New York Siate College of Agriculture At Gorucl! University Sthaca, N. VU. Library Cornell University Library imal life, “mia Cornell University Library The original of this book is in the Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu3 1924003399098 ANIMAL LIFE A SWARM OF MAY-FLIES From ‘ Riverside Natural History’ By permission of Messrs. Houghton, Mifflin & Co., Boston, USA. ANIMAL LIFE BY Fy Ws TIE, J Ras EDITOR OF *A JUNIOR COURSE OF PRACTICAL ZOOLOGY ’ WITH 63 ILLUSTRATIONS NEW YORK E Py DUTTON & COMPANY 31 WEST TWENTY-THIRD STREET 1908 PRINTED BY SPOTTISWOODE LTD., NEW-STREET SQUARE LONDON PREPACE THE want of a small work dealing with the adaptations and factors of animal life in a broad and connected manner is my excuse for writing this book. In the simplest form and with the least amount of descriptive structural detail that I can compass, I have attempted to describe the moving spectacle : its abundance and variety, its modes of maintenance and of development, the safeguards of its individual and racial welfare. The evolutionary standpoint is adopted throughout, and in developing the subject I have proceeded by the use of three leading motives that differentiate animals from plants—movement, the acquisition of solid food, and the nervous control of response to changing order. To have included the factors of animal evolution, so far as they are known, would have unduly swollen the volume, and partly on that account, partly also because of such excellent recent accounts as those by J. A. Thomson (‘ Heredity,’ Progressive Sci. Series: Murray) and by R. H. Lock (‘ Heredity, Variation, and Evolution’: Murray), I have omitted consideratio,, of them. vill ANIMAL LIFE The work is written in the first instance for those who wish to learn or teach such a survey of the animal pageant as can ally itself with observation and experi- ment ; and in the second place for those who wish to organise their knowledge of animal life. References to fuller treatment of many topics are given at the close of the chapters. I am indebted to Mr. Gordon Hewitt for the loan of the two figures illustrating the house-fly and for revising the proofs; to the Director and staff of the Manchester Museum and to Mr. Greenwood for aid in obtaining the half-tone photographs ; and to the publishers and authors specified under the respective illustrations. Miss Emily Dust (Manchester School of Art) has executed the design for the cover. My textual indebtedness to the work of others cannot be clearly indicated, but I may mention that the chapter of Insect life-histories owes much to the writings of Fabre, Peckham, Miall, and Wasmann, and that the latter part of the chapter on colour (especially as regards ‘ effacing gradation ’) owes much to the writings of the American artist Thayer. F. W. GAMBLE, MANCHESTER UNIVERSITY : March 12, 1908. CONTENTS CHAPTER I THE INTEREST OF ANIMAL LIFE The contrast between animal and plant life—The value of the study of animal life CHAPTER II THE FULNESS OF THE EARTH Its appeal to hunting and pastoral races—The discovery of animals—The richness of the sea—The sea as the mother of life—The abundance of life as revealed by travellers and naturalists—Examples of the prevalence of animal life—Scale insects—Green-fly—The hidden life of winter— Animals as rock-formers CHAPTER III THE ORGANISATION OF ANIMAL LIFE Individuality—Classification into groups subordinate to groups—The classes of vertebrate and invertebrate animals—Evolution of animal life—The rise of fish, amphibia, reptiles, and mammals—The three main pro- blems of animal life—The maintenance of self—The development of self—The progress of the race PAGE 16 E. ANIMAL LIFE CHAPTER IV MOVEMENT The spectacle of movement : 1. Increasing finish of movement is ‘sgeentipanis d by elevation in the scale of being—Insects—Fish 2. The finish and unweariedness of movement 3. Its highest manifestation—The migration of animals The modes of animal motion—The analogy of a boat— Leverage in swimming, walking, and flight—Other forms of locomotion : : ; : The movements of anivalaules Clare movement—The value of cilla—Movement essentially innate 1. The movement of worms and crustacea 2. Swimming, walking, and flight of insects . The locomotion of vertebrates : 1. Fish—Their methods of swimming—The use of the tail and fins—Free swimming and ground fish—Attempts at walking and flight ‘ , : ‘ : 2, Movement on land—Support and propulsion— Movement and rest in an erect position—The changes which have converted aquatic locomotor organs into ter- restrial ones ‘ 3. Amphibia and Reptile Maral nae ein. ing anid aquatic mammals—Whales and seals—Flying mammals—Bats : P : . , é : : 4+. Birds—Theiw flight—Adaptation of the body— gs—Feathers—Methods of gliding and active flight— Their adaptation for perching, running, and swimming— The structure of the legs and feet CHAPTER V THE QUEST FOR FOOD The source of animal food : the quest for plants : 1. The need for food—Dependence of animal on plant hte—The feeding of fixed animals—The value of higher plants to animals—Windfalls—Leaf mould. 2. The feeding of crustacea and insects—Their hips, and tongues—The services of insects to plants . jaws, pe Oo te N CONTENTS . The methods of snails and slugs—The es of ‘alanis against their attacks 4. Vegetarian mammals—The need ee iheroueh: mas- tication 5. Fruit- eating eee . 6. Evolution of plants aeeGrapnnten, by nee eens com- plexity of animal life that depends upon them B. The quest for prey : the supply of food in the sea: 1. The origin of the carnivorous diet—Scarcity of plant life in the open sea—At the poles and in deserts—Fixed animals not consistent vegetarians—Hydroids, Medusz, and anemones are carnivorous—The food of star-fish 2. The demands of active swimming life—The food of fish—Pre-occupation of the mouth with breathing— Rarity of grinders—Choice of shrimp and oily food— The food of ground fish—Dab—John Dory—Dog-fish 3. Cuttle-fish—Their activity and mode of overcoming prey—Their enemy the sperm-whale 4. The food of sea-birds : C. The quest for prey: adaptations of ina anime 1. The stress of land life—Land plants abundant but protected against the attacks of animals—The chief causes that favour a carnivorous diet . 2. The food of carnivora—Voracious inseots Spiders and their allies—How the web is made CHAPTER VI THE BREATH OF LIFE Life as a combustion—The need for oxygen—Our unconscious- ness of daily waste and pacers eae of the metaphor of flame The relative abundance of oxy a in wate Te air as diterent depths—Evolution following the quest for oxygen i Modes of breathing among animals—Protozoa, fixed animals, sponges, corals ; the irrigation of their bodies with water, and the power of pigment in combining with oxygen —The respiration in higher animals is carried out by an internal fluid, the blood, which is aerated in the skin cover- ing the gills—The adaptation to secure thorough aeration (shells), and greater oxygen-holding capacity of the blood, 73 XU ANIMAL LIFE blood pigments—The respiration of free-living and burrow- ing crustacea ; of bivalve and univalve molluscs ; of cuttle- fish—Air-breathing worms, crabs, and molluscs—The respiration of fish; their gills and muscle-pigments— Adaptations to avoid the suffocating influences of drought on fish-life—The air-bladder and its gases; its varying uses, leading to the formation of lungs—The respiration of amphibia and the conquest of the land—The breathing of reptiles—The evolution of more perfect lungs in birds and mammals associated with the development of the voice and of a higher organisation—The maintenance of the heat produced by breathing and the production of a constant temperature ‘ ; s = é . c + 104 CHAPTER VIT THE STOR ANIMALS The orderliness of animal organisation implies controlled adaptation—The nervous system a visible sign of this harmonic grace—It mediates between the stimuli that fall upon an animal and the resulting responses—It is the seat of traditional and individual memory, and sets going periodic as well as immediate actions—The nature of periodic nervous action—Organic memory—The light it throws on animal development—The nervous system the earliest and most important organ to appear—The influence of glands in stimulating the development of the body 2. -135 the senses considered as the necessary means of maintaining a station in life, gaining food, and avoiding danger—These senses bound up with essential adjustments to meet the exigencies of life—The contrast between the few essential sensations common toall living things and the vast array of organised form in which they find expression—The habits of a shrimp or prawn taken as an example of the w ay in which the conduct of these animals is built up out of responses to light, pressure, taste . : : 432 the double nature of stimuli that affect Sais Sania: from without that affect the skin, and others, from within, that affect the internal organs—The correlation between the two effected by the nervous system—The skin as the seat of origin of sense-organs for interpreting external con- CONTENTS xili ditions—The origin of the eye and ear from the skin—The zor origin of the central nervous system in the skin—The origin of the nerves in (a) a primitive connection between the central system and muscle ; and (b) an equally primitive con- nection between the internal movements and the governing central system ; and (c) a correlation between (a) and (0). 140 The stiffening of these inward and outward responses into habit and tradition—The evolution of more complex responses based upon a groundwork of muscular and sensitive re- sponse—The greater strenuousness of life on land and in air has led to the evolution of complex instincts—The power of profiting by experience—The domestication of animals, and its far-reaching effects on man’s social life . 144 CHAPTER VIII THE COLOURS OF ANIMALS 1. The primary meanings of animal colours: Colours the outcome of inward processes—The relation of animal pigments to light—Exposed surfaces of the body more deeply coloured than shaded ones—Experi- mental evidence on the colouring action of light—The bleaching effect of darkness—Agreement between plant foliage and animals in colour distribution—The green pigment of plants concerned in nourishment—The red pig- ment of blood and muscle a respiratory substance, and only secondarily a decorative one—The relation between the two in chemical composition—Loss of green pigment in parasitic plants; temporary loss in minute flagellate organisms when supplied with organic food, reacquire- ment of the green colour under inorganic nourishment— Nature of these Flagellata: a connecting-link between animals and plants—The adoption of solid food and the origin of muscle gave the animal branch of this family ereater facilities for distribution and involved more efficient Evolution of the blood pigments ; 149 te evolution of red and yellow fatty pigments—W tie distribution of these in animals and plants—Association of these pigments with stores of reserve food—aAssociation of fat with these pigments in the skin and other tissues of the ZZsop prawn—Evidence for the formation of this XIV ANIMAL LIFE VAGE fat independently of the food—The original mode of nutrition in animals a double one (a) by photosynthesis ; (L) by elaboration of solid organic food—The fatty pig- ments in animals are a vestige of the first mechanism which has been supplanted by the second and more efficient one—Pigments arising through climination of waste substances from the tissues and their deposition in the skin—The white colour of butterflies. Summary : pigments originally nutritive or respiratory ; excretory pigments a by-product of vital activity—The original function may be lost and a decorative meaning and use gained secondarily . : ‘ : . « 60 2, The secondary meanings of acral ite : Harmony between animals and their surroundings the note of animal life—Sympathetic colouration a case of such harmonious adaptation—Instances of colour-sym- pathy ; the Zsop prawn—The development of colour- sympathy in the life of the prawn—Critical period in its career—The abundance of similar sympathetic colouration in other marine animals—Scarcity of such in fresh-water —Colour sympathy in land-animals—Arctic and desert colouration—Forest and field renderings of background and foliage on the skins of animals—Effacive gradation in the shading of the skin—Cryptic colouring, form, and posture amongst stick-caterpillars, moths, and butterflies —The leaf-butterhy and Mantis of India—Spiders— Mimetic resemblance of certain unrelated butterflies— Seasonal differences of colouration and habit—Protective meaning Experiments on cater- pillars and mantises—Warning colouring associated with distastefulness—The pigments of animals older than the effect they produce . : ‘ : ; ‘ ; : = hOF CHAPTER IX THE WELFARE OF THE RACE Kacial welfare a stimulus to which all beings respond—Personal acquisitions of racial value—The heritage of animals and ot man—The response of animals to the stimulus of racial welare—The stringency of the test by which the value of this response is measured—The ornaments of sex CONTENTS among mating animals—Battles to ensure the healthiest mating among spiders, fish, birds, and mammals—Testing of the powers in drones of the bee and males of other insects—Unequal severity of the test for survival among young males in contrast to the young females of many animals _ ; ? ; : : F Egys and jeune —Deration Tie sea as a nursery—The advantages of pelagic larval life—Modes of defending the eggs and young of aquatic animals by fixing them to some holdfast and by the guardianship of the parents—The nests and nurses of tish—The protection of the eggs by frogs and reptiles—The secretiveness of birds and insects in their choice of nesting sites—Brief review of the nests of birds— Small birds construct the most carefully woven nests—The significance of the relation between size and incubating methods employed by insects—The elaboration of nurseries by social insects CHAPTER X THE LIFE*HISTORIES OF INSECTS The influence of climate in stimulating the development of insect life—The cyclic changes of its abundance—The insects of early spring—Selection of nesting sites—Ditfer- ences between families of great and of lesser eae in the food of the young The life-histories of primitive fnssots—The spring- ere sine thelr allies—The straight-winged insects—Grasshoppers, locusts —The difficulty of shedding the old skin—The development a gradual one—The life-history of the ee and their larve . More complex life- iivterice-—Mebymonphons2 The dnitroduies tion of the pupal stage—Caddis-flies and caddis-larva— The development of the pupal stage and the emergence of the fly—Beetles—The life-history of the oil-beetle. : The life-histories of more modern insects—Butterflies and their adaptations to aerial life—The development of the cabbage-white butterfly — Complex structural changes during the pupal stage—The Diptera or two-winged flies— Their economic importance—The mosquito and midge XV PAGE 201 bo N xvi ANIMAL LIFE family—The life-history of the common gnat—The breath- ing pores of the larva and of the active pupa—The emer- gence of the fly—The development of the mosquito and its relation to malarial fever—The life-history of the harlequin- fly (Chironomus)—Its larva the ‘ bloodworm’—Variation in its colour related to the nature of the water—The phantom-larva of Corcthra—The life-history of Midges : the owl-midge (Ceratopogon)—The black-fly (Sumulium)—The adaptations of its larva and pupa to life in running water— The drone-fly (Evistalis)—Adaptations to larval life in stag- nant water—General conclusions on the life-histories of Diptera : The Hymenoptera : Efficiency of their care for their young—Complexity of their communal life—The less highly organised families of this order—The saw-flies, gall-flies and ichneumons—The nature of gallsand their mode of origin—The two generations of gall-flies—The solitary wasps—The key-hole wasp—The nest and its stores of food—The sand wasp (4 mmophila)— Mode of construction of its nest—Mode of capturing prey and storing the nest—The social wasps—Their nests and workers—Solitary bees—Prosopis a primitive type—The burrowing and carder bees—Cuckoo bees : F Evolution of the hive-bee—The first indications of association in burrowing bees—The first attempts at comb- construction—The appearance of workers at first casual in Halictus, becoming a settled habit in bumble-bees—The construction and ventilation of bumble nests foreshadowing the perfect comb of the honey bee—The importance of good seasons in assisting the evolution of the higher bees— Behaviour of Arctic and Mediterranean bumble-bees—The tropical MJeliponas—The high degree of perfection attained in the colonies of the hive-bee. : 3 : : The nests of ants—The care of ants for their young—The swarming of ants—Longevity of ant-queens—Foundation of an ant-colony—Conditions that produce queens, drones, or workers—Aberration of the nursing instinct PAGE bo oo £ LSet - OF Wo bUSTRATIONS FIGURE PAGE A SWARM OF MAY-FLIES . : . . frontispiece 1. EGGS OF THE Sguip (Loligo) ; : é or II 2. SHOAL OF JELLY-FISH . ‘ ‘ i : : ; : iN 3. ComMMON Brown Lizarp . i ; ; ; : en 18 4. THE SLOW-worM (Anguis fragilis). . , : ; 18 5. NewtTs : F _— 20 6, THE RELATION BETWEEN ‘Cesaieanes. AND cr , 7. SWALLOW ON THE WING . : : ’ : z a9 Ai 8. GREATER Horsesnuor Bar. . ’ : ‘ : = ME 9g. WHITE SEAL ‘ , : : : : . : anh 54 10. DISSECTION OF BIRD (PIGEON) . i : . : : 59 Il. SAND-HOPPER (Gammarus) ; : 4 ‘ ¥ cae 68 12. TUBE-BUILDING SAND-HOPPERS : 3 : ; ; ee 13. Group oF BuRYING BEETLES : : ; : rae 70 14. ORCHESELLA: A PRIMITIVE INSECT . : : : § ra 15. MUSSELS AND PEA-CRABS . ie 81 16. How a STAR-FISH OPENS AND EATS AN 1 OvsTER : : 83 17. BLACK-HEADED GULL, NEST AND YOUNG . : Sue 86 18. TonGuE oF HoUSsE-FLY : 3 : . g 2 OT 19. WHEEL-WEB OF GARDEN SPIDER . : : : we 8 20. WEB OF Agelena ON GRASS : : ‘ : : = 205 21. Nest oF YOUNG Agelena ON FURZE . ‘ : bd 96 22. NEesT OF CAVE SPIDER : : : : : : = “OF 23. BRINE-SHRIMP (Branchipus) . ‘ : é : 4. 106 24. DAPHNIA, THE WATER FLEA A = be 25. HEAD AND THORAX OF CRAYFISH, SHOWING Gtits F TI2 26. A GROUP OF SAND-BURROWING ANIMALS (Hare URCHIN, LuGWorM, COcKLE, MuUD-CLAM, AND MASKED CRAB) . i ‘ : ‘ . ‘ ; 4 + Joa 27. THE aise ‘ ‘ . a . ° ‘ . : 12 Xvi ANIMAL LIFE THe Cave Newr (Proteus angurncus) ? 29. THe DEVELOPMENT OF COLOUR-PATTERN IN ffippolyte . 172 30, FEMALE ORANGE-TIP) BUTTERFLY, SHOWING SYMPA- THETIC COLOURATION : : ‘ : : F » AL7O 31. HEN PARTRIDGE AND YOUNG ‘ , : : 2% ee 32. Cock ARGUS PHEASANT DISPLAYING HIS PLUMAGE 2 TIO4 33. THE RUFF IN MATING PLUMAGE . é : g 3 TS 34. Black Cock DISPLAYING BEFORE THE GREY-HEN. * 196 38. TRANSFORMATION OF A SEA-worM (Nereis) : : 200 36. THE PALOLO-WORM OF SAMOA . : : : » BOs 37. EcGs oF HERRING . : : i . 3 : = i. 208 38. EGos oF CUTTLE-FISH (Sepia). ‘ ; ‘ : . 204 39. SAND-MaRTIN AND YOUNG ‘ : . ; z + oh 9 BOF 4o. SWALLOW, NEST AND YOUNG . : : : . 208 41. Nest oF Litrte Tern. ; ; ; j = a $200) 42. NEST OF SKYLARK : ; 4 : ; ; : f. 3300 3. Nest oF LONG-TAILED TIT-MOUSE. , : : : 213 44. Cuckoo IN Nest oF TITLARK 45. Harvest-Mousr AND NEST 46. SomE Primitive INSECTS : ‘ 47. THE DEVELOPMENT OF THE GRASSHOPPER 48. Lire-History oF THE DRAGON-FLY 49. SKIPJACK BEETLES AND LARVA (WIREWORM) . 2 im 2390 30, Lire-History oF CABBAGE-WHITE BUTTERFLY p wae st. THE Houskt-Fry : ‘ ; : ; : : ich SBAZ 32. LARVA OF GNAT . , ‘ : e ; ; , 2 33 53. Pupa oF GNaT . : : 3 34. NEst oF COMMON Wasp. ; : i i , ma Se 55. LEAF-CUTTER BEE. . ; : : : ‘ ne re 56. EvoLutTion or THE TONGUES oF : : » 280) 57. ADAPTIVE STRUCTURES OF THE LeGs OF THE HIvE- Ber. ' x . : : : ‘ é , gk. OE 58. HIND-LEGS OF SOLITARY BEES 39. Burrow or LEAF-cUTTER BEE ‘ : : iva 5 60. BURROW OF SOLITARY BEE (.didrena) : ; : ~ 28H 4 5 61. NEST oF BUMBLE BEE. : ‘ ' : : ores eo! 62, WORKER-CELLS FROM BE -COML \ ¥f € ie f 29 ANIMAL LIFE CHAPTER I THE INTEREST OF ANIMAL LIFE THE contrast in impressiveness between plant life and animal life is a reflection that every countryside arouses. By the plants we may know the wetness or dryness of a district, its cultivation or wildness, the run of the watercourses, the season of the year, and even the time of day. In civilised countries, where the scenery has been largely determined by man, the national character finds expression, and shows in our own country a generous capacity for half measures, a toleration of opposites, a compromise between formality and freedom, and controls in a charac- teristic manner the growth of native plants and the cultivation of alien ones. With the fields and heaths, the woodlands and uplands, in all their varying expressions, genera- tions of countryfolk have had close alliance. Be- tween them and this ‘furniture of the earth’ there has grown a tie, the strength of which is not realised B 2 ANIMAL LIFE until it is broken, and the Devonshire combe or West- morland fell are images in exile. To this the animal life of a countryside offers a sharp contrast. Its bulk, in a bird’s-eye view, is in- significant, its tenure of the ground is short. It is evasive, and offers no large characters distinctive of the highlands and lowlands, or of the cultivated and open country. It is remote, and for the discovery of its genius a closer attention and a minuter acquaint- ance than the farmer’s or gamekeeper’s is requisite. Its individuality is never wholly subdued by the country around it or the breeder who cultivates it. Alone among animals the horse and dog have been trained to a willing understanding of man’s wishes. Mass, stationariness, and pliability—the notes of plant lfe—are replaced in animals by purposeful evasion, activity, and intractability. The abundance of animals, far from always giving the pleasure wakened by the advent, growth, and even the decay of rich masses of plant life, raises feelings of dis- gust and alarm as often as those of satisfaction or enjoyment. The evolutions of shoals of fish, the concerted flight of birds, the winding homeward of a herd of cattle, give but an evanescent sense of beauty in comparison with the intimate sense of relief aroused by the sight of a woodland after traversing stretches of bare country. The sense of animal intractability 1s enhanced when we discover in them no merely passive feature of the scene, but independent and even hostile beings. INTEREST OF ANIMAL LIFE 3 a A slight acquaintance, however, with the enthralling mysteries of animal behaviour awakens the latent sympathy between animals and ourselves that is one mark of our community of origin. Many of us begin that acquaintance through the sheer pleasure we find in observing and collecting animals, and in watching their habits. To such field-work the most experienced naturalist returns with increasing wonder at the infinite significance of what he sees, at the unexpected number of fresh problems that lie in every shell and feather, in each insignificant worm or insect, in the colours of organisms, in the very games of chil- dren, and even in social customs. The shell brings up in his mind the image of an organism with brain, muscles, and glands woven into a fabric that has no caprice in its most delicate folds, whose care for itself and its offspring implies ceaseless evasion of fish and shrimp and cunning defence against the destructive power of the waves. The feather, with its perfect system of hooks and eyes, by which its plumes form a firm, airtight membrane for flight or for retaining warmth, is another casual object of beauty and sig- nificance. The meaning of its colours, its position on the bird’s body, its replacement at the moult- ing time, are but the first of many problems that a feather suggests. The worm remains no longer a degraded creature or one remote from human interest, for the study of worms has suggested the most effective of modern treatments of that most terrible of skin diseases—lupus. It was by the behaviour of B2 4 ANIMAL LIFE earthworms under the influence of special rays of light that the treatment known by Finsen’s name owes its origin. Finsen noticed that when the prismatic colours of sunlight are successively cast on the worm, the blue and violet rays—and they alone—cause irritation and distress. Accordingly, he began a systematic work on the different effects which coloured light exerted in virtue of its properties on healthy and diseased skin, and the beneficial effects of his dis- covery are now restoring to health and activity every year hundreds who but for this work on worms would have received no effective assistance. But the earth- worm is far more than the corpus vile of a successful experiment. It is the unseen agriculturist, bringing the subsoil to the surface for light, air, and rain to vivify and replenish. It is the preserver of ancient monuments, protecting them by an encasement of earth from destruction. More significant still, it is one of a tribe whose ancestors have had a great share in the origin of higher forms of life. The links that bind together the crab and lobster—the Crustacea—the insects, and probably even the vertebrate animals, find their common starting-point in the lowly worm, and as we trace back some natural characteristics of our race to an obscure tribe, such as the Frisian, so does the naturalist trace the hidden peculiarities of the structure of the higher animals to the worm, in which those features are more manifest. Perhaps the most unexpected results of this historic INFLUENCE OF ANIMAL LIFE 5 and genealogical treatment of Nature have been obtained in the games and customs of mankind. What seems more irresponsible than the behaviour of village children who come every evening to a chosen spot and sing and dance? What further meaning can there be in a harvest supper than a thanksgiving for the ingathering of the crop? Yet the words children sing are often charms said before hunting, over water, or at burial, altered almost be- yond recognition from the invocation they represent ; and the harvest supper, like our birthdays, Christmas Day, and Midsummer Day, links us with pagan man and the worship of the spirit of vegetation. As there is no known limit to the significance of animal life and behaviour, so we cannot set bounds to the influence of such knowledge on human life. Whether we consider its effect on our physical, zsthetic, or scientific faculties, we find that a biological education offers an unrivalled field for observation, to which even children turn with an enthusiasm that needs rather restraining than encouraging. The magic of life in the hidden ways and half- lights that field-observation discovers, stimulates the sensitive and artistic nature to a new sense of wonder. ‘The cry of the curlew is one of the three oldest cries of the world.’! The elevating effect of the quest of significance, the practical advances that biological research has made and will make in hygienic and agricultural practice, and a more vivid and intelligent 1 W. B. Yeats. 6 ANIMAL LIFE sense of our community with living nature, are but some of the influences which the study of animal life confers, and will confer beyond any limits we can at present assign. REFERENCES Finsen, N. R. (Light Treatment of Disease). ‘ Photo- therapy.’ Edward Arnold, 1901. A most useful summary will be found in the ‘Quarterly Review,’ January 1906, Ppp. 138-62. Haddon, A. C. ‘The Study of Man.’ The Progressive Science Series. John Murray. Darwin, C. ‘Formation of Mould through the Action of Worms.’ John Murray. CHAPTER Il] THE FULNESS OF THE EARTH THE greatness of living nature hes in its bounty. To the earlier races of mankind this fulness was brought home by the increase of herds and crops, on which their sustenance depended. ‘The cattle upon a thousand hills, ‘The valleys also are covered over with corn ’—such were the images that conveyed a joyful sense of the full measure of earth’s ungrudging- ness. From time immemorial, men have acknowledged their dependence on the fertility of nature by appeals to the spirit of vegetation and by charms against malevolent influences. They realised that success in raising foodstuffs and stocks was only possible by opposing the inroads of weeds and beasts of prey. In the abundance of locusts or lions, of weeds or rust, they saw that the fertility of nature was not directed to the good of man only, and also that through the powers of increase which man shares with animals and plants, arises the keenest of all forms of the struggle for existence. Small wonder the early shepherds cele- brated successful harvests or increasing herds. In later times the wonderful diversity and rich- ness of human and animal life became more widely 8 ANIMAL LIFE recognised. The voyages of the Spaniards and Por- tuguese, of Cook and his successors, revealed the presence of new races of men in many parts of the globe, while only sixteen years ago Stanley discovered a race of pigmies living in the equatorial forests of Africa. Strange stories of manlike apes were brought from Africa and Asia by travellers who described the ferocity and strength of these gorillas and orang-utans. From American settlers came news of the herds of bison that roamed the prairies, travelling from grazing- ground to salt-lick with the same mysterious and unfaltering precision that the camel of Eastern deserts shows in adopting its line of march. Hunters told of the life of the jungle, with its strange midday silence, that each night and morning wakens into a roar of activity ; and sailors brought back from their voyages parrots and monkeys, pearl-shells and coral, mementos of their travels that added emphasis to the recital of their beach-combing adventures and opened vistas of new worlds to their enthralled hearers. And still there return, from the exploration of lands untrodden before by white men, travellers laden with tidings of new animals. The tale of earth’s fulness is not yet complete. Life in water as well as on land has become known to us in similar ways. The cratt of fishing and the need for water-transport brought the abundance of aquatic life early to the notice of men. In pursuit of their livelihood, fishermen could not fail to notice the birds of the marshes, the ABUNDANCE OF SHORE LIFE a) frogs of the swamp, the watering-places of deer, the footprints and bruised reeds where wild pigs had wallowed or cattle had come down to drink. To the coast fishers the flocking of gulls indicated the shoals of fry; anda school of dolphins or porpoises in pur- suit of mackerel or bigger game pointed out to them those waves of migration that set in towards the shore, and after an interval as mysteriously recoil to other coasts or into deep water, carrying their pursuers along in the chase. Floating helplessly off the shore or cast up on the beach even of our own coasts, there have been found from time to time strange creatures that justify the widespread feeling of the unplumbed possibilities of the ocean: ribbon-like fish twenty feet long, huge turtles with leathery skins, grotesque sun-fish, and eagle-rays of gigantic size. When searching for bait among rocks encrusted with animals, men found, even as we find to-day, cuttlefish and conger-eels sheltering in their crevices, strange worms of unusual size and agility that broke into pieces which crept and wriggled along as though the severance had endowed them with fresh life. With the coming of spring the longshoreman would notice a change in the beach. Over the sands, under the stones, and round the weeds he would find pears, grapes, purses, and strings of jelly hardly firmer than the stinging medusz or the fleshy polyps and anemones that meet him the year round. He knows that, like the foam, the meduse soon dry to a film, and is 10 ANIMAL LIFE therefore led to conclude that the sea-jellies are sprung from the foam, and that even the more substantial creatures of the summer are also of halcyon birth. The very names ot the animal jetsam that we pick up on the beach keep this Greek idea—that the sea is the mother of life—fresh in our minds: the common fleshy pink polyp, our ‘dead men’s fingers,’ is named Alcyonium ; the jelly-like, shapeless, brownish polyp thrown up in ribands is Alcyonidium ; the kingfisher that flies arrowy as foam before the wind is Halcyon ; the days most children recall with greatest glee—the days spent on the sands are the halcyon ones. That the sea-jellies are the egg-cases of fish, worms, snails, and cuttlefish (fig. 1) is a discovery of recent times. And yet so unwilling is the mind of seamen to accept such a reasonable origin, that these Greek traditions of the rise of creatures from inanimate nature, and of the transformation of the egg-cases of worms into young fish, survive as lustily as ever the spread of modern education. This acquaintance with the larger forms of animal life, begun by the shepherd and hunter, the fisherman and explorer, has been continued by naturalists, with the result that an altogether fresh idea of the fulness of the earth has been obtained. By the use of magni- fying-glasses it was found that creatures far smaller than insects abounded in sea and fresh water, even as the midges in the air or ants and greenfly on the ground. The furry coating of weeds, the scum round farm- ABUNDANCE OF ANIMAL LIFE II yards and decaying plants, the very dust of the air and the depths of the sea, contain an abundance of Fic. 1,—Group of Egg-capsules of a Squid (Loézgo), one of the Cuttlefish. The dark spots indicate the eggs. Natural size. --(/vom a specimen tn the Manchester Aluseum.) animal life. In the far north and south, as explorers sought the Poles, they found birds and seals in plenty ; 12 ANIMAL LIFE whilst, under the ice, so numerous were the shrimps that a seal’s head let down amongst them at night was a clean skull next morning. As ships sailed through the ice-packs the patches of discoloured water showed the whales’ food—myriads of small organisms drifting south with the cold Labrador current. Voy- agers to the southward saw the water aflame with phosphorescent light, each glowing point a living animal. From the surface downwards, for some twelve hundred feet, tow-nets showed the sea teeming with animals, and, at greater depths, a peculiar but less abundant deep-sea life flourishing amid intense cold and darkness. The bountifulness of nature lies on every hand if we have but the second sight to discover it. The little brown scales on an orange, for instance, are sedentary female insects, other kinds of which attack the apple and hawthorn, the larch and birch. These the tomtits know better than we, and take for their winter food. Greenfly, unseen in winter, becomes a plague in summer, covering our flowers and shrubs, crops and trees ; blown from overhanging boughs on to the corn beneath ; eating the roots at one stage, the leaf at another; and finally, some close, warm day, drifting in a winged swarm over the countryside. The hum of life, now faint, now clear, is the sign of summer’s abundance. But even winter is not lifeless to those who know how to seek. Where leaves have drifted out of the wind into shelter, under the warm covering of moss, among clods of hedge-banks, in the earth under 2 er wae ee — 4 * , Fic. 2.—A shoal of Jelly-fish, about one of which (A/7zoestoma) a group of young Horse-mackerel are finding shelter. A Chrysaora in the foreground, Azreléa in the background.—(4fter Haeckel and Kuckuck, by permission of J. B. Baillidre et Fils.) I4 ANIMAL LIFE stones, in the mud under water, animals and their eggs abound. When brought into a warm room a bag of leaves and moss, searched on a white surface, breaks out into a solitary bumble-bee stirs, a newt unexpected life stretches its body, beetles uncurl their limbs and creep about, caterpillars wake, spiders lie entranced, ants that lay sleeping wake in agitation. Clods broken up under warm water show as clear evidence of the hidden life within them. Dried mud from distant countries will then develop the eggs of shrimps, weeds, and Infusoria from those lands. In this manner cultures of many kinds mav be made. Boundless as is the profusion of animal life, we know that in the near and remote past its abundance was no less. If the Pyramids of Egypt are monu- ments of human endurance and skill, the animalcules that compose those buildings have left therein a record not less impressive than the tale of slaves worn out in hodman’s service. In the fells of northern England, in the cliffs and downs of the south, the very rock represents the labour of innumerable hosts of animals that have secreted salts from the ocean and deposited them as coral and shell, sea-lily and sea-mat. Limestone and chalk, with all the buildings and walls made from them, are due—and exclusively due—to living organisms, though trace of their presence may have REFERENCES 15 disappeared on account of the heat and pressure to which the rock has been subjected. REFERENCES The discovery of man-like apes: Huxley’s ‘Man’s Place in Nature.’ Collected Essays, vol. vii. Greek views on evolution: H. F. Osborn, ‘From the Greeks to Darwin.’ Macmillan & Co. The nature of chalk: Husley’s Collected Essays, vol. viii. pp. 1-36. 16 ANIMAL LIFE CHAPTER III THE ORGANISATION OF ANIMAL LIFE Tue thought of this abounding animal life brings to mind its multitudinous variety ; the individuality of man; the personal distinctness of animals, more evident as we grow more familiar with them; the separation of creatures into kinds or species, marked off one from another by intangible and yet seemingly impassable boundaries; the mighty gamut of the scale of being. In variety, as in number, animal life witnesses to ungrudgingness. Yet this prolific variety is limited by orderly control. Life everywhere displays organisation. In plan, as in execution, this is true of the relationships and also of the bodies of animals. That original ‘we’ is no unattached, new thing. We are body and soul of our ancestors. In features, behaviour, and constitution we acknowledge their gifts. Nor does our indebtedness stop there. Brought face to face with our poor relations, the apes and monkeys, we see, but do not acknowledge, remoter ties. The plan and construction of our bodies and of theirs is the same, but we are unwilling to accept this because we are possessed by the idea that they have too little CLASSIFICATION 17 intelligence to be likened to man, and we forget that it is their having intelligence at all which justifies us in regarding them as fundamentally related to him. From the apes we may pass to all the remaining animals that suckle their young and are coated with hair. These—the Mammalia—are interconnected by ties of structural agreement which investigation dis- covers in almost every bone and tissue, and even in the very blooditself. As proof of relationship, blood has lately vindicated its claim to pre-eminence. There is a test to which the blood of each mammal responds, and the nature of this response given by one species, compared with that of any other species, shows the close or remote connection between the two animals. Ranking below the hairy animals, those of feather and scale flock together. Unlike as birds and reptiles seem, the connection between them is closer than that between either and any known third group of animals. It is seen in the construction of the bony framework, of the muscles and tendons, in the blood and in the eye, in the brain and in the egg. All the differences which exalt the bird—warmth and sustained activity, voice and exuberance—are the outcome of reptilian characters. After the reptiles come the sluggish Amphibia, creatures of the swamps—the newts, salamanders, frogs, and toads. Breathing both through the skin and by the lungs, these animals are only partially emancipated from aquatic life. In this and other respects they stand halfway between reptiles and fish. is 18 ANIMAL LIFE Fic. 3.—Lacerta vivipara, Fic. 4.—The Common Slow-worm, a the Common Brown footless Lizard (Angats fray?lis). Lizard. —(From a spect- The thin, small specimens are ten men tn the Alanchester days old; the larger one above is Afuseunt.) three weeks old; the largest, below, is five weeks old. —(/7 0m speetinens tn the Manchester Museum.) VERTEBRATE ORGANISATION 19 Fish alone have true median fins, and usually also the two pairs of fins that correspond to our arms and legs. The gills, reduced in ourselves to the framework of the larynx and parts of the middle ear, are seen in their full development as tufts with elaborate bars for their support, and with muscles for conducting gulps of water in at the mouth, over the tufts, and out through the gill-slits. Movements of the body are carried out mainly by the muscles of the back and tail, which are flattened either laterally or from above downwards; and to steady the unstable fish and increase its propelling force the surface of its trunk and tail is expanded into median fins. The paired fins, so essential to higher animals for locomo- tion, are mere steering-organs for fish, and in the lowest fish of all—the lamprey and its allies—are entirely dispensed with. Between these four divisions: mammals, reptiles and birds, amphibia, and fish, there is a deep-seated fundamental likeness. Differing as they do in the execution of the design, these groups agree in the plan of their bodily structure, and for this reason they can be classed together as vertebrate animals. In a similar way, the bewildering variety of in- vertebrate life can be reduced to groups subordinate to these six larger groups: the Protozoa (simplest and most primitive of animals); the Ccelenterates (zoophytes, anemones and corals) ; the Molluscs ; the Arthropods (insects, centipedes, and Crustacea) ; the Echinoderms (sea-urchins, sea-lilies and starfish) ; the C2 Fic. §.—Group of Newts (77elon cr7status), showing the differences between the Crested Male (right hand and top figures) and the smoother I’emales (left and central figures). # natural size. — (/7vom specimens in the Manchester Mitseum.) RISE AND FALL OF BYGONE RACES ar earth and water worms. Through each of these six divisions there runs an air or theme, of which the animals themselves are the innumerable variations or fugal developments. Amongst the members of each of these principal groups we find one dominant tendency—to possess the earth. Having realised this, they are in turn replaced by others, so that if by the aid of fossils we look at the history of vertebrate life, we find as we recede further and further from the present that in the order of their supremacy animal groups suffer eclipse. First, all traces of man disappear; then at a still greater distance of time the mammals and birds vanish; another stage further back and the reptiles, hitherto so abundant, are no longer found; whilst in a still more ancient time the newts die away, leaving only fish of a few kinds analogous to our sharks and to the garpike of American lakes. At the most remote epoch of which we have any recog- nisable animal records, no vertebrates are found amongst them. From invertebrate beginnings we find fish de- veloping into a multitude of forms, peopling the rivers and lakes by immigration from the sea, to which many return, as to their true home, when their life is ending. From the ancient armoured types to lamprey and shark and bony fish, each division becomes more and more complex and highly organised as its dominion increases and its circumstances improve, and remains simple if its life remains uniform. i) nN ANIMAL LIFE In the rivers and swamps armoured newts arose and wandered over the damp coal-forests and lake shores as the alligators do to-day, whilst their descend- ants, the multitudinous frogs and toads, have still only partially emancipated themselves from aquatic life in order to gain that life on land which favours the height of animal development and gives it new impetus and variety. The history of reptiles is a chronicle of more stirring events. From a remote epoch, and dim as all such origins are, the first reptiles appear, almost indistinguishable from the armoured newts, their contemporaries. They were the colonists of those days, and, with an adaptive power of meeting new circumstances that the newts had never shown, became masters not only of the swamps but of the sea and land. Some grew to the size and acquired the habits and shape of whales. On land they stood upright, high as houses, and with their hands reached to the greener boughs of lofty trees. That most difficult of all such conquests, the dominion of the air, they effected, and in their own way solved the problem of flight. Success such as this opened up still other paths of life, for which further variety of form was needed. Small as well as great could find places in these newly acquired kingdoms. The development of vertebrate life seemed a lasting work, finished in its main outlines. Yet in this heyday of reptilian life another group, SUCCESSION OF ANIMAL LIFE 23 destined for supremacy on land and sea, was beginning its career. From small rat-like creatures the earliest mammals soon rose to manifestations of size, strength, and pliability which only reptiles had hitherto shown ; andas the medieval periods of the earth’s history were ages of reptiles, so the prehistoric and historic periods form the ages of mammals. Wave after wave of life has risen from the inexhaustible depths of nature, towered to a great height, and has then fallen; yet undelayed the onward movement continues. In variety of life the period of mammals is the richest of all. As heir of the ages, it has the offshoots of verte. brates and invertebrates whose first exuberance is past. Holding the promise of the future, it contains the seed of the coming dominant races: and to those at their prime, those which have overcome and taken possession, the earth yields her heaped measure of variety and abundance. It is therefore clear that an animal does not enter upon its life unrelated in structure or habits either with those about it or unadapted to the station in which its lot is cast. Its body displays to the practised eye unmistakable marks of its place in the organised system of life ; and its structure bears witness to the precise place or specific niche which it occupies in that system. If a member of a dominant race, it may soon step into a position which less specialised animals of more lowly birth never attain. The land- owner’s son has the start over the labourer’s. 24 ANIMAL LIFE The problems by which animals and ourselves are confronted can be resolved into three :— 1. The maintenance of self. 2. The development of self. 3. The welfare of the race. To the maintenance of self a station in life is necessary, power to acquire food and to repel enemies, ability to build up the food into that frame which is the outcome of past history bequeathed to its possessor by its parents. In this activity an animal is guided by a faculty for orderly response that shapes its behaviour. Through these responses it gains a sense of the world around, and the habits so formed are as original, and yet as much the outcome of latent inherited capacity, as the body which they direct. But an animal is not born fully formed or com- pletely endued with all the psychic experience that it needs. Not merely to maintain itself, but to develop, is its task, to which every impulse awakened by the outer world of light, water, and air, or the inner stimulus of hunger, activity, and desire, impels it. Impressions keener than any subsequent ones teach a newborn creature the unexpectedness of events. If a marine animal, it learns the difficulties of balance, the rise and fall of the tide, the brightness of day and darkness of night, the qualities of surface and of deep water. If a land animal, it encounters the varying heat and cold of air and earth, discovers the weight of its body, and the difficulty of sustaining and propelling it. If sufficient food is obtained, it grows DEVELOPMENT AND THE RACE 25 both in size and complexity ; and so imperious is this demand for development that, to satisfy it and give material for elaboration, the very tissues of an animal may be sacrificed, and remoulded by a process to which it passively submits. Fresh impulses fit to guide this altered self are developed in it, and are evoked perfectly at the first trial, or after afew failures. If this experience leads to a wider range of activity, the animal rises in the scale of being; if it leads to a narrow range or fixed habit, development becomes retrograde. As the responses govern the behaviour of an animal and give it character, so this advance or retreat of the individual is governed by the supreme factor of racial welfare. The welfare of the race is the end to which indi- vidual well-being is subjected and often sacrificed. It is rather a motive that possesses animals than is possessed by them. It determines the formation and policy of hives, the building of nests, the colours of eggs, the care of the young. It transmutes inactive fish and beasts into vigilant and ferocious defenders of their young. It is the highest motive that governs individual and national conduct, and has produced that heritage of freedom and social stability which we enjoy as we inherit the physical and psychical organi- sation that constitutes our being. REFERENCES Past history of animals: Siv Ray Lankester, ‘ Extinct Animals.’ Blood-relationship : Nuitad/, ‘ Blood-immunity and Blood- relationship ’ 20 ANIMAL LIFE CHAPTER IV MOVEMENT MovEMENT, more than any other feature of animals, brings to us the meaning and working of their Hfe. Activity is the sign of life, and as its manifestations exhibit control and adaptation, so does the organism that displays them rise in the scale of being. Begin- ning with the animalcules and jelly-fish, which have at best but feeble swimming movements, we pass to the creeping things that cling to the ground or dart spasmodically from one resting-place to another, and then to the Crustacea and insects, in which the prob- lems of walking on land and of flight through air are first solved. The flight of insects is not only the most perfect movement known, but it has also raised these animals to the highest place amongst invertebrates. Their flight may be only temporary, but it is upon the superiority so gained that their life exhibits organisa- tion, and cven civilisation of the most complex kind. The movements of vertebrates in water, on land, and through the air, bring home the same con- clusion. Fish born and bred in the water are the lowest members of the group ; and the most specialised THE STUDY OF MOVEMENT 27 families of fish are those in which, as in mackerel or tunny, the art of swimming is most masterly. Am- phibia, that lie motionless for long intervals, have remained stationary in the scale of being, whilst reptiles, though capable of the most rapid running, gliding, and striking movements, are, owing to their fre- quent lethargy, only mediocre vertebrates, surpassed by both mammals and birds, which in virtue of their more sustained activity have attained the premier position. There is an esthetic side to the movements of animals that makes us never tire of the spectacle. The ease with which fish and porpoises advance, turn, and press onwards under a sudden impulse, the sense of restrained strength in the taut muscles of a horse or dog, the freedom and masterliness of flight, the graceful form and manifold rich colouring of birds, lend inexhaustible attraction to the study of motion. The energy of many animals has something of that enduring and periodically varying quality that belongs to river, wind, and sea. Gulls and albatross follow in the wake of vessels for days, and even weeks, with no sign of weariness, sleeping on the water and only stooping to feed. Fish when not in active move- ment are untiringly adjusting their balance by small muscular contractions. The beating of the heart, on which all other motion depends, endures night and day, and exhibits a rhythm of diurnal quickening and nocturnal slackening which is symbolic of the flow and ebb that rules living and inanimate nature. 28 ANIMAL LIFE The full epiphany of animal movement is scen in the behaviour of migratory flocks. Migration is essentially an oscillation between breeding-ground and feeding-ground. On the first, nests are made and the young reared and educated ; on the second, parents and young have no connection. Each lives to himself and the young grow to maturity. When the nesting season approaches, an impulse, the most powerful and selective in animal life, draws mate to mate and fills unmated migrants with a longing that cannot be satisfied save in a far river, or sea, or country. Mated couples of birds desire the particular cottage eaves or hollow on a moorland that has served them for nesting so long ; the pride of the hook-jawed salmon is only satisfied by the river that he left last year for the sea; while the upstream eels that leap with the first autumn spate, congregate in a thick mass on their start for the sea. In this rush for the breeding-ground a new appear- ance envisages the migrants, a new strength possesses them; instincts that lay dormant rise up and direct their way, notes unknown save at this time of dangerous travel are heard. Then all our migrant birds make for the north. The ducks, geese and waders, the fieldfares and redwings, leave us for the Arctic, for Norway and Siberia. From the south come our swallows, warblers, cuckoos. Wave after wave, starting from Algiers, Tunis, Syria, and even the coasts of the far south, send north- ward their migrants secking homes. Larcly do they THE MIGRATIONS OF BIRDS 29 rest. In one or at most two flights at night is the journey done. Flying low down over the earth and sea if the night be dark, filling the air with their strange migratory cries, they are carried on through all weathers by an instinct that only errs, moth-like, at light in the gloom ; or if the night be clear, high up, often out of sight, where the cold and lightness of the air would numb and overcome us, they take their way and arrive at the haven where they would be. But even before summer is over the return move- ment southward begins. First the unmated birds slip away. Then the birds of the year, perhaps under pressure of circumstances, yield to this new migratory impulse, that leads them to forswear the county and country of their birth and to find their way unaided across water to lands not their own. Lastly come the parents, flock by flock, not in the solid phalanx that they presented as a northward-going host, but silently and in detachments, with the dress of spring worn out by the summer’s housekeeping or replaced by a new but duller garb. More leisurely now and by less direct routes they make their way to the Mediterranean, to the Aigean, and to southward-lying lands. Modes of Animal Movement.—If we imagine a man in a boat provided with oars and boathook we can think of four different ways in which he may effect movement: by punting with one of the oars against the bottom of the water; by hauling against brush- wood or other obstacles on the banks ; by sculling from the stern with a single oar, or by rowing with a pair 30 ANIMAL LIFE of oars. The effort necessary to move the boat slowly through calm water is but slight in comparison with the shove and lift which we have to give in order to bring the boat down to the water. On the water the boat is relieved of its weight and becomes buoyant ; on land the weight tells; never, even in our dreams, do we imagine a boat drifting along the land. The movements of animals are of these kinds. The body is the boat, its muscles represent the man, and its limbs replace the oars and boathook. Those animals which creep over the ground use their legs as the boat- man uses his punt-oar, pressed against the rock, sand, or mud. Many animalcules, most worms, Crustacea, insects, and the vertebrates except fishes, press off in this way against some resistant medium. Burrowing animals lay hold of the sides of their retreat with hooks and claws as a boathook can be used to draw craft along river banks—of such are worms, many Crustacea, and insects. Swimming animals undulate the muscles of their back and tail as an oarsman twists a scull in the stern of a boat and lays hold of new columns of water with the blade first in one direction and then in another. In this way, bending the body from side to side into S and @ shaped curves, the tail of the fish, the body of water-worms and of aquatic Jarvie, grip a mass of water, and, using this as a resistant mass, bring the power of their muscles to bear upon it momentarily, then, instantly twisting into an inverse curve, grip anew mass, and so gain a new forward impetus. In a somewhat different way FLIGHT 31 the broad tail of a dog may be seen lashing wildly from side to side in the effort of steering round a turn when under full speed. The act of rowing with a pair of oars leads us to a partial understanding of that perfect and difficult mode of movement—flight. The weight is brought to bear on the oar at the rowlock; the fulcrum is the advancing blade, and the power is applied at the handle. But, though far more clumsily, we can also row by facing forwards, grasping the oar outside the rowlock, and paddling. It is in that position that birds exert their muscular force; whilst in insects there is a muscle pulling on the inside of the rowlock for the forward stroke, as in ordinary rowing, and another on the outside for the backward stroke. In both cases the weight and inertia of the animal have to be supported by the attachment of the wings to the body ; the muscular force is applied near that inner end, whilst the fulcrum, or point of support, is near the tip of the wing, which lays hold of the elusive columns of air, lifts the body, and, twisting like the sculling oar to avoid the eddy, falls slightly, grips a new column, and presses off against it. The faster the wing beats the better grip of the air does it obtain; for, as we know by motor travelling, air becomes almost a solid medium to cut a way through when our speed raises its resistance to a great amount. ‘ Feathering’ the wing, therefore, even more than the similar trick with an oar, becomes a necessity if a bird is to get its wing up and to the front for another of those 32 ANIMAL LIFE powerful down strokes that give effectiveness to its flight. But whilst we may in this way gain some acquaint- ance with animal movement by the analogy of a boat, there are features in the build and movements of animals not easily paralleled. A boat is a stiff unyielding structure, whilst an animal is provided with mobile muscular walls, which clongate and become thinner, or contract and thicken. Thus we may see worms, leeches, and caterpillars extend their bodies and, laying hold of some projection, draw themselves up to it, measuring in this way by looping movements the ground over which they travel, and so earning the sobriquet geometers; or, by more rapidly repeating the movement, the separate events of tension and extension become merged into a continuous gliding. Thus the snake uses the special scales arranged down its belly as projections for performing those rippling movements by which it almost swims over the ground, and in so doing helps the forward movement by lateral undulations of the tail. A method commonly employed amongst lower animals, and one that has no analogy in the working of a boat, consists in the expulsion of water from their bodies, and of a consequent rebound in the opposite direction. By this means jelly-fish swim in a series of jerks, which are due to the hollow bell or bell-clapper alternately expanding and taking a draught of water, then contracting and expelling it. In a similar manner cuttlefish, octopus, and the MOVEMENTS OF AQUATIC ANIMALS JO nautilus inhale deep draughts of water under their gill-covers and expel them through a funnel, strongly when at rest, violently when they wish to make a great backward leap. Many aquatic insect-larve, for instance those of dragon-flies, continually inhale draughts of water, and merely increase the force with which they expel the draught when they wish to make a darting movement. Prawns and lobsters leap back- wards by a somewhat different artifice, laying hold of the water by the broad, concave under-surface of the tail, and then bending this smartly beneath the body. Another mode of motion is that adopted by star- fish and sea-urchins. The five arms or five hoops that surround the bodies of these creatures are provided with serried ranks of hollow tentacles ending in suckers. When the starfish wishes to move it advances one arm, stretches out the suckers belonging to it, and draws the body up behind. In the same way a sea-urchin emits long slender tentacles from its shell, and, advancing these, draws the body in tow. The brittle stars which have such tentacles but no suckers at their tips, stretch out one arm in the direction they wish to follow, and, using the others as fins, strike the ground with a backward sweep, and shuffle over it in an un- gainly fashion. The movements of ammalcules: Ciliary move- ment.