigree of Back-boned
Animals _To face page_ 222

FIGURES.

8.—Protamœba Primitiva 52

9.—Bathybius Hæckelii 53

10.—Amœba Sphærococcus 54

11.—Euglena Striata 57

12.—Magosphæra Planula 58

13.—Labyrinthula Macrocystis 59

14.—Navicula Hippocampus 60

15.—Physarum Albipes 61

16.—Cyrtidosphæra Echinoides 66

17.—Caulerpa Denticulata 87

18.—Euastrum Rota 88

19.—Fucus Vesiculosus (egg of) 90

THE HISTORY OF CREATION.

CHAPTER XV.

PERIODS OF CREATION AND RECORDS OF CREATION.

The revolutionary influence which the Theory of Descent must exercise
upon all sciences, will in all probability affect no branch of science,
excepting Anthropology, so much as the descriptive portion of natural
history, that which is known as systematic Zoology and Botany. Most
naturalists who have hitherto occupied themselves with arranging the
different systems of animals and plants, have collected, named, and
arranged the different species of these natural bodies with much the
same interest as antiquarians and ethnographers collect the weapons and
utensils of different nations. Many have not even risen above the degree
of intelligence with which people usually collect, label, and arrange
crests, stamps, and similar curiosities. In the same manner as some
collectors find their pleasure in the similarity of forms, the beauty or
rarity of the crests or stamps, and admire in them the inventive art of
man, so many naturalists take a delight in the manifold forms of animals
and plants, and marvel at the rich imagination of the Creator, at His
unwearied creative activity, and at His curious fancy for forming, by
the side of so many beautiful and useful organisms, also a number of
ugly and useless ones.

This childlike treatment of systematic Zoology and Botany is completely
annihilated by the Theory of Descent. In the place of the superficial
and playful interest with which most naturalists have hitherto regarded
organic structures, we now have the much higher interest of the
intelligent understanding which detects in the _related forms_ of
organisms their true _blood relationships_. The _Natural System of
animals and plants_, which was formerly valued either only as a registry
of names, to facilitate the survey of the different forms, or as a table
of contents for the short expression of their degrees of similarity,
receives from the Theory of Descent the incomparably higher value of a
true _pedigree of organisms_. This pedigree is to disclose to us the
genealogical connection of the smaller and larger groups. It has to show
us in what way the different classes, orders, families, genera, and
species of the animal and vegetable kingdoms correspond with the
different branches, twigs, and groups of twigs of the pedigree. Every
wider and higher category or stage of the system (for example a class,
or an order) comprises a number of larger and stronger branches of the
pedigree; every narrower and lower category (for example a genus, or a
species) only a smaller and thinner group of twigs. It is only when we
thus view the natural system as a pedigree that we perceive its true
value. (Gen. Morph. ii. Plate XVII. p. 397.)

Since we hold fast this genealogical conception of the Organic System,
to which alone undoubtedly the future of classificatory Zoology and
Botany belongs, we should now turn our attention to one of the most
essential, but also one of the most difficult, tasks of the
“non-miraculous history of creation,” namely, to the actual construction
of the Organic Pedigree. Let us see how far we are already able to point
out all the different organic forms as the divergent descendants of a
single or of some few common original forms. But how can we construct
the actual pedigree of the animal and vegetable group of forms from our
knowledge of them, at present so scanty and fragmentary? The answer to
this question lies in what we have already remarked of the parallelism
of the three series of development—in the important causal relation
which connects the palæontological development of all organic tribes
with the embryological development of individuals, and with the
systematic development of groups.

In order to accomplish our task we shall first have to direct our
attention to _palæontology_, or _the science of petrifactions_. For if
the Theory of Descent is really true, if the petrified remains of
formerly living animals and plants really proceed from the extinct
primæval ancestors and progenitors of the present organisms, then,
without anything else, the knowledge and comparison of petrifactions
ought to disclose to us the pedigree of organisms. However simple and
clear this may seem in theory, the task becomes extremely hard and
complicated when it is actually taken in hand. Its practical solution
would be very difficult even if the petrifactions were to any extent
completely preserved. But this is by no means the case. The obvious
records of creation which lie buried in petrifactions are imperfect
beyond all measure. Hence it is necessary critically to examine these
records, and to determine the value which petrifactions possess for the
history of the development of organic tribes. As I have previously
discussed the general importance of petrifactions as the records of
creation, when we were considering Cuvier’s merits in the science of
fossils, we may now at once examine the conditions and circumstances
under which the remains of organic bodies became petrified and preserved
in a more or less recognizable form.

As a rule we find petrifactions or fossils enclosed only in those stones
which have been deposited in layers as mud by water, and which are on
that account called neptunic, stratified, or sedimentary rocks. The
deposition of such strata could of course only commence after the
condensation of watery vapour into liquid water had taken place in the
course of the earth’s history. After that period, which we considered in
our last chapter, not only did life begin on the earth, but also an
uninterrupted and exceedingly important transformation of the rigid
inorganic crust of the earth. The water began that extremely important
mechanical action by which the surface of the earth is perpetually,
though slowly, transformed. I may surely presume that it is generally
known what an extremely important influence, in this respect, is even
yet exercised by water at every moment. As it falls down as rain,
trickling through the upper strata of the earth’s crust, and flowing
down from heights into hollows, it chemically dissolves different
mineral parts of the ground, and mechanically washes away the loose
particles. In flowing down from mountains water carries their debris
into the plains, or deposits it as mud in stagnant lakes. Thus it
continually works at lowering mountains and filling up valleys. In like
manner the breakers of the sea work uninterruptedly at the destruction
of the coasts and at filling up the bottom of the sea with the debris
they wash down. The action of water alone, if it were not counteracted
by other circumstances, would in time level the whole earth. There can
be no doubt that the mountain masses—which are annually carried down as
mud into the sea, and deposited on its floor—are so great that in the
course of a longer or shorter period, say a few millions of years, the
surface of the earth would be completely levelled and become enclosed by
a continuous sheet of water. That this does not happen is owing to the
perpetual volcanic action of the fiery-fluid centre of the earth. The
surging of the melted nucleus against the firm crust necessitates
continual alternations of elevation and depression on the different
parts of the earth’s surface. These elevations and depressions for the
most part take place very slowly; but, as they continue for thousands of
years, by the combined effect of small, interrupted movements, they
produce results no less grand than does the counteracting and levelling
action of water.

Since the elevations and depressions of the different parts of the
earth alternate with one another in the course of millions of years,
first this and then that part of the earth’s surface is above or below
the level of the sea. I have already given examples of this in the
preceding chapter (vol. i. p. 361). Hence, in all probability, there is
no part of the outer crust of the earth which has not been repeatedly
above and also below the level of the sea. This repeated change explains
the variety and the different composition of the numerous neptunic
strata of rocks, which in most places have been deposited one above
another in considerable thickness. In the different periods of the
earth’s history during which these deposits took place there lived
various and different populations of animals and plants. When their dead
bodies sank to the bottom of the waters, the forms of the bodies
impressed themselves upon the soft mud, and imperishable parts, such as
hard bones, teeth, shells, etc., became enclosed in it uninjured. These
were preserved in the mud, which condensed them into neptunic rock, and
as petrifactions they now serve to characterise the respective strata.
By a careful comparison of the different strata lying one above another,
and the petrifactions preserved in them, it has become possible to
decide the relative age of the strata and groups of strata, and to
establish, by direct observation, the principal eras of phylogeny, that
is to say, the stages in history of the development of animal and
vegetable tribes.

The different strata of neptunic rocks deposited one above another,
which are composed in very various ways of limestone, clay, and sand,
geologists have grouped together into an ideal System or Series, which
corresponds with the whole course of the organic history of the earth,
or with that portion of the earth’s history during which organic life
existed. Just as so-called “universal history” falls into larger and
smaller periods, which are characterized by the conditions of
development of the most important nations at the respective epochs, and
are separated from one another by great events, so we also divide the
infinitely longer organic history of the earth into a series of greater
and less periods. Each of these periods is distinguished by a
characteristic flora and fauna, and by the specially strong development
of certain vegetable or animal groups, and each is separated from the
preceding and succeeding period by a striking change in the character of
its animal and vegetable inhabitants.

In relation to the following survey of the historical course of
development which the large animal and vegetable tribes have passed
through, it will be desirable to say a few words first as to the
systematic classification of the neptunic groups of strata, and the
larger and smaller periods corresponding to them. As will be seen
directly, we are able to divide the whole of the sedimentary rocks lying
one above another into five main groups or periods, each period into
several subordinate groups of strata or _systems_, and each system of
strata again into still smaller groups or _formations_; finally, each
formation can again be divided into stages or sub-formations, and each
of these again into still smaller layers or beds. Each of the five great
rock-groups was deposited during a great division of the earth’s
history, during a long _era_ or _epoch_; each system during a shorter
_period_; each formation during a still shorter _period_. In thus
reducing the periods of the organic history of the earth, and the
neptunic strata containing petrifactions deposited during those periods
into a connected system, we proceed exactly like the historian who
divides the history of nations into the three main divisions of
Antiquity, the Middle Ages, and Modern Times, and each of those sections
again into subordinate periods and epochs. But the historian by this
sharp systematic division, and by fixing the boundary of the periods by
particular dates, only seeks to facilitate his survey, and in no way
means to deny the uninterrupted connection of events and the development
of nations. Exactly the same qualification applies to our systematic
division, specification, or classification of the organic history of the
earth. Here, too, a continuous thread runs through the series of events
unbroken. We must therefore distinctly protest against the idea that by
sharply bounding the larger and smaller groups of strata, and the
periods corresponding with them, we in any way wish to adopt Cuvier’s
doctrine of terrestrial revolutions, and of repeated new creations of
organic populations. That this erroneous doctrine has long since been
completely refuted by Lyell, I have already mentioned. (Compare vol. i.
p. 127.)

The five great main divisions of the organic history of the earth, or
the palæontological history of development, we call the primordial,
primary, secondary, tertiary, and quaternary epochs. Each is distinctly
characterized by the predominating development of certain animal and
vegetable groups in it, and we might accordingly symbolically designate
the five epochs, on the one hand by the names of the groups of the
vegetable kingdom, and on the other hand by those of the different
classes of vertebrate animals. In this case the _first_, or primordial
epoch, would be the era of the Tangles (Algæ) and skull-less
Vertebrates; the _second_, or primary epoch, that of the Ferns and
Fishes; the _third_, or secondary epoch, that of Pine Forests and
Reptiles; the _fourth_, or tertiary epoch, that of Foliaceous Forests
and of Mammals; finally, the _fifth_, or quaternary epoch, the era of
Man, and his Civilization. The divisions or _periods_ which we
distinguish in each of the five _long eras_ (p. 14) are determined by
the different _systems_ of strata into which each of the five great
_rock-groups_ is divided (p. 15). We shall now take a cursory glance at
the series of these systems, and at the same time at the populations of
the five great epochs.

The first and longest division of the organic history of the earth is
formed by the _primordial epoch_, or _the era of the Tangle Forests_. It
comprises the immense period from the first spontaneous generation, from
the origin of the first terrestrial organism, to the end of the Silurian
system of deposits. During this immeasurable space of time, which in all
probability was much longer than all the other four epochs taken
together, the three most extensive of all the neptunic systems of strata
were deposited, namely, the _Laurentian_, upon that the _Cambrian_, and
upon that the _Silurian_ system. The approximate thickness or size of
these three systems together amounts to 70,000 feet. Of these about
30,000 belong to the Laurentian, 18,000 to the Cambrian, and 22,000 to
the Silurian system. The average thickness of all the four other rock
groups, the primary, secondary, tertiary, and quaternary, taken
together, may amount at most to 60,000 feet; and from this fact alone,
apart from many other reasons, it is evident that the duration of the
primordial period was probably much longer than the duration of all the
subsequent periods down to the present day. Many thousands of millions
of years were required to deposit such masses of strata. Unfortunately,
by far the largest portion of the primordial group of strata is in the
metamorphic state (which we shall directly explain), and consequently
the petrifactions contained in them—the most ancient and most important
of all—have, to a great extent, been destroyed and become
unrecognisable. Only in one portion of the Cambrian strata have
petrifactions been preserved in a recognizable condition and in large
quantities. The most ancient of all distinctly preserved petrifactions
has been found in the lowest Laurentian strata (in the Ottawa
formation), which I shall afterwards have to speak of as the “Canadian
Life’s-dawn” (Eozoon canadense).

Although only by far the smaller portion of the primordial or
archilithic petrifactions are preserved to us in a recognizable
condition, still they possess the value of inestimable documents of the
most ancient and obscure times of the organic history of the earth. What
seems to be shown by them, in the first place, is that during the whole
of this immense period there existed only inhabitants of the waters. As
yet, at any rate, among all archilithic petrifactions, not a single one
has been found which can with certainty be regarded as an organism which
has lived on land. All the vegetable remains we possess of the
primordial period belong to the lowest of all groups of plants, to the
class of Tangles or Algæ, living in water. In the warm primæval sea,
these constituted the forests of the period, of the richness of which in
forms and density we may form an approximate idea from their present
descendants, the tangle forests of the Atlantic Sargasso sea. The
colossal tangle forests of the archilithic period supplied the place of
the forest vegetation of the mainland, which was then utterly wanting.
All the animals, also, whose remains have been found in archilithic
strata, like the plants, lived in water. Only crustacea are met with
among the animals with articulated feet, as yet no spiders and no
insects. Of vertebrate animals, only a very few remains of fishes are
known as having been found in the most recent of all primordial strata,
in the upper Silurian. But the headless vertebrate animals, which we
call _skull-less_, or _Acrania_, and out of which fishes must have been
developed, we suppose to have lived in great numbers during the
primordial epoch. Hence we may call it after the _Acrania_ as well as
after the _Tangles_.

The _primary epoch_, or _the era of Fern Forests_, the second main
division of the organic history of the earth, which is also called the
palæolithic or palæozoic period, lasted from the end of the Silurian
formation of strata to the end of the Permian formation. This epoch was
also of very long duration, and again falls into three shorter periods,
during which three great systems of strata were deposited, namely,
first, the _Devonian_ system, or the old red sandstone; upon that, the
_Carboniferous_, or coal system; and upon this, the _Permian_ system.
The average thickness of these three systems taken together may amount
to about 42,000 feet, from which we may infer the immense length of time
requisite for their formation.

The Devonian and Permian formations are especially rich in remains of
fishes, of primæval fish as well as enamelled fish (Ganoids), but the
bony fish (Teleostei) are absent from the strata of the primary epoch.
In coal are found the most ancient remains of animals living on land,
both of articulated animals (spiders and insects) as well as of
vertebrate animals (amphibious animals, like newts and frogs). In the
Permian system there occur, in addition to the amphibious animals, the
more highly-developed reptiles, and, indeed, forms nearly related to our
lizards (Proterosaurus, etc.). But, nevertheless, we may call the
primary epoch that of _Fishes_, because these few amphibious animals and
reptiles are insignificant in comparison with the immense mass of
palæozoic fishes. Just as Fishes predominate over the other vertebrate
animals, so _Ferns_, or Filices, predominate among the plants of this
epoch, and, in fact, real ferns and tree ferns (leafed ferns, or
Phylopteridæ), as well as bamboo ferns (Calamophytæ) and scaled ferns
(Lepidophytæ). These ferns, which grew on land, formed the chief part of
the dense palæolithic island forests, the fossil remains of which are
preserved to us in the enormously large strata of coal of the
Carboniferous system, and in the smaller strata of coal of the Devonian
and Permian systems. We are thus justified in calling the primary epoch
either the era of _Ferns_ or that of _Fishes_.

The third great division of the palæontological history of development
is formed by the _secondary epoch_, or the _era of Pine Forests_, which
is also called the mesolithic or mesozoic epoch. It extends from the end
of the Permian system to the end of the Chalk formation, and is again
divided into three great periods. The stratified systems deposited
during this period are, first and lowest, the _Triassic_ system, in the
middle the _Jura_ system, and at the top the _Cretaceous_ system. The
average thickness of these three systems taken together is much less
than that of the primary group, and amounts as a whole only to about
15,000 feet. The secondary epoch can accordingly in all probability not
have been half so long as the primary epoch.

Just as Fishes prevailed in the primary epoch, _Reptiles_ predominated
in the secondary epoch over all other vertebrate animals. It is true
that during this period the first birds and mammals originated; at that
time, also, there existed important amphibious animals, especially the
gigantic Labyrinthodonts, in the sea the wonderful sea-dragons, or
Halisaurii, swam about, and the first fish with bones were associated
with the many primæval fishes (Sharks) and enamelled fish (Ganoids) of
the earlier times; but the very variously developed kinds of reptiles
formed the predominating and characteristic class of vertebrate animals
of the secondary epoch. Besides those reptiles which were very nearly
related to the present living lizards, crocodiles, and turtles, there
were, during the mesolithic period, swarms of grotesquely shaped
dragons. The remarkable flying lizards, or Pterosaurii, and the colossal
land-dragons, or Dinosaurii, of the secondary epoch, are peculiar, as
they occur neither in the preceding nor in the succeeding epochs. The
secondary epoch may be called the era of _Reptiles_; but on the other
hand, it may also be called the era of _Pine Forests_, or more
accurately, of the _Gymnosperms_, that is, the epoch of _plants having
naked seeds_. For this group of plants, especially as represented by the
two important classes—the pines, or _Coniferæ_, and the palm-ferns, or
_Cycadeæ_—during the secondary epoch constituted a predominant part of
the forests. But towards the end of the epoch (in the Chalk period) the
plants of the pine tribe gave place to the leaf-bearing forests which
then developed for the first time.

SURVEY

_Of the Palæontological Periods, or of the Greater Divisions of the
Organic History of the Earth._

I. _First Epoch_: ARCHILITHIC ERA. _Primordial Epoch._

(Era of Skull-less Animals and Forests of Tangles.)

1. Older Primordial Period or Laurentian Period.
2. Middle Primordial Period ” Cambrian Period.
3. Later Primordial Period ” Silurian Period.

II. _Second Epoch_: PALÆOLITHIC ERA. _Primary Epoch._

(Era of Fish and Fern Forests.)

4. Older Primary Period or Devonian Period.
5. Mid Primary Period ” Coal Period.
6. Later Primary Period ” Permian Period.

III. _Third Epoch_: MESOLITHIC ERA. _Secondary Epoch._

(Era of Reptiles and Pine Forests.)

7. Older Secondary Period or Trias Period.
8. Middle Secondary Period ” Jura Period.
9. Later Secondary Period ” Chalk Period.

IV. _Fourth Epoch_: CÆNOLITHIC ERA. _Tertiary Epoch._

(Era of Mammals and Leaf Forests.)

10. Older Tertiary Period or Eocene Period.
11. Newer Tertiary Period ” Miocene Period.
12. Recent Tertiary Period ” Pliocene Period.

V. _Fifth Epoch_: ANTHROPOLITHIC ERA. _Quaternary Epoch._

(Era of Man and Cultivated Forests.)

13. Older Quaternary Period or Ice or Glacial Period.
14. Newer Quaternary Period ” Post Glacial Period.
15. Recent Quaternary Period ” Period of Culture.

(The Period of Culture is the Historical Period, or the Period of
Tradition.)

SURVEY

_Of the Palæontological Formations, or those Strata of the Earth’s Crust
containing Petrifactions._

--------------------+-------------------+----------------------+--------------
_Rock-Groups._ | _Systems._ | _Formations._ | _Synonyms of
| | | Formations._
--------------------+-------------------+----------------------+-------------
V. _Quaternary { |
Group_, { XIV. Recent { 36. _Present_ | Upper alluvial
or { (Alluvium) { 35. _Recent_ | Lower alluvial
Anthropolithic { |
(Anthropozoic) { XIII. Pleistocene { 34. _Post glacial_ | Upper diluvial
groups of { (Diluvium) { 33. _Glacial_ | Lower diluvial
strata { |

IV. _Tertiary { XII. Pliocene { 32. _Arvernian_ | Upper pliocene
Group_, { (Late tertiary) { 31. _Sub-Appenine_ | Lower pliocene
or { |
Cænolithic { XI. Miocene { 30. _Falunian_ | Upper miocene
(Cænozoic) { (New tertiary) { 29. _Limburgian_ | Lower miocene
groups of { |
strata { { 28. _Gypsum_ | Upper eocene
{ X. Eocene { 27. _Nummulitic_ | Mid eocene
{ (Old tertiary) { 26. _London clay_ | Lower eocene

{ { 25. _White chalk_ | Upper cretaceous
{ IX. Cretaceous { 24. _Green sand_ | Mid cretaceous
{ { 23. _Neocomian_ | Lower cretaceous
III. _Secondary { { 22. _Wealden_ | The Kentish Weald
Group_, {
or { { 21. _Portlandian_ | Upper oolite
Mesolithic { VIII. Jura { 20. _Oxfordian_ | Mid oolite
(Mesozoic) { { 19. _Bath_ | Lower oolite
groups of { { 18. _Lias_ | Lias formation
strata {
{ { 17. _Keuper_ | Upper trias
{ VII. Trias { 16. _Muschel-kalk_ | Mid trias
{ { 15. _Bunter sand_ | Lower trias

{ VI. Permian { 14. _Zechstein_ | Upper Permian
II. _Primary { { 13. | Lower Permian
Group_, { { 12. _Carboniferous |
or { V. Carbonic sandstone_ | Upper carbonic
Palæolithic { (coal) { 11. _Carboniferous |
(Palæozoic) { { limestone_ | Lower carbonic
groups of { IV. Devonian { 10. _Pilton_ | Upper Devonian
strata {(Old red sandstone){ 9. _Ilfracombe_ | Mid Devonian
{ 8. _Linton_ | Lower Devonian

I. _Primordial { { 7. _Ludlow_ | Upper Silurian
Group_, { III. Silurian { 6. _Llandovery_ | Mid Silurian
or { { 5. _Llandeilo_ | Lower Silurian
Archilithic {
(Archizoic) { II. Cambrian { 4. _Potsdam_ | Upper Cambrian
groups of { { 3. _Longmynd_ | Lower Cambrian
strata {
{ I. Laurentian { 2. _Labrador_ | Upper Laurentian
{ { 1. _Ottawa_ | Lower Laurentian

The fourth main division of the organic history of the earth, the
_tertiary epoch_, or _era of Leafed Forests_, is much shorter and less
peculiar than the three first epochs. This epoch, which is also called
the cænolithic or cænozoic epoch, extended from the end of the
cretaceous system to the end of the pliocene system. The strata
deposited during it amount only to a thickness of about 3000 feet, and
consequently are much inferior to the three first great groups. The
three systems also into which the tertiary period is subdivided are very
difficult to distinguish from one another. The oldest of them is called
_eocene_, or old tertiary; the newer _miocene_, or mid tertiary; and the
last is the _pliocene_, or later tertiary system.

The whole population of the tertiary epoch approaches much nearer, on
the whole as well as in detail, to that of the present time than is the
case in the preceding epochs. From this time the class of _Mammals_
greatly predominates over all other vertebrate animals. In like manner,
in the vegetable kingdom, the group—so rich in forms—of the
_Angiosperms_, or _plants with covered seeds_, predominates, and its
_leafy forests_ constitute the characteristic feature of the tertiary
epoch. The group of the Angiosperms consists of the two classes of
single-seed-lobed plants, or _Monocotyledons_, and the double-seed-lobed
plants, or _Dicotyledons_. The Angiosperms of both classes had, it is
true, made their appearance in the Cretaceous period, and mammals had
already occurred in the Jurassic period, and even in the Triassic
period; but both groups, the mammals and the plants with enclosed seeds,
did not attain their peculiar development and supremacy until the
tertiary epoch, so that it may justly be called after them.

The fifth and last main division of the organic history of the earth is
the _quaternary epoch, or era of Civilization_, which in comparison with
the length of the four other epochs almost vanishes into nothing, though
with a comical conceit we usually call its record the “history of the
world.” As the period is characterized by the development of _Man_ and
his _Culture_, which has influenced the organic world more powerfully
and with greater transforming effect than have all previous conditions,
it may also be called the era of Man, the anthropolithic or anthropozoic
period. It might also be called the era of Cultivated Forests, or
Gardens, because even at the lowest stage of human civilization man’s
influence is already perceptible in the utilization of forests and their
products, and therefore also in the physiognomy of the landscape. The
commencement of this era, which extends down to the present time, is
geologically bounded by the end of the pliocene stratification.

The neptunic strata which have been deposited during the comparatively
short quaternary epoch are very different in different parts of the
earth, but they are mostly of very slight thickness. They are reduced to
two “systems,” the older of which is designated the _diluvial_, or
_pleistocene_, and the later the _alluvial_, or _recent_. The diluvial
system is again divided into two “formations,” the older _glacial_ and
the more recent _post glacial_ formations. For during the older diluvial
period there occurred that extremely remarkable decrease of the
temperature of the earth which led to an extensive glaciation of the
temperate zones. The great importance which this “ice” or “glacial
period” has exercised on the geographical and topographical distribution
of organisms has already been explained in the preceding chapter (vol.
i. p. 365). But the _post glacial period_, or the more recent diluvial
period, during which the temperature again increased and the ice
retreated towards the poles, was also highly important in regard to the
present state of chorological relations.

The biological characteristic of the quaternary epoch lies essentially
in the development and dispersion of the human organism and his culture.
Man has acted with a greater transforming, destructive, and modifying
influence upon the animal and vegetable population of the earth than any
other organism. For this reason, and not because we assign to man a
privileged exceptional position in nature in other matters, we may with
full justice designate the development of man and his civilization as
the beginning of a special and last main division of the organic history
of the earth. It is probable indeed that the corporeal development of
primæval man out of man-like apes took place as far back as the earlier
pliocene period, perhaps even in the miocene tertiary period. But the
actual development of _human speech_, which we look upon as the most
powerful agency in the development of the peculiar characteristics of
man and his dominion over other organisms, probably belongs to that
period which on geological grounds is distinguished from the preceding
pliocene period as the pleistocene or diluvial. In fact the time which
has elapsed from the development of human speech down to the present
day, though it may comprise many thousands and perhaps hundreds of
thousands of years, almost vanishes into nothing as compared with the
immeasurable length of the periods which have passed from the beginning
of organic life on the earth down to the origin of the human race.

The tabular view given on page 15 shows the succession of the
palæontological rock-groups, systems, and formations, that is, the
larger and smaller neptunic groups of strata, which contain
petrifactions, from the uppermost, or Alluvial, down to the lowest, or
Laurentian, deposits. The table on page 14 presents the historical
division of the corresponding eras of the larger and smaller
palæontological periods, and in a reversed succession, from the most
ancient Laurentian up to the most recent Quaternary period.

Many attempts have been made to make an approximate calculation of the
number of thousands of years constituting these periods. The thickness
of the strata has been compared, which, according to experience, is
deposited during a century, and which amounts only to some few lines or
inches, with the whole thickness of the stratified masses of rock, the
succession of which we have just surveyed. This thickness, on the whole,
may on an average amount to about 130,000 feet; of these 70,000 belong
to the primordial, or archilithic; 42,000 to the primary, or
palæolithic; 15,000 to the secondary, or mesolithic; and finally only
3,000 to the tertiary, or cænolithic group. The very small and scarcely
appreciable thickness of the quaternary, or anthropolithic deposit
cannot here come into consideration at all. On an average, it may at
most be computed as from 500 to 700 feet. But it is self evident that
all these measurements have only an average and approximate value, and
are meant to give only a rough survey of the _relative_ proportion of
the systems of strata and of the spaces of time corresponding with them.

Now, if we divide the whole period of the organic history of the
earth—that is, from the beginning of life on the earth down to the
present day—into a hundred equal parts, and if then, corresponding to
the thickness of the systems of strata, we calculate the relative
duration of the time of the five main divisions or periods according to
percentages, we obtain the following result:—

I. Archilithic, or primordial period 53.6
II. Palæolithic, or primary period 32.1
III. Mesolithic, or secondary period 11.5
IV. Cænolithic, or tertiary period 2.3
V. Anthropolithic, or quaternary period 0.5
-----
Total 100.0

According to this, the length of the archilithic period, during which no
land-living animals or plants as yet existed, amounts to more than one
half, more than 53 per cent.; on the other hand the length of the
anthropolithic era, during which man has existed, amounts to scarcely
one-half per cent. of the whole length of the organic history of the
earth. It is, however, quite impossible to calculate the length of these
periods, even approximately, by years.

The thickness of the strata of mud at present deposited during a
century, and which has been used as a basis for this calculation, is of
course quite different in different parts of the earth under the
different conditions in which these deposits take place. It is very
slight at the bottom of the deep sea, in the beds of broad rivers with a
short course, and in inland seas which receive very scanty supplies of
water. It is comparatively great on the sea-shores exposed to strong
breakers, at the estuaries of large rivers with long courses, and in
inland seas with copious supplies of water. At the mouth of the
Mississippi, which carries with it a considerable amount of mud, in the
course of 100,000 years about 600 feet would be deposited. At the bottom
of the open sea, far away from the coasts, during this long period only
some few feet of mud would be deposited. Even on the sea-shores where a
comparatively large quantity of mud is deposited the thickness of the
strata formed during the course of a century may after all amount to no
more than a few inches or lines when condensed into solid stone. In any
case, however, all calculations based upon these comparisons are very
unsafe, and we cannot even approximately conceive the enormous length of
the periods which were requisite for the formation of the systems of
neptunic strata. Here we can apply only relative, not absolute,
measurements of time.

Moreover, we should entirely err were we to consider the size of these
systems of strata alone as the measure of the actual space of time which
has elapsed during the earth’s history. For the elevations and
depressions of the earth’s crust have perpetually alternated with one
another, and the mineralogical and palæontological difference—which is
perceived between each two succeeding systems of strata, and between
each two of their formations at any particular spot—corresponds in all
probability with a considerable intermediate space of many thousands of
years, during which that particular part of the earth’s crust was raised
above the water. It was only after the lapse of this intermediate
period, when a new depression again laid the part in question under
water, that there occurred a new deposit of earth. As, in the mean time,
the inorganic and organic conditions on this part had undergone a
considerable transformation, the newly-formed layer of mud was
necessarily composed of different earthy constituents and enclosed
different petrifactions.

The striking differences which so frequently occur between the
petrifactions of two strata, lying one above another, are to be
explained in a simple and easy manner by the supposition that the same
part of the earth’s surface has been exposed to _repeated depressions
and elevations_. Such alternating elevations and depressions take place
even now extensively, and are ascribed to the heaving of the fiery fluid
nucleus against the rigid crust. Thus, for example, the coast of Sweden
and a portion of the west coast of South America are constantly though
slowly rising, while the coast of Holland and a portion of the east
coast of South America are gradually sinking. The rising as well as the
sinking takes place very slowly, and in the course of a century
sometimes only amounts to some few lines, sometimes to a few inches, or
at most a few feet. But if this action continues uninterruptedly
throughout hundreds of thousands of years it is capable of forming the
highest mountains.

It is evident that elevations and depressions, such as now can be
measured in these places, have uninterruptedly alternated one with
another in different places during the whole course of the organic
history of the earth. This may be inferred with certainty from the
geographical distribution of organisms. (Compare vol. i. p. 350.) But to
form a judgment of our palæontological records of creation it is
extremely important to show that permanent strata can only be deposited
during a slow sinking of the ground under water, but not during its
continued rising. When the ground slowly sinks more and more below the
level of the sea, the deposited layers of mud get into continually
deeper and quieter water, where they can become condensed into stone
undisturbed. But when, on the other hand, the ground slowly rises, the
newly-deposited layers of mud, which enclose the remains of plants and
animals, again immediately come within the reach of the play of the
waves, and are soon worn away by the force of the breakers, together
with the organic remains which they on close. For this simple but very
important reason, therefore, abundant layers, in which organic remains
are preserved, can only be deposited during a continuous sinking of the
ground. When any two different formations or strata, lying one above the
other, correspond with two different periods of depression, we must
assume a long period of rising between them, of which period we know
nothing, because no fossil remains of the then living animals and plants
could be preserved. It is evident, however, that those _periods of
elevation_, which have passed without leaving any trace behind them,
deserve a no less careful consideration than the greater or less
alternating _periods of depression_, of whose organic population we can
form an approximate idea from the strata containing petrifactions.
Probably the former were not of shorter duration than the latter.

From this alone it is apparent how imperfect our records must
necessarily be, and all the more so since it can be theoretically proved
that the variety of animal and vegetable life must have increased
greatly during those very periods of elevation. For as new tracts of
land are raised above the water, new islands are formed. Every new
island, however, is a new centre of creation, because the animals and
plants accidentally cast ashore there, find in the new territory, in
the struggle for life, abundant opportunity of developing themselves
peculiarly, and of forming new species. The formation of new species has
evidently taken place pre-eminently during these intermediate periods,
of which, unfortunately, no petrifactions could be preserved, whereas,
on the contrary, during the slow sinking of the ground there was more
chance of numerous species dying out, and of a retrogression into fewer
specific forms. The intermediate forms between the old and the
newly-forming species must also have lived during the periods of
elevation, and consequently could likewise leave no fossil remains.

In addition to the great and deplorable gaps in the palæontological
records of creation—which are caused by the periods of elevation—there
are, unfortunately, many other circumstances which immensely diminish
their value. I must mention here especially the _metamorphic state of
the most ancient formations_, of those strata which contain the remains
of the most ancient flora and fauna, the original forms of all
subsequent organisms, and which, therefore, would be of especial
interest. It is just these rocks—and, indeed, the greater part of the
primordial, or archilithic strata, almost the whole of the Laurentian,
and a large part of the Cambrian systems—which no longer contain any
recognizable remains, and for the simple reason that these strata have
been subsequently changed or metamorphosed by the influence of the fiery
fluid interior of the earth. These deepest neptunic strata of the crust
have been completely changed from their original condition by the heat
of the glowing nucleus of the earth, and have assumed a crystalline
state. In this process, however, the form of the organic remains
enclosed in them has been entirely destroyed. It has been preserved only
here and there by a happy chance, as in the case of the most ancient
petrifactions known, the _Eozoon canadense_, from the lowest Laurentian
strata. However, from the layers of crystalline charcoal (graphite) and
crystalline limestone (marble), which are found deposited in the
metamorphic rocks, we may with certainty conclude that petrified animal
and vegetable remains existed in them in earlier times.

Our record of creation is also extremely imperfect from the circumstance
that only a small portion of the earth’s surface has been accurately
investigated by geologists, namely, England, Germany, and France. But we
know very little of the other parts of Europe, of Russia, Spain, Italy,
and Turkey. In the whole of Europe, only some few parts of the earth’s
crust have been laid open, by far the largest portion of it is unknown
to us. The same applies to North America and to the East Indies. There
some few tracts have been investigated; but of the larger portion of
Asia, the most extensive of all continents, we know almost nothing; of
Africa nothing, excepting the Cape of Good Hope and the shores of the
Mediterranean; of Australia almost nothing; and of South America but
very little. It is clear, therefore, that only quite a small portion,
perhaps scarcely the thousandth part of the whole surface of the earth,
has been palæontologically investigated. We may therefore reasonably
hope, when more extensive geological investigations are made, which are
greatly assisted by the constructions of railroads and mines, to find a
great number of other important petrifactions. A hint that this will be
the case is given by the remarkable petrifactions found in those parts
of Africa and Asia which have been minutely investigated,—the Cape
districts and the Himalaya mountains. A series of entirely new and very
peculiar animal forms have become known to us from the rocks of these
localities. But we must bear in mind that the vast bottom of the
existing oceans is at the present time quite inaccessible to
palæontological investigations, and that the greater part of the
petrifactions which have lain there from primæval times will either
never be known to us, or at best only after the course of many thousands
of years, when the present bottom of the ocean shall have become
accessible by gradual elevation. If we call to mind the fact that
three-fifths of the whole surface of the earth consists of water, and
only two-fifths of land, it becomes plain that on this account the
palæontological record must always present an immense gap.

But, in addition to these, there exists another series of difficulties
in the way of palæontology which arises from the nature of the organisms
themselves. In the first place, as a rule only the hard and solid parts
of organisms can fall to the bottom of the sea or of fresh waters, and
be there enclosed in the mud and petrified. Hence it is only the bones
and teeth of vertebrate animals, the calcareous shells of molluscs, the
chitinous skeletons of articulated animals, the calcareous skeletons of
star-fishes and corals, and the woody and solid parts of plants, that
are capable of being petrified. But soft and delicate parts, which
constitute by far the greater portion of the bodies of most organisms,
are very rarely deposited in the mud under circumstances favourable to
their becoming petrified, or distinctly impressing their external form
upon the hardening mud. Now, it must be borne in mind that large classes
of organisms, as for example the Medusæ, the naked molluscs without
shells, a large portion of the articulated animals, almost all worms,
and even the lowest vertebrate animals, possess no firm and hard parts
capable of being petrified. In like manner the most important parts of
plants, such as the flowers, are for the most part so soft and tender
that they cannot be preserved in a recognizable form. We therefore
cannot expect to find any petrified remains of these important
organisms. Moreover, all organisms at an early stage of life are so soft
and tender that they are quite incapable of being petrified.
Consequently all the petrifactions found in the neptunic stratifications
of the earth’s crust comprise altogether but a very few forms, and of
these for the most part only isolated fragments.

We must next bear in mind that the dead bodies of the inhabitants of the
sea are much more likely to be preserved and petrified in the deposits
of mud than those of the inhabitants of fresh water and of the land.
Organisms living on land can, as a rule, become petrified only when
their corpses fall accidentally into the water and are buried at the
bottom in the hardening layers of mud. But this event depends upon very
many conditions. We cannot therefore be astonished that by far the
majority of petrifactions belong to organisms which have lived in the
sea, and that of the inhabitants of the land proportionately only very
few are preserved in a fossil state. How many contingencies come into
play here we may infer from the single fact that of many fossil mammals,
in fact of all the mammals of the secondary, or mesozoic epoch, nothing
is known except the lower jawbone. This bone is in the first place
comparatively solid, and in the second place very easily separates
itself from the dead body, which floats on the water. Whilst the body is
driven away and dissolved by the water, the lower jawbone falls down to
the bottom of the water and is there enclosed in the mud. This explains
the remarkable fact that in a stratum of limestone of the Jurassic
system near Oxford, in the slates of Stonesfield, as yet only the lower
jawbones of numerous pouched animals (Marsupials) have been found. They
are the most ancient mammals known, and of the whole of the rest of
their bodies not a single bone exists. The opponents of the theory of
development, according to their usual logic, would from this fact be
obliged to draw the conclusion that the lower jawbone was the only bone
in the body of those animals.

Footprints are very instructive when we attempt to estimate the many
accidents which so arbitrarily influence our knowledge of fossils; they
are found in great numbers in different extensive layers of sandstone;
for example, in the red sandstone of Connecticut, in North America.
These footprints were evidently made by vertebrate animals, probably by
reptiles, of whose bodies not the slightest trace has been preserved.[1]
The impressions which their feet have left on the mud alone betray the
former existence of these otherwise unknown animals.

The accidents which, besides these, determine the limits of our
palæontological knowledge, may be inferred from the fact that we know of
only one or two specimens of very many important petrifactions. It is
not ten years since we became acquainted with the imperfect impression
of a bird in the Jurassic or Oolitic system, the knowledge of which
has been of the very greatest importance for the phylogeny of the whole
class of birds. All birds previously known presented a very uniformly
organized group, and showed no striking transitional forms to other
vertebrate classes, not even to the nearly related reptiles. But that
fossil bird from the Jura possessed not an ordinary bird’s tail, but a
lizard’s tail, and thus confirmed what had been conjectured upon other
grounds, namely, the derivation of birds from lizards. This single
fossil has thus essentially extended not only our knowledge of the age
of the class of birds, but also of their blood relationship to reptiles.
In like manner our knowledge of other animal groups has been often
essentially modified by the accidental discovery of a single fossil. The
palæontological records must necessarily be exceedingly imperfect,
because we know of so very few examples, or only mere fragments of very
many important fossils.

Another and very sensible gap in these records is caused by the
circumstance that the _intermediate forms_ which connect the different
species have, as a rule, not been preserved, and for the simple reason
that (according to the principle of divergence of character) they were
less favoured in the struggle for life than the most divergent
varieties, which had developed out of one and the same original form.
The intermediate links have, on the whole, always died out _rapidly_,
and have but rarely been preserved as fossils. On the other hand, the
most divergent forms were able to maintain themselves in life for a
longer period as independent species, to propagate more numerously, and
consequently to be more readily petrified. But this does not exclude the
fact that in _some_ cases the connecting intermediate forms of the
species have been preserved so perfectly petrified, that even now they
cause the greatest perplexity and occasion endless disputes among
systematic palæontologists about the arbitrary limits of species.

An excellent example of this is furnished by the celebrated and very
variable fresh-water snail from the Stuben Valley, near Steinheim, in
Würtemburg, which has been described sometimes as _Paludina_, sometimes
as _Valvata_, and sometimes as _Planorbis multiformis_. The snow-white
shells of these small snails constitute more than half of the mass of
the tertiary limestone hills, and in this one locality show such an
astonishing variety of forms, that the most divergent extremes might be
referred to at least twenty entirely different species. But all these
extreme forms are united by such innumerable intermediate forms, and
they lie so regularly above and beside one another, that Hilgendorf was
able, in the clearest manner, to unravel the pedigree of the whole group
of forms. In like manner, among very many other fossil species (for
example, many ammonites, terebratulæ, sea urchins, lily encrinites,
etc.) there are such masses of connecting intermediate forms, that they
reduce the “dealers in fossil species” to despair.

When we weigh all the circumstances here mentioned, the number of which
might easily be increased, it does not appear astonishing that the
natural accounts or records of creation formed by petrifactions are
extremely defective and incomplete. But nevertheless, the petrifactions
actually discovered are of the greatest value. Their significance is of
no less importance to the natural history of creation than the
celebrated inscription on the Rosetta stone, and the decree of Canopus,
are to the history of nations—to archæology and philology. Just as it
has become possible by means of these two most ancient inscriptions to
reconstruct the history of ancient Egypt, and to decipher all
hieroglyphic writings, so in many cases a few bones of an animal, or
imperfect impressions of a lower animal or vegetable form, are
sufficient for us to gain the most important starting-points in the
history of the whole group, and in the search after their pedigree. A
couple of small back teeth, which have been found in the Keuper
formation of the Trias, have of themselves alone furnished a sure proof
that mammals existed even in the Triassic period.

Of the incompleteness of the geological accounts of creation, Darwin,
agreeing with Lyell, the greatest of all recent geologists, says:—

“I look at the geological record as a history of the world imperfectly
kept, and written in a changing dialect; of this history we possess the
last volume alone, relating only to two or three countries. Of this
volume, only here and there a short chapter has been preserved; and of
each page, only here and there a few lines. Each word of the
slowly-changing language, more or less different in the successive
chapters, may represent the forms of life which are entombed in our
consecutive formations, and which falsely appear to us to have been
abruptly introduced. On this view, the difficulties above discussed are
greatly diminished, or even disappear.”—_Origin of Species_, 6th
Edition, p. 289.

If we bear in mind the exceeding incompleteness of palæontological
records, we shall not be surprised that we are still dependent upon so
many uncertain hypotheses when actually endeavouring to sketch the
pedigree of the different organic groups. However, we fortunately
possess, besides fossils, other records of the history of the origin of
organisms, which in many cases are of no less value, nay, in several
cases are of much greater value, than fossils. By far the most important
of these other records of creation is, without doubt, _ontogeny_, that
is, the history of the development of the organic individual (embryology
and metamorphology). It briefly repeats in great and marked features the
series of forms which the ancestors of the respective individuals have
passed through from the beginning of their tribe. We have designated the
palæontological history of the development of the ancestors of a living
form as the history of a tribe, or _phylogeny_, and we may therefore
thus enunciate this exceedingly important _biogenetic fundamental
principle_: “_Ontogeny is a short and quick repetition, or
recapitulation, of Phylogeny, determined by the laws of Inheritance and
Adaptation_.” As every animal and every plant from the beginning of its
individual existence passes through a series of different forms, it
indicates in rapid succession and in general outlines the long and
slowly changing series of states of form which its progenitors have
passed through from the most ancient times. (Gen. Morph. ii. 6, 110,
300.)

It is true that the sketch which the ontogeny of organisms gives us of
their phylogeny is in most cases more or less obscured, and all the more
so the more Adaptation, in the course of time, has predominated over
Inheritance, and the more powerfully the law of abbreviated inheritance,
and the law of correlative adaptation, have exerted their influence.
However, this does not lessen the great value which the actual and
faithfully preserved features of that sketch possess. _Ontogeny is of
the most inestimable value for the knowledge of the earliest
palæontological conditions of development_, just because no petrified
remains of the most ancient conditions of the development of tribes and
classes have been preserved. These, indeed, could not have been
preserved on account of the soft and tender nature of their bodies. No
petrifactions could inform us of the fundamental and important fact
which ontogeny reveals to us, that the most ancient common ancestors of
all the different animal and vegetable species were quite simple cells
like the egg-cell. No petrifaction could prove to us the immensely
important fact, established by ontogeny, that the simple increase, the
formation of cell-aggregates and the differentiation of those cells,
produced the infinitely manifold forms of multicellular organisms. Thus
ontogeny helps us over many and large gaps in palæontology.

[Illustration: Hand of Nine different Mammals. Pl. IV.

_1. Man_, _2. Gorilla_, _3. Orang_, _4. Dog_, _5. Seal_, _6. Porpoise_,
_7. Bat_, _8. Mole_, _9. Duck-bill_.]

To the invaluable records of creation furnished by palæontology and
ontogeny are added the no less important evidences for the blood
relationship of organisms furnished by _comparative anatomy_. When
organisms, externally very different, nearly agree in their internal
structure, one may with certainty conclude that the agreement has its
foundation in Inheritance, the dissimilarity its foundation in
Adaptation. Compare, for example, the hands and fore paws of the nine
different animals which are represented on Plate IV., in which the bony
skeleton in the interior of the hand and of the five fingers is visible.
Everywhere we find, though the external forms are most different, the
same bones, and among them the same number, position, and connection. It
will perhaps appear very natural that the hand of _man_ (Fig. 1) differs
very little from that of the _gorilla_ (Fig. 2) and of the
_orang-outang_ (Fig. 3), his nearest relations. But it will be more
surprising if the fore feet of the _dog_ also (Fig. 4), as well as the
breast-fin (the hand) of the _seal_ (Fig. 5), and of the _dolphin_ (Fig.
6), show essentially the same structure. And it will appear still more
wonderful that even the wing of the _bat_ (Fig. 7), the shovel-feet of
the _mole_ (Fig. 8), and the fore feet of the _duck-bill_
(Ornithorhynchus) (Fig. 9), the most imperfect of all mammals, is
composed of entirely the same bones, only their size and form being
variously changed. Their number, the manner of their arrangement and
connection has remained the same. (Compare also the explanation of Plate
IV., in the Appendix.) It is quite inconceivable that any other cause,
except the common inheritance of the part in question from common
ancestors, could have occasioned this wonderful homology or similarity
in the essential inner structure with such different external forms.
Now, if we go down further in the system below the mammals, and find
that even the wings of birds, the fore feet of reptiles and amphibious
animals, are composed of essentially the same bones as the arms of man
and the fore legs of the other mammals, we can, from this circumstance
alone, with perfect certainty, infer the common origin of all these
vertebrate animals. Here, as in all other cases, the degree of the
internal agreement in the form discloses to us the degree of blood
relationship.

CHAPTER XVI.

PEDIGREE AND HISTORY OF THE KINGDOM OF THE PROTISTA.

Special Mode of Carrying out the Theory of Descent in the
Natural System of Organisms.—Construction of Pedigrees.—Descent
of all Many-Celled from Single-Celled Organisms.—Descent of
Cells from Monera.—Meaning of Organic Tribes, or Phyla.—Number
of the Tribes in the Animal and Vegetable Kingdoms.—The
Monophyletic Hypothesis of Descent, or the Hypothesis of one
Common Progenitor, and the Polyphyletic Hypothesis of Descent,
or the Hypothesis of Many Progenitors.—The Kingdom of Protista,
or Primæval Beings.—Eight Classes of the Protista
Kingdom.—Monera, Amœbæ, or Protoplastæ.—Whip-swimmers, or
Flagellata.—Ciliated-balls, or Catallacta.—Labyrinth-streamers,
or Labyrinthuleæ.—Flint-cells, or Diatomeæ.—Mucous-moulds, or
Myxomycetes.—Root-footers (Rhizopoda).—Remarks on the General
Natural History of the Protista: Their Vital Phenomena,
Chemical Composition, and Formation (Individuality and
Fundamental Form).—Phylogeny of the Protista Kingdom

By a careful comparison of the individual and the palæontological
development, as also by the comparative anatomy of organisms, by the
comparative examination of their fully developed structural
characteristics, we arrive at the knowledge of the degrees of their
different structural relationships. By this, however, we at the same
time obtain an insight into their true _blood relationship_, which,
according to the Theory of Descent, is the real reason of the structural
relationship. Hence by collecting, comparing, and employing the
empirical results of embryology, palæontology, and anatomy for
supplementing each other, we arrive at an approximate knowledge of “the
Natural System,” which, according to our views, is the _pedigree_ of
organisms. It is true that our human knowledge, in all things
fragmentary, is especially so in this case, on account of the extreme
incompleteness and defectiveness of the records of creation. However, we
must not allow this to discourage us, or to deter us from undertaking
this highest problem of biology. Let us rather see how far it may even
now be possible, in spite of the imperfect state of our embryological,
palæontological, and anatomical knowledge, to establish a probable
scheme of the genealogical relationships of organisms.

Darwin in his book gives us no answer to these special questions of the
Theory of Descent; at the conclusion he only expresses his conjecture
“that animals have descended from at most only four or five progenitors,
and plants from an equal or less number.” But as these few aboriginal
forms still show traces of relationship, and as the animal and vegetable
kingdoms are connected by intermediate transitional forms, he arrives
afterwards at the opinion “that probably all the organic beings which
have ever lived on the earth have descended from some one primordial
form, into which life was first breathed by the Creator.” Like Darwin,
all other adherents of the Theory of Descent have only treated it in a
general way, and not made the attempt to carry it out specially, and to
treat the “Natural System” actually as the pedigree of organisms. If,
therefore, we venture upon this difficult undertaking, we must take up
independent ground.

Four years ago I set up a number of hypothetical genealogies for the
larger groups of organisms in the systematic introduction to my General
History of Development (Gen. Morph. vol. ii.), and thereby, in fact,
made the first attempt actually to construct the pedigrees of organisms
in the manner required by the theory of development. I was quite
conscious of the extreme difficulty of the task, and as I undertook it
in spite of all discouraging obstacles, I claim no more than the merit
of having made the first attempt and given a stimulus for other and
better attempts. Probably most zoologists and botanists were but little
satisfied with this beginning, and least so in reference to the special
domain in which each one is specially at work. However, it is certainly
in this case much easier to blame than to produce something better, and
what best proves the immense difficulty of this infinitely complicated
task is the fact that no naturalist has as yet supplied the place of my
pedigrees by better ones. But, like all other scientific hypotheses
which serve to explain facts, my genealogical hypotheses may claim to be
taken into consideration until they are replaced by better ones.

I hope that this replacement will very soon take place; and I wish for
nothing more than that my first attempt may induce very many naturalists
to establish more accurate pedigrees for the individual groups, at least
in the special domain of the animal and vegetable kingdom which happens
to be well known to one or other of them. By numerous attempts of this
kind our genealogical knowledge, in the course of time, will slowly
advance and approach more towards perfection, although it can with
certainty be foreseen that we shall never arrive at a complete
pedigree. We lack, and shall ever lack, the indispensable
palæontological foundations. The most ancient records will ever remain
sealed to us, for reasons which have been previously mentioned. The most
ancient organisms which arose by spontaneous generation—the original
parents of all subsequent organisms—must necessarily be supposed to have
been Monera—simple, soft, albuminous lumps, without structure, without
any definite forms, and entirely without any hard and formed parts. They
and their next offspring were consequently not in any way capable of
being preserved in a petrified condition. But we also lack, for reasons
discussed in detail in the preceding chapter, by far the greater portion
of the innumerable palæontological documents, which are really requisite
for a safe reconstruction of the history of animal tribes, or phylogeny,
and for the true knowledge of the pedigree of organisms. If we,
therefore, in spite of this, venture to undertake their hypothetical
construction, we must chiefly depend for guidance on the two other
series of records which most essentially supplement the palæontological
archives. These are ontogeny and comparative anatomy.

If thoughtfully and carefully we consult these most valuable records, we
at once perceive what is exceedingly significant, namely, that by far
the greater number of organisms, especially all higher animals and
plants, are composed of a great number of cells, and that they originate
out of an egg, and that this egg, in animals as well as in plants, is a
single, perfectly simple cell—a little lump of albuminous constitution,
in which another albuminous corpuscle, the cell-kernel, is enclosed.
This cell containing its kernel grows and becomes enlarged. By division
it forms an accumulation of cells, and out of these, by division of
labour (as has previously been described), there arise the numberless
different forms which are presented to us in the fully developed animal
and vegetable species. This immensely important process—which we may
follow step by step, with our own eyes, any day in the embryological
development of any animal or vegetable individual, and which as a rule
is by no means considered with the reverence it deserves—informs us more
surely and completely than all petrifactions could do as to the original
palæontological development of all many-celled organisms, that is, of
all higher animals and plants. For as ontogeny, or the embryological
development of every single individual, is essentially only a
recapitulation of phylogeny, or the palæontological development of its
chain of ancestors, we may at once, with full assurance, draw the simple
and important conclusion, that _all many-celled animals and plants were
originally derived from single-celled organisms_. The primæval ancestors
of man, as well as of all other animals, and of all plants composed of
many cells, were simple cells living isolated. This invaluable secret of
the organic pedigree is revealed to us with infallible certainty by the
egg of animals, and by the true egg-cell of plants. When the opponents
of the Theory of Descent assert it to be miraculous and inconceivable
that an exceedingly complicated many-celled organism could, in the
course of time, have proceeded from a simple single-celled organism, we
at once reply that we may see this incredible miracle at any moment, and
follow it with our own eyes. For the embryology of animals and plants
visibly presents to our eyes in the shortest space of time the same
process as that which has taken place in the origin of the whole tribe
during the course of enormous periods of time.

Upon the ground of embryological records, therefore, we can with full
assurance maintain that all many-celled, as well as single-celled,
organisms are originally descended from simple cells; connected with
this, of course, is the conclusion that the most ancient root of the
animal and vegetable kingdom was common to both. For the different
primæval “original cells” out of which the few different main groups or
tribes have developed, only acquired their differences after a time, and
were descended from a common “primæval cell.” But where did those few
“original cells,” or the one primæval cell, come from? For the answer to
this fundamental genealogical question we must return to the theory of
plastids and the hypothesis of spontaneous generation which we have
already discussed (vol. i. p. 327).

As was then shown, we cannot imagine _cells_ to have arisen by
spontaneous generation, but only _Monera_, those primæval creatures of
the simplest kind conceivable, like the still living Protamœbæ,
Protomyxæ, etc. (vol. i. p. 186, Fig. 1). Only such corpuscules of mucus
without component parts—whose whole albuminous body is as homogeneous in
itself as an inorganic crystal, but which nevertheless fulfills the two
organic fundamental functions of nutrition and propagation—could have
directly arisen out of inorganic matter by autogeny at the beginning (we
may suppose) of the Laurentian period. While some Monera remained at the
original simple stage of formation, others gradually developed into
cells by the inner kernel of the albuminous mass becoming separated from
the external cell-substance. In others, by differentiation of the
outermost layer of the cell-substance, an external covering (membrane,
or skin) was formed round simple cytods (without kernel), as well as
round naked cells (containing a kernel). By these two processes of
separation in the simple primæval mucus of the Moneron body, by the
formation of a kernel in the interior and a covering on the outer
surface of the mass of plasma, there arose out of the original most
simple cytods, or Monera, those four different species of plastids, or
individuals, of the first order, from which, by differentiation and
combination, all other organisms could afterwards develop themselves.
(Compare vol. i. p. 347.)

The question now forces itself upon us, Are all organic cytods and
cells, and consequently also those “original cells” which we previously
considered to be the primary parents of the few great main groups of the
animal and vegetable kingdoms, descended from a single original form of
Moneron, or were there several different organic primary forms, each
traceable to a peculiar independent species of Moneron which originated
by spontaneous generation? In other words, _Is the whole organic world
of a common origin, or does it owe its origin to several acts of
spontaneous generation?_ This fundamental question of genealogy seems at
first sight to be of exceeding importance. But on a more accurate
examination, we shall soon see that this is not the case, and that it is
in reality a matter of very subordinate importance.

Let us now pass on to examine and clearly limit our conception of an
_organic tribe_. By _tribe_, or _phylum_, we understand all those
organisms of whose blood relationship and descent from a common primary
form there can be no doubt, or whose relationship, at least, is most
probable from anatomical reasons, as well as from reasons founded on
historical development. Our tribes, or phyla, according to this idea,
essentially coincide with those few “great classes,” or “main classes,”
of which Darwin also thinks that each contains only organisms related by
blood, and of which, both in the animal and in the vegetable kingdoms,
he only assumes either four or five. In the animal kingdom these tribes
would essentially coincide with those four, five, or six main divisions
which zoologists, since Bär and Cuvier, have distinguished as “main
forms, general plans, branches, or sub-kingdoms” of the animal kingdom.
(Compare vol. i. p. 53.) Bär and Cuvier distinguished only four of them,
namely:—1. The vertebrate animals (Vertebrata); 2. The articulated
animals (Articulata); 3. The molluscous animals (Mollusca); and 4. The
radiated animals (Radiata). At present six are generally distinguished,
since the tribe of the articulated animals is divided into two tribes,
those possessing articulated feet (Arthropoda), and the worms (Vermes);
and in like manner the tribe of radiated animals is subdivided into the
two tribes of the star animals (Echinodermata) and the animal-plants
(Zoophyta). Within each of these six tribes, all the included animals,
in spite of great variety in external form and inner structure,
nevertheless possess such numerous and important characteristics in
common, that there can be no doubt of their blood relationship. The same
applies also to the six great main classes which modern botany
distinguishes in the vegetable kingdom, namely:—1. Flowering plants
(Phanerogamia); 2. Ferns (Filicinæ); 3. Mosses (Muscinæ); 4. Lichens
(Lichenes); 5. Fungi (Fungi); and 6. Water-weeds (Algæ). The last three
groups, again, show such close relations to one another, that by the
name of “Thallus plants” they may be contrasted with the three first
main classes, and consequently the number of phyla, or main groups, of
the vegetable kingdom may be reduced to the number of four. Mosses and
ferns may likewise be comprised as “Prothallus plants” (Prothallophyta),
and thereby the number of plant tribes reduced to three—Flowering
plants, Prothallus plants, and Thallus plants.

Very important facts in the anatomy and the history of development, both
in the animal and vegetable kingdoms, support the supposition that even
these few main classes or tribes are connected at their roots, that is,
that the lowest and most ancient primary forms of all three are related
by blood to one another. Nay, by a further examination we are obliged to
go still a step further, and to agree with Darwin’s supposition, that
even the two pedigrees of the animal and vegetable kingdom are connected
at their lowest roots, and that the lowest and most ancient animals and
plants are derived from a single common primary creature. According to
our view, this common primæval organism can have been nothing but a
Moneron which took its origin by spontaneous generation.

In the mean time we shall at all events be acting cautiously if we avoid
this last step, and assume true blood relationship only within each
tribe, or phylum, where it has been undeniably and surely established by
facts in comparative anatomy, ontogeny, and phylogeny. But we may here
point to the fact that two different fundamental forms of genealogical
hypothesis are possible, and that all the different investigations of
the Theory of Descent in relation to the origin of organic groups of
forms will, in future, tend more and more in one or the other of these
directions. The unitary, or _monophyletic_, hypothesis of descent will
endeavour to trace the first origin of all individual groups of
organisms, as well as their totality, to a single common species of
Moneron which originated by spontaneous generation (vol. i. p. 343). The
multiple, or _polyphyletic_, hypothesis of descent, on the other hand,
will assume that several different species of Monera have arisen by
spontaneous generation, and that these gave rise to several different
main classes (tribes, or phyla) (vol. i. p. 348). The apparently great
contrast between these two hypotheses is in reality of very little
importance. For both the monophyletic and the polyphyletic hypothesis of
descent must necessarily go back to the Monera as the most ancient root
of the one or of the many organic tribes. But as the whole body of a
Moneron consists only of a simple, formless mass, without component
particles, made up of a single albuminous combination of carbon, it
follows that the differences of the different Monera can only be of a
chemical nature, and can only consist in a different atomic composition
of that mucous albuminous combination. But these subtle and complicated
differences of mixture of the infinitely manifold combinations of
albumen are not appreciable by the rude and imperfect means of human
observation and are, consequently, at present of no further interest to
the task we have in hand.

The question of the monophyletic or polyphyletic origin will constantly
recur within each individual tribe, where the origin of a smaller or of
a larger group is discussed. In the vegetable kingdom, for example, some
botanists will be inclined to derive all flowering plants from a single
form of fern, while others will prefer the idea that several different
groups of Phanerogama have sprung from several different groups of
ferns. In like manner, in the animal kingdom, some zoologists will be
more in favour of the supposition that all placental animals are derived
from a single pouched animal; others will be more in favour of the
opposite supposition, that several different groups of placental animals
have proceeded from several different pouched animals. In regard to the
human race itself, some will prefer to derive it from a single form of
ape, while others will be more inclined to the idea that several
different races of men have arisen, independently of one another, out of
several different species of ape. Without here expressing our opinion in
favour of either the one or the other conception, we must, nevertheless,
remark that in general _the monophyletic hypothesis of descent deserves
to be preferred to the polyphyletic hypothesis of descent_. In
accordance with the chorological proposition of a single “centre of
creation” or of a single primæval home for most species (which has
already been discussed), we may be permitted to assume that the original
form of every larger or smaller natural group only originated _once_ in
the course of time, and only in _one part_ of the earth. We may safely
assume this simple original root, that is, the monophyletic origin, in
the case of all the more highly developed groups of the animal and
vegetable kingdoms. (Compare vol. i. p. 353.) But it is very possible
that the more complete Theory of Descent of the future will involve the
polyphyletic origin of very many of the low and imperfect groups of the
two organic kingdoms.

For these reasons I consider it best, in the mean time, to adopt the
_monophyletic hypothesis of descent_ both for the animal and for the
vegetable kingdom. Accordingly, the above-mentioned six tribes, or
phyla, of the animal kingdom must be connected at their lowest root,
and likewise the three or six main classes, or phyla, of the vegetable
kingdom must be traced to a common and most ancient original form. How
the connection of these tribes is to be conceived I shall explain in the
succeeding chapters. But before proceeding to this, we must occupy
ourselves with a very remarkable group of organisms, which cannot
without artificial constraint be assigned either to the pedigree of the
vegetable or to that of the animal kingdom. These interesting and
important organisms are the _primary creatures_, or _Protista_.

All organisms which we comprise under the name of Protista show in their
external form, in their inner structure, and in all their vital
phenomena, such a remarkable mixture of animal and vegetable properties,
that they cannot with perfect justice be assigned either to the animal
or to the vegetable kingdom; and for more than twenty years an endless
and fruitless dispute has been carried on as to whether they are to be
assigned to this or that kingdom. Most of Protista are so small that
they can scarcely, if at all, be perceived with the naked eye. Hence the
majority of them have only become known during the last fifty years,
since by the help of the improved and general use of the microscope
these minute organisms have been more frequently observed and more
accurately examined. However, no sooner were they better known than
endless disputes arose about their real nature and their position in the
natural system of organisms. Many of these doubtful primary creatures
botanists defined as animals, and zoologists as plants; neither of the
two would own them. Others, again, were declared by botanists to be
plants, and by zoologists to be animals; each claimed them. These
contradictions are not altogether caused by our imperfect knowledge of
the Protista, but in reality by their true nature. Indeed, most Protista
present such a confused mixture of several animal and vegetable
characteristics, that each investigator may arbitrarily assign them
either to the animal or vegetable kingdom. Accordingly as he defines
these two kingdoms, and as he looks upon this or that characteristic as
determining the animal or vegetable nature, he will assign the
individual classes of Protista in one case to the animal and in another
to the vegetable kingdom. But this systematic difficulty has become an
inextricable knot by the fact that all more recent investigations on the
lowest organisms have completely effaced, or at least destroyed, the
sharp boundary between the animal and vegetable kingdom which had
hitherto existed, and to such a degree that its restoration is possible
only by means of a completely artificial definition of the two kingdoms.
But this definition could not be made so as to apply to many of the
Protista.

For this and other reasons it is, in the mean time, best to exclude the
doubtful beings from the animal as well as from the vegetable kingdom,
and to comprise them in a third organic kingdom standing midway between
the two others. This intermediate kingdom I have established as the
_Kingdom of the Primary Creatures_ (Protista), when discussing general
anatomy in the first volume of my General Morphology, pp. 191-238. In my
Monograph of the Monera,(15) I have recently treated of this kingdom,
having somewhat changed its limits, and given it a more accurate
definition. Of independent classes of the kingdom Protista, we may at
present distinguish the following:—

1. The still living Monera; 2. The Amœboidea, or Protoplasts; 3. The
Whip-swimmers, or Flagellata; 4. The Flimmer-balls, or Catallacta; 5.
The Tram-weavers, or Labyrinthuleæ; 6. The Flint-cells, or Diatomeæ; 7.
The Slime-moulds, or Myxomycetes; 8. The Ray-streamers, or Rhizopoda.

The most important groups at present distinguishable in these eight
classes of Protista are named in the systematic table on p. 51. Probably
the number of these Protista will be considerably increased in future
days by the progressive investigations of the ontogeny of the simplest
forms of life, which have only lately been carried on with any great
zeal. With most of the classes named we have become intimately
acquainted only during the last ten years. The exceedingly interesting
Monera and Labyrinthuleæ, as also the Catallacta, were indeed discovered
only a few years ago. It is probable also that very numerous groups of
Protista have died out in earlier periods, without having left any
fossil remains, owing to the very soft nature of their bodies. We might
add to the Protista from the still living lowest groups of organisms—the
Fungi; and in so doing should make a very large addition to its domain.
Provisionally we shall leave them among plants, though many naturalists
have separated them altogether from the vegetable kingdom.

_The pedigree of the kingdom Protista_ is still enveloped in the
greatest obscurity. The peculiar combination of animal and vegetable
properties, the indifferent and uncertain character of their relations
of forms and vital phenomena, together with a number of several very
peculiar features which separate most of the subordinate classes sharply
from the others, at present baffle every attempt distinctly to make out
their blood relationships with one another, or with the lowest animals
on the one hand, and with the lowest plants on the other hand. It is not
improbable that the classes specified, and many other unknown classes of
Protista, represent quite independent organic tribes, or phyla, each of
which has independently developed from one, perhaps from various, Monera
which have arisen by spontaneous generation. If we do not agree to this
polyphyletic hypothesis of descent, and prefer the monophyletic
hypothesis of the blood relationship of all organisms, we shall have to
Look upon the different classes of protista as the lower small
off-shoots of the root, springing from the same simple monera root, out
of which arose the two mighty and many-branched pedigrees of the animal
kingdom on the one hand, and of the vegetable kingdom on the other.
(compare pp. 74, 75.) before i enter into this difficult question more
accurately, it will be appropriate to premise something further as to
the contents of the classes of protista given on the next page, and
their general natural history.

SYSTEMATIC SURVEY

_Of the Larger and Smaller Groups of the Kingdom Protista._

----------------+--------------------+------------------+-----------------
_Classes of | _Systematic Name | _Orders of | _A name of a
the Protista | of the Classes_. | Families of the | Genus
Kingdom._ | | Classes._ | as an example._
----------------+--------------------+------------------+-----------------
{ 1. Gymnomonera Protogenes
1. MONERS Monera { 2. Lepomonera Protomyxa

{ 1. Gymnamœbæ Amœba
2. PROTOPLASTS Amœboida { 2. Leptamœbæ Arcella
{ 3. Gregarinæ Monocystis

{ 1. Nudiflagellata Euglena
3. WHIP-SWIMMERS Flagellata { 2. Cilioflagellata Peridinium

4. FLIMMER-BALLS Catallacta 1. Catallacta Magosphæra

5. TRAM-WEAVERS Labyrinthuleæ 1. Labyrinthuleæ Labyrinthula

{ 1. Striata Navicula
6. FLINT-CELLS Diatomea { 2. Vittata Tabellaria
{ 3. Areolata Coscinodiscus

{ 1. Physareæ Æthalium
7. SLIME-MOULDS Myxomycetes { 2. Stemoniteæ Stemonitis
{ 3. Trichiaceæ Arcyria
{ 4. Lycogaleæ Reticularia

{ I. Acyttaria { 1. Monothalamia Gromia
{ { 2. Polythalamia Nummulina
8. RAY-STREAMERS {
OR RHIZOPODS. { II. Heliozoa 1. Heliozoa Actinosphærium
(Root-feet) {
{ { 1. Monocyttaria Cyrtidosphæra
{ III. Radiolaria { 2. Polycyttaria Collosphæra

[Illustration: FIG. 8.—Protamœba primitiva, a fresh-water Moneron, much
enlarged. _A._ The entire Moneron with its form-changing processes. _B._
It begins to divide itself into two halves. _C._ The division of the two
halves is completed, and each now represents an independent individual.]

It will perhaps seem strange that I should here again begin with the
remarkable _Monera_ as the first class of the Protista kingdom, as I of
course look upon them as the most ancient primary forms of all organisms
without exception. Still, what are we otherwise to do with the _still
living Monera_? We know nothing of their palæontological origin, we know
nothing of any of their relations to lower animals or plants, and we
know nothing of their possible capability of developing into higher
organisms. The simple and homogeneous little lump of slime or mucus
which constitutes their entire body (Fig. 8) is the most ancient and
original form of animal as well as of vegetable plastids. Hence it would
evidently be just as arbitrary and unreasonable to assign them to the
animal as it would be to assign them to the vegetable kingdom. In any
case we shall for the present be acting more cautiously and critically
if we comprise the still living Monera—whose number and distribution is
probably very great—as a special and independent class, contrasting them
with the other classes of the kingdom Protista, as well as with the
animal kingdom. Morphologically considered, the Monera—on account of the
perfect homogeneity of the albuminous substance of their bodies, on
account of their utter want of heterogeneous particles—are more closely
connected with anorgana than with organisms, and evidently form the
transition between the inorganic and organic world of bodies, as is
necessitated by the hypothesis of spontaneous generation. I have
described and given illustrations of the forms and vital phenomena of
the still living Monera (Protamœba, Protogenes, Protomyxa, etc.) in my
Monograph of the Monera,(15) and have briefly mentioned the most
important facts in the eighth chapter (vol. i. pp. 183-187). Therefore,
only by way of a specimen, I here repeat the drawing of the fresh-water
Protamœba (Fig. 8). The history of the life of an orange-red _Protomyxa
adrantiaca_, which I observed at Lanzerote, one of the Canary Islands,
is given in Plate I. (see its explanation in the Appendix). Besides
this, I here add a drawing of the form of Bathybius, that remarkable
Moneron discovered by Huxley, which lives in the greatest depths of the
sea in the shape of naked lumps of protoplasm and reticular mucus (vol.
i. p. 344).

[Illustration: FIG. 9.—Bathybius Hæckelii, the “creature of primæval
slime,” from the greatest depths of the sea. The figure, which is
greatly magnified, only shows that form of the Bathybius which consists
of a naked network of protoplasm, without the discoliths and cyatholiths
which are found in other forms of the same Moneron, and which perhaps
may be considered as the products of its secretion.]

The _Amœbæ_ of the present day, and the organisms most closely connected
with them, _Arcellidæ_ and _Gregarinæ_, which we here unite as a second
class of Protista under the name of _Amœboidea_ (Protoplasta), present
no fewer genealogical difficulties than the Monera. These primary
creatures are at present usually placed in the animal kingdom without
its in reality being understood why. For simple naked cells—that is,
shell-less plastids with a kernel—occur as well among real plants as
real animals. The generative cells, for example, in many Algæ (spores
and eggs) exist for a longer or shorter time in water in the form of
naked cells with a kernel, which cannot be distinguished at all from the
naked eggs of many animals (for example, those of the Siphonophorous
Medusæ). (Compare the figure of a naked egg of a bladder-wrack in
Chapter xvii. p. 90.) In reality every naked simple cell, whether it
proceeds from an animal or vegetable body, cannot be distinguished from
an independent Amœba. For an Amœba is nothing but a simple primary cell,
a naked little lump of cell-matter, or plasma, containing a kernel. The
contractility of this plasma, which the free Amœba shows in stretching
out and drawing in its changing processes, is a general vital property
of the organic plasma of all animal as well as of all vegetable
plastids. When a freely moving Amœba, which perpetually changes its
form, passes into a state of rest, it draws itself together into the
form of a globule, and surrounds itself with a secreted membrane. It can
then be as little distinguished from an animal egg as from a simple
globular vegetable cell (Fig. 10 _A_).

[Illustration: FIG. 10.—Amœba sphærococcus, greatly magnified. A
fresh-water Amœba without a contractile vacuole. _A._ The enclosed Amœba
in the state of a globular lump of plasma (_c_) enclosing a kernel and a
kernel-speck (_a_). The simple cell is surrounded by a cyst, or cell
membrane (_d_). _B._ The free Amœba, which has burst and left the cyst,
or cell-membrane. _C._ It begins to divide by its kernel parting into
two kernels, and the cell-substance between the two contracting. _D._
The division is completed, and the cell-substance has entirely separated
into two bodies. (_Da_ and _Db_).]

Naked cells, with kernels, like those represented in Fig. 10 _B_, which
are continuously changing, stretching out and drawing in formless,
finger-like processes, and which are on this account called amœboid, are
found frequently and widely dispersed in fresh water and in the sea;
nay, are even found creeping on land. They take their food in the same
way as was previously described in the case of the Protamœba (vol. i. p.
186). Their propagation by division can sometimes be observed. (Fig. 10
_C_, _D_.) I have described the processes in an earlier chapter (vol. i.
p. 187). Many of these formless Amœbæ have lately been recognized as the
early stages of development of other Protista (especially the
Myxomycetæ), or as the freed cells of lower animals and plants. The
colourless blood-cells of animals, for example, those of human blood,
cannot be distinguished from Amœbæ. They, like the latter, can receive
solid corpuscles into their interior, as I was the first to show by
feeding them with finely divided colouring matters (Gen. Morph. i. 271).
However, other Amœbæ (like the one given in Fig. 10) seem to be
independent “good species,” since they propagate themselves unchanged
throughout many generations. Besides the real, or _naked_, Amœbæ
(Gymnamœbæ), we also find widely diffused in fresh water _case-bearing_
Amœbæ (Lepamœbæ), whose naked plasma body is _partially_ protected by a
more or less solid shell (Arcella), sometimes even by a case (Difflugia)
composed of small stones. Lastly, we frequently find in the body of many
lower animals parasitic Amœbæ (Gregarinæ), which, adapting themselves to
a parasitic life, have surrounded their plasma-body with a delicate
closed membrane.

