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REESE LIBRARY
UNIVERSITY OF CALIFORNIA.
BIOLOGY
LIBRARY
G
Class
UNIVERSITY EXTENSION MANUALS
EDITED BY PROFESSOR KNIGHT
THE STUDY OF ANIMAL LIFE
EDITORS PREFACE
This Series is primarily designed to aid the University Extension
Movement throughout Great Britain, and to supply the need so
widely felt by students, of Text-books for s-tudy and reference, in
connection with the authorised Courses of Lectures.
The Manuals differ from those already in existence in that they
are not intended for School use, or for Examination purposes ; and
that their aim is to educate, rather than to inform. The statement
of details is meant to illustrate the working of general laws, and the
development of principles ; while the historical evolution of the
subject dealt with is kept in view, along with its philosophical
significance.
The remarkable success which has attended University Extension
in Britain has been partly due to the combination of scientific treat-
ment with popularity, and to the union of Duplicity with thorough-
ness. This movement, however, can only reach those resident in the
larger centres of population, while all over the country there are
thoughtful persons who desire the same kind of teaching. It is for
them also that this Series is designed. Its aim is to supply the
general reader with the same kind of teaching as is given in the
Lectures, and to reflect the spirit which has characterised the move-
ment, viz. the combination of principles with facts, and of methods
with results.
The Manuals are also intended to be contributions to the Literature
of the Subjects with which they respectively deal, quite apart from
University Extension ; and some of them luill be found to meet a
general rather than a special want.
They will be issued simultaneously in England and America.
Volumes dealing with separate sections of Literature, Science,
Philosophy, History, and Art have been assigned to representative
literary men, to University Professors, or to Extension Lecturers
connected with Oxford, Cambridge, London, and the Universities of
Scotland and Ireland.
A list of the works in this Series will be found at the end of the
volume.
The Study
of
Animal Life
BY
J. ARTHUR THOMSON, M.A., F.R.S.E.
LECTURER ON^ZOOLOGY, SCHOOL OF MEDICINE, EDINBURGH
JOINT-AUTHOR OF ' THE EVOLUTION OF SEX '
AUTHOR OF 'OUTLINES OF ZOOLOGY'
SECOND EDITION
WITH ILLUSTRATIONS
LONDON
JOHN MURRAY, ALBEMARLE STREET
i 892
OG T
G
"But, for my part, which write the English story, I acknowledge
that no man must looke for that at my hands, which I have not
received from some other : for I would bee unwilling to write anything
untrue, or uncertaine out of mine own invention ; and truth on every
part is so deare unto me, that I will not lie to bring any man in love
and admiration with God and his works, for God needeth not the lies
of men. ' , and S indicate the positions of Peripatus. Balanoglossus, and
Sphenodon or Hatteria respectively.
CHAP, i The Wealth of Life 13
There is of course no doubt as to the fact that some forms
of life are more complex than others. It requires no faith
to allow that the firstlings or Protozoa are simpler than
all the rest ; that sponges, which are more or less loose
colonies of unit masses imperfectly compacted together, are
in that sense simpler than jellyfish, and so on. The animals
most like ourselves are more intricate and more perfectly
controlled organisms than those which are obviously more
remote, and associated with this perfecting of structure there
is an increasing fulness and freedom of life.
We may arrange all the classes in series from low to high,
from simple to complex, but this will express only our most
generalised conceptions. For within each class there is
great variety, each has its own masterpieces. Thus the
simplest animals are often cased in shells of flint or lime
whose crystalline architecture has great complexity. The
simplest sponge is little more than a double-walled sack
riddled by pores through which the water is lashed, but
the Venus' Flower-Basket {Euplectella), one of the flinty
sponges, has a complex system of water canals and a
skeleton of flinty threads built up into a framework of
marvellous intricacy and grace. The lowest insect is not
much more intricate, centralised, or controlled than many
a worm of the sea-shore, but the ant or the bee is a very
complex self-controlled organism. More exact, therefore,
than any linear series, is the image of a tree with branches
springing from different levels, each branch again bearing
twigs some of which rise higher than the base of the branch
above. A perfect scheme of this sort might not only express
the facts of structure, it might also express our notions of
the blood-relationships of animals and the way in which we
believe that different forms have arisen.
But the wealth of form is less varied than at first sight
appears. There is great wealth, but the coinage is very
uniform. Our first impression is one of manifold variety ;
but that gives place to one of marvellous plasticity when
we see how structures apparently quite different are redu-
cible to the same general plan. Thus, as the poet Goethe
first clearly showed, the seed-leaves, root-leaves, stem-leaves,
i4 The Study of Animal Life PART i
and even the parts of the flower sepals, petals, stamens,
and carpels, are in reality all leaves or appendages more
or less modified for diverse work. The mouth-parts of a
lobster are masticating legs, and a bird's wing is a modified
arm. The old naturalists were so far right in insisting on
i\ the fact of a few great types. Nature, Lamarck said, is
\\ never brusque ; nor is she inventive so much as adaptive.
4. Wealth of Numbers. Large numbers are so unthink-
able, and accuracy in census-taking is so difficult, that we
need say little as to the number of different animals. The
census includes far over a million living species a total so
vast that, so far as our power of realising it is concerned,
'it is hardly affected when we admit that more than half
are insects. To these recorded myriads, moreover, many
newly-discovered forms are added every year now by the
individual workers who with fresh eye or improved micro-
scope find in wayside pond or shore pool some new thing,
or again by great enterprises like the Challenger expedition.
Exploring naturalists like Wallace and Semper return from
tropical countries enriched with new animals from the dense
forests or warm seas. Zoological Stations, notably that of
Naples, are "register -houses" for the fauna of the neigh-
bouring sea, not merely as to number and form, but in
many cases taking account of life and history as well. Nor
can we forget the stupendous roll of the extinct, to which
the zoological historians continue to add as they disentomb
primitive mammals, toothed birds, giant reptiles, huge
amphibians, armoured fishes, gigantic cuttles, and a vast
multitude of strange forms, the like of which no longer
live. The length of the Zoological Record, in which the
literature and discoveries of each year are chronicled, the
portentous size of a volume which professes to discuss with
some completeness even a single sub-class, the number of
special departments into which the science of zoology is
divided, suggest the vast wealth of numbers at first sight so
bewildering. More than two thousand years ago Aristotle
recorded a total of about 500 forms, but more new species may
be described in a single volume of the Challenger Reports.
We speak about the number of the stars, yet more than one
CHAP, i The Wealth of Life 15
family of insects is credited with including as many different
species as there are stars to count on a clear night. But far
better than any literary attempt to estimate the numerical
wealth of life is some practical observation, some attempted
enumeration of the inmates of your aquarium, of the tenants
of some pool, or of the visitors to some meadow. The
naturalist as well as the poet spoke when Goethe celebrated
Nature's wealth : " In floods of life, in a storm of activity,
she moves and works above and beneath, working and
weaving, an endless motion, birth and death, an infinite
ocean, a changeful web, a glowing life ; she plies at the
roaring loom of time and weaves a living garment for God."
5. Wealth of Beauty. To many, however, animal life
is impressive not so much because of its amazing variety
and numerical greatness, nor because of its intellectual
suggestiveness and practical utility, but chiefly on account
of its beauty. This is to be seen and felt rather than
described or talked about.
The beauty of animals, in which we all delight, is usually
in form, or in colour, or in movement. Especially in the
simplest animals, the beauty of form is often comparable to
that of crystals ; witness the marvellous architecture in flint
and lime exhibited by the marine Protozoa, whose empty
shells form the ooze of the great depths. In higher animals
also an almost crystalline exactness of symmetry is often
apparent, but we find more frequent illustration of graceful
curves in form and feature, resulting in part from strenuous
and healthful exercise, which moulds the body into beauty.
Not a little of the colour of animals is due to the
physical nature of the skin, which is often iridescent ;
much, on the other hand, is due to the possession of pig-
ments, which may either be of the nature of reserve-products,
and then equivalent, let us say, to jewels, or of the nature of
waste-products, and thus a literal "beauty for ashes." It
is often supposed that plants excel animals in colour, but
alike in the number and variety of pigments the reverse is
true. Then as to movement, how much there is to admire ;
the birds soaring, hovering, gliding, and diving; the monkey's
gymnastics ; the bat's arbitrary evolutions ; the grace of the
i6
The Study of Animal Life PART
fleet stag; the dolphin gamboling in the waves; the lithe
lizards which flash across the path and are gone, and the
snake flowing like a silver river ; the buoyant swimming of
fishes and all manner of aquatic animals ; the lobster darting
backwards with a powerful tail-stroke across the pool ; the
butterflies flitting like sunbeams among the flowers. But
FIG. 3. Humming-birds {Florisiiga mellivora) visiting flowers. (From Belt.)
are not all the delights of form and colour and movement
expressed in the songs of the birds in spring ?
I am quite willing to allow that this beauty is in one
sense a relative quality, varying with the surroundings
and education, and even ancestral history, of those who
appreciate it. A flower which seems beautiful to a bee
may be unattractive to a bird, a bird may choose her mate
for qualities by no means winsome to human eyes, and a
CHAP, i The Wealth of Life 17
dog may howl painfully at our sweet music. We call the
apple - blossom and the butterfly's wings beautiful, partly
because the rays of light, borne from them to our eyes,
cause a pleasantly harmonious activity in our brains, partly
because this awakens reminiscences of past pleasant experi-
ences, partly for subtler reasons. Still, all healthy organisms
are harmonious in form, and seldom if ever are their colours
out of tone with their surroundings or with each other, a
fact which suggests the truth of the Platonic conception that
a living creature is harmonious because it is possessed by
a single soul, the realisation of a single idea.
The plants which seem to many eyes to have least
beauty are those which have been deformed or discoloured
by cultivation, or taken altogether out of their natural set-
ting ; the only ugly animals are the products of domestica-
tion and human interference on the one hand, or of disease
on the other ; and the ugliest things are what may be called
the excretions of civilisation, which are certainly not beauty
for ashes, but productions by which the hues and colours of
nature have been destroyed or smothered, where the natural
harmony has been forcibly put out of tune in short, where
a vicious taste has insisted on becoming inventive.
CHAPTER II
THE WEB OF LIFE
I. Dependence upon Surroundings 2. Inter-relations of Plants and
Animals 3. Relation of Animals to the Earth 4. Nutritive
Relations 5. More Complex Interactions
IN the filmy web of the spider, threads delicate but firm
bind part to part, so that the whole system is made one.
The quivering fly entangled in a corner betrays itself
throughout the web ; often, it is felt rather than seen by the
lurking spinner. So in the substantial fabric of the world
part is bound to part. In wind and weather, or in the
business of our life, we are daily made aware of results
whose first conditions are remote, and chains of influence
not difficult to demonstrate link man to beast, and flower to
insect. The more we know of our surroundings, the more
we realise the fact that nature is a vast system of linkages,
that isolation is impossible.
i. Dependence upon Surroundings. Every living body
is built up of various arrangements of at least twelve
" elements," viz. Oxygen, Hydrogen, Carbon, Nitrogen,
Chlorine, Phosphorus, Sulphur, Magnesium, Calcium, Pot-
assium, Sodium, and Iron. All these elements are spread
throughout the whole world. By the magic touch of life
they are built up into substances of great complexity and
instability, substances very sensitive to impulses from, or
changes in, their surroundings. It may be that living matter
differs from dead matter in no other way than this. The
CHAP, ii The Web of Life 19
varied forms of life crystallise out of their amorphous
beginnings in a manner that we conceive to be analogous to
the growth of a crystal within its solution. Further, we do
not believe in a " vital force." The movements of living
things are, like the movements of all matter, the expression
of the world's energy, and illustrate the same laws. But
to these matters we shall return in another chapter.
Interesting, because of its sharply defined and far-reaching
significance, and because the essential mass is so nearly
infinitesimal, is the part played by iron in the story of life. For
food-supply we are dependent upon animals and plants, and
ultimately upon plants. But these cannot produce their
valuable food-stuffs without the green colouring-matter in
their leaves, by help of which they are able to utilise the
energy of sunshine and the carbonic acid gas of the air.
But this important green pigment (though itself perhaps
free from any iron) cannot be formed in the plant unless
there be, as there almost always is, some iron in the soil.
Thus our whole life is based on iron. And all our supplies
of energy, our powers of doing work either with our own
hands and brains, or by the use of animals, or through the
application of steam, are traceable if we follow them far
enough to the sun, which is thus the source of the energy
in all creatures.
2. Inter-relations of Plants and Animals. We often
hear of the "balance of nature," a phrase of wide appli-
cation, but very generally used to describe the mutual
dependence of plants and animals. Every one will allow
that most animals are more active than most plants,
that the life of the former is on an average more intense
and rapid than that of the latter. For all typical plants
the materials and conditions of nutrition are found in water
and salts absorbed by the roots, in carbonic acid gas
absorbed by the leaves from the air, and in the energy of
the sunlight which shines on the living matter through a
screen of green pigment. Plants feed on very simple sub-
stances, at a low chemical level, and their most char-
acteristic transformation of energy is that by which the
kinetic energy of the sunlight is changed into the potential
20 The Study of Animal Life PART i
energy of the complex stuffs which animals eat or which
we use as fuel. But animals feed on plants or on creatures
like themselves, and are thus saved the expense of build-
ing up food - stuffs from crude materials. Their most
characteristic transformation of energy is that by which the
power of complex chemical substances is used in locomotion
and work. In so working, and eventually in dying, they
form waste-products water and carbonic acid, ammonia
and nitrates, and so on which may be again utilised by
plants.
How often is the inaccurate statement repeated "that
animals take in oxygen and give out carbonic acid,
whereas plants take in carbonic acid and give out oxygen " !
This is most misleading. It contrasts two entirely dis-
tinct processes a breathing process in the animal with
a feeding process in the plant. The edge is at once
taken off the contrast when the student realises that plants
and animals being both (though not equally) alive, must
alike breathe. As they live the living matter of both is oxi-
dised, like the fat of a burning candle ; in plant, in animal,
in candle, oxygen passes in, as a condition of life or com-
bustion, and carbonic acid gas passes out as a waste-pro-
duct. Herein there is no difference except in degree between
plant and animal. Each lives, and must therefore breathe.
But the living of plants is less intense, therefore the breath-
ing process is less marked. Moreover, in sunlight the
respiration is disguised by an exactly reverse process
peculiar to plants the feeding already noticed, by which
carbonic acid gas is absorbed, its carbon retained, and part
of its oxygen liberated.
There is an old-fashioned experiment which illustrates
the "balance of nature." In a glass globe, half- filled
with water, are placed some minute 'water-plants and water-
animals. The vessel is then sealed. As both the plants
and the animals are absorbing oxygen and liberating car-
bonic acid gas, it seems as if the little living world enclosed
in the globe would soon end in death. But, as we have seen,
the plants are able in sunlight to absorb carbonic acid and
liberate oxygen, and if present in sufficient numbers will
CHAP, ii The Web of Life 21
compensate both for their own breathing and for that of
animals. Thus the result within the globe need not be
suffocation, but harmonious prosperity. If the minute
animals ate up all the plants, they would themselves die
for lack of oxygen before they had eaten up one another,
while if the plants smothered all the animals they would
also in turn die away. Some such contingency is apt to
spoil the experiment, the end of which may be a vessel of
putrid water tenanted for a long time by the very simple
colourless plants known as Bacteria, and at last not even
by them. Nevertheless the " vivarium " experiment is both
theoretically and practically possible. Now in nature there
is, indeed, no closed vivarium, for there is no isolation and
there is open air, and it is an exaggeration to talk as if our
life were dependent on there being a proportionate number
of plants and animals in the neighbourhood. Yet the
" balance of nature " is a general fact of much importance,
though the economical relations of part to part over a wide
area are neither rigid nor precise.
We have just mentioned the very simple plants called
.Bacteria. Like moulds or fungi, they depend upon other
organisms for their food, being without the green colouring
stuff so important in the life of most plants. These very
minute Bacteria are almost omnipresent ; in weakly animals
and sometimes in strong ones too they thrive and
multiply and cause death. They are our deadliest foes, but
we should get rid of them more easily if we had greater love
of sunlight, for this is their most potent, as well as most
economical antagonist. But it is not to point out the
obvious fact that a Bacterium may kill a king that we have
here spoken of this class of plants ; it is to acknowledge
their beneficence. They are the great cleansers of the
world. Animals die, and Bacteria convert their corpses
into simple substances, restoring to the soil what the plants,
on which the animals fed, originally absorbed through
their roots. Bacteria thus complete a wide circle ; they
unite dead animal and living plant. For though many a
plant thrives quite independently of animals on the raw
materials of earth and air, others are demonstrably raising
22 The Study of Animal Life PART i
the ashes of animals into a new life. A strange partner-
ship between Bacteria on the one hand and leguminous and
cereal plants on the other has recently been discovered.
There seems much likelihood that with some plants of
the orders just named Bacteria live in normal partner-
ship. The legumes and cereals in question do not thrive
well without their guests, nay more, it seems as if the
Bacteria are able to make the free nitrogen of the air
available for their hosts.
3. Relation of Animals to the Earth. Bacteria are
extremely minute organisms, however, and stories of
their industry are apt to sound unreal. But this cannot
be said of earthworms. For these can be readily seen
and watched, and their trails across the damp footpath,
or their castings on the grass of lawn and meadow, are
familiar to us all. They are distributed, in some form or
other, over most regions of the globe ; and an idea of their
abundance may be gained by making a nocturnal expedition
with a lantern to any convenient green plot, where they
may be seen in great numbers, some crawling about, others,
with their tails in their holes, making slow circuits in search
of leaves and vegetable debris. Darwin estimated that there
are on an average 53,000 earthworms in an acre of garden
ground, that 10 tons of soil per acre pass annually through
their bodies, and that they bring up mould to the surface at
the rate of 3 inches thickness in fifteen years. Hensen found
in his garden 64 large worm-holes in 14 J square feet, and
estimated the weight of the daily castings at about 2
cwts. in two and a half acres. In the open fields, how-
ever, it seems to be only about half as much. But whether
we take Darwin's estimate that the earthworms of England
pass annually through their bodies about 320,000,000 tons
of earth, or the more moderate calculations of Hensen, or
our own observations in the garden, we must allow that the
soil-making and soil -improving work of these animals is
momentous.
In Yorubaland, on the West African coast, earthworms
(Siphonogaster) somewhat different from the common Lum-
bricus are exceedingly numerous. From two separate square
CHAP, ii The Web of Life 23
feet of land chosen at random, Mr. Alvan Millson collected
the worm-casts of a season and found that they weighed
when dry lof Ibs. At this rate about 62,233 tons of sub-
soil would be brought in a year to the surface of each
square mile, and it is also calculated that every particle of
earth to the depth of two feet is brought to the surface once
in 27 years. We do. not wonder that the district is fertile
and healthy.
Devouring the earth as they make their holes, which are
often 4 or even 6 feet deep ; bruising the particles in their
gizzards, and thus liberating the minute elements of the soil ;
burying leaves and devouring them at leisure ; preparing the
way by their burrowing for plant roots and rain-drops, and
gradually covering the surface with their castings, worms have,
in the history of the habitable earth, been most important
factors in progress. Ploughers before the plough, they
have made the earth fruitful. It is fair, however, to
acknowledge that vegetable mould sometimes forms inde-
pendently of earthworms, that some other animals which
burrow or which devour dead plants must also help in the
process, and that the constant rain of atmospheric dust, as
Richthofen has especially noted, must not be overlooked.
In 1777, Gilbert White wrote thus of the earthworms
"The most insignificant insects and reptiles are of much more
consequence and have much more influence in the economy of
nature than the incurious are aware of. ... Earthworms, though in
appearance a small and despicable link in the chain of Nature, yet,
if lost, would make a lamentable chasm. . . . Worms seem to be
the great promoters of vegetation, which would proceed but lamely
without them, by boring, perforating, and loosening the soil, and
rendering it pervious to rains and the fibres of plants ; by drawing
straws and stalks of leaves and twigs into it ; and, most of all, by
throwing up such infinite numbers of lumps of earth called worm-
casts, which, being their excrement, is a fine manure for grain and
grass. Worms probably provide new soil for hills and slopes where
the rain washes the earth away ; and they affect slopes probably to
avoid being flooded. . . . The earth without worms would soon
become cold, hard-bound, and void of fermentation, and con-
sequently sterile. . . . These hints we think proper to throw out, in
order to set the inquisitive and discerning to work. A good mono-
24 The Study of Animal Life PART i
graph of worms would afford much entertainment and information
at the same time, and would open a large and new field in natural
history."
After a while the discerning did go to work, and Hensen
published an important memoir in 1877, while Darwin's
"good monograph" on the formation of vegetable mould
appeared after about thirty years' observation in 1881 ; and
now we all say with him, "It may be doubted whether there
are many other animals which have played so important a
part in the history of the world as have these lowly-organised
creatures."
Prof. Drummond, while admitting the supreme import-
ance of the work of earthworms, eloquently pleads the claims
of the Termite or White Ant as an agricultural agent. This
insect, which dwelt upon the earth long before the true ants,
is abundant in many countries, and notably in Tropical
Africa. It ravages dead wood with great rapidity. "If
a man lay down to sleep with a wooden leg, it would be a
heap of sawdust in the morning," while houses and decaying
forest trees, furniture and fences, fall under the jaws of the
hungry Termites. These fell workers are blind and live
underground ; for fear of their enemies they dare not show
face, and yet without coming out of their ground they cannot
live.
" How do they solve the difficulty? They take the ground out
along with them. I have seen white ants working on the top of a
high tree, and yet they were underground. They took up some of
the ground with them to the tree-top. They construct tunnels
which run from beneath the soil up the sides of trees and posts ;
grain after grain is carried from beneath and mortared with a sticky
secretion into a reddish sandpaper-like tube ; this is rapidly ex-
tended to a great height even of 30 feet from the ground till
some dead branch is reached. Now as many trees in a forest are
thus plastered with tunnels, and as there are besides elaborate
subterranean galleries and huge obelisk-like ant-hills, sometimes
10-15 feet high, it must be granted that the Termites, like the
earthworms, keep the soil circulating. The earth-tubes crumble
to dust, which is scattered by the wind ; the rains lash the forests
and soils with fury and wash off the loosened grains to swell the
alluvium of a distant valley."
CHAP, ii The Web of Life 25
The influences of plants and animals on the earth are
manifold. The sea- weeds cling around the shores and
lessen the shock of the breakers. The lichens eat slowly
into the stones, sending their fine threads beneath the sur-
face as thickly sometimes " as grass-roots in a meadow-land,"
so that the skin of the rock is gradually weathered away.
On the moor the mosses form huge sponges, which mitigate
floods and keep the "streams flowing in days of drought.
Many little plants smooth away the wrinkles on the earth's
face, and adorn her with jewels ; others have caught and
stored the sunshine, hidden its power in strange guise in
the earth, and our hearths with their smouldering peat or
glowing coal are warmed by the sunlight of ancient summers.
The grass which began to grow in comparatively modern
(i.e. Tertiary) times has made the earth a fit home for flocks
and herds, and protects it like a garment ; the forests affect
the rainfall and temper the climate, besides sheltering multi-
tudes of living things, to some of whom every blow of the
axe is a death-knell. Indeed, no plant from Bacterium to
oak tree either lives or dies to itself, or is without its
influence on earth and beast and man.
There are many animals besides worms which influence
the earth by no means slightly. Thus, to take the minus
side of the account first, we see the crayfish and their
enemies the water-voles burrowing by the river banks and
doing no little damage to the land, assisting in that process
by which the surface of continents tends gradually to
diminish. So along the shores in the harder substance
of the rocks there are numerous borers, like the Pholad
bivalves, whose work of disintegration is individually slight,
but in sum-total great. More conspicuous, however, is the
work of the beavers, who, by cutting down trees, building
dams, digging canals, have cleared away forests, flooded
low grounds, and changed the aspect of even large tracts
of country. Then, as every one knows, there are injuri-
ous insects innumerable, whose influence on vegetation, on
other animals, and on the prosperity of nations, is often
disastrously great.
But, on the other hand, animals cease not to pay their
26 The Study of Animal Life PART i
filial debts to mother earth. We see life rising like a mist
in the sea, lowly creatures living in shells that are like
mosques of lime and flint, dying in due season, and sinking
gently to find a grave in the ooze. We see the submarine
volcano top, which did not reach the surface of the ocean,
slowly raised by the rainfall of countless small shells. Inch
by inch for myriads of years, the snow-drift of dead shells
forms a patient preparation for the coral island. The
tiniest, hardly bigger than the wind-blown dust, form when
added together the strongest foundation in the world. The
vast whale skeleton falls, but melts away till only the ear-
bones are left. Of the ruthless gristly shark nothing stays
but teeth. The sea-butterflies (Pteropods), with their frail
shells, are mightier than these, and perhaps the microscopic
atomies are strongest of all. The pile slowly rises, and the
exquisite fragments are cemented into a stable foundation
for the future city of corals.
At length, when the height at which they can live is
reached, coral germs moor themselves to the sides of the
raised mound, and begin a new life on the shoulders of death.
They spread in brightly coloured festoons, and have often
been likened to flowers. The waste salts of their living
perhaps unite with the gypsum of the sea-water, at any rate
in some way the originally soft young corals acquire strong
shells of carbonate of lime. Sluggish creatures they, living
in calcareous castles of indolence ! In silence they spread,
and crowd and smother one another in a struggle for stand-
ing-room. The dead forms, partly dissolved and cemented,
become a broad and solid base for higher and higher growth.
At a certain height the action of the breakers begins, great
severed masses are piled up or roll down the sloping sides.
Clear daylight at last is reached, the mound rises above the
water. The foundations are ever broadened, as vigorously
out-growing masses succumb to the brunt of the waves and
tumble downwards. Within the surface -circle weathering
makes a soil, and birds resting there with weary wings, or
perhaps dying, leave many seeds of plants the begin-
nings of another life. The waves cast up forms of
dormant life which have floated from afar, and a ter-
CHAP, ii The Web of Life 27
restrial fauna and flora begin. It is a strange and beautiful
story, dead shells of the tenderest beauty on the rugged
shoulders of the volcano ; corals like meadow flowers
on the graveyard of the ooze ; at last plants and trees,
the hum of insects and the song of birds, over the coral
island.
4. Nutritive Relations. What we may call " nutritive
chains " connect many forms of life higher animals feed-
ing upon lower through long series, the records of which
sound like the story of "The House that Jack built." On
land and on the shore these series are usually short, for
plants are abundant, and the carnivores feed on the
vegetarians. In the open sea, where there is less vegeta-
tion, and in the great depths, where there is none, carni-
vore preys upon carnivore throughout long series fish feeds
upon fish, fish upon crustacean, crustacean upon worm,
worm on debris. Disease or disaster in one link affects
the whole chain. A parasitic insect, we are told, has killed
off the wild horses and cattle in Paraguay, thereby influencing
the vegetation, thereby the insects, thereby the birds. Birds
of prey and small mammals so-called "vermin" are killed
off in order to preserve the grouse, yet this interference seems
in part to defeat itself by making the survival of weak and
diseased birds unnaturally easy, and epidemics of grouse-
disease on this account the more prevalent. A craze of vanity
or gluttony leads men to slaughter small insect-eating birds,
but the punishment falls unluckily on the wrong shoulders
when the insects which the birds would have kept down
increase in unchecked numbers, and destroy the crops of
grain and fruit. In a fuel -famine men have sometimes
been forced to cut down the woods which clothe the sides
of a valley, an action repented of when the rain-storms wash
the hills to skeletons, when the valley is flooded and the
local climate altered, and when the birds robbed of their
shelter leave the district to be ravaged by caterpillar and
fly. American entomologists have proved that the ravages
of destructive insects may be checked by importing and
fostering their natural enemies, and on the other hand, the
sparrows which have established themselves in the States
28 The Study of Animal Life PART i
have in some districts driven away the titmice and thus
favoured the survival of injurious caterpillars.
5. More Complex Interactions. The flowering plants
and the higher insects have grown up throughout long
ages together, in alternate influence and mutual per-
fecting. They now exhibit a notable degree of mutual
dependence ; the insects are adapted for sipping the
nectar from the blossoms ; the flowers are fitted for
giving or receiving the fertilising golden dust or pollen
which their visitors, often quite unconsciously, carry from
plant to plant. The mouth organs of the insects have
to be interpreted in relation to the flowers which they
visit ; while the latter show structures which may be
spoken of as the " footprints " of the insects. So exact is
the mutual adaptation that Darwin ventured to prophesy
from the existence of a Madagascar orchid with a nectar-
spur 1 1 inches long, that a butterfly would be found in the
same locality with a suctorial proboscis long enough to
drain the cup ; and Forbes confirmed the prediction by
discovering the insect.
As information on the relations of flowers and insects is
readily attainable, and as the subject will be discussed in
the volume on Botany, it is sufficient here to notice that, so
far as we can infer from the history half hidden in the
rocks, the floral world must have received a marked impulse
when bees and other flower-visiting insects appeared ; that
for the successful propagation of flowering plants it is
advantageous that pollen should be carried from one indi-
vidual to another, in other words, that cross -fertilisation
should be effected ; and that, for the great majority of
flowering plants, this is clone through the agency of insects.
How plants became bright in colour, fragrant in scent, rich
in nectar, we cannot here discuss ; the fact that they are so
is evident, while it is also certain that insects are attracted
by the colour, the scent, and the sweets. Nor can there be
any hesitation in drawing the inference that the flowers
which attracted insects with most success, and insects which
got most out of the flowers, would, ipso facto, succeed better
in life.
CHAP, ii The Web of Life 29
No illustration of the web of life can be better than the
most familiar one, in which Darwin traced the links of
influence between cats and clover. If the possible seeds in
the flowers of the purple clover are to become real seeds,
they must be fertilised by the golden dust or pollen from
some adjacent clover plants. But as this pollen is uncon-
sciously carried from flower to flower by the humble-bees,
the proposition must t>e granted that the more humble-bees,
the better next year's clover crop. The humble-bees, how-
ever, have their enemies in the field-mice, which lose no
opportunity of destroying the combs ; so that the fewer
field-mice, the -more humble-bees, and the better next year's
clover crop. In the neighbourhood of villages, however, it
is well known that the cats make as effective war on the
field-mice as the latter do on the bees. So that next year's
crop of purple clover is influenced by the number of humble-
bees, which varies with the number of field-mice, that is to
say, with the abundance of cats ; or, to go a step farther,
with the number of lonely ladies in the village. It should
be noted, however, that according to Mr. James Sime there
were abundant fertile clover crops in New Zealand before there
were any humble-bees in that island. Indeed, many think
that the necessity of cross-fertilisation has been exaggerated.
Not all insects, however, are welcome visitors to plants ;
there are unbidden guests who do harm. To their visits,
however, there are often obstacles. Stiff hairs, impassably
slippery or viscid stems, moats in which the intruders
drown, and other structural peculiarities, whose origin may
have had no reference to insects, often justify themselves
by saving the plant. Even more interesting, however, is
the preservation of some acacias and other shrubs by a
bodyguard of ants, which, innocent themselves, ward off
the attacks of the deadly leaf-cutters. In some cases the
bodyguard has become almost hereditarily accustomed to
the plants, and the plants to them, for they are found in
constant companionship, and the plants exhibit structures
which look almost as if they had been made as shelters
for the ants. On some of our European trees similar
little homes or domatia constantly occur, and shelter small
30 The Study of Animal Life TART i
insects which do no harm to the trees, but cleanse them
from injurious fungi.
In many ways plants are saved from the appetite of
animals. The nettle
has poisonous hairs ;
thistles, furze, and holly
are covered with spines ;
the hawthorn has its
thorns and the rose
its prickles ; some have
repulsive odours ; others
contain oils, acids, fer-
ments, and poisons
which many animals
dislike ; the cuckoo-pint
{Arum) is full of little
crystals which make our
lips smart if we nibble
a leaf. In our studies
of plants we endeavour
to find out what these
qualities primarily mean
to their possessors ; here
we think rather of their
secondary significance
as protections against
animals. For though
snails ravage all the
plants in a district ex-
cept those which are
repulsive, the snails are
at most only the second-
FIG. 4. Acacia (A. spharocephala), with hoi- ary factors in the CVOlu-
(After h SchLperJ hlch *"*' find shGher ' tion of the repulsive
qualities.
The strange inter-relations between plants and animals
are again illustrated by the carnivorous, generally insecti-
vorous, plants. It is not our business to discuss the
original or primary import of the pitchers of pitcher-plants
CHAP, ii The Web of Life 31
or of the mobile and sensitive leaves of Venus' Fly-Trap ;
nowadays, at any rate, insects are attracted to them,
captured by them, and used. Let us take only one case,
that of the common Bladderwort (Utricularia). Many of
the leaflets of this plant, which floats in summer in the
marsh pond, are modified into little bladders, so fashioned
that minute " water-fleas " which swarm in every corner of
the pool can readily enter them, but can in no wise get out
again. The small entrance is guarded by a valve or door,
which opens inwards, but allows no egress. The little crusta-
ceans are attracted by some mucilage made by the leaves, or
sometimes perhaps by sheer curiosity ; they enter and cannot
return ; they die, and their ddbris is absorbed by the leaf.
Again, in regard to distribution, there are numerous
relations between organisms. Spiny fruits like those of
Jack-run-the-hedge adhere to animals, and are borne from
place to place ; and minute water-plants and animals are
carried from one watercourse to another on the muddy
feet of birds. Darwin removed a ball of mud from the
leg of a bird, and from it fourscore seeds germinated. Not
a bird can fall to the ground and die without sending a
throb through a wide circle.
A conception of these chains or circles of influence
is important, not only for the sake of knowledge, but also as
a guide in action. Thus, to take only one instance among
a hundred, it may seem a far cry from a lady's toilet-table
to the African slave-trade, but when we remember the ivory
backs of the brushes, and how the slaves are mainly used for
transporting the tusks of elephants a doomed race from
the interior to the coast, the riddle is read, and the respon-
sibility is obvious. Over a ploughed field in the summer
morning we see the spider-webs in thousands glistening
with mist-drops, and this is an emblem of the intricacy of
the threads in the web of life to be seen more and more
as our eyes grow clear. Or, is not the face of nature like
the surface of a gentle stream, where hundreds of dimpling
circles touch and influence one another in an infinite com-
plexity of action and reaction beyond the ken of the wisest ?
CHAPTER III
THE STRUGGLE OF LIFE
I. Nature and Extent of the Struggle 2. Armour and Weapons
3. Different Forms of Struggle 4. Cruelty of the Struggle
i. Nature and Extent of the Struggle. If we realise
what is meant by the " web of life," the recognition of
the " struggle for existence " cannot be difficult. Animals
do not live in isolation, neither do they always pursue
paths of peace. Nature is not like a menagerie where
beast is separated from beast by iron bars, neither is it
a melee such as would result if the bars of all the cages
were at once removed. It is not a continuous Waterloo,
nor yet an amiable compromise between weaklings. The
truth lies between these extremes. In most places where
animals abound there is struggle. This may be silent and
yet decisive, real without being very cruel, or it may be
full of both noise and bloodshed.
This struggle is very old ; it is older than the conflicts
of men, older than the ravin of tooth and claw, it is as old
as life. The struggle is often very keen often for life or
death. But though few animals escape experience of the
battlefield and for some there seems no discharge from
this war we must not misinterpret nature as "a continual
free-fight." One naturalist says that all nature breathes a
hymn of love, but he is an optimist under sunny southern
skies ; another compares nature to a huge gladiatorial
show with a plethora of fighters, but he speaks as a pes-
CHAP, in The Struggle of Life 33
simist from amid the din of individualistic competition.
Nature is full of struggle and fear, but the struggle is
sometimes outdone by sacrifice, and the fear is sometimes
cast out by love. We must be careful to remember
Darwin's proviso that he used the phrase "struggle for
existence " " in a large and metaphorical sense, including the
dependence of one being on another, and including (which
is more important) not only the life of the individual, but
success in leaving progeny." He also acknowledged the
importance of mutual aid, sociability, and sympathy among
animals, though he did not carefully estimate the relative
importance of competition on the one hand and sociability
on the other. Discussing sympathy, Darwin wrote, "In
however complex a manner this feeling may have originated,
as it is one of high importance to all those animals which
aid and defend one another, it will have been increased
through natural selection ; for those communities which
included the greatest number of the most sympathetic
members would flourish best, and rear the greatest number
of offspring." I should be sorry to misrepresent the
opinions of any man, but after considerable study of
modern Darwinian literature, I feel bound to join in the
protest which others have raised against a tendency to
narrow Darwin's conception of " the struggle for existence,"
by exaggerating the occurrence of internecine competitive
struggle. Thus Huxley says, " Life was a continuous free-
fight, and beyond the limited and temporary relations of
the family, the Hobbesian war of each against all was the
normal state of existence." Against which Kropotkine
maintains that this "view of nature has as little claim to
be taken as a scientific deduction as the opposite view of
Rousseau, who saw in nature but love, peace, and harmony
destroyed by the accession of man." . . . " Rousseau has
committed the error of excluding the beak -and- claw fight
from his thoughts, and Huxley is committing the opposite
error ; but neither Rousseau's optimism nor Huxley's pessi-
mism can be accepted as an impartial interpretation of
nature."
2. Armour and Weapons. If you doubt the reality
D
34 The Stiidy of Animal Life FART i
of the struggle, take a survey of the different classes ot
animals. Everywhere they brandish weapons or are forti-
fied with armour. " The world," Diderot said, " is the
abode of the strong." Even some of the simplest
animals have offensive threads, prophetic of the poison-
ous lassoes with which jellyfish and sea -anemones are
equipped. Many worms have horny jaws; crustaceans
have strong pincers ; many insects have stings, not to
speak of mouth organs like surgical instruments ; spiders
give poisonous bites ; snails have burglars' files; the cuttle-
fish have strangling suckers and parrots' beaks. Among
backboned animals we recall the teeth of the shark and the
sword of the swordfish, the venomous fangs of serpents, the
jaws of crocodiles, the beaks and talons of birds, the horns
and hoofs and canines of mammals. Now we do not say
that these and a hundred other weapons were from their
first appearance weapons, indeed we know that most of
them were not. But they are weapons now, and just as we
would conclude that there was considerable struggle in a
community where every man bore a revolver, we must
draw a similar inference from the offensive equipment of
animals.
As to armoured beasts, we remember that shells of lime
or flint occur in many of the simplest animals, that most
sponges are so rich in spicules that they are too gritty to
be pleasant eating, that corals are polypes withfn shells
of lime, that many worms live in tubes, that the members
of the starfish class are in varying degrees lime-clad, that
crustaceans and insects are emphatically armoured animals,
and that the majority of molluscs live in shells. So among
backboned animals, how thoroughly bucklered were the
fishes of the old red sandstone against hardly less effect-
ive teeth, how the scales of modern fishes glitter, how
securely the sturgeon swims with its coat of bony mail !
Amphibians are mostly weaponless and armourless, but
reptiles are scaly animals par excellence, and the tortoise,
for instance, lives in an almost impregnable citadel. Birds
soar above pursuit, and mammals are swift and strong,
but among the latter the armadillos have bony shields of
CHAP, in The Struggle of Life 35
marvellous strength, and hedgehog and porcupine have
their hair hardened into spines and quills. Now we do not
say that all these structures were from the first of the
nature of armour, indeed they admit of other explanations,
but that they serve as armour now there can be no doubt.
And just as we conclude that a man would not wear
a chain shirt without due reason, so we argue from the
prevalence of animal" armour to the reality of struggle.
For a moment let me delay to explain the two saving-
clauses which I have inserted. The pincers of a crab are
modified legs, the sting of a bee has probably the same
origin, and it is likely that most weapons originally served
some other than offensive purpose. We hear of spears
becoming pruning-hooks ; the reverse has sometimes been
true alike of animals and of men. By sheer use a structure
not originally a weapon became strong to slay ; for there
is a profound biological truth in the French proverb : "A
force de forger on dement for geron?
And again as to armour, it is, or was, well known that a
boy's hand often smitten by the " tawse " became callous as
to its epidermis. Now that callousness was not a device
providential or otherwise to save the youth from the pains
of chastisement, and yet it had that effect. By bearing
blows one naturally and necessarily becomes thick-skinned.
Moreover, the epidermic callousness referred to might be
acquired by work or play altogether apart from school
discipline, though it might also be the effect of the blows.
In the same way many structures which are most useful as
armour may be the " mechanical " or natural results of
what they afterwards help to obviate, or they may arise
quite apart from their future significance.
3. Different Forms of Struggle. If you ask why
animals do not live at peace, I answer, more Scottico^
Why do not we ? The desires of animals conflict with
those of their neighbours, hence the struggle for bread
and the competition for mates. Hunger and love solve
the world's problems. Mouths have to be filled, but
population tends locally and temporarily to outrun the
means of subsistence, and the question "which mouths"
CHAP, in The Struggle of Life 37
has to be decided sometimes by peaceful endeavour, as
in migration, sometimes with teeth clenched or ravenous.
Many animals are carnivorous, and must prey upon weaker
forms, which do their best to resist. Mates also have to
be won, and lover may fight with lover till death is stronger
than both. But these struggles for food and for mates are
often strivings rather than strife, nor is a recognition of the
frequent keenness and fierceness of the competition incon-
sistent with the recognition of mutual aid, sociability, and
love. There is a third form of the struggle, that between
an animal and its changeful surroundings. This also is a
struggle without strife. Fellow competitors strive for their
share of the limited means of subsistence ; between foes
there is incessant thrust and parry ; in the courtship of
mates there are many disappointed and worsted suitors ;
over all are the shears of fate a changeful physical
environment which has no mercy.
An analysis of the various forms of struggle may be
attempted as follows :
(a) Between animals of the same kind which
compete for similar food and other
necessaries of life Struggle between
For
Food
fellows-.
(b) Between animals of different kinds, the
one set striving to devour, the other set
endeavouring to escape their foes, e.g.
between carnivores and herbivores
Struggle between foes.
( (c) Between the rival suitors for desired
mates Struggle between rivals in
[ love.
For \
Foot- I ^ Between animals and changeful surround-
hold j ings Struggle with fate.
In most cases, besides the egoism or individualism, one
must recognise the existence of altruism, parental love and
sacrifice, mutual aid, care for others, and sociality.
38 The Study of Animal Life PART i
Before we consider these different forms of struggle, let
us notice the rapid multiplication of individuals which
furnishes the material for what in " a wide and meta-
phorical sense" may be called a "battlefield."
A single Infusorian may be the ancestor of millions by
the end of a week. A female aphis, often producing one
offspring per hour for days together, might in a season be
the ancestor of a progeny of atomies which would weigh
down five hundred millions of stout men. " The roe of a
cod contains sometimes nearly ten million eggs, and sup-
posing each of these produced a young fish which arrived
at maturity, the whole sea would immediately become a
solid mass of closely packed codfish." The unchecked
multiplication of a few mice or rabbits would soon leave no
standing-room on earth.
But fortunately, with the exception of the Infusorians, these
multiplications do not occur. We have to thank the
struggle in nature, and especially the physical environment,
that they do not. The fable of Mirza's bridge is continually
true, few get across.
(a) It is often said that the struggle between fellows of the
same kind and with the same needs is keenest of all, but
this is rather an assumption than an induction from facts.
The widespread opinion is partly due to an a priori con-
sideration of the problem, partly to that anthropomorphism
which so easily besets us. We transfer to the animal
world our own experience of keen competition with fellows
of the same caste, and in so doing are probably unjust.
Thus Mr. Grant Allen says
" The baker does not fear the competition of the butcher in the
struggle for life ; it is the competition of the other bakers that
sometimes inexorably crushes him out of existence. ... In this
way the great enemies of the individual herbivores are not the
carnivores, but the other herbivores. . . . It is not so much the
battle between the tiger and the antelope, between the wolf and
the bison, between the snake and the bird, that ultimately results
in natural selection or survival of the fittest, as the struggle between
tiger and tiger, between bison and bison, between snake and snake,
between antelope and antelope. . . . Homo homini lupus, says
the old proverb, and so, we may add, in a wider sense, lupus lupo
CHAP, in The Struggle of Life 39
hiptis, also. . . . The struggle is fierce between allied kinds, and
fiercest of all between individual members of the same species."
I have quoted these sentences because they are clearly and
cleverly expressed, after the manner of Grant Allen, but I
do not believe that they are true statements of facts. The
evidence is very unsatisfactory. In his paragraph sum-
marised as " struggle, for life most severe between indi-
viduals and varieties of the same species ; often severe
between species of the same genus," Darwin gave five
illustrations : one species of swallow is said to have ousted
another in North America, the missel-thrush has increased
in Scotland at the expense of the song-thrush, the brown
rat displaces the black rat, the small Asiatic cockroach
drives its great congener before it, the hive -bee imported
to Australia is rapidly exterminating- the small, stingless
native bee. But the cogency of these instances may be
disputed : thus what is said about the thrushes is denied by
Professor Newton. And on the other hand, we know that
reindeer, beavers, lemming, buffaloes and many other
animals migrate when the means of subsistence are unequal
to the demands of the population, and there are other
peaceful devices by which animals have discovered a way
out of a situation in which a life-and-death struggle might
seem inevitable. Very instructive is the fact that beavers,
when too numerous in one locality, divide into two parties
and migrate up and down stream. The old proverb which
Grant Allen quotes, Homo homini lupus, appears to me a
libellous inaccuracy ; the extension of the libel to the
animal world has certainly not been justified by careful
induction. For a discussion of the alleged competition
between fellows, I refer, and that with pleasure and grati-
tude, to Kropotkine's articles on " Mutual Aid among
Animals," Nineteenth Century ', September and November
1890.
(/;) Of the struggle between foes differing widely in kind
little need be said. It is very apparent, especially in wild
countries. Carnivores prey upon herbivores, which some-
times unite in successful resistance. Birds of prey devour
40 TJie Study of Animal Life PART i
small mammals, and sometimes have to fight hard for their
booty. Reptiles also have their battles witness the combats
between snake and mongoose. In many cases, however,
carnivorous animals depend upon small fry ; thus many
birds feed on fishes, insects, and worms, and many fishes
live on minute crustaceans. In such cases the term
FIG. 6. Weasel attacking a grouse. (From St. John's Wild Sports.}
struggle must again be used " in a wide and metaphorical
sense."
(c) In a great number of cases there is between rival males
a contest for the possession of the females, a competition
in which beauty and winsomeness are sometimes as im-
portant as strength. Contrast the musical competition
between rival songsters with the fierce combats of the stags.
CHAP, in The Struggle of Life 41
Many animals are not monogamous, and this causes strife ;
a male seal, for instance, guards his harem with ferocity.
(d) Finally, physical nature is quite careless of life. Changes
of medium, temperature, and moisture, continually occur,
and the animals flee for their lives, adapt themselves to
new conditions, or perish. Cataclysms are rare, but
changes are common, and especially in such schools of
experience as the sea'-shore we may study how vicissitude
has its victims or its victors.
The struggle with Fate, that is to say, with changeful
surroundings, is more pleasant to contemplate than the
other kinds of struggle, for at the rigid mercilessness of
physical nature we shudder less than at the cruel competi-
tion between living things, and we are pleased with the
devices by which animals keep their foothold against wind
and weather, storm and tide, drought and cold. One illus-
tration must suffice : drought is common, pools are dried up,
the inhabitants are left to perish. But often the organism
draws itself together, sweats off a protective sheath, which
is not a shroud, and waits until the rain refreshes the pools.
Not the simplest animals only, but some of comparatively
high degree, are thus able to survive desiccation. The
simplest animals encyst, and may be blown about by the
wind, but they rest where moisture moors them, and are
soon as lively as ever. Leaping a long way upwards, we
find that the mud- fish (Protopterus) can be transported
from Africa to Northern Europe, dormant, yet alive,
within its ball of clay. We do not believe in toads appear-
ing out of marble mantelpieces, and a palaeontologist will
but smile if you tell him of a frog which emerged from an
intact piece of old red sandstone, but amphibians may
remain for a long time dormant either in the mud of their
native pools or in some out-of-the-way chink whither they
had wandered in their fearsome youth.
A shop which had once been used in the preparation
of bone-dust was after prolonged emptiness reinstated in a
new capacity. But it was soon fearfully infested with mites
(Glytiphagus), which had been harboured in crevices in a
strange state of dry dormancy. Every mite had in a sense
42 The Study of Animal Life PART i
died, but remnant cells in the body of each had clubbed
together in a life-preserving union so effective that a return
of prosperity was followed by a reconstitution of mites and
by a plague of them. Of course great caution must be
exercised with regard to all such stories, as well as in
regard to the toads within stones. Of common little
animals known as Rotifers, it is often said, and sometimes
rightly, that they can survive prolonged desiccation. In a
small pool on the top of a granite block, there flourished a
family of these Rotifers. Now this little pool was period-
ically swept dry by the wind, and in the hollow there
remained only a scum of dust. But when the rain returned
and filled the pool, there were the Rotifers as lively as
ever. What inference was more natural than that the
Rotifers survived the desiccation, and lay dormant till
moisture returned ? But Professor Zacharias thought he
would like to observe the actual revivification, and taking
some of the dusty scum home, placed it under his micro-
scope on a moist slide, and waited results. There were the
corpses of the Rotifers plain enough, but they did not revive
even in abundant moisture. What was the explanation ?
The eggs of these Rotifers survived, they developed rapidly,
they reinstated the family. And of course it is much easier
to understand how single cells, as eggs are, could survive
being dried up, while their much more complex parents
perished. I do not suggest that no Rotifers can survive
desiccation, it is certain that some do ; but the story I
have told shows the need of caution. There is no doubt,
moreover, that certain simple "worms," known as "paste-
eels," " vinegar-eels," etc., from their frequent occurrence
in such substances, can survive desiccation for many years.