—The movement of most animalcules is due to minute elastic hairs, which act as so many oars projecting from the body. Unlike oars, however, these D 34 ANIMAL LIFE hairs derive their force not from a muscle connecting them with the body, but from an inherent flexibility, conferring on them the power of beating more rapidly in one direction than in the reverse; and as they maintain this vibratory movement with almost perfect constancy, rarely stopping to rest, still more rarely reversing their action, the body of the animalcule is carried through the water in a direction opposite to that of the more forceful stroke. If we imagine the body provided with a membrane which bends rapidly into a curve, straightens backwards, and again bends forwards, we should have in this membrane an organ acting not unlike the tail of a prawn or the effective bend of a fish-tail. Now let us imagine the membrane to be composed of hairs which flex and straighten of their own accord ; then, if close set and synchronous in their stroke, their effectiveness in propelling the animal would hardly be less than that of a continuous membrane, and as the animalcules are excessively minute aquatic creatures, very small hairs, exerting a comparatively weak force, are sufficient to move them. These hairs, or ‘cilia, as they are called, from a supposed likeness to eyelashes, are not confined to animalcules. They are found on the bodies of flat, gliding worms of our streams and ponds and on the foot of snails. They are the means whereby the minute young of all sorts of marine animals, which crawl or walk when older, swim about. The sea- jellies, eggs of worms and snails, hatch out as micro- THE NATURE OF CILIA 35 J scopically small creatures, which even before birth spin round inside their egg-capsules by the aid of these cilia, and when out in the water glide through it by their aid ; and the bodies of zoophytes and corals, sea-mats and sea-mosses, of oysters, scallops, and cockles, which appear so hard and motionless when old, are rippled when young by the constant play of the waving bands of cilia that, aided by the currents, enable them to swim from the depths to the surface and from the open sea to the shore. Cilia such as these are not confined to the surface of animals, nor is their only use that of locomotion. If we buy a pennyworth of mussels from a fishmonger, and place them in a dish of sea-water, the shellfish will soon open their valves and protrude their yellow skin fringed with tentacles. If a little Indian ink is added by a pipette, a movement in the water previously invisible will be rendered clear. The ink will be drawn between the tentacles into the valves ; some- thing is at work inhaling a current of water. If now we open one of the mussels and cut off a piece of one of the yellow gills and place it in the water, the reason of the current will be made clear. The morsel of gill begins to move steadily along the bottom of the dish, as though endowed with independent life, and, if held up to the light in a glass dish and examined with a magnifying-glass, the filmy margin due to innumerable cilia can be seen. These vibrating rods, which when held by the weight of the intact gill sucked in a current of water, now, when attached to D2 36 ANIMAL LIFE a small fragment, cause this to move. Mahomet, as it were, comes to the mountain. But the gill of shellfish is not the only place where cilia are found inside the bodies of complex animals. Right up through the invertebrates and vertebrates, with the curious exception of the insect, spider, shrimps, and millepedes, cilia occur in some part or other of the internal organs. Even in ourselves the cavities of the nose and windpipe, of the brain and spinal cord, are lined with these vibrating rods, which bear witness to a community of substance which links us with the animalcules themselves. As the organs of movement, whether displacing a minute creature or sluicing a fluid inside a large one, these cilia bear witness to the deep-seated cause of movement. Their activity is innate. So long as they are bathed by water or their natural medium, their movement is only indirectly controlled by the action of the body, or even by its presence. If de- tached, as they frequently are, from the dying body of spherical jelly-fish (fig. 2) that come drifting to our shores in summer, their movement continues for a time unchanged in strength or pace; and while able to survive severance from the body temporarily, they are equally their own masters in the starting as in the maintenance of that unresting beat. Small wonder that organs so self-contained have been treasured, and that scope for their energy is found in highest and lowhest alike. Yet all movement partakes of this mysterious, INNATE CAUSE OF MOVEMENT 37 J innate} character, self-caused and __ self-sustained. Undisguised as is the control that the nervous system exerts on our hearts, there is a cause of the heart-beat that lies in the organ itself, and not in any governance, however subtle and effective it may be. The fundamental spontaneity of movement is disguised, controlled, and rendered effectual in a hundred ways, from the obvious exercise of our will upon voluntary movement to the drilled soldier’s unthinking response to the word of command, the unconscious acts of sleep and the automatic actions of animals. But underlying that controlled muscular force is the older, innate contractility perfected in one special form—ciliary movement. Evolution of locomotor organs in anmmals.—In a lowly organism, such as an earth- or water-worm, the body consists of a muscular tube capable of elongation and contraction, and of lateral undulating wriggling movements. It is divided into rings, each of which bears a number of hooks for the purpose of creeping over the ground. In the more complex annelids, as these creatures are called from their segmented bodies, each ring grows out into two pairs of leg-like processes, whereby the efficiency of pro- gression over ground is increased. Special muscles to move these limbs are formed, and the limbs them- selves, in addition to bearing hooks, possess a leaf- like outgrowth. Pairs of appendages occur on each segment, and by their rhythmical action perform the part of oars, sculling the body through the water, as 38 ANIMAL LIFE well as enabling it to punt over the sea-bottom or to climb up burrows of earth (fig. 35, p. 200). Among Crustacea we encounter precisely the same arrangement. Paired appendages are found on each segment, but now, being placed nearer together on the under-side of the body, their action is stronger and more precise. Moreover, the appendage is divided into inner and outer divisions, the outer one bearing the leaf-like structures and the inner branch becoming jointed and lobed. Such animals swim either on their backs by strong sculling movements inwards and backwards, or (Daphnia, fig. 24), standing vertically, they tread the water, rising at each stroke and falling slightly between the strokes. In higher Crustacea the outer division disappears from the limbs of most segments, and the inner one is converted, in the middle of the body, into a substantial jointed leg, capable both of clinging to holdfasts against currents and of supporting the weight of the body in walking ; but the original character of the hmb is seen in the swimmerets found under the tail of prawns and lobsters. These still beat from before backwards and ensure the forward swimming of the animal. Thus the body becomes divided into three portions— a head provided with jaws and antenne, a firmer middle part for walking, and a flexible tail for swimming. The highest Crustacea, crabs, depend altogether on the mobility and strength of their legs for walking or swimming. In these animals the swimmerets are turned to other accounts, and are chiefly used for CENTIPEDE AND INSECT 39 a) the carriage and protection of the eggs, or, in hermit crabs, for grasping shells. In insects we find a great variety of modes of motion. Their larve, terrestrial or aquatic, recall Fic. 6.—Illustrating the common starting-point of both Centipedes, or many-legged air-breathing animals, and of the insects with six legs. A. A Common Garden Centipede (Lzthobtus: from Koch’s ‘ Myria- poden’). 3B. Scolopendrel/a, the connecting link between A and C.-- (Ajter Lang.) c. A primitive Insect (J/achz7?'s) found under stones and on the seashore. It shows the typical six-legged condition, but traces of the abdominal feet are shown by the minute spines. - - (///er Oudemans.) 40 ANIMAL LIFE the less complex worms in their simple muscular bodies, in their wriggling movements that serve for swimming, and the looping or stretching evolutions by which they creep. Their bodies, too, are sub- divided into rings or segments, which bear a certain number of appendages arranged segmentally. These limbs, as we pass from the lower forms, such as Scolo- pendrella, to the higher insects (fig. 5), become de- finitely limited to three pairs for progression, and thus entail a correspondingly greater nicety of balance. The body becomes divided into three portions and is balanced about the middle one of these; carrying, in fact, to a further degree the division of the body into head, thorax, and abdomen, already seen in Crustacea. It is from this middle section of the body that the wings arise. Vertically over the second and third legs, pouch-like outgrowths of the body-wall form two pairs of flattened lamelle, strengthened by ribs and veinings like leaves. The arrangement of the muscles that raise and depress the wings 1s a most complex one, but consists essentially of a double lever, both elevator and depressor acting vertically but on opposite sides of the fulcrum. These muscles are of great size and power, and where the wing meets most resistance and does most work, namely, at its front edge, it is stiffened by a selvage of veins. To solve the problem of flight the economy and distribution of weight, the intensity and application of the muscular power have to be completely studied. The body requires to balance about the middle, 41 PROBLEMS OF FLIGHT and the wings to strike so that not only an upward but a forward or turning movement may be produced. (unosnyy 197sayunyy ay) U2 wout2Ia/s D 10-47 )— "YF 2OYSASIOF] Iayeaigy—"e * (vnasnyy aajsaysunyy oy) ue uaiiveds v wo.u7)—*yYyBIy Ut s12q way [re] pu Sura ay} jo juawasuvue oy] Moys 01 ‘Surw ayy uo Mopeans y --Z ‘Ory This is done by the wing-muscles not only producing but rotating the wing so an up-and-down stroke, 42 ANIMAL LIFE that its tip describes a figure of eight between every two up or down strokes; and in so doing uses the effective stroke for forward movement, just as a boat’s sail, set at any angle with the wind, plays off the greater part of its breeze into a propelling force brought to bear on the front edge of the sail. For turning, the two sides of the body require to act inde- pendently, and to lower the wing on that side towards which it is desired to turn. The intensity and rapidity of muscular vibration during flight are extreme; indeed, the efficiency of insect muscle is quite extra- ordinary, both for strength, mobility, and persistence, and the wing-muscles are the most perfectly qualified ot any in the body for sustained control and strong action. We have only to watch a hovering fly in still air, or attempt to seé a humming-bird hawk-moth flash, hover, and dart as it passes over flowers like a sunbeam, to realise that such insects have brought flight to a degree of perfection that seems astounding, unnatural, and unnecessary. So far are we behind the meanest fly in agility that we marvel, if at all, very much as a savage at machinery. The problem of effectively using two pairs of wings simultaneously is, however, too difficult for most insects, and we find a tendency in many groups for the reduction of one of them. Like a boat sailing just astern another, the back-wash and eddies in the air caused by the front wings render the effective working of the hind wings a great problem. Never- FLIGHT AND SWIMMING 43 theless, the supreme exemplars of flight—dragon- fles and hawk-moths—are amongst four-winged insects, though even in these the hind wings tend to become smaller than the front ones. In most moths a hook links front and hind wings together, and the absence of this hook serves to distinguish butterflies from them. In beetles the fore-wings are converted into shards or covers, held stiffly in flight, whilst the movement itself is entirely due to the hind-wings, which are curiously bent near the tip, so that we do not wonder that few shard-bearers are good fliers. In bees and wasps the fore-wings are strongly developed and securely hooked on the front edge of the other pair, which in flies become reduced to balancers. They take no part in flight, but are converted into highly sensitive, nervous organs. Movements of vertebrates: I. The adaptations of fsh.—In vertebrates, the problem of movement in water, on land, and in air has been solved time after time. There are walking and flying fish, swimming and darting lizards, gliding and swimming snakes; and winged reptiles, though now extinct, were once abun- dant. Birds fly both in water and air, whilst bats, amongst mammals, are almost as exclusively animals of flight as whales and seals are animals of the water. In the lowest fish, as in worms and insect larve, the body is essentially a muscular tube, capable of being thrown into wriggling, eel-like movements, by which pressure is brought to bear on the water at each 44 ANIMAL LIFE concavity. The tail is provided with a fin, shaped like the propeller of a steamer, by which its grip of the water is increased. In forward movement the body and tail of the fish are thrown into two or more curves, and as the body straightens, and before it takes an opposite curvature, the pressure of the tail on the water at the hollows, and especially the grip of the tail-fin, is greater than when the reverse curvature is obtained. The straightening stroke is more power- ful than the bending one. Moreover, the tail does not merely undulate, but twists about its own axis, meeting the water first with one of its flat surfaces as it straightens, then feathering as it prepares for the next stroke, and again straightening out with full force of the opposite surface and the expanded fin. The swirl helps the fish to gain additional purchase, the eddy helps it to elude the water and eases the feathering stroke. In order to render these undulations more effective the swimming-muscles that run down the body start from an elastic spinal rod, which gives them a central origin, and form not a continuous sheath, but a segmented mass of bundles, each bundle being bent into a V or W shape, with the points turned towards the head. The skin into which these muscle-bundles are inserted is elastic and lubricated; and if scaly, the points of the scales project backwards, so as not to impede the forward movement. Moreover, the amount of muscular tissue is increased by reducing the space in which the internal organs are packed to THE ADAPTATIONS OF FISH 45 a small compass, and converting the tail into a solid mass of muscle—the main driving power of the fish. And, further, since the animal floats, or is but slightly heavier than its own bulk of fresh water, the vertical strain on its body is reduced to a minimum, and there- fore the vertebree may remain—as in sharks—gristly or undemarcated. The provisions for altering the direction of move- ment are of the nicest adaptation. Since in most fish the muscular arrangement is employed for hori- zontal progression, and gives no great facility for change of depth, a special provision is made to meet this want: an air-bladder under the backbone is developed, the gaseous contents of which can be increased or decreased in amount, and so the relative weight of the fish increased where descent is needed and reduced where ascent is required. To this end also the paired fins are employed, as well as for turning and steering; and as the use of these two pairs of fins incurs difficulties of the same order as those already seen in insects, we find in fish, as amongst insects, a tendency to reduce one pair—the hind fins—and to give them another office, whilst at the same time enlarging the fore-fins in accordance with the increased work of guidance thrown upon them ; to which work must be added the maintenance of the unstable equilibrium, over which they keep constant guard. The vertically compressed shape of a_ well- built, active fish is such that it can never remain upright and still. It is ceaselessly making small 46 ANIMAL LIFE adjustments to overcome the tendency to float upon its back. As a help towards steadying the body it has developed fins along the middle line of the back and tail. These ‘median’ fins act as keels or centre- boards. They are supported by a series of spines, which can elevate or depress the membrane they support. The first of these spines is often stronger than the rest, and acts as a cut-water. Moreover, to diminish the resistance of such fins in a turning move- ment the spines can be lowered, so that the fin collapses, and raised again when the new tack is begun. Thus rapidly can a shark unstep the peg that stretches his dorsal fin and ship it again in the notch at its base. If such complex adjustments are needed by active fish, we do not wonder that a change in the shape or attitude of the body has been developed in those which seek their food on the bottom, or wish to escape the constant exertion of a mid-water life. Of these, the flat-fish and skates are the most remark- able. Connected with the dory family by many ties of structure and mode of occurrence, the sole and plaice, turbot and dab, agree with their relative, the John Dory, in being flattened, but differ in resting on or in the sand instead of hovering over it. It might be thought that this result was merely due to a compression of the body parallel to the ground, but examination shows that both eyes in.a flat-fish appear on the upper coloured side, that the mouth is awry, and that the skull-orbits are also skew-whiffed. ADAPTATIONS OF FLAT-FISH 47 In fact, a flat-fish, which begins life as a round fish, balancing vertically, slips on to its right or left side, which then becomes the colourless under surface, whilst the other side is converted into a variably tinted upper surface. The eye belonging to the side upon the sea-bottom has rotated owing to a twist of the orbit to the upper surface, upon which both eyes thus appear to lie, and the animal, though flapping through the water by vertical instead of horizontal strokes, is still using its muscles relatively to itself as they were employed before rotation. The skates and rays attain their flattened shape by compression of the more rounded body seen in sharks and dogfish, and by an enormous extension of the first pair of fins to form the wings, which, grow- ing and fusing with the body, give rise to that diamond shape so characteristic of the skates. These fins are now the chief organs of locomotion, and suitably so, since they are specially adapted to a vertical move- ment such as the skate requires, whilst the somewhat slender tail gives the propulsion necessary for forward movement. The attempts that fish have made from time to time to walk and fly are of great interest. Many balance themselves on their two pairs of fins and grub or nose about the rocks under water ; but owing to the unjointed nature of their limbs, this attitude is extremely difficult to maintain on land. Yet here and there shore-fish have adapted themselves to a temporary land life. The gobies that swarm on 48 ANIMAL LIFE our coasts have a relative on Eastern shores that hops with great vigour on its front fins, keeping its tail in water. A perch with the same implements manages to shuffle up overhanging boughs, and the bat-fish has actually developed an elbow-joint, whereby it can rest its weight on the flat part of the fin. But no amount of ingenuity has conferred on any fish we know the ability to walk freely. On the other hand, at least two groups of the most active swimming fish have developed that power of leaping into the air, often found in the most varied groups, into a sustained, gliding movement which resembles flight. For this purpose the flying-fish employ their powerful breast fins, which they keep spread out like a parachute. By the aid of this acroplane their descent is delayed; and so powerful is the initial jump from the sea into the air that, with a favouring breeze, they may rise on to the deck of a steamer or go clean over a fishing-boat. Il. The adaptations of terrestrial vertebratcs.—It is, however, only when we ascend above fish to the higher vertebrates that we find the problems of move- ment on land and in the air completely solved. On land, weight enters into the problem. Support, unneeded in the sustaining water, becomes now a necessity ; and in order that this weight may be upborne and moved, all the skeletal parts require to be denser, both on account of the vertical strain they support and the greater muscular tension requisite for movement. The limbs become props whilst ADAPTATION FOR LAND-LIFE 49 still organs of locomotion. To combine the advan- tages of short limbs for support, and of long ones for speed, is only one of the problems that press for solution. To relieve the muscles of the body’s weight, a vertical pillar-like leg is necessary. To gain the leverage needed for propulsion, a bent leg capable of straightening out is requisite. Hence we find that great size in quadrupeds involves columnar limbs, with the segments placed vertically, as in elephants; but in smaller animals, such as horses, the fore-limb only has this linear character, and bears greater weight, whilst the hind-limb is thrown into a zigzag form when at rest, and into a straighter line in movement. Movement and rest in an erect position, as in man, some apes, and birds, require a still greater change in the disposition of the weight, muscles, and ligaments. The mass of the body now falls upon the hind-limbs, which therefore become straighter than in quadrupeds, and the spine is sustained by ligaments that relieve the back muscles of an otherwise constant strain. The muscles of the shank become more strongly developed, not only to sustain but also to propel the weight now thrown altogether upon them. For these purposes also the foot is not elongated into a slender organ delicately poised on the toe-tips, as in many active quadrupeds, but is flattened and the heel brought down to the ground. Lastly, as an additional prop for support, the tail may be retained and thickened, as in the kangaroo. A survey of the vertebrates shows how the changes E 50 ANIMAL LIFE to meet the needs of terrestrial movement have been brought about from fish. Throughout the Amphibia, with a few interesting exceptions, two pairs of limbs corresponding to the paired fins of fishes serve in various ways. In the newts the body is still fishlike, but the limbs have acquired that division into upper, middle, and lower segments (arm, forearm, and hand, thigh, shank, and foot), that is so strikingly a character of all the higher vertebrates. The movements of these animals and their rela- tives, the salamanders, are exceedingly slow. The legs are short and bent—good, therefore, neither for bearing weight nor as levers; and the only powerful stroke is the fishhke, lateral bending performed by the tail under water. Frogs and toads, however, show an advance in their locomotive powers by the leaping and thrusting power of their long bent hind limbs. In the reptiles the powerful longitudinal muscles of the back and tail, so characteristic of fish, are still employed, and serve to assist the feet, which are short, bent, and flattened. The movements of these animals consist of short, violent rushes from point to point. For sustained, rapid action neither the hmbs nor the disposition of the weight 1s suitable ; and reptilian life enjoys extreme speed for short periods, alternating with immobility for long ones. Their degeneracy is shown in the disuse of limbs, a distinctively fishlike character, which we find in snakes and many lizards. As com- pensation for this loss the scales of the belly become enlarged, and into them are inserted the ends of the MOVEMENTS OF LIZARDS 51 very numerous ribs. When the snake desires to move, the ribs are raised one after another by the lateral body-muscles, and the scales, pressing against the ground, serve to propel the body forward. At the same time, owing to the singular flexibility of the back- bone, the lateral, eel-like movements bring the lithe body over the ground with great rapidity. Although the reptiles of to-day are inferior to those of the past, which walked erect, ran doglike or flew, there is at least one group among them—that of lizards—which is at its prime, and amongst these one or two may be specially mentioned. In zoological gardens geckos may sometimes be seen. They are small, extremely active when roused, and provided with padded adhesive fingers and toes. By the aid of these pads geckos are able to perform the strangest feats. When hunting for flies they run up and down papered walls, and even glass windows. So sure is their hold that they can run up a wall, bend over, and slide along the ceiling. Like other lizards, geckos often lie motionless for a long time, but evade capture not by arun that can be seen but in a flash of gliding. Such geckos are household pets in the East. But perhaps the most agile of all is a lizard found in Malay, which is so active as to run securely over the tops of grass shoots. In mammals the organs of movement are far more effective. The tail is reduced and the longitudinal muscles of the back—heirlooms from fishes—are employed for the work of the shoulder and hip. The 52 ANIMAL LIFE body is carried clear of the ground and supported mainly on the straight fore-limbs, whilst propulsion is effected by the more bent hind-limbs, which are straight- ened by very powerful muscles and tendons; and to provide a sufficiently firm point @appur for these the hip-girdle and vertebrz of the small of the back are greatly enlarged. To give them additional leverage the bones of the shank and foot are elongated. To ensure elasticity of tread, fleshy pads are developed in carnivores under the middle joint of the toes, and in cats the claw-bearing ones are held back in walking by means of a tendon in a protecting sheath, and only dart out by the action of prehensile muscles. For support on slippery ground the heel is raised still higher than in carnivores, and only the end joint of the toe converted into a horny hoof. Among these mammals, the so-called Ungulates, a remarkable reduc- tion in the number of toes has taken place. Instead of the five which only elephants have retained, rumi- nants have only two—the third and fourth; pigs and rhinoceros four, peccaries three, and horses one. The cloven hoof, characteristic of those that chew the cud, alone touches the ground, but traces of the second and fifth toes are seen in the deer, and are of use in spreading out the animal’s weight when soft ground is encountered. Of the many special modes of motion adopted by mammals only a few can be mentioned. In monkeys and apes the habit of climbing and of sitting nearly erect throws the weight of the body ARBOREAL AND SWIMMING MAMMALS 353 more and more on to the hind-quarters, and the arms, thus relieved of their primitive supporting function, are used for prehension; whilst in South American monkeys the tail is converted into a sensitive fifth hand for grasping boughs and giving support. In this way many of the Quadrumana have lost the power of rapid and effective running on the ground, and have acquired a wholly new arboreal mode of life and a new dexterity in the performance of their won- derful gymnastics. For grasping the twigs monkeys employ the hand as we do, with the grasp between the thumb and the palm, and the most arboreal of all are either thumbless or their fingers partially adhere, so that their limbs are converted into mere grasping hooks. Ill. Adaptations for swimming and fight in mammals.