The simple naked Amœbæ are, next to the Monera, the most important of
all organisms to the whole science of biology, and especially to general
genealogy. For it is evident that the Amœbæ originally arose out of
simple Monera (Protamœbæ), by the important process of segregation
taking place in their homogeneous viscid body—the differentiation of an
inner kernel from the surrounding plasma. By this means the great
progress from a simple cytod (without kernel) into a real cell (with
kernel) was accomplished (compare Fig. 8 _A_ and Fig. 10 _B_). As some
of these cells at an early stage encased themselves by secreting a
hardened membrane, they formed the first vegetable cells, while others,
remaining naked, developed into the first aggregates of animal cells.
The presence or absence of an encircling hard membrane forms the most
important, although by no means the entire, difference of form between
animal and vegetable cells. As vegetable cells even at an early stage
enclose themselves within their hard, thick, and solid cellular shell,
like that of the Amœbæ in a state of rest (Fig. 10 _A_), they remain
more independent and less accessible to the influences of the outer
world than are the soft animal cells, which are in most cases naked, or
merely covered by a thin pliable membrane. But in consequence of this
the vegetable cells cannot combine, as do the animal cells, for the
construction of higher and composite fibrous tracts, for example, the
nervous and muscular tissues. It is probable that, in the case of the
most ancient single-celled organisms, there must have developed at an
early stage the very important difference in the animal and vegetable
mode of receiving food. The most ancient single-celled animals, being
naked cells, could admit solid particles into the interior of their soft
bodies, as do the Amœbæ (Fig. 10 _B_) and the colourless blood-cells;
whereas the most ancient single-celled plants encased by their membranes
were no longer able to do this, and could admit through it only fluid
nutrition (by means of diffusion).

[Illustration: FIG. 11.—A single Whip-swimmer (Euglena striata), greatly
magnified. Above a thread-like lashing whip is visible; in the centre
the round cellular kernel, with its kernel speck.]

The _Whip-swimmers_ (Flagellata), which we consider as a third class of
the kingdom Protista, are of no less doubtful nature than the Amœbæ.
They often show as close and important relations to the vegetable as to
the animal kingdom. Some Flagellata at an early stage, when freely
moving about, cannot be distinguished from real plants, especially from
the spores of many Algæ; whereas others are directly allied to real
animals, namely, to the fringed Infusoria (Ciliata). The Flagellata are
simple cells which live in fresh or salt water, either singly or united
in colonies. The characteristic part of their body is a very movable
simple or compound whip-like appendage (whip, or flagellum) by means of
which they actively swim about in the water. This class is divided into
two orders. Among the fringed whip-swimmers (Cilioflagellata) there
exists, in addition to the long whip, a short fringe of vibrating hairs,
which is wanting in the unfringed whip-swimmers (Nudoflagellata). To the
former belong the flint-shelled yellow Peridinia, which are largely
active in causing the phosphorescence of the sea; to the latter belong
the green Euglenæ, immense masses of which frequently make our ponds in
spring quite green.

[Illustration: FIG. 12.—The Norwegian Flimmer-ball (Magosphæra planula)
swimming by means of its vibratile fringes, as seen from the surface.]

A very remarkable new form of Protista, which I have named
_Flimmer-ball_ (Magosphæra), I discovered only three years ago (in
September, 1869), on the Norwegian coast (Fig. 12), and have more
accurately described in my Biological Studies(15) (p. 137, Plate V.).
Off the island of Gis-oe, near Bergen, I found swimming about, on the
surface of the sea, extremely neat little balls composed of a number
(between thirty and forty) of fringed pear-shaped cells, the pointed
ends of which were united in the centre like radii. After a time the
ball dissolved. The individual cells swarmed about independently in the
water like fringed Infusoria, or Ciliata. These afterwards sank to the
bottom, drew their fringes into their bodies, and gradually changed into
the form of creeping Amœbæ (like Fig 10 _B_). These last afterwards
encased themselves (as in Fig. 10 _A_), and then divided by repeated
halvings into a large number of cells (exactly as in the case of the
cleavage of the egg, Fig. 6, vol. i. p. 299). The cells became covered
with vibratile hairs, broke through the case enclosing them, and now
again swam about in the shape of a fringed ball (Fig. 12). This
wonderful organism, which sometimes appears like a simple Amœba,
sometimes as a single fringed cell, sometimes as a many-celled fringed
ball, can evidently be classed with none of the other Protista, and must
be considered as the representative of a new independent group. As this
group stands midway between several Protista, and links them together,
it may bear the name of _Mediator_, or _Catallacta_.

[Illustration: FIG. 13.—Labyrinthula macrocystis (much enlarged). Below
is a large group of accumulated cells, one of which, on the left, is
separating itself; above are two single cells which are gliding along
the threads of the retiform labyrinth which form their “tramways.”]

The Protista of the fifth class, the _Tram-weavers_, or _Labyrinthuleæ_,
are of a no less puzzling nature; they were lately discovered by
Cienkowski on piles in sea water (Fig. 13). They are spindle-shaped
cells, mostly of a yellow-ochre colour, which are sometimes united into
a dense mass, sometimes move about in a very peculiar way. They form, in
a manner not yet explained, a retiform frame of entangled threads
(compared to a labyrinth), and on the dense filamentous “tramways” of
this frame they glide about. From the shape of the cells of the
Labyrinthuleæ we might consider them as the simplest plants, from their
motion as the simplest animals, but in reality they are neither animals
nor plants.

[Illustration: FIG. 14.—Navicula hippocampus (greatly magnified). In the
middle of the cell the cell-kernel (nucleus) is visible, together with
its kernel speck (nucleolus).]

The _Flint-cells_ (Diatomeæ), a sixth class of Protista, are perhaps the
most closely related to the Labyrinthuleæ. These primary creatures—which
at present are generally considered as plants, although some celebrated
naturalists still look upon them as animals—inhabit the sea and fresh
waters in immense masses, and offer an endless variety of the most
elegant forms. They are mostly small microscopic cells, which either
live singly (Fig. 14), or united in great numbers, and occur either
attached to objects, or glide and creep about in a peculiar manner.
Their soft cell-substance, which is of a characteristic brownish yellow
colour, is always enclosed by a solid and hard flinty shell, possessing
the neatest and most varied forms. This flinty covering is open to the
exterior only by one or two slits, through which the enclosed soft
plasma-body communicates with the outer world. The flinty cases are
found petrified in masses, and many rocks—for example, the Tripoli slate
polish, the Swedish mountain meal, etc.,—are in a great measure composed
of them.

A seventh class of Protista is formed by the remarkable _Slime-moulds_
(Myxomycetes). They were formerly universally considered as plants, as
real Fungi, until ten years ago the botanist De Bary, by discovering
their ontogeny, proved them to be quite distinct from Fungi, and rather
to be akin to the lower animals. The mature body is a roundish bladder,
often several inches in size, filled with fine spore-dust and soft
flakes (Fig. 15), as in the case of the well-known puff-balls
(Gastromycetes). However, the characteristic cellular threads, or hyphæ,
of a real fungus do not arise from the germinal corpuscles, or spores,
of the Myxomycetes, but merely naked masses of plasma, or cells, which
at first swim about in the form of Flagellata (Fig. 11), afterwards
creep about like the Amœbæ (Fig. 10 _B_), and finally combine with
others of the same kind to form large masses of “slime,” or “plasmodia.”
Out of these, again, there arises, by-and-by, the bladder-shaped
fruit-body. Many of my readers probably know one of these plasmodia, the
Æthalium septicum, which in summer forms a beautiful yellow mass of soft
mucus, often several feet in breadth, known by the name of “tan
flowers,” and penetrates tan-heaps and tan-beds. At an early stage these
slimy, freely-creeping Myxomycetes, which live for the most part in damp
forests, upon decaying vegetable substances, bark of trees, etc., are
with equal justice or injustice declared by zoologists to be animals,
while in the mature, bladder-shaped condition of fructification they are
by botanists defined as plants.

[Illustration: FIG. 15.—A stalked fruit-body (spore-bladder, filled with
spores) of one of the Myxomycetes (Physarum albipes) not much enlarged.]

The nature of the _Ray-streamers_ (Rhizopoda), the eighth class of the
kingdom Protista, is equally obscure. These remarkable organisms have
peopled the sea from the most ancient times of the organic history of
the earth, in an immense variety of forms, sometimes creeping at the
bottom of the sea, sometimes swimming on the surface. Only very few live
in fresh water (Gromia, Actinosphærium). Most of them possess solid
calcareous or flinty shells of an extremely beautiful construction,
which can be perfectly preserved in a fossil state. They have frequently
accumulated in such huge numbers as to form mountain masses, although
the single individuals are very small, and often scarcely visible, or
completely invisible to the naked eye. A very few attain the diameter
of a few lines, or even as much as a couple of inches. The name which
the class bears is given because thousands of exceedingly fine threads
of protoplasm radiate from the entire surface of their naked slimy body;
these rays are quasi-feet, or pseudopodia, which branch off like roots
(whence the term Rhizopoda, signifying root-footed), unite like nets,
and are observed continually to change form, as in the case of the
simpler plasmic feet of the Amœboidea, or Protoplasts. These
ever-changing little pseudo-feet serve both for locomotion and for
taking food.

The class of the Rhizopoda is divided into three different legions, viz.
the chamber-shells, or Acyttaria, the sun-animalcules, or Heliozoa, and
the basket-shells, or Radiolaria. The _Chamber-shells_ (Acyttaria)
constitute the first and lowest of these three legions; for the whole of
their soft body consists merely of simple mucous or slimy cell-matter,
or protoplasm, which has not differentiated into cells. However, in
spite of this most primitive nature of body, most of the Acyttaria
secrete a solid shell composed of calcareous earth, which presents a
great variety of exquisite forms. In the more ancient and more simple
Acyttaria this shell is a simple chamber, bell-shaped, tubular, or like
the shell of a snail, from the mouth of which a bundle of plasmic
threads issues. In contrast to these _single-chambered forms_
(Monothalamia), the _many-chambered forms_ (Polythalamia)—to which the
great majority of the Acyttaria belong—possess a house, which is
composed in an artistic manner of numerous chambers. These chambers
sometimes lie in a row one behind the other, sometimes in concentric
circles or spirals, in the form of a ring round a central point, and
then frequently one above another in many tiers, like the boxes of an
amphitheatre. This formation, for example, is found in the nummulites,
whose calcareous shells, of the size of a lentil, have accumulated to
the number of millions, and form whole mountains on the shores of the
Mediterranean. The stones of which some of the Egyptian pyramids are
built consist of such nummulitic limestone. In most cases the chambers
of the shells of the Polythalamia are wound round one another in a
spiral line. The chambers are connected with one another by passages and
doors, like rooms of a large palace, and are generally open towards the
outside by numerous little windows, out of which the plasmic body can
stream or strain forth its little pseudo-feet, or rays of slime, which
are always changing form. But in spite of the exceedingly complicated
and elegant structure of this calcareous labyrinth, in spite of the
endless variety in the structure and the decoration of its numerous
chambers, and in spite of the regularity and elegance of their
execution, the whole of this artistic palace is found to be the secreted
product of a perfectly formless, slimy mass, devoid of any component
parts! Verily, if the whole of the recent anatomy of animal and
vegetable textures did not support our theory of plastids, if all its
important results did not unanimously corroborate the fact that the
whole miracle of vital phenomena and vital forms is traceable to the
active agency of the formless albuminous combinations of protoplasm, the
Polythalamia alone would secure the triumph of that theory. For we may
here at any moment, by means of the microscope, point out the wonderful
fact, first established by Dujardin and Max Schulze, that the formless
mucus of the soft plasma-body, this true “matter of life,” is able to
secrete the neatest, most regular, and most complicated structures. This
secretive skill is simply a result of _inherited adaptation_, and by it
we learn to understand how this same “primæval slime”—this same
protoplasm—can produce in the bodies of animals and plants the most
different and most complicated cellular forms.

It is, moreover, a matter of special interest that the most ancient
organism, the remains of which are found in a petrified condition,
belongs to the Polythalamia. This organism is the “Canadian Life’s-dawn”
(_Eozoon canadense_), which has already been mentioned, and which was
found a few years ago in the Ottawa formation (in the deepest strata of
the Laurentian system), on the Ottawa river in Canada. If we expected to
find organic remains at all in these most ancient deposits of the
primordial period, we should certainly look for such of the most simple
Protista as are covered with a solid shell, and in the organization of
which the difference between animal and plant is as yet not indicated.

We know of but few species of the _Sun-animalcules_ (Heliozoa), the
second class of the Rhizopoda. One species is very frequently found in
our fresh waters. It was observed even in the last century by a
clergyman in Dantzig, Eichhorn by name, and it has been called after
him, Actinosphærium Eichhornii. To the naked eye it appears as a
gelatinous grey globule of mucus, about the size of a pin’s head.
Looking at it through the microscope, we see hundreds or thousands of
fine mucous threads radiating from the central plasma body, and perceive
that the inner layer of its cell-substance is different from the outer
layer, which forms a bladder-like membrane. In consequence of its
structure, this, the little sun-animalcule, although wanting a shell,
really rises above the structureless Acyttaria, and forms the transition
from these to the Radiolaria. The genus Cystophrys is of a nature akin
to it.

The _Basket-shells_ (Radiolaria) form the third and last class of the
Rhizopoda. Their lower forms are closely allied to the Heliozoa and
Acyttaria, whereas their higher forms rise far above them. They are
essentially distinguished from both by the fact that the central part of
their body is composed of many cells, and surrounded by a solid
membrane. This closed “central capsule,” generally of a globular shape,
is covered by a mucous layer of plasma, out of which there radiate on
all sides thousands of exceedingly fine threads, the branching and
confluent so-called pseudopodia. Between these are scattered numerous
yellow cells of unknown function, containing grains of starch. Most
Radiolaria are characterized by a highly developed skeleton, which
consists of flint, and displays a wonderful richness of the neatest and
most curious forms. Sometimes this flinty skeleton forms a simple
trellice-work ball (Fig. 16 _s_), sometimes a marvellous system of
several concentric trelliced balls, encased in one another, and
connected by radial staves. In most cases delicate spikes, which are
frequently branched like a tree, radiate from the surface of the balls.
In other cases the whole skeleton consists of only one flinty star, and
is then generally composed of twenty staves, distributed according to
definite mathematical laws, and united in a common central point. The
skeletons of other Radiolaria again form symmetrical many-chambered
structures, as in the case of the Polythalamia. Perhaps no other group
of organisms develop in the formation of their skeletons such an amount
of various fundamental forms, such geometrical regularity, and such
elegant architecture. Most of the forms as yet discovered, I have given
in the atlas accompanying my Monograph of the Radiolaria.(23) Here I
shall only give as an example the picture of one of the simplest forms,
the _Cyrtidosphæra echinoides_ of Nice. The skeleton in this case
consists only of a simple trelliced ball (_s_), with short radial spikes
(_a_), which loosely surround the central capsule (_c_). Out of the
mucous covering, enclosing the latter, radiate a great number of
delicate little pseudopodia (_p_), which are partly drawn back
underneath the shell, and fused into a lumpy mass of mucus. Between
these are scattered a number of yellow cells (_l_).

[Illustration: FIG. 16.—Cyrtidosphæra echinoides, 400 times enlarged.
_c._ Globular central capsule. _s._ Basket-work of the perforated flinty
shell. _a._ Radial spikes, which radiate from the latter. _p._ The
pseudo-feet radiating from the mucous covering surrounding the central
capsule. _l._ Yellow globular cells, scattered between the latter,
containing grains of starch.]

Most Acyttaria live only at the bottom of the sea, on stones and
seaweeds, or creep about in sand and mud by means of their pseudopodia,
but most Radiolaria swim on the surface of the sea by means of long
pseudopodia extending in all directions. They live together there in
immense numbers, but are mostly so small that they have been almost
completely overlooked, and have only become accurately known during the
last fourteen years. Certain Radiolaria living in communities
(Polycyttaria) form gelatinous lumps of some lines in diameter. On the
other hand, most of those living isolated (Monocyttaria) are invisible
to the naked eye; but still their petrified shells are found accumulated
in such masses that in many places they form entire mountains; for
example, the Nicobar Islands in the Indian Archipelago, and the Island
of Barbadoes in the Antilles.

As most readers are probably but little acquainted with the eight
classes of the Protista just mentioned, I shall now add some further
general observations on their natural history. The great majority of all
Protista live in the sea, some swimming freely on the surface, some
creeping at the bottom, and others attached to stones, shells, plants,
etc. Many species of Protista also live in fresh water, but only a very
small number on dry land (for example, Myxomycetes and some
Protoplasta). Most of them can be seen only through the microscope,
except when millions of individuals are found accumulated. Only a few of
them attain a diameter of some lines, or as much as an inch. What they
lack in size of body they make up for by producing astonishing numbers
of individuals, and they very considerably influence in this way the
economy of nature. The imperishable remains of dead Protista, for
instance, the flinty shells of the Diatomeæ and Radiolaria and the
calcareous shells of the Acyttaria, often form large rock masses.

In regard to their _vital phenomena_, especially those of nutrition and
propagation, some Protista are more allied to plants, others more to
animals. Both in their mode of taking food and in the chemical changes
of their living substance, they sometimes more resemble the lower
animals, at others the lower plants. _Free locomotion_ is possessed by
many Protista, while others are without it; but this does not constitute
a characteristic distinction, as we know of undoubted animals which
entirely lack free locomotion, and of genuine plants which possess it.
All Protista have a _soul_—that is to say, are “animate”—as well as all
animals and all plants. The soul’s activity in the Protista manifests
itself in their _irritability_, that is, in the movements and other
changes which take place in consequence of mechanical, electrical, and
chemical irritation of their contractile protoplasm. Consciousness and
the capability of will and thought are probably wanting in all Protista.
However, the same qualities are in the same degree also wanting in many
of the lower animals, whereas many of the higher animals in these
respects are scarcely inferior to the lower races of human beings. In
the Protista, as in all other organisms, the activities of the soul are
traceable to molecular motions in the protoplasm.

The most important _physiological characteristic_ of the kingdom
Protista lies in the exclusively _non-sexual propagation_ of all the
organisms belonging to it. The higher animals and plants multiply almost
exclusively in a sexual manner. The lower animals and plants multiply
also, in many cases, in a non-sexual manner, by division, the formation
of buds, the formation of germs, etc. But sexual propagation almost
always exists by the side of it, and often regularly alternates with it
in succeeding generations (Metagenesis, vol. i. p. 206). All Protista,
on the other hand, propagate themselves exclusively in a non-sexual
manner, and in fact, the distinction of the two sexes among them has not
been effected—there are neither male nor female Protista.

The Protista in regard to their vital phenomena stand midway between
animals and plants, that is to say, between their lowest forms; and the
same must be said in regard to the _chemical composition_ of their
bodies. One of the most important distinctions between the chemical
composition of animal and vegetable bodies consists in the
characteristic formation of the skeleton. The skeleton, or the solid
scaffolding of the body in most genuine plants, consists of a substance
called cellulose, devoid of nitrogen, but secreted by the nitrogenous
cell-substance, or protoplasm. In most genuine animals, on the other
hand, the skeleton generally consists either of nitrogenous combinations
(chitin, etc.) or of calcareous earth. In this respect some Protista are
more like plants, others more like animals. In many of them the skeleton
is principally or entirely formed of calcareous earth, which is met with
both in animal and vegetable bodies. But the active vital substance in
all cases is the mucous protoplasm.

In regard to the _form_ of the Protista, it is to be remarked that the
_individuality_ of their body almost always remains at an extremely low
stage of development. Very many Protista remain for life simple plastids
or individuals of the first order. Others, indeed, form colonies or
republics of plastids by the union of several individuals. But even
these higher individuals of the second order, formed by the combination
of simple plastids, for the most part remain at a very low stage of
development. The members of such communities among the Protista remain
very similar one to another, and never, or only in a slight degree,
commence a division of labour, and are consequently as little able to
render their community fit for higher functions as are, for example, the
savages of Australia. The community of the plastids remains in most
cases very loose, and each single plastid retains in a great measure its
own individual independence.

A second structural characteristic, which next to their low stage of
individuality especially distinguishes the Protista, is the low stage of
development of their stereometrical fundamental forms. As I have shown
in my theory of fundamental forms (in the fourth book of the General
Morphology), a definite geometrical fundamental form can be pointed out
in most organisms, both in the general form of the body and in the form
of the individual parts. This ideal fundamental form, or type, which is
determined by the number, position, combination, and differentiation of
the component parts, stands in just the same relation to the _real_
organic form as the ideal geometrical fundamental form of crystals does
to their imperfect _real_ form. In most bodies and parts of the bodies
of animals and plants this fundamental form is a pyramid. It is a
regular pyramid in the so-called “regular radiate” forms, and an
irregular pyramid in the more highly differentiated, so-called
“bilaterally symmetrical” forms. (Compare the plates in the first volume
of my General Morphology, pp. 556-558.) Among the Protista this
pyramidal type, which prevails in the animal and vegetable kingdom, is
on the whole rare, and instead of it we have either quite irregular
(amorphous) or more simple, regular geometrical types; especially
frequent are the sphere, the cylinder, the ellipsoid, the spheroid, the
double cone, the cone, the regular polygon (tetrahedron, hexahedron,
octahedron, dodecahedron, icosahedron), etc. All the fundamental forms
of the pro-morphological system, which are of a low rank in that system,
prevail in the Protista. However, in many Protista there occur also the
higher, regular, and bilateral types, fundamental forms which
predominate in the animal and vegetable kingdoms. In this respect some
of the Protista are frequently more closely allied to animals (as the
Acyttaria), others more so to plants (as the Radiolaria).

With regard to the _palæontological development of the kingdom
Protista_, we may form various, but necessarily very unsafe,
genealogical hypotheses. Perhaps the individual classes of the kingdom
are independent tribes, or phyla, which have developed independently of
one another and independently of the animal and the vegetable kingdoms.
Even if we adopt the monophyletic hypothesis of descent, and maintain a
common origin from a single form of Moneron for all organisms, without
exception, which ever have lived and still live upon the earth, even in
this case the connection of the neutral Protista on the one hand with
the vegetable kingdom, and on the other hand with the animal kingdom,
must be considered as very vague. We must regard them (compare p. 74) as
lower off-shoots which have developed directly out of the root of the
great double-branched organic pedigree, or perhaps out of the lowest
tribe of Protista, which may be supposed to have shot up midway between
the two diverging high and vigorous trunks of the animal and vegetable
kingdoms. The individual classes of the Protista, whether they are more
closely connected at their roots in groups, or only form a loose bunch
of root offsets, must in this case be regarded as having nothing to do
either with the diverging groups of organisms belonging to the animal
kingdom on the right, or to the vegetable kingdom on the left. They must
be supposed to have retained the original simple character of the common
primæval living thing more than have genuine animals and genuine plants.

But if we adopt the polyphyletic hypothesis of descent, we have to
imagine a number of organic tribes, or phyla, which all shoot up by
spontaneous generation out of the same ground, by the side of and
independent of one another. (Compare p. 75.) In that case numbers of
different Monera must have arisen by spontaneous generation whose
differences would depend only upon slight, to us imperceptible,
differences in their chemical composition, and consequently upon
differences in their capability of development. A small number of Monera
would then have given origin to the animal kingdom, and, again, a small
number would have produced the vegetable kingdom. Between these two
groups, however, there would have developed, independently of them, a
large number of independent tribes, which have remained at a lower stage
of organization, and which have neither developed into genuine plants
nor into genuine animals.

A safe means of deciding between the monophyletic and polyphyletic
hypotheses is as yet quite impossible, considering the imperfect state
of our phylogenetic knowledge. The different groups of Protista, and
those lowest forms of the animal kingdom and of the vegetable kingdom
which are scarcely distinguishable from the Protista, show such a close
connection with one another and such a confused mixture of
characteristics, that at present any systematic division and arrangement
of the groups of forms seem more or less artificial and forced. Hence
the attempt here offered must be regarded as entirely provisional. But
the more deeply we penetrate into the genealogical secrets of this
obscure domain of inquiry, the more probable appears the idea that the
vegetable kingdom and the animal kingdom are each of independent origin,
and that midway between these two great pedigrees a number of other
independent small groups of organisms have arisen by repeated acts of
spontaneous generation, which on account of their indifferent neutral
character, and in consequence of their mixture of animal and vegetable
properties, may lay claim to the designation of independent Protista.

II. III.

||| ||||||||||| |||||
||| ||||||||||| |||||
||| ||||||||||| |||||
Vegetable Monera Neutral Monera Animal Monera
| ||||| |
| ||||| |
| ||||| |
\--------------------------v------------/

|
|
=Archigonic Monera=

(Pieces of Protoplasm which have originated by Spontaneous Generation)

----------------------------------------------------------------

POLYPHYLETIC PEDIGREE.

II. I. III.

=Vegetable= =Protista= =Animal=
=Kingdom= =Kingdom= =Kingdom=
Vegetabilia Protista Animalia
\------v------/ | \-----v----/
| | |
| | |
| /-----------------------------------^--------------------------------\ |
| Slime-moulds, |
| or |
| Mucous Fungi Ray-streamers |
| _Myxomycetes_ _Rhizopoda_ |
| \-----v------/ \-----v------/ |
| | | |
| | Flint-cells | Flimmer-balls |
| | _Diatomæ_ | _Catallacta_ |
| | \-----v------/ | \-----v------/ |
| | | | | |
| | | Whip-swimmers | | |
| | | _Flagellata_ | | |
| | | \-----v------/ | | |
| | | | | | |
| | | Tram-weavers | | | |
| | | _Labyrinthulea_ | | | |
| | | \-----v------/ | | | |
| | | | | | | |
| | | | Amœbæ, | | | =Primæval=
=Primæval Plants= | | | or | | | =Animals=
Protophyta | | | Protoplasta | | | Protozoa
\------v------/ | | | \-----v------/ | | | \-----v------/
||| | | | ||||| | | | |||||||
||| | | | ||||| | | | |||||||
||| | | | ||||| | | | |||||||
||| | | | ||||| | | | |||||||
=Vegetable= | | | =Neutral= | | | =Animal=
=Monera= | | | =Monera= | | | =Monera=
| | | | | | † | † † | † |
† | | † | | † | | † | | | | † | |† | †
|† | † | †| | † | |† | † | | | | |†| | | ||† | † |†
||† | |† | || | | | || | |† | |†| | |||†| | |||† | | ||
†|||† | †||† | ||† | †|† | ||† | ||† | ||| | ||||| | |||| | |†||†
||||| | |||| | ||| | ||| | ||| | ||| | ||| | ||||| | |||| | |||||
||||| | |||| | ||| | ||| | ||| | ||| | ||| | ||||| | |||| | |||||
-------------------------------------------------------------------------------------------

N.B.—The lines marked with a † indicate extinct tribes of Protista,
which have arisen independently by repeated acts of Spontaneous Generation.

Thus, if we assume one entirely independent trunk for the vegetable
kingdom, and a second for the animal kingdom, we may set up a number of
independent stems of Protista, each of which has developed, quite
independently of other stems and trunks, from a special archigonic form
of Monera. In order to make this relation more clear, we may imagine the
whole world of organisms as an immense meadow which is partially
withered, and upon which two many-branched and mighty trees are
standing, likewise partially withered. The two great trees represent the
animal and vegetable kingdoms, their fresh and still green branches the
living animals and plants; the dead branches with withered leaves
represent the extinct groups. The withered grass of the meadow
corresponds to the numerous extinct tribes, and the few stalks, still
green, to the still living phyla of the kingdom Protista. But the common
soil of the meadow, from which all have sprung up, is primæval by
protoplasm.

CHAPTER XVII.

PEDIGREE AND HISTORY OF THE VEGETABLE KINGDOM.

The Natural System of the Vegetable Kingdom.—Division of the
Vegetable Kingdom into Six Branches and Eighteen Classes.—The
Flowerless Plants (Cryptogamia).—Sub-kingdom of the Thallus
Plants.—The Tangles, or Algæ (Primary Algæ, Green Algæ, Brown
Algæ, Red Algæ).—The Thread-plants, or Inophytes (Lichens and
Fungi).—Sub-kingdom of the Prothallus Plants.—The Mosses, or
Muscinæ (Water-mosses, Liverworts, Leaf-mosses,
Bog-mosses).—The Ferns, or Filicinæ (Leaf-ferns, Bamboo-ferns,
Water-ferns, Scale-ferns).—Sub-kingdom of Flowering Plants
(Phanerogamia).—The Gymnosperms, or Plants with Naked Seeds
(Palm-ferns = Cycadeæ; Pines = Coniferæ).—The Angiosperms, or
Plants with Enclosed Seeds.—Monocotylæ.—Dicotylæ.—Cup-blossoms
(Apetalæ).—Star-blossoms (Diapetalæ).—Bell-blossoms
(Gamopetalæ).

Every attempt that we make to gain a knowledge of the pedigree of any
small or large group of organisms related by blood must, in the first
instance, start with the evidence afforded by the existing “_natural
system_” of this group. For although the natural system of animals and
plants will never become finally settled, but will always represent a
merely approximate knowledge of true blood relationship, still it will
always possess great importance as a hypothetical pedigree. It is true,
by a “natural system” most zoologists and botanists only endeavour to
express in a concise way the subjective conceptions which each has
formed of the objective “_form-relationships_” of organisms. These
form-relationships, however, as the reader has seen, are in reality the
necessary result of true _blood relationship_. Consequently, every
morphologist in promoting our knowledge of the natural system, at the
same time promotes our knowledge of the pedigree, whether he wishes it
or not. The more the natural system deserves its name, and the more
firmly it is established upon the concordance of results obtained from
the study of comparative anatomy, ontogeny, and palæontology, the more
surely may we consider it as the approximate expression of the true
pedigree of the organic world.

In entering upon the task contemplated in this chapter, the genealogy of
the vegetable kingdom, we shall have, according to this principle, first
to glance at the _natural system of the vegetable kingdom_ as it is at
present (with more or less important modifications) adopted by most
botanists. According to the system generally in vogue, the whole series
of vegetable forms is divided into two main groups. These main
divisions, or sub-kingdoms, are the same as were distinguished more than
a century ago by Charles Linnæus, the founder of systematic natural
history, and which he called _Cryptogamia_, or secretly-blossoming
plants, and _Phanerogamia_, or openly-flowering plants. The latter,
Linnæus, in his artificial system of plants, divided, according to the
different number, formation, and combination of the anthers, and also
according to the distribution of the sexual organs, into twenty-three
different classes, and then added the Cryptogamia to these as the
twenty-fourth and last class.

The _Cryptogamia_, the secretly-blossoming or flowerless plants, which
were formerly but little observed, have in consequence of the careful
investigations of recent times been proved to present such a great
variety of forms, and such a marked difference in their coarser and
finer structure, that we must distinguish no less than fourteen
different classes of them; whereas the number of classes of flowering
plants, or _Phanerogamia_, may be limited to four. However, these
_eighteen classes of the vegetable kingdom_ can again be naturally
grouped in such a manner that we are able to distinguish in all _six
main divisions_ or _branches_ of the vegetable kingdom. Two of these six
branches belong to the flowering, and four to the flowerless plants. The
table on page 82 shows how the eighteen classes are distributed among
the six branches, and how these again fall under the _sub-kingdoms_ of
the vegetable kingdom.

The one sub-kingdom of the _Cryptogamia_ may now be naturally divided
into _two_ divisions, or sub-kingdoms, differing very essentially in
their internal structure and in their external form, namely, the Thallus
plants and the Prothallus plants. The group of _Thallus plants_
comprises the two large branches of Tangles, or Algæ, which live in
water, and the Thread-plants, or Inophytes (Lichens and Fungi), which
grow on land, upon stones, bark of trees, upon decaying bodies, etc. The
group of _Prothallus plants_, on the other hand, comprises the two
branches of Mosses and Ferns, containing a great variety of forms.

All _Thallus plants, or Thallophytes_, can be directly recognized from
the fact that the two morphological fundamental organs of all other
plants, stem and leaves, cannot be distinguished in their structure. The
complete body of all Algæ and of all Thread-plants is a mass composed of
simple cells, which is called a _lobe_, or _thallus_. This thallus is
as yet not differentiated into axial-organs (stem and root) and
leaf-organs. On this account, as well as through many other
peculiarities, the Thallophytes contrast strongly with all remaining
plants—those comprised under the two sub-kingdoms of Prothallus plants
and Flowering plants—and for this reason the two latter sub-kingdoms are
frequently classed together under the name of _Stemmed plants_, or
_Cormophytes_. The following table will explain the relation of these
three sub-kingdoms to one another according to the two different views:—

{ A. Thallus Plants } I. Thallus Plants
{ (_Thallophyta_) } (_Thallophyta_)
I. Flowerless Plants. {
(_Cryptogamia_) {
{ B. Prothallus Plants }
{ (_Prothallophyta_) }
} II. Stemmed Plants
} (_Cormophyta_)
}
II. Flowering Plants { C. Flowering Plants }
(_Phanerogamia_) { (_Phanerogamia_) }

The stemmed plants, or Cormophytes, in the organization of which the
difference of axial-organs (stem and root) and leaf-organs is already
developed, form at present, and have, indeed, for a very long period
formed, the principal portion of the vegetable world. However, this was
not always the case. In fact, stemmed plants, not only of the flowering
group, but even of the prothallus group, did not exist at all during
that immeasurably long space of time which forms the beginning of the
first great division of the organic history of the earth, under the name
of the archilithic, or primordial period. The reader will recollect that
during this period the Laurentian, Cambrian, and Silurian systems of
strata were deposited, the thickness of which, taken as a whole,
amounts to about 70,000 feet. Now, as the thickness of all the more
recent super-incumbent strata, from the Devonian to the deposits of the
present time, taken together, amounts to only about 60,000 feet, we were
enabled from this fact alone to draw the conclusion—which is probable
also for other reasons—that the archilithic, or primordial, period was
of longer duration than the whole succeeding period down to the present
time. During the whole of this immeasurable space of time, which
probably comprises many millions of centuries, vegetable life on our
earth seems to have been represented exclusively by the sub-kingdom of
Thallus plants, and, moreover, only by the class of marine Thallus
plants, that is to say, the Algæ. At least all the petrified remains
which are positively known to be of the primordial period belong
exclusively to this class. As all the animal remains of this immense
period also belong exclusively to animals that lived in water, we come
to the conclusion that at that time organisms adapted to a life on land
did not exist at all.

For these reasons the first and most imperfect of the great provinces or
branches of the vegetable kingdom, the division of the Algæ, or Tangles,
must be of special interest to us. But, in addition, there is the
interest which this group offers when viewed by itself. In spite of the
exceedingly simple composition of their constituent cells, which are but
little differentiated, the Algæ show an extraordinary variety of
different forms. To them belong the simplest and most imperfect of all
forms, as well as very highly developed and peculiar forms. The
different groups of Algæ are distinguished as much by size of body as by
the perfection and variety of their outer form. At the lowest stage we
find such species as the minute Protococcus, several hundred thousands
of which occupy a space no larger than a pin’s head. At the highest
stage we marvel at the gigantic Macrocysts, which attain a length of
from 300 to 400 feet, the longest of all forms in the vegetable kingdom.
It is possible that a large portion of the coal has been formed out of
Algæ. If not for these reasons, yet the Algæ must excite our special
attention from the fact that they form the beginning of vegetable life,
and contain the original forms of all other groups of plants, supposing
that our monophyletic hypothesis of a common origin for all groups of
plants is correct. (Compare p. 83.)

SYSTEMATIC VIEW

_Of the Six Branches and Eighteen Classes of the Vegetable Kingdom._

{ { 1. Primæval algæ 1. _Archephyceæ_
{ { (Protophyta)
{ {
{ I. { 2. Green algæ 2. _Chlorophyceæ_
A. { Tangles { (Chloroalgæ)
=Thallus Plants= { _Algæ_ {
Thallophyta { { 3. Brown algæ 3. _Phæophyceæ_
{ { (Fucoideæ)
{ {
{ { 4. Red algæ 4. _Rhodophyceæ_
{ { (Florideæ)

{ II. { 5. Lichens 5. _Lichenes_
{ Thread-plants {
{ _Inophyta_ { 6. Fungi 6. _Fungi_
{
{ { 7. Tangle-mosses 7. _Charobrya_
{ { (Characeæ)
{ {
{ III. { 8. Liverworts 8. _Thallobrya_
{ Mosses { (Hepaticæ)
{ _Muscinæ_ {
{ { 9. Frondose-mosses 9. _Phyllobrya_
B. { { (Frondosæ)
=Prothallus= { {
=Plants= { { 10. Turf-mosses 10. _Sphagnobrya_
Prothallophyta { (Sphagnaceæ)
{
{ { 11. Shaft-ferns 11. _Calamariæ_
{ { (Calamophyta)
{ IV. {
{ Ferns { 12. Frondose-ferns 12. _Filices_
{ _Felicinæ_ { (Pterideæ)
{ {
{ { 13. Aquatic ferns 13. _Rhizocarpeæ_
{ { (Hydropterides)
{ {
{ { 14. Scale-ferns 14. _Selagineæ_
{ { (Lepidophyta)

{ V. {
{ Plants with { 15. Palm-ferns 15. _Cycadeæ_
C. { Naked Seeds {
=Flowering Plants= { _Gymnosperma_ { 16. Pines 16. _Coniferæ_
Phanerogamia {
{ VI. { 17. Plants with 17. _Monocotylæ_
{ Plants with { one seed lobe
{ Enclosed Seeds {
{ _Angiosperma_ { 18. Plants with 18. _Dicotylæ_
{ { two seed lobes

----------------------------------------------------------------

_Gamopetalæ_
(Flowers with corolla)
|
_Dialypetalæ_
(Star-shaped flowers)
|
_Monochlamydeæ_ MONOCOTYLEDONÆ
(Flowers with calyx) (One seed-lobed plants)
| |
DICOTYLEDONÆ |
(Two seed-lobed plants) |
| |
\--------------------v-------------/
CONIFERÆ +Angiospermæ+
CYCADEÆ (Pines) (Plants with enclosed seeds)
(Palm-ferns) | GNETACEÆ |
| | | |
\-----------v-----------------------/
+Gymnospermæ+
(Plants with naked seeds) _Phanerogamæ_
| (Flowering plants) _Pterideæ_
_Selagineæ_ | _Rhizocarpeæ_ | (Frondose-ferns)
(Scaled-ferns) |(Water-ferns) | | _Calamariæ_
| | | | | (Shaft-ferns)
| | | | | |
\-------------------------------v------------------------/
+Filicinæ+
_Frondosæ_ _Sphagnaceæ_ (Ferns)
(Leaf-mosses) (Turf-mosses) |
| | | CHARACEÆ
\----------------v------------/ (Tangle-mosses)
| |
_Hepaticæ_ (Liverworts) |
| |
\------------------v--------------------/
+Muscinæ+ (Mosses)
_Fucoideæ_ |
_Florideæ_ (Brown Algæ) | _Lichenes_
(Red Algæ) | _Chlorophyceæ_ (Lichens)
| | (Green Algæ) |
| | | |
\------------------v-----------------/ +Fungi Inophyta+
+Algæ+ (Tangles) (Thread-plants)
| |
\-------v------------------------------/
_Protophyta_
(Primæval Plants)
|
_Vegetable Monera_

Most people living inland can form but a very imperfect idea of this
exceedingly interesting branch of the vegetable kingdom, because they
know only its proportionately small and simple representatives living in
fresh water. The slimy green aquatic filaments and flakes of our pools
and ditches and springs, the light green slimy coverings of all kinds of
wood which have for any length of time been in contact with water, the
yellowish green, frothy, and oozy growths of our village ponds, the
green filaments resembling tufts of hair which occur everywhere in fresh
water, stagnant and flowing, are for the most part composed of different
species of Algæ. Only those who have visited the sea-shore, and wondered
at the immense masses of cast-up seaweed, and who, from the rocky coast
of the Mediterranean, have seen through the clear blue waters the
beautifully-formed and highly-coloured vegetation of Algæ at the bottom,
know how to estimate the importance of the class of Algæ. And yet, even
these marine Algæ-forests of European shores, so rich in forms, give
only a faint idea of the colossal forests of Sargasso in the Atlantic
ocean, those immense banks of Algæ, covering a space of about 40,000
square miles—the same which made Columbus, on his voyage of discovery,
believe that a continent was near. Similar but far more extensive
forests of Algæ grew in the primæval ocean, probably in dense masses,
and what countless generations of these archilithic Algæ have died out
one after another is attested, among other facts, by the vast thickness
of Silurian alum schists in Sweden, the peculiar composition of which
proceeds from those masses of submarine Algæ. According to the recently
expressed opinion of Frederick Mohr, a geologist of Bonn, even the
greater part of our coal seams have arisen out of the accumulated dead
bodies of the Algæ forests of the ocean.

Within the branch of the Algæ we distinguish four different classes,
each of which is again divided into several orders and families. These
again contain a large number of different genera and species. We
designate these four classes as Primæval Algæ, or Archephyceæ, Green
Algæ, or Chlorophyceæ, Brown Algæ, or Phæophyceæ, and Red Algæ, or
Rhodophyceæ.

The first class of Algæ, the _Primæval_ Algæ (Archephyceæ), might also
be called _primæval plants_, because they contain the simplest and most
imperfect of all plants, and, among them, those most ancient of all
vegetable organisms out of which all other plants have originated. To
them therefore belong those most ancient of all vegetable Monera which
arose by spontaneous generation in the beginning of the Laurentian
period. Further, we have to reckon among them all those vegetable forms
of the simplest organization which first developed out of the Monera in
the Laurentian period, and which possessed the form of a single
plastid. At first the entire body of one of these small primary plants
consisted only of a most simple cytod (a plastid without kernel), and
afterwards attained the higher form of a simple cell, by the separation
of a kernel in the plasma. (Compare above, vol. i. p. 345.) Even at the
present day there exist various most simple forms of Algæ which have
deviated but little from the original primary plants. Among them are the
Algæ of the families Codiolaceæ, Protococcaceæ, Desmidiaceæ,
Palmellaceæ, Hydrodictyeæ, and several others. The remarkable group of
Phycochromaceæ (Chroococcaceæ and Oscillarineæ) might also be comprised
among them, unless we prefer to consider them as an independent tribe of
the kingdom Protista.

The monoplastic Protophyta—that is, those primary Algæ formed by a
single plastid—are of the greatest interest, because the vegetable
organism in this case completes its whole course of life as a perfectly
simple “individual of the first order,” either as a cytod without
kernel, or as a cell containing a kernel.

Among the primary plants consisting of a single cytod are the
exceedingly remarkable Siphoneæ, which are of considerable size, and
strangely “mimic” the forms of higher plants. Many of the Siphoneæ
attain a size of several feet, and resemble an elegant moss (Bryopsis),
or in some cases a perfect flowering plant with stalks, roots, and
leaves (Caulerpa) (Fig. 17). Yet the whole of this large body,
externally so variously differentiated, consists internally of an
entirely simple sack, possessing the negative characters of a simple
cytod.

[Illustration: FIG. 17.—Caulerpa denticulata, a monoplastic Siphonean
_of the natural size_. The entire branching primary plant, which appears
to consist of a creeping stalk with fibrous roots and indented leaves,
is in reality only _a single plastid_, and moreover a cytod (without a
kernel), not even attaining the grade of a cell with nucleus.]

These curious Siphoneæ, Vaucheriæ, and Caulerpæ show us to how great a
degree of elaboration a single cytod, although a most simple individual
of the first order, can develop by continuous adaptation to the
relations of the outer world. Even the _single-celled primary
plants_—which are distinguished from the monocytods by possessing a
kernel—develop into a great variety of exquisite forms by adaptation;
this is the case especially with the beautiful _Desmidiaceæ_, of which
a species of Euastrum is represented in Fig. 18 as a specimen.

[Illustration: FIG. 18.—Euastrum rota, a single-celled Desmid, much
enlarged. The whole of the star-shaped body of this primæval plant has
the formal value of a simple cell. In its centre lies the kernel, and
within this the kernel corpuscle, or speck.]

It is very probable that similar primæval plants, the soft body of
which, however, was not capable of being preserved in a fossil state, at
one time peopled the Laurentian primæval sea in great masses and
varieties, and in a great abundance of forms, without, however, going
beyond the stage of individuality of a simple plastid.

The group of _Green Tangles_ (Chlorophyceæ), or _Green Algæ_
(Cloroalgæ), are the second class, and the most closely allied to the
primæval group. Like the majority of the Archephyceæ, all the
Chlorophyceæ are coloured green, and by the same colouring matter—the
substance called leaf-green, or chlorophyll—which colours the leaves of
all the higher plants.

To this class belong, besides a great number of low marine Algæ, most of
the Algæ of fresh water, the common water hair-weeds, or Confervæ, the
green slime-balls, or Glœosphæræ, the bright green water-lettuce, or
Ulva, which resembles a very thin and long lettuce leaf, and also
numerous small microscopic algæ, dense masses of which form a light
green shiny covering to all sorts of objects lying in water—wood,
stones, etc.

These forms, however, rise above the simple primary Algæ in the
composition and differentiation of their body. As the green Algæ, like
the primæval Algæ, mostly possess a very soft body, they are but rarely
capable of being petrified. However, it can scarcely be doubted that
this class of Algæ—which was the first to develop out of the preceding
one—most extensively and variously peopled the fresh and salt waters of
the earth in early times.

In the third class, that of the _Brown Tangles_ (Phæophyceæ), or _Black
Algæ_ (Fucoideæ), the _branch_ of the Algæ attains its highest stage of
development, at least in regard to size and body. The characteristic
colour of the Fucoid is more or less dark brown, sometimes tending more
to an olive green or yellowish green, sometimes more to a brownish red
or black colour.

Among these are the largest of all Algæ, which are at the same time the
longest of all plants, namely, the colossal giant Algæ, amongst which
the Macrocystis pyrifera, on the coast of California, attains a length
of 400 feet. Also, among our indigenous Algæ, the largest forms belong
to this group. Especially I may mention here the stately sugar-tangle
(Laminaria), whose slimy, olive green thallus-body, resembling gigantic
leaves of from 10 to 15 feet in length, and from a half to one foot in
breadth, are thrown up in great masses on the coasts of the North and
Baltic seas.

To this class belongs also the bladder-wrack (Fucus vesiculosus) common
in our seas, whose fork-shaped, deeply-cut leaves are kept floating on
the water by numerous air bladders (as is the case, too, with many other
brown Algæ). The freely floating Sargasso Alga (Sargasso bacciferum),
which forms the meadows or forests of the Sargasso Sea, also belongs to
this class.

Although each individual of these large alga-trees is composed of many
millions of cells, yet at the beginning of its existence it consists,
like all higher plants, of a single cell—a simple egg. This egg—for
example, in the case of our common bladder-wrack—is a naked, uncovered
cell, and as such is so like the naked egg-cells of lower marine
animals—for example, those of the Medusæ—that they might easily be
mistaken one for another (Fig. 19).

[Illustration: FIG. 19.—The egg of the common bladder-wrack (Fucus
vesiculosus), a simple naked cell, much enlarged. In the centre of the
naked globule of protoplasm the bright kernel is visible.]

It was probably the Fucoideæ, or Brown Algæ, which during the primordial
period, to a great extent constituted the characteristic alga-forests of
that immense space of time. Their petrified remains, especially those
of the Silurian period, which have been preserved, can, it is true,
give us but a faint idea of them, because the material of these Algæ,
like that of most others, is ill-suited for preservation in a fossil
state. As has already been remarked, a large portion of coal is perhaps
composed of them.

Less important is the fourth class of Algæ, that of the _Rose-coloured
Algæ_ (Rhodophyceæ), or _Red Sea-weeds_ (Florideæ). This class, it is
true, presents a great number of different forms; but most of them are
of much smaller size than the Brown Algæ. Although they are inferior to
the latter in perfection and differentiation, they far surpass them in
some other respects. To them belong the most beautiful and elegant of
all Algæ, which on account of the fine plumose division of their
leaf-like bodies, and also on account of their pure and delicate red
colour, are among the most charming of plants. The characteristic red
colour sometimes appears as a deep purple, sometimes as a glowing
scarlet, sometimes as a delicate rose tint, and may verge into violet
and bluish purple, or on the other hand into brown and green tints of
marvellous splendour. Whoever has visited one of our sea-coast watering
places, must have admired the lovely forms of the Florideæ, which are
frequently dried on white paper and offered for sale.

Most of the Red Algæ are so delicate, that they are quite incapable of
being petrified; this is the case with the splendid Ptilotes, Plocamia,
Delesseria, etc. However, there are individual forms, like the Chondria
and Sphærococca, which possess a harder thallus, often almost as hard as
cartilage, and of these fossil remains have been preserved—principally
in the Silurian, Devonian, and Carboniferous strata, and later in the
oolites. It is probable that this class also had an important share in
the composition of the archilithic Algæ flora.

If we now again take into consideration the flora of the primordial
period, which was exclusively formed by the group of Algæ, we can see
that it is not improbable that its four subordinate classes had a share
in the composition of those submarine forests of the primæval oceans,
similar to that which the four types of vegetation—trees with trunks,
flowering shrubs, grass, and tender leaf-ferns and mosses—at present
take in the composition of our recent land forests.

We may suppose that the submarine tree forests of the primordial period
were formed by the huge Brown Algæ, or Fucoideæ. The many-coloured
flowers at the foot of these gigantic trees were represented by the gay
Red Algæ, or Florideæ. The green grass between was formed by the
hair-like bunches of Green Algæ, or Chloroalgæ. Finally, the tender
foliage of ferns and mosses, which at present cover the ground of our
forests, fill the crevices left by other plants, and even settle on the
trunks of the trees, at that time probably had representatives in the
moss and fern-like Siphoneæ, in the Caulerpa and Bryopsis, from among
the class of the primary Algæ, Protophyta, or Archephyceæ.

With regard to the relationships of the different classes of Algæ to one
another and to other plants, it is exceedingly probable that the Primary
Algæ, or Archephyceæ, as already remarked, form the common root of the
pedigree, not merely for the different classes of Algæ, but for the
whole vegetable kingdom. On this account they may with justice be
designated as primæval plants, or Protophyta.

Out of the naked vegetable Monera, in the beginning of the Laurentian
period, enclosed cytods were probably the first to arise (vol. i. p.
345), by the naked, structureless, albuminous substance of the Monera
becoming condensed in the form of a pellicle on the surface, or by
secreting a membrane. At a later period, out of these enclosed cytods
genuine vegetable cells probably arose, as a kernel or nucleus separated
itself in the interior from the surrounding cell-substance or plasma.

The three classes of Green Algæ, Brown Algæ, and Red Algæ, are perhaps
three distinct classes, which have arisen independently of one another
out of the common radical group of Primæval Algæ, and then developed
themselves further (each according to its kind), and have variously
branched off into orders and families. The Brown and Red Algæ possess no
close blood relationship to the other classes of the vegetable kingdom.
These latter have most probably arisen out of the Primæval Algæ, either
directly or by the intermediate step of the Green Algæ.

It is probable that Mosses (out of which, at a later time, Ferns
developed) proceeded from a group of Green Algæ, and that Fungi and
Lichens proceeded from a group of Primæval Algæ. The Phanerogamia
developed at a much later period out of Ferns.

As a second class of the Vegetable Kingdom we have above mentioned the
_Thread-plants_ (Inophyta). We understood by this term the two closely
related classes of _Lichens_ and _Fungi_. It is possible that these
Thallus plants have not arisen out of the Primæval Algæ, but out of one
or more Monera, which, independently of the latter, arose by spontaneous
generation. It appears conceivable that many of the lowest Fungi, as for
example, many ferment-causing fungi (forms of Micrococcus, etc.), owe
their origin to a number of different _archigonic_ Monera (that is,
Monera originating by spontaneous generation).

In any case the Thread-plants cannot be considered as the progenitors of
any of the higher vegetable classes. Lichens, as well as fungi, are
distinct from the higher plants in the composition of their soft bodies,
consisting as it does of a dense felt-work of very long, variously
interwoven, and peculiar threads or chains of cells—the so-called
_hyphæ_, on which account we distinguish them as a province under the
name Thread-plants. From their peculiar nature they could not leave any
important fossil remains, and consequently we can form only a very vague
guess at their palæontological development.

The first class of Thread-plants, the _Fungi_, exhibit a very close
relationship to the lowest Algæ; the Algo-fungi, or Phycomycetes (the
Saprolegniæ and Peronosporæ) in reality only differ from the
bladder-wracks and Siphoneæ (the Vaucheria and Caulerpa) mentioned
previously by the want of leaf-green, or chlorophyll. But, on the other
hand, all genuine Fungi have so many peculiarities, and deviate so much
from other plants, especially in their mode of taking food, that they
might be considered as an entirely distinct province of the vegetable
kingdom.

Other plants live mostly upon inorganic food, upon simple combinations
which they render more complicated. They produce protoplasm by the
combination of water, carbonic acid, and ammonia. They take in carbonic
acid and give out oxygen. But the Fungi, like animals, live upon organic
food, consisting of complicated combinations of carbon, which they
receive from other organisms and assimilate. They inhale oxygen and
give out carbonic acid like animals. They also never form leaf-green, or
chlorophyll, which is so characteristic of most other plants. In like
manner they never produce starch. Hence many eminent botanists have
repeatedly proposed to remove the Fungi completely out of the vegetable
kingdom, and to regard them as a special and third kingdom, between that
of animals and plants. By this means our kingdom of Protista would be
considerably increased. The Fungi in this case would, in the first
place, be allied to the so-called “slime moulds,” or Myxomycetes (which,
however, never form any hyphæ). But as many Fungi propagate in a sexual
manner, and as most botanists, according to the prevalent opinion, look
upon Fungi as genuine plants, we shall here leave them in the vegetable
kingdom, and connect them with lichens, to which they are at all events
most nearly related.

The phyletic origin of Fungi will probably long remain obscure. The
close relationship already hinted at between the Phycomycetes and
Siphoneæ (especially between the Saprolegniæ and Vaucheriæ) suggests to
us that they are derived from the latter. Fungi would then have to be
considered as Algæ, which by adaptation to a parasitical life have
become very peculiarly transformed. Many facts, however, support the
supposition that the lowest fungi have originated independently from
archigonic Monera.

The second class of Inophyta, the _Lichens_ (Lichenes), are very
remarkable in relation to phylogeny; for the surprising discoveries of
late years have taught us that every Lichen is really composed of two
distinct plants—of a low form of Alga (Nostochaceæ, Chroococcaceæ), and
of a parasitic form of Fungus (Ascomycetes), which lives as a parasite
upon the former, and upon the nutritive substances prepared by it. The
green cells, containing chlorophyll (gonidia), which are found in every
lichen, belong to the Alga. But the colourless threads (hyphæ) which,
densely interwoven, form the principal mass of the body of Lichens,
belong to the parasitic Fungus. But in all cases the two forms of
plants—Fungus and Alga—which are always considered as members of two
quite distinct provinces of the vegetable kingdom, are so firmly united,
and so thoroughly interwoven, that nearly every one looks upon a Lichen
as a single organism.

Most Lichens form small, more or less formless or irregularly indented,
crust-like coverings to stones, bark of trees, etc. Their colour varies
through all possible tints, from the purest white to yellow, red, green,
brown, and the deepest black.

Many lichens are important in the economy of nature from the fact that
they can settle in the driest and most barren localities, especially on
naked rocks upon which no other plant can live. The hard black lava,
which covers many square miles of ground in volcanic regions, and which
for centuries frequently presents the most determined opposition to the
life of every kind of vegetation, is always first occupied by Lichens.
It is the white or grey Lichens (Stereocaulon) which, in the most
desolate and barren fields of lava, always begin to prepare the naked
rocky ground for cultivation, and conquer it for subsequent higher
vegetation. Their decaying bodies form the first mould in which mosses,
ferns, and flowering plants can afterwards take firm root. Hardy Lichens
are also less affected by the severity of climate than any other plants.
Hence the naked rocks, even in the highest mountains—for the most part
covered by eternal snow, on which no plant could thrive—are encrusted by
the dry bodies of Lichens.

Leaving now the Fungi, Lichens, and Algæ, which are comprised under the
name of Thallus plants, we enter upon the second sub-kingdom of the
vegetable kingdom, that of the _Prothallus plants_ (Prothallophyta),
which by some botanists are called phyllogonic Cryptogamia (in
contradistinction to the Thallus plants, or thallogonic Cryptogamia).
This sub-kingdom comprises the two provinces of _Mosses_ and _Ferns_.

Here we meet with (except in a few of the lowest forms) the separation
of the vegetable body into two different fundamental organs,
axial-organs (stem and root) and leaves (or lateral organs). In this the
Prothallus plants resemble the Flowering plants, and hence the two
groups have recently often been classed together as stemmed plants, or
Cormophytes.

But, on the other hand, Mosses and Ferns resemble the Thallus plants, in
the absence of the development of flowers and seeds, and even Linnæus
classed them with these, as Cryptogamia, in contradistinction to the
plants forming seeds; that is, flowering plants (Anthophyta or
Phanerogamia).

Under the name of “Prothallus plants” we combine the closely-related
Mosses and Ferns, because both exhibit a peculiar and characteristic
“alternation of generation” in the course of their individual
development. For every species exhibits two different generations, of
which the one is usually called the _Prothallium_, or _Fore-growth_, the
other is spoken of as the _Cormus_, or actual _Stem_ of the moss or
fern.

The first and original generation, the Fore-growth, or Prothallus, also
called Protonema, still remains in that lower stage of elaboration
manifested throughout life by all Thallus plants; that is to say, stem
and leaf-organs have as yet not differentiated, and the entire cell-mass
of the Fore-growth corresponds to a simple thallus. The second and more
perfect generation of mosses and ferns—the Stem, or Cormus—develops a
much more highly elaborate body, which has differentiated into stalk and
leaf (as in the case of flowering plants), except in the lowest mosses,
where this generation also remains in the lower stage of the thallus.

With the exception of these latter forms the first generation of Mosses
and Ferns (the thallus-shaped Fore-growth) always produces a second
generation with stem and leaves; the latter in its turn produces the
thallus of the first generation, and so on. Thus, in this case, as in
the ordinary cases of alternation of generation in animals, the first
generation is like the third, fifth, etc., the second like the fourth,
sixth, etc. (Compare vol. i. p. 206.)

Of the two main classes of Prothallus plants, the Mosses in general are
at a much lower stage of development than the Ferns, and their lowest
forms (especially in an anatomical respect) form the transition from the
Thallus plants through the Algæ to Ferns. The genealogical connection of
Mosses and Ferns which is indicated by this fact can, however, be
inferred only from the case of the most imperfect forms of the two
classes; for the more perfect and higher groups of mosses and ferns do
not stand in any close relation to one another, and develop in
completely opposite directions. In any case Mosses have arisen directly
out of Thallus plants, and probably out of Green Algæ.

Ferns, on the other hand, are probably derived from extinct unknown
Mosses, which were very nearly related to the lowest liverworts of the
present day. In the history of creation, Ferns are of greater importance
than Mosses.

The branch of _Mosses_ (Muscinæ, also called Musci, or Bryophyta)
contains the lower and more imperfect plants of the group of
Prothallophytes, which as yet do not possess vessels. Their bodies are
mostly so tender and perishable that they are very ill-suited for being
preserved in a recognizable state as fossils. Hence the fossil remains
of all classes of Mosses are rare and insignificant. It is probable that
Mosses developed in very early times out of the Thallus plants, or, to
be more precise, out of the Green Algæ. It is probable that in the
primordial period there existed aquatic forms of transition from the
latter to Mosses, and in the primary period to those living on land. The
Mosses of the present day—out of the gradually differentiating
development of which comparative anatomy may draw some inferences as to
their genealogy—are divided into two different classes, namely: (1)
Liverworts; (2) Leafy Mosses.

The first and oldest class of Mosses, which is directly allied to the
Green Algæ, or Confervæ, is formed by the _Liverworts_ (Hepaticæ, or
Thallobrya). The mosses belonging to them are, for the most part, small
and insignificant in form, and are little known. Their lowest forms
still possess, in both generations, a simple thallus like the Thallus
plants; as for example, the Ricciæ and Marchantiaceæ. But the more
highly developed liverworts, the Jungermanniaceæ and those akin to them,
gradually commence to differentiate stem and leaf, and their most
highly-developed forms are closely allied to leaf-mosses. By this
transitional series the liverworts show their direct derivation from
the Thallophytes, and more especially from the Green Algæ.

The Mosses, which are generally the only ones known to the
uninitiated—and which, in fact, form the principal portion of the whole
branch—belong to the second class, or _Leafy Mosses_ (Musci frondosi,
called Musci in a narrow sense, also Phyllobrya). Among them are most of
those pretty little plants which, united in dense groups, form the
bright glossy carpet of moss in our woods, or which, in company with
liverworts and lichens, cover the bark of trees. As reservoirs,
carefully storing up moisture, they are of the greatest importance in
the economy of nature. Wherever man mercilessly cuts down and destroys
forests, there, as a consequence, disappear the leafy mosses which
covered the bark of the trees, or, protected by their shade, clothed the
ground, and filled the spaces between the larger plants. Together with
the leafy mosses disappear the useful reservoirs which stored up rain
and dew for times of drought. Thus arises a disastrous dryness of the
ground, which prevents the growth of any rich vegetation. In the greater
part of Southern Europe—in Greece, Italy, Sicily, and Spain—mosses have
been destroyed by the inconsiderate extirpation of forests, and the
ground has thereby been robbed of its most useful stores of moisture;
once flourishing and rich tracts of land have been changed into dry and
barren wastes. Unfortunately in Germany, also, this rude barbarism is
beginning to prevail more and more. It is probable that the small
frondose mosses have played this exceedingly important part in nature
for a very long time, possibly from the beginning of the primary period.
But as their tender bodies are as little suited as those of all other
mosses for being preserved in a fossil state, palæontology can give us
no information about this.

We learn from the science of petrifactions much more than we do in the
case of Mosses of the importance which the second branch of Prothallus
plants—that is, Ferns—have had in the history of the vegetable world.
Ferns, or more strictly speaking, the “plants of the fern tribe”
(Filicineæ, or Pterideæ, also called Pteridophyta, or Vascular
Cryptogams), formed during an extremely long period, namely, during the
whole primary or palæolithic period, the principal portion of the
vegetable world, so that we may without hesitation call it the _era of
Fern Forests_. From the beginning of the Devonian period, in which
organisms living on land appeared for the first time, namely, during the
deposits of the Devonian, Carboniferous, and Permian strata, plants like
Ferns predominated so much over all others, that we are justified in
giving this name to that period. In the stratifications just mentioned,
but above all, in the immense layers of coal of the Carboniferous or
coal period, we find such numerous and occasionally well preserved
remains of Ferns, that we can form a tolerable vivid picture of the very
peculiar land flora of the palæolithic period. In the year 1855 the
total number of the then known palæolithic species of plants amounted to
about a thousand, and among these there were no less than 872 Ferns.
Among the remaining 128 species were 77 Gymnosperms (pines and
palm-ferns), 40 Thallus plants (mostly Algæ), and about 20 not
accurately definable Cormophyta (stem-plants).

As already remarked, Ferns probably developed out of the lower
liverworts in the beginning of the primary period. In their
organization Ferns rise considerably above Mosses, and in their more
highly developed forms even approach the flowering plants. In Mosses, as
in Thallus plants, the entire body is composed of almost equi-formal
cells, little if at all differentiated; but in the tissues of Ferns we
find those peculiarly differentiated strings of cells which are called
the vessels of plants, and which are universally met with in flowering
plants. Hence Ferns are sometimes united as “vascular Cryptogams” with
Phanerogams, and the group so formed is contrasted as that of the
“vascular plants” with “cellular plants,”—that is, with “cellular
cryptogams” (Mosses and Thallus plants). This very important process in
the organization of plants—the formation of vessels—first occurred,
therefore, in the Devonian period, consequently in the beginning of the
second and smaller half of the organic history of the earth.

The branch of Ferns, or Filicinæ, is divided into five distinct classes:
(1) Frondose Ferns, or Pteridæ; (2) Reed Ferns, or Calamariæ; (3)
Aquatic Ferns, or Rhizocarpeæ; (4) Snakes Tongues, or Ophioglossæ; and
(5) Scale Ferns, or Lepidophyta. By far the most important of these five
classes, and also the richest in forms, were first the Frondose Ferns,
and then the Scale-ferns, which formed the principal portion of the
palæolithic forests. The Reed Ferns, on the other hand, had at that time
already somewhat diminished in number; and of the Aquatic Ferns, we do
not even know with certainty whether they then existed. It is difficult
for us to form any idea of the very peculiar character of those gloomy
palæolithic fern forests, in which the whole of the gay abundance of
flowers of our present flora was entirely wanting, and which were not
enlivened by any birds. Of the flowering plants there then existed only
the two lowest classes, the pines and palm ferns, with naked seeds,
whose simple and insignificant blossoms scarcely deserve the name of
flowers.

The phylogeny of Ferns, and of the Gymnosperms which have developed out
of them, has been made especially clear by the excellent investigations
which Edward Strasburger published in 1872, on “The Coniferæ and
Gnetaceæ,” as also “On Azolla.” This thoughtful naturalist and Charles
Martins, of Montpellier, are among the few botanists who have thoroughly
understood the fundamental value of the Theory of Descent, and the
mechanical-causal connection between ontogeny and phylogeny. The
majority of botanists do not even yet know the important difference
between homology and analogy, between the morphological and
physiological comparison of parts—which has long since been recognized
in zoology—but Strasburger has employed this distinction and the
principle of evolution in his “Comparative Anatomy of the Gymnosperms,”
in order to sketch the outlines of the blood relationship of this
important group of plants.

The class among Ferns which has developed most directly out of the
Liverworts is the class of real Ferns, in the narrow sense of the word,
the _Frondose Ferns_ (Filices, or Phyllopterides, also called Pteridæ).
In the present flora of the temperate zones this class forms only a
subordinate part, for it is in most cases represented only by low forms
without trunks. But in the torrid zones, especially in the moist,
steaming forests of tropical regions, this class presents us with the
lofty palm-like _fern trees_. These beautiful tree-ferns of the present
day, which form the chief ornament of our hot-houses, can however give
us but a faint idea of the stately and splendid frondose ferns of the
primary period, whose mighty trunks, densely crowded together, then
formed entire forests. These trunks, accumulated in super-incumbent
masses, are found in the coal seams of the Carboniferous period, and
between them, in an excellent state of preservation, are found the
impressions of the elegant fan-shaped leaves, crowning the top of the
trunk in an umbrella-like bush. The varied outlines and the
feather-like forms of these fronds, the elegant shape of the branching
veins or bunches of vessels in their tender foliage, can still be as
distinctly recognized in the impressions of the palæolithic fronds as in
the fronds of ferns of the present day. In many cases even the clusters
of fruit, which are distributed on the lower surface of the fronds, are
distinctly preserved. After the Carboniferous period, the predominance
of frondose ferns diminished, and towards the end of the secondary
period they played almost as subordinate a part as they do at the
present time.

The Calamariæ, Ophioglossæ, and Rhizocarpeæ seem to have developed as
three diverging branches out of the Frondose Ferns, or Pteridæ. The
Calamariæ, or Calamophyta, have remained at the lowest level among these
three classes. The Calamariæ comprise three different orders, of which
only one now exists, namely, the Horse-tails (Equisetaceæ). The two
other orders, the Giant Reeds (Calamiteæ), and the Star-leaf Reeds
(Asterophylliteæ), are long since extinct. All Calamariæ are
characterized by a hollow and jointed stalk, stem, or trunk, upon which
the branches and leaves (in cases where they exist) are set so as to
encircle the jointed stem in whorls. The hollow joints of the stalk are
separated from one another by partition walls. In Horse-tails and
Calamiteæ the surface is traversed by longitudinal ribs running
parallel, as in the case of a fluted column, and the outer skin contains
so much silicious earth in the living forms, that it is used for
cleansing and polishing. In the Asterophylliteæ, the star-shaped whorls
of leaves were more strongly developed than in the two other orders.
There exist, at present, of the Calamariæ only the insignificant
Horse-tails (Equisetum), which grow in marshes and on moors; but during
the whole of the primary and secondary periods they were represented by
great trees of the genus Equisetites. There existed, at the same time,
the closely related order of the Giant Reeds (Calamites), whose strong
trunks grew to a height of about fifty feet. The order of the
Asterophyllites, on the other hand, contained smaller and prettier
plants, of a very peculiar form, and belongs exclusively to the primary
period.

Among all Ferns, the history of the third class, that of the _Root_, or
_Aquatic Ferns_ (Rhizocarpeæ, or Hydropteridæ), is least known to us. In
their structure these ferns, which live in fresh water, are on the one
hand allied to the frond ferns, and on the other to the scaly ferns, but
they are more closely related to the latter. Among them are the but
little known moss ferns (Salvinia), clover ferns (Marsilea), and pill
ferns (Pilularia) of our fresh waters; further, the large Azolla which
floats in tropical ponds. Most of the aquatic ferns are of a delicate
nature, and hence ill-suited for being petrified. This is probably the
reason of their fossil remains being so scarce, and of the oldest of
those known to us having been found in the Jura system. It is probable,
however, that the class is much older, and that it was already
developed during the palæolithic period out of other ferns by adaptation
to an aquatic life.

The fourth class of ferns is formed by the _Tongue Ferns_ (Ophioglossæ,
or Glossopterides). These ferns, to which belongs the Botrychium, as
well as the Ophioglossum (adder’s-tongue) of our native genera, were
formerly considered as forming but a small sub-division of the frondose
ferns. But they deserve to form a special class, because they represent
important transitional forms from the Pterideæ and Lepidophytes towards
higher plants, and must be regarded as among the direct progenitors of
the flowering plants.

The fifth and last class is formed by the _Scale Ferns_ (Lepidophytes,
or Selagines). In the same way as the Ophioglossæ arose out of the
frondose forms, the scale ferns arose out of the Ophioglossæ. They were
more highly developed than all other ferns, and form the transition to
flowering plants, which must have developed out of them. Next to the
frondose ferns they took the largest part in the composition of the
palæolithic fern forests. This class also contains, as does the class of
reed ferns, three nearly related but still very different orders, of
which only one now exists, the two others having become extinct towards
the end of the Carboniferous period. The scaled ferns still existing
belong to the order of the club-mosses (Lycopodiaceæ). They are mostly
small, pretty moss-like plants, whose tender, many-branched stalk creeps
in curves on the ground like a snake, and is densely encompassed and
covered by small scaly leaves. The pretty creeping Lycopodium of our
woods, which mountain tourists twine round their hats, is known to all,
as also the still more delicate Selaginella, which under the name of
creeping moss is used to adorn the soil of our hot-houses in the form of
a thick carpet. The largest _club-mosses_ of the present day are found
in the Sunda Islands, where their stalks rise to the height of
twenty-five feet, and attain half a foot in thickness. But in the
primary and secondary periods even larger trees of this kind were widely
distributed, the most ancient of which probably were the progenitors of
the pines (Lycopodites). The most important dimensions were, however,
attained by the class of scale trees (Lepidodendreæ), and by the seal
trees (Sigillarieæ). These two orders, with a few species, appear in the
Devonian period, but do not attain their immense and astonishing
development until the Carboniferous period, and become extinct towards
the end of it, or in the Permian period directly following upon it. The
scale trees, or Lepidodendreæ, were probably more closely related to
club-mosses than to Sigillarieæ. They grew into splendid, straight,
unbranching trunks which divided at the top into numerous forked
branches. They bore a large crown of scaly leaves, and like the trunk
were marked in elegant spiral lines by the scars left at the base of the
leaf stalks which had fallen off. We know of scale-marked trees from
forty to sixty feet in length, and from twelve to fifteen feet in
diameter at the root. Some trunks are said to be even more than a
hundred feet in length. In the coal are found still larger accumulations
of the no less highly developed but more slender trunks of the
remarkable seal trees, Sigillarieæ, which in many places form the
principal part of coal seams. Their roots were formerly described as
quite a distinct vegetable form (under the name of Stigmaria). The
Sigillarieæ are in many respects very like the scale-trees, but differ
from them and from ferns in general in many ways. They were possibly
closely related to the extinct Devonian _Lycopterideæ_, combining
characteristic peculiarities of the club-mosses and the frondose ferns,
which Strasburger considers as the hypothetical primary form of
flowering plants.

In leaving the dense forests of the primary period, which were
principally composed of frond ferns (Lepidodendreæ and Sigillarieæ), we
pass onwards to the no less characteristic pine forests of the secondary
period. Thus we leave the domain of the Cryptogamia, the plants forming
neither flowers nor seeds, and enter the second main division of the
vegetable kingdom, namely, the sub-kingdom of the _Phanerogamia_,
_flowering plants_ forming seeds. This division, so rich in forms,
containing the principal portion of the present vegetable world, and
especially the majority of plants living on land, is certainly of a much
more recent date than the division of Cryptogamia. For it can have
developed out of the latter only in the course of the palæolithic
period. We can with full assurance maintain that, during the whole
archilithic period, hence during the first and longer half of the
organic history of the earth, no flowering plants as yet existed, and
that they first developed during the primary period out of Cryptogamia
of the fern kind. The anatomical and embryological relation of
Phanerogamia to the latter is so close, that from it we can with
certainty infer their genealogical connection, that is, their true blood
relationship. Flowering plants cannot have directly arisen out of
thallus plants, nor out of mosses; but only out of ferns, or Filicines.
Most probably the scaled ferns, or Lepidophyta, and more especially
amongst these the Lycopodiaceæ, forms closely related to the
Selaginella of the present day, have been the direct progenitors of the
Phanerogamia.

On account of its anatomical structure and its embryological
development, the sub-kingdom of the Phanerogamia has for a long time
been divided into two large branches, into the _Gymnosperms_, or plants
with naked seeds, and the _Angiosperms_, or plants with enclosed seeds.
The latter are in every respect more perfect and more highly organized
than the former, and developed out of them only at a late date during
the secondary period. The Gymnosperms, both anatomically and
embryologically, form the transition group from Ferns to Angiosperms.

The lower, more imperfect, and the older of the two main classes of
flowering plants, that of the _Archispermeæ_, or _Gymnosperms_ (with
naked seeds), attained its most varied development and widest
distribution during the mesolithic or secondary epoch. It was no less
characteristic of this period, than was the fern group of the preceding
primary, and the Angiosperms of the succeeding tertiary, epoch. Hence we
might call the secondary epoch that of Gymnosperms, or after its most
important representatives, the era of Pine Forests. The Gymnosperms are
divided into three classes: the Coniferæ, Cycadeæ, and Gnetaceæ. We find
fossil remains of the pines, or Conifers, and of the Cycads, even in
coal, and must infer from this that the transition from scaled ferns to
Gymnosperms took place during the Coal, or possibly even in the Devonian
period. However, the Gymnosperms play but a very subordinate part during
the whole of the primary epoch, and do not predominate over Ferns until
the beginning of the secondary epoch.

