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1653 East Main Streal RochMter, N«» York 14609 (716) 482 - 0300- Phon. (716) 288 - 5969 - Fo»
JSA
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EDITED BY PKOEESiyQR KNIGHT
THE STUDY OF ANIMAL LIFE
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 OK 'outlines OF ZOOLOGY '
THIRD EDITION
WITH JLLUSTNAT/OXS
TORONTO G. N. MORANG & COMPANY LIMITED
LONDON
JOHN MURRAY
1902
0L4 i^'^
" Rut. for my part, wluch write the English story. 1 acknowledge that no man must looke for that at my hands, which I have not received from some other : .or I would bee unwilling to.write anythmg untrue, or uncertaine out of mine own invention ; and truth on every part is so deare unto me. that 1 will not lie to bring any man m love and admiration with God and his works, for God needeth not the hes
"^ "'^'^- TOPSELL'S Apologia (1607).
J^ %' -^ ^ 5
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 joyousncss of observation and freedom of judgment, rather than to satisfy that thirst for knowledge which leads many to intellectual r'nsobriety. In pursu- ance 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
15914
v!
Preface
societies. To each of these class s 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 bibliut^aphy ; 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 chapter, c. " The Powers of Life," pp. 1 2 5-1 66, and I am also inu-^' jd 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 1893
CONTENTS
PART I
The Everyday Life of Animals
CHAPTER I
THE WEALTH OF LIFE
f Variety of life— ^. Haunts of life— :^. Wealth of form— ^ Wealth of numbers— $. Wealth of beauty . . . Pages 1-17
CHAPTER II
THE WEB OF LIFE
I. Dependence upon surroundings -^a. /nter- relations <f plants and animals— 2. Relation of animals to the earth— ^. Nutritive rela- tions—^. More complex interactions . . , jg.^
CHAPTER III
THE STRUGGLE OF LIFE
X. Nature and extent of the struggU—i. Armour and weapons— 3. Different forms of struggU-^. Cruelty of the struggle . 32-45
VIU
Contents
PART 1
CHAPTER IV
SHIFTS FOR A LIVING
I. Insulation — 2. Concealment — 3. Parasitism — 4. General resem- blance to surroundings— $. Variable colouring — 6. Rapid change of colour — 7. Special protective resemblance — 8. Warning colours — 9. Mimicry — 10. Masking— ii. Combination of advantageous qualities — 12. Surrender of parts , . Pages 46-66
CHAPTER V
SOCIAL LIFE OF ANIMALS
Partnerships — 2. Co-operation and division of labour — 3. C7r«- garious 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. Con- clusions ....... 67-94
CHAPTER VI
THE DOMESTIC LIFE OF ANIMALS t. The love of mates — 2. Love and care for offspring
9S-"6
CHAPTER VII
THE INDUSTRIES OF ANIMALS
I. Hunting — 2. Shepherding — 3. Storing — 4. Making of homes — 5. Movements ..... 117-134
PAKT II
Contents
ix
PART II The Powers of Life
CHAPTER VIII
VITALITY
I. The task of physiology — 2. The seat 0/ life — 3. 7 he energy 0/ lift — 4. Cells, the elements of life — 5. The machinery of life — 6. Proto- plasm— 7. The chemical elements of lift — 8. Growth — 9. Origin of life ...... Pages 125-142
CHAPTER IX
THE DIVIDED LABOURS OF THE BODY
I. Division of labour — 2. The functions of the body: Movement; Nutrition; Digestion; Absorption; The work of the liwr and the kidneys; Respiration; Circulation; The changes within the cells ; The activities of the nervous system — 3. Sketch of Psychology ...... 143.152
CHAPTER X
INSTINCT
I. Genetal usage of the term— 2. Cartful usage of the term— 3. Examples of instinct— ^. The origin of instinct , 153-166
i ! ! t
X Contents part m
PART III
The Forms of Animal Life
CHAPTER XI
THE ELEMENTS OF STRUCTURE
I. The resemblances and contrasts between plants and animals— z.
The relaHon of the simplest animals to those which are more com-
plex—^ The parts of the animal body , , Pages 167-183
CHAPTER XII
THE LIFE-HISTORY OF ANIMALS
I. Modes of reproduction— 2. Divergent modes— 2. Historical—,^. The egg-cell or ovum-*s. The male-cell or spermatozoon— 6. Matura- tioncf the ovum— T. Fertilisation— Z. Segmentation and the ^rst stages in development — <j. Some generalisations: the ovum theory, the Gastraa theory, fact of recapitulation, organic con- *■««»<>' 184-203
CHAPTER XIII
THE PAST HISTORY OF ANIMALS
I. The two records — 2. Imperfection of the geological record 3.
Palaontological series—^ Extinction of types — 5. Various diffi- culties— 6. Relative antiquity of animals , . 204-209
CHAPTER XIV
THE SIMPLEST ANIMALS
The simplest forms of life— Q^. Surv^ of Protoaoa—^. The common Amcaa—^. Structure of the Prototoa—i. Life cf Prototoa-d, Psychical life of the Prototoa— J. History of the ProtoMoa—i. Rela- lion to the earth— ^. Relation to other forms (f life— 10, Relation t«man ...... 2io-a2X
XI
PART IV Contents
CHAPTER XV
BACKBONELESS ANIMALS
T. Sponges — 3. Stinging - animals or Cailenteraia—^. "Worms" — 4. £cAinoderms—s. Arthropods — 6. Molluscs . Pages 932-347
CHAPTER XVI
BACKBONED ANIMALS
I. Balanoglossus—3. Tunicates—^. The LnnctUt—4. Round-mouths or Cyclostomata — s. Fishes — 6. Amphibians — 7. Reptiles— 9. Birds— g. Mammals ..... 248-272
PART IV
The Evolution of Animal Life
CHAPTER XVII
THE EVIDENCES OF EVOLUTION
I. The idea of evolutior—a. Arguments for evolution : Physiological, Morphological, Historical— -i. Origin of life . . 273-281
CHAPTER XVIII
THE EVOLUTION OF EVOLUTION THEORIES
1. Greek philosophers— 3. AristotU—^. Lucretius— 4. Evolutionists before Darwin-i. Three old masters : Bujfbn, Erasmus Darwin, Lamarck— 6. Darwin— 7. Darwin's fellow -workers— i. The present state of opinion .... 282.302
CHAPTER XIX
THE INFLUENCE OF HABITS AND SURROUNDINGS
I. The influence of funcHon—a. The influence of surroundings— 2. Our own environment . .... 303.319
xii
Contents
TAKT IV
CHAPTER XX
HEREDITY
X. The facts tf heredity— i. Theories of heredity, historical retrospect— 3. The modem theory of heredity— /^. The inheritance cf acquired characters— $. Social and ethical aspects— 6. Social inheritance
Pages 330-339
APPENDIX I
ANIMAL LIFE AND OURS
A. Our relation to animals : 1. Affinities and differences between man and monkeys— t. Descent cf man — 3. Various opinions about the descent of man— /^. Ancestors of man—S- Possible factors in the ascent of man. B. Our relation to Biology : 6. The utility of science— 7. Practical justification of biology ~-Z. Intellectual justification of biology ..... 340-35°
APPENDIX II
SOME OF THE BEST BOOKS ON ANIMAL LIFE
A. Books on " Zoology "^ti. Books on "Natural History" —C. Books or "Biology" ..... 3S1-369
Index
37I-37S
PART I
THE EVERYDAY LIFE OF ANIMALS
CHAPTER I
THE WEALTH OF LIFE
I. Variety of Life— 2. Haunts of Life~i. Wealth of f-^m— 4. Wealth of Numbers— s^. Wealth of Beaut;,
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
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3 TAe Study of Animal Life part i
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 Wilt- shire 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 Presi- dential Address to the Royal Microscopical Society, that he " wanders among fields and hedges, by moor and river, sea- washed 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 (Edicnemus 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. F -. has watched the cun- ning 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."
til
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t^jviSWiStX,^-. -
CHAP. I
The Wealth of Life
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-^. id, and the woods, or for neglecting to gain the confiden.e of fishermen and gamekeepers, or of any whose knowledge of natural history has been gathered from the experience of their daily life.
I. 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 am- phibian and the lithe fish, the limpet on the ruck and the energetic squid, the barnacle passively pendent on the float- ing log and the frolicsome shrimp, the cochineal insect like a gall upon the leaf and the busy bee, the sedentaiy 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 <"incy 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 swimmmg thmgs innumerable, our modem giants the whales the seals and walruses and the sluggish sea-cows, the flipl
i
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4 The Study of Animal Life part \
pered 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 jelly- fish, 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 seris 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 thty endle e seem in estimation, Then to recount ihe seas posterity ; So fertile be the flouds in generation. So huge their numbers, and so numberlcsse 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-ktUice, vast lii liens, strange tluwers and seeds,— the thick tang'e, the openings, and tlic 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 . sistcnccs grazing tlicre, suspended, or slowly crawling close to tlie bottom :
The sperm whale nt the surface, blowing air and .piay, or dis- porting with his flukes,
Tiie Icaden-eyed shaik, ilie walrus, tie turtle, tlie hairy sea- leopard, and the sting r.iy.
I'assions 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 sceir to have migrated to the shore and thence to the land, but also to the <,'cat depths. Of the life of the depp sea wc have had certain knowledge only
CHAP. I
The Wealth of Life
I
Fi.;. I. -Suggestion of ilccj,-..-.. llf,-. (|„ |,,„t fi.mi .i figure by W. Marshall.)
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rSBK.ra&^trznMHK'.Aut^'B^-iii^BEIRf^ii ::'S1.
TAe Study of Animal Life
PART I
within the last quarter of a century, since the Challenger expedition (1872-76), under Sir Wyville Thomson's leader- ship, 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 3^ years the Challenger explorers cruised over 68,900 nautical miles, reached with the long ann 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 ucw world has not on'y 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 unifoimity 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, a^d ultimately upon the small organ- isms which in dying sink gently from the surface like snow- flakes 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 miglit naturally seek to trace a migration of animals from sea to estuary, ond from the brackish \/ater to river and lake. But this pa^'i, though followed by some animals, does not seem to have
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CHAP. I
The [Vealth of Life
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 .merous 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 eggs 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 ^e 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, i^natching at Us prey, fleeing from its enemy, chasing its mate (th lercest of our passions blazing in an invisib'e 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 th's siglit, 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 crust.iceans or water-fleas which row swiftly through the clear water, and are eaten in hundreds by the fishes. Hut there are higher forms still : crayfish, and the larvjc of mayflies and dragonflies, mussels
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The Study of Animal Life
PART I
and water-snails, fishes and newts, the dipper and the king- fisher, 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 Hve on land. The lowest animals are mostly aquatic — the sponges and stinging-animals wholly so; worm-like forms which are truly terrestrial are few com- pared 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 mollusrs 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 tim- ashore ; the mud-fish, which can survive being brought fronj 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 ihe 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 empnasise ^he 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 f Form. — As our observations accumjJate, the desire for order asserts itself, and we should at first classify for ourselves, like the savage before us, allowing similar impressions to drav/ together into groups, such as
CHAP. I
The Wealth of Life
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 distin- guish as higher animals those which have a supporting rod along the back, and a nerve cord lying above this ; while the Imver 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 seiies 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 in- cluded along with them, are the Round-mouths— the half- parasitic hag-fish, and the palatable lampreys, with quaint young sometimes called "nine-eyes." Near the ba^e 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. Ju't at the threshold of the higher school of life, the sea-squirts or Tunicates have for the most part stumbled ; for though the active younj^ 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 Balattoglossus, 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
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The Study of Animal Life
PART I
!l
.i
i
!l
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 Arthro- pods, 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 centi- pedes, 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," heart- breaking 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 i emerteans, round hair- worms or Nematodes, flat tapeworms and flukes, and many
l<
CHAP. I
The Wealth of Life
II
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 king- dom— to secure representative specimens, to arrange them in a suitably shelver' 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 wliv>se 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.
12
fl
The Study of Animal Life part i
11
letters Sphenex
Fig. 2 —Genealogical Ti.-,-
.e Mn.,11 tranche, in tl.e centre indicate the ..lasses of "norms- ,1„
I
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 .lint 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 {Euplcctella\ 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 womi 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 ihan 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,
14
The Study of Animal Life
VKKt I
and even he parts of the flower-sepals, petals, stamens, and carpels are m reality all leaves or appendages more or less modified for diverse work. The mouth-plrts Ta lobster are masticating legs, and a bird's wing is a modified
fh^V 7 r c "^^"'■^^'^^^ ^^^'•e so far right in insisting on the fact of a few great types. Nature, Lamarck said, is never ^usque ; nor is she inventive so much as adaptive
4. Wealth of Numbers— Large numbers are so unthink- n..^ f^.^'-^'^'^^y \ 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 rf. ^''^f° i ^%°"r 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 m wayside pond or shore pool some new thine or again by great enterprises like the Challenger expedition / Exploring naturalists like Wallace and Semptr return from / tropical countries enriched with new animals from the dense forests or warm seas. Zoological Stations, notably that Si , Naples, are "register-houses" for the fauna of the neX bpuring sea, not merely as to number and form, 2t in many cases taking account of life and history as wdl 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 ho longer • . Tf" °^ '^" 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 newfpedes 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 'o 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
x6
The Study of Animal Life part i
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 fliuing like sunbeams among the flowers. But
Fig. 3.— Humming-birils {Floristiga 'iiellivora) 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 frcm 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 heaWiy organisms are harmonious in form, and seldom if ever are their colours out of tone with their surroundings or with each other, — a fact v/hich 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
Dependence upon Surroundings — 2. Inter-relations of Plants and Animals — 3. Relation of Animals to the Earth — 4. NutHti', e Relations — 5. Afore 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 fiy entangled in a comer betrays itself throughout the web ; often it is felt rather than seen Vy 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 SorroandinffS. — 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 lion. All these elements are spread throughout the whole world. By the magic touch of life they ai-e 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 diflfers from dead matter in no other way than thi; Th-
I
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 moveme-i* o*" all matter, the expression of the world's energy, an I iilusu.tte the same laws; But to these matters we shall efrn in anoti.er chapter.
Interesting, because of • s larply dc nned ?nd far-reaching significance, and because ihc p^^c'^tiai 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 fonned in the plant unless there be, as there almost always is, some iron in the soil. Thus our whole life is baseu 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 absoibed by the roots, in carbonic acid gas absorbed by the leaves from the air, and in the energy of tlic 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
I
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f
ao
The Study of Animal Life
PAST t
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 con rast when the student realises that plants and animals being both (though not equally) ahve, 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 li'"e or com- bustion, and carbonic acid gas p sses out as a waste-pro- duct. Herein there is no difference except in degree between plant and animal. Each lives, and n>ust 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
33F*
^
(.>:'
CHAP. II
TAg WehofLife
ai
I.;
compensate both *or their own breathing and for that of animals. Thus ti e 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 fcr a long time by the very simple colourless plants known as Bacteria, and at last not even by them. Nevertheless the " vivarium " experinient is both theoretically and practically possible. Now in nature th^re 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 u 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 call'-d 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 thcT 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 ; th»;y 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 raisin^j
H
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33
The Study of Animal Life
PART
r':
the ashes of animals into a new life. A strange pat ship between Bacteria on the one hand and leguminous .md 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 ddbris. 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 I4| 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
% U r
;i>,«f .iiifi^. S2^' , *tjafcsik26>-:= m-i
cha;. 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 io| lbs. 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 th3 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, perforatiny;. and loosening the soil, and rendering it pervious to rains and the litres of plants ; by drawing straws and stalks of leaves and twij^s into it ; and, most of all, by throwint; 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 piobably to avoid being flooded. . . . The earth without worms would soon l)ecome 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-
n
.^tii
r^
.fn-
^^•IdSRiSw'^^
24
The Study of Animal Life
PART 1
graph of worms would afford much entertainment and information hLJoryT" '""'' '"' "°"'' "P^" ^ '^^^^ ^"^ "- fieldTn natural
After a while the discerning did go to work, and Hensen pubhshed an important memoir in 1877, while Darwin^ "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
prrtTnTh^h'r "V"f "''f' '^^" P'^y^^ - important a cStures." "^ """"^^ "' ^"'*^ '^''' lowly-organised
Prof Drummond, while admitting the supreme imoort ance of the work of earthworms, eloquently ple'lds the Ss'
Tn, ? Tul °',^^'^'^' "^"^ ^' ^" agricultural agent. TWs insect, which dwelt upon the earth long before thf true ant •s abunoant in many countries, and notably in Tropical Atrica. 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 hf hungry Termites. These fell workers are blind and 1 ve underground ; for fear of their enemies they dare not show fac:e. and yet without coming out of their ground they cannm
along" it! them'' TL" "'' ''""'l^'' ^ ^'^^J' '^'^^ '^'^ 8-""^ out earthworms, keep the soil circulating. The earth tu£ cr,Vn
lief s;t:?^;::;nii^?d^ ' ^^^^^^"^
alluvium of a distZit vall'J/' " '°°''"'^ grains to swell the
i:i
T.*apjMBiirwi vrft ifc
CHAP. II
The Web of Life
*l
The influences of plants and animals on the earth are manifold. The sea- weeds cHng 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-vohs 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 .arder 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
"■*«< "/a««aBsw!WKA • '-'^-<».rij^?^-'%it:i
- 1
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 fonns 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 gvpsum of the sea-water, at any rate in some way the originahy 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-
■" " "' ^Ei
mm
CHAP. 11
The Web of Life
27
restrial fauna and flora begin. It is a strange and beautiful story, dead shells of the tenderest beauty on th^ 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 stoty 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 .i flooded and the local climate altered, and when the birdi 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
i- 1 ■
?^^s^
38
The Study of Animal Life
PART I
have in some districts driven away the titmice and thus tavoured the survival of injurious caterpillars.
b. More Complex Interactions.— The flowering plants and the higher insects have grown up throughout lone ages together, in alternate influence and mutual per- fectmg. They now exhibit a notable degree of mutual dependence; the insects are adaoted for sipping the nectar from the blossoms; the flov >rs are fitted for givmg 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 thev 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 dram the cup ; and Forbes confirmed the prediction bv discovering the insert.
As informatioii 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 wond 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 done through the agency of insects How plants became bright in colour, fragrant in scent, rich m 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 ihe 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 propositi r 1 must be 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 efiective 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
f1
I: -y^
30
The Study of Animal Life
f
I'ART I
insects which do no harm to the trees, but cleanse them from mjurious 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 .vhich 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-
"^J^ ^'t t^'^^ft^'t^, -y ^f »-^in the evolu- (After Schimper.) tion of the repulsive
T,, . qualities,
are atif Mhf^ >nter-relations between plants and animals are agam .llustrated by the carnivorous, generally insecti- vorous plants. It is not our busine;s%o discu s the ongmal or primary import of the pitchers of pitcher-plants,
CHAP. 11
The Web of Life
3>
or of the mobile and sensitive leaves of Venus' \ ly-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 {Utricularid). Many of the leaflets of this plant, which floats in summer in the marsh ponJ, are modified into little bladders, so fashioned that minute " water-fleas " — which swarm in every comer 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 inwar-^s, 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 debris 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 ivoiy 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 c'ear. 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 ?
A
■%
''4|
CHAPTER III
THE STRUGGLE OF LIFE
I. Nature and Extent of tkeStruggl,-2. Armcur and Weaiom- 3. Different Forms of Struggle -4. Cruelty of the Stru^le
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 m isolation, neither do they always pursue paths of peace. Nature is not iike a menagerie where beast IS separated from beast by iron bars, neither is it a mfilde 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 ^f men, older than the ravin of tooth and claw, it U 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 •kies ; another compares nature to a huge gladiatorial show with a plethora of fighters, but he speaks as a pes-
CHAP. lit
The Struggle of Life
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 natt z 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."
a. Armour and Weapons.— If you doubt the reality
o
34
TJie Study of Animal Life part i
of the struggle, take a survey of the different classes of animals. Ever)rwhere 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 aot. 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 within shells of lime, that many wonns 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 moiiuscs live in shells. So among backboned animals, how thoroi'^hly bucklered were the fishes of the old red sandstone aJ,^^inst hardly less effect- ive teeth, how the scales of modem fishes glitter, how securely the sturgeon swims with its coat of bony 'mail ! -Amphibians arc mostly weaponless and armourless, but reptiles are scaly animals par exxcllence, 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 liave 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 explanah'ons, 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 ether 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 proN jrb : " A force de forger on devient forgeron"
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. Hy 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 Porms of Struggle.— If you ask why animals do not live at peace, I answer, more Scoitko, Why do not we ? The desires of animals conflict with those of their neighbours, hence the struggle for bread ind 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"
r^w
ip^^?*
CHAP. Ill
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 withoit 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 tli« le 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 fellows.
{b) Between animals of diffefent kinds, the one set striving to devour, the other set endeavouring to escape their foes, e.g. between carnivores and herbivores — Struggle between foes.
(f) Between the rival suitors for desired mates — Struggle between rivals in love.
For Food
For Love
For Foot- hold
{(i) Between animals and changeful surround- ings — Struggle with fate.
In most cases, besides the egoism or individualism, one must recognise the existence of altruism, paren, 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 eg^s, 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 witli 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 aiiakc between antelope and antelope. . . . Homo komini lupus, says the old proverb, and so, we may add, in a wider sense, lupus lupo
CHAP. Ill
Ike Struggle of Life
39
lupus, also. . . . The struggle i.; fierce between allici. 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," Nineieenth Century, September and November 1890.
{V) Of the struggle between foes difTering 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
mnp
40
"V
if
The 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 mid Sports.)
Struggle must again be used " in a wide and metaphorical
i/Mihv-
sense
(r) In a great number of cases there is between rival males a contest for the possession of the females,-a competition m 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. Ill
The Struggle of Life
41
Many animals are not monogamous, and this causes strife ; a male seal, for instance, guards his harem with ferocity.
(rf) Finally, physical nature is qui te 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 {Glyciphagus\ which had been harboured in crevices in a strange state of dry dormancy. Every mite had in a sense
49
The Study of Animal Life
PART
^ s'
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 doi-mant 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 tiot 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
CRAP. Ill
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 mariner 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. Ornelty 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 ccnception 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 starvatioii 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
'' '"''^iwWIipWWMIiiii'.tii'yiiii 11 /I'm
The Study of Animal Life
PART I
herbivorous animals "which have been tormented and devoured by carnivores " ; of both alike " subject to all the
tTr"'' f"S^'?"' '° °'^ "«"' ^•^^^^' ^"d 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 to ments and niisenes 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
aL'n?«t r"\ '^""'f ""' '''' ^^^"^^"'^ ^°r existence among animals ,s altogether insignificant." " Animals are spared from the pain of anticipating death ; violent deaths, f not too prolonged, are painless and easy; neither do those which die of cold or hunger suffer much the popula Idea of the struggle for existence entailing misery and paL on the animal worid is the very reverse of the tmth " ^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 ha
healthy, and the happy survive and multiply." Yet i was Darwin who confessed that he found in the world "oo much misery." ^"°
We have so little security in appreciating the real life- the mental and physical pain or happiness-of anima^hat there is apt to be exaggeratio. on both sides, according a 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 aS half frozen animals have to endure "an altogether insignificant
"TuM° vT' '"''""^ '" ^^^ =^-^^'« ^- existen";?" whi^ M w n *^ """'' ''"^'"'' '^^' ^^^'^ is much truth in what Mr. Wallace urges. Moreover, the term cruelty can hardly be used with accuracy when the involved infliction
less'f'ruel-rth?- • I" ""^ ^^"^ ^^^ camivoresTr IL " 1,.'° ?"L"^ '!?^ *^- - -« to our domesti-
.... — - "•«" wc arc lo OU
cated animals. We must also remember that the
struggle
<Tl9?«veW4f«.
isMaas&''iS!S'^-if. °r^!wiiii'''$^r:viF^E2fia?ssBSHE&>
CHAP. Ill
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 ov^ 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.
^^^'^^ESWa^v-:.
CHAPTER IV
:•'
SHIFTS FOR A LIVING
I. Insulation -2. ConccahncH-i. Parasitism-^. General Re- semblance to Surroundings -i. Variable Colouring~6. Rat^id Chanse of Colour —t. Special Protective Resemblance -%. IVarnmg Colours -q. Mimicry— lo. Afasiimr-ii. Com- bmatton of Advantageous Qualities— 12. Surrender of Parts
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. InBUlation.— 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 ihe 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. Ooncealment. — 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 pwlar 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 reLitive 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 S/ri/tgops, 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 th^t this transition, and also that from diurnal to nocturnal habits, oft. brought only a temporary relief.
3. Parasitism. — i-rom the simple Protozoa up to the beginning of the backboned sei s, 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 arc temporr-ry 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 l)cgun 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, liun;;er and the search for shelter led to the estabUshment of the thievish haLit. 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—^ 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 afTccted by their laiy 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 1 She winnows, winnows roughly, sifts, To dip her chosen in her source. Contention is the vital force Whence pluck they brain, her pri«e of gifts."
4« Ckntnd Reiemblance to Snrroimdinfi. 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 m"!(^ 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 n»ust be gra' ful. 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 H certain that the pigmented feathers and hairs become white, in other cases the old feathers and hairs drop
, TV^QJg'
■"wic^MnwB^imT-'riraTW.Tniiiju .w.^:'*
so
The Study of Animal Life
PART I
oflf 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 .my pigment that may be present, but in the case of new growths it is not likely that any pig- ment is formed. In sc ue cases, e.g. Ross's lemming and the American hare {Lepus americanus), 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 those of the surroundmgs, 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 urtica\ garden whites {Pieris brassica and Pieris rapa\ and many others. Caterpillars of the small tortoise-shell in black surroundings tend to be- come darker as pupae ; in a white environment the pupx 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 statr," "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
5>
" It appears to be certain that it is the skin of the larva which is influenced by surroundinjj colours during the sensitive period, and it is probable that the cfifects are wrought through the medium of the nervous system."
Accepting the facts that caterpillars are subtly affected by surrounding colours, so that the quiescent pupie 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." Foulton'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 \\ere 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- ated by mheritance 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.
f
5a The Study of Animal Life part i
6. Bapid Ohange of Oolonr. — 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, Goinus ruthtnsparri.
. BWIWP'Jft '-<■•*?• A-iVt»SThJ»
CHAP. !▼
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, <r.^. 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 rai-ed wings ; the leaf-insects {Phyllium) have leaf-like wings and legs ;' the "walking-sticks" {Phasmid(f\ with legs thrown out at all angles, resemble irregular twigs ; many caterpillars (of Geometra moths especially) sit motionless on a branch, supported in a strained attitude by a thin thread of silk, and exactly resemble twigs ; others are like bark, moss, or li "len. Among caterpillars protective resemblance is very common, and Mr. Poulton associates its frequent occurrence with the peculiarly defenceless condition of these young animals. •• The body is a tube which contains fluid under pressure ; a slight wound entails great loss of blood, while a moderate injury must prove fatal." •• Hence larvai are so coloured as to avoid detection or to warn of some unplea- sant attribute, the object in both cases being the same— to leave the larva untouched, a touch being practically fatal." Among backboned animals we do not expect to find many
■^ryS- ,-&.
54
The Study of Animal Life
PART I
examples of precise resemblance to surrounding objects ; but one of the sea-horses {Phyllopteryx eques) is said to be exceedingly like the seaweed among which it lives. It is very difficult at present to venture suggestions as to the constitutional tendencies which may have resulted in " walking-leaves " and " walking-sticks," but forms related to these tend to resemble leaves or sticks sufficiently to deter
Fu;. 7.— r.taf-in-ccl -cata.l on a bran, h (From Heit.)
one from postulating a mere sport as the origin of the p('( iili.'uity which distinguishes riiyllium or riuuituu On the other hand, some of the strangely precise minute resemblances n1^■^' be the fostered results of slight indefinite sports. It is aiso possible that some of the cleverer animals, such as spiders, learn to hide among the lichens and on the bark which they most resemble. But in every case, and especially where there are many risks, as among
^U
CHAP. IV
Shifts for a Living
55
caterpillars, the protective resemblance would be '"ostered in the course of natural selection.
Fig. 8.— Moss insect. (From Belt.)
8. Warning Colours. — While many animals are con- cealed by their colouring, others are made the more conspicuous. But, as the latter arc often unpalatable or dangerous, Wallace suggested that the colours were warnings, which, as Poulton says, "assist the education of enemies, enabling them to easily learn and remember the animals which arc to be avoided.' Expressing the same idea. Belt says, " the skunk goes leisurely along, holding up his white tail as a danger-flag for none to come within range of his nauseous artillery," So, the brightness of the venomous coral-snake {Elafis) is a warning; the rattlesnake, excitedly shaking its rattle, "warns an intruder of its presence"'; the cobra " endeavours to terrify its enemy by the startling appearance of its expanded hood and con- spicuous eye-like marks." The language in which conspicu- ous colours are described by many naturalists tends to exaggerate the subtlety of animals, for the intentional warning of possible molesters involves rather complex ideas. Belt's description of the skunk, for instance, recalls a more familiar sight — a cat showing fight to a dog — in regard to \\\\\d\ Mantegazza gravely tells us that the cat " bristles up her fur, and inflates herself to appear larger, and to frighten the dog who threatens her " ! In our desire to be fair to the subdety of animals, it is indeed difficult to avoid being credulous.
' llJUijlJl'J
56
The Study of Animal Life
PART I
Perhaps the best illustration which Belt gives is that of a certain gaily-coloured frog : —
" In the woods around Santo Domingo there are many frogs. Some are green or brown, and imitate green or dead leaves, and live amongst foliage. Others are dull earth-coloured, and hide in holes and under logs. All these come out only at night to feed, and they are all preyed upon by snakes and birds. In contrast to these obscurely-coloured species, another little frog hops about in the daytime dressed in a bright livery of red and blue. He cannot be mistaken for any other, and his flaming vest and blue stockings show that he does not court concealment. He is very abundant in the damp wood, and I was convinced that he was uneatable so soon as I had made his acquaintance, and saw the happy sense of security with which he hopped about. I took a few specimens home with me, and tried my fowls and ducks with them, but none of them would touch them. At last, by throwing down pieces of meat, for which there was a great competition amongst them, 1 managed to entice a young duck into snatching up one of the little frogs. Instead of swallowinjj it, however, it instantly threw it out of its mouth, and went alinut jerking its head, as if trying to throw off some unpleasant taste.'
Admirable, also, are the illustrations given by Mr. Poulton in regard to many caterpillars, such as the larva of the currant or magpie moth (^Abraxas grossulariata), which is conspicuous with orange and black markings on a cream ground, and is refused altogether, or rejected with disgust, by the hungry enemies of other caterpillars. Professor Herdman and Mr. Garstang have also shown that the Eolid Nudibranchs (naked sea-slugs), with brightly-coloured and stinging dorsal papillae, are rarely eaten by fishes ; and the same is true of some other conspicuous and unpalat- able marine animals.
The general conclusion seems fairly certain that the conspicuousness of many unpalatable or noxious animals is imprinted on the memory of their enemies, who, after pay- ing some premiums to experience, learn to leave animals with "warning colours" alone. It will be interesting to discover how far the bright colour, the nauseous taste, the poisonous properties, the distasteful odour, sometimes found associated, are physiologically related to one another, but to answer these questions we are still unprepared.
CHAP. IV
Shifts for a Living
57
9. Mimicry. — Mr. Poulton has carefully traced the transi- t.vjn from warning to mimetic appearance, and it is evident that if hungry animals have been so much impressed with the frequent association of unpalatableness and conspicuous colours that they do not molest certain bright and nauseous forms, then there is a ch;uice that palatable forms may also escape if they are sufficient y like those which are passed by. The term mimicry is restricted to those cases
Fig. 9.— Hornet {Priocnemis) above, .nnd mimetic bug {Spinigcr) beneath.
(From Belt.)
" in which a group of animals in the same habitat, character- ibed by a certain type of colour and pattern, are in part specially protected to an eminent degree (the mimicked), and in part entirely without special protection (the mimickers) ; so that the latter live entirely upon the reputation of the former." Tlie fact was " discovered by Bates in Tropical America (1862), then by Wallace in Tropical Asia and Malaya ( 1 866), and by Trimen in South Africa (1870)"; while Kirby, in 18 1 5, referred to the advantage of a certain fly being like a bee, and of a certain spider resembling an ant
58
The Study of Animal Life
PART I
r
The constant conditions of mimicry are clearly and tersely summed up by Wallace. They are : —
1. That the imitative species occur in the same area, and occupy the very same station, as the imitated.
2. That the imitators are always the more defenceless.
}'. ^^^^ ^^^ imitators ire always less numerous in individuals.
4. That the imitators differ from the bulk of their allies.
Fig. la— Hunimin'-bird moth (Macroglossa titan), and humming-bird (. >./>,\jmis GouUit), (From Bates.)
S. That the imitation, however minute, is external and visible only, never extending to internal characters or to such as do not aftect the external appearance.
Many inedible butterflies are mimicked by others quite different. Many longicorn beetles exactly mimic wasps, bees, or ants. The tiger- beetles are mimicked by more harmless insects ; the common drone-fly {Eristalis) is like a bee; spiders are sometimes ant-like. Mr. Bates relates that he repeatedly shot humming-bird moths in mistake for humming-birds. Among Vertebrates genuine mimicry is rare, but it is well known that some harmless snakes mimic
CHAP. IV
Shifts for a Living
59
lue swollen
poisonous species. Thus, the very poisonous coral-snakes {Elaps), which have very characteristic markings, are mimicked in din';i ;nt localities by several harmless forms. Similarly in regard to birds, Mr. Wallace notices that the powerful "friar-birds" {Tropidorhynckus) of Malaya are mimicked by the weak and timid orioles. *' In each of the great islands of the Austro-Malayan region t\ere is a dis- tinct species of Tropidorhynchus, -md thpr. is al^^ays along with it an oriole that exactly mimics it."
That there may be mimetic resembla uc I <. - • (_n d'£tii,«.\ forms there can be no doubt, and tbt» v ii kj{ ii\^ -:».■- txw- blance has been verified ; but there ?'~ -oir.r ,;m . u ;_i,d«' .rv to weaken the case by citing instan.jt - ; j ,ii . t- = . liici liave been insuflSciently criticised. flu.- f^ i,> ;? i ,. -dlv justify us in saying that the larvae ot t'.r . .^^ lar*. tl^u.k 'Slolh {Chirrocatnpn) " terrify their en- r.ii . ' , r^> .ujij/o tion of a cobra-like serpent ; " or that the 'ob . , nluch spi'-es abrrii by the large eye-like 'specac dilated h' od, offers an appropriate model foi interior end of the caterpillar, with its terrifying markings."
Th°re is only on*; theory of mimicry, namely, that among the min.icking animals varieties occurred which prospered by bei.ig somewhat like the mimicked, and that in the course of natural selection this resemblance was gradually increased until it became domirant and, in many cases, remarkably exact.
As to the primary factors giving rise to the variation, we can only speculate. To begin with, indeed, there must have been a general resemblance between the ancestors of the mimicking animal and those of the mimicked, for cases like the Humming-Bird and its Doppel-Ganger moth are very rare. But this does not take us very far. The beginning of the mimetic change is usually referred to ore of those "indefinite," "fortuitous," "spontaneous" variations which are believed to be common among animals. It is logically possible that this may have been the case, and that there was at the very beginning no relation between the variation of the mimicker and the existence of the mimicked. But as illustrations of mimicry accumulate — ar.d they are already
m
Mi
Hi
6o
TJie Study of Animal Life
PART I
c
o
J £
O 1.
X 'J
s ;
- I
S§i
'.--, iiiy-A r .
CHAP. IV
Sh'"s for a Living
6i
very numerous — one ii tempted to ask whether there may not be in many cases some explanation apart from the action of natural selection upon casual changes. May not the similar surroundings and habits of mimickers and mimicked have sometimes something to do with their resemblance ; may it not be that the presence of the n 'micked has had a direct, but of course very subtle, influence on the mimickers ; is it altogrether absurd to suppose that there may be an element of consciousness in the resemblance between oriole and friar-bird ?
10. *< Masking" is one of the most interesting ways in which animals strengthen their hold on life. It is best illustrated on the sea-shore, where there is no little struggle for existence and much opportunity for device. There many animals, such as crabs, are covered by adventitious dis- guises, so that their real na«^ure is masked. Elsewhere, however, the same may be seen ; the cases of the caddis- worms — made of sand particles, small stones, minute shells, or pieces of bark — serve at once for protection and conceal- ment ; the cocoons of various caterpillars are often masked by extrinsic fragments. The nests of birds are often well disguised with moss and lichen.
But among marine animals masking is more frequent. "Certain sea-urchins," Mr Poulton says, "cover themselves so completely with pebbles, bits of rock and shell, that one can see nothing but a little heap of stones ; and many marine molluscs have the same habits, accumulating sand upon the s'.'.rface of the shell, or allowing a dense growth of Algas to cover them."
This masking is in many cases quite involuntar>'. Thus the freshwater snails [LytttMcrus) may be so thickly covered with Algae that they can hardly move, and some marine forms are unable to favour or prevent the growth of other orjjanisms upon their shells, but how far this is from be- injj the whole story is well known to all who are ac([uain»'!(! with our shore crabs. F"or though they also may be invol- untarily masked, there is ample evi<ience that they some- times disguise themselves.
The hermit-crabs are to some extent masked wiihin
62
The Study of Animal Life part i
their stolen shells, especially if these be covered by I'no Hydroid Hydractinia or other ortjanisms. Various other crabs {Stenorhynchus^ Inachus^ Maitt, Drottiia, Pisa) arc masked by the seaweeds, sponges, and zoophytes which cover their carapace. Moreover, the interest of this mask- ing is increased by the fact observed by Mr. Bateson at Plymouth that the crabs sometimes fix the seaweeds for
Fig. la. -Sack-bearing caterpillar (.Vaff(>/Apra). (Ktani Mates.)
themselves. Mr. Hatesnn describes how the nah seizes a piece of weed, tears off a piece, chews the end in his moufli. and then nibs it firmly on his head and legs until it i- raugh- by the turved hairs and fi.xed " Ihe whole pri (ceding is most human and piirimseful. Many substance-, as hydroids, spong« s I'oly/oa, and weetls of many kin<! and colour?, arc thus used; but these various substaiu' ate nearly always ..>minetrica!!y i>!attd on c orrt^ponduK;
M HA ,
CHAP. IV
Shifts for a Living
63
parts of the body, ar.d particularly long plume-like pieces are fixed on the head." Thus, as Carus Sterne says, is the story of " Bin am's walking wood " re-enacted on the sea- shore. Furthermore, a Stenorhynchus which has been cleaned will immediately begin to clothe itself again, with the same care and precision as before. Mr. Robertson of Millport often saw Stennrhynchus longirostris — a common crab — picking about its limbs and conveying the produce to its mouth. " If other observations confirm the view that this animal is a true vegetarian, we shall have one example at least of an independent agriculturist, who is not only superior of his lands, but carries them with him when he removes." I also have seen the crab doing what " tlie naturalist of Cumbrae " observed. In further illustration of masking we may cite Dromia vulgaris, often covered with sponge ; Dromia excavata, with compound ascidians ; the Amphipod Atylus, with seaweed ; while a species of Dorippe is said to bear a bivalve shell, or even a leaf, as a shield, and another crab cuts off the tunic of a sea-squirt and hitches it on his own shoulders.
Sometimes this masking serves as a warning or deterrent ; witness that hermit-crab {Pagurns cvamnsis) whose stolen shell is surrounded by a bright orange sponge (Suberiles domuncula). As this sponge is full of flinty needles, has a strong odour and a disagreeable taste, we do not wonder tint Mr. Garstang finds that fish dislike it intensely, noi ran we doubt that the hennit-crab trades on the reputation of its associate. In other cases the masking will aid in con- icalment and favour attack. To the associations of crabs and sea-anemones we shah afterwards refer.
II. OombinAtion of AdTantageoiw Qualities. — Mr I'oulton describes, in illustration of the combination of many methods of defence, the case of the larva of the puss moth {Cerura vinula). It resembles the leaves of the poplar and willow on which it lives. When disturbed it assumes a terrifyinjj attitude, mimetic of a Vertebrate appearance ! The effect is heightened by the protrusion of two pink whips from the tenninal prongs of the body, an<l tinally the (feature defemis itself hy squirting' formic acid.
64
The Study of Animal Life
I'ART I
!-:i J
Yet in spite of all this power of defence, the laira often falls a victim to ichneumon-flies. These manage to lay their egys
within the caterpillar, which by and by succumbs to the voracity of the hatched ichneumon maggots. Mr. I'oulton believes that the puss moth larva " has been saved from extennination by the repeated acquisition of new defensive measures. But any improvement in Fig. 13. -" Terrifying attitude" of the the means of defence ha^
caterpillar of Crura vmuta (From ^^^^^ ,„et ^y j^e greater Chambers s ^(•O'c/o'/. ; after Poultoii.) , ,1
mgenuity or boldness of foes ; and so it has come about that many of the besl- protected larv;e are often those which die in the largest numbers from the attacks of enemies. The exceptional standard of defence has been only reached through the pressure of an exceptional need."
13. Surrender of Parts.— Among the strange life -pro- serving powers which animals exhibit, we must also include that of surrendering parts of the body in 'lu' panic of capture or in the struggle to escape. A rat will gnaw off a leg to free itself from a trap, and I ha\ r heard of a stoat which did not refrain from amputatin* more than one limb. But the cases to which we now refi r are not deliberate amputations, but rctlex and unconsciou-^ surrenders. Many lizards (such as our British " slowworm " ) will readily leave their tails in their captor's grasp ; cnis- tarcans, insects, and spiders part with their limbs and scramljlc off maimed but safe ; starfishes, brittle-stars, and feather-stars resign their arms, and the sea-cucumbers their viscera. A large number of cases have been studied I'V Kredericq and (liard.
Among Crustacea the habit is most perfectly developed in the crabs, e.^. the common shore-rrab (('(/n///wj///(r«(/.»), and in the spiny lobster {Pitlinitrus), but it is also exhibited by the cra\ tish (As/uius), the common lobster (^llotnarus).
CHAP. IV Shifts for a Living 5c
the shrimp (frangon\ and the prawn {Palamon). In crabs and in the spiny lobster the surrender of a limb is effected by the forcible contraction of the basal muscles, and the line of rupture is through the second-lowest joint. FrtJde- ricq's researches seem to prove conclusively that the sur- render is a reflex and unconscious act, but its protective value is not less great. The chances are in favour of the crab escapmg, the residue of muscle prevents haemorrhage from the stump, and in the course of time the lost limb is replaced by a new growth. The crab does not know what It IS doing, but It unconsciously illustrates that it is better that one member should perish than that the whole life should be lost.
Not a few insects readily surrender their legs, but these are not replaced. Spiders arc captured if the legs are fixed without irritating the nerves, for that is an essential con- dition of the reflex amputation. In regard to lizards, also, It has been shown that a reflex nervous excitement, and not mere brittleness, is the condition of surrender. Here how- ever, the lost tail may be replaced. Among Mollilsca a surrender of parts has been recorded of Harpa veniricosa, Dons cruenta, Stenopus, some species of Helix, the razor- shell Solen ; while it is well known that male cuttle-fishes sometimes part with one of their arms for special sexual purposes. A great many « woms " break very easily, and the severed parts are sometimes able to regrow the whole organism.
Among the Echinoderms the tendency to disrupt is exhi- bued to an extraordinary degree. Thus Professor Preyer has ^liown that the seven-rayed ^l^x^^h {Asterias ienuisfiina) urrenders its arms with great readiness, often giving off three or four at a time. Hut each ray may reproduce an entire starhsh. Professor Edward Forbes tells how a speci- men of LuMa which lie had dredged, was disappearing -r the side of the boat wlu.i he cau«ht it by one of its ■«'n s; It surrendered the arm and escaped, giving "a wink - ension " wi.b one of its eyes. Brittle-sta's (Ophiuroil) >r many kinds are true to their popular name, and the C rmoKis are not less disruptive. Not only are the arms
66 The Study of Animal Life part i
readily given off, but these break into many fiagments. There can be no doubt that this habit, combined with the marvellous power of regrowth which these animals possess, is of great protective value, while it is also probable in regard to both Echinoderms and some worms, that the disruption of parts may really increase the number of individuals.
There is no need to enumerate all the protective habits and devices which animals exhibit. Some " feign " death, by falling in panic into a state allied to hypnotic trance, perhaps in some of the higher animals by conscious decep- tion ; others roll themselves up into balls, as in forms so different as myriapods and armadillos ; but, finally, I shall cite from Dr. Hickson's Naturalist in North Celebes one other device. '* I often saw advancing slowly over the sea- ardens, in parties of from four to six, a group of cutt -fish, swimming with an even backward movement, the inges of their mantles and their arms trembling, »»• ttei' colour gradually changing to what seemed to n nost infinite variety of hues as they passed jv. he rious beds of the sea -bottom. Then suddenly ihe would be a commotion in what was previously a cah md placid scene, the striped and speckled reef fishes wo be sen darting away in all directions, and of the cut ishef U that remained were four or five clouds of ink in t,H clftfl Iter. They had thrown dust in the eyes of some -OS* ark or voracious fish."
liu. should not like to suggest the ide.i that animals are alw;» i careful and anxious, or forced to continual struggle and shift.
•• They do not iweat and whine alwut their condition,
They do not lie awake in the dark and weep for their sins,
They do not make me sick discussing their duty to CJotl,
Not one is dissatisfied, not one is demented
With the mania of owning things ;
Not one kneels to another, nor to his kind that lived thous.^n(b
of years ago ; Not one is respectable or unhappy over the whole earth."
Walt V.'iiitmak.
CHAPTER V
SOCIAL LIFE OF ANIMALS
I. Partnerships— 2. Co-operation and Division of Labour— % Gre- gartous Life and Combined Action—/^. Beai>ers—s Bees— 6 't"?"^; ^f':^'''"-^- Evolution of Social Life-^. Advanta^res of Soaal Ltfe—io. A Note on the Social Organism — ii Conditstons
The over- fed plant bears many leaves but its flowers are few ; the animal which eats too much becomes fat • and we know that within the living body one part may K'row out of proportion to the others. It seems as if organ competed with organ within the living engine, as .f one tissue outgrew its neighbors in the living web, as If there were some struggle for existence between the individual units which form the city of cells in any of the higher animals. This idea of internal competition has been elaborated by a Gennan biologist, Roux, in a work entitled 7-^^ Struggle of Parts within (he Organism, and It IS full of suggestivencss. It can be verified from our own experience ; but yet it seems strange. For we rightly '»nk of an organism as a unity in which the parts are Iranothef '" '""'"^' helpfulness, being members one
Now, just as a biologist would exaggerate greatly if he maintained that the struggle of parts was tht most inv Fitant fact about an organism, so would a naturalist if he
t.
ill
i \
I «
68 TAe Study of Animal Life pakt i
Coherence and harmony and mutual helpfulness of parts— whether these be organs, tissues, or cells— are certainly facts in the life of individuals ; we have now to see how far the same is true of the larger life in which the many are considered as one.
I. Partnersliips. —Animals often live together in strange partnerships. The «« beef-eater" birds {Buphagus) perch on cattle and extract grubs from the skin ; a kind of plover {Pluvianus agyptius) removes leeches and other parasites from the. back of the crocodile, and perhaps "picks his teeth," as Herodotus alleged ; the shark is attended by the pilot-fish {Naucrates ductor\ who is shielded by the shark's reputa- tion, and seems to remove parasites from his skin.
Especially among marine animals, we find many almost constant associations, the meaning of which is often obscure. Two gasteropods Rhizochilus and Magilus grow along with certain corals, some barnacles are common on whales, some sponges and polypes are always found together, with- out there being in any of these cases either parasitism or partnership. But when we find a little fish living con- tentedly inside a large sea -anemone, or the little pea-crab (Pinnotheres) within the horse-mussel, the probable explana- tion is that the fish and the crab are sheltered by their hosts and share their food. They are not known to do harm, while they derive much benefit. They illustrate one kind of " commensalism," or of eating at the same table.
But the association between crabs and sea -anemones
affords a better illustration. One of the hermit-crabs of
our coast {Pagurus f»ideauxii) has its borrowed shell
always enveloped by a sea-anemone {Adamsia palliaia),
and Pagimis bernJumius may be similarly cnsheathed by
Adamsia rondeletii. Mobius describes two crabs from
Mauritius which bear a sea-anemone on each claw, and m
some other crab? a similar association occurs. It seems
that in some cases the crab deliberately chooses its ally and
plants it on its shell, and that it does not leave it behind at
the period of shell -chanKim Deprived of its polype c-Mn-
panion, one was seen to : restlessly ill at ease imtil
It obtained another of the same kind. The use of the sea-
CHAP. V
Social Life of Animals
69
anemone as a mask to the crab — and also perhaps as aid in attack or defence — is obvious ; on the other hand, the sea-anemone is carried about by the crab and may derive food from the crumbs of its bearer's repast.