—The most remarkable adaptations to aquatic and atrial life are found in a few groups of mammals; amongst the seals and whales for swimming and the bats for flight. Mammals are so emphatically land animals, only swimming by the aid of their limbs to reach new feeding-grounds, that the existence of two aquatic groups, one of which passes the whole of its life in the sea, is a striking fact. So different are whales and porpoises from ordinary mammals that the idea of their being fish is still widely prevalent, and, though erroneous, is intelligible by the many fishlike characters which these animals possess. The seal is amphibious, spending the greater part 54 ANIMAL LIFE of its time in the sea near the coast, and only going ashore to rest and to bring up its family. The body is thick in front and flattened behind. The tail has almost disappeared, and on either side of it the hind limbs are held rigidly out at full length. Between the fingers and toes the skin has grown so as to convert the fore-limbs into paddles and the hind-limbs into a propeller. On land a seal shuffles awkwardly on its belly, only using its hands if pressed; but at sea the flattened hind-limbs, together with the lateral muscles Fic. 9. —-The White Seal (Zobodon) of Antarctic shores. —( 770m a specimen in the Manchester Museum x 35.) of the body, enable it both to swim with great ease and to ascend periodically to the surface for air. The forepaws are used for steering. The porpoises and dolphins, the baleen and toothed whales, are as perfect in the art of swimming as any fish. Their bodies, denuded of hair, are usually of a build so completely adapted for cleaving the water that boat-builders could design the lines of their craft from models of whales. The head is a cone pointed in ADAPTATIONS OF WHALES 55 front; the neck is not marked; the back rises in a curve that gives easiest passage through the water, and finishes off behind in a tail flattened from above downwards. The general aspect and build resemble those of a free-swimming fish, but, whilst fish have a vertically flattened tail for horizontal movement, whales require a horizontally compressed tail to make those periodical ascents requisite for breathing air. Forward movement is maintained slowly or at a prodigious speed by the huge longitudinal tail- muscles swaying the body from side to side and making effective undulations on the principle of a fish. The legs are hidden and rudimentary, and their muscles are added to those of the back: whilst the arms are converted into steering-paddles as near a return to fins as is well possible. The fingers, though still five in number, are composed of more joints than the other- wise universal number, three. The nails have dis- appeared. Weight and size, no longer limited by the supporting power of the limb, may reach colossal dimensions; whales of eighty feet in length and weighing eighty tons still abound. To acquire powers of flight is perhaps an even greater feat than the conversion of a terrestrial animal into a whale. Amongst various groups of mammals the first stage of flight—the arrest of the body in a gliding descent, instead of in a straight fall, has been accomplished. Some of the opossums have extended that fold of skin which allows movement of our arms at the armpit, into a membrane that stretches from 56 ANIMAL LIFE the arm to the toes. By its aid their leap off a branch takes the form of a rise into the air, then a gentle downward curve. Amongst the squirrels two forms of such ‘ aéroplanes ’ have been devised independently, and by the aid of these, flying leaps can be made from tree to tree without descending to the ground. But it is only amongst the bats that true flight has been attained. Like huge moths, these animals come out every summer evening from the ivy, hollow tree, or barns in which they lie hidden by day, hanging down- wards from some projection, often in great clusters, with their head enfolded by the wings. These wings are folds of skin stretched from the altered hands and arms to the legs. To increase their extent the fingers are drawn out to an immense length and the wing-membrane continued to the very tips, leaving only the thumb free. The muscles for flight are strongly developed, and, as in a bird, lead to the formation of a keel-like breast-bone, from which they arise (fig. 8, p. 41). The unerring certainty of a bat’s flying and alighting movements is a marvel of skill. In a room they explore the furniture and recesses, sail through pas- sages a few inches wide without touching anything, dive under a sofa, and, turning a somersault, alight on the webbing head downwards, ready for the next flight. Then they spring clean into the air, even from a flat surface, and are on the wing at once. The inclusion of the hind-limbs in the formation of the wings has the effect of bending the knee out- ADAPTATIONS OF BIRDS oy wards and backwards, instead of forwards as in all other mammals, and this, together with the pre- occupation of all the hand but the thumb, renders walking difficult. On a flat surface some bats cannot walk; but others, such as the long-eared bat, progress in the usual way—first a hind-foot is advanced, then the fore-foot of the same side, followed by similar move- ments of the opposite limbs. IV. The adaptations of birds for faght and perching.—But it is amongst birds that we encounter the greatest freedom and most sustained powers of movement. To gain the dominion of the air by the use of wings, whilst yet retaining the power of balancing on the two legs, is a double problem of the utmost difficulty, and in the solution every part of a bird’s body has undergone some adaptive change. What a feat this is we may judge on considering the imperfect attempts man has made towards constructing an efficient flying-machine, though he has tried for a century. But in a bird, so little cumbrous is the mechanism that its sails can be folded evenly with the contour of the body; so efficient, that flight at express- train speed and sailing in great winding circles with outstretched, motionless wings are both performed with the same easy mastery as perching or hopping ; so well guided, that migratory birds sweep through immense tracts of air and reach their destination witha punctuality so sure that the Persian calendar is based on their arrival. The general shape of a bird fits it for rapid flight. 58 ANIMAL LIFE The pointed head serves to form a passage through the air, into which the rising slope of the body follows, whilst the falling slope of the tail allows the air to glide off rapidly. The weight is taken off all the peripheral parts and centred in the massive muscles of the breast and the parts adjoining ; yet so delicately poised that by extending its mobile neck the bird, gliding with outstretched wings, descends where it will. By letting the legs fall the head is thrown upwards, the point of balance being thus moved slightly for- wards or backwards without the aid of the wings. These wings or sails are essentially fore-limbs, similar to our own, but modified in every feature for the needs of flight. The arm rises upwards and back- wards, the forearm forwards and upwards, the hand backwards and upwards, forming at rest a zigzag, with the elbow pointing backwards and the wrist forwards, but in action extending into a straight line, Fic. 10.—The Pigeon. Dissection of the male from the right side. Ialf the liver and the greater part of the intestine have been removed. In the right wing, the bones and the arrangement of the primary and secondary feathers are shown. —(Z70m Marshall and Hurst, « Practical Zoology.’) A, nostril. AD, ad-digital primary feather. B, external auditory meatus. BW, bastard wing. C, cesophagus. CA, right carotid artery. D, crop. D:z A, aorta. E, keel of the sternum. YF, right auric he G, right ventricle. HV, heps atic vein. H1, left bile- duct. Ha, right bile-duct. distal end of stomach. ty right innominate artery. IV, posterior vena cava. JA, tat innominate artery. JV, right jugular vein. K, gizzard. L, liver. M, proximal limb of duodenum. MD, the two aie digital primary feathers. MP the six metacarpal primary feathers. Mz, first metacarpal. Me, second metacarpal. M3, third metacarpal. N, cloacal aperture. Ni, first digit of manus. O, bursa Fabricii. Q1, proximal phalanx of second digit of manus. O2, distal phalanx of second digit of manus. P, pancreas. PA, right pectoral artery. PD, pre-digital primary feather. PV, portal vein. Pr, first pancreatic duct. P2, second pancreatic duct. P3 3), third pancreatic duct. Q, pygostyle. R, rectum. RC, radial carpal bone. RX, rectrices or tail-feathers. Ru, third digit of manus. S, ureter. SA, right subclavian artery. SV, right anterior vena cava. ‘T, rectal diverticulum. U, kidney. UC, ulnar carpal bone. V, pelvis. Wy, lung. X, bumerus, Y, radius. Z, ulna. oo 20 dd gw OW NeW EW wg nt to 60 ANIMAL LIFE which, moving freely at the shoulder, sweeps the tip of the wings in spirals. Length of wing is given in two ways: by elongation of the arm and hand, as in storks, or by increase of the feathers in length, as in swallows ; and as we saw that in the fleetest mammals length of limb and reduction in the number of fingers or toes went together, so in birds we find that only two of the usual five fingers are used for the support of the greater part of the wing. The skin between these fingers and at each side of the wing grows into flaps, which, being covered with feathers, form an atroplane triangular in surface-outline, and yet curved so as to furnish a concavity below and a con- vexity above. Upon such a membrane, only flying leaps like those of squirrels could be carried out. To convert the feathered membrane into a true wing it must be provided with muscles sufficiently powerful to lift the bird into the air; and since not only upward but also forward movement is required, the direction of the wing has to be so inclined to that of the air- current as to convert the oblique thrust into a large, forwardly-acting component and a small, inactive one at right angles to this, just as a boat’s sail plays off the force of wind into a propelling and a drifting force, or as an insect’s wing or fish’s tail solves the same problem of resolution. Hence the need for the powerful breast muscles, mainly for depressing the wing not in one vertical plane but obliquely downwards and backwards. And since the efficiency of stroke is guided by the speed of the bird relative to that of the ADAPTATIONS OF BIRDS 61 air, in a calm rapidity, in a breeze slowness, of succes- sional stroke will characterise the beating of the wing. Further, since the resistance of the air increases with great rapidity as the speed freshens, the wing after one downstroke has to be lifted home edgewise for the next, so as not to stop the momentum; and this turning movement brings the wing not full-sail up to the vertical, but slews the front edge, somewhat flexed, to the front, and then extends it high above the head ready for another powerful sweep. To gain support from the air and to assist flight, the details of shape and feathering of the wing are modified. The lower surface grips the air chiefly by its front edge and tip, and as a jib sail, though narrow and triangular, must be strengthened on its front edge, so good fliers need strong edge feathers and narrow, pointed wings. The feathers are elaborately airtight to enhance that grip, yet are disposed so as to allow air to flow edgewise between them and over the convexity of the upper surface as it comes forward. The difference in the width of the vane on either side of the feather’s stem is not without its meaning, for, when a flat body is falling obliquely through the air, the pressure be- comes greatest not at the centre but towards the front edge, which tends to rise. If, therefore, the front webs of the first eight flight feathers were equal in width to the hind vanes, the outstretched wings would tilt up and the bird’s balance would be destroyed. It is to avoid this disturbance that the outer webbing of the feathers, upon which the main stress falls, is reduced 62 ANIMAL LIFE in width (fig.8). The form, then, not only of the wing, but of every flight feather—hollow and sustaining below, rounded and unresistant above, short and rounded for more laborious flight, long and pointed for easy, sustained flight—has a definite significance for all the varied needs of birds and their more elaborate evolutions, such as sailing and soaring. And in those cases in which flight is abandoned and the wing, as in penguins, is converted into a fin, the feathers take on the form most suitable to the needs of an aquatic life and form scale-like coverings. Flight, however, is not the only movement for which birds are fitted; and if the fore part of the body is exquisitely adapted to meet the require- ments of aérial life, the hinder part is mainly a mechanism for terrestrial and aquatic existence, for running, perching, or swimming. Such a double adaptation is a rare thing in animals, and is only shared by insects. All others that specialise in movement—fish, whales, bats—have become incap- able of rapid and sustained travel in an alternative manner. Birds alone are capable of both flight and bipedal movement. The legs of a bird have a double office. They sustain and propel the body’s weight, which is disposed so as to fall about the knee-joint. For sustenance the limbs are pillar-like, and distribute the pressure over four divergent toes. For propulsion the joints are elongated, and the hip- girdle, or ‘back’ of the bird, affords a large area, ADAPTATIONS FOR PERCHING 63 from which the powerful leg-muscles send down their tendons, which bend the knee and the toes, and, so doing, thrust the body forward. The thigh is short and the knee buried in the body’s side. What appears to be the backwardly pointing knee is in reality the ankle-joint, and separates the shank from those bones which in ourselves he flat, but which in a bird are drawn up to form a vertical column extending the length of the ihmb, and giving it additional power of movement. Just as in a horse or antelope great speed is gained by the larger joints of shank and foot bone, so in a bird the corresponding bones are drawn out into an elongated zigzag. In the most perfect runner amongst birds—the ostrich—the reduc- tion in the number of toes and the elastic padding for treading over sand have followed precisely on the lines adopted by the camel. The majority of birds possess feet suitable for perching or swimming, and the ease with which they securely alight, sleep resting on one leg, or paddle through water, involves a mechanism as perfect in its adaptation to these ends as is that of the wings for flight. Of the four toes usually present, one corre- sponding to the first of lizards is commonly opposed to the rest, so that the claw of the middle toe in front over- laps that of the hind toe and holds the twig between. Now by a labour-saving mechanism this hold, appar- ently so precarious, is rendered automatically secure. Along the front of the knee there runs a tendon which passes down the leg and ends on the under-side of the 64 ANIMAL LIFE toes. Any bending of the knee, therefore, tightens the hold of the feet; and this hold is rendered still more secure by another tendon which runs at the back of the leg and divides into three—one for each toe. When the bird perches, the weight of the body thrusts the knee out and the ankle back, and simultaneously tightens both sets of tendons, and through them the hold of the feet. In swimming-birds this flexure is the means whereby the membrane between the toes is opened and brought to bear on the water; but, in order that the resistance of the feet may be overcome, when the forward stroke is to be made, the membrane is_ rendered capable of opening and shutting, and the toes are spread out during the swimming, or back-stroke, and brought together during the forward one. In a grebe’s foot the vanes down the toes can be pulled out flat by the back tendon and turned down vertically by the front one. The foot of a bird, no less than any other part of its body, gives evidence of the most exquisite finish and usefulness. REFERENCES Animal locomotion: Peiligrew, J. B., ‘Inter. Sci. Series,’ vol. vii. Marey, ‘Animal Mechanism.’ Jbid. vol. xi. Flight: Headley, F., ‘The Structure and Life of Birds.’ Macmill in. 65 CHAPTER V THE QUEST FOR FOOD THe need for self-maintenance leads an animal to feed. To whatever end its energy is directed, loss of substance is incurred by its movement, and even by its rest. When we are lying down the breast still rises and falls, the heart beats, the blood flows, the glands secrete, digest, and store; the brain is not altogether still, and may plan in sleep works and compositions beyond the power of our waking selves to execute. Even the muscles, quiet as they seem, are doing internal work. By day and night, actively or restfully, the basis of life is used up and needs renewal. How to meet this urgent demand for material we have now to consider. The source of animal food : the quest for plants.— The kindly fruit of the earth is the source of animal food. Directly or indirectly, animal life is depen- dent on plants, visible or invisible, and so great is the supply that a flesh diet becomes anomalous. The earth is covered with verdure ; the sea is fringed with weeds and teems with minute plants. Soil is the remains of the vesture that waves in the wind and water, held in a meshwork of moulds. Diatoms, F 66 ANIMAL LIFE minute plants enclosed in flinty cases, surpass sand- grains in multitude; they encrust the shore, fill the beds of rivers, and, borne on the air, are showered down upon sea and land from the tropics to the poles. The oldest and simplest way of catching food is that practised by the lower aquatic animals : sponges, corals, animalcules, and all encrusting organisms. It consists in drinking the water and sifting from it the minute organisms that abound therein. It is carried out by the aid of those minute, vibratile hairs or cilia which, originally used for drawing the animal through the water, now draw water through the animal. Into the vortex created by the beating of these organs will be haled from the surrounding catchment-area all those particles which cannot resist suction, however gentle; and as animal and plant spores abound in fresh and salt water during the spring and summer, the particles inhaled will consist partially, at least, of minute organisms, and upon these the sponge or coral is able to live. Ina similar manner, barnacles throw out and draw in their casting-nets and collect the fine wreckage of the coast which constitutes their food. Most of the animals that feed in this way are fixed, and when at the approach of winter the supply of minute organisms falls off, they have no means of leaving the coast or lake shore for more teeming water. In order that they shall not starve during this season, most encrusting animals lay up during THE QUEST FOR PLANTS 67 the autumn stores of highly concentrated nourish- ment, such as starch and oil, within their tissues. Having done this they hibernate, and such food as they require until the next spring is supplied out of these reserves. The larger plants afford nourishment to larger or more active animals, and there is hardly a weed or flower or tree that does not support a varied assemblage of adherents. The tangles of submarine groves of seaweed and pondweed are cropped by fish and scoured by snails. Every part of land plants— the roots and young succulent leaves, the nectar, the sap, the fruits, wood, and even the galls—furnishes nourishment to insects and their young. Nor is the plant merely food to them. Shelter can be found in the innumerable crevices of bark and leaf. Air is afforded by the spaces and tubes that traverse the tissues. The very sheddings of plants are true wind- falls for other creatures. The bud-scales of spring, the leaves and fruits of autumn, all the fine débris that rain down on to the earth beneath, are gathered by ants and birds, eaten by slugs, and remoulded by worms. Weed jetsam is similarly refined. The ebb- tide, that leaves the seaweed stranded in heaps, exposes the burrows of innumerable hungry scavengers in the sand. Each evening, when the tide serves, the sand- hoppers creep out of their hiding-places near high- water mark and begin their mazy dance in search of drift-weed; whilst myriads of smaller shrimps, each enclosed in a minute bivalve shell, career F2 68 ANIMAL LIFE unceasingly over their food. Dustman service is the lot of many. Earth and water are kept clean by their unwearied efforts (fig. IT). In order to gather their food-plants, insects and Crustacea employ a similar series of mouth - part diversely shaped according to the special needs of each class. Their mouth is overhung by a mobile upper lip, and enclosed at the sides by a pair of appen- dages constructed on the same plan as the swimming or walking legs, but modified to form jaws, that Fic. 11.—The Common Sand-Hopper (Gammarus locusta). A similar form is common in fresh water.—(.4/ler Della Valle.) x 4. work from side to side and chew the food between them. Behind these a lower lip is formed by a pair of limbs that still show that division into inner and outer lobes that betrays their alliance with swimmerets ; and usually there is added to these yet another pair of members of similar bifid nature. These parts of the lower lip were originally sensitive vibrating paddles, and their accustomed movements had to be but slightly altered to fit them for chewing and tasting, instead of paddling. Provided with these, insect and SAND-HOPPERS 69 shrimp can test the weed, cut out parts of their food- plant, and masticate it. the two The large specimen is a Male ; others, partially concealed in their tubes of mud, are Females.—(From Della Valle.) 12. —Tube-forming Sand-Hoppers (Corephiun). Fic. But fas insects became adapted to subsist on the higher plants, their biting habits led to a great discovery. Once through the bark or leaf their jaws 70 ANIMAL LIFE would mect with a sweet, sticky sap; through the hole made more and more would rise. Such a fragrant bouquet no water plant possesses. Such a rising sap no seaweed or pondweed exudes. To be able to ic. 13.—A group of Mecrophorus and Aphodius Beetles burying a Bird.—(/'rom a specimen tn the Manchester Museum.) lick or suck now becomes the insect’s advantage, for sap is not only more fragrant, but far more easily digested than almost any other vegetable food, and all manner of brushes, tubes, and tongues have been INSECTS IN SEARCH OF HONEY 7] evolved for the purpose. The lower lip is drawn out spoutwise to catch and then to drink or lap up the juice, or else becomes hairy to absorb it. Finally, of its two parts, that forming the tongue becomes Fic. 14.—A small primitive Insect (Orchesed/a céncta) found under stones, representative of an early group of insects from which the sucking forms have since developed.—(Afler Lubbock. Ke- produced by permission of Lord Avebury Srom his Monograph, published by the Ray Society.) x 10. drawn out into a tube of marvellous complexity, up which the sap is pumped by a piston developed inside the throat. When gathering honey, insects perform the memor- ie ANIMAL LIFE able service of cross-fertilisation to the plants they visit. In the act of dipping the tongue into the corolla to tap the nectaries the insect dusts its head and legs with mealy pollen. Thus powdered, it flies to the next flower or another plant of the same kind, and when unfurling its proboscis strikes gently against the pillared stigma that stands central in the corolla and cross-fertilises it. The advantages of cross-breeding over inbreeding are many and great. In vigour, colour, abundance of fruit, crossbred plants are superior to inbred ones. But since plants are fixed organisms, the pollen has to be borne from flower to flower, or from a male tree to a female, by one of the three moving agencies, water, air, or animals. Flowers are in the main devices to attract the notice of animals and to ensure pollination. Brilliancy of colour, definiteness of pattern, attractiveness of odour, serve to draw the curiosity of animals. The opening of strong-smelling plants by night entices nocturnal creatures to visit them. Of the numerous applicants drawn by this bounty not all are helpful. Sparrows confer no benefit on crocuses by their ruthless destruction of early blooms. Slugs are the gardener’s greatest foe. But the great majority of flying insects are drawn, not to an indiscriminate destruction of the flower, but to the nectaries, or honey-sacs, which secrete the odour from within it. The interaction between flowers and the insects that visit them is one of the most interesting chapters THE FOOD OF SNAILS 73 in natural history. So intimately are they dependent on one another that some plants, such as certain figs and the Yucca palm, would die out were it not for a small wasp in the one case and a minute moth in the other, that serve, and alone serve, to ensure fertilisation. Another method of obtaining vegetable food is that practised by snails and slugs. These animals browse on aquatic and terrestrial plants by rasping away the surface of the plant between their prickly tongue and horny upper jaw. This method is, on a small scale, the one adopted by ruminants, such as cows and sheep, which grip their food between the tongue and horny pad of the upper jaw, and in both cases the lips are used to bring the food to the teeth. But in the snail the tongue is covered with a ribbon bearing horny teeth, which as fast as they wear away are replaced by new ones, and the action of these teeth is not unlike that of the cutter in a lawn-mower, while the fixed upper jaw of the snail corresponds to the bar against which the cutter clips off the grass. By the aid of this rasping tongue snails and slugs are able to obtain food in almost all circumstances. The covering of slimy algz on the seashore, the green scum that appears on pools and roadsides, the liver- worts, mosses, fungi, lichens, and most of the higher plants, provide an endless store of provender. So great is the injury done by snails, without any counter- balancing advantage, such as many insects confer, that plants have sought to protect themselves against these attacks by various methods. 5o general is this 74 ANIMAL LIFE need for protection that every flowering plant possesses some means of defence: hardness or prickliness, irri- tating lime salts, or acrid and oily juices. Against the attacks of some slugs, however, even such defences as poison may fail. The great black Arion will eat almost anything; but all the slugs of our gardens are not equally to blame for the immense damage to bulbs, seedlings, and plants that is often set down to them indiscriminately. The field Limax and the keeled Limax are the two most culpable destroyers, and it is to these that the disappearance of bulbs is largely due. The great Limax, on the other hand, does not appear to touch green food, but subsists on moulds; the margined slug on lichens only. They forage night after night over the same beat, and return by day to the same hiding-places. Latter’s work (quoted on p- 300) helps one to identify them. Forest, moor, and plain support an abundance of mammals. Herbs are sought after by the largest and smallest of beasts. All the ‘ ungulates ’—elephants, horses, cattle, and deer—are herbivorous, and live in troops led by an old male. Less imposing, but more numerous than these, are the rabbits, mice, squirrels, and beavers, great in their powers of destruction, though individually small, and some, such as harvest- mice, scarcely bigger than insects. Monkeys, where protected, as in India, become a pest, and not only destroy the fruit of the forest, but do immense damage to gardens. The different ways in which mammals gather HERBIVOROUS MAMMALS 75 their food are of interest. The majority use their teeth, which, in such cases, are chisel-shaped in front. All the ruminants press the grass between their tongue and upper toothless gums. The horse grasps with his lips, the tapir with the longer flexible snout which, in the elephant, is drawn out into a trunk of the utmost sensitiveness and strength, serving not only to reach up to lofty boughs for the juicier leaves, but also to overturn trees whose summits are out of reach. Squirrels and monkeys, on the contrary, use their hands for conveying food to the mouth. The need for thoroughly chewing such food has entailed great modifications of the teeth and face. The long face of the horse is due to the lodgment of many grinders. The complex form and large size of these teeth enable them to act as a mill, those of the upper jaw fitting into the hollows and bosses of the lower teeth ; whereas, since the upper and lower jaws of the ruminants are not equally wide, the teeth act intermittently on one side first and then on the other. To equip themselves for encountering dusty herbage, the Herbivora have developed an elaborate arrangement for separating dust and pollen from the air which enters the nose in order to gain the lungs. The bones that form the framework and support of the nasal passages are converted into labyrinths, so that the air whirls round on its way to the lungs, and in so doing deposits the heavier particles on the sticky walls, as a ‘separator’ divides the cream from themilk. The dust, pollen, and spores are then carried 76 ANIMAL LIFE outwards by the set of the ciliary current, which, as we saw, maintains an outgoing flow. The ‘ turbinals,’ as these labyrinths are called, help in other ways, by warming and scenting the air, and serve to build up the long and stout face that distinguishes herbivorous animals. Another means of rendering the food easily digestible is known as chewing the cud. The cud is not the herbage taken straight from the field, but consists of a mass of pulpy grass which has undergone partial digestion, and has been sent back into the mouth for a thorough mastication. All animals with a cloven hoof, except pigs, are ruminants, . whilst those which have more than two complete toes or only one, are not provided with this singular mechanism. Among the birds, devices of a much less complex kind are adopted for obtaining a vegetarian diet. But few birds subsist on leaves, for their innutritious character makes it necessary to gather large supplies in order to furnish even a small amount of food, and then it is only obtained at the expense of much hard mastication. For a bird such a diet is eminently unsuitable, since it neither wishes to overweight itself with a heavy meal nor has it teeth to grind with. Unlike the ruminants, which graze in safety, most birds appear perpetually harassed by real or imaginary fears, and need a light, stimulating diet to replace the great loss of material and energy which they expend in active, sustained movement, and many other ways. For them, therefore, oil, starch, and other FOOD AND EVOLUTION 79 essences of seeds and fruits are the most suitable nutriment, and to obtain these the beak is strengthened and sharpened. The necessary crushing is done by the action of the gizzard, which is usually aided by stones or gravel. The hard, conical beak of the finches serves to crack the seeds and fruits of the garden and hedgerow; the still more massive jaws of the