THE NEW

EVOLUTION

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THE NEW

EVOLUTION

ZOOGENESIS

By
AUSTIN H. CLARK

U. S. National Museum

Author of Animals of Land and Sea, The Birds of

THE Southern Lesser Antilles, The Crinoids

OF the Indian Ocean, Die Crinoiden

der Antarktis, etc.

BALTIMORE

THE WLLLIAMS & WELKINS COMPANY

1930

Copyright, 1930
THE WILLIAMS & WILKINS COMPANY

Made in the United States of America

Published May, 1930

FTKST EDITION

Composed and Printed at the
WAVERLY PRESS, INC.

FOR

The Williams & Wilkins Cohpany
Baltimore, Md., U. S. A.

~^\ryt^ <V^»'^r7? ^^f^ '^^yiOT' '\^QT> '\^*Q7} '\^^^7} 'X^iQT) 'X^^QT '\^tC^ 'X^'^^

CONTENTS

PAGE

Preface vii

Introduction xi

CHAPTER I
Man and His Relation to the Living World i

CHAPTER II
Features Common to Man and the Lower Animals i6

CHAPTER III
Man and the Apes 15

CHAPTER IV
The World and the Butterfly 30

CHAPTER V
Life's Background 37

CHAPTER VI
Factors Affecting Animal Life 43

CHAPTER VII
More About Animal Life ^2.

CHAPTER VIII
Land and Sea Compared 58

CHAPTER IX
Special Relationships and Contacts 73

CHAPTER X
The Most Ancient and the Living Animals 91

CHAPTER XI
The Past and the Present 100

[V]

"^"^ CONTENTS "^^"^

CHAPTER XII
More About Fossils io6

CHAPTER XIII
The Dual Relationship of Animals 114

CHAPTER XIV
What is a Species? 130

CHAPTER XV
Animal Forms 149

CHAPTER XVI

The Continuity of Life 155

CHAPTER XVII

Life 164

CHAPTER XVIII
Developmental Lines and Trees — Evolution 170

CHAPTER XIX
Gaps in the Evolutionary Lines — Mutations 180

CHAPTER XX
The Origin of the Earliest Animals — Eogenesis 189

CHAPTER XXI
Summary io8

Appendix A 13 5

Appendix B 2.61

[vi]

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PREFACE

FOR more than thirty years the author has been
engaged in the study of the interrelationships of
the different forms of animal life. This study has
included both intensive research on the forms within
certain restricted groups, particularly the birds, in-
sects, onychophores, echinoderms and certain other
types of marine invertebrates, and extensive investiga-
tions concerning the relationships of all of the various
groups of animals each to the other.

It has also included a detailed survey of the fossils
of the Cambrian, with the late Dr. Charles D. Wal-
cott, the Secretary of the Smithsonian Institution, and
more or less intensive investigations of other fossils,
especially the past representatives of the great group
of sea-lilies — the Crinoidea — in cooperation with the
late Mr. Frank Springer.

Intensive laboratory work has been supplemented
by extensive field work in various parts of North
America, in South America, in the West Indies (par-
ticularly in the Lesser Antilles), in Europe, in eastern
Asia and Japan, and in the Aleutian and Hawaiian
Islands.

Studies on land and along the sea coasts have been
broadened into detailed investigations of the animals of
the open ocean and of the sea bottom down to a depth
of 11,838 feet beneath the surface. These investi-
gations were carried out during the cruise of the
United States Bureau of Fisheries steamer Albatross in

[vii]

PREFACE

the north and northwest Pacific in 1906, on which
cruise the author served as acting naturalist in charge
of the scientific work of the vessel.

No proper appreciation of the conditions under
which life in the sea exists is possible without some
acquaintance with the subject of oceanography, and
this subject has therefore somewhat extensively en-
gaged the attention of the author.

Of itself the personal history of any individual
means nothing. It merely indicates that the indi-
vidual has had a certain range of opportunities for
becoming interested in, and later following out, cer-
tain lines of investigation. Whether the individual
has shown himself alive to those opportunities and
has profited by them can be judged only by his work.

The subject of the interrelationships of animals in-
volves an extensive acquaintance with all types of
animals in their adult, young and embryonic stages.
It also involves an acquaintance with the fossil re-
mains of the animals which have existed in past ages.
So any presentation of this subject in a volume of
reasonable size means a very rigid selection of essen-
tial facts from an enormous mass of pertinent material.

Fifty years ago it was possible to include in a vol-
ume of this kind a series of footnotes or a bibliography
giving an adequate list of references to original records
and sources of information. But such a procedure is
no longer possible. An adequate list of references to
the thousands of books and articles consulted in the
preparation of this work would occupy more pages
than the book itself.

[viii]

^^^^ PREFACE "^^^^

For assistance in the preparation of this volume I
am indebted to many of my colleagues, particularly
to Dr. Leland O. Howard, Principal Entomologist
(until recently Chief), Bureau of Entomology, Depart-
ment of Agriculture; to Dr. William M. Mann,
Director of the National Zoological Park and for-
merly of the Bureau of Entomology; Dr. Adam B0ving
of the Bureau of Entomology; Dr. Waldo L. Schmitt,
Curator of Marine Invertebrates, U. S. National Mu-
seum; Mr. Charles W. Gilmore, Curator of Vertebrate
Paleontology, U. S. National Museum; and Dr. Carl
Heinrich, of the Bureau of Entomology; all of whom
were so kind as to read the entire manuscript. To
Dr. James W. Gidlcy, Assistant Curator of Vertebrate
Palaeontology, U. S. National Museum, I am under
obligations for checking my statements regarding fos-
sil mammals, and for his kindness in verifying my
statements concerning the fossils of the Cambrian and
immediately following periods I am indebted to Dr.
Charles E. Resser, Associate Curator of Invertebrate
Paleontology, U. S. National Museum.

[ix]

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INTRODUCTION

MAN is today the central figure in the living world.
Therefore the study of the life about us must
be approached through the application of
the human yardstick. First of all we must appraise
the living world in terms of its direct relationship to
man. Beginning with the known — ourselves — we
may measure the nearer portions of the unknown; and
not till this is done may we with any confidence take
up the broader problems of the world of animals
and plants.

But the human yardstick has its limitations. To a
very large extent we are detached from the world in
which we live. Our environment we modify to suit
ourselves. We are therefore quite unfamiliar with
the terrible realities of existence that must be faced
by all other living things — that were faced also by
our ancestors.

So overwhelming are the odds against all living
things, so precarious is the existence of any indi-
vidual, that it is not practicable to discuss the varied
contacts of all forms of life from the human aspect.
Yet an appreciation of these contacts is essential to
an understanding of the living world. In order to
overcome this difficulty we shall present this subject
in terms of its relation to the life of a butterfly. From
the infinity of different contacts which we find in our
contemplation of a butterfly we shall select a few for
more detailed exposition.

[xi]

^^^^ INTRODUCTION '^^''"

All animals must eat. It is essential therefore that
we understand the origin of foods and just how the
necessary foodstuffs are continuously provided for the
plants and animals. We must also understand the
very varying conditions under which foodstuffs are
available and which therefore must be met by any
animal or plant making use of them. The very di-
verse ways of meeting these conditions and nature's
safeguards which prevent the increase of any form of
life to a point endangering its food supply have a most
important bearing on the origin and development of
animal forms. Especially important is an adequate
understanding of the differences in the conditions
which affect the animals living on the land and in
the sea.

In addition to the animals living at the present time
we know many other kinds which flourished in past
ages, the remains of which have been preserved as fos-
sils in the rocks. As we go back further and further
^ into the geologic past we find that animal life becomes
more and more different from the animal life we know
today. This fact is obvious and undeniable. Equally
obvious and undeniable are certain other facts which
hitherto have passed unnoticed. A rather detailed
survey of the fossils is therefore essential to a proper
understanding of the development of animal forms.

Fossil or living, all animals are divided into differ-
ent kinds or species. The species is the unit by which
the animal world is measured and in terms of which it
is discussed. How may this unit be defined? Is it a
fixed and stable entity, or is it a repressed force kept

bdi]

^'^ INTRODUCTION ^^'^

within bounds by rigid limitations which it is unable
to escape?

But the discussion of a species is quite inadequate
and meaningless without a survey of the life histories
of animals and a mention of the varied and complex
forms more or less widely different from the adult
form which most animals assume at one time or an-
other in the passage from the egg to the final stage.
And in addition we must review the varied processes
by which the continuity of life from one generation
to the next and from one individual to another is
assured and the significance and relative importance
of these processes.

Such is the background with which any tenable
theory of the development and diversification of
animal forms must harmonize. The idea that the
earliest forms of life were feeble helpless things exist-
ing in an ideal world especially adapted to them has
nothing to support it. So far as we can learn the
conditions on the earth since life began have always
been essentially the same — varying widely in climatic
and other details from age to age and from place to
place but always in their broader features essentially
the same.

No matter what they are, all animals arise from a
single cell, and the body of every animal is composed
of one or many cells which are always similar in
structure. All animals must therefore be interpreted
in terms of a single cell. Furthermore, all living
things arise only as the children of other living things.

So the problem is to construct a figure which, begin-

[xiii]

INTRODUCTION

ning with a single cell, contemplating unbroken con-
tinuity of life from parent to child indefinitely, having
due regard for the rigorous conditions of environment
v^hich all forms of life must meet, and taking account
of all the known peculiarities of animals, shall allo-
cate in its proper place each and every form of animal
life, and give us as a finished picture man in the domi-
nant position in the world which he holds today.

[xiv]

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CHAPTER I

MAN AND HIS RELATION TO THE

LIVING WORLD

UNDISPUTED master of the world, man dominates
the earth at the present time. But this was
not always so. In the geologic age just past,
the Pleistocene or Ice Age, the earth was dominated
by a great array of different mammals many of which
were of large size and occurred in great abundance.

Though man existed at this time, his potentialities
for development were restricted and more or less
closely circumscribed by the competition of these
four-footed creatures which threatened his food plants
and his meager crops and menaced his relatively
feeble body.

So during the Pleistocene man played only a minor
part and left scarcely an imprint beyond mere records
of his existence which in the earlier portion of the
Pleistocene become extremely scanty.

Long before the Pleistocene, in those far distant
periods known to geologists as the Cretaceous and
Jurassic, there was no trace of man. The mammals,
though numerous — at least in the Cretaceous — were
all very small and insignificant. Then the earth was
dominated by a vast and formidable array of reptiles,
on the land, in the sea, and in the air, many of which
were very large and some of gigantic size, several
times as large as the largest elephants.

^M THE NEW EVOLUTION t^'^^

The successive domination of the earth by the
reptiles, by the mammals, and by man, is an illustra-
tion— the most striking illustration — of the successive
and more or less intermittent changes that have taken
place in the balance of animal life upon the earth
since the earliest times of which we have a record.

In a consideration of the relationships of the various
types of animal life each to the other and of the
changes in these relationships at different periods in
the past, the first essential is accurately to determine
the position of man in regard to all other forms of
life.

Man is a mammal, and it is indubitable that in his
structure and anatomy man is very close to the man-
like or anthropoid apes. This is an easily demon-
strable fact which is quite beyond dispute. But a
knowledge of the structure and anatomy of man is
not sufficient in itself alone to enable us to judge of
his true relations to the other forms of life and
correctly to appraise his status in the world today.

Unfortunately at the present time the broader
viewpoint of man's relation to the world at large has
among biologists been almost completely superseded
by the very narrow viewpoint that the position of
man is to be explained entirely on the basis of his
dissected body.

This narrow viewpoint has been developed in such
a way and to such extremes as to lead to conclusions
which in their total disregard of man as man cannot
but give offense and arouse antagonism.

No one can deny that a detailed comparative

w

ZOOGENESIS

knowledge of the structure of any creature is essential
to the determination of its position in relation to the
other animals. But those who study animals both in
the field and in the laboratory soon become aware of
the important fact that no animal form can properly
be understood from the facts revealed by the study
of its structure and anatomy alone. An animal is
something more than the sum total of the organic
compounds, the secretions and the deposits that make
up its body. There is something in addition to the
tangible physical complex represented by its structure
and anatomy.

The bodily mechanism of every animal in life is
operated and controlled by a mental mechanism which
as yet we are unable to explain in terms of physics
and of chemistry. In each sort and kind of animal
this mental mechanism takes the form of a definite
complex peculiar to the species.

These mental complexes are as much a part of the
individuality of each species as are the tangible struc-
tures of the body. To base our conclusions upon a
single set of characters and to dismiss others as irrele-
vant is simply to confess our inability to comprehend
and to interpret the whole in its true relations.

Descriptions of the different breeds of dogs would be
considered wholly incomplete without some mention
of the mental traits of each. This is because we
appraise the dogs on the basis of all the characters
which enter into their relations to us. The diverse
mental traits peculiar to the different breeds of dogs
therefore become a matter of great interest.

_

THE NEW EVOLUTION

But if in the case of dogs we are always careful to
consider the mental differences as well as the structural
variations more or less peculiar to each of the several
breeds, why should we not admit that the habits of
all animals should be considered in connection with
their structure? Why should we be so careful as to
emphasize the terrier's peculiar propensity for dig-
ging, the spaniel's curious love for water and occa-
sional dexterity in catching fish, the stupidity and
ferocity of bull-dogs, and all the other traits char-
acteristic of the other breeds of dogs and then main-
tain that man in his relation to the apes must be con-
sidered solely on the basis of his structure?

How can we acknowledge the importance of the
mental differences between the greyhounds and the
hounds, between both of these and collies, and be-
tween all three and bull-dogs, and then deny, or at
least minimize, the importance of the mental differ-
ences between the orangs and the chimpanzees, be-
tween both and the gorillas, and between all three
and man?

To do this is to admit that the science of biology —
the science which deals with living things — has crys-
tallized into a narrow orthodoxy, a science of dead
remains, a sort of common meeting ground of geology,
chemistry and physics, a science with no bearing upon
those deeper problems which concern cosmic qualities
and values.

If we regard the relationship of man to the world
in which he lives, and to the other forms of life with
which he lives, from the broader viewpoint of man

[4]

Illustrations of Animal Symmetries

FOR AN explanation OF THE FIGURES SEE P. 277

THE NEW EVOLUTION

as a living being we at once uncover a whole array
of most interesting facts.

Of these interesting facts perhaps the most impor-
tant from the point of view of man as man is that man
is the only vertebrate which has a family normally
composed of a series of dependent young in all stages
of development ranging from newly born and wholly
helpless through various stages of decreasing depend-
ency to subadult or adult. This serial family of
dependent children requires the continuous care of
both parents or its equivalent for a long period
of years.

In all the other vertebrates — the other mammals,
the birds, the reptiles, the amphibians and the fishes
— the young, whether born singly or in a litter or
issuing from eggs, are always under normal conditions
independent of the parents before new young are born.

So far as we are able to judge from the actual evi-
dence, the use of fire and the use of tools were human
attributes from the very first appearance of mankind.
It may with reasonable assurance be assumed that the
same is true of speech and the use of clothing and of
ornaments. There is not the slightest evidence that
these human attributes were acquired one by one as
man departed more and more widely from an ape-
like ancestor.

While these attributes separate man sharply from
the apes, greatly accentuating the distinct and clean-
cut, though rather slight, structural differences be-
tween man and the apes, they are by no means confined
to man. Incredible though it at first may seem, never-

[6]

ZOOGENESIS

theless it is a fact that the closest parallel to the
activities of man is to be found in the activities of the
insects and their allies and not among the vertebrates
or backboned animals. And furthermore, among the
vertebrates the birds as a w^hole come rather nearer to
man in the scope of their activities than do the other
mammals, while among the mammals the rodents —
rats, mice, squirrels, beavers and their relatives — are
the most similar.

The use of fire and of fashioned tools is confined to
man. Certain ants and other insects, some reptiles,
as the crocodiles and alligators, and certain of those
strange birds called brush-turkeys or megapodes (Meg-
apodida^) make use of artificial heat of bacterial origin
derived from decaying vegetation consciously and
knowingly gathered and assembled for that purpose.
But the ignition point is never reached.

Certain digger wasps use little pebbles or little bits
of stick held in the jaws to smooth down the earth
over a buried victim. The spinning ants of the Old
World tropics build their silk nests by using their
own grubs which they hold in their jaws and pass
back and forth from leaf to leaf. The grubs have silk
glands which the adults lack, so that the construction
of silken nests by ants is only possible through a curi-
ous system of enforced child labor. There are various
other cases of the use of tools and implements by
insects. But the tools they use are never made
by them.

Very many insects in their early stages clothe them-
selves. They encase their bodies in a little jacket

[7]

THE NEW EVOLUTION

(fig. 13, p. 2.1) made of various substances bound to-
gether with a web of silken threads. For instance,
the caterpillar of the common clothes-moth makes a
little tubular jacket for itself out of hairs cut from
your furs or woollen clothes. The larvas of the cad-
dis-flies, which live in water, make somewhat similar
coverings out of sticks or parts of leaves or sand
grains. Very many insects construct an elaborate
cocoon, which may be waterproofed inside, as a pro-
tection during the pupal stage.

Many youthful insects, as the larvas of certain lace-
winged flies and the caterpillars of some lyca^nid
butterflies, cover themselves with the empty skins of
the aphids or other insects they have eaten or with
foreign substances which they impale upon or en-
tangle among their spines. This may be primarily
for the purpose of concealment or deception, but in
many cases it seems to be simply for adornment. At
any rate, the larva of a lace-winged fly or the cater-
pillar of an aphid-feeding butterfly draped in dead
aphids' skins strongly brings to mind a primitive
human being draped in furs.

Many insects have highly developed social systems
which, superficially at least, seem much like those of
man. Such social systems are to be seen among the
ants, wasps, bees and termites. Some of these social
insects seem to be able to exchange a considerable
range of information, though on principles which are
quite different from those of articulate human speech.

Some social ants make use of slaves, just as man used
to do — and still does in some places. Many make use

[8]

ZOOGENESIS

of other types of insects — aphids (figs. 7-9, p. xi),
coccids (figs. 16, p. zi; 17, p. 33), jassids, membracids
and the caterpillars of various lycasnid butterflies —
much as we make use of cattle. From these insect-
cattle they obtain honey-dew or other sweet or some-
times spicy liquids of which they are inordinately
fond. They often tend these insect-cattle with the
very greatest care, building shelters over them and
looking after them in various ways and protecting
them from their enemies. A number of different
kinds of ants have developed elaborate forms of
agriculture.

All insect societies are protected by formidable
armaments consisting of poison stings, squirt-guns
filled with acid, or powerful cutting jaws. But these
armaments are always parts of the bodies of some or
all of the insects in the social units.

All insect societies support scavengers and parasites
(fig. 14, p. xi) of various characteristic and peculiar
types. Many ant colonies contain queer helpless in-
sects which the ants assiduously feed with substances
gathered for their own young, though they get noth-
ing in return.

Some insects make use of others which are much
more powerful than themselves in traveling from place
to place, somewhat as we make use of horses, yaks and
camels. For instance, the young of some of the oil
beetles are transported to their victims on the bodies
of the parents or the attendants of the latter.

Chemical processes are extensively used by insects.
These are, however, almost entirely concerned with

[9]

THE NEW EVOLUTION

special bodily secretions. There are the various
types of silk produced by insect larvas and by spiders,
the paper made by wasps, the wax produced by bees,
aphids (figs. 7-9, p. 2.1) and other insects, sweet sub-
stances secreted by aphids and other types, narcotics
used to stupefy the prey, poisons used to kill the prey,
antiseptic substances used to protect the eggs of
internal parasites, and various kinds of poisons and
reagents for special and restricted uses.

But here we become involved with the chief differ-
ence, other than the structural, between the insects
and the vertebrates. In their relations to the world
about them the insects are mainly guided by the chem-
ical senses which in us are represented by taste and
smell, whereas in the vertebrates the eyes and ears
are commonly the main controlling organs, often com-
bined with a delicate sense of touch, and smell and
taste are relatively unimportant, even though the
former may be, as in the dogs, highly developed. So
the extensive use of chemical processes by the insects
is quite in line with the largely chemical nature of
their external contacts.

The very diverse, ingenious and effective snares of
spiders and of some insect larvae, as the young of some
caddis-flies and the New Zealand glow-worm, are
really most extraordinary structures. They show,
most of them at least, an almost perfect adjustment
in the relation of each part to the strains and stresses
which that part must meet. The pit-falls dug by
the young of ant-lions are equally effective and
ingenious.

ZOOGENESIS

The tunnels and galleries made by many insects in
wood or in the ground, which are often very compli-
cated, and the tunnels and chimneys made by spiders,
the former sometimes provided with a strong hinged
lid, show an engineering skill and a knowledge of
many of the laws of physics which is really quite
remarkable.

The sometimes enormous nests of termites, the mud
and other cells of solitary wasps, and the cells of car-
penter, leaf-cutting, Varnisher, and other solitary bees
and of wood-boring wasps also may be mentioned as
structures which are mechanically and physically per-
fect, or at least very nearly perfect.

Interesting as are these parallels between the activi-
ties of man and of the insects, they are perhaps not so
surprising as the fact that, except in man, serial fami-
lies of helpless and dependent young are found only
in certain insects. Successive and overlapping broods
of helpless young requiring continuous attention are
characteristic of the social ants, bees and wasps and,
elsewhere than in man, occur among these insects
only.

The only birds to make use of artificial heat are
some of the megapodes or brush-turkeys which are
found in the Malayan and Australian regions. These
brush-turkeys scratch together a loose mound of
leaves, rubbish and earth, lay their eggs in it, and then
cover them. The heat arising from the decaying vege-
tation in this natural incubator furnishes the warmth
necessary for the hatching of the eggs. The same pro-
cedure is followed by the alligators and the crocodiles.

THE NEW EVOLUTION f^^^

Other kinds of brush-turkeys, as those in the Sol-
omon Islands, and the crocodile-bird of northern
Africa, simply bury their eggs in warm sand, like
turtles.

In the formation of their nests birds display the
most extraordinary skill in the use of fibers, sticks
and mud, or in some cases of the secretions from theii
salivary glands. They also show great skill in hew-
ing out holes in the trunks and branches of dead trees
and in constructing burrows in banks and in the
ground.

Extraordinary ingenuity often is exhibited in select-
ing situations for their nests, both when they do the
work of making them themselves and when they ap-
propriate the deserted nest or nesting site of some
other species.

Many types of nests are very complicated, especially
such nests as are entered from the side. Among the
most curious are the ingeniously sewn nests of the
oriental tailor-birds, the long pendent nests of the
cassiques, related to our orioles, and the more or less
similar nests of some of the weaver-birds of Africa . A
few birds, as a certain weaver-bird and a small parrot
in Argentina, build community nests, like apart-
ment houses.

Some birds show much flexibility in the construc-
tion of their nests. For instance in Bermuda where
there are no suitable holes in the native cedars, the
blue-birds build open cup-shaped nests in trees, like
our chipping-sparrows. But in Bermuda I once found
a blue-bird's nest in a hole in a capstan of a wrecked

ZOOGENESIS

ship, suggesting that they would build in holes if
only they could find them. The English sparrow,
which is not a true sparrow but a weaver-bird, if it
cannot find a hole suitable for a nest will construct a
bulky nest of straw with a side entrance in a tree, thus
indicating its affinities. Flickers in treeless regions
will burrow into cliffs, and robins in sandy regions
make their nests without the usual cup of mud.
Many other similar cases could be cited.

Some of the grebes build floating nests, like rafts,
that can be towed from place to place. The motmots
build their nests in the nests of termites, and certain
kingfishers of southeastern Asia make their nests in
holes in trees which are tenanted by bees.

Many birds ornament their nests. Our common
Baltimore oriole often weaves into its pendent nest
bits of bright colored yarn or string, the indigo bird
incorporates bits of paper, the crested flycatchers use
the case skins of snakes, and other birds use other
objects, such as shells or bits of shiny stones or
brightly colored pebbles. One bird in India enlivens
the vicinity of its nest with fire-flies stuck in the
ground.

But it is not only in the formation of their nests
that birds show mental traits which are more or less
parallel to those of man. The bower-birds of Aus-
tralia build curious runs or play-houses which they
ornament with bright and conspicuous objects of all
sorts and which have no connection with their nests.
Many other birds, particularly of the crow family, as
ravens, crows, magpies and jays, are very fond of

[^3]

-■^^« ^p^g -^^^ EVOLUTION

gathering and secreting bright and conspicuous ob-
jects, especially metallic objects.

It may perhaps be mentioned that many different
kinds of birds, especially among the larger parrots,
crows and mynahs, are able to duplicate more or less
extensively and correctly the sounds, though not the
intent, of human speech. They are the only creatures
which are able to do this.

Among the mammals only the rodents can be com-
pared to birds in the diversity of their mental traits.
Many make rather elaborate nests on or in the ground,
in grass or rushes, or among the branches or in holes
in trees. The nests of rodents are almost always
entered from the side or from below and are seldom
open above like the nests of many birds. Perhaps the
most interesting of the peculiarities of rodents is to
be found in the construction of dams by beavers.

Some of the insectivores, as the moles and shrews,
make more or less perfect nests, and some of the
Madagascan lemurs make rather complicated nests
entered from the side high in the trees, like birds.
But in neither of these groups is this habit so general
or so well developed as it is in rodents.

A number of rodents, as the wood-rats and the
Norway rat, have the interesting habit of accumulat-
ing bright and conspicuous objects more or less after
the fashion of the crows.

Very many rodents have the hoarding habit, storing

up large quantities of food to last them through the

winter, or through the dry season, or through some

other time when food may be expected to be scarce.

___ _

ZOOGENESIS

Among the mammals this hoarding habit is entirely
confined to rodents and to man. But it is character-
istic of some birds, as the California woodpecker,
and of various insects, particularly of the bees and
ants.

[15]

CHAPTER II

FEATURES COMMON TO MAN AND THE

LOWER ANIMALS

THE existence in man, in the insects, in the birds,
and in the rodents of so many strikingly similar
mental traits which are conspicuously absent in
the monkeys and in nearly all the other mammals
must have some significance. There must be some
underlying basic reason for this curious distribution
of corresponding mental attributes. What have
these various groups in common wherein they differ
from the other creatures inhabiting the land? Can
such diverse types of living things have anything in
common?

Among the insects man-like mental attributes are
almost exclusively confined to types in which the
young are very different from the adults, either soft,
delicate and apparently headless grubs as in the case of
the ants, bees, and social, parasitic and predacious
wasps — the mud-daubers, digger wasps and others —
or soft bodied worm-like things as the young of
caddis-flies and the caterpillars of small and feeble
moths and butterflies. But they also occur in the
white-ants or termites, which are weak and feeble in
all stages, and in a few other types. What may be
considered as the clothing of the insect body — the
construction about it of a more or less dense cocoon
of silk, of itself alone or used as a binder for other sub-

ZOOGENESIS

stances — is common to nearly all insects which have
an inactive helpless pupal stage.

Among the birds mental attributes which parallel
the human are almost exclusively confined to those
types with helpless young which for their upbringing
require the constant attention of both parents, and
among these they are most obvious and marked in
the smaller and weaker forms such as the tailor and
the weaver-birds and in the wrens and swallows.
Birds with active and more or less self-reliant young
which are tended by one parent only, large and power-
ful birds, and sea-birds nesting where they are safe
from enemies, as a rule show little or no skill in
making nests and scorn the use of ornaments.

Weak and helpless young are especially character-
istic of the rodents, particularly of the small mouse-
like or rat-like rodents, in which the man-like mental
attributes are particularly to be remarked.

The nests of rodents, like the nests of birds, are
primarily incubators designed to facilitate the main-
tenance of a proper temperature. Many rodent nests,
as those of various mice, the muskrats, and some
squirrels, would seem to be constructed in such a
fashion as to create within them a temperature higher
than that outside through bacterial action. Whereas
among the birds nests are used only as incubators for
the young, many northern rodents pass the winter
in their nests in a state of hibernation. Correspond-
ingly in Madagascar some lemurs pass the hot dry
season in their nests in a state of aestivation.

So a survey of the animal world seems to point to

^^^"" THE NEW EVOLUTION T~^^

the conclusion that mental alertness and ingenuity
wherever it is found is developed as an offset to some
physical weakness in the animals involved. This
physical weakness usually has to do with helpless
younger stages, as in the social and other insects and
in the birds and rodents, but it may involve the later
stages, as the inactive helpless pupal stage of those
insects having such a stage, all stages in the termites,
and the hibernation period in rodents.

Thus physical weakness in the animal world is
counterbalanced by the appearance of mental attri-
butes comparable with, or at least parallel to, those of
man, and the more pronounced the weakness the more
man-like do these attributes become.

No one can deny that at the present time the insects
are the most formidable competitors of man. There
are more than three times as many different kinds of
insects as there are of all other types of animal life
taken together. Among the insects by far the most
numerous, both in kinds and in number of individuals,
are those forms, as the ants, bees, wasps and their
allies, flies and moths, and many beetles (fig. lo,
p. xi), which have weak and feeble worm-like young.
They are the most successful and resourceful of the
insects. They include the largest as well as the
smallest of all the insect species, but their average
size is considerably less than that of other insects.

Among the mammals the dominant type at the
present day is the rodent type, and especially the
murine or rat-like rodents. Here again we find as the
dominant group, most numerous both in species and

Us]

ZOOGENESIS

in individuals, a group including forms of which the
average size is very small, and which have help-
less young.

Among the birds the dominant types, most numer-
ous both in species and in individuals, are again those
of small size with helpless young.

Here we seem to be confronted with a paradoxical
situation. For we find, in the animal world taken
as a whole, that where the greatest weakness lies
there also lies the greatest strength — evidenced by the
greatest degree of material success. Everywhere we
see as the dominant types of animal life, at least on
land, types with marked inherent weaknesses — small
feeble bodies and dependent helpless young — which
we might offhand assume would imperil their ex-
istence.

But in all these types weakness of body and the
many liabilities resulting from the helpless young are
more than offset by the occurrence of more or less
manlike mental alertness and ingenuity.

Do the physical liabilities give rise to the mental
alertness and ingenuity? Do the mental attributes
permit the existence of liabilities? Or are mental
alertness and physical liabilities both correlated in
some way with definite structural features? These
questions we shall answer later.

From the physical viewpoint man is relatively one
of the least efficient of all living creatures. His feeble
body is no match for the powerful bodies of the great
grass-feeding mammals which in the relatively recent
past roamed all the open areas of the world and also

[19]

THE NEW EVOLUTION

wandered through the forests. Unarmed, he is no
match for the great cats, wolves and other predacious
creatures which preyed upon these other mammals.
He is relatively slow of foot, and is a poor and inexpert
climber. And in addition to all this the young of
man are at first helpless and then dependent for many
years, while the human family consists of a series of
several or m.any of these helpless and dependent young.

Feeble and frail of body, with helpless and depend-
ent young and the further handicap of a serial family,
man is the dominant living creature in the world
today by virtue of his extraordinary mental attributes.
Man must have an intellect superior to that of all
other living things because he has the maximum
number of liabilities to meet.

In the insects, birds and rodents, and in a lesser
degree in other forms of life, we see foreshadowed here
and there, appearing in a curiously sporadic, isolated
and disconnected manner, many of the mental attri-
butes of man. But in man we find all of the mental
attributes found in all other living things combined,
together with greatly augmented curiosity, inventive-
ness and ingenuity.

Is there a physical basis for the development of this
superior intellect in man?

Strange as it may seem, one of man's greatest weak-
nesses appears to have been his greatest asset. For
the serial family of dependent young probably lies
at the base of all human societies and probably was
responsible for the development of human culture.

Elsewhere than in man a serial family of dependent

Different Types of Insects
for an explanation of the figures see p. 277

THE NEW EVOLUTION

young is found only in the social ants, bees and wasps,
and it is impossible not to see in this an important
and far-reaching correlation. It is impossible not to
believe that the serial family lies at the foundation of
the development of social systems, alike of men and
of the hymenopterous insects. It is impossible also
not to wonder what may be the cause of or reason for
the serial family.

Seen from the point of view of predacious creatures,
a society composed of numerous individuals means
abundant food. So a society, either of social insects
or of man, must at all times be adequately defended.
Insect societies are defended by the use of formidable
and poisonous stings, acid-squirting apparatus, or
more rarely strong cutting jaws. Human societies
are defended by the use of man-made weapons, which
grow more and more effective with the increase in
size of the social units.

It is commonly asserted that the mental reactions
of insects, birds and rodents are due to instinct and
not to intelligence as in the case of man, and therefore
that the mental attributes of the insects and of man
are in no way comparable.

We marvel at the fact that every insect at birth and
at the commencement of every subsequent stage there-
after is endowed with a technical education which for
its particular needs is quite sufficient — indeed it is
complete. Very much the same is true of birds and
rodents, though they do not pass abruptly from one
stage to the next as do the insects.

Instinct is defined as "a special innate propensity,

ZOOGENESIS

in any organized being, but more especially in the
lower animals, producing effects which appear to be
those of reason and knowledge, but which transcend
the general intelligence or experience of the creature."
In the Century Dictionary we read further that
"instinct is said to be blind — that is, either the end
is not consciously recognized by the animal, or the
connection of the means with the end is not under-
stood." Intelligence is defined as "discernment or
understanding," and as "cultivated understanding."

Now if intelligence is really discernment or under-
standing, as according to definition it is, it is difficult
to see wherein it differs from instinct as displayed by
insects, birds and rodents.

For instance, the mud-daubers, the fossorial, or
digger, and other solitary wasps (fig. xo, p. 33) display
great discernment and understanding in providing for
the welfare of their young, which they will never see.
Their actions are certainly based upon definite and
detailed knowledge of the conditions which must be
met. How they acquired that knowledge is wholly
unknown to us, but it is indubitable that the knowl-
edge is there. Whether their actions have anything
to do with reason or not is a matter of opinion.

Reason is variously defined, but all definitions of
reason are based upon the general idea that reason
is a faculty characteristic of and peculiar to man, or
perhaps shared in a small way with the more familiar
domestic animals, such as dogs and cats. As a com-
parative term, therefore, the word reason is quite
without meaning.

t3]

THE NEW EVOLUTION

Whether the actions of the solitary wasps transcend
their general intelligence or experience we do not
know. We have no measure whatsoever of their
intelligence, and we cannot tell how much or how
little they may remember from their larval life.

There is no object in prolonging this discussion.
On examining the facts we see that intelligence and
reason are supposed to be peculiar to man. Actions
which in man are acknowledged to be the result of
intelligence and reason, such as the use of heat, tools
and clothing, if duplicated in insects are assumed to
be the result of blind instinct. But in the absence of
indubitable proof the same or very similar actions
cannot be supposed to arise from wholly different
causes. So after all we are forced to admit that intel-
ligence and reason are simply mental attributes we
think we understand, while instinct is a mental
attribute we know we do not understand. That
seems to be the only tangible difference between them.

This raises some very interesting questions. Can it
be possible that after all the animal world is really a
much more unified whole than it is commonly con-
sidered? Can it be possible that all forms of animal
life, although so very widely different in their struc-
ture, are merely diverse and concurrent manifestations
of the same broad principles? Are we to look upon
the numerous animal types not as higher and lower
but as representing a different grouping of features,
both physical and mental, inherent throughout the
animal world and in some way combined in the origi-
nal prototype? Or is there some other explanation?

_

-^O^ '^-^^^ <\\^,^2^ 'V^»j27? \V::5k^ '\^^k7t "X^^:^ 'X:^^:^ '^^^r^ '^^■^^ T:^3^

CHAPTER III
MAN AND THE APES

UNDENIABLE IS thc fact that man and the man-
like apes — the chimpanzees, the gorillas, the
orangs and the gibbons — show numerous points
of similarity. Man is obviously much more nearly
like these apes than he is like any other living crea-
tures. Yet equally undeniable is the fact that the
differences between man and the apes are significant
and striking.

The most interesting and the most significant of the
differences between the apes and man are connected
with their very early life.

Although they develop very slowly, none of the
apes or monkeys have a true baby stage except of
relatively brief duration. Their young very soon
acquire what might be called a subadult mentality.
Early in life the actions of young apes and monkeys
begin to resemble more or less closely the actions of
their parents — or perhaps it should be said recall the
actions of their parents. This is not at all the case
with human children in the normal human family,
though neglected or abandoned children rather
quickly leave behind them the typical child stage.

All human children have one marked peculiarity
which seems to be confined to them. When babies
first begin to touch and to hold objects they seem to
show an extraordinary preference for hard, and espe-

THE NEW EVOLUTION

daily rough, objects. Babies are very fond of passing
their fingers over sand-paper, which they usually
much prefer to ordinary paper. So far as I know this
is not at all true of young monkeys.

When they are given a hard object, such as a watch,
babies usually first put it to their mouths, and when
they begin to lose interest in it they commonly end
by whacking it against something. Of course they
sometimes simply drop it. If monkeys lose interest
in anything which they are holding in the hand they
always simply drop it. The whacking propensity
of babies certainly is not learned from their parents.
Indeed, it commonly results in tangible forms of
parental resentment. It is, perhaps, the most impor-
tant and significant instinctive reaction of babies, at
once proclaiming them as fundamentally different
from young monkeys. Their preference for hard and
rough objects tells the same story.

It is probably safe to assume that these two reac-
tions of young babies lie at the bottom of all material
human progress. For we see in these reactions an
inherent and characteristic impulse to acquire hard
rough objects and, holding them in the hand, to make
use of them. Apparently blind and undirected as
this instinct is, it is easy to suppose that it would lead
directly to the use of tools.

Another peculiarity of babies is a more or less
marked desire constantly to hold something in the
hand. Young monkeys like to cling to the mother,
but show little, if any, desire to hold anything in the
hand. In man this curious desire to have something

[16]

ZOOGENESIS

in the hand is continued throughout life. We notice
it in both men and women, and we find it equally
conspicuous in the streets of a large city and along
country lanes.

The predilection for hard and rough objects, the
whacking propensity, and the constant desire to hold
something in the hand are so very characteristically
human and appear so very early that there must be
something of fundamental import and significance
behind them. They seem to point especially to the
human hand and in some way to show that there is a
deep seated and a far-reaching difference between the
human hand and the monkey's paw.

Every parent has noticed that at times babies are
fearfully destructive. They delight especially in de-
stroying books and magazines and flimsy toys. De-
struction for destruction's sake seems to be a peculi-
arity of the baboons, for baboons if they gain entry
to a house will more or less completely wreck every-
thing that can be wrecked. But it is not a peculiarity,
so far as can be learned from the literature, of the
more man-like monkeys.

Leaving the individual baby, let us now consider
the human family. Perhaps the most important
social difference between man and the apes is corre-
lated with the fact that in man the ministrations of
both parents or their equivalent are necessary in the
raising of a family. A woman cannot raise a family
unaided. She must have the assistance of a husband
or, in the more complicated social systems, of other
members of the social unit. Interdependent with this

t7]

THE NEW EVOLUTION

we find in man a socially effective sentiment of love
which creates and makes a unit of the family.

So far as the available information enables us to
say, all monkeys live together in promiscuous hordes
or troops in which each female raises her own young
unaided. Family attachments are not necessary and
do not occur.

That family life was from the first a fundamental
human institution would seem to be shown conclu-
sively by the existence in all human races of taboos
and laws directed toward the maintenance of the
family or of some social form to be interpreted as
derived from the family. Now so far as we know
taboos and laws are not invented to mold society into
new and preconceived forms, but on the contrary
they are designed to correct evils recognized as pos-
sessing disruptive or destructive tendencies which
from time to time appear.

Through a natural process of development from the
human family arose the various human social units.
In highly developed social units including large
numbers of individuals the human social system tends
more or less extensively to break down. Promiscuity
becomes frequent, attachments between individuals of
opposite sex become increasingly transient, families
commonly consist of a single child or of two children
of very different ages, and in general the human so-
ciety seems to approach the system characteristic of
the apes.

From this it has been argued that the human social
system was originally derived from that of the apes

t8]

ZOOGENESIS 'S^^^''

and that such a breakdown simply indicates a return
to fundamentals. This is not at all the case. The
breakdown of the human social system, which orgi-
nated from large serial families of dependent children,
is invariably the result of economic causes arising
from the complexities of the system itself when so
very highly developed as to become artificial. It
arises from the love of gain or show and the associated
desire to be free of the liabilities inherent in family
ties which becomes so exaggerated as to thrust into
the background the normal sex relations. It is
rendered possible by the fact that in large communi-
ties family responsibilities, instead of remaining local-
ized and concentrated in the heads of families, become
increasingly distributed over the social unit as a
whole. It is actually the reverse of a return to
fundamentals.

It is not necessary here to discuss the use of fire,
tools, ornaments and clothing, or the development of
articulate speech. It is sufficient to point out that
the origin of all the distinctively human attributes
must be satisfactorily explained by any adequate
theory of the development of animal forms, and fur-
ther that these cannot be explained by any theory
which assumes the origin of man from the man-
like apes.

[^9]

CHAPTER IV
THE WORLD AND THE BUTTERFLY

•an's contacts with the world about him are
singularly limited. To a large extent he
himself creates the environment in which he
lives. Houses or other shelters or appropriate cloth-
ing or sometimes a simple covering of grease protect
him from the rain. Clothing and fire provide warmth,
and fire also light. Most of man's food is produced
under his control. Man is therefore more or less
completely independent of many factors that have a
most important — indeed a vital — bearing on the
existence of every other living thing.

True appreciation of any form of animal life is
quite impossible unless we constantly bear in mind
the intricate and varied contacts of that form of life
with other forms of life, both animal and vegetable,
and also with the inanimate or inorganic world.

In order to understand and to appreciate the intri-
cate nature of the complex, both living and non-
living, that enmeshes every living thing, holding it
rigidly to its proper and appointed place in the cosmic
plan, let us briefly consider the numerous and varied
contacts of a butterfly (fig. ix, p. zi).

Did you ever realize that for their existence butter-
flies depend upon the sea? The young of butterflies
are known to us as caterpillars. Caterpillars eat
leaves — or at least the great majority eat leaves.

%M ZOOGENESIS "^^^

Leaves are produced by plants. In order to grow
plants must have water. To them water comes in the
form of rain. Rain is moisture condensed from the air
passing in the form of winds above the earth. Most
of this moisture gets into the air through evaporation
from the surface of the seas which cover seven-tenths
of the area of the world.

So there really is a close connection between the
butterflies and the ocean. This connection is made
up of many links which involve almost every line of
science. For instance, astronomy plays a part. The
emanations from the sun provide the energy by means
of which the water is evaporated from the surface of
the sea, which causes the winds to blow, and which,
acting on the green substance in the leaves of plants,
enables them to form organic out of inorganic sub-
stances. In other words, the emanations from the
sun make possible the physical processes and chemical
reactions on which the existence of the butterflies
depends. And besides this, the element of time, so
far as it affects life, is an astronomical phenomenon
dependent upon the spinning of the earth upon its
axis and on its course about the sun.

Weather and climate play an important part in di-
rectly affecting the lives of all the butterflies. They
also affect them indirectly through their action on the
sea, in some cases thousands of miles away. As an
example, the alpine butterflies on the mountain tops
in south central Asia depend on snow and rain which
is brought to that region in the form of water vapor
by the higher currents of the air from the Atlantic

[31]

"Wi THE NEW EVOLUTION T^^

ocean across the plains of Europe and of western
Asia.

Soils are formed from the disintegration of the
rocks. Rocks are continually breaking up and being
washed away as mud or sand or gravel. In this way
there is formed the basic food of the plants which sup-
port the butterflies.

Besides this, the muds and sands and gravels de-
posited in water are continually being reformed and
consolidated into the so-called sedimentary rocks.
Once in a while a butterfly gets stuck in mud and
covered up. This mud may later turn to rock. When
this happens we have a record of the sort of butterflies
that existed at the time when that rock was mud. It
is quite unusual to find butterflies as fossils in the
rocks, though a fair number have been found and
studied. These all belong to that far distant period
known as the Miocene and lived many millions of
years ago. In spite of their very great antiquity,
they differ very little from the kinds we know today.
Most of their living representatives, however, are
found in different regions. Thus in Colorado we find
a type now confined to Africa, and in Germany we find
other types which today live only in America.

Most caterpillars are able to subsist only on a very
limited number of different kinds of plants which are
closely related to each other in their chemical compo-
sition. Thus the cabbage butterfly feeds only on cab-
bages and a few closely related plants, and on nas-
turtiums. Some enormous groups of butterflies feed
only on a single type of plant, as the so-called Aristo-

Different Types of Insects
for an explanation of the figures see p. 278

THE NEW EVOLUTION

lochia (or pipe-vine) swallowtails which feed only on
Aristolochias and on very closely allied plants, and
also our fritillaries which feed almost exclusively
on violets. Very many kinds of butterflies feed only
on a single kind of plant, like our beaked butterfly
and tawny emperor which as caterpillars are found
only on hackberry trees. But a few kinds of butter-
flies, like our common yellow swallowtail, feed on a
very great variety of different and unrelated plants.

From this it becomes evident that female butterflies
must be expert botanists, for they must be able accu-
rately to identify those plants which are suitable for
use as food by the caterpillars of the coming genera-
tion. Or perhaps it should be said that they must be
expert chemists, for not infrequently they will pick
out a plant chemically suitable as food, but botani-
cally widely different from any other plant which
they or their ancestors, at least for thousands of gener-
ations, could be supposed to know.

As an illustration, the female of the common cab-
bage butterfly will freely lay her eggs on garden nas-
turtiums (Tropaolurn) which belong to a family of
plants (Tropasolacea^) confined to Central and South
America and not at all like any of the plants of the
cabbage family (Brassicaceas) upon which ordinarily
this Old World insect feeds.

Butterflies have very many enemies of every con-
ceivable description. The Australian natives are very
fond of certain kinds of butterflies, and grow fat on
them if they can get them in sufficient quantities.
In Central and South America and especially in Africa

ZOOGENESIS

the caterpillars of several different kinds of butterflies
used to be, and in some places are still, in much
demand as food. Certain bats are very fond of butter-
flies, and mice and shrews eagerly devour them.
Some birds feed partly, and in the tropics largely, on
them. Certain small lizards and some of the smaller
snakes are very fond of them. Among their insect
enemies are mantes (fig. 19, p. 33), various preda-
cious bugs (fig. 2.3, p. 33), robber-flies, dragon-flies
(fig. 11, p. 33), hornets, ants, and the so-called cater-
pillar v^asps.

But their worst and most destructive enemies are
various sorts of small wasp-like flies which lay their
eggs upon or in their eggs, their caterpillars, or their
chrysalids. The small maggots which hatch from
the minute eggs of these small parasites feed upon
the contents of the egg of the butterfly or upon the
juices of the caterpillars or upon the contents of the
chrysalids. Some of the true flies which in their
appearance are much like little blue-bottles also have
this parasitic habit.

Many of the parasitic grubs which live unseen
within the bodies of the caterpillars have parasites
that feed on them. Although these live within the
caterpillars, they feed only on the parasites which
are themselves engaged in feeding on the caterpillars.

And besides these enemies butterflies have many
more, for instance nematode worms (cf. fig. 81, p. 161),
bacteria and protozoans (cf. fig. 87, p. 161), spiders
and mites, sometimes even mosquitoes. Indeed so
numerous and varied are the enemies of the butterflies

THE NEW EVOLUTION

that one often wonders how it is that any butterfly
is left alive.

Such in brief are the more important contacts of a
butterfly. In considering the living world it is impor-
tant constantly to bear in mind that every sort of
animal no matter what it is has just as many and just
as varied contacts as has a butterfly.

[36]

CHAPTER V
LIFE'S BACKGROUND

1 LL animals must eat. Therefore in a considera-

/\ tion of the living world it is important clearly
Jl jL to understand the origin of the food which
supports the animals. It is essential that we appre-
ciate just how the necessary substances are made
available for them. It is important that we under-
stand the mechanism of the formation of the food of
animals.