Repeated experiments have shown that they can lie dormant
for as long as, but not longer than, fourteen years ! and it
is interesting to notice that the more prolonged the period
of desiccation has been, the longer do these threadworms
take to revive after moisture has been supplied. It seems
as if the life retreated further and further, till at length it
may retreat beyond recall. In regard to plants there are
many similar facts, for though accounts of the germination
CHAP, in The Struggle of Life 43
of seeds from the mummies of the pyramids, or from the
graves of the Incas, are far from satisfactory, there is no
doubt that seeds of cereals and leguminous plants may
retain their life in a dormant state for years, or even for
tens of years.
But desiccation is only one illustration out of a score
of the manner in which animals keep their foothold against
fate. I need hardly say that they are often unsuccessful ;
the individual has often fearful odds against it. How many
winged seeds out of a thousand reach a fit resting-place
where they may germinate ? Professor Mobius says that
out of a million oyster embryos only one individual grows
up, a mortality due to untoward currents and surroundings,
as well as to hungry mouths. Yet the average number of
thistles and oysters tends to continue, " So careful of the
type she seems, so careless of the single life." Yet though
the average usually remains constant, there is no use trying
to ignore, what Richard Jefferies sometimes exaggerated,
that the physical fates are cruel to life. But how much
wisdom have they drilled into us ?
" For life is not as idle ore,
But iron dug from central gloom,
And heated hot with burning fears,
And dipt in baths of hissing tears,
And battered by the shocks of doom
To shape and use."
4. Cruelty of the Struggle. Opinions differ much as
to the cruelty of the " struggle for existence," and the
question is one of interest and importance. Alfred Russel
Wallace and others try to persuade us that our conception
of the " cruelty of nature" is an anthropomorphism; that,
like Balbus, animals do not fear death ; that the rabbit
rather enjoys a run before the fox ; that thrilling pain soon
brings its own anaesthetic ; that violent death has its
pleasures, and starvation its excitement. Mr. Wallace,
who speaks with the authority of long and wide ex-
perience, enters a vigorous protest against Professor
Huxley's description of the myriads of generations of
44 The Study of Animal Life PART i
herbivorous animals " which have been tormented and
devoured by carnivores " ; of both alike " subject to all the
miseries incidental to old age, disease, and over-multiplica-
tion " ; of the " more or less enduring suffering " which is
the meed of both vanquished and victor ; of the whole
creation groaning in pain. " There is good reason to
believe," says Mr. Wallace, " that the supposed torments
and miseries of animals have little real existence, but are
the reflection of the imagined sensations of cultivated men
and women in similar circumstances ; and that the amount
of actual suffering caused by the struggle for existence
among animals is altogether insignificant." " Animals are
spared from the pain of anticipating death ; violent deaths,
if not too prolonged, are painless and easy ; neither do
those which die of cold or hunger suffer much ; the popular
idea of the struggle for existence entailing misery and pain
on the animal world is the very reverse of the truth." He
concludes by quoting the conclusion of Darwin's chapter on
the struggle for existence : " When we reflect on this
struggle, we may console ourselves with the full belief that
the war of nature is not incessant, that no fear is felt, that
death is generally prompt, and that the vigorous, the
healthy, and the happy survive and multiply." Yet it was
Darwin who confessed that he found in the world "too
much misery."
We have so little security in appreciating the real life
the mental and physical pain or happiness of animals, that
there is apt to be exaggeration on both sides, according as
a pessimistic or an optimistic mood predominates. I there-
fore leave it to be settled by your own observation whether
hunted and captured, dying and starving, maimed and half-
frozen animals have to endure " an altogether insignificant
amount of actual suffering in the struggle for existence."
But I think we must admit that there is much truth in
what Mr. Wallace urges. Moreover, the term cruelty can
hardly be used with accuracy when the involved infliction
of pain is necessary. In many cases the carnivores are
less " cruel " to their victims than we are to our domesti-
cated animals. We must also remember that the " struggle
CHAP, in The Struggle of Life 45
for existence " is often applicable only in its " wide and
metaphorical sense." And it is fair to balance the happiness
and mutual helpfulness of animals against the pain and
deathful competition which undoubtedly exist.
What we must protest against is that one-sided inter-
pretation according to which individualistic competition is
nature's sole method of progress. We are told that animals
have got on by their struggle for individual ends ; that they
have made progress on the corpses of their fellows, by a
" blood and iron " competition in which each looks out for
himself, and extinction besets the hindmost. To those who
accept this interpretation the means employed seem justified
by the results attained. But it is only in after-dinner talk
that we can slur over whatever there is of pain and cruelty,
overcrowding and starvation, hate and individualism, by
saying complacently that they are justified in us their
children; that we can rest satisfied that what has been
called "a scheme of salvation for the elect by the damnation
of the vast majority " is a true statement of the facts ; that
we can seriously accept a one-sided account of nature's
regime as a justification of our own ethical and economic
practice.
The conclusions, which I shall afterwards seek to
substantiate, are, that the struggle for existence, with its
associated natural selection, often involves cruelty, but
certainly does not always do so ; that joy and happiness,
helpfulness and co-operation, love and sacrifice, are also
facts of nature, that they also are justified by natural
selection ; that the precise nature of the means employed
and ends attained must be carefully considered when
we seek from the records of animal evolution support
or justification for human conduct ; and that the tragic
chapters in the history of animals (and of men) must be
philosophically considered in such light as we can gather
from what we know of the whole book.
CHAPTER IV
SHIFTS FOR A LIVING
I. Insulation 2. Concealment 3. Parasitism 4. General Re-
semblance to Surroundings 5. Variable Colouring 6. Rapid
Change of Colour 7. Special Protective Resemblance 8.
Warning Colours 9. Mimicry 10. Masking n. Com-
bination of Advantageous Qtialities 12. Surrender of Paris
GRANTING the struggle with fellows, foes, and fate, we are
led by force of sympathy as well as of logic to think of the
shifts for a living which tend to be evolved in such con-
ditions, and also of some other ways by which animals
escape from the intensity of the struggle.
i. Insulation. Some animals have got out of the
struggle through no merit of their own, but as the result
of geological changes which have insulated them from
their enemies. Thus, in Cretaceous times probably, the
marsupials which inhabited the Australasian region were
insulated. In that region they were then the only re-
presentatives of Mammalia, and so, excepting the " native
dog," some rodents and bats, and more modern imports,
they still continue to be. By their insulation they were
saved from that contest with stronger mammals in which
all the marsupials left on the other continents were
exterminated, with the exception of the opossums, which
hide in American forests. A similar geological insulation
accounts for the large number of lemurs in the island of
Madagascar.
CHAP, iv Shifts for a Living 47
2. Concealment. A change of habitat and mode of life
is often as significant for animals as it is for men. It is
easy to understand how mammals which passed from
terrestrial to more or less aquatic life, for instance beaver
and polar bear, seals, and perhaps whales, would enjoy
a period of relative immunity after the awkward time
of transition was over. So, too, many must have passed
from the battlefield of the sea -shore to relative peace
on land or in the deep-sea. In a change from open air
to underground life, illustrated for instance in the mole,
many animals have sought and found safety, and the
change seems even now in progress, as in the New
Zealand parrot Stringops, which, having lost the power
of flight, has taken to burrowing. Similarly the power
of flight must have helped insects, some ancient saurians,
and birds out of many a scrape, though it cannot be
doubted that this transition, and also that from diurnal to
nocturnal habits, often brought only a temporary relief.
3. Parasitism. From the simple Protozoa up to the
beginning of the backboned series, we find illustrations of
animals which have taken to a thievish existence as unbidden
guests in or on other organisms. Flukes, tapeworms, and
some other "worms," many crustaceans, insects, and mites,
are the most notable. Few animals are free from some kind
of parasite. There are various grades of parasitism ; there
are temporary and permanent, external and internal, very
degenerate, and very slightly affected parasites. Some-
times the adults are parasitic while the young are free -liv-
ing, sometimes the reverse is true ; sometimes the parasite
completes its life in one host, often it reaches maturity only
after the host in which its youth has been passed is de-
voured by another. In many cases the habit was probably
begun by the females, which seek shelter during the period
of egg-laying; in not a few crustaceans and insects the
females alone are parasitic. Most often, in all probability,
hunger and the search for shelter led to the establishment
of the thievish habit. Now, the advantages gained by a
thoroughgoing parasite are great safety, warmth, abund-
ant food, in short, " complete material well-being." But
48 The Study of Animal Life PART i
there is another aspect of the case. Parasitism tends to be
followed by degeneration of appendages, food - canal,
sense-organs, nervous system, and other structures, the
possession and use of which make life worth living. More-
over, though the reproductive system never degenerates,
the odds are often many against an embryo reaching a fit
host or attaining maturity. Thus Leuckart calculates that
a tapeworm embryo has only about I chance in 83,000,000
of becoming a tapeworm, and one cannot be sorry that
its chance is not greater. In illustration of the degenera-
tion which is often associated with parasitism, and varies
as the habit is more or less predominant, take the case of
Sacculina a crustacean usually ranked along with bar-
nacles and acorn-shells. It begins its life as a minute free
"nauplius," with three pairs of appendages, a short food-
canal, an eye, a small brain, and some other structures
characteristic of many young crustaceans. In spite of this
promiseful beginning, the young Sacculina becomes a para-
site, first within the body, and finally under the tail, of a
crab. Attached by absorptive suckers to its host, and
often doing no slight damage, it degenerates into an oval
sac, almost without trace of its former structure, with
reproductive system alone well developed. Yet the
degeneration is seldom so great as this, and it is fair to
state that many parasites, especially those which remain as
external hangers-on, seem to be but slightly affected by their
lazy thievish habit ; nor can it be denied that most are well
adapted to the conditions of their life. But on the whole
the parasitic life tends to degeneration, and is unprogress-
ive. Meredith writes of Nature's sifting
" Behold the life of ease, it drifts.
The sharpened life commands its course :
She winnows, winnows roughly, sifts,
To dip her chosen in her source.
Contention is the vital force
Whence pluck they brain, her prize of gifts. "
4. General Resemblance to Surroundings. Many
transparent and translucent blue animals are hardly
CHAP, iv Shifts for a Living 49
visible in the sea ; white animals, such as the polar bear,
the arctic fox, and the ptarmigan in its winter plumage,
are inconspicuous upon the snow ; green animals, such
as insects, tree-frogs, lizards, and snakes, hide among the
leaves and herbage ;(. tawny animals harmonise with sandy
soil ; and the hare escapes detection among the clods. So
do spotted animals such as snakes and leopards live unseen
in the interrupted light" of the forest, and the striped tiger
is lost in the jungle. Even the eggs of birds are often well
suited to the surroundings in which they are laid. There
can be no doubt that this resemblance between the colour
of an animal and that of its surroundings is sometimes of
protective and also aggressive value in the struggle for
existence, and where this is the case, natural selection
would foster it, favouring with success those variations
which were best adapted, and eliminating those which were
conspicuous.
But there are many instances of resemblance to sur-
roundings which are hard to explain. Thus Dr. A. Seitz
describes a restricted area of woodland in South Brazil, where
the great majority of the insects were blue, although but
a few miles off a red colour was dominant. He maintains
that the facts cannot in this case be explained as due either
to general protective resemblance or to mimicry.
I have reduced what I had written in illustration of
advantageous colouring of various kinds, because this
exceedingly interesting subject has been treated in a readily
available volume by one who has devoted much time and
skill to its elucidation. Mr. E. B. Poulton's Colours of
Animals (International Science Series, London, 1890) is a
fascinating volume, for which all interested in these aspects
of natural history must be grateful. With this a forth-
coming work (Animal Coloration^ London, 1892) by Mr.
F. E. Beddard should be compared.
5. Variable Colouring. Some animals, such as the
ptarmigan and the mountain-hare, become white in winter,
and are thereby safer and warmer. In some cases it
is certain that the pigmented feathers and hairs become
white, in other cases the old feathers and hairs drop
E
50 TJie Study of Animal Life PART i
off and are replaced by white ones ; sometimes the
whiteness is the result of both these processes. It is
directly due to the formation of gas bubbles inside
the hairs or feathers in sufficient quantity to antagonise
the effect of any pigment that may be present, but in
the case of new growths it is not likely that any pig-
ment is formed. In some cases, e.g. Ross's lemming and
the American hare (Lepus americamis\ it has been clearly
shown that the change is due to the cold. It is likely that
this acts somewhat indirectly upon the skin through the
nervous system. We may therefore regard the change as
a variation due to the environment, and it is at least
possible that the permanent whiteness of some northern
animals, e.g. the polar bear, is an acquired character of
similar origin. There are many objections to the theory
that the winter whiteness of arctic animals arose by the
accumulation of small variations in individuals which, being
slightly whiter than their neighbours, became dominant by
natural selection, though there can be no doubt that the
whiteness, however it arose, would be conserved like other
advantageous variations.
To several naturalists, but above all to Mr. Poulton, we
are indebted for much precise information in regard to the
variable colouring of many caterpillars and chrysalides.
These adjust their colours to ithose of the surroundings, and
even the cocoons are sometimes harmoniously coloured.
There is no doubt that the variable colouring often has
protective value. Mr. Poulton experimented with the
caterpillars of the peacock butterfly (Vanessa to\ small
tortoise-shell ( Vanessa urticce), garden whites (Pieris
brassica and Pieris rapce), and many others. Caterpillars
of the small tortoise-shell in black surroundings tend to be-
come darker as pupae ; in a white environment the pupae
are lighter ; in gilded boxes they tend to become golden.
The surrounding colour seems to influence the caterpillar
" during the twenty hours immediately preceding the last
twelve hours of the larval state," " and this is probably the
true meaning of the hours during which the caterpillar
rests motionless on the surface upon which it will pupate."
CHAP, iv Shifts for a Living 51
"It appears to be certain that it is the skin of the larva
which is influenced by surrounding colours during the
sensitive period, and it is probable that the effects are
wrought through the medium of the nervous system."
Accepting the facts that caterpillars are subtly affected
by surrounding colours, so that the quiescent pupae har-
monise with their environment, and that the adjustment has
often protective value, we are led to inquire into the origin
of this sensitiveness. That the change of colour is
not a direct result of external influence is certain, but
of the physiological nature of the changes we know little
more than that it must be complex. It may be main-
tained, that " the existing colours and markings are at any
rate in part due to the accumulation through heredity
of the indirect influence of the environment, working
by means of the nervous system;" "to which it may
be replied," Poulton continues, " that the whole use and
meaning of the power of adjustment depends upon its
freedom during the life of the individual ; any hereditary
bias towards the colours of ancestors would at once destroy
the utility of the power, which is essentially an adaptation
to the fact that different individuals will probably meet with
different environments. As long ago as 1873 Professor
Meldola argued that this power of adjustment is adaptive,
and to be explained by the operation of natural selection."
Poulton's opinion seems to be, that the power of producing
Variable colouring arose as a constitutional variation apart
from the influence of the environment, that the power was
fostered in the course of natural selection, and that its
limits were in the same way more or less defined in adapta-
tion to the most frequent habitat of the larvae before
and during pupation. The other theory is that the power
arose as the result of environmental influence, was accumu-
lated by inheritance throughout generations, and was fostered
like other profitable variations by natural selection. The
question is whether the power arose in direct relation
to environmental influence or not, whether external influence
was or was not a primary factor in evolving the power of
adapting colour, and in defining it within certain limits.
52 The Study of Animal Life PART i
6. Rapid Change of Colour. For ages the chamaeleon
has been famous for its rapid and sometimes striking
changes of colour. The members of the Old World
genus Chamceleo quickly change from green to brown
or other tints, but rather in response to physical irrita-
tion and varying moods than in relation to change of
situation and surrounding colours. So the American
" chamaeleons " (Anolis) change, for instance, from emerald
to bronze under the influence of excitement and various
kinds of light. Their sensitiveness is exquisite ; " a pass-
ing cloud may cause the bright emerald to fade." Some-
times they may be thus protected, for " when on the broad
green leaves of the palmetto, they are with difficulty per-
ceived, so exactly is the colour of the leaf counterfeited.
But their dark shadow is very distinct from beneath." Most
of the lizards have more or less of this colour-changing
power, which depends on the contraction and expansion
of the pigmented living matter of cells which lie in layers
in the under-skin, and are controlled by nerves.
In a widely different set of animals the cuttle-fishes
the power of rapid colour-change is well illustrated. When
a .cuttle-fish in a tank is provoked, or when one almost
stranded on the beach struggles to free itself, or, most
beautifully, when a number swim together in strange unison,
flushes of colour spread over the body. The sight suggests
the blushing of higher animals, in which nervous excitement
passing from the centre along the peripheral nerves influ-
ences the blood-supply in the skin ; but in colour-change the
nervous thrills affect the pigment-containing cells or chroma-
tophores, the living matter of which contracts or expands
in response to stimulus. It must be allowed that the colour-
change of cuttle-fish is oftenest an expression of nervous
excitement, but in some cases it helps to conceal the
animals.
More interesting to us at present are those cases of
colour -change in which animals respond to the hues of
their surroundings. This has been observed in some
Amphibians, such as tree-frogs ; in many fishes, such as
plaice, stickleback, minnow, trout, Gobius rutkensparri,
v Shifts for a Living 53
Serranus ; and in not a few crustaceans. The researches
of Briicke, Lister, and Pouchet have thrown much light on
the subject. Thus we know that the colour of surround-
ings affects the animals through the eyes, for blind plaice,
trout, and frogs do not change their tint. The nervous
thrill passes from eye to brain, and thence extends, not down
the main path of impulse the spinal cord but down the
sympathetic chain. If this be cut, the colour-change does
not take place. The sympathetic system is connected with
nerves passing from the spinal cord to the skin, and it is
along these that the impulse is further transmitted. The
result is the contraction or expansion of the pigment in the
skin-cells. Though the path by which the nervous influence
passes from the eye to the skin is somewhat circuitous, "the
change is often very rapid. As the resulting resemblance
to surroundings is often precise, there can be no doubt that
the peculiarity sometimes profits its possessors.
7. Special Protective Resemblance. The likeness
between animals and their surroundings is often very precise,
and includes form as well as colour. Thus some bright butter-
flies, e.g. Kallima, are conspicuous in flight, but become
precisely like brown withered leaves when they settle upon
a branch and expose the under sides of their raised wings ;
the leaf-insects (Phylliuin) have leaf-like wings and legs ;
the " walking-sticks " (Phasmid^
- c c
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They absorb soluble food
They obtain the requisite carbon
bonic acid gas in the air or water
They obtain the requisite nitre
simple nitrogenous compounds,
the nitrates of the soil. They c
rid of nitrogenous waste-products
The majority possess chlorophyll,
pigment by aid of which the livi
utilises the energy of sunlight ii
carbonic acid (with liberation c
and in building up complex subsU
The component cells are walled ir
lose, a material chemically allied i
The cells exhibit on an average
division of labour
They build up crude, chemically sii
material into complex substances ;
vert the kinetic energy of sunligr
potential chemical energy of the.s
food-stuffs ; they are characteris
ducers (of carbonic acid), exp
paratively little energy in motion (
work, and are predominantly pass
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sugar, fat, ei
animals
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demonstrabl
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! Marked divisi
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3 J3 a rf J^
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Ascidians
CHAP, xi The Elements of Structure 1 7 1
The net result of this contrast is that animals are more
active than plants. Life slumbers in the plant ; it wakes
and works in the animal. The changes associated with the
living matter of an animal are seemingly more intense and
rapid ; the ratio of disruptive, power-expending changes to
constructive power-accumulating changes is greater ; most
animals live more nearly up to their income than most
. plants do. They five on richer food ; they take the pounds
which plants have accumulated in pence, and spend them.
Of course plants also expend energy, but for the most part
within their own bodies ; they neither toil nor spin. They
stoop to conquer the elements of the inorganic world, but
have comparatively little power of moving or feeling. They
are more conservative and miserly than the liberally spend-
thrift animals, and it is possible that some of the most
characteristic possessions of plants, e.g. cellulose, may be
chemical expressions of a marked preponderance of con-
structive and up-building vital processes. It is enough,
however, if we have to some extent realised the common-
places that plants and animals live the same sort of life,
but that the animals are on an average more active and
wide-awake than the plants.
2. The Relation of the Simplest Animals to those
which are more Complex. From the pond-water catch in
a glass tube one of the small animals, suppose it be a tiny
water-flea or a minute " worm " ; how does it differ from one
of the simplest animals, such as an Infusorian ? It consists of
many units of living matter instead of only one. The con-
trast is like that between an egg and the bird which is
hatched from within it. The simplest animals are single
cells, all the others from sponge to man are many-celled.
The Protozoa are units ; all others the Metazoa are
composite aggregates of units, or cities of cells.
Compare the life of one of the Protozoa with that of
a worm, a frog, or a bird. Both are alive, both may be
seen moving, shrinking away from what is hurtful, drawing
near to what is useful, engulfing food, and getting rid of
refuse. Both are breathing, for carbonic acid will poison
them, and dearth of oxygen will kill them ; both grow and
172 The Study of Animal Life PART in
multiply. But in the single -celled Protozoon all the pro-
cesses of life occur within a unit mass of living matter. In
the many-celled Metazoon the various processes occur at
different parts of the body, are discharged by special sets* of
cells, among which the labour of life has been divided. The
life of the Protozoon is like that of a one -roomed house
which is at once kitchen and work-room, nursery and coal-
cellar. The life of the Metazoon is like that of a mansion
where there are special rooms for diverse purposes.
In having no " body " the Protozoa are to some extent
relieved from the necessity of death. Within the compass
of a single cell they perform a crowd of functions, but tear
and wear are often made good again, the units have great
power of self- recuperation. They may, indeed, be crushed
to powder, and they lead no .charmed life safe from the
appetite of higher forms. But these are violent deaths.
What Weismann and others have insisted on is that
the unicellular Protozoa, in natural conditions, need never
die a natural death, being in that sense immortal. It
is true that a Protozoon may multiply by dividing into two
or more parts, but only a sort of metaphysical individuality
is thus lost, and there is nothing left to bury. We would
not, however, give much prominence to a strange idea of
this kind. For the " immortality of the Protozoa " is little
more than a verbal quibble ; it amounts to saying that our
common idea of death, as a change which makes a living
body a corpse, is hardly applicable to the unit organisms.
I believe, moreover, that the idea has been exaggerated ;
for instance, the Protozoa in the open sea, in their natural
conditions, seem to die in large numbers.
The combination of all the vital activities within the
compass of a single-cell involves a very complex life within
the unit, not more complex than the entire life of a many-
celled animal, but fuller than that of one of its component
cells. While a Protozoon is relatively simple in structure,
its life of crowded functions, such as moving, digesting,
breathing, is exceedingly complex. The simpler an organism
is in structure the more difficult will it be to study its separate
functions. Physiological or functional simplicity is in inverse
CHAP, xi The Elements of Structure 173
ratio to structural or morphological simplicity. Thus the
physiologist makes most progress when he seeks to under-
stand animals with many parts, for there he can find a large
number of units, all as it were working at one task. The
life of a Protozoon is more manifold and complex than that
of any unit from a higher animal, just as the daily life of
the savage at once hunter, shepherd, warrior is more
varied than ours. .
Already it has been recognised that every many-celled
animal begins its life as a single cell, as an egg-cell with
which a male element has united. Every Metazoon begins
its life as a Protozoon, no matter how large the animal,
for the whales arise from ova "no larger than fern-seed,"
no matter how lofty the result, for man himself has to begin
his life at the literal beginning. The fertilised egg- cell
divides and re-divides, its daughter- cells also divide, the
resultant units are arranged in layers, clubbed together to
form tissues, compacted to form young organs, and the
result is such a multicellular body as we possess ; but while
this body-making proceeds, certain units are kept apart, in
some way insulated from the process of growth, to form the
future reproductive elements, which, freed from the adult
body, will begin a new generation. Back to the beginning
again every Metazoon has to go, and if we believe that the
Protozoa are not only the simplest, but also represent the first
animals, we have here the first and perhaps most important
illustration of the fact that in its development the individual
more or less recapitulates the history of the race. The
simplest animals are directly comparable with the repro-
ductive cells of higher animals, but the divided cells of the
ovum remain clubbed together to form a young animal, while
the daughter-cells of a Protozoon separate from one another,
each as a new life.
The gulf between the single -celled and many- celled
animals is a deep one, but it has been bridged. Otherwise
we should not exist. Traces of the bridge now remain in
what are called " colonial Protozoa," which, however trouble-
some to those who like crisp distinctions, are most instruc-
tive to those who would appreciate the continuity of the
174 The Study of Animal Life PART in
tree of life. These exceptional Protozoa are loose colonies
of cells, descendants or daughter- cells of a parent unit,
which have remained persistently associated instead of
going free with the usual individualism of Protozoa. They
illustrate to some minds a primitive co-operation of cells ;
they show us how the Metazoa or multicellular animals may
have arisen.
3. The Parts of the Animal Body. The physiologist
investigates life or activity at different levels, passing from
his study of the animal as a unity with habits and a tem-
perament, to consider it as an engine of organs, a web of
tissues, a city of cells, or finally as a whirlpool of living
matter. So the morphologist investigates the form of the
intact animal, then in succession its organs, their component
tissues, the minuter elements or cells, and finally the struc-
ture of the living stuff itself. Moreover, as there is no real
difference between studying a corpse and a fossil, the palae-
ontologist is also among the students of morphology ; and
most of embryology consists of studies of structure at dif-
ferent stages in the animal's life-history.
The outer form of normal animals seems to be always
artistically harmonious. It has a certain hardly definable
crystalline perfection which pleases our eyes, but those who
have not already perceived this will not see much meaning
in the assertion, nor in Samuel Butler's opinion that " form
is mind made manifest in flesh through action."
" I believe a leaf of grass is no less than the journey-work of the
stars,
And the pismire is equally perfect, and the grain of sand, and
the egg of the wren,
And the tree-toad is a chef-d'oeuvre for the highest,
And the running blackberry would adorn the parlours of heaven,
And the narrowest hinge in my hand puts to scorn all machinery,
And the cow crunching with depressed head surpasses any statue,
And a mouse is miracle enough to stagger sextillions of infidels ! "
WALT WHITMAN.
It is also important to think of the different kinds of
symmetry, how for instance the radiating sea-anemones and
jellyfishes, which are the same all round, differ markedly
CHAP, xi The Elements of Structure 175
from bilaterally symmetrical worms, lobsters, fishes, and
most other animals. Then there is the difference between
unsegmented animals which are all one piece (like the
lower worms and the molluscs), and those whose bodies
consist, as in earthworm and crayfish, of a series of more or
less similar rings or segments, due to conditions of growth
of which we know almost nothing.
Organs are well-defined parts, such as limb or liver, heart
or brain, in which there is a predominance of one or a few
kinds of vital activity. Gradually, alike in the individual
and in the race, do they take form and function. There is
contractility before there are definite contractile organs or
muscles ; there is diffuse sensitiveness before there are
defined nerves or sense-organs. The progress of structure,
alike in the individual and in the race, is from simplicity
to complexity, as the progress of function is from homo-
geneous diffuseness to heterogeneous specialisation. The
two great kinds of progress may be illustrated by contrasting
a sea- anemone and a bird. The higher animal has more
numerous parts or organs, the division of labour within its
body has brought about more differentiation of structure,
but it is also a more perfect unity, its parts are more
thoroughly knit together and harmonised. There is pro-
gress in integration as well as in differentiation.
" The shoulder-girdle of the skate," W. K. Parker says, " may he
compared to a clay model in its first stages, or to the heavy oaken
furniture of our forefathers that stood ponderous and fixed by its own
massy weight. As we ascend the vertebrate scale, the mass becomes
more elegant, more subdivided, and more metamorphosed, until,
in the bird class and among mammals, these parts form the frame-
work of limbs than which nothing can be imagined more agile or
more apt. So also as regards the sternum ; at first a mere outcrop
of the feebly developed costal arches in the amphibia, it becomes
the keystone of perfect arches in the true reptiles, then the fulcrum
of exquisitely constructed organs of flight in the bird ; and lastly,
forms the mobile front wall of the heaving chest of the highest
vertebrate."
Of the order in which organs appear or have appeared
we can say little. The simplest sponges and polypes are
176 The Study of Animal Life PART in
little more than two-layered cups of cells, the cavity of the
cup being the primitive food -canal. A parallel stage
occurs in the early life-history of most animals, when the
embryo has the form of a two-layered sac of cells, or is in
technical language a gastrula. Both in the racial and
individual life-history the formation of this primitive food-
canal occurs very early. But it is not certain that it the
primitive stomach was not at a still earlier stage an in-
ternal brood-cavity !
But instead of speculating about this, let us seek to
understand what is meant by the correlation of organs.
Certain parts of the body stand or fall together, they are
physiologically knit, they have been evolved in company.
Thus heart and lungs, muscles and nerves, are closely
correlated. Sometimes it is obvious why two or three
structures should be thus connected, for it is of the very
essence of an organism that its parts are members one of
another. In other cases the reason of the connection is
obscure.
When organs either in the same or in different animals
have a similar origin, and are built up on the same funda-
mental plan, they are called homologous. Those whose
resemblance is merely that they have similar functions are
termed analogous. Even Aristotle recognised that some
structures apparently different were fundamentally the
same, and no small part of the progress of morphology has
consisted in the recognition of homologies. Thus it was a
great step when Goethe and others showed that the sepals,
petals, stamens, and carpels of a flower were really modified
leaves, or when Savigny discerned that the three pairs of
jaws beside an insect's mouth were really modified legs.
To Owen the precision of our conceptions in regard to
homologies is in great part due, though subsequent studies
in development have added welcome corroboration to many
of the comparisons which formerly were based solely on the
results of anatomy. Thus an organ derived from the outers?
embryonic layer cannot be homologous with one derived
from the innermost stratum of embryonic cells. Homo- :
logous organs in one animal are well illustrated by the
CHAP, xi The Elements of Structure
177
nineteen pairs of appendages borne by a crayfish. or lobster.
These differ greatly in form and in function ; many of them
are not analogous with their neighbours, one feels and
another bites, one seizes and another swims, but they are
all homologous. So are the different forms of fore-limb,
the pectoral fin of a fish, the fore-leg of a frog or lizard, the
wing of a bird, the flipper of a whale, the fore-leg of a tiger,
the arm of man. -But the wing of an insect is merely
analogous not homologous with that of a bird, while the
wings of bats and birds are both analogous and homo-
logous.
FIG. 33. Bones of the wing in pigeon (A), bat (B), extinct pterodactyl (C).
(From Chambers's Encyclop.)
Change of Function. Organs are not mechanisms rigidly
adapted for only one purpose. In most cases they have a
main function and several subsidiary functions, and changes
may take place in organs by the occasional predominance
of a subsidiary function over the original primary one.
Thus the swim- or air-bladder which grows out dorsally
from the food-canal of most fishes, seems usually to be a
hydrostatic organ ; in a few cases it helps slightly in
respiration, but in the double -breathing mud -fishes or
Dipnoi it has become a genuine lung. An unimportant
(allantoic) bladder at the hind end of the gut in frogs, is
represented in the embryos of reptiles and birds by a very
important respiratory (and sometimes yolk-absorbing) birth-
N
178 The Study of Animal Life PART in
robe, and in almost all mammals by part of the placenta
which unites mother and unborn offspring.
Substitution of Organs. To the embryologist Kleinen-
berg we owe a suggestive conception of organic change,
which he speaks of as the development of organs by sub-
stitution : An organ may supply the stimulus and the
necessary condition for another which gradually supersedes
and replaces it. In the simplest backboned animals, such
as the lancelet, there is a supporting gristly rod along the
back ; among fishes the same rod or notochord is largely
replaced by a backbone ; in yet higher Vertebrates the
adults have almost no notochord, its replacement by the
backbone is almost complete. So in the individual life-
history, all vertebrate embryos have a notochord to begin
with ; in the lancelet and some others this is retained
throughout life, in higher forms it is temporary and serves
as a scaffolding around which, from a thoroughly distinct
embryological origin, the backbone develops. What is the
relation between these two structures notochord and
backbone ? According to Kleinenberg, the notochord
supplies the necessary stimulus or condition for the
development of the backbone which replaces it.
Rudimentary Organs. (a) Through some ingrained
defect it sometimes happens that an organ does not
develop perfectly. The heart, the brain, the eye may be
spoilt in the making. Such cases are illustrations of
arrested development, (b) A parasitic crustacean, such as
the Sacculina which shelters beneath the tail of a crab,
begins life with many equipments such as legs, food-canal,
eye, and brain, which are afterwards entirely or nearly
lost ; the sedentary adult sea-squirt or ascidian has lost the
tail, the notochord, the spinal cord which its free-swimming
tadpole-like larva possessed. Such cases are illustrations
of degeneration. In these instances the retrogression is
demonstrable in each lifetime, in other cases we have to
compare the animal with its ancestral ideal. Thus there
are many cave -animals whose eyes are always blind and
abortive. The little kiwi of New Zealand has only apologies
for wings. We need have no hesitation in calling these
CHAP, xi The Elements of Structure 179
animals degenerate in eyes and fore -limbs respectively.
(c) But somewhat different are such structures as the
following : The embryonic gill-clefts of reptiles, birds, and
mammals, which have no respiratory significance, or the
embryonic teeth of whalebone whales, of some parrots and
turtles, which in no case come to anything. They are
vestigial structures, which are partly explained on the
assumption, justified also in other ways, that the ancestors
of reptiles, birds, and mammals used the gill-clefts as fishes
and tadpoles do, that the ancestors of whalebone whales,
birds, and turtles had functional teeth. No one can say
with certainty of vestigial structures that they are entirely
useless, nor can one precisely say why they persist after
their original usefulness has ceased. They remain because
of necessities of growth of which we are ignorant, and
they may be useful in relation to other structures though
in themselves functionless.
Classification of Organs. We may arrange organs
according to their work, some, such as limbs and weapons,
being busied with the external relations of the organism ;
others, such as heart and liver, being concerned with
internal affairs. Or we may classify them according to
their development from the outer, middle, or inner layer of
the embryo. Thus brain and sense-organs are always mainly
due to the outer stratum (ectoderm or epiblast), muscles
and skeleton arise from the middle mesoderm or mesoblast,
the gut and its outgrowths such as lungs and liver primarily
originate from the inner endoderm or hypoblast. Or we
may arrange the various structures more or less arbitrarily
for convenience of description as follows : the skin and its
outgrowths, appendages, skeleton, muscular system, nervous
system, sense-organs, the food-canal and its outgrowths,
the body-cavity, the heart and blood-vessels, the respiratory
organs, the excretory system, the reproductive organs.
Tissues. To the school of Cuvier we owe the analysis
of the animal organism into its component organs ; but as
early as 1801 Bichat published his Anatomic Generate, in
which the analysis was carried a step farther. He reduced
the organs to their component tissues, and maintained that
180 The Study of Animal Life PART m
the function of an organ might be expressed in terms of the
properties of its tissues.
If we pass to the next step of analysis, and think of the
body as a complex city of cells, we are better able to
understand what tissues are. Each cell corresponds to a
house, a tissue corresponds to a street of similar houses.
In a city like Leipzig many streets are homogeneous, formed
by houses or shops in which the predominant activity is the
same throughout. A street is devoted to the making of
clothes, or of bread, or of books. So in the animal body
aggregates of contractile cells form muscular tissue, of
supporting cells skeletal tissue, of secreting cells glandular
tissue, and so on.
It is enough to state the general idea that a tissue is an
aggregate of more or less similar cells, and to note that the
different kinds may be grouped as follows :
I. Nervous tissue, consisting of cells which receive,
transmit, or originate nerve-stimuli.
II. Muscular tissue, consisting of contractile cells.
III. Epithelial tissue, consisting of lining and covering
cells, which often become glandular, exuding the
products of their activity as secretions.
IV. Connective tissue, including cells which bind,
support, and store.
Cells. To the discovery and perfecting of the micro-
scope we owe the analysis of the body into its unit masses
of living matter or cells. From 1838-39, when Schwann
and Schleiden stated in their "cell doctrine" that all
organisms plants and animals alike were built up of
cells, cellular biology may be said to date. It was soon
shown as a corollary that every organism which reproduced
in the ordinary fashion arose from a single egg -cell or
ovum Nvhich had been fertilised by union with a male-cell
or spermatozoon. Moreover, the position of the simplest
animals and plants was more clearly appreciated ; they are
single cells, the higher organisms are multicellular.
Now the cells of the animal body are necessarily varied,
for the existence of a body involves division of labour
CHAP, xi The Elements of Structure
181
among the units. Some, such as the lashed cells lining
the windpipe, are very active, like the Infusorian Protozoa ;
others, for instance the fat-cells and gristle-cells of connective
tissue, are very passive, something like the Gregarines ;
others, such as the white blood corpuscles or leucocytes,
are between these extremes, and resemble the amoeboid
Protozoa.
But it is true of most of them that they consist ( i ) of a
FIG. 34. Animal cell, showing the coiled chromatin threads of the nucleus (a),
and the protoplasmic network (b) round about. (From Evolution of Sex ;
after Carnoy.)
complex, and in part living cell -substance, in which keen
eyes looking through good microscopes detect an intricate ^
network, or sometimes the appearance of a fine foam ; (2)
of a central kernel or nucleus, which plays an important
but hardly definable part in the life of the cell, especially
during the process of cell-division ; (3) of a slight outer
membrane, varying much in definiteness and sometimes
quite absent, through which communications with neigh-
1 82 The Study of Animal Life PART in
bouring cells are often established ; and (4) of cell contents,
which can be chemically analysed, and which are products
of the vital activity rather than parts of the living substance,
such as pigment, fat, and glycogen or animal starch.
The growth of all multicellular animals depends upon a
multiplication of the component cells. Like organisms,
cells have definite limits of growth which they rarely exceed ;
giants among the units are rare. When the limit of
growth is reached the cell divides.
The necessity for this division has been partly explained
by Spencer and Leuckart. If you take a round lump of
dough, weighing an ounce, another of two ounces, a third
of four ounces, you obviously have three masses success-
ively doubled, but in doubling the mass you have not
doubled the surface. The mass increases as the cube, the
surface only as the square of the radius. Suppose these
lumps alive, the second has twice as much living matter as
the first, but not twice the surface. Yet it is through the
surface that the living matter is fed, aerated, and purified.
The unit will therefore get into physiological difficulties as
it grows bigger, because its increase of surface does not
keep pace with its increase of mass. Its waste tends to
exceed its repair, its expenditure gains on its income.
What are the alternatives ? It may go on growing and die
(but this is not likely), it may cease growing at the fit
limit, it may greatly increase its surface by outflowing
processes (which thus may be regarded as life-saving), or
it may divide. The last is the usual course. When the
unit has grown as large as it can conveniently grow, it
divides ; in other words, it reproduces at the limit of
growth, when processes of waste are gaining on those
of construction. By dividing, the mass is lessened, the
. surface increased, the life continued.
But although we thus get a general rationale of cell-
division, we are not much nearer a conception of the
internal forces which operate when a cell divides ; for in
most cases the process is orderly and complex, and is
somehow governed by the behaviour of the nucleus. Few
results of the modern study of minute structure are more
ciiAr. xr The Elements of Structure 183
marvellous than those which relate to dividing cells. From
Protozoa to man, and also in plants, the process is strik-
ingly uniform. The nucleus of the cell becomes more
active, the coil or network of threads which it contains is
undone and takes the new and more regular form of a
spindle or barrel. The division is most thorough, each of
the two daughter- cells getting an accurate half of the
original nucleus. "Recent investigators, moreover, assert
that from certain centres in the cell-substance an influence
is exerted on the nuclear threads, and they talk of an archo-
plasm within the protoplasm, and of marked individuality of
behaviour in the nuclear threads.
From the cell as a unit element we penetrate to the
protoplasm which makes it what it is. Within this we
discern an intricate network, within this, special centres of
force " attractive spheres " and " central corpuscles," or
an " archoplasm " within the protoplasm ! We study the
nucleus, first as a simple unit which divides, years after-
wards as composed of a network or coil of nuclear threads
which seem ever to become more and more marvellous,
" behaving like little organisms." We split these up
into " microsomata," and so on, and so on. But we do
not catch the life of the cell, we cannot locate it, we cannot
give an account of the mechanics of cell-division. It is a
mystery of life. After all our analysis we have to confess
that the cell, or the protoplasm, or the archoplasm, or the
chromatin threads of the nucleus, or the " microsomata "
which compose them, baffle our analysis ; they behave as
they do because they are alive. Were we omniscient
chemists, such as Laplace imagined in one of his specula-
tions, and knew the secret of protoplasm, how its touch
upon the simpler states of matter is powerful to give them
life, we should but have completed a small part of those
labours that even now lie waiting us ; what further investi-
gations will present themselves we cannot tell.
CHAPTER XII
THE LIFE-HISTORY OF ANIMALS
I. Modes of Reproduction 2. Divergent Modes of Reproduction
3. Historical 4. The Egg -Cell or Ovum $. The Male-
Cell or Spermatozoon 6. Maturation of the Ovum 7.
Fertilisation 8. Segmentation and the first stages in
Development 9. Some Generalisations The Ovum Theory ',
the Gastrcza Theory ', Fact of Recapitulation ^ Organic Con-
tinuity
IN his exercitation " on the efficient cause of the
chicken," Harvey (1651) confesses that "although it be a
known thing subscribed by all, that the foetus assumes its
original and birth from the male and female, and conse-
quently that the egge is produced by the cock and henne,
and the chicken out of the egge, yet neither the schools of
physicians nor Aristotle's discerning brain have disclosed
the manner how the cock and his seed doth mint and
coine the chicken out of the egge." The marvellous
facts of growth are familiar to us the sprouting corn
and the opening flowers, the growth of the chick within
the egg and of the child within the womb ; yet so
difficult is the task of inquiring wisely into this marvel-
lous renewal of life that we must reiterate the old
confession : " ingratissimum opus scribere ab iis quae,
multis a natura circumjectis tenebris velata, sensuum
lucis inaccessa, hominum agitantur opinionibus."
i. Modes of Reproduction. The simplest animals
divide into two or into many parts, each of which becomes a
full-grown Protozoon. There is no difficulty in understanding
CHAP, xii The Life- History of Animals 185
why each part should be able to regrow the whole, for each
is a fair sample of the original whole. Indeed, when a
large Protozoon is cut into two or three pieces with a knife,
each fragment is often able to retain the movements and
life of the intact organism. Among the Protozoa we find
some in which the multiplication looks like the rupture of a
cell which has become too large ; in others numerous buds
are set free from the surface ; in others one definitely-formed
bud (like an overflow of the living matter) is set free ; in
others the cell divides into two equal parts, after the
manner of most cells ; and numerous divisions may also
occur in rapid succession and within a cyst, that is, in
limited time and space, with the result that many " spores"
are formed. These modes of multiplication form a natural
series.
In the many-celled animals multiplication may still pro-
ceed by the separation of parts ; indeed the essence of
reproduction always is the separation of part of an organ-
ism to form or to help to form a new life. Sponges bud
profusely, and pieces are sometimes set adrift ; the Hydra
forms daughter polypes by budding, and these are set free ;
sea-anemones and several worms, and perhaps even some
star-fishes, multiply by the separation of comparatively large
pieces. But this mode of multiplication which is called
asexual has evident limitations. It is an expensive way
of multiplying. It is possible only among comparatively
simple animals in which there is no very high degree of
differentiation and integration. For though cut-off pieces
of a sponge, Hydra, sea -anemone, or simple worm may
grow into adult animals, this is obviously not the case
with a lobster, a snail, or a fish. Thus with the excep-
tion of the degenerate Tunicates there is no budding
among Vertebrates, nor among Molluscs, nor among
Arthropods.
The asexual process of liberating more or less large
parts, being expensive, and possible only in simpler animals,
is always either replaced or accompanied by another
method that of sexual reproduction. The phrase " sexual
reproduction " covers several distinct facts : (a) the separa-
1 86 The Study of Animal Life PART m
tion of special reproductive cells ; (b) the production of two
different kinds of reproductive cells (spermatozoa and ova),
which are dependent on one another, for in most cases an
ovum comes to nothing unless it be united with a male-cell
or spermatozoon, and in all cases the spermatozoon comes
to nothing unless it be united with an ovum ; (c) the pro-
duction of spermatozoa and ova by different (male and
female) organs or individuals.
(a) It is easy to think of simple many-celled animals
being multiplied by liberated reproductive cells, which
differed but little from those of the body. But as more
and more division of labour was established in the bodies
of animals, the distinctness of the reproductive cells from
the other units of the body became greater. Finally, the
prevalent state was reached, in which the only cells able
to begin a new life when liberated are the reproductive
cells. They owe this power to the fact that they have not
shared in making the body, but have preserved intact the
characters of the fertilised ovum from which the parent
itself arose.
(b) But, in the second place, it is easy to conceive of a
simple multicellular animal whose liberated reproductive
cells were each and all alike able to grow into new
organisms. In such a case, we might speak of sexual
reproduction in one sense, for the process would be different
from the asexual method of liberating more or less large
parts. But yet there would be no fertilisation and no sex,
for fertilisation means the union of mutually dependent
reproductive cells, and sex means the existence of two
physiologically different kinds of individuals, or at least
of organs producing different kinds of reproductive cells.
We can infer from the Protozoa how fertilisation or the union
of the two kinds of reproductive cells may have had a
gradual origin. For in some of the simplest Protozoa, e.g.
Protomyxa,) a large number of similar cells sometimes flow
together ; in a few cases three or more combine ; in most a
couple of apparently similar units unite ; while in a few
instances, e.g. Vorticella^ a small cell fuses with a large one,
just as a spermatozoon unites with an ovum.
CHAP, xii The Life- History of Animals 187
(c) But the higher forms of sexual reproduction imply
more than the liberation of special reproductive cells, more
than the union of two different and mutually dependent
kinds of reproductive cells, they imply the separation
of the sexes. The problem of sexual reproduction becomes
less difficult when the various facts are discussed separ-
ately, and if you grant that there is no great difficulty
in understanding the liberation of special cells, and
no great difficulty in understanding why two different
kinds should in most cases have to unite if either is to
develop, then I do not think that the remaining fact
the evolution of male and female individuals need remain
obscure.
If we study those interesting Infusorian colonies, of
which Volvox is a good type, the riddle may be at least
partially read. Though Protozoa, they are balls of cells, in
which the component units are united by protoplasmic
bridges and show almost no division of labour. From
such a ball of cells, units are sometimes set free which
divide and form new colonies. In other conditions a less
direct multiplication occurs. Some of the cells apparently
better fed than their neighbours become large ; others,
less successful, divide into many minute units. The large
kind of cell is fertilised by the small kind of cell, and there
is no reason why we should not call them ova and sperma-
tozoa respectively. In such a Volvox, two different kinds
of reproductive cell are made within one organism. But
we also find Volvox balls in which only ova are being
made, and others in which only spermatozoa are being
made. The sexes are separate. Indeed we have in Vol-
vox, as Dr. Klein an enthusiastic investigator of this form
rightly says, an epitome of all the great steps in the
evolution of sex.
So far I have stated facts ; now I shall briefly state the
theory by which Professor Geddes has sought to rationalise
these facts.
All through the animal series, from the active Infusorians
and passive Gregarines, to the feverish birds and sluggish
reptiles, and down into the detailed contrasts between order
1 88 The Study of Animal Life PART in
and order, species and species, an antithesis may be read
between predominant activity and preponderant passivity,
between lavish expenditure of energy and a habit of storing,
between a relatively more disruptive (katabolic) and a re-
latively more constructive (anabolic) series of changes in
the protoplasmic life of the creature. The contrast between
the sexes is an expression of this fundamental alternative of
variation.
The theory is confirmed by contrasting the characteristic
product of female life passive ova, with the characteristic
product of male life active spermatozoa ; or by summing
up the complex conditions (abundant food, favourable
temperature, and the like) which favour the production of
female offspring, with the opposite conditions which favour
maleness ; or by contrasting the secondary sexual char-
acters of the more active males (e.g. bright colours, smaller
size) with the opposite characteristics of their more passive
mates.
Apart from the general problem of the evolution of sex,
those who find the subject interesting should think about
the evolution of the so-called " sexual instincts," as illus-
trated in the attraction of mate to mate. As to the actual
facts of pairing and giving birjh, it seems to me that I have
suggested the most profitable way of considering these in a
former part of this book where courtship and parental care
are discussed, though I believe firmly with Thoreau, that
" for him to whom sex is impure, there are no flowers in
nature."
2. Divergent Modes of Reproduction. (a) Herma-
phroditism. Especially among lower animals, both ova
and spermatozoa may be produced by one individual,
which is then said to be hermaphrodite. So most common
plants produce both seeds and pollen. Some sponges and
stinging animals, many " worms," e.g. earthworm and leech,
barnacles and acorn-shells among crustaceans, one of the
edible oysters, the snail, and many other molluscs, the sea-
squirts, and the hagfish, are all hermaphrodite. But it
should be noted that the organs in which ova and sperma-
tozoa are produced are in most cases separate, that the two
CHAP, xii The Life- History of Animals 189
kinds of cells are usually formed at different times, and
that the fertilisation of ova by spermatozoa from the same
animal very rarely occurs. It is very likely that the
bisexual or hermaphrodite state of periodic maleness and
femaleness is more primitive than that of separate sexes,
which, except in tunicates, a few fishes and amphibians,
and casual abnormalities, is constant among the backboned
animals.
(b) Parthenogenesis seems to be a degenerate form of
sexual reproduction in which the ova produced by female
organisms develop without being fertilised by male cells.
Thus " the drones have a mother but no father," for they
develop from ova which are not fertilised. In some rotifers
the males have never been found, and yet the fertility of the
females is very great ; in many small crustaceans (" water-
fleas ") the males seem to die off and are unrepresented for
long periods ; in the aphides males may be absent for a
summer (or in a greenhouse for years) without affecting the
rapid succession of female generations.
