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

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.

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; ge,  gill cover; af,  arm-fin; lf,  leg-fins; sf,  single fins; ms,  mucous scales.

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 arc 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 to 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 sec, 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. p. 23) 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 (ca ), 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. p. 2 3) 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 therewas another veryancient 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.

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 sea-weed 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.

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 or V-shaped, but in the sharks the top point is usually longer than the lower one, and in some, such as the Thresher, it is very remarkably so.

Carcharias glaucus. The Blue Shark (from Brehm ). To show the five slits in the neck, the uneven tail, and the mouth opening under the pointed snout.

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 (Acipenser sturio.) 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 arc covered by a horny flap like the bony fish, and like them too they have an air-bladder under the backbone. 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, 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, 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, of the Amazons, of the Nile, and of the rivers of Queensland in Australia. 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. 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 seawccds 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 w ay 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 sharklike 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.

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 Dragonflies, 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 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, 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 hauntcd 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 Chimera 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.