The study of animal life

Front matter

I II

22102090474

Med

Preface

This book is intended to help those who would study animal life. From different points of view I have made a series of sketches. I hope that when these are united in the mind of the reader, the picture will have some truth and beauty.

My chief desire has been to give the student some impulse to joyousness of observation and freedom of judgment, rather than to satisfy that thirst for knowledge which leads many to intellectual insobriety. In pursuance of one of the aims of this series, I have also tried to show how our knowledge of animal life has grown, and how much room there is for it still to grow.

A glance at the table of contents will show the plan of the book ; first, the everyday life of animals, next, their internal activities, thirdly, their forms and structure, and finally, the theory of animal life. This is a commonly accepted mode of treatment, and it is one by which it is possible in different parts of the book to appeal to students of different tastes. For, in lecturing to those who attend University Extension Courses, I find that seniors are most interested in the general problems of evolution, heredity, and environment; that others care more about the actual forms of life and their structure ; that many desire to have a clear understanding of the functions of the animal body ; while most wish to study the ways of living animals, their struggles and loves, their homes and

VI

Preface societies. To each of these classes of students a quarter of this volume is dedicated ; perhaps they will correct their partiality by reading the whole.

As to the two Appendixes, I may explain that instead of giving references at the end of each chapter, I have combined these in a connected bibliography ; the other Appendix on “ Animal Life and Ours ” may show how my subject is related to some of the others usually discussed in University Extension Courses.

My friend Mr. Norman Wyld has written the three chapters on “ The Powers of Life/’ pp. 125-166, and I am also indebted to him for helpful suggestions in regard to other parts of the book. I have to thank Mr. Murray, Messrs. Chambers, and Mr. Walter Scott, for many of the illustrations; while several original drawings have been made for me by my friend Mr. William Smith.

Professor Knight and Mr. John Murray have given me many useful hints while the book was passing through the press, and Mr. Ricardo Stephens was good enough to read the proof sheets.

J. A. T.

School of Medicine,

Edinburgh, May 1892

The Everyday Life of Animals

CHAPTER I i. Variety of life — 2. Haunts of life — 3. Wealth of form — 4. Wealth of numbers — 5. Wealth of beauty . . . Pages 1-17

Chapter II

1. Dependence upon surroundings — 2. I ?iter- relations of plants and animals — 3. Relation of animals to the earth — 4. Nutritive relations— 5. More complex interactions . . , 18-31

Chapter III

1. Nature and extent of the strtiggle — 2. Armour and weapons — 3. Different forms of struggle — 4. Cruelty of the struggle . 32-45 vm

CHAPTER IV i. Insulation — 2. Concealment — 3. Parasitism — 4. General resemblance to surroundings — 5. Variable colouring — 6. . Rapid change of colour — 7. Special protective resemblance — 8. Warning colours — 9. Mimicry — 10. Masking — 11. Combination of advantageous qualities — 12. Surrender of parts . . Pages 46-66

Chapter V

1. Partnerships — 2. Co-operation and division of labour — 3. Gregarious life and combined action — 4. Beavers — 5. Bees — 6. Ants — 7. Termites — 8. Evolution of social life — 9. Advantages of social life — 10. A note on “ the social organism" — 11. Conclusions ....... 67-94

Chapter VI The Domestic Life Of Animals

r. The love of mates — 2. Love and care for offspring . 95-116

Chapter VII The Industries Of Animals

1. Hunting — 2. Shepherding — 3. Storing — 4. Making of homes — 5. Movei?ients . 1 17-124

PART IT ix

The Powers of Life

Chapter VIII Vitality

i. The task of physiology — 2. The seat of life — 3. The energy of life — 4. Cells , the elements of life — 5. The machinery of life — 6. Protoplasm— 7. The chemical elements of life — 8. Growth — 9. Origin of life ...... Pages 125- 142

Chapter IX The Divided Labours Of The Body

1. Division of labour — 2. The functions of the body: Movement ; Nutrition ; Digestion; Absorption ; The work of the liver and the kidneys; Respiration; Circulation; The changes within the cells ; The activities of the nervous system — 3. Sketch of Psychology ...... 143-152