(c) Alternation of Generations. A fixed asexual zoophyte
or hydroid sometimes buds off and liberates sexual swim-
ming bells or medusoids, whose fertilised ova develop into
embryos which settle down and grow into hydroids. This is
perhaps the simplest and clearest illustration of alternation
of generations.
In autumn the freshwater sponge (Spongilla) begins
to suffer from the cold and the scarcity of food. It dies
away ; but some of the units club together to form
" gemmules " from which in spring male and female
sponges are developed. The males are short-lived, but
their spermatozoa fertilise the ova of the females. The
fertilised ovum develops into a ciliated embryo, and this
into the asexual sponge, which produces the gemmules.
The large free-swimming and sexual jellyfishes of the
genus Aurelia produce ova and spermatozoa ; from the
fertilised ovum an embryo develops not into a jellyfish, but
into a sessile Hydra-\f&.e animal. This grows and divides
and gives origin asexually to jellyfish.
Similar but sometimes more complicated alternations
190
The Study of Animal Life PART in
occur in some worm types (some flukes, threadworms, etc.),
and as high up in the series as Tunicates ; while among
plants analogous alternations are very common, e.g. in the
life-cycles of fern and moss.
FIG. 35. Diagram of a hydroid colony, some of the individuals of which have
been modified as swimming - bells or medusoids ; one of these has been
liberated.
3. Historical, In the seventeenth and eighteenth cen-
turies, naturalists had a short and easy method of dealing with
embryology. They maintained that within the seed of a
plant, within the egg of a bird, the future organism was
already present in miniature. Every germ contained a
miniature model of the adult, which in development was
CHAP, xii The Life-History of Animals 191
simply unfolded. It was to this unfolding that the word
evolution (as a biological term) was first applied. But not
only did they compare the germ to a complex bud hiding
the already formed organs within its hull, they maintained
that it included also the next generation and the next and
the next. Some said that the ovum was most important,
that it required only the sperm's awakening touch and it
began to unfold ; others said that the animalcules or
spermatozoa produced by male animals were most im-
portant, that they only required to be nourished by the
ova. The two schools nicknamed one another " ovists "
and " animalculists." The preformation-theories were false,
as Harvey in the middle of the seventeenth century discerned,
and as Wolff a century later proved, because germs are
demonstrably simple, and because embryos grow gradually
part by part. But in a later chapter we shall see that the
theories were also strangely true.
4. The Egg-cell or Ovum produced by a female animal,
or at least by a female organ (ovary), exhibits the usual
characteristics of a cell. It often begins like an Amoeba,
and may absorb adjacent cells ; in most cases it becomes
surrounded by an envelope or by several sheaths ; in
many cases it is richly laden with yolk derived from various
sources. In the egg of a fowl, the most important part
(out of which the embryo is made) is a small area of trans-
parent living matter which lies on the top of the yellow
yolk and has a nucleus for its centre ; round about
there is a coating of white-of-egg ; this is surrounded by
a double membrane which forms an air-chamber at the
broad end of the egg ; outermost is the porous shell of
lime.
While there must be a general relation between the size
of the bird and that of the egg, there are many inconsisten-
cies, as you will soon discover if you compare the eggs
of several birds of the same size. It is said that the eggs
of birds which are rapidly hatched and soon leave the nest
tend to be large, and that there is some relation between the
size of eggs and the number which the bird has to cover.
It seems probable, however, from what one notices in the
i9 2 The Study of Animal Life PART in
poultry yard and in comparing the constitution of different
birds, that a highly-nourished and not very energetic bird
will have larger eggs than one of more active habits and
sparser diet.
The egg-shell consists almost wholly of carbonate of
lime, and the experiments of Irvine have shown that a hen can
form a carbonate of lime shell from other lime salts. It is
formed around the egg in the lower part of the oviduct, and
is often beautifully coloured with pigments allied to those of
blood and bile. These colours often harmonise well with
the surroundings, but how this advantageous result has
been wrought out is uncertain.
Eggs differ greatly in regard to the amount of yolk which
they contain ; thus those of birds and reptiles have much, while
those of all mammals except the old-fashioned Monotremes
have hardly any. This is related partly to the number of
eggs which are produced, and partly to the amount of food-
capital which the embryo requires before other sources
of supply become available. The young of birds and
reptiles feed on the yolk until they are hatched, the unborn
young of all the higher (placental) mammals absorb food
from the mothers. The different sizes of egg usually
depend upon the amount of yolk, for the really vital portion
out of which the embryo is made is always very small.
There are many differences also in regard to the outer
envelopes, witness the jelly around the spawn of frogs, the
firm but delicate skin around the ova of cuttlefish, the
"horny" mermaid's -purse enclosing the skate's egg, the
chitinous sheath surrounding the ova of many insects, the
calcareous shell in birds and most reptiles.
5. The Male-Cell or Spermatozoon produced from a male
animal, or at least from a male organ (testis), is very differ-
ent from the ovum. It is very minute and very active. If
we compare an ovum to an Amoeba or to an encysted
Gregarine among Protozoa, we may liken the spermatozoon
to a minute monad Infusorian. It is a very small cell,
bearing at one end a "head," which consists mostly of
nucleus, prolonged at the other end into a mobile " tail,"
which lashes the head along.
CHAP, xii The Life- History of Animals 193
The spermatozoon, though physiologically the comple-
ment of the ovum, is not its morphological equivalent.
The precise equivalent of the ovum is a primitive male-cell
or mother-sperm-cell, which divides repeatedly and forms a
ball or clump of spermatozoa. This division is to be com-
pared with the division or segmentation of the ovum, which
we shall afterwards discuss.
In some cases spermatozoa which have been transferred
to a female may lie long dormant there. Thus those
received by the queen-bee during her nuptial flight may last
for a whole season, or even for three seasons, during which
they are used in fertilising those ova which develop into
workers or queen-bees. Quite unique is the case of one of
Sir John Lubbock's queen-ants, which, thirteen years after
the last sexual union with a male, laid eggs which
developed.
6. Maturation of the Ovum. Most ova before they are
fertilised are subject to a remarkable change, the precise
meaning of which is not certainly known. The nucleus of
the ovum moves to the surface and is halved twice in rapid
succession. Two minute cells or polar globules are thus
extruded, and come to nothing, while the bulk of the
nucleus is obviously reduced by three-fourths. It may be
that the ovum is only behaving as other cells do at the
limit of growth, or that it is exhibiting in an ineffective sort
of way the power of independent division which all the re-
productive cells of very simple many-celled animals perhaps
possessed ; it may be that it is parting with some surplus
material which is inconsistent with or no longer necessary
to its welfare, and there are other theories. One fact,
however, seems well established, that parthenogenetic ova,
which are able to develop into embryos without being
fertilised, extrude only one polar globule, a fact which
suggests that the amount of nucleus thus retained some-
how makes up for the absence of a spermatozoon.
7. Fertilisation. When a pollen grain is carried by an
insect or by the wind to the stigma of a flower, it grows
down through the tissue of the pistil until it reaches the
ovule and the egg-cell which that contains. Then a nuclear
O
194
The Study of Animal Life PART m
element belonging to the pollen cell unites with the nucleus
of the egg-cell. The union is intimate and complete.
When spermatozoa come in contact with the egg-shell
of a cockroach ovum, they move round and round it in
varying orbits until one finds entrance through a minute
aperture in the shell. It works its way inwards until its
nuclear part unites with that of the ovum. The union is
again intimate and complete.
FIG. 36. Diagram of the development of spermatozoa (upper line), of the
maturation and fertilisation of the ovum (lower line).
a, primitive amoeboid sex-cell; A, ovum with nucleus (); B, ovum extruding
the first polar body (/!) and leaving the nucleus (n\) reduced by half ; C,
extrusion of the second polar body (/ 2 ), the nucleus ( 2 ) now reduced to a
fourth of its original size ; i, a mother-sperm-cell, dividing (2 and 3) into
spermatozoa (sp) ; D, the entrance of a spermatozoon into the ovum ; E, the
male nucleus (sp.n) and the female nucleus (n 2 ) approach one another, and
are about to be united, thus consummating the fertilisation. (From the
Evolution of Sex.}
Both in plants and in animals the male cell is attracted
to the female cell, the two nuclei unite thoroughly, and,
when fertilisation is thus effected, the egg-cell is usually
impervious to other sperms.
A single nucleus of double origin is thus established,
and the egg-cell begins to divide. Some idea both of the
orderly complexity of the nuclear union and of the careful-
ness of modern investigation may be gained from the fact
that the nuclei of the two daughter-cells which result from
CHAP, xii The Life- History of Animals 195
the first division of the egg-cell have been shown to consist
in equal proportions of material derived from the male-
nucleus and from the ovum-nucleus.
Yet in the last century naturalists still spoke of an " aura
seminalis," and believed that a mere breath, as it were, of
the male cell was sufficient to fertilise an egg, and it was
only in 1843 that Martin Barry discerned the presence of
the spermatozoon within the ovum.
8. Segmentation and Development. The fertilised
egg-cell divides, and by repeated division and growth of
cells every embryo, of herb and tree, of bird and beast, is
formed. On the quantity and arrangement of the yolk the
character of the segmentation depends. When there is
little or no yolk the whole ovum divides into equal parts, as
in sponge, earthworm, starfish, lancelet, and higher mammal.
When there is more than a little yolk, and when this sinks
to the lower part of the egg-cell, the division is complete
but unequal, and this may be readily seen by examining
freshly-laid frog spawn. When the yolk is accumulated in
the core of the egg-cell, the more vital superficial part
divides, as in insects and crustaceans. Lastly, when the
yolk is present in large quantity as in the ova of gristly
fishes, reptiles, and birds, the division is very partial, being
confined to a small but rapidly extending area of formative
living matter, which lies like a drop on the surface of the
yolk.
As the result of continued division, a ball of cells is
formed. This may be hollow (a blastosphere\ or solid
(a morula, i.e. like a mulberry), or it may be much modi-
fied in form by the presence of a large quantity of yolk.
Thus in the hen's egg what is first formed is a disc of cells
technically called the blastoderm^ which gradually spreads
around the yolk.
The hollow ball of cells almost always becomes dimpled
in or invaginated, as an india-rubber ball with a hole in it
might be pressed into a cup-like form. The dimpling is the
result of inequalities of growth. The two-layered sac of cells
which results is called a gastrula, and the cavity of this sac
becomes in the adult organism the digestive part of the
196
The Study of Animal Life TART in
food- canal. Where there is no hollow ball of cells, but
some other result of segmentation, the formation of a gastrula
is not so obvious. Yet
in most cases some
analogous infolding is
demonstrable.
In the hollow sac
of cells there are
already two layers.
The outer, which is
called the ectoderm
or epiblast, forms in
the adult the outer
skin, the nervous
system, and the most
important parts of the
sense - organs. The
inner, which is called
the endoderm or hypo-
blast, forms the lining
of the most import-
ant part of the food-
canal, and of such
appendages as lungs,
liver, and pancreas
FIG. 37. The formation of the two-layered gas- . '
trula from the imagination of a hollow sphere which are Outgrowths
of cells. (From the Evolution of Sex ; after fj-Qni it But in all
Haeckel.)
animals above the
Sponges and Ccelenterates, a middle layer appears between
the other two. From this the mesoderm or mesoblast
the muscles, the internal skeleton, the connective-tissue, etc.,
are formed.
9. Some Generalisations. (a) The " Ovum - Theory}'
To realise that almost every organism from the sponge to
the highest begins its life as a fertilised egg-cell, and is
built up by the division and arrangement, layering and fold-
ing of cells, should not lessen, but should greatly enhance,
the wonder with which we look upon life. If the end
of this constantly repeated process of development be
CHAP, xii The Life- History of Animals 197
something to marvel at, the same is equally true of its
beginning.
(b) The Gastrcea Theory. From the frequent, though
not universal occurrence of the two-layered gastrula stage in
the development of animals, Haeckel concluded that the
first stable form of many -celled animal must have been
something very like a gastrula. He called this hypothetical
ancestor of all many-celled animals a Gastrcea, and his infer-
ence has found favour with many naturalists. Some of the
simplest sponges, polypes, and " worms " are hardly above
the gastrula level.
(c) Recapitulation. When we take a general survey
of the animal series, we recognise that the simplest animals
are single cells, that the next simplest are balls of cells like
Volvox, and that the next simplest are two-layered sacs of
cells like the simple sponges, polypes, and worms above
referred to. These represent the three lowest steps in the
evolution of the race. They are not hypothetical steps in a
hypothetical ladder of ascent, they are realities.
When we take a general survey of the individual
development of many-celled animals, we recognise that all
begin as single egg-cells, and that the ova divide into balls
of cells, which become in most cases two -layered sacs of
cells. It is therefore evident that the first three chapters in
individual history are precisely the first three steps in racial
history.
Von Baer, one of the pioneer embryologists in the first
half of this century, discerned that the individual life-history
was in its general course a recapitulation of the history of
the race. He recognised that even one of the higher
animals, let us say a rabbit, began at the beginning as a
Protozoon, that it slowly acquired the features of a primitive
Vertebrate, that it subsequently showed the character of a
young fish, afterwards of a young reptile, then of a young
mammal, then of a young rodent, finally of a young rabbit.
He confessed his inability to distinguish whether three very
young embryos, freed from their surroundings, were those
of reptiles, birds, or mammals. In stating Von Baer's
vivid idea of development as progress from the simple
198 The Study of Animal Life PART in
to the complex, from the general to the special, we must
be careful to notice that he did not say that the young
mammal was once like a little fish, afterwards like a reptile,
and so on ; he compared the embryo mammal at one stage
with the embryo fish, at another stage with the embryo
reptile, which is a very different matter.
FIG. 38. Embryos of fowl, a ; dog, b \ man, c. (From Chambers's Encyclop. \
after Haeckel.)
Fritz Miiller, in his Facts for Darwin, illustrated the
same idea in relation to Crustacea. When a young cray-
fish is hatched, it is practically a miniature adult. When
a young lobster is hatched, it differs not a little from the
adult, and is described as being at a Mysis stage, Mysis
being a prawn-like crustacean. It grows and moults and
becomes a little lobster. When a crab is hatched, it is
quite unlike the adult, it is liker one of the humblest
Crustacea such as the common water-flea Cyclops, and is
described as a Zoea. This Zoea grows and moults and
becomes, not yet a crab but a prawn-like animal with ex-
tended tail, a stage known as the Megalopa. This grows and
moults, tucks in its tail, and becomes a young crab. And
again, when the shrimp-like crustacean, known as Pcnceus,
is hatched, it is simpler than any known crustacean, it is
an unringed somewhat shield -shaped little creature with
three pairs of appendages and a median eye. It is known
as a Nauplius and resembles the larvae of most of the simpler
crustaceans. It grows and moults and becomes a Zoea,
grows and moults and becomes a Mysis, grows and moults
and becomes a Penczus,
CHAP, xii The Life-History of Animals 199
Now these life -histories are hardly intelligible at all
unless we believe that Penceus does in some measure recapi-
tulate the steps of racial progress, that the crab does so
to a slighter extent, that the lobster has abbreviated its
obvious recapitulation much more, while the crayfish has
found out a short cut in development. Let us exercise our
imagination and think of the ancestral Crustacea perhaps
not much less simple than the Nauplius larvae which many
FIG. 39. Life-history of Penaus ; the Nauplius.
of them exhibit. In the course of time some pushed for-
ward in evolution and attained to the level of structure
represented by the Zoea larva?. At this station some
remained and we have already mentioned the u water-flea "
Cyclops as a crustacean which persists near this level. But
others pushed on and reached a stage represented by
Mysis, and finally the highest crustaceans were evolved.
Now to a certain extent these highest crustaceans have
to travel in their individual development along the rails
laid down in the progress of the race. Thus Penaus,
200 The Study of Animal Life PART m
starting of course as an ovum at the level of the Protozoa,
has to stop as it were at the first distinctively crustacean
station the Nauplius stage. After some change and
delay, it continues to progress, but again there is a halt and
a change at the Zoea station. Finally there is another
FIG. 39#. Life-history of Penteus \ the Zoea.
delay at the My sis stage before the Penaus reaches its
destination. The crab, on the other hand, stops first at
the Zoea station, the lobster at the Mysis station, while the
crayfish though progressing very gradually like all the
others has if you do not find the simile too grotesque a
through-carriage all the way.
FIG. 39<5. Life-history of PenfPus; a later stage.
202
The Study of Animal Life PART in
One must be careful not to press the idea of recapitulation
too far, (i) because the individual life-history tends to skip
stages which occurred in the an-
cestral progress ; (2) because the
young animal may acquire new
characters which are peculiar to
its own near lineage and have
little or no importance in connec-
tion with the general evolution of
its race ; (3) because, in short,
the resemblance between the indi-
vidual and racial history (so far
as we know them) is general, not
precise. Thus we regard Nauplius
and Zoea rather as adaptive larval
forms than as representatives of
ancestral crustaceans. More-
over, if one insists too much on
the approximate parallelism be-
tween the life-history of the indi-
vidual and the progress of the
race, one is apt to overlook the
deeper problem how it is that
the recapitulation occurs to the
extent that it undoubtedly does.
The organism has no feeling for
history that it should tread a
sometimes circuitous path, be-
cause .its far-off ancestors did so.
To some extent we may think of
inherited constitution as if it were
the hand of the past upon the
organism, compelling it to become
thus or thus, but we must realise
that this is a living not a dead
hand ; in other words these meta-
morphoses have their efficient causes in the actual con-
ditions of growth and development. The suggestion of
Kleinenberg referred to in a preceding chapter helps us, for
CHAP, xii The Life- History of Animals 203
if we ask why an animal develops a notochord only to have
it rapidly replaced by a backbone, part of the answer surely
is that the notochord which in the historical evolution supplied
the stimulus necessary for the development of a backbone, is
still necessary in the individual history for the same purpose.
But there is no doubt that the idea of recapitulation is a
very helpful one, in regard to our own history as well as in
regard to animals, and we would do well to think of it
much, and to read how Herbert, Spencer (Principles of
Biology, Lond. 1864-66) has discussed it in harmony with his
general formula of evolution as a progress from the homo-
geneous to the heterogeneous ; how Haeckel (Generelle Mor-
phologie, Berlin, 1866) has illustrated it, and pithily summed
it up in his " fundamental law of biogenesis " (Biogenetisches
Grundgesetz\ saying that ontogeny (individual develop-
ment) recapitulates phylogeny (racial history) ; how Milnes
Marshall (see Nature^ Sept. 1890) has recently tested and
criticised it, defining the limits within which the notion
can be regarded as true, and searching for a deeper rationale
of the facts than the theory supplies.
(d) Organic Continuity. In a subsequent chapter on
heredity, which simply means the relation of organic
continuity between successive generations, I shall explain
the fundamental idea that the reproductive cells owe their
power of developing, and of developing into organisms like
the parents, to the fact that they are in a sense continuous
with those which gave origin to the parents. A fertilised
egg-cell with certain qualities divides and forms a " body "
in which these qualities are expressed, distributed, and
altered in many ways by division of labour. But it also
forms reproductive cells, which do not share in the up-
building of the body, which are reproductive cells in fact
because they do not do so, because they retain the intrinsic
qualities of the original fertilised ovum, because they
preserve its protoplasmic tradition. If this be so, and
there is much reason to believe it, then it is natural and
necessary that these cells, liberated in due time, should
behave as those behaved whose qualities they retain. It is
necessary that like should beget like.
CHAPTER XIII
THE PAST HISTORY OF ANIMALS
i. The two Records 2. Imperfection of the Geological Record
3. Palaontological Series 4. Extinction of Types 5. Various
Difficiilties 6. Relative Antiquity of Animals
i. The Two Records. Reviewing the development of the
chick, W. K. Parker said, " Whilst at work I seemed
to myself to have been endeavouring to decipher a palimp-
sest, and that not erased and written upon just once, but
five or six times over. Having erased, as it were, the
characters of the culminating type those of the gaudy
Indian bird I seemed to be amongst the sombre grouse,
and then, towards incubation, the characters of the Sand-
Grouse and Hemipod stood out before me. Rubbing these
away, in my downward walk, the form of the Tinamou
looked me in the face ; then the aberrant Ostrich seemed
to be described in large archaic characters ; a little while
and these faded into what could just be read off as per-
taining to the Sea Turtle ; whilst, underlying the whole,
the Fish in its simplest Myxinoid form could be traced
in morphological hieroglyphics."
There is another palimpsest the geological record
written in the rocks. For beneath the forms which dis-
appeared, as it were, yesterday, the Dodo and the Solitaire,
the Moa and the Mammoth, the Cave Lion and the Irish
Elk, there are mammals and birds of old-fashioned type the
like of which no longer live. Beneath these lie the giant
CHAP, xin The Past History of Animals 205
reptiles, beneath these great amphibians, preceded by hosts
of armoured fishes, beyond the first traces of which only
backboneless animals are found. Yet throughout the
chapters of this record, written during different aeons on the
earth's surface, persistent forms recur from age to age,
many of them, such as some of the lamp-shells or Brachio-
pods, living on from near the apparent beginning even until
now. But other races, like the Trilobites, have died out,
leaving none which we can regard as in any sense their
direct descendants. Other sets of animals, like the Ganoid
fishes, grow in strength, attain a golden age of prosperous
success, and wane away. As the earth grew older nobler
forms appeared, and this history from the tombs, like
that from the cradles of animals, shows throughout a
gradual progress from simple to complex.
2. Imperfection of the Geological Record, If complete
records of past ages were safely buried in great treasure-
houses such as Frederic Harrison proposes to make for the
enlightenment of posterity, then palaeontology would be easy.
Then a genealogical tree connecting the Protist and Man
would be possible, for we should have under our eyes what
is now but a dream a complete record of the past.
The record of the rocks is often compared to a library
in which shelves have been destroyed and confused, in
which most of the sets of volumes are incomplete, and
most of the individual books much damaged. When we
consider the softness of many animals, the chances against
their being entombed, and the history of the earth's crust,
our wonder is that the record is so complete as it is, that
from " the strange graveyards of the buried past " we can
learn so much about the life that once was.
We must not suppose the record to be as imperfect as
our knowledge of it. Thus many regions of the earth's
surface have been very partially studied, many have not
been explored at all, many are inaccessible beneath the sea.
As to the record, the rocks in which fossils are found
are sedimentary rocks formed under water, often they have
been unmade and remade, burnt and denuded. The
chances against preservation are many.
UNIVERSITY
/
206 The Study of Animal Life PART in
Soft animals rarely admit of preservation, those living
on land and in the air are much less likely to be preserved
than those living in water, the corpses of animals are
often devoured or dissolved. Again the chances against
preservation are many.
3. Palaeontological Series. Imperfect as the geological
record is, several marvellously complete series of related
animals have been disentombed. Thus, a series of fossilised
freshwater snails (Planorbis) has been carefully worked
out ; its extremes are very different, but the distinctions
between any two of the intermediate forms are hardly
perceptible. The same is true in regard to another set of
freshwater snails (Paludind), and on a much larger scale
among the extinct cuttlefishes (Ammonites, etc.) whose shells
have been thoroughly preserved. The modern crocodiles
are linked by many intermediate forms to their extinct
ancestors, and the modern horse to its pigmy progenitors.
In cases like these, the evidences of continuously progress-
ive evolution are conclusive.
4. Extinction of Types. A few animals, such as some
of the lamp-shells or Brachiopods, have persisted from almost
the oldest rock-recorded ages till now. In most cases,
however, the character of the family or order or class has
gradually changed, and though the ancient forms are no
longer represented, their descendants are with us. There
is an extinction of individuals and a slow change of
species.
On the other hand there are not a few fossil animals
which have become wholly extinct, whose type is not
represented in the modern fauna. Thus there are no
animals alive that can be regarded as the lineal descendants
of Trilobites and Eurypterids, or of many of the ancient
reptiles. There is no doubt that a race may die out.
Many different kinds of heavily armoured Ganoid fishes
abounded in the* ages when the Old Red Sandstone was
formed, but only seven different kinds are now alive.
The lamp-shells and the sea-lilies, once very numerous, are
now greatly restricted. Once there were giants among
Amphibians, now almost all are pigmies.
CHAP, xiii The Past History of Animals 207
It is difficult to explain why some of the old types
disappeared. The extinction was never sudden. Formid-
able competitors may have helped to weed out some ; for
cuttlefish would tend to exterminate trilobites, and voracious
fishes would decimate cuttlefish, just as man himself is
rapidly and inexcusably annihilating many kinds of beasts
and birds. But, apart from the struggle with competitors,
it is likely that some types were insufficiently plastic to save
themselves from changes of environment, and it seems likely
that others were victims to their own constitutions, becoming
too large, or too sluggish, or too calcareous ; or> on the
other hand, too feverishly active. The " scouts " of evolution
would be apt to become martyrs to progress; the " laggards "
in the race would tend to become pillars of salt ; the
path of success was oftenest a ma media of compromise.
Samuel Butler has some evidence for saying that " the race
is not in the long run to the phenomenally swift, nor the
battle to the phenomenally strong ; but to the good average
all-round organism that is alike shy of radical crotchets and
old world obstructiveness."
5. Various Difficulties, Nowadays it seems natural
to us to regard the fossils in the rocks as vestiges of a
gradual progress or evolution. As some still find difficulty
in accepting this interpretation, I shall refer to three
difficulties occasionally raised.
(a) It is said that the number of fossils in successive
strata does not increase steadily as we ascend to modern
times that the numerical strength of the fauna is strangely
irregular. Thus (in 1872) it was computed that 10,000
species were known from the early Silurian rocks, while the
much later Permian yielded only 300. But those who use
such arguments should mention that a large number of the
Silurian species were discovered by the marvellous industiy
of one man in a favourable locality, and that the rocks of
the Permian system are ill adapted for the preservation of
fossils. Moreover, we cannot compute the relative dura-
tion of the different periods, we cannot infer evolutionary
progress from the number of species, and we must make
many allowances for the imperfections of the record.
208 TJie Study of Animal Life PART in
(U) It is said that the occurrence of Fishes in the
Silurian, and of many highly organised Invertebrates in the
still earlier Cambrian, is inconsistent with a theory which
would lead us to expect very simple fossil forms to begin
with. But to say so is to forget that we have no concep-
tion of the vast duration of periods like the Silurian and
Cambrian, while the antecedent Archaean rocks in which we
might look for traces of simple ancestral organisms have
been shattered and altered too thoroughly to reveal any
important secrets as to the earliest animals.
(c) It is maintained that organic evolution proceeds very
slowly, and that the geologists and biologists demand more
millions than the experts in astronomical physics can grant
them. But there is considerable difference of opinion as to
the unthinkable length of time during which the earth may
have been the home of life ; we are apt to measure the rate
of evolutionary change by the years of a man's lifetime which
lasts but for a geological moment ; and there is reason to
believe that the simpler animals would change and take
great steps of progress much more rapidly than those of
high degree.
6. Relative Antiquity of Animals, I have not much
satisfaction in submitting the following table showing
the relative antiquity of the higher animals. Such a table
is only an approximation ; it does not suggest the great
differences in the duration of the various periods, nor how
the classes of animals waxed and waned, nor how some types
in these classes dropped off while others persisted. But the
general fact which the table shows is true, in the course
of time higher and higher forms of life have come into
being. It is true that the remains of mammals are of more
ancient date than those of birds, but it is likely that the
remains of the earliest birds have still escaped discovery ;
moreover, the earliest known mammalian remains seem to
be of those of very simple types.
CHAP, xiii
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52. 52.
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CHAPTER XIV
THE SIMPLEST ANIMALS
i. The Simplest Forms of Life 2. Survey of Protozoa 3. The com-
mon Amceba 4. Structure of the Protozoa 5. Life of Protozoa
6. Psychical Life of the Protozoa 7. History of the Protozoa
8. Relation to the Earth 9. Relation to other Forms of Life
10. Relation to Man
I. The Simplest Forms Of Life. It is likely that the first breath
of life was in the water, for there most of the simplest animals and
plants have their haunts. Simple they are, as an egg is simple
when contrasted with a bird. They are (almost all) unit specks of
living matter, each comparable to, but often more complex than, one
of the numerous unit elements or cells which compose any higher
plant or animal, moss or oak-tree, sponge or man. It is not merely
because they are small that we cannot split them into separate parts
different from one another, size has little to do with complexity,
but rather because they are unit specks or single cells. But they are
not "structureless " ; in fact, old Ehrenberg, who described some of
them in 1838 as "perfect organisms" and fancied he saw stomachs,
vessels, hearts, and other organs within them, was nearer the truth
than those who reduce the Protozoa to the level of white of egg.
Nor are they omnipresent, swarming in any drop of water. The
clear water of daily use will generally disappoint, or rather please
us by showing little trace of living things. But take a test-tube of
water from a stagnant pool, hold it between your eyes and the light,
and it is likely that you will see many forms of life. Simple plants
and simple animals are there, the former represented by threads,
ovals, and spheres in green, the latter by more mobile almost
colourless specks or whitish motes which dance in the water. But
besides these there are jerky swimmers whose appearance almost
suggests theirpopular name of " water-fleas," and wriggling "worms,"
CHAP, xiv The Simplest Animals 211
thinner than thread and lither than eels : both of these may be very
small, but closer examination shows that they have parts and organs,
that they are many-celled not single-celled animals.
Vary the observations by taking water in which hay stems or other
parts of dusty dead plants have been steeped for a few days, and even
with the unaided eye you will see a thick crowd of the mobile whitish
motes which, from their frequent occurrence in such infusions, are
usually called Infusorians. Or if a piece of flesh be allowed to rot in
an open vessel of water, the fluid becomes cloudy and a thin flaky scum
gathers on the surface. If a drop of this turbid liquid be examined
with a high power of the microscope, you will see small colourless
rods and spheres, quivering together or rapidly moving in almost
incalculable numbers. These, though without green colour, are the
minutest forms of plant life ; they are Bacteria or Bacilli, the
practically omnipresent microbes, some of which as disease germs
thin our human population, while others as cleansers help to make
the earth a habitable dwelling-place.
2. Survey Of Protozoa. Three great types of unicellular
animals or Protozoa have been recognised in almost every classi-
fication.
(a) The Infusorians, so abundant in stagnant water, have a
common character of activity expressed in the possession of actively
mobile lashes of living matter known as cilia or flagella. Thus
the slipper-animalcule (Paramacium} is covered with rows of lash-
ing cilia, while smaller, equally common forms, generally known
as Monads, are borne along by the undulatory movement of one or
two long whips or flagella. The bell-animalcules ( Vorticella] which
live in crowds, a white fringe on the water weeds, are generally
fixed by stalks, but are crowned with active cilia at the upper end of
the somewhat urn-shaped cell.
(b) In marked contrast to these are the parasitic Protozoa, the
Gregarines, which infest most backboneless animals, notably the
male reproductive organs of the earthworm or the gut of lobster and
cockroach. Sluggishness and the absence of all locomotor pro-
cesses are their characteristics.
(c) Between these two extremes of activity and passivity there
is a third type well represented by the much-talked-of Amoeba which
glides about on the mud of the pond, by the sun -animalcules
(Actinosph&rium] which float in the clear water of brooks, by the
limy-shelled, chalk-forming Foraminifera which move slowly on
seaweeds or at the bottom of shallow water, or in some cases float
at the surface of the sea, and by the flinty-shelled Radiolarians
which live in the open ocean. In all these the living matter
spreads out in thick or thin, stiff or plastic, free or interlacing pro-
cesses, which often admit of a slow gliding motion, and are still
The Study of Animal Life PART in
more useful in surrounding minute food particles. To these root-
like processes, which are capable of very considerable, often almost
constant, change, these
Protozoa owe their gen-
eral name of Rhizopods.
In contrast to the two
preceding types which
have definite boundaries
or ''skins," the Rhizo-
pods are naked, and their
living matter may over-
flow at any point.
As the Infusorians ' ,
are for the most part
provided with cilia from
which flagella differ only
in detail, we may speak
of the type as ciliated ;
the self-contained Gre-
garines, often wrapped
up within a sheath, we
may call predominantly
encysted ; while those
forms which, are inter-
. mediate between these
FIG. 40. jkiora.rt\\mfer(Polysto)nellastrigillata) ,
with interlacing processes of the living matter two extremes, and ex-
hibit outflowing pro-
cesses of living matter,
are called amoeboid in
reference to their most familiar type, the common Amceba.
But though the members of each class are characterised by the
predominance of one of the three phases of cell-life, they sometimes
pass from one phase to another. Thus the ciliated or the amoeboid
units may become encysted. J
J P r . ^
flowing out on all sides. Magnified 10 times.
(From Chambers's Encyclop. ; after Ma
Schultze.)
4 5
FIG. 41. Protomyxa. i, encysted ; 2, dividing into many units ; 3, these escap-
ing as flagellate cells ; 4, sinking into an amoeboid phase ; 5, fusing into a
plasmodium. (From Chambers's Encyclop. ; after Haeckel.)
As the three phases represent the three physiological possibilities
CHAP, xiv The Simplest Animals 213
ot cell-life, it is natural to find that the very simplest Protozoa, such
as Protomyxa,) exhibit a cycle of amoeboid, encysted, and flagellate
phases, not having taken a decisive step along any one of the three
great paths. Moreover, the cells of higher animals may be classified
in the same way. The ciliated cells of the windpipe or the mobile
spermatozoa correspond to Infusorians ; mature ova, fat-cells, de-
generate muscle-cells, correspond to Gregarines, while white blood-
corpuscles and young ova are amoeboid.
3. The common AmOBba. To find Amoebae, which is not
always easy, some water and mud from a pond should be allowed
to settle in a glass vessel. Samples from the surface of the sediment
should then be removed in a glass tube or pipette, dropped on a
slide, and patiently examined under the microscope. Among the
debris, traversed in most cases by swift Infusorians, the sought -for
Amoeba may be seen, as an irregular mass of living matter, often
obscured with various kinds of particles and minute Algae which it
has engulfed, but hardly mistakable as it ploughs its way leisurely
among the sediment, sending out blunt and changeful finger-like
processes in the direction towards which it moves, and drawing
in similar processes at the opposite side. From some objects it
recoils, while others of an edible sort it surrounds with its blunt
processes and gets outside of. Intense light makes it contract, and
a minute drop of some obnoxious reagent causes it to round itself off
and lie quiescent. Such is the simple animal which, in 1755, an
early microscopist Rosel von Rosenhof was delighted to describe,
calling it the " Proteus animalcule."
4. Structure of the Protozoa. Most of these Protozoa are
units or single cells, but this contrast between them and the higher
animals is lessened by the fact that many Infusorians, some
Radiolarians, and some of the very lowest forms live inclose combina-
tion, a number of apparent individuals being substantially united in
co-operation. In two quite different ways this compound life of some
Protozoa arises. The ' * Flower of Tan " (Fuligo or ^Ethalium
septicum] which in the summer months spreads as a yellowish slime
on the bark of the tanyard, and supplies the student with the
" largest available masses of undifferentiated protoplasm," arises from
the flowing together and fusion of a number of smaller amoeboid
units. But in some Infusorians and Radiolarians the colony
arises quite otherwise. Protozoa multiply by division ; each unit
splits into two which thenceforth live separate lives, and by and
by themselves divide. Suppose, however, that the unit divide
incompletely; suppose that the daughter -units, distinct though
unsevered, redivide, and that the process is continued ; a " colonial "
Protozoon is the result. In this case the units do not flow together,
they were never separated. But the "wisdom" of some of these
214 The Study of Animal Life PART in
early associations has been justified in their far-off children, for in
this way the many-celled animals began.
The cell-substance of a Protozoon is living matter, along with
nutritive materials which are approaching that climax, and waste
materials into which some of the cell substance has disintegrated.
The cell has a kernel or nucleus, or more than one, essential to its
complete life. There are bubbles of water taken in along with
food particles, and in nearly all freshwater forms there are one or
two special regions of internal activity, pulsating cavities or con-
tractile vacuoles, which become large and small sometimes rhythmic-
ally, and may burst open on the surface of the cell. They are be-
lieved to help in getting rid of waste, and also in internal circulation.
There is a rind in the Infusorians and Gregarines, and shells of flint
and lime are characteristic of most Foraminifers and Radiolarians.
5- Life of Protozoa. The life -histories of the Protozoa are
very varied, but some chapters are common to most. They expend
energy in movement ; they regain this by feeding ; their income
exceeds their expenditure, and they grow ; at the limit of growth
they reproduce by dividing into two or many daughter - units ; in
certain states two individuals combine, either interchanging nuclear
elements (in the ciliated Infusorians) or fusing together (as in some
Rhizopods) ; in drought or in untoward conditions, or before
manifold division, they often draw themselves together and encyst
within a sweated-off sheath.
The Protozoa often multiply very rapidly. One divides into
two, the two become four, and in rapid progression the numbers
increase. On Maupas's calculation a single Infusorian may in four
days have a progeny of a million. The same observer has shed a
new light on another process that of conjugation, the temporary
or permanent union of two Protozoa, which in the ciliated Infusorians
involves an interchange of nuclear particles. In November 1885,
Maupas isolated an Infusorian (Stylonichid) and observed its genera-
tions till March 1886. By that time there had been two hundred and
fifteen generations produced by ordinary division, but since these
lowly organisms do not conjugate with near relatives, conjugation
had not occurred. The result, corroborated in other cases, was
striking. The whole family became exhausted, small, and
"senile"; they ceased to divide or even to feed; their nuclei
underwent a strange degeneration ; they began to die. But
individuals removed before the process had gone too far were
observed to conjugate with unrelated forms and to live on. The
inference was obvious. Conjugation in these Infusorians is of little
moment to any two individuals ; during long periods it need never
occur, but it is essential to the continued life of the species. " It
is a necessary condition of their eternal youth."
CHAP, xiv The Simplest Animals 215
We must return, however, to the everyday life of the Protozoa.
Rhizopods move by means of outflowing processes of their living
matter which stream out at one corner and are drawn in at another ;
the Infusorians move more rapidly by undulating flagella or by
numerous cilia which work like flexible oars ; the parasitic
Gregarines without any definite locomotor structures sometimes
writhe sluggishly. A few Infusorians have a spasmodic leaping or
springing motion, while the activity of others (like Vorticella) which
in adult life are fixed; is restricted to the contraction and expansion
of a stalk and to the action of cilia around the opening which serves
as a mouth. Arcella is aided in its movements by the formation of
gas bubbles in different parts of its cell-substance.
The food consists of other Protozoa, of minute Algae, and of
organic debris, simply engulfed by the Amoebae, wafted by cilia
into the " mouth" of most Infusorians. The parasitic Gregarines
absorb the debris of the cells or tissues of the animals in which they
live, while not a few suck the cell-contents of freshwater Algse like
Spirogyra. A few Protozoa are green, and some are able to .use
carbonic acid after the manner of plants. Almost all Radiolarians
and a few Foraminifers live in constant and mutually helpful
partnership or symbiosis with small Algae which flourish within
their cell-substance.
As to the other functions, the cells absorb oxygen and liberate
carbonic acid, digest the food-particles and excrete waste, produce
cysts or elaborate shells.
6. Psychical Life Of the Protozoa. We linger over the
Protozoa because they illumine the beginnings of many activities,
and we cannot leave them without asking what light they cast upon
the conscious life of higher animals. Is the future quite hidden in
these simple organisms or are there hints of it ?
According to some, the Protozoa, with frequently rapid and
useful movements, with capacities for finding food and avoiding
danger, with beautiful and intricate shells, are endowed with the
will and intelligence of higher forms of life. According to others,
their motions are arbitrary and without choice, they are only much
more complex than those of the potassium ball which darts about
on the surface of water, the organisms are drawn by their food
instead of finding it, their powers of selection are sublimed chemical
affinities, their protective cysts are quite necessary results of partial
death, and their houses are but crystallisations. In both interpreta-
tions there is some truth, but the first credits the Protozoa with too
much, the second with too little.
Cienkowski marvelled over the way in which Vampyrella sought
and found a Spirogyra filament and proceeded to suck its contents ;
Engelmann emphasised the wonderful power of adjustment in Arcella
216 The Study of Animal Life PART in
which evolves gas bubbles and thus rises or rights itself when cap-
sized, and also detected perception and decision in the motions of
young Vorticella or in the pursuit of one unit by another ; Oscar
Schmidt granted them only "a very dim general feeling" and the
power of responding in different ways to definite stimuli ; Schneider
believed that they acted on impulses based upon definite impressions
of contact ; Moebius would credit them with the power of reminis-
cence and Eimer with will.
Romanes finds evidence of the power of discriminative selection
among the protoplasmic organisms, and he quotes in illustration Dr.
Carpenter's account of the making of shells. "Certain minute
particles of living jelly, having no visible differentiation of organs
. . . build up * tests ' or casings of the most regular geometrical
symmetry of form and of the most artificial construction. . . .
From the same sandy bottom one species picks up the coarser quartz
grains, cements them together with phosphate of iron (?) which must
be secreted from their own substance, and thus constructs a flask-
shaped 'test' having a short neck and a single large orifice. Another
picks up the finer grains and puts them together with the same
cement into perfectly spherical ' tests ' of the most extraordinary
finish, perforated by numerous small tubes, disposed at pretty regular
intervals. Another selects the minutest sand-grains and the terminal
points of sponge spicules, and works these up together apparently
with no cement at all, but by the * laying ' of the spicules into
perfect spheres, like homoeopathic globules, each having a single
fissured orifice." This selecting power is marvellous ; we cannot
explain it ; the animals are alive and they behave thus. But it
must be -remembered that even* * dead ' substances have attractive
affinities for some things in preference to others, that the cells of
roots and those lining the food-canal of an animal or floating in its
blood show a power of selection. Moreover, if we begin with a
unit which provides itself with a coating of sponge spicules,
at first perhaps because they were handiest, it is not difficult to
understand why the future generations of that species should con-
tinue to gather these minute needles. Being simply separated parts
of their parents, whose living matter had become accustomed to
the stimulus of sponge spicules, the descendants naturally sustain
the tradition. This organic memory all Protozoa must have,
for the young are separated parts of the parents.
Ilaeckel was one of the first (1876) to urge the necessity of
recognising the "soul" of the cell. He maintained that the con-
tinuity of organic life led one to assume a similar continuity of
psychical life, that an egg-cell had in it not only the potency of
forming tissues and organs but the rudiments of a higher life as well,
that the Protozoa likewise must be regarded not only as physical
CHAP, xiv The Simplest Animals 217
but as psychical, in fact that the two are inseparable aspects of one
reality. " The cell-soul in the monistic sense is the sum-total of
the energies embodied in the protoplasm, and is as inseparable
from the cell-substance as the human soul from the nervous
system." For several years Verworn has been investigating the
psychical life of the Protozoa. He has conducted his researches
with great care and thoroughness, observing the animals both in
their natural life and in artificial conditions. I shall cite his con-
clusions, translating them freely : "An investigator of the psychical
processes in Protists (simple forms of life) has to face two distinct
problems. The first is comparative, and inquires into the grade of
psychical development which the Protists may exhibit the known
standard being found of course in man ; the second is physiological,
and inquires into the nature of these psychical processes. Since
we know these only through the movements in which they are
expressed, the investigation is primarily a study of the movements
of Protists.
" On a superficial observation of these movements the impression
arises in the observer's mind that they are the result of higher
psychical processes, like the consciously willed activities of men.
Especially the spontaneous movements of advance and recoil, of
testing and searching, give us the impression of being intentional
and voluntary, since no external stimulus can account for them ;
while even some of the movements provoked by stimuli appear on
account of their marked aptness to arise from conscious sensation
and determination.
" But a critical study of the results yielded by an investigation
of spontaneous and stimulated movements warrants a more secure
judgment than that of the superficial observer, and leads to a con-
clusion opposed to his. To this conclusion we are led, that none
of the higher psychical processes, such as conscious sensations,
representations, thoughts, determinations, or conscious acts of will,
are exhibited by Protists. A number of criteria show that the
movements are in part impulsive and automatic, and in part reflex,
and in both cases expressions of unconscious psychical processes.
"This opinion is corroborated by an examination of the structure
of these Protists, for this does not seem such as would make it
possible for the individual to have an idea of its own unified self,
and the absence of self-consciousness excludes the higher psychical
processes. Small fragments cut from a Protist cell continue to
make the same movements as they made while parts of the intact
organism. Each fragment is an independent centre for itself.
There is no evidence that the nucleus of the organism is a psychical
centre. There is no unified Psyche.
"Since the characteristic movements persist in such small frag-
218 The Study of Animal Life PART in
ments, they cannot be the expression of any individual consciousness,
for the individuality has been cut in pieces."
The dilemma is obvious ; either there are no psychical processes
in the Protists, or they are inseparable from the molecular changes
which occur in the parts of the material substance.
If no psychical processes occur in the Protists, where do they
begin ? There is no distinct point in the animal series at which a
nervous system may be said to make its first appearance. If there
are none, even rudimentarily, in the Protists, then these simple
organisms do not potentially include the life of higher organisms.
If there are none in the Protists, are there any in the germs from
which men develop ?
Verworn seizes the other horn of the dilemma, maintaining that
the superficial observers are wrong in crediting the Protozoa with
their own intelligence or with some of it, but right in concluding
that psychical processes of some sort are there. But since he
cannot in any way locate these processes, since he finds that even
small fragments retain their life for a time and behave much as the
entire cells did, he maintains that all life is psychical.
7- History Of the Protozoa. We know that the Protozoa
have lived on the earth for untold ages, for the shells of Fora-
minifera and others may be disentombed from almost the oldest
rocks. The word Protozoa, a translation of the German Urthiere or
primitive animals, suggests that the Protozoa are not only the
simplest, but the first animals, or the unprogressive descendants of
these. Nowadays we can hardly feign to consider this proposition
startling, for we know that all the higher animals, including our-
selves, begin life at the beginning again as single cells. From the
division and redivision of an apparently simple fertilised egg-cell an
embryo is built up which grows from stage to stage till it is
hatched, let us say, as a chick. It is only necessary to extend this
to the wider history of the race. What the egg is to the chick the
original Protozoa were to the animal series ;. the present Protozoa
are like eggs which have lived on as such without making much
progress.
We do not know how the Protozoa began to be upon the earth,
whether they originated from not living matter or in some yet more
mysterious way. The German naturalist Oken, a prominent type
of the school of " Natural Philosophers" who flourished about the
beginning of this century, dreamed of a primitive living slime
( Urschleini) which arose in the sea from inorganic material. His
dream was prophetic of the modern discovery of very simple forms
of life, in connection with one of which there is an interesting and
instructive story. That one, perhaps I should say that supposed
one, was called Bathybius, and since those who are eager to make
CHAP, xiv The Simplest Animals 219
points against science (that is to say against knowledge) always tell
the story wrongly, I shall make a digression to tell it rightly.
In 1857 Captain Dayman, in charge of a vessel engaged in con-
nection with cable -laying, discovered on the submarine Atlantic
plateau the abundant presence of slimy material which looked as if
it were alive. Preserved portions of this formless slime were after-
wards described by Huxley, and he named the supposed organism,
partly from its habitat, partly after ^his friend Haeckel, Bathybius
Haeckelii. On the Porcupine expedition Professors Wy ville Thomson
and Carpenter observed it in its fresh state, and Haeckel afterwards
described some preserved specimens. Its interest lay in its
simplicity and apparent abundance ; Oken's dream seemed to be
coming true ; it seemed as if life were a-making in the still depths.
But when the Challenger expedition went forth, and the bed of
the ocean was explored for the first time carefully, the organism
Bathybius was nowhere to be found. But this was not all ; the
cruellest blow was yet to come. Dr. John Murray saw reason to
suspect that Bathybius was not an organism at all, that it could be
made in a test-tube, and was nothing but a gelatinous form of
sulphate of lime precipitated from the sea water by the action of the
alcohol in the preserving vessels. He renounced Bathybius,
Wyville Thomson acquiesced, Huxley surrendered his organism to
the chemists, and the obscurantists rejoiced exceedingly over the
mare's nest. Bathybius became famous, it was trotted out to
illustrate the fallibility of science, a useful if it were not a somewhat
superfluous service.
But the non-existence of Bathybius was not proved by the fact
that the Challenger explorers failed to find it, nor was it certain
that Murray's destructive criticism covered all the facts. Haeckel
clung with characteristic pertinacity to Bathybius, and his con-
stancy has been to some extent justified by the fact that in 1875
Bessels, on a North Polar expedition, dredged from 92 fathoms of
water in Smith's Sound abundant quantities of a closely -similar
slime. He observed its vital movements, and called it Proto-
Bathybius. It may be that it consists of the broken-off portions
of Foraminifera ; we require to know yet more about it, but I have
said enough to show that it is unfair to stop telling the story with
the words "mare's nest." But whether there be a Bathybius, a
Proto-Bathybius, or no Bathybius at all, we are as students of science
compelled to confess our complete ignorance as to the origin
of life.
8. Relation to the Earth. The floor of the sea for a
variable number of miles (not exceeding 300) from the shore is
covered with a heterogeneous deposit, washed in great part from
the nearest continent. In this deposit shells of Foraminifera usually
220 The Study of Animal Life PART in
occur, but they become more numerous farther from the land,
where the floor of the sea is often covered with a whitish "ooze,"
most of which consists of Foraminifera which in dying have sunk
from the surface to the bottom. They are forming the chalk of a
possible future, just as many chalk-cliffs and pure limestones repre-
sent the ooze of a distant past. In other regions the hard parts
of Radiolarians or Diatoms (small plants) or Pteropods (minute mol-
luscs) are very abundant. As the Foraminifers have made much
of the chalk, so Radiolarians have formed less important siliceous
deposits, such as the Barbados Earth, from which Ehrenberg
described no fewer than 278 species. At marine depths greater
than 2500 fathoms the Globigerina or other Foraminifer shells are
no longer present, not because there are none at the surface, but
apparently owing to the solution of the shells before they reach
such a vast depth. Here the floor is covered with a very fine
reddish or brownish deposit, often called "red -clay," a very
heterogeneous deposit of meteoric and volcanic dust and of residues
of surface-animals. Along with this, in some of the very deepest
parts, e.g. of the Central Pacific, there are accumulations of Radio-
larian shells, which do not readily dissolve. 1
9- Relation to other Forms of Life. On the one hand
the Protozoa are devourers of organic debris and the enemies of
many small plants ; on the other hand they form the fundamental
food of higher animals, helping, for instance, to make that thin sea-
soup on which many depend. Moreover, among them there are
many parasites both on vegetable and animal hosts.
