We have seen also that, as in all families of long standing, many branches have become extinct altogether; the great enamel-plated fish, the large armour-covered newts, the flying, swimming, and huge erect-walking reptiles, the toothed and long-tailed birds, the gigantic marsupials, the enormous ground-loving sloths, and many others, have lived out their day and disappeared; their place being filled either by smaller descendants of other branches of the group, or by new forms in the great armies of fish, birds, and milk-givers which now have chiefly possession of the earth.

Still, on the whole, the history has been one of a gradual rise from lower to higher forms of life; and if we put aside for a moment all details, and, forgetting the enormous lapse of time required, allow the shifting scene to pass like a panorama before us, we shall have a grand view indeed of the progress of the great backboned family.

First, passing by that long series of geological formations in which no remains of life have been found, or only those of boneless or invertebrate animals, we find ourselves in a sea abounding in stone-lilies and huge crustaceans, having among them the small forms of the earliest fish known to us, those having gristly skeletons. Then as the scene passes on, and forests clothe the land, we behold the descendants of these small fish becoming large and important, wearing heavy enamelled plates or sharp defensive spines; some of them with enormous jaws, two or three feet in length, wandering in the swamps and muddy water, and using their air-bladder as a lung. But these did not turn their air-breathing discovery to account; they remained in the water, and their descendants are fish down to the present day.

It is in the next scene, when already the age of the huge extinct fishes is beginning to pass away, and tree ferns and coal forest plants are flourishing luxuriantly, that we find the first land animals, which have been growing up side by side with the fish, and gradually learning to undergo a change, marvellous indeed, yet similar to one which goes on under our eyes each year in every country pond. For now, mingling with the fish, we behold an altogether new type of creatures which, beginning life as water-breathers, learn to come out upon the land and live as air-breathers in the swamps of the coal forests.

A marvellous change this is, as we can judge by watching our common tadpole, and seeing how during its youth its whole breathing organs are remade on a totally different principle, its heart is remodelled from an organ of two chambers into one of three, the whole course of its blood is altered, some channels being destroyed and others multiplied and enlarged, a sucking mouth is converted into a gaping bony jaw, and legs with all their bones and joints are produced where none were before, while the fish's tail, its office abandoned, is gradually absorbed and lost.

The only reason why this completely new creation, taking place in one and the same animal, does not fill us with wonder is, that it goes on in the water where generally we do not see it, and because the most wonderful changes are worked out inside  the tadpole, and are only understood by physiologists. But in truth the real alteration in bodily structure is much greater than if a seal could be changed into a monkey.

Now this complete development which the tadpole goes through in one summer is, after all, but a rapid repetition, as it were, of that slow and gradual development which must have taken place in past ages, when water-breathing animals first became adapted to air-breathing. Any one, therefore, who will take the spawn of a frog from a pond, and watch it through all its stages, may rehearse for himself that marvellous chapter in the history of the growth and development of higher life.

And he will gain much by this study, for all nature teaches us that this is the mode in which the Great Power works. Not "in the whirlwind," or by sudden and violent new creations, but by the "still small voice" of gentle and gradual change, ordering so the laws of being that each part shall model and remodel itself as occasion requires. Could we but see the whole, we should surely bend in reverence and awe before a scheme so grand, so immutable, so irresistible in its action, and yet so still, so silent, and so imperceptible, because everywhere and always at work. Even now to those who study nature, broken and partial as their knowledge must be, it is incomprehensible how men can seek and long for marvels of spasmodic power, when there lies before them the greatest proof of a mighty wisdom in an all-embracing and never-wavering scheme, the scope of which is indeed our intelligence, but the partial working of which is daily shown before our very eyes.

But to return to our shifting scene where the dense forests of the Coal Period next come before us. There, while numerous fish, small and great, fill the waters, huge Newts have begun their reign (Labyrinthodonts ), wandering in the marshy swamps or swimming in the pools, while smaller forms run about among the trees, or, snake-like in form, wriggle among the ferns and mosses; and one and all of these lead the double-breathing or amphibian life.

In the next scene the coal forests are passing away, though still the strange forms of the trees and the gigantic ferns tell us we have not left them quite behind; and now upon the land are true air-breathers, no longer beginning life in the water, but born alive, as the young ones of the black salamander are now (see p. 81). The Reptiles have begun their reign, and they show that, though still cold-blooded animals, they have entered upon a successful line of life, for they increase in size and number till the world is filled with them.