CPIAPTER X

1. General usage of the term — 2. Careful usage of the term — 3. Examples of instinct — 4. The origin of instinct . x =53-166

X

The Forms of Animal Life

Chapter XI The Elements Of Structure

r. The resemblances and contrasts between plants and animals — 2. The relation of the simplest animals to those which are more complex— 3. The parts of the animal body . . Pages 167-183

Chapter XII The Life-history Of Animals

r. Modes of reproduction- — 2. Divergent modes — 3. Historical — 4. The egg-cell or ovum — 5. 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 Gastrcea theory, fact of recapitulation, organic continuity ...... 184-203

Chapter XIII The Past History Of Animals

i. The two records — 2. Imperfection of the geological record — 3. Palceontological series — 4. Extinction of types — 5. Various difficulties— 6. Relative antiquity of animals . . 204-209

Chapter XIV The Simplest Animals

1. The simplest forms of life — 2. Survey of Protozoa — 3. The common 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 ...... 2 10-221 xi

CHAPTER XV t. Sponges — 2. Stinging - animals or Ccelenterata — 3. Worms

4. Echinoderms — 5- Arthropods — 6. Molluscs . Pages 222-247

CHAPTER XVI i. Balanoglossus — 2. Tunicates — 3. The Lancelet — 4. Round-mouths or Cyclostomata — 5. Fishes — 6. Amphibians — 7. Reptiles — 8. Birds — 9. Mammals ..... 248-272

The Evolution of Animal Life

CHAPTER XVII

THE EVIDENCES OF EVOLUTION

1. The idea of evolution — 2. Arguments for evolution : Physiological , Morphological, Historical — 3. Origin of life . . 273-281

CHAPTER XVIII

THE EVOLUTION OF EVOLUTION THEORIES

1. Greek philosophers — 2. Aristotle — 3. Lucretius — 4. Evolutionists before Darzoin — 5. Three old masters : Buffon, Erasmus Darwin , Lamarck — 6. Darwin — 7. Darwin' s fellow - workers — 8. The present state of opinion .... 282-302

CHAPTER XIX

THE INFLUENCE OF HABITS AND SURROUNDINGS

i. The influence of function — 2. The influence of surroundings — 3. Our own environment . .... 303-3x9

Xll

CHAPTER XX i. The facts of heredity — 2. Theories of heredity, historical retrospect — 3. The modern theory of heredity — 4. The inheritance of acquired characters — 5. Social and ethical aspects — 6. Social inheritance

APPENDIX I

ANIMAL LIFE AND OURS

A. Our relation to animals : 1. Affinities and differences between man and monkeys — 2. Descent of man — 3. Various opinions about the descent of man — 4. Ancestors of man — 5. Possible factors in the ascent of man. B. Our relation to Biology : 6. The utility of science — 7. Practical justification of biology — 8. Intellectual justification of biology ..... 340-350

APPENDIX II

A. Books on “ Zoology B. Books on "Natural History" — C. Books

Index

• 371-375

THE EVERYDAY LIFE OF ANIMALS

Chapter I

I. Variety of Life — 2. Haunts of Life — 3. Wealth of Form —

4. Wealth of Numbers — 5. Wealth of Beauty

The first steps towards an appreciation of animal life must be taken by the student himself, for no book-lore can take the place of actual observation. The student must wash the quartz and dig for the diamonds, though a book may help him to find these, and thereafter to fashion them into a treasure.

Happily, however, the raw material of observation is not rare like gold or diamonds, but near to us as sunshine and rain-drops. Within a few hours’ walk of even the largest of our towns the country is open and the animals are at home. Though we may not be able to see “ the buzzard homing herself in the sky, the snake sliding through creepers and logs, the elk taking to the inner passes of the woods, or the razor-billed auk sailing far north to Labrador,” we can watch our own delightful birds building their “homes without hands,” we can study the frogs from the time that they trumpet in the early spring till they or their offspring seek winter quarters in the mud, we can follow the bees and detect their adroit burglary of the

