By DAVID STARR JORDAN.

Long ago, in the old Devonian times, when life was very leisurely, all the beasts and people that there were lived in the sea together. The air was dull and murky on the land. It was so light that it gave no support to the body, and so those that ventured about in it had to lie prone on the ground all the time wherever they went. So they preferred to stay in the water, where motion is much easier. Then, too, water is so much better to breathe than air, if one has gills fitted for it! He has only to open his mouth and the water rushes in. Then he has only to shut his mouth and the water rushes out backward, bathing his gills on the way. Thus, the air dissolved in the water purifies all the little drops of blood that run up and back through the slender tubes of which the gills are made.

But in those days, besides the gills, some of the beasts of the sea had also a sac in the throat above the stomach in which they could stow away air which they took from the atmosphere itself. This served them in good stead when they were in crowded places, in which the air dissolved in the water would fail them.

And those which were so provided used to venture farther and farther out of the water, pushing their way heavily on the ground. And those which could put forth most effort survived, until at last their descendants were able to maintain themselves on the land altogether. These gave rise to the races of reptiles and birds and mammals, the ancestors of all the land beasts that you know, as well as men and women and all the monkey people. But it was very long ago when this happened, and because these ancestors came finally out of the water they have no part in the story I am trying to tell to-day.

Those that remained in the water grew more and more contented with their condition. Because the medium in which they lived was as heavy as their bodies, they swam without much effort, and effort not being needed, it was not put forth. As there was food enough in the water, they did not need to go on land. As they did not go on land, they did not use their lungs for breathing, the air sac gradually shrank away, or was used for some other purpose, and all the parts of the body became adjusted for life in water, as those of their cousins who left the sea became fitted for the life in air. Being now fishes for good, all the progress since then has made them with each succeeding century more and more decidedly fishy.

And because they are fishes they are contented to live in little brooks, which would not satisfy you and me at all. But our ancestors in the early days were more ambitious, and by struggle and effort won what seems to us a larger heritage.

So it happened one spring when the ice melted out from some little brook that flows down from somebody's hills somewhere toward some river that sets toward the Mississippi, the little fishes began to run.

And first of all came the lampreys, but they hardly count as fishes, for they have yet to learn the first principles of fishiness. A fish is a creature whose arms and legs are developed as fins, having cartilaginous rays spreading out fanlike to form an oar for swimming. But the lamprey has no trace of arm or leg, not even a bone or cartilage hidden under the skin. And its ancestors never had any limbs at all, for the earliest lamprey embryo shows no traces of them. If the ancestors ever had limbs, the descendants would never quite forget it. Some little trace would be kept by the clinging force of heredity, and at some time or another this rudiment would appear. And the lower jaw they lack too, for that is really another pair of limbs joined together in front—as it were, a pair of short hands clasped together and never unlocked.

But though the lampreys have no limbs and no jaws and are not fishes anyhow, they do not know the difference, and come up the brook in the spring, rushing up the rapids, swirling about in the eddies, just as if they were real fishes and owned the brook themselves. They are long, slender, and slippery, shaped like eels, without any scales and with only a little fin, and that along the back and tail, an outgrowth from the vertebral column. The vertebral column itself is limp and soft, the vertebrÆ only imperfectly formed and made of soft cartilage. In front the lamprey seems to be cut off short, but if we look carefully we see that the body ends in a round disk of a mouth, and that this disk is beset by rows of sharp teeth. A row of the sharpest of these is placed on the tongue, and two of these are above the gullet, for the tongue to scrape against them. And the rest are all blunt and are scattered over the surface of the mouth, which has no lips nor jaws, but is surrounded by a belt of fringes. When the lamprey is hungry he puts his mouth against the side of some fish, exhausts the water between, and then the pressure of the outside water holds him there tightly. When this is done, the fish swims away and the lamprey rides with it, giving no thought to where he is going, but all the while scraping away the flesh with his rasplike teeth. When he has filed off enough fish flesh to satisfy his hunger he lets go, and goes off about his business. The fish, who does not know what hurt him, goes off to get well if he can. Usually he can not, for the water of the brook is full of the germs of little toadstool-like plants, and these fasten themselves on the fish's wounds and make them bigger and bigger, until at last the cavity of the abdomen is pierced and little creatures of many kinds, plant and animal, go in there and plunder all this fish's internal organs, to carry them away for their own purposes.