Of the two classes of Gymnosperms just mentioned, that of the _Palm
Ferns_ (Zamiæ, or Cycadeæ) stands at the lowest stage, and is directly
allied to ferns, as the name implies, so that some botanists have
actually included them in the fern group. In their external form they
resemble palms, as well as tree ferns (or tree-like frond ferns), and
are adorned by a crown of feathery leaves, which is placed either on a
thick, short trunk, or on a slender, simple trunk like a pillar. At the
present day this class, once so rich in forms, is but scantily
represented by a few forms living in the torrid zones, namely, by the
coniferous ferns (Zamia), the thick-trunked bread-tree (Encephalartos),
and the slender-trunked Caffir bread-tree (Cycas). They may frequently
be seen in hot-houses, and are generally mistaken for palms. A much
greater variety of forms than occurs among the still existing palm ferns
(Cycadeæ) is presented by the extinct and fossil Cycads, which occurred
in great numbers more towards the middle of the secondary period, during
the Jura, and which at that time principally determined the character of
the forests.

The class of _Pines_, or _coniferous trees_ (Coniferæ), has preserved
down to our day a greater variety of forms than have the palm ferns.
Even at the present time the trees belonging to it—cypresses, juniper
trees, and trees of life (Thuja), the box and ginko trees (Salisburya),
the araucaria and cedars, but above all the genus Pinus, which is so
rich in forms, with its numerous and important species, spruces, pines,
firs, larches, etc.—still play a very important part in the most
different parts of the earth, and almost of themselves constitute
extensive forests. Yet this development of pines seems but weak in
comparison with the predominance which the class had attained over other
plants during the early secondary period, that of the Trias. At that
time mighty coniferous trees—with but proportionately few genera and
species, but standing together in immense masses of individuals—formed
the principal part of the mesolithic forests. This fact justifies us in
calling the secondary period the “era of the pine forests,” although the
remains of Cycadeæ predominate over those of coniferous trees in the
Jura period.[2]

From the pine forests of the mesolithic, or secondary period, we pass on
into the leafy forests of the cænolithic, or tertiary period, and we
arrive thus at the consideration of the sixth and last class of the
vegetable kingdom, that of the _Metaspermæ_, _Angiospermæ_, or _plants
with enclosed seeds_. The first certain and undoubted fossils of plants
with enclosed seeds are found in the strata of the chalk system, and
indeed we here find, side by side, remains of the two classes into which
the main class of Angiosperms is generally divided, namely, the _one
seed-lobed plants_, or _monocotylæ_, and the _two seed-lobed plants_, or
_dicotylæ_. However, the whole group probably originated at an earlier
period during the Trias. For we know of a number of doubtful and not
accurately definable fossil remains of plants from the Oolitic and Trias
(sic) periods, which some botanists consider to be Monocotylæ, whilst
others consider them as Gymnosperms. In regard to the two classes of
plants with enclosed seeds, the Monocotylæ and Dicotylæ, it is
exceedingly probable that the Dicotyledons developed out of the
Gnetaceæ, but that the Monocotyledons developed later out of a branch of
the dicotyledons.

The class of _one seed-lobed plants_ (Monocotylæ, or Monocotyledons,
also called Endogenæ) comprises those flowering plants whose seeds
possess but one germ leaf or seed lobe (cotyledon). Each whorl of its
flower contains in most cases _three_ leaves, and it is very probable
that the mother plants of all Monocotyledons possessed a regular triple
blossom. The leaves are mostly simple, and traversed by simple, straight
bunches of vessels or “nerves.” To this class belong the extensive
families of the rushes, grasses, lilies, irids, and orchids, further a
number of indigenous aquatic plants, the water-onions, sea grasses,
etc., and finally the splendid and highly developed families of the
Aroideæ and Pandaneæ, the bananas and palms. On the whole, the class of
Monocotyledons—in spite of the great variety of forms which it
developed, both in the tertiary and the present period—is much more
simply organized than the class of the Dicotyledons, and its history of
development also offers much less of interest. As their fossil remains
are for the most part difficult to recognize, it still remains at
present an open question in which of the three great secondary
periods—the Trias, Jura, or chalk period—the Monocotyledons originated.
At all events they existed in the chalk period as surely as did the
Dicotyledons.

[Illustration:

_Haeckel History of Creation._

_PL. V._

Relative lengths of the 5 Epochs in percentages.

Quarternary Epoch 0.5
Tertiary Epoch 2.3
Secondary Epoch 11.5
Primary Epoch 32.1
Primordial Epoch 53.6
-----
_Total_ 100.0

Single-stemmed or
MONOPHYLETIC PEDIGREE
of the
VEGETABLE KINGDOM
based on Palæontology.]

The second class of plants with enclosed seeds, the _two seed-lobed_
(Dicotylæ, or Dicotyledons, also called Exogenæ) presents much greater
historical and anatomical interest in the development of its subordinate
groups. The flowering plants of this class generally possess, as their
name indicates, two seed lobes or germ leaves (cotyledons). The number
of leaves composing its blossom is generally not three, as in most
Monocotyledons, but four, five, or a multiple of those numbers. Their
leaves, moreover, are generally more highly differentiated and more
composite than those of the Monocotyledons; they are traversed by
crooked, branching bunches of vessels or “veins.” To this class belong
most of the leafed trees, and as they predominate in the tertiary period
as well as, at present, over the Gymnosperms and Ferns, we may call the
cænolithic period that of leafed forests.

Although the majority of Dicotyledons belong to the most highly
developed and most perfect plants, still the lowest division of them is
directly allied to the Gymnosperms, and particularly to the Gnetaceæ. In
the lower Dicotyledons, as in the case of the Monocotyledons, calyx and
corolla are as yet not differentiated. Hence they are called _Apetalous_
(Monochlamydeæ, or Apetalæ). This sub-class must therefore doubtless be
looked upon as the original group of the Angiosperms, and existed
probably even during the Trias and Jura periods. Among them are most of
the leafed trees bearing catkins—birches and alders, willows and
poplars, beeches and oaks; further, the plants of the nettle
kind—nettles, hemp, and hops, figs, mulberries, and elms; finally,
plants like the spurges, laurels, and amaranth.

It was not until the chalk period that the second and more perfect class
of the Dicotyledons appeared, namely, the _group with corollas_
(Dichlamydeæ, or Corollifloræ). These arose out of the Apetalæ from the
simple cover of the blossoms of the latter becoming differentiated into
calyx and corolla. The sub-class of the Corollifloræ is again divided
into two large main divisions or legions, each of which contains a large
number of different orders, families, genera, and species. The first
legion bears the name of star-flowers, or Diapetalæ, the second that of
the bell-flowers, or Gamopetalæ.

The lower and less perfect of the two legions of the Corollifloræ are
the star-flowers (also called Diapetalæ or Dialypetalæ). To them belong
the extensive families of the Umbelliferæ, or umbrella-worts (wild
carrot, etc.), the Cruciferæ, or cruciform blossoms (cabbage, etc.);
further, the Ranunculaceæ (buttercups) and Crassulaceæ, the Mallows and
Geraniums, and, besides many others, the large group of Roses (which
comprise, besides roses, most of our fruit trees), and the Pea-blossoms
(containing, among others, beans, clover, genista, acacia, and mimosa).
In all these Diapetalæ the blossom-leaves remain separate, and never
grow together, as is the case in the Gamopetalæ. These latter developed
first in the tertiary period out of the Diapetalæ, whereas the Diapetalæ
appeared in the chalk period together with the Apetalæ.

The highest and most perfect group of the vegetable kingdom is formed by
the second division of the Corollifloræ, namely, the legion of
bell-flowers (Gamopetalæ, also called Monopetalæ or Sympetalæ). In this
group the blossom-leaves, which in other plants generally remain
separate, grow regularly together into a more or less bell-like,
funnel-shaped, or tubular flower. To them belong, among others, the
Bell-flowers and Convolvulus, Primroses and Heaths, Gentian and
Honeysuckle, further the family of the Olives (olive trees, privet,
elder, and ash), and finally, besides many other families, the
extensive division of the Lip-blossoms (Labiatæ) and the Composites. In
these last the differentiation and perfection of the Phanerogamic
blossoms attain their highest stage of development, and we must
therefore place them at the head of the vegetable kingdom, as the most
perfect of all plants. In accordance with this, the legion of the
Gamopetalæ appear in the organic history of the earth later than all the
main groups of the vegetable kingdom—in fact, not until the cænolithic
or tertiary epoch. In the earliest tertiary period the legion is still
very rare, but it gradually increases in the mid-tertiary, and attains
its full development only in the latest tertiary and the quaternary
period.

Now if, having reached our own time, we look back upon the _whole
history of the development of the vegetable kingdom_, we cannot but
perceive in it a _grand confirmation of the Theory of Descent_. The two
great principles of organic development which have been pointed out as
the necessary results of natural selection in the Struggle for Life,
namely, the laws of _differentiation_ and _perfecting_, manifest
themselves everywhere in the development of the larger and smaller
groups of the natural system of plants. In each larger or smaller period
of the organic history of the earth, the vegetable kingdom increases
both in _variety_ and _perfection_, as a glance at Plate IV. will
clearly show. During the whole of the long primordial period there
existed only the lowest and most imperfect group, that of the Algæ. To
these are added, in the primary period, the higher and more perfect
Cryptogamia, especially the main-class of Ferns. During the coal period
the Phanerogamia begin to develop out of the latter; at first, however,
they are represented only by the lower main-class, that of Gymnosperms.
It was not until the secondary period that the higher main-class, that
of Angiosperms, arose out of them. Of these also there existed at first
only the lower groups without distinct corollas, the Monocotyledons and
the Apetalæ. It was not until the chalk period that the higher
Corollifloræ developed out of the latter. But even this most highly
developed group is represented, in the chalk period, only by the lower
stage of Star-flowers, or Diapetalæ, and only at quite a late date, in
the tertiary period, did the more highly developed Bell-blossoms,
Gamopetalæ, arise out of them, which at the same time are the most
perfect of all flowering plants. Thus, in each succeeding later division
of the organic history of the earth the vegetable kingdom gradually rose
to a higher degree of perfection and variety.

CHAPTER XVIII.

PEDIGREE AND HISTORY OF THE ANIMAL KINGDOM.

I. ANIMAL-PLANTS AND WORMS.

The Natural System of the Animal Kingdom.—Linnæus and Lamarck’s
Systems.—The Four Types of Bär and Cuvier.—Their Increase to
Seven Types.—Genealogical Importance of the Seven Types as
Independent Tribes of the Animal Kingdom.—Derivation of
Zoophytes and Worms from Primæval Animals.—Monophyletic and
Polyphyletic Hypothesis of the Descent of the Animal
Kingdom.—Common Origin of the Four Higher Animal Tribes out of
the Worm Tribe.—Division of the Seven Animal Tribes into
Sixteen Main Classes, and Thirty-eight Classes.—Primæval
Animals (Monera, Amœbæ, Synamœbæ), Gregarines, Infusoria,
Planæades, and Gastræades (Planula and Gastrula).—Tribe of
Zoophytes.—Spongiæ (Mucous Sponges, Fibrous Sponges, Calcareous
Sponges).—Sea Nettles, or Acalephæ (Corals, Hood-jellies,
Comb-jellies).—Tribe of Worms.

The natural system of organisms which we must employ in the animal as
well as in the vegetable kingdom, as a guide in our genealogical
investigations, is in both cases of but recent origin, and essentially
determined by the progress of comparative anatomy and ontogeny (the
history of individual development) during the present century. Almost
all the attempts at classification made in the last century followed the
path of the artificial system, which was first established in a
consistent manner by Charles Linnæus. The artificial system differs
essentially from the natural one, in the fact that it does not make the
whole organization and the internal structure (depending upon the blood
relationship) the basis of classification, but only employs individual,
and for the most part external, characteristics, which readily strike
the eye. Thus Linnæus distinguished his twenty-four classes of the
vegetable kingdom principally by the number, formation, and combination
of the stamens. In like manner he distinguished six classes in the
animal kingdom principally by the nature of the heart and blood. These
six classes were: (1) Mammals; (2) Birds; (3) Amphibious Animals; (4)
Fishes; (5) Insects; and (6) Worms.

But these six animal classes of Linnæus are by no means of equal value,
and it was an important advance when, at the end of the last century,
Lamarck comprised the first four classes as vertebrate animals
(Vertebrata), and put them in contrast with the remaining animals (the
insects and worms of Linnæus), of which he made a second main
division—the invertebrate animals (Invertebrata). In reality Lamarck
thus agreed with Aristotle, the father of Natural History, who had
distinguished these two main groups, and called the former
_blood-bearing animals_, the latter _bloodless animals_.

The next important progress towards a natural system of the animal
kingdom was made some decades later by two most illustrious zoologists,
Carl Ernst Bär and George Cuvier. As has already been remarked, they
established, almost simultaneously and independently of one another, the
proposition that it was necessary to distinguish several completely
distinct main groups in the animal kingdom, each of which possessed an
entirely peculiar type or structure (compare above, vol. i. p. 53). In
each of these main divisions there is a tree-shaped and branching
gradation from most simple and imperfect forms to those which are
exceedingly composite and highly developed. The _degree of development_
within each type is quite independent of the peculiar _plan of
structure_, which forms the basis of the type and gives it a special
characteristic. The “type” is determined by the peculiar relations in
position of the most important parts of the body, and the manner in
which the organs are connected. The degree of development, however, is
dependent upon the greater or less division of labour among organs, and
on the differentiation of the plastids and organs. This extremely
important and fruitful idea was established by Bär, who relied more
distinctly and thoroughly upon the history of individual development
than did Cuvier. Cuvier based his argument upon the results of
comparative anatomy. But neither of them recognized the true cause of
the remarkable relationships pointed out by them, which is first
revealed to us by the Theory of Descent. It shows us that the common
_type_ or plan of structure is determined by _inheritance_, and the
degree of development or differentiation by _adaptation_. (Gen. Morph.
ii. 10).

Both Bär and Cuvier distinguished four different types in the animal
kingdom, and divided it accordingly into four great main divisions
(branches or circles). The first of these is formed by the vertebrate
animals (Vertebrata), and comprises Linnæus’ first four classes—mammals,
birds, amphibious animals, and fishes. The second type is formed by the
articulated animals (Articulata), containing Linnæus’ insects,
consequently the six-legged insects, and also the myriopods, spiders,
and crustacea, but besides these, a large number of the worms,
especially the ringed worms. The third main division comprises the
molluscous animals (Mollusca)—slugs, snails, mussels, and some kindred
groups. Finally, the fourth and last circle of the animal kingdom
comprises the various radiated animals (Radiata), which at first sight
differ from the three preceding types by their radiated, flower-like
form of body. For while the bodies of molluscs, articulated animals, and
vertebrated animals consist of two symmetrical lateral halves—of two
counterparts or antimera, of which the one is the mirror of the
other—the bodies of the so-called radiated animals are composed of more
than two, generally of four, five, or six counterparts grouped round a
common central axis, as in the case of a flower. However striking this
difference may seem at first, it is, in reality, a very subordinate one,
and the radial form has by no means the same importance in all “radiated
animals.”

The establishment of these natural main groups or types of the animal
kingdom by Bär and Cuvier was the greatest advance in the classification
of animals since the time of Linnæus. The three groups of vertebrated
animals, articulated animals, and molluscs are so much in accordance
with nature that they are retained, even at the present day, little
altered in extent. But a more accurate knowledge soon showed the utterly
unnatural character of the group of the radiated animals. Leuckart, in
1848, first pointed out that two perfectly distinct types were
confounded under the name, namely, the _Star-fishes_ (Echinoderma)—the
sea-stars, lily encrinites, sea-urchins, and sea-cucumbers; and, on the
other hand, the _Animal-plants_, or _Zoophytes_ (Cœlenterata or
Zoophyta)—the sponges, corals, hood-jellies, and comb-jellies. At the
same time, Siebold united the Infusoria with the Rhizopoda, under the
name of Protozoa (lowest animals), into a special main division of the
animal kingdom. By this the number of animal types was increased to six.
It was finally increased to seven by the fact that modern zoologists
separated the main division of the articulated animals into two groups:
(_a_) those possessing _articulated feet_ (Arthropoda), corresponding to
Linnæus’ Insects, namely, the Flies (with six legs), Myriopods, Spiders,
and Crustacea; and (_b_) the footless _Worms_ (Vermes), or those
possessing non-articulated feet. These latter comprise only the real or
genuine Worms (ring-worms, round worms, planarian worms, etc.), and
therefore in no way correspond with the Worms of Linnæus, who had
included the molluscs, the radiates, and many other lower animals under
this name.

Thus, according to the views of modern zoologists, which are given in
all recent manuals and treatises on zoology, the animal kingdom is
composed of seven completely distinct main divisions or types, each of
which is distinguished by a characteristic plan of structure peculiar to
it, and perfectly distinct from every one of the others. In the natural
system of the animal kingdom—which I shall now proceed to explain as its
probable pedigree—I shall on the whole agree with this usual division,
but not without some modifications, which I consider very important in
connection with genealogy, and which are rendered absolutely necessary
in consequence of our view as to the history of the development of
animals.

We evidently obtain the greatest amount of information concerning the
_pedigree of the animal kingdom_ (as well as concerning that of the
vegetable kingdom) from comparative anatomy and ontogeny. Besides
these, palæontology also throws much valuable light upon the historical
succession of many of the groups. From numerous facts in comparative
anatomy, we may, in the first place, infer the _common origin of all
those animals which belong to one of the seven “types.”_ For in spite of
all the variety in the external form developed within each of these
types, the essential relative position of the parts of the body which
determines the type, is so constant, and agrees so completely in all the
members of every type, that on account of their relations of form alone
we are obliged to unite them, in the natural system, into a single main
group. But we must certainly conclude, moreover, that this conjunction
also has its expression in the pedigree of the animal kingdom. For the
true cause of the intimate agreement in structure can only be the actual
blood relationship. Hence we may, without further discussion, lay down
the important proposition that all animals belonging to one and the same
circle or type must be descended from one and the same original primary
form. In other words, the idea of the circle or type, as it is employed
in zoology since Bär and Cuvier’s time to designate the few principal
main groups or “sub-kingdoms” of the animal kingdoms, coincides with the
idea of “tribe” or “phylum,” as employed by the Theory of Descent.

If, then, we can trace all the varieties of animal forms to these seven
fundamental forms, the following question next presents itself to us as
a second phylogenetic problem—Where do these seven animal tribes come
from? Are they seven original primary forms of an entirely independent
origin, or are they also distantly related by blood to one another?

[Illustration: _PL. VI._

Historical Growth of the six great stems of Animals. _See the
Explanation._]

At first we might be inclined to answer this question in a
_polyphyletic_ sense, by saying that we must assume, for each of the
seven great animal tribes, at least one independent primary form
completely distinct from the others. On further considering this
difficult problem, we arrive in the end at the notion of a
_monophyletic_ origin of the animal kingdom, viz., that these seven
primary forms are connected at their lowest roots, and that they are
derived from a single, common primæval form. _In the animal as well as
in the vegetable kingdom, when closely and accurately considered, the
monophyletic hypothesis of descent is found to be more satisfactory than
the polyphyletic hypothesis._

It is _comparative ontogeny_ (embryology) which first and foremost leads
to the assumption of the monophyletic origin of the whole animal kingdom
(the Protista excepted of course). The zoologist who has thoughtfully
compared the history of the individual development of various animals,
and has understood the importance of the biogenetic principle (p. 33),
cannot but be convinced that a common root must be assumed for the seven
different animal tribes, and that all animals, including man, are
derived from a single, common primary form. The result of the
consideration of the facts of embryology, or ontogeny, is the following
genealogical or phylogenetic hypothesis, which I have put forward and
explained in detail in my “Philosophy of Calcareous Sponges” (Monograph
of the Calcareous Sponges, vol. i. pp. 464, 465, etc.,—“the Theory of
the Layers of the Embryo, and the Pedigree of Animals”).

The first stage of organic life in the Animal kingdom (as in the
Vegetable and Protista kingdoms) was formed by perfectly simple
_Monera_, originating by spontaneous generation. The former existence
of this simplest animal form is, even at present, attested by the fact
that the egg-cell of many animals loses its kernel directly after
becoming fructified, and thus relapses to the lower stage of development
of a cytod without a kernel, like a Moneron. This remarkable occurrence
I have interpreted, according to the law of latent inheritance (vol. i.
p. 205), as a phylogenetic _relapse_ of the cellular form into the
original form of a cytod. The _Monerula_, as we may call this egg-cytod
without a kernel, repeats then, according to the biogenetic principle
(vol. ii. p. 33), the most ancient of all animal forms, the common
primary form of the animal kingdom, namely, the Moneron.

The second ontogenetic process consists in a new kernel being formed in
the Monerula, or egg-cytod, which thus returns again to the value of a
true _egg-cell_. According to this, we must look upon the simple animal
cell, containing a kernel, or the single-celled primæval animal—which
may still be seen in a living state in the _Amœbæ_ of the present day—as
the _second_ step in the series of phylogenetic forms of the animal
kingdom. Like the still living simple Amœbæ, and like the naked
egg-cells of many lower animals (for example, of Sponges and Medusæ,
etc.), which cannot be distinguished from them, the remote phyletic
primary Amœbæ also were perfectly simple naked-cells, which moved about
in the Laurentian primæval ocean, creeping by means of the ever-changing
processes of their body-substance, and nourishing and propagating
themselves in the same way as the Amœbæ of the present day. (Compare
vol. i. p. 188, and vol. ii. p. 54.) The existence of this Amœba-like,
_single-celled primary form_ of the whole animal kingdom is unmistakably
indicated by the exceedingly important fact that the egg of all
animals, from those of sponges and worms up to those of the ant and man,
is a simple cell.

Thirdly, from the “single-cell” state arose the _simplest multicellular
state_, namely, a heap or a small community of simple, equi-formal, and
equivalent cells. Even at the present day, in the ontogenetic
development of every animal egg-cell, there first arises a globular heap
of equi-formal naked cells, by the repeated self-division of the primary
cell. (Compare vol. i. p. 190 and the Frontispiece, Fig. 3.) We called
this accumulation of cells the _mulberry state_ (Morula), because it
resembles a mulberry or blackberry. This Morula-body occurs in the same
simple form in all the different tribes of animals, and on account of
this most important circumstance we may infer—according to the
biogenetic principle—that the _most ancient, many-celled, primary form
of the animal kingdom_ resembled a Morula like this, and was in fact a
simple heap of Amœba-like primæval cells, one similar to the other. We
shall call this most ancient community of Amœbæ—this most simple
accumulation of animal cells—which is recapitulated in individual
development by the Morula—the _Synamœba_.

Out of the Synamœbæ, in the early Laurentian period, there afterwards
developed a fourth primary form of the animal kingdom, which we shall
call the ciliated germ (Planæa). This arose out of the Synamœba by the
outer cells on the surface of the cellular community beginning to extend
vibrating fringes called cilia, and becoming “ciliated cells,” and thus
differentiating from the inner and unchanged cells. The Synamœbæ
consisted of completely equi-formed and naked cells, and crept about
slowly, at the bottom of the Laurentian primæval ocean, by means of
movements like those of an Amœba. The Planæa, on the other hand,
consisted of two kinds of different cells—inner ones like the Amœbæ, and
external “ciliated cells.” By the vibrating movements of the cilia the
entire multicellular body acquired a more rapid and stronger motion, and
passed over from the creeping to the swimming mode of locomotion. In
exactly the same manner the _Morula_, in the ontogenesis of lower
animals, still changes into a ciliated form of larva, which has been
known, since the year 1847, under the name of _Planula_. This Planula is
sometimes a globular, sometimes an oval body, which swims about in the
water by means of a vibrating movement; the fringed (ciliated) and
smaller cells of the surface differ from the larger inner cells, which
are unfringed. (Fig. 4 of the Frontispiece.)

Out of this Planula, or fringed larva, there then develops, in animals
of all tribes, an exceedingly important and interesting animal form,
which, in my Monograph of the Calcareous Sponges, I have named
_Gastrula_ (that is, larva with a stomach or intestine). (Frontispiece,
Fig. 5, 6). This Gastrula externally resembles the Planula, but differs
essentially from it in the fact that it encloses a cavity which opens to
the outside by a mouth. The cavity is the “_primary intestine_,” or
“primary stomach,” the _progaster_, the first beginning of the
alimentary canal; its opening is the “_primary mouth_” (prostoma). The
wall of the progaster consists of two layers of cells: an outer layer of
smaller ciliated cells (outer skin, or ectoderm), and of an inner layer
of larger non-ciliated cells (inner skin, or entoderm). This exceedingly
important larval form, the “Gastrula,” makes its appearance in the
ontogenesis of all tribes of animals—in Sponges, Medusæ, Corals, Worms,
Sea-squirts, Radiated animals, Molluscs, and even in the lowest
Vertebrata (Amphioxus: compare p. 200, Plate XII., Fig. _B_ 4; see also
in the same place the Ascidian, Fig. _A_ 4).

From the ontogenetic occurrence of the Gastrula in the most different
animal classes, from Zoophytes up to Vertebrata, we may, according to
the biogenetic principle, safely draw the conclusion that during the
Laurentian period there existed a common primary form of the six higher
animal tribes, which in all essential points was formed like the
Gastrula, and which we shall call the Gastræa. This Gastræa possessed a
perfectly simple globular or oval body, which enclosed a simple cavity
of like form, namely, the progaster; at one of the poles of the
longitudinal axis the primary intestine opened by a mouth which served
for the reception of nutrition. The body wall (which was also the
intestinal wall) consisted of two layers of cells, the unfringed
entoderm, or intestinal layer, and the fringed ectoderm, or skin-layer;
by the motion of the cilia or fringes of the latter the Gastræa swam
about freely in the Laurentian ocean. Even in those higher animals, in
the ontogenesis of which the original Gastrula form has disappeared,
according to the laws of abbreviated inheritance (vol. i. p. 212), the
composition of the Gastræa body has been transmitted to the phase of
development which directly arises out of the Morula. This phase is an
oval or round disc consisting of two cell-layers or membranes: the outer
cell-layer, the _animal or dermal layer_ (ectoblast), corresponds to the
ectoderm of the Gastræa; out of it develops the external, loose skin
(epidermis), with its glands and appendages, as well as the central
nervous system. The inner cell-layer, the _vegetative or intestinal
layer_ (hypoblast), is originally the entoderm of the Gastræa; out of it
develops the inner membrane (epithelium) of the intestinal canal and its
glands. (Compare my Monograph of the Calcareous Sponges, vol. i. p. 466,
etc.)

By ontogeny we have already gained five primordial stages of development
of the animal kingdom: (1) the Moneron; (2) the Amœba; (3) the Synamœba;
(4) the Planæa; and (5) the Gastræa. The former existence of these five
oldest primary forms, which succeeded one another, and which must have
lived in the Laurentian period, follows as a consequence of the
biogenetic principle; that is to say, from the parallelism and the
mechanico-causal connection of ontogenesis and phylogenesis. (Compare
vol. i. p. 309.) In our genealogical system of the animal kingdom we may
class all these animal forms, long since extinct, and, which on account
of the soft nature of their bodies could leave no fossil remains, among
the tribe of Primæval animals (Protozoa), which also comprises the still
living Infusoria and Gregarinæ.

The phyletic development of the six higher animal tribes, which are all
derived from the Gastræa, deviated at this point in two directions. In
other words, the _Gastræads_ (as we may call the group of forms
characterized by the Gastræa-type of structure), divided into two
divergent lines or branches; the one branch of Gastræads gave up free
locomotion, adhered to the bottom of the sea, and thus, by adopting an
adhesive mode of life, gave rise to the _Protascus_, the common primary
form of the _Animal-plants_ (Zoophyta). The other branch of the
Gastræads retained free locomotion, did not become adherent and later
on developed into the _Prothelmis_, the common primary form of _Worms_
(Vermes). (Compare p. 133.)

This latter tribe (as limited by modern zoology) is of the greatest
interest in the study of genealogy. For among Worms, as we shall see
later, there are, besides very numerous peculiar families, and besides
many independent classes, also very remarkable forms, which may be
considered as _forms of direct transition_ to the four higher animal
tribes. Both comparative anatomy and the ontogeny of these worms enable
us to recognize in them the nearest blood relations of those extinct
animal forms which were the original primary forms of the four higher
animal tribes. Hence these latter, the Molluscs, Star-fishes,
Articulated animals, and Vertebrate animals, do not stand in any close
blood relationship to one another, but have originated independently in
four different places out of the tribe of Worms.

In this way comparative anatomy and phylogeny lead us to the
_monophyletic pedigree of the animal kingdom_, the outlines of which are
given on p. 133. According to it the seven phyla, or tribes, of the
animal kingdom are of different value in regard to genealogy. The
original primary group of the whole animal kingdom is formed by the
Primæval animals (Protozoa), including the Infusoria and Gastræads. Out
of these latter arose the two tribes of Animal-plants (Zoophyta) and
Worms as diverging branches. Out of four different groups of the Worm
tribe, the four higher tribes of the animal kingdom were developed—the
Star-fishes (Echinoderma) and Insects (Arthropoda) on the one hand, and
the Molluscs (Mollusca) and Vertebrated animals (Vertebrata) on the
other.

Having thus sketched out the monophyletic pedigree of the animal kingdom
in its most important features, we must now turn to a closer examination
of the historical course of development which the seven tribes of the
animal kingdom, and the classes distinguished in them, have passed
through (p. 132). There is a much larger number of classes in the animal
than in the vegetable kingdom, owing to the simple reason that the
animal body, in consequence of its more varied and perfect vital
activity, could differentiate and develop in very many more different
directions than could the vegetable body. Thus, while we were able to
divide the whole vegetable kingdom into six main classes and nineteen
classes, we have to distinguish, at least, sixteen main classes and
thirty-eight classes in the animal kingdom. These are distributed among
the seven different tribes of the animal kingdom in the way shown in the
Systematic Survey on pages 132 and 133.

The group of _Primæval animals_ (Protozoa) within the compass which we
here assign to this tribe, comprises the most ancient and the simplest
primary forms of the animal kingdom; for example, the five oldest
phyletic stages of development previously mentioned, and besides these
the Infusoria and Gregarinæ, as well as all those imperfect animal
forms, for which, on account of their simple and indifferent
organization, no place can be found in any of the other six animal
tribes. Most zoologists, in addition to these, include among the
Protozoa a larger or smaller portion of those lowest organisms, which we
mentioned in our neutral kingdom of Protista (in Chapter XVI.). But
these Protista, especially the large division of the Rhizopoda, which
are so rich in forms, cannot be considered as real animals for reasons
previously given. Hence, if we here leave them out of the question, we
may accept two main classes or provinces of real Protozoa, namely, _Egg
animals_ (Ovularia) and _Germ animals_ (Blastularia). To the former
belong the three classes of Archezoa, Gregarinæ, and Infusoria, to the
latter the two classes of Planæads and Gastræads.

SYSTEMATIC SURVEY

_Of the 16 Main Classes and 38 Classes of the Animal Kingdom._

A. {
=Primæval= { I. Egg-animals { 1. Archaic animals 1. Archezoa
=Animals= { _Ovularia_ { 2. Gregarines 2. Gregarinæ
{ { 3. Infusoria 3. Infusoria
+Protozoa+ {
{II. Mulberry animals { 4. Planæads 4. Planæadas
{ _Blastularia_ { 5. Gastræads 5. Gastræadas

B. {
=Animal= { III. Sponges { 6. Sponges 6. Porifera
=Plants= { _Spongiæ_ {
{
+Zoophyta+ { IV. Sea-nettles { 7. Corals 7. Coralla
{ _Acalephæ_ { 8. Hood-jellies 8. Hydromedusæ
{ { 9. Comb-jellies 9. Ctenophora

C. {V. Bloodless worms {10. Planary worms 10. Platyhelminthes
=Worms= { _Acœlomi_
{ {11. Round worms 11. Nemathelminthes
+Vermes+ { VI. Blood-bearing {12. Moss-polyps 12. Bryozoa
{ worms {13. Sac-worms 13. Tunicata
{ _Cœlomati_ {14. Proboscideans 14. Rhynchocœla
{ {15. Star-worms 15. Gephyrea
{ {16. Wheel animalcules 16. Rotatoria
{ {17. Ring-worms 17. Annelida

D. {VII. Headless shellfish {18. Lamp-shells 18. Spirobranchia
=Molluscs= { _Acephala_ {19. Mussels 19. Lamellibranchia
{
+Mollusca+ { VIII. Head-bearing {20. Snails 20. Cochlides
{ _Eucephala_ {21. Cuttles 21. Cephalopoda

E. { IX. Ringed-arms {22. Sea-stars 22. Asterida
=Star-fishes= { _Colobrachia_ {23. Lily-stars 23. Crinoida
{
+Echinoderma+ { X. Armless {24. Sea-urchins 24. Echinida
{ _Lipobrachia_ {25. Sea-cucumbers 25. Holothuriæ

F. { XI. Gill-breathers {26. Crab-fish 26. Crustacea
=Articulated= { _Carides_ {
=Animals= {
{ XII. Tube-breathers {27. Spiders 27. Arachnida
+Arthropoda+ { _Tracheata_ {28. Centipedes 28. Myriopoda
{ {29. Flies 29. Insecta

{ XIII. Skull-less {30. Lancelets 30. Leptocardia
{ _Acrania_ {
G. {
=Vertebrate= { XIV. Single-nostriled {31. Lampreys 31. Cyclostoma
=Animals= { _Monorrhina_ {
{
+Vertebrata+ { XV. Amnion-less {32. Fishes 32. Pisces
{ _Anamnia_ {33. Mud-fish 33. Dipneusta
{ {34. Sea dragons 34. Halisauria
{ {35. Amphibians 35. Amphibia
{
{ XVI. Amnion-bearing {36. Reptiles 36. Reptilia
{ _Amniota_ {37. Birds 37. Aves
{ {38. Mammals 38. Mammalia

----------------------------------------------------------------

The first province of the Protozoa consists of the _Egg animals_
(Ovularia); we include among them all _single-celled animals_, all
animals whose body, in the fully developed state, possesses the
form-value of a _simple plastid_ (of a cytod or a cell), also those
simple animal forms whose body consists of an aggregation of several
cells perfectly similar one to another.

The _Archaic animals_ (Archezoa) form the first class in the series of
Egg animals. It contains only the most simple and most ancient primary
forms of the animal kingdom, whose former existence we have proved by
means of the fundamental law of biogenesis; they are, (1) Animal Monera;
(2) Animal Amœbæ; (3) Animal Synamœbæ. We may, if we choose, include
among them a portion of the still living Monera and Amœbæ, but another
portion (according to the discussion in Chapter XVI.) must on account of
their neutral nature be considered as Protista, and a third portion, on
account of their vegetable nature, must be considered as plants.

A second class of the egg animals consists of the _Gregarines_
(Gregarinæ), which live as parasites in the intestines and body-cavities
of many animals. Some of these Gregarines are perfectly simple cells
like the Amœbæ; some form chains of two or three identical cells, one
lying behind the other. They differ from the naked Amœbæ by possessing
a thick, simple membrane, which surrounds their cell-body; they can be
considered as animal Amœbæ which have adopted a parasitical mode of
life, and in consequence have surrounded themselves with a secreted
covering.

As a third class of egg animals, we adopt the real _Infusoria_
(Infusoria), embracing those forms to which modern zoology almost
universally limits this class of animals. The principal portion of them
consists of the small _ciliated Infusoria_ (Ciliata), which inhabit all
the fresh and salt waters of the earth in great numbers, and which swim
about by means of a delicate garb of vibratile fringes. A second and
smaller division consists of the adherent _sucking Infusoria_ (Acinetæ),
which take their food by means of fine sucking-tubes. Although during
the last thirty years numerous and very careful investigations have been
made on these small animalcules,—which are mostly invisible to the naked
eye,—still we are even now not very sure about their development and
form-value. We do not even yet know whether the Infusoria are single or
many-celled; but as no investigator has as yet proved their body to be a
combination of cells, we are, in the mean time, justified in considering
them as single-celled, like the Gregarines and the Amœbæ.

The second main class of primæval animals consists of the _Germ animals_
(Blastularia). This name we give to those extinct Protozoa which
correspond to the two ontogenetic embryonic forms of the six higher
animal tribes, namely, the Planula and the Gastrula. The body of these
Blastularia, in a perfectly developed state, was composed of many cells,
and these cells moreover differentiated—in two ways at least—into an
external (animal or dermal) and an internal (vegetative or gastral)
mass. Whether there still exist representatives of this group is
uncertain. Their former existence is undoubtedly proved by the two
exceedingly important ontogenetic animal forms which we have already
described as Planula and Gastrula, and which still occur as a transient
stage of development in the ontogeny of the most different tribes of
animals. Corresponding to these, we may, according to the biogenetic
principle, assume the former existence of two distinct classes of
Blastularia, namely, the _Planæada_ and _Gastræada_. The type of the
_Planæada_ is the _Planæa_—long since extinct—but whose historical
portrait is still presented to us at the present day in the widely
distributed _ciliated larva_ (Planula). (Frontispiece, Fig. 4.) The type
of the _Gastræada_ is the _Gastræa_, of whose original nature the
mouth-and-stomach larva (Gastrula), which recurs in the most different
animal tribes, still gives a faithful representation. (Frontispiece Fig.
5, 6.) Out of the Gastræa, as we have previously mentioned, there were
at one time developed two different primary forms, the Protascus and
Prothelmis; the former must be looked upon as the primary form of the
Zoophytes, the latter as the primary form of Worms. (Compare the
enunciation of this hypothesis in my Monograph of the Calcareous
Sponges, vol i. p. 464.)

The _Animal-plants_ (Zoophyta, or Cœlenterata) which constitute the
second tribe of the animal kingdom, rise considerably above the
primitive animals in the characters of their whole organisation, while
they remain far below most of the higher animals. For in the latter
(with the exception only of the lowest forms) the four distinct
functions of nutrition—namely, digestion, circulation of the blood,
respiration, and excretion—are universally accomplished by four
perfectly different systems of organs: by the intestines, the vascular
system, the organs of respiration, and the urinary apparatus. In
Zoophytes, however, these functions and their organs are not yet
separate, and are all performed by a single system of alimentary canals,
by the so-called gastro-vascular system, or the cœlenteric apparatus of
the intestinal cavity. The mouth, which is also the anus, leads into a
stomach, into which the other cavities of the body also open. In
Zoophytes the body-cavity, or “cœloma,” possessed by the four higher
tribes of animals is still completely wanting, likewise the vascular
system and blood, as also the organs of respiration, etc.

All Zoophytes live in water; most of them in the sea, only a very few in
fresh water, such as fresh-water sponges (Spongilla) and some primæval
polyps (Hydra, Cordylophora). A specimen of the pretty flower-like forms
which are met with in great variety among Zoophytes is given on Plate
VII. (Compare its explanation in the Appendix.)

The tribe of animal-plants, or Zoophytes, is divided into two distinct
provinces, the _Sponges_, or _Spongiæ_, and the _Sea-nettles_, or
_Acalephæ_ (p. 144). The latter are much richer in forms and more highly
organized than the former. In all Sponges the entire body, as well as
the individual organs, are differentiated and perfected to a much less
extent than in Sea-nettles. All Sponges lack the characteristic
_nettle-organs_ which all Sea-nettles possess.

The common primary form of all Zoophytes must be looked for in the
_Protascus_, an animal form long since extinct, but whose existence is
proved according to the biogenetic principle by the Ascula. This Ascula
is an ontogenetical development form which, in Sponges as well as in
Sea-nettles, proceeds from the Gastrula. (Compare the Ascula of the
calcareous sponge on the Frontispiece, Fig. 7, 8.) For after the
Gastrula of zoophytes has for a time swum about in the water it sinks to
the bottom, and there adheres by that pole of its axis which is opposite
to the opening of the mouth. The external cells of the ectoderm draw in
their vibrating, ciliary hairs, whereas, on the contrary, the inner
cells of the entoderm begin to form them. Thus the Ascula, as we call
this changed form of larva, is a simple sack, its cavity (the cavity of
the stomach or intestine) opening by a mouth externally, at the upper
pole of the longitudinal axis (opposite the basal point of fixture). The
entire body is here in a certain sense a mere stomach or intestinal
canal, as in the case of the Gastrula. The wall of the sack, which is
both body wall and intestinal wall, consists of two layers or coats of
cells, a fringed _entoderm_, or gastral layer (corresponding with the
inner or vegetative germ-layer of the higher animals), and an unfringed
exoderm or dermal layer (corresponding with the external or animal
germ-layer of the higher animals). The original _Protascus_, a true
likeness of which is still furnished by the Ascula, probably formed
egg-cells and sperm-cells out of its gastral layer.

The Protascads—as we will call the most ancient group of vegetable
animals, represented by the Protascus-type—divided into two lines or
branches, the Spongiæ and the Sea-nettles, or Acalephæ. I have shown in
my Monograph of the Calcareous Sponges (vol. i. p. 485) how closely
these two main classes of Zoophytes are related, and how they must both
be derived, as two diverging forms, from the Protascus-form. The primary
form of Spongiæ, which I have there called Archispongia, arose out of
the Protascus by the formation of pores through its body-wall; the
primary form of Sea-nettles, which I there called Archydra, developed
out of the Protascus by the formation of nettle-organs, as also by the
formation of feelers or tentacles.

The main-class or branch of the _Sponges_, _Spongiæ_, or _Porifera_,
lives in the sea, with the single exception of the green fresh-water
Sponge (Spongilla). These animals were long considered as plants, later
as Protista; in most Manuals they are still classed among the primæval
animals, or Protozoa. But since I have demonstrated their development
out of the Gastrula, and the construction of their bodies of two
cellular germ-layers (as in all higher animals), their close
relationship to Sea-nettles, and especially to the Hydrapolyps, seems
finally to be established. The _Olynthus_ especially, which I consider
as the common primary form of calcareous sponges, has thrown a complete
and unmistakable light upon this point.

The numerous forms comprised in the class of Spongiæ have as yet been
but little examined; they may be divided into three legions and eight
orders. The first legion consists of the soft, gelatinous _Mucous
Sponges_ (Myxospongiæ), which are characterized by the absence of any
hard skeleton. Among them are, on the one hand, the long-since-extinct
primary forms of the whole class, the type of which I consider to be the
Archispongia; on the other hand there are the still living, gelatinous
sponges, of which the _Halisarca_ is best known. We can obtain a notion
of the Archispongia, the most ancient primæval sponge, if we imagine the
Olynthus (see Frontispiece), to be deprived of its radiating calcareous
spiculæ.

The second legion of Spongiæ contains the _Fibrous Sponges_
(Fibrospongiæ), the soft body of which is supported by a firm, fibrous
skeleton. This fibrous skeleton often consists merely of so-called
“horny fibres,” formed of a very elastic, not readily destructible,
organic substance. This is the case for instance in our common bathing
Sponge (Euspongia officinalis), the purified skeleton of which we use
every morning when washing. Blended with the horny, fibrous skeleton of
many of these Sponges, there are numerous flinty spicula; this is the
case for example with the fresh-water Sponge (Spongilla). In others the
whole skeleton consists of only calcareous or silicious spicula which
are frequently interwoven into an extremely beautiful lattice-work, as
in the celebrated Venus’ Flower Basket (Euplectella). Three orders of
fibrous sponges may be distinguished according to the different
formation of the spicula, namely, Chalynthina, Geodina, and
Hexactinella. The natural history of the fibrous sponges is of especial
interest to the Theory of Descent, as was first shown by Oscar Schmidt,
the greatest authority on this group of animals. In no other group,
perhaps, can the unlimited pliability of the specific form, and its
relation to Adaptation and Inheritance, be so clearly followed step by
step; perhaps in no other group is the species so difficult to limit and
define.

[Illustration: Pl. VII.

E. Haeckel del. Lagesse sc.]

This proposition, which applies to the great legion of the Fibrous
Sponges, applies in a still higher degree to the smaller but exceedingly
interesting legion of the calcareous sponges (Calcispongiæ), on which in
1872, after five years’ careful examination, I published a comprehensive
Monograph. The sixty plates of figures accompanying this Monograph
explain the extreme pliability of these small sponges “good species” of
which, in fact, cannot be spoken of in the usual systematic sense. We
find among them only varying series of forms, which do not even
completely transmit their specific form to their nearest descendants,
but by adaptation to subordinate, external conditions of existence,
perpetually change. It frequently occurs here, that there arise out of
one and the same stock different form-species, which according to the
usual system would belong to several quite distinct genera; this is the
case, for instance, with the remarkable Ascometra (Frontispiece, Fig.
10.) The entire external bodily form is much more pliable and protean in
Calcareous Sponges than in the silicious sponges, which are
characterized by possessing silicious spicula, forming a beautiful
skeleton. Through the study of the comparative anatomy and ontogeny of
calcareous sponges, we can recognise, with the greatest certainty, the
common primary form of the whole group, namely, the sack-shaped
_Olynthus_, whose development is represented in the Frontispiece
(compare its explanation in the Appendix). Out of the Olynthus (Fig. 9
on the Frontispiece), the order of the Ascones was the first to develop,
out of which, at a later period, the two other orders of Calcareous
Sponges, the _Leucones_ and _Sycones_, arose as diverging branches.
Within these orders, the descent of the individual forms can again be
followed step by step. Thus the Calcareous Sponges in every respect
confirm the proposition which I have elsewhere maintained: that “the
natural history of sponges forms a connected and striking argument in
favour of Darwin.”

The second main class or branch in the tribe of Zoophytes is formed by
the Sea-nettles (Acalephæ, or Cnidæ). This interesting group of animals,
so rich in forms, is composed of three different classes, namely, the
Hood-jellies (Hydromedusæ), the Comb-jellies (Ctenophora), and the
Corals (Coralla). The hypothetical, extinct Archydra must be looked upon
as the common primary form of the whole group; it has left two near
relations in the still living fresh-water polyps (Hydra and
Cordylophora). The Archydra was very closely related to the simplest
forms of Spongiæ (Archispongia and Olynthus), and probably differed from
them only by possessing nettle organs, and by the absence of cutaneous
pores. Out of the Archydra there first developed the different Hydroid
polyps, some of which became the primary forms of Corals, others the
primary forms of Hydromedusæ. The Ctenophora developed later out of a
branch of the latter.

The Sea-nettles differ from the Spongiæ (with which they agree in the
characteristic formation of the system of the alimentary canal)
principally by the constant possession of nettle organs. These are small
bladders filled with poison, large numbers—generally millions—of which
are dispersed over the skin of the sea nettles, and which burst and
empty their contents when touched. Small animals are killed by this; in
larger animals this nettle poison causes a slight inflammation of the
skin, just as does the poison of our common nettles. Any one who has
often bathed in the sea, will probably have at times come in contact
with large Hood-jellies (Jelly-fish), and become acquainted with the
unpleasant burning feeling which their nettle organs can produce. The
poison in the splendid blue Jelly-fish, Physalia, or Portuguese
Man-of-war, acts so powerfully that it may lead to the death of a human
being.

The class of Corals (Coralla) lives exclusively in the sea, and is more
especially represented in the warm seas by an abundance of beautiful and
highly-coloured forms like flowers. Hence they are also called
_Flower-animals_ (Anthozoa). Most of them are attached to the bottom of
the sea, and contain an internal calcareous skeleton. Many of them by
continued growth produce such immense stocks that their calcareous
skeletons have formed the foundation of whole islands, as is the case
with the celebrated coral reefs and atolls of the South Seas, the
remarkable forms of which were first explained by Darwin.(13) In corals
the counterparts, or antimera—that is, the corresponding divisions of
the body which radiate from and surround the central main axis of the
body—exist sometimes to the number of four, sometimes to the number of
six or eight. According to this we distinguish three legions, the
Fourfold (Tetracoralla), Sixfold (Hexacoralla), and Eightfold corals
(Octocoralla). The fourfold corals form the common primary group of the
class, out of which the sixfold and eightfold have developed as two
diverging branches.

SYSTEMATIC SURVEY

_Of the 4 Classes and 30 Orders of the Animal Plants, or Zoophytes._

----------------+--------------------+--------------------+---------------
_Class of the_ | _Legions of the_ | _Orders of the_ | _A Genus Name_
_Zoophytes._ | _Zoophytes._ | _Zoophytes._ | _as example._
----------------+--------------------+--------------------+---------------
I. { I. Myxospongiæ { 1. Archispongina | Archispongia
{ _Mucous Sponges_ { 2. Halisarcina | Halisarca
=Sponges= { |
{ II. Fibrospongiæ { 3. Chalynthina | Spongilla
+Spongiæ+ {_Fibrous Sponges_ { 4. Geodina | Ancorina
or { { 5. Hexactinella | Euplectella
+Porifera+ { |
{ III. Calcispongiæ { 6. Ascones | Olynthus
{_Calcareous Sponges_ { 7. Leucones | Dyssycus
{ { 8. Sycones | Sycurus
|
|
II. { IV. Tetracoralla { 9. Rugosa | Cyathophyllum
{_Fourfold Corals_ { 10. Paranemeta | Cereanthus
=Corals= { |
{ V. Hexacoralla { 11. Cauliculata | Antipathes
+Coralla+ {_Sixfold Corals_ { 12. Madreporaria | Astræa
or { { 13. Halirhoda | Actinia
+Anthozoa+ { |
{ VI. Octocoralla { 14. Alcyonida | Lobularia
{_Eightfold Corals_ { 15. Gorgonida | Isis
{ { 16. Pennatulida | Veretillum
|
|
III. { VII. Archydræ } 17. Hydraria | Hydra
{_Primæval Polyps_ } |
=Jelly-polyps= { |
{ VIII. Leptomedusæ { 18. Vesiculata | Sertularia
+Hydromedusæ+ {_Soft Jelly-fish_ { 19. Ocellata | Tubularia
{ { 20. Siphonophora | Physophora
or { |
{ IX. Trachymedusæ { 21. Marsiporchida| Trachynema
=Hood-jellies= { _Hard Jelly-fish_ { 22. Phyllorchida | Geryonia
{ { 23. Elasmorchida | Charybdæ
+Medusa+ { |
{ X. Calycozoa } 24. Podactinaria | Lucernaria
{ _Stalked Jellies_ } |
{ |
{ XI. Discomedusæ { 25. Semæostomeæ | Aurelia
{ _Disc-jellies_ { 26. Rhizostomeæ | Crambessa
|
|
IV. { XII. Eurystoma } 27. Beroida | Beroe
{ _Wide-mouthed_ } |
=Comb-jellies= { |
{ XIII. Stenostoma { 28. Saccata | Cydippe
+Ctenophora+ { _Narrow-mouthed_ { 29. Lobata | Eucharis
{ { 30. Tæniata | Cestum

----------------------------------------------------------------

The second class of Sea-nettles is formed by the _Hood-jellies_ (Medusæ)
or _Polyp-jellies_ (Hydromedusæ). While most corals form stocks like
plants, and are attached to the bottom of the sea, the Hood-jellies
generally swim about freely in the form of gelatinous bells. There are,
however, numbers of them, especially the lower forms, which adhere to
the bottom of the sea, and resemble pretty little trees. The lowest and
simplest members of this class are the little fresh-water polyps (Hydra
and Cordylophora). We may look upon them as but little changed
descendants of those _Primæval polyps_ (Archydræ), from which, during
the primordial period, the whole division of the Sea-nettles originated.
Scarcely distinguishable from the Hydra are the adherent Hydroid polyps
(Campanularia, Tubularia), which produce freely swimming medusæ by
budding, and out of the eggs of these there again arise adherent polyps.
These freely swimming Hood-jellies are mostly of the form of a mushroom,
or of an umbrella, from the rim of which many long and delicate
tentacles hang. They are among the most beautiful and most interesting
inhabitants of the sea. The remarkable history of their lives, and
especially the complicated alternation of generation of polyps and
medusæ, are among the strongest proofs of the truth of the theory of
descent. For just as Medusæ still daily arise out of the Hydroids, did
the freely swimming medusa-form originally proceed, phylogenetically,
out of the adherent polyp-form. Equally important for the theory of
descent is the remarkable _division of labour_ of the individuals, which
among some of them is developed to an astonishingly high degree, more
especially in the splendid _Siphonophora_.(37) (Plate VII. Fig. 13.)

The third class of Sea-nettles—the peculiar division of Comb-jellies
(Ctenophora), probably developed out of a branch of the Hood-jellies.
The Ctenophora, which are also called Ribbed-jellies, possess a body of
the form of a cucumber, which, like the body of most Hood-jellies, is as
clear and transparent as crystal or cut glass. Comb or Ribbed-jellies
are characterized by their peculiar organs of motion, namely, by eight
rows of paddling, ciliated leaflets, which run in the form of eight ribs
from one end of the longitudinal axis (from the mouth) to the opposite
end. Those with narrow mouths (Stenostoma) probably developed later out
of those with wide mouths (Eurystoma). (Compare Plate VII. Fig. 16.)

The third tribe of the animal kingdom, the phylum of _Worms_ or
worm-like animals (Vermes, or Helminthes), contains a number of
diverging branches. Some of these numerous branches have developed into
well-marked and perfectly independent classes of Worms, but others
changed long since into the original, radical forms of the four higher
tribes of animals. Each of these four higher tribes (and likewise the
tribe of Zoophytes) we may picture to ourselves in the form of a lofty
tree, whose branches represent the different classes, orders, families,
etc. The phylum of Worms, on the other hand, we have to conceive as a
low bush or shrub, out of whose root a mass of independent branches
shoot up in different directions. From this densely branched shrub, most
of the branches of which are dead, there rise four high stems with many
branches. These are the four lofty trees just mentioned as representing
the higher phyla—the Echinoderma, Articulata, Mollusca, and Vertebrata.
These four stems are directly connected with one another at the root
only, to wit, by the common primary group of the Worm tribe.

The extraordinary difficulties which the systematic arrangement of Worms
presents, for this reason merely, are still more increased by the fact
that we do not possess any fossil remains of them. Most of the Worms had
and still have such soft bodies that they could not leave any
characteristic traces in the neptunic strata of the earth. Hence in this
case again we are entirely confined to the records of creation furnished
by ontogeny and comparative anatomy. In making then the exceedingly
difficult attempt to throw a few hypothetical rays of light upon the
obscurity of the pedigree of Worms, I must therefore expressly remark
that this sketch, like all similar attempts possesses only a provisional
value.

The numerous classes distinguished in the tribe of Worms, and which
almost every zoologist groups and defines according to his own personal
views, are, in the first place, divided into two essentially different
groups or branches, which in my Monograph of the Calcareous Sponges I
have termed Acœlomi and Cœlomati. For all the lower Worms which are
comprised in the class of Flat-worms (Platyhelminthes), (the
Gliding-worms, Sucker-worms, Tape-worms), differ very strikingly from
other Worms, in the fact that they possess neither blood nor body-cavity
(no cœlome); they are, therefore, called Acœlomi. The true cavity, or
cœlome, is completely absent in them as in all the Zoophytes; in this
important respect the two groups are directly allied. But _all other
Worms_ (like the four higher tribes of animals) possess a genuine
body-cavity and a vascular system connected with it, which is filled
with blood; hence we class them together as _Cœlomati_.

The main division of _Bloodless Worms_ (Acœlomi) contains, according to
our phylogenetic views, besides the still living Flat-worms, the unknown
and extinct primary forms of the whole tribe of Worms, which we shall
call the Primæval Worms (Archelminthes). The type of these _Primæval
Worms_, the ancient Prothelmis, may be directly derived from the Gastræa
(p. 133). Even at present the Gastrula-form—the faithful historical
portrait of the Gastræa—recurs in the ontogenesis of the most different
kinds of worms as a transient larva-form. The ciliated Gliding-worms
(Turbellaria), the primary group of the present Planary or Flat-worms
(Platyhelminthes), are the nearest akin to the Primæval Worms. The
parasitical Sucker-worms (Trematoda) arose out of the Gliding-worms,
which live freely in water, by adaptation to a parasitical mode of life;
and out of them later on—by an increasing parasitism—arose the
Tape-worms (Cestoda).

Out of a branch of the Acœlomi arose the second main division of the
Worm tribe, the Worms with blood and body-cavity (Cœlomati): of these
there are seven different classes.

The Pedigree on p. 151 shows how the obscure phylogeny of the seven
classes of Cœlomati may be supposed to stand. We shall, however, mention
these classes here quite briefly, as their relationships and derivation
are, at present, still very complicated and obscure. More numerous and
more accurate investigations of the ontogeny of the different Cœlomati
will at some future time throw light upon their phylogenesis.

The Round Worms (Nemathelminthes) which we mention as the first class of
the Cœlomati, and which are characterized by their cylindrical form,
consist principally of parasitical Worms which live in the interior of
other animals. Of human parasites, the celebrated Trichinæ, the
Maw-worms, Whip-worms, etc., for example, belong to them. The Star-worms
(Gephyrea) which live exclusively in the sea are allied to round worms,
and the comprehensive class of Ring-worms (Annelida) are allied to the
former. To the Ring-worms, whose long body is composed of a number of
segments, all alike in structure, belong the Leeches (Hirudinea),
Earth-worms (Lumbricina), and all the marine bristle-footed Worms
(Chætopoda). Nearly akin to them are the Snout-worms (Rhynchocœla), and
the small microscopic Wheel-worms (Rotifera). The unknown, extinct,
primary forms of the tribe of Sea-stars (Echinoderma), and of the tribe
of the articulated animals (Arthropoda), were nearest akin to the
Ring-worms. On the other hand, we must probably look for the primary
forms of the great tribe of Molluscs in extinct Worms, which were very
closely related to the Moss-polyps (Bryozoa) of the present day; and for
the primary forms of the Vertebrata in the unknown Cœlomati, whose
nearest kin of the present day are the Sea-sacs, especially the Ascidia.

SYSTEMATIC SURVEY

_Of the 8 Classes and 22 Orders of the Worm Tribe._

(Compare Gen. Morph. ii. Plate V. pp. 75-77.)

------------------+-------------------------+----------------------+------------------
_Classes_ | | _Systematic_ |
_of the_ | _Orders of the_ | _Name of the_ | _Name of a Genus_
_Worm Tribe._ | _Worm Tribe._ | _Orders of Worms_. | _as example._
| | |
------------------+-------------------------+----------------------+------------------
1. _Flat_ { 1. Primæval worms | 1. Archelminthes | Prothelmis
_Worms_ { 2. Gliding-worms | 2. Turbellaria | Planaria
Platyhel- { 3. Sucker-worms | 3. Trematoda | Distoma
minthes { 4. Tape-worms | 4. Cestoda | Tænia
| |
2. _Round_ { 5. Arrow-worms | 5. Chætognatha | Sagitta
_Worms_ { 6. Thread-worms | 6. Nematoda | Trichina
Nemathel- { 7. Hook-headed | 7. Acanthocephala | Echinorhynchus
minthes { worms | |
| |
3. _Moss_ } 8. Horse-shoe-lipped | 8. Lophopoda | Alcyonella
_Polyps_ } 9. Circle-lipped | 9. Stelmopoda | Retepora
Bryozoa } | |
| |
4. _Sea-sacs_ { 10. Sea-squirts | 10. Ascidia | Phallusia
Tunicata { 11. Sea-barrels | 11. Thaliacea | Salpa
| |
5. _Proboscideans_ } 12. Tongue-worms | 12. Enteropneusta | Balanoglossus
Rhynchocœla } 13. Cord-worms | 13. Nemertina | Borlasia
| |
{ 14. Star-worms without | 14. Sipunculida | Sipunculus
6. _Star-Worms_ { bristles | |
Gephyrea { 15. Star-worms with | 15. Echiurida | Echiurus
{ bristles | |
| |
7. _Wheel_ } | |
_Animalcule_ } 16. Wheel-worms | 16. Rotatoria | Hydatina
Rotifera } | |
| |
{ 17. Bear-worms | 17. Arctisca | Macrobiotus
{ 18. Worms with claws | 18. Onychophora | Peripatus
8. _Ring_ { 19. Leeches | 19. Hirudinea | Hirudo
_Worms_ { 20. Land-worms | 20. Drilomorpha | Lumbricus
Annelida { 21. Mailed worms | 21. Phracthelminthes | Crossopodia
{ 22. Bristle-footed | 22. Chætopoda | Aphrodite
{ worms | |

----------------------------------------------------------------

The class of Sea-sacs (Tunicata) is one of the most remarkable among
Worms. They all live in the ocean, where some of the Ascidiæ adhere to
the bottom, while others (the sea-barrels, or Thaliacea) swim about
freely. In all of them the non-jointed body has the form of a simple
barrel-shaped sack, which is surrounded by a thick cartilaginous mantle.
This mantle consists of the same non-nitrogenous combination of carbon,
which, under the name of cellulose, plays an important part in the
Vegetable Kingdom, and forms the largest portion of vegetable cellular
membranes, and consequently also the greater part of wood. The
barrel-shaped body generally possesses no external appendages. No one
would recognise in them a trace of relationship to the highly
differentiated vertebrate animals. And yet this can no longer be
doubted, since Kowalewsky’s investigations, which in the year 1867
suddenly threw an exceedingly surprising and unmistakable light upon
them. From these investigations it has become clear that the individual
development of the adherent simple Ascidian Phallusia agrees in most
points with that of the lowest vertebrate animal, namely, the Lancelet
(Amphioxus lanceolatus). The early stages of the Ascidia possess the
beginnings of the _spinal marrow_ and the _spinal column_ (chorda
dorsalis) lying beneath it, which are the two most essential and most
characteristic organs of the vertebrate animal. Accordingly, of all
invertebrate animals known to us, the _Tunicates are without doubt the
nearest blood relations of the Vertebrates_, and must be considered as
the nearest relations of those Worms out of which the vertebrate tribe
has developed. (Compare Plates XII. and XIII.)

While thus different branches of the Cœlomatous group of the Worms
furnish us with several genealogical links leading to the four higher
tribes of animals, and give us important phylogenetic indications of
their origin, the lower group of Acœlomi, on the other hand, show close
relationships to the Zoophytes, and to the Primæval animals. The great
phylogenetic interest of the Worm tribe rests upon this peculiar
intermediate position.

CHAPTER XIX.

PEDIGREE AND HISTORY OF THE ANIMAL KINGDOM.

II. MOLLUSCA, STAR-FISHES, AND ARTICULATED ANIMALS.

The great natural main groups of the animal kingdom, which we have
distinguished as TRIBES, or PHYLA (“types” according to Bär and Cuvier),
are not all of equal systematic importance for our phylogeny or history
of the pedigree of the living world. They can neither be classed in a
single series of stages, one above another, nor be considered as
entirely independent stems, nor as equal branches of a single
family-tree. It seems rather (as we saw in the last chapter) that the
tribe of Protozoa, the so-called primæval animals, is the common radical
group of the whole animal kingdom. Out of the Gastræada—which we class
among the Protozoa—the Zoophytes and the Worms have developed, as two
diverging branches. We must now in turn look upon the varied and
much-branching tribe of Worms as the common primary group, out of which
(from perfectly distinct branches) arose the remaining tribes, the four
higher phyla of the animal kingdom. (Compare the Pedigree, p. 133.)

Let us now take a genealogical look at these four higher tribes of
animals, and try whether we cannot make out the most important outlines
of their pedigree. Even should this attempt prove defective and
imperfect, we shall at all events have made a beginning, and paved the
road for subsequent and more satisfactory attempts.

It does not matter in what succession we take up the examination of the
four higher tribes. For these four phyla have no close relationship
whatever among one another, but have grown out from entirely distinct
branches of the group of Worms (p. 133). We may consider the tribe of
Molluscs as the most imperfect and the lowest in point of morphological
development. We nowhere meet among them with the characteristic
articulation or segmented formation of the body, which distinguishes
even the Ring-worms, and which in the other three higher tribes—the
Echinoderma, Articulata, and Vertebrata—is most essentially connected
with the high development of their forms, their differentiation, and
perfection. The body in all Molluscs—in mussels, snails, etc.—is a
simple non-jointed sack, in the cavity of which lie the intestines. The
nervous system consists not of a cord but of several distinct (generally
three) pairs of knots loosely connected with one another. For these and
many other anatomical reasons, I consider the tribe of Molluscs (in
spite of the high physiological development of its most perfect forms)
to be morphologically the lowest among the four higher tribes of
animals.

Whilst, for reasons already given, we exclude the Moss-polyps, and
Tunicates—which have hitherto been generally classed with the tribe of
Molluscs—we retain as genuine Molluscs the following four classes:
Lamp-shells, Mussels, Snails, and Cuttles. The two lower classes of
Molluscs, the Lamp-shells and Mussels, possess neither head nor teeth,
and they can therefore be comprised under one main class, or branch, as
headless animals (Acephala), or toothless animals (Anodontoda). This
branch is also frequently called that of the clam-shells (Conchifera, or
Bivalvia), because all its members possess a two-valved calcareous
shell. In contrast to these the two higher classes of Molluscs, the
snails and cuttles, may be represented as a second branch with the name
of Head-bearers (Cephalophora), or Tooth-bearers (Odontophora), because
both head and teeth are developed in them.

The soft, sack-shaped body in most Molluscs is protected by a calcareous
shell or house, which in the Acephala (lamp-shells and mussels) consists
of two valves, but in the Cephalophora (snails and cuttles) is generally
a spiral tube (the so-called snail’s house). Although these hard
skeletons are found in large quantities in a petrified state in all the
neptunic strata, yet they tell us but little of the historical
development of the tribe, which must have taken place for the most part
in the primordial period. Even in the Silurian strata we find fossil
remains of all the four classes of Molluscs, one beside the other, and
this, conjointly with much other evidence, distinctly proves that the
tribe of Molluscs had then obtained a strong development, when the
higher tribes, especially the Articulates and Vertebrates, had scarcely
got beyond the beginning of their historical development. In subsequent
periods, especially in the primary and secondary periods, these higher
tribes increased in importance more and more at the expense of Molluscs
and Worms, which were no match for them in the struggle for life, and
accordingly decreased in number. The still living Molluscs and Worms
must be considered as only a proportionately small remnant of the vast
molluscan fauna, which greatly predominated in the primordial and
primary periods over the other tribes. (Compare Plate VI. and
explanation in the Appendix.)

No tribe of animals shows more distinctly than do the Molluscs, how very
different the value of fossils is in geology and in phylogeny. In
geology the different species of the fossil shells of Molluscs are of
the greatest importance because they serve as excellent marks whereby to
characterize the different groups of strata, and to fix their relative
ages. As far as relates to the genealogy of Molluscs, however, they are
of very little value, because, on the one hand, the shells are parts of
quite subordinate morphological importance, and because the actual
development of the tribe belongs to the earlier primordial period, from
which no distinct fossils have been preserved. If therefore we wish to
construct the pedigree of Molluscs, we are mainly dependent upon the
records of ontogeny and comparative anatomy from which we obtain
something like the following result. (Gen. Morph. ii. Plate VI. pp.
102-116.)

The lowest stage of the four classes of genuine Molluscs known to us, is
occupied by the Lamp-shells or Spiral-gills (Spirobranchia), frequently
but inappropriately called Arm-footers (Brachiopoda), which have become
attached to the bottom of the sea. There now exist but few forms of
this class; for instance, some species of Lingula, Terebratula, and
others akin to them, which are but feeble remnants of the great variety
of forms which represented the Lamp-shells in earlier periods of the
earth’s history. In the Silurian period they constituted the principal
portion of the whole Mollusc tribe. From the agreement which, in many
respects, their early stage of development presents with the Moss
animals, it has been concluded that they have developed out of Worms,
which were nearly related to this class. Of the two sub-classes of
Lamp-shells, the Hinge-less (Ecardines) must be looked upon as the lower
and more imperfect, the Hinged (Testicardines) as the higher and more
fully developed group.

The anatomical difference between the Lamp-shells and the three other
classes of Molluscs is so considerable that the latter may be
distinguished from the former by the name of Otocardia. All the
Otocardia have a heart with chamber (ventricle) and ante-chamber
(auricle), whereas Lamp-shells do not possess the ante-chamber.
Moreover, the central nervous system is developed only in the former
(and not in the latter) in the shape of a complete pharyngeal ring.
Hence the four classes of Molluscs may be grouped in the following
manner:—

{ 1. Lamp-shells } I. Haplocardia
I. Molluscs { (Spirobranchia). } (with simple heart).
without head. {
_Acephala._ { 2. Mussels }
{ (Lamellibranchia). } II. Otocardia
} (with chamber
II. Molluscs { 3. Snails } and ante-chamber
with head. { (Cochlides). } to the heart).
_Cephalophora._ { 4. Cuttles }
{ (Cephalopoda). }

The result of these structural dispositions for the history of the
pedigree of Molluscs, which is confirmed by palæontology, is that
Lamp-shells stand much nearer to the primæval root of the whole tribe of
Molluscs than do the Otocardia. Probably Mussels and Snails developed as
two diverging branches out of Molluscs, which were nearly akin to the
Lamp-shells.

Mussels, or Plate-gills (Lamellibranchia), possess a bivalved shell like
the Lamp-shells. In the latter, one of the two valves covers the back,
the other the belly of the animal; whereas in Mussels the two valves lie
symmetrically on the right and left side of the body. Most Mussels live
in the sea, only a few in fresh water. The class is divided into two
sub-classes, Asiphonia and Siphonida, of which the latter were developed
at a later period out of the former. Among the Asiphonia are Oysters,
mother-of-pearl Shells, and fresh water Mussels; among the Siphonida,
which are characterized by a respiratory tube, are the Venus-shells,
Razor-shells, and Burrowing Clams. The higher Molluscs seem to have
developed at a later period out of those without head and teeth; they
are distinguished from the latter by the distinct formation of the head,
and more especially by a peculiar kind of tooth apparatus. Their tongue
presents a curious plate, armed with a great number of teeth. In our
common Vineyard Snail (Helix pomatia) the number of teeth amount to
21,000, and in the large Garden Slug (Limax maximus) to 26,800.

SYSTEMATIC SURVEY

_Of the 4 Classes, 8 Sub-classes, and 21 Orders of Molluscs._

------------------+-----------------------+------------------------+-------------------
_Classes of_ | _Sub-classes of_ | _Orders of_ | _Systematic Name_
_Molluscs._ | _Molluscs._ | _Molluscs._ | _of the Orders._
------------------+-----------------------+------------------------+-------------------
I. _Molluscs without head or teeth_: ACEPHALA _or_ ANODONTODA.
---------------------------------------------------------------------------------------
I. { I. Ecardines { 1. Stalked 1. Lingulida
=Lamp-shells= { _Hinge-less_ { 2. Flattened 2. Craniada
{
+Spirobranchia+ {
or {
+Brachiopoda+ { II. Testicardines { 3. Fleshy armed 3. Sarcobrachia
{ _Hinge-less_ { 4. Calcareous-armed 4. Sclerobrachia

II. { III. Asiphonia { 5. One-muscled 5. Monomya
=Mussels= { _Mussels without_ { 6. Uneven-muscled 6. Heteromya
or { _respiratory tubes_ { 7. Even-muscled 7. Isomya
=Plate-gills= {
{
+Lamellibranchia+ { IV. Siphonida { 8. Round-mantled 8. Integripallia
or { _Mussels with_ { 9. Ray-mantled 9. Sinupalliata
+Phyllobranchia+ { _respiratory tubes_ { 10. Tube-mussels 10. Inclusa

---------------------------------------------------------------------------------------
II. _Molluscs with head and teeth_: CEPHALOPHORA _or_ ODONTOPHORA.
---------------------------------------------------------------------------------------

{ V. Stump-headed { 11. Tube-snails 11. Scaphopoda
III. { _Perocephala_ { 12. Butterfly-snails 12. Pteropoda
=Snails= {
{ { 13. With hind gills 13. Opisthobranchia
+Cochlides+ { { 14. With fore gills 14. Prosobranchia
or { VI. Large-headed { 15. Swimming-snails 15. Heteropoda
+Gasteropoda+ { _Delocephala_ { 16. Beetle-snails 16. Chitonoida
{ { 17. Snails with lungs 17. Pulmonata

VII. Chamber-Poulps { 18. Pearl boats 18. Nautilida
IV. with four gills { 19. Ammon’s horns 19. Ammonitida
=Cuttles= } _Tetrabranchia_ {
or }
=Poulps= } VIII. Ink-Poulps with { 20. Ten-armed 20. Decabrachiones
} two gills {
+Cephalopoda+ } _Dibranchia_ { 21. Eight-armed 21. Octobrachiones

----------------------------------------------------------------

We distinguish two sub-classes among the Snails (Cochlides, or
Gasteropoda), namely, the Stump-headed and the Large-headed Snails. The
Stump-headed Snails (Perocephala) are very closely allied to Mussels
(through the Tooth-shells), and also to the Cuttle-fish (through the
Butterfly-snails). The more highly developed Snails, with large heads
(Delocephala), can be divided into Snails with gills (Branchiata) and
Snails with lungs (Pulmonata). Among the latter are the Land-snails, the
only Molluscs which have left the water and become habituated to a life
on land. The great majority of Snails live in the sea, only a few live
in fresh water. Some River-snails in the tropics (the Ampullaria) are
amphibious, living sometimes on land, sometimes in water, and at one
time they breathe through gills, at another through lungs. They have
both kinds of respiratory organs, like the Mud-fish and Gilled Newts
among the Vertebrata.

The fourth and last class, and at the same time the most highly
developed class of Molluscs, is that of the Cuttles, or Poulps, also
called Cephalopoda (foot attached to the head). They all live in the
sea, and are distinguished from Snails by eight, ten, or more long arms,
which surround the mouth in a circle. The Cuttles existing in our recent
oceans—the Sepia, Calamary, Argonaut, and Pearly Nautilus—are, like the
few Spiral-gill Lamp-shells of the present time, but a poor remnant of
the host which represents this class in the oceans of the primordial,
primary, and secondary periods. The numerous fossil “Ammon’s horns”
(Ammonites), “pearl boats” (Nautilus), and “thunderbolts” (Belemnites)
are evidences of the long since extinct splendour of the tribe. The
Poulps, or Cuttles, have probably developed out of a low branch of the
snail class, out of the Butterfly-snails (Pteropoda) or kindred forms.

The different sub-classes and orders, distinguished in the four classes
of Molluscs, whose systematic succession is given on the Table (p.
160), furnish various proofs of the validity of the law of progress by
their historical development and by the systematic development
corresponding to it. As however these subordinate groups of Molluscs are
in themselves of no further special interest, I must refer to the sketch
of their pedigree on p. 161, and to the detailed pedigree of Molluscs
which I have given in my General Morphology, and I shall now at once
turn to the consideration of the tribe of Star-fishes.