B flowers. And if we are discontented with our opportunities, let us read Gilbert White’s History of Selborne , or how Darwin watched earthworms for half a lifetime, or how Richard Jefferies saw in the fields and hedgerows of Wiltshire a vision of nature, which seemed every year to grow richer in beauty and marvel. It is thus that the study of Natural History should begin, as it does naturally begin in childhood, and as it began long before there was any exact Zoology, — with the observation of animal life in its familiar forms. The country schoolboy, who watches the squirrels hide the beech nuts and pokes the hedgehog into a living ball, who finds the nest of the lapwings, though they decoy him away with prayerful cries, who catches the speckled trout in spite of all their caution, and laughs at the ants as they expend hours of labour on booty not worth the having, is laying the foundation of a naturalist’s education, which, though he may never build upon it, is certainly the surest. For it is in such studies that we get close to life, that we may come to know nature as a friend, that we may even hear the solemn beating of her heart.

The same truth has been vividly expressed by one whose own life-work shows that thoroughness as a zoologist is consistent with enthusiasm for open-air natural history. Of the country lad Dr. C. T. Hudson says, in a Presidential Address to the Royal Microscopical Society, that he “ wanders among fields and hedges, by moor and river, seawaslied cliff and shore, learning zoology as he learnt his native tongue, not in paradigms and rules, but from Mother Nature’s own lips. He knows the birds by their flight and (still rarer accomplishment) by their cries. He has never heard of (Edi enemas crepitans , the Charadrius pluvialis , or the Squatarola cinerea , but he can find a plover’s nest, and has seen the young brown peewits peering at him from behind their protecting clods. He has watched the cunning flycatcher leaving her obvious and yet invisible young in a hole in an old wall, while she carries off the pellets that might betray their presence ; and has stood so still to see the male redstart that a field-mouse has curled itself on his warm foot and gone to sleep.”

But the student must also attempt more careful studies of living animals, for it is easy to remain satisfied with vague “general impressions.” He should make for himself — to be corrected afterwards by the labours of others — a “Fauna” and “Flora” of the district, or a “Naturalist’s Year Book ” of the flow and ebb of the living tide. He should select some nook or pool for special study, seeking a more and more intimate acquaintance with its tenants, watching them first and using the eyes of other students afterwards. Nor is there any difficulty in keeping at least freshwater aquaria — simply glass globes with pond water and weeds — in which, within small compass, much wealth of life may be observed. Those students are specially fortunate who have within reach such collections as the Zoological Gardens and the British Museum in London ; but this is no reason for failing to appreciate the life of the sea-shore, the moor-pond, and the woods, or for neglecting to gain the confidence of fishermen and gamekeepers, or of any whose knowledge of natural history has been gathered from the experience of their daily life.

1. Variety of Life. — Between one form of life and another there often seems nothing in common save that both are alive. Thus life is characteristically asleep in plants, it is generally more or less awake in animals. Yet among the latter, does it not doze in the tortoise, does it not fever in the hot-blooded bird ? Or contrast the phlegmatic amphibian and the lithe fish, the limpet on the rock and the energetic squid, the barnacle passively pendent on the floating log and the frolicsome shrimp, the cochineal insect like a gall upon the leaf and the busy bee, the sedentary corals and the free-swimming jellyfish, the sponge on the rock and the minute Night-Light Infusorians which make the waves sparkle in the summer darkness. No genie of Oriental fancy was more protean than the reality behind the myth — the activity of life.

2. Haunts of Life. — The variety of haunt and home is not less striking. There is the great and wide sea with swimming things innumerable, our modern giants the whales, the seals and walruses and the sluggish sea-cows, the flippered penguins and Mother Carey’s chickens, the marine turtles and swift poisonous sea-serpents, the true fishes in prolific shoals, the cuttles and other pelagic molluscs ; besides hosts of armoured crustaceans, swiftly -gliding worms, fleets of Portuguese Men-of-War and throbbing jellyfish, and minute forms of life as numerous in the waves as motes in the sunlit air of a dusty town.

“ But what an endless worke have I in hand,

To count the seas abundant progeny,

Whose fruitful seede farre passeth those on land,

And also those which wonne in th’ azure sky ;

For much more eath to tell the starres on hy,

Albe they endlesse seem in estimation,

Then to recount the seas posterity ;

So fertile be the flouds in generation,

So huge their numbers, and so numberlesse their nation.”

