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WINNERS IN LIFE’S RACE

Frontispiece. Luminous Fish of the Deep Sea. (For description see [Footnote 25], and [List of Illustrations].)

THE
WINNERS IN LIFE’S RACE

OR THE
GREAT BACKBONED FAMILY.

BY
ARABELLA B. BUCKLEY,
AUTHOR OF “THE FAIRYLAND OF SCIENCE,” ETC.

NEW YORK:
D. APPLETON AND COMPANY,
1, 3, AND 5 BOND STREET,
1883.

PREFACE.

Although the present volume, as giving an account of the vertebrate animals, is a natural sequel to, and completion of, my former book, Life and her Children, which treated of invertebrates, yet it is a more independent work, both in plan and execution, than I had at first contemplated.

This arises from the nature of the subject. The structure and habits of the lower forms of life are sufficiently simple to be treated almost without reference to geological history. When, however, I began to sketch out the lives and structure of the vertebrate animals, which are so closely interlinked one with another and yet so sharply separated into groups, I soon found that I must carry my readers into the past in order to give any intelligible account of the present.

I have therefore endeavoured to describe graphically the early history of the backboned animals, so far as it is yet known to us, keeping strictly to such broad facts as ought in these days to be familiar to every child and ordinarily well-educated person, if they are to have any true conception of Natural History. At the same time I have dwelt as fully as space would allow, upon the lives of such modern animals as best illustrate the present divisions of the vertebrates upon the earth; my object being rather to follow the tide of life, and sketch in broad outline how structure and habit have gone hand-in-hand in filling every available space with living beings, than to multiply descriptions of the various species. If my younger readers will try and become familiar with the types selected, either alive in zoological gardens or preserved in good museums, they will, I hope, acquire a very fair idea of the main branches of the Backboned Family.[1]

In order to treat so vast a subject simply and within narrow limits, it has often been necessary to pass lightly over new and startling facts. I trust, however, it will not be inferred that such passages have been lightly or carelessly written, for in all cases I have sought, and most gratefully acknowledge, the assistance of some of our best authorities; and I have endeavoured that what little is said upon difficult subjects shall be a true foundation for wider knowledge in the future.

Among the many friends who have rendered me valuable assistance, I cannot sufficiently express my obligations to Professor W. Kitchen Parker for his unwearying kindness in explaining obscure points of anatomical structure, and to my friends Mr. Alfred R. Wallace, Professor A. C. Haddon of Dublin, and Mr. Garnett of the British Museum, for constant suggestion and encouragement. I am also indebted to Mr. J. P. Anderson of the British Museum for aid in the arrangement of the Index.

The geological restorations given as picture-headings (some of which are here attempted, I believe, for the first time) have been most carefully considered, though the exact forms of such strange and extinct animals must necessarily be somewhat conjectural. My thanks are due to the artist, Mr. Carreras, jun., for the patience and care with which he has followed my instructions regarding them, and also to Mr. Smit for his masterly execution of the [frontispiece].[2]

I have been asked why, in this and the former work, I have not given genealogical tables to help the reader to follow the relations of the various groups. My reason is, that it is impossible to construct tables of this kind without giving a false idea of the fixity of natural divisions and of the extent of our knowledge. To men of science, who know how provisional such tables are, they have a certain value, but they would be positively harmful in a work of this kind, which will have fully accomplished its purpose if it only awakens in young minds a sense of the wonderful interweaving of life upon the earth, and a desire to trace out the ever-continuous action of the great Creator in the development of living beings.

Arabella B. Buckley.

London, September 1882.

CONTENTS.

LIST OF ILLUSTRATIONS.

Picture-Headings described under “[Contents].”

THE GREAT BACKBONED FAMILY

CHAPTER I.
THE THRESHOLD OF BACKBONED LIFE.

Life, life, everywhere life! This was the cry with which we began our history of the lowest forms of Life’s children, and although we did not then pass on to the higher animals, is it not true that before we reached the end we were overwhelmed with the innumerable forms of living beings? The microscopic lime and flint builders, the spreading sponges, the hydras, anemones, corals, and jelly-fish filled the waters; the star-fish, sea-urchins, crabs, and lobsters crowded the shores; the oysters, whelks, and periwinkles, with their hundreds of companions, struggled for their existence between the tides; while in the open sea thousands of crustaceans and molluscs, with cuttle-fish and terribly-armed calamaries, roamed in search of food. Upon the land the snails and slugs devoured the green foliage, while the vast army of insects filled every nook and cranny in the water, on the land, or in the air. Yes! even among these lower forms we found creatures enough to stock the world over and over again with abundant life, so that even if the octopus had remained the monarch of the sea, and the tiny ant the most intelligent ruler on the land, there would have been no barren space, no uninhabited tracts, except those burning deserts and frozen peaks where life can scarcely exist.

Yet though the world might have been full of these creatures, they would not have been able to make the fullest use of it, for all animal life would have been comparatively insignificant and feeble, each creature moving within a very narrow range, and having but small powers of enjoyment or activity. With the exception of the insects, by far the greater number would, during their whole lives, never wander more than a few yards from one spot, while, though the locust and the butterfly make long journeys, yet the bees and beetles, dragon-flies and ants, would not cross many miles of ground in several generations.

What a curious world that would have been in which the stag-beetle and the atlas-moth could boast of being the largest land animals, except where perhaps some monster land snail might bear them company; while cuttle-fish and calamaries would have been the rulers of the sea, and the crabs and lobsters of the shores! A strangely silent world too. The grasshopper’s chirp as he rubbed his wings together, the hum of the bee, the click of the sharp jaws of the grub of the stag-beetle, eating away the trunk of some old oak tree, would have been among the loudest sounds to be heard; and though there would have been plenty of marvellous beauty among the metallic-winged beetles, the butterflies, and the delicate forms of the sea, yet amid all this lovely life we should seek in vain for any intelligent faces,—for what expression could there be in the fixed and many-windowed eye of the ant or beetle, or in the stony face of the crab?

These lower forms, however, were not destined to have all the world to themselves, for in ages, so long ago that we cannot reckon them, another division of Life’s children had begun to exist which possessed advantages giving it the power to press forward far beyond the star-fish, the octopus, or the insect. This was the Backboned division, to which belong the fish of our seas and rivers; the frogs and toads, snakes, lizards, crocodiles, and tortoises; the birds of all kinds and sizes; the kangaroos; the rats, pigs, elephants, lions, whales, seals, and monkeys.

Is it possible, then, that all these widely different creatures, which are fitted to live not only in all parts of the land, but also in the air above, and the seas and rivers below, and which are, in fact, all those popularly known as “animals,” only form one division out of seven in the real animal kingdom?

Can it be true that while the chalk-builders have one division all to themselves, the sponges forming a transition group, the lasso-throwers another division, the prickly-skinned animals a third, the mollusca a fourth, the worms a fifth, and the insects a sixth, yet the innumerable kinds of birds and beasts, reptiles and fishes, are all sufficiently alike to be included in one single division—the seventh? It seems at first as if this arrangement must be unequal and unnatural; but let us go back for a moment to the beginning, and we shall see that it is not only true, but that quite a new interest attaches to the higher animals when we learn how wonderfully life has built up so many different forms upon one simple plan.

Starting, then, with the first glimmerings of life, we find the minute lime and flint builders, without any parts, making the utmost of their little lives, filling the depths of the sea, and wandering in pools and puddles on the land; acting, in fact, as scavengers for such matter as is left them by other animals. But here their power ends; to take a higher stand in life a more complicated creature is needed, and the sponge-animal, with its two kinds of cells and its numerous eggs, is the next step leading on to the curious division of lasso-throwers. These, in their turn, do their utmost to spread and vary in a hundred different ways. Possessed of a good stomach, of nerves, muscles, powerful weapons, and means for producing eggs and young ones, they fill the waters as hydras, sea-firs, jelly-fish, anemones, and corals. But here they too find their limit, and, without advancing any farther, continue to flourish in their lowly fashion. Meanwhile the tide of life is flowing on in two other channels, striving ever onwards and upwards. On the one hand, the walking star-fish and sea-urchin push forward into active life under the sea, forming, with their relations, a strange and motley group, but one which could scarcely be moulded into higher and more intelligent beings. On the other hand, the oyster and his comrades, with their curious mantle-working secret protect their soft body within by a shelly covering, and by degrees we arrive at the large army of mollusca, headed by the intelligent cuttle-fish. And here this division too ceases to advance. The soft body in its shelly home does not lend itself to wide and great changes, and it was left for other channels to carry farther the swelling tide of life. These take their rise in the lowly, insignificant division of the worms, which may, perhaps, have had something to do with the earliest forms even of the star-fish and mollusca, but which soon shot upwards, on the one hand along a line of its own, while, on the other, we have seen[3] how, in its many-ringed segments, each bearing its leg-like bristles and its line of nerve-telegraph, the worm foreshadowed the insects and crustacea, or the jointed-footed animals of sea and land, forming the sixth division.

Here surely at last we must have reached animals which will answer any purposes life can wish to fulfil. We find among them numberless different forms, spreading far and wide through the water and over the land, and it would seem as if the sturdy crab and fighting lobster need fear no rival in the sea, while the intelligent bee and ant were equal to any emergency on dry ground. But here the tide of life met with another check. It must be remembered that the jointed-footed animals, whether belonging to land or water, carry their solid part or skeleton outside them; their body itself is soft, and cased in armour which has to be cast off and formed afresh from time to time as they grow. For this reason they are like men in armour, heavily weighted as soon as they grow to any size, while the body within cannot become so firmly and well knit together as if all the parts, hard and soft, were able to grow and enlarge in common. And so we find that large-sized armour-covered animals, such as gigantic crabs and lobsters, are lumbering unwieldy creatures, in spite of their strength, while the nimble intelligent insects, such as the ant and bee, are comparatively small and delicate.

It would be curious to try and guess what might have happened if the ant could have grown as large as man, and built houses and cities, and wandered over wide spaces instead of being restricted to her ant-hills for a home, and few acres for her kingdom; but she too has found the limit of her powers in the impossibility of becoming a large and powerful creature. Thus it remained for Life to find yet another channel to reach its highest point, by devising a plan of structure in which the solid skeleton should be—not a burden for the soft body to carry, as in the sea-urchins, snails, insects, and crabs—but an actual support to the whole creature, growing with it and forming a framework for all its different parts.

This plan is that of the backboned animals. They alone, of all Life’s children, have a skeleton within their bodies embedded in the muscular flesh, and formed, not of mere hardened, dead matter, but of bones which have blood-vessels and nerves running through them, so that they grow as the body grows, and strengthen with its strength. This is a very different thing from a mere outer casing round a soft body, for it is clear that an animal with a living growing skeleton can go on increasing in size and strength, and its framework will grow with the limbs in any direction most useful to it.

Here, then, we have one of the secrets why the backboned animals have been able to press forward and vary in so many different ways; and especially useful to them has been that gristly cord stretching along the back, which by degrees has become hardened and jointed, so as to form that wonderful piece of mechanism, the backbone.

Look at any active fish darting through the water by sharp strokes of its tail,—watch the curved form of a snake as it glides through the grass, or the graceful swan bending his neck as he sails over the lake,—and you will see how easily and smoothly the joints of the backbone must move one upon the other. Then turn to the stag, and note how jauntily he carries his heavy antlers; look at the powerful frame of the lion, watch an antelope leap, or a tiger bound against the bars of his cage, and you will acknowledge how powerful this bony column must be which forms the chief support of the body, and carries those massive heads and those strong and lusty limbs.

Nor is it only by its flexibility and strength that this jointed column is such an advantage to its possessors; the backbone has a special part to play as the protector of a most valuable and delicate part of the body. We have already learnt in Life and her Children to understand the importance of the nerve-telegraph to animals in the struggle for life. We found its feeble beginnings in the jelly-fish and the star-fish; we saw it spreading out over the body of the snail; we traced it forming a line of knots in the worm, with head-stations round the neck, which became more and more powerful in the intelligent insects. But in all these creatures the stations of nerve-matter from which the nerves run out into the body are merely embedded in the soft flesh, and have no special protection, with the exception of a gristly covering in the cuttle-fish. We ourselves, and other backboned animals, have unprotected nerve-stations like these in the throat, the stomach, and the heart, and cavity of the body. But we have something else besides, for very early in the history of the backboned animals the gristly cord along the back began to form a protecting sheath round the line of nerve-stations stretching from the head to the tail, so that this special nerve-telegraph was safely shut in and protected all along its course.

A careful examination of the backbone of any fish, after the flesh has been cleared off, will show that on the top of each joint (or vertebra) of the backbone is a ring or arch of bone; and when all the joints are fastened together, these rings form a hollow tube or canal, in which lies that long line of nervous matter called the spinal cord, which thus passes, well protected, all along the body, till, when it reaches the head, it becomes a large mass shut safely in a strong box, the skull, where it forms the brain.

Here, then, besides the unprotected nerve-stations, we have a much more perfect nerve-battery, the spinal cord, carried in a special sheath formed of the arches of the backbone, which is at once strong and yielding, so that the delicate telegraph is safe from all ordinary danger. Now when we remember how important the nerves are,—how they are the very machinery by which intelligence works, so that without them the eye could not see, the ear hear, nor the animal have any knowledge of what is going on around it,—we see at once that here was an additional power which might be most valuable to the backboned division. And so it has proved, for slowly but surely through the different classes of fish, amphibia (frogs and newts), reptiles, birds, and mammalia, this cord, especially that larger portion of it forming the brain, has been increasing in vigour, strength, and activity, till it has become the wonderful instrument of thought in man himself.