Commensalism must be distinguished from parasitism, in which the one orgapism feeds upon its host, though it is quite possible that a commensal might degenerate into a parasite. Quite distinct also is that intimate partnership known as symbiosis, illustrated by the union of algoid and fungoid elements to form a lichen, or by the occurrence of minute Algae as constant internal associates and helpful partners of Radiolarians and some Coelenterates.
2. Co-operation and Division of Labour.— The idea of division of labour has been for a long time familiar to men, but its biological importance was first satisfactorily recognised by Milne-Edwards in 1827.
Among the Stinging-animals there are many animal colonies, aggregates of individuals, with a common life. These begin from a single individual and are formed by prolific budding, as a hive is formed by the prolific egg- laying of a queen-bee. The mode of reproduction is asexual in the one case, sexual in the other ; the resulting individuals are physically united in the one case, psychically united in the other ; but these differences are not so great as they may at first sight appear. Many masses of coral are animal colonies, but among the members or " persons," as they are technically called, division of labour is very raie ; moreover, in the growth of coral the younger individuals often smother the older. In colonial zoophytes the arl)orescent mode of growth usually obviates crushing ; and tliere is sometimes very marked division of labour. Thus in the colony of Hydractittia polypes, which is often found Kiowing on the shells tenanted by hermit-crabs, there may be a hundred or more individuals all in organic connection. Ihe polypes are minute tubular animals, connected at their bases, and stretching out from the surface of the shell into the still water of the pool in which the hermit-crab is rciimif. But among the hundred individuals there are three or four castes, the differences between which probably
^SiSimX^.
■ I
alii
1*. • I
70
T/t£ Study of Auimal Life
PAR r I
result from the fact that in such a large colony perfect uniformity of nutritive and other conditions is impossible. Individuals which are fundamentally and originally like one another grow to be different, and perform different func- tions according to the caste t > which they belong.
Many are nutritive in form like the little freshwater Hydra— iv\m\7cc animals with an extensile body and with .1 terminal mouth wreathed round by mobile tentacles. On
these the whole nutrition of tlie colony depends. Beside the>e there are reproductive " per- sons," which cannot feed, being mouthless, but secure the continuance of the species and give rise to embryos which start new colonies. Then there are Ion,;, lank, sensitive mem- bers, also mouthless, which serve as the sense-organs of tlic colony, and are of use in tlc- tccting food or danger. Wht 11 danger threatens, the polypo cower down, and there are IcU projecting small hard spines, which some regard as a fourtli
Fig. t4. -Colony of lfy.i,act!,.;<x class of individuals— star\c(l, tchinata. a, luitritivo iiniividiiais ; abortive members like the
h, reproductive individiinl> ; c> ^, .^i i »i i _ i
abortive spines; and there are thoms On the hawthom hed^e.
.ilso louK mouthlps individii.-ils j^ rccognising their utility to
specialised m sensitiveness. (From ° ° '
charnVjers's h'.ncyciop. ; .iftcr All- the colony as a whole we can '"'"'>• hardly overlook the fact that
their life as individuals is prarticaliy nil.
trate the dark side of division of labour.
They well illus-
i! ■ I
Ilcriwrt .^pcnrer .nnd Krnst Ilacckel Imve cxiilnincl voiy rlc.TiIy one l.tw of jir )j^rcss aiiionif those animals \v)iich form colonics. 'I'lio crmlo form nf a colciy is an ai,'::,'rij;aU of siniilat inilivi(hi.il^, the perfected colony is an intcip-aie in wliich by division of lalimir greater harmony of life li > resulted, and in which the whole colony is more thoroughly compacted into a unity. Among the Stinging-
:i,
CHAP. V Social Life of Animals 71
animals, we find some precise illustrations of such integrated colonies, especially in the Siphonophora of which the Portuguese Man-of-War i/'kysalia) is a good example. There is no doubt that these beautiful organisms are colonies of individuals, which in structure are all referable to a " medusoid " or jellyfish-like type. But the division of labour is so harmonious, and the compacting or oi^nisation of the colony is so thorough, that the whole moves and lives as a single organism.
E. Perrier in his work entitled Les Colonies Animales (Paris, 1882), shows how organic association may lead from one grade of organisation and individuality to another, and explains very clearly how sedentary and passive life tends to develop mere aggregates, while free and active life tends to integrate the colony. With this may be compared A. Lang's interesting study on the influence of sedentary life and its connection with asexual reproduction — Das Einfluss des Festsitten (Jena, 1889). Haeckel, in his GmtrelU MorpkologU (a vols,, Berlin, 1866), was one of the first to shed a strong clear light on the difficult subject of organic individuality, its grades and its progressive complexity. To Spencer, Principles of Biology (2 vols., London, 1863-67), we owe in this connection the elucidation of the transition from aggregates to integrates, and of the lines of differentiation, i.e. the progressive complication of structure which is associated with division of lalwur.
3- Gregarious Life and Combined Action.— Most mammals are in some degree gregarious. The solitary kinds are in a distinct minority. The isolated are ex- posed to attack, the associated are saved by the wisdom of their wisest members and by that strength which union gives. Many hoofed animals, such as deer, antelopes, goats, and elephants, live in herds, which are not mere crowds, but organised bands, with definite conventions and with a power of combined resistance which often enables them to withstand the attacks of carnivores. Marmots and prairie-dogs, whose " cities " may cover vast areas, live peace- ful and prosperous lives. Monkeys furnish many illustra- tions of successful gregarious life. As individuals most of them are comparatively defenceless, and usually avoid com- ing to close quarters with their adversaries ; yet in a body tliey are formidable, and often help one another out of scrapes. Brehm tells how he encountered a troop of baboons which defied his dogs and retreated in good order up the
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72
The Study of Animal Life
PART I
heights. A young one about six months old being left behind called loudly for aid. *' One of the largest males, a true hero, came down 3:sain from the mountain, slowly went to the young one, co.xed him, and triumphantly led him away — the dogs being too much astonished to make an attack."
Fig. 15. — Chimpanzee (. ! hropopUhc. us or Troglodytts calvui). (I .uiuDuChaillu.)
Many birds, such as rooks and swallows, nest together, and the sociality is citen advantageous. Kropotkine cites from Dr. Coucs an observation in regard to some little clirt"- svvallows which nested in .1 colony quite near the home of a prairie-falcon. "The little peaceful birds had no fear of their rapacious neighbour ; they did not let it even approach to their colony. They immediately surrounded it an<l
■^Mwm
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CHAP. V
Social Life of Animals
73
chased it, so that it had to make oflF at once." Of the cranes, Kropotkine notes that they are extremely "sociable and hve m fnendly relations, not only with their congeners but also with most aquatic birds." They post sentries, send scouts, have many friends and few enemies, and are very intelligent. So is it also with panots. «' The members of each band remam faithfully attached to each other, and they share m common good or bad luck." They feed together fly together, rest together ; they send scouts and post sen- tinels ; they find protection and pleasure in combination. Like the cranes, they are very intelligent, and safe from most enemies except man.
On the other hand, some of the most successful carni- vores, e.g. wolves, hunt in packs, and not a few birds of prey (some eagles, kites, vultures) unite to destroy their quarry. Combination for defence has its counterpart in combination for attack. In both cases the collective action IS often associated with the custom of posting sentinels, who warn the rest, or of sending scouts to reconnoitre. Pecu- liarly mteresting are those cases in which the relatively weak unite to attack the strong ; thus a few kites will rob an eagle and wagtails will persecute a sparrow-hawk. Kropot- kine has noticed how the aquatic birds which crowd on the shores of lakes and seas often combine to drive off intrud- ing birds of prey. « In the face of an exuberant life, the Ideally armed robber has to be satisfied with the off-fall of that life.
Among many animals there is co-operation in labour, as well as combination for attack or defence. Brehm relates that baboons and other monkeys act in thorough concert in plundering expeditions, sending scouts, posting sentinels, and even forming a long chain for the transport of the spoil. It IS said that several Hamadryad baboons will unite to turn over a large stone, sharing the booty found underneath. When the Brazilian kite has seized a prey too large for it to carry ,t summons its friends; and Kropotkine cites a re- markable case in which an eagle called others to the car- Lin'' I u'''.''^"%^'!' ^°^^'''^'" '" «^«t companies, forming a wide half-circle facing the shore and catching the fish thus
k%
! f i
S ■ .. 'A
74
The Study of Animal Life
PART 1
If!!-.
enclosed. Burial beetles unite to buty the dead mouse or bird in which the eggs are laid, and the dung-beetles help one another in rolling balls of food. But of all cases of combined activity the migration of birds is at once the most familiir and the most beautiful — the gathering together, the excitement before starting, the trial flights, the reliance placed in the leaders. Migration is usually social, and is sustained by tradition.
4. Beavers. — That the highly -socialised beavers have been extenninated in many countries where they once abounded is no argument against their sociaUty, for man has ingenuity enough to baffle any organisation. A family of about si . members inhabits one house, and in suitable localities — secluded and rich in trees — many families con- gregate in a village community. The young leave the par- ental roof in the summer of their third year, finu mates for themselves, and establish new homesteads. The community becomes overcrowded, however, and migrations take place up and down stream, the old lodges being sometimes left to the young couples. It is said, moreover, ihat lazy or other- wise objectionable members may be expelled from the society, and condemned to live alone. Under constraint of fear or human interference, and away from social impulse, beavers may relapse into lazy and careless habits, and in many cases each family lives its life apart; but in propitious conditions their achievements are marvellous. Th*; burrow may rise into a constructed home, and the members of many families may combine in wood-cutting and log-rolling, and yet more markedly in constructing dams and digging canals. Make allowances for the exaggeration of enthusiastic observers, but lead Mr. Lewis Morgan's stories of the evolu- tion of a broken burrow into a comfortable lodge, varying according to the local conditions ; of the adaptation of the dams against the rush of floods ; of canals hundreds of feet in length — labours without reward until they are finished ; of the short-cut waterways across loops of the river ; an \ cf " locks " where continuous canals are, from the nature of the ground, impossible. The Indians have invested beavers with immortality, but it is enough for us to recognise that
CHAP. V
Social Life of Animals
75
they exhibit more sagacity than can be explained by heredi- tary habit, for they often adapt their actions to novel condi- tions in a manner which must be described as intelligent. Especially when we remember that the beaver belongs to a somewhat stupid rodent race, are we inclined to believe that it is the cleverest of its kind because the most socialised.
5. Bees.— Many centuries have passed since men first listened to the humming of the honey-bees, and found in the hive a symbol of the strength of unity. From Aristotle's time till now naturalists have been studying the life of bees, without exhausting either its facts or its suggestions. The society is very large and complex, yet very stable and successful. Its customs seem now like those of children at play, and now like the real- ised dreams of social refor- mers. The whole life gives one the impression of an old- established business in which all contingencies have been so often experienced that they have ceased to cause hesitation or friction. There is indeed much mortality, some apparent cruelty, and the constantly recurring ad- venture of migration ; but though hive may war against hive, inter-civic competition has virtually ceased, and the life proceeds smoothly with the hannony and effectiveness of a perfected organisation.
The mother-bee, whom wc call a " queen " — though she is without the wits and energy of a ruler — is to this extent lic.ul of the community, that, by her prolific egg-laying, she increases or restores the population. \'ery sluggish in tlieir ordinary life are the numerous males or ♦• drones,' one of whom, fleet and vigorous beyond his fellows, w ill pair
G. 16. — Honey-bee {A fits mellifica). A,_ queen ; 1!, drone ; C, worker. (From Chambers's Khij\/o/>.)
» 1
m IP
^m
76
The Study of Animal Life
PART I
with a queen in her nuptial flight, himself to die soon after, saved at least fiom the expulsion and massacre which await all the sex when the supplies of honey run short in autumn. The queen and drones are important only so far as multiplica- tion is concerned. The sustained life of the hive is wholly in the hands of the workers, who in brains, in activity, and general equipment are greatly superior to their " queen." " The queen has lost her domestic arts, which the worker pos- sesses in a perfection never attained by the ancestral types ; while the worker has lost her maternal functions, although she still possesses the needed organs in a rudimentary state." What a busy life is theirs, gathering nectar and pollen unwearyingly, while the sunshine lasts, neatly slippinj into the secrets of the flowers or stealing their treasures by force, carrying their booty home in swift sweeping flight, often over long distances unerringly, unloading the pollen from their hind-legs and packing it into some cells of the comb, emptying out the nectar from their crop or honey- sac into store-cells, and then off again for more — s.ich is their socialised mania for getting. But, besides these •' foragers " — for the most part seniors — there are younger stay-at-home " nurses," whose labours, if less energetic, are not less essential. For it is their part to look after the grubs in their cradles, to feed them at first with a " pap " of digested nectar, and then to wean them to a diet of honey, pollen, and water ; to attend the queen, guiding her move- ments and feeding her while she lays many eggs, sometimes 2000 to 3000 eggs in a day. Mr. Cheshire, in his incom- parably careful book on Bees and Beekeeping^ laughs at the "many writers who have given the echo to a mediaeval fancy by stating that the queen is ever surrounded by a circle of dutiful subjects, reverently watching her move- ments, and liable to instant banishment upon any neglect of duty. These it was once the fashion to compare to the twelve Apostles, and, to make the ridiculous suggestion complete, their number was said to be invariably twelve ! ' But Mr. Cheshire's own account of the nurses' work, and of the whole life of the hive, is more marvellous than any mediaeval fancy.
hi
CHAP. V
Social Life of Animals
77
We have not outlined nearly all the labours of the workers. There is the exhausting though passive labour of forming the wax which oozes out on the under-surface of the body, and then there is the marvellous comb-building, at which the bees are very neat and clever workers, though they do not deserve the reputation for mathematical insight once granted them. "Their combs," Mr. Cheshire says, "are rows of rooms unsurpassably suitable for feeding and nurtur- ing the larvae, for giving safety and seclusion during the mystic sleep of pupa-hood, for ensconcing the weary worker seeking rest, and for safely warehousing the provisions ever needed by the numerous family and by all during the winter's siege. Corridors run between, giving sufficient space for the more extensive quarters of the prospective mother, and affording every facility to the busy throng walking on the ladders the edges of their apartments supply ; while the exactions of modern hygiene are fully met by air, in its native purity, sweeping past the doorway of every inhabitant of the insect city."
We shall not seek to penetrate into the more hidden mysteries of the life of bees ; for instance, " how the drones have a mother but no father," or how high feeding makes the difference between a queen and a worker. An outline of the yearly life is more appropriate. From the v/inter's rest the surviving bees reawaken when the early-flowering trees begin to blossom ; the workers engage in a *' spring cleaning," and the queen restores the reduced population by egg-laying. New supplies of food are brought in, new bees are bom, and in early summer we see the busy life in all its energy. The pressure of increased population makes itself felt, and migration or " swarming " becomes impera- tive. In due time and in fair weather " the old mother departs with the superabundance of the population." Meanwhile in the parent-hive drones have been born, and several possible queens await liberation. The first to be set free has to hold her own against newcomers, or it may be to die before one of them. The successful new queen soon becomes restless, issues forth in swift nuptial flight, is fertilised by a drone, and returns to her home to begin
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The Study of AninuU Life
PART 1
prolific egg-laying, and perhaps after a time to lead off another swarm. During the busy summer, when food is abundant, the lazy males are tolerated ; but when their function is fulfilled, and when the supplies become scarce, they are ruthlessly put to death. " No sooner does income fall below expenditure, than their nursing sisters turn their executioners, usually by dragging them from the hive, biting at the insertion of the wing. The drones, strong for their especial work, are, after all, as tender as they are defenceless, and but little exposure and abstinence is required to terminate their being. So thorough is the war of extermination, that no age is spared ; even drone eggs are devoured, the larvae have their juices sucked and their ' remains ' carried out — a fate in which the chrysalids are made to take part, the maxim for the moment being, He that will not work, neither shall he eat." This Lycurgan tragedy over, the equilibrium of the hive is more secure, and the winter comes.
The social life of hive-bees is of peculiar interest, because it represents the climax of a series of stages. Hermann Miiller has traced the plausible history of the honey-bee from an insect like the sand -wasp, and has shown in other kinds of bees the various steps by which the pollen-gathering and nectar-collecting organs have been developed. The habits of life gradually lead up to the consummately social life of the hive. Thus Prosopis, which lays its eggs in the pith of bramble-stems ; the wood-boring Xylophaga ; and the leaf-cutting Megachile, which lines its burrows with circles ct' om rose leaves, are solitary bees. The various species of humble- or bumble-bee {Bombus), so familiarly industrious ^rom the spring, when the willows bear their catkins, till the autumn chill benumbs, are half way to the hive-bees ; for they live in societies of mother, drones, and workers during summer, while the sole surviv- ing queens hibernate in solitude. From the humble-bee, moreover, we gain this hint, thr.t the home is centred in the cradle, for it is in a nest with honey and pollen stored around the eggs that the hive seems to have begun.
6. Ants.— Even more suggestive of our own social organ-
'*Me
CHAP. V Socta/ Li^e ^f Animals
79
isation is the LUiputian wor\,d of the ants, who, like micro- scopic men, build bams and h^y ^p stores, divide their labour and indulge m play, wage warig and make slaves. Like the bee-hive, the ant-nest includes , three kinds of individuals- a queen mother or more than c.^e, a number of short-lived males, and a crowd of workers. ^ The queen is again pre- eminently maternal, and if we , can trust the enthusiastic observers, she is attended with k^y^i devotion, not without some judicious control. Farren white describes how the workers attend the queen m her. pe^mbulations : -They formed round her when she rested ; s-^^e showed their regard for her by gently waking over her, ot^^ers by patiently watch- mg by her and cherishing her wito^ their antenL, and in every way endeavouring to testifyl to their affectionate attachment and generous submission « Qould ventures further, alleging that «'m whatever \ apartment a queen condescends to be present, she commands obedience and respect, and a universal gladness spreacjs itself through the who e cell, which is expressed by partici ,iar acts of joy and exultation. They have a peculiar way ok cWinnmo- iAo«;«,r and standing up on their Ld legs, a'nd ,;SwXhe others. These frolics they make use of ^"oth'o^congratu- late each other when they meet, and to shuw their rLard for the queen." These are wonderful hG of assumed emotions 1 Should an indispensable queei,, Up dp«:;rn„« f« quit the nest, the workers do not hesitatt'! t ^3 l^d tn keep her by force, and to tear off her wingCg to secure her stay. It is certain at least that as the queens settle down to the labour of maternity, their wings are lo^t—Derhans in obedience to some physiological necessity. FLom th*» mnrh greater number of the wingless workers, we zxL ^JtI fnm?t that the males and mothers of the social ant^ are win/ed insects ; but this fact becomes impressive if in > «„„ „nmm.r weather we are fortunate enough to see therm alesTnd young queens leaving the nest in the nuptial flight during which fertilisation take place. Rising in th? 'j^ Xv glitter like sparks, pale into curling smoke, an^ vanish "Sometimes the swarms of a whole district hav.» y.' noticed to unite their countless myriads, and, seen at' a dis-
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The Study of Animal Life
I'AKT I
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tance, produce an effect resei^tibling the flashing of the Aurora BoreaHs ; sometimes the effect is that of rainbow- hues in the spray of laughing waterfalls ; sometimes that of fire ; sometimes that of a smoke- wreath." *' Each column looks like a kind of slender metwork, and has a tremulous undulating motion. The poise emitted by myriads and myriads of these creatures does not exceed the hum of a single wasp. The sliightest zephyr disperses them."' After this midsummer d^y's delight of love, death awaits many, and sometimes mo/st. The males are at best short- lived, but the surviving /queens, settling down, may begin
^--^!^
FiG. 17.— Sauba aiyts at work ; to the left below, an ordinary worker ; to the right a large-headyd worker ; above, a subterranean worker. (From Hates.)
to form nests, jgathering a troop of workers, or sometimes proceeding alojne to found a colony.
A caste o.f workers {i.e. normally non -reproductive females) disti/nct from the males and queens, involves, nf course, some J division of labour ; but there is more tliau this. Worke/rs of different ages perform different tasks — foraging or /lousekeeping, fighting or nursing, as the case may be ; amd just as the various human occupations lea\ e marks botln for good and ill in those who follow them, so the divisybn of labour among ants is associated with differ- ences ofif structure. Thus, in the Saiiba or Umbrella Ant of ^rdizW JyCEcodof/ia ccpJialotcs\ so well described by Bates in
/
/
CHAP. V
Social Lt/e of Aninuds
8i
\ix% Naturalist on the Amazons, there are three classes of workers. All the destructive labour of cutting sixpence-like disks froin the leaves of trees is done by individuals with smal heads, while others wiifh enormously large heads simply walk about looking on. These «« worker-majors " are not soldiers, nor is there \any need for supervising office.3. "I think," Bates say^/.<they serve, bsomf sort, as passive instruments of < protection to the real workers. Their enormously large, .hard, and indestructible heads may be of use in protecting them against the attacks of insectivorous animals. T>hey would be, on this vievv, a kind ofpzkes de resistance, sf^rving as a foil against onslaughts made on the main body of workers." The third order of workers includes very .strange fellows, with he same kind of head as the worker-majors have, but "the ront IS clothed with hairs instead of b-eing polished, and hey have in the middle of the forehead a^win simple
n' ; /.T^ °^ '^^ ^^^"'■^ P°^^^^s«- Among the honey ants {Myrmecocystus mexicanus) .described by Dr M'Cook from the "Garden of the Gods "tin Colorado, the division of labour is almost like a joke*. The woiers
fn!r-??u^^" ^'T '''^^'" ^^"^' and discharge their spoils mto the mouths of some of their stay-at-home fellows These passive " honey-pots " store it up, till' the abdomen becomes tense and round like a grape, but e^ventuaUy they have even more tantalisingly to disgorge it foV other mem-
exhibited, as Forel has shown, by many sp^^cies of ants. The hungry apply to the full for food, anld get it. A reiusal is said to be sometimes punished by de;ath »
Marvellous in peace, the ants may also ^practise the anti-social "art of war," sometimes against i^other com! ™rbl^>TrP"'"' --times lith other kind" and^^. H . ''^^'^y '^y^' "^^^^ ^"'^^ b^^" c-^lebrated; fmnn ^^l °^.*^'"'' ^' '^ '* ^^'^ ^" event o{f the firs mportance, has been formally recorded." ^neas x Sylvius
S TJS X^"^ circumstantial account of one contested the tn^I obstinacy between a great and small species on the tnmk of a pear tree, gravely states, "This actioA was
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83 TAe Study of /animal Life part i
fought in the pontificate of Eufenius IV., in the presence of Nicholas Pistoriensis, an eminent lawyer, who related the whole history of the battle w«th the greatest fidelity." In the fray the combatants are thoroughly absorbed, yet at a little distance other worker's are uninterruptedly Heading their daily paths ; the mel^;e is intense, yet every ant seems to know those of its own j/party ; the result of it all is often nothing. We laugh at tK>e ants— the laugh comes back on ourselves. /
In some cases an ex/pedition has the definite end of slave- making, as is known ,^^0 be true of Formica sanguinea—s. British species, and oi j°olyergus rufescens, found on the Con- tinent. The former c/aptures the larvae of Formica fusca, carries them home, /and owns them henceforth as well- treated slaves ; whjfie the Amazon Ant {Polyergus) draws its supply from t >oth F. fusca and F. cunicularia, and seems to have be come almost dependent on its captives. Indeed, Huber sa ys that he never knew the Amazons take nourishment but / from the mouth of the negro captives ; while Lubbock riotes that every transition exists between bold and active b/)aron-like marauders and enervated masters, who are virtuallly helpless parasites upon their slaves— a suggestive illusjtration of laziness outwitting itself.
Slaves som-'ewhat painfully suggest domesticated animals, and these ar e also to be found among ants. For what Linnjeus said long ago, that the ants went up trees to " milk their cows, th e Aphides," is true. The ants tickle these little plant-lice wit' h their antennae, and lick the juice \vhich oozes from them ; 'nay more, according to some, they inclose and tend these , -milch kine, and even breed them at home. Seed-harves 'ting and the like may be fairly called agricul- tural, and d' o not the leaf-cutters grow mushrooms, or at least feed 'on the fungi which 2^iow on the leaves, stored some say '" with that end in view ? The driver ants, "whose "dread is upon every living thing," when they are on 'the stampede, remind us of the ancient troops of non:Aad hunters, though some of them are blind. Thus there/ are hunting, agricultural, and pastoral ants — three type/vs, as Lubbock remarks, offering a strange analogy
/
CHAF. V Social Life of Animais
H
to^the three great phases in the history of human develop- Very quaint is another habit of thi. "little people, so
hZt" T-r'' ^^"' °?''P^"^ °^ ^°^^^^^'^^ guests in'the home These are mostly little beetles, and have been carefiilly studied by Dr. Weismann, who distinguishes trSe guests {Atemeles, Lomechusa, Claviger) which are caredTor and fed by the ants, from others {Dinarda, H^^terius Form^oxenu^ wh.ch are tolerated, though not Ireated whh special fnendlmess, and which feed on dead ants or vege table debris ; while a third set are tolerated-like mice in our houses-only because they cannot be readily tumTout
Z^l^ ^'""'f ^T'''' '^^ ''^'' ^"°^" '^ ^^^'«^^-^, a lively an mal, constantly moving its feelers, and experimenting with everything. If one be attacked by a hostile ant k
ut i/^htis?","' '-^ ^"^^^°"'^^ '^y -^--'y --S e but If this IS hopeless it emits a strong odour, which seems
to narcotise the ant. These little^ familiarr are reX
dependent upon their hosts, who feed them and get
caresses in return. It is easy to understand the presence
are pets, taken away by the owners when there is a flitting
relations, since they can be shifted from one nest to another, or even from spe-.ies to species. It seems hkev ;rfre mo-^^"!? ^TT^ '""I ''^'^ semi-d;rsuS
I cannot Img.-r longer over the interestin? character
tu^e r^h'""'" V"""'" ''"' '" '^'^ of'theirS: lecture, oi their roads, tunnels, bridges and rnv^r^H
r:Lh,ed''ofT-'°' "■' r??' -" --'^« -" f°
me aisabled, of their proverbial industry, and vet of th.ir
* tf r itr\°eTan'?z"ci';i:rj;^ trr r
C^tht? *^"^ ''^ "^'^ n.mi„n're"de«sf oraZ;
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84 The Study of Animal Life part i
about their power of recognising their fellow-citizens (even when intoxicated), and of communicating definite impres- sions to one another by a subtle language of touch and gesture ; or about their instincts and intelligence, and the limitations of these. But it will be better to read some of the detailed observations, endeavouring, though necessarily with slight success, to think into the nature of ants, — their pertinacity, their indomitable "pluck," their tireless in- dustry, their organic sociality. Surely all will agree with Sir John Lubbock, to whose patient observations we ewe so much, that, "when we see an ant-hill, tenanted by- thousands of industrious inhabitants, excavating chambers, forming tunnels, making roads, guarding their home, gathering food, feeding the young, tending their domestic animals, each one fulfilling its duties industriously and without confusion, it is difficult altogether to deny them the gift of reason," or, perhaps more accurately, intelligence, for we cannot rscape the conviction •* that their mental powers differ hum those of men not so much in kind as in degree."
Kropotkine says that the work of ants is performed "according to the principles of voluntary mutual aid." " Mutual aid within the community, self-devotion grown into a habit, and very often self-sacrifice for the common wel- fare, are the rule." The marvels of their history are " the natural outcome of the mutual aid which they practise at every stage of their busy and laborious lives." To this mode of life is also due " the immense development of indi- vidual initiative." Ants are not well protected, but *' their force is in mutual support and mutual confidence." " And if the ant stands at the very top of the whole class of In- sects for its intellectual capacities; if its courage is only equalled by the most courageous Vertebrates, and if its brain~to use Darwin's words— * is one of the most mar- vellous atoms of matter in the world, perhaps more so tlian the brain of man,' is it not due to the fact that mutual aid has entirely taken the place of mutual struggle in the com- munities of ants ? "
7. Ttrmites. — The true ants are so supremely interest-
iilit
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CHAP. ▼ Social Life of Animals 85
ing, that the Termites or « white ants " (which are not ants at all) are apt to receive scant justice. Perhaps inferior in intel- ligence, they have the precedence of greater antiquity and all the interest which attaches to an old-established society Nor IS their importance less either to practical men or to speculative biologists. In 1781 Smeathman gave some account of their economy, noting that there were in everv spec.es three castes, "first, the working insects, which, for brevity, I shall generally call labourers-, next, the fighting m^sox soldters, which do no kind of labour ; and, last of all, the wmged ones, or perfect insects, which are male and female, and capable of propagation "
The "workers," blind and wingless, and smallest in the ant-hill, do all the work of foraging and mining, attending the royal pair and nursing the young. The soldiers, also blind and wingless, are much larger than the workers, but diere are relatively only a few in each hill. « They stand " Prof Drummond says, "or promenade about as sentries, it the mouths of the tunnels. When danger threatens, in the shape of true ants, the soldier termite advances to the fight " With a few sweeps of its scythe-like jaws it clears the
thai 'work'"' A?/ ""^^^-j?- ^^ '^e fray, quietly Continue
vhnL 7 / "'"^', '" '^^ ^"^■^•"' ^'^"^ "P i" a chamber whose door admits workers but is much too small for the
enants to pass out if they would, a fortunate investigator
ome times finds the royal pair. The male is sometimes
though by no means extraordinary. The queen-mother
oTxTcits' ;7 T"^^°^^^"•^"^• ''^•^ -easur's two to SIX inches while the worker is only about a fifth of an
witr iS • ^"^^ \'' T'^ '''' ''''' '-^"^ ^^^ -- '-"
Drt of it K% ' ^'^"^ ^^''^ ^'■"PP^^ ^fl^- The hind
^iLi ^ K^^ 's enormously distended with eggs, and
the head bears about the same proportion to the rest of
m n.5^ V. • ^" ^^' P^''''''^>' ^"'J " phenomenal cor-
-^'' h ' ' V T 1 ''''^'''''' -^-'^'*-^"»* of femaleness a Iari,e. cylindrical package, in shape like a sausage,
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The Study of Animal Life
PART I
and as white as a bolster." But have some admiration for her: she sometimes lays 60 eggs per minute, or 80,000 in a day, and continues reproducing for months. As she lays, she is assiduously fed by the nursing-workers, while the eggs are carried off to be hatched in the nurseries. At the breeding season, numerous winged males and females leave
Fig. 18.— Diagrammalic section of a termite's iie»t (after Houssay). In tin- walls there are winiliiig passajjes (/) ; uppermost is a well-aired empty aliii' (D) the next story (C) is a nursery where the young termites are hatclicil mi shelves (r») and (*) ; the next is a hall (H) snpporte<l by pillars ; Ix-neaili iliis is a royal chamber (>) in which the kinjj and queen are imprisoned ; aniuiul this the chambers of workcr-tcrniites (v) and some store chambers (/'.); excavated in the grnuiul arc holes (i) out of which the materi.d umcI in making the termitary was dug. 'J'he whole structure is sometimes lu-is feet in height.
the hill and its workers in swarms, most of them simply 10 die, others to mats with individuals from another hill and to begin to form new colonics.
The plot of the story becomes more intricate, however, when we notice Fritz Miiller's observations, that " besides
CHAP. V
Social Life of Animals
87
the winged males and females which are produced in vast numbers, and which, leaving the termitary in large swarms, may intercross with those produced in other communities, there are (in some if not all of the species) wingless males and females which never leave the termitary where they are born, and which replace the winged males or females whenever a community does not find, in due time, a true king or queen." There is no doubt as to the existence of both winged and wingless royal pairs. According to Grassi, the former fly away in spring, the others ascend the throne in summer. The complementary kings or viceroys die before winter ; their mates live on, widowed but still maternal, till at least the next summer.
This replacement of royalty reminds us that hive bees, bereft 0/ their queen, will rear one from the indifferent grub, but the termites with which we are best acquainted seem almost always to have a reserve of reproductive members. This other difference between termites and ants or bees should be noticed, that in the latter the "workers" are highly-developed, though sterile females, while in the former the workers seem to be arrested forms of both sexes. They are children which do not grow up.
8. Evolution of Social Life.— To Professor Alfred Espinas both naturalists and sociologists are greatly in debted for his careful discussion of the social life of animals. It may be useful, therefore, to give an outline of the mode of treatment followed in his work — Des Sodith Animates : Etude de Psychologic Compart'e (Paris, 1877) :
Co-operation, which is an essential characteristic of all society, implies some degree of organic afT.nity. There are, indeed,' occasional associations between unrelated forms—" mutualism," in which both associates are benefited; "commensalism," in which »he benefit is mainly one-sided ; parasitism, which is distinctly anti-social, deteriorating the host and also the rank of the tempor- arily benefited parasite. Of normal societies whose members are mutually dependent, two kinds may be distinguished— (a) the organically connected colonies of animals, in which there is a common nutritive life ; {b) those associations which owe their origin nnd meaning to reproduction. Of the latter, some do not become more than domestic, and these are distinguished as conjugal (in
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T/ie Study of Animal Life
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whi h the parents alone are concerned), maternal (in wliich the mother is the head of the family), and paternal (in which the male becomes prominent). But higher than the pair and the family is what Espinas calls the "peuplade," what we usually call the society, whose bonds are, for the most part, psychical.
But 'et us consider this problem of the evolution of sociality. The body of every animal — whether sponge or mammal — is a city of living units or cells. But there are far simpler animals than sponges. The very simplest animals, which we call firstlings or Protozoa, differ from all the rest, in being themselves units. The simplest animals are single cells ; each is comparable to one of the myriad units which make up a sponge, a coral, a worm, a bird, a man.
Here, therefore, there is an apparent gulf. The simplest animals are units — single cells ; all other animals are com- binations of units — cities of cells. How is this gulf to be bridged ? It is strange that evolutionists have not thought more about this, for on the transition from a unit to" a com- bination of units the possibility of higher life depends.
Every higher animal begins its individual life as a single cell, comparable to one of the firstlings. This single cell, or egg-cell, divides ; so do most of the Protozoa. But when a Protozoon divides, the results separate and live in- dependent lives ; when an egg- cell divides, the results of division cohere. Therefore, the whole life of higher animals depends upon a coherence of units.
But how did this begin ? What of the gulf between single-celled Protozoa and all the other animals which arc many-celled .'' Fortunately we are not left to mere specula- tion. The gu'*" has been bridged, else we should not exist ; but, more than 'hat, the bridge, or part of it, is still left. There are a few > ^ the simplest animals which form loose colonies of units, wnich, when they divide, remain together. Whether it was through weakness, as I am inclined to believe, that the transition forms between Protozoa and higher animals became strong, or for some hidden reason, we do not know. Some speak of this coherence of firstlings as a primal illustration of organic ;issociation,
CHAP. V
Social Life of Animals
89
co-operation, surrender of individuality, of sociality at a low level, but it is unwise to apply these words to creatures so simple. All that we certainly knov/ is that some of the simplest animals form loose colonies of units, that the gulf between them and the higher animals is thus bridged, and that the bridging depends on coherence. Our first con-
(.:>=a>^
".• !<>•— Siphonophore colony, showing the float (<i), tlie swimmiiiKbclls I It nutntivo, reproductive, and other nieniljcrb of the colony Uiiealh (\ the Hrolutio)! o/Scx ; after Haeckel.)
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elusion, therefore, is, that the possibility of there being any lii^;her animals depends, primarily at least, not on competition Itut on the coherence of units.
')ur next step is this: When we study spong?s, or zt'ophytes, or most corals,- or some t> pes usually classed as
"H%
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90 The Study of Animal Life part i
«* worms," we see that the habit of forming colonies is common. Every sponge is a simple sac to begin with, but it buds off others like itself, and the result is a coherent colony. A zoophyte is not one individual, but a connected colony of individuals. Throughout the colony there is one life ; all the individuals have a common origin, and all are members one of another. In varying degrees of perfection the life of the whole is unified. Moreover, the unity is often increased, not diminished, by the fact that the indivi- duals are not all alike. There is division of labour among them; some may feed while others reproduce, some feel much while others may be quite callous. Thus, as we already mentioned, the Portuguese Man-of-War, a colony of small jellyfish -like individuals, has much division of labour, and yet there is much, though by no means perfect,
unity of life.
Our second conclusion is that among many animals- beginning with sponges and ending with the searsquirts, which are acknowledged to be animals of high degree— the habit of forming colonies is common, and that these colonies, though organically continuous, illustrate the essence of society ; for in them many individuals of common descent and nature are united in mutual dependence and help- fulness.
The next step towards an understanding of the social relations of animals is very different from that in which we have recognised the habit of forming colonies. The factor which we have now to acknowledge is the love of mates. This also has its history, this also has its prophecies among the firstlings, but we shall simply assume as a fact that among crustaceans and insects first, in fishes and amphi- bians afterwards, in reptiles too, but most conspicuously among birds and mammals, the males are attracted to. the females, and in varying degrees of perfection enter into relations of mutual helpfulness. The relations and the attractions may be crude enough to begin with, but perhaps even we hardly know to what heights of devotion their highest expressions may attain. To mere physical fondness are added subtler attractions of sight and hearing, and
CHAP. V
Social Life of Animals
9>
these are sublimed in birds and mammals to what we call love. This love of mates broadens out ; it laps the family in its folds ; it diffuses itself as a saturating influence through the societies of animals and of men. ** Sociability," Espinas says, " is based on the friendliness of mates."
The fourth step is the evolution of the family. From monkeys and beavers and many kinds of birds, to ants and bees and diverse insects, many animals illustrate family life. There is no longer the physical continuity charac- teristic of the colony, but there is a growing psychical unity. It is natural that the first ties of family life should be those between mother and young, and should be strong- est when the number of offspring is not very large. But even in some beetles, and more notably in certain fishes and amphibians, the males exhibit parental care and affec- tion ; while in higher animals, especially among birds, the parents often divide the labours of the family. " Children," Lucretius said, "children with their caresses broke down the haughty temper of parents."
The fifth step is the combination of families into a society, such as we find illustrated by monkeys and beavers, cranes and parrots, and in great perfection by ants. The members are less nearly related than in the family, but there may be even more unity of spirit.
I do not say that it is easy to understand how coherence of units led to the formation of a " body," how colonies became integrated and the labours of life more and more distributed, how love was evolved from apparently crude attractions between the sexes, how the love of mates was broadened into parental and filial affection, or how families well knit together formed the sure foundations of society ; but I believe that it is useful to recognise these steps in the history.
We hardly know how to express ourselves in regard to the origin of affection. But I cannot get beyond Aristotle's fundamental principle of evolution, that there is nothing in the end which was not also in the beginning.
Yet we may fairly say that the sociality and helpfulness of animals are flowers whose roots are in kinship. Off-
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The Study of Animal Life
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spring are continuous in nature with their parents ; the family has a unity though its members be discontinuous and scattered ; "the race is one and the individual many."
9. Advantages of Social Life. — But animals are social, not only because they love one another, but also because sociahty is justified of her children. " The world is the abode of the strong," but it is also the home of the loving ; " contention is the vital force," but the struggle is modified and ennobled by sociality.
(a) Darwin^s Position. — Darwin observed that "the individuals which took the greatest pleasure in society would best escape various dangers ; while those that cared least for their comrades, and lived solitary, would perish in greater numbers." He distinctly emphasised that the phrase "the struggle for existence" was to be used in a wide and metaphorical sense — to include all the endeavours which animals make both selfishly and un- selfishly to strengthen their foothold and that of their offspring. But he was not always successful in retaining this broad view, nor was he led to compute with sufficient care to what extent mutual aid is a factor in evolution counteractive of individualistic struggle.
Without losing sight of the reality of the struggle for existence ; without disputing the importance of natural selection as a condition of evolution — securing that the relatively fittest changes succeed ; without ignoring what seems almost a truism, that love and social sympathies have also been fostered in the course of natural selection ; we maintain— (i) that many of the greatest steps of progress — such as those involved in the existence of many -celled animals, loving mates, family life, mammalian motherhood, and societies — were not made by the natural selection of indefinite variations ; (2) that affection, co-operation, mutual helpfulness, sociality, have modified the struggle for material subsistence by lessening its intensity and by ennobling its character.
(b) Kropotkitte's Posilion.—hgaSnst. Prof. Huxley's con- clusion that " Life was a continual free- fight, and beyond the limited and temporary relations of the family the
I
CHAF. V
Social Life of Animals
93
Hobbesian war of each against all was the normal slate of existence," let me place that of Kropotkine, to whose admir- able discussion of mutual aid among animals I again acknowledge my indebtedness.
" Life in societies is no exception in the animal world. It is the rule, the law of nature, and it reaches its fullest development with the higher Vertebrates. Those species which live solitary, or in small families only, are relatively few, and their numbers are limited. . . . Life in societies enables the feeblest mammals to resist, or to protect them- selves from, the most terrible birds and beasts of prey ; it permits longevity ; it enables the species to rear its pro- geny with the least waste of energy, and to maintain its numbers, albeit with a very slow birth-rate ; it enables the gregarious animals to migrate in search of new abodes. Therefore, while fully admitting that force, swiftness, pro- tective colours, cunning, and endurance of hunger and cold, which are mentioned by Darwin and Wallace as so many qualities making the individual or the species the fittest under certain circumstances, we maintain that under any circumstances sociability is the greatest advantage in the struggle for life. . . The fittest are thus the most soci- able animals, and sociability appears as the chief factor ot evolution, both directly, by securing the well-being of the species while diminishing the waste of energy, and indirectly by favouring the growth of intelligence. . . . Therefore combine — practise mutual aid ! That is the surest means for giving to each and to all the greatest safety, the best guarantee of existence and progress — bodily, intellectual, and r.ioral. That is what nature teaches us."
lo. A Note on "The Social Organism." — It is com- mon nowadays to speak of society as " the social organism," and the metaphor is not only suggestive but convpnient — suggestive because it is profitable to biologist and soci- ologist alike to follow out the analogies between an organism and society, convenient because there is among organisms — in aggregates like sponges, in perfected integrates Ike birds — a variety sufficient to meet all grades and views of society, and because biologists differ almost as much in
1 4
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94 The Study of Animal Life part i
their conceptions of an " organism " as sociologists do in regard to ** society."
It may be questioned, ho\ ever, whether we need any other designation for society than the word society sup- plies, and whether the biological metaphor, with physical associations still clinging to it, is not more illusory than help- ful. For the true analogy is not between society and an individual organism, but between human society and those incipient societies which were before man was. Human society is, or ought to be, an integrate — a spiritual integrate
of organisms, of which the bee-hive and the ants' nest,
the community of beavers and the company of monkeys, are like far-oflf prophecies. And in these, as in our own societies, the modem conception of heredity leads us to recognise that there is a very real unity even between members physically discontinuous.
The peculiarity of human society, as distinguished from animal societies, depends mainly on the fact that man is a social person, and knows himself as such. Man is the realis- ation of antecedent societies, and it is man's realisation of himself as a social person which makes human society what it is, and gives us a promise of what it will be. As bio- logists, and perhaps as philosophers, we are led to conclude that man is determined by that whole of which he is a part, and yet that his life is social freedom ; that society is the means of his development, and at the same time its end ; that man has to some extent realised himself in society, and that society has been to some extent realised in man.
But I am slow to suppose that we, who in our ignorance and lack of coherence are like the humbler cells of a great body, have any adequate conception of the social organism of which we form part.
II. Conclusions. — I would in the main agree with Kropotkine that " sociability is as much a law of nature as mutual struggle " ; with Espinas that " Le milieu social est la condition ndcessaire de la conservation et du renouvelle- ment de la vie"; and with Rousseau that "man did ait make society, but society made man."
CHAPTER VI
THE DOMESTIC LIFE OF ANIMALS
I. The Love cf Mates — 2. Love and Care for Offspring
Winter in our northern climate sets a spell upon life. The migrant birds escape from it, but most living things have to remain spell-bound, some hiding with the supreme patience of animals, others slumbering peacefully, others in a state of " lat ife " stranger than death. But within the hard rind of e trees, or lapped round by bud scales, or imprisoned within the husks of buried see ' '^ life of plants is ready to spring forth when the south wi. ' iws ; beneath the snow lie the caterpillars of summer butterflies, the frogs are waiting in the mud uf the pond, the hedgehog curled up sleeps soundly, and everywhere, under the seeming death, life rests until the spring. '* For the coming of Ormuzd, the Light and Life Bringer, the leaf slept folded, the butterfly was hidden, the germ concealed, while the sun swept upwards towards Aries."
But when spring does come, heralded by r*- turning migrants — swallows and cuckoos among the n- t — how marvellous is the reawakening ! The buds swell a J burst, the corn sends up its light green shoots, the primrose and celandine are in blossom, the mother humble-bee conies out from her hiding-place and booms towards the willow catkins, the frogs croak and pair, none the worse of their fast, the rooks caw noisily, and the cooing of the dove is heard from the wood. Then, as the pale flowers are sue-
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The Study of Animal Life part i
ceeded by those of brighter tints, as the snowy hawthorn gives place to the laburnum's " dropping wells of fire " and the bloom of the lilac, the butterflies flit in the sunshine, the chorus of birds grows stronger, and the lambs bleat in the valley. Temperature rises, colours brighten, life becomes strong and lusty, and the earth is filled with love.
I. The Love of Mates.— In human life one of the most complex musical chords is the love of mates, in the higher forms of which we distinguish three notes — physical, emotional, and intellectual attraction. The love of animals, however, we can only roughly gauge by analogy; our knowledge is not sure enough to appreci- ate it justly, though we know beyond any doubt that in many the physical fondness of one sex for another is sub- limed by the addition of subtler emotional syinpathies. Among mammals, which frequently pair in spring, the males are often transformed by passion, the " tirnid " I.. becomes an excited combatant with his rivals, while in t' beasts of prey love often proves itself stronger than hunger. There is much ferocity in mammalian courtship— savage jealousy of rivals, mortal struggles between them, and suc- cess in wooing to the strongest. In many cases the love- making is like a storm— violent but passing. The animals pair and separate— the females to motherhood, the males to their ordinary life. A few, like some small antelopes, seem to remain as mates from year to year ; many monkeys are said to be monogamous ; but this is not the way of the
majority.
Birds are more emotional than mammals, and their love- making is more refined. The males are almost always more decorative than their mates, and excel in the power of song. They may sing, it is true, from sheer gladness of heart, from a genuine joy of life, and their lay rises "like the sap in the bough"; b.t the main motive of their music is certainly love. It may not always be music to us, but it is sweet to the ears for which it is meant— to which in many tones the song says ever " Hither, my love ! Here I am ! Here ! " Nor do the male birds woo by singing alone, but by love dances and by fluttering displays
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CHAP. VI The Domestic Life of Animals
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of their bright plumage ; with flowers, bright pods, and I • i\hells the bower-birds decorate tents of love for :S hUytool The mammals woo chiefly by force ; the Wrds arToften moved to love by beauty, and mates often hven prolonged partnership with mutual dehght and help- fulness ^xty years before Darwin elaborated h.s theory of exual selection'according to which males have grown more auractive because the most captivating svutors were mos sucSul in 'ove. the omitholorist Bechstem noted how the female canary or finch would choose the best smger among a^rowd oTsIitors ; and there seems some reason to beheve ^ha^The female's Choice of the most --ca^ or tne .^^^^^^ handsome has been a factor m progress. Wallace on he contrar^ maintains that the females are plamly dressed because of the fate which has befallen the conspicuous durmg Sation and surely they must thus be handicapped. To others it s;ems more natural to admit that there ts truth ,n both Darwin's and Wallace's conclusions, bufto regard ,1 c ml^es as stronger, handsomer, or more musical sinM;! because hey are males, of more active constitutional hab.t ?han their mates. To this view Mr Wallace himself mchnes, clpard w th the lion', thundei, the elephant's trunv oetS or the stag's resonant bass, and the might wn.ch Tes beWnd tbese, or with the warble of the nightingale, he caroUf the thrush, the lark's blithe lay, or the n.ocking- Wrd? n!.cm,^e, and the en.utional wealth which these ex- nress tne challenges and calls of love among jther classe ranimaL are apt'to seem lacking in force or beauty^ 1 u our human judgment affords no sure criterion. The f.ogs Td newts which lead on an average a somewhat sluggish Ufe wake up at pairing time, and croak according to .he,r strength The males'are often furnished with two rcsoiv at n/sacs at the back of the mouth, and how they can c 0 k TeUersb; marsh-land know ; the North American bu frog bellows by himself, and the South American tree f.ogs ViniH a rnncert in the branches.
'°'of the mJ^ing of fishes we know little, but there are ...ne well known cases alike of display and o tournament T stickleback fights with his rivals, leads h.s mate tc
cH»p. VI The Domestic Life of Animals 99
the nest by captivating wiles, dances round lier in a frenzy,
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Fi'i . I.— Male and female bird of paradise {P.ir.uiiua minor). (From ICvolu tioH e/SiX ; after Catalogue of Dii.:,Jcn .Museum.)