Realise Walt Whitman’s vivid picture : —

“ The World below the brine.

Forests at the bottom of the sea — the branches and leaves,

Sea-lettuce, vast lichens, strange flowers and seeds — the thick tangle, the openings, and the pink turf,

Different colours, pale grey and green, purple, white, and gold — the play of light through the water,

Dumb swimmers there among the rocks — coral, gluten, grass, rushes — and the aliment of the swimmers,

Sluggish existences grazing there, suspended, or slowly crawling close to the bottom :

The sperm-whale at the surface, blowing air and spray, or disporting with his flukes,

The leaden-eyed shark, the walrus, the turtle, the hairy sealeopard, and the sting ray.

Passions there, wars, pursuits, tribes — sight in those ocean depths — breathing that thick breathing air, as so many do.”

The sea appears to have been the cradle, if not the birthplace, of the earliest forms of animal life, and some have never wandered out of hearing of its lullaby. From the sea, animals seem to have migrated to the shore and thence to the land, but also to the great depths. Of the life of the deep sea we have had certain knowledge only

Fig. i.— Suggestion of deep-sea life. (In part from a figure by W. Marshall.)

within the last quarter of a century, since the Challenger expedition (1872-76), under Sir Wyville Thomson’s leadership, following the suggestions gained during the laying of the Atlantic cables and the tentative voyages of the Lightning (1868) and the Porcupine (1870), revealed what was virtually a new world. During 3b years the Challe7iger explorers cruised over 68,900 nautical miles, reached with the long arm of the dredge to depths equal to reversed Himalayas, raised sunken treasures of life from over 300 stations, and brought home spoils which for about twenty years have kept the savants of Europe at work, the results of which, under Dr. John Murray’s editorship, form a library of about forty huge volumes. The discovery of this new world has not only yielded rich treasures of knowledge, but has raised a wave of wider than national enthusiasm which has not since died away.

We are at present mainly interested in the general picture which the results of these deep-sea explorations present,-— of a thickly -peopled region far removed from direct observation, sometimes three to five miles beneath the surface — a world of darkness relieved only by the living lamps of phosphorescence, of silent calm in which animals grow into quaint forms of great uniformity throughout wide areas, and moreover a cold and plantless world in which the animals have it all their own way, feeding, though apparently without much struggle for existence, on their numerous neighbours, and ultimately upon the small organisms which in dying sink gently from the surface like snowflakes through the air.

Far otherwise is it on the shore — sunlight and freshening waves, continual changes of time and tide, abundant plants, crowds of animals, and a scrimmage for food. The shore is one of the great battlefields of life on which, through campaign after campaign, animals have sharpened one another’s wits. It has been for untold ages a great school.

Leaving the sea-shore, the student might naturally seek to trace a migration of animals from sea to estuary, and from the brackish water to river and lake. But this path, though followed by some animals, does not seem to have been that which led to the establishment of the greater part of our freshwater fauna. Professor Sollas has shown with much conclusiveness that the conversion of comparatively shallow continental seas into freshwater lakes has taken place on a large scale several times in the history of the earth. This has been in all likelihood accompanied by the transformation of marine into freshwater species. It is thus, we believe, that our lakes and rivers were first peopled. Many freshwater forms differ from their marine relatives in having suppressed the obviously hazardous free-swimming juvenile stages, in bearing young which are sedentary or in some way saved from being washed away by river currents. Minute and lowly, but marvellously entrancing, are numerous Rotifers, of which we know much through the labours of Hudson and Gosse. These minute forms are among the most abundant tenants of fresh water, and their etrsrs are carried from one watershed to another on the wings of the wind and on the feet of birds, so that the same kinds may be found in widely separate waters. Let us see them in the halo of Hudson’s eulogy: “To gaze into that wonderful world which lies in a drop of water, crossed by some atoms of green weed ; to see transparent living mechanism at work, and to gain some idea of its modes of action ; to watch a tiny speck that can sail through the prick of a needle’s point ; to see its crystal armour flashing with ever-varying tints, its head glorious with the halo of its quivering cilia ; to see it gliding through the emerald stems, hunting for its food, snatching at its prey, fleeing from its enemy, chasing its mate (the fiercest of our passions blazing in an invisible speck) ; to see it whirling in a mad dance to the sound of its own music — the music of its happiness, the exquisite happiness of living,— can any one who has once enjoyed this sight, ever turn from it to mere books and drawings, without the sense that he has left all fairyland behind him?” Not less lively than the Rotifers are crowds of minute crustaceans or water-fleas which row swiftly through the clear water, and are eaten in hundreds by the fishes. But there are higher forms still : crayfish, and the larvae of mayflies and dragonflies, mussels and water-snails, fishes and newts, the dipper and the kingfisher, the otter and the vole.