parrots break the hard-shelled fruits of the tropics ; the twisted beak of the crossbill extracts the seeds of pine-cones. In the delicate humming-birds of South America the bill is elongated and the tongue con- verted into a double tube like that of insects. It is used for tapping insects and the nectaries of flowers, which thus give meat and drink to the most exquisite and airy of known beings. This brief ‘summary’ of vegetarian dietary sug- gests the relation of food to evolution. Plants them- selves have a long history, in which alge and fungi occupy the earlier pages, lichens, liverworts, and ferns the medizeval sections, whilst gymnosperms and flowering plants bring us to modern times ; and we can follow the adoption of simple plants as food by the more primitive land animals, and the assimilation of the higher plants by animals which had become more specialised. That many-limbed animals live amongst moulds and the few-limbed creatures feed delicately on fruit or nectar is no casual association, but a fact that testifies to the antiquity of the one and the novelty and high place of the other. We shall also find that as many plants chequer the monotony of their diet 78 ANIMAL LIFE by a side-dish of fly-juice, so vegetarian animals may lose their strictness and vary their menu with flesh, and only after obtaining a commanding station do their succeeding generations revert to that safe but laborious habit of grazing from which they set out. The quest for prey: I. The supply of food wn the sea. We speak, and rightly speak, of the heaped measure of plant lite and of the dependence of animals upon the pastures so provided. But there are common- wealths in which plants shrink to an invisible factor where yet animal life abounds. The high seas and the depths of the ocean teem with animals, yet it is only in the Sargasso Sea that weeds are visible, and much below the surface they are unable to live. Lakes and broad rivers, Arctic and Antarctic lands, sandy coasts and volcanic districts, are only fringed or powdered, as it were, with plant life. Yet in all these regions animals are found, and it would only be pos- sible for them to maintain a strictly vegetarian diet by an enormous reduction in their numbers. As a matter of experience we know that many animals are carnivorous by preference and nature. The mole would die in the richest garden mould that contained no worms, and the spider would starve in a well-kept hothouse. How this carnivorous mode of life has been attained is the problem before us. Drifting on the waters and raining down into its depths is a motley collection of flotsam, part plant, part animal. Covering the rocks and weeds are the infusoria, sponges and barnacles, hydroids and coral CAPTURE OF ANIMAL FOOD 79 polyps, sea-squirts and bivalves, whose irrigation works are ceaselessly straining the water, filtering off and digesting the drift life. Between the two con- stituent kinds of filtrates, plant and animal, they do not distinguish, but swallow and digest them both. A plant, however, is more difficult to digest, as around each element of its tissues there is a tough covering such as animals only possess on their outer surface. Hence an animal once captured and torn is quickly digested, whereas a marine or aquatic plant is only dissolved with great difficulty. We are not surprised, therefore, to find that plants may live for a consider- able time in the body of an animal, and, on the other hand, that animal food, being juicy and stimulating, would force the growth of those fixed creatures which attempted the diet. The hydroids, jelly-fish, and anemones have made both these discoveries, and the larger they grow the more confirmed becomes their carnivorous habit. Little by little the power of holding and then numbing moving prey was deve- loped. Stickiness was a necessity to prevent the tissues becoming waterlogged and the cilia from flagging, and to this slimy covering these resourceful creatures added the power of poisoning their captives by the aid of nettle-cells, with which jelly-fish and anemones sharply annoy us when bathing or wading. To digest this animal food was no new or great dif- ficulty, for the lower animals feed upon their own tissues when other food is lacking, as it often is in winter, and a jelly-fish the size of a saucer becomes, 80 ANIMAL LIFE if starved, microscopic and ultimately dissolves. Right down at the base of the animal kingdom, there- fore, we find the body feeding on itself or on some other animal—in times of famine diminishing, in times of plenty growing, budding and overflowing into its children. As the jelly-fish are budded off they leave the shore, pass into deep water, and find themselves amongst less and less vegetable food. Their activity demands nourishment, and a deliberate choice of prey is made from amongst their fellows. It is to the sea with its stress of life that we may look for one explanation of the varied food of animals. The strand itself, barren and lifeless as it appears, is full of buried minuscules, plant and animal. On this supply the larger animals depend, and in it they bury themselves. The lugworm (fig. 26, E) and heart- urchin (fig. 26,A) are but two examples out of many that eat the very strand in order to gain its hidden nutriment. Mollusc and urchin, though protected by armour and spines, are the resort of parasitic sea- worms and crabs that when young have gained a hold or an entrance into these citadels and grow to maturity on the secretions and crumbs of their host. The mussel shelters the pea-crab (fig. 15), the prickly urchin a sea-worm or a small bivalve. These feeders on the minuscular life of the shore are in turn the prey of other animals. Scallop and oyster, seemingly so well protected by their shells and strong muscles, are the particular food of the starfish. Humping itself over the bivalve, the star- Fic. 15.—A Mussel opened to show the Pea-Crabs (Male gf and Female 9 ) within it. The Female is the larger of the two Sexes.—(From specimens tn the Manchester Museum.) G 82 ANIMAL LIFE fish plants its suckered feet firmly on the ground, and then applies two or more ranks of these suckers against the valves (fig. 16), straining to separate them. The oyster claps its shell together at the first touch, but after the tireless starfish has maintained an even strain for a time, the oyster from fatigue and want of oxygen opens its valves. Through the opening the starfish inserts its acid stomach, and the secretion of this falling on the oyster’s muscle weakens it. The valves gape open, and the starfish at its leisure absorbs the contents. Away from the shore great activity is employed. The maintenance of equilibrium, the pursuit of food, and the avoidance of powerful agitation imply sus- tained movement. Jelly-fish, cuttlefish, fish of all kinds, are in constant muscular tension. Hunger follows ; the cold open sea and strong aérated water sharpen the appetite that constant exercise produces. Around these hungry swimmers is a drifting stream of wriggling, darting, whirling particles—the offspring of the shore. These enter into every mouthful of water that a fish takes to discharge over its gills, or that a jelly-fish inhales for a fresh spurt, and the choice of food is soon determined. Fish rarely masticate their food. Their jaws, preoccupied with breathing, can only momentarily hold and bolt it; and since plants above all other aliments need grinding, they form the least desirable choice. Hence it is that the oily rowing-shrimp becomes the mackerel’s bonne bouche and the favourite Fic. 16.--The mode in which a Starfish opens and eats an Oyster. A. The Starfish gathered over its prey. B. Section to show the position of the sucker-feet on |the valves. c. The long |stomach of the Starfish absorbing the Oyster through the open valves.—(d/ter Schemensz. Permisston to use granted by Professor Henking, Berlin.) G2 84 ANIMAL LIFE titbit of the herring, in pursuit of which these migratory fish travel in bands from sea to sea with an avidity that is never surfeited. In like manner, though with the help of a vast baleen sieve, the right-whales thin out the stream of minute animal life that sets from the Arctic to the temperate zone. Should the sea fail, as it does in winter, to break out into this dance of drifting life, the active swimmers retire to the bottom or deeper water, where they discover an abundance of food in the vegetarian Crustacea and molluscs, in the oily eggs of the herring and the newly hatched fry of the plaice and cod. Let but a shrimp stir a tentacle and the hungry dab seizes him. The John Dory stalks the swimming shrimp, going forward with his flat body edgewise and unseen, and at last lunging out with his sucking, extensible jaws. The dogfish, no longer sustained by nourishing herring, bolts crabs and whelks to satisfy his raging hunger. Marine invertebrate life teaches the same con- clusion. Cuttlefish, masters of marine invertebrates, are the most active swimmers it produces, and dart in vast shoals through the water, first in one direction, and then in a tangential track, forwards and backwards with equal facility. In shape and movement they resemble fish. To supply the de- mands for such energy the scanty alge of the mid- ocean are inadequate and a richer diet is requisite. This the squid, as they are called, find in the herring and mackerel. They follow the migratory shoals THE FOOD OF CUTTLEFISH 85 with an energy that sometimes sends them leaping high out of the water. Pouncing upon a fish, the squid opens a circlet of arms till then kept close like the ribs of an umbrella, and with these and the two long tentacles which can be shot out from their cases on either side of the head, it grasps its prey. Its hold is rendered secure by the suckers and hooks that stud the tips of the tentacles and the whole length of the arms. Then, bringing the fish up to the mouth and horny beak, it rasps off the flesh by the horny tongue that is the common heritage of all molluscs. So great is the strength which these fringe-finned squid obtain from their food that we have no engines quick enough to catch the larger kinds, and it is only as storm- tossed corpses that we know of monsters with arms as thick as one’s thigh and suckers as big as saucers. Yet, great as they are, there is one still mightier, the epitome of the hungry life of the high seas. This is the sperm-whale, which sculls almost at destroyer rate, thrashing the water into foam. Of his seventy feet of length, thirty feet is sheer head and jaws, and with these he despatches the colossal squid ; and it is from the interior of sperm-whales that we have found out what manner of cuttlefish are roaming through the ocean unseen and unsuspected. Sea birds also are carnivorous. Their activity, the maintenance of their bodily warmth, no less than the feeding of their young, demand more nourishment than the watery seaweeds can furnish. The year round gulls haunt the coast for any flesh diet that the 86 ANIMAL LIFE sea affords. They herald the shoals of migratory fish and the advent of their fry ; some decimate the cockle- beds. From the far north to Australia wading birds forage along the coast, and find in sand-worms, mol- luscs, and sand-hoppers a never-failing food-supply. On our rocky coasts, from April to July, the puffin, the guillemot, and other spring migrants of the sea t. i hy’ ts aie ao Fic. 17.—The Black-headed Gull, Nest, and Young. (from specimens in the Manchester Museu.) have made the rocks musical with their chorus, fishing the day through, and disappearing in late summer as mysteriously as they came. With autumn the stream of southward-going shore birds take their place, and in the hardest winter flocks more dense than those of spring cover the sand flats, and find abundant nourishment on the inexhaustible shore. THE PREY OF LAND-ANIMALS 87 The quest for prey: II. Adaptations of land animals.—On land the problem of maintenance is more complex. The extent of pasture is greatly increased ; plant sheddings and mould correspondingly denser. The supply of vegetal life is beyond computation, and if animals dominate the sea, plants characterise the land. On the other hand, there are no fixed encrusting animals—no barnacles, sponges, zoophytes or bivalves— whose families can swell the drift life of air. Food must be sought mainly on the ground, and has to be actively gathered by movement in which the weight as well as the resistance of the body has to be overcome. This added strain increases the need for nourishment which the pursuit of food seeks to satisfy, and as the climate is no longer one of great uniformity, such as that of the sea or large inland waters, the hardships of heat and cold aggravate those of hunger. More- over, plant-life also protects itself by thick coatings against the inclement effects of drought and frost, of excessive moisture and dryness. The result of this is to render such food very difficult of mastication. How widespread this difficulty has been and still remains we realise but slowly. We think with facility of plants as food for animals, and we overlook the fact that whilst such is the rule, exceptions meet us on every hand. The abundant mosses are scarcely touched by a single animal, though no form of shelter is more popular than their crevices. The ferns uncoil their fronds in undiminished numbers every summer, 88 ANIMAL LIFE and when autumn comes the roll-call is complete, for there is no plant more secure from animal interference. The lycopods, the mare’s tail, and the vast host which form the vascular cryptogams are passed by and avoided. But when we come to the primitive seed- bearing plants—the pines, the cycads—we find primitive insects, a sawfly, a few wood-borers, squirrels, and a few birds capable of obtaining nourishment from them. It is mainly the flowering plants at the top and the fungi at the bottom of the plant kingdom which constitute the supplies of vegetable food of which animals can avail themselves. And neither by birth nor adaptation have all land animals the taste or the capacity for the requisite work of getting at that nourishment and assimilating it. How an alternative diet—that of flesh—has been maintained or adopted by so many terrestrial animals we may now consider. By three paths land animals have become car- nivorous. We have seen that the primitive air-breath- ing animals—e.g., Orchesella (fig. 12) fed on moulds and lichens, which are found everywhere. From moulds, and especially from fungi, it is but a short step to a flesh diet. In the second place, we saw that piercing and sucking organs were developed as the higher insects discovered the sap or honey of flowering plants, and found that for flight such a diet was emi- nently suitable. For such creatures the transition to parasitism on either plant or animal, or to the habit of sucking the juices of active prey, was an easy one. THE FOOD OF INSECTS 89 Lastly, in the higher animals the appetite for a flesh diet acquired in the sea persists after the change to fresh water, and thence to land, has been accomplished, and it is only as the result of a happy and complex combination—good grinders and strong digestion—that the power of assimilating sufficient vegetable food has been acquired by the Herbivora. We may now consider how these habits have conduced to the welfare of land animals. Insects show well the strain of life. The most primitive are feeders on moulds and lichens ; the most degraded are parasites—fixed sucking animals; the most highly organised are pre-eminently active sucking creatures. As the tiger is a lord among mammals, so is the tiger-beetle among the huge tribe which his name heads ; and no more ferocious, active, or bloodthirsty beetle exists. From his youth up the two curved jaws that signalise his ferocity are in constant employ in attack, as he beats up and down hot roads and sandy commons, quartering the ground in arrowy darts from fly to fly. The dragon-fly is an equally dominant member of its tribe, and in brilliancy, power of flight, and rapacity is perhaps supreme amongst insects. Sup- ported throughout life on a flesh diet, it represents to many another fly the long arm of circumstance. The dragon-fly attacks its prey with equal celerity on the ground or in the air, and, as it possesses both excellent sight and flexible lips and a strong pair of jaws, it is 90 ANIMAL LIFE able to secure the prey by their aid, and then holds it in the basket formed by its feet. Again, the Emperor butterfly and hawk-moth are severally at the head of these two groups, and are fine examples of insects adapted for sucking flowers; and to satisfy its thirst the Emperor descends from the tree-top for a puddle or some dead creature. The mantis is the most elaborate of the class to which it belongs, and though maintaining a still attitude, waits but for a fly to alight near to display the ferocity and blood-sucking in- stinct that animates it. Even the grasshoppers, that haunt sandhills and match the colour of their surroundings so closely, feed upon the flies that perch unsuspectingly near them. The true flies specialise in sucking, and for the delicate probe that can pierce a tough land plant the hide of a beast is no impene- trable armour. Drawn by the sense of smell from plants to fungi, from fungi to dead animals, and thence to living ones, various families of flies have discovered the stimulant of blood. The mother-fly in particular, having but a summer to work in, discovers the greater fertility which such a diet ensures and the greater number of broods which may be reared when warm- blooded animals are drawn upon for nourishment. Ants, bees, and wasps, the highest members of that vast class, the Hymenoptera, employ the most varied methods for obtaining nutritive fluids. Plant or animal juices in a concentrated form are their favourite nourishment. Ants milk their cows—the aphides—from whose bodies flows the nectar or honey- WP Tic. 18.—Tongue of House-fly. Left side of head removed to show internal structure. The empty space is filled with air-sacs not shown in the figure.—(MW2th C. Gordon Hewitl’s permisston, The University, Manchester.) P2., eversible ‘frontal sac’; /.c., fat-cells ; C.G., s.o., brain; P.O., portion of brain supplying nerves tocompound eyes ; av.v., oc.2., nerves to anteune and simple eyes ; ph.n., lb.n., nerves to suction pump and proboscis; 74., £4., 7.7., ~7., muscles for retraction (or withdrawal) of proboscis; 7./u., ~.d@s., con.2., muscles opening mouth and controlling the flow of fluid along the ‘throat’; af#., £2.A., muscles controlling the bending and unbending of the proboscis ; af., rod concerned in the same process; ¥F., sheath of ‘suction pump,’ with its processes a.c., g.c.; d.fn., muscles working ‘suction pump’; 4, sheath keeping open beginning of ‘throat’; ves., ‘throat’: Z.cf., upper lip; ¢%., lower lip, also formed by parc of 24., d@.s., and 7, skeletal structures of the oral lobes, one of which is shown; gs., channels, and g/., ‘taste pits,’ of the oral lobe ; 2/.s7., one of the two saliva glands of the oral lobes ; saé.a., duct of large saliva gland, with ts valve, s.v., and muscles, s.7., controlling the same ; mexp., maxillary palp. 92 ANIMAL LIFE dew which they laboriously secrete. Bees so much prefer the dew to the trouble of securing honey that in some years hives are a failure. Wasps both sop up fruit juice and devour other insects, killing them with a sting and storing them in their burrows. The higher Arachnids, the spiders and scorpions, contrast with their degenerate allies, the mites and ticks, by their large brain and complex structure, which bear witness to their high place among invertebrates ; and this conclusion is borne out by their nourishment and the means they adopt in obtaining it. If to feed by sucking the juices of a captured organism is a sign of superiority, spiders and scorpions are sure of a high place, for their methods show exquisite adaptation to secure this end. So exclusively is the whole class of Arachnids a race of sucking animals, that it has lost the jaws which all but the most modified insects retain. In their place these animals possess a pair of small sharp nippers, within which hes a poison-bag, so that every nip injects some venom into the prey. The second pair of limbs is usually leg-like, but in spiders it so far differs from the four remaining pairs of legs that its base is expanded to form a jaw-like process which helps to hold, though not to chew, the food. In the scorpion the second limbs form a pair of claws, and in the mites a sheath, within which the first pair or piercing organs can be held. The act of sucking is performed not through a proboscis as in insects; the tiny mouth is applied direct to a wound in the prey, SPIDERS 93 and its juices are sucked by the alternate expansion and contraction of the throat. By this means mites, red spiders, and ticks devastate our currant-bushes and hop-plantations, destroy cheese, books, and fur- niture, become blood-suckers of man and most ter- restrial animals, and in tropical countries are one of the AK Mt Fic. 19.—Wheel-web of the Garden Spider. —(4fler Blanchard.) means whereby such diseases as relapsing fever are transmitted. Spiders are one of the dominant races of animals, and in hunting instincts excel all others. Their power of constructing webs, underground traps, and even sub-aquatic snares, is well known, but the variety of traps and the ways in which these snares Q4 ANIMAL LIFE are formed and concealed and managed are scarcely appreciated. The web of the garden spider is essentially the work of the mother. It is she who constructs it, she who watches it and feels the pulse of its lines from her hiding-place. When a mote is blown into the web it is the mother who sallies forth to remove it. When a fly is entangled it is she who emerges and, enveloping the struggling prey with more silk, retires to enjoy the feast. Her mate is but a casual incident, whose presence is tolerated for a time, but soon forgotten in the stress of capture and the care of young. In times of unusual hunger he may even be devoured. The web of spiders is unique. There is but one other example of a net stretched out to catch prey, and that is the seine-net of a caddis-fly larva, into which river-borne flotsam drifts and is devoured by the watcher (see p. 237). But spiders are the only animals which have found a means of intercepting the humming life of the air. The silk of which it is spun is the finest and strongest natural product. In itself it is no new thing. A gum which, when drawn out to a fine thread forms silk, is produced by a gland opening into the mouth of most caterpillars, of which the silkworm is but one. That which distinguishes a spider’s silk is its variety. One kind of silk is used for the outer frame- work and the radial lines, a second for the circular lines, a third for the enwrapping of prey, and a fourth SPIDERS’ WEBS 95 for the construction of the cocoon. Each sort of silk is made by a collection of glands that open near the end of the body by a little spout called the spin- neret. The lines of a geometrical web are laid down in the following way. First an outline is drawn; to form this the female shoots out the requisite thread, fastens it to some support, carries it in her hind feet, streaming out of the spinneret and Fic. 20.—Web and Nest of Agelena, spread on grass.—(‘ Riverside Natural History, by permission of Messrs. Houghton, Mifflin & Co., Boston, U.S.A.) hardening as it emerges. Presently it touches a twig or leaf, to which the spider fastens it and stretches it tight with her claws. Then, letting herself straight down and drawing out the silk behind her, she forms one of the vertical sides. Afterwards the other sides are completed in the same fashion. Across this framework the spider draws a thread, fastens it with her claws, and tightens it, so as to form the diagonals. From the centre of this she travels to another point of the 96 ANIMAL LIFE framework and draws the first radius, up which she travels to the centre again, and by repetition of the process the spokes of the wheel-shaped web are run across from the centre to the circumference. Once lic. 21.—Nest of Ageleza made by the young on surface of furze. (from a specimen in the Manchester Museum.) more running to the centre, the spider constructs a temporary spiral, the turns of which are looser as she travels outwards. Finally the finished spiral lines are spun of a second store of glands. These are more sticky than the rest, and serve, of course, to entangle the SPIDERS’ WEBS 97 prey. The temporary line or scaffolding is then cut away. The whole process of making a web takes about half an hour, and after finishing it the spider retires. Her object now is to keep in touch with the movements of the web. This she does through her feet, which are sensitive to the slightest vibration, and her complex nervous system probably enables her to interpret each kind of vibration as signifying a definite disturb- ance. In response to the tug she feels her action takes several forms. It may be that a gust of wind will immediately destroy the web, or that a large insect may blunder into it. But in the event of calm weather and no accidents the advent of prey may be, and no doubt is, yy¢, 22.—Nest of Cave Spider eagerly and confidently ex- (Aleta menardt), to show the way in which the eggs are pected. Should a fly become surrounded by silk and sup- entangled, the spider is at ported by a stalk. —(From a once aware, and adapts her nee a tht DEGREES behaviour accordingly. She evolves her stickiest silk, seizes the fly, and, running round and round her prey, envelops it somewhat as she spun the circular web lines. She now plunges her poison-organs into the fly and proceeds to suck its juices, thereafter casting out the skin and smoothing H 98 ANIMAL LIFE down the web. A butterfly is similarly treated ; but a wasp is sometimes allowed to escape with the utmost eclerity by biting through the lines that bind it. The variety of webs is great. There is the funnel- shaped web, so common under stones and among old walls, from which at the least touch out rushes the artificer. This funnel plays upon the weakness which so many insects have for investigating dark corners and for seeing where tracks lead to. Other spiders choose stations over water where gnats and midges abound. The surface of meadows and heaths are covered by flat webs, which in the frost of an early autumn morning form an almost continuous gauzy covering (fig. 21). REFERENCES The relation of insects to flowers : Lubbock, ‘ Nature Series.’ Macmillan. Spiders: McCook, * American Spiders,’ Philadelphia ; Romanes,* Animal Intelligence,’ Inter. Sci. Series, vol. xli.: Cambridge Natural History. Macmillan. 99 CHAPTER VI THE BREATH OF LIFE It is a faithful saying that we do not live on food alone. Life is a fire, now slow, now fierce, and therefore needs air as well as fuel. Changefulness is of the very essence of being, and all our rest is but hidden activity. Growth, movement, development—all the expenditure of force, which are the shows of life—involve trans- formation of our substance. We burn that others may have light; and just as the sparks fly upward under a fire’s breath, so we and all beings need a fan if the fires of life are to become active. Food is but the laid fuel; oxygen, that which fans it. The fire was lighted long ago. The twinkling flames hidden in thought, patent in conduct, have come from the vestal lights of other generations. Every moment of restful or restless activity they maintain the trans- formation of our bodies. We are renewed year by year, and to make way for the new being the old is slowly burnt away. We breathe out coal-gas, we radiate warmth, our muscles work by innate explosion. For every breakdown which is the necessary preface to this constant renewal, oxygen is essential. We rise on our dead selves only by their combustion. But so EH 2 naeye) ANIMAL LIFE generous and ungrudging is the renewal, so serenely is the new man made, that we forget that all balance is complex adjustment and all progress hardly won. We mark, not the loss that energy entails, but its sus- tained and transforming activity. Artists by nature, we rightly overlook the pains of effort. But if we are to comprehend the working of that mysterious life the activities of which arrest us, then we must be possessed by the conception of the downfall which precedes every uplifting in the transformation of living tissues. The more thorough the burning, the more complete will be the reconstruction, and health is as dependent on the one as on the other. We rise Pheenix-like out of our own ashes. As we obtain explosion by confining the area and increasing the rate of expanding activity, so a muscle gives out in one convulsive movement a force which at other times is spent in gentle and repeated efforts. But whether gentle or explosive, muscular action is only sustained by oxygen, and the more vigorous the effort, the greater the demand. As for muscles, so for other tissues. Our very bones are constantly being renewed. Where the sceming waste is greatest, there the new growth is most active ; and should this new growth be no reproduction of the preceding part, but an addition or new develop- ment, then it is subjected still more fiercely to the alternate tides of waste and repair. Breakdown by oxygenation, reconstruction by feeding, is the rule by which we live and move and work out our being. VARIETY OF VITAL ACTIVITY IOL This strange instability, as of a fountain summit or of a flame, is of the very essence of life and creates the need for oxygen as well as the need for control. If the demand or supply is small, the life will be inactive ; if ample, vivacious ; if greater still, feverish. At one end of life’s scale we have the latent life of seeds, the suspended animation of winter sleepers ; at the other the consummation of a Shelley. Between the two we have the periodic sleep and growth of plants, the gradual rise of animal activity in water, on land, and in the air, and the final achievement of permanent activity of body and mind. Life, however, outruns our metaphors. In variety of working, inwardness, and thrift it transcends our figure of flame. Biological activity is not exhausted by combustion. Muscle and nerve are most complex tissues, and their inward changes are correspondingly complex. Movement, whether of plant or animal, in- volves a change of its electric tension which may be too delicate for perception unless studied by a sensitive electrometer, or so powerful (as in the torpedo or electric eel) as to disable us. Nervous activity, again, is akin to electric action. Even respiration is not always the slow combustion we have described. A molecular as well as a mass exchange of gases is known in plants and animals. Leavening prepares for life. The inwardness no less than the variety of biological action contrasts with our simple figure. A fire is an affair of surface changes. Living things, on the other hand, burn from within outwards. Fuel burns only 102 ANIMAL LIFE in free oxygen. Plants and lowly animals possess a disruptive faculty, by which they can in the absence of free oxygen break up their store of carbonic gas and set it free. From reserves in seed or muscle fresh energy is obtained by this analytic action. Moreover, in ordinary muscle-breathing the oxygen in the blood is not directly used by the tissue, but is first stored, controlled, and delivered subtly to the muscle, under the pressure of that inward, invisible governor that converts the breath of air into the breath of life. Nor, again, is the contrast of economy in vital actions with the waste of fuel a less conspicuous feature of their work than variety or inwardness. The best coal-motors are wasteful, and give out in the desired form of work but one-eighth to one-ninth of the energy imparted, the rest escaping by conduction, in- complete combustion, and other wasteful outlets. Beings are rather more productive and less wasteful. A man given 0°44 kilos of food, representing a millon units of energy, gives out in a day, work estimated at one-fifth to one-sixth of this. This economy, unequalled in other carbon-combustions, is due to the central and peripheral control of the nervous system playing upon the fitful external supply, and is signalised in our constant temperature, equable pulse, and regular breathing. The quest for oxygen : respiration and evolution.