■ind .ifterwurds guards the eggs with jealous care. The
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The Study of Animal Life
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XOO
male salmon, with their hooked lower jaws, fight with their rivals sometimes to the death. ,• i . i :i.^
5S.t,ht sr :f *e,n are ™f .. u.„g «, Lrrl leas and wing-edges as mstruments. The crickets S mem"fth« LL "sing," and the death-watch tap.
" t frslmer^lgh., when co.ours are put out by the darlne* the"tow.woL 'shines brightly on the mossy bank^ 7 r. Rritifh soecies (Ijvnpyr nccHlucct) the wingKl LV'»d the IgCfetiale Z. both luminous ; the latter ^^.M Mcels n brightness, while her mate has larger eyes. ^tv« Ae pho Jhorescence may mean to the const,tu.,o„ Srh^«ct!i^ is certainly a love-slgnal between the sexc . But U know most about the Italian glowworm (Luaoh, te to^ of whose behaviour we have a lively picture-tha„b « PmfessoT Emerys nocturnal observations u; the meadows .Li Moena The females sit among the grass i the Zl" s «y^Kn search of them. When a female catches
Skh«s::.^-e^^rrg^;t;n:H S^rifn"ti::^irThV'^m:i^^^^^^^^^^^
coquette s ?»<"«• ' ij^„,.,jj ^nd the intensity seems ^mth th S;J t.^te >«« W the fem^e is .,we restricted The most noteworthy difference »s that tw Smrnous rhythm of the male is more rapid, with br,e^ flaThes while that of the female is more prolonged ith fonger inTervals, and more tremulous-iUummed symbols of
J^'U. we did not ignore that the courtship o au«t mammals is somewhat rough So, ^«^J^J"'"f ,; ,^ dances of many butterflies, the merry songs of the tra
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CHAP. VI The Domestic Life of Animals loi
hoppers, and the flashing signals of the glow-insects, it is just that we should turn to the strange courtship of spiders, which is less ideal. Of what we may be prepared to find we get a hint from a common experience. Not long ago I found in a gorge some spiders which I had never seen before. Wishing to examine them at leisure, I captured a male and a female, and, having only one box, put them, with misgivings, together. When I came to examine them, however, the male was represented by shreds. Such unnatural conduct, though by no means universal among spiders, is common. The tender mercies of spiders are cruel. We have lately obtained an account of the courtship of spiders from George W. and Elizabeth G. Peckham, from whose careful observations I select the following illustrations :
According to these observers, "there is no evidence that the male spiders possess greater vital activity ; on the contrary, it is the female that '<; the more ac*'ve and pugnacious of the two. There is no rel- . in either sex between development of colour and activity. 'Itie Lycosida, which are the most active of all spiders, have the least colour-development, while the sedentary orb- weavers show tlie most brilliant hues. In the numerous cases where the male differs from the female by brighter colours and ornamental appendages, these adornments are not only so placed as to be in full view of the female during courtship, but the atti- tudes and antics of the male spider at that time are actually such as to display them to the fullest extent possible. The fact that in the Altida the m.les vie with each other in making an elaborate dis- play, ^ only of their grace and agility, but also of their beauty, befor- t. females, and that the females, after attentively watching the dances and tournaments which have been executed for their Rraiification, select for their mates the males that they find most pleasing, points strongly to the conclusion that the great differences in colour and in ornament between these spiders are the result of sexual selection."
These conclusions support Darwin's position that the female's choice is a great factor in evolving at'ractiveness, and are against Wallace's contention that bright colours express greater vitality, and that the females are less brilliant because enemies eliminate the conspicuous. It is quite likely that Darwin's view is true in some cases (e.g. these spiders), and Wallace's conclusion true in others (<^. birds and butterflies), m that both may be true in
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Tlie Study of Animal Life
PART I
„„v c.^, »H.e ...fact ^^ tufS^l ^^ " '-\" Xays more brilliant than t^^l'X'l^y of maleness, which brSncy is wrapped «P^-lo"g ^ J ^^ superabundant vitality, or as it is not sufficient to ^f^^^f^i^^ey towards a relative increase greater activity, but rather as ^Jj^^^^^ges over those >.hich are ^f destructive or d.srupUve ^^'^^^ ^^^ Wem is very complex, constructive or ^^"^^f"^'':^' J't.^J^.^. We need to know and dogmatic conclusions are prcm . ^^ to winch 0 .
?Je chemical nature and ^^^^°7,e ,n apprSmate balance-sheet colour is due ; we "--'^., ° ^^^JheU s'^xes. Knough of th.s, of the income and expenditure of the ^^^ ^^^^ romance-
however ; let us return to the pictures. Su to these: patient observers:
G W und E. G. Peckham.)
e 1 tVint the males of Saiih .. On reaching the country we found that ^ .^ ^^^^ ^.^^
;>„/.. were nuti.e and were waunjg f- hc^ej^ ^^^^ ,^ ,„niulc Cilh both spiders and msccts. In U^is i ^^ ^^^^^^^ ^ difference l^tween the sexes On May 4 ^^^ ^^^ ,, y
female and placed her m one of Ojc larg« ^ ^^ ^,^^ ^^^^, ,,,1 we put a male m wuh her. He sa ^^ ^^^.^^
still, twelve =nches away. The glance .^^^^^^ f^,^„, ^et
he at once moved toward her. ^^^^y^^J^^.^Uable performances he stood still, and then ^^^^^'^^ ^^dmnng female. She cyca that an amorous male <^°»l^;^^ "^^^^.r time to time, so that h him eagerly, changmg her f-'^ ^^^.;^\.„ ^.hde Ix^dy on one sj might always be '" -^^-j J'*^' J owering it on the other by foW- by straishtemng out th^ legs, aim
CHAP. VI The Domestic Life of Animats 103
ing the first two pairs of legs up and under, leaned so far over as to be in danger of losing his balance, which he only maintained by sidling rapidly toward the lowered side. The palpus, too, on this side was turned back to correspond to the direction of the legs nearest it. He moved in a semicircle of about two inches, and then instantly reveised the position of the legs and circled in the opposite direction, gradually approachins; nearer and nearer to the female. Now she das'^es toward him, while he, raising his first pair of legs, extends them upward and forward as if to hold her off, but withal slowly retreats. Again and again he circles from side to side, she gazing toward him in a softer mood, evidently admiring the grace of his antics. This is repeated until we have counted one hundred and eleven circles made by the ardent little male. Now he approaches nearer and nearer, and when almost within reach whirls madly around and around her, she joining and whirling with him in a giddy maze. Again he falls back, and resumes his semi- circular motions with his body tilted over ; she, all excitement, lowers her head and raises her body, so that it is almost vertical. Both draw nearer, she moves slowly under him, he crawling over her head, and the mating is accomplished." The males are quarrel- some and fight with one another ; but after watching "hundreds of seemingly terrible battles " between the males of twelve differ- ent species, the obser- vers were forced to the conclusion that "they are all sham affairs gotten up for the pur- pose of displaying be fore the females, who commonly stand by in- terested spectators." "It seemed cruel sirait at first to put eight or ton males (of Dendiy- phaii/,s capitatiis) into abox to see them fight.
Yxc, i — I'wo male spiders (Zygoballus btttini) fighting. (After O. W. and E. G. Peckh.im.)
but it was soon apparent that they were very prudent little fellows, and were fully conscious that 'he who fii;hts and runs away will live t(. fight another d.ry.' In fact, after two weeks of hard fi hting we were unable to discover one wounded warrior. . . . The single female (of Phidippm morsitans) that we caught duung the
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The Study of Animal Life
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I
FIG. .4.-Malc argus pheasant di>pbylng its plumage, tl'ron, l)arw»,.)
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CHAP. VI The Domestic Life of Animals 105
upon them and killed them." ''The female of Deudryphantes tlegam is much larger than the male, and her loveliness is accom- panied by an extreme irritability of temper, which the male seems to r^ard as a constant menace to his safety ; but his eagerness being great, and his manners devoted and tender, he gradually overcomes her opposition. Her change of mood is only brought about after much patient courting on his part." In other species (Philaus militaris) the males take possession of young females and keep guard over them until they become mature. We sometimes hear of courtship by telephone. In the Epeiridse spiders " it seems to be carried on, to some extent at least, by a vibration of web lines," as M'Cook and Termeyer have also observed.
Surely it is a long gamut this, from a mammal's clamant call and forcible wooing, or from the sweet persuasiveness of our singing birds, and the fluttering displays of others, to the trembling of a thread in the web of a spider. But, however varied be the pitch of the song and the form of the dance, all are expressions of love.
Mates are also attracted to one another by odours. These are best known in mammals {e.g. beaver and civet) and in reptiles ; they predominate in the males, and at the breeding season. They usually proceed from skin glands ; but we understand little about them. They serve as incense or as stimulant, but perhaps this usefulness is secondary. The zoologist Jaeger regards the odoriferous substances in plants and animals as characteristic of and essentially associated with each life ; but without going so far we may recognise that in the general life of flowers and animals alike odours are very important. We know, too, that certain odours make much impression upon us ; such as those of hawthorn and of the hay-field, of newly- mown grass and of withered leaves, of violet and of lavender; and furthermore, that in some mysterious way some fragrances excite or soothe the system, and have become associated with sexual and other emotions,
2. Love and Care for Offspring. — Gradual as the incoming of spring has been the blossoming of parental love among animals. We can: at tell in what forms it first appeared in distinctness. We cannot say Lo here ! or 1.0 there ! for it is latent in them all
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io6 TJie Study of Animal Life part j
In many of the lower animals the units which begin new lives are readily separated from the parent ; but in others, e.g. some of the simplest, or some by no means simple "worms," and even some insects, the parent life disappears in giving birth to the young. Reproduction or the continuance of the species often involves a sacrifice of
the individual life.
It is strangely true, even in the highest forms, that reproduction, though a blossoming of the whole life, is also the beginning of death. It is costly, and brings death as well as life in its train. This is tragically illustrated by many insects, such as butterflies, who die soon after repro- ducing, though often not before they have, in obedience to instinctive impulse, cared most effectively for their eggs— the results of which they do not live to see. Think also of the mayflies, or Ephemeridae, who, after a prolonged aquatic life as larva, become winged, dance in the sunlight for an hc'ir, mate and reproduce, and die. ^ , ,
Picture the long larval life in the water, and the short aerial happiness lasting for an evening or two. Long life, compared with the span of many other insects but short love ; there may be years of patience, and but a day of pleasure; great preparations, and the anli-climax of death. The eggs lie half conscious m the water, faintly stirred by the growing life within, lapped round about by peace, — though the trout thin them sorely. In the survivors the embryos become conscious, awaken from their rocking, and turn themfelves in their cradles. See the larvae creep forth, wash themselves gaily m the water, and hungrily fall upon their prey, some smaller insects. The little " water-wings " grow, and the air soaks into the blood ; the larvae cast their skins many times, and hide from the fishes. At length comes the final moult, md the making oi the air-wings, of which in the summer e ening you may see the first short flight as the insects rise hke a living mist from the pool. But even yet a thin veil, too truly suggestive of a shroud, encumbers them ; and they rest wearily on the grass or on the branches of the willow. Watch them writhe and jerk, as it
CHAP. VI The Domestic Ltfe of Animals 107
impatient, till at length their last encumbrance — their "ghost," as naturalists call it — is thrown off. Now the other life, the life of love, begins. Merrily they dance up and down, dimpling the smooth water into smiling with a touch— chasing, embracing, separating. See the filmy fairy wings, the large lustrous eyes of the males, the tail fila- ments gracefully sweeping in the dance ! They never pause to eat — they could not if they tried ; hunger is past, love is present, and in the near future is death. The evening shadows grow longer, — shadows of death to the Ephemerides. The trout jump at them, a few rain-drops thin the throng, the stream bears others away. The mothers lay their eggs in the water, and wearily die forth- with— cradle and tomb are side by side ; the males seem to pass in a sigh from the climax of loving to the other crisis of dying. But the eggs are in the water, and the dance of love is more than a dance of death. Turning homewards, we cannot but think sadly of other Ephemerides, of patient larval life, of the gradual revealing of the higher self, of shrouds thrown aside and wedding robes put on, of hunger eaten up by love, of the sacrifice of maternity, of cradle and tomb together. Yet we remember the eggs in the water, the promise of the future beneath the surface of the stream. Under the horse- chestnut tree, too, the wind has blown the shed petals like white foam, but the tree itself is strong like Ygdrasil, and among the branches a bird sings in the twilight.
Returning in more matter-ot-fact mood to parental care, we need not dwell upon those cases where the young are simply sheltered for a while about the body of the mother, hanging to a jellyfish, on some sea-urchins hidden in tents of spines, in one or two sea-cucumbers half buried in tht skin, adhering to the naked ventral surface of the common little leech {Clepsine\ imprisoned in modified tentacles in some marine worms, carried about in a dorsal brood-chamber in many water-fleas, or under the curved tail of higher crustaceans, retained within the gills of bivalves^ and so on. Such adaptations are interesting, they involve prolonged physical contact between mother
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io8 The Study of Animal Life parti
and offspring, but we are in search of cases where the parent acts as if she cared for her young. ^ But this care, as we said, begins very gradually. Thus, in some lowly crustaceans the young may return to the brood -chamber of the mother, even after hatchmg and moulting; and young crayfish are said to jeturn to the Tdter of the maternal tail after they have been se adnft. Strange, too, are the males of some sea-spiders (Pycno- gonidl) who carry about the ova on their legs. It is con- Idently stated that the headless freshwater mussel keeps the embryos imprisoned even after the norma period, until some freshwater fish be present, to which they may attach themselves ; while some cuttle-fishes are said to exert themselves in keeping their egg-clusters dean an., safe
But it is among insects, with their full, free life that we see the best examples of parental care in backboneless animals. Some scoff at the « beetle-pricker » or the scara- be!st.-and such genial laughter as that of the Profes^o:at the Breakfast Table has a healthy resonance,-but those who scoff have not read Kirb/s Utters, else they would feel that the student of insects watches at a wdUhead o romance and marvel inexhaustibly fresh. What, for nsmce, shall we say of -e workerjees. who, though no parents, tend and nurse the grubs with constant care ; or o ^e likewise sexless worker-ants, whose first endeavou when the nest is disturbed is to save, not themselves bu the young ; or of the care that flies, moths, and other insects wUl take to lay their eggs in ^"^stances and suua- tions best fitted for the future young ? We must think back nto the past history of climatic and other conditions if rwould understand the frequently elaborate provision which mother insects make for offspring which they neve see • the ancestors had probably a longer life, and had the gr^ ification of seeing the result of their labours, and no. fhe inherited habit works on, perhaps with no vision of the future. We must also allow that the offspnng mis- takenly deposited by an imperfect maternal instinct would most likely die, and thus leave the race more seleit. But after thinking out these explanations, the facts remain mar-
iT-it--'
CHAP. VI The Domestic Life of Animals
109
vellous. Thus W. Marshall saw an Ichneumon fly {Polynema natans) remain twelve hours under water, without special adaptations for such a life, swimming about with her wings, and depositing her eggs within the larvae of caddis-flies I
We are accustomed, the same naturalist says, to look upon a hen which gathers her brood under her wings as a picture of loving care, but we must recognise that the same is true of earwigs, spiders, and scorpions. Many of us have lifted a large stone on the dry bank, and seen the hurry-scurry of small animals ; there are earwigs among the rest, and the pale-yellowish young crowd quickly under the shelter of their mothers, who stand guard with open pincers. Female spiders, too, so fierce and impatient as mates, are most "respectable mothers." Some make nests, guard, feed, and even fight for the young ; others carry the eggs about with them. " I have often," Marshall says, "made fun of the little creatures, taking away their precious egg-sac and removing it to a slight distance. It was interesting to see how eagerly they sought, and how joyously, one may even say, they sprang upon their * one and all ' when they found it again. Sometimes I cheated them with a little ball of wool of the size, form, and colour of the egg-sac, which they quickly seized, and as rapidly rejected."
Many fishes lay their eggs by hundreds in the water, and thenceforth have .lothing more to do with them, but even among these cold-blooded animals there are illustra- tions of parental care. From a bridge over the river you may be able to watch the female salmon ploughing a furrow in the gravelly bed, and there laying her eggs, care- ful not to disturb the places where others have already spawned. In quiet by-pools you may find the gay male stickleback guarding the nest which he has made of twined fibres partly glued together with mucus. There the female has laid eggs, but he has driven her forth : he will do all the nursing himself. No approaching enemy is too large for him to attack ; his courage equals his seeming pride. When the youn^ are hatched, but not yet able to fend for
no The Study of Animal Life part i
themselves, his cares are increased tenfold. It is hard to keep the youngsters in the cradle. "No sooner has he brought one bold truant back, than two others are out, and so it goes on the whole day long."
We are not clever enough to understand why the males among many fishes are so much more careful than the females For the stickleback is not alone m his excellent behavio'ir The male Chinese macropod {Polyacanthus) makes .rothy nest of air and mucus, in which he places his mates eggs. He, too, watches jealously over the brood, and "has his hands— or rather his mouth— full to recover the hasty throng when they stray, and to pack them again into their cradle." Of all strange habits, perhaps that is strangest which some male fish {e.g. Arius) have of hatching the eggs in their mouths ; what external danger s must have threatened them before this quaint brooding- chamber was chosen ! Or is if not almost like a joke to see
the male sea-horse swelling up as the eggs which he has stowed away in an external pocket hatch and mature, "till one day we see emerging from the aperture a number of small, almost transpar- ent creatures, something like marks of interrogation." Hut . some female fishes also carry
S their eggs about, attached to the ventral surface (in the Siluroid fish, Aspredo), or stowed away in a ventral pouch (in Solenostovui, allied to pipe-fishes), arrange- ments which recur among amphi- FiG. as. — Sea-horse (Hippo- ^,;ans, but On the dorsal surface
campus guttulatus). (b rom , ^, ' , , Evolution of Sex; after Atlas of the DOdy.
of Naples Station.) Amphibians, like fishes, to
which they are linked by many ties, are either quaint or careless parents. Again, the males assume the responsi- bilities of nurture. The obstetric frog {^lytes obstetnoim), common in some parts of the Continent, takes the eggs from
CHAP. VI The Domestic Life of Animals iii
his mate, winds them round his hind-legs, and retires into a hole, whence, after a fortnight or so, he betakes himself to the water, there to be relieved by the speedy hatching of his precious burden. Even quainter is the habit of the male of a Chilian irog{Rhinodenna darwinii), who keeps the eggs and the young in a pouch near the larynx, turning a resonating sac in a most inatter-of-fact way into a cradle. He is some- what leaner after it is all over. It is interesting to notice how similar forms and habits recur among animals of dif- ferent kinds, like the theme in some musical compositions. The spiral form of shell common in the simple, chalk-forming Foraminilers recurs in the pearly nautilus ; the eye of a fish is practically like that of many a cuttle, though the two are made in quite different ways ; and an extraordinary development of paternal care may signalise animals so distinct as sea-spider, stickleback, and frog.
But we must not be unfair to the female amphibians. Without doubt most of them are willing to be quickly rid of their eggs or young, and as these are usually very numerous, the mortality in the pools is of little moment. In some cases, however, water-pools are less available than in Britain, and then we find adaptations securing the welfare of the young. The black salamander of the Alps, living at elevations where pools are rare, retains her twin oiibpring until more than half of the tadpole life is past. They breathe and feed in a marvellous way within the body of the mother, and are bom as lung-breathers. In the case of the Surinam Toad {Pipa), the male places half a hundred eggs on the back of the female, where they become surrounded by small pockets of skiii, from which the young toads writhe out fully formed. In two other cases {Nototrema and Notodelphys\ the above somewhat expensive adaptation, which involves a great destruction of skin, is replaced by a dorsal pouch in which the eggs hatch, an arrangement dimly suggestive of the pouch of kangaroos and other marsupial mammals.
Fishes and amphibians are linked closely by their likeness in structure, and, as we t,.ve seen, they are somewhat alike in parental habits ; bui ixow great is the contrast between
Irti
iia The Study of Animal Life fart i
the habits of birds and reptiles, in spite of their genuine blood-relationship. Yet the python coiled round her eggs is a prophecy of the brooding birds as in past ages the flopping Saurians prophesied their sw.ft-wmged fl.gh . ^ The sharpness of the contrast is also lessened by the fac* u,' <. few birds, like the mound-builders, do not brood at a I , \vli.k others, it must be confessed, are somewhat carde .. But, exceptions and ciiminals apart, birds are so lav.sl, n, the. love so constant i.i iheir carefulness, that it is difficuii t<. speak of them without exaggeration. I am quite willing to allow that they often act without thought (that is hall the beauty of it) ; nor do I doubt that many spec.es would have gone to the wall long since m the stioiggle of life if the parents had not t„ken so much care of the young ; but I would rather emphasise at present the reality that they do sacrifice themselves for the sake of their young to a most remarkable degree,.and spend themselves not for individual ends, but for their offspring. .,,,..
Before the time of egg-laying the birds build the.r nests, eageily but without hurry, instinctively yet with some plas- tidty, and often with much beauty. On the laid eggs, whi-^h require warmth to develop, the mothers brood, and though to rest after reproduction is natural, the brood- ing is not without its literal patience. Among polygamous birds the males are, as one would expect, more or less carclc.s of their mates, but most of the monogamous males are careful either in sharing the duty of brooding or m supplying the females with food. After the eggs hatdi the degree of care required vanes according to the state of the young; for many are precociously energetic and able to look after themselves, while others still requ.re prolonged nurture. They need large quantities of food, [o supply which all the energies of both parents seem sometimes no more than adequate ; they may still require o l2 brooded over, and certainly to be protected from rain and enemies. After they are reared, they have o be tr ht to fly, to catch food, to avoid danger, and a dozen o a.ts. With what apparent love-willing and joyow - s al' this done for them I
MiiM
CHAP. VI The Domestic Life /Animals 113
Consider the cunning often displayed in leaving or approaching the nest, in removing debris which would betray the whereabouts of the young, or in distracting attention to a safe distance ; remember, too, that some birds
Fii;. 26.— NcM of tail'ir-bird (prthotoinm heHettif). (AOer Firehni.)
Will shift cither eggs or yoiuig to a new resting-place when extreme danger threatens ; estimate the energy spent in feeding the brood, sometimes on a diet quite different from that of adult life ; and acknowledge that the parental instmrt is very deeply rooted, since fostering young not their ouu may be practisc.l by orphaneil birds of both i>tMs. Listen to the bird vvhi( h h is been bereaved, and tell mc IS not the "lone singer wonderful, causing tears"?
riic female of the Indian and African hombill nests in a hole in a tree, the entrance to which she plasters up so that no room is left either for exit or entrance. The
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Tfu Study of Animal Life
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Malays imagined that this was the work >f ,|^e J-l-s male but it is the female's own domg. ^tie sus, M^hTsays "securely hidden, safe from any carnivore ^r m^Sievous ape or snake stealthily climbing, whde the irfxlns him'self lovingly to bring h.s mate those drfiehtfol things in which the tropical forest is nch-fruus aW a 1, but occasionally a delicate mouse or juicy C^ He flies with his booty to the tree and gives a oTculiar knock, which his mate knows as his signal, and ?h" "herbeak through the na-ow window welco^^^^g^^^^^^ meal." At the end of the period of incubation. C. M Wood forf says "the devoted husband is worn to a skeleton.
BSml. like men. have their vices, and birds, gener- ally soTdeal i^ their behaviour, are sometimes criminal. OmiAologists assure us that the degree of parental care v^S^nofonly in neariv -related species, but also among TrTberofthe same species. We need not ay muc stress on the fact that a bird occasionally slips its egg So a neighbour's nest, for when a partridge thus uses a
^hLln^^'rough bed. or a V^^ ^^^^^ ^K^l^^^t^C^ is likely enough that the mtruder had been disturbed
from her own resting-place when ^b«"% *° ^^^^ -^^J approach something diflferent in the case of the American SSrich (/?A.a). the female of which ^^^^^'^^^l^^^ utilise a neighbour's burrow; nor does the owner seem to oWect. for all the brooding is discharged by the mal I^a^' t is no great art to be paUent and ^gn^--^
know HS^'^Sibe7of females sometimes lay their eggs
■" wra^s^glad to hear the cuckoo's call in spring that we almost foi/et the wickedness of the voluble bird. Ih ;:.rs have h?ped us. for they have generously .demised, n fact idolised, the cuckoo, the "darhng f ^^V P^'^l;^ „ , wandering voice babbling of sunshine ^^^f^^^'^^Xoo. "sweet." nay more, a "blessed bird." But the cue k harhoaxJ the p;>ets. for they are even worse than h.r Tegwdary reputati^of being sparrow-hawks m d.sgu.se.
CHAP. VI The Domestic Life of Animals 115
they are "greedy feeders," says Brehm, "discontented, ill- conditioned, passionate fellows; in short, decidedly unamiable birds." The truth must be told, the cuckoo is an immoral vagabond, an Ishmaelite, an individualist, a keeper of game "preserves." There are so many males that they have perverted and thoroughly demoralised the females ; there is no true pairing ; they are polyandrous. The birds are too hungry for genuine love, though there is no lack of passion ; while by voraciously devouring hairy caterpillars they have acquired a gizzard-fretting feltwork in their stomachs, and for all I know are cursed by dyspepsia as well as by a con- stitutionally evil character. It is not quite correct to say that the cuckoo-mother is immoral because she shirks the duties of maternity; it is rather that she puts her young out to nurse because she is immoral.^ The so-called " parasitic " trick is an outcrop of an egoistic constitution which shows Itself m many different ways. The young bird, "a dog in the manger by birth," evicts the helpless rightful tenants whether they are still passive in the eggs or more assertive as nestlings, and as he grows up a spoilt child his foster parents lead no easy life. But though the poet? have been hoaxed, I do not believe that the nurses of the fledgling are; it seems rather as if the naughtiness of their changelmg had some charm.
Of course there is another way of looking at the cuckoo's crime. It is advantageous, and there is much art m the well-executed trick by which the mother foists her several eggs, at intervals of several days, into the nests of various birds, which are usually insectivorous and suited for the upbnngmg of the intruder. I think there is at least some deliberation m this so-called instinct. Nor should one forget that the mother occasionally returns to the natural habit of hatching her own eggs,--£i pleasant fact which several trust- worthy observers have thoroughly established. Still, in spite of the poets, the note of this " blessed bird » must be regarded ^ suggestive of sin I
whkhil !I«.''TJ1 T*" "***'" '^** ^ *'*^«^ occasionally used word, do „5.^ir^ !^*'"^ ***"*'*• * "-y '»»««'«« »*y definitely that I «tS^^^!L*' "* ^^^^^ in crediting animals with morU wihet , or. indoed, any conceptions. ^
j^a*,:'
'*"j(L.t .-^,,
^mMk
The Study of Animal Life
PART I
ii6
There IS much to be said about the domestic life of animaU-their courtship, their helpful partnership, and the.r parrtage-but perhaps I have said enough to jnduce you fortSnk about these Things more carefully. Many of the deep St problems of biology-the origin and evolution o sex the delation of reproduction to the individual and to the spec es-should be considered by those who feel themselves naSly inclined to such inquiries ; moreover, m connection "h our own lives, it is profitable to investigate among ri mals the different grades of the love of "^^^^^./^^ the Son between the rate of reproduction and the degree o development. First, however, it were better that we should waTchTe ways of animals and seek after some sympathy wkh them, that we may respect their love, and salute hem nf with stone or bullet, but with the praise of gladdened
^^'Ruskin's translation of what Socrates said in regard to the halcyon is suggestive of the mood in which we should consider these things.
^"^iiSr^ Not great ; but it has received great honour from the all others in their calmness, though in the mids of °™;
Sir.r.ol.'r.hinr»aTt ho„ou? .ho„ h„. for i. r™
""S^'li.« " It is nghlly due imlMd, O Socralcs, for O.er. i. . SZtlJl .hU.U for men »d women, rn .he, ..l-
'"l^^'r-Sh'Ilt « no. then ».«.. .he h.lc,on, .nd « go W to the city by the sands, fo' »l « time ?
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CHAPTER VII
it
THE INDUSTRIES OF ANIMALS
I. Hunting— 2. Shepherding— t,. Storing— a,. Making of Homei
5. Movements
It is likely that primitive man fed almost wholly upon fruits. His early struggles with animals were defensive rather than aggressive, though with growing strength he would become able for more than parrying. We can fancy how a band of men who had pursued and slain some ravaging wild beast would satisfy at once hunger and rage by eating the warm flesh. Somehow, we know, hunting became an habitual art. We can also fancy how hunters who had slain a mother animal kept her young alive and reared them. In this or in some other way the custom of domesticating animals begar, and men became shepherds. And as the hunter's pursuits'were partially replaced by pastoral life, so the latter became in some regions accessory to the labours of agriculture, with the development of which we may reascnably associate the foundation of stable homesteads. Around these primary occupations arose the various human industries, with division oflabour between mnn and woman, and between man and man.
Thesft human industries suggest a convenient arrange- ment for those practised by animals. For here again there are hunters and fishers— beasts of prey of all kinds— pursuing the chase with diverse degrees of art ; shepherds, too, for some ants use the aphides as cows ; and farmers without doubt.
1 18 TJie Study of Animal Life part i
if we use the word in a sense wide enough to include those who collet, modify, and store the various fruUs of the
"""t; illustrating these industries, I shall follow a charming volume by Fr J^ric Houssay. Les Industries des Ammaux,
^^t' a^W-Of this primary activity there are many kinds The crocodile lies in wait by the ^^ucer's edge, ^python hangs like a ^an fro^ t.e Uee, ^t^^^
fSr -Se angler-fish ^Lophius piscatorius) is some- what protectively coloured as he lies on the sand among what Proiecuvc y filaments dangle, and
the seaweeds; on nis oacK uu.^
nossiblv suggest worms to curious little fishes ^^nlc^, vrturing nSr, areengulfed by the angler's horrid maw,
^h^^zi :tr Ttr^ j^.
,1- - Thmir of the Indian Toxctes, a nsn wnun
SS&,^e':^>nra%s^rcr^;tt
^«1ref.sSe (i». J^Wor), which spite .ts v.cum
tions of the Amazon ants. AU sircngui «!•« Thst^nding, ,h. *- J'jf- ^; "^nr.- <^«'«
CHAP. VII The Industries of Animals
119
are often utilised, the weak combine against the strong, and the victims of even the strong carnivores often show fight valiantly.
2. Sbepherding. — Although the ants are the only animals which show a pastoral habit in any perfection, and that only in four or five species {e.g. Lasius niger and Lasius brunneus), ! think that the fact is one about which we may profitably exercise our minds. I shall follow Espinas's admirable discussion of the subject.
We may begin with the simple association of ants and aphides as commensals eating at the same bountiful table. But as ants discovered that the aphides were overflowing with sweetness, they formed the habit of licking them, the aphides submitting with passive enjoyment. Moreover, as the ants nesting near the foot of a tree covered with aphides would resent that others should invade their pre- serves, it is not surprising to find that they should continue their earthen tunnels up the stem and branches, and should eventually build an aerial stable for some of their cattle. Thither also they transport some of their own larvae to be sunned, and as they carried these back again when the rain fell, they would surely not require the assistance of an abstract idea to prompt them to take some aphides also downstairs. Or perhaps it is enough to suppose that the aphides, by no means objecting to the ants' attentions, did not require any coaxing to descend the tunnels, and eventually to live in the cellars of the nests, where they feed comfortably on roots, and are sheltered from the bad weather of autumn. In autumn the aphides lay eggs in the cellars to which they have been brought by force or coaxing or otherwise, and these eggs the ants take care of, putting them in safe cradles, licking them as tenderly as they do those of their own kind. Thus the domestication of aphides by ants is completed.
Now what is the theory of this sljepherding ? (1) We have no warrant for saying that the ants have deliberately domesticated these aphides, as men have occasionally added to the number of their domesticated animals. It does not seem to me probable that even primitive man
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The Study of Animal Life
PART I
&i5r
I30
domestications. (2) Nor is it u y dominant
began i"; -^^^ '^^^^^^ selection.
V l^ Jw! is more a luxury than a necessity, and >°L not Ukdy to have been e^volved before the estab- !• hment of the sterile caste of workers, who have no means
lV^!n»., mistake of an individual worker ant, but the Imcle oT he community's progressive development ,n "TnteUectual somnambulism," helped in some -neasur' ^j the sSsh habits of the aphides. And, .f you wish, the ferula C be added, " which was justified m the course
°' Tst«S-Not a few animals hide their prey or |he;r eathertoT^d with marvellous memory for locahnes Sum to them after a short time. But genmne stonng wTmore Snt future is illustrated by the squirrels, wh.C, Wde the"t«rrls like misers. Many mice and other rodents do likewl^and in some cases the habit seems to become f si« :f?»e, so large are the supplies la,d >n aganjst h :«t*r'« .irarcitv Very quaint are the sacrc scaraDees X'L ""^^^^^^^ of dung to their holes, an
Ifme^imercollect supplies at which they gnaw for a couple of weeks Some anfs'(..^. Atta barhara) accumulate stores of ^afn occasionally large enough to be worth robbing and^heti is no doubt that they are able to keep the se d from germinating for a considerable t-e, while thysto he germination after it has begun ^Y gnawing off pbmd Ind radicle and drying the seeds afresh. Dr. M Cooks ^count of the agricdtural ant of Texas {Pogomynnex nrJ.) gives even more marv.Uous illustrations 0 famitng habits, for these ants to a certain extent at least cuSe in front of their nests a kind of grass with a ncc
^-%^^=^!-^
CHAP. VII The Industries of Animals 121
like seed. They cut off all other plants from their fields, aiid thus their crops flourish.
But animals store for their offspring as well as for themselves. The habit is very characteristic of insects, and is the more interesting because the parents in many cases do not survive to see the rewards of their industry. Sometimes, indeed, there is no industry, for the stores of other insects may be utilised. Thus a little beetle {Sitaris muralis) enters the nest of a bee {Anthophora pilifera) and lays its eggs in the cells full of honey. More laudable are the burying-beetles {Necrophorus), which unite in har- monious labour to bury the body of a mouse or a bird, which serves as a resting-place for their eggs and as a larder for the larvae. The Spkex wasp makes burrows, in which there are many chambers. Each chamber con- tains an egg, and is also a larder, in which three or four crickets or other insects, paralysed by a sting in the nervous system, remain alive as fresh meat for the Sphex larva when that is hatched. After the Sphex has caught and stung its cricket and brought it to the burrow, it enters at first alone, apparently to see if all is right within. That this is thoroughly habitual is evident from Fabre's experiment. While the Sphex was in the burrow, he stole away the paralysed cricket, and restored it after a little ; yet the wasp always reconnoitred afresh, though the trick was played forty times in succession. Yet when he substi- tuted an unparalysed cricket for the paralysed one, the Sphex did not at once perceive what was amiss, but soon awoke to the gravity of the situation, and made a fierce onslaught on the recalcitrant victim. So it is not wholly the slave of habit.
4- Making of Homes. — Houssay arranges the dwellings of animals in three sets — (a) those which are hollowed out in the earth or in wood; (p) those which are constructed of light materials often woven together ; and (f) those which are built of clay or similar material. We may compare these to the caves, wigwams, and buildings in which men find homes.
Burrows are simplest, but they may be complex io
■--. Ifri
5».
122
The Study of Animal Life
V.\RT 1
details Those of the land-crabs (Gccardnus), <h'= J"";!- c S^S bees (Xy,oc.p.y .he sand-n,ar,ens t c „a™ , ; rabbitt the prairie dogs, ilUrstrale th,» kmd of dwe.l.,r„
™XtSr:.SS'°o\.W«.) weaves and glues
FIG. ,7.-SwaUows iflulidonaria urkka) and their nest. (After lirch.n.)
the leaves and stems of water-plants ; the minutest mouse
ir/xs SeT -^' tosr;!"'--
""' WbuMings, the swallows' nests by the window, a.ul .k
CHAP. VII The Industries of Animals
123
paper houses which wasps construct, are well known ; but we should not forget the architecture of the mason-bees, the gre.it towers of the termites, and the lodges of the beavers.
Perhaps I may be allowed to notice once again, whrit I have suggested in another chapter, that while many of the shelters which animals make are for the young rather than for the adults, the hne of definition is not strict, and some which were nests to begin with have expanded into homes
an instance of a kind of evolution which is recognisable
in many other cases.
5. Movements. — But animals are active in other ways. All their ways of moving should be considered — the marvel-
FiG. 28.— Flight of crested heron, ten images per second. (From Chambers's EncycloJ>. ; after Murey.)
lous flight of birds and insects, the power of swimming and diving, the strange motion of serpents, the leap, the heavy tread, the swift gallop of Mammals. All their gainbolings and playful frolics, their travels in search of food, and their migrations over land and sea, should be reckoned up.
Most marvellous is the winged flight of birds. As a boat is borne along when the wind fills the sails, or when the oars strike the water, and as a swimmer beats the water with his hands, so the bird beating the air backwards with its wings Is borne onward in swift flight. But the air is not so resistent as the water, and no bird can float in the air as a boat floats in the water. Thus the stroke has
\n
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Hi
mmmi
^^wpMiiivg
i^w:0!m
124 T/ie Study of Animal Life part 1
a downward as well as a backward direction. When there is more of the downward direction the bird rises, when there is more of the backward direction it speeds forward ; but usually the stroke is both downwards and backwards for the lightest bird has to keep itseir from falling as it fl.es. The hoUowness and sponginess of many of the bones com- bine strength of material with lightness, and the balloon- like air-sacs connected with the lungs perhaps help the birds in rising from the ground; but, buoyant as many buds are, all have to keep themselves up by an effort. But he possibility of flight also depends upon the fac that the raising of the wing in preparation for each stroke can be accomplished with very little effort ; the whole wing and its individual feathers are adjusted to present a^maxinuun surface during the down-stroke, a minimuin surface dunng the elevation of the wing. There are many different kmds 0 flight, which require special explanation— the fluttering 0 humming-birds, the soaring of the lark, the masterful hovering of the kestrel, the sailing of the albatross. The effortless sailing motion of many birds is comparable to that of a kite, » the weight of the bird corresponding to the tail of the kite ;" it is possible only when there is wind or when great velocity has been previously attained.
WW.'^^':
PART II
THE POWERS OF LIFE
CHAPTER VIII
VITALITY
'J
I- «!
I. The Task of Physiology— 2. The Seat of Life— i. The Eturgy of Life — 4. Ceils, the Elements of Life — 5. The Machinery oj Life — 6. Protoplasm — 7. Thi Chemical Elements of Life — 8. Growth — 9. Origin of Life
I. The Task of Physiology. — So far we have been considering the ways of living creatures, as they live and move, feed and grow, love and fight ; as they build their homes and tend their young. We shall now turn to the inner mysteries, and seek, so far as we may, to fathom the wisdom of the hidden parts. We shall describe the machinery — the means by which the forces of life cause those movements by which we recognise their presence.
This study is called physiology ; and the plan of our sketch of present knowledge will be as follows : We shall first try to realise what we mean by life ; we shall then limit ourselves to the consideration of certain kinds of life, and attempt to make plain in what parts of all living creatures are the forces of life most active. Having done this, we shall describe the life processes of the simplest creatures, and then those of the higher animals.
It is not easy to say clearly what we mean by li^" ; but we recognise as one of its characteristics the pt ^r of movement.
,'r;
■yrxi
126 The Study of Animal Lift partu
Stiil, this gives no distinction between the blowing of wind and the life of man ; but the other charactenstics of life wiU be realised as we proceed in our ^^^"^^ V^ certain that without movement there is no life. Further thought may lead us to define life as that 'complex of forces which produces form." Thus the sta- like crystals of a snowflake, the diamond drops of dew, the over- shadowing mountains, wodd all be '^naged in our minds as living, though of more lowly life than the Uchens of the bare hill-tops, the grass of the plains, or man himself. We have no space here to trace the connections between such an idea and the beliefs of all simple peoples, and the inspirations of aU poets, but the similarity is evident, and the usefulness in philosophy of such general- ised conceptions is great.
But the physiology which we shall sketch here will be a narrower one; it will be confined to the life of plants and animals, and we shall attempt to show precisely how that life is separated from the life of the dust and of the air.
2 The Seat of Life.— Now in what parts within the living body are the life forces most actively at work ?
When we look at any living creature we are all too willing, even if the wonder of life stirs within us, to remain satisfied with a vague apprehension of a mystery. It is strange that so many generations of men passed away befoi- any steps were taken towards a conception of the intimate material processes of life and growth and death The moving train has been watched, but the engine and the stoker have been almost unnoticed.
Let us consider the growth of a tiee. The outward manner of its growth we can observe, a few superficial details of its inner life we already know, and of this knowledge we may look fo- great expansion, but the ultimate processes of its life are still a complete mystery to us.
The tree is alive, but is A all alive ? Cut a stake from its heart and olant it in the ground ; it will not grow, and shows no sig..J of life, but we are not puizled ; the tree, wc think, can only live as a whole, and we know how easily most Uving things are killed by local injuries. But if we
CHA». VIII
Vitality
ta7
cat a stake from the outer part of the tree, leaving the bark on, and set it in the ground, it may happen that buds will appear, pushing through the bark, and stretching out into shoots.
There is a mystery for us to begin with : some parts of a tree may have a life of their own. Indeed, we all know that gardeners do not rear geraniums and other plants from seeds, but from cutti igs. Potatoes, as we know, will give origin to new plan .3, and even small parts of potatoes will do so. Roses are grafted into the stems of the wild brier, and in this way two life -currents are mingled. We may remember, too, that all seeds are only parts that have become separated from the parent plant. We ourselves, formed in the darkness of the womb, were separated at birth from the mothers who bore us.
Let us think of the seeds of plants for a little. Formed in the warmth and brightness of the summer sun, ripened in the glow of autumn, they fall to the ground, are carried hither and thither bv trickling runlets of water, by the winds, by animals, and. scattered over new pastures. Through the long chill of winter they remain asleep ; but not dead, — slow preparation is being made for the new day. With the warm winds of spring — when the birds come back to us and sing their first songs of love and courtship — the countless buds of the woods, the gardens, and the hedgerows, all the seeds we sowed in the autumn, all the com we scattered in the first hours of the new morning, awake ; the buds burst, the tiny leaves unroll ; in the seeds there is a great activity, — the slender shoots stretch forth — spring passes into summer — and we await the harvest.
3- The Eneivy of Life.— What is the cause ot this strength of life ? How is it that in an acre of forest tons of solid matter are lifted high into the air, while thf branches waving under the blue sky seem to enjoy the bri^^^ iness of the sun after the gloom of winter ? 1 his assertion of the poets of the gladness of nature at the springtime is no mere wandering fancy, it is simple truth ; the intensity of life at that time is due entirely to the greater warmth of the air
/
X
,a8 The Study of Animal Life
reason why '^ '"", . , creatures, that consciousness 3S°S.;"b^i«^ 1^- «iO.' inc^ased vigour or
;;::^aX. "x^n^r 'energ, of sUJ^n jh.H by
--hanic^' .rsrj rr>,"t.*:uera"5
;S' .h m^inTi" *e plant, b, which ^h. en.g,
^ the sun', mys is transmuted ;>»o W'' J^S
answer to this riddle '^» 'J!"JZ'a J wUh a water
r ''^""u'roperatd «V XSmy stuff agai^ shmy sap. If we open a duu ^.^
under the l>ark of '«■=' ^.f * l^'teTnid-d. in all .he tissues of a butt, and mgr^.nss« ^^ .^^^^^^^^
lifrJ^afw^^ fin* vha we may call for the moment
li!, sTmy^'sT; while in the ha.. >-'„ P^ ° „f „ ^i which we know can hve no more, we »";^ "°;" J". ^^
Z^^Z^^^l rJorenTne. - we do ™.
•"'T'Sli."S/S»*' of Uf..-1-e. us ,ea.e .ho .aes now'foTT'lMe, and turn to .he simplest of all 1> ^«.,rM which Hve in water and In damp places. Ihcj S^'r LthUt only a few of the larger ones can be .
»•«« .n#.fka movine about in the water m whicn mcy L 'BuHhe; cTnXf seen quite easily with a micrcscop.^ We find them to be little transparent drops f J « matter. They are not really drops; many of them ha>e
iPx-msacrW^.r^^Xi:- "Jt;.
'^^r^pmrk^-^
CHAF. VIII
Vitality i«9
distinct shapes, others constantly change their form. They move, indeed, by a kind of flowing ; one part of their body is pushed out and a part on the farther side drawn in. Some of these lowly creatures have skeletons or shells of lime or of flint. Great numbers of these shells, when the little inmates are dead, form beds of chalk and ooze. Now all living creatures begin life in this way; at first they are tiny masses of a jelly-like translucent stuflT. Each mass gets a skin or surrounding wall ; if fed, it grows hrger, and a wall is built up inside it, making its house a two-roomed one. This process goes on and on ; the whole mass grows larger and larger, and becomes divided up into a corresponding number of compartments. The chambers are not quite separated ; there are always holes left in the walls, through which strands of the jelly-like stuff pass, and so all of them are connected. The divisions in each separaie kind of animal or plant take place in a special way, until at last the whole body is built up, with all its peculiarities of form and internal arrangement. The cells of an animal's body do not, however, form walls as definitely as do those of plants.
In an ordinary plant there are millions of those com- partments ; they are called cells, from their likeness in general appearance to the cells of a honeycomb ; and the enclosed stuff that we have spoken of as jelly is called protoplasm, because it is believed that the first living things that were formed were little drops of jelly-like stuflT, not unlike that within the cells, or composing the animalculae in water. Protoplasm, wherever it occurs, from the highest to the lowest forms of life, is supposed to have, within certain limits, a similarity of nature.
In some plants the cells are large enough to be visible to the naked eye, but the cells of most plants and animals are so small that they can only be seen with a microscope.
We can now give a complete answer to the question, What parts of a tree are alive ? It is only the protoplasm of the cells. The walls of the cells are more or less dead. As the cells grow older and larger, and the walls become thicker, the amount of protoplasm within gets relatively
K
The Study of Animal Life
FAKT II
^^
less • at last it slowly dies and withers awg^; the ceUs are ^iiMtr and that is why the stake cut from the old hard '^T£e toddle of the t Jee could not grow.-it was quite
^^*f The Machinery of Idfe—We have found that, in
.om*; ^ Ae^rotoplasm within the cells is the machmery
of^L For sLplicity, we shall speak of protoplasm as
?•«;%«»«« •Ais uUng matter in plants is such that
S t^^nn^eUrgy'of sunlight into potential en.^
l.i'^mnlicated substances such as wood. This trans-
? Tnn^lnerev is one of the chief labours of plants in
Horir A SSt d^l of the energy that reaches the.r
formatter is W for their own upward growth ; so that.
rweSJJ^ore, thousands of 1 >ns of matter are every
Tearover every acre of forest, raised high into the air.
^nlimals^he Uvin^ ^c^^^^^^ X^ s^/h
f:Z:X:,o.^:^^trS^^or.^ - these is used by it I^^llf about and so transformed into energy of motion. CSSsIs chiefly shown in the storage of energy, Xe life^o? aSm2s in the use of that store. Chiefly we say, for itits X move to a slight extent; as a whole, when hey tw^etround a tree or bend towards the sun ; and m h'fr wS^ when the sap rises and falls. Animals also, to a St^nV build up substances of high potential energy. ^So S lis certain, but when we inquire by what an-angc ment of parts the liv ng matter is able to be a machme for r^isfo^ation of energy, we are unable to fo- any co. xDc «*t discovery of the cells and their living
Sd fte nTessary physical condition,, arguing from *
Z .^vitie. of .h. living ■""'•'"nhr^U tht s«^ from the stnictural arrangements of the ceUs , '"'J ' f; ^ that the living matter, a part wuhm « "« '« SScteus, and the cell-wall, were m A«™«''" *« Pf^„ a mach ne, and that the various activities of the cells w«e SuT^TlH^ing shapes of wall, and dispo«,t.on of, « ™.* puts. It WM soon shown, however, that the wall «as "»
CHAP. Till
Vitality
131
a necessary part of the living matter, and that the nucleus did not always occur. The cell is a machine, not in virtue of the disposition of its visible parts, but as a consequence of the arrangement of its molecules. We know this much about the living machinery, that it is far more perfect than the machinery of our steam-engines, the perfection of a machine being measured by the relation between the energy which enters it and that which leaves it as work done.