We see, then, that our interest in the backboned or vertebrate animals will be of a different kind from that which we found in the boneless or invertebrate ones. There we watched Life trying different plans, each successful in its way, but none broad enough or pliable enough to produce animals fitted to take the lead all over the world. Now we are going to trace how, from a more promising starting-point, a number of such different forms as fish, reptile, bird, and four-footed beast, have gradually arisen and taken possession of the land, the water, and the air, pressing forward in the race for life far beyond all other divisions of animal life.

On the one hand, these forms are all linked together by the fact that they have a backbone protecting a nerve-battery, and that they have never more than two pair of limbs; while every new discovery shows how closely they are all related to each other. On the other hand, they have made use of this backbone, and the skeleton it carries, in such very different ways that out of the same bones and the same general plan unlike creatures have been built up, such as we should never think of classing together if we did not study their structure.

What the lives of these creatures are, and what they have been in past time, we must now try to understand. And first we shall naturally ask, Where did the backboned animals begin? Where should they begin but in the water, where we found all the other divisions making their first start, where food is so freely brought by passing currents, where movement from place to place is much easier, and where there are no such rapid changes as there are on the land from dry to damp, from heat to cold, or from bright leafy summer, with plenty of food, to cold cheerless winter, when starvation often stares animals in the face?

It is not easy to be sure exactly how the backboned animals began, but the best clue we have to the mystery is found in a little half-transparent creature about two inches long, which is still to be found living upon our coast. This small insignificant animal is called the “Lancelet,”[4] because it is shaped something like the head of a lance, and it is in many ways so imperfect that naturalists believe it to be a degraded form, like the acorn-barnacle; that is to say, that it has probably lost some of the parts which its ancestors once possessed. But in any case it is the most simple backboned animal we have, and shows us how the first feeble forms may have lived.

Fig. 1.

The Lancelet, the lowest known fish-like form.

m, mouth. e, eye-spot. f, fin. r, rod or notochord, the first faint indication of a backbone. nv, nerve cord. g, gills. h, hole out of which water passes from the gills. v, vent for refuse of food.

Flitting about in the water near the shore, eating the minute creatures which come in his way, this small fish-like animal is so colourless, and works his way down in the sand so fast at the slightest alarm, that few people ever see him, and when they do are far more likely to take him, as the naturalist Pallas did, for an imperfect snail than a vertebrate animal. He has no head, and it is only by his open mouth (m), surrounded by lashes with which he drives in the microscopic animals, that you can tell where his head ought to be. Two little spots (e) above his mouth are his feeble eyes, and one little pit (n) with a nerve running to it is all he has to smell with. He has no pairs of fins such as we find in most fishes, but only a delicate flap (f) on his back and round his tail; neither has he any true breathing-gills, but he gulps in water at his mouth, and passes it through slits in his throat into a kind of chamber, and from there out at a hole (h) below. Lastly, he has no true heart, and it is only by the throbbing of the veins themselves that his colourless blood is sent along the bars between the slits, so that it takes up air out of the water as it passes.

But where is his backbone? Truly it is only by courtesy that we can call him a backboned animal, for all he has is a cord of gristle, r r, pointed at both ends, which stretches all along the middle of his body above his long narrow stomach, while above this again is another cord containing his nerve-telegraph (nv.) All other backboned animals that we know of have brains; but, as we have seen, he has no head, and his nerve-cord has only a slight bulge just before it comes to a point above his mouth. Now when the higher backboned animals are only just beginning to form out of the egg, their backbone (which afterwards becomes hard and jointed) is just like this gristly rod or notochord (r r) of the lancelet, with the spinal cord (nv) lying above it; so that this lowest backboned animal lives all his life in that simple state out of which the higher animals very soon grow.

This imperfect little lancelet has a great interest for us, because of his extremely simple structure and the slits in his throat through which he breathes. You will remember that when we spoke of the elastic-ringed animals in Life and her Children, we found that the free worms were very active sensitive creatures, whose bodies were made up of segments, each with a double pair of appendages; the whole being strung together, as it were, upon a feeding tube and a line of nerve-telegraph, but without any backbone. Now among these worms we find many curious varieties; some have the nerve-lines at the sides instead of below, and one sea-worm, instead of breathing by outside gills like the others, has slits in its throat through which the water can pass, and so its blood is purified.

You may ask, What this has to do with backboned animals? Nothing directly, but these odd worms are like fingerposts in a deserted and grass-grown country, showing where roads may once have been. The lancelet, like the worm, has a line of nerve-telegraph and a feeding-tube, only with him the nerve-telegraph lies above instead of below. He has also slits in his throat for breathing, only they are covered by a pouch. Thus he is so different from the worms that we cannot call them relations; but at the same time he is in many ways so like, that we ask ourselves whether his ancestors and those of the worms may not have been relations.

Fig. 2.

Diagram of the growth of a Sea-Squirt or Ascidian.

A a, Young free swimming stage. a², Intermediate stage when first settling down. B b, Full-grown Sea-Squirt.

m, mouth; e, hollow brain with eye; g, gill slits; h, heart; r, rod of gristle in free swimming form; nv, nerve cord in same; t, tail in process of absorption in intermediate form.

But you will say he is quite different in having a gristly cord. True—but we shall find that even this does not give us a sharp line of division. By looking carefully upon the seaweed and rocks just beyond low tide, we may often find some curious small creatures upon them, called Sea-Squirts or Ascidians (B, [Fig. 2]).[5] These creatures are shaped very like double-necked bottles, and they stand fixed to the rock with their necks stretching up into the water. Through one neck (m) they take water in, and after filtering it through a kind of net so as to catch the microscopic animals in it and taking the air out of it, they send it out through the other neck, thus gaining the name of sea-squirts. So far, they are certainly boneless animals. But they were not always stationary, as you see them fixed to the rock. In their babyhood they were tiny swimming creatures with tails (A and a), and in the tail was a gristly cord (r), with a nerve cord (nv) above it, like those we find in the lancelet. For this reason we were obliged to pass them by among the lower forms of life, because, having this cord (r), they did not truly belong to the animals without backbones; and yet now we can scarcely admit them here, because when they are grown up they are not backboned animals. They belong, in fact, to a kind of “No Man’s Land,” behaving in many ways like the lancelet when they are young, as if they had once tried to be backboned; and yet they fall back as they grow up into invertebrate animals.

So we begin to see that there may have been a time when backbones had not gained quite a firm footing, and our lancelet, with his friends the sea-squirts, seems to lie very near the threshold of backbone life.

And now that we are once started fairly on our road, let us turn aside before beginning the history of the great fish-world and pay a visit to a little creature whose name, at least, we all know well, and which stands half-way between the lancelet and the true fish. This is the Lamprey, represented by two kinds; the large Sea-Lamprey, caught by the fishermen for bait as it wanders up the rivers to lay its eggs, and the true River-Lamprey or Lampern, which rarely visits the sea.

What country boy is there who has not hunted in the mud of the rivers or streams for these bright-eyed eel-like fish, with no fins, and a fringe on back and tail? If you feel about for them in the mud they will often come up clinging to your hand with their round sucker-mouth, while the water trickles out of the seven little holes on each side of their heads. The small river-lampreys do not hurt in the least as they cling, though the inside of their mouth is filled with small horny teeth. But the larger sea-lamprey uses these teeth as sharp weapons, scraping off the flesh of fish for food as he clings to them.

Fig. 3.

Figure of a full-grown Lamprey[6] and of the young Lamprey, formerly called Ammocœtes.

Showing the seven holes through which it takes in water to breathe.

These Lampreys, together with some strange creatures, the “Hags” or “Borers,”[7] belong to quite a peculiar family, called the Round-mouthed fishes,[8] and, though they stand much higher in the world than the lancelet, yet they are very different from true fish. Like the lancelet they have only a gristly cord for a backbone, but this cord has begun to form arches over the nerve battery, and it swells out at the end into a gristly skull covering a true brain. They have clear bright eyes too, and ears, which if not very sharp, are at least such as they can hear with; they have only one nostril, and their mouth is both curious and useful. When it is shut it looks like a straight slit, but when it is open it forms a round sucker with a border of gristle, and this sucker clings firmly to anything against which it is pressed, so that a stone weighing twelve pounds has been lifted by taking a lamprey by the tail. Inside the mouth the palate and tongue are covered with small horny teeth, and these are the lamprey’s weapons.

Salmon have been caught in the rivers with lampreys hanging to them, and where the mouth has been the salmon’s flesh is rasped away, though he does not seem much to mind it.

Lastly, the lamprey has a peculiar way of breathing. He has seven little holes on each side of his head, reminding us of the slits in the worm’s throat and those hidden under the skin of the lancelet, and behind these holes are seven little pouches lined with blood-vessels, which take up air out of the water. These pouches are all separate, but they open by one tube into his throat. When the lamprey is swimming about it is possible that he may gulp water in at his mouth and send it out at the slits. But when he is clinging to anything he certainly sends water both in and out at the slits, so that he can still breathe, though his mouth is otherwise occupied.

And now, what is the history of his life? For three years he lives as a stupid little creature, with a toothless mouth surrounded by feelers, and tiny eyes covered over with skin, and he is so unlike a lamprey that for a long time naturalists thought he was a different animal and called him Ammocœtes. But at the end of the three years he changes his shape, and then he is as bright and intelligent as he was dull and heavy before. His one thought is to find a mate and help her to cover up her eggs. To do this a number of lampreys find their way up the river and set to work. Sometimes one pair go alone, sometimes several together, and they twirl round and round so as to make a hole in the sand, lifting even heavy stones out with their mouths if they come in the way. Then they shed the spawn into the hole, where it is soon covered with sand and mud, to lie till it is safely hatched, and when this is done the marine lampreys swim out to sea to feed on the numberless small creatures in it, or to fasten upon some unfortunate fish.

But there are round-mouthed fishes even more greedy than these. It is not only among the lower forms of life that some creatures, such as worms, which are driven from the outer world, find a refuge inside other animals. But here again we meet with the same thing, for those relations of the lampreys, the hags or borers, which we mentioned above, use their sharp teeth to bore their way into other fish so as to feed upon them. These greedy little creatures actually drill holes in the flesh of the cod or haddock and other fish, and eat out the inside of their bodies, so that a haddock has been found with nothing but the skin and skeleton remaining while six fat hags lay comfortably inside.

So the round-mouthed fishes, feeble though they are, hold their own in the world. How long ago it is since they first began the battle of life we shall probably never know for certain; but if some little horny teeth[9] found in very ancient rocks belong to their ancestors, they were most likely among the first backboned animals on our globe. At any rate they are very interesting to us now, for they have wandered far away from the true fishes, and give us a glimpse of some of the strange by-paths which the backboned animals have followed in order to win for themselves a place in the race for life.

THE ANCIENT FISH & THEIR HUGE RIVAL

Note.—For description of the Picture-Headings see the [Table of Contents].

CHAPTER II.
HOW THE QUAINT OLD FISHES OF ANCIENT TIMES HAVE LIVED ON INTO OUR DAY.

Who is there among my readers who wishes to understand the pleasures, the difficulties, and the secrets of fish life? Whoever he may be he must not be content with merely looking down into the water, as one peeps into a looking-glass, or he may, perchance, only see there the reflection of his own thoughts and ideas, and learn very little of how the fishes really feel and live. No! if we want really to understand fish-life we must forget for a time that we are land and air-breathing animals, and must plunge in imagination into the cool river or the open sea, and wander about as if the water were our true home. For the fish know no more about our land-world than we do about their beautiful ocean-home. To them the water is the beginning and end of everything, and if they come to the top every now and then for a short air-bath they return very quickly for fear of being suffocated. Their great kingdom is the sea—the deep-sea, where strange phosphorescent fish live, lying in the dark mysterious valleys where even sharks and sword-fish rarely venture;—the open sea, where they roam over wide plains when the ocean-bottom makes a fine feeding-ground, or where they thread their way through forests of seaweed, while others swim nearer the surface and come up to bask in the sun or rest on a bank of floating weed;—and the shallow sea, where they come to lay their eggs and bring up their young ones, and out of which many of them venture up the mouths of rivers, while others have learnt to remain in them and make the fresh water their home.

The tender little minnows that bask in the sunny shallows of the river have never even seen the sea, their ancestors left it so long long ago; yet to them, too, water is life and breath and everything. The green meadow through which the river flows is just the border of their world and nothing more, and the air is boundless space, which they never visit except for a moment to snap at a tiny fly, or when they jump up to escape the jaws of some bigger fish. Every one knows the minnow, and we cannot do better than take him as our type of a fish in order to understand how they live and move and breathe. Go and lie down quietly some day by the side of the clear pebbly shallows of some swiftly-flowing river where these delicate little fish are to be seen; but keep very still, for the slightest movement is instantly detected. There they lie

“Staying their wavy bodies ’gainst the streams

To taste the luxury of sunny beams

Tempered with coolness. How they ever wrestle

With their own sweet delight, and ever nestle

Their silver bellies on the pebbly sand!

If you but scantily hold out the hand,

That very instant not one will remain;

But turn your eye and they are there again.”

Fig. 4.

The structure of the Minnow and the living fish.

A n, nose-pit; e, eye-nerve; ea, ear-nerve; g, gills; h, heart; t, food-tube; s, stomach; k, kidney; v, vent; da, dorsal-artery. a, air-bladder; b, backbone; nv, nerve cord or spinal cord.

B n, nose; gc, gill cover; af, arm-fin; lf, leg-fins; sf, single fins; ms, mucous scales.