10. Relation to Man. In many indirect ways these firstlings
affect human life, nor are there wanting direct points of contact ;
witness a few Protozoa parasites in man, an Amoeba, some Gre-
garines, and some Infusorians, which are very trivial, however, in
comparison with the numerous plant-parasites the Bacteria.
Among the earliest human records of Protozoa is the notice
which Herodotus and Strabo take of the large coin-like Nummu-
lites, the "Pharaoh's beans" of popular fancy. But the minute-
ness of most Protozoa kept them out of sight for ages. They were
virtually discovered by Leeuwenhoek (b. 1632) about the middle of
the seventeenth century, and soon afterwards demonstrated by
Hooke to the Royal Society of London, the members of which
signed an affidavit that they had really seen them ! In 1755 Rosel
von Rosenhof discovered the Amceba, or "Proteus animalcule;"
but his discovery was ineffective till Dujardin in 1835 demonstrated
the simplicity of the Foraminifers, and till Von Siebold in 1845
1 For details, see conveniently H. R. Mill's Realm of Nature (Lond.
1892).
CHAP, xiv The Simplest Animals 221
showed that Infusoria were single cells comparable to those which
make up a higher animal. For the resemblance between some of
the spirally twisted shells of Foraminifera and those of the
immensely larger Molluscan Ammonites and Nautili led many to
maintain that the Foraminifera were minute predecessors or else
dwindling dwarfs of the Ammonites. So Ehrenberg (1838) figured
the presence of many organs within the Infusorian cell. But as
the microscope was perfected naturalists were soon convinced that
the Protozoa were unit masses of living matter. This is their great
interest to us ; they are, as it were, higher organisms analysed into
their component elements. We see them passing through cycles
of phases, from ciliated to amoeboid, from amoeboid to encysted,
cycles which shed light upon changes both of health and of disease
in higher animals. Again, they seem like ova and spermatozoa
which have never got on any farther.
CHAPTER XV
BACKBONELESS ANIMALS
I. Sponges 2. Stinging- Animals or Cctlenterata 3. " Worms"
4. Echinoderms 5. Arthropods 6. Molluscs
i. Sponges. Sponges are many -celled animals without organs,
with little division of labour among their cells. A true " body " is
only beginning among sponges.
Adult sponges are sedentary, and plant -like in their growth.
With the exception of the freshwater sponge (Spongilla) they live
in the sea fixed to the rocks, to seaweeds and to animals, or to the
muddy bottom at slight or at great depths. They feed on micro-
scopic organisms and particles, borne in with currents of water
which continually flow through the sponge. The sponge is a
Venice-like city of cells, penetrated by canals, in which incoming
and outflowing currents are kept up by the lashing activity of
internal ciliated cells. These ciliated cells, on which the whole life
of the sponge depends, line the canals, but are especially developed
in little clusters or ciliated chambers. The currents are drawn in
through very small pores all over the surface ; they usually flow out
through much larger crater-like openings.
Sponges feed easily and well, and many of them grow out in
buds and branches. A form which was at first a simple cup may
grow into a broad disc or into a tree-like system. And as trees are
blown out of shape by the wind, so sponges are influenced "by the
currents which play around them, as well as by the nature of the
objects on which they are fixed. Like many other passive
organisms, sponges almost always have a well-developed skeleton,
made of flinty needles and threads, of spicules of lime, or of fibres
of horn -like stuff. While sponges do not rise high in organic
rank, they have many internal complications and much beauty.
Sponges may be classified according to their skeleton, as
CHAP, xv Backboneless Animals 223
calcareous, flinty, and horny. (a) The calcareous forms with
needles of lime have a world-wide distribution in the sea, from
between tide-marks to depths of 300 to 400 fathoms. They often
retain a cup -like form, but vary greatly in the complexity of their
canals. The sac-like Sycandra (or Grantia} compressa is common
on British shores. (<) The siliceous sponges are more numerous,
diverse, and complicated, and the flinty needles or threads are often
combined with a fibrous " horny " skeleton. Venus' -Flower-Basket
(Euplectella) has a glassy skeleton of great beauty, Mermaids'
Gloves (Chalina oculata) with needles of flint and horny fibres is
often thrown up on the beach, the Crumb -of -Bread Sponge
(Halichondria panicea) spreads over the low -tide rocks. Some
have strange habits, witness Clione which bores holes in oyster
shells, or Suberites domunciila which clothes the outside of a whelk
or buckie shell tenanted by a hermit-Crab. Unique in habitat is
the freshwater sponge (Spongilla] common in some canals and lakes,
notable for plant-like greenness, and for the vicissitudes of its life-
history, (c) The "horny" sponges which have a fibrous skeleton
but no proper spicules are well represented by the bath-sponges
(Euspongid] which thrive well off Mediterranean coasts, where they
are farmed and even bedded out.
Sponges are ancient but unprogressive animals. Their sedentary
habits, from which only the embryos for a short time escape, have
been fatal to further progress. They show tissues as it were in the
making. They are living thickets in which many small animals
play hide-and-seek. Burrowing worms often do them much harm,
but from many enemies they are protected by their skeletons and by
their bad taste.
2. Stinging- Animals or Ccelenterata. It is difficult to
find a convenient name for the jellyfish and zoophytes, sea-anemones
and corals, and many other beautiful animals which are called
Ccelenterates ; but the fact that almost all have poisonous stinging
lassoes in some of their skin-cells suggests that which we now use.
Representatives of the chief divisions may be sometimes found
in a pool by the shore. Ruddy sea-anemones, which some call
sea-roses, nestle in the nooks of the rocks ; floating in the pool and
throbbing gently is a jellyfish left by the tide ; fringing the rocks
are various zoophytes, or, if we construe the name backwards plant-
like animals ; besides these, and hardly visible in the clear water,
are minute translucent bells some of which have a strange relation-
ship with zoophytes ; and there are yet other exquisitely delicate,
slightly iridescent globes the Ctenophores which move by comb-
like fringes of cilia. But we must search an inland pool to find
one of the very simplest members of this class the freshwater
Hydra which hangs from the floating duckweed and other plants.
224 The Study of Animal Life PART in
This Hydra is a tubular animal often about quarter of an inch in
length. One end of the tube is fixed, the other bears the mouth
surrounded by a crown of mobile tentacles. It is so simple that
cut-off fragments if not too minute may grow into complete animals ;
when well fed, the Hydra buds out little polypes like itself, and
these are eventually set free.
If we suppose the budding of Hydra continued a hundred-
fold, till a branched colony of connected individuals is formed,
we have an idea of a hydroid or zoophyte colony. For a zoophyte
is a colony of many hydra-like polypes, which are supported by a
continuous outer framework and share a common life. Numerous
as may be the "persons" on a branched hydroid, all have arisen
from one more or less Hydra-like individual.
Sometimes, however, there is a marked division of labour in such
a colony, as in Hydradinia which has nutritive, reproductive,
sensitive, and perhaps also protective " persons," three or four
castes into which the colony is divided. The difference between
nutritive and reproductive members is often well marked, and
this has a special interest in the case of many zoophytes. For
many of these, especially among those known as Tubularians and
Campanularians, have reproductive individuals which are set adrift
as small swimming-bells or medusoids, somewhat like miniature
jellyfish. \ A fixed plant -like, asexual hydroid colony buds off
free- swimming, sexual medusoids, from the fertilised eggs of which
embryos develop which grow into hydroicls. This is known as
alternation of generations, and is a remarkable illustration of
activity and passivity combined in one life-cycle.
But all the miniature jellyfish in the sea are not the liberated
reproductive buds of hydroid colonies. Some which are in
structure exceedingly like the liberated medusoids never have any
connection with a hydroid. Their embryos grow into medusoids
like the parents. Quite distinct from these medusoids, though
sometimes superficially like them, are the true jellyfishes which are
sometimes stranded in great numbers on the beach. These medusae
belong to a different series, and some of their features link them
rather to the sea-anemones than to the hydroids.
The sea -anemones and the corals are tubular animals whose
mouths are encircled by tentacles, but they are more complicated
internally than the polypes of the Hydra or hydroid type. For the
latter are simple tubes, while the sea-anemones and their relatives
have turned -in lips which make a kind of gullet, and the inside
tube thus formed is connected with the outer wall of the body by
many radiating partitions some idea of which can be gained by
looking at the skeletons or shells of many corals. Related to the
sea-anemones but different in some details, are many colonies, of
CHAP, xv Backboncless Animals 225
which Dead -men's -fingers (Alcyonium digitalum} is a common
type. Animals resembling sea -anemones have often much lime
about them, and the same is true of others which resemble
Alcyonium ; in both cases we call these calcareous forms corals.
In this bird's-eye view of Stinging-animals, we have recognised
the great types, but we have left others of minor importance out of
account, especially certain corals belonging to the hydroid series
and known as Millepores, also the Portuguese Man -of -War and
its relatives (Siphonophora), which are colonies of more or less
inedusoid individuals with much division of labour, and lastly the
Ctenophores, such as Beroe and Pleurobrachia, which represent the
climax of activity among Coalenterates.
A brief recapitulation will be useful :
First Series Hydroid and Medusoid types (Hydrozoa) :
1 i ) The freshwater Hydra and a few forms like it.
(2) The hydroids or zoophytes, each of which may be regarded
as a compound much-branched Hydra ; including (a) many
whose reproductive persons are not liberated, especially
Sertularians and Plumularians ; (b) many whose repro-
ductive persons are liberated as swimming bells or
medusoids, especially Tubularians and Campanularians.
(3) Free medusoids, anatomically like- the liberated bells of 2 (),
but without any connection with zoophytes.
(4) A few colonial medusoids such as the Portuguese Man-of-
War (Physalid].
(5) A few hydroid corals or Millepores.
Second Series Jellyfish and Sea- Anemone types (Scyphozoa) :
(1) The true jellyfishes or Medusae, including (a) a form like
Pelagia which is free-swimming all its life through, (b) the
common Aurelia whose embryos settle down and become
polypes from which the future free - swimming jellyfishes
are budded off, (c) the more or less sedentary jellyfish
known as Lucernarians.
(2) The sea -anemones and their relatives, including (a) sea-
anemones proper (e.g. Actinia) and their related reef-
building coral-colonies (e.g. star-corals Astrcea, brain-coral
Maandrina} ; and (b} Dead-men's-fingers (Alcyonium} and
others like it, also with related corals, e.g. the organ-pipe
coral (Tiibipora musica} and the " noble coral" of com-
merce (Coral Hum rub rum}.
Third Series
The Ctenophores, which are markedly contrasted with corals,
being free and light and active. Many (e.g. Beroe and
Pleurobrachia} swarm in our seas in summer, iridescent in
daylight, phosphorescent at night. They differ in many
Q
226
The Study of Animal Life PART in
ways from other Coelenterates, thus the characteristic
stinging cells are modified into adhesive cells.
The first and second series, separated by differences of structure
and development, are yet parallel. In both there are polype-types ;
in both medusoid types ; in both there are single individuals and
colonies of individuals; in both there are "corals." We may
compare a Hydra with a sea -anemone, a medusoid with a jelly-
fish, a hydroid colony with Dead -men's- fingers, Millepores with
FIG. 42. The alternation of generations in the common jellyfish Aurelia. i?
the free-swimming embryo ; 2, the embryo settled down ; 3, 4, 5, 6, the de-
veloping asexual stages, or hydra-tubae; 7, 8, the formation of a _pile of
individuals by transverse budding ; 9, the liberation of these individuals ;
10, 1 1, their progress towards the free-swimming sexual medusa form. (From
the Evolution of Sex \ after Haeckel.)
the commoner reef-corals. Moreover, we may compare a medusoid
liberated from a hydroid with Aurelia liberated from its fixed polype-
stage, and permanently-free medusoids with jellyfishes like Pelagia*
These are physiological parallels.
The sedentary polypes are somewhat sluggish, with a tendency
to bud and to form shells or skeletons of some kind. The free-
swimming medusoid types are active, they rarely bud, they do not
form skeletons, but their activity is sometimes expressed in
CHAP, xv Backboneless Animals 227
phosphorescence, and their fuller life is associated with the develop-
ment of sense-organs and a more compacted nervous system. In
both sets the food usually consists of small organisms, in securing
which the tentacles and the stinging cells are of use.
All the Stinging-animals are marine except the species of Hydra^
a minute relative called Microhydra^ the hydroid Cordylophora which
occurs in brackish water and in canals, a strange form Polypodium
which is parasitic in its youth on the eggs of the Russian sturgeon
or sterlet, and a freshwater jellyfish (Limnocodium) which was
found in the tanks at Kew. The rest live in the sea. Hydroids
grow on rocks and shells and on the backs of crabs and other
animals which they mask ; sea -anemones live on the shore -rocks
but not a few are found at considerable depths ; the medusoid
types frequent the opener sea where Siphonophores and Ctenophores
bear them company.
Various kinds of corals should be contrasted. Dead-men's-
fingers with numerous jagged spicules of lime in its flesh is just
beginning to be coralline. Similar spicules have been fused together
in an external tube in the organ -pipe coral. In* the red coral
the calcareous material forms an axis around which the individuals
are clustered. Very different are the reef- building corals, where
the cup in which each individual lived is more or less well marked
according as it has remained distinct or fused with its neighbours,
and where an image of the fleshy partitions of the sea -anemone-
like animal is seen in the radiating septa of lime.
Corals are passive, and like many animals of similar habit have
calcareous shells, but how do they get the carbonate of lime of
which these are composed ? Is that salt by no means abundant in
sea-water plentiful near coral-reefs, or is there a double-decomposi-
tion between the abundant calcium sulphate and the coral's waste-
products, as has been suggested by Irvine and Murray ? On what
do the corals feed, for they seem always to be empty ? Do their
bright pigments enable them, as Hickson suggests, to feed like
plants on carbonic acid ?
The struggle for standing-room should also be thought of, and
the throngs of gaily-coloured animals which browse and hide on
the coral banks.
Many of the Stinging-animals have forms and colours which
delight our eyes, and the quaint partnerships between sea-anemones
and crabs are interesting.
But it is through corals that Ccelenterates come into closest touch
with human life. For the stinging of bathers by jellyfish is a
minor matter, and the thousands which are cast upon the beach
are of no use as manure, being little more than animated sea-
water.
228 The Study of Animal Life PART m
As sponges showed tissues in the making, so among Stinging-
animals organs begin eyes and ears, nerve -rings, and special
reproductive structures. The zoologist has much to learn in regard
to the alternation of hydroid and medusoid in one life-cycle, the
division of labour in Hydractinia and other colonies, and the
meaning and making of a skeleton. Nor can we forget the long
past in which there were ancient coral reefs, and types of coral
hardly represented now, and strange Graptolites whose nature we
do not yet clearly understand.
We begin the series of many-celled animals with Sponges and
Ccelenterates, partly because they are on the whole simplest, but
more precisely because their types of structure are least removed
from that two-layered sac-like embryo .or gastrula which recurs in
the life-history of most animals, and which we have much warrant
for regarding as a hint of what the first successful many-celled
animals were like. The Sponges and Ccelenterates differ from the
higher animals : (l) In retaining the symmetry of this gastrula, in
being like it radially symmetrical, and in so growing that the axis
extending from the mouth to the opposite pole corresponds to the
long axis of the embryo; (2) in being two -layered animals, for
between the outer skin and the lining of the internal food-cavity
there is only a more or less indefinite jelly instead of a definite
stratum of cells ; (3) in having only one internal cavity, instead of
having, like most other animals, a body-cavity within which a dis-
tinct food-cavity lies.
3. "Worms." This title is one of convenience, without
strict justification. For there is no class of "worms," but an
assemblage of classes which have little in common. "Worm"
is little more than a name for a shape, most of the animals so
called differing from anemones and jellyfish in having head, tail, and
sides. The simplest worms were apparently the first many-
celled animals to move persistently head foremost, thus acquiring
distinct bilateral symmetry, and a definite nervous centre or brain
in that region which had most experience the head. In our
survey we are helped a little by the fact that many consist of a
series of rings or segments, while others are all one piece or unseg-
mented. It is generally true that the latter are in structure simpler
and more primitive than the former.
ist Set of Worms. Plathelminthes or flat worms, ist
Class. Turbellaria or Planarians. These are small worms,
living in the sea or in fresh water, or occasionally in damp earth,
covered externally with cilia, very simple in structure, usually
feeding on minute animals. The genus Planaria, common in fresh
water ; green species of Vortex and Convoluta, which are said by
some to owe their colour to minute partner algae ; Microstoma, which
CHAP, xv Backboneless Animals 229
by budding forms temporary chains of eight or sixteen individuals
as if suggesting how a ringed worm might arise ; Gunda, with a hint
of internal segmentation ; and two parasitic genera Graffilla and
Anoplodium may be mentioned as representatives of this class.
You will find specimens by collecting the waterweeds from a pond
or seaweeds from a shore-pool, and the simplicity of some may be
demonstrated by observing that when they are cut in two each half
lives and grows.
2nd Class. Trematoda or Flukes. These are parasitic "worms,"
living outside or inside other animals, often flat or leaf -like in
form, provided with adhesive and absorbing suckers. Those which
live as ectoparasites, e.g. on the skin of fishes, have usually a
simple history ; while those which are internal boarders have an
intricate life-cycle, requiring to pass from one host to another of a
different kind if their development is to be fulfilled. Thus the
liver-fluke (Distonium hepaticum], which causes the disease of liver-
rot in sheep, and sometimes destroys a million in one year in Britain
alone, has an eventful history. From the bile-ducts of the sheep
the embryos pass by the food-canal to the exterior. If they reach a
pool of water they develop, quit their egg-shells, and become for
a few hours free-swimming. They knock against many things, but
when they come in contact with a small water -snail (Lymnceus
truncatulus} they fasten to it, bore their way in, and, losing their
locomotor cilia, encyst themselves. They grow and multiply in a
somewhat asexual way. Cells within the body of the encysted
embryo give rise to a second generation quite different in form.
The second generation similarly produces a third, and so on.
Finally, a generation of little tailed flukes arises ; these leave the
water-snail, leave the water too, settle on blades of grass, and lose
their tails. If they be eaten by a sheep they develop into adult
sexual flukes. Others have not less eventful life-cycles, but that of
the liver-fluke is most thoroughly known. If you dissect a frog
you are likely to find Polystomum integerrimum in the lungs or
bladder ; it begins as a parasite of the tadpole, and takes two or
three years to become mature in the frog. Quaint are the little
forms known as Diporpa which fasten on the gills of minnows, and
unite in pairs for life, forming double animals (Diplozoori) ; and
hardly less strange is Gyrodactylus^ another parasite on freshwater
fishes, for three generations are often found together, one within
the other. The most formidable fluke-parasite of man is Bilharzia y
or Distomum h
but we are more familiar with the Amphipods (e.g. Gammarns]
which jerk themselves along sideways or shelter under stones both
in fresh and salt water. The wood-louse Oniscus has counterparts
(Asellus, Idotea] on the shore, and several remarkable parasitic
relatives. Among the highest forms are the long -tailed lobsters
(Homarus, Palinitrus\ and crayfishes (Astacus\ and shrimps
(Crangon], and prawns (Palczmon, Pandalus] ; the soft -tailed
hermit crabs (Pagiirus} ; and the short - tailed crabs (e.g. Cancer,
CarcimiS) Dromia].
(b) Protracheata. Peripatus. This remarkable genus, repre-
FIG. 46. Peripatus. (From Chambers's Encyclop. ; after Moseley.)
sented by about a dozen widely-distributed species, seems to be a
survivor of the ancestral insects. Worm-like or caterpillar-like in
Backboneless A n imals
241
appearance, with a soft and beautiful skin, with unjointed legs, with
the halves of the ventral nerve-cord far apart, and with many other
remarkable features, it has for us this special interest that it
possesses the air -tubes characteristic of insects and also little
kidney- tubes similar to those of Annelids.
(?) Myriapoda. Centipedes and Millipedes. These animals
have very uniform bodies, there is little division of labour among the
numerous appendages. The head is distinct, and bears besides the
pair of antennae (which Peripatus and Insects also have) two pairs
of jaws. The Centipedes are flattened, carnivorous, and poisonous ;
the Millipedes are cylindrical, vegetarian, and innocuous ; moreover,
they have two pairs of legs to most of their segments.
FIG. 47. Winged male and wingless female of Pneumora, a kind of
grasshopper. (From Darwin.)
(if) Insecta. Insects are the birds of the backboneless series.
Like birds they are on an average active, most have the power of
flight, many are gaily coloured, sense-organs and brains are often
highly developed.
Contrasted with Peripatus and Myriapods, they have a more
compact body, with fewer but more efficient limbs. They are
Arthropods, which are usually winged in adult life, breathe air
by means of tracheae, and have frequently a metamorphosis in their
life-history. To this definition must be added the anatomical facts
that the adult body is divided into three regions, ( I ) a head with
three pairs of mouth -appendages ( = legs) and a pair of sensitive
outgrowths (antennae or feelers) in front of the mouth, (2) a thorax
with three pairs of walking legs, and usually two pairs of wings,
and (3) an abdomen without appendages, unless occasional stings,
egg-laying organs, etc., be remnants of these.
R
242 TJie Study of Animal Life PART in
The wings are very characteristic. They are flattened sacs of
skin, into which air-tubes, blood-spaces, and nerves extend. It is
possible that they had originally a respiratory, rather than a
locomotor function, and that increased activity induced by bettered
respiration made them into flying wings.
The breathing is effected by means of the numerous air-tubes
{ v or tracheae which open externally on the sides and send branches
/ to every corner of the body. As the air is thus taken to all
' [ the tissues, the blood-vascular system has little definiteness, though
there is (as in other Arthropods) a dorsal contractile heart. The
larvae of some insects, e.g. dragonflies, mayflies, etc., live in
the water, and the tracheae cannot open to the exterior (else the
creature would drown), but they are sometimes spread out on
wing-like flaps of skin (" tracheal gills"), or arranged around the
terminal portion of the food-canal in which currents of water are
kept up.
The student should learn something about the different mouth-
organs of insects and the kinds of food which they eat ; about the
various modes of locomotion, for insects " walk, run, and jump with
the quadrupeds, fly with the birds, glide with the serpents, and
swim with the fish ; " about the bright colours of many, and the
development of their senses.
In the simplest insects the old-fashioned wingless Thysanura
and Collembola the young creature which escapes from the egg-
shell is a miniature adult. There is no metamorphosis. So with
cockroaches and locusts, lice and bugs ; except that the young are
small, have undeveloped reproductive organs, and have no wings,
they are like the parents, and all the more when the parents (e.g.
lice) also are wingless.
In cicadas there is a slight but instructive difference between
larvae and adults. The full-grown insects live among herbage, the
young live in the ground, and the anterior legs of the larvae are
adapted for burrowing. Moreover, the larval life ends in a sleep
from which an adult awakes. But much more marked is the differ-
ence between the aquatic larvae of mayflies and dragonflies and the
aerial adults, in which we have an instance of more thorough though
still incomplete metamorphosis.
Different, however, is the life of all higher insects butterflies
and beetles, flies and bees. From the egg-shell there emerges a
larva (maggot, grub, or caterpillar), which often lives an active
voracious life, growing much, and moulting often. Rich in stores
of fatty food, it falls into a longer quiescence than that associated
with previous moults and becomes a pupa, nymph, or chrysalis.
In this stage, often within the shelter of a silken cocoon, great
transformations occur ; the body is undone and rebuilt, wings bud
CHAP, xv Backboneless Animals 243
out, the appendages of the adult are formed, and out of the pupal
husk there emerges an imago, an insect fully formed.
(e) Arachnida. Spiders, Scorpions, Mites, etc. This class is
unsatisfactorily large and heterogeneous. In many the body is
divided into two regions, the head and breast (cephalothorax), with
two pairs of mouth parts and four pairs of walking legs, the
abdomen with no appendages. Respiration may be effected by
the skin in some mites, by trachese in other mites, by tracheae plus
"lung-books" in many spiders, by "lung-books" alone in other
spiders, by " gill-books" in the divergent king-crab.
The scorpions with a poisoning weapon at the tip of the tail,
the little book-scorpions (Chelifer\ the long-legged harvest-men
(e.g. Phalangium}\ the spiders proper spinners, nest -makers,
hunters ; the mites ; the strange parasite (Pentastomum] in the
dog's nose ; the quaint king-crab (Limulus) last of a lost race,
with which the ancient Trilobites and Eurypterids were connected ;
all these are usually ranked as Arachnids !
6. MollllSCS. It seems strange that animals, the majority of
which are provided with hard shells of lime, should be called
mollusca ; for that term first used by Linnaeus is a Latinised version
of the Greek malakia, which means, soft. Aristotle applied it
originally to the cuttlefish, which are practically without shells, so
that its first use was natural enough, but the subsequent history of
the word has been strange.
Cockle, mussel, clam, and oyster ; snail and slug, whelk and lim-
pet ; octopus, squid, and pearly nautilus ; what common character-
istics have they ? Most of them have a bias towards sluggishness,
and on the shields of lime which most of them bear, do we not read
the legend, " castles of indolence " ? But this sluggishness is only
an average character, and the shell often thins away. The scallop
(Pec fen] and the swimming Lima are active compared with the
oyster, and they have thinner shells ; the snails which creep slowly
between tides or on the floor of the sea are heavily weighted, while
the sea-butterflies (Pteropods) have light shells, and most cuttlefish
have none at all.
The shell is very distinctive, but we are not able to state
definitely how it is formed or what it means. In most of the
embryo molluscs which have been studied there is a little pit or
" shell-gland" in which a shell begins to be formed, but the shell
of the adult is in all cases made by a single or double fold of skin
known as the " mantle." In some cases where the shell seems to
be absent, e.g. in some slugs, a degenerate remnant is still to be found
beneath the skin, while in other cases (e.g. most cuttlefish) its
absence is to be explained as a loss, since related ancestral species
possess it. There are, however, two or three primitive forms
244 The Study of Animal Life PART m
(Chatoderma, Neomenia) where an incipient shell is represented
only by a few spicules or plates of lime.
The shell is made by the folded skin or "mantle" ; it consists
for the most part of carbonate of lime along with a complex organic
substance called conchiolin ; it shows three layers, of which the
outermost is somewhat soft and without lime, while the innermost
shines with mother-of-pearl iridescence. The whole product is a
cuticle something formed from the skin ; its varied colours and
forms are beautiful ; it is a protective shield ; but there are many
FIG. 48. The common octopus. (From Chambers' s Encyclop. ; after Urchin.)
questions about shells which we cannot answer. Where does the
carbonate of lime come from, since that salt is often far from
abundant in the water in which most molluscs live ? Have they
the power of changing the abundant sulphate of lime in sea- water
into carbonate of lime, perhaps by an interaction with waste products
excreted from the skin ? Is the shell an expression of the constitu-
tional sluggishness of the animal since it seems on the whole to be
most massive in the most sluggish, least so in the most active forms ?
Most molluscs are marine, on the shore, in the open sea, in the
great depths ; there are also many freshwater forms, e.g. the
mussels Anodon and Unio, and the snails, Lymnaus t Planorbis,
CHAP, xv Backboneless Animals 245
and Pahidina ; the terrestrial snails and slugs are legion. Among
those of the shore the naked Nudibranchs are often in colour and
form protectively adapted to their surroundings ; those of the open
sea (Ileteropods, Pteropods, and many cuttlefish) are active and
carnivorous, with light shells or none ; in the dark depths many
are blind or in other ways rudimentary, but food seems to be so
abundant that there is almost no need to struggle for it.
As to diet, there are three kinds of eaters carnivores, such as
the active swimmers- we have mentioned, besides the whelks and
many other burglars who bore through their neighbours' shells, and
the Testacella slugs ; vegetarians, like the periwinkle, the snail, and
most slugs ; and thirdly, almost all the bivalves, which feed on
microscopic plants and animals, and on organic debris wafted to
the mouth by the lashing of the cilia on the gills and lips. In this
connection it is important to notice that all molluscs except bivalves
have in their mouths a rasping ribbon or toothed tongue (radula,
odontophore) by which they grate, file, or bore with marked effect.
Of parasites there are few, but one Gasteropod, Entoconcha
mirabilis, which lives inside the Holothurian Synapta^ is very
remarkable in its degeneration. It starts in life as a vigorous
embryo like that of most marine snails, it becomes a mere sac of
reproductive organs and elements.
In structure, molluscs differ remarkably from the arthropods \
and higher "worms" in the absence of segments and serial \
appendages. They are not divided into rings, and they have no 1
legs.
To begin with, they were doubtless (bilaterally) symmetrical
animals, and this symmetry is retained in primitive forms like the
eight-shelled Chiton and in the bivalves. But most of the snails
are twisted and lop-sided, they cannot be symmetrically halved.
For this asymmetry the strange dorsal hump formed by the viscera,
and the tendency that the single shell would have to fall to one side,
are sometimes blamed. That this lop-sidedness is not necessarily
a defect) but rather the reverse, is evident from the success not
only of the snail tribe but of many other asymmetrical animals.
The skin has a remarkable fold (double in the bivalves) known/
as the "mantle," the importance of which in making the shell we\
have already recognised. Another very characteristic structure is
the so-called " foot," a muscular protrusion of the ventral surface,
an organ used in creeping and swimming, leaping and boring, but
almost absent in the sedentary oysters.
We rank the molluscs high among backboneless animals, partly
because of the nervous system, which here as elsewhere is a ;
dominating characteristic. There are fewer nerve centres than in
most Arthropods or in higher "worms," but this is in most cases
246 The Study of Animal Life PART m
a sign of concentration. There is a {cerebral} pair with nerves
which supply the head region, another (pleural) pair with nerves to
the sides and viscera, a third (pedal] pair whose nerves govern the
foot, and often other accessory centres of which the most important
are visceral. In the somewhat primitive eight-shelled Chiton and its
neighbours, the nervous system is the most readily harmonised with
that of other Invertebrates ; in bivalves the three pairs of centres
are far apart ; in most snails and in cuttlefish the three are con-
centrated in the head-regions, and it is those forms with concentrated
ganglia which show some signs of cleverness and emotion.
Life -History. Most molluscs pass through two larval stages
before they acquire their characteristic adult appearance. The
first is interesting because it is virtually the same as the young
stage of many "worms." It is a barrel - shaped or pear -like
embryo with a ring of locomotor cilia in front of the mouth, and is
known as a Trochosphere.
After a while this changes into a more characteristic form called
the Veliger. It bears on its head a ciliated cushion or velum often
produced into lobes ; the body has a ventral " foot" and a dorsal
"shell-gland." In aquatic Gasteropods the visceral hump begins
to appear at this stage.
The eggs of cuttlefish differ from those of other molluscs in their
rich supply of yolk, which serves for a prolonged period as capital
for the young, and the two larval stages noticed above are skipped
over. There are other interesting modifications in the life-history
of terrestrial and freshwater forms, witness the little larvae of the
freshwater mussel which are kept within the gills of the mother till
the approach of some sticklebacks or other fish, to which the
liberated young then fix themselves.
History. The shells of molluscs are well preserved in the rocks,
and palaeontologists have been very successful in tracing long series.
The chief types are all represented in the Cambrian strata a
fact which forcibly suggests the immensity of yet earlier ages.
They are abundant from the Silurian onwards. The snails have
gone on increasing, and are now more abundant than ever ; the
bivalves cannot be said to have diminished, but the Cephalo-
pod tribe has dwindled. Of the Nautiloid type of Cephalopods,
of which there are crowds of fossil forms, only the pearly Nautilus
now survives, and though there are many kinds of naked cuttle-
fish in our seas there are ten times as many shelled ancestors
in the rocks. The geological record confirms what we should
otherwise expect, that the lung-breathing snails and the freshwater
bivalves were somewhat late in appearing.
Prof. Ray Lankester has reconstructed an ideal ancestor which
combines the various molluscan characteristics in a satisfactory
CHAP, xv Backboneless Animals 247
fashion, and may be something like the original mollusc. Whence
that original sprang is uncertain, but the common occurrence of the
trochosphere larva and some of the characters of the primitive
Gasteropods (Neomenia, Chcztoderma^ Chiton] suggest the origin
of molluscs from some " worm " type or other. We can be sure of
this, however, that the series must have divided at a very early
epoch into two sets, the sluggish, sedentary, headless bivalves on
the one hand, and the more active and aggressive snails and cuttle-
fish on the other.
Relation to Man. Irresistibly we think first of oysters, which
Huxley describes as "gustatory flashes of summer lightning,"
and over which neolithic man smacked his lips. But many others,
cuttlefish, ear -shells (Haliotis\ mussels (Mytilus edttlis), peri-
winkles (Littorina littorea], cockles (Cardium cordatum\ etc. etc., are
used as food, and many more as bait. In ancient days, as even
now, the shells of many were used for ornaments, instruments,
lamps, vessels, coins, etc. ; the inner layer of the shell furnishes
mother-of-pearl ; concretions around irritating particles become
pearls in the pearl-oyster (Margaritana) and in a few others ; the
Tyrian purple was a secretion of the whelk Purpura and the
related Murex ; and the attaching byssus threads of the large bivalve
Pinna may be woven like silk.
On the other hand, a few cuttlefish are large enough to be
somewhat dangerous ; the bivalve Teredo boring into ship-bottoms
and piers is a formidable pest, baulked, however, by the pre-
valent use of metal sheathing ; the snails and slugs are even more
voracious than the birds which decimate them.
Conchology was for a while a craze, rare shells have changed
hands at the cost of hundreds of pounds, such is the human " mania
of owning things." But the shells are often fascinating in their
beauty, and poetic fancy has played lovingly with such as the
Nautilus.
CHAPTER XVI
BACKBONED ANIMALS
I. Balanoglossus 2. Timicates 3. The Lancelet 4. Round-
Mouths or Cyclostomata 5. Fishes 6. Amphibians
7. Reptiles 8. Birds 9. Mammals
ACCORDING to Aristotle, fishes and all higher animals were " blood-
containing," and thus distinguished from the lower animals, which
he regarded as "bloodless." He was mistaken as to the absence of
blood in lower animals, for in most it is present, but the line which
he drew between higher and lower animals has been recognised in
all .subsequent classifications. - Fishes, amphibians, reptiles, birds,
and mammals differ markedly from molluscs, insects, crustaceans,
" worms," and yet simpler animals. The former are backboned
(Vertebrate), the latter backboneless (Invertebrate).
It is necessary to make the contrast more precise. ( its relative in Southern
Seas.
(2) The Ganoid fishes are almost, if not quite, as ancient as the
Elasmobranchs, but their golden age, long since past, was in Devonian
and Carboniferous ages. There are only some seven different kinds
now alive. Two of these are the sturgeons (Acipenser} and the
bony pike (Lepidosteus). The latter has a bony skeleton ; the
sturgeon is in part gristly. An armature of hard scales is very
characteristic of this decadent order.
(3) In Permian times, when Reptiles were beginning, a third
type of fish appeared, of which the Queensland mud-fish (Ceratodus]
seems to be a direct descendant. In this type the air-bladder is
used as a lung, thus suggesting the transition from Fishes to Am-
phibians. Perhaps this order was always small in numbers ; now-
adays at least there are only two genera Ceratodus^ from the
fresh water of Queensland, and Protopterus^ from west and tropical
Africa ; while another form, sometimes called a different genus
(Lepidosiren}) is recorded from the Amazons. Double-breathers or
Dipnoi we call them, for they do not depend wholly upon gills, but
come to the surface and gulp air into their air-bladder. Mud-
fishes they are well named, for as the waters dry up they retire into
the mud, forming for themselves a sort of nest, within which they
lie dormant.
(4) In the Chalk period the characteristically modern fishes
(Teleosteans), with completely bony skeletons, began. Herring
and salmon, cod and pike, eel and minnow, and most of the com-
monest fishes belong to this order. Heavy ironclads yield to swift
gunboats, and the lithe Teleosteans have succeeded better than the
armoured Ganoids.
The wedge-like form of most fishes is well adapted for rapid
swimming. Most flat fish, whether flattened from above down-
wards like the gristly skate, or from side to side like the flounders
and plaice, live at the bottom; those of eel -like shape usually
wallow in the sand or mud ; the quaint globe-fish float passively.
The chief organ of locomotion is the tail ; the paired fins help to
raise or depress the fish, and serve as guiding oars. In the climb-
ing perch they are used in scrambling ; in the flying fish they are
sometimes moved during the long swooping leaps. In eels and
pipe-fish they are absent ; in the Dipnoi they have a remarkable
median axis. The unpaired fins on the back and tail and under
surface are fringes of skin supported by rays.
Fishes are often resplendent in colours, which are partly due to
CHAP, xv Backboned Animals 255
pigments, partly to silvery waste-products in the cells of the outer
skin, and partly to the physical structure of the scales. Some-
times the males are much brighter than the females, and grow
brilliant at the breeding season. In some cases the colours har-
monise with surrounding hues of sand and gravel, coral and sea-
weed ; while the plaice and some others have the power of rapidly
changing their tints.
Fishes feed on all sorts of things. Some are carnivorous, others
Fia. 52. The gemmeous drngonet (Callionymus lyra\ the male above,
the female beneath. (From Darwin.)
vegetarian, others swallow the mud. By most of them worms,
crustaceans, insect-larvae, molluscs, and smaller fishes are greedily
eaten. Strange are some of large appetite (e.g. Chiasmodon niger\
who manage to get outside fishes larger than their own normal
size !
Of their mental life little is known. Yet the cunning of trout,
the carefulness with which the mother salmon selects a spawning-
ground, the way the archer-fish (Toxotes) spits upon insects, the
nest-making and courtship of the stickleback and others, the pug-
nacity of many, show that the brain of the fish is by no means asleep.
256 The Study of Animal Life PART m
The males are often different from the females smaller, brighter,
and less numerous. In some cases they court their mates, and
fight with their rivals. Most of the females lay eggs, but a few
bony fishes and many sharks bring forth living young. In two
sharks there is a prophecy of that connection between mother and
offspring which is characteristic of mammals. The fish's egg is
usually a small thing, but those of Elasmobranchs are large, being
rich in yolk and often surrounded by a mermaid's purse. This
egg-case has long tendril-like prolongations at the corners, these
twine automatically around seaweed, and the embiyos may be
rocked by the waves until the time of hatching. When the egg is
enclosed in a sheath, or when the young are hatched within the
body of the mother, fertilisation must take place internally, but in
most cases the male accompanies the female as she spawns, and
with his milt fertilises the eggs in the water or on the gravelly
spawning-ground. As love for offspring varies inversely with their
number, there is little parental care among the prolific fishes.
Most fishes live either wholly in the sea or wholly in fresh
water, but some are indifferent, and pass, at spawning time espe-
cially, from one to the other. A few, such as the climbing
perch,* venture ashore, while the mud -fishes and a few others
can survive drought for a season. In caves several blind fishes
live, and species of Fierasfer find more or less habitual lodging
inside sea-cucumbers and some other animals.
The fishes which live in deep water are interesting in many
ways. Giinther has shown that from 80 to 200 fathoms the eyes
are rather larger than usual, as if to make the most of the dim
light. Beyond 200 fathoms "small-eyed fishes as well as large-eyed
occur, the former having their want of vision compensated for by
tentacular organs of touch, whilst the latter have no such accessory
organs," and can see only by the fitful light of phosphorescence.
" In the greatest depths blind fishes occur, with rudimentary eyes,
and without special organs of touch." The phosphorescence is pro-
duced by numerous marine animals and by the fishes themselves.
6. Amphibians. The Amphibians which now live are neither
numerous nor large. Giant Amphibians or Labyrinthodonts began
to appear in the Carboniferous period, but most of the modern
frogs and toads, newts and salamanders, are relatively pigmies.
Young Amphibians always breathe by gills, as Fishes do, and in
some cases these gills persist in adult life. But whether they do
or not, the full-grown Amphibians have lungs and use them. The
skin is characteristically soft, naked, and clammy. Amphibians
are the first Vertebrates with hands and feet, with fingers and toes.
Unpaired fringes are sometimes present on the back and tail as in
Fishes, but are never supported by fin-rays.
CHAP, xvi Backboned Animals 257
The class includes four orders, of which the Labyrinthodonts
are wholly extinct, the other three being represented by tail-less
frogs and toads (Anura), by newts and salamanders (Urodela) with
distinct tails, and by a few of worm-like form and burrowing
habit, e.g. C&cilia. Some, the last for example, are terrestrial, but
usually live in damp places ; most pass their youth at least in fresh
water ; none can endure saltness, and they are therefore absent from
almost all oceanic islands. The common British newts (Triton and
Lissotriton), and the often brightly-coloured salamanders (Sala-
mandrd] have in adult life no trace of gills ; the rice-eel (Amphiuma)
and the genus Menopoma lose their gills, but persistent clefts indi-
cate their position ; the blanched blind Proteus from caves and the
genus Menolranchus keep their gills throughout life. The remark-
able Axolotl from North American lakes occurs in two forms, both
of which may bear young ; the one form (Axolotl) has persistent
gills, the other form (Amblystomd) loses them, and the change
from the Axolotl to the Amblystoma is in part associated with the
passage from the water to the swampy shore. A large fossil dis-
covered by Scheuchzer in the beginning of the eighteenth century
was quaintly regarded as a fossil man and as a testimony of the
deluge. But Cuvier showed that Scheuchzer's Homo diluvii testis
was but a large newt.
The common frogs (Rana), the Surinam toad (Pipa), the
common toads (Bufo), and the tree-frogs (Hyla) illustrate the tail-
less order Anura. In none of them is there in adult life any trace
of gills.
The worm-like, limbless, burrowing Amphibians (Gymnophiona)
must not be confused with the blind- or slow-worms, which are
lizards. There are only very few genera, Siphonops, Rhinatrema^
Epicrium, Ccecilia. The newly-born Cacilia has external gills,
but these are soon lost. The eyes are covered with skin, but are
well developed.
The race of Amphibians began in the Carboniferous ages.
Most of the Labyrinthodonts which flourished then and in the two
succeeding periods were newt-like in form, but some were serpen-
tine. They seem to have been armoured, and were sometimes
large.
Amphibians are naturally sluggish. For long periods they can
fast and lie dormant ; they can survive being frozen quite stiff,
and though tales of toads within stones are mostly due to mistakes
or fancies, there are some authentic cases of prolonged imprison-
ment.
Few are found far from water, and the gilled condition of
the young is skipped over only in a few cases. In the black
salamander (Salamandra atra) of the Alps, which lives where
S
258
TJie Study of Animal Life PART in
pools are scarce, the young, after living and breathing for a time
within the mother, are born as lung-breathers ; also in some
species of tree-frogs (Hylodes)^ which live in situations where water
is scarce, the gilled stage is omitted.
The development of the common frog should be studied bj
every student of natural history. The eggs are fertilised as they
are being laid. The division of the ovum can be readily observed.
In its early stages the tadpole is fish-like, with a lamprey-like
JF'-W - m&+ ^ ^z^ib**^-, <
rS"*c^---~^*iehL
FIG. 53. -The life-history of the Frog.
mouth. External gills are replaced by an internal set, and as
metamorphosis is accomplished these disappear and the lungs
become active. The larva feeds first on its own yolk, then on
freshwater plants, then on small animals or even on its own
relatives ; then it fasts, absorbing its tail, and finally it becomes an
insect-catching frog.
The food of adult Amphibians usually consists of insects, slugs,
and worms ; most of the larvae are for a time vegetarian. Though
Amphibians often live alone, crowds are often found together at the
breeding season. Then the sluggish life wakes up, as the croak-
ings of frogs remind us. Quaint are many of their reproductive
habits, to some of which allusion has already been made. Such
CHAP, xvi Backboned Animals 259
animals as the Surinam toad (Pipa americana] and the Obstetric
frog (Alytes obstetric an s] suggest that the Amphibians make ex-
periments in eugenics.
7- Reptiles. Fishes and Amphibians are closely allied ; so
Reptiles are linked to Birds, and more remotely to Mammals also.
Those three highest classes Reptiles, Birds, and Mammals are
very different from one another, but they have certain characters in
common. Most of them have passed from the water to dry land ;
none of them ever breathe by gills ; all of them have two embryonic
birth-robes amnion and allantois which are of great importance
in early life. Compared with the other Vertebrates, the brains are
more complex, the circulation is more perfect, the whole life has a
higher pitch. As symbols of mammal, bird, and reptile, take the
characteristic coverings of the skin hair, feathers, and scales.
Hair typifies strength and perhaps also gentleness ; feathers suggest
swift flight, the beauty which wins love, and the down which lines
the warm nest ; scales speak of armour and cold-blooded stealth.
But we need not depreciate reptiles, nor deny the justice of that
insight which has found in them the fittest emblems of the omni-
potence of the earth. If Athene of the air possesses the birds,
surely the power of the dust is in the grovelling snakes. Few
colour arrangements are more beautiful than those which adorn the
lithe lizards. The tortoise is an example of passive energy, self-
contained strength, and all but impenetrable armature. The
crocodiles more than the others recall the strong ferocity of the
ancient extinct dragons. Nor should we judge reptiles exclusively
by their living representatives, any more than we should judge
the Romans by those of the decadent Empire. It is interesting to
remember the long-tailed toothed Archaopteryx, the predecessor of
modern birds, just as it is to recall the giant sloths which pre-
ceded the modern Edentate mammals ; but it is essential to include
in our appreciation of Reptiles the giant dragons of their golden
age. Most modern forms are pigmies beside an Ichthyosaurus 25
feet long, a Megalosaurus of 30, a Titanosaurus of 60, or an
Atlantosaurus of 100, all fairly broad in proportion. We have still
pythons and crocodiles and other reptiles of huge size, and we do
not deny Grant Allen's remark that a good blubbery " right whale "
could give points to any deinosaur that ever moved upon Oolitic
continents, but the fact remains that in far back times (Triassic,
Jurassic, and Cretaceous) reptiles had a golden age with a pre-
dominance of forms larger than any living members of the class.
Besides size, however, the ancient saurians had another virtue,
apparently possessed by both small and great they were pro-
gressive. For, with toothed birds on the one hand and flying or
flopping reptiles on the other, it seems probable that birds had
260 The Study of Animal Life PART in
their origin from feverish saurians which acquired the power of
flight, and it is also possible that some, perhaps pathological,
mother reptile, -overflowing in the milk of animal kindness, and
retaining her young for a long time within her womb, was the fore-
runner of the mammalian race.
While there are many orders of extinct reptiles Ichthyosaurs,
Plesiosaurs, Deinosaurs, Pterosaurs, and other saurians not yet
classified with certainty the living forms belong to four sets the
lizards, the snakes, the tortoises, and the crocodiles to which a
fifth order should perhaps be added for the New Zealand "lizard"
Hatteria or Sphenodon, which is in several respects a living fossil.
The Lizards (Lacertilia). The lizards form a central order of
Reptiles, but the members are a motley crowd, varied in detailed
structure and habit. Usually active in their movements, though
fond, too, of lying passive in the sunshine, they are often very
beautiful in form and colour, and not uncommonly change their
tints in sympathetic response to their surroundings. Most lay eggs,
but in some, e.g. the common British lizard (Lacerfa or Zootoca
vivipard), and the slow-worm, the young are hatched within the
mother.
Among the remarkable forms are the Geckos, which with
plaited adhesive feet can climb up smooth walls ; the large Monitors
( Varanus\ which may attain a length of 6 feet, and prey upon
small mammals, birds, frogs, fishes, and eggs ; the poisonous
Mexican lizard (Heloderma horridum), with large venom -glands
and somewhat fang -like teeth; the worm-like, limbless Amphis-
bcena ; the likewise snake-like slow-worm (Anguis fragilis\ which
well illustrates the tendency lizards have to break in the spasms of
capture ; the large Iguanas, which frequent tropical American
forests, and feed on leaves and fruit ; the sluggish and spiny
"Horned Toad" (Phrynosoma] ; the Agamas of the Old World
comparable to the Iguanas of the New ; the Flying Dragon (Draco
volant), which, with skin outstretched on extended ribs, swoops
from tree to tree ; the Australian frilled lizards (Chlamydosaurus)
and the quaint thorny Moloch ; the single marine lizard (Oreo-
cephalus or Aniblyrhynchus cristatus] from the Galapagos ; and the
divergent Chamaeleons, flushing with changeful colour.
The New Zealand Hatteria or Sphenodon is quite unique, and
seems to be the sole survivor of an extinct order Rhynchocephalia.
It was in it first of all that the pineal body an upgrowth from the
mid-brain of backboned animals was seen to be a degenerate
up ward -looking eye.