«« Joule pointed out that not only does an animal much more nearly resemble in its functions an electro-magnetic engine than it resembles a steam-engine, but also that it is a much more efficient engine ; that is to say, an animal, for the same amount of potential energy of food or fuel supplied to it— call it fuel to compare it with other engines —gives you a larger amount converted into work than any engine which we can construct physically," And Joly has expressed the contrast between an inanimate material system and an organism as follows : " While the transfer of energy into any inanimate material system is attended by effects retardative to the transfer and conducive to dis- sipation, the transfer of energy into any animate material system is attended by effects conducive to the transfer and retardative of dissipation."
It is from protoplasm that we must start in our study of living machinery ; let us see how far we can attain to exact conceptions of its nature. We will first describe shortly what is known as to the structure of protoplasm 01 living matter, chiefly to show how hopeless is any attempt at a solution of the problem in terms of visible structure. The powers of the microscope are limited by the physical nature of light, and that limit has already nearly been reached ; and yet we know the structure of matter is so ex- cessively minute that within the compass of the finest fibre visible with the microscope there is room for th- most intri- cate structural arrangements.
6. Protoplasm.— Protoplasm used commonly to be de- scnbed as a structureless mass ; we now know that it often ^ structure somewhat like a heap of network. It is a complex of finely-arranged strands, with knots or sweUings
'ia'fjsis^
,3a The Study of Animal Life part n
at the junctions of the strands, and with in each cell, one nr more central and larger swellings, probably of a highly sLda Used nSure, called nuclei. The size of the meshes vE and they are filled "now with a fUud, now wjth a mTre solid substance, or with a finer and more dehcate network, minute particles or granules of vanable sue be.ng someUmes lodged in the open meshes, sometimes deposited
identkal in refractive power with the bars or films .,f he network, that the whole substance appears ho,„ogenc^^^^^ The only means we have of getting any further kno.le of this arrangement is by staining U wuh various d>cs and observing the effects of the dyes upon the vanous part. " A^l with various staining and other reagents leads to
CHAT, irtti
Vifa/ify
«33
the conclusion that the substance of the network is of a different character from the substance filling up the meshes. Similar analysis shows that at times the bars or films of the network are not homogeneous, but composed of different kinds of stuff; yet even in these cases it is difl5cult, if not im- possible, to recognise any definite relation of the components to each other such as might deserve the name of structure." Plainly there is not much light to be got by further investi- gations in this direction. Ordinary chemical analysis, too, is of little avail ; for how can we say what parts of the mass are alive, even if we could separate part from part ? Is it only the meshwork that is really living matter, or are the granules part of it, or are the fluid contents the chiefly vital substance ?
Let us turn now to the activities of the living stuff, and see what we can learn from them. We have already spoken of one of the activities of living matter, especially of plant protoplasm, that of surrounding itself with a wall Now we might at first be inclined to suppose that the wall was simply due to a hardening and drying of the soft substance at those places where it touched the air. It is possible that that may have been the stimulus which caused, as a reaction, the wall-making at the dawn of life, and which may still have some connection with it ; but what we have to take note of is the fact that the walls, as they are made by the higher plants, have always a definite structure and chemical natur .
If we examine the cells of the leaves of a plant growing in the sunlight, we find the green colouring matter to be generally collected in little rounded masses. Looking more closely, we find it to be the fluid which fills the meshwork of the masses. At certain points in the meshwork we find minute masses of starch constantly being formed. They seem to pass along the strands and collect in the centre of the net- work, until quite a large mass of starch is accumulated there. If we examine the plant at night, some time afcer darkness has set in, we find no traces of starch in the cells of the Icares, There is evidence that the starch has been trans- formed into sugar, and can then, by osmotic and perhaps by other processes, be removed from the leaves, and
;z TOar«^scscXEK»trS»i~:.
134 TAe Study of Animal Lift mm u
carried by -the vessds to aU parts of the plant. So we get a first notion of how a plant is fed. Starch is a com- pound containing carbon and the elements of water. The carbon, we know, comes from the carbonic acid of the air; the water is absorbed by the roots from the soil. In some way the Uving matter of the cells, by means partly of the green colouring matter, is able to transform the energy of the sun's rays into potential energy of a combustible substance
starch ; so we get clear evidence of a machinery for the
transformation of energy. We have taken a plant as our example throughout, partly because the cells are more evident than in anunals, and partly because the chemical processes give evidence of a transformation of kmetic mto potential energy more clearly than do those of animals ; for the animals eat the plants, and so by using the potential energy of plant substance are able to live and move.
We have now some idea of the sources of the energy of life. Plants get their food from the air by their leaves, and from the soil by their roots, which absorb water and salts dissolved in water. By aid of the energy of sunlight they build these up into complex substances, which they use for the growth of their living matter, for the formation of sup- porting structures, and for other purposes. Animals eat these substances. They build up their own bodies of living matter and supporting structures, and they move about.
In order to get a clearer notion of the nature of living matter we must attempt to trace the manner in which these various substances are built up. We have first to discover what arc the substances that are made. In all living creatures there are, in addition to water and salts, such as common salt and soda, three groups of stuffs :— ■
Carbohydrates, such as starch and sugar, made of carbon with hydrogen and oxygen in the same proportions as they
occur in water ; ' , , .c
F«/j— substances containing the same three elements,
but with a smaller proportion of oxygen ;
/»«?/«<&— substances containing always carbon, hydrogen, oxygen, and nitrogen, with a small percentage of sulphur.
The constitution of protcids is difficult to determine.
cbjlT. Tin
Vitality
«3S
The above elonents are always present, and in proportions which vary within narrow limits; but in addition to these substances there seem to be always present others which, wheti the proteids are burnt, remain as ash in the form of salts chiefly chlorides of sodium and potassium, but also small quantities of calcium, magnesium, and iron, as chlorides, phosphates, sulphates, and carbonates. The mole- cule of a proteid must be very complex ; thus that of albumen is, at its smallest, Cggg, H^gj, N^^,, Ogg, S^; most probably it is some multiple of this.
The food-stuflFs of plants, then, are salts, water, and car- bonic acid, and a certain amount of oxygen. Of these, by means of the sun's energy, they build up complex substances — carbohydrates, fats, proteids, which, with salts, water, and oxygen, serve as the food of animals. The living matter, the machinery by which all this is done, is, if it can be classed at all, a proteid. But this only means that all living matter contains the five essential elements and some others which in the ash exist as salts.
The various services which the different food-materials are set to within the body will be described later, when we are considering the details of the animal economy. Here we shall take note of the elements that enter into the construction of the food-stuffs.
7. The Chemical Elements of Life. — There are sixty- eight elements to be found in varying abundance upon the earth, but by analysis of the food-stuffs and of living matter itself, we find that only twelve of these occur with any con- stancy in oi:ganisms. They are carbon, hydrogen, oxygen, nitrogen, sulphur, phosphorus, chlorine, potassium, sodium, calcium, magnesium, and iron.
Now nine of these elements form sixty-four per cent by weight of the earth's crust; while aluminium and silicon, substances that are only very occasionally found in living creatures, form thirty-five per cent, being the chief consti- tuents of quartz and felspar, sand and clay, in short the greater part of all rocks. All the other elements, three of which — hydrogen, nitrogen, and phosphorus — enter into life, form the remaining one per cent
13*
The Study of Animal Life part n
Since the ultimate analysis of the objective side of life seems to show that life is to be pictured as matter in an unstable and constantly altering condition, it will be of interest to find the conditions that determine which of the elements are to take part in it.
It seems that matter in order to enter into life must be —
(i) Common, (2) mobile, that is capable of easily entering into solution or becoming gaseous, and (3) capable of forming many combinations with other elements.
Nine of the elements fulfil the first condition ; a tenth, nitrogen, is the chief constituent of the atmosphere; while hydrogen is present everywhere in water. Why do not aluminium and silicon take their share in life ? Because they do not fulfil conditions (2) and (3). Their oxides are quartz and aluminia, two of the hardest substances known. Emery and ruby are two forms of aluminia ; while the oxide of carbon, the source of all the carbon used in life, is a gas.
CsLrbon, which takes so great a part in life processes that the chemistry of organic substances is commonly spoken of as the chemistry of the compounds of carbon, fulfils all three requirements in an eminent degree. For although in its pure form a solid, and sometimes a very hard substance, yet it readily forms an oxide which is present in the atmosphere, and, as we know, serves as one of the chief foods of plants. Its power of entering into combination with other elements is practically infinite. Nitrogen, although by itself an inert form of matter, is able to combine with carbon compounds and add fresh complexity.
It is easy to see why water is so important in life. It dissolves the other substances, and so allows them to come into closer contact, and to change in position more easily, than if they were solid. So the first stuff that was complex and unstable enough to be properly described as living was almost certainly formed in water, long ago, when the condi- tions of greater heat, and consequently greater mobility of all substances, made chemical changes more active.
The importance of the solvent power of water m a com- plex organism is obvious when we think of the blood, the great food stream and drain. It is shown in an interesting
CHAP, vni
Vitality
m
way by the suspended animation of a dried seed, which will remain for years dormant, but ready when moistened to spring mto active life.
How, then, are these substances built" up into living aeatures ? Let us, that we may see this matter clearly, think for a moment of the conditions of life of the simplest creatures, the formless masses of living matter. All that the simplest plants need is water holding oxygen, carbonic acid, and salts in solution. Out of these simple materials by the magic touch of their living bodies, they can build up
Z' - ~- \
B
P V- ...
y
^ /
y"
/
X
the complex matter of which those bodies are made; so that they can grow and divide until there may be hundreds in place of a single one. The image we must form of this •ncrease of hving matter is that step by step substances of an ever-growing complexity are made, one from the other, unt.l at last a substance so unstable is made that it begins to break down into simpler forms of matter at the least deviation from the precise conditions in which it was made and perhaps also with a ferment-like action causes changed
138 The Study of Animal Lift partii
in aU that it touches; and this we caU the living matter As this living matter breaks down into simpler substances, or as it causes surrounding substances to break down, energy is set ffee for use in movement. We may make a diagram of this process. The steps go up and down ; the top one we call protoplasm (Fig. A). This shows only one line of ascent and one of descent There niay be many, al going on at the same time, as is shown m Fig. B. But these are much too simple ; they show contmuou« ascending and descending stairs, but each step does not really result directly from the one below, but must result from two or more stairs meeting; and at each meeting there must be substances formed -^hich are useless, and begin to break down, or are cast out of the system at once.
8 Orowth.— The power of growth, of adding to itself subslance of the same nature as itself, is the real mystery of living matter. A crystal grows out of its solution he star or pyramid is built up with perfect regu anty, but the process is much simpler than the growth of living matter. The substance of which it will be formed is already there, but the protoplasm has to make its own substance as U grows. This is the true difference between the two pro- cesses, and not, as is usually stated, that a crystal grows by depositing matter on its surface, while a cell grows by putting matter within itself. For when two cells fuse, which of en occurs, growth is really as much by aggregation as in the case of a crystal, and such manner of growth is made possible simply because the two cells are masses of matter of equal complexity. But when less complex matter is given to a cell it cannot add that matter to itself until it has been transformed into substance as complex as itself, ims change can only be effected within the little laboratory of the cell itself. The fact that the growth of a crystal may be endless, while that of a cell is limited, which is usually cited as the distinctive difference, is a consequence of the necessity of the protoplasm for forming its own substance within its own substance. For when a cell grows m sue the ratio of its surface to its volume constantly decreases, and therefore, since new material can only be absorbea
CHAT. VIII
Vitality
139
through the surface, there must be a certain size of cell at which the rate of absorption is just sufficient for the nourish- ment of the protoplasm. Beyond this point a cell cannot grow ; but if it divides, then the mass to be fed remains the same, while the absorbing surface is increased. This, then, is the necessitating cause of cell-division. But it would be unwise to suppose that there are not other causes that help to produce this result, which has as a consequence the possibility 01 Timense variety of disposition of the daughter cells, and therefore of organic forms ; for, to begin with, a more obvious means of obtaining increased surface would be for the cell merely to become flattened or to spread out irregularly, which, indeed, we see in many of the Protozoa.
Since their growth implies cell-division as one of its con- sequences, and since cell-division is the basis of reproduc- tion, synonymous, indeed, in the Protozoa with reproduc- tion, we get the idea of successive generations of animals as merely the continued growth of former generations. This makes intelligible to us all the facts of heredity which are so surprising if we conceive of each generation as a number of untried souls that have left some former dwelling-place to come and live among us. Our children are, in truth, abso- lutely portions of ourselves. If this be so, we must imagine in the ovum — the tiny mass of protoplasm from which we are formed by continued division — a most extraordinary subtlety of constitution.
Try to picture the complexity of the arrangement of parts. There are two tiny masses of protoplasm ; so far as we can see they are the same, yet from one will grow a man, from the other a tree. If the germ that will grow into a human being could only properly be fed outside the body of the mother, so far as we know it might leave that body as an almost invisible cell, and would grow and divide, add cell to cell, until the creature was fully formed — sculp- tured out of dust and air. Our early life within the womb, our nourishment by the blood of our mother, is only nature's way of preserving us from injury. What we shall be is already marked out before the t%% begins to grow.
It is only the highest animals who are thus shielded.
:ll;j
I40 The Study of Animal Life »a»t n
The birds cover their eggs with their wings. The butterfly lays hers where the grubs will find their food. The star- fish cast theirs adrift in the sea. The same story is true of the flowers. They are the nursing mothers. In their heart the young plant grows until the first leaves appear ; not till then does it drop away, and not without food prepared and placed ready for use— enclosed in what we call the seed. But the seaweed, like the star- fish that crawls upon it, allows its young seeds quite unformed to be floated away by the tide.
All seeds, then, are parts of the living matter of the parent ; some leave naked and without food ; others are protected by shells or by husks which are filled with food ; others live within the mother until they have ceased really to be seeds, and are fully formed new creatures.
Now the living matter of any sir'nie organism is so much
the same throughout the whole bouy that almost any part
of it will do to build the new generation om. Thus,
although the sea-anemone does sometimes set apart certain
cells as seeds, yet any part of the body will, if cut off, gi w
mto a complete creature. The same thing is true of a moss
pUnt But the more highly organised animals have their
living matter set to such different service in their various
organs that most of it does not keep all the qualities of the
whole creature, but only of that part to which it belongs.
Thus if a starfish lose its arm, another will grow from the
stump. A snail can in this way repeatedly regrow its horns.
Even so highly developed an animal as a lizard can grow a
new tail. With ourselves this power is confined to growing
new skin if we lose part of it, or mending a bone if it be
broken, and other similar processes.
When we clearly understand in what way the offspring of all creatures arise from their parents, how they are, as Erasmus Darwin said long ago, like separated buds, then we see the truth of the often-made comparison between any or all species of animals and an organism. The individuals of a species are not indeed bound togethei by protoplasmic strands, but thei? interdependence is not less complete. A •ingle species utterly destroyed might modify the life of the
CHAV. VIII
Vitality
141
whole earth. Life itself is dependent upon the invariable presence of minute quantities of iron in the soil A wan- dering tribe of savages is an organism not quite so high in the scale of social organisms as is the hydra in the scale of individuals ; for the cells of the hydra, although divided broadly into an outer and an inner layer, are yet more divided in their functions than are the members of a savage tnL?. For there are only two kinds of person in such a tribe — hunters and cooks ; while a highly civilised community, with its immense variety of workmen, is prob- ably not so well organised as any mammal ; for there are in such a state thousands of persons, untrained to any special labour, merely a burden to themselves and to the nation.
9. Origin of Life.— We have said that life probably began when the conditions of heat and solubility of sub- stance were more fovourable to the formation of peculiar and complex matter than at present But such a state- ment is often thought to be unphilosophical in view of the fact that we have at present no experience of the foiiuation of such substances, and that it has been conclusively proved that living creatures always proceed from pre-existing life. But those who urge such objections forget that all that has been proved is, that the simplest creatures known to be alive at present can be formed only by cell -division one from another, and not from simple chemical materials. But we must remember that those simplest animals are highly developed in comparison with the complex matter from which we conceive life to have sprung; and no one would now expect that such comparatively highly developed animals could arise from simple matter. There is certainly no evidence of the formation at present of the very simplest and original living matter. But, in the first place, could we see it, even with a microscope, if it were to be formed ? Might it not be formed molecule by molecule ? And, secondly, what chance of survival would such elementary creatures have among the voracious animals that swann in all places where such simplest creatures might possibly be formed ? Instantly they would be devoured, before they could grow large enough to be seen.
ift
f~ •■'?*i;;'*5
I4«
The Study of Animal Lift part ii
Lastly, let it be carefully observed, such a belief as this as to the origin of life, and of the basis of all life in chemical processes, carries with it no necessary adherence to the doctrines of Materialism. The materialist analyses the whole objective world of phenomena into matter and motion. So fiu:, his conclusion is perfectly legitimate ; but when he maintains that matter and motion are the only realities of the world, he is making an unwarrantable assumption. Matter in motion is accompanied by consciousness in our- selves. We infer a similar consciousness in creatures like ourselves. As the movements and the matter differ from those that occur within our body, so will the accompanying consciousness. The simplest state of affairs or " body " we can imagine is that of a gas such as hydrogen. But such a simple sUte of matter may have its accompanying consciousness, as different from ours as is the structure of our bodies from that of a hydrogen molecule. This is, of course, also an assumption, but it is one that harmonises with the facts of experience.
The opposite extreme to Materialism is Idealism, and in this school of philosophy an assumption precisely similar, and exactly opposite to that of Materialism, is made. The idealist says the objective world of phenomena has no exist- ence at all, it is the creation of mind. An objection to such a theory lies in the question. If matter and energy are the creation of mind, how is it that we find them to be indestructible ?
Popular philosophy has mi.le an assumption which lies midway between these extremes. It postulates two reali- ties, matter and spirit, having little effect upon one another, but acting harmoniously together.
But the view that is here set forth postulates neither matter nor spirit, but an entity which is known objectively as matter and energy, and subjectively as consciousness. This philosophy goes by the name of Monism. The term consciousness is used for lack of any other to express the constant subjective reality. Carefull/ speaking, it is, of course, only the more complex subjective processes that form consciousneAt.
CHAPTER IX
THE DIVIDED LABOURS OF THE BODY
I. Divisim of l3b<mr—%. The FutuHons of tkt Body : Movement; Nutrition', Digestion; Absorption; The Work of the Liver and th* Kidn^t; Respiralitn; Circulation; The Chtmges within th* CeU$ ; The AcHvititt of th* Nervous System— 3. Shetch of Psychology
I. DiTision of Lftboor.— The simplest animals are one- celled ; the higher animals are built up of numberless cells. All the processes of life go on within a single cell In a many-celled animal the labours of life are divided among the various groups of cells which form tissues and organs. The history of physiological development is the history of this division of labour.
When a dividing cell, instead of separating into two distinct masses, remained, after the division of its nucleus, with the two daughter masses lying side by side, joined together by strands of protoplasm, then the evolution of organic form took a distinct step upwards, and at the same time arose the possibility of greater activity, by means of the division of labour. For when the process had resulted in the formation of an organism of a few doien cells, arranged very likely in the form of a cup, the outer cells might devote the greater part of their energies to movement Md the inner cells to the digestion of food. In the com- men Hydru the body consists of two kyers of cells arranged to form a tub^ the mouth <rf which is encircled by tentacle*,
ii
^iL_
T:^^
V;^,>.
144
TAe Study of Animal Life part n
The cells of the outer layer are protective, nervous, and muscular ; the cells of the inner layer are digestive and muscular. The cells of Hydra are therefore not so many- sided in function as are Amoebae. In animals higher than the simplest worms, a middle layer of cells is always formed which discharges muscular, supporting, and other functions.
With advancing complexity of structure the specialisa- tion of certain cells for the performance of certain functions has become more pronounced. In the human body the division of labour has reached a state of great perfection ; we shall give a slight sketch of its arrangements.
2. Th« Functioiis of the Body.— Our objective life consists of movement, and of feeding to supply the energy for that movement Growth, reproduction, and decay are elsewhere treated o£
Movement. — We move by the contraction of cells massed into tissues called muscles. Contractility is a property of all living matter ; in muscle-cells this function is predomi- nant This is all that need be said here of movement ; the processes of nutrition we must follow more closely.
Nutrition.— AM the cells of our bodies are nourished by the stream of fluid foodstuff, the blood, which flows in a number of vessels called arteries, veins, or capillaries, according to their place in the system. From this stream each cell picks out its food; and into another stream— the lymph stream — moving in separate channels — the lymphatics, which, however, join the blood channels, each cell casts its waste material ; just as a single-celled animal takes food from the water in which it lives and casts its waste into it
Nutrition must therefore consist of two series of activi- ties. One series will have for its object the preparation of food-matter so that it may enter the blood, and the excretion of waste products out of the blood. The other series will consist of the activities of the individual cells,— the manner in which they feed themselves.
The first step in the preparation of the blood is digestion Most food-stuff is solid and indiffusible ; before it can enter the Wood it must be made soluble and diffusible. The
CHAR a "^^ I>ivided Labours of the Bcdy 145
supply of ojqrgen to the tissues is also a part of these first processes of nutntion. Being a gas, it is treated in a special way which will be described imiiediately.
Dtgestwn.—T^^ various food-stuffs have various chemi- cal qualities. After being swallowed they enter a.C ube, the digestive tract or alimentary canal. ^Jithif this canal they are subjected to the action of variois digestive juices prepared by masses of cells called glands Saliva IS one of these juices, gastric juice is another pancreatic juice is another. The effect of these juices upon the food IS that most of it is dissolved in the juice and made diffusible. Thus we see an example of the division of labour. An amoeba flows jound a soHd particle of food and digests it. In the higher animals the Ss of
tt tTriiS^elr ^^^^"'^'"^' ^°^ '""^ ^^-'- «^-
AbsarpHoru-m^x the food is digested it leaves the alimentary canal, and is absorbed into the blood-vessels and lymphatics in the walls of the canal. Absorption Ts not a mere process of diffusion. It is diffusion modified by ?he cells hnmg the alimentary tract Certain chemical changes are effected at the same time. Most of the absorb^ ?^
TbUd t ""/' '",! *'^ '^* ^^^ not go directly t^ the blood being first absorbed into that other system of
S\**u^'"P^"*'*^- Eventually it also getsTnto the blood ; for the two streams are connected
.f2!v ^'^^ "-^ tf^ Liver and the Kidneys.~.T\,^ cells of the liver secrete a juice called bile, which is poured into ?n ^'T.*?"^ ^^^ "^^ «^^* ft^-^ction of this j^dis
u t° is ? • }' ''' ' '"^.^" "'* '" ^^« '^•^^^'on o" fat .0 nc^^^' .K f ^^ ^" *'5''^''°"- "^^ »t^«^ of food-stuff going to the hver contains sugar, the result of the digest"" 0 carbohydrates ; albumen, the result of the digest b^^S absorption of proteids ; and certain waste Sgen^us matter, formed during the digestion of proteids "'*'°^*"°"
themseh'e'^lli^' "'^"' "^'^ *^* '"^"' '^^''^ »» '^'thin « InJ " •. ""' '°'* °^**y *^^» ^ Pot«^t° »to«s up
*r as IS known they do not affect the albumen in any way,
«iS«j5::-.<«"#=«^«' ;
146 The Study of Animal Life part n
but the waste nitrogenous matter is altered and then sent on in the blood stream to the kidneys.
The cells of the kidneys take this stuff, which was pre- pared in the liver, and other waste nitrogenous products out of the blood, pass them and a certain amount of water along'to the urinary bladder, which empties itself from time
to time.
Respiration. — Breathing consists of two distinct acts, inspiration and expiration. During an inspiration air is drawn into lungs. Thence the oxygen passes by diffusion, modified by the fact that the essential membrane is a living one, into the blood. There it enters into a loose combina- tion with haemoglobin, the red colouring matter of the blood cells, and is thus carried to the cells of the tissues to be absorbed into their living matter. During an expiration we breathe out air which has less oxygen and more carbonic acid gas than normal air. The carbonic acid is a waste- product formed by the cells of the body ; it first enters the blood, is then carried to the lungs, and leaves the blood- vessels by a process of diffusion similar to that by which the oxygen entered. The close association of these two processes is simply due to the fact that an organ fitted for the diffusion of one gas in one direction will do for the diffusion of all gases in any direction.
Circulation. — The blood is maintained in a healthy state by the processes we have described. By the active con- traction of the heart it is pumped round and round the body, continually carrying with it fresh food to the tissues, and carrying away with it the waste matter cast out of the tissues. All the blood-vessels, except the very smallest, have muscular walls. The heart is a large hollow mass of muscles, is a part of a pair of large blood-vessels that have been bent upon themselves, and arranged so as to foni\ four separate chambers, two upper and two lower, an upper and a lower opening directly into one another on exich side. By the contraction of the lower chamber of the left pair the blood is forced through all the vessels of the body ; these collect and empty the blood into the upper chamber of the right pair ; from this it passes into the lower chamber on
CHAP. « Tks Divided Labours of the Body 147
the »me side, and from this it is forced through the vessels of the lungs, returning to the upper chamber of the left side, and so to the lower chamber of the left side
The way in which the blood is able to nourish the
tissues isasfollowsr—The outgoing vessels-arteries-enter each mass of tissue; within it they break up into number- less very small, very thin-walled vessels-capiUaries ; the blood oozes through these into the smaU spaces— lymph spaces-that occur throughout the tissues ; adjacent to these
rf?n"l *" "^^.l^'' ^^•'^^ ^^''^ ^•^""^ ^^^ lymph-the fluid that fills the small spaces and the vessels connected with them— what they need, and cast into it their waste. The lymph spaces open into lymph vessels, which, as has been noted, jom the blood-vessels. Oxygen and carbonic acid, being gases, pass directly from the blood through the walls of the vessels to the tissues, and from the tissues to the Dlood.
The Changes within the Cells.-ln speaking of proto- pbsm an outhne of the kind of knowledge that ^ve possess of the chemical changes that take place within the cells has been given. We know little more than the sub- stances that enter the cells and the substances that leave tnem.
Perhaps even this is too much to say ; n ,re exacUy, we know the substances that enter the body by the mouth and nose, and through the alimentary canal and lungs: we know the substances that leave the body through the kidneys, and, in expiration, through the nose. A laree amount of water and traces of other matters leave the body M perspiration ; but the chief use of sweating is probably 7ZT IT °/»^« temperature of the body, and the skin
way that the kidneys are. The undigested matter that
^^ITa '*'' ^"^-"^J^^ ^''^ "ever been within the blood, and does not therefore concern us in this inquiry. • But we know very little more than this ; the analysis of
ur^n'Z'J,*'^"^'^ *\" *"y particular mass of tissue exerts u^n he blood-,.* the differences that must exist between "« substances entering it and the substances leaving it— i«
i I
148
Thi Study of Animal Lift faet n
very difficult of detenzunation, because of the immense quantity of blood that passes through any tissue in a short time. This concludes our sketch of the interchange of matter within the body.
The Activities of the Nervous Systetn. — We have now to consider the arrangement of the nervous system — first merely as the means by which all the varied activities of the tissues of the separate parts of the body are co-ordi- nated and wrought into an harmonious series of artions, and then as the associate of consciousness and of mental processes.
Just as protoplasm may be called the physical basis of life, so is nervous tissue par excellence the physical basis of consciousness and of mind. Throughout the whole animal kingdom it has a superficial similarity of structure, and consists of the same three parts.
(i) First there are cells adapted to receive notice of change in the outer world. Changes in the sur- rounding medium and affecting such cells are called stimuli. These cells sensitive to stimuli form the chief part of the sense organs — the eyes, ears, nose, tongue. Also in the skin there are cells sensitive to alterations of touch and temperature. The effect of stimuli upon such cells is probably to set them into a state of molecular agitation, which may or may not result in chemical changes. (3) There are connecting fibres or nerves, which, being connected with the sensory cells, take up the vibrations or possibly the chemical changes of the sensory cells and transmit them to the « centre." (3) There are "central" cells, in which the nerves end, and which are set in molecular agitation by the vibrations of the nerves. This molecular agitation is often, when the central cells are in the brain, accompanied by consciousness. Ap- parently also agitations may arise <* spontane- ously" within these central cells and stimulate
CHAP. IX The Divided Labours of the Body 149
Aft outgobg neives, and cause muscular move, ments, or the activity of glands, or other cellular activities.
In many ways analogous to the nervous system is
i%hlT^^ ^^^ °^ * ^°""^' *^« receiving rt^ons are the nerve cells, among which are the cells of the se^se organs; the connecting wires are the nerve fibres ^he cen^ stations are the groups of cells called ^ll ?« ch,ef of wh.ch are in the brain and spinal corA^fhe less important gangha are like the bmnch offices, they recdve
are like the offices of a government, in which messages are received, plans elaborated on the strength of the news and orders sent out to various parts of the country Tl 'such
anUL'lr?'" '''.' ?^^^ •" ''^ nervouTsysVl are called reflex actions, whether a received messasre be s^nf
on unaltered, or whether the receiving cTu refSla^s the body. The analogy of telegraph stations, even with the iS^f .V°/'' them and with responiible pe"o„s to
t^^^ti^^S'nt: -"ir ' "^"^^ '"- --^'^^ ^^- ^
3- Sketch of Psychoicgy.—The following is lanrelv
iT^' to which we refer the reader, and to which^e acknowledge our indebtedness. '
caulLr*b!^°tL^P^"!.*** "^^"S^'^^ » "ervous matter. »used by changes m the outer world, result in what we call a change of consciousness * m wnai we
ner^t^er t^'cllirs^^^^^^^^^ ^'^^^ '^^ ^^-^^-- «' imp^reSs.°^'°°'''*'"'"*'' P"^"^^^ ^^ »*'°^"»' "* called
WvL orllJ • "P°° ™'"°'^' "^^ memory is the re
'^val of past impressions, which, we must suppose, have b
-■-v-;rg<Vi'.!^t^^j«lg
I i
1
!
150 The Study of Animal Life part n
some way been stored within the cells of the brain in the form, from the objective point of view, of a certain arrangement of its particles.
When, after the revival of past impressions, we are able to discriminate between them, we call them sensations.
Now sensations are referred, in consciousness, not to
Fig. 31.— Attitude of a hen protecting her brood against a dog (From Darwin's Expression 0/ Emotions.)
the brain cells which discriminate between them, but to the cells of the sense organs which received them.
Further, we refer, by experience, the causes of sen- sations to the outer world. We do this by a mental pro- cess which is called perception.
Now out of perceptions, and through associations, there arise expectations. The mental process involved in the formation of an expectation is called inference.
CHAP. IX The Divided Labours of the Body 151
Inference is of two kinds :
(1) Perceptual, drawn from direct experience, as in
the inference as to a rain storm from a black cloud.
(2) Conceptual, which, though based upon experience,
yet can predict events that have never been experienced. For instance, one who had studied in books only the causes of volcanic activity, might predict with a certain amount of confidence a flow of lava from a volcano, when he saw it in that state of activity which he knew usually pre- ceded an eruption of lava. What we call the emotions, love, hate, fear, and others, are, so far as we can tell, agitations of nervous matter which affect consciousness. Their exciting stimuli— infer- ences for example— proceed, immediately, from within the brain, ultimately, from changes in the outer world.
We have, therefore, the following orders of conscious- ness, which are easily distinguishable in theory :
(1) Impressions, or the effects of environmental
changes upon nervous matter ; the retaining and revival of these constitutes the basis of memory.
(2) Sensations, which occur when the differences that
exist between impressions are discriminated.
(3) Perceptions, which are the outward projections
into the world, by mental acts, of the molecular disturbances caused in the brain by environ- mental changes. For example, light falls upon the retina, stimulates the optic nerve, and causes a molecular disturbance in the brain, but the consciousness excited in us is not of the brain disturbance, but of the light. It is most essential that the distinction between per- ceptual and conceptual inference be cleariy realised, as it is probable that it is the faculty for the latter which more than anything else separates man from the lower animals. We may be nearly certain that many animals exercise per- ceptual inference, and we may affirm with little doubt that none has ever performed a conceptual one. It has been
iSa
Th Study of Animal Lift pakt ii
stated that a monkey that had learned to screw and unscrew a handle from a broom had learned " the principle of the screw." This is entirely erroneous. The monkey merely observed that a certain move-^-^nt given to the handle caused it to separate from the bioom, and inferred perceptually that the same result would always follow from the same action.
It is evident that a sound comparative psychology of the animal kingdom, or even of a few of the highest species, is beyond the present possibilities of science.
A^as^^aaa^'szz-.^ sx.-
^I^»
CHAPTER X
INSTINCT
'%
X i.,fii-rai
3-
U
lagsofthe Term— 2. Carefvl Usage of the Term— rumples of Instinct-^ TAeOrigii^fiJsii^''^^
--iuermg the mental life of animals, we must settle /ar r. is comparable to that of man. We judge of the v.er.J p ocesses of human beings, other thin furSveT dTr '^'''?i^''^^^\^^ we can only do the sa^e whe2 deahng with ammals. If we often err in irSiiT Ae mental states of our feUow-men, how much more^^efiaSe
uX: ItiTw ~""'^""^ ^"^^""^ different Sm h1 kTI u?^ believmg as we do in the continuity of
IS probable that m time we may arrive at a certain state ^^Z"^t^T'^ '" comparative psycho^
surely from sensations, the world of every creatui/mtS be largely constructed from its dominant sense ; i^ a X for instance, fro: . scent. . m a aog,
ta 5l".^°!^°2n*^ '^'^^ *^* *^^'*^"« o^ animals are all ascribed
wW^e the a^^' r °° "'^^ ""^^^"^ '^- termis £tt While the actiors of men are determined by reason, those of
hTt ^' f \P«>°»Pted by a blind power of doing Sat which « fitted to the successful conduct of their livl This. aS
iT' ?T? "°*'°° *"* ^'^"»«» modification. ' • «neS^ y!^*^'''*?* **™ Iiurtliict-Every one has •geneml notion of what is meant by insimct, but few ar^
l.-y
X i k
MHii
i|P
iiMM
I I
»54
The Study of Animal Lift part n
agreed as to the precise usage of the word ; thus when the birds build their nests, or when the bees collect honey and form the:: combs, their acts are vrith one accord said to be mstinctive ; but some would demur at using such a term to describe the love of parents for their children, the courage of brave men, or the artisf s perception of beauty. But, even supposing we agree to mean by instinct all those actions which are neither simply reflex nor purely rational, there will still remain great difference of opinion as to its origin. Thus the love of parents will not be imagined as due to practice, either in the individual or its ancestors, but rather to take origin in some hidden necessity of nature ; while the rapid closure of the eyes as protection from an expected blow would seem in all likelihood to have begun in a rapid exercise of intelligence, which, by being often repeated, had ceased to be accompanied by conscious effort.
It seems to us that there is still need of a vast amount of observation and experiment before a theory of the origin of instinct that will be at all satisfactory can be framed. As already remarked, it is not easy to decide even in what sense the term ought to be used. This being so, we shall content ourselves with mapping the field of thought and indicating the lines of inquiry that must be followed before a just view of the subject will be possible.
If we arrange examples of all the movements of animals in the order in which they are performed in the lifetime of the individuals, not limiting ourselves to those acts which involve the whole organism, but considering also those which a single organ or mass of tissue may execute, wi shall see at a glance all the possible varieties of activity with which we can be concerned. It is, of course, only the move- ments of comparatively large masses of tissue with which we can deal at present. The molecular movements which lie at the base of all the visible ones are as yet a'nost unknown.
Even before birth, visible movements of the parts of the higher animals occur ; as, for instance, the beating of the heart Such movements may be either " automatic " or reflex. At birth, in addition to such movements of its parts,
OUBiZ
InsHttct
"55
VA
%
(2
(3)
the oisranism a^ as a whole ; it reacts to its environment, and m fame performs " voluntary " actions.
The acts of the parts of an organism may be—
(1) "Automatic," as, for example, the beating of the
heart
(2) Reflex, as, for example, the intestinal movements
which force the food through the alimentary canal, or the movements involved in sneezing.
(3) Mixed actions which are partly automatic and
partly reflex, such as the respiratory movements. The movements of the entire organism may be of a verv complex nature. They may be—
(i) Reflex ; as when we start at a sudden noise.
"Innate," commonly called instinctive ; these are best observed in newly-born animals, for in them intelligence, which must be based upon experience. IS necessarily at a minimum. "Habitual," such as are rapidly learned and are then performed without mental effort, which imply an mnate capacity, and are therefore allied to (2)
(4) Intelligent, such as imply mental activity, which
consists in the combining and rearranging all the other possible acts of the order— (i), (2) or (3) • and which may be recognised in all adaptations to novel circumstances. ^ This classification possesses most obvious faults, but it
tlT^'^l "^^Tl' J^ '^""^^^ »«'"« °f th«= difficulties th deUy the would-be definer of instinct. For the essen- tial criterion of an instinctive action is that all the machinery
^'.H %^ L""''"^^ " * '^^^'' *° * ""**" «i'«"Iu», lies ^ady formed within the organism ; but the apparently in- soluble questions present themselves, How soon may not actions be modified by intelligence ? "and How in a mature ^rirT- "^"'"^'^•■^♦''^ experience i. one to separate L^inTvlract'sr'" "'' '^°" ^'^ •"^^"'^^"''y "^^^''«-^ Also it !, evidem that "habitual- actions may be "instinct- ive actions deferred until the creature be further dev-1- opeu, as the flight of many birds is deferred j or they may
'■i
156
The Study of Animal Life »a»t i
be actions in the formatiott of which intelligence has had a cosiidetable share.
Now all these activities of an entire oigmnism may be studied from four points of view : —
(i) Of natural history, or general description, such as
occurs here and there throughout this work : (a) Of physiology, or the analysis of the muscular, nervous, and other mechanisms involved ; as treated generally in the last chapter :
(3) Of psychology, or the investigation into the states
of consciousness and mental processes concerned ; as sketched in the last chapter :
(4) Of aetiology, or study of the factors in their origin
and development.
We shall first define more carefully than we have yet done what we shall speak of as instinct, then give a few examples, and finally discuss the aetiology of it.
2. The Oareftil Uiage of tbe term Instinct.— We Iiave enumerated all the possible varieties of action, and the pos- sible states of consciousness with which they may be asso- ciated have been described in the last chapter. If we retain the use of the term instinct we must explain to what ordei of activity we shall apply it. In our use of the term we shall not strive after any great precision ; for, as already noted, the difficulty of precision seems to us to be at present msurmountable. In a general way we shall call any action which does not require for its execution any immediate exertion of perceptual inference an instinctive action. Thus a burned child dreads the fire ; such dread and its const quent avoidance of fires may, with propriety, be termed instinctive. After the first bum the avoidance will, for a short time, be the result of perceptual inference ; but in perhaps a few days only the avoidance becomes " instinct- ive" ; or it might be called " habitual," as hinted previoubiy. It is, of course, to be understood that an "instinctive"' action is not necessarily the result of this *' lapsed intelli gence," as it has been called. Thus, when a worci wrigg!es away from a fire it probably has not at any tin« reasoned out to itself the advantages of such procedure,
JV.-::
dUK t
Tmsimei
'57
yrt It may wdl be said to avoid the fire instinctively. It is obvious that, If we agree to use the tenn as defined, we must call aU the actions of the lower animals, whose con- saousness has never risen to the level of perceptual infer- jaice, instinctive. This definition is based upon the assump- Uon that we can determine the CMiscious states of animals • but, as we have repeatedly said, it ,s only within very wide' limits that we can with any certainty do this. The inten- tion, however, is to preclude all those actions which are certainly or probably rational, and at the same time include adaptive reflex actions.
Mr. Herbert Spencer has defined instinct as compound reflex action, while Mr. Romanes separates it from reflex
action and from reason as follows :
•• Reflex action is non-mentai neuro-muscular adjustment due to the inherited mechanism of the nervous system, which IS found to respond to particular and often-recurring sttmuli, by giving nse to particular movements of an adaptive though not of an intentional kind."
" Instinct is reflex action into which there is imported the element of consciousness. The term is therefore a generic one, comprismg all these faculties of mind which are concerned in consciousness and adaptive action, antecedent to individual experience, without necessary knowledge of the relation between means employed and ends attained, but similarly performed under similar and requently-recurring circumstances by all the individuals of the same species."
"Reason or intelligence is the faculty which is con- amed m the intentional adaptation of means to ends. It ^rcfore imphes the conscious knowledge of the relation Detween means employed and ends attained, and may be "wcised m adaptauon to circumstances novel alike to the ttpcncnce of the individual and that of the species."
Mr. Romanes therefore separates reflex action from ^mct,ve action by limiting the term instinct to th"^
Hbd,fin^?' •^'^' ^ * '"^"" °^ *^«' 'conscious reflexes. «tt definition is open to objection on the same ground that «« 's. only m a greater degree ; for it it easier to deter
rsd
The Study of Animal Life »a»t ii
mine the presence of perceptual inference than the absence of consciousness; this criterion may be of theoretical interest, — ^it is of no practical use. The other attributes he enumerates should be carefully studied.
Pro£ Lloyd Morgan also separates, but by no hard-and- fast line, the automatic and reflex actions, which are reactions to definite stimuli, from instinctive actions, which, according to him, are ♦* sequences of co-ordinated activities, performed by the individual in common with all the mem- bers of the same more or less restricted group, in adaptation to certain circumstances, oft recurring or essential to the continuance of the species."
He separates these from intelligent actions, which are ••performed in special adaptation to special circumstances." Instinctive activities he conceives to be perfonned " without learning or practice." If the actions need a Httle practice he calls them •• incomplete instincts" ; if a great deal of practice be necessary they are called " habitual activities' ; if they are not perfectly developed at birth but after further development can be performed without practice they may be called "deferred instincts." A further useful classification of instincts is into " perfect " and •' imperfect," according to the precision of their adaptation to the desired end.
Mr. Lloyd Morgan's definition, like the others, implies that one can separate rational from non-rational actions ; but he safeguards himself by defining instincts as " oft-recurrin!,' or essential to the continuance of the species," in ciutra- distinction to intelligent actions which are performed in special adaptation to special circumstances. It is important to notice that the terms of the definition are that instincts are either oft-recurring or essential, and not oft-recurrins,- and essential, for many instincts are only either one or the other and not both. But it is not always possible to say of a certain action that it is a special adaptation to a special circumstance, and is therefore rational, and not in reality an instinctive adaptation to circumstances that are of frequeiu occurrence although we have not observed them to be so.
This definition, however, emphasises the fact that instincts are common to species ; it is, however, not easy to cstimaie
CRAP. X
Instinct
«59
the exact significance of this fact, for the apparent similarity m the actions of individuals of the same species must, to a certam taUao^ be due to incomplefeness of observation.
It IS after <^SHi^ring all these definitions that we have come to the c<*c?usv>n that it is convenient to describe all those actions of animals which are not immediately rational or mtelhgent as instincts, li we classify an instinct as reflex m cases where the exact chain of internal events is known and use the other <^ifications already enumerated, we reach a simplicity and pw^^ioo of speech that is convenient
At the same time all such enteral m adaptiveness and similarity of performance in all the individuals of a species can obviously be applied as they are discovered.
The essential distinction, we believe, between non- mtelhgent, that is, instinctive, and intelligent actions, is that non-intelligent actions are performed in virtue of the innate and co-ordinated mechanisms of the organism whereas for an intelligent action the organism has to do a greater or less amount of the co-ordination for itself.
3. Ettmples of Inatinct-If we classify aU the actions
of animals accordmg to the period of life at which they are
performed, we shall find that there are three distinct clLses
Laratd ""^ *'*^ convenience be considered
They are —
(1) Those which are performed at birth, or shortly
afterwards, as perfectly, or neariy so, as at anv future time ; '
(2) Thoso more varied actions which are characteristic
of tiie mature life of any animal :
Ti^^/:^**°^* ^^'"^^ ^'■'^ associated with reproduction ihe first of these classes must evidently consist of very
pure mstmcts since the creature cannot be supposed to
reason before it has any store of experience
actions' n^•°"^ "'''".'' ^"" 'yP'^^*^ ^y '^^ marvellous actions of insects, such as ants, bees, and wasps. These
«iv l)e instinctive, but it is very probable that many of
Acni are, at least, improved by intelligence ^
i6e
TJIt Studf of Animal Lift paut u
(a) They may be perfected by perceptual inferences on the part of the individuals, and die mental efforts may or may not, after a certain number of repetitions, be replaced by reflexes.
{b) They may be perfected by less complex mental efforts, such as those involved in imitation or in receiving instruction from other members of the species.
Actions of the third class may be as purely instinctive as any of those in the first class, or may be improved by intelligence like those of the second class; but among them are many ot the most wonderfril performances of animals, for they often seem to show a prevision of an unknown future.
Some interesting experiments have been made upon instincts of the first class. The observations show that the precision of the neuro- muscular co-ordinations of some newly-born creatures is very surprising. Mr. Spalding blindfolded some chickens immediately after they were hatched, and removed the hood after two or three days when they were stronger. He says that " almost invariably they seemed a little stunned by the light, remained motion- less for several minutes, and continued for some time less active than before they were unhooded. Their behaviour, however, was in every case conclusive against the theory that the perceptions of distance and direction by the eye are the result of experience, or of associations formed in the history of each individual life."
«« Often at the end of two minutes they followed with their eyes the movements of crawling insects, turning their heads with all the precision of an old fowl. In from two to fifteen minutes they pecked at some speck or insect, show- ing not merely an instinctive perception of distance, but an original ability to judge, to measure distance, with some- thing like infallible accuracy. They did not attempt to seize things beyond their reach, as babies are said to grasp at the moon , and they may be said to have invariably hit the objects at which they struck, they never missed by a hair's-breadth, and that too when the specks at which they aimed were no bigger and less visible than the smallest A(A
CBAP. X
Instinct
i6z
of an i To seize between the points of the mandibles at the very instant of striking, seemed a more difficult opera- non. I have seen a chicken seize and swallow an insect at Uie first attempt; most frequentiy, however, they struck ive or SIX times, lifhng once or twice before they succeeded in swaUowing their first food." Again, « The art of scrap- mg m «»rch of food, which, if anything, might be acquired by mutation, for a hen with chickens spends the half of her time m scratching for them, is nevertheless another indis- puti^ case of instinct Without any opportunities of umtatioo, when kept quite isolated fi:Dm their kind, chickens began to scrape when from two to six days old. GeneraUy the condition of the ground was suggestive; but I have several tunes seen the first attempt, which consists of a sort of ntfvous dance, made on a smooth table." Another eiyerunenter "hatched out some chickens on a carpet where he kept them for several days. They showed no inclination to scrape, because the stimulus supplied by the carpet to the soles of their feet was of too novel a character to caU mto action the hereditary instinct ; but when a litUe gravel was sprinkled on the carpet, and so the appropriate or customary stimulus supplied, the chickens immediately Degan their scraping movements."
Another instance of the first class of instincts is the fear wd to be shown by many animals for their natural foes • but on this pomt we find a certain conflict of evidence' S"blS!!'o! "^ «5'd t° 'how disgust at a dog, and, while «»U blind, at a hand that has touched and smells of a dog. or to tremble with excitement at the smell of a mouse. A chicken « young turkey wiU show evident signs of fear at hearing «« cry of a hawk. Ants of various species that are mutually hosnle recognise an enemy, and fight; but, on the other ftand, there are observations to the effect that, if taken youne enough, ants of several such species may be brought up together as a happy family. orougnt up
,J^ instinctive lameness or wildness of many animals towards man is probably the effect of intelligence L infor
ZTLT?* '"^ T ^"°''''''= ^ » ^^*= «^°i<ian^« of the wae kmd of trap, after a short experience of its properties, by
II' '■
11 i
itffl TA€ Study of Animal Lift part ii
all the mice of a house or birds of a district The wild rabbit is extremely timid, but the domesticated variety is as tame as possible. In explanation of such cases we might easily invoke the ud of " the principle of cessation of natural selec- tion" when the safety of the species ceased to depend upon wildness, but we prefer to suppose that the direct action of intelligence is to a great extent operative.
As already noted, what are perhaps the most striking examples of instinct of the second class occur among in- sects. The comb-building of bees, the wars, the slave-using, the agricultural pursuits of ants, have been so often de- scribed that they need not detain us here. The brain of an ant was to Darwin the most wonderful piece of matter in the world. Wonderful, indeed, it would be if we supposed that all the acts of an ant were truly instinctive, that is, that the nervous machinery of co-ordination was ready, waiting only the appropriate stimulus to evoke any one of that scries of nicely-adjusted actions. But if we suppose that individual intelligence has a considerable share in that co-ordination, then the brain of an ant, though still very- wonderful, is not to us quite so astounding an arrangement of particles as it was to Darwin.
The third class of instincts, those connected with reproduction, comprise such actions as the building of homes and nests, the storage of food for the use of young that may never be seen, and the care of young after
birth.