Air, water, rocks — from these three ultimate sources
do all living things secure those substances which are
necessary for their existence and their increase. The
energy by means of which these substances are re-
leased and through recombination made available for
use by living things comes from the sun. This energy
radiated from the sun reaches the earth in the form of
sunlight and of similar but invisible emanations of
wave lengths longer or shorter than those which
our eyes are able to perceive.

The interaction of the water and air upon the rocks
which is made possible by the energy provided by
the sun is perhaps best understood by the considera-
tion of a bleak and desolate mountain top. The
exposed summit of a mountain would seem to be the
last place in the world in which to contemplate life's
mysteries, but from the crags and rough and broken
rocks drenched by the rain or covered with snow or
ice or wrapped in clouds or mists we may learn first

[37]

THE NEW EVOLUTION ^^

hand very many things which are by no means so
evident elsewhere.

The most important thing we learn is that rocks,
no matter how solid they may seem, are far from inde-
structible. The rocks of the bare mountain tops are
always cracked and broken. The expansion caused
by the sun's heat and the contraction caused by the
cold of night or of the winter and the freezing and
thawing of such water as penetrates the fissures are
continually chipping off larger or smaller bits from
their exposed surfaces. Besides this, the various
minerals which compose the rocks are all more or less
soluble in water so that part of the substance of the
rocks is continually being washed away.

The bits chipped off fall down the mountain side
and gradually are reduced to smaller and smaller
fragments. The substances dissolved are partly held
in the water in the soils, and partly are carried by the
rivers to the sea.

This process of rock destruction in most mountain-
ous regions is hastened by earthquakes which by
shaking the fragments down into the valleys expose
new surfaces to the destructive forces.

In many places volcanoes are continually, or from
time to time, bringing to the surface great masses of
rock in the form of lava or of dust or ash and together
with this water vapor and other gases of various sorts
which add to the supply of substances available for
the support of life on the earth's surface.

Rocks appear to us as solid, unyielding, and more
or less unattractive objects. But they contain.

ZOOGENESIS

securely locked up in the various minerals of which
they are composed, all of the chemical elements which
make up the substance of the bodies of the plants and
animals. These are released and freed by the destruc-
tion of the rocks by air, water, heat and frost. It is
the continuous destruction of the rocks and the release
thereby of the elements necessary for the formation
of their bodies that makes possible the existence both
of plants and animals.

The finely divided particles of rock form soils which
cover the mountain sides and the valley floors, and
more deeply all of the more level regions of the land.
Soils are of many different types, and their ability to
support life is dependent upon the temperature, sea-
sonal changes and rainfall of the region as well as
on the type.

On the soils grow plants of all descriptions, some-
times in small amount as on coarse gravels or on
areas of shifting sands, but sometimes in great abun-
dance forming extensive forests and broad grass
covered plains.

Obtaining all the materials necessary for their
growth from the soil and air and water are the green
and comparable plants alone. By means of the green
substance, known as chlorophyll, and allied sub-
stances, these plants are able to form organic out of
inorganic compounds. No form of animal life is able
to exist on inorganic foods.

So all of the animals living on the land depend for
their existence on the green plants, either directly or
indirectly. Every portion of a green plant — leaves,

b9]

THE NEW EVOLUTION

stems, trunk, roots, seeds and flowers — is used as food
by some animal type or other.

Not only are all the animals supported by the green
plants, but multitudes of other kinds of plants, such
parasitic plants as the mistletoes and gold-threads and
many other less familiar sorts, and especially the
fungi, molds and rusts and many bacteria, live either
on them or on their dead remains.

Such animals as are not plant feeders live on other
animals that feed on plants or on the parasitic or
saprophytic plants feeding on the living or the dead
green plants, or on the partially decomposed remains of
plant or animal substances. A few animals have been
described as capable of existing on mineral material
alone. But it is doubtful whether any animal can
do this without the intervention of some associated
plant.

And besides all these there are numerous kinds of
parasitic plants, particularly bacteria and molds,
which live on or within the bodies of every sort of
animal, whether plant feeding or carnivorous.

In short, we find plant feeding plants, plant feeding
animals, animal feeding plants and animal feeding
animals of every conceivable variety. There is no
reservoir or source of food of any kind, permanent
or temporary, that is not utilized by some sort of
living thing.

At the beginning of the winter, or in the tropics of
the dry season, the leaves of the green plants cease to
function. In most of our plants and in many in the
tropics they wither and drop off. The dying and

[40]

ZOOGENESIS

falling of the leaves in autumn and at the beginning of
the dry season, and more or less constantly at other
times as well, means the accumulation of a vast
reservoir of foodstuffs for anything capable of making
use of it.

Bacteria and fungi thrive on this detritus, and earth-
worms and many other kinds of snails and slugs and
insects, as well as other creatures, feed either on this
decaying vegetation, or on the bacteria or fungi in it,
or on the living things that feed on them.

Much of this material is consumed where it lies
upon the ground, but a vast amount is washed into
the rivers, especially by the floods of spring and at the
breaking of the rains, and is carried to the sea. A
large part of this is still in a condition to be eaten by
detritus feeding animals, while a great deal more,
especially in the form of organic substances in suspen-
sion or solution, is available as food for the ma-
rine plants.

Our knowledge of the origin of the substances on
which the plants of the sea depend for their existence
is rather vague. But the evidence seems to indicate
that very largely, possibly for the most part, life in
the oceans is dependent, through the necessities of the
ocean plants, on food substances brought down from
the exposed land areas.

The plants of the sea, at least those which support
the greater part of the ocean's animal life — minute
free floating plants invisible to the naked eye (cf.
fig. 86, p. i6i) — seem to require the presence in the
water of something that comes to them from the land.

[4^]

^^ THE NEW EVOLUTION

This is presumably some organic substance chiefly
derived from the decayed remains of land plants.
Whatever it may be, if it is not essential at any rate
the oceanic plants grow much more luxuriantly if it
be present, exactly as many of the plants on land will
grow much better if they are well manured.

Strange as it may seem, life in the sea is for the
greater part confined to the regions bordering the
shores of continents, though also abundant about
large mountainous and wooded islands such as those
of the Malayan archipelago. So we find all of the
important fisheries of the world situated in shallow
water near the land. Furthermore, these are all in
the northern hemisphere along the coasts of those
continents which have the greatest area exposed to
the action of the sun and rain and frost.

With increasing distance from the land life in the
sea becomes progressively less and less abundant, and
toward the middle of the oceans, especially in the
southern hemisphere, it almost completely, perhaps
even entirely, disappears. Sea animals are largest and
most abundant on those shores which have a copious
rainfall, and especially on rugged and on cold coasts
where it may be assumed that material from the land
would reach the sea in the greatest quantity and
would remain unaltered for the longest time.

M

CHAPTER VI
FACTORS AFFECTING ANIMAL LIFE

VARIATIONS in the several different types of ani-
mal life from place to place on the earth's
surface or in the oceans, and from one geolog-
ical epoch to another, are directly or indirectly brought
about as a response to variations in the factors which
bear more or less directly upon the animals involved.

Frogs are not found in deserts, nor are there any
lizards in cold regions. Elephants, rhinoceroses and
tapirs now live only in restricted areas in the tropics,
but in the Pleistocene all three ranged far to the
northward of their present habitats. On the New
Siberian Islands in the Arctic Ocean the bones of
Arctic elephants or mammoths are to be found in
great abundance.

So before we can discuss the problem of the changes
in and the development of animal forms it is essential
that we understand just what the most important of
these factors are.

The chief factors affecting all living things are the
great diversity in the form in which the supply of
necessary new materials is offered, and the great
diversity in the chemical and physical environment
or surroundings in which they must be taken up
and used.

Only the plants containing chlorophyll or some
similar substance are able to build up organic out of

[43]

THE NEW EVOLUTION

inorganic substances. As they can do this only with
the aid of sunlight, the animal life of the entire world
is supported by plants growing on the surface of the
exposed land areas, or attached to the bottom, freely
floating, or suspended in water of not more than six
hundred feet in depth. So the sun-lit surface of the
land and the sun-lit surface of the sea provide the basic
food for all forms of life from the highest mountain
tops to the depths of the deepest caves and down to
the great abysses in the sea.

The plants containing chlorophyll or a comparable
substance get the materials necessary for their growth
from substances dissolved in the water in the soil, or
in the water of ponds, lakes, rivers, or the sea, and
from gases in the air or dissolved in water.

Just as water is essential to the life of every plant, so
also is it essential to the life of every animal. Since
foodstuffs are available for use by animals and plants
only when they are accompanied by an adequate sup-
ply of water, the very unequal distribution of this
liquid is the chief controlling factor affecting all life
on land.

Some regions are extremely wet, while others are
extremely dry; in others the supply of water is very
variable at different seasons of the year, or the hu-
midity may vary very greatly between the night and
day. In the north for a greater or lesser portion of
the year the water becomes ice — in other words it
changes over into a form in which it is not avail-
able for use by the very great majority of plants and
animals.

[44]

^^"^ ZOOGENESIS T^"

So every living thing on land, whether plant or
animal, must have some provision to counteract the
variability in the available supply of water, and espe-
cially to guard against the loss of moisture.

Thus all adult insects living in the open, like house-
flies, June-bugs, wasps, bees, moths and butterflies,
are protected by a tough impervious covering.
Among the backboned animals or vertebrates the rep-
tiles and the birds are best protected against the loss
of moisture. Consequently reptiles and birds with a
few insects having an insatiable thirst for nectar, sap
or blood are the characteristic creatures of hot and
extremely arid regions in the daytime.

In the cool and relatively damp nights in the same
regions mammals take the place of reptiles, issuing
from their holes and other hiding places and ranging
widely everywhere, while many different kinds of
insects take the place of the very few that are abroad
by day. In less arid regions mammals become more
varied and abundant, and are seen by day as well as
after nightfall; birds and insects also become more
varied and abundant, and amphibians (toads) appear.
In still moister regions frogs are also found.

The young of insects — maggots, grubs or caterpil-
lars, or, in the case of grasshoppers, bugs (fig. X3,
p. 33) and other types, small wingless replicas of the
fully grown — are always less well protected against a
loss of moisture than are the adults. The young of
house-flies, which live in moist decaying substances,
the young of June-bugs, which live in moist soil and
are commonly called "white-grubs," and the young

[45]

THE NEW EVOLUTION

of bees and wasps which live in cells carefully pre-
pared so as to avoid a loss of moisture, are soft and
flabby, more or less like earthworms.

Compared with the grubs of bees and wasps most of
those caterpillars which are the young of butterflies
have a thick tough skin, though they nearly all live
in more or less humid situations and of course take
in water all the time with the portions of the leaves
they eat. Many caterpillars, like those of the fritil-
laries, conserve their moisture by feeding only in the
night time, in the day hiding beneath sticks and stones
or among fallen leaves.

The caterpillars of some of those curious butterflies
that feed on ants live in the ants' nests mostly below
the surface of the ground. They are soft and their
skin is very thin, so that they look much more like
the grubs of beetles than they do like the young
of butterflies.

Much as the soft and thin skinned young of house-
flies, June-bugs, bees and wasps differ from their
parents do the marsh-living and aquatic frogs and
salamanders differ from the toads.

It is the same with plants as with the animals. All
the plants on land have some special adaptation to
prevent damage through their drying up. In many
cases plants flourish in the rainy or the warm summer
season and when that passes go into a drought-resist-
ing resting stage, or go to seed, the seeds living over,
on or in the ground, until the rainy or the summer
season comes again.

Very many insects do about the same. They live

[46]

Different Types of Crustaceans
for an explanation of the figures see p. 278

THE NEW EVOLUTION

their active life in the wet or summer season and pass
the dry or winter season in a resting stage, commonly
the pupa, buried in the ground or in some other situa-
tion where they will not lose their moisture.

Temperature is commonly regarded as an important
factor in controlling life both on the land and in the
sea. And so it is. Yet it seems to be not so impor-
tant of itself as in its indirect relation to organic life.
On land, changes in temperature, seasonal or diurnal
or irregular, profoundly affect every living thing.
This is due in part to their effect on the chemical
processes taking place within the body, but prob-
ably in equal part to the complexities they create
in the vital problem of securing and conserving
water.

So far as plants and animals are concerned, one of
the most important things concerning water is that
at low temperatures it suddenly changes over into
ice — that is, it passes over into a form in which it
cannot be used without a considerable expenditure
of energy.

So in the northern winter when the ground and
ponds and streams are frozen the plants cease to
grow and become dormant. The turtles, snakes,
lizards and frogs, the butterflies, bees, ants and other
insects, and the snails and earthworms, all pass into
the long sleep known as hibernation. All birds are
perpetually active, and all that cannot find sufficient
food fly south. But some mammals, like the bears
and woodchucks and certain of the mice, sleep like
the insects, while others, like the squirrels, sleep most

[48]

^^ ZOOGENESIS 1^"^

of the time but appear at intervals on warm and
sunny days.

When the weather gets extremely cold the air, with
any rise in temperature, becomes extremely dry and,
speaking generally, dryness is more dangerous to life
than cold. This raises an interesting question. Why
do the small birds that visit us each winter from the
north, such as the horned larks, snowflakes, kinglets,
creepers and others, leave their summer homes? Is
it not probable that they are induced to visit warmer
regions not so much on account of the cold itself as
because of the dryness which accompanies the cold?

For most of these birds there is quite as much food
available in winter in their northern homes as there is
with us, but the water content of that food is consider-
ably less. It is to be remarked that when they visit
us these little birds keep mainly in damp localities,
in low damp woodlands, about ponds and streams, or
near the sea coast.

Much as the animals and plants with us pass
through the winter do tropical animals and plants
pass the dry hot season. For instance, some of the
lemurs in Madagascar spend the dry season in a state
of torpor coiled up in a cavity of a tree or in a nest
just as some of our squirrels spend the winter.

In some places in the tropics at the end of the wet
season the trees for the most part shed their leaves,
and the insects almost completely disappear. A
photograph of such a region at this time much re-
sembles one of a snowless day in winter in the north.
Conditions are the opposite in that in one case nature

[49^

THE NEW EVOLUTION Wi

is sleeping from the effect of excessive heat and in
the other from the effect of excessive cold, but they
are the same in that in both cases the plants and
animals are sleeping over a period when they are
unable to obtain sufficient water.

Temperature affects directly only such animals as
are so very delicately balanced that they require a
fixed and usually high degree of heat for the main-
tenance of their internal chemical reactions. In this
category fall the most active vertebrates, the mam-
mals, birds and reptiles.

In the mammals and birds the body is insulated
from the temperature changes in the air about it by
a layer of air which is held in place by a covering of
hair or feathers. Their body temperature is high and
constant and, excepting in the monotremes or egg-
laying mammals, and in hibernating mammals, it is
quite independent of the outer temperature. The
bodies of whales are insulated from the temperature
of the surrounding water by a layer of fat, while the
seals have both hair and fat.

Reptiles require a relatively high temperature, but
have no mechanism for controlling it. Therefore all
of the more active and all of the larger reptiles are
tropical or subtropical, only the smaller representa-
tives of less active types, the turtles and the snakes,
occurring in the colder regions. The amphibians are
all relatively inactive and the frogs, toads and sala-
manders range far into the colder regions.

Among the other forms of life temperature seems
to have the most effect in delimiting the activity of

[5^]

ZOOGENESIS

bacteria and protozoans, many of which will thrive
only within curiously narrow limits and most, though
by no means all, of which require a considerable
degree of heat.

It is a curious fact that these very features which are
characteristic of bacteria and of protozoans are
equally characteristic of the reproductive cells of all
other animals. Reproductive cells in their tempera-
ture relations as well as in the broader features of
their structure are always more like protozoans than
they are like the animals from which they were
derived.

This is well illustrated by the narrow temperature
range within which the different sorts of fishes and
amphibians will spawn, and within which normal
development of their ova will take place, and on land
by the narrow temperature range within which the
different kinds of insects lay their eggs.

This interesting disharmony between the tempera-
ture range of adult animals and that of their eggs and
very early stages probably has played an important
part in the diversification of animal life.

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CHAPTER VII
MORE ABOUT ANIMAL LIFE

THERE is a most important trinity of factors affect-
ing life in general that is not sufficiently ap-
preciated. For all living things, no matter
what they are, water, air and food are the prime neces-
sities. Everything else is in importance wholly
secondary.

Physiological adaptations enable both animals and
plants to exist through the entire range of tempera-
tures found upon the earth, and also through the
entire range of illumination. Indeed, in the absence
of light many animals and plants are able to produce
themselves, through the phenomenon known as lumi-
nescence, a sufficiency of light of the quality necessary
for their well being, just as the birds and mammals
are able to create and to maintain the temperatures
necessary for the proper functioning of their bodily
reactions.

While by various bodily adaptations, and especially
by diverse habits, certain types of animals are able to
store up and to conserve an adequate supply of water,
or at a time when water lost cannot be replaced to
enter, sometimes abruptly, a resting stage, none can
do without it. Furthermore, all living things when
active require a considerable amount of water. It is
the same with air, and again the same with food.

From this it naturally follows that life, or rather

ZOOGENESIS

living substance, will be most abundant for each unit
of area — for instance per acre — where there is a maxi-
mum of water permanently in the liquid state, a
maximum of air, and a maximum of food.

Thus on land the optimum conditions for the
greatest development of plant and animal life, so far
as concerns mere bulk alone, are to be found in the
moister regions of the tropics where the rains are not
so heavy as to be destructive by the weight of water
falling, and the temperature is high and constant.

But in the sea these factors find their most perfect
balance in a region wholly different. Here the chief
problem is securing a sufficiency of air. Now the
colder water gets the greater the amount of air it is
capable of holding in solution. Everyone has no-
ticed that in a glass of cold water standing in a room
bubbles of air appear on the sides and bottom as the
water warms. So in the sea the optimum conditions
for both plant and animal life are in the coldest oceans,
in the polar seas in the summer time when the sun is
at its highest, and in the cold currents flowing out
from these.

In the hot wet portions of the tropics chemical dis-
integration of the rocks takes place with great rapid-
ity, continually replenishing the mineral constituents
in the food supply of the endemic plants. In the cold
polar seas the dead organic matter either in suspension
in the water or lying on the bottom is preserved, as
in an ice-box, for the longest time.

So on land food supplies, in the form of new mate-
rials made available for use by plants, are especially

[53]

Ha THE NEW EVOLUTION

abundant in the tropics, while in the sea, due to con-
servation by indefinite preservation, they are most
abundant in the coldest water.

The regions supporting the greatest density of life
both on the land and in the sea are the regions show-
ing the least deviation from the optimum conditions.
Naturally in the regions showing the least deviation
from the optimum conditions there is the least incen-
tive to or necessity for variety among the endemic
types of plants and animals. Therefore the regions
wherein is to be found the greatest density of life are
not the regions where animals and plants occur in
the maximum variety. The greatest variety both in
plants and animals is to be found in regions where
there are the most diversified conditions to be met
which may be met through minor adaptations.

Conditions which involve the passage by animals
and plants through a resting stage, more or less pro-
longed, necessitate what might be termed major adap-
tations. For an enforced resting stage necessitates
ability to prepare for it, or to recover from it, or for
both previous preparation and subsequent recovery.

The necessity for such major adaptations renders
life impossible for many types which are quite capable
of meeting the requirements for minor adaptations,
as for instance those called for to counteract daily
variations in the essentials for existence.

The fact that minor adaptations may take many dif-
ferent forms whereas the possible variety in major
adaptations is rather closely circumscribed furnishes
the explanation of the interesting fact that the great-

Some Fossil Animals

FOR AN EXPLANATION OF THE FIGURES SEE P. 279

THE NEW EVOLUTION

est variety of life is found where conditions vary more
or less extensively, but not too widely, from the
optimum.

On land the greatest variety in the plants and ani-
mals is to be found in the less humid and cooler
regions of the tropics where seasonal change is slight
or absent, but the temperature and humidity vary
considerably between the night and day, and in those
regions in the tropics with a more or less marked,
though not severe, dry season.

Among the animals of the sea the greatest variety
occurs on tropical and subtropical coasts at moderate
depths where the temperature of the water is just
about half way between the temperature of the
abysses and the temperature at the shore line. This
region is a sort of meeting ground wherein are found
many representatives of abyssal types which rise no
higher, and also representatives of many shore line
forms which descend no lower, while at the same time
very many different creatures occur in this band alone.
Much the same conditions are to be found on land in
mountainous regions in the tropics.

There is still to be considered the region producing
the greatest amount of life, that is, the maximum
amount of living substance. One might suppose that
this would be the region where the greatest amount
of disintegration of the basic rocks is constantly
taking place. And so it is. On land the maximum
amount of living substance is found in the northern
hemisphere between about the Tropic of Cancer and
about 60° north latitude where there is the greatest

[56]

ZOOGENESIS

exposed land area under conditions of rapid chemical
and physical disintegration. This region includes by
far the greater part of all the forests of the world and
of the fertile grassy plains. In the sea the region
that supports the greatest amount of life is that which
receives the drainage from this same area, that is,
the north Atlantic and the north Pacific oceans.
Here the maximum intensity of life is in bands along
the shores, narrow in the south but broadening in the
north, lying mostly in water of not more than six
hundred feet in depth.

[57]

CHAPTER VIII
LAND AND SEA COMPARED

IN ORDER properly to understand the conditions
under which life in the sea exists it is necessary
first of all to compare them closely with condi-
tions on the land in order to bring out the corre-
sponding features and to emphasize the contrasts.

We all have a pretty good idea of conditions on the
land. On land life exists at the bottom of a sea of air
which entirely surrounds the earth. The thickness
of this blanket of air about the earth is such that
each square inch of the earth's surface supports a
weight of nearly fifteen pounds of air. So we say that
at the surface of the earth there is an air pressure of
approximately fifteen pounds to each square inch.

Air is very light, much lighter than the living
substance — protoplasm — of which the bodies of the
plants and of the animals are composed. Conse-
quently all land living things, both plants and ani-
mals, must live on or just beneath the surface of the
ground at the bottom of the sea of air.

But in spite of its lightness as compared with flesh,
air is fairly heavy. Therefore it has considerable
supporting power. Besides, it is constantly in mo-
tion in one direction or another, and this constant
motion gives it transporting power.

The transporting power of air is of very great im-
portance both to the plants and to the animals. Very

[58]

^^^^ ZOOGENESIS '^M

many plants depend on air to carry the pollen from
one flower to another. We see this best in such trees
as oaks, chestnuts, alders, willows and birches in
which the male or staminate flowers are in long cat-
kins. From such trees we sometimes see the pollen
blown away in a thick cloud by a sudden gust of
wind.

The spores of molds and fungi and of more or less
similar types of plants and the spore-like stages of
many of the microscopic animals, especially the
protozoans and the rotifers, and also of a number of
the minute organisms that cause disease in man, in
animals and in plants, are almost constantly present
in the air floating about in the same way as, and
together with, minute particles of dust.

Air in stronger motion is essential for the distribu-
tion of those plants which have wind transported
seeds. Such seeds may, like the seeds of orchids, be
of such extremely minute size as to act like particles
of dust. More commonly, however, they are pro-
vided with various devices such as the wings of the
seeds of pines, elms and maples, or the tuft of hairs
or ' 'coma" of the seeds of the dandelion and the milk-
weed, which delay their falling and aid in their
transportation.

Some insects, so far as their capabilities for trans-
portation are concerned, are comparable to specks of
dust. Such for instance are the excessively minute
wasp-like things that live as parasites mostly in the
eggs of other insects or of spiders, and certain equally
small fungus-living beetles. Some of these little

[59]

THE NEW EVOLUTION

parasitic wasps and fungus beetles are scarcely more
than one one-hundredth of an inch in length, and
some of the wasps are wingless. If these were forced
to depend on their own ability to travel they would
be placed under an insuperable handicap, for what is
a single mile for us is the equivalent of six million
miles for them. We, however, have to walk that
mile while for them the wind performs the labor.

Very many living creatures have discovered that
the air is sufficiently dense to enable them to use it
to support their bodies in passing rapidly from place
to place. In other words, they have learned to fly.
This is the case with all of the bats, most of the birds,
and most of the insects in the adult stage.

Many creatures, although they do not actually fly
like the birds and bats, have their body surface in-
creased by expansions of various kinds whereby they
are enabled to glide diagonally downward through
the air from one place to another. We see this
especially in the flying-squirrels, and in the flying
lemur (Galeopithecus) and the flying lizards of the
oriental regions.

Still other creatures have various adaptations
which, by acting on the air, serve to protect them in
one way or another. Thus a cobra when it strikes
rises on the extreme end of its body and falls forward;
as it falls the expanded hood acts as an air-brake and
lessens the shock of its contact with the ground.
Tree-living squirrels have long and bushy tails. They
can fall from almost any height without danger to
themselves. If they fall out of a tree they keep their

[60]

ZOOGENESIS

tail waving, and the tail acts as a drag lessening the
shock of landing.

I have remarked that in their last stage w^hen they
are fully grown and sexually mature most insects are
capable of flight. In this stage most of them eat but
little, and many of them do not eat at all. Most
insects eat enough, or nearly enough, in their early or
larval stages to last them all their lives.

For young insects rapid or extensive locomotion in
most cases is not necessary. Their preoccupation is
to keep as close as possible to their food supply, which
usually is localized. Young insects, especially in the
later stages, gorge themselves so that when adult they
can fast. It is in the adult stage that, in most insects,
all the traveling is done; the adults wander far and
wide searching for new supplies of food for the
coming generation. Through their capacity for long
continued flight, which is greatly increased by the
absence of the necessity for feeding, the insects
largely overcome the handicap to their powers for
distribution imposed by their small size.

Most spiders are distributed by a different method.
All of the spiders are predacious, feeding on creatures
weaker than themselves, mostly on insects. Natu-
rally in catching prey strong spiders have the advan-
tage over weaker ones, and large ones over smaller
ones. Therefore the logic of the case would seem to
be that spiders should fly in their early weaker stages
and not as fully grown and powerful adults, and this
is what actually happens.

Spiders are wingless, but their lack of wings is

^^ THE NEW EVOLUTION f^'^

counterbalanced by uncanny ingenuity. On a calm
warm day in the late summer you will often see a little
spider standing on a stone or post with the abdomen
elevated and spinning out a thread or group of threads
of silk which by the warm air rising up the sides of
the stone or post is carried upward. When the spider
feels a strong enough upward pull from the rising
threads of silk it lets go its hold and is drawn up into
the air often to a great height where it is wafted about
for a greater or lesser distance before it comes to
earth again.

It should perhaps be mentioned that there are many
caterpillars which in their youngest stage are provided
with numerous long hairs. Such, for example, are
the caterpillars of many of the moths in which the
females are incapable of flight. These caterpillars
are wind distributed after the same fashion as the
seeds of the milkweed and the dandelion, and the
young of spiders.

Flight in one form or another is common to about
two-thirds of all known kinds of animals, and to
about three-fourths of all the kinds of animals in-
habiting the land. Most creatures fly simply in order
to get rapidly from place to place, but some, like
dragon-flies, most bats, and many of the birds, are
especially adapted to feed on other flying things.

Being much heavier than air, a greater or lesser
part of the food of plants and all of the food of animals
lies on the ground or buried in the ground or sup-
ported by it. It is therefore fixed in its position. To
utilize this food land animals and plants must be

"^"^ ZOOGENESIS Hi'

capable of locomotion, or in some form or other they
must be adaptable to transportation by the winds
or other agencies.

Plants are distributed almost exclusively as seeds
or spores, chiefly by the winds. But a few seeds are
adapted to become attached to the fur of animals and
thus to be transported, while some are carried about
in various other ways. Animals mostly get about by
walking or by flying, either throughout their lives or
at some special stage, but some are wind-transported
in a spore-like or other special form after the manner
of the plants.

The immobility of the food supply and the necessity
of seeking or being carried to it are the chief control-
ling features governing all types of life on land.
Therefore land animals are almost wholly of those
types, arthropods or jointed footed creatures — the in-
sects, spiders and their allies — and backboned animals
or vertebrates, which are best adapted for locomotion,
with a few representatives of some other types with
fair locomotor powers, as the mollusks — snails and
slugs — and earthworms.

While powers of active locomotion or else capacity
for transportation in some form or other through a
medium much lighter than themselves during at least
one period of their existence is an essential requisite
for all animals living on the land, no such necessities
present themselves in the case of the animals living
in the sea.

For water is about 814 times as heavy as air. It is
almost as heavy as protoplasm, the material making

THE NEW EVOLUTION

up the living portion of the bodies of the plants and
animals. Since water, and especially sea water, is
nearly as heavy as protoplasm, it naturally follows
that plants and animals may live suspended in it main-
taining a position at any desired distance beneath the
surface with little effort on their part. A drop or two
of oil or a little gas or some other minor adaptation
is sufficient to enable small animals or plants to main-
tain hydrostatic equilibrium. This simple fact is of
immense importance.

As in the case of plants on land, the plants living
in the sea require sunlight to enable them to build
up their tissues. All sea plants, therefore, are con-
fined to a thin surface layer of water of not more than
six hundred feet in depth, below which there is not
sufficient light to permit their growth.

Within this thin illuminated surface layer of water
there are found along the shores attached firmly to the
bottom many different kinds of algas, commonly
known as sea-weeds, some of which are very large.
On muddy bottoms in quiet bays and estuaries the eel-
grass and some other types of flowering plants belong-
ing to the pond-weed family (Najadacex) often occur
in great abundance, rooted in the mud. But the sum
total of all the marine plants growing along the shores
in water of less than six hundred feet in depth yields
only a small fraction of the vegetable material which
is required to support the animals of the sea.

How, then, are the sea animals supported? Most
of the vegetation in the sea is in the form of micro-
scopic plants which are quite invisible to the naked

[6^]

^^"^ ZOOGENESIS ^8^

eye. These float suspended in the water all the way
from the brightly illuminated surface down to the
greatest depths at which they are able to secure
enough effective light to enable them to grow.

So life in the sea for the most part is supported by
plants which are invisible to us. This gives us the
impression as we view the sea at some distance from
the land that all sea life is animal life, consisting of
fish, jellyfish (fig. 3, p. 5), whales, porpoises and
other creatures. Conditions in the sea may perhaps
best be understood if we compare the sea, in its
richest portions, to a sort of fog or mist in which each
little particle is a minute plant.

Many different kinds of creatures feed upon these
little plants. Of these the most important and most
numerous are various minute crustaceans of the sort
known as copepods (fig. 64, p. iii). Crustaceans be-
long to the same group (Arthropoda) as the insects,
and it is interesting to find that in the sea crustaceans,
as on the land the insects, are the chief plant feeders — ■
at least the chief plant feeders which serve as food for
other types of life.

Drifting about suspended in the water swarming
with minute plants, and the crustaceans and other
creatures feeding on them, are many other types of
animals, such as many kinds of jellyfishes (fig. 3,
p. 5) and the curious arrow-worms (fig. 6i, p. iii)
and pyrosomas (fig. 59, p. iii) which thus exist sur-
rounded by and suspended in their food supply. And
together with these live many creatures possessed of
powers of active locomotion, especially squid (fig. 45,

"^"^ THE NEW EVOLUTION '^^^^

p. 97), fishes, whales and porpoises, while in the air
above live many sea-birds.

Besides being almost as heavy as protoplasm and
thus rendering easily possible free floating or sus-
pended life, sea water is constantly in motion, though
in the deep sea this motion may become extremely
slow. This means that everywhere in shallow water
where the waves and tides create a constant movement
animals are able to attach themselves firmly to the
bottom (figs. 60, 63, 67, 68, p. iii;figs. 76, 80, p. 143)
or to root themselves or burrow in the mud and then
let the motion of the restless water do the work of
bringing food to them.

In progressively deeper water where the motion
gradually becomes so very slight as almost to be
absent, the wanderings of suspended creatures en-
dowed with feeble locomotor powers render attached
existence for such larger creatures as are able to over-
come and feed on them just as advantageous as
attached existence is along the shores.

So we are not surprised to find that various types of
animals which, attached firmly to the rocky bottom or
rooted in the mud, both grow and look like plants,
are especially characteristic of the sea. Such types of
animals are the corals (fig. 80, p. 143), sea-pens (fig.
77, p. 143), sea-fans, gorgonians, sea-squirts, hydroids
(figs. 75,76, p. 143) and sea-mosses (figs. Gj^ 68, p. iii),
belonging to a great array of different groups. More
familiar to us are the oysters, barnacles (fig. 30, p. 47)
and mussels, the mud-boring clams and razor-clams,
the sponges, and various sorts of encrusting and plant-

[66]

^^^^ ZOOGENESIS '^

like polyzoans, all common and familiar objects on
our shores.

While not an essential as it is for all animals in-
habiting the land, yet power of locomotion is a useful
asset for the creatures of the sea. So in the sea we
find great numbers of swimming creatures, as whales,
porpoises, seals, fish, squid (fig. 45, p. 97) and various
other types, and numerous crawling creatures, as for
instance worms (fig. 85, p. 161), crabs (fig. 19, p. 47),
starfishes (fig. 41, p. 71) and sea-urchins (fig. 41, p. 71).

It is important to remember that while on land all
animals must seek their food and hence must be
endowed with powers of locomotion, or must in some
stage be capable of transportation, the animals of the
sea have a choice of three different methods of secur-
ing food.

Firsf, sea animals may secure their food through
searching for it by crawling or by swimming, in other
words by the use of locomotor powers. Second, they
may attach themselves and let the motion of the
water do the work of bringing food to them. Third,
they may simply float and drift about suspended in
the midst of their food supply.

Three different ways of securing food instead of one
means three times as many possibilities for major vari-
ations in the structure of the animals involved. So
we are not surprised to find that in the sea there are
three times as many major groups of animals as are
found upon the land. In the relative proportion of
the major groups found in the sea and on the land we
seem to find a close agreement with the relative pos-

THE NEW EVOLUTION

sibilities for major diversifications offered in each of
these two regions.

But while three times as many major groups of ani-
mals are found in the sea as are found upon the land,
the relatively few major groups of animals inhabiting
the land include more than three times as many differ-
ent kinds of animals as are found in the sea.

This curious discordance results mainly from the
enormous diversity which occurs among the insects,
these creatures in number of different sorts exceeding
all other forms of life together by about three to one.

How can this condition be explained? It is in
simple correlation with the fact that conditions on the
land are almost infinitely more diversified than the
conditions in the sea.

In the first place the range of temperature from the
hottest desert region in the tropics under the noon-day
sun to the coldest spot under the Arctic winter night
in northern Siberia or in northern Canada is vastly
greater than the range in temperature from the warm-
est to the coldest seas. In the second place diurnal
variations in the temperature, which are always pres-
ent and sometimes extreme on land, in the sea are
absent, or at least quite negligible. In the third
place seasonal variations, which are more or less
marked everywhere on land and are very important
in the northern regions, affect the sea only in limited
areas and there only in relatively slight degree and
only in shallow or superficial waters. In the fourth
place the available supply of water on the land is
extremely variable, from place to place, from season

[68]

ZOOGENESIS

to season, and at different hours of the day and night.
It is always constant in the sea.

These physical variables on the land, which are
much reduced in importance and almost or even
wholly absent in the sea, create an infinite number of
different combinations each of which must be met by
a special complex of defensive or protective adapta-
tions in the land living animals. Not only that, they
must also be met through adaptations by all land
living plants as well. These adaptations on the part
of land living plants affect all the animals that feed
on them, but especially the insects which feed upon
all parts of plants. Diversity among plant feeding
insects means a corresponding diversity among their
parasites and the creatures feeding on them.

The enormous diversity of conditions on the land,
both in regard to physical conditions of environment
and to food supply, is reflected in the diversity of all
land living types of animals, but particularly of the
insects which, because of their small size, are able to
penetrate into almost every economic niche.

Zoology abounds with apparent paradoxes. In
spite of the great difference between conditions on the
land and conditions in the sea the dominant animal
types are the same both on the land and in the sea.
These are the backboned animals or vertebrates, the
arthropods or jointed footed animals — insects, spiders,
crustaceans and their allies — the mollusks, and the
jointed worms or annelids. These, with the pro-
tozoans and the nematodes (fig. 8i, p. i6i), are the
most successful and most widely spread of all animal

^^^^ THE NEW EVOLUTION "^^"^

types. Other animal types which we commonly re-
gard as characteristic of the sea, as the coelenterates
(figs. 69-73, p. 117; figs. 75-80, p. 143), the polyzoans
(figs. 67-68, p. iii)and thenemerteans, are represented
in fresh water.

It is worthy of special note that of the phyla or
major groups of animals no less than ten are exclu-
sively marine, having no representatives either on the
land or in fresh water. Of these ten major groups
seven are each composed of a very small number of
related and very similar species and play a wholly in-
significant part in the economy of the sea. These
seven groups which are structurally and anatomically
of the greatest interest, but otherwise of no impor-
tance, are the priapulids, the sipunculids, the pho-
ronids, the chastognaths or arrow- worms (fig. 6i,
p. Ill), thebalanoglossids, thecephalodiscids,andthe
cephalochordates. All are bottom livers except the
chastognaths, which live suspended in the water from
the surface down to a considerable depth. Except
for a single cha^tognath, none of these are known to
have any fossil representatives. But this means little,
as all are soft bodied creatures whose preservation in the
fossil state could result only from the merest accident.

Another group which is exclusively marine includes
the brachiopods or lamp-shells (fig. 60, p. iii). They
live on the bottom attached to rocks or other solid
objects, or burrowing in mud. There are less than
two hundred different kinds of brachiopods in the
present seas; but in the distant past they were vastly
more numerous and important.

Sea-urchin and Starfish

FOR AN EXPLANATION OF THE FIGURES SEE P. 279

THE NEW EVOLUTION

Also exclusively marine are the echinoderms — the
starfishes (fig. ^z, p. 71), brittle-stars (fig. 44, p. 87),
sea-urchins (fig. 41, p. 71), sea-cucumbers and sea-
lilies (fig. 6, p. 5) and feather-stars (fig. 43, p. 87),
or crinoids. There are many hundreds of different
kinds of these, and they are found from between tide
marks down to the greatest depths at which animal
life exists. They are relatively most important in the
deeper portions of the seas, but on all coasts they are
among the most familiar and characteristic of sea
animals. A single type of curious sea-cucumber (Pela-
gothurid), which is shaped more or less like an um-
brella, lives floating freely in the sea some distance
beneath the surface. All other echinoderms are bot-
tom livers.

The last group of animals which is exclusively
marine includes the ascidians or tunicates. Some of
these, as the sea-peaches and the sea-squirts, are
familiar to every fisherman. Like the echinoderms,
the tunicates live from the shore line down to the
deepest portions of the seas; but in contrast to the
echinoderms many different kinds, such as the salps
(fig. 58, p. Ill), pyrosomas (fig. 59,p. III)andappen-
dicularians (fig. 56, p. Ill), live suspended freely in
the water.

The great differences and at the same time the curi-
ous correspondences between the animals of the land
and the creatures of the sea are important to remember
in considering the problem of the development of
animal types.

[72.]

Vs^^ SV^^ !\^^ !\^^^ )^tSM )^SM )^^/( l\si§

CHAPTER IX

SPECIAL RELATIONSHIPS AND

CONTACTS

THE broad relationships of animals to the world
in which they live are often characterized by
an extraordinary development of certain special
contacts which may become the dominating and con-
trolling influences to which all others are more or
less subordinated. These special contacts are com-
monly overlooked, or at least minimized, and are not
considered in their true import and perspective.

Perhaps the most interesting of these special con-
tacts is that having to do with light. Light in some
form and in some degree seems to be essential for all
animal life. It may well be doubted whether any
animal lives in absolute darkness. Those inhabiting
deep subterranean streams appear to do so, but the
subject has never been investigated. They certainly
live in a minimum of light.

In the deeper portions of the sea there is no light,
or at least no effective light. But sea creatures, espe-
cially those remaining always beneath the illumi-
nated surface layer of water, are remarkable for the
luminescence developed in all types save for a few
that feed on luminescent organisms.

This general occurrence of luminescence among the
creatures of the sea has never been satisfactorily ex-
plained. Luminescence is not known to occur in any

b3]

^"^^ THE NEW EVOLUTION "^f

of the animals of fresh water excepting in the aquatic
young of certain Old World fire-flies.

Luminescence certainly would not be of such general
occurrence in the creatures of the sea if there were not
some outstanding reason for it common to all groups
of animals. The only possible explanation is that
luminescence fulfils some function of importance for
the well being of every type of animal. In other
words, the type of light produced by luminescence
must be a physiological necessity.

The black color so general in the deep sea fishes,
sometimes replaced by red, which is also common in
certain other deep sea creatures, probably serves pri-
marily to retain within their bodies the light from
the luminous things on which they feed. Were this
black color merely correlated with the darkness of the
regions where they live, we should expect to find it
also in cave living creatures. But all of these are
colorless or pink.

A very striking illustration of the necessity of light
for certain animals is afforded by the hard shelled
(but not the soft shelled) pond and river turtles. All
of these, no matter where they live, spend a consider-
able portion of their time, especially in spring and
early summer, sunning themselves on logs or sand-
bars. Their skeleton is extremely heavy, the heaviest
in proportion to total body weight that is found
among the vertebrates, excepting in certain land
tortoises. The land tortoises all live in sunny
regions, and all of the larger ones in arid or semi-arid
regions. These creatures seem to have developed the

b4l

^^^ ZOOGENESIS '^'^^^

maximum amount of internal living bony structure
that can be nourished and maintained by animals of
their size. Their skeleton therefore is in a state of
very delicate adjustment to their general bodily con-
dition. This is particularly true of rapidly grow-
ing young.

Young hard shelled pond turtles kept in a house
and deprived of sunlight in spring or early summer
show within two days a noticeable deterioration in
their skeletons, and within a week the deterioration
has become marked. Older individuals of some spe-
cies are affected almost as quickly.

When replaced in sunlight the affected individuals
almost at once begin to show improvement, and unless
the deterioration has progressed too far soon return
to normal.

Since light is so essential for the well being of the
turtles, all turtles have good eyes, and none of them
is blind.

The crocodiles and alligators seem to be almost as
dependent upon sunlight for their well being as are
the turtles.

While light in some form and in some degree is
apparently essential for all animal life, an excess of
light, especially of certain types of light, is distinctly
harmful.

There are two ways of guarding against the possible
injurious effect of too much light. In the first place,
the possession of a transparent glassy body permits
the passage of light through it without injury. We
find such transparent bodies in many of the jelly-

[75]

^""^ THE NEW EVOLUTION "^^^^

fishes, salps (fig. 58, p. iii), crustaceans, young
fishes, mollusks, arrow-worms (fig. 6i, p. iii) and
other creatures which live at or near the surface of
the sea.

But we find no transparent creatures on the land.
All land mollusks and land crustaceans are opaque,
though some of their relatives in the sea are beauti-
fully transparent. The reason seems to be that all
land animals must of necessity rest upon an opaque
surface. They therefore must be protected against
light as it comes to them from the sky and also as it is
reflected in modified form from beneath and all about
them. Besides, on land transparency would not mean
invisibility, for the difference in the refractive index
between air and protoplasm is too great ever to be
overcome. So any transparent creature on the land
would be as readily visible as a glass model of itself.
But in the sea, especially if the light be dim, trans-
parency means from partial to almost complete
invisibility.

The second means of protecting the animal body
against an excess of light is through the development
of pigment or coloring matter in the superficial body
covering or its outgrowths — in the skin or in hair,
feathers, plates, scales, or other structures. This
method is seen in all the animals which live exposed
on land, and in most of the animals of the sea. Even
the transparent marine creatures develop pigment
more or less extensively about such internal organs as
would be injured by too much light.

Thus all land animals as well as most sea creatures

^^"" ZOOGENESIS ^^^^

really exist in darkness more or less complete, for all
is dim twilight within the outer body covering.

From its original function as a protection against
an excess of light, coloration has secondarily been
developed toward the end of making sunlight useful
through the formation of endless varied and often
complicated color patterns by which the eyes of
enemies are more or less deceived.

Animals with bodies adequately protected against
harm from sunlight find sunlight extremely useful in
enabling them to find their food and to avoid their
enemies. This they do by means of eyes.

Every land creature living in the open, no matter
what it is, possesses eyes which, though they vary
greatly in perfection, are always adequate for the
needs of each. Even nocturnal creatures possess eyes,
most of them good eyes and some extraordinary eyes,
though a few have eyes which are only serviceable in
distinguishing night from day.

Taken collectively, eyes serve three different pur-
poses. They may be, as with us, organs of vision
giving a continuous photographic record of the sur-
roundings. This is the usual type of eye found in the
creatures of the land, as in all the vertebrates and in
practically all insects in the adult stage. Eyes may
simply be organs to record the varying intensity of
illumination and without a visual function, or at least
with a very limited visual capacity. Such are the
eyes of snails, slugs and caterpillars. Or eyes may
simply record the relative intensity of heat. In this
case they are usually represented by black spots more

1i? THE NEW EVOLUTION ^^^^

or less scattered over the surface of the body. In the
birds and in some reptiles which have the body unusu-
ally well insulated from the surrounding air there is a
special heat recording apparatus called the pecten
within the visual eye.

It is obvious that good vision is without value to
any creature with a bodily structure of such a nature as
to render it incapable of rapid locomotion. It is of no
advantage to be able to see food if a creature cannot
reach it, or to be able to see an enemy if escape from
that enemy is impossible. So all fixed animals, like
corals (fig. 80, p. 143), sea-pens (fig. 77, p. 143), hy-
droids, polyzoans (figs. 67, 68, p. iii), clams and
oysters, are either wholly blind or have eyes without
a visual function. Creatures with feeble locomotor
powers, like caterpillars, scallops, snails (fig. 51,
p. 97), sea-urchins (fig. 41, p. 71) and starfishes (fig.
41, p. 71), have eyes with at most a very limited
capacity for vision, and are often blind.

Perfect visual eyes are of advantage only to animals
able to profit by an acute visual capacity, which means
animals whose structure renders rapid locomotion pos-
sible. Such creatures are extremely few, and are
entirely confined to three of the major groups, the
vertebrates, the arthropods and the mollusks.

All vertebrates are capable of locomotion which,
because of their large size, is always relatively rapid.
But not all of the vertebrates are capable of sight.
Blind forms with defective or quite sightless eyes are
found among the mammals, reptiles, amphibians and
fishes, though not among the birds.

" [78]

ZOOGENESIS

Practically all insects in the adult stage are capable
of active locomotion either by flying or by running.
Most adult insects therefore have exceedingly good
eyes, though the structure of the insect eye is very
different from the structure of the eyes of the verte-
brates. But many sluggish insects incapable of flight
have eyes of very limited capacity and some, chiefly
cave insects, have no eyes at all. Active crustaceans,
such as the land-crabs, crabs (fig. 19, p. 47), hermit-
crabs (fig. xy, p. 47) and lobsters, have good eyes v^hich
are patterned after the insect model. The inactive
kinds have much reduced, simple, or more or less rudi-
mentary eyes, or else are v^holly blind.

Among the mollusks the cuttle-fish and squid (fig.
45, p. 97), w^hich are powerful and active creatures,
many of them capable of swimming with great speed
and a few even of flying like the flying-fishes, all have
large and perfect eyes. So do the octopuses which are
very active crawlers and also, for short distances,
swimmers of no mean ability. Superficially the eyes
of the squid and of the octopus appear quite the same
as the eyes of fish and other vertebrates, but their
development is very different.

The eyes of the vertebrates, arthropods and mol-
lusks, all equally efficient for the purpose which they
serve, are wholly independent structures. Each of
these types of animals has a type of eye wholly con-
fined to it and differing in origin from the other two.
But regardless of their origin all three types of per-
fect visual eyes are the same in function and in
purpose.