Meanwhile other remarkable forms now appear leading off to two new branches of backboned life. On the one hand, little insect-eating warm-blooded marsupials scamper through the woods, having started we scarcely yet know when or where, except that we learn from their structure that they probably branched off from the amphibians in quite a different line from the reptiles, and certainly gained a footing upon the earth in very early times. On the other hand, birds come upon the scene having teeth in their mouths, long-jointed tails, Ibid.  Chap. VII.") ?> and many other reptilian characters. We have indeed far more clue to the relationship of the birds than we have of the marsupials, for while we have these reptile-like birds, we have also the bird-like reptiles such as the little Compsognathus, which hopped on two feet, had a long neck, bird-like head and many other bird-like characters, though no wings or feathers.

The birds, however, even though reptile-like in their beginning, must soon have branched out on a completely new line. They for the first time among this group of animals, have the perfect four-chambered heart with its quick circulation and warm blood; while not only do they use their fore limbs for flying (for this some reptiles did before them), but they use them in quite a new fashion, putting forth a clothing of feathers of wondrous beauty and construction, and with true wings taking possession of the air, where from this time their history is one of continued success.

And now we have before us all the great groups of the backboned family—fish, amphibia, reptiles, birds and mammalia; but in what strange proportions! As the scenery of the Chalk Period with its fan-palms and pines comes before us, we find that the gristly fish, except the sharks and a few solitary types, are fast dying out, while the bony fish are but just beginning their career. The large amphibians are all gone long ago; they have run their race, enjoyed their life and finished their course, leaving only the small newts and salamanders, and later on the frogs and toads, to keep up the traditions of the race. The land-birds are still in their earliest stage; they have probably scarcely lost their lizard-like tail, and have not yet perfected their horny beak, but are only feeling their way as conquerors of the air. And as for the milk-givers, though we have met with them in small early forms, yet now for a time we lose sight of them again altogether.

It is the reptiles—the cold-blooded monster reptiles—which seem at this time to be carrying all before them. We find. them everywhere—in the water, with paddles for swimming; in the air, with membranes for flying; on the land hopping or running on their hind feet. From small creatures not bigger than two feet high, to huge monsters thirty feet in height, feeding on the tops of trees which our giraffes and elephants could not reach, they fill the land; while flesh-eating reptiles, quite their match in size and strength, prey upon them as lions and tigers do upon the grassfeeders now. This is no fancy picture, for in our museums, and especially in Professor Marsh's wonderful collection in Yale Museum in America, you may see the skeletons of these large reptiles, and build them up again in imagination as they stood in those ancient days when they looked down upon the primitive birds and tiny marsupials, little dreaming that their own race, then so powerful, would dwindle away, while these were to take possession in their stead.

And now in our series of changing scenes comes all at once that strange blank which we hope one day to fill up; and when we look again the large reptiles are gone, the birds are spreading far and wide, and we come upon those early and primitive forms of insect-eaters, gnawers, monkeys, grass-feeders, and large flesh-eaters, whose descendants, together with those of the earlier marsupials, are henceforward to spread over the earth. We need scarcely carry our pictures much farther. We have seen how, in these early times, the flesh-feeders and grass-feeders were far less perfectly fitted for their lives than they are now; how the horse has only gradually acquired his elegant form; the stag his branching antlers; and the cat tribe their scissor-like teeth, powerful jaws, and muscular limbs; while the same history of gradual improvement applies to nearly all the many forms of milk-givers.

But there is another kind of change which we must not forget, which has been going on all through this long history, namely, alterations in the level and shape of the continents and islands, as coasts have been worn away in some places and raised up or added to in others, so that different countries have been separated from or joined to each other. Thus Australia, now standing alone, with its curious animal life, must at some very distant time have been joined to the mainland of Asia, from which it received its low forms of milk-givers, and since then, having become separated from the great battlefield of the Eastern Continent, has been keeping for us, as it were in a natural isolated zoological garden, the strange primitive Platypus and Echidna, and Marsupials of all kinds and habits.

So too, Africa, no doubt for a long time cut off by a wide sea which prevented the larger and fiercer animals from entering it, harboured the large wingless ostriches, the gentle lemurs, the chattering monkeys, the scaly manis, and a whole host of insect-caters; while South America, also standing alone, gave the sloths and armadilloes, the ant-bears, opossums, monkeys, rheas, and a number of other forms, the chance of establishing themselves firmly before stronger enemies came to molest them. These are only a few striking examples which help us to see how, if we could only trace them out, there are reasons to be found why each animal or group of animals now lives where we find it, and has escaped destruction in one part of the world when it has altogether disappeared in others.