If you can be motionless and not frighten them you may see a good deal, for while some are dashing to and fro, others, with just a lazy wave of the tail and the tiny fins, will loiter along the sides of the stream, where you may examine their half-transparent bodies. Look first at one of the larger ones, whose parts are easily seen, and notice how every moment he gulps with his mouth, while at the same time a little scaly cover (g c, B, [Fig. 4]) on each side of the head, just behind the eye, opens and closes, showing a red streak within. This is how he breathes. He takes in water at his mouth, and instead of swallowing it passes it through some bony toothed slits (g, A [Fig. 4]) in his throat into a little chamber under that scaly cover; in that chamber, fastened to the bony slits, are a number of folds of flesh full of blood-vessels, which take up the air out of the water; and when this is done he closes the toothed slits and so forces the bad water out from under the scaly cover back into the river again. It is the little heart (h), lying just behind the gills, which pumps the blood into the channels in those red folds, and as it keeps sending more and more, that which is freshened is forced on and flows through the rest of the body. It goes on its way slowly, because a fish’s heart has only two chambers instead of four as we have, and these are both employed in pumping the blood into the gills, so that for the rest of the journey through the body it has no further help. For this reason, and also because taking up air out of the water is a slow matter, fish are cold-blooded animals, not much warmer than the water in which they are.

But while our minnow breathes he also swims. He is hardly still for a moment, even though he may give only the tiniest wave with his tail and fins, and he slips through the water with great ease, because his body is narrow and tapers more or less at both ends like a boat. At times, too, if he is frightened, he bounds with one lash of his tail right across the river; and if you look at one of the small transparent minnows you will see that he has power to do this because his real body, composed of his head and gills, heart and stomach, ends at half his length (see [Fig. 4], A), and all the rest is tail, made of backbone and strong muscles, with which he can strike firmly. This is one great secret of fish strength, that nearly one half of their body is an implement for driving them through the water and guiding them on their way. Still although the tail is his chief propeller, our minnow could not keep his balance at all if it were not for his arm and leg fins. You will notice that it is the pair of front fins (af) which move most, while the under ones (lf) are pressed together and almost still. Besides these two pairs he has three single fins (sf), one under his body, one large V-shaped one at the end of his tail, and another single one upon his back. All these different fins help to guide him on his way; but while the single ones are fish-fringes, as it were, like the fringe round the lancelet’s body, only split into several parts, the two pair under his body are real limbs, answering to the two pair of limbs we find in all backboned animals, whether they are all four fins, or all four legs, or wings and legs, or arms and legs.

These paired wings are most important to the minnow, for, if his arm-fins were cut off, his head would go down at once, or, if one of them was gone he would fall on one side, while, if he had lost his fins altogether, he would float upside down as a dead fish does, for his back is the heaviest part of his body. It is worth while to watch how cannily he uses them. If you cannot see him in the stream you can do so quite well in a little glass bowl, as I have him before me now. If he wants to go to the left he strikes to the right with his tail and moves his right arm-fin, closing down the left, or if he wants to go to the right he does just the opposite; though often it is enough to strike with his tail and single fin below, and then he uses both the front fins at once to press forward.

But how does he manage to float so quietly in the water, almost without moving his fins? If your minnow is young and transparent you will be able to answer this question by looking at his body just under his backbone, and between it and his stomach. There you will see a long, narrow, silvery tube (a, [Fig. 4]) drawn together in the middle so that the front half near his eyes looks like a large globule of quicksilver, and the hinder half like a tiny silver sausage. This silvery tube is a bladder full of gas, chiefly nitrogen, and is called the air-bladder. Its use has long been a great puzzle to naturalists, and even now there is much to be learnt about it. But one thing is certain, and that is, that fish such as sharks, rays, and soles, which have no air-bladders, are always heavier than the water, and must make a swimming effort to prevent sinking. Fish, on the contrary, which have air-bladders, can always find some one depth in the water at which they can remain without falling or rising, and we shall see later on that this has a great deal to do with the different depths at which certain fish live. Our minnow floats naturally not far from the top, and, even if he were forced to live farther down, the gas in his bladder would accommodate itself after a few hours if the change was not too great, and he would float comfortably again.

And now the question remains, What intelligence has the minnow to guide him in all these movements? If you will keep minnows and feed them yourself every day you will soon find out that they see, smell, and feel very quickly, though their hearing and taste are not so acute. They are cunning enough too, and will often steal a march upon heavier and slower fish, snatching delicate morsels from under their very noses. For our little minnow can boast of a real brain, though it is a small one in comparison with his size. All along, above his delicate backbone, the thread of nerve telegraph (nv, [Fig. 4]) runs under protecting bony arches, and sends out nerves on all sides to the body and fins; and when it reaches the head it swells out, under a bony covering, into a small brain, sending out two nerves to the ears (ea), in front of which is a second part, with two nerve-stations (e) for the eyes, and beyond this a third part, with two more for the nostrils, besides others which go to the face. Look on the top of a minnow’s head and you will see two little raised bumps (n). These are its nostrils, but remember they have nothing to do with breathing; they have not even any connection with the mouth, but are simply little covered cups, each with two openings for water to flow in and out, and they are lined with nerves, which, tickled by good or bad scents in the water, carry to the brain a warning, or a promise of good things.

Such, then, is our little minnow, and the different parts of his body are supported by a slender bony-jointed backbone, with ribs growing from it, supporting a strong mass of flesh on his sides. He is a delicate tender creature, but is protected and buoyed up by the water, out of which he never attempts to go. The thin, rounded, transparent scales which cover his body, growing out of little pockets in his skin, just like our nails on the tips of our fingers, protect this skin from the water and from rough treatment; while they themselves are kept soft by a slimy fluid which oozes out from under them, and especially through the dark line of larger scales (ms. [Fig. 4]) running along his body.

* * * * *

Now the minnow is a bony fish, and from it we can learn very fairly what bony or modern fishes are like. But these fish were not the founders of the race; long before they existed there was another very ancient group of fishes in the world, which were in many ways more like the lancelet and the lamprey; and to find such descendants of this ancient group as are now living we must leave the river and find our way into the open sea.

If we do this, we shall travel not many miles from the shore in summer, wending our way through shrimps and lobsters, gurnards, cod-fish, soles, and turbot, before we may chance to come across a great Blue shark, with his slaty-coloured back and fins, swimming heavily but strongly through the water, and turning sharply from time to time to seize a passing fish, his white belly gleaming like a flash of light as it comes uppermost, and then disappearing again in the dark water.

“His jaws horrific, armed with threefold fate,

Here dwells the direful shark.”

Or if this formidable monster does not happen to be in the neighbourhood another kind, the Dogfish, may cross our path, perhaps the Smooth hound, crushing the crabs and lobsters in his tooth-lined mouth, or the Rough hound fastening her purse-like egg to the seaweed by its long string-like tendrils; or, farther out still, we may perhaps see the Thresher shark lashing the water with his long pointed tail, to drive the frightened fish within his reach; or, if we were off the west coast of Ireland, the huge but harmless Basking shark might be floating calmly by in the warm sunshine. For sharks travel all over the ocean, and though they prefer the warm seas, where they sometimes reach a size of forty feet long and more, yet many of the smaller kinds visit our coasts in summer.

Fig. 5.

The Blue Shark[10] (from Brehm).

To show the five slits in the neck, the uneven tail, and the mouth opening under the pointed snout.

Now, at first sight we might imagine that these huge monsters, the terrible tyrants of the sea, must be the last and most finished production of fish-life; but if we look a little closer we shall be undeceived. Examine a shark in any good museum, and you cannot fail to be struck with his strange form. Look first at his tub-like body, so different from the narrow wedge-shape of the minnow, the herring, or the salmon. Then observe his skin, which is either tough, more like that of other animals, or thickly covered with short blunt teeth, which sometimes, especially in front of the fins, become long pointed spines. There is no trace of fish-scales here. Look at his mouth opening under his pointed snout, and you will see that as the skin turns over the lips these blunt teeth line his mouth, so that he has several rows fit for biting, and they are sometimes so formidable that they can cut a man in two at one snap. Then look more especially at the sides of his throat, and there you will see on each side from five to seven slits, reminding you at once of the slits of the lamprey, though they are long instead of round. For the shark has never arrived at having true gills under a horny cover like the minnow, but still breathes by pouches and slits somewhat after the way of the lowly round-mouthed fishes. Lastly, observe his curious tail. In nearly all living fish the tail is even[11] or V-shaped, but in the sharks the top point is usually longer than the lower one,[12] and in some, such as the Thresher, it is very remarkably so.

This uneven tail is the badge of a very ancient race; out of the shark family we scarcely find it anywhere now except among the sturgeons, who, we shall see, are old-fashioned too.

And now when we inquire into the growth of the shark and the kind of backbone he has, we find that he has still more links with the lower fish-like animals. For when he is young he has nothing but a rod of gristle or cartilage running between the long narrow feeding-tube and the spinal cord; but this rod is flattened in front, and as the young shark grows up the flat part enlarges so as to form a boat-like box—the skull, round the swollen end of the nerve telegraph—the brain. Meanwhile the rod becomes divided into rings, and from each ring an arch of gristle growing upwards surrounds the nerve cord so as to protect it from injury, and the whole skeleton becomes firm and strong. But though the shark is one of the strongest of sea-animals he never loses this gristly state of his backbone or his skeleton; however much he may strengthen it by hard matter it never becomes true bone, but remains quite distinct from the skeleton of the bony or osseous fish.

Fig. 6.

The Sturgeon[13] entering a Russian river.

We see, then, that there is a race of gristly or cartilaginous fishes, which, though they have grown strong and powerful, still hold to many primitive habits in forming both their body and skeleton. Nor do the sharks stand alone, for the large sturgeons, which live partly in the sea and partly in fresh water, crowding up the rivers of Russia and America to grope in the river mud for food, and to lay their millions of eggs, are also remnants of the ancient type. It is true that with them the slits in the neck are covered by a horny flap like the bony fish, and like them too they have an air-bladder under the backbone.[14] But they too have a gristly skeleton, and the gristly rod more or less hardened runs right along their back. In other respects they are perhaps even more peculiar than the sharks; for the sturgeon’s head is covered with hard bony shields, and five rows of bony bucklers are arranged along his body. We seem almost to have got back among the armour-covered animals as we look at his shiny plates, reminding us that with a mere gristly skeleton within, it may have been wise for the early types of fish to wear some outward protection. His snout is long and pointed, with four delicate feelers hanging down from it, and his mouth, which is quite under his head, is a soft open tube without teeth, which he can draw up or push out to suck up fish or any animal matter he finds in the mud.

Fig. 7.

The Sturgeon’s head seen from below, showing the tube-like mouth and the four barbels or feelers.

Clearly the sturgeon is an old-fashioned fellow, as you may see for yourself, when specimens caught at the mouths of our rivers are shown in the fishmongers’ shops. I have often wondered, when standing looking at him and at the sharks in the British Museum, whether the people who stroll by have any idea what a strange history these quaint old fishes have, or how they stand there among the scaly and bony fishes lying in the cases around, just as an Egyptian and a Chinaman might stand in an English crowd, descendants of old and noble races of long long ago, whose first ancestors have been lost in the dim darkness of ages, whose day of strength and glory was at a time when the modern races had not yet begun to be, and whose representatives now live in a world which has almost forgotten them.

In the silent depths of the large lakes of North America there is a fish called the Bony pike,[15] a huge fellow often six feet long, with a long beak-shaped mouth, which he snaps as he goes, devouring everything that comes in his way. This fish has his body covered with lozenge-shaped, bony, enamelled scales, like the fish of long ago, and so too has the strange Bichir,[16] which wanders above the cataracts of the Nile, with its row of eight to eighteen fins raised upon its back like tiny sails. Then again there are the curious calf-fish of North America,[17] of the Amazons,[18] of the Nile,[19] and of the rivers of Queensland in Australia.[20] These all have gristly skeletons, and together with the sharks and sturgeons make up all that remains of those strange shadows of the past moving among the bony fishes of to-day.

The mud-fishes are indeed the most curious of all, for they breathe both water and air, and in the Nile and Gambia often coil themselves round in the mud when the water goes down, and, lining their bed with slime, sleep comfortably till the rains refill the pools with water.[21] The fact is they have two quite separate ways of breathing. They have gills with which they can take air out of the water like other fish, and these they always use when they can. But they have a tube in their throat leading into the air-bladder lying under their backbone, and through this they can breathe in air when they cannot get it from the water. In Amia especially, which is a true enamel-scaled fish, this air-bladder is divided into numerous cells, and it breathes with it just as with a lung.

Fig. 8.

The Ceratodus of Queensland, an air-breathing and water-breathing mud-fish of the ancient type, with paddle-fins.

It was in the year 1870 that the Ceratodus, or the “Barramunda,” as the Australian natives call him, was discovered in the rivers of Queensland; and since then he has become very famous, for, more than any of the others, he is like the fishes of long ago. He is a lumpy fish, sometimes as much as six feet long, with a gristly cord for a backbone. His body is covered with large rounded scales, and he has a broad fringe round his pointed tail. His fins are more like paddles than fish fins, having several joints, and he uses them, together with his fringed tail, to flap along in the water, or even to wander over the reedy flats at night, chewing the weeds with his broad ridged teeth. And as he flaps along, from time to time, when the water is too muddy for his liking, he comes up to the top, and with a great gulp swallows air into the air-chamber. But before he can do this he must send out the bad air within, and in doing so he gives a grunt which is often heard far away at night in those still Australian wilds. He need not come up for air-breathing, however, if the water is pure, for, strange to say, the whole course of his blood can be altered to suit his wants. When he can get clear water to breathe through his gills the blood flows to them to be freshened, and his air-bladder simply takes in gas from the body as it does in other fishes, and wants feeding with good blood. But when he comes up to breathe then the blood is carried the other way, and comes to the air-bladder to be freshened.