Snakes or Serpents (Ophidia). These much modified
reptiles mostly cleave to the earth, though there are among them
clever climbers, swift swimmers, and powerful burro wers. Though
CHAP, xvi Backboned Animals
261
262 The Study of Animal Life PART in
they are all limbless, unless we credit the little hind ciaws of some
boas and pythons with the title of legs, they flow like swift living
streams along the ground, using ribs and scales instead of their lost
appendages, pushing themselves forward with jerks so rapid that
the movement seems continuous. Without something on which to
raise themselves they must remain at least half prostrate, but in the
forest or on rough grdund there are no lither gymnasts. Their
united eyelids give them an unlimited power of staring, and, accord-
ing to uncritical observers, of fascination ; yet most of them seem
to see dimly and hear faintly, trusting mainly for guidance to the
touch of their restless protrusible tongue and to their sense of
smell. Their only language is a hiss or a whine. Most of them
have an annual period of torpor, and all periodically cast off their
scales in a normally continuous slough, which they turn outside-in
as they crawl out. Almost all lay eggs, but in a few cases (e.g.
the adder) the young are hatched within the mothers, and this
mode of birth may be induced by artificial conditions. Think not
meanly of the serpent, "it is the very omnipotence of the earth.
That rivulet of smooth silver how does it flow, think you ? It
literally rows on the earth with every scale for an oar ; it bites the
dust with the ridges of its body. Watch it when it moves slowly
a wave, but without wind ! a current, but with no fall ! all the
body moving at the same instant, yet some of it to one side, some
to another, or some forward, and the rest of the coil backwards ;
but all with the same calm will and equal way no contraction, no
extension ; one soundless, causeless, march of sequent rings, and
spectral procession of spotted dust, with dissolution in its fangs,
dislocation in its coils. Startle it the winding stream will become
a twisted arrow ; the wave of poisoned life will lash through the
grass like a cast lance. It scarcely breathes with its one lung (the
other shrivelled and abortive) ; it is passive to the sun and shade,
and cold or hot like a stone ; yet ' it can outclimb the monkey,
outswim the fish, outleap the zebra, outwrestle the athlete, and
crush the tiger.' It is a Divine hieroglyph of the demoniac power
of the earth of the entire earthly nature. As the bird is the
clothed power of the air, so this is the clothed power of the dust ;
as the bird is the symbol of the spirit of life, so this of the grasp and
sting of death." 1
This well-known and eloquent passage is not perfectly true,
thus the serpent breathes not scarcely but strongly with its one
lung, but, while you may correct and complete it as you will, I am
sure that you will find here more insight into the nature of serpents
than in pages of anatomical description.
1 Ruskin's Queen of the Air.
CHAP, xvi Backboned Animals 263
A few snakes have mouths which do not distend, skull bones
which are slightly movable, teeth in one jaw (upper or lower)
only, and rudiments of hind legs. These are included in the
genera Typhlops and Anomalepsis, and are small simple ophidians.
Many are likewise non-venomous snakes, but with wider gape
and more mobile skull bones, and with simple teeth on both jaws. if
Some are very large and have great powers of strangling. Such
are the Pythons, the Boa, and the Anaconda. To these our grass
snake (Tropidonotus-natrix} is allied.
Many poisonous snakes have large permanently erect grooved fangs
in the upper jaw, and a salivary gland whose secretion is venomous.
Such are the cobra (Naja tripudians), the Egyptian asp {Naja haje\
the coral snakes (Elaps), and the sea snakes (Hydrophis).
Other poisonous snakes have perforated fang teeth, which can
be raised and depressed. Such are the vipers ( Vipera), the British
adder (Pelias berus]^ the copperhead (Ancistrodon contortrix), the
rattlesnakes ( Crotalus}.
Tortoises and Turtles (Chelonia). Boxed in by a bony
shield above and by a bony shield below, and often with partially
retractile head and tail and legs, the Chelonians are thoroughly
armoured. On the average the pitch of their life is low, but their
tenacity of life is great. Slow in growth, slow in movement, slow
even in reproduction are rn^iny of them, and they can endure long
fasting. It is said that a tortoise walked at least 200 yards, twenty-
four hours after it was decapitated, while it is well known that the
heart of a tortoise will beat for two or three days after it has been
isolated from the animal. In connection with their sluggishness it
is significant that the ribs which help to some extent in the respira-
tory movements of higher animals are soldered into the dorsal
shield, thus sluggish respiration may be in part the cause, as it is
in part the result, of constitutional passivity. All the Chelonians
lay eggs in nests scooped in the earth or sand.
The marine turtles (e.g. Sphargis, Chelone], the estuarine soft-
shelled turtles (e.g. Aspidonectes\ the freshwater turtles (e.g.
Emys\ and the snapping turtle ( Chelydrd] are more active than the
land tortoises, such as the European Testtido grceca, often kept as
a pet. The tortoise of the Galapagos Islands ( Testudo elephantopus],
the river tortoise (Podocnemys expansa) of the Amazon, the bearded
South American turtle (Chelys matamatd}, and the green turtle
(Chelone my das) attain a large size, sometimes measuring about
3 feet in length.
CrocodiliailS (Crocodilia). Crocodiles, alligators, and ga vials
seem in our present perspective very much alike strong, large,
heavily armoured reptiles, at home in tropical rivers, but clumsy
and stiff-necked on land, feeding on fishes and small mammals,
264
The Study of Animal Life PART in
growing slowly and without that definite limit which punctuates
the life -history of most animals, attaining, moreover, a great
age, freed after youth is past from the attacks of almost every
foe but man. The teeth are firmly implanted in sockets ; the
limbs and tail are suited for swimming, and also for crawling ; the
^heart is more highly developed than in other reptiles, having four
instead of three chambers. The animals lie in wait for victims,
and usually drown them, being themselves able to breathe while
the mouth is full of water, if only the nostrils be kept above the
surface.
In many ways Reptiles touch human life, the poisonous snakes
are very fatal, especially in India ; crocodilians are sometimes
destructive ; turtles afford food and " tortoise shell ;" lizards are
delightfully beautiful.
8. Birds. What mammals are to the earth, and fishes to the
sea, birds are to the air. Has anything truer ever been said of
FiG. 55. The Collocalia, which from the secreted juice of its salivary glands
builds the edible-bird's-nest. (Adapted from Brehm.)
them than this sentence from Ruskin's Queen of ihe Air! "The
bird is little more than a drift of the air brought into form by
plumes ; the air is in all its quills, it breathes through its whole
frame and flesh, and glows with air in its flying, like a blown
CHAP, xvi Backboned Animals 265
flame : it rests upon the air, subdues it, surpasses it, outraces it ;
is the air, conscious of itself, conquering itself, ruling itself."
Birds represent among animals the climax of activity, an index to
which may be found in their high temperature, from 2-i4 Fahren-
heit higher than that of mammals. In many other ways they rank
high, for whether we consider the muscles which move the wings
in flight, the skeleton which so marvellously combines strength
with lightness, the breathing powers perfected and economised by a
set of balloons around the lungs, or the heart which drives and
receives the warm blood, we recognise that birds share with
mammals the position of the highest animals. And while it is true
that the brains of birds are not wrinkled with thought like
those of mammals, and that the close connection between mother
and offspring characteristic of most mammals is absent in birds, it
may be urged by those who know their joyousness that birds feel
more if they think less, while the patience and solicitude con-
nected with nest-making and brooding testify to the strength of
their parental love. Usually living in varied and beautiful sur-
roundings, birds have keen eyes and sharp ears, tutored to a sense
of beauty, as we may surely conclude from their cradles and love
songs. They love much and joyously, and live a life remarkably
free and restless, qualities symbolised by the voice of the air in
their throat, and by the sunshine of their plumes. There is more
than zoological truth in saying that in the bird " the breath or spirit
is more full than in any other creature, and the earth power least,"
or in thinking of birds as the purest embodiments of Athene of
the air.
But just as there are among mammals feverish bats with the power
of true flight, and whales somewhat fish-like, so there are excep-
tional birds, runners like the ostriches and cassowaries, swimmers
like the penguins, criminals too like the cuckoos and cow-birds in
which the maternal instincts are strangely perverted. As we go
back into the past, strange forms are discovered, with teeth, long
tails, and other characteristics which link the birds of the air to the
grovelling reptiles of the earth. Even to-day there lives a
"reptilian-bird" Opisthocomus which has retained more than
any other indisputable affinities with the reptiles. Professor W. K.
Parker, one of the profoundest of all students of birds, described
this form in one of his last papers, and there used a comparison
which helps us to appreciate birds. They are among backboned
animals what insects are among the backboneless winged pos-
sessors of the air, and just as many insects pass through a cater-
pillar and chrysalis stage before reaching the acme of their life as a
flying imago, so do the young birds within the veil of the egg-
shell pass through somewhat fish-like and somewhat reptile-like
266 The Study of Animal Life PART m
FIG. 56. Decorative male and less adorned female of Spathura a genus of
Humming-birds. (From Darwin, after Brehm.)
CHAP. XVI
Backboned Animals
267
stages before they attain to the possession of wings and the enjoy-
ment of freedom.
The great majority of birds are fliers, and possess a keeled
breast-bone, to which are fixed the muscles used in flight. To
this keel or carina they owe their name Carinatae. The flying
host includes the gulls and grebes, the plovers and cranes, the
ducks and geese, the storks and herons, the pelicans and cormo-
rants, the partridges and pheasants, the sand grouse, the pigeons,
the birds of prey, the- parrots, the pies, and about 6000 Passerine or
sparrow-like birds, including thrushes and warblers, wrens and
swallows, finches and crows, starlings and birds of paradise. To
these orders we have to add Opisthocomus, from which it is perhaps
easier to pass to some of the keeled fossil birds, some of which
possessed teeth.
Distinct from the keeled fliers, both ancient and modern,
are the running-birds, which
are incapable of flight, and
therefore possess a flat raft-
like breast bone, to which
they owe their title Ratitae.
Nowadays these are few in
number, the Ostrich and the
Rhea, the Cassowary and
Emu, and the small Kiwi.
Beside these must be ranked
the giant Moa of New Zea-
land, not long extinct, and
the more ancient, not less
gigantic ALpyornis of Mada-
gascar, while farther back
still, from the Chalk strata
of America, the remains of
toothed keelless birds have
been disentombed.
The most reptilian, least
bird -like of birds is the
oldest fossil of all, placed in
a sub -class by itself, the
ArcJuzopteryx (lit. ancient
bird) from strata of Jurassic
age.
9. Mammalia. Of the
highest class of animals the Mammalia I need say least for they
are most familiar. Most of them are terrestrial, four-footed, and
hairy. Bats arrd whales, seals and sea-cows, are obviously excep-
FIG. 57. Restoration of the extinct moa.(Dzn-
ornis ingens), and alongside of it the little
kiwi (Apteryx mantelli). (From Cham-
' after F. v. Hochstetter.)
268 The Study of Animal Life PART m
tional. The brain of mammals is more highly developed than
that of other animals, and in the great majority there is a prolonged
(placental) connection between the unborn young and the mother.
In all cases the mothers feed the tender young with milk.
In the class there are three grades :
(1) In the Duckmole (Ornithorhynchus) and the Porcupine
Ant-Eater (Echidna), and perhaps another genus Proechidna, the
females lay eggs. In many other ways these exclusively Austral-
asian mammals are primitive, exhibiting affinities with reptiles.
(2) In the Marsupials, which, with the exception of some
American Opossums, are also Australasian, the young are born at
a very tender age, as it were, prematurely. In the great majority
of genera, the mothers stow them away in an external pouch, where
they are fed and sheltered till able to fend for themselves. In
Australia the Marsupials have been saved by insulation from stronger
mammals, which seem to have exterminated them in other parts
of the earth, the Opossums which hide in American forests being
the only Marsupials surviving outside Australasia, though fossils
show that the race had once a much wider distribution. In their
Australian retreat, apart from all higher Mammalia (mice, rabbits,
and the like being modern imports) the Marsupials have evolved
along many lines, prophetic of the higher orders of mammals.
There are "carnivores" like the Thylacine and the Dasyure,
"herbivores" like the Kangaroos, " insectivores " like the banded
ant-eater Myrmecobius, and "rodents" like the Wombat.
(3) In all the other orders of mammals there is a close con-
nection between mother and unborn offspring.
Two orders are lowly and distinctly separate from the others
and from one another the Edentata represented by sloths,
ant-eaters, armadillos, pangolins, and the Aard-Vark ; and the
Sirenia or Sea-Cows which now include only the dugong and the
manatee.
Along one fairly definite line we may rank three other orders
the Insectivores, the Bats, and the Carnivores. The hedgehog,
which is at once a lowly and a central type of mammal, may be
taken as the beginning of this line. Along with shrews, moles,
porcupines, the hedgehogs form the order Insectivora. To these
the Bats (Cheiroptera), with their bird-like powers of flight, are
linked, while the Carnivora (cats, dogs, bears, and seals), though
progressive in a different direction, seem also related.
Comparable to the Insectivores, but on a different line, are the
gnawing Rodents, rabbits and hares, rats and mice, squirrels and
beavers. This line leads on to the Elephants, from the company
of which the mammoths have disappeared since man arose on the
earth. With the Elephants, the rock-coneys or Hyraxes " a feeble
CHAP. XVI
Backboned Animals
269
folk " seem to be allied. Both are often included in the great
order of hoofed animals or Ungulates, along with the odd-toed
FIG. 58. Phenacodtts frtmavus t a primitive extinct mammal from the lower
Eocene of N. America. The actual size of the slab of rock on which it rested
was 49 inches in length. (From Chambers's Encyclop. ; after Cope.)
animals hors.e, rhinoceros, and tapir, and a larger number of
even-toed forms, hog and hippopotamus, camel and dromedary,
FIG. 59. Head of gorilla. (From Du Chaillu.)
and the true cud-chewers or ruminants such as sheep and cattle,
deer and antelopes. From the ancient predecessors of the modern
270
The Study of Animal Life PART in
Ungulates, it seems likely enough that the Cetaceans (whales and
dolphins) diverged.
A third line, which we may call median, leads through the
Lemurs on to Monkeys. It must be noted, however, that these
lines, which seem distinct from one another if we confine our
attention to living mammals, are linked by extinct forms. Thus a
FIG. 60. Head of male Semnopithecus. (From Darwin.)
remarkable fossil type, Phenacodus, is regarded by Cope as pre-
senting affinities with Ungulates, Lemurs, and Carnivores.
The monkeys which most closely resemble man in structure,
habits, and intelligence, are the so-called anthropoid apes, the
gorilla, the chimpanzee, the orang-utan, and the gibbon. A
second grade is represented by the more dog-like, narrow-nosed
Old World apes, such as the baboons and mandrills. Lower in
many ways are the broad-nosed New World or American monkeys,
e.g. the numerous species of Cebus, some of which are the familiar
CHAP. XVI
Backboned Animals
271
companions of itinerant musicians, while lowest and smallest among
true monkeys are the South American marmosets. Distinct from
all these, probably outside the monkey order altogether, are the
so-called half-monkeys or Lemurs.
We might describe the clever activities of monkeys, the shelters
which some of them make, their family life, parental care and
sociality, their docility, their intelligent habits of investigation, and
their quickness to profit by experience ; but it would all amount to
this, that their life a"t many points touches the human, that they
are in some ways like growing children, in other ways like savage
men, though with more circumscribed limits of progress than either.
ORDERS OF MAMMALS.
MON
KEYS
URS
CETACEANS
CARNI/VORES
BATS
IN/SECTIVORES
SIRENIA
EDENTATA
MARSUPIALS
MONOTREMES
272 The Study of Animal Life PART
SURVEY OF THE ANIMAL KINGDOM
BIRDS.
Flying-Birds. Running-Birds.
Placentals.
MAMMALS. Marsupials.
Monotremes
Snakes. Lizards. REPTILES. Crocodiles. Tortoises
FISHES.
Double- Breathers.
Bony-Fishes.
Ganoids.
Elasmobranchs.
LANCELET.
AMPHIBIANS.
Newt. Frog.
CYCLOSTOMATA.
Lamprey. Hagfish.
TUNICATES.
Insects. Arachnids
Myriapods.
Peripatus.
ARTHROPODS.
Crustaceans.
BALANOGLOSSUS
ANNELIDS.
WORMS."
FLAT-WORMS.
Cuttlefish.
Gasteropods.
MOLLUSCS.
Bivalves.
Feather-stars.
Brittle-stars.
Starfish.
ECHINODERMS
Sea-urchins.
Sea-cucumbers.
Ctenophores. Jellyfish. Sea-Anemones. Corals.
STINGING-ANIMALS or CCELENTERATES,
Medusoids and Hydroids.
SPONGES.
Infusorians. Rhizopods. Gregarines.
SIMPLEST ANIMALS.
PART IV
THE EVOLUTION OF ANIMAL LIFE
CHAPTER XVII
THE EVIDENCES OF EVOLUTION
I. The Idea of Evolution 2. Arguments for Evolution : Physio-
logical ', Morphological^ Historical 3. Origin of Life
WE observe animals in their native haunts, and study their
growth, their maturity, their loves, their struggles, and their
death ; we collect, name, preserve, and classify them ; we
cut them to pieces, and know their organs, tissues, and
cells ; we go back upon their life and inquire into the secret
working of their vital mechanism ; we ransack the rocks for
the remains of those animals which lived ages ago upon the
earth ; we watch how the chick is formed within the egg,
and yet we are not satisfied. We seem to hear snatches of
music which we cannot combine. We seek some unifying
idea, some conception of the manner in which the world of
life has become what it is.
i. The Idea of Evolution. We do not dream now,
as men dreamed once, that all has been as it is since all
emerged from the mist of an unthinkable beginning ; nor
can we believe now, as men believed once, that all came
into its present state of being by a flash of almighty volition.
We still dream, indeed, of an unthinkable beginning, but
we know that the past has been full of change ; we still
T
274 The Study of Animal Life PART iv
believe in almighty volition, but rather as a continuous reality
than as expressed in any event of the past. Thus Erasmus
Darwin (1794), speaking of Hume, says "he concluded
that the world itself might have been generated rather than
created ; that it might have been gradually produced from
very small beginnings, increasing by the activity of its
inherent principles, rather than by a sudden evolution of
the whole by the Almighty fiat." In short, we have
extended to the world around us our own characteristic
perception of human history ; we have concluded that in all
things the present is the child of the past and the parent
of the future.
But while we dismiss the theory of permanence as
demonstrably false, and the theory of successive cataclysms
and re-creations as improbable, 1 without feeling it necessary
to discuss either the falsity or the improbability, we must
state on what basis our conviction of continuous evolution
rests. " La nature ne nous offre le spectacle d'aucune
creation, c'est d'une continuation eternelle." "As in the
development of a fugue," Samuel Butler says, " where,
when the subject and counter-subject have been announced,
'there must thenceforth be nothing new, and yet all must
be new, so throughout organic nature which is a fugue
developed to great length from a very simple subject
everything is linked on to and grows out of that which
comes next to it in order errors and omissions excepted."
2. Arguments for Evolution. What then are the facts
which have convinced naturalists that the plants and the
animals of to-day are descended from others of a simpler
sort, and the latter from yet simpler ancestors, and so on,
back and back to those first forms in which all that suc-
ceeded were implied ? I refer you to Darwin's Origin of
Species (1859), where the arguments were marshalled in
such a masterly fashion that they forced the conviction
1 I use the word in its literal sense ' ' not admitting of proof. " It is
not my duty nor my desire to discuss the poetical, or philosophical,
or religious conceptions which lie behind the concrete cosmogonies of
different ages and minds. To many modern theologians creation
really means the institution of the order of nature, the possibility of
natural evolution included.
CHAP, xvii The Evidences of Evolution 275
of the world. To the statements of the case by Spencer,
Haeckel, Huxley, Romanes, and others, I have given
references in the chapter on books. Darwin's arguments
were derived ($) from the distribution of animals in space ;
(b) from their successive appearance in time, (c) from actual
variations observed in domestication, cultivation, and in
nature ; (rf) from facts of structure, e.g. homologous and
rudimentary organs, (e) from embryology. I shall simply
illustrate the different kinds of evidence, and that under
three heads (a) physiological, (b) structural, (c) his-
torical. ,/
(a) Physiological. A study of the life of organisms
shows that the ancient and even Linnaean dogma of the
constancy or immutability of species was false. Organisms
change under our eyes. They are not like cast-iron ; they
are plastic. One of the most striking cases in the Natural
History Collection of the British Museum is that near the
entrance, where on a tree are perched domesticated pigeons
of many sorts fantail, pouter, tumbler, and the like
while in the centre is the ancestral rock-dove Columba lima^
from which we know that all the rest have been derived.
In other domesticated animals, even when we allow that
some of them have had multiple origins, we find abundant
proof of variability. But what occurs under man's super-
vision in the domestication of animals and in the culti-
vation of plants occurs also in the state of nature. Natural
" varieties " which link species to species are very common,
and the offspring of one brood differ from one another and
from their parents. How many strange sports there are
and grim reversions ! and, as we shall afterwards see,
modifications of individuals by force of external conditions
are not uncommon. Those who say they see no variation
now going on in nature should try a month's work at identi-
fying species. I have known of an ancient man who dwelt
in a small town ; he did not believe in the reality of railways
and to him the testimony of observers was as an idle tale ;
he was not daunted in his scepticism even when the railway
was extended to his town, for he was aged, and remained
at home, dying a professed unbeliever in that which he had
276 The Study of Animal Life PART iv
FIG, 61. Varieties of domestic pigeon arranged around the ancestral rock-dove
(Cohimba lima). (Based on Darwin's figures.)
CHAP, xvn The Evidences of Evolution 277
never seen. Conviction depends on more than intelligence,
often on emotional vested interests.
(b) Morphological. There are said to be over a million
species of living animals, about half of them insects.
Even their number might suggest blood-relationship, but our
recognition of this becomes clear when we see that species
is often united to species, genus to genus, and even class
to class, by connecting links. The fact that we can make
at least a plausible genealogical tree of animals, arranging
them in series along the lines of hypothetical pedigree, is
also suggestive.
Throughout long series, structures fundamentally the
same appear with varied form and function ; the same bones
and muscles are twisted into a variety of shapes. Why this
adherence to type if animals are independent of one
another ? How necessary it is if all are branches of one
tree.
By rudimentary organs also the same conclusion is
suggested. What mean the unused gill-clefts of reptiles,
birds, and mammals, unless the ancestors of these classes
were fish-like ; what mean the teeth of very young whale-
bone whales, of an embryonic parrot and turtle, unless they
are vestiges of those which their ancestors possessed ? There
are similar vestigial structures among most animals. In
man alone there are about seventy little things which might
be termed rudimentary ; his body is a museum of relics. We
are familiar with unsounded or rudimentary letters in many
words ; we do not sound the " o " in leopard nor the " 1 "
in alms, but from these rudimentary letters we read the
history of the words.
(c) Historical. Every one recognises that animals have
not always been as they now are ; we have only to dig to
be convinced that the fauna of the earth has had a history.
But it does not follow that the succession of fauna after
fauna, age after age, has been a progressive development.
What evidence is there of this ?
In the first place, there is the general fact that fishes
appear before amphibians, and these before reptiles, and
these before birds, and that the same correspondence
278
The Study of Animal Life PART iv
between order of appearance and structural rank is often
true in detail within the separate classes of animals. There
are some marvellously complete series of fos-
sils, especially, perhaps, that of the extinct
cuttlefishes, in which the steps of progressive
evolution are still traceable. Moreover, the
long pedigree of some animals, such as the
horse, has been worked out so perfectly that
more convincing demonstration is hardly pos-
sible. In Professor Huxley's American Ad-
dresses^ or in that pleasant introduction to
zoology afforded by Professor W. H. Flower's
little book on the horse (Modern Science
Series, Lond., 1891), you will find the story
of the horse's pedigree most lucidly told :
how in early Eocene times there lived small
quadrupeds about the size of sheep that
walked securely upon five toes, how these
animals lost, first the inner toe, while the
third grew larger, and then the fifth ; how the
third continued to grow larger and the second
and fourth to become smaller until they dis-
appeared almost entirely, remaining only as
small splint bones ; and how thus the light-
footed runners on tiptoe of the dry plains
were evolved from the short - legged splay-
footed plodders of the Eocene marshes. Fin-
ally, there are many extinct types which link
and hi 2 nd~feetof order to order and even class to class, such
the horse and as that strange mammal Phenacodus. which
some of its an- . . ' .
cestors, show- seems to occupy a central position in the
reducdo^Tn ser i es > so numerous are its affinities, or such
the number of as those saurians which link crawling reptile
digits. (From A ....
Chambers^*- to soaring bird.
Another historical argument of great im-
portance is that derived from the study of
the geographical distribution of animals, but this cannot be
appreciated without studying the detailed facts. These
suggest that the various types of animals have spread from
CHAP, xvn The Evidences of Evolution
279
definite centres, along convenient paths of diffusion, varying
into species after species as their range extended.
But the history of the individual is even more instructive.
The first three grades of structure observed among living
animals are: (i) Single cells (most Protozoa), (2) balls of
cells (a few Protozoa which form colonies), and (3), two-
layered sacs of cells (e.g. the simplest sponges). But these
three grades correspond to the first three steps in the indi-
vidual life-history of any many-celled animal. Every one
begins as a single cell, at the presumed beginning again ;
this divides into a ball of cells, the second grade of struc-
ture ; the ball becomes a two-layered sac of cells. The
FIG. 63. Antlers of deer (1-5) in successive years; but the figure might almost
represent at the same time the degree of evolution exhibited by the antlers
of deer in successive ages. (From Chambers's EucycloJ>.)
correspondence between the first three grades of structure
and the first three chapters in the individual's life-history is
complete. It is true as a general statement that the indi-
vidual development proceeds step by step along a path
approximately parallel to the presumed progress of the
race, so far as that is traceable from the successive grades
of structure and from the records of the rocks. Even in
regard to details such as the development of antlers on stags
the parallelism of racial and individual history may be
observed. Of this correspondence it is difficult to see any
elucidation except that the individual in its life-history in
great part re-treads the path of ancestral evolution.
I have illustrated these evidences of Devolution very
280 The Study of Animal Life PART iv
briefly, for they have been stated many times of late years.
The idea of evolution has also justified itself by the light
which it has cast not only on biological, but on physical,
psychological, and sociological facts. There has never been
a more germinal idea ; it is fast becoming organic in all
our thinking.
To those who feel a repugnance to the doctrine of
descent, I suggest the following considerations :
(1) In so far as conclusions do not affect conduct, it
seems wise to conserve what makes one happiest. If your
intellectual and emotional necessities are better satisfied,
for instance, by any one of the creationist theories than
by that of a gradual and natural progress from simple
beginnings to implied ends, and if you feel that your sense
of the marvel, beauty, and sacredness of life would be
impoverished by a change of theory, then I should not seek
to persuade you.
(2) But as we do not think a tree less stately because
we know the tiny seed from which it grew, nor any man
less noble because he was once a little child, so we ought
not to look on the world of life with eyes less full of wonder
or reverence, even if we feel that we know something of its
humble origins.
(3) Finally, we should be careful to distinguish between
the doctrine of natural descent, which, to most naturalists,
seems a solemn fact, and the theories of evolution which
explain how the progressive descent was brought about.
For in regard to the causal, as distinguished from the modal
explanation of the world, we are or ought to be uncertain.
3. Origin of Life. It is no dogma, nor yet a "law
of Biogenesis," but a fact of experience, to which no excep-
tion has been demonstrated, that living organisms arise
from pre-existent organisms Omne vivum e vivo.
As to the origin of life upon the earth we know nothing,
but hold various opinions, (i) Thus it is believed that life
began independently of those natural conditions which come
within the ken of scientific inquirers ; in other words, it is
believed that the first living things were created. That
this belief presents intellectual difficulties to many minds
CHAP, xvii The Evidences of Evolution 281
may mean that its fittest expression in words has not been
attained, or is unattainable. (2) It has been suggested
that germs of life reached this earth in the bosom of
meteorites from somewhere else. This at least shifts the
responsibility of the problem off the shoulders of this planet.
(3) It is suggested that living matter may have been evolved
from not-living matter on the earth's surface. If we accept
this suggestion, we must of course suppose that in not-living
matter the qualities characteristic of living organisms are
implicit. The evolutionist's common denominator is then
as inexpressibly marvellous as the philosopher's greatest
common measure.
CHAPTER XVIII
THE EVOLUTION OF EVOLUTION THEORIES
i. Greek Philosophers 2. Aristotle 3. Lucretius 4. Evolution-
ists before Darwin 5. Three old Masters : Buffon^ JSrasmus
Darwin, Lamarck 6. Charles Darwin 7. Darwin's Fellow-
workers 8. The Present State of Opinion
THE conception of evolution is no new idea, it is the human
idea of history grown larger, large enough to cover the
whole world. The extension of the idea was gradual, as
men felt the need of extending it ; and at the same moment
we find men believing in the external permanence of one
set of phenomena, in the creation of others, in the evolution
of others. One authority says human institutions have been
evolved ; man was created ; the heavens are eternal. Ac-
cording to another, matter and motion are eternal ; life was
created ; the rest has been evolved, except, perhaps, the
evolution theory which was created by Darwin.
i. Greek Philosophers. Of the wise men of Greece
and what they thought of the nature and origin of
things, I shall say little, for I have no direct acquaintance
with the writings of those who lived before Aristotle.
Moreover, though an authority so competent as Zeller has
written on the "Grecian predecessors of Darwin/' most of
them were philosophers not naturalists, and we are apt to
read our own ideas into their words. They thought, indeed,
as we are thinking, about the physical and organic universe,
and some of them believed it to be, as we do, the result of
CH. xviii The Evolution of Evolution Theories 283
a process ; but here in most cases ends the resemblance
between their thought and ours.
Thus when Anaximander spoke of a fish-like stage in the
past history of man, this was no prophecy of the modern
idea that a fish-like form was one of the far-off ancestors of
backboned animals, it was only a fancy invented to get over
a difficulty connected with the infancy of the first human
being.
Or, when we read that several of these sages reduced
the world to one element, the ether, we do the progress of
knowledge injustice if we say that men are simply returning
to this after more than two thousand years. For that
conception of the ether which is characteristic of modern
physical science has been, or is being, slowly attained by
precise and patient analysis, whereas the ancient conception
was reached by metaphysical speculation. If we are
returning to the Greeks, it is on a higher turn of the spiral,
so far at least as the ether is concerned.
When we read that Empedocles sought to explain the
world as the result of two principles love and hate
working on the four elements, we may, if we are so inclined,
call these principles " attractive and repulsive forces " ; we
may recognise in them the altruistic and individualistic
factors in organic evolution, and what not ; but Empedocles
was a poetic philosopher, no far-sighted prophet of evolu-
tion.
But the student cannot afford to overlook the lesson
which Democritus first clearly taught, that we do not
explain any result until we find out the natural conditions
which bring it 'about, that we only understand an effect
when we are able to analyse its causes. We require a so-
called "mechanical," or more strictly, a dynamical explana-
tion of results. It is easy to show that it is advantageous
for a root to have a root-cap, but we wish o know how the
cap comes to be there. It is obvious that the antlers of a
stag are useful weapons, but we must inquire as precisely
as possible how they first appeared and still grow.
2. Aristotle. As in other departments of knowledge,
so in zoology the work of Aristotle is fundamental. It is
284 The Study of Animal Life PART iv
wonderful to think of his knowledge of the forms and ways
of life, or the insight with which he foresaw such useful dis-
tinctions as that between analogous and homologous organs,
or his recognition of the fact of correlation, of the advan-
tages of division of labour within organisms, of the gradual
differentiation observed in development. He planted seeds
which grew after long sleep into comparative anatomy and
classification. Yet with what sublime humility he says : "I
found no basis prepared, no models to copy. Mine is the
first step, and therefore a small one, though worked out with
much thought and hard labour." Aristotle was not an
evolutionist, for, although he recognised the changefulness of
life, the world was to him an eternal fact not a stage in a
process.
" In nature, the passage from inanimate things to animals is so
gradual that it is impossible to draw a hard-and-fast line between
them. After inanimate things come plants, which differ from one
another in the degree of life which they possess. Compared with
inert bodies, plants seem endowed with life ; compared with
animals, they seem inanimate. From plants to animals the passage
is by no means sudden or abrupt ; one finds living things in the
sea about which there is' doubt whether they be animals or plants."
~" Animals are at war with one another when they live in the same
place and use the same food. If the food be not sufficiently
abundant they fight for it even with those of the same kind. "
3. Lucretius. Among the Romans Lucretius gave
noble expression to the philosophy of Epicurus. I shall
not try to explain his materialistic theory of the concourse
of atoms into stable and well-adapted forms, but rather
quote a few sentences in which he states his belief that the
earth is the mother of all life, and that animals work out
their destiny in a struggle for existence. He was a cosmic,
but hardly an organic evolutionist, for, according to his
poetic fancy, organisms arose from the earth's fertile bosom
and not by the gradual transformation of simpler predecessors.
" In the beginning the earth gave forth all kinds of herbage and
verdant sheen about the hills and over all the plains ; the flowery
meadows glittered with the bright green hue, and next in order to
the different trees was given a strong and emulous desire of grow-
CH. xviii The Evolution of Evolution Theories 285
ing up into the air with full unbridled powers. . . . With good
reason the earth has gotten the name of mother, since all things
have been produced out of the earth. . . .
" We see that many conditions must meet together in things in
order that they may beget and continue their kinds ; first a supply
of food, then a way in which the birth-producing seeds throughout
the frame may stream from the relaxed limbs. . . . And many
races of living things must then have died out and been unable to
beget and continue their breed. For in the case of all things which
you see breathing the breath of life, either craft or courage or else
speed has from the beginning of its existence protected and pre-
served each particular race. And there are many things which,
recommended to us by their useful services, continue to exist con-
signed to our protection.
" In the first place, the first breed of lions and the savage races
their courage has protected, foxes their craft, and stags their prone-
ness to flight. But light-sleeping dogs with faithful heart in breast,
and every kind which is born of the seed of beasts of burden, and at
the same time the woolly flocks and the horned herds, are all con-
signed to the protection of man. For they have ever fled with
eagerness from wild beasts, and have ensued peace, and plenty of
food obtained without their own labour, as we give it in requital of
their useful services. But those to whom nature has granted none
of these qualities, so that they could neither live by their own
means nor perform for us any useful service, in return for which
we should surfer their kind to feed and be safe under our protection,
those, you are to know, would lie exposed as a prey and booty
of others, hampered all in their own death-bringing shackles, until
nature brought that kind to utter destruction."
4. Evolutionists before Darwin. From Lucretius I
shall pass to Buffon, for the intervening centuries were un-
eventful as regards zoology. Hugo Spitzer, one of the histo-
rians of evolution, finds analogies between certain mediaeval
scholastics and the Darwinians of the nineteenth century,
but these are subtle comparisons. Yet long before Darwin's
day there were evolutionists, and the first of these who can
be called great was Buffon.
We must guard against supposing that the works of
Buffon, or Lamarck, or Darwin were inexplicable creations
of genius, or that they came like cataclysms, without warning,
to shatter the conventional traditions of their time. For all
great workers have their forerunners, who prepare their
286 The Study of Animal Life PART iv
paths. Therefore in thinking out the history of evolutionist
theories before that of Buffon, we must take account of
many forces which began to be influential from the twelfth
century onwards. " Evolution in social affairs has not
only suggested our ideas of evolution in the other sciences,
but has deeply coloured them in accordance with the
particular phase of social evolution current at the time." 1
In other words, we must abandon the idea that we can
understand the history of any science as such, without
reference to contemporary evolution in other departments
of activity. The evolution of theories of evolution is bound
up with the whole progress of the world.
In trying to determine those social and intellectual forces
of which the, modern conception of organic evolution has
been a resultant, we should take account of social changes,
such as the collapse of the feudal system, the crusades, the
invention of printing, the discovery of America, the French
Revolution, the beginning of the steam age ; of theological
and religious movements, such as the Protestant Reforma-
tion and the spread of Deism ; of a long series of evolu-
tionist philosophers, some of whom were at the same time
.students of the physical sciences, notably Descartes,
Spinoza, Leibnitz, Herder, Kant, and Schelling ; of the
acceptance of evolutionary conceptions in regard to other
orders of facts, especially in regard to the earth and the
solar system ; and, finally, of those few naturalists, like De
Maillet and Robinet, who, before Buffon's day, whispered
evolutionist heresies. ( The history of an idea is like that
of an organism in which cross-fertilisation and composite
inheritance complicate the pedigree.
5. Three old Masters. Among the evolutionists before
Darwin I shall speak of only three Buffon, Erasmus Darwin,
and Lamarck.
BUFFON (1707-1788) was born to wealth and was wedded
to Fortune. He sat in kings' houses, his statue adorned their
gardens. As Director of the Jardin du Rot he had oppor-
tunity to acquire a wide knowledge of animals. He com-
manded the assistance of able collaborateurs, and his own
1 Article "Evolution" (P. Geddes) in Chambers's Encyclopedia.
CH. xvtn The Evolution of Evolution Theories 287
industry was untiring. He was about forty years old when
he began his great Natural History, and he worked till he
was fourscore. He lived a full life, the success of which
we can almost read in the strong confidence of his style.
' Le style, c'est 1'homme meme," he said ; or again, " Le
style est comme le bonheur ; il vient de la douceur de Fame."
Rousseau called him " La plus belle plume du siecle ; "
Mirabeau said, ""Le plus grand homme de son siecle et de
bien d'autres ; " Voltaire first mocked and then praised him ;
and Diderot also eulogised. Buffon was first a man then
a zoologist, which seems to be the natural, though by no
means universally recognised, order of precedence, and we
have pleasant pictures of his handsome person, his magnifi-
cence, his diplomatic manners, and a splendid genius, which
he himself called "a supreme capacity for taking pains."
Buffon's culture was very wide. He had an early
training in mathematics, and translated Newton's Fluxions ;
he seems to have been familiar with the chemistry and
physics of his time ; he was curious about everything.
Before Laplace, he elaborated an hypothesis as to the origin
of the solar system ; before Hutton and Lyell, he realised
that causes like those now at work had in the long past
sculptured the earth ; he had a special theory of heredity
not unlike Darwin's, and a by no means narrow theory of
evolution, in which he recognised the struggle for existence
and the elimination of the unfit, the influence of isolation
and of artificial selection, but especially the direct action of
food, climate, and other surrounding influences upon the
organism. It is generally allowed that there is in BufTon's
writings something of that indefiniteness which often charac-
terises pioneer works, and a lack of depth not unnatural in
a survey so broad, but they exhibit some remarkable illustra-
tions of prophetic genius, and a lively appreciation of
nature.
It is probable that Buffon's treatment of zoology gained
freedom because he wrote in French, having shaken off the
shackles which the prevalent custom of writing in Latin
imposed, and it cannot be doubted that his works did some-
thing to prepare the way for the future reception of the
288 The Study of Animal Life PART iv
doctrine of descent. He had a vivid feeling of the unity
of nature, throwing out hints in regard to the fundamental
similarity of different forms of matter, suggesting that heat
and light are atomic movements, denying the existence of
hard-and-fast lines " Le vivant et 1'animd est une propriete'
physique de la matiere !" protesting against crude distinctions
between plants and animals, and realising above all that
there is one great family of life. Naturalists had been
wandering up and down the valleys studying their charac-
teristic contours ; BufFon took an eagle's flight and saw the
connected range of hills, " 1'enchainement des etres."
ERASMUS DARWIN (1731-1802), grandfather to the
author of the Origin of Species , was a large-hearted, thought-
ful physician, whose life was as full of pleasant eccentricities,
as his stammering speech of wit, and his books of wisdom.
We have pleasant pictures of the philosophical physician
of Lichfield and Derby, driving about in a whimsical un-
stable carriage of his own contrivance, prescribing abundant
food and cowslip wine, rich in good health and generosity.
Comparing his writings with those of Buffon, an acquaint-
ance with which he evidently possessed, we find more
emotion and intensity, more of the poet and none of the
diplomatist. He approached the study of organic life on
the one hand as a physician and physiologist, on the other
hand as a gardener and lover of plants ; and, apart from
poetic conceits, his writings are characterised by a direct-
ness and simplicity of treatment which we often describe as
" common-sense."
He believed that the different kinds of plants and animals
were descended from a few ancestral forms, or possibly
from one and the same kind of " vital filament," and that
evolutionary change was mainly due to the exertions which
organisms made to preserve or better themselves. He
showed that animals were driven to exertion by hunger, by
love, and by the need of protection, and explained their
progress as the result of their endeavours. Buffon under-
rated the transforming influence of action, and laid emphasis
upon the direct influence of surroundings ; Erasmus Darwin
emphasised function, and regarded the influence of the
CH. xviii The Evolution of Evolution Theories 289
environment as for the most part indirect. Let us quote
some conclusions from his Zoonomia (1794):
" Owing to the imperfection of language the offspring is termed
a new animal, but is in truth a branch or elongation of the
parent, since a part of the embyron animal is, or was, a part of the
parent, and therefore in strict language cannot be said to be entirely
new at the time of its production ; and therefore it may retain
some of the habits of the parent-system."
"The fetus or embryon is formed by apposition of new parts,
and not by the distention of a primordial nest of germs included
one within another like the cups of a conjuror."
" From their first rudiment, or primordium, to the termination
of their lives, all animals undergo perpetual transformations ; which
are in part produced by their own exertions in consequence of
their desires and aversions, of their pleasures and their pains, or
of irritations, or of associations ; and many of these acquired forms
or propensities are transmitted to their posterity. "
" As air and water are supplied to animals in sufficient profusion,
the three great objects of desire, which have changed the forms of
many animals by their exertions to gratify them, are those of lust,
hunger, and security."
"This idea of the gradual generation of all things seems to have
been as familiar to the ancient philosophers as to the modern ones,
and to have given rise to the beautiful hieroglyphic figure of the
TTp&Tov yd?, or first great egg, produced by night, that is, whose
origin is involved in obscurity, and animated by fyws, that is, by
Divine Love ; from whence proceeded all things which exist."
On LAMARCK (1744-1829) success did not shine as it
did on the Comte de BufTon or on Dr. Erasmus Darwin.
His life was often so hard that we wonder he did not say
more about the struggle for existence. As a youth of six-
teen, destined for the Church, he rides off on a bad horse
to join the French army, then fighting in Germany, and
bravely wins promotion on his first battle-field. After the
peace he is sent into garrison at Toulon and Monaco,
where his scientific enthusiasm is awakened by the Flora
of the south. Retiring in weakened health from military
service, he earns his living in a Parisian banker's office,
devotes his spare energies to the study of plants, and
writes a Flore fran^aise in three volumes, the publica-
tion of which (1778) at the royal press was secured by
U
290 The Study of Animal Life PART iv
Buffon's patronage. As tutor to Buffon's son, he travels
in Europe and visits some of the famous gardens, and we
can hardly doubt that BufFon influenced Lamarck in many
ways. After much toil as a literary hack and scientific
drudge, he is elected to what we would now call a Professor-
ship of Invertebrate Zoology, a department at that time
chaotic. In 1794 he began his lectures, and each year
brought increased order to his classification and museum
alike. At the same time, however, he was lifting his anchors
from the orthodox moorings, relinquishing his belief in the
constancy of species, following (we know not with what
consciousness) the current which had already borne Buffon
and Erasmus Darwin to evolutionary prospects. In 1802
he published Researches on the Organisation of Living
Bodies ; in 1809 a Philosophic Zoologique\ from 1816-
1822 his Natural History of Invertebrate Animals , a large
work in seven volumes, part of which the blind naturalist
dictated to his daughter. Busy as he must have been with
zoology, his restless intellect found time to speculate it
must be confessed to little purpose on chemical, physical,
and meteorological subjects. Thus he ran an unsuccessful
tilt against Lavoisier's chemistry, and published for ten
years annual forecasts of the weather, which seem to have
been almost always wrong. Nor did Lamarck add to his
reputation by a theory of Hydrogeology, and his scientific
friends who were loyal specialists shrugged their shoulders
more and more over his intellectual knight-errantry.
Poverty also clouded his later years, his treasured
collections had to be sold for bread, his theories made no
headway, his merits were unrecognised. Yet now a La-
marckian school is strong in France and in America, and
even those who deny his doctrines admit that he was one
of the bravest of pioneers.
Of Lamarck's Philosophic Zoologique, Haeckel says,
" This admirable work is the first connected and thoroughly
logical exposition of the theory of descent." And again, he
says, "To Lamarck will remain the immortal glory of
having for the first time established the theory of descent
as an independent scientific generalisation of the first order,
CH. xvni The Evolution of Evolution Theories 291
as the Toundation of the whole of Biology." But the verdict
of the majority of naturalists in regard to Lamarck's doctrines
has not tended to be eulogistic. Cuvier, in his Eloge de M.
de Lamarck delivered before the French Academy in 1832,
said, "A system resting on such foundations may amuse
the imagination of a poet, etc., . . . but it cannot for a
moment bear the examination of any one who has dissected
the hand, the vis'cera, or even a feather." The great Cuvier
was a formidable obscurantist.
But let us hear Lamarck himself:
" Nature in all her work proceeds gradually, and could not pro-
duce all the animals at once. At first she formed only the simplest,
and passed from these on to the most complex."
" The limits of so-called species are not so constant and unvary-
ing as is commonly supposed. Spontaneous generation started
each particular series, but thereafter one form gives rise to another.
In life we should see, as it were, a ramified continuity if certain
species had not been lost."
" The operations of Nature in the production of animals show
that there is a primary and predominant cause which gives to
animal life the power of progressive organisation, of gradually
complicating and perfecting not only the organism as a whole, but
each system of organs in particular. "
" First Law. Life by its inherent power tends continually to
increase the volume of every living body, and to extend the
dimensions of its parts up to a self-regulated limit.
* * Second Law. The production of a new organ in an animal body
results from the occurrence of some new need which continues to
make itself felt, and from a new movement which this need origin-
ates and sustains.
" Third Law. The development of organs and their power of
action are constantly determined by the use of these organs.
"Fourth Law. All that has been acquired, begun, or changed in
the structure of individuals during the course of their life is pre-
served in reproduction and transmitted to the new individuals
which spring from those which have experienced the changes."
These four laws I have cited from Lamarck's Histoire Naturelle t
but in illustration of the emphasis with which he insisted on use
and disuse, I take the following passages, translated by Samuel
Butler, from the Philosophic Zoologique :
" Every considerable and sustained change in the surroundings
of any animal involves a real change in its needs."
292 TJie Study of Animal Life PART iv
"Such change of needs involves the necessity of changed
action in order to satisfy these needs, and, in consequence, of new
habits."
"It follows that such and such parts, formerly less used, are
now more frequently employed, and in consequence become more
highly developed ; new parts also become insensibly evolved in the
creature by its own efforts from within."
"These gains or losses of organic development, due to use or
disuse, are transmitted to offspring, provided they have been com-
mon to both sexes, or to the animals from which the offspring have
descended."
The historian of the evolution of evolution theories
should take account of many workers besides Buffon,
Erasmus Darwin, and Lamarck; of Treviranus (1776-
1837), whose Biology or Philosophy of Living Nature (i 802-
1805) is full of evolutionary suggestions; of Geoffroy St.
Hilaire, who in 1830, before the French Academy of
Science, fought with Cuvier, the fellow-worker of his youth,
an intellectual duel on the question of descent ; of Goethe
who, in his eighty-first year, heard the tidings of Geoffrey's
defeat with an interest which transcended the political
anxieties of the time, and whose own epic of evolution sur-
passes that of Lucretius ; of Oken's speculative mist, amid
which the light of evolutionary ideas danced like a will-o'-
the-wisp ; of many others in whose mind the truth grew if
it did not blossom. But we must now recognise the work
of Charles Darwin. .
6. Darwin. Though the general tenor of Darwin's life
the impression of an industrious open-minded observer
and thinker, the picture of a man full of mercy, kindliness,
and peace was familiar to many, his biography has filled
in those little details which make our impression living.
We see him now, as in a Holbein picture, with all the
paraphernalia of daily pursuit round about him. His high
chair, his orderly shelves, his torn-up reference books, his.
window-sill laboratory, his yellow-back novels, his snuff-
box, and a hundred little touches, make the picture alive.
We learn, too, his methods of laborious but never toilsome
work, and the gradual progress of his thought from the con-
ventionalism of youth to the convictions of matured man-
CH. xviii The Evolution of Evolution Theories 293
hood. We read the curve of his moods, steadier than that
of most men, without any climax of speculative ecstasy, free
from any fall to a depth of pessimism. We hear his own
sincere voice in his simple autobiography, and even more
clearly perhaps in the unconstrainedness of his abundant
letters. There was seldom a great life so devoid of little-
ness, seldom a record of thought so free from subtlety.
There seems to' be almost nothing hid which we could
wish revealed, or uncovered which we could wish hidden.
Darwin's life was as open as the country around his her-
mitage.
Marcus Aurelius gives thanks in his roll of blessings
that he had net been suffered to keep quails ; so Darwin, in
recounting his mercies, does not forget to be grateful for
having been preserved from the snare of becoming a
specialist. From a more partial point of view, we have
reason to be thankful that he became a specialist, not in
one department, but in many. As a disciple of Linnaeus,
he described the species of barnacles in one volume, and
followed in the steps of Cuvier in anatomising them in
another. Of tissues and cells he knew less, being as
regards these items an antediluvian, and outside the guild
of those who dexterously wield the razor, and in so doing
observe the horoscope of the organism. Of protoplasm,
in regard to which modern biology says so much and knows
so little, he was not ignorant, for did he not study the
marvels of the state known as " aggregation " ?
But it is not for special research that men are most
grateful to Darwin. Undoubtedly, if clear insight into the
world around us be esteemed in itself of value, the author
of Insectivorous Plants, The Fertilisation of Orchids, The
Movements of Plants, The Origin of Coral Reefs, The
Formation of Vegetable Mould, etc., runs no risk of being
forgotten. But though our possession of these results swells
the meed of praise, we usually regard them as outside of
Darwin's real work, which, as every one knows, was his
contribution to the theory of organic life.
This contribution was threefold (a) He placed the
theory of descent on a sure basis ; (b) he shed the light
294 The Study of Animal Life PART iv
of this doctrine on various groups of phenomena ; and (c) he
essayed the problem of the factors in evolution.