The nest-building of birds would form a very good sub- ject upon whjch to experiment, in order to determine how far such a complex act may be truly instinctive, and how far it is perfected by training, by imitation, and by intelli- gent practice and observation. The method would be to isolate young birds from their parents and firom all other creatures of their kind, so as to preclude training and imitation, and then see how far the nests that they built resembled the typical nest of their species. Then one might remove other birds from their parents but allow them the society of the members of an allied species, but one whose nests diflfered to some observable extent from thoM
CHAP. X
Instinct
i«3
It IS stated tJiat the nests of RriHeiT u- j . Australia differ very grea!w from thl ^"'''u '^' ^"^"^ "" build at home. No«f S mt^ hi h "'''' '^' '''"^ *°"'^ training and the possil^Hues ^f' imitate thl' ^'^ ^^ °' or it may be due to th.. ah««^ 'minting the specific nest,
to build the charaJJeristifn:^^^^^ °'^^ ""^^"^^ "'^^ -^ch
or the selection S^rbune'r^^ofThrlt "'" "^^^^ ^^'^ ' lays her eggs, the only sort ofkaf it J.^LTk" ^^'"'^ ^'^^ the grubs, when hatched for ft^' f I^^>,*''^* '"'" ^^"^e butterfly herself d^s not eat^' Jl 1? ^'"^ ^^^'^^^ ^^e of instincts most ^vonderfunn Tk '^ ^^°'^ "' '^^"'P'w obscure in their or^^^ The ?J^' • ^"^^^^'^^ and most Plex for us to believe that th! nt' "'^°''''^ ^'"'^ *°° ^"n^- intelligence. sHa^as we c^nrat'" ''^ "^"'^ °^ mstmcts can only be accounted for by ^e Natu^%"!', T' of fortunate varieties of habit Th^/o T Selection habit of incubation are Sinrf? '^ °^J°""S^ ^"^ the amount of thought harLenS^^^ /'"'^ ^ *^^«-" incline to the idea whiVh ml ^°'* ourselves, we
such habits ar;t.:'o LTeSeT';^ ? ^°'"^' ^^^^ nearly related to the ^■^^ ^sTlf^'"'' '"^ ^^^*'* ^°
an explanation of suchlla^s'in tetsTat;. '''^ '^^^?« naturalists have suggested thi- '" ^™s of affect,on^ certain
that birds sit upon their ee«t ^J^^^^'^ ^'^^"^^ "ot'°n breast. If such were her o£ th^ *' '° '*^' ^ ^^^'^'^ a bird could select as her S m "l ""^^^ P'*^« ^^at nest containing egi whtl .'^^^°"'d ^e a wooUy hairy
changes gene^:^^aronhem^^^^^^^^^ °^ ^"^^^^ ^^--S
tion'o f instin^s t^^t^^i:^^' '''^^^ °^ ^''^ -- 'J^y by various otheTau^hnr! ^'■^1^^'^'^^ and since his A- R. Wallace and Prl^ ' ""^-^^'^ ^^- Romanes. Mr.
Weismann's S^trines hale T ^'"^^^ ' "''"^ ^^^^^^^o certain plausibirhy^^'er ^''^''''^'^^ '^^ revision of
'"""' o^ course, supposed that Natural Selection
i64 The Study of Animal Lift part ii
was the means of the evolution of habit as much as of
form. .
Mr. Romanes, starting from this as a basis, has con- structed a well-reasoned and lucid theory. He supposes that while many instincts have been evolved by Natural Selection, such instincts being called Primary, other habits become instinctive through the " lapse of intelligence." Actions performed at first with mental effort, becoming after suffi cient repetition so ingrained upon the nervous system that a mechanism of neuro- muscular co-ordination has been established, are referred to as Secondary Instincts. He imagines also a third class of Mixed Instincts in which there are primary instincts that have been altered and improved by intelligent variations of habit, or secondary instincts that have been modified by natural selection.
Obviously, therefore, he supposes that intelligence may be a factor in the formation of any habit that may be under consideration.
But this theory of instinct becomes impossible if we accept Professor Weismann's doctrine that acquired characters can not be inherited (this doctrine will be discussed in a later chapter). If this be true, the only possibilities are primar>' instincts, and secondary instincts formed afresh during each individual lifetime, and mixed instincts of the same nature. The exact antithesis to Professor Weismann's theory is upheld by Professor Eimer, who believes that instincts have been evolved chiefly by the perpetuation of what Mr. Romanes calls secondary instincts. There is little evidence that this is the case. The value of Elmer's work really lies in his insistence upon the intelligent action of animals as apart from purely instinctive action.
Mr. Wallace has begun the analysis of the particular forms which the intelligence of animals takes. He supposes that imitation of parents and other members of the species has a great influence upon the actions of individuals He has dwelt especially upon such cases as the song and nest- building of birds. . , .u,, It may be pointed out as a matter for consideration t.iat. granted that parents teach their offspring, as, for instance,
^vSiB^S?-
CHAP. X
Instinct
'<SS
birds teach the.r fledglings to fly, and ants their young their place m the community of the nest, and that animals imi- tate each other, it is quite possible, and indeed probable that an mstmct may be steadily improved throughout sud
!• 10. j..-Vuui.g duck* calcliiDg mollis. (iVom St. JoJu.s lyud S^U.)
cessivc generations by the intelligence of the individuals of a sivecies, without any acqiiirccl character being inherited therefore^"'''''' ^'''''"''' '" ''"' evolution of instinct are (0 Natural Selection, which miKht develop innate capacity; this is certainly insufficient for the devciopnient of form, and therefor.,-, probably, also of mind.
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(2) Individual intelligence, which directly modifies the
actions of individuals, and is also used when, by imitation and education, the habits of a species are steadily improved.
(3) The " lapsing of intelligence," forming " second-
ary," and helping to form " mixed " instincts. But the probable factors are the first twa
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i ii
PART III
THE FORMS OF ANIMAL LIFE CHAPTER XI
THE ELEMENTS OF STRUCTURE
I. ThtResemblanca and Contrasts between Plaftts and Animals- 2. The Relation of the simplest Animals to those which are
I^f 'f"^^K°^ ^T? ^"? '*™'=*"'"^ (Morphology), and the study of habu and function (Physiology), are both as essen- tial to science as the realities are in life. It is with the forms of animal life and their structure that we have now to do, but It seems useful at the outset to compare plants and animals.
i.ThB Besomblances and Contrasts between Plants and Animals.— Every one could point out some differences between a tree and a horse, but many might be puzzled to d.stmgursh clearly between a sponge and a mushroom, while all have to confess their inability to draw a firm line between the simplest plants and the simplest animals. For the tree of life is double like the letter V, with divergent branches, the ends of which, represented, let us say by a daisy and a bird, are far apart, while the bases gradually approach and unite in a common root.
Plants and animals are alike, though not equally, alive
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Diverse as are the styles of animal and vegetable archi- tecture, the materials are virtually the same, and the individuals in both cases grow from equally simple beginnings.
Even movement, the chief characteristic of animals, occurs commonly, though in a less degree, among plants. Young shoots move round in leisurely circles, twining stems and tendrils bend and bow as they climb, leaves rise and sink, flowers open and close with the growing and waning light of day. Tendrils twine round the lightest threads, the leaves of the sensitive plant respond to a gentle touch, the tentacles of the sundew and the hairs of the fly-trap compare well with the sensitive structures of many animals. The stamens of not a few flowers move when jostled by the legs of insects, and the stigma of the musk closes on the pollen.
Plants and animals alike consist of cells or unit masses of living matter. The structure of the cell and the apparent structure of the living stuff is much the same in both. We may liken plants and animals to two analogous manufac- tories, both very complex ; we study the raw materials which pass in, many of the stages and by-products of manufacture, and the waste which is laid aside or thrown out, but in neither case can we enter the secret room where the mystery of the process is hidden.
In the pond we find the eggs of water-snails and water- insects attached to the floating leaves of plants; in the ditches in spring we see in many places the abundant spawn of frogs and toads ; we are familiar with the heavily yolk-laden eggs of birds. Now, with a little care it is quite easy to convince ourselves that an egg or ovum is to begin with a simple mass of matter, in part, at least, alive, and that by division after division the egg gives rise to a young animal. We are also well aware that in mosi cases the egg-cell, for cell it is, only begins to divide after it has been penetrated, and in some subtle way stimulated, by a male unit or sperm. The great facts of individual history or development tlicn are, the apparent simplicity in the beginning, the joc liminary condition that the egg-cell be united with a male
CHAP. XI ne Elements of Structure ,69
unit, and the mode of growth by repeated division of the ovum and its daughter-cells. In those plants with wh ch we arc most familiar, the facts seem different, for we wa ch bean and oak growing from seeds which, in tead ofben^ simple units, are very complex structures. But the seed"! not the begmnmg of a plant, it has already a long Sil behmd ,t, and when that history is traced back tofhe sleZ box and possible seeds of the parent plant, there t wilt be seen that the beginning of the future he'rb o; tree is a s^'e cell This IS the equivalent of the animal ovum, and ifke •t, begins Its course of repeated divisions after k has been joined by a kernel or nucleus from the pollen g^n
Thus, to sum up, along three different paths we reach th same conclusion, that there is a fundament umty
T^^rttl thf st'"'"^^\ '" *'^ ^"^"^'^^ -'-" - .IhTm • u '^°"^^ ^"^ '"ortar of their structure and lastly, m the way in which each individual berins and grows, there is a real unity. ^
ThJf' *f^.^'/"'.PJa"ts and animals are very different
wide^ and bear diffelt^U^.^^Tie^'cTs^or^^^^^^^^^ and diversity are as undeniable as the inseparable S^ol he basal trunk and the genuine sameness of life throughout the whole tree. I have stated the chief contrast between plants and animals in a tabulated summary—
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The net result of this contrast is that animals are more active than plants. Life slumbers in the plant; it wakes and works m the animal. The changes associated with the
2T ? 'i^"''"^^^''^ seemingly more intense and rapid , the ratio of disruptive, power-expending changes to constructive power-accumulating changes is greater? most
nlan'tsdo %r"r "'''■^^. "^ ^° '''''' '^"-^ ^^an most plants do. They live 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 paT w.thin 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 thnft animals, and it is possible that some of the most chZvlTf ' r'^'^'-f °f 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.
whi'.'w! ^'^^*i?'' °{ *^' ®^Pl«»* ^inials to those r^Jat tnhT' ^rfle^-F'-on^ the pond-water catch in
t.Sfl °"' '^^ '"'^" ^"''"''*'^' ^"PP«^^ '^ ^^ ^ tiny
uater-flea or a mmute " worm » ; how does it differ from one
nnnv n,T 'f T^"^"' '"'^ "' ^" Ir^in.on^r. ? It consists of
nst is L i'Tf T'^' '"''^•'^^ °^«"'y °"^- The con-
hitchoH f '^^.\^*^^!^-^^" an ^^^ and the bird which is
cds J^I fr r'""."- '^'^^ ^'"^P'^^' '-^"""als are single cells, a 1 he others from sponge to man are many-celled.
cmlnJ? ^'■' """' '■ ^" others-the Metazoa-are
coniposite aggregates of units, or cities of cells
•I uormTf'*'' "'"' "f-°:^° "^ '•^^ Protozoa with that of ien Z' \ ^\ -^ ''"■^- ^^"'h ^'-^ ^'i^«. both may be
Se, S'^ " "sefu,, engulfing food, and getting rid of
1 nn %n??i T ^^^^'^'"S-' ^o-- «^^rbonic acid will poison
t'^nn. and dearth of oxygen will kill them ; both grow and
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Tfie Study of Animal Life part m
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 o the savage-at once hunter, shepherd, warrior-is more varied than ours.
Already it has been recognised that every many-celled ammal begins ts life as a single cell,.-as an egg-cell with .hich a male element has united. Every Metazoon begins Its hfe as a Protozoon, no matter how large the animal
Iti: t" f?''r"^ °^" ""° '^^^^^ ^han fern-seS" no matter how lofty the result, for man himself has to beg n his life at the literal beginning. The fertilised egg-ceH 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 whHe this body-making proceeds, certain units are ke^t apart in some way insulated from the process of growth, to form 'the future reproductive elements, which, freed from the aduU body, will begin a new generation. Back to the beginning again every Metazoon has to go, and if we believe that thf Protozoa are not only the simplest, but also represent the first ninials we have here the first and perhaps most importan .llustration of the fact that in its developnfent the individua more or less recapitulates the history of the race The simplest animals are directly comparable with the repro- luu .e 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 0^0^^ each as a new life. «t"uiner,
The gulf between the single-celled and many-celled an.mals IS a deep one, but it has been bridged. Otherwise we should net exist. Trace, of the bridge now rema n n
l?t"tf '"' 'I'i^if"' ^^°*°^°^'" -hichfhowever tTo?bl " some to those who like cnsp distinctions, are most instruc- tive to those who would appreciate the continuity of the
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174
The Study of Animal Life part hi
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 physioloj^ist 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 finaliy as a whirlpool of livitiL; 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 pale- 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 o\x\.tx 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 "foim is mind made manifest in flesh through action."
" I believe a leaf of grass is no less than the journey-work of tht 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 machinny, And the cow cruhching with depressed head surpasses any si.', no, And a mouse is miracle enough to stagger sextillions of infukl> !'
Walt Whitman.
It is also important to think of the differ nt kind? of symmetry, how for instance the radiating sea-anemones and jellyfishes, which are the same all round, differ m rkedly
CHAP. XI The Elements of Structure 175
from bilaterally symmetrical worms, lobsters, fishes and most other animals. Then there is 'the differ^.ce beJween unsegmented anniials which are all one piece (like the lower worms and the molluscs), and those\vhose bodies consist, as m earthworm and crayfish, of a series of nwe o less snmlar nngs or segments, due to conditions of growth of which we know almost nothing {,ro\Mn
Organs are well-defined parts, such as hmb or liver hean or bram m which there is a predominance of one or a few
and fnl: ""T''l '"''^^"^"y' ^"^^^ '" ^he ind v!du^ and in the race do they take form and function. There is contractility before there are definite contractile organTo muscles ; there ,s diffuse sensitiveness before the^e are defined nerves or sense-organs. The progress of structure ahke m the individual and in the race, i^ from siS^ c ty to complexity, as the progress of function is from homo^
twoTreLt H^r '" ^^^^^^^ us specialisatio" The uvo great kinds of progress may be illustrated by contrastim! a sea-anemone and a bird. The higher animal ha mort numerous parts or organs, the division of labour withiri s body has brought about more differentiation of st ull but It IS also a more perfect unitv it<; n^rfc , ^'"'^^' Ujoroughly knit together^nrha^Jiisel '^TLrisTo' gress in integration as well as in differentiation ^
" The shoulder-girdle of the skate," W. K. Parker savs " mo„ 1
for^s ^the .obile front waif of the ILS, "^l^ ^^^^
we«'^SL'''' xf '^'"^r '^^-^'^^^ °^ ^--^ appeared can say little. The simplest sponges and polypes are
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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 sta^e 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 ae 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, anc' 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 hen 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 besidt an insect's mouth were really modified legs. To Owen tiie 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 anaton < . Thus an organ derived from the outer emVryonic 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
all homo OKOUS. So tri^ rl.o ,!;«• . f ' ^ *^
the oeclor-H fin „f , «l ;''^,'''''if™' forms of fore-limb,
analogous „„. homolo'o *\ .hi^: oT a'"bW ^hUe't iZr' "''= '"^ ''^"^ -' ^°"> analogous and' W
Fig. 33.— Bones of the wing in pigeon CA) h:,t iv.\
(Frol ChambeA^^:^^:.^J.g;.;^""^' pterodactyl (C).
hvHr,« f *• nsfies, seems usua v to bp t
■mportant respiratory (and sometimes yolk-absorbing) bLth^
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178 The Study of Animal Life part in
robe, and in almost aU mammals by part of the placenta which unites mother and unborn oflFspring.
Substitution of Organs.~To the embryologist Klemen- 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 U ncelet 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 embn'ological origin, the backbone develops. What is the relation between these two structures — notochord anu 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-swimmmg
tadpole-like larva possessed. Such cases are illustrations
of degeneration. In these instances the retrogression is
demonstrable ia each lifetime, in other casf^s we havx to
compare the animal with its ancestral ideal. Thus there
are many cave-anim.ils 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
CHAF. XI The Elements of Structure ,79
animals degenerate in eyes and fore-limbs respectively if) But somewhat different are such structures as the
«!•■ Jhkh t'^^"'^ ^'"-^^^^^^ °^ reptiles birds ^d mammals, which have no respiratory significance, oJ the embryonic teeth of whalebone whales, of £me paiTots and turtles, which in no case come to anything. ^ They ^e vestigia^ structures, which are partly expllined on t^e
n!^ Li ', ^'^'' ^^ "'^'"^'^ "^^d ^h« &i»<lefts as fishes and tadpoles do, that the ancestors of whalebone unales birds, and turtles had functional teeth. No one can sav with certamty of vestigial structures that they are entirely useless, nor can one precisely say why they persist S their original usefulness has ceased. They remairbecmise of necessities of growth of which we are ignomnt and they may be useful in relation to other struSureTthough m themselves functionless. mougn
Classification of Organs.~^Ne may arrange omans according to their work, some, such as limbs and wea^ns being busied with the external relations of the orS^^ '
bte^L "It- ^ n "" '"' ^'^^^' ^^'"^ concen^fT whh ntemal affairs. Or we may classify them according o heir development from the outer, middle, or inner layfr of he embryo. Thus brain and sense-organs 'are ar/ys maTnly due to the outer stratum (ectoderm or epiblast); muscles and skeleton arise from the middle mesodeL or ^^1' the gut and its outgrowths such as lungs and liver primarilv ongmate from the inner endodenn or hypoblast Or we may arrange the various structures more oVless arbitr^nMy In ?."""'" °^ description as follows : the skin and its outgrowths, appendages, skeleton, muscular system"nervcu h hoH '""^.'=-°'-«;^"«' the food-canal and its outgrowths the body-cavity, the heart and blood-vessels, the resoirrton; organs, the excretory system, the reproductive organ ^ rtssues.-To the school of Cuvier we owe the analvsis
t^yTZ\ bS" T^ r^"^"^ organ:;'S'^;^ whichThi . ^ ^ published his^««/^;«,> G^„^rale,\n
w organs to their component tissues, and maintained that
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the function of an organ might be expressed in terms of the
properties of its tissues. , .,• i r *u
If we pass to the next step of analysis, and thmk 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 m the ammal 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 ceUs 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 al organisms-plants and animals alike-were bu.lt 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 which had Loen fertilise-! by union with a male-eel. or spermatozoon. Moreover, the position of the snnple. animals and plants was more clearly appreciated ; they are sinjfle 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 lalxjur
CHAP. XI Tfte Elements of Structure ,8i
among the units. Some, such as the lashed cells lining t e w.ndp.pe, are very active, like the I nfusorfan Protozoa^
t sue ' te'"?"" ''' ''^"^"^ '^"^ ^"^^'-^^»« of connective tissue, are very passive, something like the Greearines
1 bet^efn tL^'^ "''^ '^'^"^ ^°'p"-'- or irufo^'s; But it is true of most of them that they consist (.) of a
complex and in part living cell -substance, in which keen e>es lookmg through good microscopes detect an TmnW
«t: c^rsir" tc~= '^^^'^
H atoenl, through which conimunicalions wiih neiKh-
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x8a The Study of Animal Life part in
boating cells are often established ; and (4) of cell cc ents, whkh can be chemically analysed, and which are pr. lucts Tnhe Tal activity rather than parts of the hymg substance, such as pigment, fat, and glycogen or animal starch.
The RrS^th if all multicellular animals depends upon a mul iplication of the component cells. Like organisms, Tells have definite limits of growth which they rarely exceed gta^ts among the units are rare. When the hmu ot erowth 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 o?fou ounL,you obvi-.-si have three masses success- °vdy doubled but in oouoling 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 lumos aU^ the second has twice as much living matter as hTfirst but not twice the surface. Yet it is through the Surface Ihat the living matter is fed, aerated, and P-^^^^^ The unit will therefore get into physiological difficulties a itLws bigger, because its increase of surface does not kee^ pace with its increase of mass. Its waste tends to exceed its repair, its expenditure gams on its income. What are the alternatives ? It may go on growing and d.e ^b- this is not likely), it may cease growing at the fit £nit it may greatly increase its surface by outflowmg pTo^Us (which thus may be regarded as I'fe-saving) or it may divide. The last is the usual course. When the unit has grown as large as it can conveniemly grc.-, divides; in other words, it reproduces at the l.m t 0 growth, when proce ~s of waste are gaining on th s of construction i iding, the mass is lessened, the
surface increased, the nfe continued. ^..^ . ,^11-
But although we thus get a general rationale of oil division, we are not much nearer a conception of th fnS forces which operate when a cell divi^^^^ ; or . most cases the process is orderly and complex, and is rmehow governed by the behaviour of the nucleus, f e. rLTs of the modem study of minute structure are more
CHAP. XI 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 m 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 corpusd^s » 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 -annot 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 ife, 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
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CHAPTER XII
THE LIFE-HISTORY OF ANIMALS
I Modti of ReproducHon—z. Divergent Modes of Reproduction- 3. Historical— A- The Egg- Cell or Ovum—S- The Malt- Cell or Spermatozoon— 6. Maturation of the Ovum—'j. Fertilisation — %. Segmentation and the first stages in Developnunt—g. Some Generalisations— The Ovum Tkcfy, the Gastrtea Theory^ Fact of Recapitulation, Organic Con- tinuity
In his exercitation "on the efficient cause of the chicken," Harvey (1651) confesses that "al'^-ough it be a known thing subscribed by all, that the fcEtus assumes i:s 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 ox physicians nor Aristotle's discerning brain have disclosea the manner how the cock and his seed doth mint an. coine the chicken out of the egge." The marvellov.; facts of growth are familiar to us — the sproutmg corn and the opening fl< weis, the growth of the chick within the egg and of the child within the womb; yet so ditficult is the task of inquiring wisely into this nianei- lous renewal of life that we must reiterate the cd confession: «' ingratissimum opus scribere ab lis qu-t, multis a natura circumjectis tencbris velata, sensuun lucis inaccessa, hominum agitantur opinionibus."
1. Modes of Eeproduction.— 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 ,85
why <^ch 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 .s often able to retain the movements and life of the intact organism. Among the Protozoa we find some .n 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 (hke an overflow of the living matter) is set free; in others the cell divides into two equal parts, after the manner of -ost 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 maily " spo^s " are formed. These modes of multiplication form a natural series.
In the many<elled 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 ; W Hydra fonns 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
S It i ". Tl' °' -"l^'Pl'-tion-which is'calle'd a.exual-has eviden limitations. It is an expensive way of multiplying. It is possible only among comparatively ^'-mple animals m which there is no very high degree of
of a sponge, Hydra sea-anemone, or simple worm may grw mo adult animals, this is obviousl/not the case
t'o^ nf ?H ;;' * '"^'^' ""' ^ ^'^- Thus with the exceo- 12 V degenerate Tunicates there is no budding
Spolr'^^^^^' "°^ --^ ^o"--. nor an.onf
Ta ;?vs ^IT"''"'', ^"'iP^^^'b'^ °"'y in ^'-"Pler animals, m4ti^ th^t nf' "^^'^ r ^«=*^on.panied by anothe; m .hod-that of sexual reproduction. The phrase " sexua' reproduction » covers several distinct (acts : (a) the separ^.'
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1 86 The Study of Animal Life part ii!
tion of special reproductive cells ; (*) 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 ot spermatozoa and ova by different (male and female) organs or individuals. ,, j • i
(rt) It is easy to think of simple many-celled animals beinc multiplied by liberated reproductive cells, which differed but little from those of the body But as mo.e and more division of labour was established m the bodies of animals, the distinctness of the reproductive eel s om 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. , • r „
(*) 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 sP^aT^^of sexua reproduction in one sense, for the process would be different from the asexual method of liberating more or less large Darts 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, ^.^. Protomyxa, a large number of similar cells sometimes flow together ; in a few cases three or more combine ; m most a couple of apparently similar units unite; while m a few instances, eg. 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
(r) 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 — nglitly 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.
AH 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 ordei
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i88 The Study of Animal Life part m
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-caUed » sexual instincts," as illus- trated in the attraction of mate to mate. As to the actual facts of pairing and giving birth, it seems to me that 1 have suggested the most profitable way of considering these in a former part of this book where courtship and parental care are discussed, though 1 believe firmly with Thoreau, that " for him to whom sex is impure, there are no flowers in
nature."
2. Divergent Modes of Reproduction.— (a) //;?mrf- i>;iro^V«w.— 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
l5!"?!i,°^/^-!' ^'■^ "'"*"y ^°'™*^** ** ^'flferent times, and that the fertihsation of ova by spermatozoa from the same animal very rarely occurs. It is very likely that the bisexu^i or hermaphrodite state of periodic maleness and femaleness is more primitive than that of separate sexes, which, except m tunicates, a few fishes and amphibians and casual abnormalities, is constant among the backboned animals.
iP) 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 niales 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 penods; m the aphides males maybe absent for a summer (or in a greenhouse for years) without affecting the rapid succession of female generations.
(^) Alternation of Generations.— Ps. 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 fi-eshwater 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
norT 7T ^'"'^ •" ^P""^ '"^•^ -"d 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.
ihe large free-swimming and sexual jellyfishes of the genus Aureba produce ova and spermatozoa j from the fertilised ovum an embryo develops not into a jellyfish, but mto a sessile ^j^^ra-like animal. This grows and divides and gives origin asexually to jellyfish.
Similar but sometimes more complicated alternations
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T/ie Study of Animal Life
I'ART 111
'Xu an^ogous alternations are very common, e.g. m .l,o life-cycles of fern and moss.
liberated.
, Wiatorical— In the seventeenth and eighteenth cen- turie;, na u\TsU had a short and easy method of deahng .n embryology. They maintained that w.thm t. . seed o a
HrjLn^n^Lntnrr^^^^^^^^^ mtaUture' mSl of the adult, which in development .a.
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 "aninialculists." 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 lay part But in a later chapter we shall see that the theories were also strangely true.
4. The Egg-cell or Ovum pro„ ed by a female animal, or at least by a female organ (cary), exhibits the usual charactenstics of a cell. It often begins like an Amoeba, and may absorb adjacent ceUs ; 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 t.%z of a fowl, the most important part (out of which the embryo is made) is a smaU area of trans- parent living matter which lies on the top of the yeUow 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 ^%g ; outermost is the porous shell of lime.
While there must be a general relation between the size of the bird and that of the ^g%, there are many inconsisten- cies, as you will soon discover if you compare the eggs of several birc^ j 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 sue of eggs and the number which the bird has to cover. It seems probable, however, from what oce notices in the
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The Study of Animal Life
PART III
ooultry yard and in comparing the constitution of different Wrds th^ a highly-nourished and not very energetic b.rd wm hat larger eggs than one of more active habits and
'^X'^egg-shell consists almost ^vholIy of carbonate of
limJ and tfe experiments of Irvine have shown that a hen can hme, ana ine «ji ^^^ ^^^^ g^^g jt is
X'o^ b.tfS^>".c.^.=U^ n,a„,.a., absorWoo young u ^ different sizes of egg usually
d^ nd' poT^^^^^^^ of yolk, for the really vital portion
nufof which the embryo is -nade is always very small. There a^e many differences also in regard to the outer
to a minute monad Infusorian. It is a very sn bearing at one end a "head," which consists mo b of nucleus, prolon,'ed at the other end into a mobile tail. which lashes the head along.
iK.'m~^.jij^A^i&
CHAP. XII The Life- History of Animals 193
The spermatozoon, though physiologically t'l" -omple- ment of the ovum, is not its morphological equivalent I he 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 10 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 th- ovum is only behaving as other cells do at the hm;; of growth, or that it is exhibiting in an ineffective sort of way the power of independent division which all the re- P'-oduct=ve 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' "hii:h are able to develop into embryos without being lertihsed, extrude only one polar globule, a fact which suggests that the amount of nucleus thus retained some- how makes up for the aljsence of a spermatozoon.
7. Fertilisatios.- -When a pollen grain is carried by an 'nsect or by the wind to the stigma of a flower, it grows down through the tissue of the pistil until it reaches the ovu'e and the egg-cell which that contains. Then a nuclear
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194 TJie Study of Animal Life part hi
element belonging to the pollen cell f ^- ^^^^^^f ^^^^^ of the egg-cell. The union is intimate and coniplete.
Whef spermatozoa come in contact with the egg-shell of a cockroach ovum, they move round and -und 't m varying orbits until one finds entrance through a minute apeVtufe in the shell. It works its way inwards ur^ul Us nuclear part unites with that of the ovum. The union ,s again intimate and complete.
-■ 3--s;:^s.t;fer i£=(S^?&i"'^ °"'"
^rr\ "T^iii^r;^) Vn^.s.^h' '^^^^^
the tir>t pol; lx)il> Kr > """ '^' A.j. . nucleus («-) now ox.rusionof theseconl polar '-^> ^ )• «h;,:;;^„, dVidins t
.,, „vum extnuling ■educed by half ; C,
I polar body ^A^,. me ""— '.N^j), -* -f;;^"=V^.o
s,*rmalozoa (x/») ; D, '^^^"V f ,.„?leu, 0^\ 'u-proach one ancther, and i^\!;-l^":^i^l^;'h.!rT^:un;;;:^u>rt^e^fcniU.tio„. (Kro. ...
Evolution o/ic.r.)
Both in plants and in animals the male cell is attracted to he female cell, the two nuclei unite t-roughly^ui , when fertilisation is thus effected, the egg-cell ,s usually
^T:i::erl::L^S^r.ble origin is tlnis establ^M •md the egg-cell begins to divide. Some idea both ol •^rdcHy complexity 'of the nuclear anion and o the caic^ net of modern investigation may be ^'^'"-^ /rom tU ^^ That the nuclei of the two daughter-cells which re.ult from
CHAP. XII The Life-History Of /inimals 195
the first division of the egg-cell have been shown to consist .n 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 semmahs," and believed that a mere breath, as it were of the male cell was sufficient to fertilise an l^^, and it was onlym 1843 that Martm Barry discerned the presence of the spermatozoon within the ovum.
8. Segmentation and Development. — The fertiliseH egg-cell divides, and by repeated division and grow h'^^f cells every embryo, of herb and tree, of bird and beast is
Zalr ?? tt '"'"'^^ ^"' arrangement of the She character c« the segmentation depends. When there is httle or no yolk the whole ovum divides into equa" parts a m sponge, ' rthworm, starfish. lancelet, and higher mamriia! VVhen there is more than a little yolk, and when tSs sii^ks to the lower part of the egg-cell, the division is complete fr"e hi "r", ; '"'^ '^'' ""'' ^^ ''^'^^y ^^^" by exaZing
^e oi of ?hV''""- n'"^!^^" ^'^ y°"^ '^ accumulated in the core of the egg-cell, the more vital superficial nart d.vides, as m insects and crustaceans. LastfyT when the yoHc IS present in large quantity as in the ovL ofTistlv fishes, reptiles, and birds, the division is very partial ^einl
onfined to a small but rapidly extending ar7a of fonnaZ hving matter, which lies like a drop ol the surface o? the
As the resuh of continued division, a ball of cells is formed. This may be hollow (a ^/aW/J.r.) or olid
Tlnis in the hen\ t^g^lL" "s^ ^^VS r^s^c of c^lt rrd t Jot' ''' ''-''''--' -'^^^^ ^-^-"^ teat The hollow ball of cells almost always becomes dimnLH . or mvagmated, as an india-rubbe, ball rth a Li "" k might be pressed into a cuo-like form tk» ^- i- . result of inequalities of erowth TlT; ,^^ "^'TP''"^ '^ ^^"^
-ii:
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196
The Study of Animal Life part m
food-canal Where there is no hollow ball of cells but some other result of segmentation, the formation of a gaslrula
is not so obvious. \et in most cases some analogous infolding i> demonstrable.
In the hollow sar of cells there arc already two layers. The outer, which is called the ectoderm or epiblast, forms in the adult the outer skin, the nervou. system, and the incist important parts of the sense - organs. 'I'he inner, which is called ( j) the endodcrm or hypo- blast, forms the linini; of the most import- ant part of the food- cana!, and (f ^ueh appendages as lunj^s. liver, and paii< reas
Fic. „._The formation of the two-l.-jyereJ ps-
Ilia
m.la from the invagination of a hollow sphere of cells. (From the Evolution 0/ Six ; .liter Haeckel.)
which are outgntwth- from it. lUit in all animals above the Sponges and Cci;lentcrates, a middle layer appears beiAeen the other two. From th-s— the mesoderm or mesobla^t- the muscles, the internal skeleton, the connective-tissue, etc..
are formed.
9. Some Oeneralisations.— 00 The " Ot •;/;«- 7 ^vn. To realise that almost every organism from the spon^i' i" the highest begins i's life as a fertilised egg-cell, and i^ built up by the divisic. and arrangement, layering aiul loUl- iag of cells, should not lessen, but should greatly tnlunce 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 ,97
Teginninl '° "'"'' '^ *^ ^^"^ '^ ^^-">^ ^-« °^ its (^) 77.^ Ga^/r^a 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 foroi of many-celled an.mal must have been somethmg very hke a gastrula. He called this hypotheS ancestor of all many-celled animals a Gastrcea, and his infer ence has found favour with many naturalists. Some of the
(0 Recapitulation. When we take a general survey jf the animal senes, we recognise that the simplest aS are smgle cells, that the next simplest are balls of cenTke
retrr^d t Th"'^ ' 'P°"^''' P^'^P^^' ^"^ *°""^ above referred to These represent the three lowest steps in the
evolution of the race. They are not hypothetical sfeps in a hypothefcal ladder of ascent, they are realities ^
When we take a general survey of the individual
development of many-celled animals, we recognise that aU
f';e".ir S tr^-'^'.-^ ^^^^ ^^e ova div^tntotn
cells lttrh.rf'°"'' -If "'"f *^^'^^ two-layered sacs of
v-A "'^ therefore evident that the first three chapters in
.n^^v^dual history are precisely the first three stepsT^rdLl
Von Baer, one of the pioneer embryoloj^jsts in the first ha^o this century, discemed that the individual lif^hLto^
he LT ^h""""* '°""'/ recapitulation of the history Z the race He recognised that even one of the hi/her an.mals. let us say a rabbit, began at the beginning fs a
vc^I fil' A ^"bsequently showed the character of a
MZJtl^ T^' °^ ^ y^""^ ^^P^"«' then of a young mammal, then of a young rodent, finally of a younjr rabbit He confessed his inability to distinguish\vhethlr t'ee ve^ cm'lTT;, "' '"'" ^'"^ --oundin«s, were thL^ vivid Idea of development as progress irom the simple
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The Study of Animcd Life part hi
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 ; mane. (From Chambers's EmyckK ; ' after Haeckel.)
Fritz MuUer, 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, — Vysis 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 anc moults, tucks in its tail, and becomes a young crab. And again, when the shrimp-like crustacean, known as rcmnis, 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 kno\\n as a Nauplius and resembles the larvie of most of the simpier crustaceans. It grows and moults and becomes a '-^oea, grows and moults and becomes a Mysis, grows nd moults and becomes a Penceus,
CHAP. XII The Life-History of Animals 199
Now these life-histories are hardly intelligible at all unless we believe that Penaus 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 rrustacea perhaps not much less simple than the Nauplius larvae which many
Fig. 39--Life.historyof/'*«««j; 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 larv.c. At this station some remained and we have already mentioned the " water-flea " tychps as a crustacean which persists near this level But others pushed on and reached a stage represented by Mysts, and finally the highest crustaceans were evolved
i\ow to a certain extent these highest crustacean^, have
o travel in their individual development along the rails
laid down m the progress of the race. Thus Penaus
1 11
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,f
I
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
Fici. 3S«-— Life-lu^>lory of I\iufus ; the Zoea.
delay at the Afysis stage before the Pcn:rus reaches its destination. The crab, on the other hand, stops first at the Zoea station, the lobster at the Mysis station, while tlie crayfish though progressing very gradually like a!! the others has— if you do not find the simile too grotesque -a through-carriage all the way.
/ i\\y\\
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i'lr,. j9^. -Life history o( I'eitiru^; a later
stage.
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202 The Study of Animal Life part m
One must l)c 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 raciul 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 ^ere 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 imta- morphoses have their efficient causes in the actual cun- dilions of growth and development. The suggestion of Kleinenberg referred to in a preceding chapter helps U5, 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, m 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 Bw/ogy Land. 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 {Generelie Mor- pho/o^e Berhn, 1866) has illustrated it, and pithily summed It up in his "fundamental law of biogenesis » {Biogenetisches Grundgesetz\ saying tha. 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.
id) 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 powtr 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" m which these qualities are expressed, distributed, and altered m 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 preserv-e 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.
I
il
Ml
m
I > 6 1
CHAPTER XIII
THE PAST HISTORY OF ANIMALS
I. ne two Records — 2. Imperfection of the Geological Record— 3. Palceontological Series — 4. Extinction of Tyfes — 5. Variom Difficulties — 6. Relative Antiquity of Animals
I. The Two Becords. — 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 ot the gaudy Indian bird — I seemed to be amongst t^" sombre g;0JS- 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 :ieemed to be described in large archaic characters ; a little while and these faded into what could just be read oflf 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
'5<«3?S'
205
CHAP, xin The Past History of Animals
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 sons on the earths surface, persistent forms recur from age to aee many of them, such as some of the lamp-shells or Brachio^ pods, hvmg on from near the apparent beginning even until now. But other races, like the Trilobites, have died out leaving none wh.ch we can regard as in any sense thei; direct descendants. Other sets of animals, like the Ganoid fishes, grow m 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 palceontology would be ea^y Then a genealogical tree connecting the Protist and Man would be possible, for we should have under our eyes what ■s now but a dream— a complete record of the past
• V u^T^ °^ ^^'^ "^^^^ ^' °^^^" compared to a library m wh,ch shelves have been destroyed and confused, in which most of the sets of volumes are incomplete, and most of the individual books much damaged. wlTen we consider the softness of many animals, the chances against their being entombed, and the history of the earth's crust our wonder ,s that the record is so complete as it is that' rem 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
su2rh ''^K °' "• "^^"^ "^'""y ^^^'^"^ °^ the earth's surface have been very partially studied, many have not
been explored at all, many are inaccessible benelth 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.
I M
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2o6
The Study of Animal Life part m
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. Palaontological 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 {Paludwa), 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 art conclusive.
4. Extinction 01 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 lias gradually changed, and though the ancient forms art no longer represented, their descendants are with us. There is an extinction of 'ndividuals and a slow chani;e of species.
On the other baud 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 Trilobit^s and Eurypterids, or of many of the ancient reptiles. There is no doubt that a rare may die out. Many different kuuls of heavily armoured Ganoiil tisbrs 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 ainon^ Amphibians, now almost all are pigmies.
CHAP, xm 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 an"':,. ..i;„.. many kinds of beasts and birds. But, apart fro n the sivn^^, with competitors, it IS hkely that some types wc o ins .fnclcatly plastic to save themselves from changes ol . n. ..o.hncnt, P.r.J it s°ems likely that others were victims to their own -..istitutions, becominL^ too large, or too sluggish, or too calcareous ; or on the otner hand, too feverishly active. The '« scouts " of evolution woula be apt to become martyrs to progress ; the " laggards " m the race would tend to become pillars of salt • the path of success was oftenesi a via 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 a 1-round organism that is ar' e shy of radLal 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 I., accepting this interpretation, I shall refer to three clifllculties occasionally raised.
(«) 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 uf the fauna is stran-elv 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 industry of one man in a .avourable locality, and that the rocks of he Permian system are ill adapt.,! for the preservation of lossils Moreover, we cannot compute the relative dura- tion of the diflferent periods, we cannot infer evolutionary progress from the number of species, and we must make many allowances for the imperfections of the record.
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The Study of Animal Life part m
(b) 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.
(f) 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 le.igth of time during which the earth may have been the home of life ; we are apt to measure the rate of evolutionary ch inge 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 ol high degree.
6. Relative Antiquity of Animals. — I have not much satisfaction in submitting the following table showing the relative antiquity of the higher .\nimals. Such a table is only an approximation ; it does not suggest the -^rcat 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 tlie general fad 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 discover)' ; moreover, the earliest known mammalian remains seem to be of those of very simple types.
CHAP. XIII The Past History of Aniniu
Primary or Pahrozoi.
»* 3
3
73
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JMesozoic
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2;
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3
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Tertiary or Cainozoic
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I
CHAPTER XIV
THE SIMPLEST ANIMALS
I. The Simplest Forms of Life— 2. Survey of Protozoa— i. The com- mon Amn-ba—^. Structure of the Prolozon-S- Life of Protozoa —6. Psychical Life of the Pro^^zoa—I. History of the Protozoa 8. Relation to the Earth— <). Relation to other Forms of Life - lo. Relation to Man
I. The Simplest Forms of Life.— It is likely that the first breati. 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 simplf when contrasted with a bird. They are (almost all) unit specks o: living matter, each comparable to, but often more complex than, or.e of the numerous unit elements or cells which compose any highei plant or animal, moss or oak-tree, spont;e 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 Ehrenberij, who described some c! them in 1838 as " perfect organisms" and fancied he sawstoniac!i?. vessels, hearts, and other organs within them, was nearer tlie tmth than those who reduce the Protozoa to the level of white of cgi;.
Nor are they omnipresent, swarming in any drop of water. I lis clear water of daily use will generally disappoint, or rather plc.ise us by showing little trace of living things. Hut take a test-tul-e of water from a stagnant pool, hold it between your eyes and theluht. and it is likely that you will see many forms of life. Simple iilant? and simple animals are there, the former represented by threah ovals, and spheres in green, the latter by more mobde almost colourless specks or whitish moles which dance in the water. Hut besides these there are jerky swimmers v hose appearance alnios^ suggests their popular name of " water-Heas," and wriggling "worms,
.im^^'^^i^
mt
CHAP. xTv T^g Simplest Animals
an
.mSi^Wll^"''"'^ ^^ "•'''■' '^"" ^^'^ = ^°'h of these may be very small, bat closer examination shows that thevhavp nnrf.o^^ ^
that they are many-celled not single-cSd animal?"''' '"' °^"''
Vary the observations by taking water in which h-iv .^t^m. «, «.»,
parts of dusty dead plants have been steeped fo a few davran 1 v
wuh the unaided eye you will see a thick^crowd of he Sile 1 iS
motes which from their frequent occurrence in such inA Ins 1
usually called Infusorians. Or if a piece of flesh be allowed to rVfn
an open vessel of water, the fluid becomes cloudy and a hrfl yscum
ga hers on the surface. If a drop of this turbkl liquid be examined
pracdcally omn.present microbes, soma of which as disease ~™^
Jlif cLLterri.iS/e';",t"Vr„ sr"' •""> -"' ^
mobile lashe, of living ™,'L, C™ as ci ia'^oTZ^na "tH ''' Ae sl,pper-animalcale l,Par<,m,t,lum) is covered wUh r^w. „f S'
:l„g* i"=oX'eSa°"%t''!' r""'"?'', '"°''™»' "' »"= °" u. i, wiups or nagella. The bell-anmia cu es {VortuflIn\ u,hi,^j,
.rfilre;"-;Lii:r.'°.'t:.rtsTi*r:o^^^^^
.•aip":i^frtz'=of'rz't"er"t'i„zr'°^V" »..s, whieh'rn' .tar^fr,,°7^,?jf;/'« ?/j"'"'f "s p-
^ '5 rnv.iun, and are siilj
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The Study of Anmal Life
PART ni
'f>?^;
„,orc useful in surnuuvUng — ^/:^yC^cv.l.lc. often alnu.; like processes, which ate capable ot vcy ^^^^^^^^^ ^^^^^^^^^ ^,^^,^^
Trolo/oa owe llicir i;c-.-. cml name of Rlu/.opo>.>. In contrast to the iw im-coiling tyiH-s ^^lv,.: \\:\\i' (Iclinitc bouml.iru: „i- "sixins," the Rhi.-, nods arc naked, and i!a.
living matter may i'\~ llow at any point.
As the I nt'usoi ';.-.', aie for il>e mo^t i- piovidca with cilia l.,! which llagclla *lilTor w in detail, wc may ^p^. of the type as cili:.u the self-contained i. ■• giwines, often wra. . . up within a sheath. \ may call prodomin.v.. encysted ; while •.: forms whicli axe i; ' juediate between .: two extremes, an.; hibit outt^owins
cesses of living i".
flowing out on .XII r'"^;^ ,,^ . ^fter Max
(From Ch.^mb<;rs> A«0'''A.
Schultze.) are called anwix .
units may become encysted.
5
lit--
, <.nc^•<t«l: 2, dividing into many unit. ;:-.t^
Fig. 41.— Protomyx.i. ing as tlagel' t,lai.modium. ,- ,
,-_-^^» t>^A three physiological p. As the three pnascs rci-rese..-. ^ »- -
CHAP, xrv Tk£ Simplest Animals 2,3
of cell-life, it is natural lo find that the very simplest Protoroa, rach :.,Protomyxa, exhibit a cycle of amaboid, encysted, and fljellate phases, not hanng taken a decisive step along any one of the three great paths. Moreover, the cells of higher animals mny be classTfiS m the same way. The ci!....ed cells of the windpipe or the mobSe spermatozoa correspond to Infusorians ; mature ova fat-cells d" generate muscle-cells, correspond to Gregarines, while white bl'ood. corpuscles and young ova are amceboid.
3- The common Amoeb0..-To find Amoebae, which is not alwaj-s easy, some wraer and mud from a pond should be allowed to seule m a glass vessel. Samples from the surface of the sediment should then be removed m a gl.xss lube or pipette, dropped on a s .de, and patiently examined under the microscope: Among the .kbns, traversed in most cases by swift InfusoiianCtlie sou^ht-for .-^«^ia may be seen, ..s an irregular mass of living matter? often obscured With vanouskmds of particles and minute Alg^ which k has engulfed, but hardly mistakable as it ploughs its way lei urely among the sediment, sending out b!unt nnd changeful fingerdike processes in the direction towards which it moves, and d^rawing m similar processes at the opposite side. From some objects il reco>ls, whUe others of an edible sort ,t surrounds with it b un processes and gets outside of. Intense light makes it contract, and a rriinu.e drop of some obnoxious reagent causes it to round itsHf off and i.e quiescent. Such is the simple animal which, in 1755, an early microscopist Rosel von Rosenhof was del,g!ued to describe calling It the " Proteus animalcule." ^"escriue,
4. StTUCtnre of the Protozoa. -Most of these Protozoa are ^.nus or single cells^ but this contrast l.etween them and the higher an;mas is lessened by the fact that manv Infusorians. tme Kaaiolanans. and some of the verj- lowest forms live inclose comU " 00-.;^"^^"% fP""'"'' individuals being substar/iully united in o-operanon. In two quite different wavs this com,, .^.id'lif- of som-
o'l" theLrL nf T> ' '""'T "'""'^^' 'P'""^'' "^ ^ ^•e.\o^^■\^. slime
■h Snl"! ■ """''"^ ^/undifferentiated protoplasm." arises fn,„, dua..v„ng together ana fusion of a nun.lH.r of ..nalier amo.lK.id Jn.-. But in some Infusorians and Kadiolarians the colonv
S:" t^\ °''""'T- , '''"T' '""'''P'^ ^y division ; eacL^^ bv tlmil"" 7'-f' tlienceforth live separate lives, and bv and f:^ '.!::™ '^'"^^ ^'^''d'=- -^"PP^.- however, that the unit d.vid. un evr?-li- '^^P°'' ''''"^^ ^^"^ claughter-unitb, distni.t thou.di
thev ir "^"''- ^" *'"' "'^ t*^*^ ""i'^ do not flow togwhe-
iney were never seiaratwl k... .^^ .. ...„j_^ - . ^^>, "c,
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The Study of Animal Life
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early associations has been justified in their far-off children, for in this wav the many-celled animals began.
tTic cell substance of a Protozoon is living matter, along v.".!. uutrive materials which are approaching that chmax, and was e materilh So which some of the cell substance has d.sm cgrate . The ce 1 has a kernel or nucleus, or more than one. essenl.al to >u complete life. There are bubbles of water taken m along with foS particles, and in nearly all freshwater orms there are one or wo special r gions of internal activity, pulsat.ng cavit.es oco,v ^ctile vacuole^ which become large and -[^^ --^^^ l^yi^;;;:; -illv and may burst open on the surface of the cell. They are 1k- & to h^lp in gettiig rid of waste, and also m mterna crculalu^n There s a iLl in the Infusorlans and Gregar.nes, and shells of fhn: Tnd itme are characteristic of most Foramin. crs and Kadiolanans. ana nnje . protoZOa— The life -histories of the Protozoa ar
very v.^^. fut^me Sters are common to most. They expend eneUyn movement ; they regain this by feedmg ; their income exceSs their expenditure, and they grow ; at the lumt of gro« 1 Sey eproduce by dividing into two or many daughter- unUs : m certain stages two individuals combine, either interchangmg nuclei Sments ( n the ciliated Infusorians) or fusing together (as in sc..e Riropods) ; in drought or in untoward conditions, or belore mSld division, they often draw themselves together and encvst within a sweated-off sheath. j- -j . ;.,.„
The Protozoa often muUiply very rapidly. One divides no two the two become four, and in rapid progression the num.a. ncr'eas^ On Maupas's calculuion a single Infus.nan may in fcur days have a progeny of a million. The same observer has shed a new St on^ a 'other process-that of conjugation, the temporan- or percent union of t\vo Protozoa, which in thecihated Inhisona . ?n?ouis an interchange of nuclear particles. In November iS^,. Maupi isoht d an Infusorian {Stylonichia) and observed its genera^ Monstm March i8S6. By that time there had been two hundied and fften generations produced by ordinaiy division, but smce t:ese owTy organisms do not conjugate with near relatives, conjug. a^ hadU^occurred. The result, «>"°borated m other case., v^ strikin- The whole family became exhaust.!, small, ^^ ''senile " ; they ceased to divide or even to feed ; their r.v.. underwen a strange degeneration; they began to die. B.. ndivSs removed' before the process had gone too far ... observed to conjugate with unrelated forms and to live on lb Sference was obvious. Conjugation in these Infusorians is of .tth moment t^any two individuals ; during l-g P-ods it need ne.« occur, but it is essential to the continued life of the species. is a necessary condiUon of their eternal youth.