The Star-fishes (Echinoderma, or Estrellæ) among which are the four
classes of Sea-stars, Sea-lilies, Sea-urchins, and Sea-cucumbers are one
of the most interesting divisions of the animal kingdom, and yet we know
less about them than about any. They all live in the sea. Every one who
has been at the sea shore must have seen at least two of their forms,
the Sea-stars and the Sea-urchins. The tribe of Star-fishes must be
considered as a completely independent tribe of the animal kingdom on
account of its very peculiar organization, and must be carefully
distinguished from the Animal-plants—Zoophytes, or Cœlenterata, with
which it is still frequently but erroneously classed under the name
Radiata (as for example, by Agassiz, who even to this day defends this
error of Cuvier’s, together with many others).

All Echinoderma are characterized, and at the same time distinguished
from all other animals, by a very remarkable apparatus for locomotion,
which consists of a complicated system of canals or tubes, filled with
sea water from without. The sea water in these aqueducts is moved partly
by the strokes of the cilia, or vibratile hairs lining their walls, and
partly by the contractions of the muscular walls of the tubes
themselves, which resemble india-rubber bags. The water is pressed from
the tubes into a number of little hollow feet, which thereby become
widely distended, and are then employed for walking and suction. The
Sea-stars are moreover characterized by a peculiar calcareous formation
in the skin, which in most cases forms a firm, well-closed coat of mail,
composed of a number of plates. In almost all Echinoderma the body
consists of five radii (counterparts, or antimera) standing round the
main axis of the body, where they meet. It is only in some species of
Sea-stars that the number of these radii amount to more than five—to
6-9, 10-12, or even to 20-40; and in this case the number of radii is
generally not constant, but varies in different individuals of one
species.

The historical development and the pedigree of the Echinoderma are
completely revealed to us by their numerous and, in most cases,
excellently preserved fossil remains, by their very remarkable
individual developmental history, and by their interesting comparative
anatomy; this is the case with no other tribe of animals, even the
Vertebrata themselves are not to be excepted. By a critical use of those
three archives, and by a careful comparison of the results derived from
their study, we obtain the following genealogy of the Star-fishes, which
I have already published in my General Morphology (vol. ii. Plate IV.
pp. 62-77.)

The most ancient and original group of the Star-fishes, the primary form
of the whole phylum, consists of the class of the true Sea-stars
(Asterida). This is established by numerous and important arguments in
anatomy and the history of development, but above all by the irregular
and varying number of the radii, or antimera, which in all other
Echinoderma is limited, without exception, to five. Every Star-fish
consists of a central, small, body-disc, all round the circumference of
which are attached five or several long articulated arms. _Each arm of
the Star-fish essentially corresponds in its organisation with an
articulated worm_ of the class of Ring-worms, or Annelida (p. 149). I
therefore consider the Star-fish as a genuine _stock or cormus of five
or more articulated worms_, which have arisen by the star-wise growth of
a number of buds out of a central mother-worm. The connected members,
thus grouped like the rays of a star, have inherited from the
mother-worm the common opening of the mouth, and the common digestive
cavity (stomach) lying in the central body-disc. The end by which they
have grown together, and which fuses in the common central disc,
probably corresponds to the posterior end of the original independent
worms.

In exactly the same way several individuals of certain kinds of worms
are united so as to form a star-like cormus. This is the case in the
_Botryllidæ_, compound Ascidians, belonging to the class of the
Tunicata. Here also the posterior ends of the individual worms have
grown together, and have formed a common outlet for discharges, a
central cloaca; whereas at the anterior end each worm still possesses
its own mouth. In Star-fishes the original mouths have probably become
closed in the course of the historical development of the cormus, or
colony, whereas the cloaca has developed into a common mouth for the
whole cormus.

SYSTEMATIC SURVEY

_Of the 4 Classes, 9 Sub-classes, and 20 Orders of Star-fishes._

(Compare Gen. Morph. II. Plate IV. pp. 62-67.)

----------------+-------------------------+---------------------------+------------------
_Classes of the | _Sub-classes of the | _Orders of the | _Systematic Name
Star-fishes._ | Star-fishes._ | Star-fishes._ | of the Orders._
----------------+-------------------------+---------------------------+------------------
|
{ I. { 1. Primary Stars | 1. Tecastra
{ Sea Stars with radiated { 2. Articulated Stars | 2. Colastra
I. { stomach { 3. Brisinga Stars | 3. Brisingastra
=Sea Stars= { _Actinogastra_ |
+Asterida+ {
{ II. { 4. Serpent Stars | 4. Ophiastra
{ Sea Stars with disc- { 5. Tree Stars | 5. Phytastra
{ shaped stomach { 6. Lily Stars | 6. Crinastra
{ _Discogastra_ { |
|
{ III. { 7. Plated Lilies with | 7. Phatnocrinida
{ Lilies with arms { arms |
{ _Brachiata_ { 8. Articulated Lilies | 8. Colocrinida
{ { with arms |
|
II. { IV. { 9. Regularly budding | 9. Pentremitida
=Sea Lilies= { Lilies with buds { Lilies |
+Crinoida+ { _Blastoidea_ { 10. Lilies budding on | 10. Eleutherocrina
{ { two sides |
|
{ V. { 11. Bladder Lilies | 11. Agelacrinida
{ Bladder Lilies { without stalks |
{ _Cystidea_ { 12. Bladder Lilies | 12. Sphæronitida
{ with stalks |
|
{ VI. { 13. Palechinida with | 13. Melonitida
{ Older Sea Urchins { more than 10 |
{ (with more than { rows of ambulacral |
{ 20 rows of plates) { plates |
III. { _Palechinida_ { 14. Palechinida with | 14. Eocidaria
=Sea Urchins= { { 10 rows of |
+Echinida+ { VII. { ambulacral plates |
{ More recent Sea { 15. Autechinida with | 15. Desmosticha
{ Urchins (with 20 { band-like ambulacra |
{ rows of plates) { 16. Autechnidia with | 16. Petalosticha
{ _Autechinida_ { leaf-like ambulacra |
|
{ VIII. { 17. Eupodia with scuti- | 17. Aspidochirota
{ Sea Cucumbers { form tentacles |
{ with aquatic feet { 18. Eupodia with | 18. Dendrochirota
IV. { _Eupodia_ { branching tentacles |
=Sea Cucumbers= { { |
{ IX. { |
+Holothuriæ+ { Sea Cucumbers { 19. Apodia with water- | 19. Liodermatida
{ without aquatic { lungs |
{ feet { 20. Apodia without | 20. Synaptida
{ _Apodia_ { water-lungs |

----------------------------------------------------------------

Hence the Star-fishes would be compound stocks of worms which, by the
radial formation of buds, have developed out of true articulated worms,
or Annelids. This hypothesis is most strongly supported by the
comparative anatomy, and by the ontogeny of some Star-fishes (Colastra),
and of segmented worms. The many-jointed Ring-worms (Annelida) in their
inner structure are closely allied to the individual arms or radii of
the Star-fishes, that is to the original single worms, which each arm
represents. Each of the five worms of the Star-fish is a chain composed
of a great number of equi-formal members, or metamera, lying one behind
the other, like every segmented Worm, and every Arthropod. As in the
latter a central nervous cord, the ventral nerve cord runs along the
central line of the ventral wall of each segment. On each metameron
there is a pair of non-jointed feet, and besides these, in most cases,
one or more hard thorns or bristles similar to those of many Ring-worms.
A detached arm of a Star-fish can lead an independent life, and can
then, by the radially-directed growth of buds at one end, again become a
complete star.

The most important proofs, however, of the truth of my hypothesis are
furnished by the ontogeny or the individual development of the
Echinoderma. The most remarkable facts of this ontogeny were first
discovered in the year 1848 by the great zoologist, Johannes Müller of
Berlin. Some of its most important stages are represented on Plates
VIII. and IX. (Compare their explanation in the Appendix.) Fig. _A_ on
Plate IX. shows us a common Sea-star (Uraster), Fig. _B_, a Sea-lily
(Comatula), Fig. _C_, a Sea-urchin (Echinus), and Fig. _D_, a
Sea-cucumber (Synapta). In spite of the extraordinary difference of form
manifested by these four representatives of the different classes of
Star-fishes, yet the beginning of their development is identical in all
cases. Out of the egg an animal-form develops which is utterly
different from the fully developed Star-fish, but very like the ciliated
larvæ of certain segmented Worms (Star-worms and Ring-worms). This
peculiar animal-form is generally called the “larva,” but more correctly
the “nurse” of these Star-fish. It is very small and transparent, swims
about by means of a fringe of cilia, and is always composed of two equal
symmetrical halves or sides. The fully grown Echinoderm, however—which
is frequently more than a hundred times larger, and quite opaque—creeps
at the bottom of the sea, and is always composed of at least five
co-ordinate pieces, or antimera, in the form of radii. Plate VIII. shows
the development of the “nurses” of the four Echinoderms represented on
Plate IX.

The fully developed Echinoderm arises by a very remarkable process of
budding in the interior of the “nurse,” of which it retains little more
than the stomach. The nurse, erroneously called the “larva,” of the
Echinoderm, must accordingly be regarded as a solitary worm, which by
internal budding produces a second generation, in the form of a stock of
star-shaped and connected worms. The whole of this process is a genuine
alternation of generations, or metagenesis, not a “metamorphosis,” as is
generally though erroneously stated. A similar alternation of
generations also occurs in many other worms, especially in some star
worms (Sipunculidæ), and cord worms (Nemertinæ). Now if, bearing in mind
the fundamental law of biogeny, we refer the ontogeny of Echinoderma to
their phylogeny, then the whole historical development of the
Star-fishes suddenly becomes clear and intelligible to us, whereas
without this hypothesis it remains an insoluble mystery. (Compare Gen.
Morph. ii. pp. 95-99.)

Besides the reasons mentioned, there are many other facts (principally
from the comparative anatomy of Echinoderma) which most distinctly prove
the correctness of my hypothesis. I established this hypothesis in 1866,
without having any idea that _fossil articulated worms_ still existed,
apparently answering to the hypothetical primary forms. Such have in the
mean time, however, really been discovered. In a treatise “On the
Equivalent of the North American Taconic Schist in Germany,”[3] Geinitz
and Liebe, in 1867, have described a number of articulated Silurian
worms, which completely confirm my suppositions. Numbers of these very
remarkable worms are found in an excellent state of preservation in the
slates of Würzbach, in the upper districts of Reusz. They are of the
same structure as the articulated arm of a Star-fish, and evidently
possessed a hard coat of mail, a much denser, more solid cutaneous
skeleton than other worms in general. The number of body-segments, or
metamera, is very considerable, so that the worms, although no more than
a quarter or half an inch in breadth, attained a length of from two to
three feet. The excellently preserved impressions, especially those of
the Phyllodocites thuringiacus and Crossopodia Henrici, are so like the
arms of many Star-fish (Colastra) that their true blood relationship
seems very probable. This primæval group of worms, which are most
probably the ancestors of Star-fish, I call Mailed worms
(Phracthelminthes, p. 150.)

[Illustration: Pl. viii.

STAR FISHES. FIRST GENERATION. WORM PERSON.]

[Illustration: Pl. ix.

STAR FISHES. SECOND GENERATION. WORM STOCK.]

The three other classes of Echinoderma evidently arose at a later period
out of the class of Sea-stars which have most faithfully retained the
original form of the stellate colony of worms. The Sea-lilies, or
Crinoida, differ least from them, but having given up the free, slow
motion possessed by other Sea-stars, they have become adherent to rocks,
etc., and form for themselves a long stalk. Some Encrinites, however
(for example, the Comatulæ, Fig. _B_, on Plates VIII. and IX.),
afterwards detach themselves from their stalk. The original worm
individuals in the Crinoida are indeed no longer preserved in the same
independent condition as in the case of the common star-fish; but they
nevertheless always possess articulated arms extending from a common
central disc. Hence we may unite the Sea-lilies and Sea-stars into a
main-class, or branch, characterized as possessing articulated arms
(Colobrachia).

In the other two classes of Echinoderma, the Sea-urchins and
Sea-cucumbers, the articulated arms are no longer present as independent
parts, but, by the increased centralization of the stock, have
completely fused so as to form a common, inflated, central disc, which
now looks like a simple box or capsule without arms. The original stock
of five individuals has apparently degenerated to the form-value of a
simple individual, a single person. Hence we may represent these two
classes as a branch characterized as being without arms (Lipobrachia),
equivalent to those which possess articulated arms. The first of these
two classes, that of Sea-urchins (Echinida) takes its name from the
numerous and frequently very large thorns which cover the hard shell,
which is itself artistically built up of calcareous plates. (Fig. _C_,
Plates VIII. and IX.) The fundamental form of the shell itself is a
pentagonal pyramid. The Sea-urchins probably developed directly out of
the group of Sea-stars. The different classes and orders of marine
lilies and stars which are given in the following table, illustrate the
laws of progress and differentiation in a striking manner. In each
succeeding period of the earth’s history we see the individual classes
continually increasing in variety and perfection. (Gen. Morph. ii. Plate
IV.)

The history of three of these classes of Star-fish is very minutely
recorded by numerous and excellently preserved fossils, but on the other
hand, we know almost nothing of the historical development of the fourth
class, that of the Sea-cucumbers (Holothuriæ). These curious
sausage-shaped Star-fish manifest externally a deceptive similarity to
worms. (Fig. _D_, Plates VIII. and IX.) The skeletal structures in their
skin are very imperfect, and hence no distinct remains of their
elongated, cylindrical, worm-like body could be preserved in a fossil
state. However, from the comparative anatomy of the Holothuriæ, we can
infer that they have arisen, by the softening of the cutaneous skeleton,
from members of the class of Sea-urchins.

From the Star-fish we turn to the fifth and most highly developed tribe
of the invertebrate animals, namely, the phylum of Articulata, or those
with _jointed feet_ (Arthropoda). As has already been remarked, this
tribe corresponds to Linnæus’ class of Insects. It contains four
classes: (1) the genuine six-legged Insects, or Flies; (2) the
eight-legged Spiders; (3) the Centipedes, with numerous pairs of legs;
and (4) the Crabs, or Crustacea, whose legs vary in number. The last
class breathe water through gills, and may therefore be contrasted as
the main-class of gill-breathing Arthropoda, or Gilled Insects
(Carides), with the three first classes. The latter breathe air by means
of peculiar wind-pipes, or tracheæ, and may therefore appropriately be
united to form the main-class of the trachea-breathing Arthropoda, or
Tracheate Insects (Tracheata).

In all animals with articulated feet, as the name indicates, the legs
are distinctly articulated, and by this, as well as by the strong
differentiation of the separate parts of the body, or metamera, they are
sharply distinguished from Ringed worms, with which Bär and Cuvier
classed them. They are, however, in every respect so like the Ringed
worms that they can scarcely be considered altogether distinct from
them. They, like the Ringed worms, possess a very characteristic form of
the central nervous system, the so-called ventral marrow, which
commences in a gullet-ring encircling the mouth. From other facts also,
it is evident that the Arthropoda developed at a late period out of
articulated worms. Probably either the Wheel Animalcules or the Ringed
worms are their nearest blood relations in the Worm tribe. (Gen. Morph.
ii. Plate V. pp. 85-102.)

Now, although the derivation of the Arthropoda from ringed Worms may be
considered as certain, still it cannot with equal assurance be
maintained that the whole tribe of the former has arisen out of one
branch of the latter. For several reasons seem to support the
supposition that the Gilled Arthropods have developed out of a branch of
articulated worms, different from that which gave rise to the Tracheate
Arthropods. But on the whole it remains more probable that both
main-classes have arisen out of one and the same group of Worms. In this
case the Tracheate Insects—Spiders, Flies, and Centipedes—must have
branched off at a later period from the gill-breathing Insects, or
Crustacea.

The pedigree of the Arthropoda can on the whole be clearly made out from
the palæontology, comparative anatomy, and ontogeny of its four
classes, although here, as everywhere else, many details remain very
obscure. Not until the history of the individual development of all the
different groups has become more accurately known than it is at present,
can this obscurity be removed. The history of the class of Gilled
Insects, or Crabs (Carides), is at present that best known to us; they
are also called encrusted animals (Crustacea), on account of the hard
crust or covering of their body. The ontogeny of these animals is
extremely interesting and, like that of Vertebrate animals, distinctly
reveals the essential outlines of the history of their tribe, that is,
their phylogeny. Fritz Müller, in his work, “Für Darwin,”(16) which has
already been referred to, has explained this remarkable series of facts
in a very able manner.

[Illustration: _Nauplius. Youth-form of six Crab-fish._ _Pl. X._

A. Limnetis.
B. Cyclops.
C. Lernacocera.
D. Lepas.
E. Sacculina.
F. Peneus.]

[Illustration: _Adult form of the same six Crab-fish._ _Pl. XI._

A. Limnetis.
B. Cyclops.
C. Lernacocera.
D. Lepas.
E. Sacculina.
F. Peneus.]

The common primary form of all Crabs, which in most cases is even now
the first to develop out of the egg, is originally one and the same, the
so-called _Nauplius_. This remarkable primæval crab represents a very
simple form of articulated animal, the body of which in general has the
form of a roundish, oval, or pear-shaped disc, and has on its ventral
side only three pairs of legs. The first of these is uncloven, the two
subsequent pairs are forked. In front, above the mouth, lies a simple,
single eye. Although the different orders of the Crustacean class differ
very widely from one another in the structure of their body and its
appendages, yet the early Nauplius form always remains essentially the
same. In order to be convinced of this, let the reader look attentively
at Plates X. and XI., a more detailed explanation of which is given in
the Appendix. On Plate XI. we see the fully developed representatives of
six different orders of Crabs, a Leaf-footed Crab (Limnetis, Fig. _A
c_); a Stalked Crab (Lepas, Fig. _D c_); a Root Crab (Sacculina, Fig.
_E c_); a Boatman Crab (Cyclops, Fig. _B c_); a Fish Louse (Lernæocera,
Fig. _C c_); and, lastly, a highly developed Shrimp (Peneus, Fig. _F
c_). These six crabs vary very much, as we see, in the entire form of
body, in the number and formation of the legs, etc. When, however, we
look at the earliest stages, or “nauplius,” of these six different
classes, after they have crept out of the egg—those marked with
corresponding letters on Plate X. (Fig. _A n-F n_)—we shall be surprised
to find how much they agree. The different forms of Nauplius of these
six orders differ no more from one another than would six different
“good species” of one genus. Consequently, we may with assurance infer a
common derivation of all those orders from a common Primæval Crab, which
was essentially like the Nauplius of the present day.

SYSTEMATIC SURVEY

_Of the 7 Legions and 20 Orders of Crabs, or Crustacea._

-------------------------+--------------------------+----------------------+--------------
_Legions of the_ | _Orders of the_ | _Systema Name_ | _Name of a_
_Crustaceæ._ | _Crustaceæ._ | _of the Orders._ | _Genus as an_
| | | _example._
-------------------------+--------------------------+----------------------+--------------
I. ENTOMOSTRACA, _Lower Crustacea_, or Segmented Crabs (not passing through the
actual Zoëa form in youth).
------------------------------------------------------------------------------------------

+I. Branchiopoda+ { 1. Primæval Crabs 1. Archicarida Nauplius
Gill-footed Crabs { 2. Leaf-foot Crabs 2. Phyllopoda Limnetis
{ 3. Trilobites 3. Trilobita Paradoxides
{ 4. Water Fleas 4. Cladocera Daphnia
{ 5. Bivalve Crabs 5. Ostracoda Cypris

+II. Pectostraca+ { 6. Barnacle Crabs 6. Cirripedia Lepas
Fixed Crabs { 7. Root Crabs 7. Rhizocephala Sacculina

+III. Copepoda+ { 8. Boatmen Crabs 8. Eucopepoda Cyclops
Oar-footed Crabs { 9. Fish Lice 9. Siphonostoma Lernæocera

+IV. Pantopoda+ {10. No-body Crabs 10. Pycnogonida Nymphon
No-body Crabs {

+V. Pœcilopoda+ {11. Spear-tails 11. Xiphosura Limulus
Shield Crabs {12. Giant Crabs 12. Gigantostraca Eurypterus

------------------------------------------------------------------------------------------
II. MALACOSTRACA, _Higher Crustacea_, or Mailed Crabs (passing through the Zoëa form
in youth).
------------------------------------------------------------------------------------------

+VI. Podophthalma+ {13. Zoëa Crabs 13. Zoëpoda Zoëa
Stalk-eyed Mailed {14. Split-legged Crabs 14. Schizopoda Mysis
Crabs {15. Mouth-footed Crabs 15. Stomatopoda Squilla
{16. Ten-footed Crabs 16. Decapoda Peneus

+VII. Edriophthalma+ {17. Cuma Crabs 17. Cumacea Cuma
Mailed Crabs with {18. Flea Crabs 18. Amphipoda Gammarus
sessile eyes {19. Wizard Crabs 19. Læmodipoda Caprella
{20. Louse Crabs 20. Isopoda Oniscus

----------------------------------------------------------------

(Articulated Worms)

The pedigree on p. 177 will show how we may at present approximately
conceive the derivation of the twenty orders of Crustacea enumerated on
p. 176, from the common primary form of the Nauplius. Out of the
Nauplius form—which originally existed as an independent genus—the five
legions of lower Crabs developed as diverging branches in different
directions, which in the systematic survey of the class are united as
Segmented Crabs (Entomostraca). The higher division of Mailed Crabs
(Malacostraca) have likewise originated out of the common Nauplius form.
The Nebalia is still a direct form of transition from the Phyllopods to
the Schizopods, that is, to the primary form of the stalk-eyed and
sessile-eyed Mailed Crabs. The Nauplius at this stage gives rise to
another larva form, the so-called Zoëa, which is of great importance.
The order of Schizopoda, those with cloven feet (Mysis, etc.), probably
originated from this curious Zoëa; they are at present still directly
allied, through the Nebalia to the Phyllopoda, those with foliaceous
feet. But of all living crabs the Phyllopods are the most closely allied
to the original primary form of the Nauplius. Out of the Schizopoda the
stalk-eyed and sessile-eyed Mailed Crabs, or Malacostraca, developed as
two diverging branches in different directions: the former through
shrimps (Peneus, etc.), the latter through the Cumacea (Cuma, etc.),
which are still living and closely allied to the Schizopoda. Among those
with stalked eyes is the river crab (cray-fish), the lobster, and the
others with long tails, or the Macrura, out of which, in the chalk
period, the short-tailed crabs, or Brachyura, developed by the
degeneration of the tail. Those with sessile eyes divide into the two
branches of Flea-crabs (Amphipoda) and Louse-crabs (Isopoda); among the
latter are our common Rock-slaters and Wood-lice.

The second main-class of Articulated animals, that of the Tracheata, or
air-breathing Tracheate Insects[4] (Spiders, Centipedes, and Flies) did
not develop until the beginning of the palæolithic era, after the close
of the archilithic period, because all these animals (in contrast with
the aquatic crabs) are originally inhabitants of land. It is evident
that the Tracheata can have developed only after the lapse of the
Silurian period when terrestrial life first began. But as fossil remains
of spiders and insects have been found, even in the carboniferous beds,
we can pretty accurately determine the time of their origin. The
development of the first Tracheate Insects out of gill-bearing
Zoëa-crabs, must have taken place between the end of the Silurian and
the beginning of the coal period, that is, in the Devonian period.

Gegenbaur, in his excellent “Outlines of Comparative Anatomy,”(21) has
lately endeavoured to explain the origin of the Tracheata by an
ingenious hypothesis. The system of tracheæ, or air pipes, and the
modifications of organization dependent upon it, distinguish Flies,
Centipedes, and Spiders so much from other animals, that the conception
of its first origin presents no inconsiderable difficulties to
phylogeny. According to Gegenbaur, of all living Tracheate Insects, the
Primæval Flies, or Archiptera, are most closely allied to the common
primary form of the Tracheata. These insects—among which we may
especially mention the delicate Day flies (Ephemera), and the agile
dragon-flies (Libellula)—in their earliest youth, as larvæ, frequently
possess _external tracheate gills_ which lie in two rows on the back of
the body, and are shaped like a leaf or paint-brush. Similar leaf or
paint-brush shaped organs are met with as real water-breathing organs or
gills, in many crabs and ringed worms, and, moreover, in the latter as
real dorsal appendages or limbs. The “tracheate gills,” found in the
larvæ of many primæval winged insects, must in all probability be
explained as “_dorsal limbs_,” and as having developed out of the
corresponding appendages of the Annelida, or possibly as having really
arisen out of similar parts in Crustacea long since extinct. The present
tracheal respiration of the Tracheata developed at a later period out of
respiration through the “tracheate gills.” The tracheate gills
themselves, however, have in some cases disappeared, and in others
become transformed into the _wings_ of the Flies. They have disappeared
entirely in the classes of Spiders and Centipedes, and these groups must
accordingly be conceived of as degenerated or peculiarly developed
lateral branches of the Fly class, which at an early period branched off
from the common primary form of Flies; Spiders probably did so at an
earlier period than Centipedes. Whether that common primary form of all
Tracheata, which in my General Morphology I have named Protracheata, did
develop directly out of genuine Ringed worms, or at first out of
Crustacea of the Zoëa form (Zoëpoda, p. 177) will probably be settled at
some future time by a more accurate knowledge and comparison of the
ontogeny of the Tracheata, Crustacea, and Annelida. However, the root of
the Tracheata, as well as that of the Crustacea, must in any case be
looked for in the group of Ringed worms.

The genuine Spiders (Arachnida) are distinguished from Flies by the
absence of wings, and by four pairs of legs; but, as is distinctly seen
in the Scorpion-spiders and Tarantulæ, they, like Flies, possess in
reality only three pairs of genuine legs. The apparent “fourth pair of
legs” in spiders (the foremost) are in reality a pair of feelers. Among
the still existing Spiders, there is a small group which is probably
very closely allied to the common primary form of the whole class; this
is the order of Scorpion-spiders, or Solifugæ, (Solpuga, Galeodes), of
which several large species live in Africa and Asia, and are dreaded on
account of their poisonous bite. Their body consists—as we suppose to
have been the case in the common ancestor of the Tracheata—of a head
possessing several pairs of feelers like legs, of a thorax, to the three
rings of which are attached three pairs of legs, and of a hinder body,
or abdomen, consisting of many distinct rings. In the articulation of
their body, the Solifugæ are therefore in reality more closely related
to flies than to other spiders. Out of the Devonian Primæval Spiders,
which were nearly related to the Solifugæ of the present day, the Long
Spiders, the Tailor Spiders, and the Round Spiders probably developed as
three diverging branches.

The _Long Spiders_ (Arthrogastres), in which the earlier articulation of
body has been better preserved than in Round Spiders, appear to be the
older and more original forms. The most important members of this
sub-class are the scorpions, which are connected with the Solifugæ
through the Tarantella (or Phrynidæ). The small book scorpions, which
inhabit our libraries and herbariums, appear as a degenerate lateral
branch from the true scorpions. Midway between the Scorpions and Round
Spiders are the long-legged Tailor-spiders (Opiliones) which have
possibly arisen out of a special branch of the Solifugæ. The
Pycnogonida, or No-body Crabs, and the Arctisca, or Bear Worms—still
generally included among Long Spiders—must be completely excluded from
the class of Spiders; the former belong to the Crustacea, the latter to
Ringed worms.

SYSTEMATIC SURVEY

_Of the 3 Classes and 17 Orders of the Tracheata._

------------------+---------------------+----------------------+----------------------
_Classes of the_ | _Sub-Classes of the_| _Order of the_ | _Two Names of_
_Tracheata._ | _Tracheata._ | _Tracheata._ |_Genera as examples._
------------------+---------------------+----------------------+----------------------
{ { 1. Scorpion spiders { Solpuga
{ { _Solifugæ_ { Galeodes
{ {
{ { 2. Tarantella { Phrynus
{ { _Phrynida_ { Thelyphonus
{ I. {
I. { Long spiders { 3. Scorpions { Scorpio
=Spiders= { _Arthrogastres_ { _Scorpioda_ { Buthus
{ {
+Arachnida+ { { 4. Book scorpions { Obisium
{ { _Pseudoscorpioda_ { Chelifer
{ {
{ { 5. Tailor spiders { Phalangium
{ { _Opilionida_ { Opilio
{
{
{ II. { 6. Spinning spiders { Epeira
{ Round spiders { _Araneæ_ { Mygale
{ { {
{ _Sphærogastres_ { 7. Mites { Sarcoptes
{ { _Acarida_ { Demodex

II. { III.
=Centipedes= { Simple-footed { 8. Simple-footed { Scolopendra
{ _Chilopoda_ { _Chilopoda_ { Geophilus
{ {
+Scolopendria+ { IV. { 9. Double-footed { Julus
or { Double-footed { _Diplopoda_ { Polydesmus
+Myriapoda+ { _Diplopoda_ {

{ { 10. Primitive flies { Ephemera
{ { _Archiptera_ { Libellula
{ {
{ { 11. Gauze-wings { Hemerobius
{ { _Neuroptera_ { Phryganea
{ V. {
{ Chewing { 12. Straight-wings { Locusta
{ _Masticantia_ { _Orthoptera_ { Forficula
{ {
III. { { 13. Beetles { Cicindela
=Flies= { { _Coleoptera_ { Melolontha
{ {
+Hexapoda+ { { 14. Bee-wings { Apis
{ { _Hymenoptera_ { Formica
{
{
{ { 15. Bugs { Aphis
{ VI. { _Hemiptera_ { Cimex
{ Sucking {
{ _Sugentia_ { 16. Two-wings { Culex
{ { _Diptera_ { Musca
{ {
{ { 17. Butterflies { Bombyx

----------------------------------------------------------------

Fossil remains of Long Spiders are found in the Coal. The second
sub-class of the Arachnida, the _Round Spiders_ (Sphærogastres), first
appear in the fossil state in the Jura, that is, at a very much later
period. They have developed out of a branch of the Solifuga, by the
rings of the body becoming more and more united with one another. In the
true _Spinning Spiders_ (Araneæ), which we admire on account of their
delicate skill in weaving, the union of the joints of the trunk, or
metamera, goes so far, that the trunk now consists of only two pieces,
of a head-breast (cephalo-thorax) with jaws, feelers, and four pairs of
legs, and of a hinder body without appendages, where the spinning warts
are placed. In _Mites_ (Acarida), which have probably arisen by
degeneration (especially by parasitism) out of a lateral branch of
Spinning Spiders, even these two trunk pieces have become united and now
form an unsegmented mass.

The class of _Scolopendria_, _Myriapoda_, or Centipedes, the smallest
and poorest in forms of the four classes of Arthropoda, is characterized
by a very elongated body, like that of a segmented Ringed worm, and
often possesses more than a hundred pairs of legs. But these animals
also originally developed out of a six-legged form of Tracheata, as is
distinctly proved by the individual development of the millipede in the
egg. Their embryos have at first only three pairs of legs, like genuine
insects, and only at a later period do the posterior pairs of legs bud,
one by one, from the growing rings of the hinder body. Of the two orders
of Centipedes (which in our country live under barks of trees, in moss,
etc.) the round, _double-footed_ ones (Diplopoda) probably did not
develop until a later period out of the older flat, _single-footed_ ones
(Chilopoda), by successive pairs of rings of the body uniting together.
Fossil remains of the Chilopoda are first met with in the Jura period.

The third and last class of the Arthropoda breathing through tracheæ, is
that of the _Flies_, or _Insects_, in the narrow sense of the word
(Insecta, or Hexapoda), the largest of all classes of animals, and next
to that of Mammalia, also the most important. Although Flies develop a
greater variety of genera and species than all other animals taken
together, yet these are all in reality only superficial variations of a
single type, which is entirely and constantly preserved in its essential
characteristics. In all Flies the three divisions of the trunk—head,
breast (thorax), and hinder body are quite distinct. The _hinder body_,
or _abdomen_, as in the case of spiders, has no articulated appendages.
The central division, the _breast_ or _thorax_, has on its ventral side
three pairs of legs, on its back _two pairs of wings_. It is true that,
in very many Flies, one or both pairs of wings have become reduced in
size or have even entirely disappeared; but the comparative anatomy of
Flies distinctly shows that this deficiency has arisen only gradually by
the degeneration of the wings, and that all the Flies existing at
present are derived from a common, primary Fly, which possessed three
pairs of legs and two pairs of wings. (Compare p. 256.) These wings,
which so strikingly distinguish Flies from all other Arthropoda,
probably arose, as has been already shown, out of the tracheate gills
which may still be observed in the larvæ of the ephemeral flies
(Ephemera) which live in water.

The head of Flies universally possesses, besides the eyes, a pair of
articulated feelers, or antennæ, and also three jaws upon each side of
the mouth. These _three pairs of jaws_, although they have arisen in all
Flies from the same original basis, by different kinds of adaptation,
have become changed to very varied and remarkable forms in the various
orders, and are therefore employed for distinguishing and characterizing
the main divisions of the class. In the first place, we may distinguish
two main divisions, namely, Flies with _chewing_ mandibles (Masticantia)
and Flies with _sucking_ mouths (Sugentia). On a closer examination each
of these two divisions may again be divided into two sub-groups. Among
chewing Flies, or Masticantia, we may distinguish the biting and the
licking ones. _Biting flies_ (Mordentia) comprise the most ancient and
primæval winged Flies, the gauzy-winged (Neuroptera), straight-winged
(Orthoptera), and beetles (Coleoptera). _Licking flies_ (Lambentia) are
represented by the one order of skin-winged (Hymenoptera) Flies. We
distinguish two groups of _Sucking Flies_, or Sugentia, namely, those
which prick and those which sip. There are two orders of pricking Flies
(Pungentia), those with half wings (Hemiptera) and gnats and blow-flies
(Diptera); butterflies are the only _sipping_ Flies (Sorbentia),
Lepidoptera.

Biting Flies, and indeed the order of _Primæval Flies_ (Archiptera, or
Pseudoneuroptera) are nearest akin to the still living Flies, and
include the most ancient of all Flies, the primary forms of the whole
class (hence also those of all Tracheata). Among them are, first of all,
the Ephemeral Flies (Ephemera) whose larvæ which live in water, in all
probability still show us in their tracheæ-gills the organs out of which
the wings of Flies were originally developed. This order further
contains the well known dragon-flies, or Libellula, the wine-glass sugar
mites (Lepisma), the hopping Flies with bladder-like feet (Physopoda),
and the dreaded Termites, fossil remains of which are found even in
coal. The order of Gauze-winged Flies (Neuroptera), probably developed
directly out of the primæval Flies, which differ from them only by their
perfect series of transformations. Among them are the gauze-flies
(Planipennia), caddis-flies (Phryganida), and fan-flies (Strepsiptera).
Fossil Flies, which form the transition from the primæval Flies
(Libellula) to the gauze-winged (Sialidæ), are found even in coal
(Dictyophylebia).

The order of _Straight-winged Flies_ (Orthoptera) developed at an early
period out of another branch of the primæval Flies by differentiation of
the two pairs of wings. This division is composed of one group with a
great variety of forms—cockroaches, grasshoppers, crickets, etc.
(Ulonata)—and of a smaller group consisting only of the well-known
earwigs (Labidura), which are characterised by nippers at the hinder end
of their bodies. Fossil remains of cockroaches, as well as of crickets
and grasshoppers, have been found in coal.

Fossil remains of the fourth order of Biting Flies, _beetles_
(Coleoptera) likewise occur in coal. This extremely comprehensive
order—the favourite one of amateurs and collectors—shows more clearly
than any other what infinite variety of forms can be developed
externally by adaptation to different conditions of life, without the
internal structure and the original form of the body being in any way
essentially changed. Beetles have probably developed out of a branch of
the straight-winged Flies, from which they differ only in their
transformations (larva, pupa, etc.).

The one order of _Licking Flies_, namely, the interesting group of the
_Bees_, or _Skin-winged Flies_ (Hymenoptera), is closely allied to the
four orders of biting Flies. Among them are those Flies which have risen
to such an astonishing degree of mental development, of intellectual
perfection, and strength of character, by their extensive division of
labour, formation of communities and states, and surpass in this not
merely most invertebrate animals, but even most animals in general. This
may be said especially of all ants and bees, also of wasps, leaf-wasps,
wood-wasps, gall-wasps, etc. They are first met with in a fossil state
in the oolites, but they do not appear in greater numbers until the
tertiary period. Probably these insects developed either out of a branch
of the primæval Flies or the gauze-winged Flies.

Of the two orders of _Pricking Flies_ (Hemiptera and Diptera), that
containing the _Half-winged Flies_ (Hemiptera), also called Beaked Flies
(Rhynchota), is the older of the two. It includes three sub-orders,
viz., the leaf-lice (Homoptera), the bugs (Heteroptera), and lice
(Pediculina). Fossil remains of the first two classes are found in the
oolites; but an ancient Fly (Eugereon) is found in the Permian system,
and seems to indicate the derivation of the Hemiptera from the
Neuroptera. Probably the most ancient of the three sub-orders of the
Hemiptera are the Homoptera, among which, besides the actual leaf-lice,
are the shield-lice, leaf-fleas, and leaf-crickets, or Cicadæ. Lice have
probably developed out of two different branches of Homoptera, by
continued degeneration (especially by the loss of wings); bugs, on the
other hand, by the perfecting and differentiation of the two pairs of
wings.

The second order of _pricking flies_, namely, the _Two-winged Flies_
(Diptera), are also found in a fossil state in the oolites, together
with Half-winged Flies; but they probably developed out of the Hemiptera
by the degeneration of the hind wings. In Diptera the fore wings alone
have remained perfect. The principal portion of this order consists of
the elongated gnats (Nemocera) and of the compact blow-flies and
house-flies (Brachycera), the former of which are probably the older of
the two. However, remains of both are found in the oolitic period. The
two small groups of lice-flies (Pupipara) forming chrysales, and the
hopping-fleas (Aphaniptera), probably developed out of the Diptera by
degeneration resulting from parasitism.

The eighth and last order of Flies, and at the same time the only one
with mouth-parts adapted to sipping liquids, consists of _moths_ and
_butterflies_ (Lepidoptera). This order appears, in several
morphological respects, to be the most perfect class of Flies, and
accordingly was the last to develop. For we only know of fossil remains
of this order from the tertiary period, whereas the three preceding
orders extend back to the oolites, and the four biting orders even to
the coal period. The close relationship between some moths (Tineæ) and
(Noctuæ), and some caddis-flies (Phryganida) renders it probable that
butterflies have developed from this group, that is, out of the order of
Gauze-winged Flies, or Neuroptera.

The whole history of Flies, and, moreover, the history of the whole
tribe of Arthropoda, essentially confirms the great laws of
differentiation and perfecting which, according to Darwin’s theory of
selection, must be considered as the necessary results of Natural
Selection. The whole tribe, so rich in forms, begins in the Archilithic
period with the class of _Crabs_ breathing by gills, and with the lowest
_Primæval Crabs_, or Archicaridæ. The form of these Primæval Crabs,
which were developed out of segmented worms, is still approximately
preserved by the remarkable _Nauplius_, in the common larval stage of so
many Crabs. Out of the Nauplius, at a later period, the curious Zoëa was
developed, which is the common larval form of all the higher or mailed
crabs (Malacostraca), and, at the same time, possibly of that Arthopod
which at first breathed through tracheæ, and became the common ancestor
of all _Tracheata_. This Devonian ancestor, which must have originated
between the end of the Silurian and the beginning of the Coal period,
was probably most closely related to the still living Primæval Flies, or
_Archiptera_. Out of these there developed, as the main tribe of the
Tracheata, the class of Flies, from the lowest stage of which the
_spiders_ and _centipedes_ separated as two diverging branches.
Throughout a long period there existed only the four biting orders of
Flies—the Primæval flies, Gauze-wings, Straight-wings, and the Beetles,
the first of which is probably the common primary form of the three
others. It was only at a much later period that the Licking, Pricking,
and Sipping flies developed out of the Biting ones, which retained the
original form of the three pairs of jaws most distinctly. The following
table will show once more how these orders succeeded one another in the
history of the earth.

CLASSIFICATION OF FLIES.

{ { 1. Primæval winged { M.I. }
{ { _Archiptera_ { A.A. }
{ { }
{ I. { 2. Gauze-winged { M.C. }
A. { Biting Flies { _Neuroptera_ { A.A. }
{ { }
=Flies= { _Mordentia_ { 3. Straight-winged { M.I. }
=with Chewing= { { _Orthoptera_ { A.D. }
=Mouths= { { }
{ { 4. Beetles { M.C. }
+Masticantia+ { { _Coleoptera_ { A.D. }
{
{
{ II. { 5. Skin-winged { M.C. }
{ Licking Flies { _Hymenoptera_ { A.A. }
{ _Lambentia_ { }
}
}
{ { 6. Half-winged { M.I. }
{ III. { _Hemiptera_ { A.A. }
B. { Stinging Flies { }
=Flies= { { 7. Tway-flies { M.C. }
=with Sucking= { _Pungentia_ { _Diptera_ { A.D. }
=Mouths= {
{
+Sugentia+ { IV. { 8. Butterflies { M.C. }
{ Sipping Flies { _Lepidoptera_ { A.A. }
{ { { }
{ _Sorbentia_ { { }

_Note._—The difference in the metamorphosis or transformation and in
the development of the wings of the eight individual orders of Flies
is also specified by the following letters: M.I. = Imperfect
Metamorphosis. M.C. = Perfect Metamorphosis. (Compare Gen. Morph. ii.
p. 99.) A.A. = Equal wings (fore and hinder wings are the same, or
differ but little). A.D. = Unequal wings (fore and hinder wings very
different in structure and texture, occasioned by strong
differentiation).

CHAPTER XX.

PEDIGREE AND HISTORY OF THE ANIMAL KINGDOM.

III. VERTEBRATE ANIMALS.

The Records of the Creation of Vertebrate Animals (Comparative
Anatomy, Embryology, and Palæontology).—The Natural System of
Vertebrate Animals.—The Four Classes of Vertebrate Animals,
according to Linnæus and Lamarck.—Their increase to Nine
Classes.—Main Class of the Tube-hearted, or Skull-less Animals
(the Lancelet).—Blood Relationship between the Skull-less Fish
and the Tunicates.—Agreement in the Embryological Development
of Amphioxus and Ascidiæ.—Origin of the Vertebrate Tribe out of
the Worm Tribe.—Main Class of Single-nostriled, or
Round-mouthed Animals (Hag and Lampreys).—Main Class of
Anamnionate Animals, devoid of Amnion.—Fishes (Primæval Fish,
Cartilaginous Fish, Osseous Fish).—Mud-fish, or Dipneusta.—Sea
Dragons, or Halisauria.—Frogs and Salamanders, or Amphibia
(Mailed Amphibia, Naked Amphibia).—Main Class of Amnionate
Animals, or Amniota.—Reptiles (Primary Reptiles, Lizards,
Serpents, Crocodiles, Tortoises, Flying-Reptiles, Dragons,
Beaked Reptiles).—Birds (Feather-tailed, Fan-tailed,
Bush-tailed).

Not one of the natural groups of organisms—which, we have designated as
tribes, or phyla, on account of the blood-relationship of all the
species included in them—is of such great and exceeding importance as
the tribe of Vertebrate Animals. For, according to the unanimous opinion
of all zoologists, man also is a member of the tribe; and his whole
organization and development cannot possibly be distinguished from that
of other Vertebrate animals. But as from the individual history of
human development, we have already recognized the undeniable fact that,
in developing out of the egg, man at first does not differ from other
Vertebrate animals, and especially from Mammals, we must necessarily
come to the conclusion, in regard to the palæontological history of his
development, that man has, historically, actually developed out of the
lower Vertebrata, and that he is directly derived from lower mammals.
This circumstance, together with the many high interests which, in other
respects, entitle the Vertebrata to more consideration than other
organisms, justifies us in examining the pedigree of the Vertebrata and
its expression in the natural system, with special care.

Fortunately, the records of creation, which must in all cases be our
guide in establishing pedigrees, are especially complete in this
important animal tribe, from which our own race has arisen. Even at the
beginning of our century Cuvier’s comparative anatomy and palæontology,
and Bär’s ontogeny of the Vertebrate animals, had brought us to a high
level of accurate knowledge on this matter. Since then it is especially
due to Johannes Müller’s and Rathke’s investigations in comparative
anatomy, and most recently to those of Gegenbaur and Huxley, that our
knowledge of the natural relationships among the different groups of
Vertebrata has become enlarged. It is especially Gegenbaur’s classical
works, penetrated as they are throughout with the fundamental principles
of the Theory of Descent, which have demonstrated that the material of
comparative anatomy receives its true importance and value only by the
application of the Theory of Descent, and this in the case of all
animals, but especially in that in the Vertebrate tribe. Here, as
everywhere else, analogies must be traced to Adaptation, homologies to
Transmission by Inheritance. When we see that the limbs of the most
different Vertebrata, in spite of their exceedingly different external
forms, nevertheless possess essentially the same internal structure;
when we see that in the arm of a man and ape, in the wing of a man or a
bird, in the breast fins of whales and sea-dragons, in the fore-legs of
hoofed animals and frogs, the same bones always lie in the same
characteristic position, articulation and connection—we can only explain
this wonderful agreement and homology by the supposition of a common
transmission by inheritance from a single primary form. On the other
hand, the striking differences of these homologous bodily parts proceed
from adaptation to different conditions of existence. (Compare Plate
IV.)

Ontogeny, or the individual history of development, like comparative
anatomy, is of especial importance to the pedigree of the Vertebrata.
The first stages of development arising out of the egg are essentially
identical in all Vertebrate animals, and retain their agreement the
longer, the nearer the respective Vertebrate animal forms, when fully
developed, stand to one another in the natural system, that is, in the
pedigree. How far this agreement of germ forms, or embryos, extends,
even in the most highly developed Vertebrate animals, I have already had
occasion to explain (vol i. pp. 306-309). The complete agreement in form
and structure, for example, in the embryos of a man and a dog, of a bird
and a tortoise, existing in the stages of development represented on
Plates II. and III., is a fact of incalculable importance, and furnishes
us with the most important data for the construction of their pedigree.

Finally, the palæontological records of creation are also of especial
value in the case of these same Vertebrate animals; for their fossil
remains belong for the most part to the bony skeleton, a system of
organs which is of the utmost importance for understanding their general
organization. It is true that here, as in all other cases, the fossil
records are exceedingly imperfect and incomplete, but more important
remains of extinct Vertebrate animals have been preserved in a fossil
state, than of most other groups of animals; and single fragments
frequently furnish the most important hints as to the relationship and
the historical succession of the groups.

The name of _Vertebrate Animals_ (Vertebrata), as I have already said,
originated with the great Lamarck, who towards the end of the last
century comprised under this name, Linnæus’ four higher classes of
animals, viz. Mammals, Birds, Amphibious animals, and Fishes, Linnæus’
two lower classes, Insects and Worms, Lamarck contrasted to the
Vertebrata as _Invertebrata_, later also called _Evertebrata_.

The division of the Vertebrata into the four classes above named was
retained also by Cuvier and his followers, and in consequence by many
zoologists down to the present day. But in 1822 Blanville, the
distinguished anatomist, found out by comparative anatomy—which Bär did
almost at the same time from the ontogeny of Vertebrata—that Linnæus’
class of Amphibious animals was an unnatural union of two very different
classes. These two classes were separated as early as 1820, by Merrin,
as two main groups of Amphibious animals, under the names of Pholidota
and Batrachia. The _Batrachia_, which are at present (in a restricted
sense) called Amphibious animals, comprise Frogs, Salamanders, gilled
Salamanders, Cæcilia, and the extinct Labyrinthodonta. Their entire
organization is closely allied to that of Fishes. The _Pholidota_, or
Reptiles, on the other hand, are much more closely allied to Birds. They
comprise lizards, serpents, crocodiles, and tortoises, and the groups of
the mesolithic Dragons, Flying reptiles, etc.

In conformity with this natural division of Amphibious animals into two
classes, the whole tribe of Vertebrate animals was divided into two main
groups. The first main group, containing Amphibious animals and Fishes,
breathe throughout their lives, or in early life, by means of gills, and
are therefore called _gilled Vertebrata_ (Branchiata, or Anallantoida).
The second main group—Reptiles, Birds, and Mammals—breathe at no period
of their lives through gills, but exclusively through lungs, and hence
may appropriately be called Gill-less, or _Vertebrata with lungs_
(Abranchiata, or Allantoida). However correct this distinction may be,
still we cannot remain satisfied with it if we wish to arrive at a true
natural system of the vertebrate tribe, and at a right understanding of
its pedigree. In this case, as I have shown in my General Morphology, we
are obliged to distinguish three other classes of Vertebrate animals, by
dividing what has hitherto been regarded as the class of fishes into
four distinct classes. (Gen. Morph. vol. ii. Plate VII. pp. 116-160.)

The first and lowest of these classes comprises the _Skull-less_ animals
(Acrania), or animals with _tubular hearts_ (Leptocardia), of which only
one representative now exists, namely, the remarkable little Lancelet
(Amphioxus lanceolatus). Nearly allied to this is the second class, that
of the _Single-nostriled_ animals (Monorrhina), or _Round-mouthed_
animals (Cyclostoma), which includes the Hags (Myxinoida) and Lampreys
(Petromyzonta). The third class contains only the genuine Fish (Pisces):
the Mud-fishes (Dipneusta) are added to these as a fourth class, and
form the transition from Fish to Amphibious animals. This distinction,
which, as will be seen immediately, is very important for the genealogy
of the Vertebrate animals, increases the original number of Vertebrate
classes from four to eight.

In most recent times a ninth class of Vertebrata has been added to these
eight classes. Gegenbaur’s recently published investigations in
comparative anatomy prove that the remarkable class of _Sea-dragons_
(Halisauria), which have hitherto been included among Reptiles, must be
considered quite distinct from these, and as a separate class which
branched off from the Vertebrate stock, even before the Amphibious
animals. To it belong the celebrated large Ichthyosauri and Plesiosauri
of the oolitic and chalk periods, and the older Simosauri of the Trias
period, all of which are more closely allied to Fish than to Amphibious
animals.

These nine classes of Vertebrate animals are, however, by no means of
the same genealogical value. Hence we must divide them, as I have
already shown in the Systematic Survey on p. 133, into four distinct
main-classes or tribes. In the first place, the three highest classes,
Mammals, Birds, and Reptiles, may be comprised as a natural main-class
under the name of _Amnion animals_ (Amnionata). The _Amnion-less
animals_ (Anamnionata), naturally opposed to them as a second
main-class, include the four classes of Batrachians, Sea-dragons,
Mud-fish, and Fishes. The seven classes just named, the Anamnionata as
well as the Amnionata, agree among one another in numerous
characteristics, which distinguish them from the two lowest classes
(the single-nostriled and tubular-hearted animals). Hence we may unite
them in the natural main group of _Double-nostriled_ animals
(Amphirrhina). Finally, these Amphirrhina on the whole are much more
closely related to those animals with round mouths or single nostrils
than to the skull-less or tube-hearted animals. We may, therefore, with
full justice class the single and double-nostriled animals into one
principal main group, and contrast them as _animals with skulls_
(Craniota), or _bulbular hearts_ (Pachycardia), to the one class of
_skull-less animals_, or animals with _tubular hearts_. This
classification of the Vertebrate animals proposed by me renders it
possible to obtain a clear survey of the nine classes in their most
important genealogical relations. The systematic relationship of these
groups to one another may be briefly expressed by the following table.

A.
=Skull-less Animals= 1. Tubular hearts 1. Leptocardia
(+Acrania+)

{ _a._ Single nostriled
{ animals { 2. Round-mouths 2. Cyclostoma
B. { _Monorrhina_ {
=Animals with= {
=Skulls= { b. Double { { 3. Fish 3. Pisces
(+Craniota+) { nostriled { I. Non-Amnionate { 4. Mud-fish 4. Dipneusta
{ animals { Anamnia { 5. Sea-dragons 5. Halisauria
or { { { 6. Batrachians 6. Amphibia
{ _Amphirrhina_ {
=Thick Hearts= { { II. Amnionate. { 7. Reptiles 7. Reptilia
(+Pachycardia+) { { Amniota { 8. Birds 8. Aves
{ { { 9. Mammals 9. Mammalia

The only one representative of the first class, the small _lanceolate
fish_, or Lancelet (Amphioxus lanceolatus) (Plate XIII. Fig. _B_),
stands at the lowest stage of organization of all the Vertebrate
animals known to us. This exceedingly interesting and important animal,
which throws a surprising light upon the older roots of our pedigree, is
evidently the last of the Mohicans—the last surviving representative of
a lower class of Vertebrate animals, very rich in forms, and very highly
developed during the primordial period, but which unfortunately could
leave no fossil remains on account of the absence of all solid skeleton.
The Lancelet still lives widely distributed in different seas; for
instance, in the Baltic, North Sea, and Mediterranean, where it
generally lies buried in the sand on flat shores. The body, as the name
indicates, has the form of a narrow lanceolate leaf, pointed at both
extremities. When full grown it is about two inches long, of a white
colour and semi-transparent. Externally, the little lanceolate animal is
so little like a vertebrate animal that Pallas, who first discovered it,
regarded it as an imperfect naked snail. It has no legs, and neither
head, skull, nor brain. Externally, the fore end of the body can be
distinguished from the hinder end only by the open mouth. But still the
Amphioxus in its internal structure possesses those most important
features, which distinguish all Vertebrate animals from all Invertebrate
animals, namely, the spinal rod and spinal marrow. The _spinal rod_
(Chorda dorsalis) is a straight, cylindrical, cartilaginous staff,
pointed at both ends, forming the central axis of the internal skeleton,
and the basis of the vertebral column. Directly above the spinal rod, on
its dorsal side, lies the _spinal marrow_ (medulla spinalis), likewise
originally a straight but internally hollow cord, pointed at both ends.
This forms the principal piece and centre of the nervous system in all
Vertebrate animals. (Compare above vol. i. p. 303.) In all Vertebrate
animals without exception, man included, these important parts of the
body during the embryological development out of the egg, originally
begin in the same simple form, which is retained throughout life by the
Amphioxus. It is only at a later period that the brain develops by the
expansion of the fore end of the spinal marrow, and out of the spinal
rod the skull which encloses the brain. As these two important organs do
not develop at all in the Amphioxus, we may justly call the class
represented by it, _Skull-less animals_ (Acrania), in opposition to all
the others, namely, to the _animals with skulls_ (Craniota). The
Skull-less animals are generally called _tubular-hearted_ (Leptocardia),
because a centralized heart does not as yet exist, and the blood is
circulated in the body by the contractions of the tubular blood-vessels
themselves. The Skulled animals, which possess a centralized,
thick-walled, bulb-shaped heart, ought then by way of contrast to be
called _bulbular-hearted_ animals (Pachycardia).

[Illustration: _Ascidia (A.) and Amphioxus (B.)_ Pl. XII.

E. Haeckel del. Legesse sc.]

Animals with skulls and central hearts evidently developed gradually in
the later primordial period out of those without skulls and with tubular
hearts. Of this the ontogeny of skulled animals leaves no doubt. But
whence are these same skull-less animals derived? It is only very lately
that an exceedingly surprising answer has been given to this important
question. From Kowalewsky’s investigations, published in 1867, on the
individual development of the Amphioxus and the adhering Sea-squirts
(Ascidia) belonging to the class of mantled animals (Tunicata), it has
been proved that the ontogenies of these two entirely different looking
animal-forms agree in the first stage of development in a most
remarkable manner. The freely swimming larvæ of the Ascidians (Plate
XII. Fig. _A_) develop the undeniable beginning of a spinal marrow (Fig.
5 _g_) and of a spinal rod (Fig. 5 _c_), and this moreover in entirely
the same way as does the Amphioxus. (Plate XIII. Fig. _B_.) It is true
that in the Ascidians these most important organs of the Vertebrate
animal-body do not afterwards develop further. The Ascidians take on a
retrograde transformation, become attached to the bottom of the sea, and
develop into shapeless lumps, which when looked upon externally would
scarcely be supposed to be animals. (Plate XIII. Fig. _A_.) But the
spinal marrow, as the beginning of the central nervous system, and the
spinal rod, as the first basis of the vertebral column, are such
important organs, so exclusively characteristic of Vertebrate animals,
that we may from them with certitude infer the true blood relationship
of Vertebrate with Tunicate animals. Of course we do not mean to say by
this, that Vertebrate animals are derived from Tunicate animals, but
merely that both groups have arisen out of a common root, and that the
Tunicates, of all the Invertebrata, are the nearest blood relations of
the Vertebrates. It is quite evident that genuine Vertebrate animals
developed progressively during the primordial period (and the skull-less
animals first) out of a group of worms, from which the degenerate
Tunicate animals arose in another and a retrograde direction. (Compare
the more detailed explanation of Plates XII. and XIII. in the Appendix.)

Out of the Skull-less animals there developed, in the first instance, a
second low class of Vertebrate animals, which still stands far below
that of fish, and which is now represented only by the Hags (Myxinoida)
and Lampreys (Petromyzonta). This class also, on account of the absence
of all solid parts, could, unfortunately, as little as the Skull-less
animals leave fossil remains. From its whole organization and ontogeny
it is quite evident that it represents a very important intermediate
stage between the Skull-less animals and Fishes, and that its few still
existing members are only the last surviving remains of a probably very
highly developed animal group which existed towards the end of the
primordial period. On account of the curious mouth possessed by the Hags
and Lampreys, which they use for sucking, the whole class is usually
called _Round-mouthed_ animals (Cyclostoma). The name of
_Single-nostriled_ animals (Monorrhina) is still more characteristic.
For all Cyclostoma possess a simple, single nasal tube, whereas, in all
other Vertebrate animals (with the exception of the Amphioxus) the nose
consists of two lateral halves, a right and a left nostril. We are
therefore enabled to comprise these latter (Anamnionata and Amnionata)
under the heading, _double-nostriled_ animals (Amphirrhina). All the
Amphirrhina possess a fully developed jaw-skeleton (upper and under
jaw), whereas it is completely wanting in the Monorrhina.

Apart also from the peculiar nasal formation, and the absence of jaws,
the Single-nostriled animals are distinguished from those with double
nostrils by many peculiarities. Thus they want the important sympathetic
nervous system, and the spleen which the Amphirrhina possess. Of the
swimming bladder, and the two pairs of legs—which all double-nostriled
animals have, at least in their embryonic conditions—not a trace exists
in the Single-nostriled animals, which is the case also in the
Skull-less animals. Hence, we are surely justified in completely
separating the Monorrhina, as we have separated the Skull-less animals,
from the Fishes, with which they have hitherto been erroneously classed.

[Illustration: _Ascidia (A.) and Amphioxus (B.)_ Pl. XIII.

E. Haeckel del. Lagesse sc.]

We owe our first accurate knowledge of the Monorrhina, or Cyclostoma, to
the great zoologist, Johannes Müller of Berlin; his classical work on
the “Comparative Anatomy of the Myxinoida” forms the foundation of our
modern views on the structure of the Vertebrate animals. He
distinguished two distinct groups among the Cyclostoma, which we shall
consider as sub-classes.

The first sub-class consists of the Hags (Hyperotreta, or Myxinoida).
They live in the sea as parasites upon other fish, into whose skin they
penetrate (Myxine, Bdellostoma). Their organ of hearing has only one
annular canal, and their single nasal tube penetrates the palate. The
second sub-class, that of Lampreys, or Prides (Hyperoartia, or
Petromyzontia) is more highly developed. It includes the well-known
Lamperns, or Nine-eyes, of our rivers (Petromyzon fluviatilis), with
which most persons are acquainted. They are represented in the sea by
the frequently larger marine or genuine Lampreys (Petromyzon marinus).
The nasal tube of these single-nostriled animals does not penetrate the
palate, and in the auricular organ there are two annular canals.

SYSTEMATIC SURVEY

_Of the 4 Main-classes, 9 Classes, and 26 Sub-classes of Vertebrata._

Gen. Morph. vol. ii. Plate VII. pp. 116-160.

======================================================================================
I. =Skull-less= (+Acrania+), or =Tube-hearted= (+Leptocardia+).

Vertebrata without head, without skull and brain, without centralized heart.
--------------------------------------------------------------------------------------
1. =Skull-less= I. Tube-hearted { 1. Lancelet 1. Amphioxus
+Acrania+ _Leptocardia_ {
--------------------------------------------------------------------------------------

II. =Animals with skulls= (+Craniota+) and with =thick-walled hearts= (+Pachycardia+).
Vertebrata with head, with skull and brain, with centralized heart.

======================================================================================
_Main-classes_ | _Classes_ | _Sub-classes_ | _Systematic Name_
_of the Skulled_ | _of the_ | _of the_ | _of the_
_Animals._ | _Skulled Animals._ | _Skulled Animals._ | _Sub-classes._
--------------------------------------------------------------------------------------
2. =Single-Nostriled= { II. Round mouths { 2. Hags, or Mucous 2. Hyperotreta
+Monorrhina+ { _Cyclostoma_ { Fish (Myxinoida)
{ { 3. Lampreys, or 3. Hyperoartia
{ { Pride (Petromyzontia)

{ III. Fish { 4. Primæval fish 4. Selachii
{ _Pisces_ { 5. Ganoid fish 5. Ganoides
{ { 6. Osseous fish 6. Teleostei
{
{ IV. Mud-fish { 7. Mud-fish 7. Protopteri
3. =Non-amnionate= { _Dipneusta_ {
{
+Anamnionata+ { { 8. Primæval 8. Simosauria
{ V. Sea-dragons { dragons
{ _Halisauri_ { 9. Snake-dragons 9. Plesiosauria
{ { 10. Fish-dragons 10. Ichthyosauria
{
{ VI. Batrachians { 11. Mailed Batrachians 11. Phractamphibia
{ _Amphibia_ { 12. Naked Batrachians 12. Lissamphibia

4. =Amnion= { VII. Reptiles { 13. Primary reptiles 13. Tocosauria
=Animals= { _Reptilia_ { 14. Lizards 14. Lacertilia
+Amnionata+ { { 15. Serpents 15. Ophidia
{ { 16. Crocodiles 16. Crocodilia
{ { 17. Tortoises 17. Chelonia
{ { 18. Flying reptiles 18. Pterosauria
{ { 19. Dragons 19. Dinosauria
{ { 20. Beaked reptiles 20. Anomodontia
{
{ VIII. Birds { 21. Long-tailed 21. Saururæ
{ _Aves_ { 22. Fan-tailed 22. Carinatæ
{ { 23. Bush-tailed 23. Ratitæ
{
{ IX. Mammals { 24. Cloacal animals 24. Monotrema
{ _Mammalia_ { 25. Pouched animals 25. Marsupialia
{ { 26. Placental animals 26. Placentalia

----------------------------------------------------------------

All existing Vertebrate animals, with the exception of the Monorrhina
and Amphioxus just mentioned, belong to the group which we designate as
Double-nostriled animals (Amphirrhina). All these animals possess (in
spite of the great variety in the rest of their forms) a nose consisting
of two lateral halves, a jaw-skeleton, a sympathetic nervous system,
three annular canals connected with the auricular sac, and a spleen.
Further, all Double-nostriled animals possess a bladder-shaped expansion
of the gullet, which, in Fish, has developed into the swimming bladder,
but in all other Double-nostriled animals into lungs. Finally, in all
Double-nostriled animals there exist in the youngest stage of growth the
beginnings of two pairs of extremities, or limbs, a pair of fore legs,
or breast fins, and a pair of hinder legs, or ventral fins. One of these
pairs of legs sometimes degenerates (as in the case of eels, whales,
etc.), or both pairs of legs (as in Cæciliæ and serpents) either
degenerate or entirely disappear; but even in these cases there exists
some trace of their original beginning in an early embryonic period, or
the useless remains of them may be found in the form of rudimentary
organs. (Compare above, vol. i. p. 13.)

From all these important indications we may conclude with full assurance
that all double-nostriled animals are derived from a single common
primary form, which developed either directly or indirectly during the
primordial period out of the Monorrhina. This primary form must have
possessed the organs above mentioned, and also the beginning of a
swimming bladder and of two pairs of legs or fins. It is evident, that
of all still living double-nostriled animals, the lowest forms of sharks
are most closely allied to this long since extinct, unknown, and
hypothetical primary form, which we may call the Primary
Double-nostriled animals (Proselachii). We may therefore look upon the
group of primæval fish, or Selachii, to which the _Proselachii_ probably
belonged, as a primary group, not only of the Fish class, but of the
whole main-class of double-nostriled animals.

The class of _Fish_ (Pisces) with which we accordingly begin the series
of Double-nostriled animals, is distinguished from the other six classes
of the series by the swimming bladder never developing into lungs, but
acting only as a hydrostatic apparatus. Agreeing with this, we find that
in fish the nose is formed by two blind holes in front of the mouth,
which never pierce the palate so as to open into the cavity of the
mouth. In the other six classes of double-nostriled animals, both
nostrils are changed into air passages which pierce the palate, and thus
conduct air to the lungs. Genuine fish (after the exclusion of the
Dipneusta) are accordingly the only double-nostriled animals which
exclusively breathe through gills and never through lungs. In accordance
with this, they all live in water, and both pairs of their legs have
retained the original form of paddling fins.

SYSTEMATIC SURVEY

_Of the 7 Legions and 15 Orders of the Fishes._

---------------------------------------------------------------------------------
_Sub-classes_ | _Legions_ | _Orders_ | _Examples_
_of_ | _of_ | _of_ | _from_
_Fishes._ | _Fishes._ | _Fishes._ | _the Orders._
---------------------------------------------------------------------------------
{
{ { 1. Sharks Sharks, dog-fish
{ I. Transverse { _Squalacei_
A. { mouths { 2. Rays Spiked rays, electric
=Primæval= { _Plagiostomi_ { _Rajacei_ rays, etc.
=Fish= {
+Selachii+ { II. Sea-Cats { 3. Sea-Cats Chimæra, Calorrhynchias
{ _Holocephali_ { _Chimæracei_

{ { 4. Buckler-heads Cephalaspidæ, Placoderma,
{ III. Mailed Ganoid { _Pamphracte_ etc.
{ Fish { 5. Sturgeons Spoon-sturgeons, sturgeons,
{ _Tabuliferi_ { _Sturiones_ sterlet, etc.
{
{ { 6. _Efulcri_ Double-finned
B. { IV. Angular-scaled { 7. _Fulcrati_ Palæoniscus, bony pike,
=Ganoid= { Ganoid Fish { etc.
=Fish= { _Rhombiferi_ { 8. _Semæopteri_ African finny pike, etc.
+Ganoides+ {
{ V. Round-scaled { 9. _Cœloscolopes_ Holoptychius, Cœlacanthides,
{ Ganoid Fish { etc.
{ _Cycliferi_ { 10. _Pycnoscolopes_ Coccolepida, Amiadæ,
etc.

{ VI. Osseous Fish {
{ with an air { 11. Herring species Herrings, salmon, carp,
{ passage to the { _Thrissogenes_ etc.
C. { swimming { 12. Eel species Eels, snake eels, electric
=Osseous= { bladder { _Enchelygenes_ eels, etc.
=Fish= { _Physostomi_ {
+Teleostei+ {
{ VII. Osseous Fish { 13. _Stichobranchii_ Perch, wrasse, turbot,
{ without an air { etc.
{ passage to the { 14. _Plectognathi_ Trunk fish, globe fish,
{ swimming { etc.
{ bladder { 15. _Lophobranchii_ Pipe fish, sea horses,
{ _Physoclisti_ { etc.

----------------------------------------------------------------

PEDIGREE OF THE NON-AMNIONATE CRANIOTA.

Genuine fish are divided into three distinct sub-classes, namely,
Primæval fish, Ganoid fish, and Osseous fish. The oldest of these, where
the original form has been most faithfully preserved, is that of the
_Primæval fish_ (Selachii). Of these there still exist Sharks (Squali),
and Rays (Rajæ), which are classed together as cross-mouthed fishes
(Plagiostomi), and the strange and grotesquely formed Sea-cats, or
_Chimæracei_ (Holocephali). These primary fish of the present day, which
are met with in all seas, are only poor remains of the prevailing animal
groups, rich in forms, which the Selachii formed in the earlier periods
of the earth’s history, and especially during the palæolithic period.
Unfortunately all Primæval fish possess a cartilaginous, never a
completely osseous skeleton, which is but little, if at all, capable of
being petrified. The only hard parts of the body which could be
preserved in a fossil state, are the teeth and fin-spikes. These are
found in the older formations in such quantities, varieties, and sizes,
that we may, with certainty, infer a very considerable development of
Primæval fish in those remote ages. They are even found in the Silurian
strata, which contain but few remains of other Vertebrata, such as
Enamelled fish (and these only in the most recent part, that is, in the
upper Silurian). By far the most important and interesting of the three
orders of Primæval fish are Sharks; of all still living double-nostriled
animals, they are probably most closely allied to the original primary
form of the whole group, namely, to the Proselachii. Out of these
Proselachii, which probably differed but little from genuine Sharks,
Enamelled fish, and the present Primæval fish, in all probability,
developed in one direction, and the Dipneusta, Sea-dragons, and Amphibia
in another.

The _Ganoid_, or _Enamelled fish_ (Ganoides), in regard to their anatomy
stand midway between the Primæval and the Osseous fish. In many
characteristics they agree with the former, and in many others with the
latter. Hence, we infer that genealogically they form the transition
from Primæval to Osseous fish. The Ganoids are for the most part
extinct, and more nearly so than the Primæval fish, whereas they were
developed in great force during the entire palæolithic and mesolithic
periods. Ganoid fish are divided into three legions according to the
form of their external covering, namely, Mailed, Angular-scaled, and
Round-scaled. The _Mailed Ganoid fish_ (Tabuliferi) are the oldest, and
are directly allied to the Selachii, out of which they originated.
Fossil remains of them, though rare, are found even in the upper
Silurian (Pteraspis ludensis of the Ludlow strata). Gigantic species of
them, coated with strong bony plates, are found in the Devonian system.
But of this legion there now lives only the small order of Sturgeons
(Sturiones), including the Spade-sturgeons (Spatularidæ), and those
Sturgeons (Accipenseridæ) to which belong, among others, the Huso, which
yields isinglass, or sturgeon’s sound, and the Caviar-sturgeon, whose
eggs we eat in the shape of caviar, etc. Out of the mailed Ganoid fish,
the angular and round-scaled ones probably developed as two diverging
branches. The _Angular-scaled Ganoid fish_ (Rhombiferi)—which can be
distinguished at first sight from all other fish by their square or
rhombic scales—are at present represented only by a few survivors,
namely, the Finny Pike (Polypterus) in African rivers (especially the
Nile), and by the Bony Pike (Lepidosteus) in American rivers. Yet during
the palæolithic and the first half of the mesolithic epochs this legion
formed the most numerous group of fishes. The third legion, that of
_Round-scaled Ganoid fish_ (Cycliferi), was no less rich in forms, and
lived principally during the Devonian and Coal periods. This legion, of
which the Bald Pike (Amia), in North American rivers, is the only
survivor, was especially important, inasmuch as the third sub-class of
fish, namely, Osseous fish, developed out of it.

_Osseous fish_ (Teleostei) include the greater portion of the fish of
the present day. Among these are by far the greater portion of marine
fish, and all of our fresh-water fish except the Ganoid fish just
mentioned. This class is distinctly proved by numerous fossils to have
arisen about the middle of the Mesolithic epoch out of Ganoid fish, and
moreover out of the Round-scaled, or Cycliferi. The Thrissopidæ of the
Oolitic period (Thrissops, Leptolepis, Tharsis), which are most closely
allied to the herrings of the present day, are probably the oldest of
all Osseous fish, and have directly arisen out of Round-scaled Ganoid
fish, closely allied to the existing Amia. In the older Osseous fish of
the legion called _Physostomi_, as also in the Ganoides, the swimming
bladder throughout life was connected with the throat by a permanent air
passage (a kind of windpipe). This is still the case with all the fish
belonging to this legion, namely, with herrings, salmon, carp, shad,
eels, etc. However, during the chalk period this air passage, in some of
the Physostomi, became constricted and closed, and the swimming bladder
was thus completely separated from the throat. Hence there arose a
second legion of Osseous fish, the _Physoclisti_, which did not attain
their actual development until the tertiary epoch, and soon far
surpassed the Physostomi in variety. To this legion belong most of the
sea fish of the present day, especially the large families of the
Turbot, Tunny, Wrasse, Crowfish, etc., further, the Lock-jaws
(Plectognathi), Trunk fish, and Globe-fish and the Bushy-gills
(Lophobranchi), viz., Pipe-fish, and Sea-horses. There are, however,
only very few Physoclisti among our river fish, for instance, Perch and
Sticklebacks; the majority of river fish are Physostomi.

Midway between genuine Fish and Amphibia is the remarkable class of
_Mud-fish_, or _Scaly Sirens_ (Dipneusta, or Protopteri). There now
exist only a few representatives of this class, namely, the American
Mud-fish (Lepidosiren paradoxa) in the region of the river Amazon, and
the African Mud-fish (Protopterus annectens) in different parts of
Africa. A third large Salamander-fish (Ceratodus Fosteri) has lately
been discovered in Australia. During the dry season, that is in summer,
these strange animals bury themselves in a nest of leaves in the dry
mud, and then breathe air through lungs like the Amphibia. But during
the wet season, in winter, they live in rivers and bogs, and breathe
water through gills like fish. Externally, they resemble fish of the eel
kind, and are like them covered with scales; in many other
characteristics also—in their internal structure, their skeleton,
extremities, etc.—they resemble Fish more than Amphibia. But in certain
features they resemble the Amphibia, especially in the formation of
their lungs, nose, and heart. There is consequently an endless dispute
among zoologists, as to whether the Mud-fish are genuine Fish or
Amphibia. Distinguished zoologists have expressed themselves in favour
of both opinions. But in fact, owing to the complete blending of
characteristics which they present, they belong neither to the one nor
to the other class, and are probably most correctly dealt with as a
special class of Vertebrata, forming the transition between Fishes and
Amphibians. The still living Dipneusta are probably the last surviving
remains of a group which was formerly rich in forms, but has left no
fossil traces on account of the want of a solid skeleton. In this
respect, these animals are exactly like the Monorrhina and the
Leptocardia. However, teeth are found in the Trias which resemble those
of the living Ceratodus. Possibly the extinct Dipneusta of the
palæolithic period, which developed in the Devonian epoch out of
primæval fish, must be looked upon as the primary forms of the Amphibia,
and thus also of all higher Vertebrata. At all events the unknown forms
of transition—from Primæval fish to Amphibia—were probably very like the
Dipneusta.