(a) The man who makes us believe a fact is to us
more important than the original discoverer. And so
Darwin gets credit for inventing the theory of descent,
which in principle is as old as clear thought itself, and in
its biological application was stated a hundred years before
the publication of the Origin of Species (1859). The con-
ception was no new one, but Darwin first made men believe
it. The idea was not his, but he gave it to many. He did
not originate ; he established. He converted naturalists to
an evolutionary conception of the organic world.
(b) Having got people to believe the theory of
descent, the theory of development out of preceding
conditions, Darwin went on to' show how the conception
would illumine all facts to which it was applicable. In his
work on the expression of emotions, and in scattered chap-
ters, he showed how the light might be shed upon the
secrets of mental activity. Whenever it was seen that
the doctrine could justify itself in regard to general organic
life, it was eagerly seized as an organon for the exploration
of special sets of facts. The phoenix revived and flew
croaking amid the smoke of burning systems. How one
discussed the evolution of language, and another that of
industry ; how the natural history of ethics was sketched
by one thinker, and the descent of institutions by another ;
how the conception has forced its way into the cloister
and the political arena, and has even found expression in
theories of literature, art, and religion, is an often-repeated
story.
(c) We have noticed that Buffon, and, let us add, Trevir-
anus, firmly maintained that the direct influence of the
external conditions of life was an important factor in evolu-
tion. We have also seen that Erasmus Darwin and Lamarck
were strongly convinced of the transforming power of use
and disuse. When Charles Darwin began to think and
write on the origin of species, he also recognised the trans-
forming influences of function and of environment. But
with the Buffonian or Lamarckian position he was never
CH. xvin The Evolution of Evolution Theories 295
satisfied ; he advanced to one of his own to the theory of
natural selection, the characteristic feature of Darwinism.
Let us state this theory, which was foreseen by Matthew,
Wells, Naudin, and others, was developed simultaneously
by Darwin and by Alfred Russel Wallace, and has attained
remarkable acceptance throughout the world.
All plants and animals produce offspring which, though
like their parents," usually differ from them in possessing
some new features or variations. These are of more or
less obscure origin, and are often termed fortuitous or in-
definite. | But throughout nature there is a struggle for
existence in which only a small percentage of the organisms
born survive to maturity or reproduction. Those which
survive do so because of the individual peculiarities which
have made them in some way more fit to survive than their
fellows. Moreover the favourable variation possessed by
the survivors is handed on as an inheritance to their off-
spring, and tends to be intensified when the new generation
is bred from parents both possessing the happily advan-
tageous character. This natural fostering of advantageous
variations and natural elimination of those less fit, explain
the general modification and adaptation of species, as well
as the general progress from simpler to higher forms of
life.
This theory that favourable variations may be fostered
and accumulated by natural selection till useful adaptations
result is the chief characteristic of Darwinism. Of this
theory Prof. Ray Lankester says : " Darwin by his discovery
of the mechanical principle of organic evolution, namely, the
survival of the fittest in the struggle for existence, completed
the doctrine of evolution, and gave it that unity and au-
thority which was necessary in order that it should reform
the whole range of philosophy." And again he says : " The
history of zoology as a science is therefore the history of
the great biological doctrine of the evolution of living things
by the natural selection of varieties in the struggle for exist-
ence, since that doctrine is the one medium whereby all
the phenomena of life, whether of form or function, are
rendered capable of explanation by the laws of physics and
296 The Study of Animal Life PART iv
chemistry, and so made the subject-matter of a true science
or study of causes." I have quoted these two sentences
because they illustrate better than any others that I have
seen to what exaggeration enthusiasm for a theory will lead
a strong intellect. But listen to a few sentences from
Samuel Butler, which I quote because they well illustrate
that the critics of Darwinism may also be extreme, and in
the hope that the contrast may be sufficiently interesting to
induce you to think out the question for yourselves.
"Bufifon planted, Erasmus Darwin and Lamarck watered,
but it was Mr. Darwin who said c That fruit is ripe/ and
shook it into his lap. . . . Darwin was heir to a dis-
credited truth, and left behind him an accredited fallacy.
. . . Do animals and plants grow into conformity with
their surroundings because they and their fathers and
mothers take pains, or because their uncles and aunts go
away ? . . . The theory that luck is the main means of
organic modification is the most absolute denial of God
which it is possible for the human mind to conceive. ..."
7. Darwin's Fellow-workers. But we must bring this
historical sketch to a close by referring to four of the more
prominent of Darwin's fellow-workers Wallace, Spencer,
Haeckel, and Huxley.
ALFRED RUSSEL WALLACE, contemporary with Darwin,
not only in years, but in emphasising the truth of evolution-
ary conceptions, and in recognising the fact of natural
selection, has been justly called the Nestor of Biology. No
one will be slow to appreciate the splendid unselfishness
with which he has for thirty years sunk himself in the Dar-
winian theory, or the scientific disinterestedness which leads
him from the very title of his last work x to its close, to
say so little perhaps too little of the important part
which he has played in evolving the doctrine. " It was,"
Romanes says, " in the highest degree dramatic that the
great idea of natural selection should have occurred inde-
pendently and in precisely the same form to two working
naturalists ; that these naturalists should have been country-
men ; that they should have agreed to publish their theory
1 Darwinism, London, 1889.
CH. xviii The Evolution of Evolution Theories 297
on the same day ; and last, but not least, that, through the
many years of strife and turmoil which followed, these two
English naturalists consistently maintained towards each
other such feelings of magnanimous recognition that it is
hard to say whether we should most admire the intellectual
or the moral qualities which, in relation to their common
labours, they have displayed.' 7
Mr. Wallace is a naturalist in the old and truest sense,
rich in a world -wide experience of animal life, at once
specialist and generaliser, a humanist thinker and a social
striver, and a man of science who realises the spiritual
aspect of the world.
He believes in the " overwhelming importance of natural
selection over all other agencies in the production of new
species," differs from Darwin in regard to sexual selection,
to which he attaches little importance, and agrees with
Weismann in regard to the non- inheritance of acquired
characters.
But the exceptional feature in Wallace's scientific philo-
sophy is his contention that the higher characteristics of
man are due to a special evolution hardly distinguishable
from creation.
Wallace finds their only explanation in the hypothesis
of " a spiritual essence or nature, capable of progressive
development under favourable conditions."
HERBERT SPENCER must surely have been an evolution-
ist by birth ; there was no hesitation even in the first strides
he took with the evolution-torch uplifted. A ponderer on
the nature of things, and the possessor of encyclopedic
knowledge, he grasped what was good in Lamarck's work,
and as early as 1852 published a plea for the theory of
organic evolution which is still remarkable in its strength
and clearness. The work of Darwin supplied corroboration
and fresh material, and in the Principles of Biology (i 863-66)
the theory of organic evolution first found philosophic, as
distinguished from merely scientific expression. To Spencer
we owe the familiar phrase "the survival of the fittest,"
and that at first sight puzzling generalisation, " Evolution is
an integration of matter and concomitant dissipation of
298 The Study of Animal Life PART iv
motion, during which the matter passes from an indefinite
incoherent homogeneity to a definite coherent heterogeneity,
and during which the retained motion (energy) undergoes a
parallel transformation." He has given his life to establish-
ing this generalisation, and applying it to physical, biological,
psychological, and social facts. As to the factors in organic
evolution, he emphasises the change-producing influences of
environment and function, and recognises that natural selec-
tion has been a very important means of progress.
ERNST HAECKEL, Professor of Zoology in Jena, and
author of a great series of monographs on Radiolarians,
Sponges, Jellyfish, etc., may be well called the Darwin of
Germany. He has devoted his life to applying the doctrine
of descent, and to making it current coin among the people.
Owing much of his motive to Darwin, he stood for a time
almost alone in Germany as the champion of a heresy.
Before the publication of Darwin's Descent of Man, Haeckel
was the only naturalist who had recognised the import of
sexual selection ; and of his Natural History of Creation
Darwin writes : " If this work had appeared before my
essay had been written, I should probably never have com-
pleted it." His most important expository works are the
above-mentioned Natiirliche Schopfungsgeschichte (ist ed.
1868 ; 8th ed. 1889) ; and his Anthropogenic (1874, trans-
lated as The Evolution of Man). These books are very
brilliantly written, though they offend many by their remorse-
less consistency, and by their impatience with theological
dogma and teleological interpretation. His greatest work,
however, is of a less popular character, namely, the Generelle
Morphologic (2 vols., Berlin, 1866), which in its reasoned
orderliness and clear generalisations ranks beside Spencer's
Principles of Biology.
HUXLEY, by whose work the credit of British schools of
zoology has been for many years enhanced, was one of the first
to stand by Darwin, and to wield a sharp intellectual sword
in defence and attack. No one has fought for the doctrine
of descent in itself and in its consequences with more keen-
ness and success than the author of Marts Place in Nature
(1863), American Addresses, Lay Sermons^ etc., and no one
CH. xviii The Evolution of Evolution Theories 299
has championed the theory of natural selection with more
confident consistency or with more skilfully handled
weapons.
8. The Present State of Opinion. As Wallace says in
the preface to his work on Darwinism, " Descent with
modification is now universally accepted as the order of
nature in the organic world." But, while this is true, there
remains much uncertainty in regard to the way in which the
progressive ascent of life has come about, as to the mechan-
ism of the great nature -loom. The relative importance of
the various factors in evolution is very uncertain. 1
The condition of evolution is variability, or the tendency
which animals have to change. The primary factors of
evolution are those which produce variations, which cause
organic inequilibrium. Darwin spoke of variations as
" fortuitous," " indefinite," " spontaneous," etc., and frankly
confessed that he could not explain how most of them arose.
Ultimately all variations in organisms must be due to
variations in their environment, that is to say, to changes in
the system of which organisms form a part. But this is
only a general truism.
1 All naturalists, however uncertain in regard to the factors in
evolution, accept the doctrine of descent the general conception of
evolution as a theory which has justified itself. It is not indeed so
demonstrable as is the doctrine of the conservation of energy, but it is
almost as confidently accepted. Few naturalists, however, have
attempted any philosophical justification of their belief. This is strange,
since it should surely give pause to the dogmatic evolutionist to reflect
that his own theory has been evolved like other beliefs, that his
scientific demonstration of it rests upon assumptions which have also
been evolved, that the entire system of evolutionary thought must be a
phase in the development of opinion, that, in short, he cannot be
dogmatic without being self-contradictory. See A. J. Balfour's Defence
of Philosophic Doubt, pp. 260-274 (London, 1879). In regard to the
philosophical aspects of the doctrine of evolution see Prof. Knight's
essay on " Ethical Philosophy and Evolution" in his Studies in Philo-
sophy and Literature (Lond. 1879), and, with additions, in Essays in
Philosophy (Boston and New York, 1890) ; Prof. St. George Mivart's
Contemporary Evolution (Lond. 1876) ; E. von Hartmann's Wahrheit
und Irrthum im Darwinismus ; an article by Prof. Tyndall on ' ' Vir-
chow and Evolution" in Nineteenth Century ', Nov. 1878 ; and articles
on " Evolution" by Huxley and Sully in Encyclopedia Britannica.
300 TJie Study of Animal Life PART iv
There are evidently three direct ways in which organic
changes may be produced : ( i ) From the nature of the
organism itself; i.e. from constitutional or germinal peculiar-
ities which are ultimately traceable to influences from
without ; (2) from changes in its functions or activity, in
other words, from use and disuse ; or (3) from the direct
influence of the external conditions of life food, temperature,
moisture, etc.
Thus some naturalists follow Buffon in emphasising the
moulding influence of the environment, or agree with
Lamarck in maintaining that change of function produces
change of structure. But at present the tide is against
these opinions, because of the widespread scepticism as to
the transmissibility of characters thus acquired.
Those who share this scepticism refer the origin of
variations to the nature of the organism, to the mingling
of the two different cells from which the individual life
begins, to the instability involved in the complexity of the
protoplasm, to the oscillating balance between vegetative
and reproductive processes, and so on.
One prevalent opinion regards variations as arbitrary
sports in " a chapter of accidents," but according to the
views of a minority variations are for the most part definite,
occurring in a few directions, fixed by the constitutional
bias of the organism. The minority are " Topsian " evolu-
tionists who believe that the modification of species has
taken place by cumulative growth, influenced by function
and environment, and pruned by natural selection. To the
majority the theory that new species result from the action
of natural selection on numerous, spontaneous, indefinite
variations, is the " quintessence of Darwinism " and of truth.
Until we know much more about the primary factors
which directly cause variations it will not be possible to
decide in regard to the precise scope of natural selection
and the other secondary factors which foster or accumulate,
thin or prune, which in short establish a new organic
equilibrium. The argument has been too much in regard
to possibilities, too little in regard to observed facts of
variation.
CH. xvin The Evolution of Evolution TJieories 301
The secondary factors of evolution may be ranked under
two heads :
i. Natural Selection, or the survival of the fittest in the
struggle for existence, and 2. Isolation, or the various means
by which species tend to be separated into sections which
do not interbreed.
Natural selection is a phrase descriptive of the course of
nature, of the survival of the fit and the elimination of the
unfit in the struggle for existence. It involves on the one
hand the survival, i.e. the nutritive and reproductive success
of the variations fittest to survive in given conditions, and
on the other hand the destruction or elimination of forms
less fit. Suitable variations pay ; nature or natural selection
justifies and fosters them. Maternal sacrifice or cunning
cruelty, the milk of animal kindness or teeth strong to
rend, distribution in space or rate of reproduction, are all
affected by natural selection. But it is another thing to say
that all the adaptations and well-endowed species that we
know have been produced by the action of natural selection
on fortuitous, indefinite variations. This is what Samuel
Butler calls the " accredited fallacy."
Secondly, there seem to be a great many ways by which
a species may be divided into two sections which do not
interbreed, and if this isolation be common it must help
greatly in divergent evolution.
Thus Romanes, who has been the chief exponent of the
importance of isolation, on which Gulick has also insisted,
says : " Without isolation, or the prevention of free inter-
crossing, organic evolution is in no case possible. It is
isolation that has been ' the exclusive means of modifica-
tion,' or more correctly, the universal condition to it.
Heredity and variability being given, the whole theory of
organic evolution becomes a theory of the causes and con-
ditions which lead to isolation."
302 The Sfady of Animal Life PART iv
SUMMARY OF EVOLUTION THEORIES.
Variations all ultimately due to External Influences.
Direct
Organism al,
Use and
O
C/Q*
action of the
constitutional,
disuse and
5'
environment
congenital,
change
produces
or germinal
of function
<-J
environ-
variations
produce
p
i-!
mental
may be either
functional
variations,
definite or indefinite.
variations
|
F
which
(certainly
wh ich,
if trans missible,
transmis-
sible).
if trans missible,
may
By the By natural
may
accumulate
persistence selection in
accumulate
as
of the original the struggle
as
o
environ-
conditions for existence
functional
*.
mental
these may these may
modi-
o
modifications
grow into give rise to
fications
of
new new
of
C/2
n>
species.
species. species.
species.
o
*
#
Allcases
may be affect ed by
"isolation,"
PH
The process of natural selection will affect all cases, but is
less essential for those marked * ,
CHAPTER XIX
THE INFLUENCE OF HABITS AND SURROUNDINGS
i. The Influence .of Function 2. The Influence of Surroundings
3. Our own Environment
i. The Influence of Function. A skilled observer can
often discern a man's occupation from his physiognomy,
his shoulders, or his hands. In some unhealthy occupa-
tions the death-rate is three times that in others. Disuse
of such organs as muscles tends to their degeneration, for
the nerves which control them lose their tone and the
circulation of blood is affected ; while on the other hand
increased exercise is within certain limits associated with
increased development. A force de forger on devient
forgeron.
If we knew more about animals we might be able to cite
many cases in which change of function produced change of
structure, but there are few careful observations bearing on
this question.
Even if we could gather many illustrations of the
influence of use and disuse on individual animals, we should
still have to find out whether the precise characters thus
acquired by individuals were transmissible to the offspring,
or whether any secondary effects of the acquired characters
were transmissible, or whether these changes had no effect
upon succeeding generations. As there are few facts to argue
from, the answers given to these questions are not reliable.
It is easy to find hundreds of cases in which the constant
304 The Study of Animal Life PART iv
characters of animals may be hypothetically interpreted as
the result of use or disuse. Is the torpedo-like shape of
swift swimmers due to their rapid motion through the
water, do burrowing animals necessarily become worm-like,
has the giraffe lengthened its neck by stretching it, have
hoofs been developed by running on hard ground, are horns
responses to butting, are diverse shapes of teeth the results
of chewing diverse kinds of food, are cave-animals blind
because they have ceased to use their eyes, are snails lop-
sided because the shell has fallen to one side, is the
asymmetry in the head of flat fishes due to the efforts made
by the ancestral fish to use its lower eye after it had formed
the habit of lying flat on the bottom, is the woodpecker's
long tongue the result of continuous probing into holes, are
webbed feet due to swimming efforts, has the food-canal in
vegetarian animals been mechanically lengthened, do the
wing bones and muscles of the domesticated duck compare
unfavourably with those of the wild duck because the habit
of sustained flight has been lost by the former ?
But these interpretations have not been verified ; they
are only probable. " It is infinitely easy," Semper says,
"to form a fanciful idea as to how this or that fact may be
hypothetically explained, and very little trouble is needed to
imagine some process by which hypothetical fundamental
causes equally fanciful may have led to the result which
has been actually observed. But when we try to prove by
experiment that this imaginary process of development is
indeed the true and inevitable one, much time and laborious
research are indispensable, or we find ourselves wrecked on
insurmountable difficulties."
Not a few naturalists believe in the inherited effects
of functional change mainly because the theory is simple
and logically sufficient. If use and disuse alter the
structure of individuals, if the results are transmitted and
accumulate in similar conditions for generations, we require
no other explanation of many structures.
The reasons why not a few naturalists disbelieve in the
inherited effects of functional change are (i) that definite
proof is wanting, (2) that it is difficult to understand how
CH. xix Influence of Habits and Surroundings 305
changes produced in the body by use or disuse can be
transmitted to the offspring, (3) that the theory of the
accumulation of (unexplained) favourable variations in the
course of natural selection seems logically sufficient. I
should suspend judgment, because it is unprofitable to argue
when ascertained facts are few.
But if you like to argue about probabilities, the following
considerations may be suggestive :
The natural powers of animals horses, dogs, birds, and
others can be improved by training and education, and
animals can be taught tricks more or less new to them, but
we have no precise information as to any changes of
structure associated with these acquirements.
Individual animals are sometimes demonstrably affected
by use or disuse. Thus Packard cites a few cases in which
some animals usually with normal eyes have had these
affected by disuse and darkness ; he instances the variations
in the eyes of a Myriapod and an Insect living in partial
daylight near the entrance of caves, the change in the eyes
of the common Crustacean Gammarus pidex after confine-
ment in darkness, the fact that the eyes of some other
Crustaceans in a lake were smaller the deeper the habitat.
There are many more or less blind animals, and Packard
says " no animal or series of generations of animals, wholly
or in part, can lose the organs of vision unless there is some
appreciable physical cause for it." If so, it is probable that
the appreciable physical cause has been a direct factor in
producing the blindness.
Not a few young animals have structures, such as eyes
and legs, which are not used and soon disappear in adult
life. Thus the little crab Pinnotheres, which lives inside
bivalves and sea -cucumbers, keeps its eyes until it has
established itself within its host. Then they are completely
covered over and degenerate. The same is true of many
internal parasites, and Semper concludes that " we must
refer the loss of sight to disuse of the organ." Perhaps the
same is true of some blind cave-animals, in which the eyes
are less degenerate in the young, and of the mole, whose
embryos have between the eyes and the brain normal optic
X
306 The Study of Animal Life PART iv
nerves which usually degenerate in each individual life-
time.
The theory that many structures in animals are due to
the inherited results of use and disuse has this advantage,
that it suggests a primary cause of change, whereas the
other theory assumes the occurrence of favourable variations
and proceeds to show how they might be accumulated in
the course of natural selection, that is to say by a secondary
factor in evolution.
When we find in a large number of entirely distinct
forms that the same habit of life is associated with the same
peculiarities, there is a likelihood that the habit is a direct
factor in evolving these. Thus sluggish and sedentary
animals in many different classes tend to develop skeletons
of lime, as in sponges, corals, sedentary worms, lamp-shells,
Echinoderms, barnacles, molluscs. Professor Lang has re-
cently made a careful study of sedentary creatures, and this
result at least is certain that the same peculiarity often occurs
in many different types with little in common except that
they are sedentary. But till one can show that sedentary life
necessarily involves for instance a skeleton of lime or some-
thing equivalent, we are still dealing only with probabilities.
2. The Influence of Surroundings. In ancient times
men saw the threads of their life passing through the hands
of three sister-fates of one who held the distaff, of another
who offered flowers, and of a third who bore the abhorred
shears of death. In Norseland the young child was visited by
three sister Norns, who brought characteristic gifts of past,
present, and future, which ruled the life as surely as did
the hands of the three Fates. So too in days of scientific
illumination, we think of the dread three, but, clothing our
thoughts in other words, speak of life as determined by the
organism's legacy or inheritance, by force of habit or
function, and by the influences of external conditions or
environment. What the living organism is to begin with,
what it does or does not in the course of its life, and what
surrounding influences play upon it, these are the_ three
Fates, the three Norns, the three Factors of Life. 'Organ-
ism, function, and environment are the sides of the bio-
CH. xix Influence of Habits and Surroundings 307
logical prism. Thus we try to analyse the light of life. But
inheritance in its widest sense is only another name for the
organism itself, and function is simply the organism's activity.
The organism is real ; the environment is real, in it we live
and move ; function consists of action and reaction between
these two realities. Yet the capital which the organism
has to begin with is very important ; conduct has some
relation to character, and function to structure ; the sur-
roundings the dew of earth and the sunshine of heaven
silently mould the individual destiny.
\^ A living animal is almost always either acting upon its
surroundings or being acted upon by them, and life is the
relation between two variables a changeful organism and
a changeful environment^ And since animals do not and
cannot live in vacuo, they should be thought of in relation
to their surroundings. You may kill the body and cut it to
pieces, and the result may be interesting, but you have lost
the animal just as you lose a picture if you separate figure
from figure, and all from the associated landscape or interior.
The three Fates are sisters, they are thoroughly intelligible
only as a Trinity.
The most certain of all the relations between an organism
and its surroundings is the most difficult to express. We
see a small whirlpool on a river, remaining for days or
weeks apparently constant, with the water circling round
unceasingly, bearing the same flotsam of leaves and twigs.
But though the eddy seems the same for many days, it is
always changing, currents are flowing in and out ; it is the
constancy of the stream and its bed which produces the
apparent constancy of the whirlpool. So, in some measure,
is it with an animal in relation to its surroundings. Streams
of matter and energy are continually passing in and out.
Though we cannot see it with our eyes, the organism is
indeed a whirlpool. It is ever being unmade and remade,
and owes much of its apparent constancy to the fact that
the conditions in which it lives the currents of its stream
are within certain limits uniform.
But as we cannot understand the material aspects of an
animal's life without considering the streams of matter and
.
308 The Study of Animal Life PART iv
energy which pass in and out, neither can we understand
its higher life apart from its surroundings.
To attempt a natural history of isolated animals, whether
alive or dead, is like trying to study man apart from society.
For it is only when we know animals as they live and move
that we discover how clever, beautiful, and human they
are. Thus Gilbert White's Selborne is a natural history ; and
therefore we began our studies with the natural life of
animals their competition and helpfulness, their adaptations
to diverse kinds of haunts, their shifts and tricks, their
industries and their loves.
At present, however, we have to do with the relation
between external and internal changes. We must find out
what the environment of an organism is, and what power it
has. In a smithy we see a bar of hot iron being hammered
into useful form. Around a great anvil are four smiths
with their hammers. Each smites in his own fashion as
the bar passes under his grasp. The first hammer falls,
and while the bar is still quivering like a living thing it
receives another blow. This is repeated many times till the
thing of use is perfected. By force of smiting one becomes
a smith, and by dint of blows the bar of iron becomes
an anchor. \ So is it with the organism. In its youth
especially, it cT5mes under the influence of nature's hammers ;
it may become fitter for life, or it may be battered out of
existence altogether. vLet us try to analyse the various
environmental factors, y
(a) Pressures. First we may consider those lateral and
vertical pressures due to air or water currents and to
the gentle but potent force of gravity. The shriek of the
wind as it prunes the trees, the swish of the water as it
moulds the sponges and water-leaves, illustrate the tunes of
those pressure-hammers. Under artificial pressure embryos
have been known to broaden ; even the division of the egg is
affected by gravity ; water currents mould shells and corals.
The influence of want of room must also be noticed, for by
artificial overcrowding naturalists have slowed the rate of
development and reared dwarf broods ; and the rate of
human mortality sometimes varies with the size of the
CH. xix Influence of Habits and Surroundings 309
dwelling. It is difficult, however, to abstract the influence
of restricted space from associated abnormal conditions.
(b) Chemical Influences. Quieter, but more potent, are
the chemical influences which damp or fan the fire of life,
which corrode the skin or drug the system, which fatten or
starve, depress or stimulate. Along with these we must
include that most important factor food.
When a lighted piece of tinder is placed in a vessel
full of oxygen it burns more actively. Similarly, super-
abundance of oxygen makes insects jump, makes the
simplest animals more agile, and causes the " phosphores-
cent " lights of luminous insects to glow more brightly ;
and young creatures usually develop more or less rapidly
according as the aeration is abundant or deficient. The
most active animals birds and insects live in the air and
have much air in their bodies ; sluggish animals often live
where oxygen is scarce ; changes in the quality of the
atmosphere may have been of importance in the historical
evolution of animals. Fresh air influences the pitch of
human life, and lung diseases increase in direct ratio to
the amount of crowded indoor labour in an area.
By keeping tadpoles in unnatural conditions the usual
duration of the gilled stage may be prolonged for two or three
years. The well-known story of the Axolotl and the Ambly-
stoma is suggestive but not convincing of the influence of
surroundings. These two newt-like Amphibians differ slightly
from one another, in this especially that the Axolotl retains
its gills after it has developed lungs, while the Amblystoma
loses them. Both forms may reproduce, and they were
originally referred to different genera. But some Axolotls
which had been kept with scant water in the Jardin des
Plantes in Paris turned into the Amblystoma form ; the two
forms are different phases of the same animal. It was a
natural inference that the Axolotls were those which had
remained or had been kept in the water, the Amblystoma
forms were those which got ashore. But both kinds may
be found in the water of the same lake and the metamor-
phosis may take place in the water as well as on the shore.
For these and for other reasons this oft -told tale is not
310
The Study of Animal Life PART iv
cogent. In another part of this book I have given examples
of the state of lifelessness which drought induces in some
FIG. 64. Axolotl (in the water) and Amblystoma (on the land).
simple animals, and from which returning moisture can
after many days recall them.
Changes may also be due to the chemical composition
of the medium, as was established by the experiments of
FIG. 65. Side view of male Artemia salina (enlarged).
(From Chambers's Encyclofi.)
Schmankewitsch on certain small Crustaceans. Among the
numerous species of the brine-shrimp Artemia^ the most
unlike are A. salina and A. milhausenii\ they differ in the
CH. xix Influence of Habits and Surroundings 311
shape and size of the tail and in the respiratory appendages
borne by the legs ; they are not found together, but live in
pools of different degrees of saltness. Now Schmankewitsch
took specimens of A. salina which live in the less salt water,
FIG. 66. Tail-lobes of Artemia salina (to the left) and of A Hernia milhausenii
(to the right) ; between these four stages in the transformation of the one into
the other. (From Chambers's Encyclop. ; after Schmankewitsch.)
added salt gradually to the medium in which they were
living, and in the course of generations turned them into
A. milhausenii. He also reversed the process by freshening
the water little by little. Moreover, he accustomed A. salina
to entirely fresh water, and then found that the form had
changed towards that of a related genus, Branchipus. This
last step has been adversely criticised, but it is allowed that
one species of brine-shrimp was changed into another.
Many interesting experiments have been made on the
effect of chemical reagents on cells, but these are perhaps
of most interest to the student of drugs. Still the fact that
the form of a cell and its predominant phase of activity
may be entirely changed in this way is important, especially
when we remember that it was in single cells that life first
began, and is now continued. Even Weismann agrees with
Spencer's conclusion that " the direct action of the medium
was && primordial factor of organic evolution."
To Claude Bernard, the main problem of evolution
seemed to be concerned with variations in nutrition :
" L'evolution, c'est 1'ensemble constant de ces alternatives
de la nutrition ; c'est la nutrition considered dans sa
realite, embrasse'e d'un coup d'ceil a travers le temps.' 7
John Hunter and others have shown how the walls of the
312 The Study of Animal Life PART iv
stomach of gulls and other birds may be experimentally
altered by change of diet, and the same is seen in nature
when the Shetland gull changes from its summer diet of
grain to its winter diet of fish. The colours of birds' feathers,
as in canaries and parrots, are affected by their food. A
slight difference in the quantity and quality of food deter-
mines whether a bee -grub is to become a queen or a
worker, royal diet evolving the reproductive queen, sparser
less rich diet evolving the more active but unfertile worker.
Abundant food favours the production of female offspring,
while sparser food tends to develop males. Thus, in frogs,
the proportion of the sexes is normally not very far from
equal ; in three lots of tadpoles an average of 5 7 per hun-
dred became females, 43 males. But Yung has shown that
the nutrition of the tadpoles has a remarkable influence on
the sex of the adults. In a set of which one half kept in
natural conditions developed into 54 females to 46 males,
the other half fed with beef had 78 females to 22 males.
In a second set of which one half left to themselves
developed 61 females to 39 males, the other half, fed with
fish, had 8 1 females to 19 males. Finally, in a third set,
of which one half in natural conditions developed 56 females
to 44 males, the other half, to which the especially nutritious
flesh of frogs was supplied, had no less than 92 females
to 8 males.
When food is abundant, assimilation active, and income
above expenditure, the animal grows, and at the limit of
growth in lower animals asexual multiplication occurs.
Checked nutrition, on the other hand, favours the higher
or sexual mode of multiplication. Thus the gardener
prunes the roots of a plant to get better flowers or repro-
ductive leaves. The plant-lice or Aphides, which infest
our pear-trees and rose-bushes, well illustrate the combined
influence of food and warmth. All through the summer,
when food is abundant and the warmth pleasant, the
Aphides enjoy prosperity, and multiply rapidly. For an
Aphis may bring forth young every few hours for days
together, so rapidly that if all the offspring of a mother
Aphis survived, and multiplied as she did, there would
CH. xix Influence of Habits and Surroundings 313
in the course of a year be a progeny which would weigh
down 500,000,000 stout men. But all through the
summer these Aphides are wholly female, and therefore
wholly parthenogenetic ; no males occur. In autumn, how-
ever, when hard times set in, when food is scarcer, and the
weather colder, males are born, parthenogenesis ceases,
ordinary sexual reproduction recurs. Moreover, if the
Aphides be kept i-n the artificial summer of a greenhouse,
as has been done for four years, the parthenogenesis con-
tinues without break, no males being born to enjoy the
comforts of that environment. Periods of fasting occur
in the life -history of many animals, and these are very
momentous and progressive periods in the lives of some,
for the tadpole fasts before it becomes a frog, and the
chrysalis before it becomes a butterfly. Lack of food, how-
ever, may stunt development, as we see every day in the
streets of our towns.
(c) Radiant Energy. Of the forms of radiant energy
which play upon the organism, we need take account only
of heat and light, for of electrical and magnetic influence
the few strange facts that we know do not make us much
wiser.
We know that increased warmth hastens motion, the
development of embryos, and the advent of sexual maturity.
An Infusorian (Stylonichia) studied by Maupas was seen
to divide once a day at a temperature of 7-io C., twice
at io-i5, thrice at I5-2O, four times at 2o-24, five
times at 24-27 C. At the last temperature one Infusorian
became in four days the ancestor of a million, in six days
of a billion, in seven days and a half of 100 billions, weigh-
ing 100 kilogrammes. By consummately patient experi-
ments, Dallinger was able to educate Monads which lived
normally at a temperature of 65 Fahr., until they could
flourish at 158 Fahr.
Cold has generally a reverse action, checking activity,
producing coma and lifelessness, diminishing the rate of
development, tending to produce dwarf or larva-like forms.
The cold of winter acting through the nervous system
changes the colour of some animals, like Ross's lemming,
314 The Study of Animal Life PART iv
to advantageous white. Not a few animals vary slightly
with the changing seasons. Thus many cases are known
where a butterfly produces in a year more than one brood,
iter form
larcellus)*
y v
FIG. 67. Seasonal dimorphism of Papilio ajax ; to the left the win
(variety Telamonides\ to the right the summer form (variety Ma
(From Chambers's Encyclop. ; after Weismann.)
of which the winter forms are so different from those born
in summer that they have often been described as different
species. It is possible that this is a reminiscence of past
climatic changes, such as those of the Ice Ages, as the
FIG. 68. Seasonal changes of the bill in the puffin (Fratcrcuta arctictt)\ to the
left the spring form, to the right .the winter form, both adult males. (After
Bureau.)
result of which a species became split up into two varieties.
Thus Araschnia levana and Araschnia prorsa are respect-
ively the winter and summer forms of one species. In the
en. xix Influence of PI ab its and Surroundings 315
glacial epoch there was perhaps only A. levana, the winter
form ; the change of climate has perhaps evolved the
summer variety A. prorsa. Both Weismann and Edwards
have succeeded, by artificial cold, in making the pupae which
should become the summer A. prorsa develop into the winter
A. levana. Nor can we forget the seasonal moulting and
the subsequent change of the plumage in birds, so marked
in the case of the "ptarmigan, which moults three times in
the year. In the puffins even the bill is moulted and
appears very different at different seasons. But in these
last cases the influence of environment must be very
indirect.
Light is very healthful, but it is not easy to explain its
precise influence. Our pulses beat faster when we go out
into the sunlight. Plants live in part on the radiant
energy of the sun, and perhaps some pigmented animals do
the same. Perhaps the hundreds of eyes which some mol-
luscs have are also useful in absorbing the light. It is also
possible that light has a direct influence on the formation of
some animal pigments, as it seems to have in the develop-
ment of chlorophyll. We know, from Poulton's experiments,
that the light reflected from coloured bodies influences the
colouring of caterpillars and pupae, but this influence seems
to be subtle and indirect, operating through the nervous
system. It is also certain that living in darkness tends to
bleach some animals, and it is probable that the absence
of light stimulus has a directly injurious effect upon the
eyes of those animals which live in caves or other dark
places. But I have already explained why dogmatism in
regard to these cases should be avoided.
One case of the influence of light seems very instructive.
It is well known that flat fishes like flounders, plaice, and
soles lie or swim in adult life on one side. This lower side
is unpigmented ; the upper side bears black and yellow
pigment-containing cells.
One theory of the presence of pigment on the upper
side and its absence on the other is that the difference is
a protective adaptation evolved by the natural selection of
indefinite variations. But it is open to question whether the
316 The Study of Animal Life PART iv
characteristic is so advantageously protective as is usually
imagined : thus the coloured upper side in soles is very
often covered with a layer of sand. Soles come out most
at night, most live at depths at which differences of colour
are probably indistinct. In shallower water the advantage
is likely to be greater, though the white under-side slightly
exposed as the fish rises from the bottom may attract atten-
tion disadvantageously. Moreover, if we find in a large
number of different animals that the side away from the
light is lighter than that which is exposed, and if we can
show that this has in many cases no protective advantage
whatever and I believe that a few hours' observation will
convince you that both my assumptions are correct then
there is a probability that the absence of light has a direct
influence on the absence of pigment.
But we are not left to vague probabilities ; Mr. J. T.
Cunningham has recently made the crucial experiment of
illuminating the under sides of young flounders. Out of
thirteen, whose under-sides were thus illumined by a mirror
for about four months, only three failed to develop black
and yellow colour-cells on the skin of the under-sides. It
is therefore likely that the normal whiteness of the under-
sides is due in some way to the fact that in nature little light
can fall on them, for they are generally in contact with the
ground.
(d) Animate Surroundings. We have given a few
instances showing how mechanical or molar pressures,
chemical and nutritive influences, and the subtler physical
energies of heat and light, affect organisms. There is a
fourth set of environmental factors the direct influence of
organism upon organism. In a previous chapter we spoke
of the indirect influences different kinds of organisms exert
on one another, and these are most important, but there are
also results of direct contact.
Much in the same way as insects produce galls on
plants, so .sea -spiders (Pycnogonidce) affect hydroids, a
polype deforms a sponge, a little worm (Myzostoma) makes
galls on Crinoids. Prof. Giard has described how certain
degenerate Crustaceans parasitic on crabs injuriously affect
CH. xix Influence of Habits and Surroundings 317
their hosts, and some internal parasites produce slight
modifications of structure. Interesting also are the shelters
or domatia of some plants, within which insects and mites
find homes.
We can speak more confidently about the influence of
surroundings than we could in regard to the influence of
use and disuse, because the ascertained facts are more
numerous. Those -interested in the theoretical importance
of these facts should attend to the following considerations.
It is essential to distinguish between cases in which
we know that external conditions influence the organism
and those in which we think they may have done so. Thus
it is probable that the degeneracy and other peculiarities of
many parasites are results of external influence and of
feeding, and also in part of disuse, but we cannot state
this as a fact.
Most of the observations on the influence of external
conditions give us no information as to the transmissi-
bility of the results. It is not enough to know that a
peculiarity observed to occur in peculiar surroundings was
observed to recur in successive generations living in the
same surroundings. For (i) it might be an indefinite
variation a sport due to some germinal peculiarity
which happened to suit. In such a case it would be
transmissible, but it would not be a change due to the
environment. And (2) even when it has been proved that
the peculiarity is due to the direct influence of the environ-
ment, and observed to recur in successive generations, still
its transmissibility is not proven, for it may be hammered
on each successive generation as it was on the first. We
can say little about the transmissibility or evolutionary
importance of changes of structure due to surroundings
because most of the observations were made before the
scepticism as to the inheritance of acquired characters
became dominant. Only in a few cases, such as that of the
brine-shrimps, was the cumulative influence traced through
many generations. In dearth of facts we should not be
confident, but eager for experiment.
Surroundings may influence the organism in varying
318 The Study of Animal Life PART iv
degrees. There may be direct results, rapid parries after
thrusts, or the results may be indirect ; they may affect the
organism visibly in the course of one generation, or only
after several have passed.
Some animals are more susceptible and more plastic
than others. Young organisms, such as caterpillars and
tadpoles, are more completely in the grasp of their environ-
ment than are the adults. Thus Treviranus, who believed
very strongly in the influence of surroundings, distinguished
two periods of vita minima in youth and in old age
during which external conditions press heavily, from the
period of vita maxima in adult life when the organism
is more free. To some kinds of influence, e.g. mechanical
pressures, passive and sedentary organisms such as sponges,
corals, shell-fish, and plants, are more susceptible than are
those of active life. And it is during a period of quiescence
that surrounding colour tells on the sensitive caterpillars.
3. Our own Environment. The human organism, like
any other, may be modified by its environment, for we
lead no charmed life. Those external influences which
touch body and mind are to us the more important, since
we have them to some extent within our own hands, and
because our lives are relatively long. Even if the changes
thus wrought upon parents are not transmissible, it is to
some extent possible for us to secure that our children grow
up open to influences known to be beneficial, sheltered from
forces known to be injurious.
As the influence of surroundings is especially potent on
young things such as caterpillars and tadpoles all care
should be taken of the young child's environment during
the earliest months and years, when the grip that externals
have is probably much greater than is imagined by those
who believe themselves emancipated from the tyranny of
the present. 1
As passive organisms are more in the thrall of their
surroundings than are the more active, we feel the import-
ance of beauty in the home, that the organism may be
1 Cf. Matthew Arnold's poem, " The Future," and Walt Whitman's
" Assimilations."
CH. xix Influence of Habits and Surroundings 319
saturated with healthful influence during the periods in
which it is most susceptible. The efforts of Social Unions,
Kyrle Societies, Verschonerungs-Vereine, and the like, are
justified not only by their results, 1 but by the biological
facts on which they more or less unconsciously depend.
There would be more progress and less invidious com-
parison of ameliorative schemes, if we realised more vividly
that the Fates are three. Though it is not easy to appre-
ciate the three sides of a prism at once, of what value is
liberty on an ash-heap, or equality in a hell, or fraternity
among an overpopulated community of weaklings ? Organ-
ism, function, and environment must evolve together, and
surely they shall.
Poets have often compared human beings to caterpillars ;
it may be that no improvement in constitutions, functions,
or surroundings will make us winged Psyches, yet it may be
possible for us to be ennobled like those creatures which in
gilded surroundings became golden. Surely art is warranted
by the results of science, as these in time may justify them-
selves in art.
1 Ideally stated in Emerson's well-known poem of "Arl\"
CHAPTER XX
HEREDITY
I. The Facts of Heredity 2. Theories of Heredity : theological,
metaphysical, mystical, and the hypothesis of pangenesis
3. The Modern Theory of Heredity 4. The Inheritance of
Acquired Characters 5. Social and Ethical Aspects 6. Social
Inheritance
WE have spoken of the three Fates which were believed to
determine of what sort a life should be. With the decay
of poetic feeling, and in the light of common science, the
forms of the three sisters have faded. But they are realities
still, for men are thinking more and more vividly about the
factors of life, which to some are " powerful principles,"
to others living and personal, to others unnameable.
Biologists speak of them as Heredity, Function, and En-
vironment : the capital with which a life begins, the
interest accruing from the investment of this in varied vital
activities, and the force of circumstances. But while it is
useful to think of Heredity, Function, and Environment as
the three fates, we must not mystify matters by talking as
if these were entities acting upon the organism. They
are simply aspects of the fact that the animal is born and
lives. The inheritance is the organism itself, and heredity
is only a name for the relation between successive genera-
tions. Moreover, the function of an organism depends
upon the nature of the organism, and so does its suscep-
tibility to influences from without,
I would at present define heredity as the organic relation
CHAP, xx Heredity 321
between successive generations, choosing this definition
because it is misleading to talk about "heredity" as a
" basal principle in evolution," as a " great law," as a
" power," or as a " cause." When I call heredity a
" Fate," it is plain that I speak fancifully, but " principle"
and " law" are dangerous words to play with. We cannot
think of life without this organic relation between parents
and offspring, and had species been created instead of being
evolved there would still be heredity.
i. The Facts of Heredity. An animal sometimes
arises as a bud from its parent, and in rare cases from an
egg which requires no fertilisation, but apart from these
exceptions, every animal develops from an egg-cell with
which a male-cell has united in an intimate way. The
egg-cell supplies most of the living matter, but the nucleus
of the fertilised egg-cell is formed in half from the nucleus
of the immature ovum, in half from the nucleus of the
spermatozoon. Let us emphasise this first fact that each
parent contributes the same amount of nuclear material to
the offspring, and that this nuclear stuff is very essential.
Another fact is more obvious, the offspring is very like
its kind. One of the first things that people say about an
infant is that it is like its father or its mother, and the
assertion does not arouse any surprise, although the truer
verdict that the infant is like any other of the same race is
received with contempt. But every one admits that " like
begets like."
This likeness between offspring and parent is often far
more than a general resemblance, for peculiar features and
minute idiosyncrasies are frequently reproduced. Yet one
must not assume that because a child twirls his thumbs
in the same way as his father did the habit has been
inherited. For peculiar habits and structures may readily
reappear by imitation, or because the offspring grow up in
conditions similar to those in which the parents lived.
Abnormal as well as normal characters, " natural " to
the parents, may reappear in their descendants, and the list
of weaknesses and malformations which may be transmitted
is long and grim. But care is required to distinguish
Y
322 The Study of Animal Life PART iv
between reappearance clue to inheritance and reappearance
due to similar conditions of life.
Then there is a strange series of facts showing that an
organism may reproduce characteristics which the parents
did not exhibit, but which were possessed by a grandparent
or remoter ancestor. Thus a lizard in growing a new
tail to replace one that has been lost has been known to
grow one with scales like those of an ancestral species. To
find out a lizard's pedigree, a wit suggests that we need only
pull off its tail. When such ancestral resemblance in ordi-
FIG. 69. Devonshire pony, showing the occasional occurrence of ancestral
stripes. (From Darwin.)
nary generation is very marked, we call it " atavism " or
u reversion," but of this there are many degrees, and
abnormal circumstances sometimes force reversion even
upon an organism with a normal inheritance. A boy
" takes after his grandfather " ; a horse occasionally exhibits
stripes like those of a wild ancestor ; a blue pigeon like the
primitive rock-dove sometimes turns up unexpectedly in a
pure breed ; or a cultivated flower reverts to the simpler
and more normal wild type. So children born during
famine sometimes show reversions, and some types of
criminal and insane persons are to be thus regarded.
CHAP, xx Heredity 323
But every animal is usually a little different from its
parents, and except in cases of " identical twins" cannot be
mistaken for one of its fellow-offspring. The proverbial
" two peas " may be very unlike. Organisms are variable,
and this is natural, for life begins in the intimate
mingling of two units of living matter perhaps very dif-
ferent and certainly very complex. The relation between
successive generations is such that the offspring is like
its parents, but various causes producing change diminish
this likeness, so that we no longer say a like begets like,"
but " like tends to beget like."
There are, I think, two other important facts in regard
to heredity, but both require discussion the one because
some of the most authoritative naturalists deny it, the other
because it is difficult to understand.
I believe that some characters acquired by the parent as
the result of what it does, and as impacts from the surround-
ing conditions of life, are transmissible to the offspring. In
other words, some functional and environmental variations
in the body of the parents may be handed on to the
offspring. This is denied by Weismann and many others.
The other fact, which has been elucidated by Galton,
is that through successive generations there is a tendency
to sustain the average of the species, by the continual
approximation of exceptional forms towards a mean.
2. Theories of Heredity historical retrospect.
Theories of heredity, like those about many other facts,
have been formulated at different times in different kinds
of intellectual language theological, metaphysical, and
scientific and the words are often more at variance than
the ideas.
(a) Theological Theories. It was an old idea, that the
germ of a new human life was possessed by a spirit, some-
times of second-hand origin, having previously belonged to
some ancestor or animal. So far as this idea persists in the
minds of civilised men, it is so much purified and sublimed
that if the student of science does not believe it true,
he cannot wisely call it false.
(b) " Metaphysical Theories." For a time it was com-
324 The Study of Animal Life PART iv
mon to appeal to "vires formativce? " hereditary tendencies,"
and " principles of heredity," by aid of which the germ
grew into the likeness of the parent, and this tendency
to resort to verbal explanations is hardly to be driven from
the scientific mind except by intellectual asceticism. For
my own part, I prefer such " metaphysical " mist to the
frost of a " materialism " which blasts the buds of wonder.
(c) "Mystical Theories" During the eighteenth cen-
tury and even, within the limits of the enlightened nineteenth,
a quaint idea of development prevailed, according to which
the germ (either the ovum or the sperm) contained a miniature
organism, preformed in all transparency, which only required
to be unfolded (or " evolved," as they said), in order to
become the future animal. Moreover, the egg of a fowl
contained not only a micro-organism or miniature model of
the chick, but likewise in increasing minuteness similar
models of future generations. Microcosm lay within micro-
cosm, germ within germ, like the leaves within a bud
awaiting successive unfolding, or like an infinite juggler's
box to the " evolution " of which there was no end. This
" preformation theory" or " mystical hypothesis " was virtu-
ally but not actually shattered by Wolff's demonstration of
" Epigenesis " or gradual development from an apparently
simple rudiment. But the preformationists were right in
insisting that the future organism lay (potentially) within
the germ, and right also in supposing that the germ involved
not only the organism into which it grew but its descendants
as well. The form of their theory, however, was crude and
false.
(d) Theories of Pangenesis. Scientific theories of here-
dity really begin with that of Herbert Spencer, who in
1864 suggested that "physiological units" derived from
and capable of growth into cells were accumulated from the
body into the reproductive elements, there tb develop the
characters of structures like those whence they arose. At
dates so widely separate as are suggested by the names of
Democritus and Hippocrates, Paracelsus and BufTon, the
same idea was expressed that the germs consist of samples
from the various parts of the body. But the theories of
CHAP, xx Heredity 325
these authors were vague and in some respects entirely
erroneous suggestions. The best-known form of this type
of theory is Darwin's " provisional hypothesis of pan-
genesis " (1868), according to which (a) every cell of the
body, not too highly differentiated, throws off characteristic
gemmules, which (b) multiply by fission, retaining their
peculiarities, and (c) become specially concentrated in the
reproductive elements, where (d} in development they grow
into cells like those from which they were originally given
off. This theory was satisfactory in giving a reasonable
explanation of many of the facts of heredity, it was unsatis-
factory because it involved many unverified hypotheses.
The ingenious Jaeger, well known as the introducer of
comfortable clothing, sought (1876) to replace the "gem-
mules " of which Darwin spoke, by characteristic " scent-
stuffs," which he supposed to be collected from the body
into the reproductive elements.
Meanwhile (1872) Francis Galton, our greatest British
authority on heredity, had been led by his experiments
on the transfusion of blood and by other considerations
to the conclusion that " the doctrine of pangenesis, pure
and simple, is incorrect." As we shall see, he reached
forward to a more satisfactory doctrine, but he still allowed
the possibility of a limited pangenesis to account for those
cases which suggest that some characters acquired by the
parents are " faintly heritable." He admitted that a cell
"may throw off a few germs" (i.e. " gemmules") "that
find their way into the circulation, and have thereby a
chance of occasionally finding their way to the sexual
elements, and of becoming .naturalised among them."