[79]

^^"^ THE NEW EVOLUTION '^^^^

When well developed visual eyes occur they usually
are the chief reliance upon which the animal possess-
ing them depends for the discovery of its food, the
avoidance of its enemies, and the recognition of
its fellows.

This is especially the case with birds which, taken
as a whole, have the most perfect vision of any group
of animals. No birds are blind, though forms which
invariably are blind occur in all the other groups of
vertebrates — the mammals, reptiles, amphibians and
fishes. It may be added that, together with extra-
ordinary sight, the birds also possess extraordinary
hearing. No birds are deaf. Smell, taste and touch,
however, are poorly developed in the birds.

Birds might almost be described as wonderfully
efficient organic mechanisms activated and controlled
by light and sound waves to which they react with a
speed and an inflexible accuracy not seen in any other
creatures.

The life-long powers of flight both by day and night
possessed by the great majority of birds, the extra-
ordinary development of sight and hearing, and the
correlated ability to seek out and find their food and
to detect and to escape from danger in unfamiliar
regions have made the birds, considered as a whole,
the most independent of their immediate surroundings
of any group of animals. Many different kinds of
birds are equally at home in far northern regions in
the summer and in the tropics in the winter. Such
an extensive economic range, involving great changes
in the immediate environment of the individuals, is

^^^^ ZOOGENESIS "^^^^

not possible in any other group of land living
vertebrates.

This relative independence of their surroundings re-
sulting from the extreme keenness of their sight,
coupled v^ith the capacity for very rapid locomotion,
is correlated v^ith a definite dependence on certain
physical conditions v^hich is by no means so strongly
marked in any other creatures.

Sight being all-important for the birds, the relative
length of day and night becomes an important factor
in their lives. For some birds, particularly in the
southern hemisphere v^here the seasons are not so
strongly marked as in the north, this probably has an
important bearing on migrations, since a longer day
means a greater proportion of the time w^hen sight is
an aid in securing food and in avoiding enemies.

Such migrations as those of the golden plover and
of the Arctic tern, v^hich annually pass from far
northern to far southern regions and back again, may
perhaps largely be explained as an endeavor always
to keep w^ithin the longest possible day.

While in the great majority of birds their interrela-
tionships v^ith other living things and with the other
objects in the world about them are governed mainly
by the sense of sight, all birds have wonderfully good
ears. For instance we notice the large thrush that
we in America call the robin listening at an earth-
worm burrow to find out whether or not the prospec-
tive victim is at home. It is probably listening for
the high pitched sounds made by the small chitinous
hooks on the earthworm's body VN^hich in small ones

^^"^ THE NEW EVOLUTION W^

such as ours are quite inaudible to us, though in the
huge oriental earthworms we can hear them easily.

In many night-flying birds, especially in most owls,
the ears seem to be almost as important as the eyes.
To anyone familiar with owls it seems quite evi-
dent that the very soft plumage of most kinds which
gives them a ghostly almost noiseless flight is pri-
marily adapted to prevent any interference with ex-
ternal sounds coming from their prey and not so that
they may steal up upon their prey unheard.

As aerial creatures feeding chiefly on insects and on
fruit the mammalian bats compete with birds. But
bats, except apparently for the large fruit-eating kinds
called "flying-foxes," living in the oriental regions,
are guided mainly by their hearing and have, at least
when compared with birds, very deficient sight.
They have, however, a high degree of sensitivity to
touch, well developed smell, and well developed taste.

Bats find their way about through the analysis of
echoes and of all the myriads of different kinds of
sounds made by the insects and the foliage. As the
very high pitched sounds give the best indication of
direction, the activities of bats mainly are controlled
by sounds which are too high pitched for us to hear.

Among the bats the flying-foxes correspond to the
owls among the birds in that their activities are con-
trolled after a manner differing from that of the great
majority of their relatives. These enormous bats are
to a large extent diurnal, at least in the more unsettled
regions. They are sometimes seen in the hottest por-
tions of the day circling in great numbers over open

[il]

ZOOGENESIS CC

grassy country close to the ground. Such flights are
probably for the purpose of cooling themselves
through increasing evaporation from their wings and
bodies. It may be mentioned that the African ele-
phant cools itself in somewhat the same way by
flapping its enormous ears. The oriental fruit-bats
seem to be guided mostly by their eyes which are
larger and much more perfectly developed than are
those of the great majority of bats.

Our common small red bat in still hot weather often
flies by day in glades and clearings in the woods. But
as its actions in the daytime are in no way different
from what they are at dusk there is no reason to sup-
pose that in its daylight flying it is not guided by its
ears as it is at night. As in the case of the great fruit-
bats, it probably flies by day merely to cool its body.

The birds and bats furnish excellent illustrations of
creatures guided almost entirely by sight and hearing.
These two senses play the major part in controlling
the actions of many other types of vertebrates.

There is another aspect of bodily control through
sight that is worthy of passing mention. This is the
effect on us of such control in other things. Subcon-
sciously we recognize the fact that our actions are
mainly controlled by sight, and we betray this recog-
nition in many different phrases. Since eyes control
our actions and also the actions of all the familiar
animals about us, eyes seem in some indefinite and
indefinable way to be the seat of the "spirit," or the
focal point of the vital force which animates and
activates the body.

THE NEW EVOLUTION

This concept greatly interferes with a true appre-
ciation of the various types of animals. We uncon-
sciously regard blind creatures as unintelligent and
stupid — as deficient in an undefinable essential — even
though they may be quite as capable in meeting com-
petition as animals with eyes.

The blind dolphins of the upper Ganges and the
blind cave and deep sea fishes and crustaceans are able
to make their way in life against strenuous competi-
tion quite as effectively as their relatives with eyes.
They are therefore quite as intelligent in spite of the
fact that their intelligence is a response to stimuli
which we ourselves find incapable of adequate inter-
pretation and analysis. Just the same is true of
oysters, starfishes and earthworms. In their own way
and so far as concerns their special needs they are as
intelligent as any other creatures, and as they need
to be.

But all creatures with eyes do not look the same to
us. For instance an octopus in a tank fascinates us
with its large unblinking eyes which to us seem bale-
ful and uncanny. The reason is that the octopus is so
strange a creature we have no notion of what he is
going to do. Hence an element of fascination based
on fear colors our concept of an octopus.

To us, depending as we do chiefly on our eyes,
bodily control through hearing as in the case of bats
seems incomprehensible and mysterious, and hence
uncanny. Besides, bats chiefly fly by night when
because of the imperfect functioning of our eyes we
are more or less fearful and suspicious. We regard

ZOOGENESIS

the bats with awe because they are primarily con-
trolled by senses which with us play a more or less
secondary part, and are most active at a time when our
chief controlling sense is least reliable. But the great
fruit-bats with their more or less dog-like heads and
large and perfect eyes we can understand, so they
appear to us simply as flying mammals.

Because of their large eyes both of which are di-
rected forward as is the case with us, wisdom is com-
monly attributed to owls. Yet they are almost uni-
versally regarded with superstitious dread. This fear
or dread is based not on their structure or incompre-
hensible bodily control as in the case of bats, but
arises from their unusual and often shrieking cries and
their mostly nocturnal habits.

"Just as the vertebrates are so frequently creatures
of the visual and auditory senses" writes Professor
Dwight E. Minnich, "so the insects are largely crea-
tures of the chemical senses. For it is chiefly by
means of these senses that most insects find their food,
their mates, and the food of their offspring, and that
the social insects are able to make the manifold dis-
criminations necessitated by their highly complex
social organization."

Professor Minnich says that a comparison between
the chemical senses of insects and the corresponding
senses of the vertebrates, including man, shows many
rather fundamental similarities. But between the
chemical senses of man and of the insects there appears
to be one outstanding difference, and that is the
greater acuteness of these senses in many insects.

THE NEW EVOLUTION

He found that the sensitivity to saccharose of the
organs of taste situated in the tarsi (feet) of that
common butterfly known as the red admiral (Cynthia
atalanta) may be on occasion two hundred and fifty-
six times as great as that of the human tongue.

Dependence on special senses, which is well illus-
trated by birds, bats and many insects, is an important
factor in biology. For such close dependence on a
narrow range of stimuli carries with it both great
advantages and great disadvantages.

The chief advantage is that extraordinary develop-
ment of a special sense overcomes competition in all
lines of activity which are dependent on or are chiefly
aided by that special sense — provided, of course, that
bodily structure and control are of such a nature as
to permit that special sense to function to the best
advantage.

The chief disadvantage is that dependence on a
special sense limits bodily control largely to that
sense and hence renders the animal dependent in
greater or lesser measure upon the maintenance un-
changed of those external conditions by which that
sense is activated. Let those conditions change, and
become such that the special sense no longer functions
to the best advantage, and the animal is placed at once
under a serious handicap duetotheunder-development
of all the other senses.

Dependence on a special sense or on a relatively
narrow range of special conditions always results in a
more or less marked subordination of all the features
of the animal type involved to the requirements of

[86]

THE NEW EVOLUTION

that special sense or of those special conditions. The
entire organization of the type tends to become con-
centric about the organs which are most important
for its welfare. The necessary uniformity in these
organs seems to impose a corresponding uniformity in
all other features. So there results a more or less
fixed uniformity of structure in all the animal types
which are activated mainly by a single special sense
or are confined within a relatively narrow range of
special conditions. An excellent illustration of this
is afforded by the birds.

Among the vertebrates the least diversified of the
included classes is that which includes the birds. All
birds exhibit a similarity in the broader features of
their structure which, considering their numbers and
the very great diversity in the minor structural details,
is surprising. In conformity with this, birds in their
later embryonic stages and in their preadult existence
exhibit a uniformity which is without parallel among
the vertebrates.

All birds lay eggs which are enclosed within a rigid
and at the same time brittle calcareous shell. There
are among them no viviparous forms such as occur
among the mammals, reptiles, fishes and amphibians.
The eggs are always large, and are provided with
abundant food material. From the egg the chick
emerges in a well developed — sometimes in a very
highly developed — stage.

In all birds except the megapodes the young are
assiduously tended by their parents, or by one parent,
until nearly or quite the full size is reached. In all

[88]

ZOOGENESIS

birds the embryo develops within a rigid envelope
permitting but little deviation from the general type
represented by the parents. Furthermore the young,
dependent on the ministrations of one or both the
parents, must be of such a nature as to be able to
receive and to profit by parental care, and also to
stimulate it. This still further restricts the pos-
sibility of wide deviation from a general type.

As a class the birds, especially the smaller birds,
are the most constantly active of all the vertebrates.
They have a fixed body temperature which is always
high, in the smaller birds more than ten degrees above
our own.

All of the birds, both fossil and living, excepting
for the ancient toothed birds of the Cretaceous period
and the two genera included in the old term Archa-
opteryx, are very closely allied, and in spite of the vast
range in size from Princess Helen's hummingbird to
the ostrich the birds form a much more unified group
than do the mammals, reptiles, amphibians or fishes.

Like the birds, the turtles and the crocodilians show
a remarkable uniformity of structure, a corresponding
uniformity in their early stages, and a similar curious
zoological isolation from all related types. In agree-
ment with the birds, there are no viviparous crocodili-
ans or turtles. The eggs of turtles may have a hard
and brittle shell, like the eggs of birds and croco-
dilians, or the shell may be tough and parchment-
like. When compared with the eggs of birds the eggs
of turtles and of crocodilians are small, but they are
much more numerous. They are carefully placed by

^^ THE NEW EVOLUTION f^'^^^

the female in suitable situations, but the young receive
no parental care.

These few examples of the extreme development of
special contacts and of the tendency of the entire
organization and life history of an animal type to
become concentric about the organs most concerned in
the interpretation and reception of the stimuli or the
physical benefits received through special contacts
show the necessity for a careful appraisal of each
animal type in terms of the details of its environment.

[so]

CHAPTER X

THE MOST ANCIENT AND THE LIVING

ANIMALS

FOR many millions of years animals have existed
on the earth just as they exist today. But the
animals of past ages were not the same as the
animals we know at the present time. Some of them
were only slightly different from their modern rep-
resentatives, but some were very widely different.
Generally speaking, the further back we go in geo-
logic time the greater the difference between the ani-
mals then existing and those of the present day.

The animals of the past are for the most part known
to us as fossils in the rocks. Fossils are the remains
or traces of animals or plants that formerly existed.
Fossils may be of any age. They may be the remains
of animals or plants that lived millions of years ago,
or only a few years previously.

Once in the West Indies I was riding along a sandy
beach when suddenly I felt my horse to be on hard
rock instead of sand. There seemed to be no change
in the aspect of the beach, but when I dismounted I
found that that particular portion had been changed
to limestone rock in which were embedded several
different kinds of shells and the remains of various
other sorts of marine animals.

But this portion of the beach had not been rock for
very many years, as some of the shells still had cling-

THE NEW EVOLUTION '^f

ing to them bits of their skin-like covering. In the
mountains of Tennessee I have seen somewhat similar
sea beaches, also with shells and other marine objects,
turned to stone; but it has been a very long time since
this region was part of any sea coast.

When animals die and after death lie on the surface
of the ground they gradually decay and their bones
become scattered and broken up. In order to be pre-
served they must be buried.

In the frozen ground of northern Siberia the woolly
arctic elephant or mammoth and the woolly rhinoc-
eros are occasionally found with the skin, hair and
wool and even the flesh preserved. The flesh can
still be eaten although it has been in cold storage for
something like fifteen thousand years. From the
plant remains found in the stomachs and in the
mouths of these frozen mammoths we even know
what they fed upon. Their food was furnished by
the same plants that now flourish in the region.

But it is only very seldom that the flesh, skin or
hair of the animals of the distant past have been dis-
covered. As a rule only the skeleton is preserved.
Yet imprints of birds' feathers have been found in
several places, and indeed the first trace of the most
ancient bird we know, the so-called Arcbaopferyx, was
the imprint of a feather.

The most spectacular of all the regions where fossils
have been found in North America is Rancho la Brea,
within the city limits of Los Angeles, California.
Here over a vast period of time asphalt has been accu-
mulating from escaping oil. In this sticky asphalt

^^"^ ZOOGENESIS M^

animals that lived during the Pleistocene or Ice Age
were caught like flies in sticky fly paper and slowly
sank beneath the surface.

Animals struggling in the sticky mass served as bait
for beasts and birds of prey, and these in turn were
trapped and perished in great numbers. Water birds
were caught along the edges of the pools of water that
collected on the asphalt.

More than three thousand giant wolves, two thou-
sand saber-toothed tigers, sixty giant ground sloths,
and mammoths, mastodons, lions, camels, tapirs,
short-faced bears, bison, peccaries, and many other
mammals, and a great variety of birds, already have
been dug out of this deposit.

In a locality recently discovered in southern Arizona
mastodons were found which had been mired in boggy
mud holes about springs, just as they frequently were
mired in the peat bogs in the northern states.

Dust blown by the wind sometimes kills and buries
animals, occasionally in great numbers. At a locality
in western Kansas the skeletons of nine peccaries or
American wild pigs were found huddled together
with their heads all pointing in the same direction.
Apparently they had been overtaken, killed and
buried by a sand storm. The wind blown dust de-
posits of the pampas of Argentina contain the remains
of many animals now extinct which seem to us most
fantastic and bizarre.

Cave deposits have yielded many interesting fossils.
Some of these caves were the homes of beasts of prey
and the bones found in such caves are the bones both

[93]

"^"^ THE NEW EVOLUTION "^^^^

of the tenants and of their victims. Other caves are
crevices in the rocks into which unfortunate creatures
fell or into which carcasses and bones were washed
by rains.

In fossil bone deposits complete skeletons of any-
kind are very rare. Most deposits consist of detached
bones and broken fragments.

In a locality in Bavaria very fine calcareous muds
were deposited in quiet lagoons behind protecting
reefs. These muds are now turned to stone which is
quarried for use in lithographic printing. In quarry-
ing this stone many fossils which are most remarkably
preserved have come to light, including the imprints
of the bodies of such delicate creatures as squid (fig.
45, p. 97) and jellyfishes, and of a feather of an an-
cient bird. In this locality the remains are those of
animals that flourished in the age called the Jurassic
which was a very long time before most of our modern
animals appeared.

By far the most abundant of all fossils are the
remains of animals and plants that in the past lived in
the sea. It makes no difference where they live,
whether on the bottom or swimming freely in the
water, when sea creatures die and after the scavengers
have done their work the hard parts that are left col-
lect on the bottom muds or sands. Here they are
gradually covered up by gravel, sand or mud brought
down by streams and distributed by the currents of
the sea.

Battered shells and various remains of other crea-
tures— just such as we see on the beaches of the present

[94]

^^"^ ZOOGENESIS '^^^'^

time — are often found in ancient beach deposits. If
the remains lie in quiet water or at a depth below the
effect of waves the fossils that we find may be as per-
fect as the corresponding parts in living animals.

Many sea animals and plants die and are buried in
the place in which they lived. For example, corals
(fig. 80, p. 143) and other reef forming animals and
plants are sometimes killed by changes in temperature
or depth or by some other cause or smothered by mud
and sand.

Incredible numbers of fossil fish are found in thin
layers of rock or other deposits in California and else-
where. In some cases these probably were killed by
stranding in shallow bays into which they had been
driven by their enemies.

Similar calamities are not infrequent at the present
day. In August, 192.5, I was so fortunate as to wit-
ness one at Manchester, Massachusetts. Immense
numbers of small herring ran into the little harbor
where by the falling of the tide they were stranded on
the mud flats. These they almost completely covered
— indeed in some places they lay two or more layers
deep. The weather was hot and they decomposed
with great rapidity. Their decomposition fouled the
water and this killed the larger fish, pollack and hake,
that had originally chased them in.

If these had been covered with mud and buried
before decomposition had progressed too far, they
eventually would have formed just such a thin layer
of fossil fish as we find in the rocks.

Fish are also destroyed wholesale in another way.

[95]

^^^^ THE NEW EVOLUTION "^f

Sometimes a minute free floating sea plant, one of the
so-called peridinians (usually or perhaps always
Goniaulax), becomes enormously abundant and then
suddenly dies away. The billions of dead plants foul
the water and give off a sulphurous odor like that
from a volcano. The fish in the affected area are
killed and go to the bottom or wash up on the shores
in enormous numbers.

Such calamities are occasional on the coast of south-
ern California and of southern Japan, in southwestern
Africa and elsewhere. On the coast of Venezuela
between Margarita island and the mainland, where I
have witnessed this phenomenon, it takes place
every summer.

If the fishes poisoned by the fouling of the sea
resulting from the death of the peridinians should be
covered up and buried and the sea bottom should
later turn to rock that rock would contain a continu-
ous thin layer of fish.

Remarkably perfect sea reptiles showing the out-
lines of the body which have been found in England
and in southern Germany represent carcasses stranded
on fine mud and subsequently buried.

When the deposits laid down in the sea are, through
the elevation of the land, brought above sea level, then
the fossils can be seen. Often in the intervening time
the originally loose muds or sands or gravels have
been changed to solid rock, and the fossils in this rock
are in their composition wholly different from what
they were originally.

Under very exceptional conditions it may happen

[96]

Various Types of Mollusks, a Planarian. a Fluke and a Foraminiferan
for an explanation of the figures see p. 279

^^^^ THE NEW EVOLUTION '"^^^

that extremely delicate things such as sea worms,
squid, or even jellyfishes, are buried in fine mud in
such a fashion as to prevent bacterial decay. In such
cases even imprints revealing the finer details of the
internal structure may be preserved. Such perfect
preservation is to be seen in some of the very earliest
fossils that have been discovered.

This briefly stated is the way the remains of the
earlier life upon the earth have been preserved. From
these remains of the animals of earlier epochs in the
earth's history we can now form a pretty good idea of
the types of life that flourished at various periods in
the more or less distant past.

How are we able to determine the relative age of
the different fossils that we find?

Ever since rain began falling on the earth muds and
sands and gravels have been continuously washing
down into the sea. While in certain places the sedi-
ments now exposed may reach a thickness of about
two miles, in no one place has this deposition been
continuous. How, then, can we measure and cor-
relate these sediments?

Movements of the surface of the earth subsequent
to the deposition of the sediments, such as those
involved in mountain building, often cut them
through or tilt them up on edge so that their cross sec-
tions may be studied. The erosion of streams by
carving great canyons through the rocks also assists
us in our study of them.

By piecing together the information gathered from
very many regions it has proved possible to arrange

[98]

ZOOGENESIS

the fossil sediments in a continuous series from the
very earliest to those now forming. We can tell
with great exactness the relative age of any fossil
bearing rock in reference to other fossil bearing rocks
elsewhere.

By studying the various fossils in formations of
different ages we are able to compare the animals of
one period with those of another and thereby to form
a picture of the ever changing aspect of animal life
as it has existed on the earth.

Table Showing the Sequence of Geological Time

Recent
Pleistocene

Post-tertiary
or

Quarternary

Pliocene
Miocene
Oligocene
Eocene

Tertiary
or
Cenozoic

Cretaceous

Jurassic

Triassic

Secondary

or
Mesozoic

Carboniferous
Devonian
Silurian
Cambrian

Primary
or
Paleozoic

Pre-Cambrian

or
Algonkian

Arch^aa

[99]

CHAPTER XI

THE PAST AND THE PRESENT

ONE of the most striking and important facts
which has been established through a study
of the fossil animals is that from the very-
earliest times, from the very first beginnings of the
fossil record, the broader aspects of the animal life
upon the earth have remained unchanged.

When we examine a series of fossils of any age we
may pick out one and say with confidence "This is a
crustacean" — or a starfish, or a brachiopod, or an
annelid, or any other type of creature as the case
may be.

In the details of their structure these fossils are not
necessarily like the crustaceans, starfishes (fig. 41,
p. 71), brachiopods (fig. 60, p. iii), annelids (fig. 85,
p. 161) or other creatures living in the present seas.
Nevertheless, if they are sufficiently well preserved we
have no difficulty in recognizing at once the group to
which each and every fossil animal belongs.

How do we recognize these fossils as members of
the various groups? We are able to recognize them
because they fall within the definition of a particular
group. But the definitions of the phyla or major
groups of animals are all drawn up on the basis of a
study of their living representatives alone.

Since all the fossils are determinable as members of
their respective groups by the application of defini-

[100]

ZOOGENESIS

tions of those groups drawn up from and based entirely
on living types, and since none of these definitions of
the phyla or major groups of animals need be in any
way altered or expanded to include the fossils, it
naturally follows that throughout the fossil record
these major groups have remained essentially un-
changed. This means that the interrelationships be-
tween them likewise have remained unchanged.

Strange as it may seem, the animals of the very
earliest fauna of which our knowledge is sufficient to
enable us to speak with confidence, the fauna of the
Cambrian period, were singularly similar to the ani-
mals of the present day. In the Cambrian crustaceans
were crustaceans, echinoderms were echinoderms,
arrow-worms (fig. 6x, p. iii) were arrow-worms, and
mollusks (figs. 45-52., p. 97) were mollusks just as
unmistakably as they are now.

In order to illustrate the diversity of life in the
Cambrian seas and to bring out its striking general
similarity to the life of the present time, let us briefly
note the types of animals which flourished at that
far distant period.

In Cambrian times crustaceans were represented by
phyllopods, trilobites (fig. 3x, p. 55) and merostomes
(fig. 31, p. 55); among the echinoderms there were
crinoids (fig. 6, p. 5), cystideans (figs. 37, 38, p. 55),
and elasipod and other holothurians; chastognaths
(fig. 62., p. Ill) or arrow-worms, lamp-shells (fig. 60,
p. Ill) or brachiopods, and graptolites (figs. 39, 40,
p. 55) were present; of the annelids or jointed worms
we know polynoids, nereids (fig. 85, p. 161), gephy-

THE NEW EVOLUTION

reans, and Tomopferis-likc forms (fig. 65, p. m); of
the mollusks we find pteropods (fig. 48, p. 97) and
gastropods (fig. 51, p. 97); and there were corals and
other coelenterates, and sponges.

Most of the fossils mentioned in the preceding list
are from a single locality in British Columbia where
they were found by the late Dr. Charles D. Walcott in
the Burgess shale. I had the pleasure of being associ-
ated with Dr. Walcott when he was working on them.

These fossils are remarkable not only on account of
their great age, but also because of their wonderfully
perfect preservation. In many of the most delicate
among them — creatures so very fragile that their
modern representatives can scarcely be satisfactorily
preserved in alcohol — even the details of the nervous
system may be made out.

In order to avoid possible criticism that too broad
generalizations are being drawn from fossils mostly
from a single locality, let us consider as a supplement
to this varied Cambrian fauna the fossils from the
Ozarkian and Ordovician rocks, representing periods
somewhat less distant than the Cambrian.

From the Ozarkian rocks come cephalopods (fig. 45,
p. 97) and pelecypods (fig. 52., p. 97) or bivalved mol-
lusks, and from the Ordovician polyzoans (figs. 67,
68, p. Ill), echinoids or sea-urchins (fig. 41, p. 71),
ophiurans or brittle-stars (fig. 44, p. 87), starfishes
(fig. 4^, p. 71), insects and fishes. There is no evi-
dence that these were not also present in the Cambrian.
Indeed, it will be most surprising if future investiga-
tion does not prove their existence there.

[101]

^^^^ ZOOGENESIS "^""^

The significance of this imposing list of Ordovician
and pre-Ordovician animals becomes more evident if
we contemplate the missing animal types. These
missing types are the ctenophores or sea-walnuts (fig.
66, p. Ill), the flat-worms (figs. 54, 55, p. 97) and
round-worms (fig. 81, p. 161), the rotifers (fig. 136,
p. 103) and gastrotrichas (fig. 134, p. 2.03), priapulids
and sipunculids, heteropods, archiannelid, oligochaete,
myzostomid (fig. 84, p. 161), hirudinid (leeches) and
onychophorid (Feripatus) worms, nemerteans, pho-
ronids, cephalodiscids (figs. 61, 63, p. m), balanoglos-
sids, tunicates, and vertebrates except for fishes.

Except for the missing vertebrates — amphibians,
reptiles, birds and mammals — which are primarily
land living, all of these various types are soft bodied
creatures which would be preserved as fossils only
under the most extraordinary circumstances. Recog-
nizable traces of them would only be present in the
rocks by the merest accident.

While from what has just been said it is evident
that there has been no change whatever in the inter-
relationships between the phyla or major groups from
the very earliest times of which we have an adequate
fossil record up to the present day, this is not of itself
conclusive evidence that these groups have always
borne the same relation to each other. For it is
undoubtedly true that the Cambrian period is nearer
to the present epoch than it is to that far distant
time when life on earth began.

Indeed, fragmentary and in some cases fairly satis-
factory fossils have been found in rocks of much earlier

THE NEW EVOLUTION

date than those of the Cambrian period. But in so
far as these are determinable all of them, like the
fossils of the Cambrian, fall into major groups on the
basis of the definition of the major groups drawn up
from living types.

The fact that these very early fossils are the remains
of calcareous algas, corals, crustaceans and protozoans
is simply correlated v^ith the circumstance that these
types of life, as is w^ell seen in the calcareous algas,
the corals and the foraminifera of the present day,
build exceptionally heavy skeletons. The existence
of these types alone in these very ancient rocks cannot
be regarded as indicating that no other types of life
existed in those ancient seas.

Since all our evidence show^s that the phyla or major
groups of animals have maintained precisely the same
relation w^ith each other back to the time when the
first evidences of life appear, it is much more logical
to assume a continuation of these parallel interrela-
tionships further back into the indefinite past, to the
time of the first beginnings of life, than it is to assume
somewhere in early pre-Cambrian times a change in
these interrelationships and a convergence toward a
hypothetical common ancestral type from which all
were derived. This last assumption has not the
slightest evidence to support it. All of the evidence
indicates the truth of the first assumption.

To this plain statement of fact the objection might
be raised "This is all very true so far as it goes, but
we must admit that the earliest evidences of life are
the traces of simple and primitive forms; and, anyway,

[104]

^""^ ZOOGENESIS '^^'^

there was an enormous lapse of time between the first
appearance of life and the period wherein are found
the earliest fossil remains. So it is easier to believe
that life gradually developed from simpler to more
complex forms than that the major groups arose
simultaneously."

The answer to this is that science is based upon
ascertained facts. We take the facts as we find them
and coordinate them into broad generalizations. The
facts are that all of the fossils, even the very earliest
of them, fall into existing major groups. This is
indisputable.

[105]

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V^M^ <\^i&^ i^tsJi )S^^Ji )^^^M sX^is^ )S^^M )S^^M iXsK

CHAPTER XII
MORE ABOUT FOSSILS

CONTRASTING Strongly with the inflexibility and
the permanence of the fundamental characters
which delimit and identify each of the phyla or
major groups of animals and the consequent absence
of any change in their relations to each other from
the very earliest times of which we have a record up
to the present day is the very great diversity which we
see within every major group when we compare the
different ages of the past.

As we trace further and further back the record in
the rocks we see fewer and fewer of the kinds of ani-
mals we know today and more and more unfamiliar
forms, until nearly all the animals are strange and
unfamiliar and we find ourselves, lost in astonishment,
viewing the relics of a world which seems to have
been entirely different from the world we know
today.

And so it was. For instance, in that period known
to geologists as the Cretaceous the mammals, though
numerous, were all very small and unimportant. The
earth was dominated by a most extraordinary and
formidable array of reptiles. Chief among these were
the dinosaurs of very many different kinds, some of
them no larger than a hen, but some of enormous size
and in appearance most fantastic and grotesque.

There were huge horned dinosaurs, strange armored

^^^ ZOOGENESIS '^'^^^

dinosaurs, duck-billed dinosaurs, and, together with
these, terrible predacious dinosaurs with a formidable
array of long sharp teeth. The giants of this group
were the great swamp-living dinosaurs with absurdly
small heads, enormously long necks and tails, heavy
bodies, and ponderous legs.

The birds which lived in the Cretaceous period were
curious things with teeth like reptiles, quite different
from any of the birds we know at the present time.
But more important than the birds were strange flying
reptiles with wings much like the wings of bats.
These bat-like reptiles are known as pterosaurs.
Some of them were small, no larger than a sparrow,
but some were very large, as much as twenty-seven
feet across the expanded wings.

Competing with fishes in the sea were plesiosaurs
of various kinds, and also mososaurs, as well as large
sea-turtles. Some of these last were more than twelve
feet long.

Together with these curious types of reptiles lived
many other forms almost equally bizarre, but also
many of the more familiar types, as for instance
crocodiles and alligators.

In spite of the great and striking differences between
most of the vertebrates of the Cretaceous period and
those of the present day, they are all instantly recog-
nizable as vertebrates as vertebrates are defined on the
basis of their representatives of the present day.

Of all invertebrate fossils none are more familiar
than the remains of those curious crustaceans known
as trilobites (fig. 31, p. 55). All of the trilobites are

^^"^ THE NEW EVOLUTION '^^^''

now extinct — in fact the last of them disappeared
many millions of years ago.

The remains of trilobites are extremely common in
the very oldest rocks in which are found fossil remains
of animals in a satisfactory state of preservation.
They are abundant in the rocks of the Cambrian
period, in which they exceed in number and in di-
versity the remains of all the other forms of animal
life. In the succeeding period, the Ordovician, they
were also very numerous and varied. They were less
numerous and varied in the Silurian, and during the
Devonian they declined in numbers and in variety.
In the Carboniferous only a few, all rather closely
related to each other, are found, and at the end of this
period they entirely disappeared.

Over two thousand different kinds of trilobites are
known. These vary in length from less than half an
inch to nearly two feet. The trilobites represent the
only large subdivision of the jointed-legged animals
or Arthropoda which has become extinct.

In the phylum Arthropoda there is another much
smaller group now wholly extinct which is of special
interest as it includes the largest members of the
phylum. This group is that containing the so-called
eurypterids (fig. 31, p. 55), some of which were nearly
ten feet long. The largest member of the phylum
Arthropoda at the present time is the Japanese giant
spider-crab which measures eleven feet or more from
claw to claw, but its body is relatively small. The
eurypterids are first known from the Cambrian, and
the last of them are found in the Carboniferous.

ZOOGENESIS

They were related to the still living king- or horse-
shoe crabs which still are to be found on the eastern
shore of North America and in the west Pacific.

Curious and unfamiliar as are the eurypterids and
the trilobites, they are quite obviously crustaceans as
crustaceans are defined on the basis of the living
species.

In the old days of sailing ships the chambered
nautilus was a very common ornament in the parlors
of the houses in the sea-port towns and cities. The
chambered nautilus is to be found only in the Indo-
Malayan seas, and there are scarcely half a dozen dif-
ferent kinds, all of which are very much alike.

But in the past the nautiluses were creatures of much
importance as inhabitants of the sea, and about ^,500
different kinds have been described which have been
found as fossils in the rocks. In some of these the
shell was straight, in some it was partly straight and
partly coiled, in others it was loosely coiled, and in
many it was tightly coiled as in the still living
chambered nautilus. In the coiled types the coil was
sometimes flat — in a single plane — as in the chambered
nautilus, and sometimes in a spire as in a gastropod
or snail.

These creatures first appeared, so the fossil record
tells us, in the Ordovician, in which period they were
found in very great variety. They were still more
numerous in the period just following — the Silurian.
They then declined, and since the time when the giant
reptiles were the dominating creatures on the earth
(the Cretaceous period) only two types persisted one

[109]

dM THE NEW EVOLUTION

of which died out in the relatively recent past, leaving
the present seas with only the chambered nautilus and
its few close relatives.

Together with the nautiloids in the very ancient
seas there flourished the ammonites (figs. 33, 34,
p. 55), creatures which were very similar but vastly
more numerous and varied. Of these more than 5 ,000
different kinds have been described. All of the am-
monites are now extinct— in fact none of them sur-
vived beyond the end of the age of reptiles (the
Cretaceous period).

A curious thing about the ammonites is that they
first appeared after the nautiloids had begun to wane.
After the end of the so-called palaeozoic era they
increased with great rapidity both in numbers and
in variety. At the end of the Cretaceous they sud-
denly disappeared, just as did the giant reptiles, for
what reason we do not know. Some of the ammo-
nites were very small, appearing as mere specks, but
some were very large forming a close spiral four feet
or more across.

In few groups of animals is the fossil record so com-
plete and satisfactory as it is in the ammonites, and
in few groups are progressive developmental lines so
clearly indicated.

The history of the brachiopods or lamp-shells (fig.
60, p. Ill) is an interesting one. More than 7,000
different kinds are known of which only about 160
are to be found living in the present seas. Brachio-
pods are well represented in the very earliest rocks
which contain recognizable fossils — the rocks of the

Various Types of Animal Life
for an explanation of the figures see p. 280

THE NEW EVOLUTION

Lower Cambrian. They increased markedly in num-
bers in the Middle Cambrian and reached a maximum
of diversity in the Ordovician and Silurian from which
periods we know more than 3,000 different kinds.
They continued plentiful in the Devonian and also
in the Carboniferous, but toward the end of the latter
period they began to decline and since the end of the
age of reptiles (Cretaceous) they have been of small
importance.

This parade of facts showing the very different
balance of life upon the earth in the distant past might
be indefinitely extended. But we have said enough
to show that in the different periods and the different
eras the continuous changes affected only the forms
within each phylum, and never the interrelationships
between the phyla.

Most interesting in this connection are the ammo-
nites, for they begin as ammonites, become enor-
mously diversified, and then disappear without ever
being anything but ammonites. Here we have a
group, a division of the cephalopod mollusks allied
to the nautiloids, of which the entire history seems
to be laid bare for our inspection. The early portion
of the history of the ammonites is not lost in the
unknown pre-Cambrian as in the case of the trilobites,
the eurypterids and the lamp-shells.

This constant change from age to age involving the
animal types within each major group or phylum com-
bined with the unchanging constancy of those broader
features of animal life by which the members of each
phylum are distinguished from the members of all the

[ill]

ZOOGENESIS

other phyla demonstrates a dual nature in the rela-
tionships of animals to the world in which they live
that has hitherto been unrecognized.

[113]

CHAPTER XlII
THE DUAL RELATIONSHIPS OF ANIMALS

A CRITICAL Study of fossil animals taken as a whole
brings out two apparently contradictory
facts.

In the first place all the major groups of animals
have maintained the same relationship to each other
from the very first. The characteristic features of these
major groups have undergone no change whatever.
Crustaceans have always been crustaceans, echino-
derms have always been echinoderms, and mollusks
have always been mollusks. There is not the slight-
est evidence which supports any other viewpoint.

Yet on the other hand within each major group
there has been constant and continual change from
age to age. All of the crustaceans, echinoderms and
mollusks of the present day are more or less, and often
very widely, different from the representatives of
those groups which flourished in the distant past.

How can such a dual relationship of animal forms —
fixed and inflexible major groups each including con-
stantly changing types — be possible? Not only is it
possible, but it is to be inferred from the facts of
geology and geography as we understand and inter-
pret them.

At the very earliest time at which life in any form
could be presumed to have existed on the earth there
was water in abundance, and there must have been

ZOOGENESIS

land rising above the water. There must also have
been winds, if only feeble winds, carrying the water
vapor back from the seas and lakes and marshes over
the land areas.

Chemical and physical disintegration of the rocks
tvas taking place in exactly the same way in which it
is taking place today. The elements which are essen-
tial for the growth of plants were being released and
recombined, and soils were being formed just as they
are at the present time. Muds and sands and gravels
were being washed into the sea, there forming
sediments.

Of course most of the rock disintegration taking
place today is affecting the so-called sedimentary rocks
which are themselves made up of the more or less
selected and consolidated residues which have resulted
from the previous disintegration of archasan rocks
and of earlier sedimentary rocks. But this does not
in any way affect the truth of the statement that rock
disintegration is releasing the same elements and form-
ing soils in the same way now as in the past.

The fact that, in so far as it concerns the sedi-
mentary rocks, geological history is interpreted en-
tirely by comparison with what is occurring at the
present time is an acknowledgment of the truth of
this. Yet if it be true then it is evident that at the
time of the first beginnings of life there were the same
potentialities for the support of a varied fauna that
there are today.

To deny this would mean to deny the validity of
the comparisons between the geological processes of

THE NEW EVOLUTION

the present day and those of the past, the accuracy of
which comparisons forms our sole criterion for the
interpretation of the latter.

All of the major groups of animals may be supported
either by the algae or related groups of plants, or by
the flowering plants, or by a mixture of plant types.
Thus in the sea we find the walrus and the seals and
whales feeding upon animals dependent for their
existence upon the diatoms, while on the land we see
the elephant and the dogs and wolves supported
wholly by flowering plants or by creatures feeding
on them.

So with an abundance of plant food quite regardless
of the kind the possibility exists for the appearance of
some representative or representatives in every major
group of animals.

In regard to plants the situation is quite different,
for in the case of plants there is a direct relation to the
amount and quality of sunlight. The amount and
quality of sunlight plays but a minor part in the
animal world taken as a whole. It is largely a neg-
ligible factor. For instance some fishes and some
crustaceans are found along the shores and on the
beaches in the sunniest portion of the tropics, while
others live in the deepest and darkest portions of the
sea and also far under ground in lightless — or prac-
tically lightless — caves. Sunlight is essential only
for relatively small groups of animals, as for instance
birds and many of the reptiles, especially the turtles
and the crocodilians. Animals as a whole are depend-
ent only on an adequate supply of plant food, air and

[ii6]

ZOOGENESIS

water. An amount of light sufficient to permit the
growth of any type of green or comparable plant ap-
pears to be sufficient for all, most, or at least some,
of the members of all the phyla or major groups of
animals.

If we examine the major animal groups we discover
a very interesting fact. Broadly speaking their rela-
tionships to each other are very different from the
relationships between the major groups of plants.
The major groups of plants are in the main competi-
tive with each other, as they feed on the same sub-
stances in the same way. The existence of one or
another of these major groups, or if they occur to-
gether the balance between them, is largely deter-
mined by the amount of water and by the amount
and quality of the available light.

The major groups of animals in their relation to
each other are on quite a different basis, for in the
main they are non-competitive, or perhaps it should
be said that they are fundamentally non-competitive.
While in their economic range the major groups, at
least the larger major groups, more or less overlap,
still there is always a certain section of their range
in which, as a result of differences in bodily structure,
they are safe from competition.

The three largest and most important of the phyla
or major groups are the backboned animals or Verte-
brata, the jointed-legged animals or Arthropoda (in-
cluding the insects, centipedes, millepeds, spiders,
crustaceans, and their allies), and the mollusks
or Mollusca.

THE NEW EVOLUTION

All three of these groups include both plant-eating
and animal-eating forms. Many vertebrates prey on
other vertebrates, as for instance hawks, owls, cats
and barracudas, very many vertebrates feed on insects,
and many, particularly many fishes, some mammals
and some birds, are mollusk feeders. Insects, spiders
and crustaceans prey largely on each other; many are
parasites on vertebrates, as lice, fleas (fig. i8, p. 33),
bot-flies and fish-lice (fig. X4, p. 47), the last being
curious crustaceans, and some, both on the land and
in the sea, are mollusk feeders. Predacious mollusks
prey mostly on each other, as for instance oyster
drills and whelks, though some feed on small crusta-
ceans and a number on other forms of life. The young
of most of the fresh- water clams (fig. 52., p. 97) are
for a time parasitic on the fishes.

In view of this, how can the members of these
three great phyla be said to be fundamentally non-
competitive?

The structure of a vertebrate with its internal
almost invariably jointed skeleton is such that the
smallest possible size permitting of effective function-
ing is relatively large. Vertebrates range between
about three-quarters of an inch in length for the small-
est fish to about no feet for the largest whale. But
very few vertebrates are less than two inches in their
total length.

The structure of an arthropod with its external
jointed skeleton is such that the maximum size per-
mitting of effective functioning is small. Arthropods
range from about one one-hundredth of an inch to

ZOOGENESIS

about ten feet in length. But relatively few, either
in the sea or on the land, exceed two inches.

So we find that the vertebrates and the arthropods
in the great majority of their included species are
really non-competitive. Each of these two major
groups for the most part occupies its special economic
niche which is determined by its structure and the
correlated limitations in efficient size.

The structure of a mollusk with its unjointed body
does not permit the development of jointed supports
or supports articulated with the body, like the legs
and wings and the paired fins of vertebrates and the
legs and wings of insects. So the mollusks cannot
compete with vertebrates or with insects in running
or flying on the land. On the other hand, since their
motions are very slow they require much less food and
air and so are able to exist in situations impossible
for any members of these other groups.

So also in the sea and in fresh water the mollusks
are capable of existing in many different ways and
under many different sets of conditions not possible
for any vertebrate or arthropod.

On the land the mollusks compete more or less
directly with some insects and a few vertebrates, such
as the small land tortoises, in consuming fungi and
soft vegetable material. In the sea some, as mussels,
oysters and others, live attached to firm supports and
feed on the same materials as the barnacles (fig. 30,
p. 47), which are curious distorted arthropods.
Others live suspended in the water of the open ocean
(fig. 48, p. 97) and feed on the minute suspended

THE NEW EVOLUTION

plants, such as the diatoms and peridinians (fig. 86,
p. i6i), as do some arthropods and the young of very
many fishes. A few, like the octopus, crawl about
the bottom and feed more or less after the fashion of
the crabs and lobsters. Still others, like the cuttle-
fish and squid (fig. 45, p. 97), live swimming freely
in the sea and successfully compete with fish.

It is somewhat curious that while on the land the
creatures capable of the most rapid locomotion, the
running and flying animals, which are the dominant
types, are all vertebrates or arthropods, in the sea the
creatures with the greatest powers of locomotion, the
dominant swimming types, and all the flying types,
belong to the vertebrates and mollusks. In view of
the correspondence which exists on land between the
vertebrates and the insects in the matter of rapid loco-
motion we might expect that in the sea there would
be a similar correspondence between the vertebrates
and crustaceans. But instead we find that in the sea
the mollusks take the place of arthropods as effec-
tive swimmers.

Perhaps the next most important of the major
groups, and a very large one, is that which includes
the jointed worms or annelids (fig. 85, p. 161). These
live mostly in the sea, but some live in fresh water
and a few upon the land — the earthworms, land-
leeches and onychophores (Peripatus).

The jointed worms have the advantage over the
vertebrates and the arthropods in lacking a rigid
skeleton, either internal or external, which gives them
great flexibility. They have the advantage over

[12.0]

ZOOGENESIS

mollusks in possessing a jointed and usually much
elongate body in which each segment is, to a greater
or lesser degree, a semi-independent unit.

While many of the jointed worms live swimming
freely in the water or crawling on the surface of sub-
merged objects, they are especially adapted to a bur-
rowing life, either boring through mud or winding
their way through the canals in sponges or through
crack and crevices in rocks, in coral heads, or in any
other objects. Their slender bodies, which are usu-
ally soft and extremely flexible and are made up of a
more or less long series of semi-independent units,
fit them for a manner of life impracticable for the vast
majority of the vertebrates, the arthropods, or the
mollusks.

The echinoderms, which include the starfishes (fig.
42., p. 71), brittle-stars (fig. 44, p. 87), sea-urchins
(fig. 41, p. 71), feather-stars (fig. 43, p. 87) and sea-
lilies (fig. 6, p. 5) and their allies, and the sea-
cucumbers or holothurians, are peculiar in having
when their final form is reached a radial symmetry
with almost invariably five divisions of the body, a
usually heavy outer — though not properly external —
skeleton which is composed of pavement-like or re-
ticulated or vertebra-like plates and is wholly unlike
the jointed external skeleton of the arthropods, and a
curious hydraulic system called the water-vascular
system by means of which they operate their tube-
feet, which are their locomotor organs, and com-
parable and other structures.

The heavy outer armor of the echinoderms, which

^^^^ THE NEW EVOLUTION ©|^

is usually reinforced with numerous sharp spines, or
the tough and leathery skin filled with limy plates
or spicules, provides a very effective defense against
aggression. They are therefore relatively safe from
enemies. This enables them to live exposed upon the
bottom in those places where food is most abundant,
there to consume it at their leisure. Many of them
simply swallow mud which is rich in the dead remains
of plants or animals.

Almost perfectly protected and living with their
food supply, or at least near it, rapid locomotion is
not an essential for the echinoderms. But they make
up for the absence of the capacity for rapid locomotion
in their ability to move equally well in any direction,
an ability not possessed by animal types with a defi-
nite head end at which the main sense organs are col-
lected as is the case with the active types in all the
phyla we have just considered.

While one echinoderm, lacking all traces of a skele-
ton, lives freely suspended in the sea, a number bore
in mud more or less like worms, others have a more or
less definite head end in spite of their radial symmetry,
and still others, permanently or temporarily attached,
feed more or less after the fashion of the barnacles
and oysters, still the echinoderms as a group fill an
economic niche which is quite different from that
occupied by the vertebrates, the arthropods, the mol-
lusks or the annelids.

There is no object in carrying this recitation fur-
ther. It is evident that a considerable part of the
economic range of each of the groups we have con-

[12.2.]

ZOOGENESIS

sidered belongs to it alone. From this it is clear that
each of these groups is safe from complete extinction
by any of the others.

The relative number of different forms in the various
groups may vary from time to time and from place to
place. We see this in the present seas where the
mollusks are mainly creatures of shallow water and
the echinoderms are chiefly characteristic of the
deeper portions of the oceans. We also see it in com-
paring the lamp-shells or brachiopods of the present
day with those that flourished in the palaeozoic seas.
But however the relative numbers in the different
groups may vary, each major group will always be
present, and not only present but well represented.

All of the other major groups of animals have some
special economic niche wherein they are safe from
direct competition by creatures belonging to any of
the other groups. The only possible exception to
this rule is furnished by the graptolites, which have
been long extinct. But whether these were of them-
selves a major group, or a division of the coelenterates,
or a division of the cestodes, we do not really know.