A very peculiar class of Vertebrate animals, long since extinct, and
which appears to have lived only during the secondary epoch, is formed
by the remarkable _Sea-dragons_ (Halisauria, or Enaliosauria, also
called Nexipoda, or Swimming-footed animals). These formidable animals
of prey inhabited the mesolithic oceans in great numbers, and were of
most peculiar forms, sometimes from thirty to forty feet in length. From
many and excellently preserved fossil remains and impressions, both of
the entire body of Sea-dragons as well as of single parts, we have
become very accurately acquainted with the structure of their bodies.
They are usually classed among Reptiles, whilst some anatomists have
placed them in a much lower rank, as directly allied to Fish.
Gegenbaur’s recently published investigations, which place the structure
of their limbs in a true light, have led to the surprising conclusion
that the Sea-dragons form quite an isolated group, differing widely both
from Reptiles and Amphibia as well as from Fish. The skeleton of their
four legs, which are transformed into short, broad, paddling fins (like
those of fish and whales) furnishes us with a clear proof that the
Halisauria branched off from the main-stock of Vertebrata at an earlier
period than the Amphibia. For Amphibia, as well as the three higher
classes of Vertebrata, are all derived from a common primary form, which
possessed only _five_ toes or fingers on each leg. But the Sea-dragons
have (either distinctly developed or in a rudimentary condition as parts
of the skeleton of the foot) more than five fingers, as have also the
Selachians or Primæval fish. On the other hand, they breathed air
through lungs, like the Dipneusta, although they always swam about in
the sea. They, therefore, perhaps, in conjunction with the Dipneusta,
branched off from the Selachii, but did not develop into higher
Vertebrata; they form an extinct lateral line of the pedigree, which has
died out.

The more accurately known Sea-dragons are classed into three orders,
distinct enough one from the other, namely, _Primæval Dragons_, _Fish
Dragons_, and _Serpent Dragons_. The _Primæval Dragons_ (Simosauria) are
the oldest Sea-dragons, and lived only during the Trias period. The
skeletons of many different genera of them are met with in the German
limestone known as “Muschel-kalk.” They seem upon the whole to have been
very like the Plesiosauria, and are, consequently, sometimes united with
them into one order as Sauropterygia. The _Serpent Dragons_
(Plesiosauria) lived in the oolitic and chalk periods together with the
Ichthyosauria. They were characterised by an uncommonly long thin neck,
which was frequently longer than the whole body, and carried a small
head with a short snout. When their arched neck was raised they must
have looked very like a swan; but in place of wings and legs they had
two pairs of short, flat, oval-paddling fins.

The body of the _Fish Dragons_ (Ichthyosauria) was of an entirely
different form; these animals may be opposed to the two preceding orders
under the name of Fish-finners (Ichthyopterygia). They possessed a very
long extended body, like a fish, and a heavy head with an elongated,
flat snout, but a very short neck. Externally, they were probably very
like porpoises. Their tail was very long, whereas it was very short in
the members of the preceding orders. Also both pairs of paddling fins
are broader and show very different structure from that seen in the
other two orders. Probably the Fish Dragons and Serpent Dragons
developed as two diverging branches out of the Primæval Dragons; but it
is also possible that the Plesiosauria alone originated out of the
Simosauria, and that the Ichthyosauria were lower off-shoots from the
common stock. At all events, they must all be directly, or indirectly
derived from the Selachii, or Primæval fish.

The succeeding classes of Vertebrata, the _Amphibia_ and the _Amniota_
(Reptiles, Birds, and Mammals), owing to the characteristic structure
which they all exhibit of five toes to each foot, may all be derived
from a common primary form, which originated from the Selachii, and
which possessed five toes on each of its four limbs. When we find a less
number of toes than five, we can show that the missing ones must have
been lost in the course of time by adaptation. The oldest known
Vertebrata with five toes are the _Batrachias_ (Amphibia). We divide
this class into two sub-classes, namely, mailed Batrachians and naked
Batrachians, the first of which is distinguished by the body being
covered with bony plates or scales.

The first and elder sub-class of Amphibia consists of the _Mailed
Batrachians_ (Phractamphibia), the oldest land living Vertebrata of
which fossil remains exist. Well-preserved fossil remains of them occur
in the coal, especially of those with _Enamelled heads_ (Ganocephala),
which are most closely allied to fish, namely, the Archegosaurus of
Saarbruck, and the Dendrerpeton of North America. There then follow at a
later period the gigantic _Labyrinth-toothed animals_ (Labyrinthodonta),
which are represented in the Permian system by Zygosaurus, but at a
later period, more especially in the Trias, by Mastodonsaurus,
Trematosaurus, Capitosaurus, etc. The shape of these formidable
rapacious animals seems to have been between that of crocodiles,
salamanders, and frogs, but in their internal structure they were more
closely related to the two latter, while by their solid coat of mail,
formed of strong bony plates, they resembled the first animals. These
gigantic mailed Batrachians seem to have become extinct towards the end
of the Triassic period. No fossil remains of mailed Batrachia are known
during the whole of the subsequent periods. However, the still living
blind Snakes, or _Cæciliæ_ (Peromela)—small-scaled Phractamphibia of the
form and the same mode of life as the earth-worm—prove that this
sub-class continued to exist, and never became completely extinct.

The second sub-class of Amphibia, the _naked Batrachia_ (Lissamphibia),
probably originated even during the primary and secondary epochs,
although fossil remains of them are first found in the tertiary epoch.
They are distinguished from mailed Batrachia by possessing a naked
smooth, and slimy skin, entirely without scales or coat of mail. They
probably developed either out of a branch of the Phractamphibia, or out
of the same common root with them. The ontogeny of the three still
living orders of naked Batrachia—the gilled Batrachia, tailed
Batrachia, and frog Batrachia—distinctly repeats the historical course
of development of the whole sub-class. The oldest forms are the gilled
Batrachia (Sozobranchia), which retain throughout life the original
primary form of naked Batrachia, and possess a long tail, together with
water-breathing gills. They are most closely allied to the Dipneusta,
from which, however, they differ externally by the absence of the coat
of scales. Most gilled Batrachia live in North America: among others of
the class is the Axolotl, or Siredon, already mentioned. (Compare above,
vol. i. p. 241.) In Europe the order is only represented by one form,
the celebrated “Olm” (Proteus anguinus), which inhabits the grotto of
Adelsberg and other caves in Carinthia, and which, from living in the
dark, has acquired rudimentary eyes which can no longer see (vol. i. p.
13). The order of Tailed Batrachia (Sozura) have developed out of the
gilled Batrachia by the loss of external gills; the order includes our
black and yellow spotted land Salamander (Salamandra maculata), and our
nimble aquatic Salamanders (Tritons). Many of them—for instance, the
celebrated giant Salamanders in Japan (Cryptobranchus Japonicus)—still
retain the gill-slits, although the gills themselves have disappeared.
All of them, however, retain the tail throughout life. Tritons
occasionally—when forced to remain in water always—retain their gills,
and thus remain at the same stage of development as gilled Batrachia.
(Compare above, vol. i. p. 241.) The third order, the _tailless_ or
_frog-like Batrachia_ (Anura), during their metamorphosis, not only lose
their gills, with which in early life (as so-called tadpoles) they
breathe in water, but also the tail with which they swim about. During
their ontogeny, therefore, they pass through the course of development
of the whole sub-class, they being at first _Gilled Batrachia_, then
_Tailed Batrachia_, and finally _Frog-like Batrachia_. The inference
from this is evidently, that _Frog-like Batrachia_ developed at a later
period out of _Tailed Batrachia_, as the latter had developed out of
_Gilled Batrachia_ which originally existed alone.

In passing from the Amphibia to the next class of Vertebrata, namely,
Reptiles, we observe a very considerable advance in the progress of
organization. All the double-nostriled animals (Amphirrhina) up to this
time considered, and more especially the two larger classes of Fish and
Batrachia, agree in a number of important characteristics, which
essentially distinguish them from the three remaining classes of
Vertebrata—Reptiles, Birds, and Mammals. During the embryological
development of these latter, a peculiarly delicate covering, the _first
fœtal membrane_, or _amnion_, which commences at the navel, is formed
round the embryo; this membrane is filled with the amnion-water, and
encloses the embryo or germ in the form of a bladder. On account of this
very important and characteristic formation, we may comprise the three
most highly developed classes of Vertebrata under the term
_Amnion-animals_ (Amniota). The four classes of double-nostriled animals
which we have just considered, in which the amnion is wanting (as is the
case in all lower Vertebrate animals, single-nostriled and skull-less
animals), may on the other hand be opposed to the others as _amnion-less
animals_ (Anamnia).

The formation of the fœtal membrane, or amnion, which distinguishes
reptiles, birds, and mammals from all other Vertebrata, is evidently a
very important process in their ontogeny, and in the phylogeny which
corresponds with it. It coincides with a series of other processes,
which essentially determine the higher development of Amnionate animals.
The first of these important processes is the _total loss of gills_, for
which reason the Amniota, under the name of _Gill-less animals_
(Ebranchiata), were formerly opposed to all other Vertebrate animals
which breathed through gills (Branchiata). In all the Vertebrate already
discussed, we found that they either always breathed through gills, or
at least did so in early life, as in the case of Frogs and Salamanders.
On the other hand, we never meet with a Reptile, Bird, or Mammal which
at any period of its existence breathes through gills, and the
gill-arches and openings which do exist in the embryos, are, during the
course of the ontogeny, changed into entirely different structures,
viz., into parts of the jaw-apparatus and the organ of hearing. (Compare
above, vol. i. p. 307.) All Amnionate animals have a so-called cochlea
in the organ of hearing, and a “round window” corresponding with it.
These parts are wanting in the Amnion-less animals; moreover, their
skull lies in a straight line with the axis of the vertebral column. In
Amniotic animals the base of the skull appears bent in on the abdominal
side, so that the head sinks upon the breast. (Plate III. Fig. _C_, _D_,
_G_, _H_.) The organs of tears at the side of the eye also first develop
in the Amniota.

The question now is, When did this important advance take place in the
course of the organic history of the earth? When did the common ancestor
of all Amniota develop out of a branch of the Non-amniota, to wit, out
of the branch of the Amphibia?

To this question, the fossil remains of Vertebrata do not give us a very
definite, but still they do give an approximate, answer. For with the
exception of two lizard-like animals found in the Permian system (the
Proterosaurus and Rhopalodon), all the fossil remains of Amniota, as yet
known, belong to the _secondary_, _tertiary_, and _quaternary epochs_.
With regard to the two Vertebrata just named, it is still doubtful
whether they are genuine reptiles, or perhaps Amphibia of the salamander
kind. Their skeleton alone is known to us, and even this not perfectly.
Now as we know nothing of the characteristic features of their soft
parts, it is quite possible that the Proterosaurus and Rhopalodon were
non-amnionate animals more closely allied to Amphibia than to Reptiles;
possibly they belonged to the transition form between the two classes.
But, on the other hand, as undoubted fossil remains of Amniota have been
found as early as the Trias, it is probable that the _main class of
Amniota_ first developed in the Trias, that is, in the beginning of the
Mesolithic epoch. As we have already seen, this very period is evidently
one of the most important turning points in the organic history of the
earth. The palæolithic fern forests were then replaced by the pine
forests of the Trias period; important transformations then took place
in many of the classes of Invertebrata. Articulated marine lilies
(Colocrina) developed out of the plated ones (Phatnocrina.) The
Autechinidæ, or sea-urchins with only twenty rows of plates, took the
place of the palæolithic Palechinidæ, the sea-urchins with more than
twenty rows of plates. The Cystideæ, Blastoideæ, Trilobita, and other
characteristic groups of Invertebrata of the primary period became
extinct. It is no wonder that transforming conditions of adaptation
powerfully influenced the Vertebrate tribes also in the beginning of the
Trias period, and caused the origin of Amniotic animals.

If, however, the two Lizard and Salamander-like animals of the Permian
system, the Proterosaurus and Rhopalodon, are considered genuine
Reptiles, and consequently the most ancient Amniota, then the origin of
this main class must necessarily have taken place in the preceding
period, towards the end of the primary, namely, in the Permian period.
However, all other remains of Reptiles, which were formerly believed to
have been found in the Permian and the Coal system, or even in the
Devonian system, have been proved to be either not remains of Reptiles
at all, or to belong to a more recent date (for the most part to the
Trias). (Compare Plate XIV.)

The common hypothetical primary form of all Amniotic animals, which we
may call _Protamnion_, and which was possibly nearly related to the
Proterosaurus, very probably stood upon the whole midway between
salamanders and lizards, in regard to its bodily formation. Its
descendants divided at an early period into two different lines, one of
which became the common primary form of Reptiles and Birds, the other
the primary form of Mammals.

Of all the three classes of Amniota, _Reptiles_ (Reptilia, or Pholidota,
also called Sauria in the widest sense), remain at the lowest stage of
development, and differ least from their ancestors, the Amphibia. Hence
they were formerly universally included among them, although their whole
organization is much more like that of Birds than Amphibia. There now
exist only four orders of Reptiles, namely,—Lizards, Serpents,
Crocodiles, and Tortoises. They, however, form but a poor remnant of the
exceedingly various and highly developed host of Reptiles which lived
during the Mesolithic, or Secondary epoch, and predominated over all
other Vertebrata. The immense development of Reptiles during the
Secondary epoch is so characteristic that we could as well name it after
those animals as after the Gymnosperms (p. 111). Twelve of the
twenty-seven sub-orders, given on the accompanying table, and four of
the eight orders, belong exclusively to the secondary period. These
mesolithic groups are marked by an asterisk. All the orders, with the
exception of Serpents, are found fossilized even in the Jura and Trias
periods.

[Illustration: _Pl. XIV._

[Horizontal axis:]
Branches,
Classes,
and Sub-Classes,
of the Vertebrate
Stem.

Prochordata
Evertebrate
Forefathers
of the
Vertebrate

Skull-less
(Acrania)
or
Tube-hearted
Fish,
(Leptocardia)

Single
nostrilled
(Monorrhina)
or
Round-mouthed
Fishes
(Cyclostoma)

Anamnia { Paired-nostrilled forms or Amphirrhina
{ with gills, without Amnion.
Fish, Pisces

Primeval
Fish,
Selachii.

Enamelled
Fish,
Ganoides.

Bony
Fish,
Teleostei.

Mud
Fish,
Dipneusta.

Sea-Dragons,
Halisauria.

Frogs and
Newts,
Amphibia.

Amniota { Paired nostrilled or Amphirrhina
{ with Amnion, without gills.

Reptiles, Reptilia.

Primæval
Reptiles,
Tocosauria.

Lizards,
Lacertilia.

Snakes,
Ophidia.

Crocodiles,
Crocodilia.

Tortoises,
Chelonia.

Flying
Reptiles,
Pterosauria.

Dragons,
Dinosauria.

Billed
Reptiles,
Anomodontia.

Birds,
Aves.

Suckling animals, Mammalia.

Billed
Animals,
Monotrema.

Pouched
Animals,
Marsupialia.

Placental
Animals,
Placentalia.

[Vertical axis:]
Cenolithic or
Tertiary Epoch.

Pliocene
Age.

Miocene
Age.

Eocene
Age.

Mesolithic or
Secondary Epoch.

Chalk
Period.

Jurassic
Period.

Triassic
Period.

Palæolithic or
Primary Epoch.

Permian
Period.

Coal
Period.

Devonian
Period.

Archilithic or
Primordial Epoch.

Silurian
Period.

Cambrian
Period.

Laurentian
Period.

[Legend:]
Single or
MONOPHYLETIC PEDIGREE
of the Stem of the
BACK-BONED ANIMALS
Based on Palæontology.

Relative lengths of the 5
Epochs in per centages.

Quarternary Epoch 0.5
Tertiary Epoch 2.3
Secondary Epoch 11.5
Primary Epoch 32.1
Primordial Epoch 53.6
------
_Total_ 100.0]

In the first order, that of _Primary Reptiles_, or _Primary Creepers_
(Tocosauria), we class the extinct _Thecodontia_ of the Trias, together
with those Reptiles which we may look upon as the common primary form of
the whole class. To the latter, which we may call _Primæval Reptiles_
(Proreptilia), the Proterosaurus of the Permian system very probably
belongs. The seven remaining orders must be considered as diverging
branches, which have developed in different directions out of that
common primary form. The Thecodontia of the Trias, the only positively
known fossil forms of Tocosauria, were Lizards which seem to have been
like the still living monitor lizards (Monitor, Varanus).

SYSTEMATIC SURVEY

_Of the 8 Orders and 27 Sub-orders of Reptiles._

(Those groups marked with * became extinct even during the Secondary
Period.)

-----------------------------------------------------------------------------------
| _Sub-orders_ | _Systematic Name_ | _A Generic Name_
_Orders_ | _of_ | _of the_ | _as_
_of Reptiles._ | _Reptiles._ | _Sub-orders._ | _an example._
-----------------------------------------------------------------------------------
I. =Primary= { 1. Primæval reptiles 1. Proreptilia * (Proterosaurus?)
=Reptiles= {
+Tocosauria+ { 2. 2. Thecodontia * Palæosaurus

{ 3. Cleft-tongued 3. Fissilingues Monitor
{ 4. Thick-tongued 4. Crassilingues Iguana
II. =Lizards= { 5. Short-tongued 5. Brevilingues Anguis
+Lacertilia+ { 6. Ringed lizards 6. Glyptodermata Amphisbæna
{ 7. Chameleons 7. Vermilingues Chamæleo

{ 8. Adders 8. Aglyphodonta Coluber
{ 9. Tree serpents 9. Opisthoglypha Dipsas
III. =Serpents= { 10. 10. Proteroglypha Hydrophis
+Ophidia+ { 11. Vipers 11. Solenoglypha Vipera
{ 12. Worm serpents 12. Opoterodonta Typhlops

{ 13. Amphicœla 13. Teleosauria * Teleosaurus
IV. =Crocodiles= { 14. Opisthocœla 14. Steneosauria * Steneosaurus
+Crocodilia+ { 15. Prosthocœla 15. Alligatores Alligator

{ 16. Sea tortoises 16. Thalassita Chelone
V. =Tortoises= { 17. River tortoises 17. Potamita Trionyx
+Chelonia+ { 18. Marsh tortoises 18. Elodita Emys
{ 19. Land tortoises 19. Chersita Testudo

{ 20. Long-tailed 20. Rhamphorhynchi * Rhamphorhynchus
VI. =Flying= { Flying lizards
=Reptiles= { 21. Short-tailed 21. Pterodactyli * Pterodactylus
+Pterosauria+* { Flying lizards

{ 22. Giant dragons 22. Harpagosauria * Megalosaurus
VII. =Dragons= { 23. Elephantine 23. Therosauria * Iguanodon
+Dinosauria+* { dragons

{ 24. Dog-toothed 24. Cynodontia * Dicynodon
VIII. =Beaked= { 25. Toothless 25. Cryptodontia * Udenodon
=Reptiles= { 26. Kangaroo reptiles 26. Hypsosauria * Compsognathus
+Anomodontia+* {
{ 27. Bird reptiles 27. Tocornithes * (Tocornis)

Of the four orders of reptiles now existing, and which, moreover, have
alone represented the class since the beginning of the tertiary epoch,
that of _Lizards_ (Lacertilia) is probably most closely allied to the
extinct Primary Reptiles, and especially through the monitors already
named. The class of _Serpents_ (Ophidia) developed out of a branch of
the order of lizards, and this probably not until the beginning of the
tertiary epoch. At least we at present only know of fossil remains of
serpents from the tertiary strata. _Crocodiles_ (Crocodilia) existed
much earlier; the Teleosauria and Steneosauria belonging to the class
are found fossil in large quantities even in the Jura; but the still
living alligators are first met with in a fossil state in the chalk and
tertiary strata. The most isolated of the four existing orders of
reptiles consists of the remarkable group of _Tortoises_ (Chelonia);
fossils of these strange animals are first met with in the Jura. In some
characteristics they are allied to Amphibia, in others, to Crocodiles,
and by certain peculiarities even to Birds, so that their true position
in the pedigree of Reptiles is probably far down at the root. The
extraordinary resemblance of their embryos to Birds, manifested even at
later stages of the ontogenesis, is exceedingly striking.

The four extinct orders of Reptiles show among one another, and, with
the four existing orders just mentioned, such various and complicated
relationships, that in the present state of our knowledge we are obliged
to give up the attempt at establishing their pedigree. The most
deviating and most curious forms are the _Flying Reptiles_
(Pterosauria); flying lizards, in which the extremely elongated fifth
finger of the hand served to support an enormous flying membrane. They
probably flew about, in the secondary period, much in the same way as
the bats of the present day. The smallest flying lizards were about the
size of a sparrow; the largest, however, with a breadth of wing of more
than sixteen feet, exceeded the largest of our living flying birds in
stretch of wing (condor and albatross). Numerous fossil remains of them,
of the long-tailed Rhamphorhynchia and of the short-tailed Pterodactylæ
are found in all the strata of the Jura and Chalk periods, but in these
only.

Not less remarkable and characteristic of the Mesolithic epoch was the
group of _Dragons_ (Dinosauria, or Pachypoda). These colossal reptiles,
which attained a length of more than fifty feet, are the largest
inhabitants of the land which have ever existed on our globe; they lived
exclusively in the secondary epoch. Most of their remains are found in
the lower cretaceous system, more especially in the Wealden formations
of England. The majority of them were fearful beasts of prey (the
Megalosaurus from twenty to thirty, the Pelorosaurus from forty to fifty
feet in length). The Iguanodon, however, and some others lived on
vegetable food, and probably played a part in the forests of the chalk
period similar to that of the unwieldy but smaller elephants,
hippopotami, and rhinoceroses of the present day.

The _Beaked Reptiles_ (Anomodontia), likewise also long since extinct,
but of which very many remarkable remains are found in the Trias and
Jura, were perhaps closely related to the Dragons. Their jaws, like
those of most Flying Reptiles and Tortoises, had become changed into a
beak, which either possessed only degenerated rudimentary teeth, or no
teeth at all. In this order, if not in the preceding one, we must look
for the primary parents of the bird class, which we may call Bird
Reptiles (Tocornithes). Probably very closely related to them was the
curious, kangaroo-like Compsognathus from the Jura, which in very
important characteristics already shows an approximation to the
structure of birds.

The class of _Birds_ (Aves), as already remarked, is so closely allied
to Reptiles in internal structure and by embryonal development, that
they undoubtedly originated out of a branch of this class. Even a glance
at Plates II. and III. will show that the embryos of birds at a time
when they already essentially differ from the embryos of Mammals, are
still scarcely distinguishable from those of Tortoises and other
Reptiles. The cleavage of the yolk is partial in the case of Birds and
Reptiles, in Mammals it is total. The red blood-cells of the former
possess a kernel, those of the latter do not. The hair of Mammals
develops in closed follicles in the skin, but the feathers of birds and
also the scales of reptiles develop in hillocks on the skin. The lower
jaw of the latter is much more complicated than that of Mammals; the
latter do not possess the quadrate bone of the former. Whereas in
Mammals (as in the case of Amphibia) the connection between the skull
and the first neck vertebra is formed by two knobbed joints, or
condyles, in Birds and Reptiles those have become united into a single
condyle. The two last classes may therefore justly be united into one
group as Monocondylia, and contrasted to Mammals, or Dicondylia.

The deviation of Birds from Reptiles, in any case, first took place in
the mesolithic epoch, and this moreover probably during the Trias. The
oldest fossil remains of birds are found in the upper Jura
(Archæopteryx). But there existed, even in the Trias period, different
Saurians (Anomodonta) which in many respects seem to form the transition
from the Tocosauria to the primary ancestors of Birds, the hypothetical
Tocornithes. Probably these Tocornithes were scarcely distinguishable
from other beaked lizards in the system, and were closely related to the
kangaroo-like Compsognathus from the Jura of Solenhofen. Huxley classes
the latter with the Dinosauria, and believes them to be the nearest
relations to the Tocornithes.

The great majority of Birds—in spite of all the variety in the colouring
of their beautiful feathery dress, and in the formation of their beaks
and feet—are of an exceedingly uniform organization, in much the same
way as are the class of insects. The bird form has adapted itself on all
sides to the external conditions of existence, without having thereby in
any way essentially deviated from the strict hereditary type of its
characteristic structure. There are only two small groups, the
feather-tailed birds (Saururæ) and those of the ostrich kind, which
differ considerably from the usual type of bird, namely, from those with
keel-shaped breasts (Carinatæ), and hence the whole class may be divided
into three sub-classes.

The first sub-class, the _Reptile-tailed_, or _Feather-tailed Birds_
(Saururæ), are as yet known only through a single, and that an
imperfect, fossil impression, which, however, in being the oldest and
also a very peculiar fossil bird, is of great importance. This fossil is
the Primæval Griffin, or Archæopteryx lithographica, of which as yet
only one specimen has been found in the lithographic slate at
Solenhofen, in the Upper Jura system of Bavaria. This remarkable bird
seems on the whole to have been of the size and form of a large raven,
especially as regards the legs, which are in a good state of
preservation; head and breast unfortunately are wanting. The formation
of the wings deviates somewhat from that of other birds, but that of the
tail still more so. In all other birds the tail is very short and
composed of but few short vertebræ; the last of these have grown
together into a thin, bony plate standing perpendicularly, upon which
the rudder-feathers of the tail are attached in the form of a fan. The
Archæopteryx, however, has a long tail like a lizard, composed of
numerous (20) long thin vertebræ, and on every vertebra are attached
the strong rudder-feathers in twos, so that the whole tail appears
regularly feathered. This same formation of the tail part of the
vertebral column occurs transiently in the embryos of other birds, so
that the tail of the Archæopteryx evidently represents the original form
of bird-tail inherited from reptiles. Large numbers of similar birds
with lizard-tails probably lived during the middle of the secondary
period; accident has as yet, however, only revealed this one fossil.

The _Fan-tailed_, or _Keel-breasted birds_ (Carinatæ), which form the
second sub-class, comprise all living Birds of the present day, with the
exception of those of the ostrich kind, or Ratitæ. They probably
developed out of Feather-tailed Birds during the first half of the
secondary period, namely, in the Jura or Chalk period, by the hinder
tail vertebræ growing together, and by the tail becoming shortened. Only
very few remains of them are known from the secondary period, and these
moreover only out of the last section of it, namely, from the Chalk.
These remains belong to a swimming bird of the albatross species, and a
wading bird like a snipe. All the other fossil remains of birds as yet
known have been found in the tertiary strata.

The _Bushy-tailed_, or _Ostrich-like Birds_ (Ratitæ), also called
_Running Birds_ (Cursores), the third and last sub-class, is now
represented only by a few living species, by the African ostrich with
two toes, the American and Australian ostrich with three toes, by the
Indian cassowary and the four-toed kiwi, or Apteryx, in New Zealand. The
extinct giant birds of Madagascar (Æpyornis) and the New Zealand
Dinornis, which were much larger than the still living ostriches, also
belong to this group. The Birds of the ostrich kind—by giving up the
habit of flying, by the degeneration of the muscles for flying resulting
from this, and of the breast bone which serves as their support, and by
the corresponding stronger development of the hinder legs for
running—have probably arisen out of a branch of the Keel-breasted birds.
But possibly, as Huxley thinks, they may be the nearest relations of the
Dinosauria and of the Reptiles akin to them, especially of the
Compsognathus; at all events, the common primary form of all Birds must
be looked for among the extinct Reptiles.

CHAPTER XXI.

PEDIGREE AND HISTORY OF THE ANIMAL KINGDOM.

IV. MAMMALS.

There are only a few points in the classification of organisms upon
which naturalists have always agreed. One of these few undisputed points
is the privileged position of the class of Mammals at the head of the
animal kingdom. The reason of this privilege consists partly in the
special interest, also in the various uses and the many pleasures, which
Mammals, more than all other animals, offer to man, and partly in the
circumstance that man himself is a member of this class. For however
differently in other respects man’s position in nature and in the system
of animals may have been regarded, yet no naturalist has ever doubted
that man, at least from a purely morphological point of view, belongs
to the class of Mammals. From this there directly follows the
exceedingly important inference that man, by consanguinity also, is a
member of this class of animals, and has historically developed out of
long since extinct forms of Mammals. This circumstance alone justifies
us here in turning our especial attention to the history and the
pedigree of Mammals. Let us, therefore, for this purpose first examine
the groups of this class of animals.

Older naturalists, especially considering the formation of the jaw and
feet, divided the class of Mammals into a series of from eight to
sixteen orders. The lowest stage of the series was occupied by the
whales, which seemed to differ most from man, who stands at the highest
stage, by their fish-like form of body. Thus Linnæus distinguished the
following eight orders: (1) Cetæ (whales); (2) Belluæ (hippopotami and
horses); (3) Pecora (ruminating animals); (4) Glires (gnawing animals
and rhinoceroses); (5) Bestiæ (insectivora, marsupials, and various
others); (6) Feræ (beasts of prey); (7) Bruta (toothless animals and
elephants); (8) Primates (bats, semi-apes, apes, and men). Cuvier’s
classification, which became the standard of most subsequent zoologists,
did not rise much above that of Linnæus. Cuvier distinguished the
following eight orders: (1) Cetacea (whales); (2) Ruminantia (ruminating
animals); (3) Pachyderma (hoofed animals, with the exclusion of
ruminating animals); (4) Edentata (animals poor in teeth); (5) Rodentia
(gnawing animals); (6) Carnassia (marsupials, beasts of prey,
insectivora, and bats); (7) Quadrumana (semi-apes and apes); (8) Bimana
(man).

The most important advance in the classification of Mammals was made as
early as 1816 by the eminent anatomist Blainville, who has already been
mentioned, and who first clearly recognised the three natural main
groups or sub-classes of Mammals, and distinguished them according to
the formation of their generative organs as _Ornithodelphia_,
_Didelphia_, and _Monodelphia_. As this division is now justly
considered by all scientific zoologists to be the best, on account of
solid foundation on the history of development, let us here keep to it
also.

The first sub-class consists of the _Cloacal Animals_, or _Breastless
animals_, also called _Forked animals_ (Monotrema, or Ornithodelphia).
This class is now represented only by two species of living mammals,
both of which are confined to Australia and the neighbouring island of
Van Diemen’s land, namely, the well-known Water Duck-bill
(Ornithorhynchus paradoxus) with the beak of a bird, and the less known
Beaked Mole (Echidna hystrix), resembling a hedgehog. Both of these
curious animals, which are classed in the order of _Beaked Animals_
(Ornithostoma), are evidently the last surviving remnants of an animal
group formerly rich in forms, which alone represented the Mammalia in
the secondary epoch, and out of which the second sub-class, the
Didelphia, developed later, probably in the Jurassic period.
Unfortunately, we as yet do not know with certainty of any fossil
remains of this most ancient primary group of Mammals, which we will
call _Primary Mammals_ (Promammalia). Yet they possibly comprise the
oldest of all the fossil Mammalia known, namely, the Microlestes
antiquus, of which animals, however, we as yet only know some few small
molar teeth. These have been found in the uppermost strata of the
Trias, in the Keuper, first in Germany (at Degerloch, near Stuttgart,
in 1847), later also in England (at Frome), in 1858. Similar teeth have
lately been found also in the North American Trias, and have been
described as Dromatherium sylvestre. These remarkable teeth, from the
characteristic form of which we can conclude that they belonged to an
insectivorous mammal, are the only remains of mammals as yet found in
the older secondary strata, namely, in the Trias. It is possible,
however, that besides these many of the other mammalian teeth found in
the Jura and Chalk systems, which are still generally ascribed to
Marsupials, in reality belong to Cloacal Animals. This cannot be decided
with certainty owing to the absence of the characteristic soft parts. In
any case, numerous Monotrema, with well-developed teeth and cloaca, must
have preceded the advent of Marsupial animals.

The designation, “_Cloacal animals_” (Monotrema), has been given to the
Ornithodelphia on account of the cloaca which distinguishes them from
all other Mammals; but which on the other hand makes them agree with
Birds, Reptiles, and Amphibia, in fact, with the lower Vertebrata. The
formation of the cloaca consists in the last portion of the intestinal
canal receiving the mouth of the urogenital apparatus, that is, the
united urinary and genital organs, whereas in all other Mammals
(Didelphia as well Monodelphia) these organs have an opening distinct
from that of the rectum. However, in these latter also the cloaca
formation exists during the first period of their embryonal life, and
the separation of the two openings takes place only at a later date (in
man about the twelfth week of development). The Cloacal animals have
also been called “_Forked animals_,” because the collar-bones, by means
of the breast bone, have become united into one piece, similar to the
well-known fork-bone, or merry-thought, in birds. In all other Mammals
the two collar-bones remain separated in front and do not fuse with the
breast bone. Moreover, the coracoid bones are much more strongly
developed in the Cloacal animals than in the other Mammalia, and are
connected with the breast bone.

In many other characteristics also—especially in the formation of their
internal genital organs, their auricular labyrinth, and their
brain—Beaked animals are more closely allied to the other Vertebrata
than to Mammals, so that some naturalists have been inclined to separate
them from the latter as a special class. However, like all other
Mammals, they bring forth living young ones, which for a time are
nourished with milk from the mother. But whereas in all other Mammals
the milk issues through nipples, or teats, from the mammary glands,
teats are completely wanting in beaked animals, and the milk comes
simply out of a flat, sieve-like, perforated patch of the skin. Hence
they may also be called _Breastless_ or _Teatless animals_ (Amasta).

The curious formation of the beak in the two still living Beaked
animals, which is connected with the suppression of the teeth, must
evidently not be looked upon as an essential feature of the whole
sub-class of Cloacal animals, but as an accidental character of
adaptation distinguishing the last remnant of the class as much from the
extinct main group, as the formation of a similar toothless snout
distinguishes many toothless animals (for instance, the ant-eater) from
the other placental animals. The unknown, extinct Primary Mammals, or
Promammalia—which lived during the Trias period, and of which the two
still living orders of Beaked animals represent but a single
degenerated branch developed on one side—probably possessed a very
highly developed jaw like the marsupial animals, which developed from
them.

_Marsupial_, or _Pouched Animals_ (Didelphia, or Marsupialia), the
second of the three sub-classes of Mammals, form in every respect—both
as regards their anatomy and embryology, as well as their genealogy and
history—the transition between the other sub-classes—the Cloacal and
Placental Animals. Numerous representatives of this group still exist,
especially the well-known kangaroos, pouched rats, and pouched dogs; but
on the whole this sub-class, like the preceding one, is evidently
approaching its complete extinction, and the living members of the class
are the last surviving remnants of a large group rich in forms, which
represented the Mammalia during the more recent secondary and the
earlier tertiary periods. The Marsupial Animals probably developed
towards the middle of the Mesolithic epoch (during the Jura) out of a
branch of the Cloacal Animals, and in the beginning of the Tertiary
epoch again, the group of Placental Animals arose out of the Marsupials,
and the latter then succumbed to the former in the struggle for life.
All the fossil remains of Mammals known to us from the Secondary epoch,
belong either exclusively to Marsupials, or partly perhaps to Cloacal
animals. At that time Marsupials seem to have been distributed over the
whole earth; even in Europe (France and England), well-preserved fossil
remains of them have been found. On the other hand, the last off-shoots
of the sub-class now living are confined to a very narrow tract of
distribution, namely, to Australia, the Australasian, and a small part
of the Asiatic Archipelago. There are also a few species still living
in America, but at the present day not a single marsupial animal lives
on the continent of Asia, Africa, or Europe.

The name of pouched animals is given to the class on account of the
purse-shaped pouch (marsupium) existing in most instances on the
abdominal side of the female animals, in which the mother carries about
her young for a considerable time after their birth. This pouch is
supported by two characteristic marsupial bones, also existing in
Cloacal animals, but not in Placental animals. The young Marsupial
animal is born in a much more imperfect form than the young Placental
animal, and only attains the same degree of development which the latter
possesses directly at its birth, after it has developed in the pouch for
some time. In the case of the giant kangaroo, which attains the height
of a man, the newly born young one, which has been carried in the
maternal womb not much longer than five weeks, is not more than an inch
in length, and only attains its essential development subsequently, in
the pouch of the mother, where it remains about nine months attached to
the nipple of the mammary gland.

The different divisions generally distinguished as families in the
sub-class of Marsupial animals, deserve in reality the rank of
independent orders, for they differ from one another in manifold
differentiations of the jaw and limbs, in much the same manner, although
not so sharply, as the various orders of Placental animals. In part they
perfectly agree with the latter. It is evident that adaptation to
similar conditions of life has effected entirely coincident or analogous
transformations of the original fundamental form in the two sub-classes
of Marsupials. According to this, about eight orders of Marsupial
animals may be distinguished, the one half of the main group or legion
of which are herbivorous, the other half carnivorous. The oldest fossil
remains of the two legions (if the previously mentioned Microlestes and
the Dromatherium are not included) occur in the Jurassic strata, namely,
in the slates of Stonesfield, near Oxford. The slates belong to the
Bath, or the Lower Oolite formation—strata which lie directly above the
Lias, the oldest Jura formation. (Compare p. 15.) It is true that the
remains of Marsupials found in the slates of Stonesfield, as well as
those which were found later in the Purbeck strata, consist only of
lower jaws. (Compare p. 29.) But fortunately the lower jaw is just one
of the most characteristic parts of the skeleton of Marsupials. For it
is distinguished by a hook-shaped process of the lower corner of the jaw
turning downwards and backwards, which neither occurs in Placental nor
in the (still living) Cloacal animals, and from the existence of this
process on the lower jaws from Stonesfield, we may infer that they
belonged to Marsupials.

SYSTEMATIC SURVEY OF CLOACAL AND MARSUPIAL MAMMALIA.

I. _First Sub-class of Mammalia:_

_Forked or Cloacal Animals (Monotrema, or Ornithodelphia)._

Mammals with Cloaca, without Placenta, with Marsupial Bones.

------------------------------------------------------------------------------------
I. }
=Primary Mammals= } Unknown extinct Mammalia from the { (Microlestes?)
+Promammalia+ } Trias Period { (Dromatherium?)

II. } 1. Aquatic beaked 1. Ornithorhynchida { 1. Ornithorhynchus
=Beaked Animals= } animals { paradoxus
+Ornithostoma+ } 2. Terrestrial 2. Echidnida { 2. Echidna hystrix
} beaked animals {
------------------------------------------------------------------------------------
II. _Second Sub-class of Mammalia:_

_Pouched or Marsupial Animals (Marsupialia, or Didelphia)._

Mammals without Cloaca, without Placenta, with Marsupial Bones.
------------------------------------------------------------------------------------
_Legions_ | _Orders_ | _Systematic Name_ | _Families of the_
_of_ | _of_ | _of_ | _Marsupialia._
_Marsupialia._ | _Marsupialia._ | _the Orders._ |
------------------------------------------------------------------------------------
{ 1. Hoofed 1. Barypoda { 1. Stereognathida
{ Marsupial animals { 2. Nototherida
III. { { 3. Diprotodontia
=Herbivorous= {
=Marsupial= { 2. Kangaroo 2. Macropoda { 4. Plagiaulacida
=Animals= { Marsupial animals { 5. Halmaturida
{ (Leaping pouched { 6. Dendrolagida
+Marsupialia+ { animals)
+Botanophaga+ {
{ 3. Root-eating 3. Rhizophaga {
{ Marsupial animals {
{ (Gnawing pouched { 7. Phascolomyida
{ animals) {
{
{ 4. Fruit eating 4. Carpophaga {
{ Marsupial animals { 8. Phascolarctida
{ (Climbing pouched { 9. Phalangistida
{ animals) { 10. Petaurida

{ 5. Insectivorous 5. Cantharophaga { 11. Thylacotherida
{ Marsupial animals { 12. Spalacotherida
{ (Primæval pouched { 13. Myrmecobida
{ animals) { 14. Peramelida
IV. {
=Carnivorous= { 6. Marsupial animals 6. Edentula {
=Marsupial= { poor in teeth {
=Animals= { (Pouched animals { 15. Tarsipedina
{ with trunks) {
{
{ 7. Rapacious marsupial 7. Creophaga { 16. Dasyurida
{ animals { 17. Thylacinida
+Marsupialia+ { (Rapacious pouched { 18. Thylacoleonida
+Zoophaga+ { animals)
{
{ 8. Ape-footed 8. Pedimana {
{ Marsupial animals { 19. Chironectida
{ (Pouched animals { 20. Didelphyida
{ with hands)

SYSTEMATIC SURVEY OF PLACENTAL ANIMALS.

III. _Third Sub-class of Mammalia:_

_Placentalia, or Monodelphia (Placental Animals)._

Mammals without Cloaca, with Placenta, without Marsupial Bones.

-----------------------------------------------------------------------------------
_Legions of_ | _Orders of_ | _Sub-orders of_ |_Systematic Name_
_the_ | _the_ | _the_ | _of_
_Placental Animals._|_Placental Animals._|_Placental Animals._ | _the Sub-orders._
-----------------------------------------------------------------------------------
III. 1. INDECIDUA. _Placental Animals without Decidua._
-----------------------------------------------------------------------------------
V. { I. Single-hoofed { 1. Tapirs 1. Tapiromorpha
=Hoofed Animals= { _Perissodactyla_ { 2. Horses 2. Solidungula
+Ungulata+ {
{ II. Double-hoofed { 3. Pigs 3. Choeromorpha
{ _Artiodactyla_ { 4. Ruminating 4. Ruminantia

{ III. Herbivorous {
VI. { Whales { 5. Sea cows 5. Sirenia
=Whales= { _Phycoceta_ {
+Cetacea+ {
{ IV. Carnivorous { 6. Whales 6. Autoceta
{ Whales { 7. Zeuglodonta 7. Zeugloceta
{ _Sarcoceta_ {

VII. { V. Digging Animals { 8. Ant-eaters 8. Vermilinguia
=Animals= { _Effodientia_ { 9. Armadilloes 9. Cingulata
=poor in teeth= {
+Edentata+ { VI. Sloths { 10. Giant Sloths 10. Gravigrada
{ _Bradypoda_ { 11. Dwarf Sloths 11. Tardigrada
-----------------------------------------------------------------------------------
III. 2. DECIDUATA. _Placental Animals with Decidua._
-----------------------------------------------------------------------------------
VIII. { VII. Rapacious {12. Rapacious land 12. Carnivora
=Placental Animals= { Animals { animals
+Zonoplacentalia+ { _Carnaria_ {13. Rapacious sea 13. Pinnipedia
{ { animals
{
{ VIII. False-hoofed {14. Hyrax 14. Lamnungia
{ Animals {15. Toxodonts 15. Toxodontia
{ _Chelophora_ {16. Dinotheria 16. Gonyognatha
{ {17. Elephants 17. Proboscidea

XI. { IX. Semi-apes {18. Fingered animals 18. Leptodactyla
=Disc Placental= { _Prosimiæ_ {19. Flying lemur 19. Ptenopleura
=Animals= { {20. Long-footed 20. Macrotarsi
+Discoplacentalia+ { {21. Short-footed 21. Brachytarsi
{
{ X. Gnawing Animals {22. Squirrel species 22. Sciuromorpha
{ _Rodentia_ {23. Mouse species 23. Myomorpha
{ {24. Porcupine species 24. Hystrichomorpha
{ {25. Hare species 25. Lagomorpha
{
{ XI. Insect-eating {26. With a cœcum 26. Menotyphla
{ Animals {27. Without a 27. Lipotyphla
{ _Insectivora_ { cœcum
{
{ XII. Flying Animals{28. Flying foxes 28. Pterocynes
{ _Chiroptera_ {29. Bats 29. Nycterides
{
{ XIII. Apes { 30. Clawed apes 30. Arctopitheci
{ _Simiæ_ { 31. Flat-nosed 31. Platyrrhinæ
{ { 32. Narrow-nosed 32. Catarrhinæ

----------------------------------------------------------------

Of _Herbivorous marsupials_ (Botanophaga), only two fossils are as yet
known from the Jura, namely, the Stereognathus ooliticus, from the
slates of Stonesfield (Lower Oolite), and the Plagiaulax Becklesii, from
the middle Purbeck strata (Upper Oolite). But in Australia there are
gigantic fossil remains of extinct herbivorous Marsupials from the
diluvial period (Diprotodon and Nototherium) which were far larger than
the largest of the still living Marsupials. The Diprotodon Australis,
whose skull alone is three feet long, exceeded even the river-horse, or
Hippopotamus, in size and upon the whole resembled it in the unwieldy
and clumsy form of body. This extinct group, which probably corresponded
with the gigantic placental hoofed animals of the present day—the
hippopotami and rhinoceroses—may be called Hoofed Marsupials (Barypoda).
Closely allied to them is the order of kangaroos, or Leaping Marsupials
(Macropoda), which all have seen in zoological gardens. In their
shortened fore legs, their very lengthened hind legs, and very strong
tail, which serves as a jumping pole, they correspond with the leaping
mice in the class of Rodents. Their jaw, however, resembles that of
horses, and their complex stomach that of Ruminants. A third order of
Herbivorous Marsupials corresponds in its jaws to Rodents, and in its
subterranean mode of life, especially, to digging mice. Hence they may
be termed Rodent Marsupials, or root-eating pouched animals
(Rhizophaga). They are now represented only by the Australian wombat
(Phascolomys). A fourth and last order of Herbivorous Marsupials is
formed by the climbing or Fruit-eating Marsupials (Carpophaga), whose
mode of life and structure resembles partly that of squirrels, partly
that of apes (Phalangista, Phascolarctus).

The second legion of Marsupials, the _Carnivorous Marsupials_
(Zoophaga), is likewise divided into four main groups or orders. The
most ancient of these is that of the primæval, or Insectivorous
Marsupials (Cantharophaga). It probably includes the primary forms of
the whole legion, and possibly also those of the whole sub-class. At
least, all the lower jaws from Stonesfield (with the exception of the
Stereognathus) belong to Insectivorous Marsupials, and the still living
Myrmecobius is their nearest relative. But some of those oolitic
Primæval Marsupials possessed a larger number of teeth than all the
other known mammals, for each half of the lower jaw of the
Thylacotherium contained sixteen teeth (three incisors, one canine
tooth, six pseudo, and six genuine molars). If the upper jaw, which is
unknown, had as many teeth, then the Thylacotherium had no less than
sixty-four teeth, just double the number possessed by man. The Primæval
Marsupials correspond, on the whole, with the Insectivora among
Placental animals, which order includes hedgehogs, moles, and
shrew-mice. A second order, which has probably developed out of a branch
of the last, consists of the Snouted, or Toothless Marsupials
(Edentula), which resemble the Toothless animals, or Edentata, among the
Placental animals by their tube-shaped snout, their degenerated jaws,
and their corresponding mode of life. On the other hand, the mode of
life and formation of the jaws of Rapacious marsupials (Creophaga)
correspond with those of the genuine Beasts of Prey, or Carnivora, among
Placental animals. This order includes the pouched marten (Dasyurus) and
the pouched wolf (Thylacinus) in Australia. Although the latter attains
to the size of a wolf, it is but a dwarf in comparison with the extinct
Australian pouched lions (Thylacoleo) which were at least as large as a
lion, and possessed huge canine teeth more than two inches in length.
Finally, the eighth and last order is formed by the marsupials with
hands, or the Ape-footed Pouched animals (Pedimana), which live both in
Australia and America. They are frequently kept in zoological gardens,
especially the different species of the genus Didelphys, and are known
by the name of pouched rats, bush rats, or opossums. The thumb on their
hinder feet is opposable to the four other toes, as in a hand, and by
this they are directly allied to the Semi-apes, or Prosimia, among
Placental animals. It is possible that these latter are really next akin
to the marsupials with hands, and that they have developed out of their
long since extinct ancestors.

It is very difficult to discover the genealogy of Marsupials, and this
more especially because we are but very imperfectly acquainted with the
whole sub-class; and the Marsupials of the present day are evidently
only the last remnants of a group that was at one time rich in forms. It
is possible that Marsupials with hands, those with snouts, as well as
rapacious Marsupials, developed as three diverging branches out of the
common primary group of Primæval Marsupials. In a similar manner, on the
other hand, the rodent, leaping, and hoofed Marsupials have perhaps
arisen as three diverging branches out of the common herbivorous primary
group, that is, out of the Climbing Marsupials. Climbing and Primæval
Marsupials might, however, be two diverging branches of the common
primary forms of all Marsupials, that is, of the _Primary Marsupials_
(Prodidelphia), which originated during the older secondary period out
of Cloacal animals.

The third and last sub-class of mammals comprises the _Placental
animals_, or _Placentals_ (Monodelphia, or Placentalia). It is by far
the most important, comprehensive, and most perfect of the three
sub-classes; for the class includes all the known mammalia, with the
exception of Marsupials and Beaked animals. Man also belongs to this
sub-class, and has developed out of its lower members.

Placental animals, as their name indicates, are distinguished from all
other mammals, more especially by the formation of a so called
_placenta_. This is a very peculiar and remarkable organ, which plays
an exceedingly important part in nourishing the young one developing in
the maternal body. The placenta (also called after-birth) is a soft,
spongy, red body, which differs very much in form and size, but which
consists for the most part of an intricate network of veins and blood
vessels. Its importance lies in the exchange of substance between the
nutritive blood of the maternal womb, or uterus, and the body of the
germ, or embryo. (See vol. i. p. 298.) This very important organ is
developed neither in marsupials nor in beaked animals. But placental
animals are also distinguished from these two sub-classes by many other
peculiarities, thus more especially by the absence of marsupial bones,
by the higher development of the internal sexual organs, and by the more
perfect development of the brain, especially of the so-called callous
body or beam (_corpus callosum_), which, as the intermediate commissure,
or transverse bridge, connects the two hemispheres of the large brain
with each other. Placental animals also do not possess the peculiar
hooked process of the lower jaw which characterizes Marsupials. The
following classification (p. 246) of the most important characteristics
of the three sub-classes will best explain how Marsupials, in these
anatomical respects, stand midway between Cloacal and Placental animals.

Placental animals are more variously differentiated and perfected, and
this, moreover, in a far higher degree, than Marsupials, and they have,
on this account, long since been arranged into a number of orders,
differing principally in the formation of the jaws and feet. But what is
even of more importance than these, is the different development of the
placenta, and the manner of its connection with the maternal uterus.
For in the three lower orders of Placental animals, in Hoofed animals,
Whales, and Toothless animals, the peculiar spongy membrane, which is
called the _deciduous membrane_, or _decidua_, and which connects the
maternal and the fœtal portions of the placenta, does _not_ become
developed. This takes place exclusively in the seven higher orders of
Placental animals, and we may, therefore, according to Huxley, class
them in the main group of _Deciduata_, or animals with _decidua_. They
are contrasted with the three first-mentioned legions of indeciduous
animals, or _Indeciduata_.

But in the various orders of Placental animals the placenta differs not
only in important internal differences of structure, which are connected
with the absence or the presence of a decidua, but also in the external
form of the placenta itself. In the Indeciduata it consists, in most
cases, of numerous, single, scattered bunches or tufts of vessels, and
hence this group may be called _tufted placental animals_
(Villiplacentalia). In the Deciduata, however, the single tufts of
vessels are united into a cake, which appears in two different forms. In
the one case it surrounds the embryo in the form of a closed band or
ring, so that only the two poles of the oval egg bladder are free of
tufts; this is the case in animals of prey (Carnaria) and the
pseudo-hoofed animals (Chelophora), which may consequently be comprised
as _girdled-placental animals_ (Zonoplacentalia). In the other
Deciduata, to which man also belongs, the placenta is a simple round
disc, and we therefore call them _disc-placentals_ (Discoplacentalia).
This group includes the five orders of Semi-apes, Gnawing animals,
Insectivora, Bats, and Apes, from the latter of which, in the zoological
system, man cannot be separated.

It may be considered as quite certain, from reasons based upon their
comparative anatomy and their history of development, that Placental
animals first developed out of Marsupials, and that this very important
development—the first origin of the placenta—probably took place in the
beginning of the tertiary epoch, during the eocene period. But one of
the most difficult questions in the genealogy of animals is the
important consideration whether all Placental animals have arisen out of
one or out of several distinct branches of Marsupials; in other words,
whether the origin of the placenta occurred but once, or several times.

When, in my General Morphology, I for the first time endeavoured to
establish the pedigree of Mammals, I here, as in most cases, preferred
the monophyletic, or one-rooted, to the polyphyletic, or many-rooted,
hypothesis of descent. I assumed that all Placental animals were derived
from a single form of Marsupial animal, which, for the first time, began
to form a placenta. In this case the Villiplacentals, Zonoplacentals,
and Discoplacentals would perhaps have to be considered as three
diverging branches of the common primary form of Placentals, or it might
also be conceived that the two latter, the Deciduata, had developed only
at a later period out of the Indeciduata, which on their part had arisen
directly out of the Marsupials. However, there are also important
reasons for the alternative; namely, that several groups of Placentals,
differing from the beginning, arose out of several distinct groups of
Marsupials, so that the placenta itself was formed several times
independently. This opinion is maintained by Huxley, the most eminent
English zoologist, and by many others. In this case the Indeciduata and
the Deciduata would perhaps have to be considered as two completely
distinct groups; then the order of Hoofed animals, as the primary group
of the Indeciduata, might be supposed to have originated out of the
Marsupial hoofed animals (Barypoda). Among the Deciduata, on the other
hand, the order of Semi-apes, as the common primary form of the other
orders, might possibly have arisen out of Handed Marsupials (Pedimana).
But it is also conceivable that the Deciduata themselves have arisen out
of several different orders of Marsupials, Animals of Prey out of
Rapacious Marsupials, Gnawing animals out of Gnawing Marsupials,
Semi-apes out of Handed Marsupials, etc. As we do not at present possess
sufficient empiric material to solve this most difficult question, we
must leave it and turn our attention to the history of the different
orders of Placental animals, whose pedigree can often be very accurately
established in detail.

We must, as already remarked, consider the order of _Hoofed animals_
(Ungulata) as the primary group of the Indeciduata, or Tuft-placentals;
the two other orders, Whales and Toothless animals, developed out of
them, as two diverging groups, probably only at a later period, by
adaptation to very different modes of life. But it is also possible that
the animals poor in teeth (Edentata) may be of quite a different origin.

Hoofed animals are in many respects among the most important and the
most interesting Mammals. They distinctly show that a true understanding
of the natural relationship of animals can never be revealed to us
merely by the study of living forms, but in all cases only by an equal
consideration of their extinct and fossil blood-relations and ancestors.
If, as is usually done, only the living Hoofed animals are taken into
consideration, it seems quite natural to divide them into three entirely
distinct orders, namely: (1) Horses, or _Single-hoofed animals_
(Solidungula, or Equina); (2) Ruminating animals, or _Double-hoofed_
(Bisulca, or Ruminantia); and (3) Thick-skinned, or _Many-hoofed_
(Multungula, or Pachyderma). But as soon as the extinct Hoofed animals
of the tertiary period are taken into consideration—of which animals we
possess very numerous and important remains—it is seen that this
division, but more especially the limitation of the Thick-skinned
animals, is completely artificial, and that these three groups are
merely top branches lopped from the pedigree of Hoofed animals, which
are most closely connected by extinct intermediate forms. The one half
of the Thick-skinned animals—rhinoceroses, tapirs, and
palæotheria—manifest the closest relationships to horses, and have like
them odd-toed feet; whereas the other half of the Thick-skinned
animals—pigs, hippopotami, and anoplotheria—on account of their
double-toed feet are much more closely allied to ruminating animals than
to the former. Hence we must, in the first place, among Hoofed animals
distinguish the two orders of Paired-hoofs and Odd-hoofs, as two natural
groups, which developed as diverging branches out of the old tertiary
primary group of Primary Hoofed animals, or Prochela.

The order of _Odd-hoofed animals_ (Perissodactyla) comprises those
Ungulata in which the middle (or third) toe of the foot is much more
strongly developed than the others, so that it forms the actual centre
of the hoof. This order includes the very ancient, common, primary group
of all Hoofed animals, that is, the _Primary-hoofed animals_ (Prochela),
which are found in a fossil state in the oldest Eocene strata
(Lophiodon, Coryphodon, Pliolophus). Directly allied to this group is
that branch which is the actual primary form of the Odd-hoofed animals,
namely, the _Palæotheria_, fossils of which occur in the upper Eocene
and lower Miocene. Out of the Palæotheria, at a later period, the
rhinoceroses (Nasicornia) and rhinoceros-horses (Elasmotherida) on the
one hand, and the tapirs, lama-tapirs, and primæval horses, on the
other, developed as two diverging branches. The long since extinct
primæval horses, or Anchitheria, formed the transition from the
Palæotheria and tapirs to the Miocene horses, or hipparions, which are
closely allied to the genuine living horses.

The second main group of Hoofed animals, the order of _Pair-hoofed
animals_ (Artiodactyla), comprises those hoofed animals in which the
middle (third) and fourth toe of the foot are almost equally developed,
so that the space between the two forms the central line of the entire
foot. The order is divided into two sub-orders—the Pig-shaped and the
Cud-chewing, or Ruminating. The _Pig-shaped_ (Chœromorpha) comprise in
the first place the other branch of Primary-Hoofed-animals, the
_Anoplotheria_, which we consider as the common primary form of all
Pair-hoofed animals, or Artiodactyla (Dichobune, etc.). Out of the
Anoplotheria arose, as two diverging branches, the primæval swine, or
Anthracotheria, on the one hand, forming the transition to swine and
river-horses, and the Xiphodonta on the other hand, forming the
transition to Ruminating animals. The oldest _Ruminating animals_
(Ruminantia) are the Primæval Stags, or Dremotheria, out of which,
possibly, the stag-shaped (Elaphia), the hollow-horned (Cavicornia), and
camels (Tylopoda), have developed as three diverging branches. Yet these
latter are, in many respects, more allied to the Odd-hoofs than to the
genuine Pair-hoofs. The accompanying systematic survey on p. 252, will
show how the numerous families of Hoofed animals are grouped, in
correspondence with this genealogical hypothesis.

SYSTEMATIC SURVEY

_Of the Sections and Families of Hoofed Animals, or Ungulata._

(N.B. Those families that are extinct are marked with an asterisk.)

----------------+--------------------------------+------------------------+-------------------
_Orders_ | | |
_of_ | _Sections_ | _Families_ | _Systematic Name_
_Hoofed_ | _of_ | _of_ | _of_
_animals._ | _Hoofed Animals._ | _Hoofed Animals._ | _the Families._
----------------+----------------------------=---+------------------------+-------------------
I. { I. Primary Hoofed { 1. Lophiodonta 1. Lophiodontia*
=Odd-toed= { Animals.* { 2. Pliolophida 2. Pliolophida*
=Hoofed= { _Prochela_
=Animals= { { 3. Primary 3. Palæotherida*
{ { Odd-hoofs
+Ungulata+ { II. Tapir-shaped { 4. Lama-tapirs 4. Macrauchenida*
{ _Tapiromorpha_ { 5. Tapirs 5. Tapirida
+Perissodactyla+ { { 6. Rhinoceroses 6. Nasicornia
{ { 7. Rhinoceros-horses 7. Elasmotherida*
{
{ III. Single-hoofs { 8. Primæval 8. Anchitherida*
{ _Solidungula_ { horses
{ { 9. Horses 9. Equina

{ { 10. Primary 10. Anoplotherida*
{ { Pair-hoofs
{ { 11. Primæval 11. Anthracotherida*
{ IV. Pig-shaped { pigs
{ _Chœromorpha_ { 12. Pigs 12. Setigera
{ { 13. River horses 13. Obesa
{ { 14. Primæval 14. Xiphodontia*
{ { ruminants
{
{ { { {15. Primæval 15. Dremotherida*
{ { { { deer
II. { { A. Stag-shaped { a. {16. Pseudo 16. Tragulida
=Pair-toed= { { _Elaphia_ { { musk deer
=Hoofed= { { {
=Animals= { { { b. {17. Musk deer 17. Moschida
{ { { {18. Deer 18. Cervina
+Ungulata+ { { {
{ V. { { c. {19. Primæval 19. Sivatherida*
+Artiodactyla+ { Ruminating { { { giraffes
{ animals { { {20. Giraffes 20. Devexa
{ _Ruminantia_ {
{ { { {21. Primæval 21. Antilocaprina*
{ { { d. { gazelles
{ { { {22. Gazelles 22. Antilopina
{ { {
{ { B. Hollow-horned { {23. Goats 23. Caprina
{ { _Caricornia_ { e. {24. Sheep 24. Ovina
{ { { {25. Oxen 25. Bovina
{ {
{ { C. Pad-footed { 26. Lamas 26. Auchenida
{ { _Tylopoda_ { 27. Camels 27. Camelida

----------------------------------------------------------------

It is probable that the remarkable legion of _Whales_ (Cetacea)
originated out of Hoofed animals, which accustomed themselves
exclusively to an aquatic life, and thereby became transformed into the
shape of fish. Although these animals seem externally very like many
genuine Fish, yet they are, as even Aristotle perceived, genuine
Mammals. By their whole internal structure—in so far as it has not
become changed by adaptation to an aquatic life—they, of all known
Mammals, are most closely allied to Hoofed animals, and more especially
agree with them in the absence of the decidua and in the tufted
placenta. Even at the present day the river-horse (Hippopotamus)
constitutes a kind of transition form to the Sea Cows (Sirenia), and
from this it seems most probable that the extinct primary forms of the
Cetacea are most closely allied to the Sea Cows of the present day, and
that they developed out of Pair-hoofed animals, which were related to
the hippopotamus. Out of the order of _Herbivorous whales_
(Phycoceta)—to which the sea cows belong, and which accordingly, very
probably, contain the primary forms of the legion—the other order of
_Carnivorous whales_ (Sarcoceta) appears to have developed at a later
period. But Huxley thinks that these latter were of quite a different
origin, and that they arose out of the Carnaria through the Seals. Among
the Sarcoceta, the extinct gigantic Zeuglodonta (Zeugloceta)—whose
fossil skeletons some time ago excited great interest, it being thought
that they were “sea serpents”—are probably only a peculiarly developed
lateral branch of genuine whales (Autoceta), which comprise, besides the
colossal whalebone whales, the cachalot or spermaceti whales, dolphins,
narwhals, porpoises, etc.

The third legion of the Indeciduata, or Sparsi-placentalia, comprises
the strange group of the animals _poor in teeth_ (Edentata); it is
composed of the two orders of burrowers and sloths. The order of
_Burrowers_ (Effodientia) consists of the two sub-orders of _ant eaters_
(Vermilinguia), to which the scaled animals also belong, and the _girdle
animals_ (Cingulata), which were formerly represented by the gigantic
Glyptodons. The order of _Sloths_ (Tardigrada) consists of the two
sub-orders of the small, still living _dwarf sloths_ (Bradypoda), and
of the extinct unwieldy _giant sloths_ (Gravigrada). The enormous fossil
remains of these colossal herbivora suggest that the whole legion is
becoming extinct, and that the Edentata of the present day are but a
poor remnant of the mighty order of the diluvial period. The close
relations between the still living South American Edentata and the
extinct gigantic forms which are found beside the latter on the same
part of the globe, made such an impression upon Darwin on his first
visit to South America, that they even then suggested to him the
fundamental idea of the Theory of Descent. (See above, vol. i. p. 134.)
But it is precisely the genealogy of this legion which is most
difficult. The Edentata are perhaps nothing but a peculiarly developed
lateral branch of the Ungulata; but it may also be that their root lies
in quite another direction.

We now leave the first main group of Placental animals, the Indeciduata,
and turn to the second main group, namely, the Deciduata, or animals
with decidua, which are distinguished from the former by possessing a
deciduous membrane, or decidua, during their embryonal life. We here
meet with a very remarkable small group of animals, for the most part
extinct, and which probably were the old tertiary (or eocene) ancestors
of man. These are the Semi-apes, or Lemurs (Prosimiæ); these curious
animals are probably the but little changed descendants of the primæval
group of Placentalia which we have to consider as the common primary
form of all Deciduata. They have hitherto been classed together in the
same order with Apes which Blumenbach called Quadrumana (four-handed).
However, I regard them as entirely distinct from these, not merely
because they differ from all Apes, much more than do the most different
Apes from one another, but also because they comprise most interesting
transitional forms leading to the other orders of Deciduata. I conclude
from this that the few still living Semi-apes, which moreover differ
very much among one another, are the last surviving remnants of a
primary group now almost extinct, but which was at one time rich in
forms, and out of which all the other Deciduata (possibly with the
single exception of Beasts of Prey, and Pseudo-hoofed animals) have
developed as diverging branches. The old primary group of Semi-apes has
probably developed out of Handed or Ape-footed Marsupials (Pedimana),
which are surprisingly like them in the transformation of their hinder
feet into grasping hands. The primæval primary forms themselves (which
probably originated in the eocene period) are of course long since
extinct, as are also the greater portion of the transition-forms between
them and all the other orders of Deciduata. However, individual remnants
of the latter are preserved among the Semi-apes of the present day.
Among these, the remarkable Finger-animal of Madagascar (Chiromys
madagascariensis) constitutes the remnant of the group of the
Leptodactyla and the transition to Rodents. The strange flying lemur in
the South Sea and Sunda islands (Galeopithecus), the only remnant of the
group of Pteropleura, forms a perfect intermediate stage between
Semi-apes and Bats. The long-footed Semi-apes (Tarsius, Otolicnus)
constitute the last remnant of that primary branch (Macrotarsi) out of
which the Insectivora developed. The short-footed forms (Brachytarsi)
are the medium of connection between them and genuine Apes. The
Short-footed Semi-apes comprise the long-tailed Lemur, the short-tailed
Lichanotus, and the Stenops, the latter of which seems to be very
closely allied to the probable ancestors of man among the Semi-apes. The
short-footed as well as the long-footed Prosimiæ live widely distributed
over the islands of southern Asia and Africa, more especially in
Madagascar; some live also on the continent of Africa. No Semi-ape,
either living or in a fossil state, has as yet been found in America.
They all lead a solitary, nocturnal kind of life, and climb about on
trees. (Compare vol. i. p. 361.)

Among the six remaining orders of Deciduata, all of which are probably
derived from long since extinct Semi-apes, the order of _Gnawing
animals_ (Rodentia), which is rich in forms, has remained at the lowest
stage. Among these the _squirrel-like_ animals (Sciuromorpha) stand
nearest akin to the Pedimanous Marsupials. Out of this primary group the
_mouse-like_ animals (Myomorpha) and the _porcupine-like_ animals
(Hystricomorpha) developed probably as two diverging branches, the
former of which are directly connected with the squirrel-like animals,
by the eocene Myoxida, the latter by the eocene Psammoryctida. The
fourth sub-order, the _hare-like_ animals (Lagomorpha), probably
developed only at a later period out of one of the other three
sub-orders.

Very closely allied to the Rodentia is the remarkable order of
_Pseudo-hoofed animals_ (Chelophora). Of these there now live but two
genera, indigenous to Asia and Africa, namely, Elephants (Elephas), and
Rock Conies (Hyrax). Both have hitherto generally been classed among
real Hoofed animals, or Ungulata, with which they agree in the formation
of the feet. But an identical transformation of nails or claws into
hoofs occurs also in genuine Rodentia and in certain hoofed Rodentia
(Subungulata) which live exclusively in South America. Beside smaller
forms (for example, guinea pigs and gold hares) the Subungulata also
include the largest of all Rodentia, namely, the Capybara Rats, which
are about four feet in length. The Rock Conies, which are externally
very nearly akin to Rodents, especially to the hoofed Rodents, were
formerly classed among Rodentia by some celebrated zoologists, as an
especial sub-class (Lamnungia). Elephants, on the other hand, when not
classed among Hoofed animals, were generally considered as the
representatives of a special order which were called Trunked animals
(Proboscidea). But the formation of the placentas of Elephants and of
Hyrax agree in a remarkable manner, and are entirely distinct from those
of Hoofed animals. These latter never possess a decidua, whereas
Elephants and Hyrax are genuine Deciduata. Their placenta is indeed not
of the form of a disc, but of a girdle, as in the case of Animals of
Prey; it is very possible that the girdle-shaped placenta is but a
secondary development of the discoplacenta. Thus, then, it might be
thought that the Pseudo-hoofed animals have developed out of a branch of
the Rodentia, and in a similar manner perhaps the Carnivora out of a
branch of the Insectivora. At all events, Elephants and Hyrax in many
respects, especially in the formation of important skeletal parts, of
the limbs, etc., are more closely allied to the Rodentia, and more
especially to hoofed Rodentia, than to genuine Hoofed animals. Moreover
several extinct forms, especially the remarkable South American
Arrow-toothed animals (Toxodontia), stand in many respects midway
between Elephants and Rodentia. That the still living Elephants and
Hyrax are but the last survivors of a group of Pseudo-hoofed animals,
which was once rich in forms, is proved not only by the very numerous
fossil species of Elephants and Mastodon (some of which are even larger,
others also much smaller than the Elephants of the present day), but
also by the remarkable miocene _Dinotheria_ (Gonyognatha), between which
and their next kindred, the Elephants, there must be a long series of
unknown connecting intermediate forms. Taking all things into
consideration, the most probable hypothesis which can be established at
present as to the origin and the relationship of Elephants, Dinotheria,
Toxodon, and Hyrax is, that they are the last survivors of a group of
Pseudo-hoofed animals rich in forms, which developed out of the
Rodentia, and probably out of relatives of the Subungulata.

The order of _Insect Eaters_ (Insectivora) is a very ancient group, and
is next akin to the common extinct primary form of the Deciduata, as
well as to the Semi-apes of the present day. It has probably developed
out of Semi-apes which were closely allied to the Long-footed Lemurs
(Macrotarsi) of the present day. It is separated into two orders,
Menotyphla and Lipotyphla; the Menotyphla are probably the older of the
two, and are distinguished from the Lipotyphla by possessing an
intestinal cœcum, or typhlon. The Menotyphla include the climbing
Tupajas of the Sunda Isles, and the leaping Macroscelides of Africa. The
Lipotyphla are represented in our country by shrew mice, moles, and
hedgehogs. The Insectivora, in the formation of their jaws and their
mode of life, are nearly akin to Carnivora, but are, on the other hand,
by their discoplacentas and by their large seminal vesicles, allied to
Rodents.

It is probable that the order of _Rapacious animals_ (Carnaria)
developed out of a long since extinct branch of Insectivora, at the
beginning of the Eocene period. It is a natural group, very rich in
forms, but still of very uniform organization. The Rapacious animals are
sometimes also called Girdle-placentals (Zonoplacentals), although the
Pseudo-hoofed animals (Chelophora), in the same way, also deserve this
designation. But as the latter, in other respects, are more closely
allied to the Rodentia than to Carnaria, we have already discussed them
in connection with the former. Animals of prey are divided into two,
externally very different, but internally very closely related,
sub-orders, namely, Land animals of prey and Marine animals of prey. The
_Land animals of prey_ (Carnivora) comprise bears, dogs, cats, etc.,
whose pedigree can be approximately guessed at by means of many extinct
intermediate forms. The _Marine animals of prey_, or _Seals_
(Pinnipedia), comprise sea bears, sea dogs, sea lions, and walruses.
Although marine animals of prey appear externally very unlike land
animals of prey, yet by their internal structure, their jaw and their
peculiar girdle-shaped placenta, they are very nearly akin to them, and
have evidently originated out of a branch of them, probably out of a
kind of weasel (Mustelina). Even at the present day the fish otters
(Lutra), and still more so the sea otters (Enhydris), present a direct
form of transition to Seals, and clearly show how the bodies of land
Carnivora are transformed into the shape of a Seal, by adaptation to an
aquatic life, and how the steering fins of marine rapacious animals have
arisen out of the legs of the former. The latter consequently stand in
the same relation to the former as do the Whales to Hoofed animals
among the Indeciduata. In the same way as the river-horse at present
stands midway between the extreme branches of oxen and sea oxen, the sea
otter still forms a surviving intermediate stage between the widely
separated branches of dogs and sea dogs. In both cases the complete
transformation of the external form, consequent upon adaptation to
entirely different conditions of life, has not been able to efface the
solid foundation of the inherited internal peculiarities.

According to Huxley’s opinion, which has already been quoted, only the
Herbivorous Whales (Sirenia) are derived from Hoofed animals; on the
other hand, the Carnivorous Cetacea (Sarcoceta) are derived from the
marine animals of prey; the Zeuglodonts would form a transition between
the two latter. But in this case it would be difficult to understand the
close anatomical relations which exist between the Herbivorous and
Carnivorous Cetacea. The strange peculiarities in the internal and
external structure which so strikingly distinguish the two groups from
all other mammals would then have to be regarded only as _analogies_
(caused by the same kinds of adaptation), not as _homologies_
(transmitted from a common primary form). The latter, however, strikes
me as being by far the more probable, and hence I have left all the
Cetacea among the Indeciduata as one group of kindred origin.

The remarkable order of _Flying Mammals_, or _Bats_ (Chiroptera), stands
near to the Carnaria as well as to the Insectivora. It has become
strikingly transformed by adaptation to a flying mode of life, just as
marine animals of prey have become modified by adaptation to a swimming
mode of life. This order probably also originated out of the Semi-apes,
with which it is even at present closely allied, through the flying
lemurs (Galeopithecus). Of the two orders of flying animals, the
insect-eating forms, or _flying mice_ (Nycterides), probably developed
out of those eating fruits, or _flying foxes_ (Pterocynes); for the
latter are, in many ways, more closely allied to Semi-apes than are the
former.

We have now still to discuss the genuine Apes (Simiæ) as the last order
of Mammals; but as, according to the zoological system, the human race
belongs to this order, and as it undoubtedly developed historically out
of a branch of this order, we shall devote a special chapter to a more
careful examination of its pedigree and history.

CHAPTER XXII.

ORIGIN AND PEDIGREE OF MAN.

The Application of the Theory of Descent to Man.—Its Immense
Importance and Logical Necessity.—Man’s Position in the Natural
System of Animals, among Disco-placental Animals.—Incorrect
Separation of the Bimana and Quadrumana.—Correct Separation of
Semi-apes from Apes.—Man’s Position in the Order of
Apes.—Narrow-nosed Apes (of the Old World) and Flat-nosed Apes
(of America).—Difference of the two Groups.—Origin of Man from
Narrow-nosed Apes.—Human Apes, or Anthropoides.—African Human
Apes (Gorilla and Chimpanzee).—Asiatic Human Apes (Orang and
Gibbon).—Comparison between the different Human Apes and the
different Races of Men.—Survey of the Series of the Progenitors
of Man.—Invertebrate Progenitors (Prochordata) and Vertebrate
Progenitors.

Of all the individual questions answered by the Theory of Descent, of
all the special inferences drawn from it, there is none of such
importance as the application of this doctrine to Man himself. As I
remarked at the beginning of this treatise, the inexorable necessity of
the strictest logic forces us to draw the special deductive conclusion
from the general inductive law of the theory, that Man has developed
gradually, and step by step, out of the lower Vertebrata, and more
immediately out of Ape-like Mammals. That this doctrine is an
inseparable part of the Theory of Descent, and hence also of the
universal Theory of Development in general, is recognized by all
thoughtful adherents of the theory, as well as by all its opponents who
reason logically.