W. K. Brooks, a well-known American naturalist, pro-
posed in 1883 an important modification of Darwin's theory,
especially insisting on the following three suppositions :
that it is in unwonted and abnormal conditions that the cells
of the body throw off gemmules ; that the male elements
are the special centres of their accumulation ; and that the
female cells keep up the general resemblance between
offspring and parents. For further modifications and for
criticism of the theories of pangenesis, I refer the student
326 The Study of Animal Life PART iv
to the works of Galton, Ribot, Brooks, Herdman, Plarre,
Van Bemmelen, and De Vries.
3. The Modern Theory of Heredity. In the midst of
much debate it may seem strange to speak of the modern
theory of heredity, but while details are disputed, one clear
fact is generally acknowledged, the increasing realisation of
which has shed a new light on heredity. This fact is the
organic continuity of generations.
In 1876 Jaeger expressed his views explicitly as follows :
" Through a long series of generations the germinal proto-
plasm retains its specific properties, dividing in develop-
ment, into a portion out of which the individual is built up,
and a portion which is reserved to form the reproductive
material of the mature offspring." This reservation, by
which some of the germinal protoplasm is kept apart, during
development and growth, from corporeal or external influ-
ences, and retains its specific or germinal characters intact
and continuous with those of the parent ovum, Jaeger
regarded as the fundamental fact of heredity.
Brooks (1876, 1877, 1883) was not less clear: "The
ovum gives rise to the divergent cells of the organism, but
also to cells like itself. The ovarian ova of the offspring
are these latter cells or their direct unmodified descendants.
The ovarian ova of the offspring thus share by direct
inheritance all the properties of the fertilised ova."
But before and independently of either Jaeger or Brooks
or any one else, Galton had reached forward to the same
idea. We have noticed that he was led in 1872 to the
conclusion that "the doctrine of v pangenesis, pure and
simple, is incorrect." His own view was that the fertilised
ovum consisted of a sum of germs, gemmules, or organic
units of some kind, to which in entirety he applied the
term stirp. But he did not regard this nest .of organic
units as composed of contributions from all parts of the
body. He regarded it as directly derived from a previous
nest, namely, from the ovum which gave rise to the parent.
He maintained that in development the bulk of Jhe stirp
grew into the body as every one allows but that a cer-
tain residue was kept apart from the development of the
CHAP, xx Heredity 327
"body" to form the reproductive elements of the offspring.
Thus he said, in a sense the child is as old as the parent,
for when the parent is developing from the ovum a residue
of that ovum is kept apart to form the germ-cells, one of
which may become a child. Besides Galton, Jaeger, and
Brooks, several other biologists suggested this fertile idea
of the organic continuity of generations. Thus it is ex-
pressed by Erasmus Darwin and by Owen, by Haeckel,
Rauber, and Nussbaum. But it is to Weismann that the
modern emphasis on the idea is chiefly due.
Let us try to realise more vividly this doctrine of organic
continuity between generations. Let us begin with a fertil-
ised egg-cell, and suppose it to have qualities abcxyz. This
endowed egg- cell divides and redivides, and for a short
time each of the units in the ball of cells may be regarded
as still possessed of the original qualities abcxyz. But
division of labour, and rearrangement, infolding and out-
folding, soon begin, and most of the cells form the " body."
They lose their primitive characters and uniformity, they
become specialised, the qualities ab predominate in one
set, be in another, xy in another. But meantime certain
cells have kept apart from the specialisation which results
in the body. They have remained embryonic and un-
differentiated, retaining the many-sidedness of the original
egg-cell, preserving intact the qualities abcxyz. They form '
the future reproductive cells let us say the eggs.
Now when these eggs are liberated, with the original
qualities abcxyz unchanged, having retained a continuous
protoplasmic tradition with the parent ovum, they are evi-
dently in almost the same position as that was. There-
fore they develop into the same kind of organism. Given
the same protoplasmic material, the same inherent quali-
ties, the same conditions of birth and growth, the results
must be the same. A single-celled animal with qualities
abcxyz divides into two ; each has presumably the qualities
of the original unit ; each grows rapidly into the form of
the full-grown cell. We have no difficulty in understanding
this. In the sexual reproduction of higher animals, the
case is complicated by the formation of the "body," but
328 The Study of Animal Life PART iv
logically the difficulty is not greater. A fertilised egg-cell
with qualities abcxyz divides into many cells, which, becom-
ing diverse, express the original qualities in various kinds
of tissue within the forming body. But if at an early stage
certain cells are set apart, retaining the qualities or charac-
ters abcxyz in all their entirety, then these, when liberated
after months or years as egg-cells, will resemble the original
ovum, and are able like it to give rise to an organism,
which is necessarily a similar organism.
To call heredity "the relation of organic continuity
between successive generations," as I define it, seems a
truism to some, but it is in the realisation of this truistic
fact that the modern progress in regard to heredity consists.
To ask how the inherent qualities of the ovum become
divergent in the different cells of the body, or how some
units remain embryonic, or how the egg-cell divides at
all, is to raise the deepest problems of biology, not of
heredity. To answer such questions is the more or less
hopeless task of physiological embryology, not that of the
student of heredity. Recognising the fact of organic con-
tinuity, various writers such as Samuel Butler, Hering,
Haeckel, Geddes, Gautier, and Berthold, have sought in
various ways to make it clearer, e.g. by regarding the re-
production of like by like as an instance of organic memory.
As these suggestions are unessential to our argument, I
shall merely notice that there are plenty of them.
How far has this early separation of the future repro-
ductive cells from the developing body been observed ? It
has been observed in several worm-types leeches, Sagitta^
thread-worms, Polyzoa, in some Arthropods (e.g. Moina
among crustaceans, Chironomus among Insects, Phalangidas
among spiders), and with less distinctness in a number of
other organisms, both animal and vegetable. In most of
the higher animals, however, the future reproductive cells
are not observable till development has proceeded for some
days or weeks. To explain this difficulty, Weismann has
elaborated a theory which he calls " the continuity of the
germ-plasma" The general idea of this theory is that of
organic continuity between generations, and this Weismann
CHAP, xx Heredity 329
has done momentous service in expounding. But for the
detailed theory by which he seeks to overcome the diffi-
culty which has been noticed above I refer those interested
to Weismann's Papers on Heredity (Trans. Oxford, 1889).
4. The Inheritance of Acquired Characters. (a) His-
torical. We have seen that variations, or changes in char-
acter, may be constitutional \ i.e. innate in the germ or
functional, i.e. due to use or disuse ; or environmental, i.e.
due to influences of nutrition and surroundings. Many
naturalists have believed that gains or losses due to any of
these three sources of change might be transmitted from
parent to offspring. But nowadays the majority, with
Profs. Weismann and Lankester at their head, deny the
transmissibility of either functional or environmental
changes, and believe that inborn, germinal, or constitu-
tional variations alone are transmissible.
This scepticism is not strictly modern. The editor,
whoever he was, of Aristotle's Historia Animalium, differed
from his master as to the inheritance of injuries and the
like. Kant maintained the non- inheritance of extrinsic
variations, and Blumenbach cautiously inclined to the same
negative position. In more recent times the veteran morpho-
logist His expressed a strong conviction against the inherit-
ance of acquired characters, and the not less renowned
physiologist Pfliiger is also among the sceptics. A few
sentences from Galton (1875), whose far-sightedness has
been insufficiently acknowledged, may be quoted : " The
inheritance of characters acquired during the lifetime of the
parents includes much questionable evidence, usually diffi-
cult of verification. We might almost reserve our belief
that the structural cells can react on the sexual elements at
all, and we may be confident that at the most they do so in
a very faint degree in other words, that acquired modifica-
tions are barely, if at all, inherited in the correct sense of
that word."
But Weismann brought the discussion to a climax by
altogether denying the transmissibility of acquired charac-
ters.
(b) Weismann's position. Weismann's reasons for
330 The Study of Animal Life PART iv
maintaining that no acquired characters are transmissible
are twofold, first because the evidence in favour of such
transmission consists of unverifiable anecdotes ; second
because the " germ -plasma," early set apart in the de-
velopment of the body, remains intact and stable, unaffected
by the vicissitudes which beset the body.
It is natural that Weismann, who realised so vividly the
continuity between germ and germ, should emphasise the
stability of the "germ-plasma," that he should regard it
as leading a sort of charmed life within the organism un-
affected by changes to which the body is subject. But has
he not exaggerated this insulation and stability ?
Of course Weismann does not deny that the body may
exhibit functional and environmental variations, but he
denies that these can spread from the body so as to affect
the reproductive cells thereof, and unless they do so, they
cannot be transmitted to the offspring.
On the other hand, innate or germinal characters
must be transmitted. They crop up in the parent be-
cause they are involved in the fertilised egg-cell. But as
the cell which gives rise to the offspring is by hypothesis
similar to and more or less directly continuous with the
cell which gave rise to the parent, similar constitutional
variations will crop up in' the offspring.
We must admit that most of the old evidence adduced
in favour of the transmission of acquired characters may
be called a "handful of anecdotes." For scepticism was
undeveloped, and when a character acquired by a parent
reappeared in the offspring, it was too readily regarded as
transmitted, whereas it may often have been acquired by
the offspring just as it was by the parent.
Weismann has two saving clauses, which make argu-
ment against his position peculiarly difficult. (i) He
admits that the germ -plasma may be modified "ever so
little " by changes of nutrition and growth in the body ;
but may not an accumulation of many " ever -so- littles "
amount to the transmission of an acquired character ? (2)
He admits that external conditions, such as climate, may
influence the reproductive cells along with, though not
CHAP, xx Heredity 331
exactly through, the body ; but this is a distinction too
subtle to be verified.
These two saving-clauses seem to me to affect the strin-
gency of Weismann's conclusion, but in his view they do
not affect the main proposition that definite somatic modifi-
cations or changes in the body due to function or environ-
ment have no effect on the reproductive cells, and therefore
no transmission to- offspring.
(c) Arguments against Weismann's position. In arguing
against Weismann's position that no acquired characters
are inherited, I shall first illustrate the arguments of others,
and then emphasise that which appears to me at present
most cogent.
(1) Some have cited against Weismann various cases
where the effects of mutilation seemed to be transmitted,
and Weismann has spent some time in experimenting with
mice in order to see whether cutting off the tails for several
generations did not eventually make the tails shorter. It
did not a result which might have been foretold. For we
have known for many years that the mutilations inflicted
on sheep and other domesticated animals had no measur-
able effect on the offspring. Even the numerous cases of
tailless kittens produced from artificially curtailed cats have
no cogency in face of the fact that tailless sports often arise
from normal parents. Moreover, it is for many reasons not
to be expected that the results of curtailment and the like
should be inherited. For there is great power of regener-
ating lost parts even in the individual lifetime ; the result
of cutting off a tail is for most part merely a minus quantity
to the organism ; the imperfectly known physiological re-
action on nerves and blood-vessels might perhaps result in
a longer rather than a shorter tail in the offspring.
(2) Various pathologists, led by Virchow, have empha-
sised the fact that many diseases are inherited, but their
arguments have usually shown how easy it is to misunder-
stand Weismann's position. No doubt many malformations
and diseases reappear through successive generations, but
there is lack of evidence to show that the pathological
variations were not germinal to begin with. It is sadly
332
The Study of Animal Life PART iv
interesting to learn that colour-blindness has been known
to occur in the males only of six successive generations,
deaf mutism for three, finger malformations for six, and so
with harelip and cleft palate, and with tendencies to con-
sumption, cancer, gout, rheumatism, bleeding, and so on.
But these facts do not prove the transmission of functional or
environmental variations ; they only corroborate what every
one allows, that innate, congenital, constitutional characters
FIG. 70. Half-lop rabbit, an abnormal variation, which by artificial selection
has become constant in a breed. (From Darwin.)
tend to be transmitted. Yet some cases recently stated by
Prof. Bertram Windle seem to suggest that some patho-
logical conditions acquired by function may be transmitted.
But even if a non-constitutional pathological state acquired
by a parent reappeared in the offspring, we require to show
that the offspring did not also acquire it by his work or
from conditions of life, as his parent did before him.
(3) Some individual cases seem to stand some criticism.
Two botanists, Hoffmann and Detmer, have noted such
facts as the following scant nutrition influenced the flowers
of poppy, Nigella, dead-nettle, and the result was trans-
CHAP, xx Heredity 333
mitted ; peculiar soil conditions altered the root of the
carrot, and the result was transmitted.
Semper gives a few cases such as Schmankewitsch's
transformation of one species of brine-shrimp (Artemid) into
another, throughout a series of generations during which
the salinity of the water was slowly altered.
Eimer has written a book of which even the title, " The
Origin of Species, according to the laws of organic growth,
through the inheritance of acquired characters," shows how
strongly he supports the affirmative side of our question.
But much as I admire and agree with many parts of Eimer's
work, I do not think that all his examples of the inheritance
of acquired characters are cogent. One of the strongest
is that cereals from Scandinavian plains transplanted to
the mountains become gradually accustomed to develop
more rapidly and at a lower temperature, and that when
returned to the plains they retain this power of rapid
development. I am inclined to think that the strongest
part of Eimer's argument is that in which he maintains that
certain effects produced upon the nervous system by peculiar
habits are transmissible.
(4) Another mode of argument may be considered. To
what conception of evolution are we impelled if we deny
the inheritance of acquired characters ? Weismann believes
that he has taken the ground from under the feet of
Lamarckians and Buffonians, who believe in the inheritance
of functional and environmental variations. The sole fount
of change is to be found in the mingling of the kernels of
two cells at the fertilisation of the ovum. On these varia-
tions natural selection works.
But even if we do not believe in the inheritance of
acquired characters, it is open to us to maintain that by
cumulative constitutional variations in definite directions
species have grown out of one another in progressive evolu-
tion. Thus we are not forced to restrict our interpreta-
tions of the marvel and harmony of organic nature to the
theory of the action of natural selection on indefinite for-
tuitous variations.
Prof. Ray Lankester's convictions on this subject are so
334 The Siudy of Animal Life PART iv
strong, and his dismissal of Lamarckian theory is so
emphatic, that I shall select one of his illustrations by way
of contrasting his theory with that of Lamarckians.
Many blind fishes and crustaceans are found in caves.
Lamarckians assume, as yet with insufficient evidence, that
the blindness is due to the darkness and to the disuse
of the eyes. Changes thus produced are believed, again
with insufficient evidence, to be transmitted and increased,
generation after generation. This is a natural and simple
theory, but it is not a certain conclusion.
What is Prof. Ray Lankester's explanation ?
" The facts are fully explained by the theory of natural
selection acting on congenital fortuitous variations. Many
animals are born with distorted or defective eyes whose
parents have not had their eyes submitted to any peculiar
conditions. Supposing a number of some species of Arthro-
pods or fish to be swept into a cavern, those individuals with
perfect eyes would follow the glimmer of light and eventually
escape to the outer air, leaving behind those with imperfect
eyes to breed in the dark place. In every succeeding
generation this would be the case, and even those with
weak but still seeing eyes would in the course of time
escape, until only a pure race of eyeless or blind animals
would be left in the cavern." This is a possible explanation,
but it is not a certain conclusion.
(5) The argument which I would urge most strongly is
based on general physiological considerations. It gives
no demonstration, but it seems to establish a presump-
tion against Weismann's conclusion. He maintains that
functional and environmental changes in the body cannot
be transmitted because such changes cannot reach the
stable and to some extent insulated reproductive elements.
But this cannot requires proof, just as much as the converse
can.
The organism is a unity ; cell is often linked to cell by
bridges of living matter ; the blood is a common medium
carrying food and waste ; nervous relations bind the whole
in harmony. Would it not be a physiological miracle if the
reproductive cells led a charmed life unaffected even by
CHAP, xx Heredity 335
influences which touch the very heart of the organism ? Is
it unreasonable to presume that some influences of habit and
conditions, of training and control, saturate the organism
thoroughly enough to affect every part of it ?
A slight change of food affects the development of the
reproductive organs in a bee-grub, and makes a queen out of
what otherwise would have been a worker. A difference of
diet causes a brood of tadpoles to become almost altogether
female. There is no doubt that some somatic changes
affect the reproductive cells in some way. Is it incon-
ceivable that they affect them in such a precise way that
bodily changes may be transmitted ?
It must be admitted that it is at present impossible to
give an explanation of the way in which a modification
of the brain can affect the cells of the reproductive organs.
The only connections that we know are by the blood, by
nervous thrills, by protoplasmic continuity of cells. But
there are many indubitable physiological influences which
spread through the body of which we can give no rationale.
Because we cannot tell how an influence spreads, we need
not deny its existence.
It is at least conceivable that a deep functional or
environmental change may result in chemical changes
which spread from cell to cell, that characteristic products
may be carried about by the blood and absorbed by the
unspecialised reproductive cells, that nervous thrills of
unknown efficacy may pass from part to part. Nor do we
expect that more than a slight change will be transmitted
in one generation.
Weismann traces all variations ultimately to the action
of the environment on the original unicellular organisms.
These are directly affected by surrounding influences, and
as they have no " body " nor specialised reproductive
elements, but are single cells, it is natural that the char-
acters acquired by a parent-cell should also belong to the
daughter-units into which it divides. And if so, is it not
possible that the reproductive cells of higher animals, being
equivalent to Protozoa, may be definitely affected by their
immediate environment, the body ? Moreover, if it were
336 The Study of Animal Life PART iv
proved that the definite changes produced on an individual
by influences of use, disuse, and surroundings, do not reach
the reproductive cells, and cannot, therefore, be transmitted,
it is not thereby proved that secondary results or some results
of such definite changes may not have some effect on the
germ-cells. The conditions are so complex that it seems
rash to deny the possibility of such influence.
Certainly it is no easy task to explain all the adapta-
tions to strange surroundings and habits, or the majority of
animal instincts, or the progress of men, apart from the
theory that some of the results of environmental influence
and habitual experience are transmitted. I am certainly
unable to reconcile myself to the opinion that the progress
of life is due to the action of natural selection on fortuitous,
indefinite, spontaneous variations.
I believe that the conclusion of the whole matter should
be an emphatic " not proven " on either side, while the
practical corollary is that we should cease to talk so much
about possibilities (in regard to which one opinion is often
as logically reasonable as another), and betake ourselves
with energy to a study of the facts.
5. Social and Ethical Aspects. All the important
biological conclusions have a human interest.
The fact of organic continuity between germ and germ
helps us to realise that the child is virtually as old as the
parent, and that the main line of hereditary connection
is not so much that between parent and child as "that
between the sets of elements out of which the personal
parents had been evolved, and the set out of which the
personal child was evolved." " The main line," Galton
says, " may be rudely likened to the chain of a necklace,
and the personalities to pendants attached to the links."
To this fact social inertia is largely due, for the organic
stability secured by germinal continuity tends to hinder
evolution by leaps and bounds either forwards or backwards.
There is some resemblance between the formula of heredity
and the first law of motion. The practical corollary is
respect for a good stock.
That each parent contributes almost equally to the off-
CHAP, xx Heredity 337
spring suggests the two-sided responsibility of parentage ;
but the fact has to be corrected by Galton's statistical con-
clusion that the offspring inherits a fourth from each
parent, and a sixteenth from each grandparent ! Inherited
capital is not merely dual, but multiple like a mosaic.
If we adopt a modified form of Weismann's conclusion,
and believe that only the more deeply penetrating acquired
characters are transmitted, we are saved from the despair
suggested by the abnormal functions and environments of
our civilisation.
And just in proportion as we doubt the transmission of
desirable acquired characters, so much the more should we
desire to secure that improved conditions of life foster the
individual development of each successive generation.
That pathological conditions, innate or congenital in the
organism, tend to be transmitted, suggests that men should
be informed and educated as to the undesirability of
parentage on the part of abnormal members of the com-
munity.
But while no one will gainsay the lessons to be drawn
from the experience of past generations, it should be noticed
that Virchow and others have hinted at an " optimism of
pathology," since some of the less adequately known abnor-
mal variations may be associated with new beginnings not
without promise of possible utility. It seems, moreover,
that by careful environment and function, or by the inter-
crossing of a slightly tainted and a relatively pure stock, a
recuperative or counteractive influence may act so as to
produce comparatively healthy offspring, thus illustrating
what may be called "the forgiveness of nature."
6. Social Inheritance. -- The widest problems of
heredity are raised when we substitute " fraternities " for
individuals, or make the transition to social inheritance
the relation between the successive generations of a society.
The most important pioneering work is that of Galton,
whose unique papers have been recently summed up in a
work entitled Natural Inheritance. Galton derived his
data from his Records of Family Faculties^ especially con-
cerning stature, eye-colour, and artistic powers ; and his
z
338 The Study of Animal Life PART iv
work has been in great part an application of the statistical
law of Frequency of Error to the records accumulated.
The main problem of his work is concerned with the
strange regularity observed in the peculiarities of great
populations throughout a series of generations. " The
large do not always beget the large, nor the small the
small ; but yet the observed proportion between the large
and the small, in each degree of size and in every quality
hardly varies from one generation to another." A specific
average is sustained. This is not because each individual
leaves his like behind him, for this is not the case. It is
rather due to the fact of a regular regression or deviation
which brings the offspring of extraordinary parents in a
definite ratio nearer the average of the stock.
" However paradoxical it may appear at first sight, it is
theoretically a necessary fact, and one that is clearly con-
firmed by observation, that the stature of the adult offspring
must on the whole be more mediocre than the stature of
their parents that is to say, more near to the median
stature of the general population. Each peculiarity of a
man is shared by his kinsmen, but on an average in a less
degree. It is reduced to a definite fraction of its amount,
quite independently of what its amount might be. The
fraction differs in different orders of kinship, becoming
smaller as they are more remote."
Yet it must not be supposed that the value of a good stock
is under-estimated by Galton, for he shows how the offspring
of two ordinary members of a gifted stock will not regress
like the offspring of a couple equal in gifts to the former,
but belonging to a poorer stock, above the average of which
they have risen.
Yet the fact of regression tells against the full transmission
of any signal talent. Children are not likely to differ from
mediocrity so widely as their parents. " The more bounti-
fully a parent is gifted by nature, the more rare will be his
good fortune if he begets a son who is as richly endowed as
himself, and still more so if he has a son who is endowed
more largely." But "The law is even-handed ; it levies an
equal succession -tax on the transmission of badness as of
CHAP, xx Heredity 339
goodness. If it discourages the extravagant hope of a gifted
parent that his children will inherit all his powers, it no less
discountenances extravagant fears that they will inherit all
his weakness and disease."
The study of individual inheritance, as in Galton's
Hereditary Genius^ may tend to develop an aristocratic and
justifiable pride of race when a gifted lineage is verifiable
for generations. It may lead to despair if the records of
family diseases be subjected to investigation.
But the study of social inheritance is at once more demo-
cratic and less pessimistic. The nation is a vast fraternity,
with an average towards which the noble tend, but to which
the offspring of the under-average as surely approximate.
Measures which affect large numbers are thus more hopeful
than those which artificially select a few.
Even when we are doubtful as to the degree in which
acquired characters are transmissible, we cannot depreciate
the effect on individuals of their work and surroundings.
In fact there should be the more earnestness in our desire to
conserve healthful function and stimulating environment of
every kind, for these are not less important if their influences
must needs be repeated on each fresh generation. " There
was a child went forth every day ; and the first object he
looked upon, that object he became ; and that object
became part of him for the day, or a certain part of the
day, or for many years, or for stretching cycles of years." 1
Nor can we forget how much a plastic physical and
mental education may do to counteract disadvantageous
inherited qualities, or to strengthen characters which are
useful.
Every one will allow at least that much requires to be
done in educating public opinion, not only to recognise all
the facts known in regard to heredity, but also to admit the
value and necessity of the art which Mr. Galton calls
" eugenics," or in frank English " good-breeding."
1 Walt Whitman's "Assimilations."
APPENDIX I
ANIMAL LIFE AND OURS
A. Our Relation to Animals
i. Affinities and Differences between Man and Monkeys.
In one of the works of Broca, a pioneer anthropologist of renown,
there is an eloquent apology for those who find it useful to con-
sider man's zoological relations.
" Pride," he says, " which is one of the most characteristic traits
of our nature, has prevailed with many minds over the calm testi-
mony of reason. Like the Roman emperors who, enervated by all
their power, ended by denying their character as men, in fact, by
believing themselves demigods, so the king of our planet pleases
himself by imagining that the vile animal, subject to his caprices,
cannot have anything in common with his peculiar nature. The
proximity of the monkey vexes him, it is not enough to be king of
animals ; he wishes to separate himself from his subjects by a deep
unfathomable abyss ; and, turning his back upon the earth, he takes
refuge with his menaced majesty in a nebulous sphere, ' the human
kingdom.' But anatomy, like that slave who followed the con-
queror's chariot crying, Memento te hominem esse, anatomy comes
to trouble man in his naive self-admiration, reminding him of the
visible tangible facts which bind him to the animals."
Let us hearken to this slave a little, remembering Pascal's
maxims : "It is dangerous to show man too plainly how like he is
to the animals, without, at the same time, reminding him of his
greatness. It is equally unwise to impress him with his greatness,
and not with his lowliness. It is worse to leave him in ignorance
of both. But it is very profitable to recognise the two facts."
It is many years since Owen now a veteran among anatomists
described the " all-pervading similitude of structure " between
APP. i Animal Life and Ours 341
man and the highest monkeys. Subsequent research has continued
to add corroborating details. As far as structure is concerned,
there is much less difference between man and the gorilla than
between the gorilla and a monkey like a marmoset. Yet differences
between man and the anthropoid apes do exist. Thus man alone
is thoroughly erect after his infancy is past, his head weighted with
a heavy brain does not droop forward, and with his erect attitude
his perfect development of vocal mechanism is perhaps connected.
We plant the soles" of our feet flat on the ground, our great toes
are usually in a line with the rest, and we have better heels than
monkeys have, but no emphasis can be laid on the old distinction
which separated two-handed men (Bimana) from the four-handed
monkeys (Quadrumana), nor on the fact that man is peculiarly
naked. We have a bigger forehead, a less protrusive face, smaller
cheek-bones and eyebrow ridges, a true chin, and more uniform
teeth than the anthropoid apes. More important, however, is the
fact that the weight of the gorilla's brain bears to that of the smallest
brain of an adult man the ratio of 2 : 3, and to the largest human
brain the ratio of I : 3 ; in other words, a man may have a brain
three times as heavy as that of a gorilla. The brain of a healthy
human adult never weighs less than 31 or 32 ounces ; the average
human brain weighs 48 or 49 ounces ; the heaviest gorilla brain
does not exceed 20 ounces. "The cranial capacity is never less
than 55 cubic inches in any normal human subject, while in the
orang and the chimpanzee it is but 26 and 27^- cubic inches
respectively. "
But differences which can be measured and weighed give us little
hint of the characteristically human powers of building up ideas and
of cherishing ideals. It is not merely that man profits by his
experience, as many animals do, but that he makes some kind of
theory of it. It is not merely that he works for ends which are
remote, as do birds and beavers, but that he controls his life
according to conscious ideals of conduct. But I need not say much
in regard to the characteristics of human personality, w r e are all
conscious of them, though we may differ as to the words in which
they may be expressed ; nor need I talk about man's power of
articulate speech, nor his realisation of history, nor his inherent
social sympathies, nor his gentleness. For all recognise that the
higher life of men has a loftier pitch than that of animals, while
many think that the difference is in kind, not merely in degree.
2. Descent of Man. The arguments by which Darwin and
others have sought to show that man arose from an ancestral type
common to him and to the higher apes are the same as those used
to substantiate the general doctrine of descent. For the Descent
of Man was but the expansion of a chapter in the Origin of Species ;
342 The Study of Animal Life APP.
the arguments used to prove the origin of animal from animal were
adapted to rationalise the ascent of man.
(a) Physiological. The bodily life of man is like that of mon-
keys ; both are subject to the same diseases ; various human traits,
such as gestures and expressions, are paralleled among the " brutes " ;
and children born during famine or in disease are often sadly
ape-like.
(b) Morphological. The structure of man is like that of the
anthropoid apes, none of his distinctive characters except that of
a heavy brain being momentous, and there are about seventy
vestigial structures in the muscular, skeletal, and other systems.
(c) Historical. There is little certainty in regard to the fossil
remains of prehistoric man, but some of these suggest more primi-
tive skulls, while the facts known about ancient life show at least
that there has been progress along certain lines. Moreover, there
is the progress of each individual life, from the apparently simple
egg-cell to the minute embryo, which is fashioned within the womb
into the likeness of a child, and being born grows from stage to
stage, all in a manner which it is hard to understand if man be
not the outcome of a natural evolution.
3. Various Opinions about the Descent of Man. But
opinion in regard to the origin of man is by no means unanimous.
(a) A few authorities, notably A. de Quatrefages, maintain a
conservative position, believing that the evolutionist's ca^e has not
been sufficiently demonstrated. But the majority of naturalists
believe the reverse, and think that the insufficiencies of evidence in
regard to man are counterbalanced by the force of the argument
from analogy.
(b} Alfred Russel Wallace has consistently maintained a position
which seems to many a very strong one. "I fully accept," he
says, " Mr. Darwin's conclusion as to the essential identity of man's
bodily structure with that of the higher mammalia, and his descent
from some ancestral form common to man and the anthropoid apes.
The evidence of such descent appears to me overwhelming and
conclusive. Again, as to the cause and method of such descent
and modification, we may admit, at all events provisionally, that
the laws of variation and natural selection, acting through the
struggle for existence and the continual need of more perfect
adaptation to the physical and biological environments, may have
brought about, first that perfection of bodily structure in which he
is so far above all other animals, and in co-ordination with it the
larger and more developed brain, by means of which he has been
able to utilise that structure in the more and more complete sub-
jection of the whole animal and vegetable kingdoms to his
service."
i Animal Life and Ours 343
" But because man's physical structure has been developed
from an animal form by natural selection, it does not necessarily
follow that his mental nature, even though developed part passu
with it, has been developed by the same causes only. " Wallace
then goes on to show that man's mathematical, musical, artistic,
and other higher faculties could not be developed by variation and
natural selection alone. "Therefore some other influence, law, or
agency is required to account for them." Indeed this unknown
cause or power may-have had a much wider influence, extending
to the whole course of his development. "The love of truth, the
delight in beauty, the passion for justice, and the thrill of exulta-
tion with which we hear of any act of courageous self-sacrifice, are
the workings within us of a higher nature which has not been
developed by means of the struggle for material existence." At
the origin of living things, at the introduction of consciousness, in
the development of man's higher faculties, " a change in essential
nature (due, probably, to causes of a higher order than those of the
material universe) took place." "The progressive manifestations
of life in the vegetable, the animal, and man which we may
classify as unconscious, conscious, and intellectual life probably
depend upon different degrees of spiritual influx."
In discussing problems such as this there is apt to be misunder-
standing, for words are "but feeble light on the depth of the un-
spoken," and perhaps no man appreciates his brother's philosophy.
Therefore, I refrain from seeking to controvert what Wallace has
said, especially as I also believe that the nature of life and mind
are secrets to us all, and that the higher life of man cannot be
explained by indefinite variations which happened to prosper in the
course of natural selection.
But it seems to me (i) to be difficult to divide man's self into
an animal nature which has been naturally evolved and " a
spiritual nature which has been superadded," or to separate man's
higher life from that of some of the beasts. (2) When we find
that any fact in our experience, such as human reason, cannot
be explained on the theory of evolution which we have adopted, it
does not follow that the reality in question has not been naturally
evolved, it only follows that our theory of evolution is imperfect.
A theory is not proved to be complete because it explains many
facts, but it is proved to be incomplete if it fails to explain any.
Thus if man's higher nature cannot be explained by the theory of
natural selection in the struggle for existence, then that theory is
incomplete, but there may be other theories of evolution which are
sufficient. (3) It is difficult to know what is meant by spiritual
influx for our opinions in regard to those matters vary with
individual experience. We may mean to suggest the interpola-
344 The Study of Animal Life APP.
tion of a power of a secret and supersensory nature, distinct from
that power which is everywhere present in sunbeam and rain-
drop, bird and flower. Then we are abandoning the theory of a
continuous natural evolution. Or we may mean to suggest that when
life and mind and man began to be, then possibilities of action and
reaction hitherto latent became real, and all things became in a
sense new. Then, while maintaining that life and mind are new
realities with new powers, we are still consistent believers in a con-
tinuous natural evolution. (4) Perhaps the simplest conception is
that more than once suggested in this book, that the world is one
not twofold, that the spiritual influx is the primal reality, that there
is nothing in the end which was not also in the beginning.
(c) Prof. Calderwood has recently stated with clearness and
conciseness what difficulties surround the task of those who would
explain the evolution of man. " So far as the human organism is
concerned, there seem no overwhelming obstacles to be encountered
by an evolution theory ; but it seems impossible under such a theory
to account for the appearance of homo sapiens the thinking, self-
regulating life, distinctively human." Again, I have no desire to
enter into controversy, for I recognise the difficulties which the
student of comparative psychology must tackle, but it seems
important that the following consideration should be kept in mind.
It is not the first business of the evolutionist to find out how one
reality has grown out of another, but to marshal the arguments
which lead him to conclude that one reality has so evolved. We
have only a vague idea how a backbone arose, but that need not
hinder us from believing that backboned animals were evolved from
backboneless if there be sufficient evidence in favour of this con-
clusion. We do not know how birds arose from a reptile stock s
but that they did so arise is fairly certain. We cannot explain the
intelligence of man in terms of the activity of the brain ; we are
equally at a loss in regard to the intelligence of an ant. What we
have to do is to compare the structure of man's brain with that of
the nearest animals, and the nature of human intelligence with that
of the closest approximations, drawing from the results of our
comparison what conclusion we can. The general doctrine of
descent may be established independently of the investigations of
physiologist and psychologist, valuable as these may be in elucidat-
ing the way in which the great steps of progress have been made.
(d] Finally there is the opinion of many that man is altogether
too marvellous a being to have arisen from any humbler form of
life. But to others this ascent seems the stamp of man's nobility.
4. Ancestors of Man. Of these we know nothing. The
anthropoid apes approach him most closely, each in some particular
respect, but none of them nor any known form of life can be called
i Animal Life and Ours 345
man's ancestor. It is possible that the race of men for of a
first man evolutionists cannot speak began in Miocene times,
as offshoots from an ancestral stock common to them and to the
anthropoids. We often hear of " the missing link," but surely no
one expects to find him alive. And while we have still much to
learn from the imperfect geological record, it must be remembered
that what most distinguishes man will not be remarkable in a fossil,
for brains do not petrify except metaphorically, nor can we look for
fossilised intelligence or gentleness.
FIG. 71. Young gorilla. (From Du Chaillu.)
5. Possible Factors in the Ascent of Man. In regard to
the factors which secured man's ascent from a humbler form of life
we can only speculate.
(a) We have already explained that organisms vary, that the
offspring differ from their parents, that the more favourable changes
prosper, and that the less fit die out of the struggle. Thus the race
is lifted. Now, from what we know of men and monkeys, it seems
likely that in the struggles of primitive man cunning was more
important than strength, and if intelligence now became, more than
ever before, the condition of life or death, wits would tend to
develop rapidly.
(b) When habits of using sticks and stones, of building shelters,
of living in families, began and some monkeys exhibit these it is
likely that wits would increase by leaps and bounds.
(c) Professor Fiske and others have emphasised the importance of
prolonged infancy, and this must surely have helped to evolve the
gentleness of mankind.
34 6 The Study of Animal Life APP.
(d) Among many monkeys society has begun. Families com-
bine for protection, and the combination favours the development
both of emotional and intellectual strength. Surely " man did not
make society, society made man."
B. Our Relation to Biology
.6. The Utility Of Science. As life is short, all too short for
learning the art of living, it 'is well that we should criticise our
activities, and favour those which seem to yield most return of
health and wealth and wisdom.
We are so curious about all kinds of things, so omnivorously
hungry for information, that the most trivial department of know-
ledge or science may afford exercise and mental satisfaction to its
votaries. The interest and pleasantness of science is therefore no
criterion.
Nor can we be satisfied with the assertion that science should
be pursued for science's sake. As in regard to the kindred dictum,
"art for art's sake," we require further explanation some ideal of
science and art. For it is not evident that knowledge is a good in
itself, especially if that knowledge be gained at the expense of the
emotional wealth which is often associated with healthy ignorance.
Nor is it safe to judge scientific activity by the material results
which the application of knowledge to action may yield. For a seed
of knowledge may lie dormant for centuries before it sends its shoots
into life, and many of the material results of applied science are not
unmixed blessings. Moreover, too narrow a view may be taken of
material results, so-called " necessaries " of existence may be exalted
over the "super-necessaries" essential to life; in short, what lies
about the mouth the nose, the ears, the eyes, the brain may be
forgotten.
We are nearer the truth if we combine the different standards of
science, and unify them by reference to the human ideal. 1 The utility
of science, and of biology among the other kinds of knowledge, is
to supply a basis of fact
(a) For the practice of useful arts (such as hygiene and
education), and for the guidance of conduct :
(b) For the satisfaction of our desire to understand and enjoy
the world and our life in it.
7. Practical Justification of Biology. The world of life
is so web-like that almost any part may touch or thrill us. It is
therefore well that we should learn what we can about it.
On plants we are very dependent for food and drink, for shelter
1 See Ruskin, The Eagles Nest (1880).
i Animal Life and Ours 347
and clothing, and for delight. Their evil influence is almost
restricted to that of disease germs and poisonous herbs.
Animals likewise furnish food (perhaps to an unwholesome
extent) ; and parts of their bodies are used (sometimes carelessly)
in manifold ways. Among those which are domesticated, some,
such as canary and parrot, cat and dog, are kept for the pleasure
they give to many ; others, such as dog, horse, elephant, and
falcon, are used in the chase ; others, notably the dog, assist in
shepherding ; horse and ass, reindeer and cattle, camel and
elephant, are beasts of burden ; others yield useful products, the
milk of cows and goats, the eggs of birds, the silk of silkworms,
and the honey of bees.
Formerly of much greater importance for good and ill as direct
rivals, animals have, through man's increasing mastery of life, become
less dangerous and more directly useful. Only in primitive con-
ditions of life and in thinly-peopled territories is something of the
old struggle still experienced. Their influence for ill is now for the
most part indirect, on crops and stocks. Parasites are common
enough, but rarely fatal. The serpent, however, still bites the
heel of progressive man.
Man's relations with living creatures are so close that systematic
knowledge about them is evidently of direct use. Indeed it is in
practical lore that both botany and zoology have their primal roots,
and from these, now much strengthened, impulses do not cease to
give new life to science.
If increase of food-supply be desirable, biology has something to
say about soil and cereals, about fisheries and oyster-culture. The
art of agriculture and breeding has been influenced not a little by
scientific advice, though much more by unrationalised experience.
If wine be wanted, the biologist has something to say about grafting
and the Phylloxera^ about mildew and Bacteria. It is enough to
point to the succession of discoveries by which Pasteur alone has
enriched science and benefited humanity.
But if we take higher ground and consider as an ideal the health-
fulness of men, which is one of the most obvious and useful
standards of individual and social conduct, the practical justification
of biological science becomes even more apparent.
Medicine, hygiene, physical education, and good-breeding (or
" eugenics ") are the arts which correspond to the science of
biology, just as education is applied psychology, as government is
applied sociology, and as many industries are applied chemistry and
physics. It would be historically untrue to say that the progress in
these arts was due to progress in the parallel sciences ; in fact the
progressive impulse has often been from art to science. " La
pratique a partout devance la theorie," Espinas says, and all
348 The Study of Animal Life APP.
historians of science would in the main confirm this. But it is
also true that science reacts on the arts and sometimes improves
them.
There may be peculiar aberrations of the art of medicine due to
the progress of the science thereof, but these are because the science
is partial, and hardly affect the general fact that scientific progress
has advanced the art of healing. The results of science have like-
wise supplied a basis to the endeavours to prevent disease and to
increase healthfulness, not only by definite hygienic practice but
perhaps still more by diffusing some precise knowledge of the
conditions of health.
The generalisations of biology, realised in men's minds, must in
some measure affect practice and public opinion. Spencer's
induction that the rate of reproduction varies inversely with the
degree of development sheds a hopeful light on the population
question ; the recognition of the influence which function and sur-
roundings have upon the organism suggests criticism of many
modes of economic production ; a knowledge of the facts and
theory of heredity must have an increasing influence on the art of
eugenics. Nor can I believe that the theory of evolution which
men hold, granting that it is in part an expression of their life and
social environment, does not also react on these.
In short, the direct application of biological knowledge in the
various arts of medicine, hygiene, physical education, and eugenics,
helps us to perfect our environment and our relations with it, helps
us to discover if not the "elixir vitae" some not despicable
substitute. And likewise, a realisation of the facts and principles of
biology helps us to criticise, justify, and regulate conduct, suggest-
ing how the art of life may be better learned, how human relations
may be more wisely harmonised, how we may guide and help the
ascent of man.
8. Intellectual Justification of Biology. But another
partial justification of Biology is found in our desire to understand
things, in our dislike of obscurities, in our inborn curiosity. There
is an intellectual as well as a practical and ethical justification of
the study of organic life.
Through our senses we become aware of the world of which we
form a part. We cannot know it in itself, for we are part of it and
only know it as it becomes part of us. We know only fractions of
reality real at least to us and these are unified in our experience.
(i) In the world around us we are accustomed to distinguish
four orders of facts. ** Matter " and " energy " we call those which
seem to us fundamental, because all that we know by our senses
are forms of these. The study of matter and energy or perhaps
we may say the study of matter in motion considered apart from
i Animal Life and Ours 349
life, we call Physics and Chemistry, of which astronomy, geology,
etc., are special departments.
(2) But we also know something about plants and animals, and
while all that we know about them is still dependent upon changes
of matter and motion, yet we recognise that the activities of the
organism cannot at present be expressed in terms of these. There-
fore we find it convenient to speak of life as a new reality, while
believing that it is the result of some combination of matters and
energies, the secret of -which is hidden.
(3) But we are also aware of another reality, our own mind. Of
this we have direct consciousness and greater certainty than about
anything else. And while some would say that what we are
conscious of when we think is a protoplasmic change in our brain
cells or is a subtle kind of motion, it is truer to say that we are
conscious of ourselves. It is our thought that we know, it is our
feeling that we feel, and as we cannot explain the thought or the
feeling in terms of protoplasm or of motion, we find it convenient to
speak of mind as a new reality, while believing it to be essentially
associated with some complex activity of protoplasm the secret of
which is hidden. For our knowledge of our own mental processes,
and of those inferred to be similar in our fellows, and of those
inferred to be not very different in intelligent animals, we establish
another science of Psychology.
(4) But we also know something about the life of the human
society of which we form a part. We recognise that it has a unity
of its own, and that its activities are more than those of its
individual members added up. We find it convenient to regard
society as another synthesis or unity though less definite than
either organism or mind and to our knowledge of the life and
growth of society as a whole, we apply the term sociology.
Thus we recognise four orders of facts and four great sciences
4. Society Sociology.
3. Mind Psychology.
2. Life Biology.
I. Matter and Energy . . . Physics and Chemistry.
Each of these sciences is dependent upon its predecessor. The
student of organisms requires help from the student of chemistry
and physics ; mind cannot be discussed apart from body ; nor can
society be studied apart from the minds of its component members.
Each order of realities we may regard as a subtle synthesis of
those which we call simpler. Life is a secret synthesis of matter
and energy ; mind is a subtle form of life ; society is a unity of
minds.
But it must be clearly recognised that the "matter and energy"
which we regard as the fundamental realities are only known to us
350 The Study of Animal Life APP. i
through what is for us the supreme reality ourselves mind. And
as in our brain activity we know matter and energy as thought, I
have adopted throughout this book what may be called a monistic
philosophy.
Having recognised the central position of Biology among the
other sciences, we have still to inquire what its task precisely is.
Our scientific data are (i) the impressions which we gather
through our senses about living creatures, and (2) the deductions
which we directly draw in regard to these. Our scientific aim
is to arrange these data -so that we may have a mental picture of
the life around us, so that we may be better able to understand
what that life is, and how it has come to be what it seems to be.
Pursuing what are called scientific methods, we try to make the
world of life and our life as organisms as intelligible as possible.
We seek to remove obscurities of perception, to make the world
translucent, to make a working thought-model of the world.
But we are apt to forget how ignorant we are about the realities
themselves, for all the time we are dealing not with realities, but
with impressions of realities, and with inferences from these im-
pressions. On the other hand, we are apt to forget that our deep
desire is not merely to know, but to enjoy the world, that the heart
of things is not so much known by the man as it is felt by the child.
APPENDIX II
SOME OF THE "BEST BOOKS" ON ANIMAL LIFE
To recommend the "best books" on any subject is apt to be like
prescribing the "best diet." Both depend upon age, constitution,
and opportunities. The best book for me is that which does me
most good, but it may be tedious reading for you. -Moreover,
books are often good for one purpose and not for another ; that
which helps us to realise the beauty and marvel of animal life may
be of little service to those who are preparing for any of the
numerous examinations in science. But the greatest difficulty is
that we are often too much influenced by contemporary opinion,
so that we lose our power of appreciating intellectual per-
spective.
The best way to begin the study of Natural History is to
observe animal life, but the next best way is to read such accounts
of observation and travel as are to be found in the works of
Gilbert White, Thoreau, Richard Jefferies, and John Burroughs,
or in Bates's Naturalist on the Amazons, Belt's Naturalist in
Nicaragua^ and Darwin's Voyage of the " Beagle" Sooner or later
the student will seek more systematic books, but it is not natural
that he should begin with a text-book of elementary biology.
In introducing you to the literature devoted to the study of
animals, I shall avoid the bias of current opinion by following the
history of zoology. I shall first name some of the more technical
books ; secondly, some of the more popular ; thirdly, some of the
more theoretical. If I may make the distinction, I shall first
mention books on zoology, secondly those on natural history,
thirdly those on biology.
A. Zoology.
(i) We can form a vivid conception of the history of zoology
by comparing it with our own. In our childhood we knew and
352 The Study of Animal Life APP.
cared more about the useful, dangerous, and strange animals than
about .those which were humble and familiar ; we had more in-
terest in haunts and habits than in structure and history ; we
were content with rough-and-ready classification, and cherished
' a feeling of superstitious awe in regard to the indistinctly-known
forms of life. We were inquisitive rather than critical ; we
accepted almost any explanation of facts, and, if we tried to inter-
pret, forced our borrowed opinions upon nature instead of trying
to study things for ourselves. So was it with those naturalists who
lived before Aristotle.
We must also recognise that the science of zoology had its
beginnings in a practical acquaintance with animals, just as botany
sprang from the knowledge of ancient agriculturists and herb-
gatherers. Much information in regard to the earliest zoological
knowledge has been gathered from researches into the history of
words, art, and religious customs, and there is still much to be
gleaned. Therefore I should recommend the student to dip into
those books which discuss the early history of man, such as
Lubbock's Prehistoric Times (1865), and Origin of Civilisation
(1870) ; Tylor's Primitive Culture (1871), and Anthropology
(1881); Andrew Lang's Myths, Ritual, and Religion ; besides
works on the history of philosophy, such as those of Schwegler and
of Zeller, which give some account of ancient cosmogonies.
(2) But just as there are precocious children, so there was an
early naturalist, whose works form the most colossal monument to
the intellectual prowess of any one thinker. The foundations of
zoology were laid by Aristotle, who lived 384-322 B.C. He
collected many observations, and argued from them to general
statements. He records over five hundred animals, and describes
the structure and habits, the struggles and friendliness, of some
of these. His is the first definite classification. His work
was dominated by the idea that animal life is a unity and part
of a larger system of things. In part his works should be read,
and besides the great edition by Bekker (Berlin, 1831-40),
there is a translation of The Parts of Animals by Dr. Ogle, and
of The History of Animals by R. Cresswell. See also G. J.
Romanes's "Aristotle as a Naturalist," Nwtitwntk Century (Feb.
1891, pp. 275-289). ^ofc/.A** n
(3) After the freedom of early childhood, and in most cases
after precocity too, there comes a lull of inquisitiveness. Other
affairs, practical tasks, games and combats, engross the attention,
and parents sigh over dormant intellects ; so the historian of
zoology sighs over the fifteen centuries during which science
slumbered. The foundations which Aristotle had firmly laid
remained, but the walls of the temple of knowledge did not rise.
n Some of the "Best Books" on Animal Life 353
The seeds which he had sown were alive, but they did not germi-
nate. Men were otherwise occupied, with practical affairs, with
the tasks of civilisation alike in peace and war, though some at
their leisure played with ideas which they did not verify. There
were some exceptions; such as Pliny (23-79 A.D.), a diligent but
uncritical collector of facts, and Galen (130-200 A.D.), a medical
anatomist, who had the courage to dissect monkeys ; besides the
Spanish bishop Isidor in the seventh century, and various Arabian
inquirers. It . will nut be unprofitable to look into the Natural
History of Pliny, which has been translated by Bostock and
Riley.
(4) But just as there is in our life a stage happy are those who
prolong it during which we delight in fables and fairy tales, so
there was a long period of mythological zoology. The schoolboy
who puts horse-hairs into the brook, and returns after many days
to find them eel-like worms, is doing what they did in the Middle
Ages. For then fact and fiction were strangely jumbled ; credulity
ran riot along the paths of science ; allegorical interpretations and
superstitious symbolisms were abundant as the fancies which flit
through the minds of dreamers. Scientific inquiry was not en-
couraged by the theological mood of the time ; and just as Scotch
children cherish The Beasts of the Bible as a pleasantly secular book
with a spice of sacredness which makes it legitimate reading on
the Sabbath, so many a mediaeval naturalist had to cloak his
observations in a semi- theological style.