Now these special niches must have been present
at the time when life on earth first began. None of
them can be assumed to have been of recent origin.
We recognize the fact that wherever there is a res-
ervoir of food, permanent or temporary, capable of
supporting animal life, there animal life of some sort
or other will be found. If it is reasonable to apply a
knowledge of geological processes based on the pres-
ent to an interpretation of the geological processes of

^^'"^ THE NEW EVOLUTION Wi

the past, it is no less reasonable to do the same with
our knowledge of zoology. If we do this we must
believe that all the various niches must have been
occupied at the very first instead of serially.

Still another aspect of the problem demands con-
sideration. No animal type can exist of itself alone.
In the first place, it must be supplied with food
through the medium of coexisting plants. In the
second place, it must be held in check so as to avoid
the danger of increasing to such an extent as to destroy
its food supply and thus bring about its own ex-
termination.

The necessary check on the excessive increase in
the numbers of any type of animal is provided by pre-
dacious animals, by internal and external parasites,
and" by various types of animal feeding plants, princi-
pally bacteria and fungi.

We recognize the necessity for an intricate and
delicate balance between the various types among the
animals and plants of the present day. Is there any
reason why in the remotest past a similar balance
should not have been as necessary?

It is probably not without significance that no
major group of animals includes exclusively plant-
eating species, though in some of the major groups all
of the included species are carnivorous; and besides
these in several large groups, such as the cestodes or
tapeworms (figs. 8x, 83, p. 161) and the spiny-headed
worms, all of the included forms are parasitic.

We cannot deny that at the time when the first
appearance of animal life was possible the poten-

[124]

ZOOGENESIS

tiality was present for the occurrence of some repre-
sentative type or types in each of the phyla or major
groups without at the same time denying the validity
of our interpretations of the processes of geology so
far as concerns the disintegration of the rocks and the
building up of soils and sediments. And such fossil
evidence as exists, fragmentary and unsatisfactory as
it is, supports the assumption that this potentiality
was an actuality and that animal life so far as the
phyla are concerned at the very first appeared in essen-
tially the same form as that in which we know it now.

While at the time of the first appearance of life the
abundant water and the winds and the disintegration
of the rocks rendered possible the existence of animals
in all the major groups, conditions on the earth were
very different from those at the present day.

We learn this from the constantly varying assem-
blages of fossils in the rocks of different ages. Thus
in the Cambrian rocks we find occurring together
animal types which now are exclusively marine, as
the sea-cucumbers, brachiopods (fig. 60, p. iii),
gephyreans and others, some of which live in shallow
water and others only in the deep sea; types, such
as the phyllopods which now are exclusively non-
marine, living in rivers, lakes and ponds; and types,
as the nereid worms (fig. 85, p. 161), with modern
representatives both in the sea and in fresh water.

All of the creatures which we know from the Cam-
brian, with the possible exception of the trilobites,
were very delicate and fragile. This suggests that
at that time the water where they lived was quiet.

THE NEW EVOLUTION

These Cambrian creatures could not have withstood
the pounding of the surf along the shores of the pres-
ent oceans. Absence of a surf line means absence of
strong winds, or frequent violent storms, which fur-
ther suggests a blanket of clouds resulting in more or
less uniform temperatures over the greater part, or
possibly all, of the earth's surface.

Speaking in less general terms, we learn from the
rocks that in the palaeozoic era coral reefs extended
into high latitudes. The luxurious and uniform
development of cryptogams over the earth during
Carboniferous time indicates a warm moist climate
which varied but little with latitude. In the Pleis-
tocene or Ice Age the remains of reindeer, lem-
ming, musk-oxen and other Arctic animals in central
Europe show clearly that at that time the climate of
central Europe was much colder than it is now.

In other words, climatic changes have been con-
stantly going on. The present distribution of heat
and cold, of dampness and of dryness, is but a passing
phase in the history of the earth's surface.

All of the changes which take place in any region
naturally affect all the animal inhabitants of that
region. Some may die out and be replaced by others
from another region, some may assume a more or less
widely different guise, and some may be able to exist
unchanged under the new conditions.

But changes in climatic conditions however severe
do not affect the basic requirements of food, water
and air, which are always present, at least up to the
point of complete desiccation or of permanent frost.

Some Coelenterates and a Solenogaster
for an explanation of the figures see p. 281

^^"^ THE NEW EVOLUTION Wf

So changes in climatic conditions affect not the exist-
ence or the occurrence of any of the major groups or
phyla, but instead the balance and the details of the
types included within the phyla, or in other words
the various forms in which the structural com-
plex characteristic of the several major groups is
manifested.

We may illustrate this point by a comparison be-
tween different portions of the earth's surface. Every
major group or phylum is represented in seas where
the temperature of the water never rises above the
freezing point of fresh water (3 2.° Fahrenheit or 0° Cen-
tigrade). Every major group is also represented in
the tropics.

But the representatives of the phyla in the very cold
and in the very warm water are in practically all
cases very different, just as on land arctic and tropical
animals are almost always very different.

In the warm water of the tropics and in the hot
tropical lowlands the number of different types of
animals included in each of the various major groups
is far greater than it is in the cold regions. But in
spite of the enormous number of different kinds of
animals found in the tropics, there is not the slightest
indication of any tendency to produce new phyla, or
inter grades between the phyla.

In regions intermediate between the two extremes
of hot and cold all grades of intermediate conditions
are to be found, and it is noteworthy that in compar-
ing different intermediate areas on the earth's surface
we find a curious disparity in the balance between the

ZOOGENESIS

different divisions within the phyla which are quite
comparable to the changes in the balance between the
different divisions seen as we pass from age to age in
the fossil record.

It is doubtful whether at any time in the past there
has ever been such a great diversity of climatic condi-
tions as is found at the present day. The present
tropics are probably hotter than the climate in any
past age since life began. This is suggested by the
fact that animal types which from their geological
history we recognize as ancient if they are of restricted
distribution are mostly found not in the hot tropics,
but in more or less warm temperate regions of equable
temperature and humidity, at moderate elevations in
the tropics, or at moderate depths in the tropical seas.

Somewhere or other on the earth today we probably
find duplicated all, or nearly all, of the climates of
the past so far as temperature and humidity are con-
cerned. But we cannot be sure of duplication when
it comes to the very important question of light or
the strength and frequency of winds.

If we may judge the past from what we know of
conditions at the present time we are in a position to
understand the constancy of the major groups or
phyla, and also the constant changes from age to age
that took place within the phyla.

[12.9]

CHAPTER XIV
WHAT IS A SPECIES?

BEFORE proceeding further we must consider the
basic unit in terms of which the animal world
is measured. This basic unit is the so-called
species. In everyday language a species is a distinct
kind or sort of animal.

The accepted definition of a species is an assemblage
of individuals which agree with each other in form,
size, color and in other characters, in one or more of
which they constantly differ from related assem-
blages of individuals; which normally and freely
interbreed; and which transmit to their offspring their
proper characters unchanged, or with that little modi-
fication which is due to conditions of environment.

While technically correct, this definition is decep-
tive. It is simply a broadening of the definition of an
individual. It contemplates primarily material in
museum collections and is based almost entirely upon
the vertebrates, especially birds and mammals. It
scarcely applies to other forms of life even as repre-
sented in museums.

What, then, is a species? That is difficult to say,
for the different kinds of animals vary very greatly in
the interrelationships of the included individuals, and
in their relations to allied types.

Each species is always separate and distinct from
every other species. But a species is not a static

ZOOGENESIS

entity. Rather a species is to be regarded as a re-
strained and repressed force — an enigmatic potenti-
ality— which, once released, will go to unknown and
unsuspected lengths.

The peculiarities of species are best appreciated
through the consideration of a few examples taken
more or less at random from the animal world.

Some species are constant in their characters and
practically invariable. Thus wherever it is found the
American eel is always the same. There is no differ-
ence between Canadian and West Indian or Brazilian
specimens. It is very closely related to the similarly
constant European eel, from which it differs in having
about seven less vertebrae in its backbone. The breed-
ing ranges of the American and of the European eels
broadly overlap, yet no American eel has ever been
taken in Europe and no European eel has ever been
taken in America. Although these eels are so very
closely related the American eel passes through its
larval stage in rather less than a year, while the larval
stage of the European eel occupies from two to
three years.

Among the butterflies the common painted lady,
which is found throughout the world except in the
polar regions, Australia and New Zealand, and South
America south of the northern coast, is also every-
where the same. It shows temporary and individual
variations resulting from temporary local factors, but
no permanent local variation. The same is the case
with the red admiral which is found in western
Europe and over a large part of North America, and

^^"^ THE NEW EVOLUTION "^^^^

with various other butterflies, mostly with very
limited distribution.

Other species, on the contrary, are so very highly
variable that they can only be defined in negative
terms. Being impossible of description, they can be
identified only by the fact that they do not conform
to the description of any other species.

Such a species is one of the commonest feather-stars
(cf. fig. 43, p. 87) of the Indian and west Pacific
oceans which is found from Japan to Madagascar. In
this extraordinary creature the arms vary in number
from eleven or twelve to about seventy, but are usually
about twenty or about forty. The arms may be all
of the same length, or the hinder arms may be only
one-third as long as the anterior, or the anterior and
posterior arms may be of any intermediate relative
proportions. The arms may be short and stout, or
greatly elongated and attenuated; sometimes the ante-
rior arms are elongate and attenuated, and the poste-
rior short and stout. The pinnule combs may be long
and low, or short and high; they are usually confined
to the first two or three pairs of pinnules, but some-
times they occur at intervals almost to the arm tips.
The arm branches are typically of four segments each,
but usually one or more of them are of two segments,
and in rare cases all of them may be of two segments.
The leg-like processes on the dorsal side — the cirri —
may be numerous, rather stout, and well developed,
or they may be few and weak, or they may be alto-
gether absent.

In Madagascar and in southern Japan this species is

[132-]

ZOOGENESIS

only slightly variable; here it is always rather small
with about twenty arms which are always rather
short and stout.

All of the most closely related feather-stars are only
slightly variable. But other feather-stars in widely
different groups both in the East and in the West
Indies show a comparable extraordinary variability.

Extreme variability is characteristic of very many
creatures in the sea and in these variability is often
carried to what seem to be fantastic lengths. But
the creatures of the sea are known to relatively few
so that a detailed discussion of them would be un-
profitable. So we shall take our examples of vari-
ability chiefly from among the butterflies, as the vari-
ations of butterflies have been widely studied and are
therefore fairly well appreciated. Furthermore ex-
amples of variation in the butterflies may be seen in
any collection, and some, at least, are easily obtain-
able almost everywhere.

One of our common butterflies varies from light
clear yellow with a wing spread of about xj inches
or rather less to deep brilliant orange with a bright
violet iridescence in the males and a wing spread of
nearly if inches. The males of the two extremes
have a different wing form and a wholly different odor.
There is no regular intergradation between the yellow
and the deep orange types. The butterflies are yel-
low, yellow faintly flushed with orange on the fore
wings, light orange, or deep orange. Intergrades be-
tween these color types are rare. The males of the
first two types are very fond of sitting on mud and

[^33]

"^^^ THE NEW EVOLUTION '^^^^

sucking up the water. The males of the light and
deep orange types will not visit mud, and are much
swifter, higher and stronger fliers. Giants and curi-
ous little dwarfs are found in all the forms.

In the yellow form one-quarter of the females are
pure white, with the black borders of the usual yellow
females. In the north these white females never
occur in spring, being found only in the summer. In
the south they occur equally both in spring and sum-
mer. In the deep orange form white females are in-
frequent, and in the light orange form they are still
less common. In the yellow form which is faintly
flushed with orange apparently the females are
never white.

So far as I have seen mating takes place only be-
tween butterflies of the same color type. The young
produced may be of the same color type as the par-
ents, or of a different color type, or of two or more
color types.

But in some localities this extraordinary butterfly
shows only most insignificant variations, and some
of its closest relatives are almost invariable.

A few butterflies exist in two quite different sizes
between which intermediates are rare, at least in most
localities. This is the case, for instance, in our com-
mon tailed blue. In many butterflies sporadic giants
and dwarfs differing abruptly in size and more or less
in habits from the normal type are not infrequent.

In many butterflies there is a regular alternation of
forms from one season to the next. Thus in our com-
mon eastern angle-wings the summer individuals are

[134]

^^^ ZOOGENESIS "^^^^

dark in color with short wings. They are more or
less sedentary and seldom stray far from their place of
origin. The autumn individuals, however, which
live through the winter, are much lighter in color
than the summer individuals and have longer wings.
These wander very widely. The dark short-winged
and light long-winged forms are very different from
each other and never intergrade.

A somewhat similar phenomenon is seen in the pro-
duction of a long-winged migratory form from time
to time, or more or less irregularly, by certain grass-
hoppers. Similar and comparable phenomena are also
seen in other insects.

In various regions certain butterflies have very
distinct alternative forms one flying in the wet and
the other in the dry season. These forms are usually
quite distinct, but in many cases intergrades occur,
and in a few intergrades are common.

Some of our butterflies in certain years will produce
typical wet forms in bogs or other damp localities
which die out without leaving any progeny. Such
forms with us are usually regarded as extreme varieties
or aberrations according to their relative abundance.

In most of our butterflies the individuals of the
spring brood increase gradually in size and change
more or less noticeably in color — showing especially
an increase in the dark markings — from the earliest
to the latest. This change is very marked in the
common cabbage and yellow clover butterflies, and
also in the zebra and the yellow swallowtails. The
color changes are perhaps most striking in the com-

[^35]

^^"^ THE NEW EVOLUTION '^^'^

mon blue. In all of these cases the latest individuals
of the spring brood closely resemble the individuals
of the summer brood in those species in w^hich there
is a summer brood.

In certain butterflies the individuals of the spring
brood may be the same, or nearly the same, through-
out the range, while the individuals of the summer
brood or broods differ very w^idely in different regions.
This is well illustrated by the common little copper
butterfly as it occurs in Europe, North America
and Asia.

Some butterflies are at all times very highly variable
in both sexes in color or in wing form or in both
features. Thus one of our common western swallow-
tails may be either predominantly yellow or predomi-
nantly black, or of any intermediate type. But the
yellow form does not occur in Arizona, while the
black form does not occur in Oregon or northward.
Great diversity of color in one region, but the occur-
rence of only a single color type in the same species
in another region, is a common phenomenon in the
insects. In South America some of those curious but-
terflies called heliconians are so very variable that
scarcely any two individuals can be found which are
quite alike.

In most wide-ranging species there is more or less
extensive variation in color, size, and wing form from
one region to another. The different forms taken by
the species in the different regions are recognized as
subspecies or geographical varieties. These sub-
species may grade imperceptibly into the correspond-

[^36] '

ZOOGENESIS

ing forms in adjacent areas over a broad territory, or
in a very narrow belt, or they may be wholly distinct
though very similar. This last is especially the case
if they occur on islands. Thus in one of the common
Aristolochia (or pipe-vine) swallowtails a single sub-
species is found from the south Atlantic states through
Central and South America as far as Buenos Aires,
while on each of the West Indian islands there is a
well marked and distinctive form. Very many sub-
species have been described, especially in birds, mam-
mals, butterflies and mollusks.

Geographical variation usually affects both sexes
equally, the sexes varying together. Thus the com-
mon northern butterfly known as the white admiral
in southern New England and New York in both sexes
passes over into a southern form which is much larger
and in which the conspicuous white band is wholly
lacking, while the hind wings are slightly angulated.

But sometimes one sex only is affected, or one sex
is affected to a much greater extent than is the other.
In the northern United States and Canada the common
yellow swallowtail is rather small, and both sexes
are almost alike in color. From New York south-
ward the insect is much larger. The males remain
almost the same in color, but the females become
black, or if remaining yellow they acquire a large
amount of blue on the hind wings. In the extreme
south they are always black, and in some regions
there are more or less well marked intermediate forms
between the black and yellow females.

In several Indo-Malayan swallowtails the males are

^37]

THE NEW EVOLUTION

the same, or practically the same, throughout their
range, but there are several or many different types
of females which differ widely in their color and often
also in their wing form. In the same species some of
these female types will have an extensive range, while
the range of others is very limited. In the two
best known of these Asiatic butterflies both sexes are
alike and constant in the northernmost portions of
their range.

In a common African swallowtail there is a single
type of male showing slight local variations, but
there are more than thirty more or less widely different
types of females nearly all of them lacking tails and
showing no resemblance to the males. Some of these
are very local, while others are widespread. In
parts of Abyssinia females have been found with tails,
though colored like other females. In Madagascar
the females are like the males both in color and in
wing form.

In one of the commonest South American swallow-
tails the males are everywhere the same, but the
females are divisible into three well marked local
races. In this butterfly the males are to be looked for
in damp woods, while the females fly in more open
places. The same sex difference in habits is found in
other South American swallowtails, and in other
butterflies elsewhere. It is characteristic of at least
one of our common eastern skippers.

Diversity of females while the males remain the
same is by no means confined to butterflies. It is even
more strikingly seen in the ants, bees and wasps with

[138]

^^~^^ ZOOGENESIS '^^^^

their "queens" and one or more forms of female
* 'workers . " In the white-ants or termites the various
"castes" are both male and female.

In a few butterflies the females are invariable, but
the males are divisible into local races. In the com-
mon black swallowtail of the eastern states the males
are much more variable than the females, and show a
tendency to divide into local races which is not seen,
or at least seen not so clearly, in the females.

Another form of geographical variation which is
well illustrated by the butterflies is variation affecting
some, most, or even all, of the animals of a certain
type in a particular region.

For instance on the island of Celebes very many of
the butterflies, including at least some in all the larger
groups and all but one of the local swallowtails, have
the fore border of the fore wings very strongly curved
with a distinct elbow near the base. These butterflies
are in no way related to each other, but each is related
to a corresponding form in the Malay region which
has the usual form of wing.

In tropical America very many butterflies, included
in all but two of the larger groups, have wings of
very curious form, the fore wings very long and
broadly rounded at the tips and the hind wings
very small.

The American Aristolochia swallowtails all differ
from those of the Old World in having the sinus of
the fifth tarsal (foot) segment, in which the claws
are inserted, much less extended.

With the exception of two species, one from the

[139]

THE NEW EVOLUTION

Amazon region and one from Ecuador, all of the
species of American Aristolochia swallowtails with
tails occur from Costa Rica northward, and from
temperate Brazil southward. All the very numerous
species in the region between Costa Rica and central
Brazil except for the two mentioned are wholly with-
out tails. Our common North American blue swal-
lowtail loses its tails in the southernmost portion of
its range. A number of Asiatic swallowtails gradu-
ally lose their tails toward the southeast, among the
islands of the Malayan archipelago.

On the West Indian island of Jamaica there is a
marked tendency toward an increase of the black
markings in the local butterflies.

On the island of New Guinea the local representa-
tives of wide-ranging butterflies are smaller than the
forms found elsewhere; the largest forms are those
which occur on the island of Amboina.

In high mountain regions butterflies become ex-
tremely variable, varying from peak to peak, from
valley to valley, and frequently in different portions
of the same valley. This is most evident in the
Himalayas and the mountains to the northward, and
in the Andes, but it is very noticeable in certain Rocky
Mountain species.

It occasionally happens that a form which is a rare
variety in one region is the sole representative of the
species in a distant region.

A species of butterfly may feed on a very great
variety of different plants, as does our yellow swal-
lowtail, or it may feed on only a single kind of plant.

[140]

^^^'1 ZOOGENESIS ^''^^

like our beaked butterfly. Most butterflies feed on
several or many closely related plants.

It often happens that a butterfly in its feeding habits
shows an abrupt departure from its nearest relatives.
Thus in that restricted group of swallowtails which
includes our common black or parsnip swallowtail
and the common yellow swallowtail of Europe all of
the species except three feed on umbelliferous plants.
One in eastern Asia feeds on plants of the rue family.
Another in Sardinia feeds on garden rue. The third,
in the Rocky Mountain region, feeds on Artemisia — a
composite plant. All three live with another species
of the same group which feeds on umbelliferous plants,
and the last two are very closely related to the forms
with which they live.

In the group of butterflies that includes the hair-
streaks, blues and coppers there is very great diversity
in food and feeding habits, with a corresponding
diversity in the caterpillars, though not in the eggs
or adults. In this group many of the species are
carnivorous, feeding on ants, aphids or other insects,
or are at first plant feeders becoming carnivorous in
the later stages. Some feed on lichens or on algas, or
bore into fruits. Nearly all are cannibals.

In some butterflies sexual development is very slow
and full maturity is not reached until some time after
emergence from the pupa. In those butterflies that
pass the winter as adults the eggs do not mature till
spring, that is, until the butterflies have been in the
adult stage for about six months. In the summer
brood of the same butterflies, however, maturity

^^^'^ THE NEW EVOLUTION '^^'^

takes place as rapidly, or almost as rapidly, as it does
in other butterflies.

In very many butterflies mating takes place, or may
take place, as soon as the wings are dry. In some
species the males may be seen fluttering about the
female chrysalids. In a few hair-streaks the full
grown caterpillars exhibit strong sex attraction, and
commonly form their chrysalids in pairs, a smaller
male just behind a larger female.

Reviewing the peculiarities of species as just given
we cannot fail to sense a temporary equilibrium.
Some species are held in narrow bounds by the opera-
tion of internal or external forces. They vary only
very slightly, or their geographical range is very
limited. Others in one portion of their range are
held in narrow bounds, but elsewhere are very vari-
able. This variation may be correlated with a shift-
ing of the bounds between which life is possible from
season to season or from one region to another, or it
may be correlated with a local separation of the limits
between which the species can exist.

The most striking feature of this variation which
we see within the species is that it is wholly, mainly,
or at least largely, discontinuous, that is, the several
forms do not intergrade, or if they do intergrade,
inter grades are rare. A striking example of the com-
plete absence of intergrades between very different
alternative forms is seen in our common eastern angle-
wings. Parents of one form will produce the same
form, or the other form, or both forms, but never
intergrades.

[14^]

Various Coelenterates
for an explah4ati0n of the figures see p. 281

^M THE NEW EVOLUTION ^^^^

The discontinuity of the forms within the species
as they normally exist in nature is emphasized by
very many cases in which the forms produced are
extremely local, or are rare varieties, or are sporadic
aberrations.

Professor William Bateson has brought together
some significant cases of such variations. He pointed
out that reversed varieties of animals are frequent.
They are not uncommon in man. They are especially
noticeable in the mollusks and the flat-fishes. Such
varieties are formed as optical or mirror images of
the body of the usual form. In both the mollusks
and the flat-fishes some species are normally right-
handed, while others are normally left-handed. But
reversed examples are found as individual variations.

In the mollusks this is not confined to the gastro-
pods or snail-like mollusks (fig. 51, p. 97), which
have spiral shells, but occurs also in the slugs and in
the bivalved mollusks (fig. 5x, p. 97).

Bateson noted that the fact that the reversed con-
dition may become a character of an established race
is familiar in the case of Fusus antiquus. This shell
is found in abundance as a fossil of the Norwich Crag.
The individuals in the Crag are normally left-handed,
though the same species at the present day is a right-
handed one. Of the left-handed form a colony was
discovered on the rocks in Vigo Bay, where the indi-
viduals were associated with certain other shells
occurring in the Norwich Crag. The same variety
occurs in Sicily.

Bateson remarked that from time to time there

[144]

ZOOGENESIS

have been records of the capture of the "hairy vari-
ety" of the moor-hen (Gallinula chloro-pus) in which
all the feathers were destitute of barbules and conse-
quently had a hairy texture, greatly changing the
general appearance of the bird. Owing to the ab-
sence of barbules, the general color of such birds
is tawny.

A few feathers of this type have been found in
hawks and gulls, and a jagana is recorded in which a
great portion of the body feathers were in this con-
dition. The feathers of the Apery x or kiwi and of
the cassowaries are also partially destitute of barbules.
A gray brahma hen has been reported with the same
peculiarity.

Bateson said that the case of the silky fowl is
similar in the absence of most of the barbules, but
in the silky fowl the point of the shaft is produced to a
delicate point and the barbs are fine and are sometimes
bifid or trifid at the apex. In the silky fowl the
skin and bones are purplish blue. The color of the
skin and bones has not been recorded in the case of
the "hairy" moor-hen.

Varieties of goats, cats, rabbits and other domestic
animals with long silky hair are well known, and
there are very similar breeds of guinea-pigs. This
variety is not confined to domestic animals, for it has
been reported in the common house-mouse.

Black mice are not infrequent. The so-called
"rhinoceros mice" are very interesting, and have
several times been reported. A male and a pregnant
female found in a straw-rick at Taplow, England,

[145]

THE NEW EVOLUTION

were entirely devoid of hair except for a few dark
colored whiskers. The skin was thrown up into nu-
merous prominent folds which crossed the body trans-
versely in an undulating manner. The ears were dark
or blackish, the tail was ash-colored, and the eyes
were black. There were no traces of hair follicles.
The animals were active and healthy, and there was
no suggestion of disease. The young when born were
similar to the parents. Other "rhinoceros mice"
have been recorded, both in England and in this
country.

Three mice were caught in a house in the town of
Elgin the bodies of which were completely naked.
There was nothing peculiar about the snout, whiskers,
ears, lower half of the legs, and tail, all of which parts
had hair of the usual length and color. At least two
others were killed in the same house where these
were found.

Naked horses have often been exhibited. A horse
taken from a half wild herd in Queensland had the
skin black and resembling rubber. Careful examina-
tion showed no trace of hair, nor any openings of hair
follicles. While in Turkestan, Professor Bateson
heard of a naked horse but failed to see it.

According to Belt the hairless dogs in tropical
America remain distinct and do not intergrade with
other dogs.

In many different kinds of domestic animals races
or breeds are known in which the bones of the face
do not grow to their full size, while the bones of the
jaw are, or may be, of normal proportions. Familiar

[146]

ZOOGENESIS

examples are the pugs, the Japanese pugs, the bull-
dogs, the Niata cattle of Argentina, short-faced pigs,
etc. A bull-dog skull has been found in an ancient
Inca grave in Peru, indicating that the bull-dog type
arose independently in America.

"Bull-dog" cod, carp, chub, minnows, mullet,
pike, salmon and trout have been described. In the
case of carp and trout the "bull-dog" variety is very
common in certain limited areas. "Bull-dog" forms
of other vertebrates have also been recorded.

A very interesting case of discontinuity is furnished
by the peach and nectarine. Darwin wrote that we
have excellent evidence of peach stones producing
nectarine trees, and of nectarine stones producing
peach trees. We see the same tree bearing both
peaches and nectarines. We find peach trees through
bud variation suddenly producing nectarines, the seeds
of which reproduce nectarines, as well as fruit which
is in part nectarine and in part peach. Finally, we
have a case of a nectarine tree first bearing half and
half fruit and subsequently true peaches.

The variation from peach to nectarine or from
nectarine to peach may be total. If it is less than
total the fruit may be divided into either halves or
quarters so that for each segment the variation is still
total. There is no evidence of intermediate forms
other than these divided fruits.

Bateson remarked that it is therefore a fair presump-
tion that intermediate forms are either rare or non-
existent, and that the peach state and the nectarine
state are thus positions of organic stability between

[M7]

^^"^ THE NEW EVOLUTION "^""^

which intermediate states, if they are chemical and
physical possibilities, are positions of instability.

Precisely the same phenomenon occurs among ani-
mals in which, however, it is usually overlooked or
misinterpreted. One scarcely expects an animal to
be partly one thing and partly another. This con-
dition is most obvious and most easily demonstrated
in the feather-stars (fig. 43, p. 87) and sea-lilies (fig.
6, p. 5) in which sometimes one or even two of the
five rays will be replaced by rays of a type belonging
to a widely different species. Several such cases
have been described.

The more we study species the more clearly do we
see that a species is a fluid unit, held to its present
form by forces which it cannot overcome. The
ability to expand and to produce new forms is inherent
in almost every species at the present time; but the
opportunity is lacking.

[148]

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CHAPTER XV
ANIMAL FORMS

ANIMALS exist in an almost infinite multiplicity
IX and complexity of form, and in most cases
Jl X. each single kind of animal exists in two or
more different — often very widely different — forms.
This is familiar to us in the case of the tadpole and
the frog, and in the case of the caterpillar, the
chrysalis and the butterfly. But these are relatively
simple illustrations. In the case of the common
eel we have the leptocephalus, the glass-eel, the
elver, and finally the eel, while in a group of shrimps
known as Pen^us the young are at first a nauplius
(cf. fig. IOC, p. 175), then in succession a metanauplius,
a protozoasa, a mysis-like creature, and finally an
adult, there being in these shrimps no less than five
different larval stages in addition to the adult form.
In only two of the major groups — the arrow-worms
or chastognaths (fig. 62., p. iii) and the rotifers (fig.
136, p. 103) — are there no larval forms in any of the
included species, the development leading directly
from the egg to the adult form. But the same is true
in many individual species, or larger or smaller assem-
blages of species, in many other groups. In the
vertebrates true larval forms leading an independent
life occur in most amphibians and a few fishes,
but are not found elsewhere. Generally speaking,
fresh water representatives of marine animals either

[149]

THE NEW EVOLUTION

greatly shorten the larval stages, or omit them
altogether.

It is a curious fact that very closely related creatures
may have v^idely different larvas. For instance, the
larvas of nearly all the brittle-stars (fig. 44, p. 87) are
strange looking things called plutei (cf . fig. 89, p. 175),
but some brittle-stars have worm-like pelagic larvas.
The larvas of most starfishes (fig. 42., p. 71) are of the
form called bipinnarias, later usually becoming brachi-
olarias (fig. 88, p. 175); but starfishes w^hich brood their
young have w^orm-like larvas.

On the other hand, very different creatures may
have very similar larvae. Thus the young of most,
but by no means all, of the mollusks and also of the
jointed w^orms or annelids are typical trochosphere
larvae. One adult rotifer has the same form. Larval
forms v^^hich are commonly considered modified tro-
chospheres are found in the echinoderms (fig. 109,
p. 175), in the balanoglossids, in the phoronids (fig.
lOi, p. 175), and in the polyzoans (fig. 90, p. 175).

Extraordinary diversification of the larval forms is
found in the echinoderms. Here we have the barrel-
shaped larvas of the feather-stars (fig. 109, p. 175), the
auricularias of most of the holothurians or sea-cucum-
bers, which resemble most nearly the so-called tor-
naria larvae (fig. 94, p. 175) of the balanoglossids, the
bipinnarias and usually later the brachiolarias (fig. 88,
p. 175) of most starfishes, the bizarre plutei of most
sea-urchins (fig. 89, p. 175) and brittle-stars, and also
some other larval forms.

Other curious larval forms among the marine ani-

ZOOGENESIS

mals are the actinotrocha larvas (fig. 102., p. 175) of
the phoronids, and the cyphonautes larvae (fig. 90,
p. 175) of most polyzoans. There are various other
larval types among the marine animals.

Not only do the different types of larvae vary very
widely in their body form, but they also vary widely
in the manner of their development. In most crusta-
ceans, whatever may be the sequence of their larval
forms, the development is more or less direct. In the
nemerteans the development is usually direct, but in
some there is a curious larva called a pilidium (fig. 106,
p. 175) which transforms to the adult by a very com-
plicated metamorphosis. There are also other forms
of larvae in the nemerteans.

In some of the trematodes the development is
direct, but in others it is extremely complicated.
Thus the first larva may be a miracidium (fig. 96,
p. 175) which transforms into a sporocyst (fig. 98,
p. 175), or rarely into a redia (fig. 97, p. 175). The
sporocyst may produce other sporocysts, but usually
produces rediae, these last — sometimes also the sporo-
cysts— producing curious tadpole-like larvae called
cercarias (fig. 99, p. 175), which grow into the adults.

During the course of their development the echino-
derms become transformed from a bilateral larva (figs.
88, 89, p. 175) into a radially symmetrical adult (figs.
41, 4^, p. 71) with the body in five divisions.

In the passage from the larval to the adult form
quite a number of the attached sea animals turn a half-
somersault. The larva attaches itself at the anterior
end just in front of the mouth and fastens itself

"Wl THE NEW EVOLUTION ®^

firmly to the supporting surface. Then the mouth
and the associated structures move upward to a posi-
tion nearly or quite opposite the point of attach-
ment. This curious process takes place in the
feather-stars (fig. 43, p. 87) (but not in the other
echinoderms), in the barnacles (fig. 30, p. 47) (though
not in the parasitic barnacles or in the other crusta-
ceans), in most tunicates, and in certain other
types.

A curious feature of animals as a whole is the recur-
rence of similar or comparable forms in widely differ-
ent groups.

Among the single celled animals or protozoans
some are attached and more or less radially sym-
metrical, like Stentor and Vorticella. Others are at-
tached and form colonies at the summit of a stalk,
like Codosiga or Epistylis. Some, as Amoeba, are free
living and capable of locomotion, but are sluggish
and creep equally well in any direction. Still others
float about freely suspended in the water. Many are
elongated and more or less bilaterally symmetrical,
and swim with great rapidity. Some are naked,
while others form beautiful regular and complicated
shells of lime or other substances, or rough aggluti-
nated tubes of sand grains, or other forms of body
covering.

Among the radially symmetrical animals some —
indeed most — are attached. Some of the attached
types form colonies on the summit of a stalk (fig. 7X,
p. 117), as the umbellularians. Others, as many sea-
anemones (figs. 4, p. 5; 79, p. 143), are free living and

[15^]

^^"^ ZOOGENESIS "^""^

capable of locomotion, but are sluggish and creep
equally well in any direction. Some, like the jelly-
fishes (figs. 3, p. 5; 78, p. 143) and the ctenophores
(fig. 66, p. Ill), float freely suspended in the water.
Others are elongated and more or less bilaterally
symmetrical, like the Venus' girdle (Cestus) and the
creeping ctenophores. Some are naked, while others
construct beautiful and complicated bases, like the
corals, or are even completely enclosed in pro-
tecting plates (Primnod), or live in tubes of sand or
mud. Thus these creatures repeat the bodily forms of
the protozoans so far as their structure will allow.

Among the bilaterally symmetrical animals derived
through a gastrula stage many are attached, as nearly
all the polyzoans (figs. 67, 68, p. iii), most sea-lilies
(fig. 6, p. 5), many crustaceans, like the barnacles
(fig. 30, p. 47), most tunicates, and certain other
types; some of the attached forms, as certain of the
polyzoans, form colonies on the summit of a long
stalk. Others, as most sea-urchins and starfishes, are
free living and capable of locomotion, but are sluggish
and creep equally well in any direction. Some, as
certain rotifers, tunicates and holothurians, float
freely suspended in the water. Very many are bilater-
ally symmetrical and swim, run or fly with great
rapidity. Some are naked, while others, as the bar-
nacles, brachiopods, mollusks and polyzoans, form
regular and complicated limy shells or, as in the case
of many worms, some rotifers, some phoronids, and
some insect larvas, construct rough agglutinated tubes
of sand grains or other forms of body covering.

^53] "

THE NEW EVOLUTION

But whatever may be the form of any animal type
either in its larval or adult stage the fundamental
features of the group of w^hich it is a member are in
it found to be unchanged.

[154]

CHAPTER XVI
THE CONTINUITY OF LIFE

No UNDERSTANDING of animal life is possible
without an appreciation of the ways in
which the perpetuation of the species is
assured. Continuity of life from one generation to
the next is brought about by three apparently quite
different processes.

In the first place, there is the usual sexual repro-
duction. Secondly, many animals are reproduced by
females only, through the development of unfertilized
eggs. In the third place, an animal may divide in
two, or may produce buds which grow into new
animals; these may separate from the parent, or may
remain attached to it.

Many different kinds of animals, such as all
sponges, all coelenterates, many flatworms, some
jointed worms or annelids, the phoronids, the poly-
zoans, some tunicates, the cephalodiscids, some brit-
tle-stars and starfishes, and a few crustaceans, either
form buds which become detached and develop into
independent animals, or, usually at an early stage,
divide into two or more parts, each of which develops
into an independent animal.

Many of these types, especially the sponges, the
coelenterates, the polyzoans and the tunicates, besides
producing buds which become detached, also produce
buds which remain attached to the parent animal.

^^^^ THE NEW EVOLUTION Wf

and in this way build up more or less extensive
colonies (figs. 59, Gy, p. iii; figs. 69-72., p. 12.7).

There are very many variations of this process.
For instance some sponges, including the sponges of
fresh water, and most of the fresh water polyzoans,
produce as they grow internal buds consisting of
masses of cells encased in a tough and usually more or
less complicated shell. After the animal dies these
little seed-like structures are liberated through the
decomposition and disintegration of the body and
drift away, to grow into a new animal, or colony, if
and when conditions become favorable.

In most polyzoans the tentacles, alimentary canal
and nervous system of the individuals from time to
time disintegrate, and a new set of these organs may
be formed through internal budding from the per-
sistent body wall of such partially disintegrated
polypides.

In the insects in which the metamorphosis is in-
complete, as for instance the grasshoppers, mantles
(fig. 19, p. 33) and bugs (fig. ^3, p. 33), the body of
the young grows gradually into the body of the adult,
and the new organs, such as the wings, are formed as
simple outgrowths.

In those insects, as the beetles, wasps, butterflies
and flies, in which the young are very different from
the adults a few of the systems of organs, such as the
reproductive, the nervous and the circulatory, persist
from the larva to the adult, but the other organs dis-
integrate, being later entirely rebuilt from special
groups of cells called imaginal disks.

ZOOGENESIS

In connection with this so-called asexual reproduc-
tion the extraordinary powers of regeneration pos-
sessed by certain types of animals deserves a special
mention. Some creatures may be cut into a great
number of small fragments, and each fragment will
subsequently grow into a perfect animal. In other
creatures fragments above a certain minimum size, or
including a greater or lesser portion of some essential
structure, will grow into a perfect animal. In still
other creatures division or mutilation of the body is
followed by the replacement, by the central portion,
of the parts removed. But the fragments not includ-
ing this central portion die.

A curious form of reproduction is seen in certain
minute parasitic wasps in which a single egg gives
rise to from two or three to about a thousand larvas.
In somewhat the same way the egg of certain poly-
zoans develops into a multinucleated mass which
buds off small pieces, each of which becomes a
larva.

To a large extent asexual reproduction is especially
characteristic of the early stages or the young of the
animal types wherein it occurs, the individuals which
are fully grown being capable only of sexual repro-
duction. Thus in certain brittle-stars very young in-
dividuals divide into two, and each half then grows
into an adult. Certain starfishes when young divide
themselves into five sections, the five arms, separating
at the base; subsequently each arm grows four more
arms, and the original single little starfish becomes
five adults. But in none of the brittle-stars or star-

[157]

THE NEW EVOLUTION ^S"

fishes is such a procedure possible after the animal
is fully grown.

While in many animal types asexual reproduction is
carried to great lengths, it never wholly takes the
place of sexual reproduction. Sometimes sexual and
asexual generations alternate, or there may be several,
many, or even very many asexual generations between
two sexual generations, or asexual reproduction may
be rare, or very rare, or merely casual.

Reproduction by females only through the develop-
ment of unfertilized eggs is not infrequent in the
animal world. In a number of different creatures
young are produced by females in the absence of any
males. This is true in all the rotifers (fig. 136, p. ^03).
Most rotifers, besides possessing this curious type of
reproduction, also are known to show — though
often very infrequently — the usual sexual reproduc-
tion. But in many kinds of rotifers males are en-
tirely unknown.

Production of eggs and young by females in the
absence of males occurs as a regular and constant
feature in the life history of many different kinds of
phyllopod and ostracod crustaceans, in many different
kinds of hymenopterous and hemipterous insects, in
some jellyfishes, in some moths, and in a few other
creatures. In some of the crustaceans and in some
insects no males have ever been discovered.

The production of young through the development
of unfertilized eggs is by no means confined to full
grown females. In a few kinds of flies young are
produced by the pupal stage, or even by the maggots.

[^58]

^^ ZOOGENESIS "^"^^

In certain insects, as in the social ants, bees and
wasps, and in the termites or white-ants, individuals
occur — the so-called workers — which have non-func-
tional reproductive organs. In the ants, bees and
wasps such individuals are always females, but in
the termites they are both males and females.

Corresponding non-breeding forms are not infre-
quent in other types of insects, and also in birds and
mammals, though in these so far as known they
serve no useful purpose. Unsexed polyps or cor-
responding units are of course common in the coelen-
terates and in the polyzoans, and occur also in some
tunicates.

The production of fertile eggs or living young by
females only is so extensively developed in some types
of animals that sexual reproduction is a very rare
occurrence — indeed in some it is entirely unknown.
In others it is casual or rare. Between the two
extremes almost every type of intermediate exists.

But throughout the animal world sexual reproduc-
tion is the usual and most widespread means of insur-
ing the perpetuation of the species, and even in those
animal types with extensive asexual reproduction or
reproduction through females only sexual reproduc-
tion almost without exception plays an important
part.

Asexual reproduction or division may take place at
any stage, though it is most frequent in the early
stages and in young animals. In the case of reproduc-
tion through the development of unfertilized eggs the
eggs are usually produced by fully grown females,

^^^^ THE NEW EVOLUTION "^^^

more rarely by young females, and very rarely by the
preadult or larval stages.

As a prerequisite to sexual reproduction it is neces-
sary that the individuals become sexually mature. It
is important to remember, however, that sexual
maturity is quite a different thing from structural
maturity. It is true that in the great majority of
animals after sexual maturity is reached structural
development abruptly ceases, very shortly ceases, or
proceeds at a much slackened pace. In certain but-
terflies, indeed, structural development ends six
months or more before full sexual maturity is reached.

But this is not always true. Even larval stages
may become sexually mature. Thus in one group of
the ctenophores the larva develops sexual cells which
mature during the summer and produce eggs which
develop normally into larvx which are, however,
smaller than the larvae produced by adults. After
the production of eggs has continued for some days
the larva loses the sexual cells, undergoes a com-
plicated metamorphosis, and develops into an adult,
when sexual cells again appear. Certain flukes also
may produce eggs in their larval stages.

In nearly all animals on land the individuals are
divided into males and females. But this is by no
means always true. In many different kinds of ani-
mals both sexes are developed in every individual so
that single individuals produce fertile eggs or young.

Both sexes equally developed and functioning at
the same time so that a single individual alone pro-
duces young are found in a number of coelenterates,

Various Types of Animal Life
for an explanation of the figures see p 231

"^^ THE NEW EVOLUTION

including all the ctenophores, in the tapeworms,
most flukes, most turbellarians, some nematodes, the
arrow-worms or chastognaths, most polyzoans, pos-
sibly a few brachiopods, most barnacles, a few fishes,
and an amphibian. In a number of fishes and some
amphibians individuals occur casually in which both
sexes are equally developed.

Both sexes are equally developed in earthworms,
leeches and snails, but in these creatures the indi-
viduals are not capable of self-fertilization. In tad-
poles both sexes are equally developed, but only one
sex continues to develop to maturity.

In some animals, as for instance in the slime-eels
and some nematodes, the individuals are at first male
and later female, while in others, as in most tunicates,
the individuals are at first female and later male.

In a number of different creatures, including some
nematodes, some barnacles, and the ceratioid fishes,
the males are wholly helpless parasites and live
attached to, or within, the body of the female.

From this brief mention of some of the more impor-
tant methods for assuring the continuity of life from
one generation to the next and so on indefinitely it
is clear that every conceivable expedient is to be found
in some animal type or other. Furthermore, in every
animal type that form of reproduction best fitted to
produce the greatest number of young under the con-
ditions which must be met is the one adopted.

These conditions differ very widely. In some cases
the greatest number of young results from the actual
production of relatively few which are cared for by

^^^^ ZOOGENESIS ^^^'^

the parents until almost the adult stage is reached,
as in the mammals and most birds. In other cases
the hazards of life are so very great that very many
young must die for each one that survives.

In the common human tapeworm it has been shown
that of the young produced only one in thirty-five
millions has any chance of becoming an adult
tapeworm.

In the case of the common eel of our ponds and
streams an average female lays from five to ten million
eggs, and large females lay from fifteen to twenty
millions. Thus the chance that any given egg will
hatch and the resulting young will grow into a
mature eel which will succeed in returning to the
spawning grounds is only one in about ten millions.

[163]

CHAPTER XVII
LIFE

|iME and again it has been shown that living
things arise only as the children of other
living things. This rule has no exceptions,
and it is inconceivable that there should be excep-
tions. It is utterly impossible for any living thing
to arise spontaneously. The continuity of life from
parent to child is not doubted by any student of ani-
mals or plants at the present day. It is a basic axiom
of biology.

Since all living things are derived from other living
things, it naturally follows that the ancestral line of
every living thing in the world at the present time
has been continuous and unbroken, going back to the
very earliest life upon the earth. No biologist today
doubts the continuity of life from parent to child
through all the ages that have passed since life's
first beginnings, or the common origin of all forms
of life.

Every living thing develops from a unit particle of
living matter — a single germ cell — in which no trace
of the adult form of that living thing is discernible.
This is a second basic axiom of biology. Further-
more, the bodies of all living things are composed
either of a single cell, as in the case of the single-celled
animals or protozoans, or of vast numbers of cells of
varied form and function grouped into the various

[164]

ZOOGENESIS

organs of the body and forming either of themselves
or as a result of their activity the diverse struc-
tural elements.

Since every animal, no matter what it is, originates
as a single cell, and the body of every animal is com-
posed of one or many cells which are always essen-
tially the same in structure, we clearly see that all
types of animal life must be explained in terms of a
single cell.

Unbroken continuity of life from its very first
appearance on the earth, and the fact that all animals
begin as single cells and no matter what their size
are always composed of a single cell or of a multitude
of cells which in their broader features resemble the
original single cells from which they are derived —
these are the fundamentals out of which we must
construct our picture of the interrelationships of ani-
mal forms.

Our first reaction to the plain statement of these
fundamentals is that the problem is a simple one.
Since all animals begin as a single cell, and since many
animals are known whose entire body consists of a
single cell, therefore these single celled animals must
be the most primitive and all other animals must have
been descended from them. So we are tempted to
construct an evolutionary line from the single celled
animals to those whose body is most complex in
terms of cells, and then to arrange all animal types as
best we may along this line. Such an assumed course
of development of animal forms, from those whose
body is composed of a single cell to the multitudes of

'^'^'^ THE NEW EVOLUTION '^^'^

multicellular types which we know today, is ex-
plained by what is called the theory of evolution.

Evolution as commonly understood assumes the
gradual development step by step of all the widely
varying forms of animal life from an original form
of simple structure. But the developmental course
which has been followed by animal life cannot be
reduced to any such simple formula. In the first
place, the study of animal life itself, whether the
study of adult forms or of embryology, shows it to be
wholly incapable of such simple interpretation. In
the second place, this hypothesis is not in accord with
the fossil history of animals as we know it. In the
third place, it is not in accord with our interpretation
of the geological processes and conditions in the very
distant past.

Any acceptable theory of animal development must
be in complete agreement with its setting. It must
take into account the geological background and
must be in accord with what we know, or believe, to
have been the condition of the earth in the very
distant past.

In tracing the history of animal life from its very
first appearance to the infinite complexity which we
see at the present day there are three entirely separate
sets of facts to be considered, and any acceptable
theory of the development of animal life must har-
monize and correlate all three.

In the first place, within each of the so-called phyla
or major groups of animals, as is well seen in the
vertebrates, particularly in the mammals and the

b66]

^^^^ ZOOGENESIS ®il

reptiles, there are many well marked, obvious, and
undeniable evolutionary lines v^hich, beginning with
a relatively simple form of creature run by easy stages
to a specialized and highly complex form.

In the second place, very few of these evolutionary
lines are perfectly continuous . Practically all of them
are more or less interrupted by gaps of various widths,
and these gaps are often very broad. Especially is it
true that these evolutionary lines tend to be separated
from each other for their entire course, running paral-
lel or more or less convergent right down to their very
earliest beginnings, and not uniting in a common type
of animal as we would expect. For instance, the
whales and the seals are always whales and seals, and
show little or no approach to any other type of
mammal. Similarly, there are no intermediates be-
tween turtles and snakes, or between turtles and
lizards, all of which are reptiles, or between squid
(fig. 45, p. 97) and oysters, though both types are
mollusks.