But if the doctrine be true, then the recognition of the animal origin
and pedigree of the human race will necessarily affect more deeply than
any other progress of the human mind the views we form of all human
relations, and the aims of all human science. It must sooner or later
produce a complete revolution in the conception entertained by man of
the entire universe. I am firmly convinced that in future this immense
advance in our knowledge will be regarded as the beginning of a new
period of the development of Mankind. It can only be compared to the
discovery made by Copernicus, who was the first who ventured distinctly
to express the opinion, that it was not the sun which moved round the
earth, but the earth round the sun. Just as the _geocentric conception_
of the universe—namely, the false opinion that the earth was the centre
of the universe, and that all its other portions revolved round the
earth—was overthrown by the system of the universe established by
Copernicus and his followers, so the _anthropocentric conception_ of the
universe—the vain delusion that Man is the centre of terrestrial nature,
and that its whole aim is merely to serve him—is overthrown by the
application (attempted long since by Lamarck) of the theory of descent
to Man. As Copernicus’ system of the universe was mechanically
established by Newton’s theory of gravitation, we see Lamarck’s theory
of descent attain its causal establishment by Darwin’s theory of
selection. This comparison, which is very interesting in many respects,
I have discussed in detail elsewhere.

In order to carry out this extremely important application of the Theory
of Descent to man, with the necessary impartiality and objectivity, I
must above all beg the reader (at least for a short time) to lay aside
all traditional and customary ideas on the “Creation of Man,” and to
divest himself of the deep-rooted prejudices concerning it, which are
implanted in the mind in earliest youth. If he fail to do this, he
cannot objectively estimate the weight of the scientific arguments which
I shall bring forward in favour of the animal derivation of Man, that
is, of his origin out of Ape-like Mammals. We cannot here do better than
imagine ourselves with Huxley to be the inhabitants of another planet,
who, taking the opportunity of a scientific journey through the
universe, have arrived upon the earth and have there met with a peculiar
two-legged mammal called Man, diffused over the whole earth in great
numbers. In order to examine him zoologically, we should pack a number
of the individuals of different ages and from different lands (as we
should do with the other animals collected on the earth) into large
vessels filled with spirits of wine, and on our return to our own planet
we should commence the comparative anatomy of all these terrestrial
animals quite objectively. As we should have no personal interest in
Man, in a creature so entirely different from ourselves, we should
examine and criticise him as impartially and objectively as we should
the other terrestrial animals. In doing this we should, of course, in
the first place refrain from all conjectures and speculations on the
nature of his soul, or on the spiritual side of his nature, as it is
usually called. We should occupy ourselves solely with his bodily
structure, and with that natural conception of it which is offered by
the history of his individual development.

It is evident that in order correctly to determine Man’s position among
the other terrestrial organisms we must, in the first place, follow the
guidance of the natural system. We must endeavour to determine the
position which belongs to Man in the natural system of animals as
accurately and distinctly as possible. We shall then, if in fact the
theory of descent be correct, be able from his position in the system to
determine the real primary relationship, and the degree of consanguinity
connecting Man with the animals most like him. The hypothetical pedigree
of the human race will then follow naturally as the final result of this
anatomical and systematic inquiry.

Now if, by means of comparative anatomy and ontogeny, we seek for man’s
position in that Natural System of animals which formed the subject of
the last two chapters, the incontrovertible fact will at once present
itself to us, that man belongs to the tribe, or phylum, of the
Vertebrata. Every one of the characteristics, which so strikingly
distinguish all the Vertebrata from all Invertebrata, is possessed by
him. It has also never been doubted that of all the Vertebrata the
Mammals are most closely allied to Man, and that he possesses all the
characteristic features distinguishing them from all other Vertebrata.
If then we further carefully examine the three different main groups or
sub-classes of Mammals—the inter-connections of which were discussed in
our last chapter—there cannot be the slightest doubt that Man belongs to
the Placentals, and shares with all other Placentals, the important
characteristics which distinguish them from Marsupials and from
Cloacals. Finally, of the two main groups of placental Mammals, the
Deciduata and the Indeciduata, the group of Deciduata doubtless includes
Man. For the human embryo is developed with a genuine decidua, and is
thus absolutely distinguished from all the Indeciduata. Among the
Deciduata we distinguish two legions, the Zonoplacentalia, with
girdle-shaped placenta (Beasts of Prey and Pseudo-hoofed animals), and
the Discoplacentalia, with disc-shaped placenta (all the remaining
Deciduata). Man possesses a disc-shaped placenta, like all
Discoplacentalia; and thus our next question must be, What is man’s
position in this group?

In the last chapter we distinguished the following five orders of
Discoplacentalia: (1) Semi-apes; (2) Rodents; (3) Insectivora; (4) Bats;
(5) Apes. The last of these five orders, that of Apes, is, as every one
knows, in every bodily feature far more closely allied to Man than the
four others. Hence the only remaining question now is, whether, in the
system of animals, Man is to be directly classed in the order of genuine
Apes, or whether he is to be considered as the representative of a
special sixth order of Discoplacentalia, allied to, but more advanced
than, that of the Apes.

Linnæus in his system classed Man in the same order with genuine Apes,
Semi-apes, and Bats, which he called _Primates_; that is, lords, as it
were the highest dignitaries of the animal kingdom. But Blumenbach, of
Göttingen, separated Man as a special order, under the name of _Bimana_,
or two-handed, and contrasted him with the Apes and Semi-apes under the
name of _Quadrumana_, or four-handed. This classification was also
adopted by Cuvier and, consequently, by most subsequent zoologists. It
was not until 1863 that Huxley, in his excellent work, the “Evidence as
to Man’s Place in Nature,”(26) showed that this classification was based
upon erroneous ideas, and that the so-called “four-handed” Apes and
Semi-apes are “two-handed” as much as man is himself. The difference
between the foot and hand does not consist in the _physiological_
peculiarity that the first digit or thumb is opposable to the four other
digits or fingers in the hand, and is not so in the foot, for there are
wild tribes of men who can oppose the first or large toe to the other
four, just as if it were a thumb. They can therefore use their “grasping
foot” as well as a so-called “hinder hand,” like Apes. The Chinese
boatmen row with this hinder hand, the Bengal workmen weave with it. The
Negro, in whom the big toe is especially strong and freely moveable,
when climbing seizes hold of the branches of the trees with it, just
like the “four-handed” Apes. Nay, even the newly born children of the
most highly developed races of men, during the first months of their
life, grasp as easily with the “hinder hand” as with the “fore hand,”
and hold a spoon placed in its clutch as firmly with their big toe as
with the thumb! On the other hand, among the higher Apes, especially the
gorilla, hand and foot are differentiated as in man. (Compare Plate IV.)

The essential difference between hand and foot is therefore not
physiological, but _morphological_, and is determined by the
characteristic structure of the bony skeleton and of the muscles
attached to it. The ankle-bones differ from the wrist-bones in
arrangement, and the foot possesses three special muscles not existing
in the hand (a short flexor muscle, a short extensor muscle, and a long
fibular muscle). In all these respects, Apes and Semi-apes entirely
agree with man, and hence it was quite erroneous to separate him from
them as a special order on account of the stronger differentiation of
his hand and foot. It is the same also with all the other structural
features by means of which it was attempted to distinguish Man from
Apes; for example, the relative length of the limbs, the structure of
the skull, of the brain, etc. In all these respects, without exception,
the differences between Man and the higher Apes are less than the
corresponding differences between the higher and the lower Apes. Hence
Huxley, for reasons based on the most careful and most accurate
anatomical comparisons, arrives at the extremely important
conclusion—“Thus, whatever system of organs be studied, the comparison
of their modifications in the Ape series leads to one and the same
result, that the structural differences which separate Man from the
Gorilla and Chimpanzee are not so great as those which separate the
Gorilla from the lower Apes.” In accordance with this, Huxley, strictly
following the demands of logic, classes Man, Apes, and Semi-apes in a
single order, _Primates_, and divides it into the following seven
families, which are of almost equal systematic value: (1) Anthropini
(Man); (2) Catarrhini (genuine Apes of the Old World); (3) Platyrrhini
(genuine American Apes); (4) Arctopitheci (American clawed Apes); (5)
Lemurini (short-footed and long-footed Semi-apes, p. 255); (6)
Chiromyini (p. 256); (7) Galeopithecini (Flying Lemurs, p. 256).

SYSTEMATIC SURVEY

_Of the Families and Genera of Apes._

-----------------+------------------------+---------------------+------------------
_Sections_ | _Families_ | _Genera_ | _Systematic Name_
_of_ | _of_ | _of_ | _of_
_Apes._ | _Apes._ | _Apes._ | _the Genera._
-----------------+------------------------+---------------------+------------------
I. APES OF THE NEW WORLD (+Hesperopitheci+), OR FLAT-NOSED APES (+Platyrrhini+).
-----------------------------------------------------------------------------------
A. =Platyrrhini= { I. Silky apes { 1. Brush ape 1. Midas
=with claws= { _Hapalida_ { 2. Lion ape 2. Jacchus
{
+Arctopitheci+ {

{ II. Flat-nosed, { 3. Squirrel ape 3. Chrysothrix
{ without prehensile { 4. Leaping ape 4. Callithrix
B. =Platyrrhini= { tail { 5. Nocturnal ape 5. Nyctipithecus
=with blunt= { _Aphyocerca_ { 6. Tail ape 6. Pithecia
=nails= {
{ III. Flat-nosed, { 7. Rolling ape 7. Cebus
+Dysmopitheci+ { with prehensile { 8. Climbing ape 8. Ateles
{ tail { 9. Woolly ape 9. Lagothrix
{ _Labidocerca_ { 10. Howling ape 10. Mycetes
----------------------------------------------------------------------------------
II. APES OF THE OLD WORLD (+Heopitheci+), OR NARROW-NOSED APES (+Catarrhini+).
----------------------------------------------------------------------------------
{ IV. Tailed Catarrhini, {
{ with { 11. Pavian 11. Cynocephalus
C. =Tailed= { cheek-pouches { 12. Macaque 12. Innus
=Catarrhini= { _Ascoparea_ { 13. Sea cat 13. Cercopithecus
{
+Menocerca+ { V. Tailed Catarrhini, {
{ without { 14. Holy ape 14. Semnopithecus
{ cheek-pouches { 15. Short ape 15. Colobus
{ _Anasca_ { 16. Nose ape 16. Nasalis

{ { 17. Gibbon 17. Hylobates
{ VI. Human apes { 18. Orang-Outan 18. Satyrus
D. =Tailless= { _Anthropoides_ { 19. Chimpanzee 19. Engeco
=Catarrhini= { { 20. Gorilla 20. Gorilla
{
+Lipocerca+ { VII. Men { 21. Ape-like man, 21. Pithecanthropus
{ _Erecti_ { or speechless man (Alalus)
{ (_Anthropi_) { 22. Talking man 22. Homo

----------------------------------------------------------------

If we wish to arrive at a natural system, and consequently at the
pedigree of the Primates, we must go a step further still, and entirely
separate the Semi-apes, or Prosimiæ, (Huxley’s last three families),
from Genuine Apes, or Simiæ (the first four families). For, as I have
already shown in my General Morphology, and explained in the last
chapter, the Semi-apes differ in many and important respects from
Genuine Apes, and in their individual forms are more closely allied to
the various other orders of Discoplacentalia. Hence the Semi-apes must
probably be considered as the remnants of the common primary group, out
of which the other orders of Discoplacentalia, and, it may be, all
Deciduata, have developed as two diverging branches. (Gen. Morph. ii.
pp. 148 and 153.) But man cannot be separated from the order of Genuine
Apes, or Simiæ, as he is in every respect more closely allied to the
higher Genuine Apes than the latter are to the lower Genuine Apes.

_Genuine Apes_ (Simiæ) are universally divided into two perfectly
natural groups, namely, the Apes of the New World, or American Apes, and
the Apes of the Old World, which are indigenous to Asia and Africa, and
which formerly also existed in Europe. These two classes differ
principally in the formation of the nose, and they have been named
accordingly. American Apes have flat noses, so that the nostrils are in
front, not below; hence they are called _Flat Noses_ (Platyrrhini). On
the other hand, the Apes of the Old World have a narrow cartilaginous
bridge, and the nostrils turned downwards, as in man; they are,
therefore, called _Narrow Noses_ (Catarrhini). Further, the jaw, which
plays an important part in the classification of Mammals, is essentially
distinct in these two groups. All Catarrhinæ, or Apes of the Old World,
have exactly the same jaws as Man, namely, in each jaw four incisors
above and below, then on each side a canine tooth and five cheek teeth,
of which two are pre-molars and three molars, altogether thirty-two
teeth. But all Apes of the New World, all Platyrrhini, have four more
cheek teeth, namely, three pre-molars and three molars on each side,
above and below: they consequently possess thirty-six teeth. Only one
small group forms an exception to this rule, namely, the _Arctopitheci_,
or _Clawed Apes_, in whom the third molar has degenerated, and they
accordingly have on each half of their jaw three pre-molars and two
molars. They also differ from the other Platyrrhini by having claws on
the fingers of their hands and the toes of their feet, not nails like
Man and the other Apes. This small group of South American Apes, which
includes among others the well-known pretty little Midas-monkey and the
Jacchus, must probably be considered only as a peculiarly developed
lateral branch of the Platyrrhini.

Now, if we ask what evidence can be drawn, as to the pedigree of Apes,
from the above facts, we must conclude that all the Apes of the New
World have developed out of one tribe, for they all possess the
characteristic jaw and the nasal formation of the Platyrrhini. In like
manner it follows that all the Apes of the Old World must be derived
from one and the same common primary form, which possessed the same
formation of nose and jaw as all the still living Catarrhini. Further,
it can scarcely be doubted that the Apes of the New World, taken as an
entire tribe, are either derived from those of the Old World, or (to
express it more vaguely and cautiously) both are diverging branches of
one and the same tribe of Apes. We also arrive at the exceedingly
important conclusion—which is of the utmost significance in regard to
Man’s distribution on the earth’s surface—that Man _has developed out
of the Catarrhini_. For we cannot discover a zoological character
distinguishing him in a higher degree from the allied Apes of the Old
World than that in which the most divergent forms of this group are
distinguished from one another. This is the important result of Huxley’s
careful anatomical examination of the question, and it cannot be too
highly estimated. The anatomical differences between Man and the most
human-like Catarrhini (Orang, Gorilla, Chimpanzee) are in every respect
less than the anatomical differences between the latter and the lowest
stages of Catarrhini, more especially the Dog-like Baboon. This
exceedingly important conclusion is the result of an impartial
anatomical comparison of the different forms of Catarrhini.

If, therefore, we recognise the natural system of animals as the guide
to our speculations, and establish upon it our pedigree, we must
necessarily come to the conclusion that _the human race is a small
branch of the group of Catarrhini, and has developed out of long since
extinct Apes of this group in the Old World_. Some adherents of the
Theory of Descent have thought that the American races of Men have
developed, independently of those of the Old World, out of American
Apes. I consider this hypothesis to be quite erroneous, for the complete
agreement of all mankind with the Catarrhini, in regard to the
characteristic formation of the nose and jaws, distinctly proves that
they are of the same origin, and that they developed out of a common
root after the Platyrrhini, or American Apes, had already branched off
from them. The primæval inhabitants of America, as is proved by numerous
ethnographical facts, immigrated from Asia, and partly perhaps from
Polynesia (or even from Europe).

There still exist great difficulties in establishing an accurate
pedigree of the Human Race; this only can we further assert, that the
nearest progenitors of man were tail-less Catarrhini (Lipocerca),
resembling the still living Man-like Apes. These evidently developed at
a late period out of tailed Catarrhini (Menocerca), the original form of
Ape. Of those tail-less Catarrhini, which are now frequently called
Man-like Apes, or Anthropoides, there still exist four different genera
containing about a dozen different species.

The largest Man-like Ape is the famous _Gorilla_ (called Gorilla engena,
or Pongo gorilla), which is indigenous to the tropics of western Africa,
and was first discovered by the missionary, Dr. Savage, in 1847, on the
banks of the river Gaboon. Its nearest relative is the _Chimpanzee_
(Engeco troglodytes, or Pongo troglodytes), also indigenous to western
Africa, but considerably smaller than the Gorilla, which surpasses man
in size and strength. The third of the three large Man-like Apes is the
_Orang_, or _Orang Outang_, indigenous to Borneo and the other Sunda
Islands, of which two kindred species have recently been distinguished,
namely, the large Orang (Satyrus orang, or Pithecus satyrus) and the
small Orang (Satyrus morio, or Pithecus morio). Lastly, there still
exists in southern Asia the genus _Gibbon_ (Hylobates), of which from
four to eight different species are distinguished. They are considerably
smaller than the three first-named Anthropoides, and in most
characteristics differ more from Man.

The tail-less Man-like Apes—especially since we have become more
intimately acquainted with the Gorilla, and its connection with Man by
the application of the Theory of Descent—have excited such universal
interest, and called forth such a flood of writings, that there is no
occasion for me here to enter into any detail about them. The reader
will find their relations to Man fully discussed in the excellent works
of Huxley,(26) Carl Vogt,(27) Büchner,(43) and Rolle.(28) I shall
therefore confine myself to stating the most important general
conclusion resulting from their thorough comparison with Man, namely,
that each one of the four Man-like Apes stands nearer to Man in one or
several respects than the rest, but that no one of them can in every
respect be called absolutely the most like Man. The Orang stands nearest
to Man in regard to the formation of the brain, the Chimpanzee in
important characteristics in the formation of the skull, the Gorilla in
the development of the feet and hands, and, lastly, the Gibbon in the
formation of the thorax.

Thus, from a careful examination of the comparative anatomy of the
Anthropoides, we obtain a similar result to that obtained by Weisbach,
from a statistical classification and a thoughtful comparison of the
very numerous and careful measurements which Scherzer and Schwarz made
of the different races of Men during their voyage in the Austrian
frigate _Novara_ round the earth. Weisbach comprises the final result of
his investigations in the following words: “_The ape-like
characteristics of Man_ are by no means concentrated in one or another
race, but are distributed in particular parts of the body, among the
different races, in such a manner that each is endowed with some
heirloom of this relationship—one race more so, another less, and even
we Europeans cannot claim to be entirely free from evidences of this
relationship.”[5]

I must here also point out, what in fact is self-evident, that not one
of all the still living Apes, and consequently not one of the so-called
Man-like Apes, can be the progenitor of the Human Race. This opinion, in
fact, has never been maintained by thoughtful adherents of the Theory of
Descent, but it has been assigned to them by their thoughtless
opponents. The Ape-like progenitors of the Human Race are long since
extinct. We may possibly still find their fossil bones in the tertiary
rocks of southern Asia or Africa. In any case they will, in the
zoological system, have to be classed in the group of _tail-less
Narrow-nosed Apes_ (Catarrhini Lipocerci, or Anthropoides).

The genealogical hypotheses, to which we have thus far been led by the
application of the Theory of Descent to Man, present themselves to every
clearly and logically reasoning person as the direct results from the
facts of comparative anatomy, ontogeny, and palæontology. Of course our
phylogeny can indicate only in a very general way the outlines of the
human pedigree. Phylogeny is the more in danger of becoming erroneous
the more rigorously it is applied in detail to special animal forms
known to us. However, we can, even now, with approximate certainty
distinguish at least the following twenty-two stages of the ancestors of
Man. Fourteen of these stages belong to the Vertebrata, and eight to the
Invertebrate ancestors of Man (Prochordata.)

THE CHAIN OF THE ANIMAL ANCESTORS, OR THE SERIES OF THE PROGENITORS, OF
MAN.

(Comp. Ch. XX., XXI.; Plate XIV. and p. 22.)

FIRST HALF OF THE SERIES OF THE ANCESTORS OF MAN.

INVERTEBRATE ANCESTORS OF MAN (Prochordata).

FIRST STAGE: +Monera+.

The most ancient ancestors of Man, as of all other organisms, were
living creatures of the simplest kind imaginable, _organisms without
organs_, like the still living Monera. They consisted of simple,
homogeneous, structureless and formless little lumps of mucous or
albuminous matter (protoplasm), like the still living Protamœba
primitiva. (Compare vol. i. p. 186, Fig. 1.) The _form value_ of these
most ancient ancestors of man was not even equal to that of a cell, but
merely that of a _cytod_ (compare vol. i. p. 347); for, as in the case
of all Monera, the little lump of protoplasm did not as yet possess a
cell-kernel. The first of these Monera _originated_ in the beginning of
the Laurentian period by _spontaneous generation_, or archigony, out of
so-called “inorganic combinations,” namely, out of simple combinations
of carbon, oxygen, hydrogen, and nitrogen. The assumption of this
spontaneous generation, that is, of a mechanical origin of the first
organisms from inorganic matter, has been proved in our thirteenth
chapter to be a necessary hypothesis. (Compare vol. i. p. 338.) A
direct _proof_ of the earlier existence of this most ancient ancestral
stage, based upon the fundamental law of biogeny, is possibly still
furnished by the circumstance that, according to the assertions of many
investigators, in the beginning of the development of the egg, the
cell-kernel, or nucleus, disappears, and the egg-cell thus relapses to
the lower stage of the cytod (Monerula, p. 124; _relapse_ of the
nucleated plastid into a non-nucleated condition). The assumption of
this first stage is necessary for most important general reasons.

SECOND STAGE: +Amœbæ+.

The second ancestral stage of Man, as of all the higher animals and
plants, is formed by _a simple cell_, that is, a little piece of
protoplasm enclosing a kernel. There still exist large numbers of
similar “single-celled organisms.” Among them the common, simple Amœbæ
(vol. i. p. 188, Fig. 2) cannot have been essentially different from
these progenitors. The _form value_ of every Amœba is essentially the
same as that still possessed by the egg of Man, and by the egg of all
other animals. (Vol. i. p. 189, Fig. 3.) The naked egg-cells of Sponges,
which creep about exactly like Amœbæ, cannot be distinguished from them.
The egg-cell of Man, which like that of most other animals is surrounded
by a membrane, resembles an enclosed Amœba. The first single-celled
animals of this kind arose out of Monera by the differentiation of the
inner kernel and the external protoplasm; they lived in the earlier
Primordial period. An irrefutable proof that such single-celled primæval
animals really existed as the direct ancestors of Man, is furnished
according to the fundamental law of biogeny (vol. i. p. 309) by the
fact that the human egg is nothing more than a simple cell. (Compare p.
124.)

THIRD STAGE: +Synamœbæ+.

In order to form an approximate conception of the organisation of those
ancestors of Man which first developed out of the single-celled Primæval
animals, it is necessary to trace the changes undergone by the human egg
in the beginning of its individual development. It is just here that
ontogeny guides us with the greatest certainty on to the track of
phylogeny. We have already seen that the egg of Man (in the same way as
that of all other Mammals), after fructification has taken place, falls
by self-division into a mass of simple and equi-formal Amœba-like cells
(vol. i. p. 190, Fig. 4 _D_). All these divided globules are at first
exactly like one another, naked cells containing a kernel, but without
covering; in many animals they show movements like those of the Amœbæ.
This ontogenetic stage of development which we called Morula (p. 125),
on account of its mulberry shape, is _a certain proof_ that in the early
primordial period there existed ancestors of man which possessed the
_form value_ of a mass of homogeneous, loosely connected cells. They may
be called a _community of Amœbæ_ (Synamœbæ). (Compare p. 127.) They
_originated_ out of the single-celled Primæval animals of the second
stage by repeated self-division and by the permanent union of the
products of this division.

FOURTH STAGE: +Ciliated Larva (Planæada)+.

In the course of the ontogenesis of most of the lower animals, and also
in that of the lowest Vertebrate animals, the Lanceolate Animals, or
Amphioxus, there first develops out of the Morula (Frontispiece, Fig. 3)
a ciliated larva (planula). Those cells, lying on the surface of the
homogeneous mass of cells, extend hair-like processes, or fringes of
hairs, which by striking against the water keep the whole body rotating.
The round many-celled body thus becomes differentiated, in that the
external cells covered with cilia differ from the non-ciliated internal
cells (Frontispiece, Fig. 4). In Man and in all other Vertebrate animals
(with the exception of the Amphioxus), as well as in all Arthropoda,
this stage of the ciliated larva has been lost, in the course of time,
by abbreviated inheritance. There must, however, have existed ancestors
of Man in the early Primordial period which possessed the form value of
these ciliated larvæ (Planæa, p. 125). A certain proof of this is
furnished by the Amphioxus, which is on the one hand related by blood to
Man, but on the other has retained down to the present day the stage of
the planula.

FIFTH STAGE: +Primæval Stomach Animals (Gastræada)+.

In the course of the individual development of Amphioxus, as well as in
the most different lower animals, there first arises out of the planula
the extremely important form of larva which we have named _stomach
larva_, or _gastrula_ (p. 126; Frontispiece, Fig. 5, 6). According to
the fundamental law of biogeny this gastrula proves the former existence
of an independent form of primæval animal of the same structure, and
this we have named primæval stomach animal, or Gastræa (pp. 127, 128).
These Gastræada must have existed during the older Primordial period,
and they must have also included the ancestors of man. A _certain
proof_ of this is furnished by the Amphioxus, which in spite of its
blood relationship to Man still passes through the stage of the gastrula
with a simple intestine and a double intestinal wall. (Compare Plate X.
Fig. _B 4_.)

SIXTH STAGE: +Gliding Worms (Turbellaria)+.

The human ancestors of the sixth stage which originated out of the
Gastræada of the fifth stage, were low worms, which, of all the forms of
worms known to us, were most closely allied to the Gliding Worms, or
Turbellaria, or at least upon the whole possessed their form value. Like
the Turbellaria of the present day, the whole surface of their body was
covered with cilia, and they possessed a simple body of an oval shape,
entirely without appendages. These acœlomatous worms did not as yet
possess a true body-cavity (cœlom) nor blood. They _originated_ in the
early primordial period out of the Gastræada, by the formation of a
middle germ-layer, or muscular layer, and also by the further
differentiation of the internal parts into various organs; more
especially the first formation of a nervous system, the simplest organs
of sense, the simplest organs for secretion (kidneys) and generation
(sexual organs). The proof that human ancestors existed of a similar
formation, is to be looked for in the circumstance that comparative
anatomy and ontogeny point to the lower acœlomatous Worms as the common
primary form, not merely of all higher Worms, but also of the four
higher tribes of animals. Now, of all the animals known to us, the
Turbellaria, which possess neither a body-cavity nor blood, are most
closely allied to these primæval acœlomatous Primary Worms.

SEVENTH STAGE: +Soft Worms (Scolecida)+.

Between the Turbellaria of the preceding stage and the Sack Worms of the
next stage, we must necessarily assume at least one connecting
intermediate stage. For the Tunicata, which of all known animals stand
nearest to the eighth stage, and the Turbellaria which most resemble the
sixth stage, indeed both belong to the lower division of the unsegmented
Worms; but still these two divisions differ so much from one another in
their organization, that we must necessarily assume the earlier
existence of extinct intermediate forms between the two. These
connecting links, of which no fossil remains exist, owing to the soft
nature of their bodies, we may comprise as _Soft Worms_, or Scolecida.
They developed out of the Turbellaria of the sixth stage by forming a
true body-cavity (a cœlom) and blood in their interior. It is difficult
to say which of the still living Cœlomati are nearest akin to these
extinct Scolecida; it may be the Acorn-worms (Balanoglossus). The proof
that even the direct ancestors of man belonged to these Scolecida, is
furnished by the comparative anatomy and the ontogeny of Worms and of
the Amphioxus. The form value of this stage must moreover have been
represented by several very different intermediate stages, in the wide
gap between Turbellaria and Tunicata.

EIGHTH STAGE: +Sack Worms (Himatega)+.

Under the name of Sack worms, or Himatega, we here allude in the eighth
place to those Cœlomati, out of which the most ancient skull-less
Vertebrata were directly developed. Among the Cœlomati of the present
day, the _Ascidians_ are the nearest relatives of these exceedingly
remarkable Worms, which connect the widely differing classes of
Invertebrate and Vertebrate animals. That the ancestors of man really
existed during the primordial period in the form of these Himatega, is
_distinctly proved_ by the exceedingly remarkable and important
agreement presented by the ontogeny of the Amphioxus and the Ascidia.
(Compare Plates XII. and XIII., also pp. 152, 200, etc.) From this fact
the earlier existence of Sack Worms may be inferred; they of all known
worms were most closely related to our recent Tunicates, especially to
the freely swimming young forms or larvæ of the simple Sea-squirts
(Ascidia, Phallusia). They originated out of the worms of the seventh
stage by the formation of a dorsal nerve-marrow (medulla tube), and by
the formation of the spinal rod (chorda dorsalis) which lies below it.
It is just the position of this central spinal rod, or axial skeleton,
between the dorsal marrow on the dorsal side, and the intestinal canal
on the ventral side, which is most characteristic of all Vertebrate
animals, including man, but also of the larvæ of the Ascidia. The form
value of this stage nearly corresponds with that which the larvæ of the
simple Sea-squirts possess at the time when they show the beginning of
the dorsal marrow and spinal rod. (Plate XII. Fig. _A 5_: compare the
explanation of these figures in the Appendix.)

SECOND HALF OF THE SERIES OF HUMAN ANCESTORS. VERTEBRATE ANIMAL
ANCESTORS OF MAN (Vertebrata).

NINTH STAGE: +Skull-less Animals (Acrania)+.

The series of human ancestors, which in accordance with their whole
organisation we have to consider as Vertebrate animals, begins with the
Skull-less animals, or Acrania, of whose nature the still living
Lancelet (Amphioxus lanceolatus, Plate XII. _B_, XIII. _B_) gives us a
faint idea. Since this little animal in its earliest embryonal state
entirely agrees with the Ascidia, and in its further development shows
itself to be a true Vertebrate animal, it forms a direct transition from
the Vertebrata to the Invertebrata. Even if the human ancestors of the
ninth stage in many respects differed from the Amphioxus—the last
surviving representative of the Skull-less animals—yet they must have
resembled it in its most essential characteristics, in the absence of
head, skull, and brain. Skull-less animals of such structure—out of
which animals with skulls developed at a later period—lived during the
primordial period, and originated out of the Himatega of the eighth
stage by the formation of the metamera, or body segments, as also by the
further differentiation of all organs, especially the more perfect
development of the dorsal nerve-marrow and the spinal rod lying below
it. Probably the separation of the two sexes (gonochorism) also began at
this stage, whereas all the previously mentioned invertebrate ancestors
(apart from the 3—4 first neutral stages) exhibited the condition of
hermaphrodites (hermaphroditism). (Compare vol. i. p. 196.) The _certain
proof_ of the former existence of these skull-less and brainless
ancestors of man, is furnished by the comparative anatomy and the
ontogeny of the Amphioxus and of the Craniota.

TENTH STAGE: +Single-nostriled Animals (Monorrhina)+.

Out of the Skull-less ancestors of man there arose in the first place
animals with skulls, or Craniota, of the most imperfect nature. The
lowest stage of all still living Craniota is occupied by the class of
round-mouthed animals, or Cyclostoma, namely, the Hag (Myxinoidea) and
Lampreys (Petromyzontia). From the internal organization of these
single-nostriled animals, or Monorrhina, we can form an approximate idea
of the nature of the human ancestors of the tenth stage. In the former,
as also in the latter, skull and brain must have been of the simplest
form, and many important organs, as for example, the swimming bladder,
the sympathetic nerve, the spleen, the jaw skeleton, and both pairs of
legs, may probably as yet not have existed. However, the pouch gills and
the round sucking mouth of the Cyclostoma must probably be looked upon
as purely adaptive characteristics, which did not exist in the
corresponding stage of ancestors. The single-nostriled animals
originated during the primordial period out of the skull-less animals by
the anterior end of the dorsal marrow developing into the brain, and the
anterior end of the dorsal chord into the skull. The _certain proof_
that such single-nostriled and jawless ancestors of man did exist, is
found in the “comparative anatomy of the Myxinoidea.”

ELEVENTH STAGE: +Primæval Fish (Selachii.)+.

Of all known Vertebrate animals, the ancestors of the Primæval Fish
probably showed most resemblance to the still living Sharks (Squalacei).
They _originated_ out of the single-nostriled animals by the division of
the single nostril into two lateral halves, by the formation of a
sympathetic nervous system, a jaw skeleton, a swimming bladder, and two
pairs of legs (breast fins or fore-legs, and ventral fins or hind-legs).
The internal organisation of this stage may probably, upon the whole,
have corresponded to the lowest species of Sharks known to us; the
swimming bladder was however more strongly developed; in the case of the
latter it exists only as a rudimentary organ. They _lived_ as early as
the Silurian period, as is proved by the fossil remains of sharks (teeth
and fin spines) from the Silurian strata. A _certain proof_ that the
Silurian ancestors of man and of all the other double-nostriled animals
were nearest akin to the Selachii, is furnished by the comparative
anatomy of the latter; it shows that the relations of organisation in
all Amphirrhina can be derived from those of the Selachii.

TWELFTH STAGE: +Mud Fish (Dipneusta)+.

Our twelfth ancestral stage is formed by Vertebrate animals which
probably possessed a remote resemblance to the still living Salamander
fish (Ceratodus, Protopterus, Lepidosiren, p. 212). They _originated_
out of the Primæval fish (probably at the beginning of the palæolithic,
or primary period) by adaptation to life on land, and by the
transformation of the swimming bladder into an air-breathing lung, and
of the nasal cavity (which now opened into the cavity of the mouth)
into air passages. The series of the ancestors of man which breathed air
through lungs began at this stage. Their organisation may probably in
many respects have agreed with that of the still living Ceratodus and
Protopterus, but at the same time may have been very different. They
probably lived at the beginning of the Devonian period. Their existence
is _proved_ by comparative anatomy, which shows the Dipneusta to be an
intermediate stage between the Selachii and Amphibia.

THIRTEENTH STAGE: +Gilled Amphibians (Sozobranchia)+.

Out of those Mud Fish, which we considered the primary forms of all the
Vertebrata which breathe through lungs, there developed the class of
Amphibia as the main line (pp. 205, 216). Here began the five-toed
formation of the foot (the Pentadactyla), which was thence transmitted
to the higher Vertebrata, and finally also to Man. The gilled Amphibians
must be looked upon as our most ancient ancestors of the class of
Amphibia; besides possessing lungs they retained throughout life regular
gills, like the still living Proteus and Axolotl (p. 218). They
_originated_ out of the Dipneusta by the transformation of the paddling
fins into five-toed legs, and also by the more perfect differentiation
of various organs, especially of the vertebral column. In any case they
existed about the middle of the palæolithic, or primary period, possibly
even before the Coal period; for fossil Amphibia are found in coal. The
_proof_ that similar gilled Amphibians were our direct ancestors, is
given by the comparative anatomy and the ontogeny of Amphibia and
Mammals.

FOURTEENTH STAGE: +Tailed Amphibians (Sozura)+.

Our amphibious ancestors which retained their gills throughout life,
were replaced at a later period by other Amphibia, which, by
metamorphosis, lost the gills which they had possessed in early life,
but retained the tail, as in the case of the salamanders and newts of
the present day. (Compare p. 218.) They _originated_ out of the gilled
Amphibians by accustoming themselves in early life to breathe only
through gills, and later in life only through lungs. They probably
existed even in the second half of the primary, namely, during the
Permian period, but possibly even during the Coal period. The _proof_ of
their existence lies in the fact that tailed Amphibians form a necessary
intermediate link between the preceding and succeeding stages.

FIFTEENTH STAGE: +Primæval Amniota (Protamnia)+.

The name Protamnion we have given to the primary form of the three
higher classes of Vertebrate animals, out of which the Proreptilia and
the Promammalia developed as two diverging branches (p. 222). It
_originated_ out of unknown tailed Amphibia by the complete loss of the
gills, by the formation of the amnion, of the cochlea, and of the round
window in the auditory organ, and of the organs of tears. It probably
originated in the beginning of the mesolithic or secondary period,
perhaps even towards the end of the primary, in the Permian period. The
_certain proof_ that it once existed lies in the comparative anatomy and
the ontogeny of the Amniota; for all Reptiles, Birds, and Mammals,
including Man, agree in so many important characteristics that they
must, with full assurance, be admitted to be the descendants of a
single common primary form, namely, of the Protamnion.

SIXTEENTH STAGE: +Primary Mammals (Promammalia)+.

We now find ourselves more at home with our ancestors. From the
sixteenth up to the twenty-second stage they all belong to the large and
well known class of Mammals, the confines of which we ourselves have as
yet not transgressed. The common, long since extinct and unknown primary
forms of all Mammalia, which we have named Promammalia, were at all
events, of all still living animals, of the class most closely related
to the Beaked animals, or Ornithostoma (Ornithorhynchus, Echidna, p.
233). They differed from the latter, however, by the teeth present in
their jaws. The formation of the beak in the Beaked animals of the
present day must be looked upon as an adaptive characteristic which
developed at a later period. The Promammalia arose out of the Protamnia
(probably only at the beginning of the secondary period, namely, in the
Trias) by various advances in their internal organisation, as also by
the transformation of the epidermal scales into hairs, and by the
formation of a mammary gland which furnished milk for the nourishment of
the young ones. The _certain proof_ that the Promammalia—inasmuch as
they are the common primary forms of all Mammals—also belong to our
ancestors, lies in the comparative anatomy and the ontogeny of Mammalia
and Man.

SEVENTEENTH STAGE: +Pouched Animals (Marsupialia)+.

The three sub-classes of Mammalia—as we have already seen—stand in such
a relation to one another that the Marsupials, both as regards their
anatomy and their ontogeny and phylogeny, form the direct transition
from the Monotrema to Placental animals (p. 247). Consequently, human
ancestors must also have existed among Marsupials. They _originated_ out
of the Monotrema—which include the primary Mammalia, or Promammalia—by
the division of the cloaca into the rectum and the urogenital sinus, by
the formation of a nipple on the mammary gland, and by the partial
suppression of the clavicles. The oldest Marsupials at all events
existed as early as the Jura period (perhaps even in the Trias); during
the Chalk period they passed through a series of stages preparing the
way for the origin of Placentalia. The certain proof of our derivation
from Marsupials—nearly akin to the still living opossum and kangaroo in
their essential inner structure—is furnished by the comparative anatomy
and the ontogeny of Mammalia.

EIGHTEENTH STAGE: +Semi-apes (Prosimiæ)+.

The small group of Semi-apes, as we have already seen, is one of the
most important and most interesting orders of Mammalia. It contains the
direct primary forms of Genuine Apes, and thus also of Man. Our Semi-ape
ancestors probably possessed only a very faint external resemblance to
the still living, short-footed Semi-apes (Brachytarsi), especially the
Maki, Indri, and Lori (p. 256). They _originated_ (probably at the
beginning of the Cenolithic, or Tertiary period) out of Marsupials of
Rat-like appearance by the formation of a placenta, the loss of the
marsupium and the marsupial bones, and by the higher development of the
commissures of the brain. The _certain proof_ that Genuine Apes, and
hence also our own race, are the direct descendants of Semi-apes, is to
be found in the comparative anatomy and the ontogeny of Placental
animals.

NINETEENTH STAGE: +Tailed Apes (Menocerca)+.

Of the two classes of Genuine Apes which developed out of the Semi-apes,
it is only the narrow-nosed, or Catarrhini, which are closely related by
blood to Man. Our older ancestors from this group probably resembled the
still living Nose-apes and Holy-apes (Semnopithecus), which possess jaws
and narrow noses like Man, but have a long tail, and their bodies
densely covered with hair (p. 271). The Tailed Apes with narrow noses
(Catarrhini Menocerci) _originated_ out of Semi-apes by the
transformation of the jaw, and by the claws on their toes becoming
changed into nails; this probably took place as early as the older
Tertiary period. The _certain proof_ of our derivation from Tailed
Catarrhini is to be found in the comparative anatomy and the ontogeny of
Apes and of Man.

TWENTIETH STAGE: +Man-like Apes (Anthropoides)+.

Of all still living Apes the large tail-less, narrow-nosed Apes, namely,
the Orang and Gibbon in Asia, the Gorilla and Chimpanzee in Africa, are
most nearly akin to Man. It is probable that these Man-like Apes, or
Anthropoides, originated during the Mid-tertiary period, namely, in the
Miocene period. They developed out of the Tailed Catarrhini of the
preceding stage—with which they essentially agree—by the loss of the
tail, the partial loss of the hairy covering and by the excessive
development of that portion of the brain just above the facial portion
of the skull. There do not exist direct human ancestors among the
Anthropoides of the present day, but they certainly existed among the
unknown extinct Human Apes of the Miocene period. The _certain proof_ of
their former existence is furnished by the comparative anatomy of
Man-like Apes and of Man.

TWENTY-FIRST STAGE: +Ape-like Men (Pithecanthropi)+.

Although the preceding ancestral stage is already so nearly akin to
genuine Men that we scarcely require to assume an intermediate
connecting stage, still we can look upon the speechless Primæval Men
(Alali) as this intermediate link. These Ape-like men, or
Pithecanthropi, very probably existed towards the end of the Tertiary
period. They originated out of the Man-like Apes, or Anthropoides, by
becoming completely habituated to an upright walk, and by the
corresponding stronger differentiation of both pairs of legs. The fore
hand of the Anthropoides became the human hand, their hinder hand became
a foot for walking. Although these Ape-like Men must not merely by the
external formation of their bodies, but also by their internal mental
development, have been much more akin to real Men than the Man-like Apes
could have been, yet they did not possess the real and chief
characteristic of man, namely, the articulate human language of words,
the corresponding development of a higher consciousness, and the
formation of ideas. The _certain proof_ that such Primæval Men without
the power of speech, or Ape-like Men, must have preceded men possessing
speech, is the result arrived at by an inquiring mind from comparative
philology (from the “comparative anatomy” of language), and especially
from the history of the development of language in every child (“glottal
ontogenesis”) as well as in every nation (“glottal phylogenesis”).

TWENTY-SECOND STAGE: +Men (Homines)+.

Genuine Men _developed_ out of the Ape-like Men of the preceding stage
by the gradual development of the animal language of sounds into a
connected or articulate language, of words. The development of this
function, of course, went hand in hand with the development of its
organs, namely, the higher differentiation of the larynx and the brain.
The transition from speechless Ape-like Men to Genuine or Talking Men
probably took place at the beginning of the Quaternary period, namely,
in the Diluvial period, but possibly even at an earlier date, in the
more recent Tertiary. As, according to the unanimous opinion of most
eminent philologists, all human languages are not derived from a common
primæval language, we must assume a polyphyletic origin of language, and
in accordance with this a polyphyletic transition from speechless
Ape-like Men to Genuine Men.

ANCESTRAL SERIES OF THE HUMAN PEDIGREE.

M N = Boundary between the Invertebrate and Vertebrate Ancestors.

---------------------------------------------------------------------------------------------------
_Epochs of the_ | _Geological Periods_ | _Animal_ | _Nearest Living_
_Organic_ | _of the_ | _Ancestral Stages_ | _Relatives of the_
_History of the_| _Organic History_ | _of_ | _Ancestral Stages._
_Earth._ | _of the Earth._ | _Man._ |
---------------------------------------------------------------------------------------------------
{ { 1. Monera { _Protogenes_
{ { (_Monera_) { _Protamœba_
{ {
{ { 2. Single-celled { Simple Amœbæ
{ { Primæval animals { (_Automœbæ_)
{ {
{ { 3. Many-celled { Communities of
{ { Primæval animals { Amœbæ
{ { { (_Synamœbæ_)
{ {
{ { 4. Ciliated planulæ { Planula larvæ
{ { (_Planæada_) {
I. { {
ARCHILITHIC { 1. Laurentian Period { 5. Primæval Intestinal { Gastrula larvæ
OR { { animals (_Gastræada_) {
{ 2. Cambrian Period {
PRIMORDIAL { { 6. Gliding Worms { _Rhabdocœla_
EPOCH { 3. Silurian Period { (_Turbellaria_) { _Dendrocœla_
{ {
{ { 7. Soft-worms { ?Between the Sea-squirts
{ { (_Scolecida_) { and Gliding worms
{ {
{ { 8. Sack worms { Sea-squirts
{ { (_Himatega_) { (_Ascidiæ_)
{ { M.................................................N
{ { 9. Skull-less { Lancelets
{ { (_Acrania_) { (_Amphioxi_)
{ {
{ { 10. Single-nostriled { Lampreys
{ { (_Monorrhina_) { (_Petromyzonta_)
{ (Compare p. 22, and {
{ Plate XIV. and its { 11. Primæval fish { Sharks
{ explanation.) { (_Selachii_) { (_Squalacei_)
---------------------------------------------------------------------------------------------------
{ 4. Devonian Period { 12. Salamander fish { Mud fish
II. { { (_Dipneusta_) { (_Protopteri_)
PALÆOLITHIC { 5. Coal Period {
OR { { 13. Gilled Amphibia { (_Proteus_)
{ 6. Permian Period { (_Sozobranchia_) { Axolotl (_Siredon_)
PRIMARY { {
EPOCH { { 14. Tailed Amphibia { Water-newts
{ { (_Sozura_) { (_Tritons_)
---------------------------------------------------------------------------------------------------
{ { 15. Primæval Amniota { ?Between the Tailed-Amphibia
III. { { (_Protamnia_) { and Primary
MESOLITHIC { 7. Trias Period { { mammals
OR { {
{ 8. Jura Period { 16. Primary Mammals { Beaked animals
SECONDARY { { (_Promammalia_) { (_Monotrema_)
EPOCH { 9. Chalk Period {
{ { 17. Pouched animals { Pouched rats
{ { (_Marsupialia_) { (_Didelphys_)
---------------------------------------------------------------------------------------------------
{ { 18. Semi-apes { Lori (_Stenops_)
{ { (_Prosimiæ_) { Maki (_Lemur_)
{ {
IV. { { 19. Tailed Narrow-nosed { Nose apes
CENOLITHIC { 10. Eocene Period { Apes { Holy apes
OR { {
{ 11. Miocene Period { 20. Men-like Apes or { Gorilla, Chimpanzee,
TERTIARY { { Tail-less Narrow-nosed { Orang,
EPOCH { 12. Pliocene Period { Apes { Gibbon
{ {
{ { 21. Speechless Men or { Deaf and Dumb,
{ { Ape-like Men { Cretins or
{ { { Microcephali
---------------------------------------------------------------------------------------------------
V. { { {
QUATERNARY { 13. Diluvial Period { 22. Talking Men { Australians and
EPOCH { 14. Alluvial Period { { Papuans

CHAPTER XXIII.

MIGRATION AND DISTRIBUTION OF MANKIND. HUMAN SPECIES AND HUMAN RACES.

Age of the Human Race.—Causes of its Origin.—The Origin of
Human Language.—Monophyletic or Single, Polyphyletic or
Multiple Origin of the Human Race.—Derivation of Man from many
Pairs.—Classification of the Human Races.—System of Twelve
Species of Men.—Woolly-haired Men, or Ulotrichis.—Bushy-haired
(Papuans, Hottentots).—Fleecy-haired (Caffres,
Negroes).—Straight-haired men, or Lissotrichi.—Stiff-haired
(Australians, Malays, Mongols, Arctic, and American
Tribes).—Curly-haired (Dravidas, Nubians, Midlanders).—Number
of Population.—Primæval Home of Man (South Asia, or
Lemuria).—Nature of Primæval Men.—Number of Primæval Languages
(Monoglottists and Polyglottists).—Divergence and Migration of
the Human Race.—Geographical Distribution of the Human Species.

The rich treasure of knowledge we possess in the comparative anatomy and
the history of the development of Vertebrate animals, enables us even
now to establish the most important outlines of the human pedigree in
the way we have done in the last chapter. One must, however, not expect
to be able to survey satisfactorily in every detail the history or
phylogeny of the human species which will henceforth form the basis of
Anthropology, and of all other sciences. The complete development of
this most important science—of which we can only lay the first
foundation—must remain reserved for the more accurate and extensive
investigations of a future time. This applies also to those more special
questions of human phylogeny at which it is desirable before concluding
to take a cursory glance, namely, the question of the time and place of
the origin of the human race, as also of the different species and races
into which it has differentiated.

In the first place, the period of the earth’s history, within which the
slow and gradual transmutation of the most man-like apes into the most
ape-like men took place, can of course not be determined by years, nor
even by centuries. This much can, however, with full assurance be
maintained, for reasons given in the last chapter, that Man is derived
from Placental animals. Now, as fossil remains of these Placentalia are
found only in the tertiary rocks, the human race can at the earliest
have developed only within the Tertiary period out of perfected man-like
apes. What seems most probable is that this most important process in
the history of terrestrial creation occurred towards the end of the
Tertiary period, that is in the Pliocene, perhaps even in the Miocene
period, but possibly also not until the beginning of the Diluvial
period. At all events Man, as such, lived in central Europe as early as
the Diluvial period, contemporaneously with many large, long since
extinct mammals, especially with the diluvial elephant, or mammoth
(Elephas primigenius), the woolly-haired rhinoceros (Rhinoceros
tichorrhinus), the giant deer (Cervus euryceros), the cave bear (Ursus
spelæus), the cave hyæna (Hyæna spelæa), the cave lion (Felis spelæus),
etc. The results brought to light by recent geology and archæology as to
these fossil men and their animal contemporaries of the diluvial period,
are of the greatest interest. But as a closer examination of them would
occupy too much of my limited space, I must confine myself here to
setting forth their great general importance, and refer for particulars
to the numerous writings which have recently been published on the
Primæval History of Man, more especially to the excellent works of
Charles Lyell,(30) Carl Vogt,(27) Friedrich Rolle,(28) John Lubbock,(44)
L. Büchner,(43) etc.

The numerous and interesting discoveries presented to us by these
extensive investigations of late years on the primæval history of the
human race, place the important fact (long since probable for many other
reasons) beyond a doubt, that the human race, as such, has existed for
more than twenty thousand years. But it is also probable that more than
a hundred thousand years, perhaps many hundred thousands of years, have
elapsed since its first appearance; and, in contrast to this, it must
seem very absurd that our calendars still represent the “Creation of the
World, according to Calvisius,” to have taken place 5821 years ago.

Now, whether we reckon the period during which the human race, as such,
has existed and diffused itself over the earth, as twenty thousand, a
hundred thousand, or many hundred thousands of years, the lapse of time
is in any case immensely small in comparison with the inconceivable
length of time which was requisite for the gradual development of the
long chain of human ancestors. This is evident even from the small
thickness of all Diluvial deposits in comparison with the Tertiary, and
of these again in comparison with the preceding deposits. (Compare p.
22.) But the infinitely long series of slowly and gradually developing
animal forms from the simplest Moneron to the Amphioxus, from this to
the Primæval Fish, from the Primæval Fish to the first Mammal, and
again, from the latter to Man, also require for their historical
development a succession of periods probably comprising many thousands
of millions of years. (Compare vol. i. p. 129.)

Those processes of development which led to the origin of the most
Ape-like Men out of the most Man-like Apes must be looked for in the two
adaptational changes which, above all others, are distinctive of Man,
namely, _upright walk_ and _articulate speech_. These two
_physiological_ functions necessarily originated together with two
corresponding _morphological_ transmutations, with which they stand in
the closest correlation, namely, the _differentiation of the two pairs
of limbs and the differentiation of the larynx_. The important
perfecting of these organs and their functions must have necessarily and
powerfully reacted upon the differentiation of the brain and the mental
activities dependent upon it, and thus have paved the way for the
endless career in which Man has since progressively developed, and in
which he has far outstripped his animal ancestors. (Gen. Morph. ii. p.
430.)

The first and earliest of these three great processes in the development
of the human organism probably was the _higher differentiation and the
perfecting of the extremities_ which was effected by the _habit of an
upright walk_. By the fore feet more and more exclusively adopting and
retaining the function of grasping and handling, and the hinder feet
more and more exclusively the function of standing and walking, there
was developed that contrast between the hand and foot which is indeed
not exclusively characteristic of man, but which is much more strongly
developed in him than in the apes most like men. This differentiation of
the fore and hinder extremities was, however, not merely most
advantageous for their own development and perfecting, but it was
followed at the same time by a whole series of very important changes in
other parts of the body. The whole vertebral column, and more especially
the girdle of the pelvis and shoulders, as also the muscles belonging to
them, thereby experienced those changes which distinguish the human body
from that of the most man-like apes. These transmutations were probably
accomplished long before the origin of articulate speech; and the human
race thus existed for long, with an upright walk and the characteristic
human form of body connected with it, before the actual development of
human language, which would have completed the second and the more
important part of human development. We may therefore distinguish a
special (21st) stage in the series of our human ancestors, namely,
Speechless Man (Alalus), or Ape-man (Pithecanthropus), whose body was
indeed formed exactly like that of Man in all essential characteristics,
but who did not as yet possess articulate speech.

The origin of _articulate language_, and the _higher differentiation and
perfecting of the larynx_ connected with it, must be looked upon as only
a later, and the most important stage in the process of the development
of Man. It was, doubtless, this process which above all others helped to
create the deep chasm between man and animal, and which also first
caused the most important progress in the mental activity and the
perfecting of the brain connected with it. There indeed exists in very
many animals a language for communicating sensations, desires, and
thoughts, partly a language of gestures, partly a language of feeling or
touch, partly a language of cries or sounds, but a real language of
words or ideas, a so-called “articulate” language, which by abstraction
changes sounds into words, and words into sentences, belongs, as far as
we know, exclusively to Man.

The origin of human language must, more than anything else, have had an
ennobling and transforming influence upon the mental life of Man, and
consequently upon his brain. The higher differentiation and perfecting
of the brain and mental life as its highest function developed in direct
correlation with its expression by means of speech. Hence, the highest
authorities in comparative philology justly see in the development of
human speech the most important process which distinguishes Man from his
animal ancestors. This has been especially set forth by August
Schleicher, in his treatise “On the Importance of Speech for the Natural
History of Man.”(34) In this relation we see one of the closest
connections between comparative zoology and comparative philology; and
here the theory of development assigns to the latter the task of
following the origin of language step by step. This task, as interesting
as it is important, has of late years been successfully undertaken by
many inquirers, but more especially by Wilhelm Bleek, who has been
occupied for seventeen years in South Africa with the study of the
languages of the lowest races of men, and hence has been enabled to
solve the question. August Schleicher more especially discusses, in
accordance with the theory of selection, how the various forms of
speech, like all other organic forms and functions, have developed by
the process of natural selection, and have divided into many species and
dialects.

I have no space here to follow the process of the formation of language,
and must refer in regard to this to the above-mentioned important work
of Wilhelm Bleek, “On the Origin of Language.”(35) But we have still to
mention one of the most important results of comparative philology,
which is of the highest importance to the genealogy of the human
species, that is, that _human language was probably of a multiple, or
polyphyletic origin_. Human speech, as such, did not develop probably
until the genus of Speechless or Primæval Man, or Ape Man, had
separated into several kinds or species. In each of these human species,
and perhaps even in the different sub-species and varieties of this
species, language developed freely and independently of the others. At
least Schleicher, one of the first authorities on the subject, maintains
that “even the beginnings of language—in sounds as well as in regard to
ideas and views which were reflected in sounds, and further, in regard
to their capability of development—must have been different. For it is
positively impossible to trace all languages to one and the same
primæval language. An impartial investigation rather shows that there
are as many primæval languages as there are races.”(34) In like manner,
Friederich Müller(41) and other eminent linguists assume a free and
independent origin of the families of languages and their primæval
stocks. It is well known, however, that the boundaries of these tribes
of languages and their ramifications are by no means always the
boundaries of the different human species, or the so-called “races,”
distinguished by us on account of their bodily characteristics. This,
as well as the complicated relations of the mixture of races, and the
various forms of hybrids, is the great difficulty lying in the way of
tracing the human pedigree in its individual branches, species, races,
varieties, etc.

In spite of these great and serious difficulties, we cannot here refrain
from taking one more cursory glance at the ramification of the human
pedigree, and at the same time considering, from the point of view of
the theory of descent, the much discussed question of the monophyletic
or polyphyletic origin of the human race, and its species or races. As
is well known, two great parties have for a long time been at war with
each other upon this question; the _monophylists_ (or monogenists)
maintain the unity of origin and the blood relationship of all races of
men. The _polyphylists_ (or polygenists), on the other hand, are of
opinion that the different races of men are of independent origin.
According to our previous genealogical investigations we cannot doubt
that, at least in a _wide sense_, the monophyletic opinion is the right
one. For even supposing that the transmutation of Man-like Apes into Men
had taken place several times, yet those Apes themselves would again be
allied by the one pedigree common to the whole order of Apes. The
question therefore would always be merely about a nearer or remoter
degree of blood relationship. In a _narrower sense_, on the other hand,
the polyphylist’s opinion would probably be right, inasmuch as the
different primæval languages have developed quite independently of one
another. Hence, if the origin of an articulate language is considered as
the real and principal act of humanification, and the species of the
human race are distinguished according to the roots of their language,
it might be said that the different races of men had originated,
independently of one another, by different branches of primæval,
speechless men directly springing from apes, and forming their own
primæval language. Still they would of course be connected further up or
lower down at their root, and thus all would finally be derived from a
common primæval stock.

While we hold the latter of these convictions, and while we for many
reasons believe that the different species of speechless primæval men
were all derived from a common ape-like human form, we do not of course
mean to say that _all men are descended from one pair_. This latter
supposition, which our modern Indo-Germanic culture has taken from the
Semitic myth of the Mosaic history of creation, is by no means tenable.
The whole of the celebrated dispute, as to whether the human race is
descended from a single pair or not, rests upon a completely false way
of putting the question. It is just as senseless as the dispute as to
whether all sporting dogs or all race-horses are descended from a single
pair. We might with equal justice ask whether all Germans or all
Englishmen are “descended from a single pair,” etc. A “first human
pair,” or “a first man,” has in fact never existed, any more than there
ever existed a first pair or a first individual of Englishmen, Germans,
race-horses, or sporting dogs. The origin of a new species, of course,
always results from an existing species, by a long chain of many
different individuals sharing the slow process of transformation.
Supposing that we had all the different pairs of Human Apes and Ape-like
Men before us—which belong to the true ancestors of the human race—it
would even then be quite impossible (without doing so most arbitrarily)
to call any one of these pairs of ape-like men “the first pair.” As
little can we derive each of the twelve races or species of men, which
we shall consider directly, from a “first pair.”

The difficulties met with in classifying the different races or species
of men are quite the same as those which we discover in classifying
animal and vegetable species. In both cases forms apparently quite
different are connected with one another by a chain of intermediate
forms of transition. In both cases the dispute as to what is a kind or a
species, what a race or a variety, can never be determined. Since
Blumenbach’s time, as is well known, it has been thought that mankind
may be divided into five races or varieties, namely: (1) the Ethiopian,
or black race (African negro); (2) the Malayan, or brown race (Malays,
Polynesians, and Australians); (3) the Mongolian, or yellow race (the
principal inhabitants of Asia and the Esquimaux of North America); (4)
the Americans, or red race (the aborigines of America); and (5) the
Caucasian, or white race (Europeans, north Africans, and south-western
Asiatics). All of these five races of men, according to the Jewish
legend of creation, are said to have been descended from “a single
pair”—Adam and Eve,—and in accordance with this are said to be varieties
of one kind or species. If, however, we compare them without prejudice,
there can be no doubt that the differences of these five races are as
great and even greater than the “specific differences” by which
zoologists and botanists distinguish recognised “good” animal and
vegetable species (“bonæ species”). The excellent palæontologist
Quenstedt is right in maintaining that, “if Negroes and Caucasians were
snails, zoologists would universally agree that they represented two
very excellent species, which could never have originated from one pair
by gradual divergence.”

The characteristics by which the races of men are gradually
distinguished are partly taken from the formation of the hair, partly
from the colour of the skin, and partly from the formation of the skull.
In regard to the last character, two extremes are distinguished, namely,
long heads and short heads. In _long-headed men_ (Dolichocephali), whose
strongest development is found in Negroes and Australians, the skull is
extended, narrow, and compressed on the right and left. In _short-headed
men_ (Brachycephali), on the other hand, the skull is compressed in an
exactly opposite manner, from the front to the back, is short and broad,
which is especially striking in the case of the Mongolians.
_Medium-headed men_ (Mesocephali), standing between the two extremes,
predominate especially among Americans. In every one of these three
groups we find men with _slanting teeth_ (Prognathi), whose jaws, like
those of the animal snout, strongly project, and whose front teeth
therefore slope in front, and men with _straight teeth_ (Orthognathi),
whose jaws project but little, and whose front teeth stand
perpendicularly. During the last ten years a great deal of time and
trouble have been devoted to the careful examination and measurement of
the forms of skulls, which have, however, not been rewarded by
corresponding results. For within a single species, as for example
within the Mediterranean species, the form of the skull may vary so much
that both extremes are met with in the same species. Much better
starting-points for the classification of the human species are
furnished by the nature of the hair and speech, because they are much
more strictly hereditary than the form of the skull.

Comparative philology seems especially to be becoming an authority in
this matter. In the latest great work on the races of men, which
Friederich Müller has published in his excellent “Ethnography,”(42) he
justly places language in the fore-ground. Next to it the nature of the
hair of the head is of great importance; for although it is in itself of
course only a subordinate morphological character, yet it seems to be
strictly transmitted within the race. Of the twelve species of men
distinguished on the following table (p. 308), the four lower species
are characterised by the woolly nature of the hair of their heads; every
hair is flattened like a tape, and thus its section is oval. These four
species of _woolly-haired men_ (Ulotrichi) we may reduce into two
groups—tuft-haired and fleecy-haired. The hair on the head of
_tuft-haired men_ (Lophocomi), Papuans and Hottentots, grows in
unequally divided small tufts. The woolly hair of _fleecy-haired men_
(Eriocomi), on the other hand, in Caffres and Negroes, grows equally all
over the skin of the head. All Ulotrichi, or woolly-haired men, have
slanting teeth and long heads, and the colour of their skin, hair, and
eyes is always very dark. All are inhabitants of the Southern
Hemisphere; it is only in Africa that they come north of the equator.
They are on the whole at a much lower stage of development, and more
like apes, than most of the Lissotrichi, or straight-haired men. The
Ulotrichi are incapable of a true inner culture and of a higher mental
development, even under the favourable conditions of adaptation now
offered to them in the United States of North America. No woolly-haired
nation has ever had an important “history.”

SYSTEMATIC SURVEY

_Of the 12 Species of Men and their 36 Races._

(Compare Plate XV.)

-------------------+--------------------------+----------------------------+-------------
_Species._ | _Races._ | _Home._ | _Immigrated_
| | | _from the_
-------------------+--------------------------+----------------------------+-------------
{ 1. =Papuan= { 1. Nigritos Malacca, Philippine West
{ +Homo Papua+ { Islands
{ { 2. New Guinea men New Guinea West
{ 2. =Hottentot= { 3. Melanesians Melanesia North-west
{ +Homo+ { 4. Tasmanians Van Diemen’s Land North-east
{ +Hottentottus+
{ { 5. Hottentots The Cape North-east
{ { 6. Bushmen The Cape North-east

{ 3. =Kaffre= { 7. Zulu Kaffres Eastern South Africa North
{ +Homo Cafer+ { 8. Beschuanas Central South Africa North-east
{ { 9. Congo Kaffres Western South Africa East
{
{ 4. =Negro= { 10. Tibu negroes Tibu district South-east
{ +Homo Niger+ { 11. Soudan negroes Soudan East
{ { 12. Senegambians Senegambia East
{ { 13. Nigritians Nigritia East
.......................................................................................

{ 5. =Australian= { 14. North Australians North Australia North
{ +H. Australis+ { 15. South Australians South Australia North
{
{ 6. =Malay= { 16. Sundanesians Sunda Archipelago West
{ +Homo Malayus+ { 17. Polynesians Pacific Archipelago West
{ { 18. Natives of Madagascar Madagascar East
{
{ 7. =Mongolian= { 19. Indo-Chinese Tibet, China South
{ +Homo+ { 20. Coreo-Japanese Corea, Japan South-west
{ +Mongolus+ { 21. Altaians } Central Asia, North Asia South
{ { 22. Uralians} North-western Asia, South-east
{ { Northern Europe,
{ { Hungary
{
{ 8. =Arctic Men= { 23. Hyperboreans Extreme N.E. of Asia South-west
{ +Homo Arcticus+ { 24. Esquimaux The extreme north of West
{ { America
{
{ 9. =American= { 25. North Americans North America North-west
{ +Homo+ { 26. Central Americans Central America North
{ +Americanus+ { 27. South Americans South America North
{ { 28. Patagonians The extreme south of North
{ { South America

{ 10. =Dravidas= { 29. Deccans Hindostan East?
{ +Homo Dravida+ { 30. Singalese Ceylon North?
{
{ 11. =Nubian= { 31. Dongolese Nubia East
{ +Homo Nuba+ { 32. Fulatians Fulu-land (Central East
{ { Africa)
{
{ 12. { 33. Caucasians Caucasus South-east
{ =Mediterranese= { 34. Basque Extreme north of Spain South?
{ +Homo+ { 35. Semites Arabia, North Africa, etc. East
{ +Mediterraneus+ { 36. Indo-germanic South-western Asia, South-east
{ { tribes Europe, etc.

----------------------------------------------------------------

In the eight higher races of men, which we comprise as _straight-haired_
(Lissotrichi), the hair of the head is never actually woolly, although
it is very much frizzled in some individuals. Every separate hair is
cylindrical (not like a tape), and hence its section is circular (not
oval).

The eight races of Lissotrichi may likewise be divided into two
groups—stiff-haired and curly-haired. _Stiff-haired men_ (Euthycomi),
the hair of whose heads is quite smooth and straight, and not frizzled,
include Australians, Malays, Mongolians, Arctic tribes, and Americans.
Curly-haired men, on the other hand, the hair of whose heads is more or
less curly, and in whom the beard is more developed than in all other
species, include the Dravidas, Nubians, and Mediterranean races.
(Compare Plate XV.)

Now, before we venture upon the attempt hypothetically to explain the
phyletic divergence of mankind, and the genealogical connection of its
different species, we will premise a short description of the twelve
named species and of their distribution. In order clearly to survey
their geographical distribution, we must go back some three or four
centuries, to the time when the Indian Islands and America were first
discovered, and when the present great mingling of species, and more
especially the influx of the Indo-Germanic race, had as yet not made
great progress. We begin with the lowest stages, with the woolly-haired
men (Ulotrichi), all of whom are prognathic Dolichocephali.

The _Papuan_ (Homo Papua), of all the still living human species, is
perhaps most closely related to the original primary form of
woolly-haired men. This species now inhabits only the large island of
New Guinea and the Archipelago of Melanesia lying to the east of it
(Solomon’s Islands, New Caledonia, the New Hebrides, etc.). But
scattered remnants of it are also still found in the interior of the
peninsula of Malacca, and likewise in many other islands of the large
Pacific Archipelago; mostly in the inaccessible mountainous parts of the
interior, and especially in the Philippine Islands. The but lately
extinct Tasmanians, or the natives of Van Diemen’s Land, belonged to
this group. From these and other circumstances it is clear that the
Papuans in former times possessed a much larger area of distribution in
south-eastern Asia. They were driven out by the Malays and forced
eastwards. The skin of all Papuans is of a black colour, sometimes more
inclining to brown, sometimes more to blue. Their woolly hair grows in
tufts, is spirally twisted in screws, and often more than a foot in
length, so that it forms a strong woolly wig, which stands far out from
the head. Their face, below the narrow depressed forehead, has a large
turned-up nose and thick protruding lips. The peculiar form of their
hair and speech so essentially distinguishes the Papuans from their
straight-haired neighbours, from the Malays as well as from the
Australians, that they must be regarded as an entirely distinct species.

Closely related to the Papuans by the tufted growth of hair, but
geographically widely separated from them, are the _Hottentots_ (Homo
Hottentottus). They inhabit exclusively the southernmost part of Africa,
the Cape and the adjacent parts, and have immigrated there from the
north-east. The Hottentots, like their original kinsmen the Papuans,
occupied in former times a much larger area (probably the whole of
Eastern Africa), and are now approaching their extinction. Besides the
genuine Hottentots—of whom there now exist only the two tribes of the
Coraca (in the eastern Cape districts) and the Namaca (in the western
portion of the Cape)—this species also includes the Bushmen (in the
mountainous interior of the Cape). The woolly hair of all Hottentots
grows in tufts, like brushes, as in the case of Papuans. Both species
also agree in the posterior part of the body, in the female sex being
specially inclined to form a great accumulation of fat (Steatopygia).
But the skin of Hottentots is much lighter, of a yellowish brown colour.
Their very flat face is remarkable for its small forehead and nose, and
large nostrils. The mouth is very broad with big lips, the chin small
and pointed. Their speech is characterised by several quite peculiar
guttural sounds.

The next neighbours and kinsmen of Hottentots are _Kaffres_ (Homo
Cafer). This woolly-haired human species is, however, distinguished,
like the following one (the genuine Negro), from Hottentots and Papuans
by the woolly hair not being divided into tufts, but covering the head
as a thick fleece. The colour of their skin varies through all shades,
from the yellowish black of the Hottentot to the brown black or pure
black of the genuine Negro. While in former times the race of Kaffres
was assigned to a very small area of distribution, and was generally
looked upon only as a variety of the genuine Negro, this species is now
considered to include almost the whole of the inhabitants of equatorial
Africa, from the 20th degree south latitude to the 4th degree north;
consequently, all South Africans, with the exception of the Hottentots.
They include especially the inhabitants of the Zulu, Zambesi, and
Mozambique districts on the east coast, the large human families of the
Beschuans or Setschuans in the interior, and the Herrero and Congo
tribes of the west coast. They too, like the Hottentots, have immigrated
from the north-east. Kaffres, who were usually classed with Negroes,
differ very essentially from them by the formation of their skull and by
their speech. Their face is long and narrow, their forehead high, and
their nose prominent and frequently curved, their lips not so
protruding, and their chin pointed. The many languages of the different
tribes of Kaffres can all be derived from an extinct primæval language,
namely, from the Bantu language.

The genuine _Negro_ (Homo Niger)—when Kaffres, Hottentots, and Nubians
are separated from him—at present forms a much less comprehensive human
species than was formerly supposed. They now only include the Tibus, in
the eastern parts of the Sahara; the Sudan people, or Sudians, who
inhabit the south of that large desert; also the inhabitants of the
Western Coast of Africa, from the mouth of the Senegal in the north, to
beyond the estuary of the Niger in the south (Senegambians and
Nigritians). Genuine Negroes are accordingly confined between the
equator and the Tropic of Capricorn, and only a small portion of the
Tibu tribe in the east have gone beyond this boundary. The Negro species
has spread within this zone, coming from the east. The colour of the
skin of genuine negroes is always more or less of a pure black. Their
skin is velvety to the touch, and characterised by a peculiar offensive
exhalation. Although Negroes agree with Kaffres in the formation of the
woolly hair of the head, yet they differ essentially in the formation of
their face. Their forehead is flatter and lower, their nose broad and
thick, not prominent, their lips large and protruding, and their chin
very short. Genuine Negroes are moreover distinguished by very thin
calves and very long arms. This species of men must have branched into
many separate tribes at a very early period, for their numerous and
entirely distinct languages can in no way be traced to one primæval
language.

To the four woolly-haired species of men just discussed, straight-haired
men (Homines Lissotrichi) stand in strong contrast, as another main
branch of the genus. Five of the eight species of the latter, as we have
seen, can be comprised as stiff-haired (Euthycomi) and three as
curly-haired (Euplocomi). We shall in the first place consider the
former, which includes the primæval inhabitants of the greater part of
Asia and the whole of America.

The lowest stage of all straight-haired men, and on the whole perhaps of
all the still living human species, is occupied by the _Australian_, or
_Austral-negro_ (Homo Australis). This species seems to be exclusively
confined to the large island of Australia; it resembles the genuine
African Negro by its black or brownish black hair, and the offensive
smell of the skin, by its very slanting teeth and long-headed form of
skull, the receding forehead, broad nose, protruding lips, and also by
the entire absence of calves. On the other hand Australians differ from
genuine Negroes as well as from their nearest neighbours the Papuans, by
the much weaker and more delicate structure of their bones, and more
especially by the formation of the hair of their heads, which is not
woolly and frizzled, but either quite lank or only slightly curled. The
very low stage of bodily and mental development of the Australian is
perhaps not altogether original, but has arisen by degeneration, that
is, by adaptation to the very unfavourable conditions of existence in
Australia. They probably immigrated to their present home from the north
or north-west, as a very early offshoot of the Euthycomi. They are
probably more closely related to the Dravidas, and hence to the
Euplocomi, than the other Euthycomi. The very peculiar language of the
Australians is broken up into numerous small branches, which are grouped
into a northern and a southern class.

The _Malay_ (Homo Malayus), the brown race of ethnographers, although
not a large species, is important in regard to its genealogy. An extinct
south Asiatic human species, very closely related to the Malays of the
present day, must probably be looked upon as the common primary form of
this and the following higher human species. We will call this
hypothetical primary species, Primæval Malays, or Promalays. The Malays
of the present day are divided into two widely dispersed races, the
_Sundanesians_, who inhabit Malacca, the Sunda Islands (Sumatra, Java,
Borneo, etc.) and the Philippine Islands, and the _Polynesians_, who are
dispersed over the greater portion of the Pacific Archipelago. The
northern boundary of their wide tract of distribution is formed on the
east by the Sandwich Islands (Hawai), and on the west by the Marian
Islands (Ladrones); the southern boundary on the east is formed by the
Mangareva Archipelago, and on the west by New Zealand. The inhabitants
of Madagascar are an especial branch of Sundanesians who have been
driven to the far west. This wide pelagic distribution of the Malays is
explained by their partiality for nautical life. Their primæval home is
the south-eastern portion of the Asiatic continent, from whence they
spread to the east and south, and drove the Papuans before them. The
Malays, in the formation of body, are nearest akin to the Mongols, but
are also nearly allied to the curly-haired Mediterranese. They are
generally short-headed, more rarely medium-headed, and very rarely
long-headed. Their hair is black and stiff, but frequently somewhat
curled. The colour of their skin is brown, sometimes yellowish, or of a
cinnamon colour, sometimes reddish or copper brown, more rarely dark
brown. In regard to the formation of face, Malays in a great measure
form an intermediate stage between the Mongols and the Mediterranese;
they can frequently not be distinguished from the latter. Their face is
generally broad, with prominent nose and thick lips, the opening for
their eyes not so narrowly cut and slanting as in Mongols. The near
relationship between all Malays and Polynesians is proved by their
language, which indeed broke up at an early period into many small
branches, but still can always be traced to a common and quite peculiar
primæval language.