11 V:
CHAP. XIV The Simplest Animals 215
We must return, however, to the eveiyday life of the Protozoa Rhizopods move by means of outflowing processes of tlieir livinL' matter winch stream out at one corner and are drawn in ac another • tlie Infusorians move more rapidly by undulating flagella or by numerous cilia wliich work like flexible oars; the parasitic Gregarines without any defmite locomotor structures sometimes writhe sluggishly. A few Infusorians have a spasmodic leaping or springing motion, while the activity of others (like Vorticelld)ss\nc\i in adult hfe 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 ^'as (nubbles in different parts of its cell-substance.
'Ihe food consists of other Protozoa, of minute Algce, and of organic debris, simply engulfed by the AmoebK, wafted by cilia into the " mouth " of most Infusorians. The parasitic Gregarines absDrb the debris ol the cells or tissues of the animals in which they live, while not a few suck the cell-contents of freshwater Algje 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 I-oraminifers live in constant and mutually helpful partnership or symbiosis with small Algae which flourish within their cell-substance.
As to the other functions, the celk 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 'Votozoa, with frequently rapid and useful movements, with cap...i[ies for finding food and avoiding I'.anger, with beautiful and intricate shells, are endowed with the will and intelligence of higher forms of life. According to others, their motions are arbitraiy 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 c^awn by their food instead of finding it, their powers of selection art jublimcd chemical aifimties, their protective cysts are quite necessary results of partial <icath, 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.
Cienkow^ki marvelled over the way in which Vampyrella sought and found a Spirogyra filament and proceeded to suck its contents ; t-ngelmann emphasiseii the wonderful power of sdjustiv-ent in Aralla
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216 The Study of Animal Life part m
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 discriir " lative 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 atnnities 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 will) 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.
Haeckel was one of the first (1876) to urge the necessity o( 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, tiiat liie 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 emlwdied in the protoplasm, and is as inseparable from the cell-substance as the human soul from the nervous system." For several years Verwom has been investigatinc the psychical hfe of the Protozoa. He has conducted his researclies with great care and thoroughness, observing tlie animals both in their natural life and m artificial conditions. I shall cite his con- elusions, translating them freely : "An investigator of the psychical processes in Pro...^ts (simple forms of life) has to face two distinct problems. Tne 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 psycliical 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 testmg and searching, give us the impression of being intentional atul 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 nnd 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- elusion 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 numl;er of criteria show that the movements are in part impulsive and automatic, and in part reflex, ^" ./xi:° '^^^^ expressions of unconscious psychical processes.
This opmion 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 1 here 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-
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ai8 The Study of Animal Life part in
ments, they cannot be the expression of any individual consciousnesa 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 rudlmentarily, in the Protists, then these simple organisms do not potentially include the life of higher organisms. If theie are none in the Protists, are there any in the germs from which men develop ? ....
Verworn seizes the other horn of the dilemma, mamtaming 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 lie 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 Urthicre or primitive animals, suggests that the Protozoa are not only tie simplest, but the first animals, or the unprogre"ive descendants ot these. Nowadays we can hardly feign to consider this proposition. startling, for we know that all the higher animals, including ot;r- selves, begin life at the beginning again as single cells. Fiom the division and redivision of an apparently simple fertilised egg-cell rx embryo is built up which grows from stage to stage till it 1- hatched, let us say, as a chick. It is only necessary to extend t! '.^ to the wider history of the race. What the egg is to the chick the original Protozoa were to the animal series ; the present Protoza 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 e.u: .. whether they originated from not living matter or in some yet more mysterious way. The German naturalist Oken, a prominent ty; : of the school of "Natural Philosophers" who flourished about t.: beginning of this century, dreamed of a primitive living shtre (Urschleim) which arose in the sea from inorganic material. Mi-- dream was prophetic of the modern discoveiy of very simple ;or'.r.s of life, in connection with one of which there is an interesimj sr.a instructive story. That one, perhaps I should say that supposea one, was called Batkybius, and since those who are eager to nr..-:e
mijiJl
CHAP. XIV TAe Simplest Anintals 219
points against science (that is to say against knowledge) always tell the stojy wrongly, I shall make a digression to tell it rightly
In 1857 Captam Dayman, in charge of a vessel engaged in con- nection with cab e - laying, discovered on the submarine Atlantic plateau the abundant presence of slimy material which looked as if It were al.ve. Preserved portions of this formless slime were after- wards descnb. d by Huxley, and he named the supposed organism,
Haeckelu. On the /Va///«^expeduion Professors Wyville 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
But when the Challenger expedition went forth, and the bed of the ocean was explored for the first time carefully, the organism Bathybius v^;,^ nowhere to be found. But this was not M : the
™? . r R T, ^'' '° '=°'"'- ^'- J°^" ^^""-y '^-' 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 sulpha e of lime precipitated from the sea water by the action of the ttt T"h P^«^^y>"g 7^f «Js- He renounced Bathybius,
llri ^ °^ acquiesced, Huxley surrendered his organism to the chemists, and the obscurantists rejoiced exceedingly over the mares nest. Bathybius became famous, it was trotted out to 1 ustrate the fallibility of science, a useful if it were not a some^hS superfluous service.
th.f';hi^^n""''''"'',°'"^''''>'^''"'^"^^ "°' P^°^'^d by the fact
ha the Chall^ger explorers failed to find it. nor was it certain
that Murray's destructive criticism covered all the facts. Haeckel
l"nMr Kf' '"'''^ pertinacity to Bathybius. and his con-
S ^ ^Tr Vrf "^'"' J"'''^''-' '^y the fact that in 1875
tarerV^'w'^^/^'f \'P''^^''°"''^^^^eed from 92 fathoms of
TZ '"^""^^ ^o""^ abundant quantities cf a closely- similar
fiTkr,,.,- n ""'"^ ''l^''^' movements, and called it Protc
Bathy,us. It may be that it consists of the broken-off portions
of Foraminifera ; we require to know yet more about it. but I have
aid enough to show that it is unfair to stop telling th; s"ory wi h
the words "mare's nest." But whether there lia Bathybhr .
IZlillT^r' °r "° ^'"'^^'"' ""' ^"' ''^ "^^ ^^ ^'"d^"«s of science compelled to confess our complete ignorance as to the origin
8. Relation to the Earth. — The floor of the sea for a
o"e?ed^T'a VI """ (-t exceeding 300) from thHlJ:: i
^"""■^•■•-jr'wa" 3"ciis of i-oraminilcia usually
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TJie Study of Animal Life ^-art m
oocur, bu; 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. ihey are ferming the chalk of a possible future, just as many dialk-cliffs and pure limestones repre- sent the ooie 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. ^
9. Belation to other Forms of Life.— On the one hand
the Protozoa are devourers of oi^nic 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. Belation 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 .^nioeba, some Gie 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 N unimu lites, the " Pharaoh's beans " of popular fancy. But the minute- ness of most Protozoa kept them out of sight for ages. Thty were virtually discovered by Leeuwenhoek (b. 1632) about the middle o( the seventeenth century, and soon afterwards demonstrated by Hooke to the Royal Society of London, the members of which signed an «ffidavit that they had really seen them ! In 1755 Kosc[ von Rosenhof discovered the Amoeba, or "Proteus animalcule:" but his discovery was ineffective till Dujardin in 1835 demonstraied the simplicity of the Foraminifers, and till Von Siebold in 184S
» For details, see conveniently H. R. Mill's Realm of Nature (Lend. 1893).
CHAP, xnr The Simplest Animats an
sb'^'ved that Infusoria were single celli comparable to those whicli make up a higher animal. For the resemblance between some of the spirally twisted shells of Foraminifera and those of the immensely larger MoUuscan Ammonites and Nautili led many to mamtain 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 uni^ 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 spermatoiot which have never got on any farther.
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CHAPTER XV
BACKBONELESS ANIMALS
Spends — 2. Stitigittg-Animah or Ccelenterata — 3. " Worms''— 4. Echitioderms—l. Arthropods— (t. 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 hie of the sponge depends, line the canals, but are especially develoi-ed in little clusters or ciliated chambers. The currents are drawn in through very small pores all over the surface ; they usually flow on 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 art blown out of shape by the wind, so sponges are influenced by the currenU which play around them, as well as by the nature o\ ti e objects on which they are fixed. Like many other ia:,>r.e organisms, sponges almost always have a well-developed skclcKn. made of flinty needles and threads, of spicules of lime, or of tilres of horn -like stuff. While sponges do not rise high in oiganic rank, they have many internal complications and much beauty.
Sponges may be classified according to their skeleton, m
CHAP. XT
BackboneUss Animals
"3
calcareous, ainty, and horny, (o) The calcareous forms with needles of bme 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
« ■•.• u t !.fc'"^''* (°' Grantia) com/r»sa is common
on Brifsh shores (*) The siliceous sponges are more numerous, diverse, and comphcated, and the flinty needles or threads are often combined with a fibrous " horny " skeleton. Venus'-Flower-Basket [EupUctella) hzs, a glassy skeleton of great beauty. Mermaids' Gloves (CAa//«a oculata) with needles of flint and horny fibres Ls often thrown up on the beach, the Crumb-of- Bread Sponge {Haltchondna pamcea) spreads over the low -tide rocks. Some have strange habits, witness Clione which bores holes in oyster shells, or Subentes domuncula which clothes the outside of a whelk or buckle shell tenanted by a hermit-Crab. Unique in habitat is the freshwater sponge {SpongHla) common in some canals and lakes, notable for plant-hke greenness, and for the vicissitudes of its life- history, (c) The " horny " sponges which have a fibrous skeleton
^f "ilP'^^u't''." "* **" represented by the bath-sponges (Euspongta) which thrive well off Mediterranean coasts, whe- they are farmed and even bedded out. '
Sponges are ancient but unpiogiessive 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,
? • '^°i "^"^ *"*™'" ^^"^ "* Protected by their skeletons and by tneir bad taste. '
2. Stinging- Anixnals or Ooelenterata.— It U difficult to
fin. 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 stincine lassoes in some of their skin-cells suggests that which we now use
Representatives of the chief divisions may be sometimes found n a pool by the shore. Ruddy sea-anemones, which some call ea-roses, nestle m the nooks of the rocks ; floating in the pool and hrohbmg gently IS a jellyfish left by the tide ; fringing thTrocks
e various toophytes, or if we construe the name backwards plant! iKc animals ; besides these, and hardly visible in the clear water are minute translucent bells some of which have a strange relation s .p wuh .oophyte, ; and there are yet other exquiSdSe'
Si. ly iridescent globes-the Ctenophore, which mo.thyTmt
7y^at^.iV "7''»» ™^"^b«." of this dass-the neshwatei a^dra which hangs from the floating duckweed and other planta.
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ii4 The Study of Animal Life part hi
TKU H^ra is a tubular animal often about quarter of an inch in
Th» ^'•<» » * S thTtXis fixed, the other bears the mouth
^'"^^a.?°bv a crSln of m^b?e tentacles. It is so simple that
StLlt. tf^t tc^ minute may grow into complete animals ;
wh^n wdf?S the Hydra buds out little polypes hke Uself. and
''TfweTpS^'the budding of Hydra continued a hundred-
"°Som:tirer tZ^^:^^'^^^^^o.oi^.^..r^n such Sometimes however in ^^^^.^.^^^ reproductive,
S n a special interest in the case of many zoophytes. Fo this nas a spcuim uu^ tnown as Tulm arians and
-Li..,.H-« hi«i« of hvdrod colonies. Some wnicn are
lik. lh« P^* « /Sm, .« "he M. jellyfish^ «hich are somelimei superficially l«e i"'™" "= ' . ni „,ednst
sometimes stranded in great numl.ers on "« ?«?*• '"' ,i„k their. talone 10 a different series, and some of tlieir fcattres hnit r,.her^th..«.-.nem«ne,.han.„theMro.d. ^^^
moilS: :::-=^^;"fjv5C'XroS"^^^^ s.rt;Seru-roSs^'.Hro»^^^^^^^^
man, radiating partition, "r ,,"'? °' """'iir R^lal d > • -l^
CHAF. XV Backboneless Animals
225
as relatives (S.phonophora). which are colonies of more or Lss meduscMd ind.v.duals with much division of labour. TdLuv the Ctenophores, such as Beroe and Pleurobrackia, which XS tJe climax of activity among Coelenterates. "^n represent the
A brief recapitulation will be useful • /»vr/ j-^,,_Hydroid and Medusoid types (Hydrozoa):- I The freshwater Hydra and a few forms like it
(2) The hydroids or zoophytes, each of which maybe regarded
as a compound much-branched Hydra ; including af many whose -eproductive persons are not liberated, espedaSy Se uwians and I'lumularians ;-(3) many whose^repro^ ductive persons are liberated as swimming bells or medusoids, especially Tubularians and Campanularians
(3) tree meduso.ds. anatomically like the liberated bells o? 2 i)
but without any connection with zoophytes. ^ ''
(5) A few hydroid corals or Millepores. Wj^/«_JeIIyfish and Sea-Anemone types (Scyphozoai-
(!) The true jellyfishes or Medus.. including S a formlke Pelasta which is free-swimming all its life IhioUgh,?^) £e common ^«,W.a who.se embiyos settle down and become polypes from which the future free -swimming jellyfishes are budded off. (.) the more or less sedenta^ry jeUyfish known as Lucernarians. ^ j-^^yjisn
The sea -anemones and their relatives, including r«) sea- anemones proper ie.g. Aainia) and their relat;d reef- building coral-colonies {e.g. star-corals Astr^a, brain-coral
clT /r V • '''° ^"h'^'-'^'l ^"r->«. 'S. the organ-pipe coral (Tubtpora musua) ^nA the '« noble coral" of com- merce (Ct>/a//,«w „,^;^;,;). *' 01 com- Third Series— Ti,e Ctenophores, which a: e n.arkedly contrasted with corals, l^mg free and bght and active. Many (e.g. Beroi and I^letirobrachm) swarm in our seas in summer, iride> ♦ in daylight, phosphorescent at night. Tlu-y differ in . ny Q
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226 Th£ 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 diflferences of structure and development, are yet parallel. In both there are polype-types ; in both medusoid types ; in both there are single mdividuals and colonies of individuals; in both there are "corals. ^ ^^e n;--*)' compare a Hydra with a sea -anemone, a medusoid with a jelly- fish a hydroid colony with Dead -men's- fingers, Millepores wiih
the Evolution o/Stx ; after Haeckel.)
lll-Ol
the commoner reef-corals. Moreover, we may compare a mod liberated from a hydroid with Aurelia liberated from its fixed polyp. stage, and permanently-free medusoids with jellyfishes like Vda^ta, These arc physiological parallels.
The sedentary polypes arc somewhat sluggish, with a tondomy to bud and to form shells or skeletons of some kind. 'I ho free- swimming medusoid types are active, they rarely bud, they d) not form skeletons, but their activity is sometijncs expressed m
CHAP. XV Backboneless Animals
phosphorescence, and their fuller life
227
J associated with the develnn wh,ch ftMe„„clcs and .h'e S^" .ST^H Zr"" » -"""«
occurs in brackish water and in .;„ni "y^'™''* f-o> dyhphora which
which is pan^siticinTts youth "n .ri.: ^fThf R°™ '''''^^'^"'" or sterlet, and a freshwater iellvfi.jf^f / • ^^^^^^^'^n sturgeon found in the tanks at Kew ^rlt ^Ltmnocodtum) which was
\^x them company Siphonophores and Ctenophores
Various kinds of corals should be contra<;tPH n . fingers with aumerous jagged suicules oMi " • •. ^,^^'|-™ens- l^nning to be coralline SimiUrc•^i™^'" "' ^^^^ '- J"st i7an external t°ut" i^' tl I'^^an 'pTp^L'rT t" S"' '^^'^J the calcareous material form.; nn a vJc*^ j "... , *^^ ""^^ '^o"' are clustered. Ve.y diSnt nr^ ^.^'"""^^M'f^ '^^ individuals the cup in which e^IhlnSuaUivxd'ir:^"'''^^ ~'^'^' "'^"^ according as it has remaiS di inct 1 "fZ' ^h^ "'" T^''' and where an imatre of the fliv. ..'"^^^ ^^'^^ "s neighbours, .ike anima, is ^::^t^l^:SZt^:tl^, '>- ™one-
ca.^":irK.T; hot'do^ trVef r °^''""^' ^-^^^^ »'-
which these are composed^ Is h^f ^1 ^^ '''^°"^*'^ ^^ '™« of sea-water-plentiful nS cLl ree^ or "T^'iL"^^ ^ n' ^'""'^"' '" tion between the abunHmt ^.\l- °^'V"^'^ ^ double-decomposi-
products, a: hls\t""suggS'b^? i'^^^^^^^^ ''^ '^^^"'^ --'- do the corals feed, for therseem alwn s f^h '"■'^^ ^" ^"'''''' bright pigmenU enable them T/r^ ^^ ^""P^^' ^° »heir plants on carbonic acid ? ' ''''°" '"^gests. to feed like
water. """' '^'"S J'ttle more than animated sea-
11
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2a8 The Study of Animal Life part m
As sDonces showed tissues in the making, so among Stinging- As sponges snow nerve- rings, and special
animals o'g"^ ^8^°-?^ ^lo^t has much to leam in regard "P/v^T™.S orhydS^dTedusoid in one life-cycle, the to he ^'7?^*^° °\„^^^^^ and other colonies, and the
division °f }*^" JV a skSe on. Nor can we forget the long meaning and makmg oj J «^;'«° ^^^j „,f,, ^^d types of coral
Sirretrett^^^^^^^^^^^ Graptolites whose nature we
'°W ?ln'?il's^ritro?m;uy-celled animals with Sponges and rXteS par?^ ic-re they are on the whole simplest, but OElenteraes. partly / ^^.^^^.yyxft are leest removed
ZmtCtt^S reT.cS^ or gastrula which recurs .n
Se Wsto^ of most animals, and which we have mucn warran the life-tastory oi mus successful many-celled
for regardmg as a hint of what ^he ^^^^^^^^ ^.^^^ ^^^^ ^j,^ animals ^ere 'ke The f ?on|es ^^ ^^.^ ^^^^^^^^ .^^
S^r^ttdii ly ^ymS^^^^^ and'in so gVowing that the axis eSi from the mouth to the opposite pole corresponds o the extending iromuic two -layered animals, for
'"'y°'Wo™^This title is one of convenience, ^vithout .3 . r^r'., Vnr there is no class of "worms," but an
sides. The ""P^'^/iSSstently head foremost, thus acquiring
CHAP. XV
Backhondess Antmals
329
by budding forms temporary chains of eight or sixteen individuals as if suggesting how a ringed wonn might arise ; Gunda, with a hint of internal s^mentation ; and two parasitic genera — Grc^la and Amplodium — 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 fiat 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 {Distornum hepaiicum), 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 (Lymtueus tmncatulus) 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 similariy 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 (Diplotoon) ; and hardly less strange is Gyrodactylm, another parasite on freshwater fishes, for three generations are often found together, one within the other. The most formidable fluke-parasite of man is Bilhartia, or Distomum kamatobium, common in Africa.
3rd Class. Ccstoda or Tapeworms. These are all internal parasites, and, with the exception of one {Ankigctes), which fulfils its life in the little river-worm Tubifex, the adults always occur in the food-canal of backboned animals. Like the flukes, they have
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836 The Study of Animal Life part ih
adhesive suckers, and sometimes hooks as well ; unlike aukes and planarians, which have a food-canal, they absorb the juices of their hosU through their skins, and have no mouth or gut. Like the endo-parasitic flukes, the tapeworms have (except Archigttes) intricate life -histories. Both Turbellarians and Trematodes are small, rarely more than an inch at most in length, but the tape- worms may measure several feet. In the adult Tania solium, which is sometimes found in the intestines of man, we see a small head like that of a pin ; it is fixed by hooks and suckers to the wall of the food-canal ; it buds off a long chain of "joints," each of which is complete in itself. As these joints are pushed by con- tinued budding farther and farther from the head, they become larger, and distended with eggs, and even with embryos, for the bisexual tapeworm seems able to fertilise itself, which is a very rare thing among animals. The terminal joints of the chain are set free, one or a few at a time, and they pass down the food-canal to the exterior. The tiny embryos which they contain when fully ripe are encased in firm shells. It may be that some of them are eaten by a pig. tbe shells are dissolved away in the food-canal, small six- ncoked embryos emerge. These bore their way into the muscles of the pig and lie dormant, increasing in size however, becoming little bladders, and forming a tiny head. They are called bladder- worms, and it was not till about the middle of this century that they were recognised as the young stages of the tapeworm. For if the diseased pig be killed and its flesh eaten (especially if half-cooked) by man, then each bladder-worm may become an adult sexual tape- worm. The bladder part is of no importance, but the head fixes itself and buds off a chain. For many others the story is similar ; the bladder-worm of the ox becomes another tapeworm {Tania saginata) in man ; the bladder-worm of the pike or turbot becomes another (Bothriocephaltis lotus) ; the tladder-worm of the rabbit becomes one of the tapeworms of the dog, that of the mouse passes to the cat, and so on. A bladder-worm which forms many heads destroys the brain of sheep, etc., and has its tapeworm stage ( Tattia ccenunis) in dog or wolf. Another huge bladder- worm, which has also many heads, and sometimes kills men, has also its tapeworm stage {Tania echinococcus) in the dog. But enough of these vicious cycles.
2nd Set of Worms. Bibbon Worms or Nemerteans—
4th Class, Nemcrtea.— In pleasing contrast to the flukes and tape- worms, the Nemerteans are free -living "worms." They are mostly marine, often brightly coloured, almost always elongated, always covered \vith cilia. There is a distinct food-canal with a posterior opening, a blood-vascular system for the first time, a well-develop nervous system, a remarkable protrusible " pro-
CHAt. XV
BcukboneUss Animals
a3*
boscu lying in a sheath along the back, a pair of enigmatical ciliated piU on the head. The sexes are almost always separate. Almost all Nemerteans are carnivorous, but two or three haunt other animals in a manner which leads one to suspect some parasitism ; thus AfalacobJella lives within the shells of bivalve molluscs. We find many of them under loose stones by the sea-shore; one beautiful form, Lineus marinus, sometimes measures over twelve feet in length. Some, such as Cerebratulm, break very readily into parts, even on slight provocation, and these parts are said to be able to r^row the whole. To speculative zoologists, the Nemer- teans are of great interest on account of the vertebrate affinities which some of their structures suggest. Thus the sheath of the ''proboscis" has been compared with the vertebrate notochord (the structure which precedes and is replaced by a backbone), and the two ciliated head -pits with gill-slits.
3rd Set of Worms. Nematbelmintlies or Bound- Worms— sth Class, Nematoda or Thread - Worms.— The " worms " of this class are usually long and cylindrical, and the small ones are like threads. The skin is firm, the body is muscular ; in most a simple food-canal extends from end to end of the body-cavity now for the first time distinct; the sexes are separate. Many of the Nematodes live in damp earth and in rottenness ; many are, during part of their life, parasitic in animals or plants. We have already noticed how long some of them — "paste -eels," "vinegar -eels," etc.— may lie in a dried-up state without dying. The life-histories are often full of vicissitudes ; thus the mildew- worm {Tylmchus tritict) passes from the earth into the ears of wheat, and many others make a similar change ; the female of Sphttrularia bombi migrates from damp earth into humble-bees, and there produces young which find their way out ; others, e.g. some of the thread-worms found in man {Oxyurii, Trichocephalus), pass from water into their hosts ; others are transferred from one host to another ; as in the case of the Trichina with which pigs are infected by eating rats, and men infected by eating diseased pigs, or the small Filaria sanguinis hominis, sometimes found in the blood of man, which seems to pass its youth in a mosquito. Somewhat different from the other Nematodes are those of which the horse-hair worm Gordius is a type. They are sometimes found inside animals (water-insects, molluscs, fish, frog, etc), at other times they appear in great numbers in the pools, being, according to popular superstition, vivified horse-hairs.
6th Class, Acanthocephsla. — Including one peculiar genus of parasites {Echinorkynchus).
4th Series of Worms. The Annelids or Ringed Wonns
-7lh Class, Chsetopoda or Bristle - footed "worms."— In the
«3« The Study of Animal Life part m
earthworms {Liimbricus, etc.), in the freshwater worms {Nais,
Tubifex, etc.), in the \o\yfioxxa& {Arenicola piscatorum), and in the
»ea-worms (Nereis, Aphrodite, etc.), all of which are ranked as
Ch8etopods,\he body is divided into a series of similar rings or
segments, and there are always some, and often very many, bristles
on the outer surface. The segments are not mere external rings,
but divisions of the body often partially partitioned off" internally,
and there is usually some repetition of internal organs. Thus in
each segment there are often two little kidney-tubes or nephridia,
while reproductive organs may occur in s^ment after segment.
Moreover, there are often two feet on each ring. The nervous
system consists of a dorsal brain and of a double nerve-cord lying
along the ventral surface. The nerve-cord has in each segment a
pair of nerve-centres or ganglia, and divides in the head region to
form a ring round the gullet united with the brain above. The
existence of nerve-centres for each segment makes each ring to some
extent independent, but the brain rules all. This type of nervous
system represents a great step of progress ; it is very different from
that of Stinging-animals, which lies diffusely in the skin or forms
a ring around the circumference ; different from that of the lower
"worms," where the nerve-cords from the brain usually run alonj,'
the sides of the body ; different from that of molluscs, where the
nerve-centres are fewer and tend to be concentrated in the head ;
different finally from the central nervous system of backboned animals,
for that is wholly dorsal. But the type characteristic of ringed
"worms" — a dorsal brain and a ventral chain of ganglia — is also
characteristic of crustaceans, insects, and related forms.
Of bristle-footed "worms," there are two great sets, the earth- worms and the sea-worms. The former, including the common soil-makers and a few giants, such as the Tasmanian Megascolides, sometimes about six feet long, have bristles but no feet ; sense- organs, feelers, and breathing organs are undeveloped as one would expect in subterranean animals. The sea-worms, on the other hand, have usually stump-like bristly feet, and eyes and tentacles and gills, but there is much difference between those which swim freely in the sea (e.g. Alciope and Tomopteris and some Nereids) and the lobworms which burrow and make countless castings upon the flat sandy shores, or those which inhabit tubes of lime or sandy particles (e.g. Serpula, Spirorbis, and Lattice or Terebdli cotichilegd). The earthworms with comparatively few bristles (Oligochseta) are bisexual, while almost all the marine worms with many bristles (Polychaeta) have separate sexes. Moreover, those of the first series usually lay their eggs in cocoons, within which the embryos develop without any metamorphosis, while the sea- worms, though they sf-metirr.PF. form r.ocoons, have free-swimming l.irva!
CHAP. XV
Backboneless Animals
m
usually v^ry different from the adults-little barrel-shaped or pear, shaped ci.iated creatures known as Trochospheres.
Some of the Chjetopods multiply not only sexually, but asexually by dividing into two or by giving off buds from various parts of their body Strange branching growths, which eventually separate mto individuals, are well illustrated by the freshwater A^a/JTand
Fig. 43.-A budding marine worm (6>//« ramosa). From Evolution of Sex ■ after M 'Intosh's Challenger Report.) '
still better by a marine worm, Syllis nvuosa, which almost forms •I iictwoi k.
Many sea-worms have much beauty, which some of their names hlv^ In'n "J"' ^Phjodiu, Alao/e, suggest, and which is said to ha^e mduced a specialist to call his seven daughters after them
Along with the Chstopods, we include some other forms' too
™" 'iTut ' "r *^^" --^'°" '^-^. ^he Myzostomata which or ^-ill-Uke growths on the feather-stars which they infest, the
wiEk T^'^"^ '" '"^''^ '^^ >»icroscopic male lives as a para i,e uuhin thefemale, and some very simple forms which are so .times ^ -.iv.. -Aiciii-.vnnends.
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»34
The Study of Animal Life part hi
8th Class, Hirudinea or Discophora or Leeches. — These are blood-sucking animais, which often cling for a long time to their victims. They live in salt and in fresh water, and sometimes on land. The body is elastic and ringed, but the external markings do not correspond to the internal segments. There are no legs, but the mouth is suctorial, and there is another adhesive sucker posteriorly. The body-cavity is almost obliterated by a growtli of spongy tissue, whereas that of Chaetopods is roomy. Leeches are hermaphrodite, and lay their eggs in cocoons, within which the young develop without metamorphosis.
The medicinal leeches {Hirudo medicinalii) live in slow streams and marshes, creeping about with their suckers or sometimes swimming lithely, preying upon fishes and amphibians, and both laiger and smaller animals. They fix themselves firmly, bite with their three semicircular saw-like tooth-plates, and gorge themselves with blood. When they get an opportunity they make the most of it, filling the many pockets of their food-canal. The blood is kept from coagulating by means of a secretion, and on its store the leech may live for many months.
The horse-leech {Hamopis sanguisuga) is common in Britain and ilsewhere The voracious Aulastoma is rather carnivorous than parasitic The land -leeches (e.g. Hamadipsa ceylonica\ though small and thin, are very troublesome, sucking the blood of man and beast Among the others are the eight-eyed Nepkelis of our ponds, the little Clepsim which sometimes is found with its young attached to it, the warty marine PontMella which fastens on rays, Piideola on perch and carp, BranchtUion with numerous lateral leaflets of skin, and the largest leech— the South American Macro- bdtlla valdiviana which is said to attain a length of over two
feet.
Possibly related to the Annelid series are two other
classes —
9th Class— Chxtognatha, including two genera of small arrow- like marine '• worms," Sagitta and Spadella.
loth Class — Rotifera, " wheel animalcvUes," abundant and exquisitely beautiful animals inhabiting fresh and salt water and damp moss. The head-region bears a ciliated structure, whose activity produces the impression of a swiftly rotating wheel. Many of them seem to !« entirely parthenogenelic. Some can survive being made as dry as dust. Fifth set of Worms— a doubtful combination including—
I ith Class— Sipunculoidea, " spoon-worms" living In the sea, freely or in tubes, e.g. Siputuulus.
lath Claa— Phoronidea, including one genus, Pk^vnis.
cHAf. XV BackboneUss AnimcUs
13th Class-Polyzoa or Bryozoa, with one exception forming colonies by budding, in fresh water or in the sea «. p. the common sea-mats or horn-wracks (Flustra)
'*''*.?«'7^'^\°P°*^* °' Lamp-shells, a clLs of marine
shelled animals once much richer in members, now
decadent. They have a superficial, but only a superficial
resemblance to Molluscs. F<:rn«ai,
I have net catalogued all these classes of "worms » without a
purpose. To ignore their diversity would have lent a false simplicity
to our survey If you gain only this idea that there U a great
Za^^TL"^"^ worm-like animals, which zoologists have not yet
reduc-;d to order, you have gained a true idea. The " worms "lie
as It were m a central pool among backboncless animals, from which
whh Frhllr"^ '""T? °^ P'^S'*^"^* "f*- They have affinities with Echinoderms, with Insects, with Molluscs, with Vertebrates. To practi<al people the study of " worms » has no little interest. The work of earthworms is pre-eminently important ; the sea-
constant companion ; numerous parasitic i^orms injure man. his domesticated ock, and the crops of his fielc'?.
.'♦• .EcWn<^erm»t» -in contrast to the " Worms," the series mcluding starfishes, brit -stars, feather- stars, sea-urchins, and sea-cucumbers, is well defined. "renins, ana
The Echinodermata are often ranker next the stinging animals, mainly becau«s many of the adults have « radiate fyi^metra; jellyfishes and sea-anemones have. But radiate sySr/b a
?K wlh olf" •*;• ^l^T *'VP'«'"y due to a sedemary habit of life in which all sid« of the animal were equally affected. More-
saT'tiel -T:?-^ Echmoderms are bilaterally symmetrical, that is to
olL /.h^n., ''"'"r '"'° >''" *'°"e . median pline. We place Echinodeims after and not before "worms." because the simplest worm-like animals are much simpler, much near" the l.yponiet.c.1 gastrula-like ancestor than are any Echinoderms. and
io^troroth^erl'^^'^''" "^''^"°''^""' ^^^^^ ^-™ «-
wa™ 's'^L'S '" i°''^ '. '''•^'^v"^ ?« *^"«^ ^'''^h *" in «»"« ways suggestive. You know the five-rayed appearance of the
animal like a conventional .tar; you ha\e perhapi watched il
moving slowly in a deep ,xH:k pJol by the^shoiT; yrtve
perhaps ducovered that it will surrender one of its armi ihen you
tor to capture it. No;v Haeckel compared the s.arfish toTcolZ
of five worms united in the centre. Each •• arm " or •« ray""^
complete in itself. £.,:h hM . nerve-cord aSng the ^tra
'::^^ Li? r • 23 ■' .*'• ^'P' P~'o"8»»ton. of the fo^.clrSiI.ro^ ' vessels, and reproductive organs Each i. wiatomically comparable
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236
The Study of Animal Life part m
to a worm. Furthermore, when an arm is separated, it may bud out other four arms and thus recreate an entire starfish. Each arm has therefore some physiological independence.
But there is no likelihood that a starfish arose as a colony of worms; the facts of development do not corroborate the sug- gestion. - , , ,
Of Echinoderms there are seven classes, two of which are wholly extinct. These— the Cystoids and Blastoids— are of great interest because of their relationship with the feather- stars or Crinoids, which stand somewhat apart from the other four extant classes. The Cystoids are more primitive than the Crmoids, and connect them with the starfishes or Asteroids. The Asteroids are nearly related to the brittle-stars or Ophiuroids, and they are also linked to the sea-urchins or Echinoids. These in turn are the nearest allies of the Holothuroids or sea-cucumbers.
The Echinoderms are all marine. The sea-urchins and Holo- thurians are mud-cleansing scavengers; the Holothurians and Crinoids feed for the most part on small organisms, though tlie former are sometimes mud-eaters ; the starfishes are more tmphatic- ally carnivorous, and often engulf small molluscs.
Among starfishes, sea-urchins, and sea -cucumbers, we find occasional cases of prolonged external connection between the
mothers and the young. . , , . u •..,
The Echinoderms are sluggish animals, though many bnttie- stars are lithe gymnasts, and though the commonest Crinoids (Comatulids, such as the rosy feather-star, Anttdon rosacea), differ from their stalked relatives and adolescent stages in being to some extent swimmers. Perhaps the sluggishness is expressed m the abundance of lime in the skin and other parts ; for, as the name suggests, the Echinoderms are thorny-skinned, being usually pro- tected by calcareous plates and spines. The sea-cucumbers are the most muscular and the least limy, indeed in some almost the only calcareous parts are a few anchors and plates scattered in the skm. Another frequent characteristic is the radial symmetry, but we remember that the larvae are bilateral.
Very important is the development ot a peculiar systciu oi canals and suctorial " tube-feet "—the water-vascular system. Hy means of the tube-feet the starfishes and sea-urchins move, m the others their chief use seems to be in connection with respir.it ion, and it is likely that in some at least they also help in excretion.
Another characteristic of the Echinoderms is the strangeness of the larval forms. For not only are they very different from the parenU, and v-iy remarkable in form, but in no case do they erow directly into the adult. The development U '''nfi'f' th€ larva does not li«:ome the adult } the fwindttioM of the
CHAP. XV
Backboneless Animals
237
Fic. 44. —A Holothurian (Cucumaria ertcfa) with iu young attached »o it't 5kin. (From Ev«iiilhH 0/Stx ; after ChailtHger Narrative.)
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The Study of Animal Life part m
adult are laid anew within the body of the larva, which is absorbed or partly rejected.
Not only the starfishes but also the brittle -stars and the Teather-stan often surrender their arms when captured, or even when slightly irritated, and a part or a remnant can in favourable conditions regrow the whole. The Holothurian Synapta breaks readily into pieces, and others contract themselves so forcibly that the internal organs are extruded.
The relations of Echinoderms t other animals are many. A little fish, Fierasfer, goes in and out of Holothurians ; the de- generate Myzostomata form galls on the arms of Crinoids ; star- fishes are deadly enemies of oysters. On the other hand, some sea-snails and fishes prey upon Echinoderms in spite of their grittiness. Except that the unlud eggs of some sea-urchins are edible, and that some sea-cucumbers are considered delicacies, the Echinoderms hardly come into direct contact with human life.
5. Arthropods. — Lobsters, centipedes, insects, spiders, agree with the Annelid " worms " in V ing built up of a series of rings or segments. .Some or all of iUv.i segments bear limbs, and these limbs are jointed, as the term Arthropod implies. The skin forms an external sheath or cuticle of a stuff called chitin, an>l this firm sheath helps us to understand how thfc limbs became well-jointed. The chiti.i seems in some way antagonistic to tlic occurrence of ciliated cells, for none seem to occur in this large series unless it be in the strange type Peripatus. The chitin \\^> also to do with the moulting or cuticle-casting which is common in the series, for the cuticle is generally rigid and does not expand as the body grows, hence it has to be cast and a new one made. Finally, Arthropods have a nervous system Kke that of Annelids— ft double dorsal brtiin connected by a ring round the gullet with a double chain of ganglia along the ver.lral surface. But the life ol most Arthropods is more highly pitched than that of Annelid>. The sense-organs are more highly developed, brains are larger and more complex, the ganglia of the ventral chain tend to become concentrated ; there is division of labour among the appendages : there are new internal organs s .ch as a heart ; the wliole bo<.!v is better knit together. A crayfish may part with his claw and grow another in its place, but the animal will not survive being cut in two as some kinds of Annelids do.
The series includes at least five classes :—
Crustacea, almost all aquatic, and breathing by gills.
Protrachcata, represented by the genus Ptripaiui.
Myriapoda, centipedes and millipedes.
Insecta, more or less aerial
Aracbnida, Riders, scorpions, mites, etc.
CHAP. XV
Backhoneless Animals
239
The members of the last four classes usually breathe by means of air-tubes or tracheae, which penetrate into every part of the body, or in the case of spiders and scorpions, by " lung-books," which seem like concentrated and plnited trachere. The King-crab (Limulus), which is very often ranked along witli Arachnids is aquatic, and breathes by peculiar "gill-books." '
(a) Omstacea.— Except the wood-lice, which live under bark .ind stones, the land-CMl)s which visit the sea only at the breeding
Fig. 45.— Nauplius of Sacculina. (From Fritz Mailer.)
time, and some shore-forms which live in great part above the tide- mark, the Crustaceans are aquatic animals, and usually breathe by gills. Each segment of the body usually bears a pair of append- ages and each aj.iwndage is typically double. Among these ap- I'tndagcs much division of labour is often exhibited, some l)eing sensoiy, others masticatory, others locomotor. In the higher forms the hfe-hjstory is often long and circuitous, with a succession of larval stages.
The lower Crustaceans arc grouped together as Enfnmostraca. riiey are often small and simple in structure; the number of
^y^^,'^
24© Tht Study of Animal Life part m
segments and appendages varies greatly. The little larva whidi hatches from the egg is usually a " Nauplius "— an unsegmentc.l creature with only three pairs of appendages and a median eye.
The brine -shrimps (A Hernia), the related genus Branchipus, the old-fashioned freshwater Apus ; the common water-flea Daphui^ and its relatives, like Lcptodora and Moina, are united in the okkt of Phyllopods.
The small "water-fleas"' of which Cyptis is a very comii\on representative, and which arc very abundant in sea and lake, foim the order of Ostr.icods.
Another " water-flea" Cyclops and many more or less degeneiaie " fish-lice " and other ectoparasites (e.g. Chondral ant hus, Cali^^u;., Lernaa) are known as Copepods. The free-swimming forms often occur in great swarms and are devoured by fishes.
The acorn -shells {Balanns) crusting the rocks, the barn.-iclcs (Ijspas) pendent from floating "timl)er," and the degenerate ^a^vw//;/,; under the tail of crabs, represent the order Cirrij^dia.
The higher Crustaceans are grouped together as Malacostracn. The bo<ly usually consists of nineteen segments, five forming the he.-id, eight the thorax, six the abdomen or tail. In most cases the larva is hatchetl at a higher level of structure than the Naupliii- represents, but the shrimp-like Peniais l)egins life as a Naupliu- while the crab is hatched as a Zoea, the lobster in a yet liighes form, and the craytish as a miniature adult.
Simplest of these higher Crustaceans, in some ways lil^i- :> survivor of their hypothetical ancestors, is the marine genus .\V/,;.'/.j, but we are more familiar with the Amphipmls (e.g. Gnnimaru \ which jerk themselves along sideways or shelter under stones luitli in fresh and salt water. The wood-louse Onisais has counieriui;-> {Asellus, LioUa) on the shore, and several remarkable paraMiic relatives. Among the highest forms are the long-tailed lob^te^^ (/lomartis, ralinitnis), and crayfishes (As/aats), and slirimi» (Crangon), and prawns {PaUcmon, randalus)\ the sofltailea hermit crabs (Pagitrns) ; and the short tailed crabs (e.g. Cuiiu-y. Carcinus, Diomia).
{h) Protracheata.— Z''''"'/'''"^- This remarkable genus. iei>rc-
FiG. 46.— Peripaiu*. (From C! ambers's Encychp. ; after Mo*«ley )
sented by about a dozen widely-distributed species, seems to ! e n survivor of the ancestral insects. Worm-like or caterpillar like sn
CHAP. XV
BackboneUss Animals
24t
app^rance, 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 jjossesses the air- tubes characteristic of insects and also little kidney-tubes similar to those of Annelids.
(0 Msrriapoda.— 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 antenncE (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.
Fiu. 47.-\Vinsed male and wingless female of Pneumora. a kind of grasshopper. (From Darwin.)
('0 Insecta.— Insects are the birds of the backboneless series. Like birds they are on an average active, most have the power of Hiyht, many are gaily coloured, sense-organs and brains are often highly developed.
Contrasted with Peripatus and Myriapods, 'hey have a more compact Ixxly, with fewer but more efficient lirSs. They are Arthropods, which are usually winged in adult life, breathe air 'y means of tracheoe, and have frequently a metamorphosis in their ijfe-history. To this definition must be added the anatomical facts "at the adult body is divided into three regions, (i) a head with tliree pairs of mouth -appendage* { = leg8) and a pair of sensitive < '"'growths (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, cgg-laying organs, etc., be remnants of these.
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243 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 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 plls "), 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 betwctn larvae and adults. The full-grown insects live among herbage, the young live in the ground, and the anterior legs of the larvre ue adapted for burrowing. Moreover, the larral life ends in a sleep from which an adult awakes. But much mure marked is the differ- ence between the aquatic larvae of mayflies and dragonflies and the aerial adults, in which we have an instance of mere 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 ini- 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 undont and rebuilt, wings bud
4XAr. XV
Sackboneiess Antmats
*43
out, the appendages of the adult are formed, and out of the pupal husk there emerges an imago, an insect fully formed.
(/) Aradmida.— Spiders, Scorpions, Mites, etc.— This ctss is unmtisfactorily large and heterc^eneous. 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 tracheae in other mites, by trarhete 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 {Cktlifer), 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 (Z»/w«/«x)— last of a lost race, with which the ancient Trilobites and Eurypterids were connected ; all these are usually ranked as Arachnids !
6. Molluscs. — 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 iU 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 slu^hness, 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 (Pecten) 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 nave 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 it to be explained as a loss, since related ancestral species possess it. There are, how«yer, two or three primitive forms
,44 The Study of Animal Life part hi
sutetance called ""*»''" •■*r^,toe, Sile'.he innc,n,», S.raTe"i:::S /n'V^.eSwfiK;? ... .he. „e ™„,
uUi;i
F.G. 48.-The common octopus (From ChamWs Encyclop. ; nfter I'.rc
Cuestions about shells whicl. we --^ jnsv^ Where .Ws^|hc
carbonate of lime come f^o".. since tha sal ^.
abundant in the water m which '"-^^J^^^^^^j/ ^^ ;, sca-ua.cr
the power of changing the =^h""^'^"^. ^"'P'^^^^^^^^^
into'carbonate of lime. V^^^^^l^^^;"^::'^:,^^^ ^^ cons.itu-
excreted from the skm ? Is the "j" ^^//^^^ °„ ,he whole to k
tional sluggishness of the animal nee u eems on ^_^^_^^^,
most massive in the most ^ "88'^'^' '^!\* ^^ '" ' ', J open sea, in the Most molluscs are marine on the ^ho e ^ t'le op ^^^^
great depths; there are also manyj^^^^^^^^^^ mussels ^noa'on and Lnt>}, ana .1- -"'!"» -
CHAP. XT
Backhoneless Animals
a45
and Paludina ; 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 , .leteropods, 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 not.ce that all molluscs except bivalves have in their mouths a rasping r.bbon or toothed tongue {radulu, 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 Ilolothurian 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 oi^ns 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 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 backhoneless animals, partly l)ecause of the nervous system, which here as elsewhere is a dominating characteristic. There are fewer nerve centres than in most .'\rthropod3 or in higher " worms," but this is m most casca
{■=. f
■I I
,46 Tht Study of Animal Life vakj iu
the sides and visara, a ^""°y««« ' ^ , . j^ ^ ^ important
foot, -jj^'^*" j^jf;^2:SpTS^^^^^ cA'^o'^^^ ^^^
are vuceral. In the «o'»«*™*»?7" most readily harmonised with thai of other InvMt™»i», m^j,,, ,i,e thrM «re con.
first »}"*"** .f°~Z.» It is a barrel -shaped or pear-hke :X-r.'ri.ro?5^»l"dU.infrontofthe.outh....U
'" M." "whutffcSe" to>o . mo,, ch^acterbtic fom <aUe<l
'° '^T^ ofc uSfoh dift. r™,n those of othe, -l^ '" S ine egg!»" f prolonged period as capita
J^h^^ fS, »^«.s *. in.»»«.y of F. "'- '4-
tSW "te •l>»n'i>"' f-O"" "« S""''° °°T^5 „, L» Tver Mh! go,? on tacreMing, and are now "^ore ,.b«nd.mt thj" »«' • *
=hiv.l«s cannot be said «»o,''»^t ^^^mIJ^ f Cep^'oV>. SrlSh t^ercltds oTf^iSl on,; he pea^ Na..J-s :lw sunrives. and though there are ">->' ''"'f ^^.^.tfj^'.^^ fish in on- -^;" - ^ 'rrdloTStSrw'e shcld i:™iin'5.c.y?h/.bXb;Lh|ng snait. and the fresh.,..- blval»es were ^c«hat late In appearing. ^^.^ Prof. Ray lankester has reconstracted ".'^™ " »°.f.<^inr, combiiK> the wrioos moUtucan cbaraccensliB .n a « '
CHAP. XV
Backbonehss Animals
847
lightning,"
u IV :.nv others,
dP,:
fashion, and may lie 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 {Neovienia^ C/uefod'-rnia, Chiton) suggest the origin of molluscs from son.j " worm " type or other. We can be sure ol this, however, that i iC series must have divid-^d 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. — Irresbtibly we think first of oysters, which Huxley describes as "gustatory flashes of su and over which neolithic man smacked his I'ps cuttlefish, ear -shells (Haiiotis), mussels (A ,'//?' winkles (Littorina httorea), cockles ( Cardium <ji J-it.i used as food, and many more as bait. In iiroic now, the shells of many were used for ■ r v >. lamps, vessels, coins, etc. ; the inner law r ■! mother-of pea.l ; concretions around i tntiiu, <.; pearls in the pearl-oyster (/!/ar^an/(7«<j cl ii TjTian purple was a secretion of the . h.ik v, related Murex ; and the attaching byssus thi. ad., o; • ' e (,iv;.V»e Pinna may be woven like silk.