In the third place, no animals are known even from
the very earliest rocks which cannot be at once as-
signed to their proper phylum or major group on the
basis of the definition of that group as drawn up from
a study of living animals alone. A backboned animal
is always unmistakably a backboned animal, a star-
fish is always a starfish, and an insect is always an
insect no matter whether we find it as a fossil or catch
it alive at the present day. There can be only one
interpretation of this entire lack of any intermediates
between the major groups of animals, as for instance

^^^"" THE NEW EVOLUTION "^^"^^

between the vertebrates, the echinoderms, the mol-
lusks and the arthropods. If we are willing to accept
the facts at their face value, which would seem to be
the only thing to do, we must believe that there never
were such intermediates, or in other words that these
major groups from the very first bore the same relation
to each other that they do at the present day. Is this
creationism? Not at all. It simply means that life
at its very first beginnings from the single cell devel-
oped simultaneously and at once in every possible
direction. All of the phyla or major groups seem to
be of simultaneous development — at least we have no
evidence that it was otherwise. From each one of
these a separate developmental line or tree arose,
growing upward through the ages.

The numerous developmental lines are explained by
the process of evolution as that term is commonly
understood, and this descriptive word should be re-
stricted to these developmental lines.

The gaps within these lines, and between related
lines which run more or less parallel, are explained by
an extension of the theory of mutations.

The complete absence of any intermediate forms
between the major groups of animals, which is one
of the most striking and most significant phenomena
brought out by the study of zoology, has hitherto
been overlooked, or at least ignored. This condition
may readily be explained by an application of the
facts gained through the study of embryology by a
theory which may be called the theory of eogenesis.

Restriction or expansion of the meaning of a well

[^68]

^^~^^ ZOOGENESIS ^1^

known word results always in confusion. The term
evolution is commonly used to cover the entire devel-
opmental history of animals. But evolution con-
templates a gradual and continuous unfolding of ani-
mal life beginning with creatures consisting of a
single cell and ending with man. A better under-
standing of the subject will result if we recognize the
fact that this process includes three distinct but inter-
related phases, first, evolution properly so called;
second, mutations; and third, eogenesis.

If we regard the complete history of the develop-
ment of animal life in this light we must, in order to
avoid confusion, use for it an entirely new term. We
may call it %po genes is.

[169]

CHAPTER XVIII

DEVELOPMENTAL LINES AND TREES-
EVOLUTION

THE first of the three sets of facts to be con-
sidered in connection with the development of
animal forms has to do with the existence
within each of the larger of the so-called phyla or
major groups of animals of well marked, obvious and
undeniable evolutionary lines which, having their
origin in far distant geologic time in a relatively
simple form of creature, run by easy stages to a spe-
cialized and highly complex form or group of forms.

Such lines of progressive bodily development are
well marked in the backboned animals or vertebrates,
particularly in the mammals and the reptiles. We
may illustrate this point by a consideration of the
history of the horses.

At present there are living on the earth about ten
different kinds of horses all but one of which, the
domestic horse, which is not found in a wild state,
are confined to Asia and to Africa, most of them,
the various kinds of zebras, living in Africa.

But in the Pleistocene or Ice Age many different
kinds of horses roamed over all the continents except
Australia. According to Dr. James W. Gidley there
were a number of different kinds in North America
where they ranged north to beyond the Arctic circle
in Alaska.

[170]

^^^^ ZOOGENESIS ""^^^

These horses were all the modern type, with rela-
tively long limbs and with a single toe and hoof on
each foot. Their skulls were long-muzzled and their
jaws were deep in order to accommodate the long and
high-crowned teeth which are so characteristic of the
modern horse. They ranged in size from little crea-
tures no larger than the smallest Shetland pony to
some that exceeded the largest draught horses.

As related by Dr. Gidley, these horses of the Ice
Age were preceded by others of a still earlier geologic
time. The fossils of the later portion of the so-called
Tertiary period, known as the Miocene and Pliocene
epochs, give abundant evidence of earlier groups of
horses which were even more varied in types and more
numerous in kinds than those of the Pleistocene.

The duration of this period was very long, being
measured by hundreds of thousands or perhaps even
millions of years, and the records show that horses
were abundant from its beginning until its close.
There were no very large horses at this time, and the
general average size was notably smaller than that of
the horses of the Pleistocene. They all resembled the
modern horses in a general way, but most of them
differed in several rather inconspicuous but very im-
portant features.

The limbs and feet of the horses of this period were
much like those of modern horses, but in addition to
the single rounded hoof most of them had on each
foot a pair of extra toes, one on either side of the main
toe. These extra toes varied in size from small ones,
resembling the so-called dew-claws of the deer or elk.

THE NEW EVOLUTION

which did not reach the ground, to larger ones which
reached the ground and must have borne some of the
weight of the animal in walking. A very few of the
horses of this period had feet like the modern horses —
that is, entirely without the lateral toes — but their
remains occur only in the later portion of the period.
Most of the horses of the earlier phases of the period
had longer and better developed lateral toes than those
of the middle and later phases.

All horses with single toes, both modern and ex-
tinct, have on each foot a pair of long splint bones, one
on either side of the main toe, which in life are covered
by the skin. The upper ends of these bones are
greatly expanded and have well developed articular
facets for contact with the small bones of the wrists
or ankles. This part of the foot is identical in struc-
ture in the one-toed and in the three-toed horses, but
in the three-toed horses there are three additional
terminal bones on the lateral toes which are absent in
the one-toed horses.

In the horses of the Pliocene and Miocene the
muzzle portion of the skull is usually relatively
shorter than in the modern horse, and the jaws are
not quite so deep, due to a difference in the relative
height of the crowns of the cheek teeth. In the
living horses and the horses of the Pleistocene or Ice
Age all the cheek teeth when fully formed have long
and nearly straight crowns from three to four inches
or more in height. These are set deeply in the jaws
and move outward as they are worn away by use. It
is this type of tooth which, as remarked by Dr.

[17^]

^^''"f ZOOGENESIS '^^^^

Gidley, gives the great depth to the jaws of modern
horses. In most of the horses of the later Tertiary
the cheek teeth are of this type, but the crowns are
less heightened and are usually much more curved.
Both of these features tend to decrease the depth of
the jaws.

A few of the kinds of horses which lived in this
period had teeth of a simpler type in which the crowns
are low and are attached to the jaws by means of
roots. For the most part these kinds are found in the
earlier portions of the period. Of the kinds with
high crowned teeth those with the least heightened
crowns are also found in the earlier phases of this time
period. This group of the earlier horses represents
in a way a transition stage between those with low
crowned and those with high crowned teeth, for the
young or colts of the horses of this group had cheek
teeth of the low crowned type which in adult life
were replaced by teeth of the high crowned type.

In the next older epoch of the Tertiary period,
known as the Oligocene, still other kinds of horses
inhabited America. These more ancient horses were
on the average smaller than those just noted. Most
of them were about the size of a shepherd dog or a
little larger; a few were somewhat smaller. There
were many different kinds of these little horses. All
were three-toed types with the lateral toes reaching
to the ground, and all had low crowned teeth, so
except for their smaller size they must have resembled
closely those of similar type belonging to the next
later period (Miocene).

li^ THE NEW EVOLUTION ' ^^^^

All through the sedimentary rocks of the earliest
epoch of the Tertiary — the Eocene or "dawn time" —
there are records of an abundance of little creatures
much resembling those of the Oligocene but still more
diminutive in size. They also had a main central toe
with well developed lateral toes on each hind foot,
but the fore feet were provided with four toes instead
of three. The muzzle portion of the skull was rela-
tively shorter in the little very early horses than in
the larger later horses, so that the eyes were about
midway between the ears and the tip of the nose
instead of being nearer the ears as in the later horses.

The oldest member of the group of four-toed horses,
which is also the oldest member of the great group to
which belong all the horses, was a little creature no
larger than a fox called Eobippus or the ' 'dawn horse. ' '

While no member of the horse family has five com-
plete toes, some of the little four-toed ones have in
the foot an extra small bone of splint-like shape which
can only be interpreted as the representative of a
fifth toe.

This account of the different types of horses, begin-
ning with those of the present day and running back
further and further through geologic time to the very
earliest creature known which can be called a horse
leads us by easy stages to an animal which is very
different from any kind of horse we ever saw. With-
out a knowledge of the intermediate types we would
never suspect that it had any affinity with horses.
Now if we reverse the picture we shall get a good
example of an evolutionary line.

^74]

Young Stages of Various Animals

FOR an explanation OF THE FIGURES SEE P. 282

^^^1 THE NEW EVOLUTION T"^^

In the Eocene there lived a curious little creature
no bigger than a fox called the "dawn horse" —
Eohippus — which had four toes on the front and three
on the hind feet and a relatively short head with the
eyes about half way between the ears and the tip of
the nose instead of nearer the ears than the tip of the
nose as in the later horses. In the same epoch,
though somewhat later, there was an abundance of
very similar little creatures.

Following these there were a number of different
kinds of horses all of which had three toes and, like
the "dawn horse," low crowned teeth which were
affixed to the jaw by means of roots.

Still later there were horses which as colts had low
crowned teeth, but when fully grown had teeth with
fairly high crowns. With these lived others in which
the teeth had high crowns at all ages. These horses
had shorter muzzles and rather less deep jaws than
the modern horses, and while they had a single hoof,
there was a toe on either side of it. These lateral
toes varied from small ones which did not reach the
ground to larger ones which reached the ground.

In the Pleistocene or Ice Age — in the epoch just
before the present — there were very many different
kinds of horses which were all of the modern type
and inhabited all the continents with the exception
of Australia.

So we see a well marked and distinct evolutionary
line beginning with the little four-toed horses in the
Eocene and culminating in the large single-toed horses
of the present day.

^^ ZOOGENESIS

While this series of horse types may broadly speak-
ing be considered as representing a single line running
from the little four-toed horses to the large single-toed
horses, the actual conditions really are not quite
so simple.

Several of the horse types after their first appearance
branched out in various directions, and these diverse
branches became more and more distinct from each
other and themselves gave off branches in the same
way, and again the process v^as repeated.

In the Pleistocene the modern type of horse, w^hich
was then of relatively recent appearance, had already
branched out in many different directions. At the
present time there exist a single sort of true wild
horse in Asia, four kinds of wild donkeys, three in
Asia and one in Abyssinia (Ethiopia), and several
different kinds of zebras, all in Africa.

The development or evolution of the horse from its
first beginnings in the Eocene to the present day may
thus be most faithfully represented by a tree-like
figure, the base of the tree-like figure being a creature
more or less closely resembling EoJhippus, and the
present wild horses, wild asses and zebras being repre-
sented by a few of the topmost twigs.

The existence of many well marked develop-
mental trees like that delineated by the fossil
horses enables us to present a general picture of the
evolutionary history of many different types of ani-
mal life.

Large sections of certain groups of animals may
even be delineated in this way and their evolutionary

^ THE NEW EVOLUTION

history described on the analogy of a tree with a
close approximation to the known facts.

Thus the reptiles first appeared in that very ancient
time known as the Carboniferous and gradually
branched out, increasing in diversity and in maximum
size. The largest land animals of which we have any
knowledge are the largest of the dinosaurs, which
flourished in the Jurassic and Cretaceous. At the
end of the Cretaceous period most of the larger and
more spectacular of the reptiles suddenly disappeared,
but many reptilian types, for instance the turtles,
lizards, snakes and crocodilians continued right
through to the present day.

The mammals first appeared in the form of very
small and insignificant creatures at the time (Jurassic)
when the great reptiles were the dominating giants
of the land and sea. After the sudden disappearance
of the giant reptiles at the end of the Cretaceous, the
mammals increased greatly in diversity and somewhat
in size, though in the earlier portion of the epoch fol-
lowing (the Eocene) the largest mammal was not so
large even as a sheep.

These mammals of the earlier portion of the "dawn
period" (Eocene) soon disappeared, but as they dis-
appeared their place was taken by other types which
were more or less comparable to the sorts we know
today. Gradually as time went on these mammals
became more and more diversified. Various extra-
ordinary types appeared, some of huge size and in
aspect most bizarre, while together with these came
others which we have no difficulty in recognizing as

ZOOGENESIS

the direct predecessors of the types which we know at
the present day.

In many other groups, especially in the mollusks,
in the echinoderms, and in the jointed-legged animals
or arthropods, similar and comparable evolutionary
figures may be constructed on the basis of the facts
available.

[179]

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Vi i^^Ii }^^/i 1^31^^ )S^^£^ >S^^Ji >\2i^« i\^^« ^3il

CHAPTER XIX

GAPS IN THE EVOLUTIONARY LINES-
MUTATIONS

THE second of the three sets of facts to be
considered in connection with the develop-
ment of animal forms concerns the imperfec-
tions in the evolutionary picture as portrayed by a
branching tree-like figure.

All the evolutionary lines are frequently interrupted
by gaps of various w^idths, and these gaps are often
very broad. Thus in the horses, as has been pointed
out by Dr. James W. Gidley and by Professor W. D.
Matthew, there is a considerable gap between the
Eocene and the next following (Oligocene) types,
and there are numerous other gaps, many of the types
of horses being more or less, and sometimes rather
widely, isolated from their nearest relatives.

In the horses, as stated by Professor Matthew, we
"have in many cases a succession of collateral ances-
tors so nearly related to the direct genetic line as to
afford, when critically studied with due recognition
of their status, a clear record of the physical evolution
of the race, sometimes in more general, sometimes in
more detailed terms according to the nearness of their
approximation to the direct ancestral line."

So we see that even in the horses the tree-like figure
is after all only an approximation to the truth. The
twigs of the tree do not actually join the branches,

^^^^ ZOOGENESIS "^""^

and the branches do not join the main trunk; and
besides, the main trunk itself is not continuous. The
gap between the very earliest horses that we know,
the horses of the Eocene, and those of the next fol-
lowing period, the Oligocene, will undoubtedly be
narrowed by future discoveries, but most of the gaps
probably will not.

Especially is it true that evolutionary lines tend to
be separated from each other for their entire course,
the trunks of the evolutionary trees running parallel
or more or less convergent right down to their very
earliest beginnings and not coming together in a
common type of animal as we would expect.

For instance, the whale line is always distinct from
every other line of mammalian development, just as
in the reptiles the corresponding ichthyosaurs always
were distinct from every other line of reptiles. So
also the seal line is always distinct. Just as whales
were always whales, seals were always seals. No
intergrades between the seals and other mammals are
known, although the seals belong to the Carnivora
and therefore must have had an ancestor common to
them and to the terrestrial members of that great
mammalian group.

Among the more familiar mammals, the cat and
the dog lines are always separate. No forms inter-
mediate between cats and their relatives and dogs and
their relatives are known, even though both cats and
dogs are collateral members, together with the seals,
of the Carnivora.

But in the case of cats and dogs the very early types

[TsT]

^^"^ THE NEW EVOLUTION '^^^^

which are found in the Oligocene are less widely dif-
ferent from each other than are the cats and dogs of
the present day. Professor Matthew says that "there
is no serious gap in the line through which the dogs
are traced back to the Lower Eocene Mmcis, but the
Lower Eocene ancestors of the Felidas [cats] are repre-
sented only by a number of European genera imper-
fectly known and apparently not very close to the
direct line of descent." Palaeontologists, however,
admit the distinctness of these three groups by placing
the cats in one family (Felidas), the dogs in another
(Canidae), and the Lower Eocene Carnivora to which
they are most closely related in still a third (Miacidas).

Among the other backboned animals or vertebrates
there are no intermediates between turtles and snakes,
or turtles and lizards, or snakes and lizards, all of
which are reptiles, and in the fishes there are no inter-
mediates between the cyclostomes (lampreys and
hagfishes), or the teleosts or bony fishes, and any
other types.

It should perhaps be emphasized that discontinui-
ties in descent and in relationship are much less con-
spicuous and marked among the backboned animals
or vertebrates than they are in the large invertebrate
groups. In the vertebrates there are no such enor-
mous gaps as those between the squid, octopus and
nautilus, and the snail or oyster, all of which are
mollusks, or between the starfishes, sea-urchins, sea-
lilies and sea-cucumbers, all of which are echinoderms.

All the backboned animals taken together form a
very homogeneous group in which the entire struc-

ZOOGENESIS 'P^"

tural range from the tadpole or the leptocephalid to
the highest mammal is scarcely greater than the
structural range found in certain individual species
of crustaceans or of insects at different stages in their
development from newly hatched young to adults.

Thus v^hile in many animal types wc are able to
trace, as in the horses, a gradual evolution from a
form which is simple and generalized in structure to a
group of forms all of which are highly specialized,
this is by no means always true. Indeed, it is the
exception rather than the rule. All lines are broken
by gaps which may be small and insignificant, or
broad and striking.

It is commonly assumed that these various gaps are
due to our lack of adequate knowledge of the animals
concerned, and especially of their fossil record. No
doubt in many cases this is partly, or even perhaps
largely, true, but in very many cases these gaps un-
doubtedly are real and never were bridged by so-called
missing links.

In the light of our present knowledge it is not pos-
sible for us to doubt that all living things are the chil-
dren of other living things, and that life has been
continuous from parent to child from its earliest
beginnings. How is it possible to harmonize this
fact with the occurrence of broad and unbridged gaps
in the evolutionary lines?

The answer is that continuity of life does not neces- -
sarily imply a similar continuity of the bodily form \
in which that life is manifested. In other words,
children may be very different from their parents. As

S0 THE NEW EVOLUTION "^^"^

an illustration of continuity of life from parent to
child coupled with abrupt and striking discontinuity
in form, and also in mental traits, let us consider
the dogs.

According to the best authorities, all of the nearly
two hundred different breeds of domesticated dogs
are descended -rom a single type of ancestor, which
was a wolf or wolves closely resembling our native
wolf but with slightly different teeth. The domestic
dogs may be grouped, following Gibson, into wolf-
dogs, greyhounds, spaniels, hounds, mastiffs and
terriers.

Some of the wolf-dogs, as for instance the dogs of
the Esquimaux and of the Kamchadales, show a more
or less close resemblance to wolves and are said to
interbreed with them, while others, as the collies,
police-dogs, sheep-dogs, Newfoundlands and St. Ber-
nards, are much less wolf-like. But the wolf-dogs
may be arranged in a fairly continuous series from
the most to the least wolf-like.

This series of dog forms is parallel to many of the
evolutionary lines which are seen in the geological
history of the mammals, as for instance in the horses,
camels and hyaenas. It is a series of types which
differ only slightly from each other running, with
many side branches and ramifications, between two
extremes which are widely different.

Of the other breeds of dogs we may select the grey-
hounds, hounds, bull-dogs and pugs — the last two
from the mastiff stock — as representative types known
to everyone.

Early Developmental Stages, and Two Curious Animal Types

FOR an explanation OF THE FIGURES SEE P. 283

"^"^ THE NEW EVOLUTION '^^"^^

It is not necessary here to describe the diverse
bodily forms characteristic of these well known breeds
of dogs. But their mental traits call for brief
consideration. Viewed in relation to the structure
of these dogs, they are extremely interesting.

The greyhounds, or as they are sometimes called
the "gaze hounds," have deficient powers of scent,
but unusually keen eyes and ears. They hunt entirely
by sight. The hounds have poor sight, and hunt
almost exclusively by scent. Bull-dogs are deficient
both in sight and scent and are stupid and ferocious,
displaying little affection. Pugs, which are much
like bull-dogs and are equally stupid, differ markedly
from them in being both timid and affectionate.

Now although the early history of the domestic
dogs is involved in complete obscurity since the com-
panionship of dogs and man runs back into the Stone
Age, far beyond the first beginnings of history, it
seems to be quite clear that certain types of dogs, at
least, appeared as wide and abrupt departures from
parents of a very different bodily form and with
widely different mental traits.

We seem to be quite within the facts in stating that
the bull-dogs, the pugs, and the strange hairless dogs
appeared suddenly as anomalous types which, appeal-
ing to human fancy, have been perpetuated and their
peculiarities accentuated, or at least preserved, by
careful breeding.

The greyhounds existed in the typical form in the
early days of ancient Egypt, and the modern hounds
go back to the later days of the Roman empire, so

ZOOGENESIS

we cannot make any really definite statement about
their ancestry.

But regarding bull-dogs, pugs and hairless dogs we
can say with reasonable certainty that they do not
intergrade, and also that there are now no intergrades,
and there never have been any intergrades, between
these and any other types of dogs, or wolves.

They therefore furnish an excellent and obvious
illustration of unbroken continuity of descent, from
wolves through other types of dogs, which is coupled
with abrupt change or discontinuity in bodily form
and in mental attributes. So far as we know, the
greyhounds, the hounds, and many other forms of
dogs had a similarly abrupt and discontinuous origin.

The question naturally arises, is it permissible to
use the domestic dogs to illustrate the course of
animal evolution during geologic time?

It is generally agreed that the changes in animal
life which took place from one geological epoch to
another occurred as a response to changes in the en-
vironment of the animals concerned — in other words
to changes in the conditions any given animal type
was forced to meet. Varieties or forms which were
best suited to meet the new conditions survived, and
the rest died out. The successful varieties or forms,
in the absence of competition, branched out into many
different forms which became more and more distinct
from each other until, with further geological
changes, most or all of these died out.

Domestication means a change in the environment
of all animals which are subjected to its influence.

[187]

"W THE NEW EVOLUTION

Biologically considered, all changes in environment
are strictly comparable whether they be brought
about by geological processes affecting large areas,
or by domestication affecting relatively small groups
of individuals.

Furthermore, there is no tangible difference betw^een
the natural elimination, by the agency of enemies or
through disease or other causes, of all the individuals
of a certain type of w^olf which are unfitted to cope with
their environment, and the development of a special
breed of domesticated dog through the elimination of
all the individuals that do not come up to the standard
set by the dog breeder.

To say that the evolutionary plan which is illus-
trated by the dogs is not comparable with the evolu-
tionary trees evidenced by the fossil animals is to deny
a similar effect as the result of similar causes. If,
however, we admit the validity of the comparison,
we at the same time admit the natural occurrence of
broad and striking gaps or discontinuities in evolu-
tionary lines.

Unbroken continuity of descent coupled with
abrupt discontinuity or change in bodily form is a
common, striking, and well known phenomenon in
all types of animal life. It is far more striking among
the invertebrates than it is among the vertebrates.

[i88]

01^/! l\siS^ )^^%/!( sV^t^/lf l\^^^ )\3J|

CHAPTER XX

THE ORIGIN OF THE EARLIEST ANI-
MALS—EOGENESIS

THE third of the three sets of facts to be con-
sidered in connection with the development of
animal forms is perhaps the most puzzling and
the most extraordinary. It has always been the chief
obstacle in the way of the successful development
of a theory of evolution which shall assign to every
animal type a fixed, definite and logical position in
relation to every other animal type.

No matter how far back we go in the fossil record
of previous animal life upon the earth we find no
trace of any animal forms which are intermediate
between the various major groups or phyla.

This can only mean one thing. There can be only
one interpretation of this entire lack of any inter-
mediates between the major groups of animals — as
for instance between the backboned animals or ver-
tebrates, the echinoderms, the mollusks and the
arthropods.

If we are willing to accept the facts we must believe
that there never were such intermediates, or in other
words that these major groups have from the very
first borne the same relation to each other that they
bear today.

Is this creationism? Not at all. All living things
are derived from other living things. Furthermore,

^^ THE NEW EVOLUTION "^^"^

all types of animal life must be explained in terms of
a primitive single cell. The seemingly simultaneous
appearance of all the phyla or major groups of ani-
mals simply means that life at its very first be-
ginnings developed at once and simultaneously from
the primitive single cell in every possible direction,
giving rise to some original form or forms in every
phylum.

So at its very first appearance animal life assumed
essentially the same form as that in which we know
it now so far as the phyla or major groups of animals
are concerned. That is, at the very beginning there
appeared a representative or representatives of the ar-
thropods (figs. 7-32., pp. zi, 33, 47 and 55), the jointed
worms or annelids (fig. 85, p. 161), the mollusks (figs.
45-51, p. 97), the arrow-worms or chastognaths (fig.
Gz, p. Ill), and so on. There is no evidence whatever
that would lead us to believe otherwise.

As age succeeded age the forms within these major
groups underwent constant and continual change.
For instance, in the arthropods the trilobites (fig. 31,
p. 55) and the eurypterids (fig. 31, p. 55) increased in
diversity and then died out, giving place to a wealth
of other types developed from other lines within the
phylum. But the characteristic features of the phy-
lum as a whole remained unchanged.

Thus the evolutionary picture that we get from a
survey of the actual facts is that at the very first there
were numerous basic forms from each of which a
separate evolutionary tree arose growing upward
through the ages. The topmost twigs of each of

[190]

ZOOGENESIS

these evolutionary trees end in the numerous forms of
animal life we know today.

What was the origin of these basic forms of life,
and how did the original representative or representa-
tives of each of the several phyla or major groups of
animals come into existence?

All animals have the body composed either of a
single cell, or of a multitude of cells all of which are
essentially the same in structure. Furthermore, all
animals in which the body is composed of numerous
cells begin their independent life as a single cell,
which divides into two, four, eight, sixteen, and so
on, until the full number of cells is reached (figs.
110-117; 1x1-1x5, p. 185).

Since all animals, no matter what they are, begin
life as a single cell, it is clear that all animal forms
must be interpreted in terms of a primitive single
cell.

A single cell cannot increase in size beyond a certain
point without serious interference with the chemical
and physical interchanges on which life depends. On
reaching the maximum size permitted by the chemical
and physical restrictions, the animal cell divides
into two; later these two cells each divide into two,
becoming four, these four become eight, these eight
sixteen, these sixteen thirty-two, and so on in-
definitely (figs. 110-117, p. 185).

In this process of division there are three paths that
may be followed (fig. A, p. 2.38). As they divide the
cells may separate from each other so that the indi-
vidual animals always remain composed of a single

^M THE NEW EVOLUTION '^^^''

cell. In other words, on the division of the original
cell into two each of these halves may separate from
the other and become a separate animal with half the
bulk of the original. Further division would giYC
rise to a corresponding number of entirely separate
animals. The so-called single-celled animals or pro-
tozoans (fig. 87, p. 161) illustrate this process.

But after the division of the original cell into two,
four, eight, sixteen, and so on, the cells resulting
from division might remain in contact, eventually
forming a body consisting of vast numbers of cells.
Here there are two alternatives. The cells may
adhere more or less irregularly (figs. 1x1-1x5, P- ^^s)
so that a poorly differentiated mass of cells results,
the mass as a whole being more or less distinctly
radial in its symmetry. The result of such develop-
ment is represented by the sponges.

On the other hand, the adhesion of the cells may
take place in a regular geometrical fashion (figs.
110-117, p. 185) until a hollow ball of cells (called a
blastula; figs. 114, 115, p. 185) is formed which, by
collapsing like a rubber ball with one side pushed in,
would form a two-layered cup (called a gastrula;
figs. 116, 117, p. 185) with an axis passing through the
center of the opening and of the opposite pole, and
the walls the same in all the radii.

We know that all animals begin life as a single cell
which divides into two, and these derivatives con-
tinue to divide in the same way. We see that this
continued division of the cells takes three different
lines. The cells resulting from the divisions may (i)

[192-]

^1^ ^OOGENESIS ^1^

separate completely, (x) adhere irregularly, or (3)
adhere in regular geometrical fashion.

There is no reason for believing that these three
paths of development w^ere not follov^ed simultane-
ously— that is, that animal life did not from the very
first develop in three divergent w^ays (fig. A, p. ^38).
There is no logic in the assumption that the earliest
animals were necessarily of the single-celled or pro-
tozoan type. All of the single celled animals that
we know are quite as highly specialized as are any
other animals, though they are specialized in a wholly
different way.

While it is most reasonable to suppose that all
three alternatives were realized from the very start,
if any one of the three alternatives were to precede
the others it would presumably be the development
of a more or less formless sponge-like mass from which
on the one hand single-celled creatures were derived
through a complete separation of the cells after divi-
sion, and on the other hand the structurally more
complex animals were derived through the arrange-
ment of the cells as they divided in regular geo-
metrical fashion. The almost complete individuality
of certain cells in sponges and especially the behavior
of dissociated sponge cells would seem to support this
view. But the most probable supposition is the
simultaneous appearance of all three lines of devel-
opment from the primitive single cell.

We have seen that regular adhesion of cells after
division in geometrical fashion results in the forma-
tion of a two layered cup called a gastrula (figs. 116,

[193]

^^ THE NEW EVOLUTION "^^"^

117, 119, p. 185), which is radially symmetrical about
its only axis. If the gastrula should continue its
development to the adult stage, following to its
logical conclusion the preceding line of geometrical
development, the result would be an animal radially
symmetrical in form with the body composed of two
layers of cells. Such an animal type we actually
find in the sea-anemones, hydras and allied creatures
— the so-called coelenterates (figs. 3, 4, p. 5; figs. 78,
79, p. 143).

But during the development of the gastrula some
irregularity might appear which would disturb the
fundamental radial symmetry either partially or com-
pletely, leading to the development of animal types
more or less elongated in form and with, instead of
radial, bilateral symmetry — that is, with the two
halves the same on either side of the central plane
(see figs. B, C, D, pp. 140, 146, and 2.50).

Excepting for the protozoans, the sponges, the
coelenterates, and the ctenophores, all animals are
either completely bilaterally symmetrical, or the body
is mainly bilaterally symmetrical with more or less
marked traces of radial symmetry. Furthermore,
during their development they all pass through a
stage which is either a more or less typical gastrula
(figs. 116, 117, p. 185), or may be interpreted as repre-
senting and derived from the gastrula. No matter
how different they may be, the gastrula is common to
them all. They all develop in comparable fashion
as far as the gastrula, but from that point they all
diverge, each in a different direction.

[134]

dS! ZOOGENESIS ®l|

This divergence, however, is not haphazard, but
on the contrary runs in certain very definite lines
resulting in the production of a series of animal types
each of which bears a definite relation to all the rest
(figs. B, C, E, pp. X40, 146, and 2.54).

The key to this relationship is furnished by four
curious groups of forms having a symmetry which is
partly radial and partly bilateral (fig. E, p. 2.54).

These four groups are made up of:

I. Types which by continuous budding produce a
linear colony;

-L. Types in which the budding takes place inter-
nally within the original unit;

3 . Types which are solitary, each individual repre-
senting a single dissociated coelenterate unit; and

4. Types which are colonial, though the indi-
viduals are independent of each other.

Between each two of these types there is another
type which combines the characters of both, but
shows no trace of radial symmetry.

Thus between the types which by continuous bud-
ding produce a linear colony and the types in which
the budding takes place internally we find a type
which is segmented externally and also possesses
internal (coelomic) budding. Between the types in
which the budding takes place internally within the
original unit and the types which are solitary, each
representing a single dissociated coelenterate unit, we
find a type which is solitary with internal budding
but no segmentation, and so on.

On the basis of their fundamental characters all of

[^95]

^^^^ THE NEW EVOLUTION ®l

the animal phyla or major groups may be arranged in
five successive series of four each, the outermost four
being the four partially radial types mentioned. The
exact center of the figure is occupied by the verte-
brates, which combine the characters of the four
groups immediately surrounding them (cephalochor-
dates, balanoglossids, cephalodiscids and tunicates)
but are not more closely related to any one of these
than they are to the other three (fig. E, p. 2.54).

Such a figure shows each phylum as related more or
less equally to four others, and more distantly to all
the rest. As we pass from the outer to the inner
series we find that the phyla become more and more
complex and, because of their increasing complexity,
seemingly less and less widely differentiated from
each other.

But how could such a curiously complicated inter-
relationship come into being? How could any single
type of animal be related more or less equally to four
others, and why should the more complexly organized
types — the cephalodiscids, balanoglossids, cephalo-
chordates, tunicates and vertebrates — be less widely
different from each other than the more simply or-
ganized types?

The answer is a simple one. Since we have not the
slightest evidence, either among the living or the
fossil animals, of any intergrading types falling be-
tween the major groups it is a fair supposition that
there never have been any such intergrading types.

We find twenty definite structural complexes which
are apparently without any direct relation to each

[196]

^^^^ ZOOGENESIS ©ll

other. All, however, as well as the coelenterates, are
derived through a gastrula stage or its equivalent,
which is the last stage common to them all.

Nothing exactly comparable to a gastrula exists as
an adult animal. It is true that all the coelenterates
are essentially adult forms reducible to a gastrula,
but all of them are developed very far beyond the
gastrula. The coelenterates are probably to be con-
sidered as having progressed quite as far beyond the
gastrula as the bilaterally symmetrical animals, al-
though they retain the original symmetry of the
gastrula sometimes quite unmodified, but usually
slightly modified (fig. B, p. 140) .

In the coelenterates the body symmetry always
remains essentially that of the gastrula no matter
how far development in other lines may go. But in
all other types which are derived through a gastrula
the body symmetry changes over from the radial
symmetry of the gastrula to a different, usually a
bilateral, symmetry during the course of the develop-
ment from the gastrula to the adult.

In the bilaterally symmetrical animals during the
course of the development from the gastrula to the
adult profound modifications in the internal structure
occur and these follow a different and divergent path
in each of the seventeen major groups of animals
concerned.

In none of these seventeen major groups of animals
is there any indication of a cessation in the course of
the development between the gastrula and the adult,
except for the appearance in most cases of a special

[197]

^^^^ THE NEW EVOLUTION '^^'^'^

larval type which is almost always adapted to insure
the wide distribution of the species . The unescapable
inference is that the balance of the internal organs
during this time is not of such a nature as to render
possible the existence of such forms as adults.

Besides this, the fact that successful development
from the gastrula to the structural complex character-
istic of each major group always follows certain defi-
nite lines which, though they may be greatly short-
ened, are always undeviatingly the same, would seem
to indicate that development outside of or between
these lines would result in structural complexes which
would be incapable of meeting successfully the con-
ditions of existence. Many gastrulas develop in va-
rious abnormal ways, but these always die.

The picture that we get of the developmental
history of animals through the study of comparative
embryology is that there is not now, and there never
has been at any time, any possibility of the existence
of economically possible animal types anywhere along
the line between a gastrula and the several structural
complexes characteristic of the coelenterates and the
bilaterally symmetrical major groups.

The natural conclusion is that the original forma-
tion of the original members of these groups resulted
from divergencies in early embryonic stages which
followed simultaneously every separate line which
could lead to an economically possible adult.

Such lines are limited in number, and for that reason
we see the major groups curiously few when we con-
sider the enormous multiplicity of minor types within

ZOOGENESIS

these major groups in the larval as well as in the
adult stages.

It is an interesting fact that the embryological
development of the cephalochordates, balanoglossids,
cephalodiscids, tunicates and vertebrates indicates a
close relationship between these five groups, which
are commonly referred to as the chordates and the
protochordates.

This indicates that the increased structural com-
plexities of these groups do not permit of much
deviation from a general mean. It cannot be inter-
preted as indicating that these five groups were ever
more closely related than they are now, or that any
one of them was derived through or from any of the
others. Each represents a separate and distinct path
from the gastrula, though these paths are but little
divergent.

According to this interpretation the various phyla
of bilaterally symmetrical animals are in effect recom-
binations of features which are inherent in animals
taken as a whole, or in other words recrystallizations
of the fundamental features of animal organization,
which occur at every focal point where an animal type
capable of existence may be formed from the elements
available in the general animal complex.

No appreciable time element is necessarily involved
in such a process of recombination or recrystalliza-
tion of fundamental animal features. Therefore at the
very first appearance of life the animal world, so far as
the phyla or major groups of animals are concerned,
probably was quite the same as it is today.

[199]

$M THE NEW EVOLUTION T"^^

The figure formed by this recombination of ele-
mental structural features into the various phyla repre-
sents the basic picture of animal life — a flat picture
with all its details of simultaneous appearance — in
which all of the evolutionary trees are rooted and
from which they rose, one from each phylum, upwards
through successive ages.

The interpretation of the origin of the major groups
or phyla as the result of recombinations — or varying
combinations — of characters inherent in animals as a
whole which took place in early embryonic stages
supplies the key to the very sharp distinctions usually
to be seen between the different classes in each phylum.

It has been mentioned that among the major
groups the cephalochordates, balanoglossids, cephalo-
discids, tunicates and vertebrates are rather more
closely related to each other than are the remaining
major groups.

These five phyla form an assemblage capable of
definition as a unit — though a very heterogeneous
unit — which to a certain extent is intermediate in
character between a collection of five major groups
and a single major group alone.

As a typical major group let us take the echino-
derms. The echinoderms agree among themselves,
and differ very markedly from all other animal types,
in being coelomate creatures with a fairly perfect
radial and usually pentamerous symmetry, with a
body wall containing calcareous plates and generally
armed with spines, with the coelome divided into two
well marked portions, the perivisceral cavity and the

[zoo]

MM ZOOGENESIS W§i

water vascular system, and with the gonads not con-
nected with the coelome in the adults. The young
larvas of all echinoderms are always bilaterally sym-
metrical instead of radially symmetrical, and are
almost always free-swimming.

The echinoderms are divided into five classes, the
sea-urchins, holothurians or sea-cucumbers, starfishes,
brittle-stars, and crinoids (sea-lilies and feather-stars)
and their allies. These five classes are entirely and
widely distinct from each other and do not intergrade.
So far as we know there never have been any inter-
grades between them. From time to time various
attempts have been made to construct evolutionary
trees which shall account for the peculiarities of these
several groups by reducing them to a hypothetical
ancestor. But these attempts have simply served to
emphasize the complete distinctness of the creatures.

The development of the feather-stars differs very
considerably from that of the forms included in the
other classes. The divergence begins with the com-
plete formation of the gastrula, and rapidly increases.
Almost immediately afterwards the embryonic stages
of the other classes begin to diverge, and as develop-
ment goes on they diverge more and more widely.

So in the echinoderms the only relationship be-
tween the five included classes is found in the embry-
onic stages immediately following the gastrula. As
it is impossible to assume that these stages could ever
have led an independent existence as adult animals, so
it is impossible to assume that any adults ever existed
which were intermediate between these five classes as

[lOl]

^'^ THE NEW EVOLUTION ^|^

we see them now and as they are represented in the
early fossils.

The principle of recombination of characters in the
echinoderms as a whole, this recombination taking
place at very early embryological stages, seems ade-
quately to explain the sharp distinctions or very
broad mutations between the starfishes, brittle-stars,
sea-urchins, sea-cucumbers, and the crinoids and
their allies.

In exactly the same way we may explain the sharp
distinctions between the gastropods, bivalves, scaph-
opods, cuttle-fish and other types among the mol-
lusks, and between the crustaceans, spiders, insects,
centipedes and other forms in the arthropods.

Coming down to finer divisions, divergence in
relatively late embryonic stages would serve to ex-
plain the curious isolation of the skippers (Hesperioi-
dea) in the butterflies, and divergence in still later
embryonic life the sharp difference between the mega-
thymids and the other skippers.

If the conclusion be justified that each phylum or
major group of animals represents the natural end
product of a special type of cell division, and that
all these special developmental lines leading from the
single cell to the different phyla appeared concur-
rently, resulting in the simultaneous formation of
some representative or other in all the major groups,
there should be further indications pointing in the
same direction.

We have traced a hypothetical course of develop-
ment from the single cell to each of the various major

[i02.]

Various Types of Animal Life
for an explanation of the figures see p. 28

^1^ THE NEW EVOLUTION "^^^^

groups. Now let us see what may be ascertained by
an analysis of animal forms.

From the study of the development of animal forms
as they are preserved in successive geological deposits
we learn that after a special line of development begins
the types involved always increase in their degree of
specialization. They divide into various subtypes
each of which becomes more and more specialized,
and these may again divide. Finally the end branches
one after another, or sometimes simultaneously, come
to an end and the type becomes extinct.

An excellent illustration of this is seen in the horses,
the tree-like figure rising from the little Eohippus as
a base and giving off a great number of increasingly
specialized branches ending in still more specialized
twigs about ten of which (the wild horse, the wild
donkeys and the zebras) still are to be found in Africa
and in Asia while the rest are all extinct.

At the base of every branching line of progressive
specialization — or developmental tree — we find a type
or form which in its structure includes all of the
features found collectively in all the later types.

Specialization, or developmental progress, is a
matter of subtraction and modification — never of addi-
tion. No structure lost ever is replaced.

Thus Eobippus, with four toes on the fore feet and
three on the hind feet, was succeeded by other horses
with three toes on all the feet. In still later horses
the middle toe increased, while the lateral toes de-
creased in size. Finally we have the living horses
with a single toe on all the feet.

[2.04]

200GENESIS

The development of animal forms, as we learn from
a study of the fossils, is not a reversible phenomenon.
Once specialization has begun it always continues —
by a process of progressive modification and subtrac-
tion— in the same general direction, becoming more
and more extreme. There is never any retrogres-
sion.

Heretofore this principle has been applied only to
more or less restricted groups of animals. But there
is no reason to suppose that it is not applicable to
animals as a whole.

If we attempt to apply it to animals as a whole —
that is, to the various major groups or phyla — we at
once discover some most interesting facts. Most
important of these facts is that we find it wholly
impossible to arrange the phyla in any sort of a line
showing progressive subtraction and no addition —
such a line as is so evident, for instance, in the horses.

Each phylum includes animals of a definite struc-
tural type of complex which is widely different from
the structural type or complex characteristic of the
animals in every other phylum. These structural
complexes characteristic of the several phyla differ
from each other by modification of fundamental
structures, including the addition of some features and
the subtraction of others.

Thus the echinoderms have acquired a radial sym-
metry apparently through the subtraction or loss of
half of each segment of the body, and in addition have
lost the nephridial system — at least in its usual form
— and all trace of chitinous structures; the annelids

[105]

$M THE NEW EVOLUTION '^'^

or jointed worms have lost all traces of an internal
calcareous skeleton, a structure very highly developed
in the echinoderms ; the mollusks are almost entirely
w^ithout a trace of segmentation; vv^hile the arthropods
are w^ithout a perivisceral coelome or internal cal-
careous structures, and their endoderm and excretory
organs are very much reduced.

There can therefore be no relationship whatever
between the developmental figure represented by the
horses from Eohippus to the modern type and the
figure representing the interrelationships of the sev-
eral phyla.

Since both addition and subtraction are involved
in the differences between the phyla we must believe
— if we are to be consistent — that all of the various
phyla are on the same developmental plane, or in
other words that they came into existence through
derivation from a common ancestor or ancestral type
which was possessed of the potentiality for producing
each and all of them.

To express this in concrete terms, it is impossible
to believe that the echinoderms, lacking half of each
body segment and a nephridial system, the annelids,
with no trace of an internal calcareous skeleton, the
mollusks, without segmentation, or the arthropods,
without a perivisceral coelome or an internal cal-
careous skeleton, can represent steps along a develop-
mental line running to the vertebrates in which the
body segments are composed of two similar halves
one on either side of the midline, in which there is
always an elaborate nephridial system, in which there

[2^06] ~

^^"^ ZOOGENESIS "^^"^

is an internal calcareous skeleton, and in which there
is always a perivisceral coelome.

Any assumption that the various invertebrate phyla
represent steps in the development of the vertebrates
must rest on the flat denial of the developmental
truths which are so clearly evident within each of the
larger phyla.

So through the application of a principle derived
from the careful and detailed study of the past history
of animal types within the phylum we reach the con-
clusion that the phyla themselves must have origi-
nated quite independently of each other from a com-
mon source. In other words, by the application of
this principle we find indubitable indications of the
origin of the various phyla through eogenesis.

[2-07]

O^y^t) (VO*^/J) tv<^^>D (t<^^>D tTN>^>r (V^^/^/d tw^/Vr (^<^^/75 (TvTvrvr («<v/Vfi (T<>/r.

?iSX< >i3t^ ^y^l^ f*^3C*< XR*!^ )^^%lA )^i%lA )^i%iA ^VSl?

CHAPTER XXI
SUMMARY

PREFACE. — The more we learn of the world in
which we live the more clearly do we see
that an orderly and definite plan underlies
and dominates all the phenomena of nature. The
living world of animals and plants is no exception.
It is not chaotic. To picture it as chaotic is simply
to confess our ignorance. What, then, is the plan
upon which the living world is based? What is
the relationship between the various types of liv-
ing things?

Four different problems are involved in the answer
to this question. F^rsf, how and in what form did
animals first appear? Second, what has been the his-
tory of animal life from its first appearance to the
present day? Third, how do animal forms giYC rise
to other and different forms? Fourth, what is the rela-
tionship of man to the living world?

Before taking up these problems let us review the
evidence which leads us to believe that these questions
can be answered. We know that some definite rela-
tionship exists between the different types of animals
because of two important facts.

In the first place, all living things arise only as the
children of other living things. This rule has no
exceptions, and it is inconceivable that there should
be exceptions. Since all living things arise only from

[2.08]

ZOOGENESIS

other living things, it naturally follows that all the
present life upon the earth is descended from other
life that flourished in the ages that are past, and that
from still earlier life, and so on back to the time when
life first appeared.

In the second place, all living things, no matter
what they are, begin their life as a single cell in which
no trace whatever of the adult form is discernible,
and all germ cells no matter from what form of life
they are produced are alw^ays strictly comparable.
The bodies of all living things are composed either of
a single cell or, more commonly, of vast numbers of
cells which are all alike in their fundamental struc-
ture. No matter how many cells there may be in
the body of an animal, and no matter how diversified
they are, all of the cells in any individual arise
through the division of the original germ cell.

So as the starting point for our search for order in
the living world we hsivc first the unbroken continuity
of life from the very earliest times until the present
day, and second the necessity of interpreting or explain-
ing the origin of all forms of life in terms of the
single cell.

These two important facts, the unbroken continuity
of life and the necessity for explaining and interpret-
ing all forms of life in terms of the single cell, must be
considered in their relation to the further obvious
fact that all living things must eat. The single cell
in order to grow and to develop and to produce other
cells must be supplied with food, and the continuity
of life from one generation to the next indefinitely is

[2.09]

%M THE NEW EVOLUTION ®^

dependent on a similarly unbroken continuity in the
supply of the necessary food materials.

Therefore in a consideration of the living world it
is essential to understand the origin of the food which
supports the animals and plants and also the widely
varying conditions under which that food is offered.
For without a proper appreciation of the setting in
which the development of animal forms took place
any discussion of the subject becomes mere futile
speculation.

Eogenesis. — From the air, the water and the rocks
do all living things secure those substances which are
necessary for their existence and their increase. Ever
since life first appeared on earth rain has been falling
on the land and the water, heat and cold have been
weathering away the rocks, and from them liberating
those substances necessary for the support of life in
the same way that it is being done at the present
time.

We cannot deny this without at the same time deny-
ing the validity of the comparisons between the geo-
logical processes of the present day and the geological
processes of the past, comparisons which furnish the
only clue to the interpretation of the latter.

Since the conditions on the earth, in so far as they
affect the basic food requirements of plants and ani-
mals, to the best of our knowledge and belief have
remained unchanged from the very earliest times at
which we may assume that plants and animals existed,
is it not reasonable to suppose that in its broader
features the world of animals and plants has from the

[2-10]

ZOOGENESIS

very first been essentially the same? The probabili-
ties are in favor — overwhelmingly in favor — of the
simultaneous development of some representative or
representatives of all, or practically all, of the phyla
or major groups of animals at the time of the very
first appearance of life.

The only acceptable hypothesis is that in its broader
features the development of animal forms took place
by concurrent evolution.

All of the actual evidence we have supports this
supposition. This evidence comes from the fossils
that we find in the very earliest rocks wherein fossils
are satisfactorily preserved. Practically all these fos-
sils are more or less widely different from the corre-
sponding animals we know today. But we recognize
them for what they are because they fall within the
definitions of their respective groups, and these defini-
tions are drawn up from a study of their living repre-
sentatives alone.