— Water contains air, as we see by the bubbles that rise on heating ; but the amount of oxygen is a mere fraction of that contained in an equal volume of the THE SUPPLY OF OXYGEN 103 atmosphere. There is at least twenty times as much oxygen in a bottle of air as in the same quantity of fresh or salt water. When we consider this, then the fact that all the higher forms of life, plant and animal, are aérial and the lower mainly aquatic becomes more intelligible. The more complex frame of the advanced classes of life demands more oxygen than that of the simple, both on account of the speedier rate at which their tissues disintegrate and re-form, and also on account of the more rapid and laborious work that theirmovements imply. The greater size as well as complexity to which land plants and animals attain is another reason for their more active respira- tion. The spacious air and abounding waters provide an unlimited store of the requisite oxygen. Unlike the search for food, which is a quest beset with difficulty and uncertainty, the breath of life is around all that live upon the earth and bounteous beyond computation. At the surface of the earth, or that of the hills, its richness is greatest, and as we descend to the waters its bounty diminishes. Above and below the surface the amount of oxygen varies. If we climb beyond the snow-line this change causes mountain- sickness ; if we enter a cave our lights burn low. As with the surface of the earth so with the surface waters. The upper strata are rich in oxygen from wave-move- ment and the imprisoned air of the foam; and this bounty is reflected in the teeming life and comparatively high development of its fauna ; below in the stillness there is poverty of oxygen, only matched by the cave 104 ANIMAL LIFE region; and yet where oxygen has diffused, the darkness is peopled by hungry strays and waifs. Whether in the earth or in the waters the highest forms of each order come to the surface, the lowest are submerged ; and emergence or submergence corre- sponds to plenty or poverty of oxygen. This air we breathe has only been reached by epochs of struggle and new departures. The possession of the earth is hardly won. Before the nimble air gave strength and impetus to the conquerors they had to pass the marsh and shore on their landward way. Plants and animals alike have striven for the face of the waters, for the beach, for the marshes, and finally for the air. Man himself carries in his ears an unmistakable sign of his gill-breathing, watery past, and of the depths he has left behind him. Evolu- tion follows the successful quest for oxygen, and there- fore earth has been peopled by the highest communities. The ancient stocks are scattered, some keeping to the beach, some lurking in dens and caves, or, as parasites and messmates, hiding away, degenerate and prolific ; some, such as whales, returning to the waters, where they maintain an unfair supremacy over the uneman- cipated fish. Refugees from the shore and from the surface of the water retire to the depths, and there, at oases in the gencral desolation, hang out their phosphorescent signal lights. Evolution of the respiratory methods of antmals.—The drama needs elaboration. Its climax—the possession of lungs and of a good circulation—comes last in the EVOLUTION OF BREATHING HABITS 105 history of every group that has attained supremacy. The earlier acts are done under water. The simplest animals, so-called Protozoa, are all characteristically aquatic. They either live freely in water, or in a water-bath which some animal or plant provides for them. Furnished with oars or ‘cilia’ they pursue and engulf their prey ; or, if station- ary, draw in liquid instead of being drawn through it. Thus both inside and outside they are bathed by constantly changing water; and from one or both of these sources they extract the minimal quantity of oxygen which is dissolved in such water, and it suffices them. By its aid, movement is maintained, the food broken down, and the living substance, after rebuilding and replenishing itself out of that food, is disintegrated as the first step in another cycle of life. Neither lungs nor gills are distinguishable. There is no blood to carry oxygen or to remove carbonic acid. The protozoon is a gill and heart in effect, though not in fact. It does with its seemingly simple tools all that taxes the complicated structure of a higher animal to accomplish in breathing, namely, to abstract oxygen from the air dissolved in the water, to convey that oxygen whither it is needed, to use the store without exhausting it, and after use to carry away the ashes and smoke of the fire. Sponges, corals, and anemones are animals whose bodies are channelled out for the passage of water. These creatures irrigate their bodies by a stream that passes in through one or more openings, then through 106 ANIMAL LIFE a sieve on which the food is collected, and finally out again by the same or a different path. This constant irrigation carries water within the reach of the various tissues, so that without any blood-vessels they are yet able to derive oxygen from the stream, and to empty into it the débris of that slow combustion that water cannot quench. This removal of the ashes of com- bustion is largely assisted by the activity of minute plants that infect and colour the coral and anemone. But growth, as well as breathing, depends on the supply of oxygen, and as these inert animals grow freely instead of moving actively, they utilise the bounty of the surf for the spread of their colonies. Sponges cover the rocks of our coasts, and each of these, if cut into a hundred pieces, will grow into a hundred sponges as large as the first. Ane- mones coat our shores and will propagate, as well as sponges, by cuttings. Corals form barriers and reefs miles in extent, and build up island and mountain by the growth of succeeding generations. Nor is their life a short one. A sea-anemone lives twenty-five years, and may live to over fifty, and corals are of equal longevity. This long-continued growth implies a rich supply of oxygen; and in two different ways these fixed animals gain a better supply than that which still water contains. First they colonise the region of surf. Sea-water when shaken up with air increases the amount of its oxygen many fold, and from the sur- face down to a depth of some twenty feet the amount BREATHING AND GROWTH 107 is considerably greater than in the stiller depths. The influence of this fact upon the growth of sea- animals is continually brought home to us. Life and foam are old associates. The region of greatest animal growth is just where the water is most sparkling. So long as the swell is not so heavy as to tear and grind all that is not solid rock it will foster growth. ‘ Full fathom five’ is the depth down to which most corals flourish, sponges cover the rocks, and anemones afforest the coast. Where the tide runs strongest, there will be the richest growth, and that not only be- cause it brings new food with every flood, but because it carries fresh supplies of oxygen. The second method that these long-shore encrusting animals adopt to gain more oxygen is to increase their capacity for holding it. The red colour of our blood has exactly that meaning, and as its tone waxes and wanes so does our energy; and for this reason, that the red pigment has a strong affinity for oxygen, binding it to itself, and in so doing deepening in tone. When richin oxygen its colour is bright and vitality great; when poor in oxygen the colour fades and the body grows faint. The sponges and their allies give us a first hint as to the origin of these respiratory pigments, for we find them of the most varied tints, but chiefly red, yellow, andgreen. These colours which, if we ever notice, we think of merely as decorative effects, possess a value to these animals which decides not life—for these tough primeval beings hold to life at many points and defy a sudden 108 ANIMAL LIFE taking off—but, what is of greater significance, their increased vitality and productiveness. Needing but little oxygen for their own consumption, they are able to utilise any small surplus with great advantage, as in growth; and it is probably this help that colour gives them. These reds and yellows, more than the uncoloured parts, on this view, seize the passing oxygen, store and then dispense it to the tissues. The vespiratory adaptations of Crustacea and Molluscs.—Among higher and mote active creatures the demand for oxygen is more insistent, and the irrigation system becomes limited to particular regions, over which astream of water flows in and out. These regions— the gills—are thin-walled folds of skin, within which there flows a fluid which is no longer water, but blood, thicker than water. Its channels lead to and away from the gills, and the streams that fill them course past the gill-walls, as they circulate. The sea-worms bear a tuft of gill-plumes on every segment, and each of the simpler sea-shrimps and pond-shrimps carries a plume on its thigh. The very effort of movement shakes the gill, brings it to fresh bodies of water, and stimulates the circulation. The movements of such creatures help to create the supply of oxygen which they demand, and if food were easy to come at and enemies few, there might be no need for more elaboration than gill-plumes and gill-circulation. Such, however, is notoriously not the case, and we find ineach kingdom—that of the worm and that of the Fic. 23.—Brine-Shrimp (Branchipus), a primitive Crustacean found in salterns in the south of England. The gills are fixed on the bases of the swimming-legs. —(/vom Lang’s ‘ Comparative Anatomy.) x 20. a,, first antenne; @,, the large second antenne ; va, unpaired eye; JZ, liver; md, mandible; ,sd, kidney; 4, heart; of, openings of heart; , male organ; br, gills. 110 ANIMAL LIFE shrimp—a variety of breathing devices adequate to the different demands of its members. To meet these varied exigencies two methods have been elaborated with great detail. First, the con- struction of a channel along which the oxygen-holding water is made to flow, and, second, an increase in the oxygen-holding power of the blood. The first of these methods is the secret of the greater advance that the shrimp family has made over that of the worm, and it is also the motive under- lying the formation of the shells of the molluscs. The buckler of a shrimp, lobster, or crab, the valves of a mussel, are tubes confining the respiratory current to a comparatively narrow area in which the gills lie, and thereby increasing the rate at which the water can be drawn over them. The second of these methods is largely effected by pigment. Our blood we know needs iron to keep it healthy, and it is a fact that gives us new affinity with lower animals that in them also the same ferruginous red blood is found. It occurs in those which have to live where oxygen is scarce or in parts of the body where muscular action is most sustained. Elsewhere we find a copper salt taking the place of the iron one, giving with oxygen not a red but a blue tint, and possessing only a quarter of the oxygen-holding power that belongs to hzmoglobin, its iron relative. Finally, in the less exigent forms the blood is hardly more than a stream of watery albumen. The working of the first method is easily tested. If some powdered carmine or indian ink is placed DAPHNIA III just behind the last leg of a crayfish at rest in a dish of water, a series of puffs of the colouring matter will Fic. 24.—Daphnia, an abundant freshwater Crustacean ; the body is enclosed in a carapace ; the limbs, less numerous than those of the Brine- shrimp, carry gills.—(/vom Lang’s ‘ Comparative Anatomy.) x 50. a,, first antenne ; @., second (rowing) antennz ; ad, abdomen au, eye; dr, branchial sac ; bru, brood cavity ; d, intestine; 7, to _f%, trunk feet ; 2, brain; %, heart ; Z, liver; sd, shell gland. issue in a few moments from beneath the eyes of the creature; and if we seize it and examine the under II2 ANIMAL LIFE surface of the head, a rapid movement may be observed at the sides of the mouth, indicating the position of the bailer ; the gills are, in fact, enclosed in such a way that the space around them is converted into a tube, open in front and behind. In a burrowing animal, however, such a method entails the danger of sucking up débris and choking Fic. 25.—Jlead and thorax of Crayfish, to show the gills and the bailer, ef,. 5 y g 3 (From Langs ‘ Comparative Anatomy.’) @,, @,, antenna ; aé,, ab., abdominal segments ; A2b,,, Ado,., PAL, gills ; Ae), first swimmeret ; 5-13, thoracic appendayes. the gills. Accordingly we find among burrowing crabs a great varicty of devices which, while per- mitting them to escape their numerous foes—the larger fish—allows them to maintain an in- and out- going current without blocking the gills. The common crab, which sinks up to the eyes in soft sand at the slightest warning, has a reversible gill-current. In general, it draws water through an opening at the BREATHING OF BIVALVES II3 base of the foot-jaws and exhales it beneath the eyes. When sunk in sand it performs the opposite movement, and drives the water out at the opening through which it had previously inhaled it. The masked crab, which burrows deeply into the sand, possesses a special breathing tube, through which it can inhale fresh draughts of water. Its antenne are brought together by interlocking hairs, so producing the tube, and the water then passes backward over the gills and out amongst the feet (fig. 19, F). The burrowing bivalves—razor-shells, rainbow- shells, cockles, and the like—provide themselves with a breathing siphon. To escape their numerous enemies and to evade the digging action of the sea, that threatens to evict and pulverise them, they possess a flattened shell, which easily passes through the sand as the spade-like foot hauls them into the burrow. But without some means of breathing surface-water these animals would be speedily choked, and their delicate gills lacerated by the flinty particles around them. Accordingly we find they have developed a long, bent siphon, the original fringe of their double tube drawn out to twice the length of the animal. Through this double tube the bivalves can reach up to the surface-water and tap a supply unmixed with sand. The current runs down one tube, bathes the delicate plate-like gills, and after passing through the body rises again to the surface, where, toavoid contaminating the supply, the outlet tube is turned away. When alarmed the animal withdraws its tubes into the shell, in which I 114 ANIMAL LIFE they lie till the disturbance has passed away. Their presence has impressed a line inside the shell, so that in place of a mark running. parallel with its Tic, 26.—A group of Burrowing Animals from a sandy shore. A. The Heart-urchin, showing its tube feet gathering food. 8B. A Bivalve (Scrobicu/arva), showing the inlet (4) for water and food and the outlet (a). c. The Cockle, showing inhalent and exhalent tubes. p. The Mud-clam (A/ya), showing the same. E. The Lugworm. F. The Masked Crab, whose antenne form the inhalent tube.—(B-D /rom Messrs. Meyer and Mobins ; A, after Graber; ¥, ¥, original.) BREATHING OF SNAILS II5 edge, the border of the contracted siphons forms a bay, and by it the bivalves with long siphons may be distinguished when we have only the shell to guide us. The univalves, or snails, have more varied breath- ing organs. The majority of sea-snails carry a tube, trunk-like, in front of their head, as they creep over the shallows at low tide, and by this trunk they inhale water which, after travelling over the gill hid within the shell, goes out by a slit near the base of the trunk. To support the trunk the snail-shell has a groove or spout, and by it the presence of the breathing-tube may be known even from the shell alone. Other sea- snails have no such canal, but are, as it were, snub- nosed, the nostrils being separated into an in-letting and an out-letting one. A few, such as the ear-shell and the key-hole limpets, have a slit, a row of holes, or a single hole, through which the water makes its escape after bathing the gills. Cuttlefish, squid, and nautilus have a short funnel, or escape pipe, for the same purpose, and in them the effort of breathing is convulsive; the whole body shakes with the effort and twists its gaping orifices as it unceasingly sucks in and transmits the gulps of water that flood its gills. The size, activity, and growth of these fierce creatures demand larger quan- tities of oxygen than are needed by other snails, and as the blood courses through their gills, it changes from a colourless to a blue fluid, a sign of the presence of that coppery blood-pigment which holds oxygen 12 116 ANIMAL LIFE with a capacity only exceeded by the red iron pig- ment which we possess. In each of these tribes—those of the worm and of the shrimp and snail—we find many air-breathers. There are earthworms and land leeches, land crabs and wood lice, land snails and land slugs. That these are descended from aquatic ancestors is shown in their dependence upon moisture. A worm shrivels by heat and is killed by frost. Its delicate netted skin is a gill that can withstand neither extremity of climate to which acrial life exposes it. Hence the tropics with their damp undergrowth, and the deeper soil with its more tenacious moisture, are the chief resorts of these adaptive air-breathers, for it is in such places that perennial damp is secured. The breathing of vertebrates. Gill-, lung-, and voice- production.—Fish differ from all animals except the zoophytes in their mode of breathing. By a succession of swallowing movements that suffer little interrup- tion, a fish fills its mouth with water, then closes it tightly, and by compressing its throat and gullet drives the water out through its gill-slits. The margins of the slits are converted into tasselled fringes, and the muscles used in swallowing are so arranged as alternately to open and shut these side exits. The gills of a fish consist of these bundles of red tassels mounted on hoops. Each thread of the tassel contains a V-shaped blood-vessel, one limb of which comes from the heart, whilst the other goes to the body. The red colour is evidence that only a thin skin inter- BREATHING OF FISH LL venes between the blood in the gills and the water which bathes them in a series of successive outgoing spurts. Through this transparent covering the oxygen of the water diffuses into the blood, which, thus invigorated, is carried to the various organs of the body. Where the activity of the organs is great the storage of needful oxygen is increased by the develop- ment of a red pigment capable of forming a reserve fund, upon which the muscles may draw for the in- creasing work that is demanded by the ceaseless adjustment of the body and by the rapid, powerful strokes required for pursuit, escape, or migration. The pink colour of salmon-trout and the red of the salmon and of the tunny are stores of this kind. This constant irrigation of the gills has brought fish into intimate touch with the qualities of water. The gradual drying of watercourses and ponds in summer, or the fouling of water by the decay of vegetation, reduces the amount of available oxygen, and to avoid the threatening suffocation many fish have adopted the plan of swallowing not water only, but air as well. The common loach rises to the surface to gulp a mouthful of air. The mudfish of Africa and of America does the same. The advantage of such a plan is patent. When the water is pure and abundant, aérial oxygen is a luxury, but when, in dry weather, the stream becomes a few isolated warm pools, which decaying weeds are rendering each day less fit for breathing, then those fish which can 118 ANIMAL LIFE breathe air are able to hold out longer than their submerged fellows, and, should the next rain be too long delayed, they will be first to meet the spate and to secure the new supplies of food that the flood carries. In order to store the air which gives them such advantage the throat of fish is puckered up into pouches ; some of these are quite shallow pockets, some are long tubes running down the body. In virtue of this supply the climbing perch makes ex- cursions overland before the dew is off the grass, and the mudfish, which tenants every sheet of water in equatorial Africa, passes through the driest season with impunity, rolled up and sleeping. The demand for storage of gases is so insistent that we find it obeyed by almost all fish, even in those which breathe solely under water. In them the storing organ is a tube lying under the backbone and opening into the throat during the first part or the whole of life. Into this chamber gas is exhaled from the blood. In marine fish oxygen is chiefly stored; in freshwater fish nitrogen preponderates. But these gas chambers, which originally no doubt served as reservoirs of respirable gas, have lost their primary function, as, indeed, the neutral nitrogen implies, and become transformed in ordinary fish into bladders, which determine their specific gravity by the alterably greater or less quantity of their contents. Thus they have entered into the problem of movement, and, by tending to lighten the fish’s back and upset its equilibrium, have led to far-reaching demands upon ORIGIN OF LUNGS 11g the fins and the muscular control of balance. Finally, in a few catfish the gas chamber becomes connected to the ear by a chain of little bones, in virtue of which the perception of vibrations in the water is notably enhanced. From some such appendages of the pharynx our lungs are derived. Fish of different orders have imdependently converted an outgrowth used at first for temporary air-storage into a sac, round the walls of which blood could be re-oxygenated and purified of its carbon dioxide. The opening of this virtual lung is even converted, in some fish, into a glottis ot voice-organ analogous to our own larynx ; and in the so-called salmon (Ceratodus) of Queensland, once wide spread over the northern hemisphere, the organ may be spoken of as a pair of lungs, which exist side by side with the gills ; it occupies the position and plays the part of the lungs in ourselves, and, whilst useful at all times, becomes of special respiratory value in foul water or times of drought. The next stage in the evolution of our breathing organs is traceable in the amphibious newts and frogs. These have gills when young ; a little older they possess both gills and lungs; and in their adult stage lose their gills and breathe mainly by lungs, reverting at times of stress and subaqueous retirement to the oldest known method of supplementing respiration, namely, breathing through the skin. This power of respiring air directly is associated with the conquest of the land. As it is done through the nose, we find 120 ANIMAL LIFE the air passage emancipated from the food passage. The reptiles exhibit a more complete solution of the air-breathing problem. In this, as in all their other faculties, we find amongst them a vast range of medio- crity. Most reptiles are only partially adapted for life on land; many at regular periods pass into a trance during which they respire mainly by the stores of air which their lungs have previously accumulated. In the reptiles we find the last traces of that primeval animal capacity for surface or skin breathing ; of true gills nothing but the framework remains. But in none of the known groups of this immense class do we find other than simple bag-like lungs, or a larynx capable of modulated sound. In none of them at the present day is the heat produced in respiration so controlled as to ensure a continuously periodic high vitality. From some unknown members of this mediocre class two offshoots have sprung in which the faculties of breathing amply, of sustained activity, and of voice production, have been perfected. Among birds we trace the evolution of the most perfect lungs that are known ; of the most continuously active of beings; of the most indefatigable of songsters. Amongst mammals we can follow the elaboration of a less atrial type of breathing; but, in accordance with their closer touch with the ground and_ the acquisition of great size, we find in them a means of inspiring and purifying great tides of air, an immense store of latent energy, and the most varied powers of voice and speech. BREATHING OF BIRDS 121 The working out of these capacities in each group is a problem of great interest. In birds the lungs are small, the windpipe long, and the organ of voice at its end, not in the throat at its commencement. Birds, therefore, are ventriloquists. From their lungs spring a number of air-sacs which buoy up the viscera as on cushions, line the skin, and often penetrate the very bones and feathers. To inflate this system a dual mechanism is provided. When stationary, the bird may raise and lower its ribs; when flying stiff- breasted, it lifts and depresses its flexible back. In either case two results follow. Compression involves not only expulsion of air from the lungs, but from the air-sacs through the lungs. Expansion entails an inrush through the lungs into the air-sacs. Thus the air in the lungs is wholly tidal. The expiration of combustion gas and the inspiration of fresh air are thoroughly carried out, in which processes the function of the air-sacs is not to act as respiratory organs directly, but to subserve this ventilation of the lungs by increasing the inward and outward wash of air and carbonic acid. This rapid rushing breathing stirs the blood. The muscles, fanned as by a draught, precipitate their activity in a series of superbly adjusted move- ments. The tissues burn well. Fuel has to be con- tinuously supplied. Food is imperiously needful, and the unappeasable, proverbial appetite of a bird becomes intelligible to us. Heat, too, increases. The feathers check its radiation and conduction. A nervous 122 ANIMAL LIFE control governs its uniformity, and there results a higher temperature than any we can healthily evolve, and one that for the first time in our résumé of living beings is unaffected by that of its surroundings. A hen’s temperature is uniformly 103 degrees Fahrenheit ; a swallow’s, 106 degrees. The production of voice is partly voluntary, partly mechanical. The adjustment of the slit just above the lungs and the rate of vibrating its edges are modi- fiable muscular actions. The call note, the migration note, the mating song, the alarm note, and the mimicry of parrots and song-birds are controllable responses to an impulse or an audible voice. But the ordinary breathing movement, which underlies it all, has become part of that unreasoning mechanism over whose starting or finishing birds have no voluntary control. The combination of superb singing powers with high vitality and spacious breathing marks the bird. In the mammals the lungs are capacious; but the amount of really tidal air is a mere fraction of the whole, and forms a top layer, from which the great mass that is stationary gains its oxygen, and into which it diffuses its carbonic acid. Thus, between the lungs and the tidal air is a diffusion-chamber. Every beast and child fills this with its first breath and never breathes as deeply again. Movements of the lungs are those of enlargement and diminution. Both of these are effected by the chest and by the diaphragm, a device peculiar to mammals. Both take place through the nose, as in all BREATHING OF MAMMALS 123 lung-breathing animals save unheeding men; and to purify the air, which for ground animals, such as mammals are wont to be, is too harsh or spore-laden for immediate diffusion in the lungs, this nose is elaborated within and without. Its chambers are subdivided by a scroll-work partition that converts them into labyrinths. Inspiration through such tubes now becomes more effective at the outset ; and as the wash of air whisks round the corners it deposits some of its impurities on to the soft membrane that lines them, and from the middle part of the nasal passage the air, toned, purified, and warmed, goes to the diffusion-chamber. The maintenance of activity in mammals, though less impressive than in birds, comports well with their needs. More groundlings than these, their quest for food is more deliberate, their meals heartier and with temperate intervals. Their reserves of strength and material are greatly in excess of immediate needs. The combustion changes of their muscles and glands furnish abundant heat, whether by the patent or hidden activity of these organs, which is evidenced by the dark colour of their flesh. Protected by both fat and hair, this heat is but slowly lost, and the relation of gain to loss is regulated by a nervous control that is centred in the capacious brain. So accurate is this adjustment that man and beast preserve their several temperatures under hot, cold, and changeable climates, and thereby ensure that continuance of activity which is one reason for their dominance. lic. 27.