On the other hand, a few cuttlefish are \..^g" nca;..!: to )e somewhat langerous ; the bivalve Teredo boring iu.^ ^jiii^-'uottoms £td p'ers is a formidable pest, baulked, however, by the pre- valent use of metal sheathing ; the snails and blugs are even more voradou* 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, a^-l poetic fancy has played lovingly with such as the Nautilus.
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CHAPTER XVI
BACKBONED ANIMALS
I. Balanegtosius—2. Tunuates—y The Lanceld—i,. Koinu- Mouths or Cyclostomata — S- Fishes — b. AMiphibuws ~ 7. Reptiles— i. Birds— 9. Mammals
A'x:oRDiNG to Aristotle, fishes and all higher animals were •« blood containing," and thus distinguished from the lower anmials, which he regarded as • ' bloodless." He was mistaken as to the abseiKc uf blood in lower animals, for in most it U present, but the line which he drew between higher and lower animals has been recognisc.l m all subsequent classifications. Fishes, amphibians, reptiles. bird>. and mammals differ markedly from molluscs, insects, crustaceans. "worms," and yet simpler animals. The former are backbuiicd (Vertebrate), the latter backboneless (Invertebrate).
It is necessary to make the contrast more precise. («) ^'^"'y Invertebrates have a well-developed nerve-cord, but this lies on tin ventral surface of the body, and is connected anteriorly, by a >>"t; round the gullet, with a dorsal brain in the head. In \ trti- bralss the whole of the central nervous system lies along the dur^al
-^
Fir, 4o.-DiMr»m of " Ideal Vertebrate " ihowing the Mgment* of the 1k.,Iv the spinal cordTthe nolochord, the gill-ciefU, the ventral heart. (After H..«cUI.)
surface of the body, forming the brain and spinal cord. Tlu -. arise by the infolding of a skin groove on the dorsad surfiue .f tlu embryo, {p) Underneath the nerve-cord in the Vertebrate ciidr)-
ft
CHAP. XVI
Backboned Animals
249
is a supporting rod or uij:t>. .< ul. It arses along the roof of the Axxl-canal, and serves as ^ supporting axis to the Ixxly. It i>er- sists in some of the lowest Vertebrates (f.^'. thelancelet) ; it i>ersists in part in some fishes ; but in most Verte!)rates it is replaced by a new growth — the backlxinc — wliich ensheaths and constricts it. (c) From the anterior region of the food-canal in fishes and tadpoles Klits, bordered by gills, open to the exterior. Through the slits water flows, washing the outsidcs of blood -ves.' -Is antl aerating the blood. These slits or clefts are represented ai the young of all Vertebrate animals, but in reptiles, birds, and mammals they are transitory and never used. Amphibians arc 'he highest animals in which they are used for breathing, and even then they may be entirely replaced by lungs in adult life. They are evident in tad- ))oles, they have disappeared in frogs. (./) Many an Invertebrate has a well-develojied heart, but this always lies on the dorsal surface of the lx)dy, while that of fish or inv^, bird or man, lies ventrally. (<•) It is characteristic of the eye of 1 ickboned animals that the greater i>art of it arises as an outgrowt!. from the brain, while that of b.acklKjneless animals is directly derived from the skin, liut this fMffcrence is less striking when we rememlxr that it is fn)iu an infolding of skin that the brain of a b.-ickboned animal arises.
Hut while the rliaractcristics of backlxjned animals can now \vi staled with a precision greater than tliat of sixty yea s igo, it is no longer possil>le to draw with a firm hand the dividing line Ulween b.icklKmed and backboneless. Thus fishes are not the simplest \'ertebrates ; the lamprey aixl tlie glutinous hag belong to a more primitive type, and are called fishes only by courte^y ; simpler stiil is the lancelet ; the Tunicates hesitate on the border line, K'ing tadpoledike in their youth, but mostly degenerate when adults ; and the w irm-like Halano^^lo'^sia is perhaps to be ranked as an incipient Vertebrate. The extension of knowledge and the appli- cation of evolutionary conceptions obliterate tiie ancient landmarks of vinrc rigid but K-ss natural classification.
1. BAlftnOCloSSttS. — lialino:;li).uMis is a worm - like animal, npresented by some half-dozen species, which ea. their way
Y\yi. 50. — B.ili«not!liJ'«»«s> 4i"wiiiK probDHcl-., collar, ami gill-slitt.
tlirnugh sandy imi<l olT the coasts of the (.'hannel Islands, Krittany, ChcsajH-ake ll-.y, and o'.hcr regions, lis In^ly i> ciliated and divided into distinct regions- a large •' piolioscis "' in front of the mouth, a
^iMx^
s t
■%v
»5Q The Study of Animal Life part m
firm collar behind the nouth, a part with numerous gill-slits behind the collar, and finally a soft coiled portion with the intestme and reproductive organs. The size varies from alwut an mch to 6 inches, the colours are bright, the odour is peculiar ; the sexes art- separate. But Bcdanoglossus is most remarkable m havmg a dorsal supporting rod (like a notochord) in the "proboscis" regon, a dorsal nerve-cord running along the back and especially devclopc.l in the collar, and a series of giU-clefls on the anterior part of ti.e food-canal. It is therefore difficult to exclude Balamglosms fr.Mu
Fig ,,.--Cephal«!i«cus a single individual, isolated from a colony, li i~ mi 1> m.i({nifiea. KV^om Chanibcrsr. tncydo/'-, after cArt//.«i'.' Kci-i > M'liilosh and Karmer.)
the Vertebrate series, and it i> likely that the same :mi-i be vii.l of another strange animal, Cfhahhiiuiis, discovered by liic <'■■■>'■
Unger explorers.
2. Tunicates. Hanging; to the jicnnon like stawtoN >^ii. t- fringe the rocky shore and arc rarely uncovercl Uy Uie ndi-. liij^i sea-sciuirls sometimes lixe. They are shaped like dnul.k-muu'.lK.; wine l«gs 2 or 3 inches in length, antl water »-. aUva>> \ i.i; drawn in at one a|M:rlure and exiK-lkd at the other. I >.uaii} !.a) live in dusters, and their life is very i^ssive. We call liuiu -•... Mjuirts localise water may si>out forth when wc squee/r i..v,i
CHAF. xn
Backboned Animals
251
bodies, while the tnle Tunicate refers to a characteristic cloak ot tunic which envelops the whole animal.
There is not much to suggest backbonedness about these Tuni- cates, and till 1866 no one dreamt that they could Ik: included in the Vertebrate series. But then the Russian naturalist Kowalevsky discovered their life-history. The young forms are free-swimming creatures like miniature tad]X)les, with a dorsal nerve-cord, a sup- porting rod in the tail region, gill-slits opening from the food canal, a little eye arising as an outgrowth of the brain, and a ventral heart.
The.e are only two or three genera of Tunicates, especially one called Apftndicularia, in which these Vertebrate characteristics are retained throughout life. The others lose them more or less com- pletely. The young Tunicates are active, perhaps too active, for a short time ; then they settle down as if fatigued, fix themselves by their heads, absorb their tails, and become deformed. The nervous system is reduced to a single ganglion between the two apertures ; the original gill-slits are replaced by a great number of a different character ; the eye is lost. From the skin of the degenerate animal the external tunic is exuded. It is a cutide, and consists, in part at least, of cellulose, the sul»tance which forms the cell-walls of plants. Thus this characteristically vegetable substance occurs almost uniquely in the most passive part of a very passive animal. The sea-squirt's metamorphosis, is one of the most signal instances of degeneration ; the larva has a higher structure than the adult ; the young Tunicate is a Vertebrate, the adult is a nondescript We cannot tell how this fate has befallen the majority, nor why a few are free-swimmers, nor why Apprndicularia retains throughout life the Vertebrate characteristics of its youth. Do the majority over- exert themselves when they are " tadpoles," or arc they constitu- tionally doomed to become sedentary ?
'i unicates are hermaphrodite — a very rare condition among Ver- tebrates ; some of them exhibit " alternation of generations," as the [Kiet Chamisso first observed ; asexual multiplication by budding is very common, and not only clusters but more or less intimate colonies are thus formed.
Tunicates live in all seas, niostly near the coast from low water to 20 fathoms, and usually fixed to stones and rocks, shells and sea- weed. A few are free-swimming, such as the fire-flame {Pyivsoma)^ a unified colony of tubular (orm, sometimes 2 or 3 feet in letigth, and brilliantly phasphorcsccnt. Very beauiiPd are the swimming thains of the genus Salpa, whose sti icture and life-history alike are complicated.
Tunicates feed on the animalcules bt>me in by the wntet currents, and some of them must feed well, so rapidly do they grow
li I
I:
II
f ' If
as* The Study of Animal Life pa»t hi
and multiply. Unpleasant to taste, they are left in peace, though a crab sometimes cuts a tunic off as a cloak for himself.
3 The LaiICel«t.-The lancelct {AmphioxusS is a simple Vertebrate, far below the structural rank of fishes. It is only about 2 inches in length, and, as both English and Greek names suggest, it is pointed at both ends. On the sandy coasis of warm and temperate seas it is widely distril>utcd.
From tip to tail of the translucent body runs a supporting noto- chord ; above this U a spinal cord, with hardly a hint of brain. The pl.a.7nx bears a hundred or so gill-shts, which m the aduh are covered over by folds of skin, so that the water which enters by the mouth finds its way out by a single postenor aperture. Although Amphioxus has no skull, nor jaws, nor bram, nor linibs, it deserves its position near the base of the Vertebrate series. The sexes are separate, and the eggs are fertilised outside of the body. The development of the embryo has been very carefully studie.l. and is for a time very like that of Tunicates.
4. Eound-MotttllB or OyclOlt01liato.-The hag -fishes and the lampreys and a few allied genera must be excluded from the class of fishes. They are survivors of a more pnimtive race. They are lawless, limbless, scaleless, and therefore not fishes.
The lampreys (Petromyzon) live in rivers and estuaries, and also
in the wider sea. They are eel-like, slimy animals. The skeleton
is gristly ; the simple brain is imperfectly roofed ; the single nostril
docs not open into the mouth ; the rounded mouth has homy teeth
on the lips and on the piston-like tongue ; there are seven pairs of
giU-pouches which open directly to the exterior and internally into
a tube lying beneath and communicating with the adult gullet : the
young are blind and otherwise different from the parents, and mny
remain so for two or three years. ,„ ,i , i
Though lampreys eat worms and other small fry, and even cieaa
animals/they fix themselves aggressively to fishes, ra.sping holes
in the skin, and sucking the flesh and juices. They aUo chng .o
stones, as the name Petromyion suggests.
Some si>ecics drag stones into a kind ot nest. They sp-awn i.i spring, usually far up rivers, for at least some of the marine lamprey, leave the sea at the time of breeding. The young are in many ways different from the parents, and that of the small riv.r lampem [Petromyion branchialU) used to be regarded as a distinct ^visL\~Ammo^<,ta. The metamorphosis was discovered t«o hundred years ago by Baklner. a Slrasburg fisherman, but vy overlooked till the strange story was worked out in ihjO i)^ August Muller. Country boys often call the young nine eyes, miscounting the gill apertures, and the Germans alio speak oJ munaugtn.
CHAP. XVI
Backboned Animals
«53
The sea lamprey (/'. marinus) may measure three feet ; the river lamprey (P. Jluviatilis) about two feet ; the small lampern or stone-grig (P. brttHchialis or planeri) about a foot The flesh is well known to be palatable.
The glutinous hag (Myxine gltUinosa) is an eel- like animal, about a foot in length, of a livid flesh colour. It is common at considerable depths (40 to 300 fathoms) oflf the coasts of Britain and Norway, and, when not feeding, lie- buried in the mud witli only its nostril protruded. Like the lamprey, it has a smooth slimy skin, a gristly skeleton, a round suctorial mouth with teeth. The single nostril communicates with the food-canal at the back of the mouth, and serves for the inflowing of water ; the six gill- pockets on each side open directly into the gullet, but each has an excurrent tube, and the six tubes of each side open at a common aperture. The animal lives away from the light, and its eyes are rudimentary, hidden beneath skin and muscles. The skin exudes so much slime that the ancients spoke of the hag " turning water into glue."
In several ways the hag is strange. Thus J. T. Cunningham discovered that it is hermaphrodite, first producing male elements, and afterwards eggs, and Nansen hao corroborated this. The eggs are large and oval, each enclosed in a •'horny" shell with knotted threads at each end, by which a number are entangled together. How they develop is unknown. The hags devour the bait and even the fish from the fisherman's lines, and some say that they bore their way into living flshes such as cod.
5. Fi(lh<>ff — Fishes .ire in the water as birds in the air, — swift, buoyant, and graceful. They are the first backboned animals with jaws, while scales, paired fins, and gills are their most character- istic structures. The scales may lie hard or soft, scattered or closely fitting, and are often very beautiful in foim and colour. The paired fins are limbs, as yet wi :iout digits, varying much in sire and position, and helping the fish to direct its course. The gills are outgrowths of skin with a plaited surface, on which the branching blood-vessels are washed by the water. They are the breathing organs of all fishes, but in the double-breathing mud- fishes {Dipnoi) the swim-bladder has come to serve as a lung, and there are hints of this in a few others.
There are at least four orders of fishes : — (l) The cartilaginous fishes (Elasmobranchs or Selachians) are for the most part quite gristly, except in teeth antl scales. Among them are the flattened skates and rays with enormous fore-fins, while the sharks and dogfish are shaped like most other fishes. Their pedigree goes back as far as the Silurian rocks, in which remains of shark-like forms are found. A J apancse shark {Ckia-
'ik I
•SI f f
254 The Study of Animal Life part iii
mydoselachm) is said to be very closely allied ^^/yP" J^J^Jj^X in the Old Red Sandstone. Allied to the Elasmobranchs, but ^metimes kept in a separate division, are two genera, the Cktmam Tr Kt^-S-the-Herrin^ and Callorhynchus, iu relative in Southern
^^''Si The Ganoid fishes are almost, if not quite, as ancient as the Elasmobranchs, but their goldenage, long since past, ^^ »" D^^" and Carboniferous ages. There are only some fJ^PJ^' J^^^J'^^J^ now alive. Two of these are the sturgeons (^«A««r) and he W pike (Lepidoslois). The latter has a bony skeleton ; the Z^n is inVrt gristly. An armature of hard scales .s very characteristic of this decadent order. ... ,11
S In Permian times, when Reptiles were begmn.ng, a thud type of fish appeared, of which the Queensland mud-fish (Ceratodus) leem to be Tdirect descendant. In this type the air-bladder ,s used as a lung, thus suggesting the transition from Fishes to Am- phlbiS^ PC haps thii order was always small m numbers ; now- adlvsT^ least there are only two genera- ara/..//«, from the S wate .f Queensland, and Protopterus, from west and trop.cal AfrTcaTv le another form, sometimes called a d.fferen genus is recorded from the Amazons. Double-breathers c.r all them, for they do not depend wholly upon g>i>s. >^"l ^ surface and gulp air into their air-bladder. Mud- rt well named, for as the waters dry up they retire into ming for themselves a sort of nest, within which they
{Ltpidosit Dipnoi V comr fishes
the n Jii, lie d' rma
( I. "^ -OStt
1 salm est fi >oats.
he Chalk period the characteristically modern fishes
will ompletely bony skeletons, begun. Ilcinni;
cod a' 1 pike, eel and minnow, and most of the com-
, belo to this order. Heavy ironclads yield to swilt
ai d 'I. le Teleosteans have succeeded better limn tin
T^rt ,vle lorm of most fishes is well adapted (or ra,.! swimming! I^ ' flat fish, whether flattened from above down wards like the .nslly bkale, or from side to side like the flounckp Td plaice, live at the bottom; those of eel -like shape usua ly "aloWlhe sand or mud; the quaint f^^ ^f.^^^^ The chief organ of locomotion is the tad ; the P»'^«^^ "'^^^^ raise or depress the fish, and serve as guiding oars. In he chml. ing perch they are used in scrambling ; .n the flymg hsh tl .7 . sometimes moved during the long swooping leaps. In ceK an 1 SsT they are absent; in the Dipnoi they have a re.narka hie InSian axil' The unpaired fins on the back «.d Uil and un.cr surface are fringes of skin 8upi»orted by rays.
Fishes are often rLsplendent in colours, which are partly ciue w
CHAP. XVI
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 jxjwer of rapidly changing their tints.
Fishes feed on all sorts of things. Some are carnivorous, others
Vm. 32. —The gemmeoiis clr.ij.inet {Cnl/ioHviuus iyrtt), the male alwvc, the fcmule beneath. (!• roiii Darwiu.)
\et;ctaiian, others swallow the mud. By niost of them worms, « lustaceans, inscct-larv.v, jiiolluscs, and smallci fishes are greedily tntcn. Stran-je are some of large appeti'e (<-.,(,■•. Chiasmodon niger\ wlio manage to get outside tishes larger than their own normal
M/L- :
Of their mental life little is known. Vet the running of tiout, the carefulness witli wliich llu- mother s.thnon selects a .spavvninj;- ^'i-ntntl, the way the archer-fish {Toxotes) spits ujwn insects, the lust. making and courtship of the stickleback and others, the img- nacity of many, show that the brain of the fish is by no means asleep.
II
11
«S6
Th€ Study of Animal Lifi pa»t in
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 fishs 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 comers, these twine automatically around seaweed, and the embryos 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 prohfic fishes.
Most fishes live either wholly in 4he sea or wholly in fresh water, but some are indifferent, ard 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 » fc* ot\^" 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 m many ways. Gunther 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 l,y tentacular orrans of touch, whilst the latter have no such accessory organs," an-i 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, (iiant Amphibiai.s or Labyrinthodonts bepin to appear in the Carboniferous period, but most of the modern frogs and toads, newts and sjilamanders, are relatively pigmies.
Young Amphibians always breathe by gills, as Fishes do, and m some cafes these gills persist in adult life. But whether they no or not, the full-grown Amphibians have lungs and use them, i de skin is characteristically soft, naked, and clammy. Amphibians are the first Vertebrates with hands and feet, with fingers and tocs. Unpaired fringes are sometimes present on the back and tail .as in Fishes, but are never supported by f vrays.
CHAP. XVI
Backboned Animals
as?
I
The class includes four orders, of which the Lab]rrinthodonts 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. Cacilia. Some, the last for example, are tensstriaJ, 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 LissoiriUm), and the often brightly-coloured salamanders (Saia- niandra) 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 Menobranchus 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 {Axoloi!) has persistent gills, the other form {Amblystoma) loses them, asd 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 frc^ {Ranct), the Surinam toad (JHfd), 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- ^r slow-worms, which are lizards. There are only very few genera, Siphonops, RhineUrema, Epicrium, Cacilia. 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 ouite stif^, 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 s'iipped over only in a few cases. In the black salamander {SalamanJra atra) of the Alps, which lives where
S
258 The Study of Animal Life part 111
pools are scarce, the young, after living and breathing for a time SSn the mother, are l^rn as lung-breathers; also m some Tpecies of tree-frogs {JJylodes), ..-hich live m situations where water
''''''^t^:£^^Tt^'^^o. frog should be studied by every student of natural history. The eggs are fertilised as they are being laid. The division of the ovum can be readily observed, "n hs early stages the tadpole is fishlike. with a lamprey-l.ke
Fig. 53. -The life-history of the Frog.
mouth. External gills are replaced by an internal set. an-l as metamorphosis is accomplished these disapiv^ar and the lui.t,'s become active. The larva feeds first on its own yolk, then en 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 larvx 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 croal:- ings of frogs remind us. Quairt are many of their reproduMive habits, to some of which allusion has already been made, buch
CHAP. XVI
Backboned Animals
259
animals as the Surinam toad (Pipa amfricana) and the Obstetric frog (Alyles obstetricans) 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 tliem the fittest emblems of the omni- ' potencc 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 Archctopteryx, 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 jiigmies beside an Ichthyosaurus 25 feet long, a Megalosaurus of 30, a Titanosaurus of 60, or an Atlantosaums of loo, 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 foi-ms larger than any living members of the class, liesides size, however, the ancient saurians had another virtue, apparently possessed by both small and great — they were pro- gressive. Yox, with toothed birds on the one hand and flying or flopping reptiles on the other, it seems probable that birds had
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a6o 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 (Lacertilla).— 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 ver>' 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 {Lacerta or Zooto^a mvipara), and the slow-worm, the young are hatched within the
mother. . ^ , v v • l
Among the remarkable forms are the Geckos, which with plaited adhesive feet can climb up smooth walls ; the large Monitors [yaranus\ which may attain a length of 6 feet, and prey upon small mammals, birds, frogs, fishes, and eggs; the poisonous Mexican lizard {Heloderma hoiridum), with large venom glands and somewhat fang -like teeth; the worm-like, limbless Amphis- bam', the likewise snake-like slow-worm (Anptis 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 slugijish and spiny " Horned Toad " (Phryiiosonta) ; the Agamas of the Old World comparable to the Iguanas of the New ; the Flying Dragon (Draco volatts), which, with skin outstretched on extended nbs, swoops from tree to tree; the Australian frilled lizards (Chlamydosaunts) and the quaint thorny Moloch ; the single marine lizard {Oreo- cephaUu or Amblyrhynchm cristatus) from the Galapago and the divergent Chameleons, 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 upward-looking eye.
Snakes or Serpents (Ophidia). — These much modified
reptiles mostly cleave to the earth, though there are among tliem devcr climbers, swift swimmers, and powerful burrowers. Though
CHAP. XVI
Backboned Animals
261
; j!
m
i . I
|
t I ; |
|
|
1! |
|
|
1 '■ !i |
i |
'}•"
a6a
The Study of Animal Life part hi
they are all limbless, unless we credit the little hind claws of some hooi 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 ground 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 'le 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 I 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 j 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 coib. 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 hiero-jlyph of the demoniac power of the earth — of the entire eartlily 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."*
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.
Ruskin's Quttn of the Air.
CttAP. 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 Anomakpsis, 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. 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 permanentlyerect grooved fangs in the upper jaw, and a salivary gland whose secretion is venomous. Such are the cobra {Naja tripudians), the Egyptian asp (Naj'a haje)y the coral snakes (Elaps), and the sea snakes {Hydrophis).
Other poisonous snakes have perforated fang teeth, which can be raised and depresseJ. Such are the vipers ( Vipera), the British adder [.Pelias derus), the copperhead (Ancisirodon contortrix), the rattlesnakes (Crota/us).
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 many 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 slu^sh 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 01 sand.
The marine turtles {«.g. Sphargis, Chelone), the estuarine soft- shelled turtles {e.g. Aspidonectes\ the freshwater turtles {e.g. Emys), and the snapping turtle {Chelydra) are more active than the land tortoises, such as the European Testudo graca, often kept as a pet. The tortoise of the Galapagos Islands ( Testudo elephautopus), the river tortoise {Podocnemys expattsa) of the Amazon, the bearded South American turtle (Chelys matamata), and the green turtle {Chelone mydas) attain a large size, sometimes measuring about 3 feet in length.
Oroccdilians (Crocodilia). — Crocodiles, alligators, and gavials •eem in our present perspective very much alike— strong, large, heavily armoured reptiles, at home in tropical rivers, but clumsy snd stiff-necked on land, feeding on fishes and small mammals,
V f
rt
f.'% m
264
The Study of Animal Life part m
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 whilo 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 fetal, especially in India ; crocodilians are sometimes destructive ; turtles afford food and " tortoise shell ;" lizards arc 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
fio. 55.— The Collocalia, whicli from the secreted juice of its salivary glands builds the cdiblc-l'iid's-ncst. (Adapted from Brehiii.)
them than this sentence from Ruskin's Queen of tic Air? "'I'hc 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 bluwn
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"- 14' 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 niore 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, swimniers 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 "—0/tjM<7f<?w«j— -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- »hell pass through somewhat fish-like and somewhat reptile-like
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The Study of Animal Life part hi
Fig. 56.— Decorative male and less adorned female of Spafhura— a genus of Humming-birds. (From Darwin, after Urehm.)
CrtAP. XVI
Backboned Animals
267
f ;
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 arc 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 Opisthocomiis, 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 modem, are the running-birds, which ai'e incapable of flight, and therefore possess a flat raft- like breast bone, to vvhicli they owe their title Ratita;. Nowadays these are few in number, the Ostrich and the Rhea, the Cassowary and Kmu, and the small Kiwi. Heside these must be ranked the giant Moa of New Zea- land, not long extinct, and the more ancient, not less gigantic yEpyornis 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 al, placed in a sub-cKass by itself, the Archaopteryx (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 and whales, seals and sea-cows, are obviously excep-
Fig. 57. — Restoration of the extinct moa (/)/«- ornts ingens), and alongside of it the little kiwi {Apteryx iiiantelii). (From Cham- bers's A^ktj'c/o/. ; after F. v. Hochstetter.)
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Tfu Study of Animal Life part 114
tional. The brain of mammals is more highly developed thap 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 {Omithorhynchus) and the Porcupine Ant-Eater lEchtdtta\ 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 distributioii. 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 Mynnecobius^ 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 -nammal, 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 Camivora (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-co' jys or Hyraxes— " a feeble
CHAP. XVX
Backboned Animals
269
folk " — seem to be allied. Both are often included in the great order of hoofed animals or Ungulates, along w-th the odd-toed
Fig. i%.—Phenacoelus f>rimarms, 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 — horse, 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
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111
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The Study of Animal Life part m
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. 6o.— Head of male Semnopithecus. (From Darwin.)
remarkable fossil type, Pkenacodus, 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 gori i t, 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.^. the numerous species of Cebus, some of which are the familiar
CHAP. XVI
Backboned Animals
II
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 ipake, 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 at 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
unXgulates
KEYS
\ CARNI/VORES
URS
CETACEANS
BATS b
\ td
IN/SECTIVORES
SIRENIA
EDENTATA
MARSUPIALS
\
MONOTREMES
a7a The Study of Animal Life part in
SURVEY OF THE ANIMAL KINGDOM T
BIRDS. Flying-Birds. Running-Birds,
Placentals. MAMMALS. Marsupials. Monotremes.
Snakes. Lizards. REPTILES. &ocodiles. Tortoises
Double-Breathers. Bony-Fishes.
Elasmobranchs.
AMPHIBIANS. Newt. Frog.
LANCELET.
CrcLOSTOMATA. Lamprey. Hagfish.
TUNICATES
Insects. Arachnids
Myriapods. Peripatus.
ARTHROPODS, Crustaceans.
BALANOGLOSSUS.
ANNELIDS. "WORMS."
FLAT-WORMS.
Cuttlefish. Gasteropods.
MOLLT'SCS.
Bivalves.
Feather-stars.
Brittle-stp-s.
Starfish.
ECHINODERMS,
Sea-urchins. Sea-cucumbers.
Ctenophorcs. Jellyfish. Sea-Anemones. Corals.
STINGING-ANIMALS or CCELENTERATES.
Medusoids and Hydroids.
SPONGES.
Infusorians. Rhiropods. Gregarines.
SIMPLEST ANIMALS.
I
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PART IV
THE EVOLUTION OF \NIMAL LIFE
CHAPTER XVII
THE EVIDENCES OF EVOLUTION
I. The Idea of Evolution — 2. Arguiiunts for Evolution : Physio- logical, Morphological, Historical — 3. Origin of Lift
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 tgg, 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 ill 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
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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 (i794), 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,^ 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 dtemelle." "As in the development of a fugue," Samuel Butler says, "where, when the subject and counter-subject have been announxd, 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 oj Species (1859), where the arguments were marshalled in sue' a masf^rly fashion that they forced the conviction 1 1 uie the word in its literal sense-- not admiuingof proof." It is not my duty nor my desire to discuss the poetical, or philosophical, or religious conceptions which lie behind the concrete cMmogomes of diffaxSt ages and minds. To many modem theologians creatior, nMdirmeanTthe institution of the order of nature, the possibility of natural evdutioa included.
CBAP. XVII The Evidences of Evolution 375
of the wwld. 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 {a) from the distribution of animals in space ; (p) from their successive appearance in time, {c) from actual variations observed in domestication, cultivation, and in nature ; {d) from facts of structure, e.g. homologous and rudiiiiftntary 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 livia, 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 I 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
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The Study of Animal Life part iv
F.G 6. -Varieties of domestir J.igeon arr.ngejl arou.,.l f--^f^ ^'^■^•'' ''^
CHAP. XVII The Evidences of Evolution
211
never seen. Conviction depends on more than intelligence, often on emotional vested interests.
(J>) 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,
(0 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
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The Study of Animal Life part iv
6
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 runn-rs 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 ■!!;dhrndfeet°o'f order to order and even class to class, such th-^ horse and as that Strange mammal Phenacodtts, which TestLf show: seems to occupy a central position in the ine the gradual ^qx\qs, SO uumerous are its affinities, or such [he numVr uf as thosc sauriaus which link crawling reptile 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
SU-s"«" to soaring bird.
cyclot. ; after Marsh.)
CHAP. XVII 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 evohition exhibited by tne antlers of deer in successive ages. (From Chambers's Encyclof.)
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 evolution very
f
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38o 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 ligbt 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 m all
our thinking. , j . • /
To those who feel a repugnance to the doctrine of descent, I suggest the following considerations :—
(i) 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 worid, 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— Ow«^ 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.
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I
CHAPTER XVIII
THE EVOLUTION OF EVOLUTION THEORIES
I. Greek Philosophers -2. Aristotle-l. Lucretius-^, Evolution, ists before Darwin-^. Three old Masters: Buffon, Erasmus Darwin, Lamarck-6. Charles Darwin— 1. Darwin s Fellom- workers-^. 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 Plulosopliers.— Of the wise men of Greece and what they thought of the nature and ongin 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 ot 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 ot
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 modem 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 modem 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 retuming 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 >o inclined, call these principles " attractive and repulsive orces " ; 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 effeci. 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 to 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 fvindamental It is
In
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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 xccognisedthe changefulness of life, the world was to him an eternal fact not a stage m 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 m the sea about which there is doubt whether they be animals or plants. «« Animals are at war with one another when they live m 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 eaith's fertile bosom and not by the gradual transform?tion 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 f?:fferent 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 fro:" ''/'. beasts, and have ensued peace, and plenty of food obtained w :out 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 suffer 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 BufTon, 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 BufTon.
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 forenmners, who prepare their
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paths. Therefore xa 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." i 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, Spinoia, Leibnitz, Herder, Kant, and Schelling ; of the acceptance cf 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 .nd Robinet. who, before Buffon's day, whispered evolutionist heresies. The history of an idea is like that of an organism in which cross-fenilisation 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- 17 88) was bom to wealth andwas wcddeu
to Fortune. He sat in kings' houses, his statue adorned their gardens. As Director of the Jardin du Roi he had oppor- tunity to acquire a wide knowledge of animals. He com- manded the assistance of able coUaborateurs, and his own 1 Article "EvoluUon" (P. Geddei) in Chambers*! Encyciofadia.
:^=^K:'aKrA •• ^A«;^J'MTtf.K£~~V'W-"y '
CH. XVIII The Evolution of Evolution Theories 287
industry was untiring. He was about forty years old when he began his gfreat Natural ^''«tory, 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 I'homme m6me," he said ; or again, " Le style est comme le bonheur ; il vient de la douceur de I'Ame." Rousseau called him " La plus belle plume du si^cle ; " Mirabeau said, " Le plus grand homme de son sifecle et de bien d'autres ; " Voltaire first mocked and then praised him ; and Diderot also eulogised. EufTon 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 pasi. 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 Bufibn'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 Bufibn's treatment of zoology gained freedom because he wrote in French, having shaken oflF 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
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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, suggestmg that heat and light are atomic movements, denying the existence of hard-and-fast lines—" Le vivant et I'animd est une propn^t^ physique de la mati^re !" protesting against crude distmctions 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 ; Buflfon took an eagle's flight and saw the connected range of hills,—" I'enchainement des ^tres.
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 stammc rjng 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 " . , • 1
He beUeved 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 tnat evolutionary change was mainly due to the exertious 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 theit progress as the result of their endeavours. Buffon under- rated the transfon.iing 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 El lution 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 withm another like the cups of a conjuror."
"From their first rudiment, or primordium, to the termination ot tneir 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." .1. "^"' ^"^ w^'<^f 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 ti,ings seems to hi/e been as familiar to the ancient philosophers r the modern ones, and to have given rise to the beautiful hieroy.yphic figure of the rpwToy if6y, or first great egg, produced by night, that is, whose ongrn IS involved in obscurity, and animated by ip^s, that is, by Divine Love ; from whence proceeded all things which exist."
On Lamarck (i 744-1 829) success did not shine as it did on the Comte de liuffon or on Dr. Erasmus Darwin. His life was often so hard that we wonder he did not say more about the struggle for existe ice. As a youth of six- teen, destined for the Church, ' rides off on a bad horse to jo... the French r.rmy, then fighting in Germany, and bravely wms 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 F/ore frafiiaise in three volumes, the publica- Hon of which (1778) at the royal press was secured by
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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 Buflfon influenced Lamarck m many wavs 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 liftmg his anchors from the orthodox moorings, relinquishing his behef 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 i8o. he published Researches on the Organisation of Uvtng Boies', in 1809 a Philosophie Zoologique , from 1816- 1 822 his Natural History of Invertebrate Animals, a large work in seven volumes, part of which the blind na -.list dictated to his daughter. Busy as he must have beea wuh zoology, his restless intellect found time to speculaie-.t 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 weathe^ which seem to have been almost always wrong. Nor d.d Lamarck add to his reputation by a theory of Hydrogeology, and his scientific Sends who were loyal specialists shrugged their shoulders more and more over bis intellectual knight-errantry.
. 1 J- J !.:_ 1™**... voarc his tr
Poverty
lore over ma ini*,..*,..*— o- - •
roveny 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 ,n Amei.ca, and even those who deny his doctrines admit that he was one
of the bravest of pioneers. „ u 1 c-,v>.
Of Lamarck's Philosophie Zoologtque, Haeckel sa>s, « This admirable work is the first connected and thoroughly logical exposition of the theory of descent." And again he savs "To Lamarck will remain the immonal glory 0 havi'ng for the first time established the theory of descent as an independent scientific generalisation of the first order,
cn.xvni The Evolution of Evolution Theories 291
as the foundation 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 iloge de M. i'^T^ ^^^'^^'■ed before the French Academy in 1832' said, "A system resting on such foundations may amuse the imagmafon of a noet, etc., ... but it cannot for a moment bear the examination of any one who has dissected the hand, the viscera, or even a feather." The great Cuvier was a formidable obscurantist.
But let us hear Lamarck himself:
ducl'SfZ '"■^" ^' """'^ P'°'"^' gradually, and could not pre duce all the ammals at once. At first she formed only the simplest and passed from these on to the most complex " amplest,
\SJ^^ ^™"' °^ f"'^"^'^ 'P^''"' "« "°' so <^onstant and unvary- mg as IS commonly supposed. Spontaneous generation staS each particular series, but thereafter one form givi rise to aulcher In hfe we should see, as it were, a ramified continuity if ierta'n species had not been lost." """.luuy u cenam
"The operations of Nature in the production of animals show Int.l Tr ':." P"""""^ '"'^ predominant cause which gves to amma hfe the power of progressive organisation, of gfadual V comphcating and perfecting not only the organism as a whole bu^ each system of organs in particular." '
incrla^^'lhf Ti ^'^^ ^) ''' '"^"^'"' P°^" *^"^^ continually to mcrease the volume of every living body, and to extend the d.mensions of its parts up to a self-regulated limit, resultf fi:om fhJ^J^" Production of a new organ in an animal body Se itseTfe \n l"r"'"'' °^ '°'^' "^^ "^'^^ ^'^''^h continues to
;• rAini Law. The development of organs and their power of
Fourth Law. All that has been acquired, begun, or -handed in the structure of individuals during ,he course ofShi life f pre
wnich spring f om tho.se which have experienced the changes."
These four aws I have cited from limarck's HistoinNXrelle nd'Lt;'?';r'.h'^ir'"'^*'''"^''^^ ^« in^lste^tnt;
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creature by iU own efforts '"■" ""'!'%,„,„„„en,, due to use or
descended." ,
The historian of the evolution of evolution theones .ho^d taije account of many w^^rsb^^^^^^^^ Buff „,
S:n5. flugh.'U'^^Vie'r. *e fellow-worker of his you^h Udmn' ; bloT^S But we must now recogn.se the work
Siw sill laboratory, his yellow-back novels h,s «^uff.
^isi%rrn-r^s^t?;ri^ - -^^^^^^^^ »?rr.rrc-»rrerr.
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 not 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 Linnsus, 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 .as 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 c^ear 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
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of this doctrine on various groups of i^'^'^^ '' ""^ ^'^ *" l^^^y^^^''V">^'^\^'^^''^tZT:\c^ Is to us
sin«^u:ro;n«£^^^
caption was no ne» ""^^^f rKavel to many. He did L"-o. J^nt';h:e"s2b^i:kea."'Hf convened natu,a>ists to
A }rL the thfory of development out of preceding
hfe, It was eage ^^.^ ^^^^^^^ ^^^ Aew
itrthinUe. and '^^^^^^'^^ T£^ how the conception to» ^"^ fven found expression In ro*e: o-flSlra^.tdJ^sC-Uan ofte^n-tepeate.
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CH. xvm 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 bom 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 va-iation possessed by the survivors is handed on as an inheritance to their oflT- 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
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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 m the hope that the contrast may be sufficiently interesting to induce you to think out the question for yourselves.
"Buffon planted, Erasmus Darwin and Lamarck watered, but it was Mr. Darwin who said '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 mam means of organic modification is the most absolute denial of God which it is possible for the human mind to conceive. . . . 7 Daxwin'8 FeUow-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 Biolo^. No one will be slow to appreciate the splendid unselfishness with which he has for thirty years sunk himself ^ the Dar- winian theory, or the scientific disinterestedness which leads him from the very title of his last work^ to its close, co 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 naturaUsts ; 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,"
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 evolulion-torch uplifted. A ponderer on the nature of things, and the possessor of encyclopaedic 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
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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 Radiolarians, Sponges, Jellyfish, etc., may be well called the Darwin of Germany. He has devoted his life to applying the doctrme 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 wa? 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 Naturliche ScKopfungsgeschichte (ist ed. 1868 ; 8th ed. 1889) ; and his Anthrcpor'-'ie {I'i^l %, trans- lated as The Evolution ./ 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 Generellc Morphologic (2 vols., Beriin, 1866), which in its reasoned orderiiness 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 doctrme of descent in itself and in its consequences with more keen- ness and success than the author of Man's Place in Nature (1863), American Addresses, Lay Sermons, etc., and no one
CH. xvin 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 relaiive importance of the various factors in evolution is very uncertain. ^
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.
> 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, lew 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 \<\s 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 Encyclopcedi^ Dritauri. :,
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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 Buffbn 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 vari- tions 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, influ< need 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 di'-ectly cause variations it will not be possiole 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 f^ observed facts 0/ variation.
cH. XVIII The Evolution of Evolution Theories 301
The secondary factors of evolution niay 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 inteiL'^ei
Natuiai selection i<; '\ phrase descriptive of the course of nature, ( mV a survival of the tit and the elimination of the unfit in li-e struggle fci existence. It involves on the one hand the survivHi. /.•♦. the nutriti/e 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 hav- been produr°d 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 possiMe. 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."
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The Study of Animal Life part iv
SUMMARY OF EVOLUTION THEORIES.
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I Variations all ultimately due to External Influences.
Direct action of the environment produces environ- mental variations,
wh ich if trans;missible,
Organismal,
constitutional,
congenital,
or germinal
variations
may be either
definite or indefinite.
Use and disuse and
chanf^e
of function
produce
functional
variations
(certainly transmis- sible).
may accumulate as environ- mental modifications of species.
All cases
By the
persistence
of the original
editions
iheso may
grow into
new
species.
By natural
selection in
the --truggle
for existence
these may
give rise to
new
species.
wh':ich, if transimissible.
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<
may
be aflfectied by
may accumulate
as functional modi- fications
of species.
"isolation."
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The process of natural selection will affect all cases, but i» less essential for those marked • .
CHAPTER XIX
THE INFLUENCE OF HABITS AND SURROUNDINGS
I. The Influence of Function — 2. The Influen,. of Surroundings — 3, Our own Environment
I. The Influence of Fnnction. — 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 cf function produced change of structure, but there are few careful observations bearing on this questior.
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 fhsm, the answers given to these questio*^'- are not reliable.
It is easy to find hundreds of cases in which the constant
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304 The Study of Animal Life paxt iv
characters of animals may be hypothetically interpreted as the result of use or disuse. Is the torpedo ' shape of swift swimmers due to their rapid motic nrough 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 blmd 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 m vegetarian anin.als been mechanically lengthened, do the wing bones and muscles of the domesticated duck compare unfavourably with those of the wild duck because the habi* of sustained flight has been lost by the former ?
But these interpretations have not been venfied ; 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 disbeheve m tne inherited effects of functional change are (i) that definite proof is wanting, (a) 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 — h rses, 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 pulex 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 disrippear 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
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3o6 The Study of Animal Life part iv
nerves which usually degenerate in each individual life-
™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 m the course of natural selection, that is to say by a secondary
factor in evolution. . , j- .• .
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 chree sister Noms, 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 scientihc 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 orgrnism 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 Noms, the three Factors of Life. Organ- ism, function, and environment are the $»des of the Die-
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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- roundinto — 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 vacuoy 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 nnceasingly, 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 it: bed which produces the apparent constancy of the whiripool. 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 curre.Us 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
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3o8 The Study of Animal Life part tv
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 Selbome 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 ou what the environment of an organism is, and what power . has In a smithy we see a bar of hot iron bemg 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 l.vmg thing u 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 esoecially. it omes under the influence of nature s hammers ; it may become fitter for life, or it may be battered out of existence altogether. Let us try to analyse the various environmental factors.
{a\ Pressures.— r\x%\. we may consider those lateral and vertical pressures due to air or water currents and to th" gentle but potent force of gravity. The shriek of the w^nd as It pruSes the trees, the swish of the water as it moulds the sponges and water-'eaves, illustrate the tunes o those pressure-hammers. Under artificial pressure embryos have been known to broaden ; even the division of the egg .s 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 d^efopment and reared dwarf broods ; and the rate of human mortality sometimes vanes with the sue of the
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CH. XIX Influence of Habits and Surroundings 309
dwelling. It is difficult, however, to abstract the influence of restricted space from associated abnormal conditions.
(J)) 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 Atnbly- 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
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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
F;<;. 64.-AxoIotl (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 ot
p,(-, 6, —Side view of male Atlnnia saliiin (uulaiged). (From Chambers's Kiicychp.)
Schmankewitsch on certain small Crustaceans. Aniong the numerous species of the brine-shrimp ^;■Av,//.^ the mos unlike are A. salina and A. milhausemt ; they difter m 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 ^. salina »vhich live in the less salt water,
Fi(j. 66. — Tail-lobcs of Artciiiia saiiiia (to the left)and o( Arte/in'a titilhausetiii (to the right) : between these four stages in the transformation of the one into the other. (From Chambers's Encyclop. ; after Schmank.:witsch.)
11
F
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 \h& primordial factor of organic evolution."'
To Claude Bernard, the main proljJem of evolution seemed to be concerned with variations in nutrition : " L'evolution, c'est I'ensemble constant dc ces alternatives dc la nutrition ; c'est la nutrition considerde dans sa reality, embrassde d'un coup d'oeil ii travers le temps."' John Hunter and others have shown how the walls of the
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stomach of gulls and other birds may be experimentally altered by cliange of diet, and the same is seen in nature when the Shetland gull changes from its summe.- 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 57 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 81 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 v xiich the especially nutritious flesh of frogs was supplied, had no less than 92 females
to 8 males.
When food is abundant, assimilation active, and mcome 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
ill
CH. XIX Influence of Habits and Surroundings 313
in the course of a year be l. progenv which would weigh down 500,000,000 stout men. \. i. 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 bom, parthenogenesis ceases, ordinary sexual reproduction recurs. Moreover, if the Aphides be kept in the artificial summer of a greenhouse, as has been done for four years, the parthenogenesis con- tinues without break, no males being bom 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.
if) 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°- 10° C, twice at lo'-is", thrice at is'-ao", 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 Hfelessness, 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 lemn^ing,
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314 Tlie 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,
(variety Telamouide^, to tl.e ri^ht I v; Nammer form (variety Marccllu.). (From Chambers's Eucydop. \ after Weismann.)
of which the winter forms are so different from those born in summer that they have often been described as different spe-ics It is possible that this is a remmiscence of past climatic changes, such as those of the Ice Ages, as the
Fig. 68.-Se.-isonal chnnse. <.f the hill in the puffin {rraU,XHln»rcik«)\ to the left the -opting form, to the right the winter form, both .idult malen. (Altir Dureau.)
result of which a species became split up into two varieties. Thus Araschnia kvana and Araschnia prorsa are respect- ively the winter and summer forms of one species. In the
CH, XIX Influence of Habits 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 arti6cial cold, in making the pupse 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 difterent at dilTerent 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 influen s 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 tha. 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 ai d 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
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3i6 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 undersides 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. -
(</) Animate Surroundings.— ^t 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 {JPycnogonida) affect hydroids, a polype deforms a sponge, a little worm {Mysostoma) makes galls on Crinoids. Prof. Giard has described how certain degenerate Crustaceans parasitic on crabs injuriouajy 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
3i8
The Study of Animal Life part iv
^'.egrees. 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— m 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.*
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 » Cf. Matthew Arnold's poem, ' ' The Future," and Walt Whitman's •' AMim!latii»s."
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,^ 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, T surroundings w"" 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.
> Ideally stated in Emerson's well-known poem of "Art."
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CHAPTER XX
HEREDITY
I. The Facts of Heredity —%. Theories of Heredity: theological^ metaphysical, mystical^ and the hypothesis of pangenesis — 3. The Modem Theory of Heredity—^. 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 bom 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
3ai
between successive generations^ choosing this definition because it is misleading to talk about "heredity" as a "basal principle ia evolution," as - "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 supphes 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 thtimbs 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 maybe transmitted is long and grim. But care is required to distinguish
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between reappearartce due 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'? nedigree, a wit suggests that we need only pull off its tail. When such ancestral resemblance in ordi-
Fig. 6a.— Devonshire pony, showing the occasional occurrence of ancestral stripes. (From Darwin.)
nary generation is very marked, we call it •' atavism " or «« 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 bom dunng famine sometimes show reversions, and some types of criminal and insane persons are to be thus regarded.
CHAP. XX
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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 " 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 T/ieories. — 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 Theoties." — For a time it was com-
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mon to appeal to <^ vires formativai* " 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 dnven 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."— Tivinvii 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 ^^% 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 WolfTs demonstration of " Epigenesis » or gradual development from an apparently simple rudiment. But the preformationists were right m 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. .- . . ex.
(d) Theories of Pangenesis.—ScitnWfic 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 to 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 parti of the body. But the theories of
CHAP. XX
Htredity
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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 (*) multiply by fission, retaining their peculiarities, and (f) become specially concentrated in the reproductive elements, where (rf) 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 ?.nd for criticism of the theories of pangenesis, I refer the student
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to the works of Galton, Ribot, Brooks, Herdman, Plarre, Van Bemmelen, and De Vries.
3 The Modem 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 ofifspring." This reservation, by which some of the germinal protoplasm is kept apart, dunng 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, Jasger 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 ofifspring 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 pangenesis, pure and simple, is incorrect." His own view was that the fertihsed ovum consisted of a sum of germs, gemmules, or organic units of some kind, to which in entirety he apphed 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 the stirp grew into the body— as every one allows— but that a cer- toin residue was kept apart from the development of the
CHAP. XX
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" 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 Hacckel, Rauber, and Nussbaum. But it is to Weismann that the modem eaiphasis 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 j 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 form?*'on of the " body," but
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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, seenis a truism to some, but it is in the realisation of this truistic fact that the modem 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 Bcrthold, 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, Phalangid;E 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, VVeismann has elaborated a theory which he calls " the continuity of the germ-plasma:* The general idea oi this theory is that of oi^anic continuity between generations, and this Weismann
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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.— («) His- torical. We have seen that variations, or changes in char- acter, may be constituHonal, 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 modem. The editor, whoever he was, of Aristotle's Historia Animalium, differed from \ master as to the inheritance of injuries and the like. Avant maintained the non- inheritance of extrinsic variations, and Blrnenbach 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 Gallon (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.
(*) Weismann's position. — Weismann't reasons for
33© 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 conusts 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 fitvour 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. ZX
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exacUy throu^ 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 cr enmon^ ment have no effect on the reproductive cells, and therefore no transmission to offspring.
lc\ 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.