In illustration of the mood of the mediaeval naturalists, which
is by no means to be carelessly laughed at, read John Ashton's
Curious Creatures (Lond., 1890), in which much old lore is retold,
often in the words of the original writers. The most characteristic
expression of mythical Zoology is a production often called Physio-
logus. It is found in about a dozen languages and in many
different forms, being in part merely a precipitate of floating
traditions. It is partly like a natural history of the beasts of the
Bible and prototype of many similar works, partly an account of
the habits of animals, the study of which modern zoologists are
apt to neglect, partly a collection of natural history fables and
anecdotes, partly a treatise on symbolism and suggestive of the
poetical side of zoology, partly an account of the medicinal and
magical uses of animals. For many centuries it seems to have
served as a text-book, a fact in itself an index to the slow progress
of the science. Its influence on art and literature has been con-
siderable, and it well illustrates the attempt to secure for the
unextinguishable interest in living things a sanction and foothold
under the patronage of theology. A series of fifty emblems is
described, among others the lion which sleeps with its eyes open,
2 A
354 The Study of Animal Life AIT.
the lizard which recovers its sight by looking at the sun, the eagle
which renews its youth, the tortoise mistaken for an island, the
serpent afraid of naked man, and the most miserable ant-lion,
which is not able either to take one kind of food or digest the
other.
(5) But delight in romance is replaced by a feeling of the need
for definite knowledge, and the earlier years of adolescent man-
hood and womanhood are often very markedly characterised by a
thirst and hunger for information. Which of us now perhaps
blase with too much learning does not recall the enthusiasm for
knowing which once swayed our minds ? Stimulated in a hundred
ways by new experiences and responsibilities, our appetite for facts
was once enormous. This was the mood of naturalists during the
next great period in the history of zoology.
The freer circulation of men and thoughts associated with the
Crusades ; the discovery of new lands by travellers like Marco
Polo and Columbus ; the founding of universities and learned
societies ; the establishment of museums and botanic gardens ; the
invention of printing and the reappearance of Aristotle's works in
dilution and translation ; and many other practical, emotional, and
intellectual movements gave fresh force to science, and indeed to
the whole life of man. If we pass over some connecting links,
such as Albertus Magnus in the thirteeenth century, we may call
the period of gradual scientific renaissance that of the Encyclo-
paedists. This somewhat cumbrous title suggests the omnivorous
habits of those early workers. They were painstaking collectors
of all information about all animals ; but their appetite was
greater than their digestion, and the progress of science was
in quantity rather than in quality. Prominent among them were
these four, the Englishman Edward Wotton (1492-1555), who
wrote a treatise De Differentiis Animalium ; the Swiss Conrad
Gesner (1516-65), author of a well-known Historia Animalium ;
the Italian Aldrovandi x (b. 1522); and the Scotsman Johnston
(b. 1603).
About the middle of the eighteenth century the best aims of the
Encyclopaedists were realised in Buffon's Histoire Naturelle, which
appeared in fifteen volumes between 1749 and 1767. This work
not only describes beasts and birds, the earth and man, with an
eloquent enthusiasm which was natural to the author and pleasing
to his contemporaries, but is the first noteworthy attempt to
expound the history or evolution of animals. Its range was very
wide ; and its successors are not so much single books as many
different kinds of books, on geology and physical geography, on
classification and physiology, on anthropology and natural history.
There is a good French edition of Buffon's complete works by
ii Some of the "Best Books " on Animal Life 355
A. Richard 1825-28), and at least one English translation. Three
large modern books on natural history correspond in some degree
to the Histoire Naturelle^ viz. CasselPs Nattiral History ', edited by
P. Martin Duncan (6 vols. ; London, 1882) ; The Standard or
Riverside Natural History, edited by J. S. Kingsley (6 vols. ;
London, 1888); and a remarkable work well known as Brehm's
Thierlebeii) of which a new (3rd) edition is at present in progress
(10 vols.; Leipzig and Wien, 1890). Those who read German
will find in Carus Sterne's (Ernst Krause's) Werden und Vergehen
(3rd ed. ; Berlin, 1886) the most successful attempt hitherto
made to combine in one volume a histoiy of the earth and its
inhabitants.
(6) From Buffon till now the history of biology shows a pro-
gressive analysis, a deeper and deeper penetration into the structure
and life of organisms. From external form to the internal organs,
from organs to the tissues which compose them, from tissues to
their elementary units or cells, and from cells to the living matter
itself, has been the progress of the science of structure Mor-
phology. From habit and temperament to the work of organs,
from the functions of organs to the properties of tissues, from these
to the activities of cells, and from these finally to the chemical and
physical changes in the living matter or protoplasm, has been the
progress of the science of function Physiology. Such is the lucid
account which Prof. Geddes has given of the last hundred years'
progress; see his article "Biology" in the new edition of
Chambers's Encyclopedia. Following the metaphor on which we
have already insisted, we may compare this century of analysis to
the period of ordered and more intense study which in the individual
life succeeds the abandonment of encyclopsedic ambitions.
We should clearly understand the histoiy of this gradually
deepening analysis of animals ; for if we would be naturalists"
we must retread the same path. The history of biology has still
to be written, but there are already some useful books and papers,
notably J. V. Carus, Geschichte der Zoologie (Miinchen, 1872) ;
J. Sachs, Geschichte der Botanik (Miinchen, 1875), translated
into English (Oxford, 1890); W. Whewell, History of the
Inductive Sciences (London, 1840) ; articles " Morphology "
and "Physiology," Encyclopedia Britannica, by P. Geddes and
M. Foster ; H. A. Nicholson, Natural History : its Rise and
Progress in Britain (Edinburgh, 1888); A. B. Buckley, Short
History of Natural Science ; E. Perrier, La Philosophie Zoologique
avant Darwin (Paris, 1884) ; Ernst Krause (Carus Sterne), Die
Allgemeine Weltanschauung in ihrer historischen Entwickelung
(Stuttgart, 1889). Very instructive, not least so in contrast,
are two articles, "Biology" (in Chambers's Encyclopedia), by
356 77/6? Study of A n imal Life A PP.
P. Geddes, and "Zoology" (in Encyclopedia Britannicd), by E.
Ray Lankester.
If we think over the sketch which Professor Geddes has given,
we shall see how easy it is to arrange the literature the first step
towards mastering it. (a) The early anatomists were chiefly
occupied with the study of external and general features, very
largely moreover with the purpose of establishing a classification.
The Sy sterna Natunz of Linnaeus (ist ed., 1735 ; I2th, 1768) is
the typical work on this heavily-laden shelf of the zoological
library. It is to such books that we turn when we wish to
identify some animal, but the shelf is very long and most of the
volumes are very heavy. Each chapter of Linne's Sy sterna has
been expanded into a series of volumes, or into some gigantic
monograph like those included in the series of " Challenger" Reports,
or The Fatina and Flora of the Gulf of Naples. If I am asked
to recommend a volume from which the eager student may identify
some British flower, I can at once place Hooker's Flora in his
hands. But it is more difficult to help him to a work by which he
may identify his animal prize. There are special works on British
Mammals, Birds, Fishes, Molluscs, Insects, etc., but a compact
British Fauna is much wanted. I shall simply ' mention Bronn's
Klassen und Ordnungen des Thierreiches, a series of volumes still
in progress; Leunis, Synopsis des Thierreiches (Hanover, 1886);
the British Museum Catalogues (in progress) ; and P. H. Gosse's
Manual of Marine Zoology of the British Islands (1856).
() Cuvier's Regne Animal (1829) is the typical book on the
next plane of research that concerned with the anatomy of organs.
I should recommend the student on this path to begin with Pro-
fessor F. Jeffrey Bell's Comparative Anatomy and Physiology (Lond. ,
1886) ; after which he will more readily appreciate the text-books
on Comparative Anatomy by Huxley, Gegehbaur, Claus, Wieders-
heim, Lang, etc. As an introduction I may also mention my
Outlines of Zoology (Edin., 1892). As a book of reference
Hatchett Jackson's edition of Rolleston's Forms of Animal Life
(Oxford, 1888) is of great value, not least on account of its
scholarly references to the literature of zoology. The zoological
articles in the Encyclopedia Britannica^ many of which are pub-
lished separately, are not less useful. As guides in serious practical
work may be noticed A Course of Elementary Instruction in
Practical Biology by Profs. T. H. Huxley and H. N. Martin,
revised by Profs. G. B. Howes and D. H. Scott (Lond., 1888);
Howes's Atlas of Practical Elementary Biology (Lond., 1885) ;
A Course of Practical Zoology by Prof. A. Milnes Marshall and
Dr. C. H. Hurst (3rd ed., Lond., 1892); Prof. C. Lloyd
Morgan's Animal Biology (Lond. , 1889); Vogt and Yung, Traite
ii Some of the " Best Books " on Animal Life 357
cTAnatomie comparee pratique (Paris, 1885-92) or in German
(Braunschweig) ; Prof. W. K. Brooks's Handbook of Invertebrate
Zoology for Laboratories and Seaside Work (Boston, 1882); Prof.
T. J. Parker's Zootomy (Lond., 1884) and Practical Biology
(Lond., 1891).
(c} As early as 1801, Bichat had penetrated beneath the organs
to the tissues which compose them, and his Anatomic Generale is
the forerunner of many works on minute anatomy or histology.
From the comparative histology of animals by Leydig (Histologie,
1867) the zoological student must begin, but to follow it up he must
have recourse to the pages of scientific journals. As a guide in
microscopic work, Dr. Dallinger's new edition of Carpenter's well-
known work, The Microscope (Lond., 1891) may be cited.
(d) In 1838-39, Schwann and Schleiden, two German naturalists,
clearly stated a doctrine towards which investigation had been
gradually tending, namely, that each organism was built up of
cells, and originated from a fertilised egg-cell. In the establish-
ment of this ' ' cell-theory " the study of structure became deeper,
and the investigation of animal cells still becomes more and more
intense. To gain an appreciation of this step in analysis, the
student may well begin with the article " Cell" in the new edition
of Chambers's Encyclopedia, and with the articles " Morphology"
and "Protozoa" in the Encyclopedia Britannica* From these he
will discover how his studies may be deepened.
(e) Finally, with the improvement of microscopic instruments
and technique, investigation has touched the bottom, as far as
biology is concerned, in the study of the living stuff or protoplasm
itself. Again, I refer you to the articles "Protoplasm" in the
Encyclopedia Britannica and in Chambers's Encyclopedia.
I shall not follow the history of physiology in detail, but content
myself with saying that (a) from the conception of a living body
ruled by spirits or dominated by a temperament, physiologists passed
to consider it (K) as an engine of living organs, then (c) as a com-
plex web of tissues, then (d] as a city of cells, and finally (e) as a
whirlpool of living matter. I recommend you to read first the
article " Physiology" in the Encyclopedia Britannica^ then Huxley's
Crayfish (Imernational Science Series), and his Elementary Text-
book of Physiology, then Jeffrey Bell's Comparative Anatomy and
Physiology and Lloyd Morgan's Animal Biology, after which you
may pass to larger works such as the text-books of Kirkes (new ed. ,
1892) ; Bunge (Lond., 1890) ; Landois and Stirling, McKendrick,
and Foster, and to the studies on comparative physiology by
Krukenberg, Vergleichend-Physiologische Studien and Vortrdge
(Heidelberg, 1882-88).
In the above summary nothing has been said about the history
358 The Study of Animal Life APP.
of animals in their individual life (embryology), nor of their gradual
appearance upon the earth (palaeontology), nor about their distri-
bution in space. As regards embryology, begin with the article
in Chambers's Encyclopedia, and pass thence to the text-books
of A. C. Haddon, F. M. Balfour, M. Foster and F. M. Balfour,
O. Herfwig, Heider and Korschelt, etc. A short account of
distribution in time will be found in A. Heilprin's Distribution of
Animals (International Science Series), from which advanced
students may pass to the Text -book of Paleontology by H. A.
Nicholson and R. Lydekker (2 vols., Lond. and Edin., 1889), to
the French work of Gaudry, Les enchainements du monde animal
dans les temps geologiques (Paris, 1888-90), or to the German
works of Zittel and of Neumayr. Heilprin's book is again the
best introduction to the study of distribution in space, while
Wallace's Geographical Distribution of Animals (Lond., 1876)
remains the principal work of reference.
For progressive research I may refer the student to the Journal
of the Royal Microscopical Society (edited by Prof. F. Jeffrey Bell),
which gives summaries of recent researches ; the Quarterly Journal
of Microscopical Science (edited by Profs. E. Ray Lankester, Klein,
Sedgwick, and Milnes Marshall) ; and of course Nature, in which
summaries and discussions are often to be found. More popular
journals are the American Naturalist and Natural Science.
Of all elementary books the best to begin with are two volumes
by "A. B. Buckley, Life and her Children (backboneless animals),
and Winners in Life's Race (backboned animals) ; but I shall now
mention other ways of beginning.
B. Natural History.
" Certain dreadfully scientific persons, who call themselves by
the name of naturalists, seem to consider zoology and comparative
anatomy as convertible terms. When they see a creature new to
them, they are seized with a burning desire to cut it up, to analyse
it, to get it under the microscope, to publish a learned book about
it which no one can read without an expensive Greek lexicon, and
to put up its remains in cells and bottles. They delight in an
abnormal heemapophysis ; they pin their faith on a pterygoid pro-
cess ; they stake their reputation on the number of tubercules on
a second molar tooth ; and they quarrel with each other about a
notch on the basisphenoid bone." Thus, in a breezy way, did the
Rev. J. G. Wood laugh at the morphological zoologists. But his
good-humoured criticism is apt to be misleading. For if science,
as such, be justifiable, the work of the anatomist is warranted as
ii Some of the " Best Books " on Animal Life 359
part of it, and is neither less nor more valuable than that of the
field naturalist. We may criticise the details of the anatomist's
analysis, we may believe that his discipline is often pressed
unnaturally upon students, we may beseech him to be less
pedantic ; but to remind him that the study of structure requires
to be supplemented by the study of life is like reminding the field
naturalist that animals have bones and muscles. Both are true
statements, but somewhat obvious.
The zoologist has deliberately given himself up to analysis, and
if the world is to become translucent to us, we must include within
our knowledge what he can tell us about the structure and activities
of animals, alike as unities and as complex combinations of organs,
tissues, and cells. Let us agree to call this serious study, including
the morphological and physiological aspects which we have already
explained, " zoology." We must acknowledge that few of us can
become zoological experts. But let not this hinder us from per-
ceiving that it is not difficult to understand towards what end and
by what method Linnaeus and Cuvier, Bichat and Claude Bernard,
and the other great masters worked ; nor let it deter us from using
all natural opportunities of practically observing the forms and
powers of animal life. We shall soon feel that "zoology" is
neither less interesting nor less essential than the work of the
field naturalist, we shall recognise that its terminology is not more
complex than that of seamanship, and we may even admit that
from clear zoological thinking our contemplation of nature acquires
an additional intensity of emotion. " Tout naturaliste cachait plus
ou moins tin amateur d'idylles ou d'eclogues." What Hamerton
says with reference to an artist's education applies also to the
student of science: "The harm is not in the study (of plants),
it is in the forgetfulness of large relations to which this minute
observation of nature has occasionally led those who were addicted
to it." Zoologists are not the only workers who sometimes lose
their sense of perspective.
Now, however, I would address those who have little time or
opportunity for "zoology," but who have an interest ^ in the life
and habits of animals, and desire to appreciate these more
thoroughly. This knowledge of animals as personalities in
struggle and friendliness, in hate and love, in birth and death,
I would call "natural history," in contrast to analytic "zoology"
on the one hand, and generalising "biology" on the other. For
I restrict the latter term to the general theory of life its nature
and origin, its growth and continuance. It matters little what
names are given to these three aspects of the study of animal life ;
thus what I call "Natural History" Prof. Ray Lankester calls
more precisely "Bionomics"; but it is important to recognise all
3 6
The Stiidy of Animal Life
the three as essential, and to cease from drawing prejudiced com-
parisons between them.
Their relations may be summarised as follows :
"NATURAL HISTORY."
Q
CD
fauna >
1
cl ^ ss in relation
1
Study of the enus tO
real life one another
w
f species ^ nd to the}r
P
families surroundings,
pairs
individuals
T3 ^
;
| e
2
?
(5) Organism.
g
S, p
8
(4) Organs.
K p.
(3) Tissues.
p i
crq.
-
(2) Cells.
5'
(i) Protoplasm.
o
p
p
Study of Structure Study of Activities
p
(Morphological) (Physiological).
1
v ' v - . '
p
"ZOOLOGY."
6u
To those interested in "Natural History," there is little need
to give the primary word of counsel "OBSERVE," for to do so is
their delight ; nor do they need to be told that sympathetic feeling
with animals, delight in their harmonious beauty, and poetical
justice of insight which recognises their personality, are qualities
of a true naturalist, as every one will allow, except those who are
given up to the idolatry of that fiction called " pure science."
There is a maniacal covetousness of knowledge which one has
no pleasure in encouraging. We do not want to know all that is
contained even in Chambers's Encyclopaedia , though we wish to
gain the power of understanding, realising, and enjoying the
various aspects of the world around us. We do not wish brains
laden with chemistry and physics, astronomy and geology, botany
ii Some of the "Best Books " on Animal Life 361
and zoology, and other sciences, though we would have our eyes
lightened so that we may see into the heart of things, our brains
cleared so that we may understand what is known and unknown
when we are brought naturally in face of problems, and our emotions
purified so that we may feel more and more fully the joy of life.
Therefore I would, in the name of education, urge students to
begin naturally, with what interests them, with the near at hand,
with the practically important. A circuitous course of study,
followed with natural eagerness, will lead to better results than the
most logical of programmes if that take no root in the life of the
student.
Let me suggest some of these indirect ways of beginning.
Begin with domesticated animals and their histoiy. See Darwin's
Variation of Animals and Plants under Domestication (1868), etc.
Concentrate your attention on some common animals. See, for
instance, Darwin's Formation of Vegetable Mould through the
action of Worms (1881); Mivart's Frog (Nature Series, London);
Huxley's Crayfish (Internat. Sci. Series, London) ; M 'Cook's
North American Spiders (2 vols., Philadelphia, 1889-90); F.
Cheshire's Bees and Bee-keeping (vol. i., Lond., 1886); Lubbock's
Ants, Sees, and Wasps (Internat. Sci. Series, London) ; Flower's
Horse (Lond., 1891).
Enjoy your seaside holiday. See Charles Kingsley's Glaucus ;
J. G. Wood's Common Objects of the Sea-Shore (1857); P. H.
Gosse's Manual of Marine Zoology (1856), and Tenby; G. H.
Lewes's Seaside Studiet(Edm. 1858); L. Fredericq, La Lutte pour
V existence chez les Animaux Marins (Paris, 1889).
Form an aquarium. See J. G. Wood's Fresh and Salt Water
Aquarium ; P. H. Gosse, The Aquarium (1854), and many similar
works.
Begin a naturalist's year-book. See the Naturalises Diary
by Roberts ; the Field Naturalists Handbook, by J. G. and
Th. Wood (Lond., 1879); and K. Russ, Das heimische
Naturleben im Kreislauf des Jahres ; Ein Jahrbuch der Natur.
(Berlin, 1889).
Observe the animals you see on your country walks. See
J. G. W T ood's Common Objects of the Country (1858), The Brook
and its Banks (1889) ; Life of a Scotch Naturalist ', Thomas
Edward, by Samuel Smiles ; The Moor and the Loch, by J.
Colquhoun (Edin. 1840, 8th ed. 1878) ; Wild Sports and Natural
History of the Highlands, by Charles St. John (Lond., illust. ed.,
1878); Woodland, Moor, and Stream, edited by J. A. Owen
(Lond., 1889); W. Marshall, Spaziergdnge eines Naturforschers
(Leipzig, 1888) ; Lloyd Morgan's Sketches of Animal Life (Lond.,
1892), etc. etc.
362 The Study of Animal Life AFP.
Another natural way of beginning is to work out some subject
which attracts you. It becomes a centre round which a crystal
grows. Muybridge's photographic demonstrations of animal loco-
motion have interested us in the flight of birds, let us follow this
up by observation and by reading, e.g., Ruskin's Love's Meinie
(1881); Pettigrew's Animal Locomotion (Internat. Sci. Series,
1873); Marey's Animal Mechanism (Internat. Sci. Series, 1874);
Marey's Le Vol des Oiseanx (Paris, 1890).
The colours of animals appeal to many people. Read E. B.
Poulton's volume (1890) in the Internat. Sci. Series, and Grant
Allen's Colour Sense, and F. E. Beddard's Animal Colouration
(Lond., 1892).
The relations between plants and animals are entrancingly
interesting. Watch the bees and other insects in their flight,
and read Darwin's volumes on the Fertilisation of Orchids (1862)
and on Cross- Fertilisation (1876); Hermann Miiller's Fertilisation
of Flowers (transl. by Prof. D'Arcy Thompson, Lond., 1883);
Kerner's Flowers and their Unbidden Guests ; the articles on
" Insectivorous Plants, "in Encyclop. Britannica, and in Chambers's
Encyclop., or Darwin's work (1875).
Again, many of us are directly interested in foreign countries.
Let the practical interest broaden, it naturally becomes geographical
and physiographical, and extends to the natural history of the
region. No more pleasant and sane way of learning about the
ways and distribution of animals could be suggested than that
which follows as a gradual extension of physiographical knowledge.
See Dr. H. R. Mill's Realm of Nature^ and the following samples
from the long list of books by exploring naturalists :
A. Agassiz, Three Cruises of the "Blake" (Boston and New York,
1888).
S. W. Baker, Wild Beasts and Ways : Reminiscences of Europe,
Asia, Africa, and America (London, 1890).
H. W. Bates, Naturalist on the Amazons (5th ed. , London,
1884).
T. Belt, Naturalist in Nicaragua (2nd ed. , London, 1888).
W. T. Blanford, Observations on Geology and Zoology of Abyssinia
(Lond., 1870).
P. B. Du Chaillu, Explorations and Adventures in Equatorial Africa,
(Lond., 1861) ; Ashango Land (1867).
R. O. Cunningham, Notes on the Natural History of the Straits of
Magellan (Edin., 1871).
Darwin, Voyage of the "Beagle" (1844, new ed. 1890).
H. Drummond, Tropical Africa (Lond., 1888).
H. O. Forbes, A Naturalist's Wanderings in the Eastern Archi~
pelago (Lond. , 1885).
Guillemard, Cruise of the " Marchesa" (Lond., 1886).
ii Some of the " Best Books " on Animal Life 363
A. Heilprin, The Bermuda Islands (Philadelphia, 1889).
S. J. Hickson, A Naturalist in North Celebes (London, 1889).
W. H. Hudson, The Naturalist in La Plata (Lond., 1892).
A. v. Humboldt, Travels to the Equinoctial Regions of America ;
Aspects of Nature (Trans. 1849); Cosmos (Trans. , 1849-58).
Lumholtz, Among Cannibals (Lond., 1889).
H. N. Moseley, Notes by a Naturalist on the " Challenger " (Lond. ,
1879, new ed. Lond., 1892).
A. E. Nordenskiold, Voyage of the " Vega" (Lond., 1881).
F. Gates, ed. by C. G. Gates, Matabele Land and the Victoria
Falls, a Naturalist's Wanderings in the Interior of S. Africa
(1881).
N. M. Przewalski, Wissenschaftliche Resultate der nach Centralasien
unternommenen Reisen (Leipzig, 1889).
H. Seebohm, Siberia in Europe (Lond., 1880) ; and Siberia in Asia
(1882).
J. E. Tennent, Natural History of Ceylon (Lond., 1861).
Wyville Thomson, The Depths of the Sea (Lond., 1873) ; Narrative of
the Voyage of the " Challenger" (1885). Cf. A. de Folin, Sous
les Mers (Paris, 1887) ; H. Filhol, La Vie au fond des Mers
(Paris, 1886) ; W. Marshall, Die Tiefsee und ihr Leben (Leipzig,
1888).
Tristram, The Flora and Fauna of Palestine.
Tschudi, Thierleben der Alpenwelt.
A. R. Wallace, Malay Archipelago (Lond., 1869); Tropical Nature
(1878) ; Island Life (1880).
Ch. Waterton, Wanderings in South America (ed. by J. G. Wood,
1878).
C. M. Woodford, Naturalist among the Head-hunters (London,
1890).
Prominent among those who have helped many to realise the
marvel and beauty of nature, a widely-felt gratitude ranks Gilbert
White, Henry Thoreau, Charles Kingsley, Richard Jefferies, J. G.
Wood, John Ruskin, and John Burroughs.
GILBERT WHITE (1720-1793) is known to all as the author of
The Natural History and Antiquities of Selborne, in the County of
Southampton (1788), a book consisting of a series of letters addressed
to a few friends. A good edition is that by J. E. Harting (6th ed.,
London, 1888), but there is a cheaper one, edited by Richard
Jefferies, in 'the Camelot Series.
HENRY THOREAU (1817-1862), the author of Walden, A Week
on Concord, and other much-loved books.
CHARLES KINGSLEY (1819-1875). See his Glancus (Lond.,
1854) ; Water-Babies ; and popular lectures.
364 TJie Study of Animal Life APP.
RICHARD JEFFERIES (1848-1887).
See The Eulogy of Richard Jefferies, by Walter Besant (London,
1888), and the following works, some of which are published in
cheap editions: The Gamekeeper at Home (1878); Wild Life
in a Souther ?i County (1879) ; The Amateur Poacher (1880) ;
Round about a Great Estate (1881) ; Nature near London
(1883) ; Life of the Fields (1884) ; Red Deer (1884) ; The Open
J. G. WOOD, whom we have lately lost, has done more than
any other to popularise natural history in Britain.
See Life of J. G. Wood, by his son, Theodore Wood (Lond., 1890) ;
My Feathered Friends (1856); Common Objects of the Seashore
(1857); Common Objects of the Country (1858); his large
Natural History (1859-63) ; Glimpses into Petland (1862) ; Homes
without Hands (1864) J The Dominion of Man (1887) ; and other
works.
JOHN RUSKIN. See the Eagle's A T est, Queen if the Air, Love's
Meinie, Proserpina, Deucalion, and 'Ethics of the Dust.
JOHN BURROUGHS.
See the neat shilling editions of Wake Robin (1871), Winter Sun-
shine (1875), Birds and Poets (1877), Locusts and Wild Honey
(1879), Pepacton (1881), Fresh Fields (1884), Signs and Seasons
(1886).
See also :
GRANT ALLEN, The Evolutionist at Large ; Vignettes from
Nature, etc.
FRANK BUCKLAND, Curiosities of Natural History (London,
1872-77), and his Life.
P. H. GOSSE. Romance of Natural History (London, 1 860-61).
P. G. HAMERTON, Chapters on Animals ; The Sylvan Year
(3rd ed., London, 1883).
W. KIRBY AND W. S PENCE, Introduction to Entomology
(London, 1815).
F. A. KNIGHT, By Leafy Ways ; Idylls of the Field (London,
1889).
PHIL ROBINSON, The Poet's Birds (London, 1883); and The
Poet's Beasts (London, 1885).
ANDREW WILSON, Leaves from a Naturalist's Note-Books;
Chapters on Evolution, etc.
ii Some of the " Best Books " on Animal Life 365
C. Biology.
Having offered counsel to those who would study the literature
of Zoology and of Natural History, I shall complete my task of
giving advice by addressing those who are strong enough to
inquire into the nature, continuance, and progress of life. It is
to students of mature years that this "biological" study is most
natural, for young folks should be left to see and enjoy as much
as possible, till theories grow in them as naturally as "wisdom
teeth." This also should be noted in regard to the study of
evolution and the related problems of biology, that though all the
generalisations reached must be based on the research and observa-
tion of zoologists, botanists, and naturalists, and are seldom fully
appreciated by those who have little personal acquaintance with
the facts, yet sound and useful conclusions may be, and often are,
obtained by those who have had no discipline in concrete scientific
work.
Besides the general question of organic evolution there are
special subjects which the student of biology must learn to think
about: Protoplasm, or "the physical basis of life;" Repro-
duction, Sex, and Heredity, or "the continuance of life;" and
Animal Intelligence, or "the growth of mind." Before passing
to the literature on these subjects, it may be noted that there are
two general works of pioneering importance, namely, Herbert
Spencer's Principles of Biology (2 vols., Lond., 1864-66), and
Ernst Haeckel's Generelle Morphologic (2 vols., Berlin, 1866).
Protoplasm. Of this the student should learn how little we
know. Yet this is not very easy, since the most important recent
contributions, such as those of Professors Hering and Gaskell, are
inaccessible to most. The gist of the matter, however, may be
got hold of by reading : (a] three articles in the Encyclopedia
Britannica, "Physiology" (Prof. M. Foster), " Protoplasm "
(Prof. P. Geddes), and " Protozoa" the large type (Prof. E. Ray
Lankester) ; (//) the Presidential Address to the Biological Section
of the British Association, 1889, by Prof. Burdon Sanderson
{Nature, xl., September 1889, pp. 521-526); and (c] the article
"Protoplasm" in the new edition of Chambers's Encyclopaedia.
Of the abundant literature on the philosophical questions which
the scientific conception of living matter raises, I shall mention
Huxley's address on "The Physical Basis of Life," published
among his collected essays; Hutchison Stirling's tract, "As
regards Protoplasm;" the chapter on "Vitalism" in ^Bunge's
Physiological Chemistry (translated, London, 1890).
Reproduction, Sex, and Heredity. For adult students,
and no others should be encouraged to face the responsibility of
366 The Study of Animal Life APF.
inquiry into such matters, the most convenient introduction will
be found in The Evolution of Sex (Contemporary Science Series,
Lond., 1889), by Prof. Geddes and myself. In that work there
are references to others. A survey of modern opinions and con-
clusions in regard to heredity may be obtained from the article in
Chambers's Encyclopedia, whence the student will pass unbiassed
to the essays of Weismann, Papers on Heredity and Kindred
Subjects (translated by E. B. Poulton, S. Schonland, and A. E.
Shipley, Oxford, 1889), to the works of Francis Gal ton, especially
his Natural Inheritance (Lond., 1889), and to other important
books mentioned in the article referred to.
Animal Intelligence. A recent work by Professor C. Lloyd
Morgan, Animal Life and Intelligence (Lond., 1890), supplies the
best introduction to those interesting questions in the discussion of
which the biologist becomes a psychologist. The most reliable
treasury of facts is certainly G. J. Romanes's Animal Intelligence
(Internat. Sci. Series, 4th ed., Lond., 1886), to which may
be added Couch's Illustrations of Instinct (1847), Lander Lindsay's
Mind in Animals (1879), Biichner's A us dem Geistesleben der Thiere
(2nd ed., Berlin, 1877) and Liebe und Liebesleben in der Thierwelt
(Berlin, 1879) ; Max Perty, Ueberdas Seelenleben der Thiere (Leipzig,
1876) ; Houzeau, Des Facultes mentales des Animaux (Brussels,
1872). Of t unique value is the work of A. Espinas, Des Societes
Animates, Etude de Psychologie comparee (Paris, 1877). See also
P. Girod, Les Societes chez les animaux (Paris, 1890). I should
also mention that Brehm's Thierleben (1863-69), a great work now
in process of re-edition (10 vols., Leipzig), is a marvellous
treasury of information in regard to the ways and wisdom of
animals, and that we have in Verworn's Psycho- Physiologische
Protisten Studien (Jena, 1889) a very interesting and important
study of the dawn of an inner life in the simplest animals or
Protozoa. Of the ingenious work of animals, an admirably terse
description is given in F. Houssay's Les Industries des Animaux
(Paris, 1889). For theories of instinct, see especially Romanes,
Mental Evolution in Animals (Lond., 1883); Darwin, Origin of
Species ; Wallace, Contributions to the Theory of Natural Selection ;
Spencer, Principles of Psychology and Principles of Biology ; G. H.
Lewes, Problems of Life and Mind (Lond., 1874-79); Samuel
Butler, Life and Habit (Lond., 1878); J. J. Murphy, Habit and
Intelligence; E. von Hartmann, Das Unbewusste vom Stand-
punkte der Physiologie und Descendenztheorie (2nd ed., Berlin,
1877) f' "Schneider, Der Thierische Wille (Leipzig, 1880); Eimer,
Organic Evolution ; Weismann, Papers on Heredity.
The Fact of Organic Evolution. The student's first task
in regard to Evolution is to make himself acquainted with the
ii Some of the " Best Books " on Animal Life 367
arguments which show that the animals and plants now alive are
descended from simpler ancestors, these from still simpler, and
so on back into the mists of life's beginnings. To realise that the
present is child of the past is to realise the fact of Evolution, and
the surest way to grasp the biological verification of this fact is to
undertake a course of practical study. Failing this, we must, I
suppose, read up the subject. Romanes's Evidences of Evolution
(Nature Series, Lond.) gives a convenient statement of the case,
and his Rosebery -Lectures will be more exhaustive. Clodd's
Story of Creation: a plain account of Evolution (Lond., 1888)
sums up the evidence in small compass ; another very terse state-
ment will be found in H. De Varigny's Experimental Evolution
(Lond., 1892); Haeckel's Natural History of Creation (Berlin,
1868) the most popular of his works, now in its eighth edition
(Jena, 1890) is available in translation (Lond., 1879); Huxley's
American Addresses (Lond., 1877) have even greater charm of
style; Carus Sterne's Werden und Vergehen (3rd ed., Berlin,
1886) is perhaps the best of all popular expositions; while the
thorough student will find most satisfaction in the relevant
portions of Darwin's Origin of Species^ and Spencer's Principles
of Biology.
History of Evolution Theories. As the idea of Evolution
is very ancient, and as it was expounded in relation to animal life
by many competent naturalists before Darwin's intellectual coin
became current throughout the world, it is unwise that students
should restrict their reading to Darwinian and post-Darwinian
literature. The student of Evolution should know how Buffon,
Erasmus Darwin, Lamarck, Treviranus, the St. Hilaires, Goethe,
even Robert Chambers, and many other pre-Darwinians dealt with
the problem. Those who desire to preserve their sense of historical
justice should read one or more of the following : Huxley's article
on " Evolution " in the Encyclopedia Brilannica ; Samuel Butler's
interesting volume on Evolution Old and New (Lond., 1879);
Perrier's Philosophie Zoologiqite avant Darwin (Paris, 1884) ; the
historical chapters of Haeckel's Natural History of Creation ;
Carus's Geschichte der Zoologie, and some other historical works
already referred to (p. 355) ; A. de Candolle's Histoire des
Sciences et des Savants depuis deux Siecles (Geneve, Bale, 1883);
Carus Sterne's (Ernst Krause's) excellent work, Die Allgemeine
Weltanschatiung (Stuttgart, 1889) ; De Quatrefages, Charles
Darwin et ses precurseurs fran$ais (Paris, 1870).
Darwinism. The best account of the Darwinian theory of
Evolution, especially of the theory of natural selection which
Charles Darwin and Alfred Russel Wallace independently elabo-
rated, is Wallace's Darwinism (Lond., 1889). From this the
368 The Study of Animal Life APP.
student will naturally pass to the works of Darwin himself The
Origin of Species by means of Natural Selection ; or, the Pre-
servation of Favoured Races in the Sttiiggle for Life (Lond.,
1859) ; The Variation of Animals and Plants under Domestication
(2 vols., Lond., 1868); The Descent of Man , and Selection in
Relation to Sex (Lond., 1871), etc. ; the earlier works of Wallace,
especially his Contributions to the Theory of Natural Selection
(Lond., 1871) ; Spencer's Principles of Biology cf. his articles
on " The Factors of Organic Evolution " (Nineteenth Century ',
1886) ; HaeckePs Generelle Morphologic ', and Natural History of
Creation. As a popular account of Darwin's life and work, Grant
Allen's Charles Darwin (English Worthies Series, 3rd ed., Lond.,
1886) has a deserved popularity; G. T. Bettany's similar work
(Great Writers Series, Lond., 1886) has a very valuable biblio-
graphy ; but for full personal and historical details reference must
be made to the Life and Letters of Charles Darwin, by his son
Francis Darwin (3 vols., Lond., 1887).
Recent Contributions to the Theory of Evolution,
At the present time there is much discussion in regard to the
factors of organic Evolution. The theory of Evolution is still
being evolved ; there is a struggle between opinions. On the
one hand, many naturalists are more Darwinian than Darwin was,
that is to say, they lay more exclusive emphasis upon the theory
of natural selection ; on the other hand, not a few are less Darwinian
than Darwin was, and emphasise factors of Evolution and aspects
of Evolution which Darwin regarded as of minor importance.
Of those who are more Darwinian than Darwin, I may cite as
representative : Alfred Russel Wallace who, in his Darwinism,
subjects Darwin's subsidiary theory of sexual selection to destructive
criticism ; August Weismann who, in his Essays on Heredity,
denies the transmissibility of characters acquired by the individual
organism, as the results of use or disuse or of external influence ;
and E. Ray Lankester, see his article "Zoology" in the Encyclo-
pedia Britannica, and his work on the Advancement of Science
(Lond., 1890). The student should also read an article by Prof.
Huxley, "The Struggle for Existence, and its Bearing upon Man"
in the Nineteenth Century, Feb. 1888.
See also :
Samuel Butler, Evolution Old and New (Lond., 1879), Luck or
Cunning (Lond., 1887), and other works.
Prof. E. D. Cope, Origin of the Fittest (New York, 1887).
Prof. G. H. T. Eimer, Organic Evolution, as the Result of the
Inheritance of Acquired Characters, accordi?ig to the Laws of
Organic Growth (Jena, 1888). Trans, by J. T. Cunningham
(Lond., 1890).
ii Some of the " Best Books " on Animal Life 369
Prof. T. Fiske, Outlines of Cosmic Philosophy (Lond., 1874), Dar ~
winism, and other Essays (Lond. , 1875).
Prof. P. Geddes, Article ' * Variation^and _ Selection," Encyclopedia
Britannica ; "Evolution," ~Chambers's Encyclopedia, new ed.
Cf. The Evolution ^of~Sex t and forthcoming work on Evolution,
Organic and Social.
E. Gilou, La Lutte pour le Bien-etre (1890).
Rev. J. T. Gulick, Divergent Evolution, through Cumulative Segre-
gation (Journ. Lirui. Soc. xx., 1888).
P. Kropotkine, "Mutual Aid among Animals," Nineteenth Century
(Sept. and Nov. 1890).
Lanessan, La Lutte pour V Existence et t Association pour la Lutte
(Paris, 1882).
Prof. St. George Mivart, The Genesis of Species (Lond., 1871),
Lessons from Nature (Lond., 1876), On Truth (Lond., 1889).
Prof. C. Lloyd Morgan, Animal Life and Intelligence (Lond.,
1890).
Prof. C. V. Nageli, Mechanisch - physiologische Abstammungslehre
(Miinchen and Leipzig, 1884).
Prof. A. S. Packard, Introduction to the Standard or Riverside
Natural History (New York and Lond., 1885).
Dr. G. J. Romanes, Physiological Selection (Journ. Linn. Soc. xix. ,
1886), and forthcoming Rosebery Lectures on the Philosophy
of Natural History.
Prof. K. Semper, The Natural Conditions of Existence as they affect
Animal Life (Internal. Sci. Series, Lond., 1881).
Dr. J. B. Sutton, An Introduction to General Pathology (Lond.,
1886). Evolution and Disease (Contempor. Sci. Series, Lond.,
1890).
2 B
INDEX
ABSORPTION, 145
Acacias guarded by ants, 29, 30
Acquired characters, 329-336
Actions, automatic, 155
habitual, 155
innate, 155
intelligent, 155
Alternation of generations, 189
Amceba, 213
Amphibians, 9, 256, 257
parental care among, no, in
Amphioxus, 252
Angler-fish, 118
Animalculists, 191
Animals, everyday life of, 1-124
domestic life of, 95, 116
industries of, 117-124
life-history of, 184-203
past history of, 204-209
social life of, 67-94
and plants, resemblances and
contrasts, 167-171
relation of simplest to more
complex, 171-174
Annelids, 231-234
Antlers, 279
Ants, 78-84
and aphides, 119, 120
and plants, 29
Aphides, 82, 312
multiplication of, 38
Arachnida, 243
Archoplasm, 183
Aristotle, 283, 284
Armour of animals, 34, 35
Artemia, 310, 311
Arthropods, 10, 238
Atavism, 322
Autotomy, 64-66
Axolotl, 309
BACKBONED animals, 9, 222-247
Backboneless animals, 9, 10, 248-
272
Bacteria, 21, 22
Balance of nature, 19-21
Balanoglossus, 9, 249, 250
Bathybius, 219
Beauty of animals, 15-17
Beavers, 25, 74, 75
Bees, 78-84 ntf^'ly
Biology, justification of, ( 34-50
Birds, 9, 264-267
parental care among, 114, 115
Blind animals, 305
Body, functions of, 144-149
parts of, 174-183
Books, 351-369
Boring animals, 25
Bower birds, 98
Brachiopoda, 235
Brine-shrimp, 310, 311
Buffon, 286
CADDIS worms, 61
Carbohydrates, ' 1 34
The Study of Animal Life
372
Caterpillars, 50, 51
Cats and clover, 29
Cave-animals, 334
livision, 158-^33
, -.128, 147, 179-183
Jentipedes, 241
Cestoda, 229
Chaetopoda, 231-233
Challenger Expedition, 5, 6
Chamseleons, 52
Chemical elements, 135
influences in environment, 309,
Circulation, 146
Classification of animals, 8-n
Coelenterates, 222-228
Cold, effect of, '313
Colonies, 70, 71
Colour-change, 52, 53
Colouring, protective, 48, 49
variable, 49-51
Colours of animals, 49-53
of flat-fishes, 315
Commensalism, 68, 69
Competition, internal, 67
Concealment of animals, 47
Conjugation, 214
Consciousness, 150-152
Co-operation, 69
Corals, 26, 27, 227
Coral snakes, 59
Courtship of birds, 96
mammals, 96
spiders, 101-105
Crabs, masking of, 61, 62
and sea-anemones, 68, 69
Cranes, gregarious life of, 73
Crayfish, 25
Crocodilians, 263, 264
Cruelty of nature, 43-45
Crustacea, 239, 240
life-history of, 198-202
Cuckoo, 114, 115
Cuttlefish, 52, 66
Cyclostomata, 252
DARWIN, Charles, 292-296
Erasmus, 288, 289
Deep-sea fishes, 256
life, 6
Descent of man, 341-345
Desiccation, 41-43
Digestion, 145
Distribution of animals, 3-8
Disuse, results of, 305, 306
Division of labour, 69-71, 143,
144
Dormant life, 41-43
Drought, effect of, 41-43
EARTHWORMS, 22-24
Echinoderms, 10, 65, 66, 235-238
Ectoderm, 196
Eggs, 191, 192
Elaps, 59
Elephant hawk-moth, 59
Encystation, 41
Endoderm, 196
Environment, 306-319
Ephemerides, 106, 107
Epiblast, 196
Epigenesis, 324
Evolution, evidences of, 273-281
factors of, 299-302
theories, history of, 282-301
of sex, 1 88
Extinct types, 206, 207
FAMILY, evolution of, 91
life, 91
Fats, 134
Feigning death, 66
Fertilisation, 193-195
Filial regression, 338
Fishes, 9, 253-256
parental care among, 109, no
Flight of birds, 123, 124
Flowers and insects, 28, 29
Flukes, 229
Food, influence of, 310-313
Freshwater fauna, 6-8
Friar-birds, 59
Frog, 258
Function, influence of, 303
GASTIUEA theory, 197
Index
373
Gastrula, 195, 196
Genealogical tree, 12, 13
Geological record, imperfection of,
205
Germ -plasma, 328
Giant reptiles, 259
Glow-worm, courtship of, 100
Gregarines, 211
Gregarious animals, 71-74
Grouse attacked by \veasel, 40
HABITAT, change of, 47
Habitual actions, 155
Haeckel, 298
Hagfish, 253
Halcyon, 116
Hatteria, 260
Heat, influence of, 313
Heredity, 320-339
Hermaphroditism, 188
Hermit-crabs, masking of, 63
Hirudinea, 234
Homes, making of, 121-123
Hornbill, brooding of, 114
Horse, pedigree of, 278
Hunting, 118, 119
Huxley, 298
Hydractinia, 69, 70
Hypoblast, 196
ICHNEUMON flies, 64
Idealism, 142
Impressions, 151
Industries of animals, 116-124
Infusorians, 211
multiplication of, 38
Innate actions, 155
Insects, 241-243
parental care of, 108
and flowers, 28
Instinct, 153-166
origin of, 163-166
Instincts defined, n
incomplete, 158
mixed, 163
primary, 163
secondary, 163
Insulation of animals, 46
Intelligence, lapse of, 166
Intelligent actions, 155
Iron, importance of, 19
Isolation, 300, 301
Ivory, 31
JELLYFISH, 226
KALLIMA, 53
Kidneys, work of, 145
LAMARCK, 289-292
Lamprey, 252
Lancelet, 9, 252
Land animals, 8
Leaf insects, 54
Leeches, 234
Lemming, Ross's, 50
Lemurs, 46
Life, chemical elements of, 135-
i37
energy of, 127
haunts of, 3-8
machinery of, 130, 131
origin of, 140-142, 280
struggle of, 32-45
variety of, 3
wealth of, 1-17
Light, influence of, 315, 316
Liver, work of, 145
Living matter, 131-135
Lizards, 260
Love of mates, 90, 91, 96
and care for offspring, 105-116
and death, 106
Luciola, courtship of, 100
Lucretius, 284, 285
MACROPOD, parental care of, no
Mammals, 9, 267-271 .
Man as a social person, 94
considered zoologically, 340-
346
Marine life, 3-6
Marsupials, 46
Masking, 61-63
Materialism, 141, 142
374
The Study of Animal Life
Mates, love of, 90, 91, 96
Mayflies, 106, 107
Metamorphosis of Insects, 243
Mesodertn or mesoblast, 196
Migration of birds, 74
Millepedes, 241
Mimicry, 57-61
Mites, desiccation of, 41, 42
Molluscs, 10, 243-247
Monkeys, 270, 271, 341
gregarious life of, 71
Monogamous mammals, 96
Moss-insect, 55
Moulting, 315
Movement, 144
Movements of animals, 123, 124
Mud-fish, 8
My gale, 36
Myriapoda, 241
NATURAL selection, 295
Nematoda, 231
Nemerteans, 230
Nervous system, 148
Nudibranchs, 56
Number of animals, 14, 15
Nutrition, 144
Nutritive relations, 27, 28
ODOURS and sexual attraction,
105
Offspring, care for, 105-116
Ontogeny, 203
Ooze, 220
Organic continuity, 203, 326-329
Organs, 175
change of function of, 178
classification of, 178
correlation of, 176
order of appearance of, 175,
176
rudimentary, 178, 179
substitution of, 178
Orioles, 59
Ovists, 191
Ovum, 191-193
theory, 196
Oysters, mortality of, 43
PAL^ONTOLOGICAL series, 206
Palaeontology, 204-209
Pangenesis, 324
Parasitic worms, 229-231
Parasitism, 47, 48
Parthenogenesis, 189-193
Partnerships among animals, 68,
69
Perception, 151
Peripatus, 10, 240
Phasmidae, 53
Phenacodus, 269, 270
Phyllopteryx, 54
Phylogeny, 203
Physiology, 125-152
Pigeon, 275, 276
Pineal body, 260
Plants and animals, 19, 20, 28-31,
168-171
Polar globules, 193
Polyzoa, 235
Preformation theories, 191, 324
Pressures, effect of, 300
Protective resemblance, 53
Proteids, 134, 135
Protomyxa, 212
Protoplasm, 131-135
Protopterus, 41
-Protozoa^ ii, 210-221
colonial, 173, 174
classes of, 211
life of, 214
"immortality" of, 172
psychical life of, 215-218
structure of, 213
andMetazoa, transition bet ween,
88, 89, 171-174
Psychology, 149
Pupoe of caterpillars, 50
Puss-moth, 63, 64
RADIANT energy, influence of,
3i3-3i6
Recapitulation, 197, 279
Reflex actions, 155
Reproduction, 184-190
Reptiles, 9, 259-264
Respiration, 146
Index
375
Reversion, 322
Rhizopods, 212
Rotifers, 7, 4 2 > 2 34
Round-mouths, 9, 252
Rudimentary organs, 277
SACCOPHORA, 62
Sacculina, 48
Sea-horse, parental care of, no
Seasonal dimorphism, 314
Segmentation, 195
Sensations, 151
Sex, 96
Sexual reproduction, 186-188
selection, 98
Shells of molluscs, 243
Shepherding, 119, 120
Shifts for a living, 46-66
Skunk, 55
Snails and plants, 30
Snakes, 260-263
Social inheritance, 337-339
life of animals, 67-94
organism, 93, 94
Societies, evolution of, 87
Song of birds, 96
Spencer, 297, 298
Spermatozoon, 192, 193
Sphex, 121
Spiders, courtship of, 101-105
bird-catching, 36
Sponges, n, 222
Spongilla, 186
Spring, biology of, 95. 9 6
Starfish, 235
ickleback, courtship of, 99
parental care of, 109, no, 122
tinging-animals, n, 223-228
toring, 120, 121
truggle for existence, 32-45
urrender of parts, 64-66
ymbiosis, 69
TAPEWORMS, 229
Termites, 24, 84-87
tissues, 179, 180
Tortoises, 263
Toxotes, 118
Trematoda, 229
Tunicates, 9, 250, 251
Turbellaria, 228
VARIATION, 299
Vertebrata, characters of, 19, 248,
249
Vital force, 19
Vivarium, 20, 21
Volvox, 187
WALLACE, 296, 297
Warning colours, 55, 5 6
Weapons of animals, 34
Web of Life, 18-31
White Ants. See Termites
Worms, 10, n, 228-235
YOLK, 195
ZOOLOGY, history of, 35 2 -357
THE END
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