So, wandering hither and thither, the backboned family, and especially the milk-givers, took possession of plains and mountain ranges, of forests and valleys, of deserts and fertile regions. But still another question remains—How has it come to pass that large animals which once ranged all over Europe and Northern Asia,—mastodons, tusked tapirs, rhinoceroses, elephants, sabre-toothed tigers, cave-lions, and hippopotamuses in Europe, gigantic sloths and llamas in North America, and even many huge forms in South America, have either been entirely destroyed or are represented now only by scattered groups here and there in southern lands? What put an end to the "reign of the milk-givers," and why have they too diminished on the earth as the large fish, the large newts, and the large lizards did before them?

To answer this question we must take up out history just before the scene at the head of our last chapter, which the reader may have observed does not refer, as the others have done, to the animals in the chapter itself. Nevertheless it has its true place in the series, for it tells of a time when the great army of milk-givers had its difficulties and failures as well as all the other groups, only these came upon them not from other animals but from the influence of snow and ice.

For we know that gradually from the time of tropical Europe, when all the larger animals flourished in our country, a change was creeping very slowly and during long ages over the whole northern hemisphere. The climate grew colder and colder, the tropical plants and animals were driven back or died away, glaciers grew larger and snow deeper and more lasting, till large sheets of ice covered Norway and Sweden, the northern parts of Russia, Germany, England, Holland, and Belgium, and in America the whole of the country as far south as New York. Then was what geologists call the "Glacial Period;" and whether the whole country was buried in ice, or large separate glaciers and thick coverings of snow filled the land, in either case the animals, large and small, must have had a bad time of it.

True, there were probably warmer intervals in this intense cold, when the more southern animals came and went, for we find bones of the hippopotamus, hyena, and others buried between glacial beds in the south of England. But there is no doubt that at this time numbers of land animals must have perished, for in England alone, out of fifty-three known species which lived in warmer times, only twelve survived the great cold, while others were driven southwards never to return, and the descendants of others came back as new forms, only distantly related to those which had once covered the land.

Moreover, when the cold passed away and the country began again to be covered with oak and pine forests where animals might feed and flourish, we find that a new enemy had made his appearance. Man—active, thinking, tool-making man—had begun to take possession of the caves and holes of the rocks, making weapons out of large flints bound into handles of wood, and lighting fires by rubbing wood together, so as to protect himself from wild beasts and inclement weather.

In America and in England alike, as well as in Northern Africa, Asia Minor, and India, we know that man was living at this time among animals, many of them of species which have since become extinct, and with his rude weapons of jagged flint was conquering for himself a place in the world.

He must have had a hard struggle, for we find these flint implements now lying among the hones of hyamas, sabre-toothed tigers, cave-lions, cave-bears, rhinoceroses, elephants, and hippopotamuses, showing that it was in a land full of wild beasts that he had to make good his ground.

Many and fierce these conflicts must have been, for the wild beasts were still strong and numerous, and man had not yet the skill and weapons which he has since acquired. But rough and savage though he may have been, he had powers which made him superior to all around him. For already he knew how to make and use weapons to defend himself, and how to cover himself at least with skins as protection from cold and damp. Moreover, he had a brain which could devise and invent, a memory which enabled him to accumulate experience, and a strong power of sympathy which made him a highly social being, combining with others in the struggle for life.

And so from that early time till now, man, the last and greatest winner in life's race, has been taking possession of the earth. With more and more powerful weapons he has fought against the wild beasts in their native haunts; and by clearing away the large forests, cutting up the broad prairies and pastures, and cultivating the land, he has turned them out of their old feeding grounds, till now we must go to the centre of Africa, the wild parts of Asia, or the boundless forests of South America, to visit in their homes the large wild animals of the great army of milk-givers.

Since, therefore, these forms are growing rarer every century, and some of them, such as the Dodo, Epyornis, and Moa among birds, and the northern sea-cow or Rhytina among milk-givers, have already disappeared since the times of history, we must endeavour, before others are gone for ever, to study their structure and their habits. For we are fast learning that it is only by catching at these links in nature's chain that we can hope to unravel the history of life upon the earth.

At one time naturalists never even thought that there was anything to unravel, for they looked upon the animal kingdom as upon a building put together brick by brick, each in its place from the beginning. To them, therefore, the fact that a fish's fin, a bird's wing, a horse's leg, a man's arm and hand, and the dipper of a whale, were all somewhat akin, had no other meaning than that they seemed to have been formed upon the same plan; and when it became, certain that different kinds of animals had appeared from time to time upon the earth, the naturalists of fifty years ago could have no grander conception than that new creatures were separately made (they scarcely asked themselves how) and put into the world as they were wanted.