The recognition of these fossils as members of cer-
tain groups through the application of definitions
based on living animals alone means that from the
very earliest times of which we have a record the
broader features of the animal life upon the earth have
remained unchanged. So from all the tangible evi-
dence that we have been able to discover we are forced
to the conclusion that all the major groups of animals
at the very first held just about the same relation to
each other that they do today.

How may the simultaneous appearance of all the
major groups of animals be harmonized with their

^^ THE NEW EVOLUTION ^^

common origin involving unbroken continuity of life
from parent to child from a primitive single cell?

Applying the knowledge that we have of the subject
of embryology — of the earlier stages in the develop-
ment of different types of animals — we may assume
without the possibility of successful contradiction
that all of the major groups of animals were formed
at the same time as the result of following different
developmental paths from the primitive single cell.
No other reasonable conclusion can be drawn from the
facts of embryology. There is no evidence of any
kind which would lead us to suppose that any one
of the major groups was derived through any of
the others.

On the contrary there is strong circumstantial evi-
dence which indicates that none of the major groups
could have been derived through any of the others.

A study of the developmental lines of animals
shows that developmental progress is always evi-
denced by increasing specialization along definite
structural lines at the expense of other structural
features. Organs may gradually become reduced and
perhaps disappear, but nothing is ever added. Spe-
cialization is always a matter of subtraction from a
well balanced whole. Such subtraction once started
may continue, or it may cease, temporarily or per-
manently. But a structural feature that has once
begun to lose importance and to dwindle never
reverses the developmental path; it never recovers any
of its lost significance.

All of the major groups of animals differ from each

[ill]

^^ ZOOGENESIS ^^

other both in the reduction of some of the bodily
structures and in the very great development of others.
Thus they differ from each other both by subtraction
and by addition. To assume that any of the major
groups are derived from any of the others is therefore
to deny the general application of a well estab-
lished principle.

Another factor which probably has a bearing on
the question of the simultaneous development of the
major animal groups is the necessity for the main-
tenance of a balance between the different forms of
life. The necessary check on the excessive increase
in the numbers of any type of animal is provided by
predacious animals, by parasites, and by various
types of animal feeding plants, principally bacteria
and fungi. It is impossible to believe that such a
check was not as essential at the time of the first
appearance of life as it is today.

The process leading to and resulting in the first
appearance of some representative or representatives
of each of the major groups may be known as eogenesis.

Evolution. — We come now to the second question,
what has been the history of animal life from its first
appearance to the present day?

The various types of animals included in each single
one of the larger major groups — for instance in the
vertebrates or backboned animals, the mollusks or
the arthropods — have varied very greatly in succes-
sive geologic ages. This is shown conclusively by a
study of the fossils. If the broader aspects of the
living world have from the first remained unchanged,

MM THE NEW EVOLUTION ®^

why should we find such extraordinary changes in
the details in successive ages?

The answer is a simple one. While all the food
substances necessary for the support of animal life
have been available from the first, the conditions
under which these food substances were available have
varied very greatly from one epoch to another. For
instance, at one time the earth was largely cloud
enveloped. The light was relatively dim, and the
temperature was about the same almost everywhere.
The winds were light, so that the seas were calm
and quiet.

Living under these conditions were representatives
of all the major groups we know today. But the
representatives of the major groups which flourished
at that time were quite different looking creatures
from the types we know at the present day. The
problems which they had to meet in securing food
and in avoiding enemies — in the struggle for existence
— were very different from the problems which must
be met by their modern representatives. A cloud
enshrouded world of about the same temperature
everywhere with only light winds and with almost
waveless seas is a very different thing from the world
of the present day.

The changes in animal life from age to age for the
most part took place according to a definite plan or
system. A small and inconspicuous creature in one
age was succeeded in the next by several more spe-
cialized and often larger creatures, and these were suc-
ceeded by many still more specialized, and so on,

^^ ZOOGENESIS ^1^

until the whole strain gradually or suddenly died out.
In the larger major groups this process occurred at
the same time, or at different times, in many dif-
ferent types.

Such a developmental or evolutionary process is
well represented by a branching or tree-like figure in
which each branch end represents a special line which
has become extinct. An excellent example of this is
seen in the developmental history of the horses.

This process of branching or tree-like development
of many different animal forms from a single original
type — as for instance the development of all the dif-
ferent kinds of dogs we know today from the original
wolf — is commonly known as evolution.

Eoge7iesis and evolution. — What is the relation of evo-
lution to eogenesis — the simultaneous formation
through following different developmental paths from
the primitive single cell of all the major types of
animals?

Through eogenesis the ground is prepared for the
growth of the evolutionary trees. Therefore the pic-
ture that we get shows a whole forest of evolutionary
trees of widely different sizes each of which arose
from a seed formed and planted by the process of
eogenesis.

Broader aspect of the development of animal forms. — The
evolutionary processes by which are formed the ulti-
mate twigs of the various evolutionary trees are
processes of specialization through the progressive
suppression of certain features, leading secondarily
to the emphasis of others. The more extreme the

THE NEW EVOLUTION

specialization in any animal type the more has it
departed from a zoologically normal balance. The
primitive types in all the major groups are those in
which the most perfect balance between all the struc-
tural features is maintained.

The several major groups exhibit a great variety
of conditions in the relation of their different struc-
tural features to each other; they show a very different
balance in their various essential organs. In their
embryonic stages the representatives of the various
major groups show a close approximation to each
other in the gastrula, but are wholly similar to each
other only in the germ cell.

Thus the only fact of cosmic significance in the
whole subject of evolution in its broadest sense is the
appearance of the single cell. The single cell has
inherent in itself the potentiality for development,
through selective and progressive reduction in various
directions and in various ways, into every form of life
which at any time may be capable of existence and of
self-perpetuation under the conditions obtaining at
that time.

All animal types are therefore to be regarded, in
their relation to cosmic evolution, simply as varied
and varying manifestations of the inherent potentiali-
ties of the fundamental substance protoplasm. Such
a concept contemplates the animal world as in reality
but a single unit finding its expression in an infinity
of equations all of which, no matter how complicated
they may seem, reduce themselves to the same funda-
mental term.

il^ ZOOGENESIS '^ll

If the animal world is fundamentally but a single
unit, definite evidence of that fact should be available.
We find the evidence in the ability of each and every
type of animal, no matter w^hat its structure or its
form, to maintain itself equally well in the face of
widely varying, though always ruthless, competition.
Further evidence of the fundamental unity of animal
life is seen in the recurrence of similar forms in crea-
tures of widely different structure whenever because
of a difference in size, or for other reasons, there is no
direct competition, and also in the frequent occurrence
in so-called abnormal or aberrant individuals of fea-
tures normally characteristic of animals of a widely
different type. More tangibly we find it in the recur-
rence of comparable and similar attributes in widely
different types of life when they are faced with similar
conditions. There is no other possible explanation
for the reappearance of such striking similarities as
those which are found in insects, in the small birds,
in the rodents, and in man.

Mutations. — The third question to be answered is,
how do animals change their form? The three factors
immediately involved in the production of new animal
species or types are; first, the production of variants
or mutants; second, the hereditability of the characters
possessed by these mutants; and third, the ability of
such mutants as are able to establish themselves on an
hereditary basis to maintain and to perpetuate them-
selves under the conditions they must meet.

Most mutations arise during the formation of the
germ cells, and they are therefore already present in

^1^ THE NEW EVOLUTION

the germ plasm. An individual is marked as a
mutant at the time when the body is composed of only
a single cell. But sometimes mutations may appear
during the course of development.

Mutants — individuals differing from the normal as
a result of mutation — may show only a very slight
departure from the usual form of the animal con-
cerned, or they may depart so very widely that the
individual is incapable of development beyond the
earliest embryonic stages, or they may be of any inter-
mediate degree.

The mutations with which we are familiar among
the wild and domestic animals and in the laboratory
are all relatively slight, showing no very wide depar-
tures from the normal form. How, then, is it possible
to assume that mutation could account for such dif-
ferences as those between flies, butterflies and bees,
or between insects and crustaceans, or between the
crustaceans and the mollusks?

The more specialized an animal type becomes the
more inflexible and unchangeable does it become, the
more closely dependent upon the maintenance of con-
ditions as they are, and hence the more liable to
extinction if conditions change.

The reason for this is that specialization is a func-
tion of progressive subtraction. The more an animal
type has lost through this process of progressive sub-
traction, the less there remains for the production of
mutants which will be capable of existence. For all
mutants arise through the subtraction of something
from the usual form. In a very highly specialized

§&! ZOOGENESIS Wii

animal type subtraction has already progressed almost
to the extreme limit compatible with existence so
there remains very little that can be taken away with-
out endangering the life of the individual. Natu-
rally, therefore, the mutants with which we are
familiar at the present day differ relatively little from
the usual type. Yet rhinoceros mice, hairless dogs
and horses, and many other unusual creatures, show
how it is quite possible for new species and even
genera to appear in such a fashion as to give but
little indication of their immediate ancestry.

As we go further and further back in geological
time we find ourselves among the ancestral forms from
which the present highly specialized animals were
descended. The ancestral form from which any as-
semblage of animals is descended combines the char-
acters which are selectively distributed among the
descendants. For instance, in the ancestral wolf there
are combined all of the features which now are widely
distributed among the various breeds of domestic
dogs. Our different breeds of dogs differ from each
other not in the appearance of any new characters,
but in the selective suppression of characters through
which one or more special features are made to stand
out prominently.

The more well developed structural characters there
are in any animal type — in other words the better
and more complete the structural balance — the greater
is the possibility for the appearance of many widely
different economically successful mutants among its
descendants.

[2-19]

^^ THE NEW EVOLUTION f^~^'^

So it is a reasonable assumption that, although
those mutants capable of existence which appear
among the young of the animals of the present day do
not differ greatly from their parents, in the geological
past successful mutants differing very widely from
their parents would from time to time appear. And
the further we went back into the geological past —
the nearer we approached the bases of the evolu-
tionary trees — the greater would be the possibility
for the production of successful mutants varying
widely from the parent type.

The primitive single cell, having within the poten-
tiality for the production of all types of animals,
might be assumed to be possessed of the ability to
produce simultaneously mutants which would be
widely different from each other, both by structural
changes in the single cell and through development
involving cell multiplication in various directions.

From this it is apparent that from what we know
of mutants — especially as we see them in nature — and
from what we know of the development of animal
forms through progressively increasing specialization
we arrive at the conclusion that from the primitive
single cell there simultaneously appeared through
mutation as many different types of animals as were
capable of successful existence, while each of these
several types through progressive mutation in each
successive geological age branched out into every
economically possible form.

In other words the study of the possibilities of
mutation, combined with the study of progressive

[2.10]

^^^1 ZOOGENESIS W&l

Specialization, leads us directly to the original simul-
taneous appearance of the major groups through eogen-
esis and the subsequent development and refinement
of each through evolution.

The flat picture of animal life presented as the result
of eogenesis — v^^hich may be regarded as mutational
development from the primitive single cell — shows
many wholly distinct and separate major groups from
each of which a phylogenetic, developmental or evo-
lutionary tree rises upward through geologic time.

The larger phyla or major groups are divided into
classes, and as a rule the classes within each major
group are entirely distinct from each other and do
not inter grade. Thus in the mollusks we find pelecy-
pods or bivalves, scaphopods, solenogasters, gastro-
pods or snail-like creatures, and cephalopods. In the
echinoderms there are starfishes, brittle-stars, sea-
urchins, sea-cucumbers, crinoids, cystids and Mas-
toids. In the arthropods there are crustaceans,
arachnids, myriopods and insects. In the vertebrates
or backboned animals there are mammals, birds, rep-
tiles, amphibians and fishes.

The distinctness of these classes each from the other
is probably of the same nature as the much broader
distinctions between the various phyla. That is,
each class should be interpreted as a selective recom-
bination through broad mutations in every eco-
nomically possible form of the features inherent in
and distinctive of the phylum. In other words, it
is a fair assumption that the differences between the
several classes within each phylum are differences

[2.2.1]

^1^ THE NEW EVOLUTION ^|^

arising in the early embryonic stages of the animal
types concerned more or less immediately after the
fixation of the structural complex characteristic of
the phyla.

Within the classes the same phenomenon is again
repeated in a less extreme form in the different orders,
as is especially well seen in the insects, crustaceans,
gastropods and brittle-stars.

Abrupt discontinuities, becoming progressively less
and less pronounced, may be followed further into
suborders, families, genera and species, as we saw
(p. 133) among the butterflies.

Discontinuities of every sort, though often obvious
and striking, are very much less conspicuous and
marked within the phylum Vertebrata than they are
in the large invertebrate phyla. In the Vertebrata
even the classes are not always sharply distinguished
from each other. Thus many fossils cannot with cer-
tainty be determined as reptiles or as amphibians.
More or less intermediate between the birds and rep-
tiles are two curious creatures from the Jurassic which
figure together in text-books under the common name
of Archaopteryx. Similarly intermediate between the
mammals on the one hand and the reptiles and am-
phibians on the other are the strange egg-laying mam-
mals or monotremes of Australia and New Guinea.

The relative homogeneity of the phylum Vertebrata
is easily understood when it is realized that the
vertebrates are the most highly specialized of all
forms of animal life, and that the entire structural
range in all the vertebrates taken together is scarcely

[2.2.1]

^"^'"'I ZOOGENESIS ^1^

greater than the structural range in certain single
species of insects or of crustaceans at different stages
in their life history. The vertebrates possess such a
delicately balanced complexity of internal structure
and, partly as a result of their large size, such a deli-
cate adjustment to their environment, that changes
brought about by a continuous series of slight altera-
tions and progressive minor readjustments are more
suited to them than the sudden wide and abrupt dis-
continuities so frequent in invertebrate types.

Because of their very high degree of specialization,
well marked and reasonably continuous evolutionary
lines are frequent among the vertebrates, and wide
discontinuities are relatively rare, while the reverse
is true in all the other phyla of comparable size.

That the gaps between the forms in individual
species and the wide discontinuities between the
several classes included in each of the larger phyla
are fundamentally of the same nature and differ only
in degree can scarcely be denied. The latter are to be
interpreted as having resulted originally from muta-
tions in creatures which were of a primitive nature and
therefore capable of producing young very widely dif-
ferent from themselves yet able to meet the require-
ments of existence.

The relationship of man. — Since he possesses a back-
bone and associated structures, man belongs to the
group of backboned animals or vertebrates, which
group includes the fishes, amphibians, reptiles, birds
and mammals . Within the vertebrates he is a member
of the group of mammals. Within the mammals he

[2.2.3]

^M THE NEW EVOLUTION ^l|

presents the greatest similarity to the anthropoid or
man-like apes of western Africa and southeastern Asia
— the gorillas, the chimpanzees, the orangs and
the gibbons.

Structurally and anatomically man is rather close
to these man-like apes. This is a readily demon-
strable fact which is quite beyond dispute. But it is
also beyond dispute that there is a sharp, clean-cut,
and very marked difference between man and the
apes. Every bone in the body of a man is at once
distinguishable from the corresponding bone in the
body of any of the apes.

Man belongs to the same division of the mammals
— the Primates — as the apes. But his similarity to
the modern apes does not imply any direct relation-
ship with them. Man is not an ape, and in spite of
the similarity between them there is not the slightest
evidence that man is descended from an ape.

The large anthropoid apes — the gorillas, the chim-
panzees and the orang-outans — are all very highly
specialized terminal twigs from the Primate stock.
They are so very delicately adjusted to their environ-
ment that they all are very difficult to keep in cap-
tivity. They represent a vanishing group all the
members of which are now restricted to very limited
areas, the orang-outans to Borneo and Sumatra and
the gorillas and chimpanzees to equatorial west
Africa. They thus have almost the same distribu-
tion as those curious lemuroids called the lorises
and pottos.

Man also is very highly specialized, though in

ZOOGENESIS

quite a different way. He also has become very deli-
cately adjusted to his environment. But in the case
of man this has been an asset instead of a liability as
it is with the great apes. Man has been able to over-
come the increasingly delicate adjustment to his en-
vironment by artificially creating for himself a special
environment in which he lives more or less completely
independent of his natural environment. For the
most part man grows his food and the materials to
make his clothing and other necessities, and he con-
trols the temperature in which he lives. Thus the
Esquimaux actually exist in a tropical temperature no
matter how low the temperature outside of their
thick clothing and their heated igloos may be.

As man and the man-like apes are both very highly
specialized, but are specialized in widely different
directions, we cannot suppose that either descended
from the other, or indeed that there really is any very
close relationship between them. The truth of this is
now very generally admitted by biologists.

Professor Henry Fairfield Osborn has pointed out
that while nature may transform an organ through
change of function, it can never restore a single lost
part, whether it be a lost tooth, a lost digit, a lost
ankle bone or rib, a lost tendon, or a lost nerve. The
evolution of anatomical or structural organs is never
reversible. By the application of this principle he
pointed out that the human hand could never have
reacquired the nerves, muscles, functions, freedom,
flexibility and separate innervation lost in the highly
specialized hand of the arboreal, or tree-living, apes.

[2-2.5]

^1^ THE NEW EVOLUTION ^^

The opposable human thumb could never have grown
out of the partly atrophied ape thumb.

Many other structural features tell the same story.
The more carefully we study the points of similarity
between man and the apes the more clearly do we see
and appreciate the importance of the differences be-
tween them. As Huxley truly said, the differences
between man and the apes are broad and striking.

From time to time various "missing links" sup-
posed to connect man with the apes have been de-
scribed. But from what has just been said it is impos-
sible to believe that such "missing links" ever
actually existed.

In a recent article on "missing links" Mr. Gerrit
S. Miller, Jr., the curator of mammals in the United
States National Museum, reviewed in great detail the
evidence and opinions regarding the "Java ape-man"
or "Trinil man" (Fithecanthro^us erectus) and the "Pilt-
down man" QEoanfbropus daivsont) which are the only
two finds that "can be seriously regarded as furnish-
ing . . . direct evidence of man's blood relation-
ship with animals resembling in some general manner
the present day gorilla and chimpanzee. ' ' Mr. Miller
concluded that while awaiting further discoveries
"we should not hesitate to confess that in place of
demonstrable links between man and the other mam-
mals we now possess nothing more than some fossils
so fragmentary that they are susceptible of being
interpreted either as such links or as something else."
So in the light of all the evidence available at the
present time there is no justification in assuming that

' [Hi]

^^^^ ZOOGENESIS '^^'^

such a thing as a "missing link" ever existed, or
indeed could ever have existed.

Yet since both man and the apes belong to the same
division of the mammals — the Primates — and we can-
not doubt the continuity of life from parent to child
from the very first, man and the apes must have had
at some time in the past a common ancestor.

Our know^ledge of man goes back only to the end
of the period — the Pliocene — just preceding the Pleis-
tocene or Ice Age at the furthest, and many authori-
ties believe that the earliest remains of man are not
older than the earlier portion of the Pleistocene.

In the case of the Piltdow^n man all authors agree
that the fragments of the brain case and the nearly
complete nasal bones are human. Sir Arthur Keith
v^rote that the brain case of v^hich the original frag-
ments formed a part was essentially the same as that
of modern man in both form and capacity, the capacity
being about 1,400 cubic centimeters. Others have
calculated the capacity as about 1,2.40, 1,100 or 1,170
cubic centimeters. In the case of the Trinil, Java,
remains, all authors agree that the skull cap is
strangely different from the corresponding part of
other known mammals, living and fossil.

This is all the tangible evidence we have regarding
early man. But the fragments of the brain case and
the nasal bones of the Piltdown find are sufficient to
indicate that man has been essentially the same since
about the beginning of the Pleistocene, or in other
words that the developmental histories of man and
of the anthropoid apes have run parallel, and have

[2-2-7]

THE NEW EVOLUTION ^^^

remained wholly separate, as far back at the very least
as the beginning of the Pleistocene.

This is important, for in the case of the horses the
various types found in the Pleistocene, though numer-
ous and varied, were all of the modern type, and the
same is true in the case of other mammalian forms.
So it is possible to assume that the developmental
history of man has run parallel to the developmental
history of other mammalian lines, as would naturally
be expected.

What, then, was the connection between man and
the other mammals, and when did man branch off
from the Primate stock?

Professor Osborn has pointed out that the geo-
logical period in which the various lines of mam-
malian development separated and radiated from each
other was the Eocene. "Even in Lower Eocene time
all the existing families of hoofed mammals, such as
the horses, tapirs, rhinoceroses and titanotheres (the
last all now extinct) had widely separated from each
other in tooth, limb, hand and foot structure. Be-
fore the close of Eocene time these branches were
further subdivided into forest-loving and plateau-
loving types; in every branch the forest-loving types
were stationary or regressive. Similarly, by the
close of Eocene time the mastodont and elephant
families are found widely separated into five greater
branches (in Oligocene time there were numerous
sub-branches and in Miocene time eighteen distinct
branches). In the succeeding Oligocene time we

discover a sharp and world-wide division between

__

^^^^ ZOOGENESIS T"''^

plateau-loving and forest-loving types; in the forests
remain all the backw^ard conservative types; on the
plateaus and uplands are found the alert, progressive,
forward-looking types, including all the long-hind-
limbed bipedal [tw^o legged] animals adapted to rapid
progression in an open or partly forested country.
It is no exaggeration to say that at the daw^n of
Oligocene time all the plateau-loving animals are
distinctly modernized both in habits and in bodily
proportions."

Professor Osborn asks, "Is it likely that the Pri-
mates alone escaped this divorce betv^een backw^ard,
forest-loving life and forv^ard, plateau, savanna and
upland life, especially as Eocene forest areas in every
continent began to contract and upland open plains
began to expand?"

It is difficult to see how anyone can take exception
to this reasoning. There are no grounds for assum-
ing that man offered an exception to the general truths
which we learn through the study of the fossil history
of the mammals as a whole. The conclusion that
man was man as early as the Eocene — as early as the
time of the little Eolnppus — has far more in its favor
than the assumption that man is directly connected
with the modern apes.

Now Eohippus was a creature which was very dif-
ferent from the modern horses, or the donkeys, or the
zebras. And besides, all of the Eocene representa-
tives of the present mammals were very different from
the present, or the Pleistocene types. So if the
human line was distinct in Eocene time it necessarily

[2-2-9]

Wl THE NEW EVOLUTION '^"^"

follows that the man of that period was very different
from what we know as man today. Similarly, the
creatures representing the modern monkeys at that
time must have been very different from them.

Therefore the common ancestor of the Primates
must have been a creature which we could not call
either man or monkey on the basis of the accepted
definitions of those terms, or of our current concepts
of the animal world.

How it is possible for both man and the apes to be
descended from a common ancestor not resembling
either is made clear by the history of the greyhounds
and the bull-dogs. These two types of dogs are very
different from each other both in bodily form and in
mentality, yet they are descended from the same an-
cestor, a wolf, which does not resemble either.

Unbroken continuity in descent from parent to
child does not necessarily imply a similar continuity
in bodily form or in mental attributes. This is well
illustrated by the bull-dogs, which suddenly appeared
as a rather broad mutation from another type of dog,
and by the hairless dogs which had a similarly abrupt
and sudden origin.

So while the general and broader features of human
structure were inherited, in accordance with the
unbroken continuity of descent from parent to child,
from some as yet unknown ancestor common to all
the Primates — but not from an ape as we understand
that term — it is possible and indeed most reasonable
to assume that man, like the bull-dogs and the hair-
less dogs, arose through a rather broad mutation and

[2-30]

^^'^l ZOOGENESIS "^i

therefore that the details of man's structure and his
mentality are, and always have been, man's alone.

Reflections. — The two chief features wh.ch distin-
guish man from all the other mammals are his ex-
tremely flexible and useful hand, and his unique family
relationships. Human children follow each other so
very closely that the second appears before the first
is independent of the parents, the third follows the
second in the same way, and so on. Other distinc-
tive attributes are the use of fashioned or manufac-
tured tools, the use of fire, the use of clothing and of
ornaments, and the use of articulate speech, which
enables man to accumulate inowledge in successive
generations. Is there any relation between these
several different types of attributes?

The flexible and adaptable hand of man lends itself
naturally to the use, as implements or weapons, of
various natural objects, such as sticks and stones.
From this it is but a step to the manufacture and the
use of tools.

The use of tools leads naturally to developments in
three directions. In the first place, it is unlikely that
any creature possessing the strength of man could use
tools long without striking sparks and thus discover-
ing the possibilities of fire. In the second place, the
use of tools would lead to the manufacture and the
use of clothing and of ornaments. In the third
place, the use of tools permits the construction of a
fixed abode or domicile wherein man would be safe
from at least the majority of his four-footed enemies.

Such an abode would presumably become the abid-

THE NEW EVOLUTION

ing place of the female in which she would find pro-
tection and to which food would regularly be brought
for joint consumption by the male. Man is the
only vertebrate with slowly developing young born
one at a time living continuously in an enclosed abode
or domicile. Such a manner of life permits the rapid
bearing of young, for with the mother protected and
provided for she may devote herself entirely to the
raising of her children. Animals kept in captivity —
fed and protected — sometimes bear young before the
preceding young are independent, although they are
not known to do so under natural conditions, so
there are some grounds for assuming that the human
family of dependent young of different ages is asso-
ciated with the fixed abode.

The development of a dependent family including
young of many different ages would necessitate the
interpretation by the parents of a great number of
different sounds and thus might be assumed to lay
the foundation for the beginnings of articulate
human speech. The basic fundaments of language are
already evident in all creatures with dependent
young.

So we find that all the things that make man human
may be traced back to the potentialities of the flexible
human hand guided by a brain capable of developing
those potentialities.

In the first chapter we saw that in the animal world
taken as a whole there were very many instances of
man-like attributes, especially among the insects and
also among the smaller birds and rodents. We also

[2-32-]

ZOOGENESIS

saw that these man-like mental attributes were always
coupled with some heavy liability, usually feeble and
defenseless young.

We now are able to see further. The man-like
attributes of the insects, birds and rodents, and a few
other creatures, are correlated with the possession of
jaws, beaks or other structures which are capable of
being used more or less after the fashion of our hands.
Wherever such occur the ability to make use of them
enables their possessors successfully to meet and to
overcome liabilities which otherwise would be in-
superable. In other words, these structures permit
the existence of liabilities without danger to the
species; the liabilities themselves do not induce the
appearance of man-like attributes.

In the complicated homes built by the ants, bees,
wasps and termites are females which never leave
them, constantly producing eggs, and hence an enor-
mous serial family of dependent young. It is the
elaborate home that makes this possible, and the deft
and skillful jaws of the adults, coupled with their
powers of defense, make the home possible.

So the lesson that we learn from the study of ani-
mal forms in the broadest sense is that it is the home
and associated features that form the foundation of
the human social structure; in the home originated,
and from the home emanated, all our social progress.

t33]

APPENDIX A

The tracing of the details of the development of animal forms
from the primitive single cell is a rather complicated process in-
volving the use of various technical terms and the names of
numerous types of animals which are quite unknown except to
specialists in zoology.

So it has seemed advisable not to incorporate the discussion of
eogenesis in the body of this work, but instead to consider this
important subject separately in an appendix.

All animals living at the present time develop from a single
cell. As this is true of every animal of which the development is
known, we have no hesitation in assuming that it has always been
true of every animal type. From this it naturally follows that
all types of animal life must be explained in terms of an original
single cell.

Since all types of animal life must be explained and interpreted
in terms of a single cell, a path must be traced from the original
and primitive single cell to the basic form or forms in every
phylum.

Some animals possess bodies which are composed only of single
cells. Such animals are always very small (fig. 87, p. 161). The
bodies of other animals are composed of cells belonging to only
two germ layers (fig. 117, p. 185), the ectoderm and endoderm.
These animals are always radial, or fundamentally radial, in sym-
metry, more or less like a flower, and for the most part live firmly
fixed to some support and grow after the fashion of a plant.
Most of them are of medium size or small, like the sea-anemones
or the hydroids, but a few, as certain jellyfishes, may be very
large. Those which live, like jellyfishes, suspended freely in the
water have only very feeble locomotor powers.

All creatures living on the land, and a very large proportion
of those living in the sea and in fresh water, have their bodies
formed of cells derived from three germ layers (fig. ixo, p. 185).
Such animals may be small, scarcely more than one one-hundredth
of an inch in length, or very large, like elephants and whales, or
of any intermediate size.

It is almost invariably assumed that the animals with bodies

[2-35]

WM THE NEW EVOLUTION ®®

composed of a single cell represent the primitive animals from
which all others are derived. They are commonly supposed to
have preceded all other animal types in their appearance. There
is not the slightest basis for this assumption beyond the circum-
stance that in arithmetic — which is not zoology — the number one
precedes the other numbers.

Arithmetical simplicity in the broader features of animal struc-
ture does not by any means imply biological simplicity of func-
tions and of reactions. In the animals with bodies composed of
a single cell that single cell is so excessively complex in its physi-
cal and chemical makeup that it is able to perform of itself alone
all of the vital and mechanical functions which in other creatures
are distributed among a greater or lesser number of special organs,
each of which is composed of more or less numerous cells fitted to
perform a more or less limited range of functions.

Two animals each able with equal success to carry on all of the
very numerous and complicated functions necessary for animal
existence, and at the same time equally efficient in meeting the
limitations and restrictions imposed by external forces, would
seem to be on quite the same footing, and therefore of an equal
degree of specialization. If this were not so — if on the other
hand the arithmetically simpler creatures were biologically more
simple than the arithmetically more complex — can anyone give
any good reason why the former should not have disappeared as
the latter appeared?

No reason can be given. All of the different major groups of
animals existing at the present time are, in their respective spheres
of action, equally efficient. If they were not, the more efficient
would soon exterminate the less efficient. Among the various
major groups of animals as we find them at the present day there
is no possible question of simplicity or of complexity, of primi-
tiveness or of specialization, from the strictly biological stand-
point.

In size, and in everything correlated with size, the fish or the
crustacean is vastly superior to the protozoan. In number of
individuals, potentiality for rapid increase, and ability to survive
adverse conditions, the protozoan is vastly superior to the crusta-
cean or the fish. While so far as the existence of the individuals
is concerned, the fish and the crustacean, because of their size,
power, locomotor ability, and capacity for offense and defense,

^3^

^^"^ ZOOGENESIS ^'^

have a vast superiority over the protozoan, so far as concerns the
existence of the species the protozoan, because of the immense
number of individuals and their minute size, has an enormous
advantage over the crustacean or the fish.

Biologically the protozoan, the fish and the crustacean are all
on an equal footing, in spite of the apparent arithmetical advan-
tage inherent in the multicellular structure of the body of the
crustacean and the fish. Indeed, whatever advantage there may
be rests with the protozoan, for very many different kinds of
protozoans live as commensals and as parasites within the bodies
of all fishes and crustaceans.

There is another way of looking at the matter. The bodies of
all animals are at first composed of a single cell (figs . i lo, 1 1 1 , iii ,
p. 185). In the case of the protozoan the body always remains a
single cell (fig. 87, p. 161), or at least special structures^ — which
may be very complicated — are formed without the division of the
cell as a whole.

In the case of the multicellular animals the original germ cell
divides into two cells, these divide in the same way, and cell divi-
sion keeps on until the final form and complexity is attained (figs.
110-117; 111-1x5, p. 185). The division of the original germ cell
into two, however, adds nothing. The original potentiality of
the germ cell is simply enclosed in two packages instead of a
single one. Further cell division adds nothing. The original
potentialities of the germ cell are simply being segregated and
distributed in an increasingly large number of units. An adult
multicellular animal may therefore be considered as merely the
most effective form in which the fundamental attributes of the
original germ cell can find expression.

It has been demonstrated by the study of genetics that muta-
tions are localized in the so-called chromosomes, which represent
a portion of the germ plasm, or contents of the germ cell. Thus
in the germ cell even minor variations in the characters or features
of any animal type are already present, although they will not be-
come evident until the germ cell has become divided up into thou-
sands or millions of cells.

Any individual animal, therefore, no matter how complicated
its body may be, is simply the elaborated equivalent of its germ
cell. As such, it is the equivalent of a single celled animal or
protozoan. Assuming that a protozoan equals the number one,

[2-37]

THE NEW EVOLUTION

COELEITTSRATE

Body radially symmetrical,
with definite organs.

Body a cellular mass,
with no definite organs.

Fig. a. — Diagram illustrating the three simultaneous paths
of development from the primitive single cell. Although both
the protozoans and the sponges are enormous groups including
great numbers of species, neither group ever gave rise to any
other type. The geometrical line of development resulting in the
radially symmetrical coelenterate leads through the gastrula (see
figs. 110-117, p. 185), an embryonic stage found in all the more
complex animals. The coelenterates and all other animals ex-
cept the sponges and the protozoans must therefore be interpreted
in terms of the gastrula (see figs. 115, 116, 12.0, p. 185).

[^38]

^^^J ZOOGENESIS '^^"^'^

any multicellular animal may be regarded as represented by a
vast number of fractions grouped in various ways which, when
added together, equal the number one, and which were all derived
from an original number one.

Coming back to the single cell, there is no reason whatever for
assuming that complete separation of dividing cells is a more
primitive condition than adhesion of cells after division, or pre-
ceded adhesion. In fact, the great rarity of complete separation
of cells after division in the animal world taken as a whole almost
suggests that adhesion, not separation, is the primitive condition.
Therefore the statement commonly made that the single celled
animals or protozoans are the most primitive of the animals, and
preceded in appearance the multicellular types, has nothing to
support it. The only logical assumption is that the appearance of
unicellular and multicellular animal types was simultaneous —
perhaps even that the latter appeared first (fig. A, p. 138).

Cells which after division remain in contact may adhere irreg-
ularly, resulting in the formation of a more or less unorganized
mass. Essentially such a condition is characteristic of the great
group of sponges, in which creatures many of the constituent cells
are almost wholly independent of each other and suggest masses
of protozoans packed closely together.

Cells which after division remain in contact may adhere regu-
larly, resulting in the appearance of a series of geometrical forms
(figs. iio-ii7,p. 185). Regular division of cells followed by regu-
lar adhesion leads to the formation of a hollow ball of cells called
a blastula (figs. 113, 114, p. 185). The blastula collapses, like a
rubber ball with one side pushed in, into a cup with an outer and
an inner layer of cells called a gastrula (figs. 116, 117, p. 185). The
typical gastrula has an axis passing through the center of the
opening and of the opposite pole, and the radii about this axis are
everywhere the same — in other words the typical gastrula is radi-
ally symmetrical about its only axis.

If the radially symmetrical two-layered gastrula (figs. 116, 117,
p. 185) should become adult, there would result a radially symmet-
rical animal composed of two layers of cells, which would be of
quite the same nature as a hydra or a sea-anemone. The whole
group of the Coelenterata — hydras, corals, sea-anemones, sea-
pens, hydroids, alcyonarians, gorgonians, antipatharians, jelly-
fishes, and numerous other types — represent animals which pos-

[2-39]

or^

!."*^

^■^/X

THE NEW EVOLUTION

A^*

^et:»^ though alwaj^s ,,^j^

Fig. B. — Although all coelenterates are developed geometri-
cally through a gastrula or strictly comparable stage, few of
them are perfectly radial in their symmetry. Many of them have
a slit-like mouth instead of a circular mouth, with the two halves
of the animal on either side of a plane passing through the long
axis of the slit-like mouth alike. This condition is known as
"biradiate" symmetry, and there are in the coelenterates all tran-
sitions between truly radial and "biradiate" symmetry. But all
coelenterates are either radial or "biradiate," and all agree in
having the body composed of only two germ layers, ectoderm and
endoderm; there is no intermediate or mesodermal layer.

From this condition of radial, or approximately radial, sym-
metry and no mesoderm there are two lines of departure. Both

[140]

^^ ZOOGENESIS ^l'

lines of departure are accompanied by the appearance of meso-
derm between tlie ectodermal and endodermal layers of the
gastrula.

I. In the ctenophores the body is divided into two similar
and equal halves by a plane passing through the long axis of the
flattened stomach, and also into two similar halves by a plane
at right angles to this which passes through the long axis of the
so-called funnel into which the stomach leads. Thus either line
in a right angled cross divides the ctenophore into two equal
halves. This very distinctive symmetry is characteristic of, and
is confined to, the ctenophores.

1. In the Vermiformes the body is divided into equal and simi-
lar halves by a plane passing through the long axis of the body
dorsoventrally. But there is always a greater or lesser amount
of radial symmetry evident in the nervous system, the digestive
system, or the head structures. The Vermiformes are bilateral,
though always showing a certain amount of radial symmetry.

sess radially symmetrical bodies composed of two layers of cells
which arise from an original single cell through regular geomet-
rical cell division.

As there is no reason for assuming that irregular adhesion of
cells after division necessarily preceded regular geometrical adhe-
sion of cells after division, there are no grounds for supposing
that the coelenterates are not as old as the sponges or the proto-
zoans.

The single celled animals or protozoans, the sponges, and the
two layered radially symmetrical animals each represent the
logical end product of a special type of cell division and of cell be-
havior after division (fig. A, p. ^38). There is not the slightest
evidence that any one of these animal types preceded the other
two in appearance.

We now come to those animals in which the body is made up
of three layers of cells. The gastrula is formed as just described
(figs. 110-117, p. 185), but a greater or lesser number of cells, aris-
ing in various ways, make their appearance within the hollow
wall of the gastrula (compare figs. 116 and 117 with fig. 12.0, p.
185) and subsequently form the mesoderm.

"^^^ THE NEW EVOLUTION T"^

In one group of animals with the body composed of three cell
layers, the ctenophores (fig. 66, p. iii), the symmetry is quadri-
lateral; there are two axes, a long and a short, crossing each other
in the middle at right angles, and the two halves on opposite sides
of either axis are the same. These curious creatures (sec fig. B,
p. 140, fig. C, p. 146, and fig. D, 4, p. ^50) may be regarded as on
a par with the coelenterates, though wholly different from them.

All other animals are always in some stage, and usually in the
adult, bilaterally symmetrical with a more or less marked head
end at which are the main nerve centers, the chief sense organs,
and usually the mouth, if a mouth be present.

The bilaterally symmetrical animals segregate themselves in
two rather well defined groups. The first group includes those
types in which the symmetry is partly bilateral and partly radial,
and there is no typical gastrula or cup stage in the development of
the individuals. The second group includes the types in which
the symmetry is wholly bilateral, and which in their development
pass through a typical gastrula stage, or a stage easily recognized
or interpreted as a modification of the gastrula.

The animals which are partly bilateral and partly radial in
their symmetry form a most extraordinary assemblage of very
widely diverse types. They are the cestodes or tapeworms, the
acanthocephalids or spiny-headed worms, the trematodes or
flukes, the turbellarians, the nematodes or thread-worms, the
nematorpha or gordian worms (the "hair-snakes" of puddles and
troughs), and a considerable number of curious small obscure
worm-like things of uncertain relationships. Although the only
features which these queer creatures share in common are the
partially bilateral and partially radial symmetry, the absence of
true ccelomic structures, and the absence of a true gastrula stage
in the development of the individuals, there are indications that
as a whole they represent a distinct zoological unit, although
a remarkably heterogeneous unit.

There are forms which are intermediate between the tape-
worms and the flukes, and others which are intermediate between
the flukes and the turbellarians. Some authorities consider the
spiny-headed worms to be related to the nematodes or thread-
worms, others believe them to be most nearly allied to the tape-
worms, while still others regard them as wholly distinct from
anything else. The gordian worms are usually considered to be

[2.42-]

ZOOGENESIS ^

related to the nematodes from which, however, they differ in
practically every detail of their structure.

All of the tapeworms, spiny-headed worms, flukes and gordian
worms are parasites, as are also many of the thread-worms and a
few of the turbellarians. The tapeworms, spiny-headed worms,
some of the nematodes, some of the turbellarians, and a few curi-
ous forms (such as Rhopalura [figs. 12.7, 12.8, p. 185], Dkj/ema,
Dicyemo-psis [fig. 12.6, p. 185], Dicyemella^ and others) which are
supposed to be allied to the trematodes or flukes have no mouth
and no digestive system. A few of the small turbellarians with-
out a digestive system are said to be able to live on inorganic
material like a green plant through the medium of the green cells
in their tissues.

In the young stages of many of these creatures, especially in
certain tapeworms and flukes and in a few turbellarians, asexual
reproduction is carried to an extraordinary degree, recalling the
conditions in the younger stages of many of the radially sym-
metrical coelenterates. Other forms, especially among the tur-
bellarians, possess the most remarkable powers of reparation and
of regeneration, being able to reproduce an entire individual from
a very small fragment. This also recalls the conditions in certain
coelenterates. On the other hand, in other forms there is simple
sexual reproduction only, and the individuals possess little or no
power of reparation. Such forms in these respects most nearly
resemble the more complex forms of bilaterally symmetrical
animals.

In some of these creatures both sexes occur in the same individ-
ual, while in others the sexes are separate. In a few, unfertilized
eggs capable of developing are produced. Rarely, larval as well
as adult forms produce eggs. Many develop directly from the
tgg to the adult, but others have one, two, three, or even four
very distinct larval forms, some of which produce great numbers
of the same, or different, larval forms through various types of
asexual reproduction. Some of the larval forms are branched and
plant-like, and in many cases the adults are practically colonial
animals.

The number of different kinds of these animals is very great,
and the part they play in the economy of nature, especially in pre-
venting the too rapid increase of other kinds of animals, is most
important.

[2-43]

^^"^ THE NEW EVOLUTION "^^""^

It might be supposed that the fact that the great majority of
these creatures are parasites indicates that they are simply
anomalous forms the peculiar characteristics of which have been
developed in accordance w^ith and as a response to their parasitic
habits.

Parasitic habits, however, cannot produce structures which
are not already potentially present. Through parasitism certain
structural details may be profoundly altered, or a parasite may lose
various structural characters and through this loss become much
altered in its general appearance. This is well illustrated by the
various parasitic crustaceans and by the parasitic barnacles. But
no new structural complex is ever formed.

Nature does not produce anomalies. To regard any creature
as anomalous is simply to confess our inability to understand it.
The living world is not chaotic — everything has its appointed
place in the general plan.

The reason that the majority of these creatures are parasitic is
that their curious structure renders them incapable of competing
as free living forms with other types, while at the same time it
lends itself with peculiar facility to the specialized requirements
of a parasitic life.

None of these creatures can be assumed to be descended from
the radially symmetrical coelenterates, or to have given rise to, or
to have been the ancestors of, any other forms of animal life. Yet
all forms of animal life must have been derived from the same
original ancestor or ancestral type. What, then, is their relation
to other animals?

In their very earliest developmental stages — those immediately
following the division of the germ cell — they resemble all other
animal types. But they very soon diverge, both from the
developmental line leading to the radially symmetrical coelenter-
ates and from each other. Their later embryonic stages are
unique and very diverse. In some these recall in certain respects
the coelenterate planula, while in others they appear more like
the early embryos of some of the more complex animals. How
can this be reconciled with any developmental plan?

The fundamental difference between the single-celled animals
or protozoans and all other animals is that the single cell of the
protozoan divides into two cells which separate completely from
each other, each half of the original cell becoming a separate

[2-44]

TfJ ZOOGENESIS l"^^^

animal with half the bulk of the parent. In all other creatures
the original germ cell divides into two as in the case of the proto-
zoans, but the two derivatives of the original germ cell remain
connected.

So the difference between the protozoans and the other animals
is chiefly and most obviously a difference in the behavior of the
single cell which lies at the base of all animal structure.

The essential and most obvious difference between the sponges
and the coelenterates is that in the sponges the cells as they divide
adhere in a more or less irregular mass in which many of them
retain to a large extent their individuality, while in the coelenter-
ates the cell division takes place geometrically and results in the
formation of a radially symmetrical body in which all of the cells
• — or practically all of them — have entirely lost their individuality
through incorporation into various organs and structures.

Thus the difference between the sponges and the coelenterates
has its inception in the very early embryonic stages. But it
would seem that the sponges and the coelenterates are more
closely related to each other than either group is to the proto-
zoans in which there is no adhesion of cells — or at least no adhe-
sion which impairs the complete individuality of the cells.

The curious assemblage of creatures with which we are at
present concerned seems clearly to be less like the sponges than
like the coelenterates. But in their embryonic stages they depart
very early from the regular geometrical line which leads to the
adult coelenterate. Their relation to the coelenterates is of
approximately the same nature as the relationship between the
sponges and the coelenterates, or as the relationship between the
sponges and the coelenterates taken together and the protozoans.

Any regular geometrical line of development would naturally
be subject to every possible deviation and departure from the
normal. Such of these deviating lines of development as would
result in producing an adult animal — no matter how bizarre —
which has an internal chemical and physical balance enabling it
successfully to carry on the necessary vital processes, and at the
same time was fortunate enough to find some niche in which it
could maintain itself, could very easily produce an apparently
wholly new type of animal.

Such new types of animals, coming into existence as the result
of deviations from the regular developmental line originating at

^45]

^N/^

THE NEW EVOLUTION

Level representing the adult stage
strictly radial ^ / «

Fig. C. — In fig. B the animal types represented are considered
as adults only. The outermost circle has no connection what-
ever with the next, nor the next with that within it. There
are, however, numerous types connecting the innermost circle
with the center. The origin of this condition is illustrated in
this diagram. The radially symmetrical coelenterates arise
through regular geometrical division from the ovum or egg
through the gastrula. Their development is represented by the
line from the bottom to the top of the figure, the top being the
small central circle in fig. B. The biradiate coelenterates, the
ctenophores and the Vermiformes arise through departures from
this regular line of geometrical figures which take their origin
at or about the early gastrula stage, or perhaps just before it.

[Z46]

ZOOGENESIS

a very early embryonic stage, would in the adult form give no
certain indication of their origin. They would appear as isolated
animal types with no close relatives.

Only in this way may the various types included in the Vermi-
formes be explained. They may be interpreted as having arisen
simultaneously with the coelenterates through deviations from
the regular geometrical course of embryonic development leading
to a radially symmetrical adult.

This deviation seems to have taken place at a slightly later
stage in some than in others, and furthermore it seems to have
been of several diverse types resulting in a curiously heterogene-
ous assemblage of forms relatively few of which are sufficiently
well balanced to be capable of independent, that is, non-parasitic
existence.

None of the Vermiformes can be assumed to have been the
ancestors of anything else. As animal forms they are quite
unique. But taken as a whole they furnish a most significant
clue to the probable relationships of the other animal types.

No matter how different they may be — whether clam, bird,
starfish, jointed worm, or other form of animal life — all of the
more complexly organized animals in the course of their develop-
ment pass through a gastrula or comparable stage. This gastrula
stage is the last stage common to them all. Since they all pass
through a gastrula stage they are all referable, as far as the gas-
trula, to a developmental line which, followed to its logical end,
leads to a radially symmetrical animal (fig. A, p. 138).

Following — or usually during — the gastrula stage they all
diverge in different directions. The radial symmetry of the
gastrula is completely lost, and subsequent development leads
in all cases to the formation of a bilaterally symmetrical creature.

All of the more complex animals agree in being bilaterally
symmetrical, and also in having the body derived from three germ
layers. Each major group, however, possesses characteristic
and distinctive features which have their origin in the very
varied behavior of the three germ layers — of themselves and in
reference to the other two — in late gastrula and subsequent
development.

Thus a mollusk is a mollusk, a vertebrate is a vertebrate, an
echinoderm is an echinoderm, a jointed worm or annelid is an
annelid, and so on, in the late gastrula, or at the furthest imme-

[M7]

Vs

1il THE NEW EVOLUTION "^^^

diately subsequent, stage, and becomes more and more obviously
so as the development progresses. Indeed, in some major groups
the early gastrulas are characteristic and distinctive.