(O 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 tor severa generations did not eventually make ^^ V* .' 1?°^;, Jl did not— a result which might have been foretold. For we have known for many years that the mutilations mflicted 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 oits have no cogency in face of the fact that taiUess 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 mtst part merely a minus quantity to the organism; the imperfectly known physiological re- action on nerves and blood-vessels might perhaps result m 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, bu there is lack of evidence to show that the pathological variations were not genninal to begin with. It is tadly
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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. liut 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.— HalWop rabbit, an abnormal variation, which by artificial selection has become ronstant in a breed. (From Darwin.)
tend to be transmitted. Ve* some cases recently stated by Prof. Bertram Windle seem to suggest that some patho- logical conditions acquired by function may be transmitted. IJut even if a ncn-constitutional pathological state acquired by a parent reappeared in the oflTspring, 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 poppvj Nigella, dead-nettle., and the result was trans-
CHAP. XX
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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 (Ariemia) 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 aflfirmative side of our question. But much as I admire and agree with many parts of Eimer's work, 1 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*! convictions on this subject are to
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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 ftiUy explained by the theory of natural selection acting on congenital fortuitous variations. Many animals are bom 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
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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 -.unrounding influences, and as they have no "body" nc* 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 afiiected by their immediate environment, the body? Moreover, if it were
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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 fi-om 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 fir-t law of motion. The practical corollary is respect for a good stock.
That each parent contributes almost equally to the off-
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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 gram narent ! 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
t
338
The Study of Animal Life pa»t i^
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 smaU 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 individuM 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 Ukely 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 Gallon'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 sc cial 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 wl '^h 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." ^
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."
^ Walt Whitman's ' ' Assimilations."
iL ii^j
APPENDIX I
ANIMAL LIFE AND OURS
A. Our Relation to Animals
I AfSnities and Differences between Man and Monkeys.
; one^ the woAs of Broca. a pioneer anthropologist of renown, fjere is an eloquent apology for those who find U useful to con-
''^'l ^^i:^V]^ «'wS!; one of the most characteristic trait.
of our nature, has prevailed with many minds over the calm tesU-
Iny of reason. Like the Roman emperors who. enervated by dl
S uowen ended by denying their character as men, in fact, by
iliev?n7th;mSve8 demigod^ so the king of our planet pltttfes
Ss^ ?IJ im^ning tha^the vile animal, subject to his caprice
rlniJ^t have alwthing in common with kis peculiar nature. The
uSity of the monkey vexes him. it is not enough to be kmg of
'^ °^!?c . he wishes to separate himself from his subjects by a deep
ShnriaWe abvS • aXturning his back upon the earth, he takes
;et« ^h his ^nLtf ;^^^ a nebulous sphere, 'the human
tS^' But anatomy, like that slave who followed the con-
nJSort chariot crying, Mmento te hominem ««, anatomy comes
double mTn in his 'naive self-admiration, reminding him of the
visible tangible facts which bind him to the animals.
visible tang ^^^^^ ^ j.^^j^^ remembenng Fa^als
maxiSs "ItTdangerous to show man too planly how like he is ^T animals without, at the same time, reminding h.m of his IreSnei Is Vlly unwise to impress him with h.s greatness, fid not with hU LliLs. It is worse to leave him m ignorance ?iL?»S B?i* it is very profitoble to recognise the two facts."
nt m^y yean sine? Owen-now a veteran among anatomists -i^SId the "all-pervading simiUtade of structure" between
APP. I
Animal Life and Ours
341
vU .1
.X
The
act that man is peculiarly less pro*' '"ive face, smaller '.(I >ore uniform '., ':.< ever, is the ;Kt ' i he smallest -\\.: a /est human > ave a brain of a healthy .-s : the average
; ■ ,.ir:, .1
}arv
•,'1 i
1,
m
ir •;-/ ou
tavie
man and the highest monkeys. Subsequent research ha« continued to add corroborating details. As far as structure is concerned, ihere is much less difference between man and the gorilla than between the gorilla and a monkey like a mamoset. Yet differences between man and the anthropoid apes do exist. Thus man alone is thorciglily trect after his infancy is past, his head weighted with a heu.y brain does not droop forward, and with his erect attitude his peiiect development of vocal mechanism is perhaps connected. We plant the soles of our feet flat on the ground, our great toes are usuaily 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 (P! . ana) from the four-handed monkeys (Quadrumana), nor on ' it- naked. We have a bigger foreh'M cheek-bones and eyebrow ridg • , a teeth than the anthropoid aper M fact that the weight of the grr'^ . ' '-.' brain of an adult man the i a" <>i : brain the ratio of I : 3 ; i. three times as heavy as 1 human adult never we-gh. I- -^ human brain weighs 48 or 40 does not exceed 20 ounces. ' than 55 cubic inches in any ncri ir 1 . ... m orang and the chimpanzee it is u ' ar 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 r laracter'stics of huu.an personality, we are all conscious of them, though w? 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. Fov all recognis hat the higher life of men has a loftier pitch than that of animi.":, while many think that the difference is in kind, not merely 'n dejjree.
2. Descent of Man. — 'I'he arg^-ments by whicl Darwin and others have sought to show that man urose 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 o/Speeiu ;
cnniai cd
gorilla brain
);...! 'v is never less
I'njcjt, while in the
, ^ cubic inches
The Study of Animal Life
KTt.
34«
the argumenU used to prove the origin of animal from animal were adapted to rationalise the ascent of man.
(a) Physiological.— 1\it bodily life of man is like that of mon- keys ; both are subject to the same diseases ; various human traits, such as ges ares and expressions, are paralleled among the " brut ;s ; and chil'.ren bom during famine or in disease are often sadly
(u) 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.
(<■) Historical.— TYittt is little certAinty in regard to the fossil remains of prehistoric man, but some of these suggest more primi- tive skulls, while the facU known about ancient life show at kast 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 withm the womb into the likeness of a child, and being bom 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 Quatrefagcs, maintain a conservative position, believing that the evolutionist's case 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 10 many a very strong one. '• I fully accept," he says, " Mr. Darwin's conclusion as to the essentia' identity of man s bodi'ly 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 struffile for existence and the continual need of 1, ore 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-ord'nation 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 bis service."
Animal Life and Ours
343
••But .^K*uie man's physical structure has been developed from an .r^; al form bynitoral selection it doc. not neces^n^r fXw that i-,:. mental Lure, even though d«v«loped /or, A««^ with it. has been developed by the same causes only." WaU.ce Thw gie. on to .how that m«n's mathemat-cal, "»««<=*> f^istic mToS« higher faculties could not be developed by vanat.on and Stural .election alone. - Therefore some °'her mfluence law.^ aeency U required to account for them." Indeed this unknown S^r^er may have had a much wider influence ex ending To the whSe cour« of his dev. : .pmerit. " Jhe Jove of ,ru h he delight in beauty, the passion for justice, and the J*"» « ""'»J tion with which we hear of any act of courageous «lf-«"ifice. are the workings within us of a higher nature which has not been deve7oid^ means of the struggle for material ««»«<=«•" ft ?he orik^n of Uving things, at ihe introduction of consc.ousn^s, in he development of man's higher faculties. •• a change ;««««« nature (due, probably, to causes of a higher order than those of the "ateriai universe) toik place." ;« i;hc P^^g-^"^^^^"!*^!"! of life in the vegetable, the animal and ,«>^°-''J ?L^* "^W chusilya. unconscious, conscious, and mtellectual hfe-ptobably depend upon different degrees of spiritual influx. „5^-a„.
In di.cus.ing problems such as this there .s apt to be «n«unrte' standing, for worf. are " but feeble light on the depth of the an- iken'^' ani^rhapsno man appreciates hi. brother'. phdo«,phy. Wiretl rSrainVm seeking to -ontrovert wjat Wallace ha. Mid esoedally as I also beUeve that the nature of life and mind SI ;J?rS.Ti. all. and that the higher life of man cannot be explained by indefinite variations which happened to prosper m tne courM of natural Klection. „ , . , .r •_._
Xt it «em. to me (.) to be difficult to divide man'. «lf mo an animal nature which has been naturally evolved and a Ipirl^lHature which ha. been .uperadded " or to ;^™'^;«»« higher life from that of wme of the beaatfc (a) When we find IL any fact in our exprrience. such -^^ ^f«" '«"^"' «S"° be expliined on the theory of evolution which we l'«r »'»oP»«i,»» doe. not follow that the reality in question has not been naturtlly JJSvSd, it only follows that our theory of evolution is imperfect AiheorV i. not proved to be complete because it rxpla ns many factsr^t U U pLed to be incomplete if it faiU to "P ;in^-y- Thui if man's higher nature cannot be «P>*'"«f. ''> J* 'J^Y ° natural selection ir the struggle for existence. «hen that theory s incomplete, but there may be other theories of «^"'"'7 *'»'^,'', "* Xent. '(3) It i» difffcult to l'"^^ -»1*'^- "l**"^'^^^^^^ in(lux-for our opinion, in regard to those matter, vary with Sdoal .xperieSce. We may mean to «igge*t the mterpola-
V^-^'.^^ '^^■:
344 The Study of Animal Life app.
tion of a power of a secret and supersensory nature, distinct from that power whi'*h is everywhere present in sunbeam and rain- drq), bird and flower. Then we are abandoning the theory of a continuous natural evolution. Or we may mean to vi^vA that wL -n life and mind and man began to be, then possibilities of action and reaction hitherto latent became real, and all things bjcame in a sense new. Then, while maintaining that life and mind are new realities with new powers, we are still consistent believf.rs in a con- tinuous natural evolution. (4) Perhaps the simpK-^st conception is that more than once su^ested in thU 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.
(e) 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 0I homo sapiens— ihe 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 Uckle, but it seems important that the following consideration should be kept in mind.
It is not the first basiness 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 Aas so evolved. We have only a vague idea how a backbone arose, but that need not hinder us from l>elieving that Ixickboned animals were evolved from bockboneless if there be sufficient evidence in favour of this con- clusion. We do not know how birds arose from a reptile stock, but that tlicy did so arise is fairly certain. We cannot explain the intelligence of m.-»n in terms of the activify 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 .>f the neare?t animals, and the nature of human intelligence with th.u of the closest approximations, drawing from the results of our comparison what conclusion we can. The general doctrine of descent may be establisheil independently of the investigations of physiologist and psychologist, valuable as these may l)e in elucidat- ing the way in which the great steps of prepress have been made.
(d) Finally there is the opinion of matiy that man is altogether too marvellous a l>eing to have arisen from any humbler form of life. But to others this ascent seems the tump of man's nobility.
4. Ancestors of Man.— Of these we know notliing. The anthropoid a|)es approach hitji most closely, each in some particular respect, but none of them nor any known form of life can be callcil
Animal Life and Ours
345
man's ancestor. It is possible that the race of men— for of a first mr^n 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.
Kii.. 71. -Young gorilla. (From I>u Chaillu)
5. Possible Factors in tho Ascent of Man.— in regard to
tlie factors which secured man's ascent from a humbler form of life we can only si>eculatc.
(a) We have already explained that organisms vary, that the offspring differ from their paients, that the more favourable changes prosper, and that the loss 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 nxire imixjrtnnt than strength, .ind if intelligence now U-cauic, more than ever U-fore, the condition of life or death, wits would tend to develop ra)>idly.
(/.) When h.ibits of using sticks and stones, of building shelters, of living in families, l)egan- and some monkcyscxhil.it these— it is likely that wits wouUl increase by leaps and Inninds.
(c) Professor Fiske and others have emphasised the importance of prolongetl infancy, and this must surely have helped to evolve the ncntlciiess of mankind.
n
'4
346
The Study of Animal Life
APF.
(«/) Among many monkeys society has begun. Families com- bine for protection, and the combination favoors the derelopment botfi of emotional and intellectual strength. Surely " man did not make society, society made man."
B. Our Relation to Bioiogy.
6. The Utility of Sdeiice.— As life is short, all too short for learning the art of Uving, it is well that we should cntiase 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. . , . u . i
Nor can we be satisfied with the assertion that saence 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 ot science and art. For it is not evident tiiat 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 Ue dormant for centuries before it sends lU 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, w.mi ues about the mouth— the nose, the ears, the eyes, the brain— u:?y be
°' WeTrc nearer the truth if we combine the different standards of science, and unify them by reference to the human ideal.* The utility of science, and of biology among the other kinds of knowledge, is to supply a basis of fact — ... i
(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 Jmstiflcation of Biology.-The world of life
is so web-like that almost any part may touch or thrill iw. it is therefore well ihat we should learn what we can about it.
On plants we are very dependent for food and dnnk, for shelter
» See Ruskin. Tkt EagUt Nttt (1880).
Animal Life and Ours
347
and clothing, and for delight. Thdr evil influen^ .s almost restricted to that of disease germs and poisonons herbfc
Animals likewise furnish food (perhaps to an unwholesoaie extent) ; and parts of their bodies are used (sometimes cafelessly) in manifold ways. Among those which are domesti<ated, some, such as canary and parrot, cat and dog, are kept for thepie^^ure they give to many ; others, such as dog, horse, elei*a«t, -mfi falcon, are used in the chase ; others, notably the dog, a*Mst .<> shepherding; horse and ass, reindeer and cattle, camei anf! elephant, are l)easts of burden ; others yield useful producte, the milk of cows and goats, the eggs of birds, the silk of silkworms, and the honey of bees.
Formerly of much greater imj ortance for good and lU 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 systentiatic 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. , u u i i
But if we take higher ground and consider as an ideal the healtli- 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 arc applied chemistry and physics. It would be historically untrue to say that the progreM in these arts was due to progress in the parallel sciences ; in fact the propretsive impulse has often been from art to science. ' La pratique a partout devanc^ la thiorie," Espinas says, and all
-ff^^t.^-
m
:^i*jr.ras?:
¥^-m
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
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 prc^ess has advanced the art of healing. The results of science have like- wise suppUed 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 m men s minds, must in some measure affect practice and public opinion. Spencer's inducUon 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 mei lold, granting that it is in part an expression of their life and soc environment, does not also react on these.
. short, the direct application of biological knowledge in the
ja» arts of medicine, hygiene, physical education, and eugenics,
us to perfect our environment and our relations with it, helps
discover— if not the "elixir vitie"— some not despicable
sui tute. And likewise, a realisation of the facts and principles of
bio ijy helps us to criticise, justify, and regulate conduct, suggest-
in. V the ft of life may be better learned, how human relations
ml <; mor wisely harmonised, how we may guide and help the
Ia*«^ HJtnal JuBtillcation of Biology.— But another
r»n!: ym» ?ion of Biology is found in our desire to understand thing -' >ur dislike of obscurities, in our inlwrn curiosity. There is an in- actual as well as a practical and ethical justification of the stucy of organic life.
Through our senses we liecome 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) Intheworid 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 i^erhaps we may say the study of matter in motion— considered apart from
, Animal Life and Ours 349
life, we call Phyria and Chemistty, of which astronomy, geology, etc. are special departments. . . , j
(2) But we also know something about plants and animals, and while all that we know about them is stiU dependent upon chuiges of matter and motion, yet we recogni^ that the acUv.tie. of the onanism cannot at present be expressed in terms of these. There- foTJre find it convenient to speak of life as a new reality, while believing that it U the result of some combination of matters and energies, the secret of which is hidden. • a c\(
(?) But we are also aware of another reahty, our own mmd. Of this we have direct consciousness and greater certamty than about anvthine 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 U truer to say that we are conscious of ourselves. It U our thought that we know .t is our feeling that we feel, and as we cannot explam the thought or the feeling in terms of protoplasm or of motion, we find it convenient o speak of mind as Tnew reality, while believing it to be essentudly 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. . ,., r .u u
(4l But we also know something about the life of the human society of which we form a part. We recognise that it has a umty of its own. and that its activities are more than those of its individual members added up. We find it '^o")'*"'*"* »° '^^'J society as another synthesis or un.ty-though less definite than either organism or mind- and to our knowledge of the life and erowth of society as a whole, we apply the term soaology.
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. Ihe 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 u a unity of
""'But it must be clearly recognised that the " matter and energy" which we regard as the fundamental realities are only known to us
II
The Study of Animal Life
APP. 1
through whiU is for us the supreme reality— ourselves— mind. And as in our brain activity we know matter and enei^ as thought, I have adopted throughout this book what may be called a monistic
philosophy. . , ,>• • u
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 11
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 ine 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, •o 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 JefTeries, and John Burroughs, or in Bates's Naturalist on the Amazons, Belt's Naturalist tn Nuaragua, and Darwin's Voyage cf 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 cunent opinion by following the history of too\ogf. 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 toology, secondly those on natural history, thirdly thc«e on biology.
A. Zoolcgy,
(i) We can form a vivid conception of the history of toology by cseiparing it with our own. In our childhood we knew and
The Study of Animal Life
APP.
35«
eaicd more about the useful, dangerous, and strange animals than about those which were humble and fiimiliar ; 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 sool<^ 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 Ctviluatton (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 loology 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 friendUness, of some of these. His is the first definite classification. His work was dominated by the idea that animal Ufe 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, 183 1-40), 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 NaturalUt," Nineteenth Century (Feb.
1891, pp. 275-289). , .
(3) After the freedom of early childhood, and m most cases after precocity too, there comes a lull of inquisitiveness. Other affaira, practical tasks, games and combats, engross the attention, and parents sigh over dormant intellects; so the historian of toology sighs over the fifteen centuries during which science slumbered. The foundations which Aristotle had firmly laid remained, but the waUs of the temple of knowledge did not nse.
n Sonu 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 monkej-s ; besides the Spanish bishop Isidor in the seventh century, and various Arabian inquirers. It will not 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 medieval 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- b^ts. It is found in about a dozen languages and in many diH'erent 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-l)Ook, 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 wliich sleeps with its eyes ojien,
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TJu Study of Animal Life
APP.
354
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 blast 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 connectmg links, such as Albertus Magnus in the thirteeenth century, we inay 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 (1492-1 555). w^o wrote a treatise De Differetttiis Animalium ; the Swiss Conrad Gesner (1516-65), author of a well-known Historia Animalium ; the Italian Aldrovandi (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 NaturelU, 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 tlie 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 histoiy. There is a goo4 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 modem books on natural history correspond in some degree to the Histoire Naturell:, viz. CasselPs Natural 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 Thierleben, of which a new (3rd) edition is at present in progress {10 vols.; Leipzig and Wien, 1890). Those who read German will find in Caius Sterne's (Ernst Krause's) Werden und Vergehtn (3rd ed. ; Berlin, 1886) the most successful attempt hitherto made to combine in one volume a history of the earth and its inhabitants.
(6) From BuflFon 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 Encydopadia. Following the metaphor on which we have already insisted, we may compare this century of analjrsis to the period of ordered and more intense study which in the individual life succeeds the abandonment of encyclopaedic 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 (MUnchen, 1872) ; J. Sachs, Geschichte der Botanik (MUnchen, 1875), translated into English (Oxford, 1890); W. Whewell, History of the Inductive Sciences (London, 1840) ; articles " Morphology " and •• Physiology," Eneyclopadia Britannica, by P. Geddes and M. Foster H. A. Nicholson, Natural History: its Rise and Progi.u in Britain (Edinburgh, 1888); A. B. Buckley, Short History tf Natural Science ; E. Terrier, La Philcsophie Zoologique avant Darwin (Paris, 1884); Ernst Krause (Carus Sterae), Die Allgemeine IVeltanschauung in ihrer historischen Entwitkelung (Stuttgart, 1889). Very instructive, not least so in contrast, are two articles, "Biology" (in Chambers's Encyclopadia), by
356
The Study of Animal Life
APP.
P. Geddes, and "Zool(^" (in Emyclopadia Briiannica^f 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 Systema Naturce of Linnaeus (ist ed., 1735 ; 12th, 1768) is the typical work on this heavily-kden 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 Linn^'s Systema h.is been expanded into a series of volumes, or into some gigantic monograph like those included in the series of " Challenger" Reports, or The Fauna 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 Britisli Mammals, Birds, Fishes, Molluscs, Insects, etc., but a compact British Fauna is much wanted. I shall simply mention Bronn's /Classen und Ordnungen des Thierreiches, a series of volumes still in pr(^ess ; 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).
(A) Cuvier's Rigne Animal (1829)13 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 atid Physiology (Lond. , 1886); after which he will more readily appreciate the text-books on Comparative Anatomy by Huxley, Gegenbaur, 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 Encychp^tdia Britannua, many of which are pub- lished separately, are not less useful. As guides in serious practical work may be loticed- -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 (Lend., 1885); A Course of Practical Zoology by Prof. A. Milnes Marshall and Dr. C. H. Hurst (jtti ed'., I^nd., 1892); Prof. C. Lloyd 'ULax^xit Animal Biology [,UmA.^ 1889); Vogt and Yung, Traiti
II Some of the " Best Books " on Animal Life 357
d^ Anatomic comparie pratique (Paris, 1885-92) or" in German (Braunschweig) ; Prof. W. K. Brooks's Handbook of ItwerUbrate Zoology for Laboratories and Seaside Work (Boston, 1882); Prof. T. J. Parker's Zootomy (Lond., 1884) and Practical Biology (Lend., 1891),
{c) As early as 1801, Bichat had penetrated beneath the organs to the tissues which compose tliem, and his Anatomie GhiSrale 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., 1 891) 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, imd 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 Etuyclopadia, and with the articles "Morphology" and "Protozoa" in the Encyclopadia Britannica. From these he will discover how his studies may be deepened.
(«) 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 Encyclopadia Britannica ai:d in Chambers's Enc^'chpadia.
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 •.o consider it {b) 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 •.vhirlpool of living matter. I recommend you to read first the article " Physiology " in the Encyclopcedia Britannica, then Huxley's Crayfish (International Science Series), and his Elementary Text- book of Physiolog}', 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 Srirling, McKendrick, and Foster, and to the studies on comparative phj liology by Krukenberg, Vergleichend - Physiologischt Studien and Vortrda (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 individ-l life^^^^^^^^^^
appearance upon the ^''''^t^ jf JXrlolofv Sn with the article buiion in space As regards embo'ology begin ^^^^^^^
^"r A^r H^L?? ttirot rUstrand F. M. Balfour
l^^nwTneiL and ^^^ teilpif^-=« of distribution in time wU be found >" A «« p„n ^^^^^^^^
students --y P-^;° Jj^^f ;oir. Ld. and Edin., ,889), to Nicholson and R. ^S" ^z« emhainements du monde animal the French work of Gaudry, /-« ««^«» j^ German
remains the principal w"'"^ °/ ^^^"7"' ^^^ ^t^dent to the>«m«/ For progressive research I may re er tne suiuc" y
which gives summanes -J-^'^^^'^^^^] ^y Lankester. Klein. ^/Mfr.5../»»Va/5«.«^« (edited by P;°'«- '^^^ ^ ^^^ ;„ ^hich 4dgwick, and Milnes Marshall) and of cou^^^^^^^ ,^ summaries and d.scus.^^^^^ are oft n .o^J^ral ScUnce. ^-SJ^IlUletnl^^^^^^
mention other ways of begmnmg.
B. Natural History.
rory\:^r::S.^s s;:;:itrcut ^^ :z^
them, they are seized w,th ^^^^J^^e^Sh a learned^ book about it. to get it under the microscope »« P« J^ ^^^^^ ,exicon, and it which no one can read w't^out an "P«"^'^*^j^ ^,1; ^j ,„ an to put up its remains m «"^^"%^"^th on a pterygoid pro- abnormal hxmapophysts ; ^^^^ P'" ^^JiVJ^, ^bT/of^ubeTc^^
„ Some of the " Best Books " on Animal Life 359 part of it. and is neither less nor jnore v^duable th^^^^^ tV.at^ of .the Lid naturalist, ^e may crmcise the d^^^^ ^^^^^ ^^^^ analysis we may believe that "^^P^^^^j^ ^m to be less unnaturally upon students, we may ^^ ^^^^^^^„ ,^q„i,es
pedantic; but »« "mmd ^»^^^^^^^^^^^^^^ field
iJrllLTtrJJ-ls Mnes and muscles. Both are true
'' ^l^ ^^d \ rhSeTa^JetrlutThe^^^^^^^^^ and activities our knowledge what 1'^ can tea ^ combinations of organs,
of animals aUke «« umtxes and a^ co^pl"^ ^^^^^
tissues, and cells. Let us ag^f« |" j^j^h we have already
the morphological and PlS:i>°^°g\^^^^^^^^^ that few of us can
explained, "zoology." We ^^f ^f*^"";";^^^^ binder us from per- become zoological experts. But ^^^ Jjj ^J^^wards what end and ceiving that it is not ^i'^'^";' *° "^j^^ Sa^^^^^^^ Claude Bernard, by what method Lmn^us and O^^^^^^^ ^^ j.^^„ „3i„g
and the other great masters worked, n^^^^^^ ^^^^ ^^^
all natural opportumt.es o^ pact c^^^^^^^^ ...oology" is
powers of ammal life. ^« .j*"^" ,_.=-! j^an the work of the Neither less interesting nor le« ^^^\^^^ ^^^^^^ is not more field naturalist, we shall '«<=°et»se that its^ermi ogy ^^^^
complex than that ^^ 5\^'"^"^J ?' *" Jk^^^^^^ nature acquires from clear zoologica^ *»f ^"^ ?« *=°^^*'™^^^^^^^ cachait plus
an additional intensity o .en>c^ °°; ^ JloJ^« » What Hamerton
ou moins "\-'"»^«'^' ^^'"'^t^ ^ also to the
says with reference to an art^ts educa PP ^
fo^r^^To^lS^:^^^^^^^^^^ --^^-" ^°"
their sense of perspective. those who have little time or
Now. however I YO^^,.f^^f;'J„7ave « interest in the life opportunity for -zoolc^, but who have ^^^^ ^^^^
and habits °f ^^^^^J^i^^^^^^ personalities -in
thoroughly. T">s Jcnowieagc ^^ ^^^y^^
struggle and friendhneg. in ha e and ^^^J^J^^j j, ..,,,iogy" I would call •• natural history, m c°°"^^ „ '^^ ^ther. For
on the one hand, and g^;"^^'"!, J°Sory of life-its nature I restrict the latter term to ^J\« general tneo y ^.^^^^ ^^^^
360 The Study of Animal Life app.
the three as essential, and to cease from drawing prejudiced com parisons between them.
Their relations may be summarised as follows : —
••NATURAL HISTORY."
Study of the
real life
of
I
fauna
class
order
genus
species
families
pairs
individuals
in relation
to one another and to their surroundings.
(S) Organism. (4) Organs. (3) Tissues, (2) Cells, (i) Protoplasm.
Study of Structure (Morphological)
Study of Activities (Physiological).
ZOOLOGY.'
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 Encyclopcedia, 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
,1 Some of the " Best Books " on Animal Life 361
and roology, 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 he most logical of programmes if that take no root in the life of the
^^Let'me suggest some of these indirect ways of beginning. Begin with domesticated animals and their histoiy. See Darwin s Vanation of A mm ah and Plants under Domestication (l866), etc. Concentrate your attention on some common animals. See, for instance, Darwin's Formation of Vegetable Mould through the action of Worms (i88l); Mivart's /r^^ (Nature Series, Lon^'on); Huxley's Crayfish (Internat. Sci. Series, London) ; M«Cook s North American S/^iders {2 vols., Philadelphia, 1889-90) ; f- Cheshire's Bees and Bee-keeping (vol. i., Lond., 1886) ; Lubbock s Ants, Bees, and Wasps (IniGrnvii. Sci. Series, London); Flowers
/A»r5«(Lond., 1891). ,,. , , „,
Enjoy your seaside holiday. See Charles Kingsley ^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 Studies (mm. 1858); L. Fred^ricq, La Lutte pour
rexistence chez les Animaux Marins {Vaxxs, 1889).
Form an aquarium. See J. G. Wood's Fresh and Salt Watei
Aquarium ; P. H. Gosse, The Aquarium (1854), and many similar
Begin a naturalist's year-book. See the Naturalist's Diary by Roberts; the Field Naturalise s Handbook, by J. G. and Th. Wood {Lond., 1879); and K. Russ, Das hetmtsche Naturleben im Kreislauf des Jahres ; Ein Jahrbuch der Natur.
(Berlin, 1889). „ _
Observe the inimals you see on your country walks. &ee T. G. Wood's Common Objects of the Country (1858), The Brook and its Bank (1889); Life of a Scotch NaturaHt, Thomas Edward, by Samuel Smiles; The Moor and the Loch, hy 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, Spaziergange eifus Natutforschers (Leipzig, 1888); Lloyd Morgan's Sketches of Animal Life (Lond., 1892), etc. etc.
The Study of Animal Life
KVV.
Another natural way of beginning is to work out some subject which attracts you. It becomes a centre round which a crystal erows. Muybridge's photographic demonstrations of animal loco- motion have interested us in the Hight of birds, et us follow this ^p iy observation and by reading, e.g., Ruskin's Z^.V Mann (i88i); Pettigrew's Animal Locomotion (Internat. Sci. Series \%Tiy,U»xti% Animal Mechanism (Internat Sci. Series. 1874); Marey's Le Vol des 0«wi«r (Paris, 1890).
The colours of animals appeal to many people. Read E. B. Poulton's volume (1890) in the Internat. Sci. Series, and Grant STcolour 5*L. aid F. E. Beddard's Animal Colo,naUon
^^The lelaUons between plants and animals are ent'^ncingly interesting Watch the bees and other insects in their flight, anSDarS volumes on the Fertilisation of OrcAJds {1S62) ^oTcross.FertilisationiiS76); Hermann Umiers Fertzhs^^on of Flowers (transl. by Prof. D'Arcy Thompson, Lond., 883) . Kemer's Flowers and their Unbidd^ Guests; the arUcles on '« Insectivorous Plants," in Encyclop. Brttanntca, and m Chambers s ^Mrvf/oA, or Darwin's work (1875). , . , . » •„,
XSn, manyof us are directly interested in foreign countries Let^e practical interest broaden, it naturally becomes geographical a^d physiograpWcal. and extends to the natural history o he rSon No more peasant and sane way of learning about the wSs and distribution of animals could be suggested than that Sh follows as a gradual extension of physiographcal knowledge. See Dr H. R. Mill's Realm of Nature, and the following samples from Xh" long list of books by exploring naturalists :— A. Agassiz. nree Cruises of the "Blake" (Boston and New York.
S W.^ Baker. Wild Beasts and Ways: Reminiscences of Europe,
jitia Africa, and America VUinAon, \Z<io). H. ^^^^ Naturalist on the Amazons (sth ed.. London.
T iJlt Naturalist in Nicaragua (2nd ed., London. 1888). liiirT:S^ioTobservatiom on Geology and Zoology of Abyss.nta
P B^^ci^m%xplorations and Adventures in Equatorial Afnca,
^ rCutln|Sll= l!^:Zl!:^ilTut^l History of the Straits of
Magellan (EAia., 1871). .
Darwin. rW e^'** " -»# '^^J "^^g^" '^^°^-
H. Drummond. Tropical Afnca (Umd. , 1888).
h! O. Forbes. A Naturalists Wanderings %n the Eastern Arc/it
ptlago {Uind. , xBSs)- ^ „ ,. . ,on^v
Gm\ltm^Td, Cruise of the -Marchesa' (Lond.. 1886).
„ Sofiu of the " Best Books " oh Animal Lift 363
187Q, new ed. Lond., 189a). .. /i «„^ tRRt^
unternommmen Reiser (L;^>Pf!S; J^^'- .^ .„ ^,,.^
H. Seebohm. 5j*ma m Europe (Lond.. i88oj . ana
J. E.^Tennent. ^'^'-ral History of Ceylon {l.c^^^^^ VyviUe Thomson. The Depths of t/ie S a (M ^1^73) .^^^ ^J^ the Voyage of the \C>taUenger (r^^S)^ Cf A^ oe ^^^.^^^^^^
Tristram. V/i/ Flora and Fauna of Palestine.
Tschndi, Thierleien der A Ipenwelt. Trotical Nature
A R. Wallace. Malay Archipelago {Lond.. 1869) . Tropicat na,
(1878) ; hland Life (i88°)- America (ed. by T. G. Wood.
Ch. Waterton, Wanderings m South America ^ea. oy j
C. M^'woodford, Naturalist among the Head-hunters (London. 1890). Prominent among those who have helped many to «alise the marveland beauty of nature, a widely-felt gratitude ranks Gilbert WWte Henry Thoreau. Charles Kingsley. Richard JefTenes. J. G. Wood, John Ruskin, and John Burroughs.
'Lento, .888), buf .her. Is a cheaper one. edited b, R,cha,d Jefferies, in the Camelot Series.
Henry Thoreau (1817-1862). the author of Walden, A Week on Concord, and other much-loved books.
CHARLES KINGSLEY (l8l9-i«75)- See his Glaucus 1854) ; Water-Babies ; and popular lecturer
(Lend.,
3^4
The Study of Animal Life
APP.
Richard Jefferies (1848- 1887).
See The Eulogy of Richard Jefferies, by Walter Besant (London, 1 883), and the following works, some of which are published in cheap editions: The Gamekeeper at Home (1878); Wild Lift in a Southern County (1879); The Amateur Poacher (1880); Round about a Great Estate (t88i) ; Nature near London (1883) ; Life of the Fields (1884) ; Red Deer (1884) ; The Open ^iV(i885).
J. G. Woou, 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 V/ood (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) ; The Dominion of Man (1887) ; and other works. John Ruskin. See the Eagle's Nest, Queen of 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), ^»'''^-' ^"^ P"^*^ (1877). iLocusts 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, 1 860-6 1 ).
P. G. Hamerton, Chapters on Animals : The Sylvan Year (3rd ed., London, 1883).
W. Kirby and W. Spence, Introdui.'ion to Entomology (London, 1815).
F. A. Knight, By Leafy Ways; Idylls of the Field (London, 1889).
Phil Robinson, The Poet's Birds (London, i8«3); and The Poet's Beasts (London, 1885).
Andrew Wilson, Leaves from a Naturalist's Note-Books; Chapters on Evolution, etc.
-■**»«!«
II
So7ne 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 advic- by addressing those who are strong enough to Tnquire 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 GemrelU Morphologie {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 Encychpadia ffritannica, "Physiology" (Prof. M. Foster), "Protoplasm" (Prof. P. Geddes), and " Protozoa"— the large type— (Prof. E. Ray Lankester) ; {p) 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 Etuyclopadia. 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 "VitUiism" in Bunge's Physiological Chemistry (translated, London, 1890).
Beprodnction, Sex, and Heredity.— For adult students,
and no others should be encouraged to face the responsibility of
t
366 The Study of Animal Life app.
inquiry into such matters, the most convenient introductionj.'iU Kund n The Evolution of Sex p^ni^^^or^rj S^^^^^^n^^ llnd 1880V by Prof. Geddes and myself. In that work there ^e ifeJcncel' Z others. A survey of modem op.mons and co„ 1 • « ;« r^Torrl to heredity may be obtamed Kom the article in
ffm^JmeriliL (Lo„d„ .889), and to other „„po.ta„t '^*n^°tot<;CD'SJ-rS wo* by Professor C. iJo,d
also mention that Brehm t n«rkU« ('S^S »9 S „„„,
in process of re-edition (10 "«''■• "^f '"'"J' ,'\„j „i,dom of „««ur, of inf«mat»n - J=8«d 'o * . X^.V-l-i-'.'
C't'o^ 'Vr >: =n'io»sTo',."of ir,.T„'''aW terse Protozoa. Ol ^^^ '"8^" „-„«av's Les Industries des Antmaux I^S^m. '''Z 5~HeJo^.i„ct «e esg=^.. K„™.cs,
in regwd to Evolution is to make mmseu »t4u».ut
II
Some of the " Best Books " on Animal Life 367
arguments ^^hich show that the animals and plan now ahve are descended from simpler ancestors, these from still s™Pl". ^J" soTback into the mists of life's begimiings. To realise that the
(Nature Series, Lond.) gives a convenient statement of the case, S hfs RSbTry Lectures will be more exhaustive. CU^d s ?LvofcLli7n: a plain accoun: of Evolution (Lond., 1888) S UP the evSence in small compass ; another very terse state- ment wm be found in H. De Varigny's Experimental EvoMxm Sd 892); Haeckel's Natural Hilary ./ Cr.a/«^ (Berim, te^tne -St popular of his works, now in its ^f ^h f mon (Tena i89o)-is available in translation (Lond.. 1879) ; Huxley s ^^AnuH^an Addressee (Lond., 1877) have even peater «:h^m f f^e; Carus Sterne's Werden und Vergehen (3rd ed.. Berlin 1886 is perhaps the best of all popular expositions; while the thorougb Sent will find most satisfaction in the relevaii iTrJbnso. Darwin's Origin of Species, and Spencer's Pnnctples
"^mZtl Of Evolution Theories.- As the idea of Evolution is v^Snt, and as it was expounded in relation to animal Ufe byTa. c^Smpetent naturalists "before Darwin's inteHectual com Scame current throughout the world, it is unwise that students S restrict tl..ir reading to Darwinian and Pos^Damiman literature. The student of Evolution should know ho«r Buffon Erasmu- Darwin. Lamarck. Treviranus. the St. Hila.res Goethe
even Robert Chambers, and many other P'^^f^^^"'''"^ .'^f ^^ ^^ the problem. Those who desire to preserv;- their sense of historical Ssti'ce should read one or more of the following : Huxley Y^^^^^^ in " Evolution " in the Encyclopadxa Bntannua ; Samuel Butler s interesting volume on Evolution Old and ^«7^(L*>"f«'- 'f J^) ; Perrkr'8/'-4.-^x«'/A'V Zoologique avant Darwtn (Pans. 1884) the hSorical chapters of H^e^kel'. Natural History of Creatton-, SZTcescLte der ZoologU, and some other histon^ works already referred to (p. 355) ; /. de CandoUe's g'^""' ^"
Sciences et des Savants d^P''"/^*' ^\i' l^ ^ h^^hL^^^^^^ Carus Sterne's (Ernst Krausc's excellent work, Dte Allgemetne mZnschauung (Stuttgart. ,889) ; De Quatrefages. CkarUs Darwin et sesprJcurseursfranfats {Funs, liJO). .,
Darwinisnu-The best account of the Darwinian theory of EvolSTespecially of the theoiy of natural selwtion which ChSs Darwi? and Alfred Russel W-Uace independently^cj^ rated, is Wallace's Darwinism (Lond.. 1889). From this the
368
The Study of Animal Life
A pp.
Student will naturally pass to the works of Darwm himself— 7A« Origin of Species by means of Natural SeUction ; or, the Pre- servation of Favoured Races in the Shuggle for Life (Lond., 1859) • The Variation of Animals and Plants under Domestuatton (2 vols., Lond., 1868); The Descent of Man, and SeUction in Relation to Sex (Lond., 1871), etc. ; the earlier works of Wallace, especially his Contrilmtions to the Theory of Natural Selection (Lond., 1 871); Spencer's Principles of Biology— cf his articles on "Thf Factors of Organic Evolution" {Nineteenth Century, 1886); Haeckel's Generelle Morphologie, and Natural History of Creation. As a popular account of Darwin's life and work. Grant Allen's Charles Danvin (English Worthies Series, 3rd ed., Lond., 1886) has a deserved popularity; G. T. Bettany's similar work (Great Writers Series, Lond., i886) has a very valuable biblio- eraphy ; 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).
Becent Contributions to the Theory of Bvolutioa—
At the present time there is much discussion m r^ard 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 Weisma.m wlio, in his Essays on Heredity, denies the transmissibiiity of characters acquired by the individual oreanism, as the results of use or disuse or of external influence ; and E. Ray Lankester, see his article "Zoology" m iht Enc^-clo. padia Britannica, and his work on tlie Advancement of Science fLond., 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.
Samuel Butler. Evolution Old and New (Lond., 1 /9). Luck or
C«««»»r (Lond.. 1887) and other works. Prof E. D. Cope. Origin of the Fittest {ii^yt \oxV., 1887). Prof G H T Elmer, Organic Evolution, as the Result of the
Inheritance of Acquired Characters, according to the Laws of
Organic Growth (Jena. 1888). Trans, by J. T. Cunnmgnam
(Lond., 1890).
II Scm4 of the " Best Books " on Animal Life 369
Ptot T. Ffake, Outlims tf Cosmic PhUmophy (Lund.. 1874). Dor- wMsm, amdoOtr Essays {Ifnd., »*75). ., „_^^,^^i,
i>r«f P Reddes Article "Variation and Sdection, MHcyeUf^ata 5^*^^' '^ution." Chambers-s Encyclopedia n^ ^. OLmEiloluHon of Sex. and forthcoming work on Evolutton,
Organic and Social. V Oflon La LutU fiour le Bien-ltrt (1090). Rc^T'Tfo^dH Divergent Evolution, through CumulaHve Segre-
P ^.^Z^'^uZ^^^^^T^r,^'' Nineteenth century Lan.S' Z'L:ur^^\E.istence et rAssociaHon pour la LutU
Prof^^^'c^rgc Mivart. The Genesis if ^pecies{U>f- . Xr"*'
U^sonsfJi Nature (U>nA., 1876). On Truth (^n±, 1889). Prof C. lioyd Morgan, Animal Life and Intelligence {Lond.,
Prof.*C°^V. NBgeU. Mechanisch . physiologischc Abstammungslehre
'(MUnchen and Leipzig. 1884). pi«„,idt
Prof. A. S. Packard, Introduction to the Standard or Rtverstde
Natural History (New York and Lond., 1885). Dr G T Romanes, Physiological Selection (Joum. Linn. Soc. xu..
1886). Sd forthcoming'^Rosebery I^tures on the PhUosophy
^ToL^liLt^Tnl'Natural Conditions of Existence as they affect J timal Life (Intrmt. Sci. Series, Lond., 18B1).
Dr. J B LtSi! Jr Int,vducHon 'to General Pathol^ (Lond, x886). Evolution and Disease (Contempor. Sci. Senes, Lond.. 1890).
3 B
INDEX
Absorption, 145 Acacias guarded by ants, 29, 30 Acquired characters, 339-336 Actions, automatic, 155
habitual, 155
innate, 155
intelligent, 155 Alternation of generations, 189
Amoeba, 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, 05, 116
industries of, 1 17-124
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, 1 71-174 Ann lids, 231-234 Antic. . 279 Ants, J '-84
and av- ides, 119, 120
and plants, 29 Aphides, 8a, 31a
mnltipUcation of, 38 Anchnida, 243 Archoplaun, 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, 2a Balance of nature, 19-21 Balanoglossus, 9, 249, 250 Bathybius, 219 Beauty of animals, 15-17 Beavers, 25, 74, 7S Bees, 78-84
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
BufTon, 286
Caddis worms, 6z Carbohydrates, 134
37«
The Study of Animal Lift
Caterpillars, 50. 51 Cau and dover. 39 Cave-animals. 334 Cdl-divMon. 158-183 Cells, ia8, 147. 179-183 Centipedes, 341 Cestoda, 339 Chsetopoda, 331-233 Challenger Expedition, 5, 6 Chamseleons, 53 Chemical elements, 135
influences in environment, 309,
313
Circulation, 146 Classification of animals, 8-ix Coelenterates, 222-228 Cold, effect of, 313 Colonies, 70, 71 Colour-change, 52, 53 Colouring, protective, 48, 49
variable, 49-51 Colours of animab, 49-53
of flat-fishes, 315 Commensalism, 68, 69 Competition, internal, 67 Concealment of animals, 47 Conjugation, 314 Consciousness, 150-153 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, 35 Crocodilians, 363, 364 Cruelty of nature, 43-45 CnisUcea, 339> 34°
life-history of, 198-202 Cuckoo, 114. "5 Cuttlefish, 53, 66 Cyclostomata, 35a
Darwin. Charles, 393-396 Brftsmuf, 388, 389
Deep-sea fishes, 356
life, 6 Descent of man, 34X>34S 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, 23-34
Echinoderms, 10, 65, 66, 235-238
Ectoderm, 196
Eggs, 191, 19a
Elaps, 59
Elephant hawk-moth, 59
Encystation, 41
Endoderm, 196
Environment, 306-319
Ephemerides, 106, 107
Epiblast, 196
Epigenesis, 324
Evolution, evidences of, 373-281
factors of, 399-303
theories, history of, 383-301
of sex, 188 Extinct types, 206, 207
Family, evolution of, 91
life, 91 Fats, 134 Feigning death, 66 Fertilisation. 193-19S Filial regression, 3^8 Fishes, 9, 253-25"
parental care among, 109, 110 Flight of birds, 123, 124 Flowers and insects, 28, 39 Flukes, 229
Food, influence of, 310-313 Freshwater fauna, 6-8 Friar-birds, 59 Frog, 258 Ftmction, influence of,. 303
Oastra^ theoty. X97
Index
373
Gastnila, 195, 196 Genealogical tree, la, 13 Geological record, imperfection of,
ao5 Germ-plasma, 338 Giant reptiles. 359 Glow-worm, courtship of, 100 Greg^nes, an Gregarious animals, 71-74 Grouse attacked by weasel, 40
Habitat, change of, 47 Habitual actions, 155 Haeckel, 398 Hagfish, 353 Halcyon, 116 Hatteria, 260 Heat, influence of, 313 Heredity, 320-339 Hermaphroditism, 188 Hermit-crabs, masking of, 63 Hirudinea, 334 Homes, making of, 121-123 Hombill, brooding of, 114 Horse, pedigree of, 278 Hunting, 118, 119 Huxley, 298 Hydractinia, 69, 70 Hypoblast, 196
Ichneumon flies, 64 Idealism, 14a Impressions, 151 Industries of animals, 116-124 Infiisorians, an
multiplication of, 38 Innate actions, 155 Insects. 341-343
parental care of, 108
and flowers. 38 Instinct, 153-166
origin of, 163-166 Instinct 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, 30X Ivory. 31
Jellyfish, 226
Kallima, S3 Kidneys, work of, 145
Lamarck, 289-292
Lamprey. 252
Lar;cdet. 9, 252
Land animals. 8
Leaf insects. 54
Leeches, 234
Lemming, Ross's, 50
Lemurs, 46
Life, chemical elements of, 135-
137
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
Macrofod, parental care of, no Mammals, 9, 267-271 Man as a social person, 94
considered loologically, 340-
346 Marine life, 3-6 Marsupials. 46 Masking, 61-63 Materialism. 141, 14*
374
The Study of Animal Life
Mates, love of, 90, 91, 96 Mayflies, 106, 107 Metamorphosis of Insects, 243 Meaoderm or mesoblast, 196 Migration of birds, 74 MiUepedes, 241 Mimicry, 57-61 Mites, desiccation oi, 41, 43 Molluscs, 10, 243-'247 Monkeys, 370, 271, 341
gregarious life of, 71 Monogamous mammals, 96 Moss-insect, 55 Moulting, 315 Movement, 144
Movements of animals, 123, 124 Mud-fish, 8 Mygale, 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,
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, nuMttality of, 43
Palaontological series, so6 Pftteeontology, 304-209 Pangenesis, 334 Parasitic worms, 229-331 Parasitism, 47, 48 Parthenogenesis, 189-193 Partnerships among animals, 68;
69 Perception, 151 Peripatus, 10, 240 Phasmidse, 53 Phenacodus, 269, 270 Phyllopteryx, 54 Phylogeny, 203 Physiology, 125-153 Pigeon, 27s, 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, 11, 210-221
colonial, 173, 174
classes of, 211
life of, 214
"immortality" of, 172
psychical life of, 215-318
structure of, 213
andMetazoa, transition between, 88, 89, 171-174 Psychology, 149 Pupae of caterpillars, 50 Puss-moth, 63, 64
Radiant energy, influence of,
313-316 Recapitulation, 197, 279 Reflex actions, 155 Reproduction, 184-190 Reptiles, 9, 359-364 RespiratioD, 146
Index
375
Revenion, ^;a» Rhinpods, ais Rotifer*, 7. 4a, 334 Round-mouths, 9, 353 Rudimentaiy organs, 377
Saccophora, 62
Sacculina, 48
Sea-borso, 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, SS
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, 131 Spiders, courtship of, iot-105
bird-catching, 36 Sponges, iz, 323 Spongilla, 186 Spring, biolo^ of. 95, 96 Starfish, 335
Stickleback, courtship of, 99
parental care of, 109, no, 133 Stinging-animals, xz, 323-338 Storing, zao, Z3X Struggle for existence. 33-45 Surrender of parts, 64-66 Symbiosis, 69
Tapeworms, 229 Termites, 34, 84-87 Tissues, 179, 180 Tortoises, 263 Toxotes, 118 Trematoda, 229 Tunicates, 9, 250, 251 Turbellaria, 328
Variation, 299
Vertebrata, characters of, 19, 348,
349 Vital force, X9 Vivarium, so, 3i Volvox, 187
Wallace, 296, 397 Warning colours, 55, 56 Weapons of animals, 34 Web of Life, 18-31 White Ants. See Termites Worms, zo, zx, 338-335
Yolk, 195
Zoology, history of, 352-357
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