And now if we want to read the history of all these strange forms, you must let me take you by the hand and lead you in imagination back, back through millions of years, to a time so long ago that we cannot even count the ages between. As we recede from our own day we shall leave behind us all the kinds of plants and animals we now know so well, and meet with strange kinds only bearing a general resemblance to them. After a long journey of thousands and thousands of years, in which the plants and animals, and even the very shape of the continents and islands, have gone through many changes, we shall get back to the time when the lime-builders were forming thin layers of chalk at the bottom of the sea, which were afterwards to become our enormous chalk hills. Still backwards we must go through all that long period, and then through three others quite as long, with ever-changing scenes of life and climate and geography, till we find ourselves in those grand old forests whose trees and plants we now dig out as coal.

Even then we must not stop to rest, though we are getting back to the dim ages of the world, for the journey is not yet ended. On, on, backwards through countless years, till we lose sight not only of beasts and birds and reptiles, but even of insects and flowering plants, which, at the time we are reaching, had not yet begun to be. At last we lose almost all life upon the land, so far as we can tell, and after another long period has passed before us we find ourselves in a scene of water, water everywhere.

True, there is a line of shore where strange ferns and unknown club-mosses and reed-like plants are growing; but these only border the vast water-world, and we have reason to believe that no living animal wanders over that wild and barren country. But the water itself is full of life, though its inhabitants are of low kinds, as if Nature herself was as yet only half-awake.

Rich and rare seaweeds carpet the floor of the ocean, mingled with delicate flint-sponges and old massive corals; beautiful feather-stars in the form of rooted stone-lilies wave their slender arms; greedy star-fish, grazing sea-urchins, and all their many relations, grope upon the rocks; and sea-snails crawl or float in countless numbers. The Nautilus, too, is there, with curious half-uncoiled companions of forms we have never seen before; and huge sea-woodlice, the Trilobites of olden time with their three-ridged shields, burrow in the sand, or roll themselves up at the bottom of the water. And above all these, among many kinds of armour-covered animals, a huge form, nine feet long, like a lobster, with an imperfect head, rows himself along with his oar-like hind feet, seizing the smaller creatures with his long nipping claws in front. For we have travelled back to a time when the crustaceans were the most powerful animals in the world, and the huge lobster-like Pterygotus was the monarch of the seas.

It was in the midst of a scene such as this that we first find the feeble ancestors of the Sturgeon and the Shark beginning to make their way in the world. It may be that creatures such as the sea-squirts, the lancelet, and the lamprey, were there to bear them company, but these soft animals could leave no trace behind except the tiny teeth of the lampreys; for they had no enamelled plates like the plated fish, no hard teeth-spines like the sharks, which could become buried in the soft mud when they died, and remain, together with the hard shell of their enemy the Pterygotus, to be dug out now in our day and bear witness to the fight they fought. But the plated-scaled fish had something to leave behind, and from their remains we can picture to ourselves a group of clumsy fish scarcely a foot long, with hind fins like paddles and single-fringe fins on their back, with enamelled lozenge-shaped plates on their bodies and unevenly pointed tails. These fish would keep well out of the way of the Pterygotus, because they were small and weak and he was large and strong. We may imagine them gliding among the seaweeds, and hugging the shore as they chewed the plants with their flat-ridged teeth, for their skeletons were probably feeble and their armour-like shields were heavy, and they would not be so active as the little shark-like animals, not bigger than a half-pound perch, with tough skins and sharp spines, which swam more boldly out to sea. These more active fish were the founders of the shark group, and those sharp spines, together sometimes with the tough skin, remained buried in the mud, and have come down to us as fossils.[22]

We should find it difficult to say exactly to what class all these early fish belonged, for there were very few kinds, and therefore fewer distinctions, between them in those days; and many peculiarities which afterwards appear in different groups either did not exist or were united in one fish. It is enough for us that they were the ancestors of our sharks and sturgeons and mud-fish of to-day; and though they were but small and weak, yet they were the beginning of a powerful race of creatures, for they had the great advantage of a growing inside skeleton, which could vary and strengthen with their bodies from generation to generation, while their rivals, the Pterygotus and his companions, had only their heavy cumbrous armour with a mass of soft flesh inside, and were but lumbering creatures at best.

And so we find that as thousands and thousands of years rolled by, the descendants of the enamel-shielded fish began to improve, and became larger and more powerful as the generations passed on, till they became masters of the shallow seas, and after awhile of the rivers and lakes. By the time that the first air-breathing creatures, the May-flies and Dragon-flies, had found their way out of the water into the forests of pines and tree-ferns on the land, and left their tender wings in the soft ground of the ponds and lakes, large fishes[23] whose tails were uneven-pointed like the sturgeon,—whose bodies were covered with lozenge-shaped enamelled scales and their heads with shields,—were grazing along the shores and in the rivers and bays, with probably swarms of smaller kinds which have left no traces behind.

These were peaceable fish which fed upon plants, and among them were some curious forms with paddle-like fins and broad-ridged teeth, which, as they swam under the shade of the huge forest trees, would come to the top and take in air through their mouth. These were the distant ancestors of our present mud-fishes, and through all the passing ages, from the time of the coal forests till now, they have kept their fish-like form, so that we have their descendants among us now in the Australian Ceratodus and the mud-loving Protopterus of the Nile.

But besides these gentle vegetarians there were in the sea huge enamel-scaled monsters, with terrible jaws and gigantic teeth, floundering about and making great havoc among the crab-like animals. One of these, whose head-shield has been found in the ancient rocks of Ohio in America,[24] must have been at least fifteen feet long, with a huge head, three feet long and a foot and a half broad; and no doubt there were many others like him, having a fine time of it now that they were the strongest creatures living. For this was the Golden Age of fishes, just before the time when the coal-forests grew; and the clumsy crab-like animals, and the trilobites, which had had their innings when the fish were small, now began gradually to be exterminated by their powerful enemies. Little by little they gave up the battle of life, and the larger ones died out altogether, leaving only those smaller crustaceans which did not clash with the fish.

So time passed on. The coal-forests grew, and died away and were buried; and as the ages rolled by a still stronger class of animals began to grow up which was to pay back upon the enamel-scaled fish the vengeance they had wreaked upon the crustaceans. For in the coal forests we first meet with creatures like our newts and salamanders, and after these came the true air-breathing reptiles (see [Chap. v.]), which swarmed over land and sea. There were the fish-lizards, with their strong swimming paddles and sharp teeth, and the swan-like lizards, with their long necks, which enabled them to strike their prey in the water; and these, together with the flying-lizards, and the huge dragon-like reptiles which haunted the shore, made the life of the heavily-moving enamelled fish a burden to them. So they, in their turn, began to give way, and became smaller and rarer as the history went on, till at the time when the chalk-building animals were at work at the bottom of the sea we begin to lose sight of all but those few forms which linger still. It was about this time that the Sturgeon, as we now know him, became the chief representative of these old cartilaginous fishes, and to this day he and his children go on travelling up the rivers of Europe, Asia, and America, or crossing from sea to sea—a living example of those ancient races which ruled the seas of long ago.

The history of the small shark-like animals was rather different. They too grew strong and powerful before the reptiles came, and they did not afterwards lose much of their greatness. With the wide ocean for their home, and not troubled with the heavy enamelled plates of their companions, they kept clear of the monster reptiles, or struggled with them bravely. Some took to the open sea, and from them are descended the giant sharks of to-day which still remain masters of the ocean. Others still lingered near the shore, where we find quite new forms springing up; some, like the Chimæra or “King of the Herrings,” formed a group of their own, half-way between sharks and sturgeons; and some, slightly flattened like the huge Monk-fish, hide themselves in the loose sand when seeking their prey. Others, the Skates and Rays, with flat bodies, and long tails serving as rudders, shoved smoothly along with a wavy flapping motion of their broad arm-fins. These too lie chiefly at the bottom of the sea, where their dusky colour hides them both from the fish they would wish to attack and those that would attack them; for while the sharks trust to their strength, the skates and rays trust to stratagem, and, coming along stealthily in the shadow, flap rapidly over their prey and suck them into their open mouth below. And for further protection we find some of them, such as the Sting-rays, armed with barbed spines; others, such as the Torpedo-fish, with electric batteries in their heads, which they can use to stun and kill their enemies; while others again, such as the Saw-fishes of the Tropics, have the front part of their skull lengthened out in a long bony weapon, armed with teeth, which they use to rip open the bodies of their prey.

All these formidable fish are descendants of the shark family, which, with powerful gristly backbones, strong fins and tails, and highly developed brains, refused to be suppressed as their plated companions were, but found room in the wide ocean to do battle for themselves, and improve in many ways upon their ancestors. They do not, like the sturgeon and the bony fish, lay their thousands of eggs, but are content with one or two at a time, such as the leathery purse-eggs of the skate and the rough hound shark; or give birth to a dozen or twenty living young ones. Yet they are so well fitted for their life that they flourish and keep their ground, so that while the enamel-scaled fish and the mud-fish are small groups, many of them fading away, the sharks and rays bid fair to be the race which will keep up the traditions of those quaint old Fishes of ancient times, which were once the masters of the world.

THE BONY FISH IN THE EARLY DAYS

CHAPTER III.
THE BONY FISH, AND HOW THEY HAVE SPREAD OVER SEA AND LAKE AND RIVER

When the palmy days of the enamel-scaled fish had passed away, and the sharks and rays had taken up their various quarters in different parts of the sea, there still remained vast tracts and many snug nooks and bays admirably fitted for fish-life. But these were not empty, for long before this time another order of fish—light, strong, and active,—had been pressing forward to take possession of every vacant space.

If we could dive under the water and watch the fishes at home we should see at once how much more agile and easy the bony fish are in their movements than their gristly companions. Look at a shoal of silvery herrings as they swim and leap and gambol, or a fine salmon sailing up the river or springing over a waterfall, or a tiny stickleback darting across the stream, and compare their graceful motion with the ponderous though powerful movements of an unwieldy shark. Any one who has done this will feel at once that though the sharks have still kept their power as tyrants of the sea, because they are so strong and big, yet these light skirmishers are much more at their ease, and move with much less effort in the water, so that it is natural they should have made their way into all parts of the rivers and seas. But where have they come from? We know very little of their early history, but what little we do know leads us to think that long ago they branched off from the enamel-scaled fish, and struck out a path of their own to make the most of the watery world.

Turn back for a moment to our little minnow, and recall his tender backbone made of joints hollowed out before and behind, with cushions of gristle between; those cushions, when the minnow was growing out of the minnow egg, were one long gristly cord, like the cord of the sturgeon, and it was only as the minnow grew that the bony joints hardened round it and separated it. Moreover, that huge bony pike which we find now wandering in the American lakes has bony joints hollowed out like the minnow’s, although by his enamel-scales and uneven tail we know him to be one of the ancient fishes. Some time or other, then, the sturgeon, the bony pike, and the modern minnow, must have had a common ancestor, though we should have to reach him through millions of generations. In the same way, too, we find the red-folded gills covered by a scaly lid, both in the sturgeon and the minnow, though in other ways they are not exactly alike; while even the V-shaped tail of the modern fish is not so different from the ancient shape as it seems, for the end of the backbone runs up into the top branch of the fork as it does in the uneven tails of the olden fish. Lastly, the delicate rounded scales on our minnow’s body are not entirely the property of bony fishes, for we find such scales on the mud-fishes, the Amia and Ceratodus (see [p. 33]); while the little modern stickleback, on the other hand, has bony plates, reminding us of those of olden times. We see, then, that the bony fish still carry upon them many signs of their origin from the older fish, and when once the coast was left clear, and they got a fair start, we can easily imagine that the fish of this younger race which was still in its childhood, and easily moulded to suit different kinds of life, would press forward in every direction and make the most of every chance.

And so we find that little by little, from the time of those chalk seas till now, the remains of enamel-scaled fish grow rarer and rarer in the hardened mud, and the bones and scales of modern fish take their place, till this bony race has spread so far and wide that in our own day, if we were to start from the head of a river and swim down into the open sea of the Atlantic or Pacific, we should meet on our way bony fish of all shapes and sizes and habits of life. River-fish and lake-fish and sea-fish; shore-fish, surface-swimming fish, and fish of the deep sea; flat-fish like the sole, half hidden in the sand, and long rounded fish like the eel, threading their way through holes and passages all over the world; flying fish with long arm-fins, and clinging fish whose fins form a sucking disk; nay, even so strange a thing as an angling-fish, whose back fin is turned into a fishing-rod to attract his prey.

All these, during the long ages since they first started in life, have been learning to make use of some area in the wide expanse of water spread over our globe, and it remains for us now to see how they have succeeded. Where shall we make our start? If we begin at home in the rivers we should have to work, as it were, backwards, for the sea is the chief home of fishes, and the rivers only the refuge of a few stray kinds. The sea-shore would be, perhaps, our truest starting-point, but then we should have to travel two different ways. Will it not be best to dive down first into the silent depths of the ocean, and learn what little is known of those which have taken refuge there? Thence we can rise up to the open sea, from there swim in to the shore, and then up the rivers and back to our own land-home.

It makes but little difference where we take our plunge into the deep sea, for changes of climate are scarcely or not at all known there, and the fish seem to wander over every part. Wherever it may be, then,—let us say in the seas of the Tropics, which have given us most of our specimens—let us dive down, down, till we reach about 1800 feet (300 fathoms).

... “For who can know

What creatures swim in secret depths below,

Unnumber’d shoals glide thro’ the cold abyss

Unseen, and wanton in unenvied bliss.”