Such a condition is capable of but a single interpretation.
The only possible conclusion is that there is not now, and there
never has been at any time in the past, any linear relationship be-
tween the major groups of animals at any stage later than the
gastrula. None of them can be assumed to have passed through
a stage represented by any of the others in the adult form.

In all of them there are the same three germ layers — the ecto-
derm, representing and arising from the outer layer of cells in the
gastrula cup, the endoderm, arising from the layer of cells lining
the gastrula cup, and the mesoderm, arising in various ways
within the hollow walls of the gastrula cup between the outer
ectoderm and the inner endoderm.

Each of the three germ layers gives rise to definite sets of
organs and of structures. Obviously, therefore, a slight modifi-
cation of the relationships between them in early embryonic life
will produce marked and profound differences in adult animals.

The relation between the various groups of the more complex
animals can only be interpreted on the basis of embryological
evidence — and no other evidence is available — as divergence from
a common center, this common center being represented by the
gastrula. There is no other possible point of common contact.

We may explain the matter in this fashion. A number of
exactly similar hollow hemispheres of modeling clay may be
taken and each modeled into a wholly different figure. In this
way we could form an infinite series of clay figures which would
not show the slightest similarity to each other. But each would
be formed of the same clay, and each would have originated as a
hollow hemisphere.

This is about what nature has done in the case of the more com-
plex animal forms. Instead of hollow hemispheres of clay, how-
ever, nature's units were hollow hemispheres with an outer, an
inner, and an intermediate layer of cells, the cells in each of these
three groups or layers being capable of forming certain organs or
structures only. And besides this, nature's remodeling of the
original available materials — the three germ layers — had to
produce as a result an animal form with a proper internal chemi-
cal and physical balance, and at the same time capable of securing

[2.48]

ZOOGENESIS

suitable food in sufEcient quantity and of defending itself against
aggression.

The possible number of forms into which the materials avail-
able in the gastrula may be modeled so as to produce an animal
type capable of successful existence is undoubtedly limited.
Probably the major groups of animals as we know them represent
the full total.

The reason for the assumption that the major groups of ani-
mals represent the entire range of structural possibilities is that
they arrange themselves in a very definite order in relation to each
other, and in this definite order there are no gaps. This order
seems to correspond in the animal world to the periodic system of
the chemical elements in the inorganic world. The key to this
order is furnished by the group Vermiformes.

We have already pointed out that these creatures, which have
a symmetry partly radial but chiefly bilateral, may be considered
as having arisen from the line of geometrical development leading
to the radially symmetrical coelenterates as a result of the appear-
ance of developmental irregularities in the early embryonic stages
leading to the formation of a mainly bilateral adult.

The developmental figure represented by the radially symmetri-
cal coelenterates and the Vermiformes (fig. B, p. 140) would be a
central spot, indicating the coelenterates, surrounded by a circle
of more or less detached spots each of which represents one of the
several groups of "worms."

So far as the adults are concerned, there is no connection be-
tween the spots. But the same figure viewed from the aspect of
the development of the individuals in each of these types of ani-
mals would show a vertical axis running from the primitive
single cell upward through a series of geometrical embryonic
stages — the two, four, eight, sixteen and thirty-two celled stage,
etc., and the blastula and gastrula — to the adult coelenterate.
From various points in this vertical line, mostly at or near the
early gastrula stage, lines would branch off and run diagonally
upward and outward to each of the spots representing one of the
flatworm or roundworm types (fig. C, p. 146).

In the circle of forms represented by the Vermiformes (fig. E,
p. ^54, outer circle) we see four distinct and widely different struc-
tural types, two or more of which, however, may occur in closely
related animals. These four structural types are the following.

t49]

m

THE NEW EVOLUTION

::^:

I

o

Fig. D. — ^The animarsymmetries. i. — The"symmetry of the
germ cells, which is also the fundamental symmetry of the proto-
zoans; the dotted lines are assumed to radiate from the center of
a sphere, x. — Coelenterate radial symmetry, viewed along the
axis through the mouth and the opposite pole. 3. — Biradiate
symmetry, a modification of the preceding (2.), found in coelen-
terates only. 4. — ^The cross symmetry of i he ctenophores. 5. —
The partly bilateral and partly radial symmetry of a tapeworm in
which the head or scolex is four sided. 6. — Bilateral symmetry,
with a single axis. 7. — ^The pseudoradial symmetry of an echino-
derm — really bilateral symmetry with the axis curved in a circle,
half of the five segments of the body failing to develop in the
adult.

[150]

ZOOGENESIS

I. The jointed tapeworms. From a head end, or "scolex,"
which is commonly radially symmetrical and often four-sided
(figs. 5, p. 5; 8i, 83, p. 161), a series of units is continually budded
off which, as they are shoved further and further from the scolex
by the budding off of new units, become more and more developed.
These units — the proglottides — are usually strongly flattened
and have a more or less well marked dorsal and ventral surface.
The proglottides usually differ more or less on either side of the
plane passing through the center of the so-called dorsal and ven-
tral surfaces.

In these jointed tapeworms we see a rather close approach to
the type of development characteristic of various jellyfishes —
for instance the common Aurellia. In these jellyfishes the t^g
gives rise to a little creature shaped like an inverted bell attached
by the handle. From the margin of this bell two tentacles arise
opposite each other in quick succession, so that at the two ten-
tacle stage the little creature is bilaterally symmetrical — or
rather biradial. After this, other tentacles appear. Subsequent
to the formation of the complete circle of tentacles, the larva
undergoes more or less extensive reproduction by the formation
of buds which separate off and grow into new and independent
animals, and also by division into two or more parts, each part
after separation becoming a new animal. In this connection it
may be mentioned that in certain tapeworms the larval form may
in somewhat comparable fashion produce from its internal walls
one or two generations of secondary vesicles which project into
it, the cestode heads originating in special small brood capsules
on these secondary vesicles. In these cases the number of sepa-
rate tapeworms which arise from a single embryo is enormous.
In the little bell-shaped jellyfish larva, after reproduction by
budding and by fission have proceeded for some time the body
begins to divide transversely, and the tentacles disappear. The
body now elongates, and little plate-like or saucer-shaped bodies
with four pairs of marginal lobes are detached one by one from
the outer end. These float away and grow into jellyfishes. The
distal proglottides of the jointed tapeworms are also detached,
one by one or in groups, but in the case of the tapeworm the pro-
glottides are fully developed before detachment. It may be re-
marked that not all of the tapeworms are jointed, some being
single units.

^^ THE NEW EVOLUTION

z. The flukes, in which the budding off of young, which are
different from the adult, takes place within the larval form. In
the flukes the first larva, a miracidium (fig. 96, p. 175), generally
becomes a sporocyst (fig. 98, p. 175), which is a hollow sack with
excretory canals in its walls containing in its interior cavity a
number of germ cells. The germ cells within the sporocyst usu-
ally develop into redia^ (fig. 97, p. 175), which resemble sporo-
cysts except in having a mouth and intestine, and two lateral
processes near the hind end. The germ cells within the redia^
usually produce cercarias (fig. 99, p. 175), which are essentially
young flukes with a slender and very mobile tail. Later the tail
is lost, and the young fluke grows into the adult (fig. 55,0. 97).

If we are to maintain that the animal world has an underlying
plan or system — that it is not chaotic — there must be some sig-
nificance in the extraordinary developmental history of the flukes.
To say that it is a response to, or was developed because of, their
parasitic habits is simply to beg the question. If parasitic crea-
tures are to be considered as derived from other forms of animal
life, then every peculiarity of a parasite must be explained by,
and may itself explain, other features found in other animals.
In other words, no parasites can add anything to their funda-
mental structural equipment or to their ontogeny that does not
exist in related types.

What structural peculiarities in the more complex animals
may be explained by the development of the flukes? The very
extensive asexual reproduction in the young stages of the flukes
recalls similarly extensive asexual reproduction in the young,
and often also later, stages in the coelenterates. Many coelen-
terates as they grow produce a large colony of interconnected ani-
mals of more or less plant-like form. In various coelenterates
the individual animals in these colonies are not all alike, but are
divided into three types. These three types are: Firsf, the nu-
tritive or sack-like individuals, which do the eating for the entire
colony; second, the reproductive individuals, which produce the
eggs; and third, the "defensive" individuals, which serve to pro-
tect the colony by means of structures the chief feature of which
is a poisonous secretion.

In the more complex animals there is developed, typically by
budding from the enteron — the digestive cavity primarily derived
from the endoderm — a structure or organ of the greatest impor-

[2-52-]

^^^ ZOOGENESIS f^^^

tance called the coelom. The coelom has three divisions. These
three divisions are: Firsf, the perivisceral, which forms the body
cavity in which the heart and other viscera lie; second^ the gona-
dial, or reproductive portion, from the walls of which the repro-
ductive cells arise; and third, the nephridial, the walls of which
secrete the nitrogenous waste.

It is impossible not to see in the three divisions of the coelom
a correspondence with the three distinct types of polyps produced
by many of the colonial coelenterates. It is likewise impossible
not to see in the extensive asexual reproduction by budding in
the flukes the same phenomenon as the extensive asexual repro-
duction in the coelenterates. In the coelenterates the buds which
grow into the new individuals — polyps — are always external,
while in the flukes they are always produced within the original
unit.

It is quite conceivable that the coelom may have arisen from
the budding internally as in the flukes instead of externally as in
the coelenterates of a sack-like, a reproductive, and an excretory
unit corresponding to each one of the three types of polyps
characteristic of many colonial coelenterates. Such an explana-
tion of the origin of the coelom is at least plausible on the basis
of the evidence, and no other explanation which does not involve
the creation of a new structure out of nothing is possible.

3. The solitary flatworms and roundworms, wholly independ-
ent of each other, each individual developing directly, or through
a larval form, from an egg without any asexual reproduction. In
this group fall the thread-worms or nematodes (fig. 81, p. 161),
most turbellarians (fig. 54, p. 97), and some other types.

4. Flatworms which are independent of each other, but form
colonies of similar perfect individuals through asexual reproduc-
tion, as in the case of Microstomum (fig. 135, p. 103).

Thus we find in the Vermiformes four main structural types.
These four chief structural types are :

I. Mainly bilateral animals taking the form of a linear and
more or less unified colony.

z. Mainly bilateral animals in which colony formation is in-
verted, the budding off of the new elements taking place within
the original unit.

3. Mainly bilateral independent animals which do not form
colonies and which show no asexual reproduction.

t53]

>/v

THE NEW EVOLUTION

^^^^

Turtellarians
Nematodes

Nemertea

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Fig. E. — Illustrating the relative positions in reference to each
other of the bilaterally symmetrical animals. The outer circle
(compare fig. B) represents the Vermiformes, a very highly di-
versified group including four distinct structural types showing
features w^hich are combined in four other types of more compli-
cated animals not directly related to them. Similar recombina-
tions of structural features account for all the other animal types,
the Vertebrata occupying the center of the figure as the most
complex of all animals. These different groups arose as a result

^54]

ZOOGENESIS

of following different developmental lines from (approximately)
the gastrula onward. The ancestral line of each radiates from the
gastrula, and the groups were therefore never connected by inter-
mediate types of adult animals, nor was any one derived through
any of the others. The appearance of all was probably simul-
taneous or nearly so, and also simultaneous with that of the types
not shown in this figure (see figs. A-C).

4. Mainly bilateral animals which, although remaining prac-
tically independent of each other, form colonies through asexual
reproduction by transverse fission.

If we place these four structural types, represented by (i)
jointed tapeworms, (2.) flukes, (3) nematodes and most turbel-
larians, and (4) Microstomum^ at equal intervals on the circum-
ference of a circle (fig. E, p. ? 54) we find that there are four other
groups of animal forms which structurally may be interpreted as
intermediate between them, or rather which combine in a single
type the characteristic features of the forms on either side. The
animal types included in this second series of four have no trace
whatever of radial symmetry, so they may be arranged on a
circle within the circle on which the Vermiformes are placed.
These types present the following characters:

I. Animals which are sharply segmented or jointed, like the
jointed tapeworms, and also in their growth develop internal
buds more or less after the fashion of the flukes, leading to the
development of a coelom. The animals which answer to these
specifications are the annelids or jointed worms.

2.. Animals which are unsegmented, like the nematodes and
turbellarians, but possess an internally budded coelom, thus in
this respect corresponding to the flukes. These animals are the
sipunculids.

3. Animals which are solitary and unsegmented without a
coelom, like the turbellarians and nematodes, but show abundant
asexual reproduction like Microstomum. These animals arc the
rotifers. Possibly the priapulids belong here.

4. Animals which are segmented but without a coelom, like
the jointed tapeworms, but less completely unified and not sub-
ject to a continual loss of the units, as in Microstomum. Probably
the graptolites belong here.

[2-55]

^^ THE NEW EVOLUTION '^'^^^

None of the animal types in this second series of four can be
assumed to have any direct connection with any of the flatworms
or roundworms, nor can it be shown that they have any connec-
tion with each other. Their development, however, where it is
known, shows that the very early stages resemble the correspond-
ing stages of the coelenterates, but that they branch off from the
regular geometrical line in such a way as to lead to the formation
of completely bilateral larvae and subsequently adults in which
the broader structural features may be interpreted as combining
those of two separate groups of Vermiformes.

As they depart from the coelenterate line of development in
very early larval stages, their origin was presumably simultane-
ous with that of the coelenterates and the Vermiformes and had
its inception in the different behavior of the gastrula. For in-
stance, while the very young jointed tapeworm embryo develops
in such a way as to produce a sharply jointed and semicolonial
animal, and the fluke embryo during its growth undergoes exten-
sive internal budding, the young embryo of the jointed worms or
annelids in its development combines both external segmenta-
tion and internal budding.

Within this second series of four animal types there is another
series of four which bears the same relation to the second series
that the second series does to the first.

The third series of four animal types includes :

I. The polyzoans, which are colonial, or at least primarily
colonial, and not at all, or only very imperfectly coelomate, fall-
ing between the rotifers and the graptolites.

-L. The arthropods, with a segmented body like that of the
annelids, but divided into two or three units showing division of
labor (in the insects one, the head, controlling and directing,
another, the thorax, bearing the legs and wings and therefore
locomotor, and the third, the abdomen, containing the digestive,
reproductive and other organs) after the graptolite or polyzoan
fashion, with a poorly developed coelom, with abundant traces
of asexual reproduction (polyembryony, parthenogenesis, frag-
mentation of larvae, etc.), with a marked tendency to form (as
in the ants) polyzoan-like colonies with division of labor among
the (independent) units, and sometimes (as in Thompsonia) even
forming dendritic colonies.

3. The mollusks, always solitary, like the sipunculids, with

^^ ZOOGENESIS |S^

a highly developed coelom, and with traces of segmentation sug-
gesting the annelids.

4. The fourth group should be composed of solitary animals
with an indication of colonial structure and a coelom, but with-
out segmentation. It is possible to place the nemerteans here by
assuming that their imperfect segmentation is of the Microstomum
and not of the tapeworm type.

Within this third series of animal types there is a fourth series
bearing the same relation to the third series that the third does
to the second. This fourth series of animal types includes the
following:

I. The echinoderms, combining a reduced body consisting in
the adults of five half segments more or less of the arthropod type
with a highly developed coelom as in the mollusks.

2.. The arrow-worms or chxtognaths, suggesting a relation-
ship with the mollusks, and also with the nemerteans.

3. The phoronids, suggesting a relationship with the poly-
zoans but with a well developed coelom and with the colonial
habit reduced to the budding off of new individuals.

4. The brachiopods or lamp-shells, suggesting both the poly-
zoans and the barnacle-like arthropods.

In this fourth series of animal types the features characteristic
of each of the four groups of types in the first series all occur in
varying proportions . A fifth series of four, bearing the same rela-
tion to the fourth that the fourth does to the third, would there-
fore be composed of types which would be structurally very
much alike.

We appear to find such a series in:

I. The tunicates, which seem to be in line with the polyzoans,
while they also suggest both the brachiopods and the phoronids.

t. The cephalochordates, which clearly stand in the cestode-
arthropod line and at the same time show indubitable affinities
with the echinoderms.

3. The balanoglossids, with no trace of asexual reproduction,
which may be considered in line with the flukes and mollusks
and between the chastognaths and the echinoderms.

4. The cephalodiscids, which seem to fall between the chaetog-
naths and the phoronids.

These four very distinctive, but structurally closely related,
types all show marked affinities with the vertebrates. It is pos-
ts?]

THE NEW EVOLUTION

sible to interpret the vertebrates as combining the features found
in all of them and therefore as occupying, as the most highly
perfected of all animal types, the center of the figure.

In the vertebrates we are able to recognize the segmentation of
the cestodes, annelids and cephalochordates, combined with the
coclomic structure first indicated in the flukes, both enclosed in
the undivided body of the turbellarians and nematodes. If the
vertebrate limbs may be compared to budded units recalling cer-
tain highly reduced and specialized units in tunicates or polyzoans,
the comparison is complete.

In these various recombinations of structural features leading
to greater and greater structural complexity, numerous secondary
features, such as visual and other sense organs, appendages of
different kinds, diverticula and other outgrowths from the enteric
canal, chitinous and calcareous skeletons, and others, became
enormously developed and specialized in correlation with the
increasing bodily efficiency resulting from the progressive im-
provement in the structural balance.

In this exposition of the development of the fundamental ani-
mal forms^ — of the original type representing each of the major
groups or phyla — no claim is made that the last word has been
spoken in regard to the placing of each phylum in relation to
the others. But it is believed that the diagrammatic representa-
tion here given is in all essential features correct.

There can be no talk of any direct relationship between the
adult forms in one phylum and the adult forms in any other.
There is not now, and we have no evidence that there ever was,
any intergradation between the phyla as represented by post-
embryonic forms.

All of the evidence points to the origin of the phyla through
modifications of the regular geometrical developmental course
which took place in the gastrula, or approximately at the gas-
trula, stage, each departure from the regular course resulting in a
different bilateral animal form.

This means that all animal types arose through various recom-
binations of features which are already present in the gastrula,
and further that the animal types differ from each other not by
the addition of certain features but, on the contrary, by the sub-
traction or repression of a varying number of the features which
are inherent in, or an integral part of, the perfect gastrula, this

^1^ ZOOGENESIS ^^

subtraction or repression of certain features causing others to
stand out with special prominence.

According to this hypothesis the most highly perfected animal
types are the protozoans, the coelenterates, and the vertebrates.

In the radially symmetrical coelenterates the gastrula passes
with the least possible change into an adult form. As the adult
coelenterate represents a gastrula which is only slightly modified
and has lost relatively little of its inherent plasticity, we natu-
rally see in the coelenterates as a group such features as asexual
reproduction by budding and by fission, colony formation, di-
versification of polyps in a colony, reparation, sexual reproduction
by larvae, and variation in individual and colonial form developed
to an extent far beyond anything seen elsewhere in the animal
world. The persistence of features inherent in the gastrula
seems to be the only reasonable explanation for the extraordinary
diversity so characteristic of this enormous and important group
of animals.

In the vertebrates all of the features inherent in the gastrula
are again present, but they are present in a very highly modified
and static form as a result of the extensive and intricate changes
which have taken place during the development of the indi-
viduals. The vertebrates therefore are so very delicately bal-
anced, both in respect to their internal mechanism and reactions
and in regard to their external contacts, that they have retained
none of the plasticity characteristic of the gastrula, or of the
coelenterates. They are incapable of asexual reproduction, of
colony formation, of extensive reparation of lost parts, or of as-
suming any great variety of form.

Structurally the least perfect animal types are those included
in the Vermiformes, because each of these types lacks the maxi-
mum number of the features inherent in the gastrula. But the
sum total of the features found widely distributed in the Vermi-
formes as we know them would be essentially the equivalent of
the features found in the coelenterates.

Such a concept of the development of animal life may be illus-
trated by comparing the primitive gastrula to a rosebud. As the
rosebud opens the petals unfold and grow out to their full size.
Each petal may be taken to represent a separate developmental
line running from the gastrula to one of the major groups, which
itself would be represented by the petal's outer edge.

[2-59]

"^^t THE NEW EVOLUTION M'

All the available facts lead to the conclusion that the major
groups of animals appeared simultaneously, or nearly so, in es-
sentially the same form as that in which we know them now by
a process of concurrent evolution. Furthermore, the animal world,
taken as a whole, forms a closely unified entity, and the more we
study animals the more clearly do we realize that this is true.

[z6o]

APPENDIX B

THE MAJOR GROUPS OF ANIMALS

Vertebrata — the backboned animals. — This very large group
includes the mammals, birds, reptiles, amphibians and fishes
which together are represented by about fifty thousand different
species. The structure is very complex, and the size ranges from
a length of no feet in the great blue whale as found in the Antarc-
tic down to about three-quarters of an inch in the smallest adult
fish. But all vertebrates are relatively large, and the average size
is far larger than in any other group. Vertebrates are found
everywhere, in every region and from the highest mountain tops
down to the ocean floor. The animal from the greatest depth
in the sea at which animals have been found (19,806 feet) is a
fish. Most vertebrates live on land. The fishes, however, live
chiefly in the sea; also living and breeding in the sea are the
whales, except for a few fresh water dolphins in South America
and Asia, ana the sea-snakes. (Fig. 2., p. 5.)

Cephalochorda — Am-phioxt&s (Branchiostoma) and its allies. —
This is a very small group including only a few species which
look like small colorless semitransparent fishes headless and
pointed at each end. They live partially buried in sand. They
are found only in the sea in shallow water and at moderate
depths, and are widely distributed, though very local.

Balanoglossida. — A small group confined to the sea wherein
they are very widely distributed. Like sponges, they have a
disagreeable and usually strong smell which sometimes imparts a
flavor to the fishes that feed on them. (Fig. 94, p. 175, young.)

Cephalodiscida. — A very small group including a very few
species of two quite different types {Ce-phalo discus [fig. 61, p. in]
and Uab do-pleura [fig. 63, p. in]). They are found only in the
sea in shallow water and in water of moderate depth and are
widely distributed, though apparently very local.

TuNicATA — the sea-squirts, sea-peaches, pyrosomas and their rela-
tives.— This is a large and highly diversified group entirely con-
fined to the sea. The various species are found in all seas at all
depths, but most of them live in shallow water. Some live
attached to the bottom, while others float freely in the water.

[z6i]

^^^^ THE NEW EVOLUTION "^1^

Many are colonial, forming incrustations on rocks or long chains
or hollow cylinders which float about suspended in the water.
Some of the bottom living types are raised on a long slender
stalk. In many the tough outer covering is largely composed
of cellulose, a substance especially characteristic of plants.
Many are very brilliantly phosphorescent. (Figs. 56-59, p. iii.)

Phoronidea. — A very small group including less than ten
species, found only in the sea where the) are widely distributed,
but very local. (Fig. 101, p. 175, young.)

SiPUNcuLoiDEA. — A small group, entirely marine, but very
widely distributed.

MoLLuscA — the mollusks. — A very large and much diversified
group including the snails, slugs, clams, oysters, shipworms,
sea-butterflies, squid, octopus, nautilus, and many other types,
which are represented by a total of about fifty thousand species.
Most mollusks live in the sea where they are especially character-
istic of shallow w^ater, but a few are found in very deep water
and some in fresh water and on land, occurring even above the
snow line in the Himalayas. A number are parasitic, a few in
the larval stage only; others as adults are internal parasites,
lacking a shell and a digestive system. (Figs. 33, 34, p. 55;
45-52., p. 97; 74, p. 12.7; 95, p. 175.)

Annelida — fbe jointed worms. — A large and much diversified
group including the earthworms, sea-worms, etc. Most of the
jointed worms live in the sea, but the earthworms and the ony-
chophores (Feripatus and its allies) live on land, and quite a
number, mostly allied to the earthworms, live in fresh water.
Some are free swimming, others live in mud or sand or in holes
in rocks or coral heads, and many construct limy or horny and
quill-like tubes. Many live in the cavities of sponges, and one
of these is branched, with a head on the end of every branch. A
few marine forms are parasitic, some being internal parasites,
chiefly in echinoderms. (Figs. 65, p. iii; 84, 85, p. 161; 104,
108, p. 175.)

Brachiopoda — the lamp-shells. — A small group including about
170 species all of which live in the sea mostly in shallow water
or in water of moderate depth; but a few live in very deep water.
(Fig. 60, p. III.)

Arthropoda — the jointed-legged (literally, footed) animals. —
This group includes the insects, spiders, scorpions, mites, crusta-

'^^^ ZOOGENESIS '^^'^

ceans (crabs, shrimps, lobsters, barnacles, sow-bugs, beach-fleas,
water-fleas, etc.), and various other types. The number of
included species — roughly six hundred thousand of which about
twenty thousand are crustaceans — is vastly greater than the
number included in all the other animal groups taken together.
But in spite of this the uniformity in the general structure is so
very great that the members of the group are always readily
recognizable, usually throughout their lives, or at least in the
adult or first stages. Arthropods are found everywhere on land
and in fresh vv^ater, and down to the greatest depths in the oceans.
Most of them are free-living, but very many are parasitic, usually
on other arthropods, but also on vertebrates and other creatures,
both on land and in the sea. Some of the so-called parasitic
barnacles can be recognized as arthropods only in the early stages,
the adults becoming almost or quite structureless. (Figs, i,
p. 5; 7-16, p. 2-1; 17-2.3, p. 33; 14-30, p. 47; 31, 32., p. 55; 64,
p. hi; 91-93, p. 175; 100, loi, p. 175; 12.9, 131-133, p. 103.)

EcHiNODERMATA. — This large group includes the starfishes,
brittle-stars, sea-urchins, holothurians or sea-cucumbers, crinoids
or sea-lilies and feather-stars, and the extinct Mastoids and
cystideans. Echinoderms are found only in the sea, where they
are represented from between tide marks dow^n to the greatest
depths. They are especially characteristic of deep water.
(Figs. 6, p. 5; 35-38, p. 55; 41, 42., p. 71; 43, 44, p. 87; 88, 89,
109, p. 175; 12.0, p. 185.)

Nemertea. — A moderate sized group including species which
are found mostly in the sea, though a few live in fresh water and
some on land. In the sea they live chiefly on the bottom, in mud
and especially under stones or other objects lying on mud. But
some live exposed, and a few others are free floating. Most of
them have the most extraordinary power of elongating and
contracting the body. Some break to pieces with the greatest
facility, each piece later developing into a complete individual.
They are all carnivorous. (Fig. 106, p. 175, young.)

Ch^tognatha — arrow-worms. — A small group living wholly in
the sea, found everywhere in shallow or moderately deep w^atcr.
They are transparent in life, appearing like small thin glassy
fishes. They live freely suspended in the water. (Fig. 62., p. 11 1.)

Priapuloidea. — A very small group wholly confined to the
sea, wherein it is widely distributed.

^M THE NEW EVOLUTION ®ll

RoTiFERA — rotifers or wheel-animalcules . — A large group of uni-
versal occurrence in fresh water, but represented by only a few
species in the sea. Many of them are able effectively to protect
themselves when the pools and ponds dry up, and many can
survive heat almost as high as the boiling point. With the dry-
ing up of water the encapsuled rotifers and their eggs are blown
about and very widely scattered. Because of the great facility
with which they are distributed by winds, rotifers are always to
be found in water which has collected in sagging gutters, in the
axils of epiphytic plants on telephone wires or high up in the
trees — in fact anywhere that water collects and stands for a few
days. Many kinds of rotifers may be obtained by letting marsh
hay or even bark from trees in moist localities soak in water for
a week or so. Even bark from logs that have been stored
for some time in a cellar will sometimes yield rotifers. They
always appear in aquaria, and usually in goldfish bowls. A few
rotifers are parasitic, living in the intestines of earthworms,
in the canals of fresh water jellyfishes, in the body cavity of
sea-cucumbers, on crustaceans, and elsewhere. (Figs. 134, 136,
p. ^03.)

PoLYzoA — moss animalcules . — A large group almost entirely
marine, occurring from between tide marks down to the deepest
portions of the sea, though most abundantly represented in
shallow water and in water of moderate depth. One section of
the group, and a few species in another section, live in fresh
water. Most polyzoans form moss-like, leaf-like, fan-like, vine-
like, or simply encrusting colonies; but a very few species are
solitary. The most conspicuous fresh water type forms large
jelly-like masses, usually in late summer, about sticks or other
supports. In one fresh water type the colony as a whole crawls
about like a worm. (Figs. 67, 68, p. iii; 90, p. 175.)

Vermiformes. — A very large and exceedingly diversified group
including the tapeworms, flukes, turbellarians, spiny-headed
worms, nematodes or thread-worms, gordian worms or "hair-
snakes," and various other types. Most of the species are
internal parasites in other animals, a few are external parasites,
some live in plants, and some are free living, these last occurring
in the sea, in fresh water, and in moist earth. Some are parasitic
at one stage and free living at another, and many are parasitic
in one type of animal in the young stages and in a wholly different

^^ ZOOGENESIS "^^^

type of animal as adults. They may develop directly from the
egg, or they may pass through one, two, or several larval forms.

The most familiar exam^ples are the tapeworms, the hook-
worms, various "worms" affecting children, dogs, cats, cattle,
etc., the "vinegar-eels," the "wafers" of oysters, and the "hair-
snakes" seen wriggling in pools and troughs in summer, which
in the young stages are parasites in insects. (Figs. 5, p. 5; 54,
55, p. 97; 81-83, p. 161; 96-99, p. 175; ii6-i2.8, p. 185; 130, p. 103;
135, p. 103.)

Ctenophora — sea-walnuts, the Venus' girdle, etc. — A fairly
large group found only in the sea, more especially in the warmer
waters. The ctenophores are nearly all free-swimming and are
most abundant below the surface zone, but occasionally appear
in great numbers at the surface. A few of them are elongated,
flattened and worm-like and creep about on objects on or growing
from the sea floor. Most of them are transparent and as clear as
glass, the vibratile plates showing a beautiful play of iridescent
colors. A few are more or less deeply colored, usually pink
or red. (Fig. GG, p. iii.)

CcELENTERATA. — A Very large and very highly diversified group
including the sea-anemones or animal-flowers, the hydras, the
hydroids, the sea-pens, the sea-fans, the corals, the millepores,
the gorgonians, the antipatharians, the alcyonarians, the jelly-
fishes, the ctenophores, and various other types. Most of the
coslenterates are marine, living in shallow water or in water of
moderate depth, but mxany are found in very deep water and a few
in fresh water, the best known of these last being the hydras and
the little fresh water jellyfishes which are so curiously erratic
in their occurrence. Many coelenterates are solitary, like the
hydras and the sea-anemones, but most of them form bush-like,
tree-like, wand-like, fan-like, mushroom-like, feather-like, en-
crusting, or solid and massive colonies. Many form semi-
transparent or beautifully and delicately colored free-floating
colonies, of which the Portuguese man-of-war is an example.
Some kinds are only found in association with other animals,
particularly crabs (fig. 17, p. 47) and annelids, while a few are
parasitic on other coelenterates, on fish-eggs, ttc. (Figs. 3, 4,

P- 55 69-73» P- 1^7; 75-So» P- 1435 io3» i^S' io7» P- i75' no"
119, p. 185.)

PoRiFERA — Sponges. — A large and much diversified group with

[l6j ^

THE NEW EVOLUTION

the body mass encrusting, cushion-shaped, cup-shaped, saucer-
shaped, globular, tubular, rod-shaped, leaf-like, trumpet-shaped,
fan-shaped, mushroom-shaped, lobed, branched or digitate,
sessile or raised on a long stalk, etc. Almost all sponges contain
a supporting skeleton which may be limy, or silicious, or horny,
or silicious and horny, and is usually exceedingly complex.
Nearly all sponges are marine, living at all depths. Some types
are especially characteristic of deep water. But a few kinds of
sponges live in fresh water. All sponges when alive possess a
strong and disagreeable odor. The common bath sponge is the
cleaned skeleton of one of the horny sponges, and the "Venus'
flower basket" is the cleaned skeleton of one of the silicious
sponges. (Figs. 1x1-114, p. 185, development.)

Protozoa — the single-celled animals. — Very small, usually
microscopic, animals, forming an enormous group, which is the
most highly diversified of all the groups in the animal kingdom.
More or less familiar examples are the foraminifera, to which we
owe the great chalk deposits, the radiolarians, the infusorians,
the gregarines, the sporozoans, etc. They are found everywhere
in the sea and in fresh water, more or less throughout the bodies
of all other creatures, and everywhere on land. In a special
drought-resisting resting stage, many kinds are blown about over
the land and lodge in quantities even on the topmost twigs of
the tallest trees. If bits of bark or hay or dead leaves be placed
in water they will appear in a day or two, and soon the water
is swarming with them. Some of those that can be secured from
the bark of fire logs are large enough to be seen with the naked
eye, and many may be seen with a low power lens. Very many
live upon or within the bodies of other creatures. Crustaceans
are sometimes almost completely covered with a veritable forest
of stalked forms, while others wander about over the surface of
sea-urchins and other sea animals. Our bodies always contain
many thousands of various harmless kinds. But very many are
dangerous parasites, causing malaria and other diseases in man,
Texas fever in cattle, etc. On the other hand, some are indis-
pensable. Thus in the case of the termites or white-ants the
cellulose swallowed is broken up not by the digestive processes
of the insects, but by the intervention of various protozoans in
their intestinal canal, and the termites digest the substances
thus made available for them. Reproduction in the protozoans

[1.66]

$M ZOOGENESIS ^^

is commonly by division of the body into two equal parts, but
in some by the formation of buds which become detached, by the
breaking up of the body into "spores," or by other means; there
is, however, never any reproduction through the formation of
special sexual cells as in all other animal types. (Figs. 53,
p. 97; 87, p. 161.)

The broader features of the interrelationships between the
major groups may be appreciated by a study of the following
key, bearing in mind that very many important structural char-
acters are not mentioned in the key.

Key to the Major Groups of Animals

a^ Body composed of a vast number of cells
b^ body with definite organs and structures
c^ symmetry completely, or almost completely bilateral;
body with a dorsal and ventral surface, and the two
halves on either side of a plane passing through the mid-
line alike
d^ no trace of radial symmetry
e^ with a vascular system
/^ with a body cavity; no protrusible proboscis the
sheath of which runs the whole length of the body
g^ no water vascular system

h^ body never completely ensheathed in a tough
or hard segmented external skeleton; jaws
never formed of modified legs
i^ body not enclosed between a dorsal and ven-
tral shell; if enclosed between shells (as
in some mollusks) these are left and right
/ with a notochord, a hollow dorsally
placed nervous system, and a pharynx
opening to the exterior by lateral pass-
ages
k^ notochord extending practically the full length of the body;
body segmented
l^ dorsal nerve cord extending for some distance in front of the
notochord, and expanded at its anterior end into a brain;
anterior portion of the axial skeleton forming a skull en-
closing the brain Vertebrata

^67]

^^ THE NEW EVOLUTION

P notochord extending forward in front of the nerve cord;
no skull; no true brain

Cephalochorda
k? notochord not extending the full length of the body; body not
segmented
l^ notochord confined to the anterior portion of the body; body
with three divisions, the proboscis, the collar and the
trunk
m^ elongated and worm-like; collar not produced; alimen-
tary canal a straight tube; without asexual reproduc-
tion; free living, inhabiting burrows in sand or mud

Balanoglossida

m

body not worm-like; collar region produced into one or
more pairs of tentaculiferous arms; alimentary canal
U-shaped; reproducing asexually by budding; inhabit-
ing tubes secreted by the animals themselves

Cephalodiscida
P notochord confined to the hinder portion of the body, and
usually absent in adults

TuNICATA

y^ no true notochord; nervous system ventral,
and not hollow; no lateral openings
from the pharynx to the exterior
h} unsegmented; no chitinous bristles or setas on the body

P- no ventral foot, mantle-fold or shell; mouth associated with

a series of hollow ciliated tentacles arranged in a circle,

horseshoe, double horseshoe or double spiral; no special

sense organs; elongated and worm-like

nz^ perivisceral cavity divided into three intercommunicating

chambers; no horny structures on anterior portion of

body; inhabiting tubes secreted by themselves and

covered with foreign materials

Phoronidea
m^ body cavity very large and undivided; anterior protrusible
portion of body often covered with rows of horny
hooks or with small imbricating scale-like papillae

SiPUNCULOIDEA

P with a ventral foot, and usually a mantle-fold, and a uni-
valve or bivalve shell; no hollow ciliated tentacles about
the mouth, which is commonly provided with very

ZOOGENESIS

numerous teeth set in a radula, or a beak; various special
sense organs present; very rarely elongated and w^orm-like

MOLLUSCA

k^ body divided into numerous segments and usually much elon-
gated; ventral nerve cord almost invariably with a swelling
or ganglion in each segment; almost invariably with chitin-
ous setas or bristles embedded in and secreted by pits in the
skin

Annelida
i"^ body enclosed within a pair of shells, one of
which is dorsal and the other ventral

Brachiopoda
h"^ body completely enclosed in a usually tough or
hard segmented external skeleton; with
jointed legs, and usually other jointed
appendages, in the young or adult, or in all
stages; jaws formed of modified legs

Arthropoda
g^ a complicated water-vascular system, derived
from the coelom, present; body in the adult
more or less perfectly radial, usually in five
divisions, but bilateral in the younger stages;
body wall with abundant calcareous deposits
usually forming plates which generally bear
spines

ECHINODERMATA

p no body cavity; a protrusible proboscis lying in a
sheath running the whole length of the animal
on the dorsal side of the intestinal canal

Nemertea
e^ without a vascular system
f- mouth armed with chitinous teeth or stout bristles;
size moderate; no asexual reproduction of any
kind
g^ body fish-like, with fins, divided internally into
three segments; coelom highly developed, with
three pairs of chambers separated by transverse
septa; both sexes in the same individual;
pelagic

Ch^tognatha

WR THE NEW EVOLUTION ^^^^

^ body worm-like, unsegmented, with a spacious
undivided body cavity not connected with the
excretory or generative organs; living on the
bottom in sand or mud; sexes separate

Priapuloidea
f^ with a complicated generally retractile ciliated
apparatus in connection with the mouth, used in
the gathering of food; size very small; abundant
asexual reproduction
^ ciliated apparatus consisting of cilia about the
mouth in the form of a ring, or in lobes or vari-
ous patterns; asexual reproduction by unfer-
tilized eggs only; sexes separate and usually
very different; solitary, though sometimes
social

ROTIFERA

^ ciliated apparatus consisting of a circular or
horseshoe-shaped crown of ciliated tentacles
with the mouth in the middle; always with
asexual reproduction by budding, sometimes
also by the formation of "statoblasts" or by
fragmentation of the larvx; usually both sexes
in the same individual; almost always colonial,
forming plant-like colonies

POLYZOA

d?- with definite traces of radial symmetry (superposed
upon the bilateral) in the nervous system, the
digestive system, or the anterior end

VeRMI FORMES

c^ individual animals entirely, or almost completely, radi-
ally symmetrical, like a flower, with tentacles or other
processes about the edge of the large central cavity,
which is bounded by solid walls
d} body divided into quadrants, with two axes, a long and
a short, at right angles to each other; eight rows of
vibratile plates formed of fused cilia; two tentacles or
none; no stinging cells; never colonial; no asexual
reproduction; mesoderm present

Ctenophora

[170]

M ZOOGENESIS Ptf^

"t^

d"^ body radially symmetrical about the central axis only;
if the body is in fours, the crossed axes are of the same
length and the quadrants are alike; no vibratile
plates; four or more tentacles, lobes, or other proc-
esses present; stinging cells always present; always
with asexual reproduction, at least in the young
stages; no mesoderm

CcELENTERATA

b"^ no definite organs or structures; body a solid mass of very
varied form pierced by innumerable small holes which lead
into a system of canals running together and eventually
leading into the exterior by one or several large openings

PORIFERA

a^ Body composed of a single cell, or the equivalent of a single
cell

Protozoa

The relationships between the different animal types are of
two sorts, differences and resemblances, and the successful divi-
sion of the animal types into phyla is dependent upon the proper
appreciation of the relative importance of the differences and the
resemblances.

The potentialities of an animal form as an effective mechanism
are largely dependent upon the basic symmetry of the form. The
basic animal symmetries therefore should be regarded as the
dominating factors in animal morphology to which all other
factors are subordinated.

In the animal world there are five distinct types of symmetry
(fig. D, p. 150). These five types of symmetry are characteristic
of (i) all germ cells and all protozoans at some stage in their life
history; (z) the Coelenterata; (3) the Ctenophora; (4) the Vermi-
formes; and (5) all other types of animal life.

The symmetry of the single celled animals or protozoans is
based primarily on the symmetry of the sphere — that is, a sym-
metry radiating equally in all directions from a central point.
But this ideal symmetry is maintained, or closely approached,
in only a very few types most conspicuous of which are certain
heliozoans and radiolarians.

The symmetry of the sponges is based upon a mass production
of cells which do not become segregated into definite organs.

[vi]

THE NEW EVOLUTION

Sponges, therefore, cannot develop any very definite symmetry,
or a head end. Having no possibility of developing organs of
locomotion or for the prehension of prey they must remain
throughout their lives attached and are forced to find their
support through the development of an efficient mechanism for
straining minute organisms from the water. No other type of
existence is possible for them. When viewed at right angles to
the plane of attachment sponges are always more or less circu-
lar— or rather irregularly circular.

The symmetry of the coelenterates is always a modification of
a hemisphere — a sphere with one side pushed in forming a double-
walled hemisphere. The coelenterates are therefore radially
symmetrical. This radial symmetry renders them incapable of
effective locomotion in any definite line, since their sense organs
and nervous system are arranged in a circle lying in a plane at
right angles to the central axis and at some distance from it —
that is, about the periphery of the open pole of the hemisphere.
But this circular arrangement of the sense organs and nerves
rendering every sector of the animal as alert and as efficient as
every other sector peculiarly fits the coelenterates for remaining
fixed in one place and reaching out and capturing the organisms
in the water about them. Most of them feed upon other animals
of considerable size. They are by far the most successful and
the most numerous of the fixed animals. They are also fairly
successful as free-swimming animals. Not a few of them are
very large. Some of the attached gorgonians reach a height of
fifteen feet, and one of the common jellyfishes of northern seas
reaches a width of seven and a half feet across the bell, from
which depend tentacles more than one hundred and twenty feet
in length.

The ctenophores are commonly regarded as representing a sec-
tion of the Coelenterata. They were separated from the Coelente-
rata as a distinct phylum by the present author in 192.1. They
differ markedly from the coelenterates in various significant ways,
especially in their symmetry, in the presence of mesoderm, in the
entire absence of asexual reproduction and therefore of colony
formation, and in the absence of stinging cells. The ctenophores
have two body axes, one long and one short, crossing each other
in the middle at right angles. The two halves of the body on
either side of these two axes are alike. The body is thus divided

[2.72.]

ZOOGENESIS

into quadrants, the quadrants diagonally opposite each other
being alike, and reversed or mirror images of the two with which
they are paired. This cross symmetry permits the development
of a greatly elongated body, such as we see in the Venus' girdle
(Cestui) and to a lesser degree in the creeping forms. But no
matter what the form of the body may be, the center of the animal
is always the axis passing through the intersection of the crossed
planes, and all the radii are always alike on either side of this
axis. So the elongated ctenophores are always double ended
with the head, so to speak, in the center of the body. This
cross symmetry is not adaptable to the requirements of a fixed
existence, so the ctenophores are all free swimming or creeping
creatures. But their locomotor powers are limited because of
the similarity of the two sides of the body on either side of the
median plane. Because of the mechanical limitations imposed
by their unique symmetry the ctenophores are much less numerous
in species than the coelenterates, sponges or protozoans.

The several animal types here grouped under the Vermiformes
are usually distributed among several different phyla because
of the great differences in bodily structure that they show. There
is no denying the fact that these differences are important. At
the same time there is no denying the equally obvious fact that
all these creatures agree among themselves and differ from all
other animals in possessing a symmetry which is in part radial
and in part — generally for the most part — bilateral. Thus in
the tapeworms the head or scolex is commonly (though not
alwaysj) radially symmetrical with four equal sectors. In the
spiny-headed worms (Acanthocephala) which have by some
authors been associated with the tapeworms, by others associated
with the nematodes, and by still others regarded as quite without
close relatives, the anterior end is radially symmetrical. In the
turbellarians the mouth is on the ventral surface at, in front of,
or behind the middle, and the digestive cavities commonly radiate
from the base of the pharynx. Various transition forms unite
the turbellarians with the wholly parasitic flukes or trematodes.
In the trematodes the mouth is always at the anterior end and
usually leads into a forked intestine. The nervous system,
however, is radially arranged, consisting of six longitudinal
cords, two ventral, two dorsal and two lateral, all of which are
connected by transverse anastomoses. There are various types

^73]

THE NEW EVOLUTION

which intergrade between the trematodes and the tapeworms.
As the spiny-headed worms are now considered to be more or less
closely related to the tapeworms, it is evident that the union
of the tapeworms, spiny-headed worms, flukes and turbellarians
in a single phylum is a logical disposition of these groups. The
nematodes or thread-worms, however, seem at first sight to have
very little in common with any one of these groups. They have
been generally associated with the spiny-headed worms and the
gordian worms in the phylum Nemathelminthes. The nervous
system of the nematodes consists of a ring about the gullet from
which six anterior and six posterior trunks arise. There are also
other suggestions of radial symmetry. These traces of radial
symmetry are the only features which definitely align the nema-
todes with anything else. The nematodes entirely lack ciliated
tissue, all of them molt, at least in the young stages, most of
them possess a spinneret, many are more or less sharply and dis-
tinctly segmented externally, and some have segmented append-
ages as in the arthropods and some rotifers. But the differences
between the nematodes, the arthropods and the rotifers are much
greater than the resemblances. The characteristic nematode
features seem in a most extraordinary way to supplement the
features found in the tapeworms, flukes, etc., thus indicating that
the Vermiformes as here understood is really a natural group.
The gordian worms or "hair-snakes" which have essentially
the body form of nematodes but are otherwise very different, are
radially symmetrical at the anterior end in the larval stage. We
may regard the tapeworms, spiny-headed worms, flukes, turbel-
larians, nematodes and gordian worms as wholly anomalous and
without any affinities to each other or to anything else — each
as a sort of zoological accident — or we may regard the occurrence
in all of them of traces of radial symmetry as significant and as
showing that they differ equally from the radially symmetrical
animals on the one hand and from the bilateral animals on the
other. We cannot adopt the former alternative without imply-
ing a lack of order in the animal world, which is an inconceivable
assumption. The only reasonable course is to accept the latter
alternative and to consider all these creatures collectively as
representing a rather heterogeneous phylum intermediate between
the radially symmetrical coelenterates and the more complex
bilaterally symmetrical animals.

[2-74]

^^ ZOOGENESIS "^^^

Except for those just mentioned, all the animal phyla include
only forms which are bilaterally symmetrical. The echinoderms
appear to be radially symmetrical, but the radial symmetry is
far from perfect, and they are always bilateral in the young stages.

In the preceding key the characters used in separating the
various phyla of bilaterally symmetrical animals are the most
obvious or the most easily understood, but not necessarily the
most important.

It is generally agreed that the supporting rod known as the
notochord is a very important structural feature, so that the use
of its presence or absence in separating the Vertebrata, Cephalo-
chorda, Balanoglossida, Cephalodiscida and Tunicata from all
the other phyla can scarcely be questioned.

The Vertebrata differ from the other four groups in having a
definite skull (they are therefore often called the Craniata), in
having the notochord surrounded by a stiff sheath and almost
invariably divided up into segments which correspond with those
of the embryonic muscular system, forming the "backbone," and
in almost invariably possessing a movable jaw and two pairs
of limbs.

In the key they are paired with the Cephalochorda solely
because the latter in their general appearance resemble fishes far
more than they do anything else. But the Cephalochorda are
undoubtedly more closely related to the Tunicata, Balanoglossida
and Cephalodiscida — especially to the first named — than they
are to the Vertebrata.