But a higher and better explanation was soon to be found, for there was growing up among us the greatest naturalist and thinker of our day, that patient lover and searcher after truth, Charles Darwin, whose genius and earnest labours opened our eyes gradually to a conception so deep, so true, and so grand, that side by side with it the idea of making an animal from time to time, as a sculptor makes a model of clay, seems too weak and paltry ever to have been attributed to an Almighty Power.

By means of the facts collected by our great countryman and the careful conclusions which he drew from them, we have learned to see that there has been a gradual unfolding of life upon the globe, just as a plant unfolds first the seed-leaves, then the stem, then the leaves, then the bud, the flower, and the fruit; so that though each part has its own beauties and its own appointed work, we cannot say that any stands alone, or could exist without the whole. Surely then Natural Ilistory acquires quite a new charm for us when we see that our task is to study among living forms, and among the remains of those that are gone, what has been the education and the development of all the different branches, so as to lead to the greatest amount of widespreading life upon the globe, each having its own duty to perform. With the great thought before us that every bone, every hair, every small peculiarity, every tint of colour, has its meaning, and has, or has had, its use in the life of each animal or those that have gone before it, a lifelong study even can never weary us in thus tracing out the working of Nature's laws, which are but the expression to us of the mind of the great Creator.

When we once realise that whether in attacking or avoiding an enemy it is in most cases a great advantage to all animals to be hidden from view, and that each creature has arrived at this advantage by slow inheritance, so that their colours often exactly answer the purpose, how wonderful becomes the gray tint of the slug, the imitation of bark in the wings of the buff-tip moth, the green and brown hues of the eatable caterpillars, the white coat of the polar bear, and the changing colour of the arctic fox, the ermine, and the ptarmigan, as winter comes on! And when, on the other hand, we find badly-tasting creatures such as ladybirds and some butterflies, or stinging animals like bees and wasps, having bright colours, because it is an actual advantage to them to be known and avoided, we see that in studying colour alone we might spend a lifetime learning how the winners in life's race are those best fitted for the circumstances under which they live, so that in ever-changing variety the most beautifully-adapted forms flourish and multiply.

Then if we turn to the skeleton and the less conspicuous framework of the body, the flippers of the whale, the manatee, or the seal, doing the work of a fish's fin and yet having the bones of a hand and arm, reveal a whole history to us when we have once learned the secret that in the attempt to increase and multiply no device is left untried by any group of animals, and so every possible advantage is turned to account.

Next, the wonderful instincts taught by long experience give us a whole field of study. We see how frogs and reptiles, and even higher animals such as marmots, squirrels, shrews and bears, escape the cold and scarcity of food in winter by burying themselves in mud, or in holes of trees or caves of the earth till spring returns; and while we find alligators burying themselves in cold weather in America, we find crocodiles, on the contrary, taking their sleep in the hot dry weather in Egypt because then is their time of scarcity.

Then we learn that the birds avoid this difficulty of change of climate in quite another manner. They with their power of flight have learned to migrate, sometimes for short distances, sometimes for more than a thousand miles, so that they bring up their young ones in the cool north in summer, when caterpillars and soft young insects are at hand for their prey, and lead them in the winter to the sunny south where food and shelter in green trees are always to be found. So long indeed has this instinct of migration been at work, that often we are quite baffled in trying to understand why they take this or that particular route for their flight, because probably, when the first stragglers chose it, even the areas of land and water were not divided as now, so that we must study the whole history of the changing geography of the earth to understand the yearly route of the swallow or the stork.

And last but not least, when we look upon the whole animal creation as the result of the long working out of nature's laws as laid down from the first by the Great Power of the Universe, what new pleasure we find in every sign of intelligence, affection, and devotion in the lower creatures! For these show that the difficulties and dangers of animal life have not only led to wonderfully-formed bodies, but also to higher and more sensitive natures; and that intelligence and love are often as useful weapons in fighting the battle of life as brute force and ferocity.

Even among the fish, which, as a rule, drop their eggs and leave them to their fate, we have exceptions in the nest-building sticklebacks and the snake-headed fish of Asia, which watch over and defend their fry till they are strong, in the pipe-fish where the fathers carry the young in a pouch, and in sharks which travel in pairs; while a pike has been known to watch for days at the spot where his mate was caught and taken away, and mackerel and herrings live in shoals and probably call to each other across the sea.