The _Mongol_ (Homo Mongolus) is, next to the Mediterranese, the richest
in individuals. Among them are all the inhabitants of the Asiatic
Continent, excepting the Hyperboreans in the north, the few Malays in
the south-east (Malacca), the Dravidas in Western India, and the
Mediterranese in the south-west. In Europe this species of men is
represented by the Fins and Lapps in the north, by the Osmanlis in
Turkey, and the Magyars in Hungary. The colour of the Mongol is always
distinguished by a yellow tone, sometimes a light pea green, or even
white, sometimes a darker brownish yellow. Their hair is always stiff
and black. The form of their skull is, in the great majority of cases,
decidedly short (especially in Kalmucks, Baschkirs, etc.) but frequently
of medium length (Tartars, Chinese, etc.) But among them we never meet
with genuine long-headed men. The narrow openings of their eyes, which
are generally slanting, their prominent cheek bones, broad noses, and
thick lips are very striking, as well as the round form of their faces.
The language of the Mongols is probably traceable to a common primæval
language; but the monosyllabic languages of the Indo-Chinese races, and
the polysyllabic languages of the other Mongol races, stand in contrast
as two main branches which separated at an early time. The monosyllabic
tribes of the Indo-Chinese include the Tibetans, Birmans, Siamese, and
Chinese. The other polysyllabic Mongols are divided into three races,
namely: (1) the Coreo-Japanese (Coreans and Japanese); (2) the Altaians
(Tartars, Kirgises, Kalmucks, Buriats, Tungusians); and (3) the Uralians
(Samoiedes, Fins). The Magyars of Hungary are descended from the Fins.

The _Polar men_ (Homo Arcticus) must be looked upon as a branch of the
Mongolian human species. We comprise under this name the inhabitants of
the Arctic Polar lands of both hemispheres, the Esquimaux (and
Greenlanders) in North America, and the Hyperboreans in north-eastern
Asia (Jukagirs, Tschuksches, Kuriaks, and Kamtschads). By adaptation to
the Polar climate, this human race has become so peculiarly transformed
that it may be considered as a distinct species. Their stature is low
and of a square build; the formation of their skull of medium size or
even long; their eyes narrow and slanting like the Mongols; their
cheek-bones prominent, and their mouth wide. Their hair is stiff and
black; the colour of their skin is of a light or dark brown tinge,
sometimes more inclined to white or to yellow, like that of the Mongols,
sometimes more to red, like that of the Americans. The languages of
Polar men are as yet little known, but they differ both from the
Mongolian and from the American. Polar men must probably be regarded as
a remnant and a peculiarly adapted branch of that tribe of Mongols which
emigrated from north-eastern Asia to North America, and populated that
part of the earth.

At the time of the discovery of America, that part of the earth was
peopled (setting aside the Esquimaux) only by a single human species,
namely, by the _Redskins_, or _Americans_ (Homo Americanus). Of all
other human species they are most closely related to the two preceding.
The form of their skull is generally a medium one, rarely short or
long-headed. Their forehead broad and very low; their nose large,
prominent, and frequently aquiline; their cheek-bones prominent; their
lips rather thin than thick. The colour of their skin is characterised
by a red fundamental tint, which is, however, sometimes pure copper-red,
or light red, sometimes a deeper reddish brown, yellow brown or olive
brown. The numerous languages of the various American races and tribes
are extremely different, yet they agree in their original foundation.
Probably America was first peopled from north-eastern Asia by the same
tribe of Mongols from whom the Polar men (Hyperboreans and Esquimaux)
have also branched. This tribe first spread in North America, and from
thence migrated over the isthmus of Central America down to South
America, at the extreme south of which the species degenerated very
much by adaptation to the very unfavourable conditions of existence. But
it is also possible that Mongols and Polynesians immigrated from the
west and mixed with the former tribe. In any case the aborigines of
America came over from the Old World, and did not, as some suppose, in
any way originate out of American apes. Catarrhini, or Narrow-nosed
Apes, never at any period existed in America.

The three human species still to be considered—the Dravidas, Nubians,
and Mediterranese—agree in several characteristics which seem to
establish a close relationship between them, and distinguish them from
the preceding species. The chief of these characteristics is the strong
development of the beard, which in all other species is either entirely
wanting or but very scanty. The hair of their heads is generally not so
lank and smooth as in the five preceding species, but in most cases more
or less curly. Other characteristics also seem to favour our classing
them in one main group of curly-haired men (Euplocomi).

The _Dravida man_ (Homo Dravida) seems to stand very near the common
primary form of the Euplocomi, and perhaps of Lissotrichi. At present
this primæval species is only represented by the Deccan tribes in the
southern part of Hindostan, and by the neighbouring inhabitants of the
mountains on the north-east of Ceylon. But in earlier times this race
seems to have occupied the whole of Hindostan, and to have spread even
further. It shows, on the one hand, traits of relationship to the
Australians and Malays; on the other, to the Mongols and Mediterranese.
Their skin is either of a light or dark brown colour; in some tribes, of
a yellowish brown, in others, almost black brown. The hair of their
heads, as in Mediterranese, is more or less curled, neither quite
smooth, like that of the Euthycomi, nor actually woolly, like that of
the Ulotrichi. The strong development of the beard is also like that of
the Mediterranese. The oval form of face seems partly to be akin to that
of the Malays, partly to that of the Mediterranese. Their forehead is
generally high, their nose prominent and narrow, their lips slightly
protruding. Their language is now very much mixed with Indo-Germanic
elements, but seems to have been originally derived from a very peculiar
primæval language.

The _Nubian_ (Homo Nuba) has caused ethnographers no fewer difficulties
than the Dravida species. By this name we understand not merely the real
Nubians (Schangallas, or Dongolese), but also their near kinsmen, the
Fulas, or Fellatas. The real Nubians inhabit the countries of the Upper
Nile (Dongola, Schangalla, Barabra, Cordofan); the Fulas, or Fellatas,
on the other hand, have thence migrated far westward, and now inhabit a
broad tract in the south of the western Sahara, hemmed in between the
Soudanians in the north and the Nigritos in the south. The Nubian and
Fula races are generally either classed with negroes or with the Hamitic
races (thus with Mediterranese), but are so essentially different from
both that they must be regarded as a distinct species. In former times
they very probably occupied a large part of north-eastern Africa. The
skin of the Nubian and Fula races is of a yellowish or reddish brown
colour, more rarely dark brown or approaching to black. Their hair is
not woolly but curled, frequently even quite smooth; its colour is dark
brown or black. Their beard is much more strongly developed than in
negroes. The oval formation of their faces approaches more to the
Mediterranean than to the Negro type. Their forehead is high and broad,
their nose prominent and not flat, their lips not so protruding as in
the negro. The language of the Nubian races seems to possess no
relationship to those of genuine negroes.

The _Caucasian_, or _Mediterranean man_ (Homo Mediterraneus), has from
time immemorial been placed at the head of all races of men, as the most
highly developed and perfect. It is generally called the Caucasian race,
but as among all the varieties of the species, the Caucasian branch is
the least important, we prefer the much more suitable appellation
proposed by Friedrich Müller, namely, that of Mediterranean, or Midland
men. For the most important varieties of this species, which are
moreover the most eminent actors in what is called “Universal History,”
first rose to a flourishing condition on the shores of the
Mediterranean. The former area of the distribution of this species is
expressed by the name of “Indo-Atlantic” species, whereas at present it
is spread over the whole earth, and is overcoming most of the other
species in the struggle for existence. In bodily as well as in mental
qualities, no other human species can equal the Mediterranean. This
species alone (with the exception of the Mongolian) has had an actual
history; it alone has attained to that degree of civilization which
seems to raise man above the rest of nature.

The characteristics which distinguish the Mediterranean from the other
species of the race are well known. The chief of the external features
is the light colour of the skin, which however exhibits all shades, from
pure white or reddish white, through yellow or yellowish brown to dark
brown or even black brown. The growth of the hair is generally strong,
the hair of the head more or less curly, the hair of the beard stronger
than in any of the other species. The form of the skull shows a great
development in breadth; medium heads predominate upon the whole, but
long and short heads are also widely distributed. It is only in this one
species of men that the body as a whole attains that symmetry in all
parts, and that equal development, which we call the type of perfect
human beauty. The languages of all the races of this species can by no
means be traced to a single common primæval language; we must at least
assume four radically different primæval languages. In accordance with
this we must also assume within this one species four different races,
which are only connected at their root. Two of these races, the Basques
and Caucasians, now exist only as small remnants. The Basques, which in
earlier times peopled the whole of Spain and the south of France, now
inhabit but a narrow tract of land on the northern coast of Spain, on
the Bay of Biscay. The remnant of the Caucasian race (the Daghestans,
Tschercassians, Mingrelians, and Georgians) are now confined to the
districts of Mount Caucasus. The language of the Caucasians as well as
that of the Basques is entirely peculiar, and can be traced neither to
the Semitic nor to the Indo-Germanic primæval languages.

Even the languages of the two principal races of the Mediterranean
species—the Semitic and Indo-Germanic—cannot be traced to a common
origin, and consequently these two races must have separated at a very
early period. Semites and Indo-Germani are descended from different
ape-like men. The _Semitic_ race likewise separated at a very early
period into two diverging branches, namely, into the _Egyptian_ and
_Arabic_ branches. The _Egyptian_, or _African_ branch, the
_Dyssemites_—which sometimes under the name of Hamites are entirely
separated from the Semites—embraces the large group of Berbers, who
occupy the whole of north Africa, and in earlier times also peopled the
Canary Islands, and, finally, also the group of the Ethiopians, the
Bedsha, Galla, Danakil, Somali, and other tribes which occupy all the
north-eastern shores of Africa as far as the equator. The _Arabic_, or
_Asiatic_ branch, that is, the _Eusemites_, also called Semites in a
narrow sense, embrace the inhabitants of the large Arabian peninsula,
the primæval family of genuine Arabians (“primæval type of the
Semites”), and also the most highly developed Semitic groups, the Jews,
or Hebrews, and the Aramæans—the Syrians and Chaldæans. A colony of the
southern Arabs (the Himjarites), which crossed the Straits of
Bab-el-Mandeb, has peopled Abyssinia.

Lastly, the Indo-Germanic race, which has far surpassed all the other
races of men in mental development, separated at a very early period,
like the Semitic, into two diverging branches, the _Ario-Romaic_ and the
_Slavo-Germanic_ branches. Out of the former arose on the one hand the
_Arians_ (Indians and Iranians), on the other the _Græco-Roman_ (Greeks
and Albanians, Italians and Kelts). Out of the Slavo-Germanic branch
were developed on the one hand the _Slavonians_ (Russian, Bulgarian,
Tchec, and Baltic tribes), on the other the _Germani_ (Scandinavians and
Germans, Netherlanders and Anglo-Saxons). August Schleicher has
explained, in a very clear genealogical form, how the further
ramifications of the Indo-Germanic race may be accurately traced in
detail on the basis of comparative philology.(6) (Compare p. 331.)

The total number of human individuals at present amounts to between
1,300 and 1,400 millions. In our Tabular Survey (p. 333) 1,350 millions
has been assumed as the mean number. According to an approximate
estimate, as far as such a thing is possible, 1,200 millions of these
are straight-haired men, only about 150 millions woolly-haired. The most
highly developed species, Mongols and Mediterranese, far surpass all the
other human species in numbers of individuals, for each of them alone
comprises about 550 millions. (Compare Friederich Müller’s Ethnography,
p. 30.) Of course the relative number of the twelve species fluctuates
every year, and that too according to the law developed by Darwin, that
in the struggle for life the more highly developed, the more favoured
and larger groups of forms, possess the positive inclination and the
certain tendency to spread more and more at the expense of the lower,
more backward, and smaller groups. Thus the Mediterranean species, and
within it the Indo-Germanic, have by means of the higher development of
their brain surpassed all the other races and species in the struggle
for life, and have already spread the net of their dominion over the
whole globe. It is only the Mongolian species which can at all
successfully, at least in certain respects, compete with the
Mediterranean. Within the tropical regions, Negroes, Kaffres, and
Nubians, as also the Malays and Dravidas, are in some measure protected
against the encroachments of the Indo-Germanic tribes by their being
better adapted for a hot climate; the case of the arctic tribes of the
polar regions is similar. But the other races, which as it is are very
much diminished in number, will sooner or later completely succumb in
the struggle for existence to the superiority of the Mediterranean
races. The American and Australian tribes are even now fast approaching
their complete extinction, and the same may be said of the Papuans and
Hottentots.

In now turning to the equally interesting and difficult question of the
relative _connection_, _migration_, and _primæval home_ of the twelve
species of men, I must premise the remark that, in the present state of
our anthropological knowledge, any answer to this question must be
regarded only as a provisional hypothesis. This is much the same as with
any genealogical hypothesis which we may form of the origin of kindred
animal and vegetable species, on the basis of the “Natural System.” But
the necessary uncertainty of these special hypotheses of descent, in no
way shakes the absolute certainty of the general theory of descent. Man,
we may feel certain, is descended from Catarrhini, or narrow-nosed apes,
whether we agree with the polyphylites, and suppose each human species,
in its primæval home, to have originated out of a special kind of ape;
or whether, agreeing with the monophylites, we suppose that all the
human species arose only by differentiation from a single species of
primæval man (Homo primigenius).

For many and weighty reasons we hold the monophyletic hypothesis to be
the more correct, and we therefore assume a _single primæval home_ for
mankind, where he developed out of a long since extinct anthropoid
species of ape. Of the five now existing continents, neither Australia,
nor America, nor Europe can have been this primæval home, or the
so-called “Paradise,” the “cradle of the human race.” Most
circumstances indicate southern Asia as the locality in question.
Besides southern Asia, the only other of the now existing continents
which might be viewed in this light is Africa. But there are a number of
circumstances (especially chorological facts) which suggest that the
primæval home of man was a continent now sunk below the surface of the
Indian Ocean, which extended along the south of Asia, as it is at
present (and probably in direct connection with it), towards the east,
as far as further India and the Sunda Islands; towards the west, as far
as Madagascar and the south-eastern shores of Africa. We have already
mentioned that many facts in animal and vegetable geography render the
former existence of such a south Indian continent very probable.
(Compare vol. i. p. 361.) Sclater has given this continent the name of
Lemuria, from the Semi-apes which were characteristic of it. By assuming
this Lemuria to have been man’s primæval home, we greatly facilitate the
explanation of the geographical distribution of the human species by
migration. (Compare the Table of Migrations XV., and its explanation at
the end.)

We as yet know of no fossil remains of the hypothetical primæval man
(Homo primigenius) who developed out of anthropoid apes during the
tertiary period, either in Lemuria or in southern Asia, or possibly in
Africa. But considering the extraordinary resemblance between the lowest
woolly-haired men, and the highest man-like apes, which still exist at
the present day, it requires but a slight stretch of the imagination to
conceive an intermediate form connecting the two, and to see in it an
approximate likeness to the supposed primæval men, or ape-like men. The
form of their skull was probably very long, with slanting teeth; their
hair woolly; the colour of their skin dark, of a brownish tint. The hair
covering the whole body was probably thicker than in any of the still
living human species; their arms comparatively longer and stronger;
their legs, on the other hand, knock-kneed, shorter and thinner, with
entirely undeveloped calves; their walk but half erect.

This ape-like man very probably did not as yet possess an actual human
language, that is, an articulate language of ideas. Human speech, as has
already been remarked, most likely originated after the divergence of
the primæval species of men into different species. The number of
primæval languages is, however, considerably larger than the number of
the species of men above discussed. For philologists have hitherto not
been able to trace the four primæval languages of the Mediterranean
species, namely, the Basque, Caucasian, Semitic, and Indo-Germanic to a
single primæval language. As little can the different Negro languages be
derived from a common primæval language; hence both these species,
Mediterranean and Negro, are certainly _polyglottonic_, that is, their
respective languages originated after the divergence of the speechless
primary species into several races had already taken place. Perhaps the
Mongols, the Arctic and American tribes, are likewise polyglottonic. The
Malayan species is, however, _monoglottonic_; all the Polynesian and
Sundanesian dialects and languages can be derived from a common, long
since extinct primæval language, which is not related to any other
language on earth. All the other human species, Nubians, Dravidas,
Australians, Papuans, Hottentots, and Kaffres are likewise
monoglottonic. (Compare p. 333.)

Out of speechless primæval man, whom we consider as the common primary
species of all the others, there developed in the first place—probably
by natural selection—various species of men unknown to us, and now long
since extinct, and who still remained at the stage of speechless ape-men
(Alalus, or Pithecanthropus). Two of these species, a woolly-haired and
a straight-haired, which were most strongly divergent, and consequently
overpowered the others in the struggle for life, became the primary
forms of the other remaining human species.

The main branch of woolly-haired men (Ulotrichi) at first spread only
over the southern hemisphere, and then emigrated partly eastwards,
partly westwards. Remnants of the eastern branch are the Papuans in New
Guinea and Melanesia, who in earlier times were diffused much further
west (in further India and Sundanesia), and it was not until a late
period that they were driven eastwards by the Malays. The Hottentots are
the but little changed remnants of the western branch; they immigrated
to their present home from the north-east. It was perhaps during this
migration that the two nearly related species of Caffres and Negroes
branched off from them; but it may be that they owe their origin to a
peculiar branch of ape-like men.

The second main branch of primæval straight-haired men (Lissotrichi),
which is more capable of development, has probably left a but little
changed remnant of its common primary form—which migrated to the
south-east—in the ape-like natives of Australia. Probably very closely
related to these latter are the South Asiatic _primæval Malays_, or
_Promalays_, which name we have previously given to the extinct,
hypothetical primary form of the other six human species. Out of this
unknown common primary form there seem to have arisen three diverging
branches, namely, the true Malays, the Mongols, and the Euplocomi; the
first spread to the east, the second to the north, and the third
westwards.

The primæval home, or the “Centre of Creation,” of the Malays must be
looked for in the south-eastern part of the Asiatic continent, or
possibly in the more extensive continent which existed at the time when
further India was directly connected with the Sunda Archipelago and
eastern Lemuria. From thence the Malays spread towards the south-east,
over the Sunda Archipelago as far as Borneo, then wandered, driving the
Papuans before them, eastwards towards the Samoa and Tonga Islands, and
thence gradually diffused over the whole of the islands of the southern
Pacific, to the Sandwich Islands in the north, the Mangareva in the
east, and New Zealand in the south. A single branch of the Malayan tribe
was driven far westwards and peopled Madagascar.

The second main branch of primæval Malays, that is, the Mongols, at
first also spread in Southern Asia, and, radiating to the east, north,
and north-west, gradually peopled the greater part of the Asiatic
continent. Of the four principal races of the Mongol species, the
Indo-Chinese must perhaps be looked upon as the primary group, out of
which at a later period the other Coreo-Japanese and Ural-Altaian races
developed as diverging branches. The Mongols migrated in many ways from
western Asia into Europe, where the species is still represented in
northern Russia and Scandinavia by the Fins and Lapps, in Hungary by the
kindred Magyars, and in Turkey by the Osmanlis.

PEDIGREE OF SEMITES

----------------------------------------------------------------

PEDIGREE OF THE INDO-GERMANI

On the other hand, a branch of the Mongols migrated from north-eastern
Asia to America, which was probably in earlier times connected with the
former continent by a broad isthmus. The Arctic tribes, or Polar men,
the Hyperboreans of north-eastern Asia, and the Esquimaux of the
extreme north of America, must probably be regarded as an offshoot of
this branch, which became peculiarly degenerated by unfavourable
conditions of existence. The principal portion of the Mongolian
immigrants, however, migrated to the south, and gradually spread over
the whole of America, first over the north, later over South America.

The third and most important main branch of primæval Malays, the
curly-haired races, or Euplocomi, have probably left in the Dravidas of
Hindostan and Ceylon, that species of man which differs least from the
common primary form of the Euplocomi. The principal portion of the
latter, namely, the Mediterranean species, migrated from their primæval
home (Hindostan?) westwards, and peopled the shores of the
Mediterranean, south-western Asia, north Africa, and Europe. The
Nubians, in the north-east of Africa, must perhaps be regarded as an
offshoot of the primæval Semitic tribes, who migrated far across central
Africa almost to the western shores. The various branches of the
Indo-Germanic race have deviated furthest from the common primary form
of ape-like men. During classic antiquity and the middle ages, the
Romanic branch (the Græco-Italo-Keltic group), one of the two main
branches of the Indo-Germanic species, outstripped all other branches in
the career of civilization, but at present the same position is occupied
by the Germanic. Its chief representatives are the English and Germans,
who are in the present age laying the foundation for a new period of
higher mental development, in the recognition and completion of the
theory of descent. The recognition of the theory of development and the
monistic philosophy based upon it, forms the best criterion for the
degree of man’s mental development.

SYSTEMATIC SURVEY OF THE TWELVE HUMAN SPECIES.

N.B.—Column A denotes the Average Number of the Population in
millions. Column B shows the Degree of the Phyletic Development of
the Species, thus Pr = Progressive Diffusion; Co = Comparative
Stability; Re = Retrogression and Extinction. Column C denotes the
Character of the Primæval Language; Mn (Monoglottonic) signifies that
the Species had one Simple Primæval Language; Pl (Polyglottonic) a
Compound Primæval Language.

----------------------+--------------------+--------+-------+--------+-----------------------------
_Tribe._ | _Human | A. | B. | C. | _Home._
| Species._ | | | |
----------------------+--------------------+--------+-------+--------+-----------------------------

TUFT-HAIRED { | | |
+Lophocomi+ { 1. PAPUAN | 2 | Re | Mn { New Guinea and Melanesia,
{ | | | { Philippine Islands, Malacca
(about 2 millions) { 2. HOTTENTOT | 1/20 | Re | Mn { The extreme south of Africa
{ | | | { (The Cape)
| | |
FLEECY-HAIRED { 3. KAFFRE | 20 | Pr | Mn { South Africa (between 30°
{ | | | { S. Lat. and 5° N. Lat.)
+Eriocomi+ { 4. NEGRO | 130 | Pr | Pl { Central Africa (between the
{ | | | { Equator and 30° N. Lat.)
(about 150 millions) { | | |
| | |
{ 5. AUSTRALIAN | 1/12 | Re | Mn { Australia
{ 6. MALAY | 30 | Co | Mn { Malacca, Sundanesia, Polynesia,
{ | | | { and Madagascar
STRAIGHT-HAIRED { | | |
+Euthycomi+ { 7. MONGOL | 550 | Pr | Mn? { The greater part of Asia
{ | | | { and northern Europe
(about 600 millions) { 8. ARCTIC | 1/25 | Co | Pl? { The extreme north-east of
{ MAN | | | { Asia and the extreme north
{ | | | { of America
{ 9. AMERICAN | 12 | Re | Mn? { The whole of America with
{ | | | { the exception of the extreme
{ | | | { north
| | |
{ 10. DRAVIDAS | 34 | Co | Mn { South Asia (Hindostan and
{ | | | { Ceylon)
{ | | |
{ 11. NUBIAN | 10 | Co | Mn? { Central Africa (Nubia and
{ | | | { Fula-land)
CURLY-HAIRED { | | | { In all parts of the world,
{ | | | { having migrated from South
+Euplocomi+ { 12. MEDITERRANEAN | 550 | Pr | Pl { Asia to North Africa and
{ | | | { South Europe
(about 600 millions) { | | |
{ | | |
| | | { In all parts of the world,
13. HYBRIDS | 11 | Pr | Pl { but predominating in America
OF THE | | | { and Asia
SPECIES | | |
--------------------+--------+ |
TOTAL 1350

CHAPTER XXIV.

OBJECTIONS AGAINST, AND PROOFS OF THE TRUTH OF, THE THEORY OF DESCENT.

Objections to the Doctrine of Filiation.—Objections of Faith
and Reason.—Immeasurable Length of the Geological
Periods.—Transition Forms between Kindred Species.—Dependence
of Stability of Form on Inheritance, and of the Variability of
Form on Adaptation.—Origin of very complicated Arrangement of
Organisation.—Gradual Development of Instincts and Mental
Activities.—Origin of a priori Knowledge from Knowledge a
posteriori.—The Knowledge requisite for the Correct
Understanding of the Doctrine of Filiation.—Necessary
Interaction between Empiricism and Philosophy.—Proofs of the
Theory of Descent.—Inner Causal Connection between all the
Biological Series of Phenomena.—The Direct Proof of the Theory
of Selection.—Relation of the Theory of Descent to
Anthropology.—Proofs of the Animal Origin of Man.—The Pithecoid
Theory as an Inseparable Part of the Theory of
Descent.—Induction and Deduction.—Gradual Development of the
Human Mind.—Body and Mind.—Human Soul and Animal Soul.—A Glance
at the Future.

If in these chapters I may hope to have made the Theory of Descent seem
more or less probable, and to have even convinced some of my readers of
its unassailable truth, yet I am by no means unconscious that, to most
of them, during the perusal of my explanations, a number of objections
more or less well founded must have occurred. Hence it seems absolutely
necessary at the conclusion of our examination to refute at least the
most important of these, and at the same time, on the other hand, once
more to set forth the convincing arguments which bear testimony to the
truth of the theory of development.

The objections which are raised to the doctrine of descent may be
divided into two large groups: objections of faith and objections of
reason. The objections of the first group originate in the infinitely
varied forms of faith held by human individuals, and need not here be
taken into consideration at all. For, as I have already remarked at the
beginning of this book, science, as an objective result of sensuous
experience, and of the striving of human reason after knowledge, has
nothing whatever to do with the subjective ideas of faith, which are
preached by a single man as the direct inspirations or revelations of
the Creator, and then believed in by the dependent multitude. This
belief, very different in different nations, only begins, as is well
known, where science ends. Natural Science believes, according to the
maxim of Frederick the Great, “that every one may go to heaven in his
own fashion,” and only necessarily enters into conflict with particular
forms of faith where they appear to set a limit to free inquiry and a
goal to human knowledge, beyond which we are not to venture. Now this is
certainly the case here in the highest degree, for the Theory of
Development applies itself to the solution of the greatest of scientific
problems—that of the creation, the coming into existence of things; more
especially the origin of organic forms, and of man at their head. It is
here certainly the right as well as the sacred duty of free inquiry, to
fear no human authority, and courageously to raise the veil from the
image of the Creator, unconcerned as to what natural truth may lie
concealed beneath. The only Divine revelation which we recognise as
true, is written everywhere in nature, and to every one with healthy
senses and a healthy reason it is given to participate in the unerring
revelation of this holy temple of nature, by his own inquiry and
independent discovery.

If we, therefore, here disregard all objections to the Doctrine of
Descent which may be raised by the priests of the different religious
faiths, we must nevertheless endeavour to refute the most important of
those objections which seem more or less founded on science, and which
we grant might, at first sight, to a certain extent captivate us and
deter us from adopting the Doctrine of Descent. Many persons seem to
think the length of the periods of time required the most important of
these objections. We are not accustomed to deal with such immense
periods as are necessary for the history of the creation. It has already
been mentioned that the periods, during which species originated by
gradual transmutation, must not be calculated by single centuries, but
by hundreds and by millions of centuries. Even the thickness of the
stratified crust of the earth, the consideration of the immense space of
time which was requisite for its deposition from water, taken together
with the periods of elevation between the periods of depression,
indicate a duration of time of the organic history of the earth which
the human intellect cannot realize. We are here in much the same
position as an astronomer in regard to infinite space. In the same way
as the distances between the different planetary systems are not
calculated by miles but by Sirius-distances, each of which comprises
millions of miles, so the organic history of the earth must not be
calculated by thousands of years, but by palæontological or geological
periods, each of which comprises many thousands of years, and perhaps
millions, or even, milliards, of thousands of years. It is of little
importance how high the immeasurable length of these periods may be
approximately estimated, because we are in fact unable with our limited
power of imagination to form a true conception of these periods, and
because we do not as in astronomy possess a secure mathematical basis
for fixing the approximate length of duration in numbers. But we most
positively deny that we see any objection to the theory of development
in the extreme length of these periods which are so completely beyond
the power of our imagination. It is, on the contrary, as I have already
explained in one of the preceding chapters, most advisable, from a
strictly philosophical point of view, to conceive these periods of
creation to be as long as possible, and we are by so much the less in
danger of losing ourselves in improbable hypotheses, the longer we
conceive the periods for organic processes of development to have been.
The longer, for example, we conceive the Permian period to have been,
the easier it will be for us to understand how the important
transmutations took place within it which so essentially distinguish the
fauna and flora of the Coal period from that of the Trias. The great
disinclination which most persons have to assume such immeasurable
periods, arises mainly from the fact of our having in early youth been
brought up in the notion that the whole earth is only some thousands of
years old. Moreover, human life, which at most attains the length of a
century, is an extremely short space of time, and is not suitable as a
standard for the measurement of geological periods. Our life is a
single drop in the ocean of eternity. The reader may call to mind the
duration of life of many trees which is more than fifty times as long;
for example, the dragon-trees (Dracæna) and monkey bread-fruit trees
(Adansonia), whose individual life exceeds a period of five thousand
years; and, on the other hand, the shortness of the individual life of
many of the lower animals, for example, the infusoria, where the
individual, as such, lives but a few days, or even but a few hours,
contrasts no less strongly with human longevity. This comparison brings
the relative nature of all measurement of time very clearly before us.
If the theory of development be true at all, there must certainly have
elapsed immense periods, utterly inconceivable to us, during which the
gradual historical development of the animal and vegetable kingdom
proceeded by the slow transformation of species. There is, however, not
a single reason for accepting a definite limit for the length of these
periods of development.

A second main objection which many, and more especially systematic
zoologists and botanists, raise against the theory of descent, is that
no _transition forms_ between the different species can be found,
although according to the theory of descent they ought to be found in
great numbers. This objection is partly well founded and partly not so,
for there does exist an extraordinarily large number of transition forms
between living, as well as between extinct species, especially where we
have an opportunity of seeing and comparing very numerous individuals of
kindred species. Those careful investigators of individual species who
so frequently raise this objection are the very persons whom we
constantly find checked in their special series of investigations by the
really insuperable difficulty of sharply distinguishing individual
species. In all systematic works, which are in any degree thorough, one
meets with endless complaints, that here and there species cannot be
distinguished because of the excessive number of transition forms. Hence
every naturalist defines the limit and the number of individual species
differently. Some zoologists and botanists, as I mentioned (vol. i. p.
276), assume in one and the same group of organisms ten species, others
twenty, others a hundred or more, while other systematic naturalists
again look upon these different forms only as varieties of a single
“good” species. In most groups of forms there is, in fact, a
superabundance of transition forms and intermediate stages between the
individual species.

It is true that in many species the forms of transition are actually
wanting, but this is easily explained by the principle of divergence or
separation, the importance of which I have already explained. The
circumstance that the struggle for existence is the more active between
two kindred forms the closer they stand to each other, must necessarily
favour the speedy extinction of the connecting intermediate forms
between the two divergent species. If one and the same species produce
diverging varieties in different directions, which become new species,
the struggle between these new forms and the common primary form will be
the keener the less they differ from one another; but the stronger the
divergence the less dangerous the struggle. Naturally therefore, it is
principally the connecting intermediate forms which will in most cases
quietly die out, while the most divergent forms remain and reproduce
themselves as distinct “new species.” In accordance with this, we in
fact no longer find forms of transition leading to those groups which
are becoming extinct, as, for example, among birds, are the ostriches;
and among mammals, the elephants, giraffes, Semi-apes, Edentata, and
Ornithorhyncus. The groups of forms approaching their extinction no
longer produce new varieties, and naturally the species are what is
called “good,” that is, the species are distinctly different from one
another. But in those animal groups where development and progress are
still active, where the existing species deviate into many new species
by the formation of new varieties, we find an abundance of transition
forms which cause the greatest difficulties to systematic naturalists.
This is the case, for example, among birds with the finches; among
mammals with most of the rodents (more especially with those of the
mouse and rat kind), with a number of the ruminants and with genuine
apes, more especially with the South American forms (Cebus), and many
others. The continual development of species by the formation of new
varieties here produces a mass of intermediate forms which connect the
so-called “good” species, which efface their boundaries, and render
their sharp specific distinction completely illusory.

The reason that this nevertheless does not cause a complete confusion of
forms, nor a universal chaos in the structure of animals and vegetables,
lies simply in the fact that there is a continual counteraction at work
between progressive _adaptation_ on the one hand, and the _retentive_
power of _inheritance_ on the other hand. The degree of stability and
variability manifested by every organic form is determined solely by the
actual condition of the equilibrium between these two opposite
functions. _Inheritance is the cause of the stability of species,
adaptation the cause of their modification._ When therefore some
naturalists say that, according to the theory of descent, there ought to
be a much greater variety of forms, and others again, that there ought
to be a much greater equality of forms, the former under-estimate the
value of inheritance and the latter the value of adaptation. _The ratio
of the interaction between inheritance and adaptation determines the
ratio of the stability and variability of organic species_ at any given
period.

Another objection to the theory of descent, which, in the opinion of
many naturalists and philosophers is of great weight, is that it
ascribes the origin of organs which act for a definite purpose to causes
which are either aimless or mechanical in their operation. This
objection seems to be especially important in regard to those organs
which appear so excellently adapted for a certain definite purpose that
the most ingenious mechanician could not invent a more perfect organ for
the purpose. Such are, above all, the higher sense-organs of animals,
the eye and ear. If the eyes and auditory apparatus of the higher
animals alone were known to us, they would indeed cause great and
perhaps insurmountable difficulties. How could we come to the conclusion
that the extraordinarily great and wonderful degree of perfection and
conformity to purpose which we perceive in the eyes and ears of higher
animals, is in every respect attained solely by natural selection?
Fortunately, however, comparative anatomy and the history of
development help us here over all obstacles; for when in the animal
kingdom we follow the gradual progress towards perfection of the eyes
and ears, step by step, we find such a finely graduated series of
improvement, that we can clearly follow the development of the most
complex organs through all the stages towards perfection. Thus, for
example, the eye in the lowest animal is a simple spot of pigment which
does not yet reflect any image of external objects, but at most
perceives and distinguishes the different rays of light. Later, we find
in addition to this a sensitive nerve; then there gradually develops
within the spot of pigment the first beginning of the lens, a refractive
body which is now able to concentrate the rays of light and to reflect a
definite image. But all the composite apparatus for the movement of the
eye and its accommodation to variations of light and distance are still
absent, namely, the various refractive media, the highly differentiated
membrane of the optic nerve, etc., which are so perfectly constructed in
higher animals. Comparative anatomy shows us an uninterrupted succession
of all possible stages of transition, from the simplest organ to the
most highly perfected apparatus, so that we can form a pretty correct
idea of the slow and gradual formation of even such an exceedingly
complex organ. The like gradual progress which we observe in the
development of the organ during the course of individual development,
must have taken place in the historical (phyletic) origin of the organ.

Many persons when contemplating these most perfect organs—which
apparently were purposely invented and constructed by an ingenious
Creator for a definite function, but which in reality have arisen by the
aimless action of natural selection—experience difficulties in arriving
at a rational understanding of them, which are similar to those
experienced by the uncivilized tribes of nature when contemplating the
latest complicated productions of engineering. Savages who see a ship of
the line, or a locomotive engine for the first time, look upon these
objects as the productions of a supernatural being, and cannot
understand how a man, an organism like themselves, could have produced
such an engine. Even the uneducated classes of our own race cannot
comprehend such an intricate apparatus in its actual workings, nor can
they understand its purely mechanical nature. Most naturalists, however,
as Darwin very justly remarks, stand in much the same position in regard
to the forms of organisms as do savages to ships of the line and to
locomotive engines. A rational understanding of the purely mechanical
origin of organic forms can only be acquired by a thorough and general
training in Biology, and by a special knowledge of comparative anatomy
and the history of development.

Among the remaining objections to the Theory of Descent, I shall here
finally refer to and refute but one more, as in the eyes of many
unscientific men it seems to possess great weight. How are we, from the
Theory of Descent, to conceive of the origin of the mental faculties of
animals, and more especially their specific expressions—the so-called
instincts? This difficult subject has been so minutely discussed by
Darwin in a special chapter of his chief work (the seventh), that I must
refer the reader to it. We must regard instincts as essentially the
habits of the soul acquired by adaptation, and transmitted and fixed by
inheritance through many generations. Instincts are, therefore, like all
other habits, which, according to the laws of cumulative adaptation
(vol. i. p. 233) and established inheritance (vol. i. p. 216), lead to
the origin of new functions, and thus also to new forms of the organs.
Here, as everywhere, the interaction between function and organ goes
hand in hand. Just as the mental faculties of man have been acquired by
the progressive adaptation of the brain, and been fixed by continual
transmission by inheritance, so the instincts of animals, which differ
from them only in quantity, not in quality, have arisen by the gradual
perfecting of their mental organ, that is, their central nervous system,
by the interaction of Adaptation and Inheritance. Instincts, as is well
known, are inherited, but experiences and, consequently, new adaptations
of the animal mind, are also transmitted by inheritance; and the
training of domestic animals to different mental activities, which wild
animals are incapable of accomplishing, rests upon the possibility of
mental adaptation. We already know a series of examples, in which such
adaptations, after they had been transmitted through a succession of
generations, finally appeared as innate instincts, and yet they have
only been acquired from the ancestors of the animals. Inheritance has
here caused the result of training to become instinct. The
characteristic instincts of sporting dogs, shepherd’s dogs, and other
domestic animals, and the natural instincts of wild animals, which they
possess at birth, were in the first place acquired by their ancestors by
adaptation. They may in this respect be compared to man’s “knowledge a
priori,” which, like all other knowledge, was originally acquired by our
remote ancestors, “a posteriori,” by sensuous experience. As I have
already remarked, it is evident that “knowledge a priori” arose only by
long-enduring transmission, by inheritance of acquired adaptations of
the brain, out of originally empiric or experiential “knowledge a
posteriori” (vol. i. p. 31).

The objections to the Theory of Descent here discussed and refuted are,
I believe, the most important which have been raised against it; I
consider also that I have sufficiently proved to the reader their
futility. The numerous other objections which besides these have been
raised against the Theory of Development in general, or against its
biological part, the Theory of Descent in particular, arise either from
such a degree of ignorance of empirically established facts, or from
such a want of their right understanding, and from such an incapacity to
draw the necessary conclusions, that it is really not worth the trouble
to go further into the refutation. There are only some general points in
regard to which, I should like, in a few words, to draw attention.

In the first place I must observe, that in order thoroughly to
understand the doctrine of descent, and to be convinced of its absolute
truth, it is indispensable to possess a general knowledge of the whole
of the domain of biological phenomena. _The theory of descent is a
biological theory_, and hence it may with fairness and justice be
demanded that those persons who wish to pass a valid judgment upon it
should possess the requisite degree of biological knowledge. Their
possessing a special empiric knowledge of this or that domain of zoology
or botany, is not sufficient; they must possess a _general insight into
the whole series of phenomena_, at least in the case of one of the three
organic kingdoms. They ought to know what universal laws result from the
comparative morphology and physiology of organisms, but more especially
from comparative anatomy, from the individual and the palæontological
history of development, etc.; and they ought to have some idea of the
deep _mechanical, causal connection_ between all these series of
phenomena. It is self-evident that a certain degree of general culture,
and especially a philosophical education, is requisite; which is,
however, unfortunately by many persons in our day, not considered at all
necessary. _Without the necessary connection of empirical knowledge and
the philosophical understanding of biological phenomena, it is
impossible to gain a thorough conviction of the truth of the Theory of
Descent._

Now I ask, in the face of this first preliminary condition for a true
understanding of the Theory of Descent, what we are to think of the
confused mass of persons who have presumed to pass a written or oral
judgment upon it of an adverse character? Most of them are unscientific
persons, who either know nothing of the most important phenomena of
Biology, or at least possess no idea of their deeper significance. What
should we say of an unscientific person who presumed to express an
opinion on the cell-theory, without ever having seen cells; or of one
who presumed to question the vertebral-theory, without ever having
studied comparative anatomy? And yet one may meet with such ridiculous
arrogance any day in the history of the biological Theory of Descent.
One hears thousands of unscientific and but half-educated persons pass a
final judgment upon it, although they know nothing either of botany or
of zoology, of comparative anatomy or the theory of tissues, of
palæontology or embryology. Hence it happens, as Huxley well says, that
most of the writings published against Darwin are not worth the paper
upon which they are written.

We might add that there are many naturalists, and even celebrated
zoologists and botanists, among the opponents of the Theory of Descent;
but these latter are mostly old stagers, who have grown grey in quite
opposite views, and whom we cannot expect, in the evening of their
lives, to submit to a reform in their conception of the universe, which
has become to them a fixed idea.

It is, moreover, expressly to be remarked, that not only a general
insight into the _whole_ domain of biological phenomena, but also a
philosophical understanding of it, are the necessary preliminary
conditions for becoming convinced of and adopting the Theory of Descent.
Now we shall find that these indispensable preliminary conditions are,
unfortunately, by no means fulfilled by the majority of naturalists of
the present day. The immense amount of empirical facts with which the
gigantic advances of modern natural science have recently made us
acquainted has led to a prevailing inclination for the special study of
single phenomena and of small and narrow domains. This causes the
knowledge of other paths, and especially of Nature as a great
comprehensive whole, to be in most cases completely neglected. Every one
with sound eyes and a microscope, together with industry and patience
for study, can in our day attain a certain degree of celebrity by
microscopic “discoveries,” without, however, deserving the name of a
naturalist. This name is deserved only by him who not merely strives to
_know_ the individual phenomena, but who also seeks to _discover_ their
causal connection. Even in our own day, most palæontologists examine and
describe fossils without knowing the most important facts of embryology.
Embryologists, on the other hand, follow the history of development of a
particular organic individual, without having an idea of the
palæontological history of the whole tribe, of which fossils are the
records. And yet these two branches of the organic history of
development—ontogeny, or the history of the individual, and phylogeny,
or the history of the tribe—stand in the closest causal connection, and
the one cannot be understood without the other. The same may be said of
the systematic and the anatomical part of Biology. There are even now,
in zoology and botany, many systematic naturalists who work with the
erroneous idea that it is possible to construct a natural system of
animals and plants simply by a careful examination of the external and
readily accessible forms of bodies, without a deeper knowledge of their
internal structure. On the other hand, there are anatomists and
histologists who think it possible to obtain a true knowledge of animal
and vegetable bodies merely by a most careful examination of the inner
structure of the body of some individual species, without the
comparative examination of the bodily form of all kindred organisms. And
yet here, as everywhere, the internal and external factors, to wit,
Inheritance and Adaptation, stand in the closest mutual relation, and
the individual can never be thoroughly understood without a comparison
of it with the whole of which it is a part. To those one-sided
specialists we should like in Goethe’s words to say:—

We must, contemplating Nature,
Part as Whole, give equal heed to:
Nought is inward, nought is outward,
For the inner is the outer.[6]

And again:—

Nature has neither kernel nor shell,
It is she that is All and All at once.[7]

What is even more detrimental to the general understanding of nature as
a whole than this one-sided tendency, is _the want of a philosophical
culture_, and this applies to most of the naturalists of the present
day. The various errors of the earlier speculative nature-philosophy
made during the first thirty years of our century, have brought the
whole of philosophy into such bad repute with the exact empirical
naturalists, that they live in the strange delusion that it is possible
to erect the edifice of natural science out of mere facts, without their
philosophic connection; in short, out of mere knowledge, without the
understanding of it. But as a purely speculative and absolutely
philosophical system, which does not concern itself with the
indispensable foundation of empirical facts, becomes a castle in the
air, which the first real experiment throws to the winds; so, on the
other hand, a purely empirical system, constructed of nothing but facts,
remains a disorderly heap of stones, which will never deserve the name
of an edifice. Bare facts established by experience are nothing but rude
stones, and without their thoughtful valuation, without their
philosophic connection, no science can be established. As I have already
tried to impress upon my reader, the _strong edifice of true monistic
science_, or what is the same thing, the _Science of Nature, exists only
by the closest interaction, and the reciprocal penetration of philosophy
and empirical knowledge_.

This lamentable estrangement between science and philosophy, and the
rude empiricism which is now-a-days unfortunately praised by most
naturalists as “exact science,” have given rise to those strange freaks
of the understanding, to those gross insults against elementary logic,
and to that incapacity for forming the simplest conclusions which one
may meet with any day in all branches of science, but especially in
zoology and botany. It is here that the neglect of a philosophical
culture and training of the mind, directly avenges itself most
painfully. It is not to be wondered at that the deep inner truth of the
Theory of Descent remains a sealed book to those rude empiricists. As
the common proverb justly says: they cannot see the wood for the trees.
It is only by a more general philosophical study, and especially by a
more strictly logical training of the mind, that this sad state of
things can be remedied. (Compare Gen. Morph. i. 63; ii. p. 447.)

If we rightly consider this circumstance, and if we further reflect upon
it in connection with the empirical foundation of the philosophical
theory of development, we shall at once see how we are placed respecting
the oft-demanded _proofs of the theory of descent_. The more the
doctrine of filiation has of late years made way for itself, and the
more all thoughtful, younger naturalists, and all truly
biologically-educated philosophers have become convinced of its inner
truth and absolute necessity, the louder have its opponents called for
actual proofs. The same persons who, shortly after the publication of
Darwin’s work, declared it to be “a groundless, fantastic system,” an
“arbitrary speculation,” an “ingenious dream,” now kindly condescend to
declare that the theory of descent certainly is a scientific
“_hypothesis_,” but that it still requires to be “_proved_.” When these
remarks are made by persons who do not possess the requisite
empirico-philosophical culture, nor the necessary knowledge in
comparative anatomy, embryology, and palæontology, we cannot be much
offended, and we refer them to the study of those sciences. But when
similar remarks are made by acknowledged specialists, by teachers of
zoology and botany, who certainly ought to possess a general insight
into the whole domain of their science, or who are actually familiar
with the facts of those scientific domains, then we are really at a loss
what to say. Those who are not satisfied with the treasures of our
present empirical knowledge of nature as a basis on which to establish
the Theory of Descent, will not be convinced by any other facts which
may hereafter be discovered; for we can conceive no circumstances which
would furnish stronger or a more complete testimony to the truth of the
doctrine of filiation than is even now seen, for example, in the
well-known facts of comparative anatomy and ontogeny. I must here again
direct attention to the fact, _that all the great and general laws, and
all the comprehensive series of phenomena of the most different domains
of biology can only be explained and understood by the Theory of
Development_ (and especially by its biological part, the Theory of
Descent), and that without it they remain completely inexplicable and
incomprehensible. _The internal causal connection_ between them all
proves the Theory of Descent to be the greatest _inductive law_ of
Biology.

Before concluding, I will once more name all those series of inductions,
all those general laws of Biology, upon which this comprehensive law of
development is firmly based.

(1.) _The palæontological history of the development of organisms_, the
gradual appearance and the historical succession of the different
species and groups of species, the empirical laws of the palæontological
change of species, as furnished to us by the science of fossils, and
more especially the _progressive differentiation and perfecting_ of
animal and vegetable groups in the successive periods of the earth’s
history.

(2.) _The individual history of development of organisms_, embryology
and metamorphology, the gradual changes in the slow development of the
body and its particular organs, especially _the progressive
differentiation and perfecting_ of the organs and parts of the body in
the successive periods of the individual development.

(3.) _The inner causal connection between ontogeny and phylogeny_, the
parallelism between the individual history of the development of
organisms, and the palæontological history of the development of their
ancestors, a connection which is actually established by the laws of
_Inheritance_ and _Adaptation_, and which may be summed up in the words:
ontogeny, according to the laws of inheritance and adaptation, repeats
in its large features the outlines of phylogeny.

(4.) _The comparative anatomy of organisms_, the proof of the essential
agreement of the inner structure of kindred organisms, in spite even of
the greatest difference of external form in the various species; their
explanation by the causal dependence of the internal agreement of the
structure on _Inheritance_, the external dissimilarity of the bodily
form on _Adaptation_.

(5.) _The inner causal connection between comparative anatomy and the
history of development_, the harmonious agreement between the laws of
the gradual development, _the progressive differentiation and
perfecting_, as they may be seen in comparative anatomy on the one hand,
in ontogeny and palæontology on the other.

(6.) _Dysteleology, or the theory of purposelessness_, the name I have
given to the _science of rudimentary organs_, of suppressed and
degenerated, aimless and inactive, parts of the body; one of the most
important and most interesting branches of comparative anatomy, which,
when rightly estimated, is alone sufficient to refute the fundamental
error of the teleological and dualistic conception of Nature, and to
serve as the foundation of the mechanical and monistic conception of the
universe.

(7.) _The natural system of organisms_, the natural grouping of all the
different forms of Animals, Plants, and Protista into numerous smaller
or larger groups, arranged beside and above one another; the kindred
connection of species, genera, families, orders, classes, tribes, etc.,
more especially, however, the _arboriform branching character of the
natural system_, which is the spontaneous result of a natural
arrangement and classification of all these graduated groups or
categories. The result attained in attempting to exhibit the
relationships of the mere forms of organisms by a tabular classification
is only explicable when regarded as the expression of their actual
_blood relationship_; _the tree shape of the natural system_ can only be
understood as the actual _pedigree of the organisms_.

(8.) _The chorology of organisms_, the science of the local distribution
of organic species, of their _geographical_ and _topographical
dispersion over the surface of the earth_, over the heights of
mountains and in the depths of the ocean, but especially the important
phenomenon that every species of organism proceeds from a so-called
“_centre of creation_” (more correctly a “_primæval home_” or “_centre
of distribution_”); that is, from a single locality, where it originated
but once, and whence it spread.

(9.) _The œcology of organisms_, the knowledge of the sum of the
_relations of organisms to the surrounding outer world_, to organic and
inorganic conditions of existence; the so-called “_economy of nature_,”
the correlations between all organisms living together in one and the
same locality, their adaptation to their surroundings, their
modification in the struggle for existence, especially the circumstances
of parasitism, etc. It is just these phenomena in “the economy of
nature” which the unscientific, on a superficial consideration, are wont
to regard as the wise arrangements of a Creator acting for a definite
purpose, but which on a more attentive examination show themselves to be
the necessary results of mechanical causes.

(10.) _The unity of Biology as a whole_, the deep inner connection
existing between all the phenomena named and all the other phenomena
belonging to zoology, protistics, and botany, and which are simply and
naturally explained by a single common principle. This principle can be
no other than the common derivation of all the specifically different
organisms from a single, or from several absolutely simple, primary
forms like the Monera, which possess no organs. The Theory of Descent,
by assuming this common derivation, throws a clear light upon these
individual series of phenomena, as well as upon their totality, without
which their deeper causal connection would remain completely
incomprehensible to us. The opponents of the Theory of Descent can in no
way explain any single one of these series of phenomena or their deeper
connection with one another. So long as they are unable to do this, _the
Theory of Descent remains the one adequate biological theory_.

We should, on account of the grand proofs just enumerated, have to adopt
Lamarck’s Theory of Descent for the explanation of biological phenomena,
even if we did not possess Darwin’s Theory of Selection. The one is so
completely and _directly proved_ by the other, and established by
mechanical causes, that there remains nothing to be desired. The laws of
_Inheritance_ and _Adaptation_ are universally acknowledged
_physiological_ facts, the former traceable to _propagation_, the latter
to the _nutrition_ of organisms. On the other hand, the _struggle for
existence_ is a _biological_ fact, which with mathematical necessity
follows from the general disproportion between the average number of
organic individuals and the numerical excess of their germs. But as
Adaptation and Inheritance in the struggle for life are in continual
interaction, it inevitably follows that _natural selection_, which
everywhere influences and continually changes organic species, must, by
making use of _divergence of character_, produce new species. Its
influence is further especially favoured by the active and passive
_migrations_ of organisms, which go on everywhere. If we give these
circumstances due consideration, the continual and gradual modification
or transmutation of organic species will appear as a biological process,
which must, according to causal law, of _necessity_ follow from the
actual nature of organisms and their mutual correlations.

That even the _origin of man_ must be explained by this general organic
process of transmutation, and that it is simply as well as naturally
explained by it, has, I believe, been sufficiently proved in my last
chapter but one. I cannot, however, avoid here once more directing
attention to the inseparable connection between this so-called “theory
of apes,” or “pithecoid theory,” and the whole Theory of Descent. If the
latter is the greatest _inductive law_ of biology, then it of necessity
follows that the former is its most important _deductive law_. They
stand and fall together. As all depends upon a right understanding of
this proposition, which in my opinion is very important, and which I
have therefore several times brought before the reader, I may be allowed
to explain it here by an example.

In all mammals known to us the centre of the nervous system is the
spinal marrow and the brain, and the centre of the vascular system is a
quadrupal heart, consisting of two principal chambers and two
ante-chambers. From this we draw the general inductive conclusion that
all mammals, without exception, those extinct, together with all those
living species as yet unknown to us, as well as the species which we
have examined, possess a like organization, a like heart, brain, and
spinal marrow. Now if, as still happens every year, there be discovered
in any part of the earth a new species of mammal, a new species of
marsupial, or a new species of deer, or a new species of ape, every
zoologist knows with certainty at once, without having examined its
inner structure, that this species must possess a quadruple heart, a
brain and spinal marrow, like all other mammals. Not a single naturalist
would ever think of supposing that the central nervous system of this
new species of mammal could possibly consist of a ventral cord with an
œsophageal collar as in the insects, or of scattered pairs of knots as
in the molluscs, or that its heart could be many-chambered as in flies,
or one-chambered as in the tunicates. This completely certain and safe
conclusion, although it is not based upon any direct experience, is a
_deductive conclusion_. In the same way, as I have shown in a previous
chapter, Goethe, from the comparative anatomy of mammals, established
the general inductive conclusion that they all possess a mid jawbone,
and afterwards drew from it the special deductive conclusion that man,
who in all other respects does not essentially differ from other
mammals, must also possess a like mid jawbone. He maintained this
conclusion without having actually seen the human mid jawbone, and only
proved its existence subsequently by actual observation (vol. i. p. 84).

The process of _induction_ is a logical system of forming conclusions
_from the special to the general_, by which we advance from many
individual experiences to a general law; _deduction_, on the other hand,
draws a conclusion _from the general to the special_, from a general law
of nature to an individual case. Thus the _Theory of Descent_ is,
without doubt, a great _inductive law_, empirically based upon all the
biological experience cited above; the pithecoid theory, on the other
hand, which asserts that man has developed out of lower, and in the
first place out of ape-like mammals, is a _deductive law_ inseparably
connected with the general inductive law.

The pedigree of the human race, the approximate outlines of which I gave
in the last chapter but one, of course remains in detail (like all the
pedigrees of animals and plants previously discussed) a more or less
approximate general hypothesis. This however does not affect the
application of the theory of descent to man. Here, as in all
investigations on the derivation of organisms, one must clearly
distinguish between the general _theory_ of descent and the special
_hypotheses_ of descent. The general _theory_ of descent claims full and
lasting value, because it is an inductive law, based upon all the whole
series of biological phenomena and their inner causal connection. Every
special _hypothesis_ of descent, on the other hand, has its special
value determined by the existing condition of our biological knowledge,
and by the extent of the objective empirical basis upon which we
deductively establish this particular hypothesis. Hence, all the
individual attempts to obtain a knowledge of the pedigree of any one
group of organisms possesses but a temporary and conditional value, and
any special hypothesis relating to it will become the more and more
perfect the greater the advance we make in the comparative anatomy,
ontogeny, and palæontology of the group in question. The more, however,
we enter into genealogical details, and the further we trace the
separate off-shoots and branches of the pedigree, the more uncertain and
subjective becomes our special _hypothesis_ of descent on account of the
incompleteness of our empirical basis. This however does no injury to
the general _theory_ of descent, which remains as the indispensable
foundation for really profound apprehension of biological phenomena.
Accordingly, there can be no doubt that we can and must, with full
assurance, regard the derivation of man—in the first place, from
ape-like forms; farther back, from lower mammals, and thus continually
farther back to lower stages of the vertebrata down to their lowest
invertebrate roots, nay, even down to a simple plastid—as a general
_theory_. On the other hand, the special tracing of the human pedigree,
the closer definition of the animal forms known to us, which either
actually belong to the ancestors of man, or at least stand in very close
blood relationship to them, will always remain a more or less
approximate _hypothesis_ of descent, all the more in danger of deviating
from the real pedigree the nearer it endeavours to approach it by
searching for the individual ancestral forms. This state of things
results from the immense gaps in our palæontological knowledge, which
can, under no circumstances, ever attain to even an approximate
completeness.

A thoughtful consideration of this important circumstance at once
furnishes the answer to a question which is commonly raised in
discussing this subject, namely, the question of scientific _proofs for
the animal origin of the human race_. Not only the opponents of the
Theory of Descent, but even many of its adherents who are wanting in the
requisite philosophical culture, look too much for “signs” and for
special empirical advances in the science of nature. They await the
sudden discovery of a human race with tails, or of a talking species of
ape, or of other living or fossil transition forms between man and the
ape, which shall fill the already narrow chasm between the two, and thus
empirically “prove” the derivation of man from apes. Such special
manifestations, were they ever so convincing and conclusive, would not
furnish the proof desired. Unthinking persons, or those unacquainted
with the series of biological phenomena, would still be able to maintain
the objections to those special testimonies which they now maintain
against our theory.

The absolute certainty of the Theory of Descent, even in its application
to man, is built on a more solid foundation; and its true inner value
can never be tested simply by reference to individual experience, but
only by a philosophical comparison and estimation of the treasures of
all our biological experiences. The inestimable importance of the Theory
of Descent is surely based upon this, that the theory follows of
necessity (as a general inductive law) from the comparative synthesis of
all organic phenomena of nature, and more especially from the triple
parallelism of comparative anatomy, of ontogeny, and phylogeny; and the
pithecoid theory under all circumstances (apart from all special proofs)
remains as a special deductive conclusion which must of necessity be
drawn from the general inductive law of the Theory of Descent.

In my opinion, all depends upon a right understanding of this
_philosophical foundation of the Theory of Descent_ and of the
_pithecoid theory_ which is inseparable from it. Many persons will
probably admit this, and yet at the same time maintain that all this
applies only to the _bodily_, not to the _mental_ development of man.
Now, as we have hitherto been occupied only with the former, it is
perhaps necessary here to cast a glance at the latter, in order to show
that it is also subject to the great general law of development. In
doing this it is above all necessary to recollect that body and mind can
in fact never be considered as distinct, but rather that both sides of
nature are inseparably connected, and stand in the closest interaction.
As even Goethe has clearly expressed it—“matter can never exist and act
without mind, and mind never without matter.” The artificial discord
between mind and body, between force and matter, which was maintained by
the erroneous dualistic and teleological philosophy of past times has
been disposed of by the advances of natural science, and especially by
the theory of development, and can no longer exist in face of the
prevailing mechanical and monistic philosophy of our day. How human
nature, and its position in regard to the rest of the universe, is to be
conceived of according to the modern view, has been minutely discussed
by Radenhausen in his “Isis,”(33) which is excellent and well worth
perusal.

With regard to the origin of the human mind or the soul of man, we, in
the first place, perceive that in every human individual it develops
from the beginning, step by step and gradually, just like the body. In a
newly born child we see that it possesses neither an independent
consciousness, nor in fact clear ideas. These arise only gradually when,
by means of sensuous experience, the phenomena of the outer world affect
the central nervous system. But still the little child is wanting in all
those differentiated emotions of the soul which the full-grown man
acquires only by the long experience of years. From this graduated
development of the human soul in every single individual we can, in
accordance with the inner causal connection between ontogeny and
phylogeny, directly infer the gradual development of the human soul in
all mankind, and further, in the whole of the vertebrate tribe. In its
inseparable connection with the body, the human soul or mind has also
had to pass through all those gradual stages of development, all those
various degrees of differentiation and perfecting, of which the
hypothetical series of human ancestors sketched in a late chapter gives
an approximate representation.

It is true that this conception generally greatly offends most persons
on their first becoming acquainted with the Theory of Development,
because more than all others it most strongly contradicts the
traditional and mythological ideas, and the prejudices which have been
held sacred for thousands of years. But like all other functions of
organisms, the human soul must necessarily have historically developed,
and the comparative or empirical study of animal psychology clearly
shows that this development can only be conceived of as a gradual
evolution from the soul of vertebrate animals, as a gradual
differentiation and perfecting which, in the course of many thousands of
years, has led to the glorious triumph of the human mind over its lower
animal ancestral stages. Here, as everywhere, the only way to arrive at
a knowledge of natural truth is to compare kindred phenomena, and
investigate their development. Hence we must above all, as we did in the
examination of the bodily development, compare the highest animal
phenomena on the one hand with the lowest animal phenomena, and on the
other with the lowest human phenomena. The final result of this
comparison is this—that _between the most highly developed animal souls,
and the lowest developed human souls, there exists only a small
quantitative, but no qualitative difference_, and that this difference
is much less than the difference between the lowest and the highest
human souls, or than the difference between the highest and the lowest
animal souls.

In order to be convinced of this important result, it is above all
things necessary to study and compare the mental life of wild savages
and of children.(32) At the lowest stage of human mental development are
the Australians, some tribes of the Polynesians, and the Bushmen,
Hottentots, and some of the Negro tribes. Language, the chief
characteristic of genuine men, has with them remained at the lowest
stage of development, and hence also their formation of ideas has
remained at a low stage. Many of these wild tribes have not even a name
for animal, plant, colour, and such most simple ideas, whereas they have
a word for every single, striking _form_ of animal and plant, and for
every single sound or colour. Thus even the most simple abstractions are
wanting. In many of these languages there are numerals only for one,
two, and three: no Australian language counts beyond four. Very many
wild tribes can count no further than ten or twenty, whereas some very
clever dogs have been made to count up to forty and even beyond sixty.
And yet the faculty of appreciating number is the beginning of
mathematics! Nothing, however, is perhaps more remarkable in this
respect, than that some of the wildest tribes in southern Asia and
eastern Africa have no trace whatever of the first foundations of all
human civilization, of family life, and marriage. They live together in
herds, like apes, generally climbing on trees and eating fruits; they do
not know of fire, and use stones and clubs as weapons, just like the
higher apes. All attempts to introduce civilization among these, and
many of the other tribes of the lowest human species, have hitherto been
of no avail; it is impossible to implant human culture where the
requisite soil, namely, the perfecting of the brain, is wanting. Not one
of these tribes has ever been ennobled by civilization; it rather
accelerates their extinction. They have barely risen above the lowest
stage of transition from man-like apes to ape-like men, a stage which
the progenitors of the higher human species had already passed through
thousands of years ago.(44)

Now consider, on the other hand, the highest stages of development of
mental life in the higher vertebrate animals, especially birds and
mammals. If, as is usually done, we divide the different emotions of the
soul into three principal groups—sensation, will, and thought—we shall
find in regard to every one of them, that the most highly developed
birds and mammals are on a level with the lowest human beings, or even
decidedly surpass them. The _will_ is as distinctly and strongly
developed in higher animals as in men of character. In both cases it is
never actually free, but always determined by a causal chain of ideas.
(Compare vol. i. p. 237.) In like manner, the different degrees of will,
energy, and passion are as variously graduated in higher animals as in
man. The _affections_ of the higher animals are not less tender and warm
than those of man. The fidelity and devotion of the dog, the maternal
love of the lioness, the conjugal love and connubial fidelity of doves
and love-birds are proverbial, and might serve as examples to many men.
If these virtues are to be called “instincts,” then they deserve the
same name in mankind. Lastly, with regard to _thought_, the comparative
consideration of which doubtless presents the most difficulties, this
much may with certainty be inferred—especially from an examination of
the comparative psychology of cultivated domestic animals—that the
processes of thinking, here follow the same laws as in ourselves.
Experiences everywhere form the foundation of conceptions, and lead to
the recognition of the connection between cause and effect. In all
cases, as in man, it is the path of induction and deduction which leads
to the formation of conclusions. It is evident that in all these
respects the most highly developed animals stand much nearer to man than
to the lower animals, although they are also connected with the latter
by a chain of gradual and intermediate stages. In Wundt’s excellent
“Lectures on the Human and Animal Soul,”(46) there are a number of
proofs of this.

Now, if instituting comparisons in both directions, we place the lowest
and most ape-like men (the Austral Negroes, Bushmen, and Andamans,
etc.), on the one hand, together with the most highly developed animals,
for instance, with apes, dogs, and elephants, and on the other hand,
with the most highly developed men—Aristotle, Newton, Spinoza, Kant,
Lamarck, or Goethe—we can then no longer consider the assertion, that
the mental life of the higher mammals has gradually developed up to that
of man, as in any way exaggerated. If one must draw a sharp boundary
between them, it has to be drawn between the most highly developed and
civilized man on the one hand, and the rudest savages on the other, and
the latter have to be classed with the animals. This is, in fact, the
opinion of many travellers, who have long watched the lowest human races
in their native countries. Thus, for example, a great English traveller,
who lived for a considerable time on the west coast of Africa, says: “I
consider the negro to be a lower species of man, and cannot make up my
mind to look upon him as ‘a man and a brother,’ for the gorilla would
then also have to be admitted into the family.” Even many Christian
missionaries, who, after long years of fruitless endeavours to civilize
these lowest races, have abandoned the attempt, express the same harsh
judgment, and maintain that it would be easier to train the most
intelligent domestic animals to a moral and civilized life, than these
unreasoning brute-like men. For instance, the able Austrian missionary
Morlang, who tried for many years without the slightest success to
civilize the ape-like negro tribes on the Upper Nile, expressly says:
“that any mission to such savages is absolutely useless. They stand far
below unreasoning animals; the latter at least show signs of affection
towards those who are kind towards them, whereas these brutal natives
are utterly incapable of any feeling of gratitude.”

Now, it clearly follows from these and other testimonies, that the
mental differences between the lowest men and the animals are less than
those between the lowest and the highest men; and if, together with
this, we take into consideration the fact that in every single human
child mental life develops slowly, gradually, and step by step, from the
lowest condition of animal unconsciousness, need we still feel offended
when told that the mind of the whole human race has in like manner gone
through a process of slow, gradual, and historical development? Can we
find it “degrading” to the human soul that, by a long and slow process
of differentiation and perfecting, it has very gradually developed out
of the soul of vertebrate animals? I freely acknowledge that this
objection, which is at present raised by many against the pithecoid
theory, is quite incomprehensible to me. On this point Bernhard Cotta,
in his excellent “Geologie der Gegenwart,” very justly remarks: “Our
ancestors may be a great honour to us; but it is much better if we are
an honour to them!”(31)

Our Theory of Development explains the origin of man and the course of
his historical development in the only natural manner. We see in his
gradually ascensive development out of the lower vertebrata, the
greatest triumph of humanity over the whole of the rest of Nature. We
are proud of having so immensely outstripped our lower animal ancestors,
and derive from it the consoling assurance that in future also, mankind,
as a whole, will follow the glorious career of progressive development,
and attain a still higher degree of mental perfection. When viewed in
this light, the Theory of Descent as applied to man opens up the most
encouraging prospects for the future, and frees us from all those
anxious fears which have been the scarecrows of our opponents.

We can even now foresee with certainty that the complete victory of our
Theory of Development will bear immensely rich fruits—fruits which have
no equal in the whole history of the civilization of mankind. Its first
and most direct result—the complete reform of _Biology_—will necessarily
be followed by a still more important and fruitful reform of
_Anthropology_. From this new theory of man there will be developed a
new _philosophy_, not like most of the airy systems of metaphysical
speculation hitherto prevalent, but one founded upon the solid ground of
Comparative Zoology. A beginning of this has already been made by the
great English philosopher Herbert Spencer.(45) Just as this new monistic
philosophy first opens up to us a true understanding of the real
universe, so its application to practical human life must open up a new
road towards moral perfection. By its aid we shall at last begin to
raise ourselves out of the state of social barbarism in which,
notwithstanding the much vaunted civilization of our century, we are
still plunged. For, unfortunately, it is only too true, as Alfred
Wallace remarks with regard to this, at the end of his book of travels:
“Compared with our wondrous progress in physical science and its
practical applications, our system of government, of administering
justice, of national education, and our whole social and moral
organisation remains in a state of barbarism.”

This social and moral barbarism we shall never overcome by the
artificial and perverse training, the one-sided and defective teaching,
the inner untruth and the external tinsel, of our present state of
civilization. It is above all things necessary to make a complete and
honest return to Nature and to natural relations. This return, however,
will only become possible when man sees and understands his true “place
in nature.” He will then, as Fritz Ratzel has excellently remarked,(47)
“no longer consider himself an _exception_ to natural laws, but begin to
seek for what is lawful in his own actions and thoughts, and endeavour
to lead a life _according_ to natural laws.” He will come to arrange his
life with his fellow-creatures—that is, the family and the state—not
according to the laws of distant centuries, but according to the
rational principles deduced from knowledge of nature. Politics, morals,
and the principles of justice, which are still drawn from all possible
sources, will have to be formed in accordance with natural laws only. An
_existence worthy of man_, which has been talked of for thousands of
years, will at length become a reality.

The highest function of the human mind is perfect knowledge, fully
developed consciousness, and the moral activity arising from it. “Know
thyself!” was the cry of the philosophers of antiquity to their
fellow-men who were striving to ennoble themselves. “Know thyself!” is
the cry of the Theory of Development, not merely to the individual, but
to all mankind. And whilst increased knowledge of self becomes, in the
case of every individual man, a strong force urging to an increased
attention to conduct, mankind as a whole will be led to a higher path of
moral perfection by the knowledge of its true origin and its actual
position in Nature. The simple religion of Nature, which grows from a
true knowledge of Her, and of Her inexhaustible store of revelations,
will in future ennoble and perfect the development of mankind far beyond
that degree which can possibly be attained under the influence of the
multifarious religions of the churches of the various nations,—religions
resting on a blind belief in the vague secrets and mythical revelations
of a sacerdotal caste. Future centuries will celebrate our age, which
was occupied with laying the foundations of the Doctrine of Descent, as
the new era in which began a period of human development, rich in
blessings,—a period which was characterized by the victory of free
inquiry over the despotism of authority, and by the powerful ennobling
influence of the Monistic Philosophy.

FOOTNOTES:

[1] With the exception of a single specimen of the bones of a foot,
preserved in the cabinet of Amherst College.—E. R. L.

[2] The primary stock of the Coniferæ divided into two branches at an
early period, into the Araucariæ on the one hand, and the Taxaceæ, or
yew-trees, on the other. The majority of recent Coniferæ are derived
from the former. Out of the latter the third class of the
Gymnosperms—the Meningos, or Gnetaceæ—were developed. This small but
very interesting class contains only three different genera—Gnetum,
Welwitschia, and Ephedra; it is, however, of great importance, as it
forms the transition group from the Coniferæ to the Angiosperms, and
more especially to the Dicotyledons.

[3] “Ueber ein Aequivalent der takonischen Schiefer Nordamerikas in
Deutschland.”

[4] The English word “Insects” might with advantage be used in the
Linnæan sense for the whole group of Arthropods. In this case the
Hexapod Insects might be spoken of as the Flies.—E. R. L.

[5] Weisbach: “Novara-Reise,” Anthropholog. Theil.

[6] Müsset im Naturbetrachten
Immer Eins wie Alles achten.
Nichts ist drinnen, Nichts ist drauszen,
Denn was innen, das ist auszen.

[7] Natur hat weder Kern noch Schale,
Alles ist sie mit einem Male.

LIST OF THE WORKS REFERRED TO IN THE TEXT BY FIGURES, THUS—(1),

_The study of which is recommended to the Reader._

1. _Charles Darwin_, On the Origin of Species by means of Natural
Selection; or, the Preservation of Favoured Races in the Struggle for
Life. London, 1859. 5th Edition, 1869.

2. _Jean Lamarck_, Philosophie Zoologique, ou Exposition des
Considérations relatives à l’histoire naturelle des animaux; à la
diversité de leur organisation et des facultés, qu’ils en obtiennent;
aux causes physiques, qui maintiennent en eux la vie et donnent lieu aux
mouvemens, qu’ils exécutent; enfin, à celles qui produisent, les unes le
sentiment, et les autres l’intelligence de ceux qui en sont doués. 2
Tomes. Paris, 1809.

3. _Wolfgang Goethe_, Zur Morphologie: Bildung und Umbildung organischer
Naturen. Die Metamorphose der Pflanzen, 1790. Osteologie, 1786. Vorträge
über die drei ersten Capitel des Entwurfs einer allgemeinen Einleitung
in die vergleichende Anatomie, ausgehend von der Osteologie, 1786. Zur
Naturwissenschaft im Allgemeinen, 1780-1832.

(Wolfgang Goethe, Contributions to Morphology: Formation and
Transformation of Organic Natures. The Metamorphosis of Plants, 1790.
Osteology, 1786. Lectures on the first three chapters of an Attempt at a
General Introduction to Comparative Anatomy, beginning with Osteology,
1786. Contributions to the Science of Nature in general, 1780-1832.)

4. _Ernst Haeckel_, Generelle Morphologie der Organismen: Allgemeine
Grundzüge der organischen Formenwissenschaft, mechanisch begründet durch
die von Charles Darwin reformirte Descendenz-theorie. I. Band,
Allgemeine Anatomie der Organismen, oder Wissenschaft von den
entwickelten organischen Formen. II. Band, Allgemeine
Entwickelungsgeschichte der Organismen, oder Wissenschaft von den
entstehenden organischen Formen. Berlin, 1866.

(Ernst Haeckel, General Morphology of Organisms; General Outlines of the
Science of Organic Forms based on Mechanical Principles through the
Theory of Descent as reformed by Charles Darwin. Vol. I., General
Anatomy of Organisms; or, the Science of Fully Developed Organic Forms.
Vol. II., General History of the Development of Organisms; or, the
Science of Organic Forms in their Origin. Berlin, 1866.)

5. _Louis Agassiz_, An Essay on Classification. Contributions to the
Natural History of the United States. Boston. Vol. I., 1857.

6. _August Schleicher_, Die Darwin’sche Theorie und die
Sprachwissenschaft. Weimar, 1863.

(August Schleicher, Darwin’s Theory and the Science of Language. Weimar,
1863.)

7. _M. J. Schleiden_, Grundzüge der wissenschaftlichen Botanik (die
Botanik als inductive Wissenschaft). 2 Bände. Leipzig, 1849.

(M. J. Schleiden, Principles of Scientific Botany (Botany as an
Inductive Science). 2 Vols. Leipzig, 1849. Translated by Edwin
Lankester, M.D., F.R.S. London, 1849.)

8. _Franz Unger_, Versuch einer Geschichte der Pflanzenwelt. Wien, 1852.

(Franz Unger, Essay on the History of the Vegetable Kingdom. Vienna,
1852.)

9. _Victor Carus_, System der thierischen Morphologie. Leipzig, 1853.

(Victor Carus, System of Animal Morphology. Leipzig, 1853.)

10. _Louis Büchner_, Kraft und Stoff. Empirisch-naturphilosophische
Studien in allgemein verständlicher Darstellung, Frankfort, 1855, 3
Auflage. 1867, 9 Auflage.

(Louis Büchner, Force and Matter. Studies in the Empirical Philosophy of
Nature, treated popularly. Frankfort, 1855, 3rd Edition. 1867, 9th
Edition.)

11. _Charles Lyell_, Principles of Geology. London, 1830. 10th Edition,
1868.

12. _Albert Lange_, Geschichte des Materialismus und Kritik seiner
Bedeutung in der Gegenwart. Iserlohn, 1866.

(Albert Lange, History of Materialism, and a Criticism of its Importance
at the Present Time. Iserlohn, 1866.)

13. _Charles Darwin_, Voyage of the _Beagle_. London.