As we review the series of animals from the simplest upwards, we find a gradual increase in the number of those which live on land. The lowest animals are mostly acpiatic — the sponges and stinging-animals wholly so ; worm-like forms which are truly terrestrial are few compared with those in water ; the members of the starfish group are wholly marine ; among crustaceans, the wood-lice, the land-crabs, and a few dwellers on the land, are in a small minority ; among centipedes, insects, and spiders the aquatic forms are quite exceptional ; and while the great majority of molluscs live in water, the terrestrial snails and slugs are legion. In the series of backboned animals, again, the lowest forms are wholly aquatic ; an occasional fish like the climbing -perch is able to live for a time ashore ; the mud-fish, which can survive being brought from Africa to Europe within its dry “ nest ” of mud, has learned to breathe in air as well as in water ; the amphibians really mark the transition from water to dry land, and usually rehearse the story in each individual life as they grow from fish -like tadpoles into frog- or newt -like adults. Among reptiles, however, begins that possession of the earth, which in mammals is established and secure. As insects among the backboneless, so birds among the backboned, possess the air, achieving in perfection what flying fish, swooping tree-frogs and lizards, and above all the ancient and extinct flying reptiles, have reached towards. Interesting, too, are the exceptions — ostriches and penguins, whales and bats, the various animals which have become burrowers, the dwellers in caves, and the thievish parasites.

But it is enough to emphasise the fact of a general ascent from sea to shore, from shore to dry land, and eventually into the air, and the fact that the haunts and homes of animals are not less varied than the pitch of their life.

3. Wealth of Form. — As our observations accumulate, the desire for order asserts itself, and we should at first classify for ourselves, like the savage before us, allowing similar impressions to draw together into groups, such as birds and beasts, fishes and worms. At first sight the types of architecture seem confusingly numerous, but gradually certain great samenesses are discerned. Thus we distinguish as higher animals those which have a supporting rod along the back, and a nerve cord lying above this ; while the lower animals have no such supporting rod, and have their nerve-cord (when present) on the under, not on the upper side of the body. The higher or backboned series has its double climax in the Birds and the furred Mammals. Indissolubly linked to the Birds are the Reptiles, — lizards and snakes, tortoises and crocodiles — the survivors of a great series of ancient forms, from among which Birds, and perhaps Mammals also, long ago arose. Simpler in many ways, as in bones and brains, are Amphibians and Fishes in close structural alliance, with the strange double-breathing, gill- and lung-possessing mud-fishes as links between them. Far more old-fashioned than Fishes, though popularly included along with them, are the Round-mouths — the halfparasitic hag-fish, and the palatable lampreys, with quaint young sometimes called “nine-eyes.” Near the base of this series is the lancelet, a small, almost translucent animal living in the sea-sand at considerable depths. It may be regarded as a far-off prophecy of a fish. Just at the threshold of the higher school of life, the sea-squirts or Tunicates have for the most part stumbled ; for though the active young forms have been acknowledged for many years as reputable Vertebrates, almost all the adults fall from this estate, and become so degenerate that no zoologist ignorant of their life-history would recognise their true position. Below this come certain claimants for Vertebrate distinction, notably one Ta/anoglossus, a worm-like animal, idolised by modern zoology as a connecting link between the backboned and backboneless series, and reminding us that exact boundary-lines are very rare in nature. For our present purpose it is immaterial whether this strange animal be a worm -like vertebrate or a vertebrate-like worm.