We shall be groping more and more in darkness as we go, for the sunlight scarcely reaches beyond 1000 feet, and we have left its last rays behind us, and the water is growing icy cold. How strange, then, that the first fish we meet should have large wide-open eyes! This is the Beryx,[25] shaped something like a perch, but about a foot and a half long, and genealogists ought to look at him with respect, for his ancestors (see [heading of Chapter]) are almost the oldest known bony fish, and lived in the chalk seas.

Has he come down here because the upper world was too rough for him? If so, he has found comparative stillness, for he is far beneath the turmoil of the waves, and only the slowly creeping currents make any movement around him. But he has not escaped from the struggle for life, for not only is a good-sized shark coming his way, but a huge monster of the bony race, six feet long,[25] with wide-opened jaw, sharp pointed teeth, and large keen eyes, is wandering near in search of prey, devouring large and small fish with great impartiality.

Still in the dense darkness the Beryx must surely escape? No! for, strangely enough, lights are travelling about in this midnight region. The monster himself carries lamps upon his body, and a shoal of small oblong fish, something of the size and shape of a gudgeon, come swimming by, carrying on their sides whole rows of shining spots giving out phosphorescent light; while not far off another fish, called in India the Bombay duck, glows all over, as if his whole body had been rubbed in phosphorus. Nay! so far as we know the Beryx himself is probably gleaming with light, for his body is covered with a large quantity of the same slimy fluid which makes the “Bombay duck” phosphorescent when he is freshly drawn out of the sea.

So these curious fish, living in eternal darkness except when they make an expedition to the surface, carry many of them their own lights; and as we go deeper still more and more of them are found with shining mother-of-pearl-like spots on their head, or sides, or tail, so that the very darkness is alive with light. What slaughter and hunting there is among them! for they all eat each other, and even their own young, there being no plants for any of them to feed on. There are the deep-sea cod-fish; strange forms with large heads, long tapering tails, and thread-like fins, chasing the smaller fish, and falling victims themselves to the fierce Stomias which comes sailing along with its row of glowing lights, and its huge sharp teeth, ready to seize its prey. Both these fish go down as deep as ten thousand feet and more, accompanied by another fish quite as ferocious, though only a foot long, with large teeth sticking out of its mouth like the tusks of a boar, and curious round spots, with lenses in them, on its side, which may be eyes, or may be lanterns to light it on its road; and among these luminous fishes are wriggling along the deep-sea Conger eels, with toothless mouths and elastic stomachs, swallowing large fish whole; while another curious cod-like fish, whose stomach can stretch to more than four times its natural size, draws itself over its prey just as a snake does, and carries it in the hanging bag till it is digested. And deeper yet in the dead calm water roam many fishes with delicate feelers hanging from their mouths, while their fins are slender and tapering, so that they feel their way along the still depths. Among these are the Ribbon-fish, twenty feet long but only a foot deep, and never more than two inches thick in any part, with their long rosy fins floating like ribbons back from their heads and from under the body.[26]

Strange monsters are all these deep-sea fish, some of them living as much as 16,000 feet under the surface of the sea, so that if Switzerland were turned upside down in mid-ocean, the peak of Mont Blanc would not reach down to where they swim. Yet they are only modified forms of ordinary fish from the world above, which have become fitted to live under that vast pressure of water. Their skeletons, though bony and well-knit together at that depth, are fibrous and slight compared to those of their surface relations, for although they have to resist a weight of from two to sixteen tons pressing all round them, a ton weight being added for every thousand feet, no special strength is required, because the dense water permeates their whole structure, and the pressures are everywhere equal. It is the same with them as with the most delicate and fragile insects living in our atmosphere, the pressure of which would tear them to pieces if unbalanced by equal pressures within and without.

But when these deep-sea fishes are brought up quickly to the surface, the outside pressure no longer balances that inside, and so their tissues loosen and their whole framework starts apart, so that they almost fall to pieces at a touch; and their air-bladder, if they have one, expands so much as to force the stomach out of the mouth, turning them almost inside out. Neither are their lanterns a special creation for their use, but merely adaptations of that slimy fluid which we saw oozing from the scales of the minnow. In some of the deep-sea fish even the outer bones are filled with this fluid, and the line of scales along the side has large openings, so that the body is bathed in glowing slime. In others it collects in glands on the sides, making the phosphorescent spots.

In this way the deep-sea fish have become fitted to make a home in the very heart of the ocean. Some with large eyes, seeing by means of their own and their neighbours’ light, others with small eyes and delicate feelers, testing each step as they go, and feeding, probably, on the shower of minute sea-animals that falls continually from above; while some, like the Beryx, the Bombay Duck, and the light-carrying Scopelus, which live nearer the top, come up on still nights to feed at the surface of the sea.

Fig. 9.

Remoras[27] clinging by their sucking-disk to the under part of a shark.—(Adapted from Brehm.)

And now, as we rise again from the dark still depths up to warm layers of the tropical seas into which the sun is pouring his penetrating rays, it may happen that a large dark body moves between us and the surface, as the Great Blue Shark, or one of his smaller relations, ploughs his way through the water. But what are these little dark brown fish, with round gaping mouths, which are hanging by the top of their head and back from under the shark’s belly? (see [Fig. 9]). Where he goes they go with him, and, as they are borne along, they feed upon the tiny sea-animals among which they are carried so easily. These cunning passengers, of whose very existence the shark seems unconscious, are the Remoras, or sucking-fish. You would scarcely think that they belong by descent to the mackerel tribe, a strong-swimming, active, and almost warm-blooded group of fish, with a large supply of nerves and blood-vessels to their muscles, so that they swim boldly out to sea, and make more use of the open ocean than almost any other group. But among all tribes there will be some weak members, and these must live by stratagem. The little remora is a feeble swimmer, and, having to live out at sea, has acquired a curious sucker by which he clings to sharks, and whales, and even ships, so that he is carried along without exertion. Yet this sucker, again, is only a special adaptation of the back-fin, which, instead of being single, as in other mackerel, has its spines divided and bent, one set to the left, the other to the right, and joined by a double set of plates, surrounded by a fringe of skin. This forms an oval disk, and, as the remora glides along under the shark’s belly, he presses the damp membrane against the fish, and, drawing together the muscles of the plates, clings as firmly as a limpet to a rock.

Nor is the remora the only companion of the shark—

“Bold in the front the little Pilot glides,

Averts each danger, every movement guides;”

for the little steel-blue striped Pilot-fish,[28] another distant connection of the mackerel tribe,[29] is hovering around, feeding upon the scraps of the shark’s food, and finding protection in his neighbourhood, though in olden times he was supposed to protect the shark. A brave little fish this, which has succeeded in making the shark his friend: while near him he is safe from other fishes.

And now, as we continue our way in the open sea, it is nearly always forms more or less related to the mackerel tribe which cross our path. The slender Bonito[30] and the heavier Tunny[31] sometimes ten feet long, are hunting below or on the surface, and the beautiful Dorados,[32] or gold-mackerel, as the Germans call them, with their silvery blue backs tinged with a sheen of gold, their dull-coloured fins, and their golden eyes, are driving by in large shoals in pursuit of the flying-fish. All these are powerful swimmers, and they have no air-bladder, which is an advantage to such active hunters which wish to turn rapidly, to go down deep or rise to the top, and change their position at every moment; for in all these movements a natural float inside is a hindrance to be overcome. And so we find that in fish, even of the same family, some have lost the air-bladder, while others have it enlarged to meet their wants, as in the case of the lovely blue and silver sun-fish[33] for example, which, though quite near relations of the dorado, have very large air-bladders, enabling them to float quietly on the top of the water, waving their deep scarlet fins.

Fig. 10.

Flying-Fish[34] pursued by the Dorado.[35]

But while we are watching all these large and strong swimmers an active and bloodthirsty struggle is going on, for the bonitos and the dorados are looking to make their meal upon the little Flying-fish, which are straining every nerve to escape them, while here and there one drops down into their very mouths. Lovely little creatures these are, of the Pike family, which have taken to the open sea, where they rise with a stroke of the tail many feet out of the water, their bright purple backs and silvery sides gleaming in the sun, as, with their long transparent arm-fins outspread, they float for as much as two hundred yards before they fall back, to spring up again with another stroke. Their air-bladder, which is half as long as their body, and contains in a six-inch fish as much as three and a half cubic inches of gas, stands them in good stead, and they rise and fall with quick rapid flights out of the reach of their foe, so that in the open sea they do fairly well on the whole, though, if they venture near land, the sea-birds persecute them in the air. Nor do they stand alone in this curious habit of flying, or rather floating, in the air, for a larger fish of quite another family, the “Flying Gurnards,”[36] with a smaller but still ample air-bladder, and long arm-fins, may also be seen rising in the Mediterranean and tropical seas, out of reach of the fish-hunters of the water.

And now we must leave the open sea and steer for the shore. It is true that many other fish are wandering in the broad watery main, but many of them, such as the globe-fish, feeding on the small crustaceans and the sea-horses,[37] whom we shall meet nearer shore, are feeble forms carried hither and thither by currents or on floating banks of seaweed, while others have no special interest. The sharks, the mackerel, and the flying-fish, are the most remarkable colonisers of the ocean-surface, for even the enormous Sword-fish,[38] which attacks the bonitos and whales with its long wedge-shaped bony jaw, and is said to sail by raising his back-fin, is a distant off-shoot of the mackerel tribe.

So we cannot do better than follow our own common Mackerel, as they migrate in shoals out of the deep sea to feed on the fry of the herring or the pilchard in shallower water, or to leave their eggs floating not many miles from land, so that the tiny mackerel, when hatched, may live in the quiet bays till their strength comes.

But stop! Long before we have come so far as this, and while we are still a hundred miles or more from the shore, let us peep down into the sea-valleys, where forests of seaweed and marine plants are growing, and myriads of tiny sea-lice and crustaceans throng the water. What is that army of thin spindle-shaped forms rising and falling in such numbers? It is a shoal of herring, which have come there to feed upon the sea-animals, keeping out of sight of the sea-birds above, and the cod and sharks and ravenous fish which hunt them without mercy, so that they only venture to come to the surface on calm dark nights. It was in valleys such as these that the herrings were living when the older naturalists thought they were gone away to the Polar Seas, because they only saw them in spring and autumn, when they come into shallower water to drop their myriads of eggs,[39] which sink down, and stick to the seaweed and stones below.

But now they are revelling in the deep ocean, rising and falling with ease, for their air-bladder has two openings, one to the stomach and one to the outside of the body, so that the gas can adjust itself to their movements; and surely if the shark is the type of the old, lumbering, powerful, slow-breeding fish, the herring, with its narrow lissome body, light playful movements, and myriads of young, is the type of the new and active race. They are as truly social animals as any herds on land, for they travel in shoals of many hundreds of millions; and as they can squeak, and have a very good apparatus for hearing, it is more than likely that they call to each other. They make both the salt and fresh water their own; for when the eggs are hatched at the mouths of rivers the tiny fish take refuge there from the violent persecutions of the cod and mullet and haddock, flat-fish and whiting, and, together with the small fry of other fish, stroll up the rivers, where we call them “white-bait.”

And now, as we come nearer to the shore, where countless numbers of small fry are filling the water, and all creatures are struggling together to accomplish three objects, namely, to get food, to avoid being turned into food, and to lay their eggs, we find many strange weapons and devices adopted by the different fish for protection and attack.

... “Each bay

With fry innumerable swarms, and shoals

Of fish, that with their fins and shining scales

Glide under the green waves, in sculls that oft

Bank the mid sea.”

There are the Mullets,[40] with tender feelers under their chin, with which they brush the ground lightly as they swim, feeding on the tiny creatures. There are the walking fish, the Gurnards,[41] which have three of the spines of their arm-fins separate, and moved by strong muscles and nerves, so that they can walk on the sea-bottom, feeling their way, while the stiff, spiny rays of their back-fin stand up to wound any enemy attacking them from above. There are the tiny Blennies which walk too, but by means of the few rays which alone remain of their leg-fins growing close under the head. Then there are the clinging-fish, the Gobies,[42] living on the rocky shores, where the waves beat and roar, and they have their leg-fins joined together, so as to form a kind of funnel under their throat, with which they cling to the rocks and then dart across the waves to feed, coming to anchor again out of the dash of the water; some of these little fellows make nests and guard their eggs after the mother has left them, till the young can shift for themselves. More curious still, the Lumpsucker[43] has its arm-fins and leg-fins all joined together into a round disk under the throat, and so holds on bravely against the dashing tide, defending the eggs which have been laid in the seaweed near the shore, and even remaining to take up the young ones when hatched, and carry them safely back into deep water as they cling to his sides.

Meanwhile, close down upon the sand are the hiding-fish, the Weevers, the Anglers, and the Flat-fish.

The weevers[44] are the most dangerous. Their shaded yellow colour hides them from view, while the sharp spines of their back-fins, which they keep raised, will inflict very severe, if not poisonous, wounds on any creature striking against them. Nor is this all, for behind the cheeks, fastened on to the horny gill cover, are daggers with which they can strike, deliberately jerking them back so as to give a sharp blow. These are fighting aggressive fish, waging the war that goes on so sharply all round our coasts.

Fig. 11.