14. _Charles Darwin_, The Variation of Animals and Plants under
Domestication. 2 Vols. London, 1868.

15. _Ernst Haeckel_, Studien über Moneren und andere Protisten, nebst
einer Rede über Entwickelungsgang und Aufgabe der Zoologie. Mit 6
Kupfertafeln. Leipzig, 1870.

(Ernst Haeckel, Studies on the Monera and other Protista, together with
a Discourse on the Evolution and the Problems of Zoology. With 6
Copper-plates. Leipzig, 1870.)

16. _Fritz Müller_, Für Darwin. Leipzig, 1864.

(Fritz Müller, For Darwin. Translated by W. S. Dallas. London, Murray.)

17. _Thomas Huxley_, On our Knowledge of the Causes of the Phenomena of
Organic Nature. Six Popular Lectures. London, Hardwicke, 1862.

18. _H. G. Brönn_, Morphologische Studien über die Gestaltungsgesetze
der Naturkörper überhaupt, und der Organischen insbesondere. Leipzig und
Heidelberg, 1858.

(H. G. Brönn, Morphological Studies on the Laws of Form of Natural
Bodies in General, and of Organic Bodies in Particular. Leipzig and
Heidelberg, 1858.)

19. _H. G. Brönn_, Untersuchungen über die Entwickelungsgesetze der
organischen Welt während der Bildungszeit unserer Erdoberfläche.
Stuttgart, 1858.

(H. G. Brönn, Investigations on the Laws of Development of the Organic
World during the Time of the Formation of the Earth’s Crust. Stuttgart,
1858.)

20. _Carl Ernst Bär_, Ueber Entwickelungsgeschichte der Thiere.
Beobachtung und Reflexion. 2 Bände. 1828.

(Carl Ernst Bär, On the History of the Development of Animals.
Observation and Reflection. 2 Vols. 1828.)

21. _Carl Gegenbaur_, Grundzüge der vergleichenden Anatomie. Leipzig,
1859. 2 (Umgearbeitete) Auflage, 1870.

(Carl Gegenbaur, Outlines of Comparative Anatomy. Leipzig, 1859. 2nd
(Revised) Edition, 1870.)

22. _Immanuel Kant_, Allgemeine Naturgeschichte und Theorie des Himmels,
oder Versuch von der Verfassung und dem mechanischen Ursprunge des
ganzen Weltgebäudes nach Newton’schen Grundsätzen abgehandelt.
Königsberg, 1755.

(Immanuel Kant, General History of Nature and Theory of the Heavens; or,
Essay on the Constitution and the Mechanical Origin of the whole
Universe treated according to Newton’s Principles. Königsberg, 1755.)

23. _Ernst Haeckel_, Die Radiolarien. Eine Monographie. Mit einem Atlas
von 35 Kupfertafeln. Berlin, 1862.

(Ernst Haeckel, The Radiolaria. A Monograph, with Atlas containing 35
Copper-plates. Berlin, 1862.)

24. _August Weismann_, Ueber den Einflusz der Isolirung auf die
Artbildung. Leipzig, 1872.

(August Weismann, On the Influence of Isolation on the Formation of
Species. Leipzig, 1872.)

25. _Ernst Haeckel_, Ueber die Enstehung und den Stammbaum des
Menschengeschlechts. Zwei Vorträge in der Sammlung gemeinverständlicher
wissenschaftlicher Vorträge, herausgegeben von Virchow und Holtzendorff.
Berlin, 1868. 2 Auflage, 1870.

(Ernst Haeckel, On the Origin and the Pedigree of the Human Race. Two
Lectures in the Collection of Popular Scientific Lectures, edited by
Virchow and Holtzendorff. Berlin, 1868. 2nd Edition, 1870.)

26. _Thomas Huxley_, Evidences as to Man’s Place in Nature. Three Parts:
1. On the Natural History of the Man-like Apes. 2. On the Relations of
Man to the Lower Animals. 3. On some Fossil Remains of Man. London,
Williams & Norgate.

27. _Carl Vogt_, Vorlesungen über den Menschen, seine Stellung in der
Schöpfung und in der Geschichte der Erde. 2 Bände. Giessen, 1863.

(Carl Vogt, Lectures on Man, his Place in Creation and in the History of
the Earth. 2 Vols. Giessen, 1863.)

28. _Friedrich Rolle_, Der Mensch, seine Abstammung und Gesittung im
Lichte der Darwin’schen Lehre von der Art-Entstehung, und auf Grund der
neueren geologischen Entdeckungen dargestellt. Frankfurt-a-M., 1866.

(Friedrich Rolle, Man, his Derivation and Civilization, in the Light of
Darwin’s Theory of the Origin of Species, based on Recent Geological
Discoveries. Frankfort-a-M., 1866.)

29. _Eduard Reich_, Die allgemeine Naturlehre des Menschen. Giessen,
1865.

(Eduard Reich, The General Natural History of Man. Giessen, 1865.)

30. _Charles Lyell_, The Antiquity of Man. London, Murray.

31. _Bernhard Cotta_, Die Geologie der Gegenwart. Leipzig, 1866.

(Bernhard Cotta, The Geology of the Present Day.)

32. _Karl Zittel_, Aus der Urzeit. Bilder aus der Schöpfungsgeschichte.
München, 1871.

(Karl Zittel, Primæval Times. Pictures from the History of Creation.
Munich, 1871.)

33. _C. Radenhausen_, Isis. Der Mensch und die Welt. 4 Bände. Hamburg,
1863. 2 Auflage, 1871.

(C. Radenhausen, Isis. Man and the Universe. 4 Vols. Hamburg, 1863. 2nd
Edition, 1871.)

34. _August Schleicher_, Ueber der Bedeutung der Sprache für die
Naturgeschichte des Menschen. Weimar, 1865.

(August Schleicher, On the Importance of Language to the Natural History
of Man. Weimar, 1865).

35. _Wilhelm Bleek_, Ueber den Ursprung der Sprache. Herausgegeben mit
einem Vorwort von Ernst Haeckel. Weimar, 1868.

(Wilhelm Bleek, On the Origin of Language. Edited and with a Preface by
Ernst Haeckel. Weimar, 1868.)

36. _Alfred Russel Wallace_, The Malayan Archipelago. London, Macmillan.

37. _Ernst Haeckel_, Ueber Arbeitstheilung in Natur- und Menschenleben.
Sammlung gemeinverständlicher wissenschaftlicher Vorträge, herausgegeben
von Virchow und Holtzendorff. 4 Serie. 1869. Heft 78.

(Ernst Haeckel, On Differentiation in Nature and in Human Life. A
Collection of Popular Scientific Lectures, edited by Virchow and
Holtzendorff. 4th Series. 1869. No. 78.)

38. _Hermann Helmholtz_, Populäre wissenschaftliche Vorträge.
Braunschweig, 1871.

(Hermann Helmholtz, Popular Scientific Lectures. Brunswick, 1871.)

39. _Alexander Humboldt_, Ansichten der Natur. Stuttgart, 1826.

(Alexander Humboldt, Views of Nature. Stuttgart, 1826.)

40. _Moritz Wagner_, Die Darwin’sche Theorie und das Migrationsgesetz
der Organismen. Leipzig, 1868.

(Moritz Wagner, Darwin’s Theory and the Law of the Migration of
Organisms. Leipzig, 1868.)

41. _Rudolf Virchow_, Vier Reden über Leben und Kranksein. Berlin, 1862.

(Rudolf Virchow, Four Discourses on Life and Disease. Berlin, 1862.)

42. _Friedrich Müller_, Ethnographie (Reise der österreichischen
Fregatte Novara. Anthropologischer Theil. 3 Abtheilung). Wien, 1868.

(Friedrich Müller, Ethnography (Voyage of the Austrian Frigate _Novara_.
Anthropological Part. 3rd Part). Vienna, 1868.)

43. _Ludwig Büchner_, Die Stellung des Menschen in der Natur, in
Vergangenheit, Gegenwart und Zukunft. Leipzig, 1870.

(Ludwig Büchner, Man’s Place in Nature in the Past, the Present, and the
Future. Leipzig, 1870.)

44. _John Lubbock_, Prehistoric Times. London, 1867.

45. _Herbert Spencer_, A System of Philosophy. (1. First Principles. 2.
Principles of Biology. 3. Principles of Psychology, etc.) London, 1867.
2nd Edition.

46. _Wilhelm Wundt_, Vorlesungen über die Menschen- und Thierseele.
Leipzig, 1863.

(Wilhelm Wundt, Lectures on the Human and Animal Soul. Leipzig, 1863.)

47. _Fritz Ratzel_, Sein und Werden der organischen Welt. Eine populäre
Schöpfungsgeschichte. Leipzig, 1869.

(Fritz Ratzel, Nature and Origin of the Organic World. A Popular History
of Creation. Leipzig, 1869.)

48. _Charles Darwin_, The Descent of Man, and Selection in Relation to
Sex. 2 Vols. London, 1871.

APPENDIX.

EXPLANATION OF THE PLATES.

PLATE FACING TITLE-PAGE.

_Developmental History of a Calcareous Sponge_ (Olynthus). Compare vol.
ii. p. 140. The egg of the Olynthus (Fig. 9), which represents the
common ancestral form of all Calcareous Sponges, is a simple cell (Fig.
1). From this there arises, by repeated division (Fig. 2), a globular,
mulberry-like heap of numerous equi-formal cells (Morula, Fig. 3; vol.
ii. p. 125.) As the result of the change of these cells into an outer
series of clear ciliated cells (Exoderm) and an inner series of dark,
non-ciliated cells (Entoderm), the ciliated larva, or Planula, makes its
appearance. This is oval in shape, and forms a cavity in its centre
(gastric cavity, or primitive stomach, Fig. 6 _g_, with an opening
(mouth-opening, or primitive mouth, Fig. 6 _o_); the wall of the gastric
cavity consists of two layers of cells, or germ-layers, the outer
ciliated Exoderm (_e_) and the inner non-ciliated Entoderm (_i_). Thus
arises the exceedingly important stomach-larva, or Gastrula, which
reappears in the most different tribes of animals as a common larval
form (Fig. 5, seen from the surface; Fig. 6, in long section. Compare,
vol. ii. pp. 126 and 281). After the Gastrula has swum about for some
time in the sea, it fastens itself securely to the sea-bottom, loses its
outer vibratile processes, or cilia, and changes into the Ascula (Fig.
7, seen from the surface; Fig. 8, in long section; letters as in Fig.
6). This Ascula is the recapitulative form, according to the biogenetic
fundamental law, the common ancestor of all Zoophytes, namely, the
Protascus (vol. ii. pp. 129, 133). By the development of pores in the
wall of the stomach and of three-rayed calcareous spicules, the Ascula
changes into the Olynthus (Fig. 9.) In Fig. 9 a piece is cut out from
the stomach-wall of the Olynthus in order to show the inside of the
stomachal cavity, and the eggs which are forming on the surface (_g_).
From the Olynthus the most various forms of Calcareous Sponges can
develop. One of the most remarkable is the Ascometra (Fig. 10), a stock
or colony from which different species, and in fact different generic
forms, grow (on the left Olynthus, in the middle Nardorus, on the right
Soleniscus, etc., etc.). Further details as to these most interesting
forms, and their high importance for the Theory of Descent, may be found
in my “Monograph of the Calcareous Sponges” (1872), especially in the
first volume. (Compare vol. ii. pp. 160, 167).

PLATE I. (_Between pages 184 and 185, Vol. I._)

_History of the Life of the most Simple Organism_, a Moneron (Protomyxa
aurantiaca). Compare vol. i. p. 184, and vol. ii. p. 53. The plate is a
smaller copy of the drawing in my “Monographie der Moneren” (Biologische
Studien, 1 Heft, 1870; Taf. 1), of the developmental history of the
Protomyxa aurantiaca; I have there also given a detailed description of
this remarkable Moneron (pp. 11-30). I discovered this most simple
organism in January, 1867, during a stay in Lanzarote, one of the Canary
Islands; and moreover I found it either adhering to, or creeping about
on the white calcareous shells of a small Cephalopod (vol. ii. p. 162),
the Spirula Peronii, which float there in masses on the surface of the
ocean, or are thrown up on the shore. The Protomyxa aurantiaca is
distinguished from the other Monera by the beautiful and bright
orange-red colour of its perfectly simple body, which consists merely of
primæval slime, or protoplasm. The fully developed Moneron is
represented in Figs. 11 and 12, very much enlarged. When it is hungry
(Fig. 11), there radiate from the surface of the globular corpuscule of
plasm, quantities of tree-shaped, branching and mobile threads
(pseudo-feet, or pseudopodia), which do not become retiformly
connected. When, however, the Moneron eats (Fig. 12), the mucous threads
become variously connected, form net-works and enclose the extraneous
corpuscule which serves as food, which the threads afterwards draw into
the interior of the Protomyxa. Thus in Fig. 12 (above on the right), a
silicious and ciliated Whip-swimmer (Peridinium, vol. ii. pp. 51, 57),
has just been caught by the extended mucous filaments, and has been
drawn into the interior of the mucous globule, in which there already
are several half digested silicious infusoria (Tintinoida), and Diatomeæ
(Isthmia). Now, when the Protomyxa has eaten and grown sufficiently, it
draws in all its mucous filaments (Fig. 15), and contracts into the form
of a globule (Fig. 16 and Fig. 1). In this state of repose the globule
secretes a simple gelatinous covering (Fig. 2), and after a time
subdivides into a large number of small mucous globules (Fig. 3). These
soon commence to move, become pear-shaped (Fig. 4), break through the
common covering (Fig. 5), and then swim about freely in the ocean by
means of a delicate whip-shaped process, like the Flagellata (vol. ii.
p. 57, Fig. 11). When they meet a Spirula shell, or any other suitable
object, they adhere to it, draw in their whip, and creep slowly about on
it by means of form-changing processes (Figs. 6, 7, 8), like Protamœbæ
(vol. i. p. 186, vol. ii. p. 52). These small mucous corpuscules take
food (Figs. 9, 10), and attain their full grown form (Figs. 11, 12),
either by simple growth or by several of them fusing to form a larger
protoplasmic mass (Plasmodium, Figs. 13, 14).

PLATES II. AND III. (_Between pages 294 and 295, Vol. I._)

_Germs or Embryos of four different Vertebrate Animals_, namely,
Tortoise (_A_ and _E_), Hen (_B_ and _F_), Dog (_C_ and _G_), and Man
(_D_ and _H_). Figs. _A_, _D_, an early stage of development; Figs. _E_,
_H_, a later stage. All the eight embryos are represented as seen from
the right side, the curved back turned to the left. Figs. _A_ and _B_
are seven times enlarged, Figs. _C_ and _D_ five times, Figs. _E_ and
_H_ four times. Plate II. exhibits the very close blood relationship
between birds and reptiles; Plate III. that between man and the other
mammals.

PLATE IV. (_Between pages 34 and 35, Vol. II._)

_The Hand, or Fore Foot, of nine different Mammals._ This plate is
intended to show the importance of Comparative Anatomy to Phylogeny, in
as much as it proves how the internal skeleton of the limbs is
continually preserved by _inheritance_, although the external form is
extremely changed by _adaptation_. The bones of the skeleton of the hand
are drawn in white lines on the brown flesh and skin which surrounds
them. All the nine hands are represented in the same position, namely
the wrist (where the arm would be joined to it) is placed above, whilst
the ends of the fingers or toes are turned downwards. The thumb, or the
first (large) fore-toe is on the left in every figure; the little
finger, or fifth toe is to the right at the edge of the hand. Each hand
consists of three parts, namely (i.) the _wrist_ (carpus), composed of
two cross rows of short bones (at the upper side of the hand); (ii.) the
_mid-hand_ (metacarpus), composed of five long and strong bones (marked
in the centre of the hand by the numbers 1-5); and (iii.) the five
_fingers_, or _fore toes_ (digiti), every one of which again consists of
several (mostly from two to three), _toe-pieces_, or _phalanges_. The
hand of _man_ (Fig. 1), in regard to its entire formation, stands
midway between that of the two large human apes, namely, that of the
_gorilla_ (Fig. 2), and that of the _orang_ (Fig. 3). The fore paw of
the _dog_ (Fig. 4), is more different, and the hand or breast fin of the
_seal_ (Fig. 5) still more so. The adaptation of the hand to the
movement of swimming, and its transformation into a fin for steering, is
still more complete in the _dolphin_ (Ziphius, Fig. 6). The extended
fingers and bones of the central hand here have remained short and
strong in the swimming membrane, but they have become extremely long and
thin in the _bat_ (Fig. 7), where the hand has developed into a wing.
The extreme opposite of the latter formation is the hand of the _mole_
(Fig. 8), which has acquired a powerful spade-like form for digging,
with fingers which have become extremely short and thick. What is far
more like the human hand than these latter forms, is the fore paw of the
lowest and most imperfect of all mammals, the Australian _beaked animal_
(Ornithorhynchus, Fig. 9), which in its whole structure stands nearer to
the common, extinct, primary form of mammalia, than any known species.
Hence man differs less in the formation of the hand from this common
primary form than from the bat, mole, dolphin, seal, and many other
mammals.

PLATE V. (_Between pages 84 and 85, Vol. II._)

_Monophyletic, or One-rooted Pedigree of the Vegetable Kingdom_,
representing the hypothesis of the common derivation of all plants, and
the historical development of the different groups of plants during the
palæontological periods of the earth’s history. The horizontal lines
denote the different smaller and larger periods of the organic history
of the earth (which are spoken of in vol. ii. p. 14), and during which
the strata containing fossils were deposited. The vertical lines
separate the different main-classes and classes of the vegetable kingdom
from one another. The arboriform and branching lines indicate, in an
approximate manner, by their greater or less number and thickness, the
greater or less degree of development, differentiation, and perfecting
which each class probably attained in each geological period. (Compare
vol. ii. pp. 82, 83.)

PLATE VI. (_Between pages 130 and 131, Vol. II._)

_Monophyletic, or One-rooted Pedigree of the Animal Kingdom_,
representing the _historical growth of the six animal tribes_ during the
palæontological periods of the organic history of the earth. The
horizontal lines _g h_, _i k_, _l m_, and _n o_ divide the five large
periods of the organic history of the earth one from another. The field
_g a b h_ comprises the archilithic, the field _i g h k_, the
palæolithic, the field _l i k m_ the mesolithic, and the field _n l o m_
the cenolithic period. The short, anthropolithic period is indicated
by the line _n o_. (Compare vol. ii. p. 14.) The height of the separate
fields corresponds with the relative length of the periods indicated by
them, as they may approximately be estimated from the relative thickness
of the neptunic strata deposited between them. (Compare vol. ii. p. 22.)
The archilithic and primordial period alone, during which the
Laurentian, Cambrian, and Silurian strata were deposited, was probably
considerably longer than the four subsequent periods taken together.
(Compare vol. ii. pp. 10, 20.) In all probability the two tribes of
worms and Zoophytes attained their full development during the
mid-primordial period (in the Cambrian system); the star-fishes and
molluscs probably somewhat later (in the Silurian system); whereas the
articulata and vertebrata are still increasing in variety and
perfection.

PLATE VII. (_Between pages 146 and 147, Vol. II._)

_Group of Animal-Trees_ (_Zoophytes, or Cœlenterata_) _in the
Mediterranean_. On the upper half of the plate is a swarm of swimming
medusæ and ctenophora; on the lower half a few bunches of corals and
hydroid polyps adhering to the bottom of the sea. (Compare the system of
Zoophytes, vol. ii. p. 132, and on the opposite page their pedigree.)
Among the adhering Zoophytes at the bottom of the ocean there is, below
on the right hand, a large coral-colony (1), which is closely akin to
the red precious coral (Eucorallium), and like the latter belongs to the
group of corals with eight rays (Octocoralla Gorgonida); the single
individuals (or persons) of the branching stock have the form of a star
with eight rays, consisting of eight tentacles, which surround the
mouth. (Octocoralla, vol. ii. p. 143.) Directly below and in front of it
(quite below on the right), is a small bush of hydroid polyps (2),
belonging to the group of bell-polyps, or Campanulariæ (vol. ii. p.
146). A larger stock of hydroid polyps (3), belonging to the group of
tube-polyps, or Tubullariæ, rises, to the left, on the opposite side,
with its long thin branches. At its base is spread a stock of silicious
sponges (Halichondria) (4), with short, finger-shaped branches (vol.
ii. p. 139). Behind it, below on the left (5), is a very large marine
rose (Actinia), a single individual from the class of six-rayed corals
(Hexacoralla, vol. ii. p. 143). Its low, cylindrical body has a crown of
very numerous and large leaf-shaped tentacles. Below, in the centre of
the ground (6), is a sea-anemone (Cereanthus) from the group of
fourfold corals (Tetracoralla). Lastly, on a small hill on the bottom
of the sea, there rises, on the right above the corals (1) a cup-polyp
(Lucernaria), as the representative of the stalked-jellies.
(Podactinaria, or Calycozoa, vol. ii. p. 144.) Its cup-shaped, stalked
body (7) has eight globular clusters of small, knotted tentacles on its
rim.

Among the _swimming Zoophytes_ which occupy the upper half of Plate
VII., the hydromedusæ are especially remarkable, on account of their
alteration of generation. (Compare vol. i. p. 206.) Directly above the
Lucernaria (7) floats a small tiara jelly (Oceania), whose bell-shaped
body has a process like a dome, the form of a papal tiara (8). From the
opening of the bell there hangs a wreath of very fine and long
tentacles. This Oceania is the offspring of a tube-polyp, resembling the
adhering Tubularia below on the left (3). Beside this latter, on the
left, swims a large but very delicate hair-jelly (Æquorea). Its
disc-shaped, slightly arched body is just drawing itself together, and
pressing water out of the cavity of the cup lying below (9). The
numerous, long, and fine hair-like tentacles which hang down from the
rim of the cup are drawn by the ejected water into a conical bunch,
which towards the centre turns upwards like a collar, and is thrown into
folds. Above, in the middle of the cavity of the cup, hangs the stomach,
the mouth of which is surrounded by four lobes. This Æquorea is derived
from a small bell-polyp, resembling the Campanularia (2). The small,
slightly arched cap-jelly (Eucope), swimming above in the centre (10),
is likewise derived from a similar bell-polyp. In these three last cases
(8, 9, 10), as in the majority of the hydromedusæ, the alternation of
generation consists in the freely swimming medusa (8, 9, 10), arising by
the formation of buds (therefore by non-sexual generation, vol. i. p.
192), from adhering hydroid polyps (2, 3). These latter, however,
originate out of the fructified eggs of the medusæ (therefore by sexual
generation, vol. i. p. 195). Hence the non-sexual, adhering generation
of polyps (I., III., V., etc.) regularly alternates with the sexual,
freely swimming generation of medusæ (II., IV., VI., etc.). This
alteration of generation can only be explained by the Theory of Descent.

The same remark applies to a kindred form of propagation, which is still
more remarkable, and which I discovered in 1864, near Nice, in the
Elephant-jellies (Geryonida), and called _allœogony_, or _allœogenesis_.
In this case two completely distinct forms of medusa are descended from
one another; the larger and more highly developed generation (11),
Geryonia, or Carmarina, is six-rayed, with six foliated sexual organs,
and six very movable marginal filaments. From the centre of its
bell-shaped cup, like the tongue of a bell, hangs a long proboscis, at
the end of which is the opening of the mouth and stomach. In the cavity
of the stomach is a long, tongue-shaped bunch of buds (which on Plate
VII. (_n_) is extended from the mouth on the left like a tongue). On
this tongue, when the Geryonia is sexually ripe, there bud a number of
small medusæ. They are, however, not Geryoniæ, but belong to an entirely
distinct but very different form of medusa, namely, to the genus Cunina,
of the family of the _Æginida_. This Cunina (12) is very differently
constructed; it has a flat, semi-globular cup without proboscis,
consists in early life of six divisions, later of sixteen, and has
sixteen bag-shaped sexual organs, and sixteen short, stiff, and strongly
curved tentacles. A further explanation of this wonderful allœogenesis
may be found in my “Contributions to the Natural History of the
Hydromedusæ.” (_Leipzig_, Englemann, 1865), the first part of which
contains a monograph of the Elephant-jellies, or Geryonida, illustrated
by six copper-plates.

Even more interesting and instructive than these remarkable relations
are the vital phenomena of the _Siphonophora_, whose wonderful
polymorphism I have frequently spoken of, and described in a popular
manner in my lecture on “Differentiation in Nature and Human Life.”(37)
(Compare vol. i. p. 270, and vol. ii. p. 140.) An example of this is
given in Plate VII. in the drawing of the beautiful Physophora (13).
This swimming stock or colony of hydromedusæ is kept floating on the
surface of the sea by a small swimming bladder filled with air, which in
the drawing is seen rising above the surface of the water. Below it is a
column of four pairs of swimming bells, which eject water, and thereby
set the whole colony in motion. At the lower end of the column of
swimming bells is a crown-shaped wreath of curved spindle-shaped
_sensitive polyps_, which also serve as a covering, under the protection
of which the other individuals of the stock (the eating, catching, and
reproductive persons) are hidden. The _ontogenesis_ of the Siphonophora
(and especially of this Physophora), I first observed in Lanzerote, one
of the Canary Islands, in 1866, and described in my “History of the
Development of the Siphonophora,” and added fourteen plates for its
explanation. (Utrecht, 1869). It is rich in interesting facts, which can
only be explained by the Theory of Descent.

Another circumstance, which is also only explicable by the Theory of
Descent, is the remarkable change of generation in the higher medusæ,
the disc-jellies (Discomedusæ, vol. ii. p. 136), a representative of
which is given at the top of Plate VII., in the centre (rather in the
background), namely, a Pelagia (14). From the bottom of the bell-shaped
cup, which is strongly arched and the rim of which is neatly indented,
there hang four very long and strong arms. The non-sexual polyps, from
which these disc-jellies are derived, are exceedingly simple primæval
polyps, differing very little from the common fresh-water polyp (Hydra).
The alternation of generation in these Discomedusæ has also been
described in my lecture on Differentiation,(37) and there illustrated by
the Aurelia by way of example.

Finally, the last class of Zoophytes, the group of comb-jellies
(Ctenophora, vol. ii. p. 142), has two representatives on Plate VII. To
the left, in the centre, between the Æquorea (9), the Physophora (13),
and the Cunina (12), is a long and thin band like a belt (15), winding
like a snake; this is the large and splendid _Venus’ girdle_ of the
Mediterranean (Cestum), the colours of which are as varied as those of
the rainbow. The actual body of the animal, which lies in the centre of
the long belt, is very small, and constructed exactly like that of the
_melon-jelly_ (Cydippe), which floats above to the left (16). On the
latter are visible the eight characteristic fringed bands, or ciliated
combs, of the ctenophora, and also two long tentacles which extend right
across the page, and are fringed with still finer threads.

PLATES VIII. AND IX. (_Between pages 170 and 171, Vol. II._)

_History of the Development of Star-fishes_ (_Echinoderma_, or
_Estrella_). The two plates exhibit their alternation of generation
(vol. ii. p. 168), with an example from each of the four classes of
Star-fishes. The sea-stars (Asterida) are represented by Uraster (_A_),
the sea-lilies (Crinoida) by Comatula (_B_), the sea-urchins (Echinida)
by Echinus (_C_), and finally, the sea-cucumbers (Holothuriæ) by Synapta
(_D_). (Compare vol. ii. pp. 166 and 176.) The successive stages of
development are marked by the numbers 1-6.

Plate VIII. represents the individual development of the first and
non-sexual generation of Star-fishes, that is, of the _nurses_ (usually,
but erroneously, called larvæ). These nurses possess the form-value of a
simple, unsegmented worm-individual. Fig. 1 represents the egg of the
four Star-fishes; and it, in all essential points, agrees with that of
man and of other animals. (Compare vol. i. p. 297, Fig. 5.) As in man,
the protoplasm of the egg-cell (the yolk) is surrounded by a thick,
structureless membrane (zona pellucida), and contains a globular,
cell-kernel (nucleus), as clear as glass, which again encloses a
nucleolus. Out of the fertilised egg of the Star-fish (Fig. _A_ 1) there
develops in the first place, by the repeated sub-division of cells, a
globular mass of homogeneous cells (Fig. 6, vol. i. p. 299), and this
changes into a very simple nurse, which has almost the same shape as a
wooden shoe (Fig. _A_ 2-_D_ 2). The edge of the opening of the shoe is
bordered by a fringe of cilia, the ciliary movements of which keep the
microscopically small and transparent nurse swimming about freely in the
sea. This fringe of cilia is marked in Fig. _A_ 2-_A_ 4, on Plate VII.,
by the narrow alternately light and dark seam. The nurse then, in the
first place, forms a perfectly simple intestinal canal for nutrition,
mouth (_o_), stomach (_m_) and anus (_a_). Later, the windings of the
fringe of cilia become more complicated, and there arise arm-like
processes (Fig. _A_ 3-_D_ 3). In sea-stars (_A_ 4) and sea-urchins (_C_
4) these arm-like processes, which are fringed with cilia, afterwards
become very long. But in the case of sea-lilies (_B_ 3) and
sea-cucumbers (_D_ 4), instead of this, the fringe of cilia, which at
first, through winding in and out, forms one closed ring, changes
subsequently into a succession of separate ciliated girdles, one lying
behind the other.

In the interior of this curious nurse there then develops, by a
non-sexual process of generation, namely, by the formation of internal
buds or germ-buds (round about the stomach), the second generation of
Star-fishes, which later on become sexually ripe. This second
generation, which is represented on Plate IX. in a fully developed
condition, exists originally as a stock or cormus of five worms,
connected at one end in the form of a star, as is most clearly seen in
the sea-stars, the most ancient and original form of the star-fishes.
The second generation, which grows at the expense of the first,
appropriates only the stomach and a small portion of the other organs of
the latter, but forms for itself a new mouth and anus. The fringe of
cilia, and the other parts of the body of the nurse, afterwards
disappear. The second generation (_A_ 5-_D_ 5), is at first smaller or
not much larger than the nurse, whereas, by growth, it afterwards
becomes more than a hundred times, or even a thousand times, as large.
If the ontogeny of the typical representatives of the four classes of
Star-fishes be compared, it is easily seen that the original kind of
development has been best preserved in sea-stars (_A_) and sea-urchins
(_C_) by inheritance, whereas in sea-lilies (_B_) and sea-cucumbers it
has been suppressed according to the laws of abbreviated inheritance
(vol. i. p. 212).

Plate IX. shows the fully developed and sexually mature animals of the
second generation from the mouth side, which, in the natural position of
Star-fishes (when creeping at the bottom of the sea), in sea-stars (_A_
6) and sea-urchins (_C_ 6), is below, in sea-lilies (_B_ 6) above, and
in sea-cucumbers (_D_ 6) in front. In the centre we perceive, in all the
four Star-fishes, the star-shaped, five-pointed opening of the mouth. In
sea-stars, from each arm there extend several rows of little sucking
feet, from the centre of the under-side of each arm to the end. In
sea-lilies (_B_ 6), each arm is split and feather-like from its base
upwards. In sea-urchins (_C_ 6) the five rows of sucking feet are
divided by broader fields of spines. In sea-cucumbers, lastly (_D_ 6),
on the worm-like body it is sometimes only the five rows of little feet,
sometimes only the feathery tentacles surrounding the mouth, from five
to fifteen (in this case ten), that are externally visible.

PLATES X. AND XI. (_Between pages 174 and 175, Vol. II._)

_Historical Development of the Crab-fish_ (Crustacea).—The two plates
illustrate the development of the different Crustacea from the nauplius,
their common primæval form. On Plate XI. six Crustacea, from six
different orders, are represented in a fully developed state, whereas on
Plate X. the early nauplius stages are given. From the essential
agreement between the latter we may, on the ground of the fundamental
law of biogeny, with full assurance maintain the derivation of the
different Crustacea from a single, common primary form, a long since
extinct Nauplius, as was first shown by Fritz Müller in his excellent
work “Für Darwin.”(16)

Plate X. represents the _early nauplius stages_ from the ventral side,
so that the three pairs of legs, on the short, three-jointed trunk are
distinctly visible. The first of these pairs of legs is simple and
unsegmented, whereas the second and third pairs are forked. All three
pairs are furnished with stiff bristles, which, through the paddling
motion of the legs, serve as an apparatus for swimming. In the centre of
the body, the perfectly simple, straight intestinal canal is visible,
possessing a mouth in front, and an anal orifice behind. In front, above
the mouth, lies a simple, single eye. All the six forms of nauplius
entirely agree in all these essential characteristics of organization,
whereas the six fully developed forms of Crustacea belonging to them,
Plate XI., are extremely different in organisation. The differences of
the six nauplius forms are confined to quite subordinate and unessential
relations in regard to size of body, and the formation of the covering
of the skin. If they could be met with in this form in a sexually mature
condition, no zoologist would hesitate to regard them as six different
species of one genus. (Compare vol. ii. p. 175.)

Plate XI. represents those fully developed and sexually mature forms of
Crustacea, as seen from the right side, which have ontogenetically
(hence also phylogenetically) developed out of the six kinds of
nauplius. Fig. _A c_ shows a freely swimming fresh-water crab (Limnetis
brachyurus) from the order of the Leaf-foot Crabs (Phyllopoda), slightly
enlarged. Of all the still living Crustacea, this order, which belongs
to the legion of Gill-foot Crabs (Branchiopoda), stands nearest to the
original, common primary form of nauplius. The Limnetis is enclosed in a
bivalved shell, like a mussel. Our drawing (which is copied from Grube)
represents the body of a female animal lying in the left shell; the
right half of the shell has been removed. In front, behind the eye, we
see the two feelers (antennæ), and behind them the twelve leaf-shaped
feet of the right side of the body, behind on the back (under the
shell), the eggs. Above, in front, the animal is fixed to the shell.

Fig. _B c_ represents a common, freely swimming fresh-water crab
(Cyclops quadricornis) from the order of Oar-legged crabs (Eucopepoda),
highly magnified. In front, below the eye, we see the two feelers of the
right side, the foremost of which is longer than the hinder one. Behind
these are the gills, and then the four paddling legs of the right side.
Behind these are the two large egg-sacks, which, in this case, are
attached to the end of the hinder part of the body.

Fig. _C c_ is a parasitic Oar-legged crab (Lernæocera esocina), from the
order of fish lice (Siphonostoma). These peculiar crabs, which were
formerly regarded as worms, have originated, by adaptation to a
parasitical life, out of freely swimming, Oar-legged crabs (Eucopepoda),
and belong to the same legion (Copepoda, vol. ii. p. 176). By adhering
to the gills on the skin of fish or other crabs, and feeding on the
juice of these creatures, they forfeited their eyes, legs, and other
organs, and developed into formless, inarticulated sacks, which, on a
mere external examination, we should never suppose to be animals. On the
ventral side only there exist, in the shape of short, pointed bristles,
the last remains of legs which have now almost entirely disappeared. Two
of these rudimentary pairs of legs (the third and fourth) are seen in
our drawing on the right. Above, on the head, we see thick, shapeless
appendages, the lower ones of which are split. In the centre of the body
is seen the intestinal canal, which is surrounded by a dark covering of
fat. At its posterior end is the ovary, and the cement-glands of the
female sexual apparatus. The two large egg-sacks hang externally (as in
the Cyclops, Fig. _B_). Our Lernæocera is represented in half profile,
and is copied from Claus. (Compare Claus, “Die Copepoden-Fauna von
Nizza. Ein Beitrag zur Characteristik der Formen und deren Abänderungen
im Sinne Darwins.” Marburg, 1866).

Fig. _D c_ represents a so-called “duck mussel” (Lepas anatifera), from
the order of the Barnacle crabs (Cirripedia). These crabs, upon which
Darwin has written a very careful monograph, are, like mussels, enclosed
in a bivalved, calcareous case, and hence were formerly (even by Cuvier)
universally regarded as a kind of mussel, or mollusc. It was only from a
knowledge of their ontogeny, and their early nauplius form (_D n_, Plate
VIII.), that their crustacean nature was proved. Our drawing shows a
“duck mussel” of the natural size, from the right side. The right half
of the bivalved shell has been removed, so that the body is seen lying
in the left half of the shell. From the rudimentary head of the Lepas
there issues a long, fleshy stalk (curving upwards in our drawing); by
means of it the Barnacle crab grows on rocks, ships, etc. On the ventral
side are six pairs of feet. Every foot is forked and divided into two
long, curved, or curled “tendrils” furnished with bristles. Above and
behind the last pair of feet projects the thin cylindrical tail.

Fig. _E c_ represents a parasitic sack-crab (Sacculina purpurea) from
the order of Root-crabs (Rhizocephala). These parasites, by adaptation
to a parasitical life, have developed out of Barnacle crabs (Fig. _D
c_), much in the same way as the fish-lice (_C c_), out of the freely
swimming Oar-legged crabs (_B c_). However, the suppression, and the
subsequent degeneration, of all of the organs, has gone much further in
the present case than in most of the fish-lice. Out of the articulated
crab, possessing legs, intestine, and eye, and which in an early stage
as nauplius (_E n_, Plate VIII.), swam about freely, there has developed
a formless, unsegmented sack, a red sausage, which now only contains
sexual organs (eggs and sperm) and an intestinal rudiment. The legs and
the eye have completely disappeared. At the posterior end is the opening
of the genitals. From the mouth grows a thick bunch of numerous
tree-shaped and branching root-like fibres. These spread themselves out
(like the roots of a plant in the ground) in the soft hinder part of the
body of the hermit-crab (Pagurus), upon which the root-crab lives as a
parasite, and from which it draws its nourishment. Our drawing (_E c_),
a copy of Fritz Müller’s, is slightly enlarged, and shows the whole of
the sausage-shaped sack-crab, with all its root-fibres, when drawn out
of the body upon which it lives.

Fig. _F c_ is a _shrimp_ (Peneus Mülleri), from the order of _ten-foot_
crabs (Decapoda), to which our river cray-fish, and its nearest
relative, the lobster, and the short-tailed shore-crabs also belong.
This order contains the largest and, gastronomically, the most important
crabs, and belongs, together with the mouth-legged and split-legged
crabs, to the legion of the stalk-eyed mailed crabs (Podophthalma). The
shrimp, as well as the river crab, has in front, on each side below the
eye, two long feelers (the first much shorter than the second), then
three jaws, and three jaw-feet, then five very long legs (the three
fore ones of which, in the Peneus, are furnished with nippers, and the
third of which is the longest). Finally, on the first five joints of the
hinder part of the body there are other five pairs of feet. This shrimp,
which is one of the most highly developed and perfect crabs, originates
(according to Fritz Müller’s important discovery) out of a nauplius (_F
n_ Plate VIII.), and consequently proves that the higher Crustacea have
developed out of the same form as the lower ones, namely, the nauplius.
(Compare vol. ii. p. 175.)

PLATES XII. AND XIII. (_Between pages 200 and 201, Vol. II._)

_Blood relationship between the Vertebrata and the Invertebrata._
(Compare vol. ii. pp. 152 and 201.) It is definitely established by
Kowalewski’s important discovery, which was confirmed by Kupffer, that
the ontogeny of the lowest vertebrate animal—the Lancelet, or
Amphioxus—agrees in all essential outlines completely with that of the
invertebrate Sea-squirts, or Ascidiæ, from the class of Sea-sacks, or
Tunicata. On our two plates, the ascidia is marked by _A_, the amphioxus
by _B_. Plate XIII. represents these two very different animal-forms in
a _fully developed_ state, as seen from the _left side_, the end of the
mouth above, the opposite end below. Hence, in both figures the dorsal
side is to the right, the ventral to the left. Both figures are slightly
magnified, and the internal organisation of the animals is distinctly
visible through the transparent skin. The full-grown ascidia (Fig. _A_
6) grows at the bottom of the ocean, from whence it cannot move, and
clings to stones and other objects by means of peculiar roots (_w_) like
a plant. The full-grown amphioxus, on the other hand (Fig. _B_ 6), swims
about freely like a small fish. The letters on both figures indicate the
same parts: (_a_) orifice of the mouth; (_b_) orifice of the body, or
porus abdominalis; (_c_) dorsal rod, or chorda dorsalis; (_d_)
intestine; (_e_) ovary; (_f_) oviduct (same as the sperm-duct); (_g_)
spinal marrow; (_h_) heart; (_i_) blind-sac of the intestine; (_k_)
gill basket (respiratory cavity); (_l_) cavity of the body; (_m_)
muscles; (_n_) testicle (in the ascidia united with the ovary into a
hermaphrodite gland); (_o_) anus; (_p_) genital orifice; (_q_)
well-developed embryos in the body cavity of the ascidia; (_r_) rays of
the dorsal fin of the amphioxus; (_s_) tail-fin of the amphioxus; (_w_)
roots of the ascidia.

Plate XII. shows the _Ontogenesis_, or the individual development of the
_Ascidia_ (_A_) and the _Amphioxus_ (_B_) in five different stages
(1-5). Fig. 1 is the egg, a simple cell like the egg of man and all
other animals (Fig. _A_ 1 the egg of the ascidia, Fig. _B_ 1 the egg of
the amphioxus). The actual cell-substance, or the protoplasm of the
egg-cell (_z_), the so-called yolk, is surrounded by a covering
(cell-membrane, or yolk-membrane), and encloses a globular cell-kernel,
or nucleus (_y_), the latter, again, contains a kernel-body, or
nucleolus (_x_); when the egg begins to develop, the egg-cell first
subdivides into two cells. By another sub-division there arise four
cells (Fig. _A_ 2, _B_ 2), and out of these, by repeated sub-division,
eight cells (vol. i. p. 190, Fig. 4 _C_, _D_). By fluid gathering in the
interior these form a globular bladder bounded by a layer of cells. On
one spot of its surface the bladder is turned inwards in the form of a
pocket (Fig. _A_ 4, _B_ 4). This depression is the beginning of the
intestine, the cavity (_d_ 1) of which opens externally by the
provisional larval-mouth (_d_ 4). The body-wall, which is at the same
time the stomach-wall, now consists of two layers of cells—the
germ-layers. The globular larva (Gastrula), now grows in length. Fig.
_A_ 5 represents the larva of the ascidia, Fig. _B_ 5 that of the
amphioxus, as seen from the left side in a somewhat more advanced state
of development. The orifice of the intestine (_d_ 1) has closed. The
dorsal side of the intestine (_d_ 2) is concave, the ventral side (_d_
3) convex. Above the intestinal tube, on its dorsal side, the neural
tube, the beginning of the spinal marrow, is being formed, its cavity
still opens externally in front (_g_ 2). Between the spinal marrow and
the intestine has arisen the spinal rod, or chorda dorsalis (Notochord)
(_c_), the axis of the inner skeleton. In the larva of the ascidia this
rod (_c_) proceeds along the long rudder-tail, a larval organ, which is
cast off in later transformation. Yet there still exist some very small
ascidiæ (Appendicularia) which do not become transformed and attached,
but which through life swim about freely in the sea by means of their
rudder-tail.

The ontogenetic facts which are systematically represented on Plate XII.
and which were first discovered in 1867, deserve the greatest attention,
and, indeed, cannot be too highly estimated. They fill up the gap which,
according to the opinion of older zoologists existed between the
vertebrate and the so-called “invertebrate” animals. This gap was
universally regarded as so important and so undeniable, that even
eminent zoologists, who were not disinclined to adopt the theory of
descent, saw in this gap one of the chief obstacles against it. Now that
the ontogeny of the amphioxus and the ascidia has set this obstacle
completely aside, we are for the first time enabled to trace the
pedigree of man beyond the amphioxus into the many-branching tribe of
“invertebrate” worms, from which all the other higher animal tribes have
originated.

If our speculative philosophers, instead of occupying themselves with
castles in the air, were to give their thoughts for some years to the
facts represented on Plates XII. and XIII., as well as to those on
Plates II. and III., they would gain a foundation for true
philosophy—for the knowledge of the universe firmly based on
experience—which would be sure to influence all regions of thought.
These facts of ontogenesis are the indestructible foundations upon which
the monistic philosophy of future times will erect its imperishable
system.

PLATE XIV. (_Between pages 206 and 207, Vol. II._)

_Monophyletic, or One-rooted Pedigree of the Vertebrate Animal tribe_,
representing the hypothesis of the common derivation of all vertebrate
animals, and the historical development of their different classes
during the palæontological periods of the earth’s history. (Compare
Chapter XX. vol. ii. p. 192.) The horizontal lines indicate the periods
(mentioned in vol. ii. p. 14) of the organic history of the earth during
which the deposition of the strata containing fossils took place. The
vertical lines separate the classes and sub-classes of vertebrata from
one another. The tree-shaped and branching lines, by their greater or
lesser number and thickness, indicate the approximate degree of
development, variety, and perfection, which each class probably attained
in each geological period. In those classes which, on account of the
soft nature of their bodies, could not leave any fossil remains (which
is especially the case with Prochordata, Acrania, Monorrhina, and
Dipneusta) the course of development is hypothetically suggested on the
ground of arguments derived from the three records of
creation—comparative anatomy, ontogeny, and palæontology. The most
important starting-points for the hypothetical completion of the
palæontological gaps are here, as in all cases, furnished by the
_fundamental law of biogeny_, which asserts the inner _causal-nexus
existing between ontogeny and phylogeny_. (Compare vol. i. p. 310, and
vol. ii. p. 200; also Plates VIII.-XIII.) In all cases we have to regard
the individual development (determined by the laws of Inheritance but
modified by the laws of Adaptation) as short and quick repetitions of
the palæontological development of the tribe. This proposition is the
“ceterum censeo” of our theory of development.

The statements of the first appearance, or the period of the origin of
the individual classes and sub-classes of vertebrate animals (apart from
the hypothetical filling in mentioned just now), are taken as strictly
as possible from palæontological facts. It must, however, be observed,
that in reality the origin of most of the groups probably took place one
or two periods earlier than fossils now indicate. In this I agree with
Huxley’s views; but on Plates V. and XIV. I have disregarded this
consideration in order not to go too far from palæontological facts.

The numbers signify as follows (compare also Chapter XX. and vol. ii.
pp. 204, 206):—1. Animal Monera; 2. Animal Amœbæ; 3. Community of Amœbæ
(Synamœbæ); 4. Ciliated Infusoria without mouths; 5. Ciliated Infusoria
with mouths; 6. Gliding worms (Turbellaria); 7. Sea-sacks (Tunicata);
8. Lancelet (Amphioxus); 9. Hag (Myxinoida); 10. Lamprey
(Petromyzontia); 11. Unknown forms of transition from single-nostriled
animals to primæval fishes; 12. Silurian primæval fish (Onchus, etc.);
13. Living primæval fishes (sharks, rays, Chimæræ); 14. Most ancient
(Silurian) enamelled fishes (Pteraspis); 15. Turtle fishes (Pamphracti);
16. Sturgeons (Sturiones); 17. Angular-scaled enamelled fishes
(Rhombiferi); 18. Bony pike (Lepidosteus); 19. Finny pike (Polypterus);
20. Hollow-boned fishes (Cœloscolopes); 21. Solid boned fishes
(Pycnoscolopes); 22. Bald pike (Amia); 23. Primæval boned fishes
(Thrissopida); 24. Bony fishes with air passage to the swimming bladder
(Physostomi); 25. Bony fishes without air passage to the swimming
bladder (Physoclisti); 26. Unknown forms of transition between primæval
fishes and amphibious fishes; 27. Ceratodus; 27_a_. Extinct Ceratodus
from the Trias; 27_b_. Living Australian Ceratodus; 28. African
amphibious fishes (Protopterus) and American amphibious fishes
(Lepidosiren); 29. Unknown forms of transition between primæval fishes
and amphibia; 30. Enamelled heads (Ganocephala); 31. Labyrinth toothed
(Labyrinthodonta); 32. Blind burrowers (Cæciliæ); 33. Gilled amphibia
(Sozobranchia); 34. Tailed amphibia (Sozura); 35. Frog amphibia (Anura);
36. Dichthacantha (Proterosaurus); 37. Unknown forms of transition
between Amphibia and Protamnia; 38. Protamnia (common primary form of
all Amnion animals); 39. Primary mammals (Promammalia); 40. Primæval
reptiles (Proreptilia); 41. (Thecodontia); 42. Primæval dragons
(Simosauria); 43. Serpent dragons (Plesiosauria); 44. Fish dragons
(Ichthyosauria); 45. Teleosauria (Amphicœla); 46. Steneosauria
(Opisthocœla); 47. Alligators and Crocodiles (Prosthocœla); 48.
Carnivorous Dinosauria (Harpagosauria); 49. Herbivorous Dinosauria
(Therosauria); 50. Mæstricht lizards (Mosasauria); 51. Common primary
form of Serpents (Ophidia); 52. Dog-toothed beaked lizards (Cynodontia);
53. Toothless beaked lizards (Cryptodontia); 54. Long-tailed flying
lizards (Rhamphorhynchi); 55. Short-tailed flying lizards
(Pterodactyli); 56. Land tortoises (Chersita); 57. Birds—reptiles
(Tocornithes), transition form between reptiles and birds; 58. Primæval
griffin (Archæopteryx); 59. Water beaked-animal (Ornithorhynchus); 60.
Land beaked-animal (Echidna); 61. Unknown forms of transition between
Cloacals and Marsupials; 62. Unknown forms of transition between
Marsupials and Placentals; 63. Tuft Placentals (Villiplacentalia); 64.
Girdle Placentals (Zonoplacentalia); 65. Disc Placentals
(Discoplacentalia); 66. Man (Homo pithecogenes, by Linnæus erroneously
called, Homo sapiens.)

PLATE XV. (_After page 369, Vol. II._)

_Hypothetical Sketch of the Monophyletic Origin and the Diffusion of the
Twelve Species of Men from Lemuria over the earth._ The _hypothesis_
here geographically sketched of course only claims an entirely
_provisional value_, as in the present imperfect state of our
anthropological knowledge it is simply intended to show how the
distribution of the human species, from a single primæval home, may be
_approximately_ indicated. The probable primæval home, or “Paradise,” is
here assumed to be _Lemuria_, a tropical continent at present lying
below the level of the Indian Ocean, the former existence of which in
the tertiary period seems very probable from numerous facts in animal
and vegetable geography. (Compare vol. i. p. 361, and vol. ii. p. 315.)
But it is also very possible that the hypothetical “cradle of the human
race” lay further to the east (in Hindostan or Further India), or
further to the west (in eastern Africa). Future investigations,
especially in comparative anthropology and palæontology, will, it is to
be hoped, enable us to determine the probable position of the primæval
home of man more definitely than it is possible to do at present.

If in opposition to our monophyletic hypothesis, the polyphyletic
hypothesis—which maintains the origin of the different human species
from several different species of anthropoid ape—be preferred and
adopted, then, from among the many possible hypotheses which arise, the
one deserving most confidence seems to be that which assumes a double
pithecoid root for the human race namely, an Asiatic and an African
root. For it is a very remarkable fact, that the African man-like apes
(gorilla and chimpanzee) are characterized by a distinctly long-headed,
or dolichocephalous, form of skull, like the human species peculiar to
Africa (Hottentots, Caffres, Negroes, Nubians). On the other hand, the
Asiatic man-like apes (especially the small and large orang), by their
distinct, short-headed, or brachycephalous, form of skull agree with
human species especially characteristic of Asia (Mongols and Malays).
Hence, one might be tempted to derive the latter (the Asiatic man-like
apes and primæval men) from a common form of brachycephalous ape, and
the former (the African man-like apes and primæval men) from a common
dolichocephalous form of ape.

In any case, tropical Africa and southern Asia (and between them
Lemuria, which formerly connected them) are those portions of the earth
which deserve the first consideration in the discussion as to the
primæval home of the human race; America and Australia are, on the other
hand, entirely excluded from it. Even Europe (which is in fact but a
western peninsula of Asia) is scarcely of any importance in regard to
the “Paradise question.”

It is self-evident that the migrations of the different human species
from their primæval home, and their geographical distribution, could on
our Plate XV. be indicated only in a very general way, and in the
roughest lines. The numerous migrations of the many branches and tribes
in all directions, as well as the very important re-migrations, had to
be entirely disregarded. In order to make these latter in some degree
clear, our knowledge would, in the first place, need to be much more
complete, and secondly, we should have to make use of an atlas with a
number of plates showing the various migrations. Our Plate XV. claims no
more than to indicate, in a very general way, the approximate
geographical dispersion of the twelve human species as it existed in the
fifteenth century (before the general diffusion of the Indo-Germanic
race), and as it can be sketched out approximately, so as to harmonize
with our hypothesis of descent. The geographical barriers to diffusion
(mountains, deserts, rivers, straits, etc.), have not been taken into
consideration in this general sketch of migration, because, in earlier
periods of the earth’s history, they were quite different in size and
form from what they are to-day. The gradual transmutation of catarrhine
apes into pithecoid men probably took place in the tertiary period in
the hypothetical Lemuria, and the boundaries and forms of the present
continents and oceans must then have been completely different from what
they are now. Moreover, the mighty influence of the ice period is of
great importance in the question of the migration and diffusion of the
human species, although it as yet cannot be more accurately defined in
detail. I here, therefore, as in my other hypotheses of development,
expressly guard myself against any dogmatic interpretation; they are
nothing but _first attempts_.

INDEX.

ABYSSINIANS, ii. 323, 330

Acalephæ, ii. 141

Acœlomi, ii. 148, 151

Acrania, ii. 196, 198, 200, 204

Acyttaria, ii. 51, 62

Adaptation, i. 90, 156, 219

—— actual, i. 225, 231

—— correlative, i. 241

—— cumulative, i. 233

—— direct, i. 225, 231

—— divergent, i. 247

—— indirect, i. 224, 227

—— individual, i. 228

—— irregular, i. 229

—— monstrous, i. 229

—— potential, i. 224, 227

—— sexual, i. 230

—— universal, i. 231

—— unlimited, i. 249

Agassiz, Louis, i. 61

Agassiz’s conception of the universe, i. 65

—— essay on classification, i. 61

—— history of creation, i. 63

—— history of development, i. 64

—— idea of species, i. 65

Albuminous bodies, i. 331

Algæ, ii. 81, 82, 83

Alluvial system, ii. 15

Altaians, ii. 309, 317

Alternation of generations, i. 206

Americans, ii. 309, 318

Amnion animals, ii. 204, 219

Amniota, ii. 204, 219

Amœbæ, ii. 53, 279

Amœboidea, ii. 53

Amphibia, ii. 209, 216

Amphioxus, ii. 198, 285

Amphirrhina, ii. 203, 205

Anamnionata, ii. 204

Animal Plants, ii. 144

Angiospermæ, ii. 83, 111

Annelida, ii. 133, 149, 151

Anorgana, i. 5, 328

Anorganology, i. 6

Anthozoa, ii. 143

Anthropocentric conception of the universe, i. 38

Anthropoides, ii. 270, 275, 292

Anthropolithic period, ii. 15, 17

Anthropology, i. 7

Anthropomorphism, i. 18, 66

Ape-like men, ii. 293, 300

Apes, ii. 241, 268, 270

Arabians, ii. 323, 330

Arachnida, ii. 180, 182

Archelminthes, ii. 148

Archezoa, ii. 132, 134

Archigony, i. 183, 338

Archilithic period, ii. 8, 14

Arians, ii. 323, 331

Aristotle, i. 55, 76

Arthropoda, ii. 132

Articulata, ii. 119

Ascidia, ii. 152, 200

Ascones, ii. 141

Asterida, ii. 164, 166

Atavism, i. 207

Australians, ii. 308, 314

Autogeny, i. 339

BÄR, CARL ERNST, i. 109

—— doctrine of filiation, i. 109

—— theory of development, i. 294

—— types of animals, i. 53; ii. 119

Basques, ii. 322

Bathybius, i. 184, 344; ii. 53

Batrachians, ii. 204

Bats, ii. 240, 261

Beaked mammals, ii. 233, 239

—— reptiles, ii. 224, 226

Belief, i. 9; ii. 335

Berbers, ii. 323, 330

Biogenesis, fundamental law of, i. 309; ii. 33

Biology, i. 6

Birds, ii. 204, 226

Brachiopoda, ii. 157

Brain, bladder of, in man, i. 304

—— development of, i. 303

Bruno Giordano, i. 22, 70

Bryozoa, ii. 150, 152

Buch, Leopold, i. 107

Büchner, Louis, i. 110

Buds, formation of, i. 192

CAFFRES, ii. 312, 333

Calcispongiæ, ii. 140, 144

Cambrian system, ii. 9, 15

Carbon, i. 330, 335

—— theory of, i. 335

Carboniferous system, ii. 11, 15

Carus Victor, i. 110

Catallacta, i. 51, 59

Catarrhini, ii. 270, 272

Caucasians, ii. 309, 321

Causa finalis, i. 34, 75

Causal conception of the universe, i. 18, 74

Cells, i. 187, 346

—— formation of, i. 347

—— theory of, i. 346

Cell-kernel, i. 188

—— membrane, i. 188

—— substance, i. 186

Cænolithic period, ii. 14, 16

Cephalopoda, ii. 160, 162

Chamisso, Adalbert, i. 206

Change of climate, i. 363

Chelophora, ii. 240, 257

Chinese, ii. 309, 317

Chorology, i. 351

Cloacal animals, ii. 234, 239

Cochlides, ii. 159, 160

Cœlenterata, ii. 136, 144

Cœlomati, ii. 148, 151

Coniferæ, ii. 82, 110

Constructive forces, i. 90, 253, 337

Copernicus, i. 39

Corals, ii. 142, 144

Coreo-Japanese, ii. 309, 317

Cormophytes, ii. 80

Correlation of parts, i. 218

Cosmogeny, i. 321

Cosmological gas theory, i. 323

Crabs, ii. 174, 176

Craniota, ii. 198, 204

Creation, centres of, i. 352

—— the, i. 8

Creator, the, i. 64, 70

Cretaceous system, ii. 12, 15

Crinoides, ii. 166, 171

Crocodiles, ii. 223, 224

Crustacea, ii. 173, 176

Cryptogamia, ii. 80, 82

Ctenophera, ii. 142, 144

Cultivated plants, i. 137

Curly-haired men, ii. 310, 333

Cuttles, ii. 160, 162

Cuvier, George, i. 50

Cuvier’s dispute with Geoffroy, i. 88

—— history of creation, i. 59

—— palæontology, i. 54

—— idea of species, i. 50

—— theory of cataclysms, i. 58

—— theory of revolutions, i. 58

—— types of animals, i. 53; ii. 118

Cycadeæ, ii. 82, 110

Cyclostoma, ii. 202, 204

Cytod, i. 346

DARWIN, CHARLES, i. 131

Darwinism, i. 149

Darwin’s life, i. 132

—— travels, i. 132

—— theory of corals, i. 133

—— theory of selection, i. 150

—— study of pigeons, i. 141

Darwin, Erasmus, i. 118

Deciduata, ii. 240, 255

Deduction, i. 85; ii. 357

Democritus, i. 22

Devonian system, ii. 11, 14

Diatomeæ, ii. 51, 60

Dicotylæ, ii. 82, 112

Didelphia, ii. 239

Differentiation, i. 270, 283

Diluvial system, ii. 15

Dipneusta, ii. 204, 212

Divergence, i. 270

Division of labour, i. 247

Domestic animals, i. 137

Dragons, ii. 225

Dravidas, ii. 308, 319

Dualistic conception of the universe, i. 20, 75

Dysteleology, i. 15; ii. 353

ECHINIDA, ii. 166, 171

Echinoderma, ii. 163, 166

Edentata, ii. 240, 254

Egg Animals, ii. 132, 134

Eggs, i. 190, 198

Egg of man, i. 190, 297; ii. 279

Egg, cleavage of the, i. 190, 299; ii. 280

Egyptians, ii. 323, 330

Elephants, ii. 257

Empiricism, i. 79; ii. 349

Eocene system, ii. 15, 16

Ethiopians, ii. 323, 330

Explanation of phenomena, i. 29

FERNS, ii. 82, 101

Fibrous plants, ii. 82

Final cause, i. 22

Fins, ii. 309, 317

Fishes, ii. 206, 208

Flagellata, ii. 51, 57

Flat-nosed apes, ii. 270, 272

Flat worms, ii. 148, 150

Flint cells, ii. 51, 60

Flowering plants, ii. 82, 108

Flower animals, ii. 143

Flowerless plants, ii. 80, 82

Flying animals, ii. 240, 261

Freke, i. 119

Fulatians, ii. 308, 320

Fungi, ii. 82

GANOID FISH, ii. 208, 210

Gastræa, ii. 127, 128, 281

Gastrula, ii. 126, 127

Gegenbaur, i. 312; ii. 179, 193

Gemmation, i. 192

Generation, i. 209

Genus, i. 41

Geocentric conception of the universe, i. 38

Geoffroy S. Hilaire, i. 86, 116

Germans, ii. 323, 331

Germ buds, formation of, i. 193

—— cells, formation of, i. 194

Gibbon, ii. 270, 275

Gilled insects, ii. 174, 176

Gill-arches in man, i. 307

God, conception of, i. 70

Goethe, Wolfgang, i. 80

Goethe’s conception of nature, i. 22

—— discovery of mid-jaw bone, i. 84

—— formative tendency i. 91, 253

—— idea of God, i. 71

—— investigations in nature, i. 81

—— materialism, i. 23

—— metamorphosis, i. 90

—— metamorphosis of plants, i. 82

—— philosophy of nature, i. 81

—— theory of development, i. 92

—— vertebræ of skull, i. 83

Genochoristus, i. 196

Gonochorism, i. 196

Gorilla, ii. 270

Grant, i. 119

Greeks, ii. 323, 331

Gregarinæ, ii. 133, 134

Gynmosperms, ii. 82, 109

HALISAURIA, ii. 204, 214

Hare-rabbit, i. 148, 275

Heliozoa, ii. 64

Herbert, i. 119

Heredity, i. 176

Hermaphrodites, i. 196

Herschel’s cosmogeny, i. 321

Holothuriæ, ii. 166, 172

Hoofed animals, ii. 249, 252

Hooker, i. 119

Hottentots, ii. 311, 333

Human races, ii. 296, 305, 308

—— soul, ii. 361

Huxley, i. 119, 145; ii. 268

Hybridism, i. 145, 210, 275

Hydromedusæ, ii. 143, 145

ICE PERIOD, i. 367; ii. 17

Indecidua, ii. 241, 249

Individual development, ii. 293

Indo-Chinese, ii. 309, 317

Indo-Germanic, ii. 323, 331

Induction, i. 85; ii. 357

Infusoria, ii. 132, 135

Inheritance, abridged, i. 212

Inheritance, acquired, i. 213

—— adapted, i. 213

—— amphigonous, i. 210

—— conservative, i. 204

—— constituted, i. 216

—— contemporaneous, i. 217

—— continuous, i. 205

—— established, i. 216

—— homochronous, i. 217

—— interrupted, i. 205

—— latent, i. 205

—— mixed, i. 210

—— progressive, i. 213

—— sexual, i. 209

—— simplified, i. 212

—— uninterrupted, i. 205

—— laws of, i. 204

Inophyta, ii. 82, 93

Insects, ii. 184

Insectivora, ii. 241, 259

Instinct, ii. 343

Invertebrata, ii. 118, 195

Iranians, ii. 323, 331

JAPANESE, ii. 309, 317

Jews, ii. 323, 330

Jura system, ii. 12, 14

KANT, IMMANUEL, i. 101, 321

Kant’s Criticism of the faculty of judgment, i. 105

—— mechanisms, i. 37, 102

—— philosophy of nature, i. 101

—— theory of descent, i. 103

—— theory of development, i. 321

—— theory of the formation of the universe, i. 101

Knowledge, à posteriori, i. 31; ii. 345

—— à priori, i. 31; ii. 344

LABYRINTHULEÆ, ii. 51

Lacertilia, ii. 223

Lamarck, Jean, i. 111

Lamarck’s anthropology, i. 115; ii. 264

—— philosophy of nature, i. 112

—— theory of descent, i. 113

Lamarckism, i. 150

Lamellibranchia, ii. 158, 160

Lancelet, ii. 198, 204, 285

Laplace’s cosmogeny, i. 321

Laurentian system, ii. 9, 14

Lemuria, i. 361; ii. 326

Leonardo da Vinci, i. 56

Leptocardia, ii. 196, 204

Leucones, ii. 141

Linnæus, Charles, i. 39

Linnæus’ classification of animals, ii. 118

—— classification of plants, ii. 78

—— designation of species, i. 41

—— history of creation, i. 44

—— system, i. 40

Lubbock, Sir John, ii. 298

Lyell, Charles, i. 126

Lyell’s history of creation, i. 128

MAGYARS, ii. 309, 316

Malays, ii. 308, 315

Malthus’ theory of population, i. 161

Mammalia, ii. 231, 239

Man-apes, ii. 271, 275, 292

Marsupials, ii. 236, 239, 290

Matagenesis, i. 206

Materialism, i. 35

Matter, i. 22; ii. 360

Mechanical causes, i. 34, 74

Mechanical conception of the universe, i. 17, 74

Mechanism, i. 37, 102

Mediterranese, ii. 308, 321

Medusæ, ii. 143, 144

Mesolithic period, ii. 14, 20

Metamorphosis of the earth’s strata, ii. 25

Metamorphosis, i. 90

Migration, laws of, i. 373

—— of organisms, i. 354

—— of the human species, ii. 325

—— theory of, i. 367

Mind, i. 22; ii. 360

—— development of the, ii. 344, 360

Miocene period, ii. 15, 16

Miracles, i. 22

Molluscs, ii. 155, 160

Monera, i. 184, 343; ii. 52, 278

Mongols, ii. 308, 316

Monism, i. 34

Monistic conception of the universe, i. 20, 74

Monocottylæ, ii. 82, 112

Monoglottonic, ii. 327, 333

Monogony, i. 183

Monophylites, ii. 44

Monophyletic hypothesis of descent, ii. 44

Monorrhina, ii. 203, 204

Monosporogonia, i. 194

Monotrema, ii. 234, 239

Morphology, i. 21

Morula, ii. 125, 127

Moses’ history of creation, i. 37

Moss animals, ii. 150, 152

Mosses, ii. 82, 97

Müller, Fritz, i. 49, 73; ii. 174

Müller, Johannes, i. 312; ii. 203

Muscinæ, ii. 82, 99

Mussels, ii. 159, 160

Myriapoda, ii. 182, 184

Myxomycetes, ii. 51, 60

NATURAL PHILOSOPHY, i. 78

Negroes, ii. 309, 313, 333

Nemathelminthes, ii. 149, 150

Newton, i. 25, 106

Non-amnionate, ii. 204, 209

Nubians, ii. 308, 320

ŒCOLOGY, ii. 354

Oken, Lorenz, i. 95

Oken’s history of development, i. 293

—— philosophy of nature, i. 96

—— theory of infusoria, i. 97

—— —— protoplasm, i. 97

Olynthus, ii. 141

Ontogenesis, i. 293

Ontogeny, i. 10; ii. 33

Orang, ii. 271, 275

Organisms, i. 5, 328

Organs, i. 5

Origin of language, ii. 302, 327

Osseous fishes, ii. 208, 211

Ovularia, ii. 132, 134

PACHYCARDIA, ii. 201

Palæolithic period, ii. 11, 14

Palæontology, i. 54

Palissy, i. 56

Palm ferns, ii. 82, 110

Pander, Christian, i. 294

Papuans, ii. 310, 333

Paradise, ii. 325

Parallelism of development, i. 313

Parthenogenesis, i. 197

Pedigree of amphibia, ii. 209

—— anamnia, ii. 209

—— apes, ii. 270

Permean system, ii. 11, 14

Petrifactions, i. 54

Phanerogama, ii. 80, 82, 108

Philosophy, i. 79; ii. 350

Phylogeny, i. 10; ii. 33

Phylum, ii. 42

Physiology, i. 21

Pithecoid, theory, ii. 356

Placentalia, ii. 240, 244

Planula, ii. 126, 135, 281

Planæa, ii. 125, 127

Planæada, ii. 280

Plasma, i. 185, 330

Plasmogony, i. 339

Plastids, i. 347

Plastids, theory of, i. 347

Platyelminthes, ii. 148, 150

Platyrrhini, ii. 270, 272

Pleistocene system, ii. 15

Pliocene system, ii. 15, 16

Polar man, ii. 308, 317

Polyglottal, ii. 327, 333

Polynesians, ii. 308, 315

Polyphyletic theory of descent, ii. 45

Polyphylites, ii. 45, 303

Polyps, ii. 142

Polyp jellies, ii. 143, 144

Polysporogonia, i. 193

Population, number of, ii. 333

Porifera, ii. 139, 144

Primary mammals, ii. 239, 290

Primary period, ii. 11, 14

Primæval algæ, ii. 82, 84

—— animals, ii. 131, 132

—— history of man, ii. 298

—— men, ii. 325

Primordial period, ii. 9, 14

Prochordata, ii. 278

Progenitors of man, ii. 279, 295

Progress, i. 277, 283

Promammalia, ii. 233, 239

Propagation, i. 183

—— amphigonic, i. 195

—— monogonic, i. 183

—— non-sexual, i. 183

Propagation, sexual, i. 195

—— virginal, i. 197

Protamnia, ii. 289, 295

Protamœbæ, ii. 52

Prothallophytes, ii. 80, 97

Prothallus plants, ii. 80, 97

Protista, ii. 48

Protophyta, ii. 82, 85

Protoplasma, i. 185, 330

Protoplasts, ii. 51, 53

Protozoa, ii. 121, 131, 132

Purpose in nature, i. 19

Purposelessness in nature, i. 20

RADIATA, ii. 120

Radiolaria, i. 333, 371; ii. 65

Rapacious animals, ii. 240, 260

Recent system, ii. 15

Reptiles, ii. 222, 224

Rhizopoda, ii. 51, 61

Ringed worms, ii. 149, 150

Rodentia, ii. 241, 257

Romans, ii. 323, 331

Rotatoria, ii. 149, 150

Rotifera, ii. 150, 152

Round worms, ii. 149, 150

Rudimentary eyes, i. 13

—— gristle, i. 12

—— legs, i. 14

—— lungs, i. 289

—— mammary glands, i. 290

—— muscles, i. 12

—— nictitating membrane, i. 13

—— organs, i. 12

—— pistils, i. 15

—— stamens, i. 15

—— tails, i. 289

—— teeth, i. 12

—— wings, i. 287

SACK WORMS, ii. 283, 295

Sauria, ii. 222

Schaaffhausen, i. 110

Schleicher, August, i. 108; ii. 301

Schleiden, J. M., i. 109

Science, i. 9; ii. 335

Scolecida, ii. 283, 295

Sea stars, ii. 164, 166

—— cucumbers, ii. 166, 171

Sea dragons, ii. 204

—— lilies, ii. 166, 177

—— nettles, ii. 141, 144

—— urchins, ii. 166, 171

Secondary period, ii. 14, 20

Selection æsthetic, i. 268

—— artificial, i. 152, 170, 254

—— homochromic, i. 263

—— medical, i. 173

—— military, i. 171

—— musical, i. 267

—— natural, i. 168, 255

—— psychical, i. 269

—— sexual, i. 265

—— Spartan, i. 170

Self-division, i. 191

Semites, ii. 322, 330

Serpents, ii. 223

Sexes, separation of, i. 244

Sexual characters, i. 209, 265

Silurian system, ii. 8, 14

Slavonians, ii. 323, 331

Snails, ii. 159, 160

Soul, the, i. 71; ii. 343, 362

Species, i. 41, 273, 304, 311

Specific development, i. 311

Spencer, Herbert, i. 119; ii. 367

Sperma, i. 197

Spiders, i. 180, 182

Spirobranchia, ii. 157, 160

Sponges, ii. 139, 144

Spores, formation of, i. 194

Stemmed plants, ii. 280

Straight-haired men, ii. 309, 314

Struggle for life, i. 161, 252

Synamœba, ii. 125, 280

Systematic development, i. 313

System of animals, ii. 132

—— apes, ii. 270

—— Arabians, ii. 330

—— arachnida, ii. 182

—— Arians, ii. 331

—— arthropoda, ii. 132

—— articulata, ii. 177, 183

—— catarrhini, ii. 270

—— cœlenterata, ii. 144

—— crustacea, ii. 176

—— didelphia, ii. 239

—— echinoderma, ii. 166

—— Egyptians, ii. 330

—— fishes, ii. 208

—— formations, ii. 15

—— Germans, ii. 331

—— gilled Insects, ii. 177

—— Græco-Romans, ii. 331

—— Hamites, ii. 330

—— hoofed animals, ii. 252

—— human ancestors, ii. 295

—— human races, ii. 308

—— human species, ii. 308, 309

—— Indians, ii. 331

—— Indo-Germani, ii. 331

—— insects, ii. 182

—— mammalia, ii. 239

—— mankind, ii. 295

—— marsupials, ii. 239

—— men and apes, ii. 271

—— molluscs, ii. 160

—— monodelphia, ii. 241

—— organisms, ii. 74, 75

—— placentalia, ii. 240

—— plants, ii. 82

—— platyrrhini, ii. 270

—— protista, ii. 51

—— reptiles, ii. 224

—— Semites, ii. 330

—— Slavonians, ii. 331

—— spiders, ii. 182

—— star fishes, ii. 167

—— strata of the earth, ii. 15

—— tracheata, ii. 182

—— ungulata, ii. 252

—— vegetable kingdom, ii. 83

—— vertebrata, ii. 204

—— worms, ii. 150

—— zoophytes, ii. 144

TAIL OF MAN, i. 289, 308

Tangles, ii. 61, 82

Tartars, ii. 209, 317

Teleology, i. 100, 291

Teleostei, ii. 208, 211

Teleological conception of the universe, i. 20, 75

Tertiary period, ii. 14, 16

Thallophytes, ii. 80, 82

Thickness of the earth’s crust, ii. 19

Thought, ii. 364

Thread plants, ii. 82, 93

Tocogony, i. 183

Tortoises, ii. 225

Tracheata, ii. 182

Transition forms, ii. 338

Transmutation, theory of, i. 4

Treviranus, i. 92

Trias system, ii. 12, 14

Tuft-haired men, ii. 307, 309

Tunicata, ii. 152, 200

Turbellaria, ii. 283

Turks, ii. 309, 316

UNGER, FRANZ, i. 109

Ungulata, ii. 249, 252

Unity in nature, i. 22, 338

Uralians, ii. 309, 317

Variability, i. 220

Variation, i. 219

Varieties, i. 276

Vertebrata, ii. 195, 205

Vital force, i. 22, 334

Vitalistic conception of the universe, i. 18

Wagner, Andreas, i. 138

Wagner, Moritz, i. 369

Wallace, Alfred, i. 135

Wallace’s chorology, i. 361, 373

—— theory of selection, i. 136

Well’s theory of selection, i. 150

Whales, ii. 240, 251

Will, freedom of the, i. 113, 237, 364

Wolff’s theory of development, i. 293

Woolly-haired men, ii. 307, 309

Worms, ii. 147, 150

ZOOPHYTES, ii. 136, 144

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