Among the other cold-blooded animals—the frogs, newts, and reptiles—it is true we find less show of feeling, but we must remember that these are only poor remaining fragments of large groups which have disappeared from the earth. Even among the amphibia however a tame toad will become attached to one person; while among reptiles, lizards are full of intelligence and affection, and snakes are well-known for their fondness for their owners. The case of the snake which died by its master's side when he fell down insensible, Animal Intelligence,  Romanes, p. 261") ?> if it can be relied upon, would show that even cold-blooded animals have tender hearts.

Yet these are all instances of affection of lower animals to man. We must turn to the birds, that group which has gone on increasing in strength and numbers down to our day, to find that tender devotion which watches over the helpless nursling, defends the young at the risk of life, nay, like the peewit with the dragging wing, will even run in the face of death to lure the cruel destroyer away from the hidden nest. Natural history teems with examples of birds faithful to each other and pining even till death for the loss of a mate; while many birds, such as rooks, starlings, wild geese, swans, and cranes, not only live in companies and exact obedience from their members, but even set sentinels to watch, the duties of the office being faithfully fulfilled.

Then again it is to the higher animals, those nearer to ourselves, that we must look for the truest affection, and the strongest proofs of that obedience and sympathy which lead them to unite and so become strong in the face of danger. Among the beasts of prey it is true that, except the wolves and jackals, none herd together, but family love is strong and true. No tiger is so dangerous as is the mother tigress if any one approaches her young ones, or the lioness whose cubs are attacked, and in our own homes we all know the tenderness and devotion of a cat to her kittens. Nevertheless, these animals have very little social feeling; theirs are the narrower virtues of courage and fidelity to home, and to the duty of providing food for wife and children. It is among the gentler vegetable-feeders,—the antelopes and gazelles, the buffaloes, horses, elephants, and monkeys,— that we find the instinct of herding together for protection, and with this the consciousness of the duty of obedience and fidelity to the herd and to one another.

It is easy to see how this was necessary to protect these feebler animals from the attacks of their ferocious neighbours, and also what an advantage they had when they had once learned to set sentinels who understood the duty of watching while others fed, as in the case of the chamois and seals, of obeying the signal of a leader like the young baboons on the march, or of putting the mothers and children in the centre for protection, as horses and buffaloes do.

And there is a real significance in this gradual education in duty to others which we must not overlook, for it shows that one of the laws of life which is as strong, if not stronger, than the law of force and selfishness, is that of mutual hdp and dependence.  Many good people have shrunk from the idea that we owe the beautiful diversity of animal life on our earth to the struggle for existence, or to the necessity that the best fitted should live, and the feeblest and least protected must die. They have felt that this makes life a cruelty, and the world a battlefield. This is true to a certain extent, for who will deny that in every life there is pain and suffering and struggle? But with this there is also love and gentleness, devotion and sacrifice for others, tender motherly and fatherly affection, true friendship, and a pleasure which consists in making others happy.

This we might have thought was a gift only to ourselves—an exception only found in the human race; now we see that it has been gradually developing throughout the whole animal world, and that the love of fathers and mothers for their young is one of the first and greatest weapons in fighting life's battle. So we learn that after all, the struggle is not entirely one of cruelty or ferocity, but that the higher the animal life becomes, the more important is family love and the sense of affection for others, so that at last a fierce beast of prey with strength and sharp tools at his command, is foiled in attacking a weak young calf, because the elders of the herd gather round him, and the destroyer is kept at bay.

Surely then we have here a proof that, after all, the highest and most successful education which Life has given her children to fit them for winning the race is that "unity is strength;" while the law of love and duty beginning with parent and child and the ties of home life, and developing into the mutual affection of social animals, has been throughout a golden thread, strengthened by constant use in contending with the fiercer and more lawless instincts.

So it becomes evident that the beautiful virtue of self-devotion, one of the highest man can practise, has its roots in the very existence of life upon the earth. It may appear dimly at first,—it may take a hard mechanical form in such lowly creatures as insects, where we saw the bees and ants sacrificing all tender feelings to the good of the community. But in the backboned family it exists from the very first as the tender love of mother for child, of the father for his mate and her young ones, and so upwards to the defence of the tender ones of the herd by the strong and well-armed elders, till it has found its highest development in man himself.

Thus we arrive at the greatest and most important lesson that the study of nature affords us. It is interesting, most interesting, to trace the gradual evolution of numberless different forms, and see how each has become fitted for the life it has to live. It gives us courage to struggle on under difficulties when we see how patiently the lower animals meet the dangers and anxieties of their lives, and conquer or die in the struggle for existence. But far beyond all these is the great moral lesson taught at every step in the history of the development of the animal world, that amidst toil and suffering, struggle and death, the supreme law of life is the law of SELF-DEVOTION AND LOVE.