Across the line, among the backboneless animals, it is more difficult to distinguish successive grades of higher io The Study of Animal Life part i

and lower, for the various classes have progressed in very different directions. We may liken the series to a school in which graded standards have given place to classes which have “ specialised ” in diverse studies ; or to a tree whose branches, though originating at different levels, are all strong and perfect. Of the shelled animals or Molluscs there are three great sub -classes, (a) the cuttlefishes and the pearly nautilus, (b) the snails and slugs, both terrestrial and aquatic, and ( c ) the bivalves, such as cockle and mussel, oyster and clam. Simpler than all these are a few forms which link molluscs to worms.

Clad in armour of a very different type from the shells of most Molluscs are the jointed-footed animals or Arthropods, including on the one hand the almost exclusively aquatic crustaceans, crabs and lobsters, barnacles and “ water-fleas,” and on the other hand the almost exclusively aerial or terrestrial spiders and scorpions, insects and centipedes, besides quaint allies like the “ king-crab,” the last of a strong race. Again a connecting link demands special notice, Peripatus by name, a caterpillar- or worm- like Arthropod, breathing with the air-tubes of an insect or centipede, getting rid of its waste-products with the kidneys of a worm. It seems indeed like “a surviving descendant of the literal father of flies,” and suggests forcibly that insects rose on wings from an ancestry of worms much as birds did from the reptile stock.

Very different from all these are the starfishes, brittle-stars, feather-stars, sea-urchins, and sea-cucumbers, animals mostly sluggish and calcareous, deserving their title of thorny-skinned or Echinodermata. Here again, moreover, the sea-cucumbers or Holothurians exhibit features which suggest that this class also originated from among “ worms.”

But “ Worms ” form a vast heterogeneous “ mob,” heartbreaking to those who love order. No zoologist ever speaks of them now as a “class” ; the title includes many classes, bristly sea- worms and the familiar earthworms, smooth suctorial leeches, ribbon-worms or Nemerteans, round hairworms or Nematodes, flat tapeworms and flukes, and many chap, i The Wealth of Life n

others with hardly any characters in common. To us these many kinds of “ worms ” are full of interest, because in the past they must have been rich in progress, and zoologists find among them the bases of the other great branches — Vertebrates, Molluscs, Arthropods, and Echinoderms. “ Worms ” lie in a central (and still muddy) pool, from which flow many streams.

Lower still, and in marked contrast to the rest, are the Stinging-animals, such as jellyfish throbbing in the tide, zoophytes clustering like plants on the rocks, sea-anemones like bright flowers, corals half-smothered with lime. In the Sponges the type of architecture is often very hard to find. They form a branch of the tree of life which has many beautiful leaves, but has never risen far.

Beyond this our unaided eyes will hardly lead us, yet the pond-water held between us and the light shows vague specks like living motes, the firstlings of life, the simplest animals or Protozoa, almost all of which have remained mere unit specks of living matter.

It is easy to write this catalogue of the chief forms of life, and yet easier to read it : to have the tree of life as a living picture is an achievement. It is worth while to think and dream over a bird’s-eye view of the animal kingdom— to secure representative specimens, to arrange them in a suitably shelved cupboard, so that the outlines of the picture may become clear in the mind. The arrangement of animals on a genealogical or pedigree tree, which Haeckel first suggested, may be readily abused, but it has its value in presenting a vivid image of the organic unity of the animal kingdom.

If the catalogue be thus realised, if the foliage come to represent animals actually known, and if an attempt be made to learn the exact nature, limits, and meaning of the several branches, the student has made one of the most important steps in the study of animal life. Much will remain indeed — to connect the living twigs with those whose leaves fell off ages ago, to understand the continual renewal of the foliage by the birth of new leaves, and finally to understand how the entire tree of life grew to be what it is.

Fig. 2 —Genealogical Tree

The small branches in the centre indicate the classes of worms ; the letters P, />, and S indicate the positions of Penpatus, balanoglossus, and Sphenodon or Hatteria respectively.

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.