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

Footnote 15. Lepidosteus.

Footnote 16. Polypterus.

Footnote 17. Amia.

Footnote 18. Lepidosiren.

Footnote 19. Protopterus.

Footnote 20. Ceratodus.

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

Footnote 21. These fish, coiled round, may be seen in the British Museum.

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,

Footnote 22. Ichthyodorulites.

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

Footnote 23. Dipterus.

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.

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