—The Common Dormouse.—(/yom a specimen in the Manchester Aluseum.) WINTER SLEEPERS 125 In this, as in all other excellences, we can trace a series of steps from the lower and more variable condition in reptiles ; for the lowest mammals have still no even temperature, nor do they suffer fever from a rise of many degrees. In the development of every child and whelp the heat-centres and heat-mechanism are only gradually steadied and rendered independent of cold or heat; whilst in the winter sleep and spring awakening of the dormouse, bat, and bear we see strength of constitu- tion that endures a quick change of 30 degrees without experiencing any harm. At such moments, which break a long sequence of still winter days and preface a still longer period of activity, these hibernators show a reptilian fluctuation and toughness. The reserve and rare display of full mammalian activity is well expressed by the voice. The calls, chatter, and songs of birds rarely cease ; their notes of warning, companionship, or exhilaration signal their presence and arrest us. But with mammals it is otherwise. The majority only roar, cry, or trumpet to sound an alarm or in rare moments of combat and excitement. Even the dog’s bark is a domestic refinement. The highest group, that of the monkeys, is the only querulous and chattering one, and this habit seems to go with active, arboreal, and social life. But, whether silent or vocal, all mammals possess a larynx similar to our own, and it is the nervous control and adjustment of the vocal cords, of the mouth and of voice-production, that give pre-eminence in 126 ANIMAL LIFE song rather than any structural difference which the anatomist can detect. In this, as in all other bodily excellences, the higher type of brain is the seat of success. Throughout this long series of breathing, heating, and sounding mechanisms we see the conquest of the air, and the inward use of oxygen for effecting move- ment, for maintaining that destructive aspect of the double process of life in virtue of which existence and growth are alone possible. But deeper than any analysis we have yet made are the adaptations of animal structure to ensure its increasingly efficient working in passing from water to land, from cold to warm blooded beings, from a silent to a vocal life. The heart and blood-vessels, even the blood itself, share in the advance, and become in birds and mam- mals divided into two systems, one of which receives acrated blood from the lungs, whilst the other receives the waste from the tissues. From this change all the tissues gain advantage. The muscles become more thoroughly oxidised, and therefore stronger. Their tone reacts on the body gencrally, and on the nervous system in particular. The heat they exhale becomes more generous, and the more abundant food they require as fuel stimulates more strongly the glands of the body. The trembling balance of life becomes steadied by a firm central nervous control, and its two emulating processes—the downward pull of oxida- are intensified tion and the upward thrust of nutrition in the maintenance and growth of every part. 127 CHAPTER VII THE SENSES OF ANIMALS The action of the Nervous System as a means of vesponse.—The procession of animal life from simplicity to complexity of structure, each phalanx fitted to an existence varying in richness of contact with itself and its surroundings, is a choric response to calls upon its nature that ages of trial have evoked. Every living thing is an old hand. Its choice of station and movement therein, its choice of food and mode of breathing, its structure and the relation - of the component parts, are traditional and reflect the heat and cold, the light and darkness, the hunger and plenty of many generations. Some mighty control has guided the steps by which each section of this complex composition comes orderly into existence, sustains itself there, develops, founds its family, and after a day, a year, or a century makes room for its fellows, leaving traces which cannot be mistaken of the part it has played. The organisation of each being, and of the pageant of which it is an assignable part, exhibits signs of that orderly control and re- lationship to the course of events within and without (oe) 12 ANIMAL LIFE itself which is one of the most impressive facts of natural history. The visible sign of this harmonic grace is the nervous system. Placed as a mediator between the conduct of an animal and the impulses that arise within it or that fall upon it, the nervous system determines that life and conduct shall not be a spas- modic response to every call that circumstances make, but that the general well-being of the race shall be consulted, and that in each life-history traditional answers shall be given at first, until education has conferred the power of a strong individual line of conduct. The nervous system co-ordinates the activities of different parts of an individual being in order to produce successful movement, good digestion, and adequate breathing. It interprets as sensations the stronger knocks that fall upon it from the outer world, and to the tapping of light, sound, heat, odours, tastes, and the like it answers by so many perceptions. It responds to the calls that arise from within an animal, and receives every moment of each day messages from the organs that tell the condition of each one. [If all be well the messages are imperceptible to us; if any part be weak, its call upon the nervous system becomes louder, and, if not silenced by adjustment of its need, we ultimately become aware of that which the nervous system has known all along, and we call it hunger, pain, desire. Besides these faculties the nervous system is the PERIODICITY 129 seat of traditional and individual memory. Through the long succession of days and nights that have lightened and darkened animal history with their alternate periods of greater activity and less, the nervous system has attained a rhythm which tones the activities of the body. This memory of bygone recurring conditions is preserved for us in the slow swing of the brain, which controls the impulse of the moment by the set of its own impetus, gathered through generations of alternate periods of rhythmic change into a fundamental beat. We awake and sleep not only because the sunrise and sun-setting call us to uprising and downsitting, but because in our life and that of our fathers the rising sun and gathering darkness have impressed on our being day by day and night after night an alternation of activity, rapid heart-beat, daytime breathing, with relaxation, slower pulse, and deeper breaths. At our usual hour for sleep or wakening we tend to either, though dark blinds or bright lights may delay our response to habit. So the flowers that close at night will shut their petals even though we turn their night into day. Our fundamental action, if not, indeed, our entire conduct, is thus no immediate response to the calls that arise within us or that fall upon our senses, but is determined to a variable extent by the tra- ditional and by the periodic response of the nervous system that has been established by habit; and to this habit it remains true, though for varying terms in different cases, even if the original stimulus that K 130 ANIMAL LIFE called it forth is removed or even opposed. This faculty of the nervous system has been happily called organic memory. If the conditions of life were un- changing, such a faculty would be unimaginable. But change—secular change—is of the essence of life, and the fuller the life the more generous in num- ber and amplitude of swing are the conditions under which it flourishes. Not only day and night, winter and summer, seedtime and harvest, set going the inward pendulum of animal life, but the life and death of their associates, the swing of the tides, all the great secular movements, beat with alternating force upon the receptive nervous tissue. Upon these leading motives that create habit others are super- imposed. We learn to walk because the brain has learnt to respond without effort along the trodden paths of nervous life, and is free to learn the new ways of upright adjustments. Organic Memory an aid to Developmental Study.— It is helpful to remember that once the nervous system has established a periodicity, that then, like a pen- dulum, it will continue to swing without the repetition of the push that started it. For by such a metaphor we are able to picture the development of an animal in a new light. Nothing is more wonderful, nor more familiar, than the moulding of a life in dark- ness, and the gradual revelation of its conduct, at first animal, then racial and traditional, and, lastly, individual. But if we admit that life preserves a memory of that which it has long experienced, and ORGANIC MEMORY 131 needs not always outward objects to assist that inner eye, then the marvel of animal development becomes a more rational process to us. The eye, which ages of experience of light and sight has brought to near perfection, is moulded without a flaw in darkness; the hands, which have developed by grasping, are formed without a movement; wings are made ready where no air is and where stillness reigns. The responses which are to govern conduct are developing there also. Each unwavering act in this bodily and psychic drama has a long history of effort and failure and success behind it, and here it is summarised in a few weeks of unchanging darkness. But if the eye re- acts without light, the formation of the eye may not require the original condition which called it forth. All we know of development seems to show that from the commencement of life each being has a memory, and that each organ plays some part in starting that memory into lite. Each part of us is a member one of another. The most important of these organs and the earliest to appear is the nervous system, for that has the most complex history to recapitulate. But for its full epiphany its memory has to be stimulated by a substance that comes from the thyroid gland, passes into the blood, and, carried to the brain and else- where, evokes the series of changes that help to build up a normal child. Should this gland fail to act efficiently, stunted mental and bodily growth result. The child is numbered with the feeble-minded. But kK 2 132 ANIMAL LIFE now, let that organ be taken from some other animal, say a sheep, and its extract be given in doses to the dwarfed being, there will often result a gradual change. The needful stimulus is taken up by the blood, carried to the brain and body, and there evokes the hidden and arrested growth of the stunted parts. In such a way many organs play their part by exciting the activity of others, perhaps far away from them; and to this principle we can attribute the strange and orderly persistence of organs whose primary use has disappeared. The gill-slits, for example, which recur with unfailing regularity in the development of all vertebrate animals, are only used in their primitive sense by fish. But in higher animals their walls give rise to thyroid and other glands that serve to excite the growth of the neck and larynx, and without these glands and gill-bars, which in fish have a totally different function, our development would be imperfect and retarded. Or, to take perhaps the most striking case—the change from youth to manhood, and the corresponding change in animals—a stimulus affects the whole body, alters the voice, broadens the chest, beards the face, and intensifies the conduct. In animals, as we have seen, so great is this change that the colour and eyes, the limbs and skin, undergo a complete metamorphosis : their movements and habitat are exchanged for new ones; the bird, fish, insect, and even certain worms, become different beings. When the change is less radical, as in the growth of antlers and resonance of voice or ferocity of manner, we SENSE-ORGANS 133 recognise the same mode of response of the animal’s nature to a stimulus that sets up new development. The Organs of Sense-—When this view of animal life and development as an orderly response to inward and outward stimuli has become familiar we are able to consider the nature of the senses of animals. The organs of sense are such as originate a message of a definite kind destined for the nervous system. Besides the five senses we have a muscular sense, one of heat, of cold and of pain. In addition to these, messages too faint for our brain to interpret are passing to it from all parts of the body and informing it of their several conditions; to which messages it is able to respond by assurances of which we are totally un- conscious. The good results of rest, fresh air, change of occupation, are the outcome of such toning effects of the nervous system on the muscles and organs generally, of whose needs we are only vaguely conscious, but to which the nervous system responds with more than a physician’s skill and promptitude. In dealing with the senses, therefore, we shall consider these subconscious senses, as well as those of sight, hearing, and outer impulses. The psychical phenomena of animals present a marked contrast with the physical. In structure and mode of development animal life presents varia- tions of endless diversity on several themes. The complications that adapt creatures for life under water, on land, and in air are of the most diverse kinds, whereas the fundamental instincts possessed by this 134 ANIMAL LIFE organised array are seven or eight only. Indeed, if we extend our researches to the lowest animalcule, we find that in it all the essential responses occur which form the themes of the fugues in higher animals. Sight, taste, touch, smell, balance, temperature, and parental instincts, are distinct although there is no eye, no ear, no tongue, and no specialised organ of any kind. Even the element of choice is not absent, and in the lowliest animal the psyche decides what to eat, what to absorb, when to retire from or advance to light or some counter-attraction. Indeed, we may go further than this and say that plants, and even the lowest plants, possess all the fundamental responses. They respond to light, they perceive odours, they choose what to absorb and what to reject. They are sensitive to shock, and even possess sense-organs of a rudi- mentary kind. In an organism devoid of a nervous system and without any organs of a specialised cha- racter all the responses are present, and they direct its life. The astounding diversity of animal and plant life, therefore, only gives expression in a thousand ways and with added clearness and fulness to the responses that their most degraded member possesses; and though writers have ascribed similar ethics to the dust, it is probable that this fundamental psychical uni- formity of living things forms one great character distinguishing them from the not living. The reason of this uniformity does not seem hard to find. The essential objects and conditions of lle are everywhere the same. Maintenance, development, LIFE AS A RESPONSE 135 and family or racial cares are its chief aims. Light, vibration or pressure, touch, odours, heat, and dryness or wetness, are its chief conditions. Each of these changes with greater or less regularity. The alterna- tion of day and night, of heat and cold, tell upon all living things. The prehension of food involves the sense of contact with bodies of many kinds; whilst movement involves changes of pressure. Growth and development introduce new factors. The presence of active enemies or of inimical conditions tests the race. For the lowest animal, therefore, some perception of these fundamental conditions, some power of response to their changing quality, some means of meeting emergencies, seems essential. The surprising result is that even the simplest organism gives no hint of any different life than that pursued by the higher ones. All the senses, dim though they be and exercised without organs, are there. The conflict of ages has totally obscured any primitive life. The simplest creatures are old hands, and tell us nothing of what life would be without the power of response. But though we are denied insight into the begin- nings of adaptive response, we can still trace its development in the many and complex forms of animal life. In fact, life depends upon these fundamental responses to living or non-living agencies. To us, in whom the enjoyment of the senses is a luxury, there is always a difficulty in appreciating the close, neces- sarily responsive touch in which the simpler organisms 136 ANIMAL LIFE live with light, water, and air. A plant moves towards the light, its roots track the watercourses, its leaves respond to the quality of air, because in these acts it finds the materials for food and new life. In the same way these old responses form the basis for animal actions. In them the senses are not emotions or per- ceptions apart. They are invariably bound up with a movement or adjustment which has to do with the preservation of life; and these adjustments are no new acquisition, but are traceable in the humblest living thing. The origin of instincts has been needlessly obscured by overlooking the fact that ‘sense’ is only a link in a chain of action, and also by treating organs of sense as things apart, instead of regarding them as inseparably linked with essential adjustments. The Senses of Shrimps.—Instincts are combinations of these old responses. We may take a shrimp as an example. By day we see it lying motionless in the sand or clasping a branch of seaweed. By night we find it swimming with great vigour at the top of its prison-water, its heart and breathing organs beating at a great rate, its colour altered from brown to blue, and its nervous system extremely highly strung and sensitive to shock. At the least alarm it will now leap out, whereas by day no ordinary disturbance would cause it to forsake its chosen spot. The tone of its being has been altered, and after persisting through the night this agility will give place at day- break to the more sluggish habit of its sleeping hours. Jn recording the behaviour of an animal, therefore, we THE RESPONSES OF SHRIMPS 137 have to consider its nervous condition, which is a function or outcome of a long succession of days and nights. By turning its night into day and day into night we find that for the first day or so of experiment the change of tone still occurs at the appropriate hour. Thus at nightfall, in spite of artificial light, the animal’s colour deepens into red, then to green, and finally to blue ; its limbs, heart. and breath take on anew rhythm, which endures for a night and then disappears. In the same way, if we prevent the morning light from making itself felt, the shrimp will still, for a day or so, time its recovery from a nocturnal bout as though informed of day’s appearing. In fact, the nervous system is the master, and for a while its innate perio- dicity determines the rate of the animal’s activity. This result shows what a supremely important part light and darkness play in animal economy. Con- tinued bright light shocks it to stillness; dim light gives it the necessary suppleness of limb. But now, suppose this action worn down by the con- stant effect of continued light or darkness; we have then the shrimp in a more responsive mood. The tone of its surroundings now influences its colour in a more direct fashion. On light backgrounds it quickly assumes a pale tint. On dark ones its red and brown pigments produce a dark tone. If we cover its eyes this faculty of sympathetic colour- change is abolished. The brown colour persists under all conditions of illumination, and we thus conclude that the skin is influenced not so much directly by light 138 ANIMAL LIFE as indirectly by the stimulus of sight, which is trans- mitted to the skin by the nervous system. Moreover, as the colour of the animal is deposited in the muscle- pigments as inuch as, or even more than, in those of the skin, and since the colour-changes of the muscles follow those of the skin, it is evident that the eyes govern changes in the muscle as well as those in the skin. We are led to look upon the eyes, therefore, not only as organs of sight, but rather as one link in a chain of response which is evoked by light from the whole animal. From this point of view the eyes, acting upon the nervous system, both govern the colour-relations of the shrimp and give the tone to its muscles and general activity. In a somewhat similar way we may look upon the response to vibration, the sense of pressure and of equilibrium. The shrimp has two ‘ears,’ placed in the first pair of horns, or in some shrimps near the end of the tail. These cars are hollow balls containing a solid body, cither grains of sand or a small block of lime; and it has been found by experiment that accurate balance during swimming or walking is de- pendent upon the healthy condition of these ears. Like the eyes, they communicate with the muscles and skin by means of the nervous system and have the faculty of compensating any tendency to upset or overturn. They register every vibration that the Waves cause or that movement induces. These ears are, in fact, organs of touch with a delicate balance and intimate connection with the muscular system ; THE RESPONSES OF SHRIMPS 139 and though almost every part of the skin of the shrimp, and in particular its legs, is provided with sensitive hairs, and is to some extent sensitive to change of pressure, such as a wave or a movement implies, yet the ears by reason of their position near the brain have a more commanding influence on the whole body —an influence they practise even in times of peace. The sense of taste or smell plays such a large part in animal life that we must consider it as a fundamental response ; yet in the shrimp, as in all animals, though so important, this sense has no well-defined organ through which it works. All we know is that certain hairs on the upper lip and antenne, like those of a cat, act as feelers, by which the neighbourhood of food is recognised. The response of the body to this sense is a complex one. In a chain of concerted action muscular events begin that stretch from one end of the body to the other and engage the activity of many limbs. The food of the shrimp consists of small bivalves, which it finds amongst the sand in which it burrows. The little shell is picked up by the big claws and transferred to the mouth. Here the excite- ment of the upper lip and jaws spreads to the lower lip, and to limbs further back, as well as to parts further inward. The mouth begins to water, that is, the digestive juices are prepared; and so the whole series of digestive processes—the dissolution of the food and its absorption—are linked up as a composite re- sponse to the smell roused by the discovery of food. Yet this response is ultimately referable to the property of 140 ANIMAL LIFE distinguishing and preferring chemical substances, which enables all living things to absorb nutritive substances when surrounded by a mixture of hetero- geneous bodies. It is only in some of the higher animals that the organs of sense become so highly developed and the perceptions arising through them so well defined that sensations become phenomena apart from those of motion, digestion, or of others immediately concerned in the welfare of the body, so that we cannot yet resolve their complex actions into the simpler responses from which they have sprung. The Origin of Sense-organs from the Skin.—The skin, upon which the outer world impinges, contains the sense-organs which receive and transmit its messages, and the deeper parts of the skin develop points from which their needs emerge. Thus, upon any organism a double set of impulses falls, one from without, another from within. Each of these is at first intimately connected with the fundamental acts of life, and in order to correlate the supply indicated from without with the demand indicated from within a nervous system has been gradually elaborated. In the first instance it appears to be related rather to the efficient response of the body to the external messages —pressure, food, ight, and so on—and in particular to movement. But it is clear that, since these responses are of vital importance, they must be cor related with the inner needs of the body ; and so there come to be not only a nervous regulation of move- ORIGIN OF THE NERVOUS SYSTEM 1q1 ment, a response to vibration or to food, but also an inner mechanism by which the food-canal, the breathing-apparatus, and the other internal organs are brought into nervous connection with the outer mechanism of skin and muscle. In other words, we see the outline of that control and perception of the outer world by movement, prehension, and touch, and the satisfaction of the needs of the inner world of hunger, growth, and racial cares, that is roughly in- dicated by the terms central nervous system and visceral nervous system. The question may perhaps be asked, Why have animals developed a nervous system? The answer, so far as we can give it, bears upon the last discussion. Animals move freely and eat solidly. These two facts go together, and have led to an inevitable distinction between the outer locomotor and inner nutritive regions. Now it is clear that, even if no formal nervous system exists, animal movement demands and _ pos- sesses a directive and controlling influence. Further, as we know, this regulated locomotor mechanism is able to transmit food to the mouth and to inhale water or air, and the body is able to move the food from place to place in satisfaction of its needs. In other words, animals, even the simple, such as polyps, have a virtual nervous control of their organs of movement and of their visceral organs, and a correlation between the two. Movement, then, and solid food have, so far as we can see, been the two factors responsible for creating the need for that control which is simply 142 ANIMAL LIFE emphasised in the primitive nervous systems, such as those which jellyfish and starfish possess. In fact, the development of these animals shows that the muscle and skin are at first continuous, and the strained threads that connect the two, as they separate for their respective functions, become the nerves for em- phasising movement. In a similar way the food-tube is at first a part of the skin, which becomes pitted in and grows inwardly, and the connection between its layers and the muscles and skin of the wall of the body furnishes the basis for its visceral nerves, and for the correlation between their demands and the exertions of the locomotor organs in the prehension and supply of food. Thus the nervous system of animals is inti- mately related to the primary conditions and needs of life, and is organically descended from the neuro- muscular skin and the neuro-muscular food-tube. The development of animals, even of ourselves, shows how close is the relation of the nervous system to this primitive plan just sketched, and how intimately the sense-organs are connected with the skin. The skin in all animals is an organ of one or more senses, and from it arise the essential sensitive parts of those sense-organs, such as the eye, the ear, and nose, which seem to be unrelated to it. It would appear incredible that the retina of the eye, the equally delicate and more complicated lining of the ear, should be a modified patch of skin; yet such is the case, not only in one group, but in all; and, indeed, in some groups it is possible to pointiout a series of stages in ORIGIN OF THE NERVOUS SYSTEM 143 which the eye commences as a mere open pit, then develops into a closed vesicle, and passes by degrees into an organ whose complexity approaches, if it does not attain, that of our own ; whilst with regard to the ear, the skates and certain other fish still retain an open tube by which their ear is placed in communica- tion with the skin. In the early life of animals the nervous system itself is at first in close contact with the embryonic skin, and only gradually sinks down to take up its position in the enclosing bony or gristly tube that is to form the vertebral column ; whilst in many primitive forms its connection with the skin is retained through- out: life. The nerves which direct movement are actually developed in ‘connection with the muscles and skin, much as in the case of a jellyfish or sea- urchin; whilst those nerves that announce hunger, desire, and generally the condition and needs of the inner organs, are derived ultimately from ingrowths of the surface layer. The two sets of organs—the outer or directive and inner or visceral—become inter-con- nected by nervous ties that provide pathways whereby the need for food or breath, for example, is able to set in motion a movement of the body that tends to supply that need. So we see a full animal is quiescent, a hungry one is active. In the reverse way, the sight or taste of food sets going the nerves that connect the prehensile organs with the digestive ones, and so prepare the way for the reception of food. So short- ness of breath induces more rapid breathing, as we see I44 ANIMAL LIFE in fish when the water of their aquarium has become partly exhausted. In short, whilst the movements of an animal are stimulated by light, heat, and outer agencies, they are controlled by a nervous mechanism that is not only related to that control, but is also concerned in satisfying the inner desires by those movements. Gradually these adjustments become not only automatic in their working, but by their repetition induce a second self, a periodic heightening and lowering uf the central governing control, through which the rate of automatic working is rendered steady for long intervals and is protected from becoming spasmodic and from changing with each change of scene. Thus we find choice becoming obedience and obedience becoming tradition, giving, as it were, a direction which the answer may take, though not determining the intensity of its response. The warm blood of the higher animals creates a further buffer between them and the changing con- ditions around their bodies; it wards off from them those changes of temperature which sink their less fortunate relations into stupor or death. The value of this mechanical and traditional tend- ency is easily misunderstood. We need not look upon it as necessarily converting the whole life of an animal into a series of purely automatic actions. For if we steadily keep our outlook on the gradual evolution of self-consciousness, we shall see in this stiffening of action the necessary prelude to advance in the FROM CHOICE TO HABIT 145 higher responses. It is not merely because we are relieved of decision about manipulation that would otherwise check our advance, that as speech, draughts- manship, or reckoning become easily performed, that therefore language, art, and astronomy have become a more perfect expression of the universe. The un- burdening transfer from act of choice to act of drill and from the strain of memory to the habit of tradition allows not only further advance to be made, but preserves the past and forms when complexity has been gained a point of departure for responses to messages which before were too high for us to in- terpret or hear. These messages, coming either from within or from without, are no new things, but, like the pulses that beat upon us all day long, were un- perceived till the insistent voices of needs were stilled and we became attuned to a more receptive pitch of nervous strain. Thus upon the solid groundwork of embodied and self-contained, self-regulating tradition the needs of maintenance are satisfied, leaving us free, not to sink into the torpor of automatism, but to respond to finer impulses which the cares of main- tenance had hidden. The needy artist must first make his bread and then practise his art; and the making of bread creates the necessary organic pre- paration for esthetic perception and work. Even so the classes of animals richest in manual work and tradition are alone they which have esthetic preceptions. ‘For to him that hath shall be given.’ 