The Fishing Frog.[45]

But there is one even more cunning than they, lying hidden in the seaweed or the sand—a large, flat, soft fish, about three feet in length, and quite half as broad as he is long, with a soft stumpy tail, stretching out behind, and a kind of wrist-joint to arm and leg fins, by which he can creep noiselessly along. His wide mouth is gaping open, so that a two-foot rule could be passed crossways into it, and his pointed teeth are bent back to allow his prey to enter. But how is this prey to be caught, for he is not going to move to fetch it? Notice all round his head and his body, the skin is fringed like blades of seaweed and plays about in the water; while above his head and back the spines of his fin stand up quite separate, and the front one is tapering and long like a fishing-rod, with a lappet at the end like a bait. And now, as the shallow water ripples over his head, the lappet plays to and fro, and the unwary fish come up to nibble at it, lower and lower he waves it, and the nibblers follow, till, opening his wide gape, he gulps them down, even if they are as large as himself, and lies passive with his swollen stomach till they are digested. This is our own Fishing-frog,[46] of which one was once found with seventy herrings in his stomach. He has relations all over the world—in the open sea and down in its depths, and all of them more or less follow his fishing habits. Yet there is no creation of special parts for these strange weapons; the altered back-fin and the jagged skin do all the work, just as in some curious fish of the weever family in the tropics, called the Stargazers,[47] the feelers on their lips, longer than those of other fishes, and a lengthened thread from below the tongue, play in the watery currents and attract the small animals, while the fish with upturned eyes watches them as they are lured to destruction.

Lastly, among all these curious forms upon our shores there is an abundance of flat-fish—soles and turbot, brill and plaice—flapping along at the bottom, covering themselves with sand, or rising up with that strange wavy movement of the whole body in which they use what look like long side-fins, but which are really the back-fin and the belly-fin.

Fig. 12.

The Common Sole.[48]

Above are two small soles as they swim when young. At that time they are not larger than a grain of rice.—(Adapted from Figuier and Malm.)

If we wanted to pick out the strangest and strongest proof of how the shape of fish is altered to suit their wants, we need seek no further than the flat-fish.

When we were speaking of the shark order we saw that the rays and skates are flattened forms suited to hide in the sand, and these fish are truly spread out as if they had been squeezed under a heavy weight, their broad arm-fins edging the sides of their body. But the bony flat-fish, the Soles and Turbot, have a far stranger history. The young sole, when it comes out of the egg, is not flat like the young skate, but a very thin spindle-shaped fish, something like a minnow. He is then about the size of a grain of rice, very transparent, and lives at the top of the sea. He has one eye on each side, like other fish, only one eye is higher up than the other, and the single fin on its back and the one under its body reach almost from head to tail. In this way he swims for about a week, but he is so thin and deep, and his fins are so small, that swimming edgeways is an effort, and soon he falls down on one side, generally the left, to the bottom of the sea. Many times he rises up again, especially at first, till he has got used to breathing at the muddy bottom, and meanwhile the eye that lies underneath is gradually working its way round to the upper side, his forehead wrinkles so as to draw the under eye up, while his whole head and mouth receive a twist which he never afterwards loses. His skeleton, it must be remembered, is still very soft, and the bones of his face are easily bent; and at last this eye is screwed round, and as he lies at the bottom he can look upwards with both eyes and save the under one from getting scratched by the sand, as it must have done if it had remained below.

Nor is this all, for while his under side, shaded from the sunlight, remains white and colourless, his upper side gradually becomes coloured like the sand in which he lies, and he is safely hidden from attack as he flaps along, feeding on worms and other animals. And now when he swims he no longer uses his arm and leg fins, which are quite small and insignificant, but bends his whole body, using the back and belly fins to help him. What we then call the top of the sole is really his side, where you may see the dark line of scales running along the middle, and one arm-fin lying close to his head. Yet he can swim strongly and to far distances, for in the winter the soles, too, migrate into the open sea, where they may be found in the deep water of the Silver Pit, between the Dogger Bank and the Well Bank.

Fig. 13.

Hippocampus, a fish commonly called the Sea-Horse.

And now, before we leave the shore, we must glance at a curious weakly little fellow clinging by his curly tail to the seaweed, whom you will certainly not take for a fish, even if you can find him out, so entangled is he generally in weeds of the same colour as himself. Yet the Sea-horse[49] is a true fish, covered not with scales but with plates, with which he makes a clicking noise by scraping them together. What look like large ears are really his arm-fins, while at the end of his long snout is a mouth shaped like an ordinary fish’s mouth, but toothless, and he breathes with fish’s gills arranged in round tufts instead of folds. What the use of his strange shape is to him we cannot tell, but at any rate his fleshless bony body must protect him from other fish, while his power of clinging causes him to be often carried by floating weed even into the open ocean, and make up for his feeble powers. In one thing he surpasses most other fishes, for he is a most careful father, carrying the mother’s eggs in a little pouch under his body till the young ones escape. There is one form of these sea-horses in tropical seas which has long red fringes floating from its body, so that it cannot be distinguished from the seaweed in which it hides.

So we see that the deep sea, the open sea, and the shore, are filled so full of different forms that there are enough not only to make use of every part, but also to provide food for each other, and we also see that by far the larger number even of widely-spread fish come near to the shore to leave their spawn, while the young ones often make their way into the brackish water at the mouths of rivers, and spend their youth in the shelter of the still fresh water.

Now it is very natural that many such fish should learn to remain in this quiet refuge, and in time to live there altogether. And because fish-life in the rivers is comparatively uneventful and little varied, we find much fewer peculiarities in river-fish. Many of them are very near relations of sea forms. There is the salmon, a true sea-fish, which wanders up the river to spawn in the pebbly shallows; and there are the trout, his near relations, which have learned to live entirely in the rivers. There are the sea-perches, large strong fish, and the smaller river perch, which have made their homes very successfully in the rivers, for their spines are so sharp that even the greedy pike hesitates to swallow them. There are the sea-sticklebacks, and the little river-stickleback.[50] This last is a very clever little fish, which hollows out the foundation of his nest very carefully in the bed of the river, and then builds it up for several inches with blades of grass and weeds ([Fig. 14]), gumming them together with the slime of his body. Then, when all is ready, he swims about to drive and coax the mother to the nest, sending her in to lay her eggs, and then driving her right through and out at the other side, so that a stream of water flows constantly over the eggs till they are hatched. Nay, his care does not end here, for when the young fish come out of the egg with a bag of yelk hanging under the body, as all young fish have at first, and so cannot swim easily and escape their enemies, the courageous little father will defend them and fight fiercely with any fish which thinks to make a meal upon them, not leaving them till all the yelk is absorbed, and they are able to swim and feed themselves.

Fig. 14.

STICKLEBACKS AND THEIR NEST. (Gasterosteus aculeatus.)

Besides these active river-fish there are the little stupid Miller’s Thumbs,[51] hiding under the stones to feed on tiny animals; they are feeble relations of the gurnards which we saw walking on the bottom of the sea. Then there are the purely freshwater fish, the Pike and the large Carp family, with its many branches, the Roach, and Dace, and Gudgeon, and Minnow; and the enormous family of Cat-fish and Sheat-fish,[52] of which we have none in England, but plenty in America and other parts of the world, a family in which the fathers sometimes carry the eggs in their mouths till hatched. And last but not least among the freshwater forms is that irrepressible family of the Eels which we saw wandering in the deep sea, and which are also to be found near the shores all over the world. These fish will even travel through pipes and into cisterns; and will climb up trees so as to drop into neighbouring streams and continue their wanderings; they sleep in the mud in winter; and even after being frozen come to life again; and in the spring they go to the sea to spawn, giving rise to those shoals of young ones from three to five inches long which come in incredible numbers up the rivers in summer, making the eel-fairs,[53]—

“The silver eel, in shining volumes rolled,”

so much spoken of in old books, when the eels will often climb high banks, nay, even pass over miles of dry land, closing down their narrow gill-openings, and so shutting in water to serve them as they go.

All these, and many other freshwater families, show us how the fish have wandered into every possible nook of the waters, so that even in those inland salt lakes of North America and Asia into which no rivers flow fish-life is abundant; and we can only suppose that the eggs must have been carried by water-birds in their flight, or by gusts of wind, or have arrived there in ages long ago, before these lakes were cut off from the rest of the watery world.

Yet some few fish besides the eels have been known to travel over land to find watery “pastures new;” the Climbing Perch[54] of India and the Doras of Tropical America will both travel many miles when their own ponds are dried, the perch breathing by the help of a special apparatus, and the doras probably shutting water into its gills; for necessity, even in fishes, proves the “mother of invention,” and in special works on fish you will find accounts of numberless strange devices and adaptations by which they manage to survive in the struggle for life.

And now, collecting together all we have learned, let us in conclusion form a rough picture of the history of the fish-world. All over our globe, from pole to pole, and from the Indian Ocean round to the east, back to the Indian Ocean again, is one vast world of waters, with inlets and land-locked seas bordering its margins, and rivers pouring into its depths. In the past ages of the world these rivers and coasts and inlets have varied innumerable times, but the great ocean-mother has always been there to bear the increasingly-varied forms in her bosom, and to enable them to wander where best they could preserve life.

And so from their beginning, when they were probably as feeble as the lancelet, these earliest and simplest backboned animals with their two pair of limbs as yet very variable both in their position and shape, have been spreading far and wide over the watery three-quarters of the globe. We have seen how the enamel-scaled fish had their time of glory, but were not able to hold their ground, because they were not agile and fish-like enough to escape their foes; and how the sharks by their strength and boldness remain monarchs of the sea to the present day. Then we have seen that in old chalk seas the new and active race of bony fish appear in force; some like the herring and the carp, with air-bladders, which had openings like the enamel-scaled fish, and these can dart from heights to depths; while others had closed air-bladders, and these remain with most ease at one level, and can sometimes, if necessary, use the gas in their bladder for breathing, if they are oppressed with muddy water; and lastly, some, such as the dorado, have lost their air-bladder altogether, and gain in freedom of action what they lose in lightness and buoyancy. And during the ages that have passed since this bony race began, different branches each in their own way have thrown out curious weapons and developed strange organs to help them in the battle of life, so that now we have deep-sea fish carrying their own light; fish with distensible stomachs swallowing prey larger than themselves; fish with large air-bladders and long arm-fins springing out of their own element and floating in air; angling-fish, walking-fish, clinging-fish, and hiding-fish; and even those whose shape is distorted, like the sole, to enable them to hide and hunt in safety; while, when the sea is full, we find new varieties pressing their way into every river and tiny stream, and even overland into enclosed waters. Nay! when we descend into the recesses of the earth and visit the underground pools of the dark caverns of Kentucky, there we come upon fish which have found a refuge in eternal darkness, and have lost not only the power of sight but actually the eyes themselves.

And here we must leave them to go to higher vertebrate animals. Although but little is known of fish-life, a very small part even of that little has been given here, and yet we take leave of it with the feeling that its changes and chances are greater than we can ever thoroughly learn. How much pleasure these creatures have in their water-world it would be difficult for us to say; but since we find them playing together, hunting together, sporting in the warm sunshine, and diving and gambolling in the open sea, and sometimes even calling to one another, we cannot but think that life has great charms for them in spite of the many dangers surrounding them. And when, low though they are in the scale of life, we find them (though curiously enough always the fathers) carrying the eggs, building nests for them, and defending the young, we see that even here, in the very beginning of backboned life, we touch the root of true sympathy, the love of parent for child.

THE HOME OF THE EARLY AIR BREATHERS

CHAPTER IV.
HOW THE BACKBONED ANIMALS PASS FROM WATER-BREATHING TO AIR-BREATHING, AND FIND THEIR WAY OUT UPON THE LAND.

So the backboned animals, as fish, have peopled the seas and rivers, and, as the ages have past on, have become more and more fitted to their watery life, little dreaming of another and different life in the world of air above them. And yet in the same pond with the little stickleback, so busy building his nest, there is a creature which could tell him that it is possible to live in both worlds, if only you have the proper machinery to do it with.

It is clear that if the backboned animals were ever to live upon land, after they had begun their career in the water, there must have been some among them which learned gradually to give up water-breathing, and to make use of free air; and we shall not have far to seek for creatures which will help us to guess how they managed it.

From almost every country pond, or ditch, or swamp, a chorus of voices rises up in the springtime of the year, calling to us to come and learn how Life has taught her children to pass from the water to the air; for it is then that the frogs lay their eggs, and every tadpole which grows up into a frog carries us through the wonderful history of an animal beginning life as a fish with water-breathing gills, and ending it as a four-legged animal with air-breathing lungs.

Come with me, then, to some stagnant pool in a country lane, towards the end of March, and there we shall no doubt find a whole company of frogs, croaking to their hearts’ content after their long winter sleep in the mud at the bottom of the pond. They are wide awake now, and are actively employed laying their eggs. Look carefully around the edges of the pond, especially in that part where the wind has driven the scum to the side, and you will doubtless find in some still corner a gluey mass (e, [Fig. 15]), which looks like a lump of jelly with dark specks in it. Take this up carefully, for it is frog spawn; carry it home together with some weeds from the pond; put it in a glass bowl with water; and then from day to day you may study the history of a frog’s life.

Fig. 15.

Metamorphosis of the Frog.

e. Eggs. 1. Tadpoles just out of the egg. 2. With outside gills. 3. With gills hidden, and beak-like mouth. 4. Hind legs appearing. 5. All legs grown, but fish-tail remaining. 6. Putting on Frog appearance; tail being absorbed. 7. Young perfect Frog.