Regarding the groups from the Phoronidea to the Polyzoa
inclusive there is no agreement among zoologists as to what the
most important structural features are, or as to what the actual
interrelationships between the groups may be.

t75]

EXPLANATION OF THE FIGURES

Illustrations of Animal Symmetries (Page 5)

Fig. I. — A bilaterally symmetrical animal, with the two sides —
right and left — of a plane passing through the mid-
dle of the body alike. The European spurge hawk-
moth (Deile-phila eu-phorbia).

Fig. X. — A bilaterally symmetrical animal. A curious fish (Hali-
eutella lappa). From Gill, after Goode and Bean.

Fig. 3. — A radially symmetrical animal — eight similar sectors
surround the central axis. A jellyfish (Discofnedusa
philippina) from the Philippines. From Mayor.

Fig. 4 — An animal with "biradiate" symmetry — that is, with
radial symmetry modified by the elongation of the
central mouth into a slit. A sea-anemone (Poly-
siphonia tuherosa) dredged from a depth of 3 ,390 feet.
From the Challenger reports.

Fig. 5.' — A jointed or segmented tapeworm (Ttxnia macrocystis)
from a wild-cat. The head, or "scolex," is radially
symmetrical (four sided) but the body is bilaterally
symmetrical. From Hall.

Fig. 6. — Pseudoradial symmetry. The body is divided into five
almost precisely similar parts, but the internal organs
are not all radially symmetrical, and the young are
bilaterally symmetrical. A sea-lily or crinoid
(Ftilocrinus pinnatus) from a depth of 9,52.8 feet,
originally described by the author.

Different Types of Insects (Page 11)

Figs. 7-9. — A plant-louse or aphid (Lachnus platanicola). Cour-
tesy of the Department of Agriculture.

Fig. 10. — The cotton-boll weevil QAnthonomus grandis) with
wings extended. Courtesy of the Department of
Agriculture.

Fig. II. — The grape leaf-hopper (Typhlocyba comes). Courtesy of
the Department of Agriculture.

Fig. II.' — A whip-cracker butterfly QAgeronia fumosa).

bTTJ

THE NEW EVOLUTION

Fig. 13. — Caterpillar of the case-making clothes-moth in its case
(Tinea pellionella). Courtesy of the Department of
Agriculture.

Fig. 14.' — A staphylinid beetle (Corymb ogastcr fniranda) found in
the nests of white-ants or termites (Cornitermes pug-
nax) in British Guiana. From W. M. Mann.

Fig. 15. — A pangonid fly (Pangonia longirostris), related to our
horse-flies. From Hardwicke.

Fig. 16. — Adult male of the fluted scale insect (leery a purchast).
Courtesy of the Department of Agriculture.

Different Types of Insects (Page 33)

Fig. 17. — An adult female scale insect (Diaspis lanatus). Cour-
tesy of the Department of Agriculture.

Fig. 18. — ^The jigger-flea or chigoe (Tunga penetrans)', a female be-
fore entering the skin. Courtesy of the Department
of Agriculture.

Fig. 19. — A mantis (Calidomantis hosia) from west Africa. From
Rehn.

Fig. -lo. — A braconid parasite of wood-boring beetle grubs (Allod-
or us tomaxia). From Aldrich.

Fig. II. — A dragon-fly (Ischnura carvula) from the western United
States. From Kennedy.

Fig. 11. — A wingless fly (Nyaeribia, sp.) which lives as a parasite
on bats. After Packard.

Fig. 13. — A "big bed-bug" (Reduvius personatus). From Riley
and Johannsen.

Different Types of Crustaceans (Page 47)

Fig. 14. — A "fish-louse," a curious crustacean — the female of a
copepod (Lernaenkus longiventris) parasitic on vari-
ous fishes. The young are typical crustaceans.
From Wilson.

Fig. 15. — A euphausian (Eupbausia pellucida). From the Chal-
lenger reports.

Fig. 16. — A curious amphipod (Eusirus cuspidatus). From Wy-
ville Thomson.

Fig. 17. — A hermit-crab (Catapagurus sharreri)\ the hinder portion
of the body is enclosed within a group of sea-anem-
ones. From A. Agassiz,

ZOOGENESIS

Fig. i8. — A curious crustacean (Cystosoma nepun'i). From the

Challenger reports.
Fig. i9. — A spider-crab QAnisonotus curvirostris) common in depths

of 180-1,800 feet in the West Indies. From A.

Agassiz.
Fig. 30. — A stalked barnacle QScalpellum penfacrinarum) known

only from sea-lilies. From Pilsbry, after A. H.

Clark.

Some Fossil Animals (Page 55)

Fig. 3 1 . — Restoration of an eurypterid (Eurypterus fischerf). After

Schmidt.
Fig. 31. — A trilobite (Dalmanites Itmulurus^. From Zittel, after

Hall.
Figs. 33-34. — An ammonite (Macrocephalites macrocephalus).

From Zittel.
Figs. 35-36.' — A blastoid (Fentremites sulcatus). From Zittel.
Figs. 37-38. — A cystid (Echinospharites aurantium). From Zittel.
Fig. 39. — A graptolite (Tetragraptus bryonoides). From Zittel,

after Hall.
Fig. 40. — A graptolite (Didymograptus pennatulus) . From Zittel,

after Hall.

Sea-urchin and Starfish (Page 71)

Fig. 41. — A sea-urchin (Forocidaris sharreri) from the West Indies.

From A. Agassiz.
Fig. 42.. — The only known individual of a starfish QAnthenea mexi-

cana) from the west coast of Mexico, originally

described by the author.

Feather-star and Brittle-star (Page 87)

Fig. 43. — The rosy feather-star QAntedon bifida). From A. H.

Clark, after W. B. Carpenter.
Fig. 44. — A long armed brittle-star (Ophiocreas spinulosus). From

A. Agassiz.

Various Types of Mollusks, a Planarian, a Fluke, and a

FORAMINIFERAN (PaGE 97)

Fig. 45. — A cephalopod moUusk — a squid (Mastigoteuthis agas-
si^it). From A. Agassiz.

[2-79]

THE NEW EVOLUTION f^'^

Fig. 46. — A pelagic mollusk (^Atalanta, sp.). From A. Agassiz.
Fig. 47. — A curious dark blue mollusk (Glaucus^ sp.) common on

the surface of the Gulf Stream. From A. Agassiz.
Fig. 48. — A pteropod (Styliola, sp.). From A. Agassiz.
Fig. 49. — A shipworm (Teredo tiavalis). From Caiman.
Fig. 50. — A pelagic mollusk Qjatithina, sp.) very common on the

surface of Gulf Stream. From A. Agassiz.
Fig. 51. — A gastropod or snail-like mollusk (Thais lamellosd).

From Dall.
Fig. 52.. — A bivalve mollusk or pelecypod. A fresh water clam

(Lampsilis salinasensis) from Mexico. From Dall.
Fig. 53. — A foraminiferan (Biloculina tenera) with the pseudo-
podia extended. From A. Agassiz, after Schultze.
Fig. 54. — A planarian (Planaria polychroa) with the pharynx,

bearing the mouth at the end, extended. From

Sedgwick.
Fig. 5 5 . — The liver fluke (Dhfomum bepaticum). From Sedgwick,

after Sommer.

Various Types of Animal Life (Page hi)

Fig. 56. — An appendicularian. From A. Agassiz.

Fig. 57. — A free-swimming tunicate (Doliolufjz). From A.

Agassiz.
Fig. 5 8.' — ^The solitary form of a salp (Salpa cahoti). From A.

Agassiz.
Fig. 59. — A pyrosoma — a colony of closely packed tunicates

forming a hollow cylinder. From A. Agassiz.
Fig. 60. — A brachiopod or lamp-shell (Terebratula cubensis). From

A. Agassiz.
Fig. 61. — A cephalodiscid (Cephalodiscus dodecalophus). From the

Challenger reports.
Fig. 6i. — An arrow-worm or ch^tognath (Sagitta, sp.). From

A. Agassiz.
Fig. 63. — A cephalodiscid (Rhabdopleura mrmanf). From Lan-

kester.
Fig. 64. — A free-living or pelagic copepod. These creatures are

of immense importance. From A. Agassiz.
Fig. 65. — An annelid or jointed worm that lives floating freely

at or near the surface of the sea (Tomopteris, sp.).

From A. Agassiz.

^^ ZOOGENESIS "^^^"^

Fig. 66. — A sea-walnut or ctenophore (Mnemiopis leideyt). From

A. Agassiz.
Fig. 67. — A colony of polyzoans {lS\ucrondla -^avondld). From

Lankester.
Fig. 68. — A portion of the preceding, much enlarged. From

Lankester.

Some Ccelenterates and a Solenogaster (Page 12.7)

Fig. 69. — A hydroid (Hippirella annulatd). From A. Agassiz,

after Fewkes.
Fig. 70. — An antipatharian {Antipathes columnaris). From A.

Agassiz, after Pourtales.
Fig. 71. — A small portion of another kind of antipatharian.

From A. Agassiz, after Pourtales.
Fig. 71. — An umbellularian (U??2belhdaria guntheri). From A.

Agassiz.
Fig. 73. — A common jellyfish of warm seas (Velella mutica).

From A. Agassiz.
Fig. 74. — A moUusk of the type known as a solenogaster (Frone-

omenia sluiteri). From Sedgwick, after Hubrecht.

Various Ccelenterates (Page 143)

Fig. 75. — Much enlarged portion of a colony of a hydroid (Obelia

artkulatd). From Fraser,
Fig. 76. — A colony of the same hydroid. From Fraser.
Fig. 77. — A sea-pen or pennatulid QAnthopikifn thomson'i). From

A. Agassiz.
Fig. 78. — A jellyfish (Glossocodon temiirostris) from the Gulf

Stream. From A. Agassiz.
Fig. 79. — A deep-sea sea-anemone QActinauge nodosa). From A.

Agassiz, after Verrill.
Fig. 80. — A stony coral or madreporarian (Forites davarid).

From A. Agassiz.

Various Types of Animal Life (Page 161)

Fig. 81. — A parasitic nematode (Trichostrongyhis fiberius). From

Hall, after Barker.
Fig. 8i. — A tapeworm (Mtdtice-ps multke-ps) from a dog. From

Hall.

"^"^ THE NEW EVOLUTION CT

Fig. 83 . — A tapeworm (Echinococcus granulosus^ found in the dog,

cat, mountain-lion, etc. From Hall, after Leuckart.
Fig. 84. — A myzostomid worm (M.y%pstomum costatu7n). From A.

H. Clark, after Boulenger.
Fig. 85. — A jointed worm or annelid QAmphinome pallasif). From

A. Agassiz.
Fig. 86. — A peridinian (Ceratium tripos^. From Sedgwick, after

Stein.
Fig. 87. — A group of single celled animals — trypanosomes (Try-

■panosoma -pecaudf) from a tsetse-fly (Glossina palpalis^.

From Hindle, after Roubaud.

Young Stages of Various Animals (Page 175)

Fig. 88. — A bipinnaria — a young stage of the common starfish

QAsterias rubens forbesit). From A. Agassiz.
Fig. 89. — A pluteus — a young stage of the common green sea-
urchin {Strongylocentrotus drdbachiensis^. From A.

Agassiz.
Fig. 90. — A cyphonautes — a young stage of a polyzoan. From

A. Agassiz.
Fig. 91. — A larval crustacean QPanopus, sp.). From A. Agassiz.
Fig. 92.. — A larval stage of a crab (Porcellana, sp.). From A.

Agassiz.
Fig. 93 . — One of the young stages of the common green crab (Car-

cinus manas^. From A. Agassiz.
Fig. 94. — A tornaria — a young stage of a balanoglossid. From

A. Agassiz.
Fig. 95 . — A young stage of the common periwinkle (Littorind) of

the New England coast. From A. Agassiz.
Figs. 96-99. — Larval stages of the liver fluke (Distomum hepati-

cum?). Fig. 96. — A miracidium. After Thomas.

Fig. 97. — A redia. After Thomas. Fig. 98. — A

sporocyst containing redi^e. After Leuckart. Fig.

99. — A cercaria. After Thomas.
Fig. 100. — The nauplius stage of a copepod (Dactylopus, sp.).

From A. Agassiz.
Fig. ioi. — A young stage of a hermit-crab (Pagurus, sp.). From

A. Agassiz.
Fig. loi. — An actinotrocha — a larval form of a phoronid. After

Masterman.

ZOOGENESIS

Fig. 103.- — The fourth larval stage of a small jellyfish (Glossocodon,

sp.); see fig. 78, p. 143 . From A. Agassiz.
Fig. 104. — A larval stage of an annelid or jointed worm (Leuco-

dore, sp.). From A. Agassiz.
Fig. 105. — The sixth larval stage of a small jellyfish (Glossocodon,

sp.) ; see fig. 103 . From A. Agassiz.
Fig. 106. — A pilidium — a larval form of a nemertean. From A.

Agassiz.
Fig. 107. — A larval stage of a small sea-anemone (Edwardsia, sp.).

From A. Agassiz.
Fig. 108. — A larval stage of one of the annelids or jointed v^^orms

(Polygordius, sp.). From A. Agassiz.
Fig. 109. — A larval stage of the Mediterranean rosy feather-star

(^Antedonmediterranea)', see fig. 43, p. 87. From A.

H. Clark, after Bury.

Early Developmental Stages, and Two Curious Animal

Types (Page 185)

Figs. 110-119. — Early developmental stages of a coral (Monoxenia
darwinit). FromHaeckel. Figs, iio-iii. — Egg or
ovum. Fig. III. — Two celled stage. Fig. 113. — ■
Four celled stage. Fig. 114. — ^The blastula. Fig.
115. — The blastula in cross section. Fig. 116. —
The gastrula at the commencement of its formation,
seen in cross section. Fig. 117. — ^The completed
gastrula, seen in cross section, showing the outer
(ectodermal) and the inner (endodermal) layers of
cells. Fig. 118. — A free-swimming blastula, with
cilia. Fig. 119. — A free-swimming gastrula, with
cilia.

Fig. 12.0. — Gastrula of a sea-urchin (Toxopneustes brevispinosus)
seen in cross section, showing the mesodermal net-
work between the outer (ectodermal) and inner
(endodermal) layers of cells. After Selenka.

Figs. 111-115. — Early developmental stages of a sponge {Sycon
ra-phanus). After F. E. Schultze. Fig. iii. —
Ovum. Fig. 111. — Four celled stage. Fig. 113. —
Sixteen celled stage. Fig. 114. — Blastosphere with
large dark granular cells at the open pole. Fig.

__

^^ THE NEW EVOLUTION ^|^

12.5. ■ — Free-swimming larva; the upper half of the

body is endodermal and the lower half is ectodermal.
Fig. 12.6. — A dicyemid (Dicyemopsis macroce-phalus), a creature

more or less closely related to the flukes. After van

Beneden.
Figs. 12.7-1x8. — A rhopaluran (Rhopalura giardif), a creature more

or less closely related to the flukes; 12.7, male; 1x8,

female. After van Beneden.

Various Types of Animal Life (Page 103)

Fig. 119. — A bird-louse (Lipeuras variabilis). From Denny.
Fig. 130. — A "Miiller's larva" — the young of a polyclad turbel-

larian (Eurylepta amiculata). After Hallez.
Fig. 131. — Maggot of a horse-fly (Tabanus kirzgt). From Hindle,

after King.
Fig. 132.. — Maggot of the European rat-flea (Ceratophyllus fasci-

afus). Courtesy of the Department of Agriculture.
Fig. 133. — A young dragon-fly (^Archilestes calijomica). From

Kennedy.
Fig. 134. — A gastrotricha {Chcztonotus maximus). After Biitschli.
Fig. 135. — M-icrostomum lineare. After von Graff.
Fig. 136. — A rotifer (Euchlaris pellucida^y side view. From Har-

ring.

[x84]

Ov^/

O/'x

-C^/'^

duw

x>^/

or-'

INDEX

Acanthocephala, 173

acanthocephalids, -l^z

actinotrocha, 151

African swallowtail, 138

agriculture of ants, 9

alcyonarians, X39, 165

Algonkian, 99

alligators, 7, 11, 107

American eel, 131, 149, 163

ammonites, no, 112.

Amaba, 15^

amphibians, 6, 45, 50, 51, 78, 80, 88,

89, 103, 149, i6i, i2.i, 2.11, 113, 161
AmphioxuSy 161

ancestry of and diversity in dogs, 184
ancestry of man, 118, 130
angle-wings, 134, 141
animal-flowers, 165
animals of the Cambrian, loi
animals of the past, xii
animals, symmetries of, 171
animal world a closely unified entity,

160
Annelida, 161, 169
annelids, 69, 100, loi, 110, m, 150,

155, 190, 105, io6, 147, 155, 156, 158
ant agriculture, 9
ant-eating butterflies, 46
anthropoid or man-like apes, 1, 6, 17,

2.8,19,114, 115,117
antipatharians, 139, 165
anfiquus, Fusus, 144
ant-lions, 10
ants, 7, 8, 9, II, 15, 16, 18, 11, 35, 48,

138,159,133

ape-man, Java, 116

apes, 15,18, 19, 117, 130

aphid-feeding butterfly, 8

aphids, 8, 9, 10

appendicularians, 71

Apferjx, 145

arachnids, 111

Archaopteryx, 89, 91, 111

archiannelid worms, 103

Arctic tern, 81

Aristolochia swallowtails, 31, 140

arrow-worms, 65, 76, loi, 149, 161,

190, 157, 163
Arthropoda, 65, 108, 117, 161, 169
arthropods, 78, 79, 118, 119, 110, iii,

111, 168, 179, 189, 190, 101, 106, 111,

156, 157, 163, 174
ascidians, 71
asexual reproduction, 155, 156, 157,

atalanta, Cynthia, 86
Aurellia, development of, 151
auricularia, 150

B

Baboons, 17

baby stage of man, 15

backboned animals, 45, 167, 181, 189,

111, X13, 16 1
bacteria, 35, 40, 41, 51
balance of animal life, changes in, z
balance of life, 114, 113
Balanoglossida, 161, 168, 175
balanoglossids, 70, 103, 150, 196, 199,

100, 157
Baltimore oriole, 13
barnacles, 66, 119, 151, 153, 161, 163

U85]

INDEX

or^

barnacles, parasitic, 152.

barracudas, 118

barrel-shaped larvx, 150

basic symmetries of animals, 171

bath sponge, z66

bats, 35, 60, 8x, 83, 85

bats, hearing of, 82.

beach-fleas, z63

beaked butterfly, 34

bears, 48

beavers, 7, 14

bees, 8, 10, 11, 13, 15, 16, 18, zz, 45,
48, 138, 159, zi8, i33

bees, carpenter, 11

bees, leaf-cutting, 11

bees, solitary, 11

bees, varnisher, 11

beetles, 18, 46, 156

bipinnaria, 150

birds, 6, 7, 11, li, 13, 14, 15, 17, 18,
19, io, i2., Z3, 35, 45, 48, 49, 60,
80, 81, 8i, 83, 88, 89, 93, 103, 107,

116, 118, 137, 159, 163, 2.17, XZI, 1.ZZ,

113, Z33,Z47, i6i
birds, hearing of, 80, 81
birds, parental care in, 88
birds' nests, 12., 13
bison, 93

bivalves, zoz, zxi
black mice, 145
blastoids, 2^.1, 163
blastula, 191, 139, Z49
blind dolphins, 84
blue, common, 135, 136
blue-birds, 12.
blue-bottles, 35
blues, 141

bony fishes or teleosts, i8z
bot-flies, 118
bower-birds, 13

brachiolaria, 150

Brachiopoda, x6z, ^69

brachiopods, 70, 100, loi, no, iiz,

IZ3, 1Z5, 153, i6z, Z57
Branchiostoma, z6i
brittle-stars, lox, izi, 150, 155, 157,

ioi, zzi, zzz, Z63
brush-turkeys, 7, 11
bugs, 35, 45, 156

bull-dog, 4, 147, 184, 186, 187, Z30
bull-dog fishes, 147
butterflies, xi, 16, 30, 3Z, 34, 35, 36, 45,

46, 48, 131, 137, 149, 156, 160, Z18
butterflies, ant-eating, 46
butterflies, asphid-feeding, 8
butterflies, beaked, 34
butterflies, fossil, 31
butterflies, lycasnid, 8
butterfly, cabbage, 3Z, 34
butterfly, carnivorous, 141
butterfly, copper, 136

Cabbage butterfly, 3Z, 34
caddis-flies, 8, 10, 16
California woodpecker, 15
Cambrian, loi, loz, 103, 104, 108, iiz,

1Z5, iz6 (see table on p. 99)
Cambrian animals, loi
camels, 93, 184
Canidas, i8z
Carboniferous, 108, iiz, iz6, 178 (see

table on p. 99)
Carnivora, 181, i8z
carnivorous butterflies, 141
carpenter bees, 11
cassiques, iz
cassowaries, 145
caterpillars, 30, 3Z, 34, 35, 46, 6z, 78,

149

[l86]

INDEX

v.'V/^'

caterpillar wasps, 35

cats, zo, 7-1, 118, 145, 181, 182.

cell behavior in early embryology, ijx,

centipedes, 117, loi
Cephalochorda, z6i, 2.68, 175
cephalochordates, 70, 196, 199, ioo, 157
Cephalodiscida, z6i, z68, Z75
cephalodiscids, 70, 103, 155, 196, 199,

xoo, Z57
Cephalodiscus, z6i
cephalopods, loz, iiz, zzi
ceratioid fishes, i6z
cercaria, 151, Z5Z
cestodes, 1Z4, Z4Z, Z58
Cestus, 153, Z73
Cha:tognatha, Z63, Z69
chxtognaths, 70, loi, 149, i6z, 190,

2-57, 2.63
chambered nautilus, 109, no
change in symmetry of echinoderms

during growth, 150
changes in the balance of animal life, z
chemical senses of insects, 85, 86
chimpanzees, 4, Z5, ZZ4
chordates, 199
clams, 66, 78, Z47, z6z
clams, fresh- water, 118
clothes moth, 8
cobra, 60
coccids, 9

cocoon of insects, 8, 16
Codosiga, 15Z

Coelenterata, Z39, Z65, Z71, Z7Z
coelenterates, 70, loz, 155, 159, 160,

i94> 195 > 197, 2-42-, 2.43, Z44, Z45, Z47,

Z49, Z5Z, Z53, Z56, Z65, Z71, Z7Z, Z73,

2-74
ccelom, Z53, Z55

collies, 4

common black swallowtail, 139, 141

common Aristolochia swallowtail, 137

common blue, 136

common western swallowtail, 136

concurrent evolution, zii

conditions on the earth when life first
began, xiii

conditions under which food is offered,
xii

contacts of living things, xi

continuity of descent with discon-
tinuity of form, 183, Z30

continuity of life, xii, 164, 189, zo8

controlling features governing life on
land, 63

controlling senses, 10

cooling of the body in bats, 8z, 83

cooling of the body in elephants, 83

copepods, 65

copper butterfly, 136

coppers, 141

corals, 66, 78, 95, loz, 104, iz6, 153,

2-39. 2.65
cosmic significance of evolution, zi6
crabs, 67, 79, izo, Z63
Craniata, Z75
creepers, 49

creeping ctenophores, 153, Z73
crested flycatchers, 13
Cretaceous, i, 89, 106, 107, 109, iiz,

178 (see table on p. 99)
crinoids, 7Z, loi, zoi, zoz, zzi, Z63
crocodile-bird, iz
crocodiles, 7, 11, 75, 107
crocodilians, 89, 116, 178
crows, 13, 14
crustaceans, 65, 69, 76, 79, 84, 100, loi,

107, 114, 116, 117, 118, izo, 151,

15Z, 153, 155, 183, zoz, Z18, ZZI, ZZ3,

z6z,z63, Z64

[^87]

INDEX

Ctenophora, 165, zyo, zyi
ctenophores, 103, 153, 160, Z41, X4z,

2.65, X72.

ctenophores, creeping, 153, X73

cuttle-fish, 79, 12.0, ioi

cyclostomes (lampreys and hag-fishes),

i8z
Cynthia atalantUy 86
cyphonautes, 151
cystideans (or cystids), loi, xxi, ^63

D

Dawn horse, 174, 176

dawsont, Eoanfbropus, 2.2.6

deep sea fishes, 74, 84

dependence of species on special senses,

86
development of Aurellia, Z5 1
Devonian, 108, iiz (see table on p. 99)
diatoms, izo
Dkyema, Z43
Dicyemella, Z43
Dicyetnopsis, Z43
digger wasps, 7, 16
dinosaurs, 106, 178
disintegration of rocks, 37, 53
dogs, 3, Z3, 146, 147, 181, 184, 186,

187, 188, Z19, Z30
dogs, hairless, 146, 186, 187, Z19, Z30
dolphins, blind, 84
domestication of animals, 187, 188
dragon-flies, 35
dying of the sea, 96

Earliest forms of life, xiii
earthworms, 41', 46, 48, 63, 81, 8z, 84,

izo, i6z, z6z, Z64
Echinodermata, Z63, Z69

echinoderms, 7Z, loi, 114, izi, izz,
150, 151, 168, 179, i8z, 189, zoo, zoi,
Z05, Z06, zzi, Z47, Z57, Z63, Z75

echinoids, loz

eel, American, 131, 149, 163

effect of climatic change on life, iz6,
iz8

elephants, i, 43

elver, 149

English sparrow, 13

Eoanthropus dawsont, 2.2.6

Eocene, 174, 176, 177, 178, 181, i8z,
zz8, ZZ9 (see table on p. 99)

Eohippus, 174, 176, 177, Z04, Z06, ZZ9

Epistylis, 15Z

erectus. Pithecanthropus, 2.2.6

eurypterids, 108, iiz, 190

evolution in its cosmic significance, zi6

evolution, concurrent, zii

evolution, problem of, xiii

evolutionary lines, 166, 167, 170, 180,
181, ziz, Z13

exchange of information by insects, 8

exclusively marine phyla, 70, 71

eyes, 77, 83

Family, the human, 6, zo, Z7, Z3Z
family, serial dependent, 6, 11, zo
faunal peculiarities of Amboina, 140
faunal peculiarities of Celebes, 139
faunal peculiarities of Jamaica, 140
faunal peculiarities of mountain re-
gions, 140
faunal peculiarities of New Guinea

(Papua), 140
faunal peculiarities of tropical America,

139
faunal variations in dififerent regions,

iz8, IZ9

[x88]

s>/^

INDEX

o^^

^1^

feather-star, variable Indo-Pacific, 131
feather-stars, 72., izi, 13^, 133, 148,

150, I5Z, xoi, 163
Felidas (cats), i8z
fire-flies as ornaments, 13
fishes, 4, 6, 51, 65, 66, 67, 78, 79, 80,

84, 88, 89, 95, 96, loi, 116, 118, lio,

149, i6i, 182., zzi, ZZ3, z6i
fishes, bull-dog, 147
fishes, ceratioid, i6z
fishes, deep sea, 74, 84
fish-lice, 118
flat-fishes, 144
flat worms, 103, 155, Z53
fleas, 118
flickers, 13

flies, 18, 35, 156, 158, Z18
flight, 60

flight of spiders, 61
flukes, 160, Z4Z, Z43, Z5Z, Z53, Z55,

Z58, Z64, Z73, Z74
flycatcher, crested 13
flying-fishes, 79
flying-foxes, 8z

flying lemur (Galeofithecus), 60
flying lizards, 60
flying squirrels, 60
food of animals, xii, 37, 39, 40, 41,

43, 44, zio
food of sea animals, 41
foraminifera, 104, z66
formation of soils, 3Z, 37
fossils, 91
fossil butterflies, 3Z
fossil feathers, 9Z, 94
fossil sea reptiles, 96
fossorial (digger) wasps, Z3
fresh-water animals, larval peculiarities

of, 149
fresh-water clams, 118

fritillaries, 34, 46

frogs, 43' 45' 46' 5O' 149
fruit-bats, 8z, 83, 85
fungi, 40, 41, 59
fungus beetles, 59
Fusus antiquus, 144

Gallinula ochropis, 145

gaps in the evolutionary lines, 167, i8o

gastropods, loz, zoz, zzi, zzz

gastrotrichas, 103

gastrula, 153, 19Z, 193, 194, 197, 198,

199, Z39, Z41, Z4Z, Z47, Z48, Z49, Z56,

Z58, Z59
gephyrean worms, loi, loz, 1Z5
giant wolves, 93
gibbons, Z5, ZZ4
glass-eel, 149
goats, 145
golden plover, 81
Goniaulax, 96

gordian worms, Z4Z, Z43, Z64, Z74
gorgonians, 6G, Z39, Z65, Z7Z
gorillas, 4, Z5, ZZ4
graptolites, loi, Z55, Z56
grasshoppers, 45, 135, 156
gray brahma hen, 145
grebes, 13
gregarines, z66

greyhounds, 4, 184, 185, 187, Z3C
ground-sloths, 93
grubs, 45
guinea-pigs, 145
gulls, 145

H

Hairless dogs, 146, 186, 187, Z19, Z30
hair-snakes, Z4Z, Z64, Z65, Z74
hair-streaks, 141, 14Z

[189]

o^^

INDEX

.^■0

hake, 95

half-somersault during development,

hand, the human, x'^, -2.6, xy, 1x5, ^31

hawks, 118, 145

hearing of bats, 82.

hearing of birds, 80, 82.

heliozoans, zyi

hemipterous insects, 158

hen, gray brahma, 145

hermit-crabs, 79

Hesperioidea, 2.02.

heteropods, 103

hirudinid worms, 103

hoarding habit, 14, 15

holothurians, loi, 12.1, 150, 153, 2.01,

2.63
hook-worms, ^65
horned larks, 49
hornets, 35
horses, 170, 171, ijx, 173, 174, 176,

177, 180, 184, Z04, 105, io6, ^2.8
horses, naked or hairless, 146, 119
horse-shoe crab, 109
hoxinds, 4, 184, 186
house-flies, 45
human attributes, 6, 7, 16, 17, 18, 12.4,

Z30, X3I
human attributes in birds, 7, 17
human attributes in insects, 7, 16
human attributes in other mammals,

7, 17
human attributes in rodents, 7, 15
human children, X5, 2.6, 2.7
human culture, origin of, ^31
human family, 6, zo, Z7, Z3Z
human hand, Z5, z6, Z7, ZZ5, Z31
human social system, zz, z8
human society, zz, z8
hyjenas, 184

hydras, 194, Z39, Z65
hydroids, 66, Z35, Z39, Z65
hymenopterous insects, zz, 158

I

Tee Age or Pleistocene, i, iz6, 170, 171,
17Z, 176, 177, ZZ7, zz8, ZZ9 (see table
on p. 99)

ichthyosaurus, 181

indigo bird, 13

infusorians, z66

insect-cattle, 9

insect societies, 8, 9, zo, zz

insectivores, 14

insects, 7, 8, 9, 10, 11, 15, 16, 17, 18,
zo, zz, Z4, 41, 45, 46, 48, 51, 59, 61,
63, 65, 68, 69, 79, 85, 86, loz, 117,
118, 119, izo, 156, 15S, 159, 167,
183, zoz, Z17, Z18, ZZI, ZZ3, Z3Z, Z33,
z6z

insects, chemical senses of, 85

insects, cocoon of, 8, 16

irreversibility of specialization, Z04,
Z05

J

Jagana, 145

Japanese giant spider-crab, 108

Japanese pugs, 147

jassids, 9

Java ape-man, zz6

jays, 13

jellyfish, 65, 75, 94, 98, 153, Z35, Z39,

Z51, Z64, Z65, Z7Z
jointed worms, 6^, loi, izo, izi, 150,

155, 190, Z06, Z47, Z55, Z56, z6z
June-bugs, 45,46
Jurassic, i, 94, 178 (see table on p. 99)

[190]

INDEX

King-crab, 109
kingfishers, 13
kinglets, 49
kiwi, 145

L

Lace-winged flies, 8

lack of competition between the animal
phyla, 117, 118, 119

lamp-shells, 70, loi, no, 113, 157, z62.

land-crabs, 79

land-leeches, no

larval peculiarities of fresh-water ani-
mals, 149

leaf-cutting bees, 11

leeches, 162.

lemming, 12.6

lemurs, 14, 17, 49

leptocephalid, 183

leptocephalus, 149

lice, 118

life, balance of, 12.4, zi3

life histories, xiii

light, 73

limits of size in vertebrates, ii8

lions, 93

living things children of other living
things, xiii

lizards, 35, 48, 167, 178, i8i

lobsters, 79, izo, 163

lorises, 12.4

loss of tails in Asiatic Aristolochia
swallowtails, 140

luminescence, 73

lycasnid butterflies, 9

M

Maggots, 45
magpies, 13

maintenance of continuity of life, xiii

mammals, i, z, 6, 7, 14, 15, 16, 19,

45. 48. 5o> 78. 80, 88, 89, 103, 106,

118, 137, 159, 166, 167, 170, 178, i8i,

183, 2.XI, 2.2.2., Z2.3, ii4, iX9, i6l

mammoth, 43, 9z

man, xi, i, x, 3, 4, 6, 7, 10, 16, 19, X5,

z6, X7, i8, Z9, 30, 85, Z17, ZZ3, ZZ4,

ZX5 , xz6, ZX7
man, ancestry of, zz8, ZZ9, Z30
man, baby stage of, Z5, z6
man, origin of, 2lz8
man, Piltdown, zz6, ZZ7
man, Trinil, zz6, ZZ7
man-like attributes in lower animals

explained, Z3Z, Z33
man-like or anthropoid apes, z, 6, Z7,

z8, ZZ4, ZZ5, zz6
mantes, 35
mastodons, 93
megapodes, 7, 11, 88
Megapodidas, 7
megathymids, zoz
membracids, 9

mental complexes and structure, 3, 4
merostomes, loi
metanauplius, 149
Miacida:, i8z
Miacis, i8z
mice,7, 17, 35,48
mice, black, 145
mice, naked, 146
mice, rhinoceros, 145, Z19
Mkrosfomum, 2.53, Z55, Z57
millepeds, 117
millipores, Z65
Miocene, 3Z, 171, 17Z, 173, zz8 (see

table on p. 99)
miracidium, 151, Z5Z
missing links, zz6, ZZ7

[2-91]

INDEX

mites, 35, 162.

molds, 40, 59

moles, 14

Mollusca, 117, z6z, 169

mollusks, 63, 69, 76, 78, 79, loi, loi,
Hi, 114, 117, 119, 1X0, lii, 1x3, 137,
M4. 153. 167, 168, 179, i8x, 189, 190,
zoz, 2.06, ii8, izi, ^47, 156, 2.57,
z6i

monkeys, 16, 15, z6, Z7, z8, Z30

monotremes (egg-laying mammals), 50,

ZiZ

moor-hen, 145
mososaurs, 107
moss-animalcules, 164
mosquitoes, 35
moths, 16, 18, 45, 158
motmots, 13
mud-daubers, 16, Z3
murine rodents, 18
musk-oxen, 116
musk-rats, 17
mussels, 66, 119
myriopods, zzi
mysis-like creature, 149
myzostomid worms, 103

N

Naked or hairless horses, 146

naked mice, 146

nauplius, 149

nautilus, 109, no, 181, 2.62.

nautilus, chambered, 109, no

necessities of life, 52.

Nemathelminthes, 174

nematodes, 35, 69, 162., -l/^z, 143, 153,

^55, 158, 2.64, X73,z74
nematomorpha, x^z
Nemertea, z6t,, x69
nemerteans, 70, 103, 151, 157

nereid worms, loi, 1x5
nests of birds, iz, 13
New Zealand glow-worm, 10
Niata cattle, 147
Norway rat, 14

O

ochropus, Gallinula, 145
octopus, 79, 84, izo, i8z, z6z
Oligocene, 173, 174, 181, 181, zz8

(see table on p. 99)
oligochaste worms, 103
onychophores, ixo, z6z
onychophorid worms, 103
ophiurans, 101
optimum conditions for life in the sea,

53

optimum conditions for life on land, 53

orangs, 4, X5, 1x4

Ordovician, 108, 109, iix (see table on

P- 99)

Ordovician and Ozarkian animals, lox

origin of all animals from a single cell,

xiii, 164, i9i,xo9, X35
origin of animal foods, 37
origin of human culture, X31
origin of man, XX7
oriole, Baltimore, 13
ostracods, 158
ostrich, 89
oyster drills, 118

oysters, 66, 78, 84, 119, 167, i8x, x6x
owls, 8x, 85, 118
Ozarkian and Ordovician animals, lox

Painted lady, 131

parasites and parasitism, X44

parasitic barnacles, 15X

Palaeozoic, 1x3, 1x6 (see table on p. 99)

[2-92-]

INDEX

parasitic wasps, i6, 35, 59, 157

parental care m birds, 88

parrots, 12., 14

peach-nectarine trees, 147

peccaries, 93

pelecypods, loi, xzi

Pelagof/juria, /Z

Penatis, 149

peridinians, 96, iio

Peripatus, i62.

Phoronidea, i6i, i68, 2.75

phoronids, 70, 103, 151, 153, 155, 157

phyllopods, loi, 12.5, 158

pigmentation in animals, 76

pilidium, 151

Piltdown man, 116, 12.7

Pithecanthropus erectiis, 2.i6

place of greatest size and abundance of

sea animals, ^2.
Pleistocene or Ice Age, i, 43, 12.6, 170,

171 > 172-, 176, 177. 2.Z7, ii8, 2.^9 (see

table on p. 99)
plesiosaurs, 107
Pliocene, 171, 172., 2.17 (see table on

P- 99)
plover, golden, 81

plutei, 150

pollack, 95

polynoid worms, loi

Polyzoa, 2.64, 170, ^75

polyzoans, 67, 70, 102., 151, 153, 155,

157, 159, 162., 2.56, 157, 2.58, x64
Porifera, x65, 2.71
porpoises, SG, 67
potentiality of the primitive single

cell, 2.2.0
pottos, 2.2.4

Pre-Cambrian, iiz (see table on p. 99)
predacious wasps, 16
priapulids, 70, 103, 155

Priapuloidea, 163, 170
Primates, 12.4, 2.17, zz8, ZZ9
primitive forms of animal life analyzed,

104
primitive single cell, potentiality of,

zzo
Primnoa^ 153

Princess Helen's hummingbird, 89
problem of evolution, xiii
protection of insect societies, 9
protochordates, 199
Protozoa, zb6, Z71
protozoasa, 149
protozoans, 35, 51, 59, 69, 104, 15Z,

194, Z41, Z44, Z71, Z73
psychological aspects of eyes, 83
pteropods, loz
pterosaurs, 107
pugs, 147, 184, 186, 187
pyro somas, 65, 7Z, z6i

R

Rabbits, 145

radiolarians, z66, Z71

rat-like rodents, 18

rats, 7

ravens, 13

razor-clams, GG

red admiral, 86, 131

redia, 151, Z5Z

region of greatest amount of life, 5Z, 53

region of greatest density of life, 54

region of greatest variety of life, 54, 56

reindeer, iz6

relative efficiency of fish, crustaceans

and protozoans, Z36
relative number of kinds of animals on

land and in the sea, 68
relative number of major groups of

animals on the land and in the sea, 67

[2-93]

INDEX

s>^^

reproduction, asexual, 155, 156, 157,

158, 159

i-eproductive cells compared with pro-
tozoans, 51

reptiles, i, 6, 45, 50, 78, 80, 88, 89, 103,
106, 107, 116, 167, 170, 178, 181,
181, izi, izi, 2.^3, 2.61

reversed varieties, 144

Khabdopleura, i6i

rhinoceros, 43, zi8

rhinoceros, woolly, 91

rhinoceros mice, 145, xi9

Rhopalura, 2.43

robber-flies, 35

robins, 13, 81

rock disintegration, 38, 53

rodents, 7, 14, 15, 16, 17, 18, lo, iz,

2-3, 2.17. 2.3Z, Z33
Rotifera, Z64, z7o
rotifers, 59, 103, 149, 150, 153, 158,

Z55, Z56, Z64, Z74
round-worms, 103
rusts, 40

Safeguards preventing undue increase

of animals, xii
salamanders, 46, 50
salps, 7Z, 76
saber -toothed tigers, 93
Sardinian swallowtail, 141
scallops, 78
scaphopods, zoz, zzi
scorpions, z6z
sea-anemones, 15Z, 194, Z35, Z39, Z53,

Z65
sea-animals, 4Z
sea-birds, 17, 66
sea-butterflies, z6z

sea-cucumbers, 7Z, izi, 1Z5, 150, i8z,

ZOZ, ZZI, Z63, Z64
sea-fans, 66, Z65
sea-lilies, 7Z, izi, 148, 153, i8z, zoi,

Z63
seals, 50, 67, 167, 181
sea-mosses, 66
sea-peaches, 7Z, z6i
sea-pens, 66, 78, Z39, Z65
sea-squirts, 66, jz, z6i
sea-turtles, 107
sea-urchins, 67, 71, 78, loz, izi, 150,

153, i8z, ZOI, ZZI, zb3
sea-walnuts, 103, Z65
sea-worms, 98, z6z
serial dependent family, 6, 11, zo, zz
sexual development in butterflies, 141
shipworms, z6z
short-faced bears, 93
short-faced pigs, 147
shrews, 14, 35
shrimps, 149, Z63
sight and migration in birds, 81
Silurian, 108, 109, iiz (sec table on p.

99)

silky fowl, 145

single-celled animals, 19Z, Z35, Z36,

2-37. 2.39, z66
sipunculids, 70, 103, Z55, Z56
Sipunculoidea, z6z, z68
skippers, zoz
slime-eels, i6z
slugs, 41, 63, z6z
small red bat, 83
snails, 41, 63, 78, i6z, i8z, z6z
snakes, 35, 48, 50, 167, 178, i8z
snowflakes, 49
social insects, 8, 18
social system, human, zz, z8
social system of insects, 8, zz

[2-34]

INDEX

social wasps, i6

societies, insect, 2.1., 159

society, human, zi, 8i

soils, formation of, 31

solenogasters, ixi

solitary bees, 11

solitary wasps, 11, 2.3

sow-bugs, ^63

spaniel, 4

specialization, irreversibility of, i04

species, xii, 130

spiders, 10, 11, 35, 59, 61, 6i, 69,117,

Z02., z6z
spiders, flight of, 6i
spinning ants, 7
spiny-headed worms, 14^, 143, 164,

2-73. 2.74
sponge, bath, -lGG

sponges, GG, loz, izi, 155, 193, 141,

Z45, 2.65, -Lji, -L-j-L, 2.73
sporocyst, 151, i.'p.
sporozoans, z66
squid, 65, 67, 79, 94, 98, 12.0, 167, 182.,

x6i
squirrels, 7, 17, 48, 60
starfishes, 67, 72., 78, 84, 100, loi, ixi,

i5o> i53> 155. 157. 167, 182., ioi, ill,

M7. 2.63
Stmt or, 151

swallowtail, African, 138
swallowtail, common Asiatic, 138
swallowtail, common black, 139, 141
swallowtail, common western, 141
swallowtail, Sardinian, 141
swallowtail, yellow, 34, 137, 140
swallowtail, yellow European, 141
swallowtails, Aristolochia, 32., 139, 140
symmetries of animals, 171

Tadpoles, i6z, 183

tailed blue, 134

tailor-birds, iz, 17

tapeworms, 1Z4, i6z, 163, Z4z, Z43,

Z51, Z55, Z56, Z64, Z65, Z73, Z74
tapirs, 43, 93, zz8
tawny emperor, 34
teleosts or bony fishes, i8z
termites, 8, 11, 13, 16, iS, 139, 159,

Z33, z66
tern, Arctic, 81
terrier, 4
Tertiary, 171, 173, 174 (see table on

P- 99)
Thompsonia, Z56

thread-worms, Z4Z, Z43,z53,z64

three methods of securing food avail-
able for sea animals, 67

titanotheres, zz8

toads, 45, 48, 50

Tomoperis-\ik.c worms, loz

tornaria, 150

tortoises, 74, 119

transparency of animals, 75, 76

transportation through the air, 58

trematodes, 151, Z4Z, Z73

Triassic, 99

trilobites, loi, 107, 108, iiz, 115, 190

Trinil man, zz6, ZZ7

trocho sphere, 150

Tunicata, z6i, z68, Z75

tunicates, 71, 103, 15Z, 153, 155, 159,
i6z, 196, 199, zoo, Z57, Z58

turbellarians, i6z, Z4Z, Z43, Z53, Z55,
Z58, Z64, Z73, Z74

turtles, IZ, 48, 50, 74, 75, 89, 116, 167,
178, i8z

[^95]

>s>/>

INDEX

O^/'x

U

Umbellularians, 151

use of antiseptics by insects, 10

use of artificial heat, 7, Z4

use of clothing, 6, 2.4

use of clothing by insects, 7, 16, X4, ^9

use of fire, 6, 7, Z9

use of narcotics by insects, 10

use of ornaments, 6, 8, 13, 14, 17, 19

use of poisons by insects, 9, 10

use of slaves, 8

use of speech, 6, 8

use of tools, 6, 7, Z4, X9

use of tools by insects, 7

Varnisher bees, 11

vegetable food of sea animals, 64, 65

Venus' flower-basket, 2.66

Venus* girdle, 153, 165, Z73

Vermiformes, X49, Z55, 7.^6, 159, 2.64,
X70, Z7I, Z73, Z74

Vertebrata, zzx, z6i, Z67, Z75

vertebrates, 6, 10, 45, 50, 63, 69, 78,
79, 80, 83, 85, 103, 117, 118, 119, izo,
izi, izz, 149, 166, 167, 168, 170, 188,
189, 196, 199, zoo, Z07, ZZI, ZZZ, ZZ3,
2-47. 2-58, Z59

vertebrates, range in size of, 118

vinegar-eels, Z65

vision, 77, 78, 79

vision of birds, 80, 81, 8z

Vonkella, 15Z

W

Wafers, Z65

wasps, 8, 10, II, 18, zz, 45, 46, 138,
156, 159, Z33

wasps, caterpillar, 35

wasps, digger, 7, 16

wasps, fossorial, Z3

wasps, parasitic, 16, 35, 59, 60, 157

wasps, predacious, 16

wasps, social, 16

wasps, solitary, 11, Z3

wasps, wood-boring, 11

water-fleas, Z63

weaver-birds, iz, 17

whales, 50, 65, 67, 167, 181

wheel-animalcules, Z64

whelks, 118

white admiral, 137

white-ants, 16, 139, 159, z66

wholesale death of small herring, 95

w^oolly rhinoceros, 9Z

wolves, zo, 184, 187, 188, Z19

wood-boring wasps, 11

woodchucks, 48

woodpecker, California, 15

wood-rats, 14

worm-like larvas of brittle-stars and

starfishes, 150
worms, 67, 153, Z49, Z64, Z65
w^orms, archiannelid, 103
w^orms, arrow, 65, 76, loi, 149, i6z,

190, Z57, Z63
worms, gephyrean, loi, loz, 1Z5
worms, gordian, Z4Z, Z43, Z74
worms, hirudinid, 103
worms, jointed, 69, loi, izo, izi, 150,

155, 190, Z06, Z47, Z55, Z56, z6z
worms, myzostomid, 103
worms, nereid, loi, IZ5

[196]

>-r^

INDEX

Ov/T^

worms, oligocha^te, 103

worms, onychophorid, 103

worms, polynoid, loi

worms, spiny-headed, 2.42., 143, z64,

2-73 > 2.74
worms, Tomoperis-Y]}^t, 102.

Yellow clover butterfly, 135
yellow swallowtail, 34, 137, 140
yellow swallowtail of Europe, 141

Zebras, 170, 177, 104, ^19

[2-97]

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'^^Wf^