146 ANIMAL LIFE The performance of work done out in the open leads in each class to a capacity for new response, and therefore to greater variety of handiwork. Amongst the Protozoa, those are the most complicated and the highest which have left shelter to inherit the fuller traditions of the open sca. Amongst the zoophytes there is one family—the siphon-bearers—that has surpassed all others in eracefulness and variety of shape, in intensity of colouring and virulence of poison, and it is this family of the blue velella and the violet ‘ Portuguese man-of- war’ that has had no rest, that has felt the unceasing beat of the sea, and without intermission has been stimulated to action. A more familiar example is the hydroid-polyp of the shore, with its simple struc- ture and plant-like responses, and the jellyfish that arises from it but strikes out to sea, where its eyes and ears, its muscles and poison-organs become elabo- rated through its constant adjustment, varying to meet the changing action of light and waves and the choice of food. But it is on land and in air that adjustment be- comes more arduous, oxygen more plentiful, and advance, though difficult, more pronounced. The play of light, heat, and vibration, the influence of weight, the sources of friction, the steepness of hills, all tell with greater force on land than under water, To those animals that can make the adjustments and endure even for a few months the rigour of a changing climate a higher place is assured than to their brethren INTELLIGENCE 147 of the sea; whilst the old, the irresponsive, adopt her- mitage in the soil away from the stress of life. So it is not till the physical adjustments become varied, sound, and performed with ease and without thought, that we find the dawn of intelligent response to the living factors of the situation; the response to an impulse, not themselves, that has been at work allalong, but is hidden from animal life until a certain stage of responsiveness has been attained. Then as racial instinct, the spirit of the hive, or by whatever name we call it, sometimes in solitude, more often in com- panies, the finer issues of hfe are felt and responded to by those that generations of manual work, delicacy of touch, and observance of open-air changes have cultivated. Birds and insects rule the air by un- thinking adjustment. Man rules the earth by thoughtful adjustment. His snecess is due to his power for profiting by experience, both in his in- dividual and corporate life, and thereby rising in capacity for response to more and more complex motives, whether for good or for evil. The domestication of animals may ilustrate what far-reaching results flow from a simple act when that act can be repeated and modified in the light of experience. In common with other carnivorous animals man kills for food, and in general with as little foresight as they. Nevertheless, here and there a genius will have noticed that, after a successful chase, to keep alive that which is not required will give power. And L. 2 148 ANIMAL LIFE these more far-seeing warriors, having begun to capture as well as to kill, acquire wealth and fame. To the consequences of this simple act more than to any other, civilisation is indebted for its development from the ‘ pack,’ through the pastoral to the political state. The Australian remains for us the nearest of all living races to that primitive hunting state ; and the nomad shepherds of the East illustrate the art which has given rise to ‘capital’ and to ‘ pecuniary’ advantage amongst the more advanced races. REFERENCES ‘Animal Behaviour’: Lloyd Morgan. ‘The Senses of Animals’: Sir J. Lubbock (Lord Avebury). “Internat. Sci. Series,’ vol. Ixv. Influence of domestic animals on civil history: Maine, ‘Ancient Law’ ; Jenks, ‘ History of Politics ’ (Temple Primers). 149 CHAPTER VIII THE COLOURS OF ANIMALS The Primary Meanings of Animal Pigments.—In man and creature colour is sacramental. Complexion in man is a sign of racial constitution and tempera- ment, and colour in animals is the expression of that hidden working which controls, and is controlled by, their life. We regard, and rightly regard, the body as fuel for fire; its activity as the outcome of a combustion which is fed by food and fanned by air, the engendered heat being carried by those hot-water pipes, the arteries, to the remotest outworks of skin and muscle, of bone and nerve, there to replenish the loss which secretion, movement, and nervous activity involve. And as from coal we can obtain not only heat, but tarry matters and aniline dyes, so from the slow combustion of the tissues does the body deposit those grains of matter which, when exposed to the light and air, become pigment, as a cut apple goes brown or a chipped toadstool blue. Colour is thus distilled, as it were, from the whole body, and resumes its essence in a seemingly surface finish. | If we now review the colours of animals, we are T50 ANIMAL LIFE struck by this influence of light on their distribution, A dark back and a pale under-surlace form the most general of all schemes of colouring. Insects and worms, shells and starfish, fish and frogs, birds and most beasts, through a vast category of marine and terrestrial forms, display the white breast. Squirrels, the most vividly coloured of mammals, still keep the rule; whales and fish agree in the contrast of their dark upper sides with their white nether surfaces. Blue and brown butterflies are only so when seen from above ; and if we turn up the palms of our sunburnt hands, we find that there too pallor is more evident than on the upper side. Colour and light-exposure, pallor and light-starvation, are correlative terms. As the green colour of plants fades in darkness and shade- leaves, so the nether parts of animals are bleached by the lack of hight. To confirm this and give the mind living hold upon its significance we must apply the test of experi- ment. If light induces colour, and darkness prevents its appearance, then we should, by inverting a young animal, obtain some evidence as to the present-day applicability of this principle. This has been done both artificially and by that age-long trial that natural experiments involve. Young plaice have been grown in a tank, lighted from below and darkened above, so that the under-surface of the fish, which is normally turned away from the light, was exposed during the hours of daylight to the light reflected: from a mirror. After an interval of a few weeks several of the bately so LIGHT AND COLOUR 151 treated were found to have developed spots of colour on their under-surface, and thus to present an ambi- colourate appearance. Ultimately one of the fish became almost totally embrowned, and lost all but mere traces of its usual silvery whiteness. More convincing even than this experiment is the one which Nature herself has carried out on the sucker- fish. The sucker-fish is a parasite hanging on to the bodies of larger tropical fish for the sake of the crumbs that fall at meal-times. To ensure its hold the fish has converted its dorsal fin into a strong, transversely ridged sucker, which it applies to the upper side of its host, and thus views the world standing on its head. Its back is in shade, its belly in light, with the result that the usual colouration of animals is here reversed—its back is white and the belly dark, almost the only exception to the otherwise universal rule ; and so accustomed are we to it, that when we first handle a sucker-fish we involuntarily turn it upside down and unconsciously acknowledge the strength of that asso- ciation that leads us to regard the dark surface of an animal as the upper one. Whilst we can thus conclude that the shaded parts of the body become pale and the exposed parts dark, there are some natural experiments upon the total bleaching of the body by generations of cave life. The cave newts of Carniola, in Hungary (fig. 28), have become famous. They are milky white blind newts, a foot or so in length, and live in the darkness and cold of subterranean waters. Unlike their allies, the 152 ANIMAL LIFE askers, which are coloured on the back, these cave newts are without any trace of pigment. That they have lost their original colouring subsequently to adopting cave life is a conclusion rendered highly probable owing to the discovery of still another colourless species in South America which is related to quite a distinct family of darkly coloured newts, and is borne out by the occurrence in the same caves Fic, 28.—The Cave Newt of Europe (Proteus anguineus). (From specimens tn the Manchester Museum.) of white shrimps and bleached insects, whose relatives lead a free life and possess a coloured skin. But this bleaching is only permanent so long as light is excluded, and if these cave newts are brought into daylight they develop in the course of time a dark skin, and after a few months become almost black, the change being most marked on the back of the animal. Experiment thus confirms the power of light rapidly to excite the formation of colour or pigment, and the power of LIGHT AND COLOUR 153 darkness to prevent the appearance of colour or to destroy a pre-established colour in the course of generations. With this thought we may look out on the colours of the animal world and observe the broad general agreement between the arrangement of these tints and the green colour of plants. The two sides of an animal differ as do the two surfaces of a leaf ; the upper one, being the more exposed to the sun, is the darker ; the lower, more shaded surface, is the lighter one. Animals, such as worms, that keep one end of their body root-like buried in the ground become at that extremity bleached, and those that are altogether excluded from the light, like a tuber, are totally colourless. A plant grown in the dark becomes pale and chlorotic ; an animal, though more slowly, becomes no less drastically etiolated. Transported from dark- ness to light, the leaves of a cellar-grown or shaded shrub reassume their green colour, and with no less certainty the colourless troglodyte becomes dusky when illuminated. Nor is the full light of the sun necessary for the development and preservation of the colours of animals and plants. In a dim light vast numbers of jungle plants, forests of brown and red seaweeds, multitudes of crepuscular, creeping things, and deep-sea fish work out their life with as full a colour as their relatives and brethren of the sun. The mole and bat are no less deeply coloured than the sparrow or skylark ; the pygmies of the dark Congo forest are brown as the tribes of open country ; the moss 154 ANIMAL LIFE of a waterfall on which no light shines is as full a glossy green as the velvety covering on a south wall, and shows us that though light and colour, darkness and pallor, are causally related, yet the intensity of the necessary light and the need for its continuous employment and the mode of its working have to be considered before we can unravel the tangled problem of animal colouration. In a plant these factors are comparatively easy to determine. The green colour we know is associated with the production of the plant’s food. In the leaf, starch or sugar is formed as a preliminary step towards building up the plant-substance by union with juices that rise as sap from the roots. For the efficiency of the leaf light is requisite. Cut off all light, and the leaf is starved in a day, and dies. Expose the leaf to a continuous direct light, and it is no less infallibly killed, though replete with starch. In the moss and fern tribe darkness and starvation may long be endured with impunity ; in the cactus group intense light and plenty are cqually well borne. But, however varied their powers of adaptivencss may be, plants require the green colour for a definite object—namely, to lift the carbon dioxide of the air to a higher power, which in one form we call starch, in another sugar ; that is, the green colour of plants subscrves nutrition, and to do this light is required. In this process of modifying the carbonic acid of the air its oxygen is set free and made available for the needs of aquatic plants, so that by day starch COLOUR DUE TO PLANTS 155 is formed and oxygen provided. The green colouring matter of plants is, consequently, concerned in the processes of replacing the matter of living substance. Its fundamental importance and its simple require- ments explain the ubiquity and abundance of green colouring in plant-life. Amongst animals there is no such fundamental, widespread, and nutritious pigment. That mysterious and seemingly simple hold upon earth, air, and water by which plants make their living, if it exists in animals, is no prominent feature of their life. Their food is no cunning mixture of gas and water. In spite of fable, the chameleon does not live on air, but on flies; nor does the possession of a green colour by many frogs, snakes, birds, insects, or worms confer upon these animals (with one remarkable exception) the ability to subsist without solid food, even where the green matter has proved to be identical with that of plants. A plant living in an animal, as plants (Flagellates) do (p. 106) in Protozoa, anemones, and some worms, is only capable of keeping its host from starvation by submitting to be eaten up piecemeal, and should further solid food be lacking the menagerie dissolves partnership. Whatever value we can attribute to animal colouration, a nutritive one would seem to be the least probable, and we turn to the other side of life’s balance-sheet, the income of energy, to see if there is any animal pigment which has the property of allying itself with the oxygen of air and of purveying that oxygen to the tissues of the body. 156 ANIMAL LIFE In this quest we soon meet with success. The red colouring matter of blood is such a vivifying substance. The acrating virtue of the blood lies in that colour, and should it fade we become weak and anemic ; should it disappear, we succumb ; our fires burn out from need of the oxygen which the red pigment, and it alone, can dispense. To most animals, as to ourselves, this pigment is essential. All the members of the vertebrate class, cold- as well as warm-blooded, possess it. It gives not only the colour to the blood, but the dark tint to the muscles. Below this class it occurs sporadically in snail, starfish, and worm, conferring upon their blood and muscles a greater efficiency than is possessed by their colourless relatives, and the ability to thrive in stagnant water or amid ill-ventilated surroundings. In producing the gross colour of the animal this pigment takes but a small share, and it is only when a given supply has done its work and steps aside to make room for the new flow that comes from the marrow of the bones that it is apparently removed from the blood-vessels, transported to the skin, con- verted into a black pigment, and stored in hair and feathers, there to give rise to the colour of the body. But the interest of the red blood-pigment is not confined to its wide distribution, its life-giving property, or its usefulness as a source of surface colouring. In its chemical nature this pigment shows a family con- nection with the green colouring matter of plants. In their purest known state each of these bodies, LOSS OF COLOUR 157 the one red, the other green, appear as cousins, related through some as yet undiscovered stock. Each has diverged at some remote epoch along a line of its own, and in course of time produced the substance that we know as the green colouring matter of plants and the red pigment of the blood of animals. Yet, in spite of this divergence and seeming dis- parity, we can detect points not only of resemblance, but of affinity. Both have a like, though hidden, family constitution, indicative of a common but remote genetic connection. They occur with un- failing regularity in the higher divisions of the two kingdoms of living nature, and become less constant in the lower members of animal and plant life. In those plants which live parasitically upon the tissues of other organisms the green colouring matter is absent. Its nutritive power of making and purveying sugar, starch, or oil is not required. In the vast class of moulds, mushrooms, and toad- stools there is not one that has the requisite green pigment. Amongst typically green plants there are still more striking examples of the loss of colour following upon the adoption of parasitic habits. The dodder that infests vetches and clover sucks the juices of its host and loses its livery. The minute colourless Flagellata which abound in organic infusions are cousins to those Euglene that fill the roadside hollows with a green scum, and if only water and light are supplied to them their colourless bodies reassume the green tint and create a food store from such 158 ANIMAL LIFE inorganic sources. Itis just among such plastic, chame- leonic Flagellates that we can trace that remote con- nection between animals and plants to which biology points from whatever side we study it—in infusions an animal, in water a plant; producing starch like a leaf, and yet such starch as only the muscles of animals evolve. Still for long intervals like an alga, and anon swarming in a dense throng like a shoal of microscopic fish ; abandoned in turn by the botanists to zoologists, and by zoologists to the botanists, this group of Januses is ever enticing the naturalist to its study, and yet refusing to fit into the categories he has made. From such Flagellates all the families of sea- weeds trace their descent, as to the founder of dynasties, and to them also many of the lowest animals and the sponges owe their genesis. The loss of green pigment amongst animals would thus seem to be due to their mode of feeding upon organic food, which was not only a richer diet, but, unlike the primitive plant food, could be obtained in dark as well as in light places. When the activity of these dual organisms increased, as it necessarily did in pursuit of fresh stores of organic débris, the need for nourishment increased also. The new and characteristic animal tissue— muscle—demanded both oxygen for contraction and also nourishment by appropriate food, and im- pressed into its service that faculty for vivifying the body with oxygen which in its green youth was associated with the body colour; and in the lower RESPIRATORY PIGMENTS 159 animals we see, following the gradual insistence of this respiratory demand, the gradual evolution of a more and more efficient oxygen-carrier. In the shellfish the blood has only a quarter of that oxygen-holding capacity which we possess. In the worms which live where little air is available, the blood is richer, and either green or red. In the vertebrates the blood is always red, richer in oxygen-holding power, and meets the demands created by the growth, bulk, and activity of the body for a continuous supply of oxygen to all the tissues. Of these demands some are more pressing than others, and we can assign the deeper colour of the more active muscles to the great stores of blood- pigment heaped up for their use. Hence the darker legs of a hen contrast with its breast, or the dark flesh of game with the white flesh of poultry, And further, if the generally accepted opinion is correct, that the yellow, brown, and black pigments of hair and skin, to which all the higher animals owe their colouring, are kinds of effete blood-pigment removed from the circulation and dumped down out of the way, then we may look upon the blood as furnishing the pigments which are worked up upon the canvas of skin into such superb embroideries. We can thus broadly trace the rise of the red colour of the blood to its source in some distant connection between plants and animals, of which its chemical affinity with plant-green is confirmatory evidence. Evolution of red and yellow fatty pigments—A no jess complex and vet fascinating quest than this of 160 ANIMAL LIFE the history of blood-pigment is that of the yellow and red colouring matters of the lower animals. We all know the red colour of boiled shrimps, lobsters, and crabs, and the change from blue to red which these Crustacea suffer in the process is but an instance of the breaking down by heat of a delicately poised and unstable substance, and of its return to the basal red pigment which we see in the change of phosphorus from red to yellow on heating. But we are not familiar with the fact that such red and yellow forms of a definite chemical substance run like a thread through animal and plant organisms, giving evidence of a similarity of constitution that appears more and more strongly to the mind as we grow acquainted with these unexpected relationships. The yellow yolk of an egg, the red shell of a lobster and yellow substance of a carrot contain a colouring matter of the same chemical nature. The same material colours the wax of our ears and the visual purple of our eyes. The eyes of birds and reptiles possess yellow globules, scattered amongst the part most sensitive to light; the eye of man and of ape has its yellow spot or centre of acutest sight; andin the eyes of nearly all vertebrates there is a reddish pigment which belongs to the same class of coloured substances. In the skin of fish and that of frogs, which are so highly nervous as to be hardly less susceptible to changes in their neighbourhood than the eye itself, the same yellow and red pigment is abun- dantly found, and there assumes the form of minute FATTY PIGMENTS 161 star-shaped masses (chromatophores), which can con- tract to a mere dot, leaving clear interspaces between one mass of pigment and another, or, again, can expand to a radiate form, branching out and filling the skin with a tracery of colouring. In the same way the skins of shrimps and prawns are dotted over with little mobile bags of pigment, now expanded into star- like forms and rendering the animal of a deep brown colour, and anon contracting to as many microscopic black-looking dots, separated by clear interspaces, and the effect of which is to give the shrimp or prawn a transparent and colourless appearance. As we go further down in the scale these pigments become still more abundant. They suffuse the skins of most starfish, sea-urchins, sea-cucumbers, and brittle- stars. This substance, which in its yellow or red form has such an extraordinarily wide distribution amongst animals, is no less common amongst plants. The green substance of ordinary leaves contains it. In all underground stems, roots, and tubers it is present, though often only in small quantities, as in the turnip, or in a concentrated form as in the carrot. In the fungi it produces most of the brilliant orange, yellow, and red effects that so strikingly catch the eye on leaves, palings, and tree-trunks which are infested by moulds. Even amongst the simplest of all forms of life—the bacteria—the same pigment is still to be found. From the lowest to the highest forms of plants, from the simplest Protozoon up to man himself, there M 162 . ANIMAL LIFE is no large class in which the yellow and red pigments are not to be found, though we may have to search in the remotest and most delicate organs before we find them ; they may confer the most brilliant colour, or be hidden and valueless as regards it. The meaning of this widespread colouring is not yet fully understood. It may well be an apparatus of extreme antiquity, which has been to some extent supplemented by newer methods. These pigments are occasionally capable of producing starch in the presence of light, but neither so effectively nor so rapidly as the green colouring matter; and it is not unlikely that the green pigment, which is perhaps the most economic machine that life has evolved, was only perfected after the simpler yellow tools had long been tried for the production of food from inorganic sources in air and water. In the lower plants the red and yellow colouring matter is related to the accumulation of fat and oils, which are stored in the seeds or spores. Similarly, in the carrot, the huge reserves of fatty materials col- lected in the roots are accompanied by a dense forma- tion of yellow pigment, and in the eggs of animals the same relation between yolk and pigment is clear. So constant is this association that these pigments have been called fatty pigments, and stand in some sort of relation to the nourishment of the young, whether plant or animal. But until recently the nature of this relation was entirely unknown. The results of some researches on the pigments of prawns FUNCTION OF FATTY PIGMENTS _ 163 have, however, suggested that they possess a definite nutritive meaning. In these animals the colour of the skin is due, as we have seen, to minute stellate masses of such substances. These mobile pigment-stars form the ‘chromatophores.’ But not only is the skin thus inter- spersed, as it were, with pores, from which the pig- ments overflow into channels or into which they retire, leaving the channels clear and colourless, but a similar system of pigmented holes and crannies traverses the muscles, the digestive system, the nerves, and the eyes. The whole prawn, in fact, is bathed within by pigment veinings. Along the courses of these channels lies a second series of tubes that contain, in green specimens, minute grains of colourless fat, and if the prawn be starved and kept in the light the fat does not disappear. If, on the other hand, both food and light are excluded, the prawns, having exhausted what food they had to start with, absorb pigment and fat also ; and if such lean specimens are taken out again into the light at the end of a fortnight, they will in the course of a single day show not only a fatty skin, but a far denser accumulation of fat than is to be seen in a fresh-caught prawn. This result points very strongly to the conclusion that the red and yellow colouring matters, even of such highly organised animals as prawns, are, as in some plants, able to form fat out of its simple elements, and are, therefore, no mere deco- ration, but factories, under the shade of which the M2 164 ANIMAL LIFE demands of the body for nourishment and of the eggs for yolk, which cannot be completely met by the usual food, are satisfied. The colour of the prawn may thus have nutritive value, though naturally of a lower order than that of the food taken in by the mouth and elaborated in the passage through the tissues. The multitudinous minute collections of pigment or chromatophores that star the skin and the interior of the body form so many rudimentary elaborating machines, independent of the digestive system, and differing from it in being able to construct and distri- bute a fatty substance under the influence of coloured light. Whether this double mode of nourishment is widely spread amongst animals is not as yet ascer- tained ; but we know that it is extremely difficult to prove, and for this reason—skin-nutrition is a mere vestige of an old process that has been supplanted by the more modern and efficient one of nutrition by the digestive system. The collections of pigment, under whose