That jelly-like mass is a collection of frog’s eggs. When they were laid, each egg was a small round dark body in a gluey covering, and they all fell to the bottom of the pond, where, by degrees, the water oozing through the envelope swelled each egg, till they clung altogether in a mass, and, rising, floated at the top. Then very soon each round dot lengthened out into a long streak, and in a few days an eyeless head appeared at one end with a soft closed mouth under it, and at the other a tail, with a soft fin round it like the tail of the lancelet; so that by the time you find the spawn, you may, most likely, be able to see the tiny creature wriggling every now and then in its watery bed. This will go on for some time, and a week or two may pass before the moving tadpole breaks through its egg skin, and coming out into the world, fastens on to a piece of weed (1, [Fig. 15]) by two little suckers behind its mouth. And now that it is out of the egg the interest begins. Look carefully day after day and you will see some branching tufts (2, [Fig. 15]) growing larger and larger on each side of its head. What are these? We have not seen them in any fish. No! but if you take a young hound-shark out of his leathery egg before his time, you will find that he has outside gills much like these, only he loses them before he comes out into the world, whereas the tadpole keeps them to breathe with a little longer. If you put the tadpole, at this stage, under the microscope, you can see the red blood flowing through these gills to take up air out of the water.

Meanwhile the tadpole’s lips are gradually forming into a round mouth, much like the lamprey’s, and by-and-by the inner part of this mouth is covered with two little horny jaws, forming a sharp beak (3, [Fig. 15]) with which he will nip off pieces of weed for food. Meanwhile, as he grows larger and larger, and eyes, nostrils, and flat ears form in the head, a covering begins to grow back over the sides of the neck, and little by little the branching tufts disappear (3, [Fig. 15]). How, then, can he breathe now? Watch carefully and you will see that he gulps every moment as we saw the minnow doing ([p. 23]). The fact is that the outside tufts have faded away, and under the cover the tadpole has six slits in his throat, like the slits of the lamprey, which are covered in somewhat similar fashion to those of the amphioxus (see [p. 11]), and he breathes through them.

Here is our tadpole, then, to all intents and purposes a fish. He swims with a fish’s tail; he gulps in water at his mouth, passing it out at the slits in his throat after it has poured over his fish’s gills. Moreover, he has a fish’s heart, of two chambers only, like the minnow’s ([p. 23]), which pumps the blood into these gills to be freshened, while, like the lamprey, he has a gristly cord, enlarged at the end to form a gristly skull, a round sucking mouth, and no limbs. All this time, however, though he has a fish’s fin round his tail, he has no arm or leg fins. Wait a while and you will see that under his tender skin far more useful limbs are being prepared. As he grows bigger and more active week by week, wriggling among the weeds and feeding greedily, two little bumps appear one on each side of his now bulky body, just where it joins the tail. These bumps grow larger every day, until, lo! some morning they have pierced through the skin, and two tiny hind legs (4, [Fig. 15]) are working between the body and the tail. The two front legs are longer in coming, for they are hidden under the cover which grew over the gills, but in about another week they too appear, and we have a small four-legged animal with a lamprey’s tail (5, [Fig. 15]). These legs are something far in advance of fish fins, for they have shoulders and thighs, arm and leg bones, wrist and ankle bones, hand and foot bones; and instead of the large number of rays in a fish’s fin they have four fingers on their short front legs, and five toes at the end of long hind ones; the toes being joined together by a web, which helps him wonderfully in striking the water as he swims.

The tadpole has now become fitted to jump and leap on the land or swim by his legs in the water; and, moreover, while these legs have been growing, another change has been taking place. You will notice by careful watching that at first he still gulps in water as he used to do, but he comes more often to the top, and, poising himself so that his mouth is out of the water, gives out a bubble of bad air, draws in some fresh, and goes down again. Why does he do this? Have you any recollection of another fish-like animal which comes up to take in air? Look back at our friends the mud-fishes ([p. 34]), and read how the Ceratodus fills his air-bladder when he is short of good air in the water. When you have re-read this, you will suspect that the tadpole, too, has something like an air-bladder, which he fills from time to time. And so he has. While his legs are growing a bag has been forming inside at the back of his throat, which afterwards divides into two, and he fills these by shutting his mouth, drawing air in at his nostrils, putting up the back of his tongue to shut it in, and then swallowing it down into the lungs; so that he is now a truly double-breathing animal, using his gills when below water and his lungs when above. Moreover, if you could watch inside his body, you would now see that little by little the blood-vessels going to the gills grow smaller and smaller, and those going to the lungs grow larger and larger; while the fish’s two-chambered heart divides into three chambers, one to receive the blood from the body, another to receive it from the lungs, and one to drive this blood back again through the whole animal. And when at last this change is so complete that all the blood goes to the lungs to be freshened, the gills shrivel up and disappear, and our tadpole is a true air-breathing animal.

Notice, though, that he is still cold and clammy, not warm like a mouse or a bird. For his blood still moves slowly, and as he has only three chambers to his heart instead of four, as warm-blooded animals have, the good blood from the lungs and the worn-out blood from his body become mixed each time they come round, so that his breathing work is still of a low kind all his life. And now that he can leap and swim with his legs, his tail is no longer of use to him, and it is gradually sucked in, growing shorter and shorter till it disappears, and the young frog is complete.

Thus our backboned animal has succeeded in getting out of the water on to the land, and in doing so he has quite changed his habits. A peaceful vegetarian before, he is now a greedy eater of insects, slugs, and other animals. His horny beak has been pushed off; his lips have stretched back farther and farther, till they now open right back as far as his flat little ear; and he is a gaping, wide-mouthed, leaping frog[55]—

... “Hoarse minstrel of a strain

Aquatic, leaping lover of the rain;”

(7, [Fig. 15]), with teeth in the roof of his mouth. But perhaps his tongue is the most curious of all, for instead of being fixed at the back, and free in the front, as in most other animals, the root of it is fastened to the front of his lower jaw, and the tip lies back in his mouth, so that when he wishes to catch an insect he throws his tongue quickly forward, captures his prey on the sticky point, and flings it back down his throat.

So he hops about the summer long, if he can only escape from ducks and rats and other frog-eating animals. He often takes to the water, for he can fill his lungs with air and use it very slowly, and, moreover, his soft skin is of great use to him in still breathing in the water or in the moist air; and when winter comes he takes refuge with many others at the bottom of the pond, and sinks into a state of torpor, till the spring brings croaking and egg-laying time round again.

Fig. 16.

The Common Smooth Newt[56]—male and young in the water; female on the bank.

Our little frog, then, is truly an animal with a double life, a genuine amphibian,[57] meaning by this, not merely an animal that can swim in the water and move on land, for seals and water-rats, white bears and hippopotamuses, can do this, but one that in the early part of its life would die if taken out of the water, while afterwards it lives and breathes in the air.

Fig. 17.

Proteus of the Carniola caverns,[58] with its external breathing gills.—(Adapted from Brehm.)

Have these double-lived creatures, then, such a great advantage over real water animals, or how can we account for their having adopted this strange life? If we only look upon them as they are now, we can scarcely call them particularly successful, compared to other animals. For though there are plenty of them, yet they are comparatively small and insignificant; and when we find large ones like the gigantic salamander of Japan, they are sluggish and feeble. Look at the common newts, or water-salamanders of our ponds, with their weak crawling limbs, as they wander round the edges of a pond, feeding on water-insects and tadpoles, the male with his crested back, the smooth mother, and the young eft-tadpole with its branching tufted gills ([Fig. 16]). They are much less active than the frog, for they never lose their tails, and they come less often out of the water, although they are true air-breathing animals. Then, when we go to other countries, there is the Proteus ([Fig. 17]), that curious half-transparent newt, with a round body and tiny helpless legs, which lives in eternal darkness in the still underground pools of the Carniola caverns near Adelsberg. He has become well fitted for his dismal life, for his tiny eyes are grown over with skin, and he never loses the feathery gills on each side of his neck, but lives like a tadpole all his life, although he has true lungs. Again, in America we have the Siren, with its long snake-like body, and only front legs, with which it cannot walk. It, too, keeps its gills as it wanders about the stagnant waters of South Carolina, feeding on worms and insects. Then in the Mexican lakes there are the curious Axolotls, which also wear outside gills, as a rule, all their lives, and fathers, mothers, and children remain breathing in the water together, although they have real lungs. But about twenty years ago, some of those axolotls, which were kept in the Jardin des Plantes in Paris lost their gills, came out upon the land, and astonished people by becoming true land salamanders, like some already well known and called Amblystomes, breathing only with their lungs. It was difficult for some time to make the world believe that grown-up water-breathing creatures which could lay eggs were able to turn into other creatures without gills. But at last a lady, Fraulein Marie von Chauvin, took some axolotls when they were full-grown, and kept them on land in wet moss, washing and feeding them every day, and thus succeeded in teaching them to breathe air, so that their gills shrivelled up and disappeared. Then there could no longer be any doubt that the axolotl is only the lower water-form of the amblystoma, which in the Mexican lakes, owing to the increased dryness of the surrounding country, has lost the habit of coming out on to the land, and remains in the water with its little ones all its life; but which, when brought to a moist climate where it can breathe comfortably on land, sometimes returns to its old double life.

Fig. 18.

Axolotl, a creature living and breeding for generations in the water. Amblystoma coming out of the water,—an axolotl which has lost the gills and acquired lungs.

We have, in fact, in Europe real land salamanders, which live in cool damp places, looking like lumpy soft-skinned lizards, but going down to the water to lay their eggs, that their little ones may go through their tadpole life—and one of these, the black salamander,[59] which lives high up in the mountains of Germany, France, and Switzerland, does not even go to the water, but carries the young tadpoles in her body till they can breathe air and run alone; and yet they are still true amphibia, for if they are taken out of their mother and put in water, they go through all their changes like common efts and newts.

Lastly, there is a strange group of legless creatures called Cæcilians, which have taken refuge underground, burrowing like worms, though they are true amphibians and their young have gills in their babyhood hidden under a slit in the neck. These cæcilians are the only amphibians which have scales something like fishes, yet they never live in the water, but in the marshy ground of tropical countries, feeding on worms and insects.

* * * * *

Now when we think that these sluggish newts, and salamanders, and cæcilians, with their more nimble but comparatively unprotected relations, the frogs, are all the amphibians now living, we cannot but wonder how Life came to produce such a feeble set of creatures to fight the battle of existence.

But if we glance back to that far-off time when the ancient fishes were wandering round the shores and in the streams of the coal-forests, we shall be better able to read the riddle. For in those days it was a great step for an animal to get out of the water at all, and those that did so had a much better time of it than our frogs and newts have now, when the country is full of land enemies.

And so we find that the amphibia were not then the small scattered groups they are now, but strong lusty animals, with formidable weapons. In the hardened mud, which in those days formed the soft swampy ground of the coal-forests, but is now stiffened into the roofs and floors of our coal-mines, footprints have been left which tell us of large and formidable creeping animals, with toed feet and long flat tails, dragging themselves over the marshes of the coal-forests, and finding their way to many places which even the mud-fish with their paddles could not reach; and from time to time, in these same roofs and floors of our mines, both here and in America, we find the bones and coverings of these amphibia, buried in Nature’s catacombs for ages, and only brought to light by the rude hand of man.

These remains remind us that

“A monstrous eft was of old the lord and master of earth,

For him did the high sun flame, and his river billowing ran.

And he felt himself in his force to be Nature’s crowning race;”

for they show us huge and powerful creatures[60] which sported in the water or wandered over the land with sprawling limbs, long tails, and bones on which gills grew, while their heads were covered with hard bony plates, and their teeth were large, with folds of hard enamel on the surface. Some of these were fish-like, with short necks and broad flat tails, but they had true legs and toes; others, more like crocodiles, and sometimes ten feet long, were able to walk firmly, but still dragging their bodies and long tails over the swampy ground on which their footprints are still found; some were small and more like lizards, with simple teeth, scaly armour, and light nimble bodies; and these, probably, ran about quickly on the land, and have sometimes left their skeletons in the hollow trunks of the old coal-forest trees.

All these plated and formidable creatures were amphibia or double-lived animals, and this was their Golden Age, as they preyed upon the fishes in the swamps and ponds, probably not sparing even their nearest connections, the mud-fishes, who, less fortunate than themselves, had followed the road of fish-life instead of coming out upon the land. They lived so long ago that we can tell but little of their daily lives, but it is clear that they played a very different part from our small frogs and newts of to-day, and in their well-formed limbs were worthy forerunners of land and air-breathing animals.

But like the old race of fishes these large amphibians were only to have their day, for as other branches of the family tree grew up, and reptiles grew strong and mighty, and other true land animals began to flourish, these huge plated forms dwindled away, and we lose sight of them; and when we find any of their relations again it is only as our present frogs and newts, salamanders and cæcilians, which have taken up their refuge in lakes, ponds, ditches, underground waters, or damp mud. And, curiously enough, those forms of to-day which are most like the huge Labyrinthodonts,[61] as they are called, of the old coal-forests, are the feeble cæcilians, with their horny scales and their numerous ribs, although they have now fallen the lowest of all amphibians, and, with their sightless eyes and ringed and legless bodies, have taken to burrowing in the ground like worms.

Not so the frogs, which, like the bony fishes, began their career in later times, and have known how to fit themselves into many nooks and corners in life. In almost all countries of the globe they hop merrily about the ponds and ditches, never wandering far from the water, into which they jump and dive whenever danger threatens. It is true they are eaten by thousands, both as tadpoles and frogs, by birds, snakes, water-rats, and fish, and even by each other, but they multiply fast enough to keep up the supply, and find plenty of insects both in and out of the ponds. Nor have they kept entirely to a watery life, for their near relations, the toads, which have toothless mouths and toes less webbed, have ventured much farther on to the land, protected partly, no doubt, by the disagreeable acrid juice which they can throw out from a gland behind the eye whenever they are attacked.

It is curious to notice the quiet leisurely waddle of the sluggish toad, as he spreads out his short fat legs and puffs out his warty skin, and to compare him with the nervous, anxious, little frog, starting at every danger. And still more curious is it to see him getting out of his skin, as he does several times a year. For his skin does not peel off in pieces as it does in the watery frogs, but splits along his back; then he wriggles about till it lies in folds on his sides and hips, and, putting one of his hind feet between the front ones, draws the skin off the leg like a stocking off a foot. With the other leg he does the same, and then, drawing out his front legs, pulls the whole skin forward, and stripping it over his head, swallows it; thus deliberately putting his old coat inside him, and appearing in one that is glossy, fresh, and new. The toad has many enemies in spite of his acrid taste, and he shows his wisdom by hiding in walls and under stones in the daytime, and coming out in the dusk of evening to hunt the beetles and grubs so often out of reach of the water-loving frog.

Fig. 19.

The Flying Tree-Frog of New Guinea[62] (Wallace).

But the toad is not the only land relation of the frog; there are others of the group that venture even farther from water; for in most parts of the world (though not in England), tree-frogs, with sucking disks at the ends of their toes and fingers, climb the trees and hunt for insects among the leaves and branches; while in Borneo Mr. Wallace found one ([Fig. 19]) with webbed feet, which it spread out, and so flew down from the trees. There are plenty of the ordinary tree-climbing frogs to be seen in the south of France, their small green bodies peeping out from under the dull gray olive-leaves; and to be heard, too, in an endless chorus all night long when the spring arrives.

But how can these tree-dwellers bring up their little ones in water? Some of them come down and lay their eggs in the ponds, and even sleep down in the mud in winter. Others lay their eggs in little puddles of water in the hollows of the trees, and there the young ones live their tadpole life; while in one curious tree-frog of Mexico, called the Nototrema, the mother has a pouch in her back, and the father places the eggs in it for the little tadpoles to live in a moist home till they leap out as perfect frogs.

Nor is this the only case in which fathers and mothers take care of their young. In one species of frogs living near Paris, the father[63] winds the long string of gluey eggs round his thighs, and buries himself in the ground till the young tadpoles are ready to come out, and then he leaps into the water. And in one of the tongueless toads, the Surinam toad,[64] the mother’s soft skin swells up, forming ridges and hollows, and when her eggs are laid the father clasps them in his feet, and, leaping on her back, puts an egg into each hollow. Then the mother goes into the water, and remains there while each tadpole completes its changes in its own hole, jumping out at last a finished toad.

Yet, in spite of curious habits such as these, the frogs and their companions on the whole lead a very monotonous life. They are, it is true, more intelligent than fish, and have learned to know more of the world, but in the long ages that have passed since their ancestors roamed in the coal-forest marshes, other and higher animals have taken possession of the land, and left room only for a few scattered groups of amphibia. Still, however, they remain hovering between two lives, and filling such spots as neither the fishes nor the land animals can occupy; and when we hear them croaking in the quiet night, or see them leaping on the marshy ground, they remind us that we have still living in our day, a link between the fish whose world is a world of waters, and the air-breathing animals which have become masters of the land.

THE REPTILES IN THEIR PALMY DAYS.

CHAPTER V.
THE COLD-BLOODED AIR-BREATHERS OF THE GLOBE IN TIMES BOTH PAST AND PRESENT.

And now the transformation is complete, for when we pass on to the next division of backboned animals, the “Reptiles,” we hear nothing more of gills, nor air taken from the water, nor fins, nor fishes’ tails. From this time onward all the animals we shall study live with their heads in the air, even if their bodies may be in the water; they swim with their legs or, as in the case of the snakes, with their wriggling bodies, and they lay their eggs on the land where their young begin life at once as air-breathers.

Yet they can often remain for a long time both under water and under ground, for they are still cold-blooded animals, breathing very slowly, and easily falling into a state of torpor when the air around them is cold and chill. They are but the first step, as it were, to active land-animals; yet they have played a great part in the world, and when we know their history we shall be surprised to find how much Life has been able to make of her cold-blooded children.

To learn how this has been, however, we must travel away from home and our own surroundings. The tiny brown lizard which runs over our heaths, while its legless relation, the slowworm, burrows in the ground,—the few snakes which glide through the grass of our meadows, and the stray turtles thrown at rare intervals on our shores,—tell us very little about true reptile life. It is to Africa, India, South America, and other warm countries, that we must go to find the formidable crocodiles, huge tortoises, large monitor-lizards, and dangerous boa-constrictors, cobras, and rattle-snakes. And even then, strong and powerful as some of these creatures are, they do not tell us half the history of the cold-blooded air-breathers. For the day of reptile greatness, like that of the sharks and enamel-scaled fish, was long long ago.

Now that we know how frogs pass from water-breathing to air-breathing, and how axolotls, accustomed to live all their life in the water, can lose their gills and become land-animals, we can form an idea how in those ancient days, while still the huge-plated newts were wandering in the marshes, some creatures which had lost their gills would take to the land, and their young ones starting at once as air-breathers, as the black salamanders do now (see [p. 80]), would in time lose all traces of the double or amphibian life, and become true air-breathing reptiles.

At any rate, there we find them appearing soon after the coal-forest period passed away, at first few and far between, in company with the large amphibians, but spreading more and more as the ages passed on, till they in their turn became monarchs of the globe. Already, when the coal-forests had but just passed away, a lizard,[65] in some points like the monitors that now wander on the banks of the Nile, was living among his humbler neighbours; and from that time onwards we find more and more reptiles, till just before the time when our white chalk was being formed by the tiny slime-animals at the bottom of the sea, we should have seen strange sights if we could have been upon the globe. For the great eft was no longer

“... lord and master of earth.”

All over the world, and even in our own little England, which was then part of a great continent, cold-blooded reptiles of all sizes, from lizards a few inches long to monsters measuring fifty or sixty feet from head to tail, swarmed upon the land, in the water, and in the air. There were among them a few kinds something like our tortoises, lizards, and crocodiles; but the greater number were forms which have quite died out since birds and beasts have spread over the earth, and a wonderful and powerful set they were.

Some were vegetable-feeders, which browsed upon the trees or fed upon the water-weeds, as our elephants and giraffes, our hippopotamuses and sea-cows do now. Others were ferocious animal-eaters, and their large pointed teeth made havoc among their reptile companions, as lions and tigers do among beasts. Some swam in the water devouring the fish, while others, like birds or bats, soared in the air.

In the open ocean were the sea-lizards, some called Fish-Lizards,[66] like huge porpoises thirty feet long, but really cold-blooded reptiles, with paddles for legs, and long flattened tails for swimming. Woe to the heavily-enamel-scaled fish when these monsters came along, their pointed teeth hanging in their widely-gaping mouths as they raised their huge heads, with large open eyes, out of the water! Then among these were others with long swan-like necks and small heads,[67] which would strike at the fish below them in the water, while other slender, long-bodied monsters,[68] measuring more than seventy feet from tip to tail, flapped along the sea-shore with their four large paddles, or swam out to sea like veritable sea-serpents, devouring all that came in their way. These were all water-reptiles, while there were also many smaller land-lizards playing about upon the shore, and among the trees and bushes. But the strangest of all were perhaps the “Flying reptiles”[69] of all sizes, from one as small as a sparrow to one which measured twenty-five feet from tip to tip of its wings. These reptiles did not fly like birds, for they had no feathers, but only a broad membrane, stretching from the fifth finger of their front claw to their body, and with this they must have flown much as bats do now, while some of them were armed not only with claws, but also with hooked beaks and sharp teeth, with which they could tear their prey.

And meanwhile upon the land were wandering huge creatures, larger than any animal now living, which were true reptiles with teeth in their mouths, yet they walked on their hind legs like birds, probably only touching the ground with their short front feet from time to time, as kangaroos do. They had strong feet with claws, the marks of which they have left in the ground over which they wandered, supporting themselves by their powerful tails as they went.

Some of them were peaceful vegetarians,[70] browsing on the tree-ferns and palms, and rearing their huge bodies to tear the leaves from the tall pine-trees. But others were fierce animal-feeders. Fancy a monster thirty feet high,[71] with a head four or five feet long, and a mouth armed with sabre-like teeth, standing upon its hind legs and attacking other creatures smaller than itself, or preying upon those other huge reptiles which were feeding peacefully among the trees. Surely a battle between a lion and an elephant now would count as nothing compared to the reptile-fights which must have taken place on those vast American lands of the west, or on the European pasture-grounds, where now the remains of these monsters are found.

But where are they all gone? We know that they have lived, for we can put together the huge joints of their backbones, restore their gigantic limbs, and measure their formidable teeth, but they themselves have vanished like a dream. As time went on, other and more modern forms, the ancestors of our tortoises, lizards, crocodiles, and afterwards snakes, began to take the place of these gigantic types; while warm-blooded animals, birds and beasts, began to increase upon the earth. Whether it was that food became scarce for these enormous reptiles, or whether the birds and beasts drove them from their haunts, we are not yet able to find out. At any rate they disappeared, as the ancient enamelled fishes and large newts had disappeared before them, and soon after the beds of white chalk were formed, which now border the south of England and north of France, only the four divisions of tortoises, lizards, crocodiles, and snakes, survived as remnants of the great army of reptiles which once covered the earth.

* * * * *

Ah! if we could only have a whole book upon reptiles to show how strangely different these four remaining groups have become during the long ages that they have been using different means of defence; and how, even in a single group, they employ so many varied stratagems to survive in the battle of life! Look at the tortoises with their hard impregnable shells, the crocodiles with their sharp-pointed teeth and tough armour-plated skins, and the silently-gliding snakes with their poisonous fangs or powerful crushing coils. See how the tiny-scaled lizard darts out upon an insect and is gone in the twinkling of an eye, and then watch the solemn chamæleon trusting to his dusky colour for protection, and scarcely putting one foot before another in the space of a minute.

Each of these has his own special device for escaping the dangers of life and attacking other animals, and yet we shall find, before we finish this chapter, that they are all formed on one plan, and that it is in adapting themselves to their different positions in life that they have become so unlike each other.

We shall all allow that the Tortoises are the most singular of any, and it is curious that they are also in many ways the nearest to the frogs and newts, although they are true reptiles. Slow ponderous creatures, with hard bony heads ([Fig. 20]), wide-open expressionless eyes, horny beaks, and thick clumsy legs, the tortoises seem at first sight to be only half alive, as they lumber along,

“Moving their feet in a deliberate measure

Over the turf,”

carrying their heavy shell, and eating, when they do eat, in a dull listless kind of way. They do, in truth, live very feebly, for they can only fill their lungs with air by taking it in at the nostrils and swallowing it as frogs do, and then letting it drift out again as the lungs collapse, for their hard shell prevents them from pumping it in and out by the movement of their ribs like other reptiles. This slowness of breathing and the fact that they have only three-chambered hearts like frogs (see [p. 76]), so that the good and bad blood mix at every round, causes them to be very inactive, and they digest their food very slowly, and have been known to live months and even years without eating.

Fig. 20.

The Greek Tortoise.

This sluggishness would, indeed, certainly be their ruin in a bustling greedy world, if it were not for the strong box in which they live. Take in your hand one of the small Greek[72] or American[73] tortoises, so often sold as pets, and you will see how well he can draw back out of harm’s way, while at the same time you will, I think, be sorely puzzled to understand how he is made. His head, his four legs, and his tail, with their thick scaly skin, are intelligible enough. But why do all these grow on to the inside of his shell, so that when you trace them up you cannot find the rest of his soft body? You would hardly guess that his shell is the rest of his body, or at least of his skeleton. But it is so. The arched dome which covers his back is made of his backbone and ribs, and the shelly plates arranged over it are his skin hardened into horny shields, which, in the Hawksbill turtle, form the tortoise-shell which is peeled off for our use; while the flat shell under his body is the hardened skin of his belly, and the bones which belong to it.

Fig. 21.

Carapace of the Tortoise.

j, Joints of the backbone grown together; r, ribs formed into a solid cover; sh, shoulder bones; h, hip bones covered by carapace, which has grown over them.

Let us make this clear, for it is a strange history. If you look at the skeleton of a lizard ([Fig. 23], [p. 103]), it is all straight-forward enough. His head fits on to his long-jointed backbone, which is able to bend in all parts freely, down to the very tip of his tail. His front legs with their shoulder bones (s), and his hind legs with their hip bones (h), are attached in their proper places to his backbone, and lastly, his ribs (r) protect the inside of his body, and by expanding and contracting pump the air in and out of his lungs, the front ribs being joined underneath in a breastbone. It is easy to see, therefore, that the lizard may be active and nimble, twisting his body hither and thither, and escaping his enemies by his quickness. But the tortoise is slow and sluggish, and has only managed to baffle the numberless animals which are looking out for a meal by fabricating a strong box to live in. But he had to make this out of the same kind of skeleton as the lizard, with the one difference that he has no breastbone. Let us see how it has been brought about. The bones of his neck are jointed and free enough as you can see ([Fig. 21]), and so are the joints of his tail, beginning from behind his hip bones (h). But with his back it is different. The backbone can be clearly seen inside the empty shell, running from head to tail so as to cover the nerve-telegraph, but the joints (j) have all grown together, and on the top they have become flattened into hard plates,[74] while the ribs (r) which are joined to them have also been flattened out and have grown firmly together so as to make an arched cover or carapace. If now you look at the back of the young tortoise ([Fig. 22]), which has been taken out of the egg before it was full-grown, you will see these plates (p) on the side where the tortoise-shell (ts) has been peeled off. They have not yet widened out enough to be joined together, and the ribs (r) are as yet only united by strong gristle. But what is that row of oblong plates (mp) round the edge? Those are the marginal plates, and they are mere skin bones, like the bony plates of the crocodile, but they are all firmly fixed together so as to bind the edges of the ribs, while plates of the same kind form the shell under the body, and the whole is covered by the horny skin.

Fig. 22.