But when the lampreys come up the April brook it is not to feed on fishes, nor is it to feed at all. Nature is insistent that the race should be kept up, and every animal is compelled to attend to the needs of the species, even though it be at the sacrifice of all else. If she were not so, the earth and the seas would be depopulated, and this is a contingency toward which Nature has never looked.

The lampreys come up the stream to spawn, and while on this errand they fasten their round mouths to stones or clods of earth, that the current may not sweep them away. When so fastened they look like some strange dark plant clinging to the bottom of the brook. When the spawning season is over some of them still remain there, forgotten by Nature, who is now busied with other things, and they wear their lives away still clinging—a strange, weird piece of brook-bottom scenery which touched the fancy of Thoreau.

When the young are hatched they are transparent as jelly, blind and toothless, with a mouth that seems only a slit down the front end of the body. These little creatures slip down the brook unobserved, and hide themselves in the grass and lily pads till their teeth are grown and they go about rasping the bodies of their betters, grieving the fishes who do not know how to protect themselves.

The lamprey is not a fish at all, only a wicked imitation of one which can deceive nobody. But there are fishes which are unquestionably fish—fish from gills to tail, from head to fin, and of these the little sunfish may stand first. He comes up the brook in the spring, fresh as "coin just from the mint," finny arms and legs wide spread, his gills moving, his mouth opening and shutting rhythmically, his tail wide spread, and ready for any sudden motion for which his erratic little brain may give the order. The scales of the sunfish shine with all sorts of scarlet, blue, green, purple, and golden colors. There is a black spot on his head which looks like an ear, and sometimes grows out in a long black flap, which makes the imitation still closer. There are many species of the sunfish, and there may be a half dozen of them in the same brook, but that makes no difference; for our purposes they are all as one. They lie poised in the water, with all fins spread, strutting like turkey-cocks, snapping at worms and little crustaceans and insects whose only business in the brook is that the fishes may eat them. When the time comes, the sunfish makes its nest in the fine gravel, building it with some care—for a fish. When the female has laid her eggs the male stands guard till the eggs are hatched. His sharp teeth and snappish ways, and the bigness of his appearance when the fins are all displayed, keep the little fishes away. Sometimes, in his zeal, he snaps at a hook baited with a worm. He then makes a fierce fight, and the boy who holds the rod is sure that he has a real fish this time. But when the sunfish is out of the water, strung on a willow rod, and dried in the sun, the boy sees that a very little fish can make a good deal of a fuss.

When the sunfish goes, then the catfish will follow—"a reckless, bullying set of rangers, with ever a lance at rest." The catfish belongs to an ancient type not yet fully made into a fish, and hence those whose paired fins are all properly fastened to the head, as his are not, hold him in well-merited scorn. He has no scales and no bright colors. His fins are small, and his head and mouth are large. Around his mouth are eight long "smellers," fleshy feelers, that he pushes out as he crawls along the bottom in search of anything that he may eat. As he may eat anything, he always finds it. His appetite is as impartial as that of a goat. Anything from a dead lamprey or a bunch of sunfish eggs to a piece of tomato can is grateful to him. In each of the fins which represent his arms is a long, sharp bone with a slimy surface and a serrated edge. These are fastened by a ball-and-socket joint, and whenever the fish is alarmed the bone is whirled over and set in place; then it sticks out stiffly on each side. There is another such bone in the fin on the back, and when all of these are set there is no fish that can swallow him. When he takes the hook, which he surely will do if there is any hook to be taken, he will swallow it greedily. As he is drawn out of the water he sets his three spines, and laughs to himself as the boy pricks his fingers trying to get the hook from his stomach. This the boy is sure to do, and because the boy of the Mississippi Valley is always fishing for catfish is the reason why his fingers are always sore. The catfish is careless of the present, and sure of the future. After he is strung on a birch branch and dried in the sun and sprinkled with dust and has had his stomach dug out to recover the hook, if he falls into the brook he will swim away. He holds no malice, and is ready to bite again at the first thing in sight.

The catfish uses his lungs as an organ of hearing. The needless lung becomes a closed sac filled with air, and commonly known as the swim bladder. In the catfish (as in the suckers, chubs, and most brook fishes) the air bladder is large, and is connected by a slender tube, the remains of the trachea, to the oesophagus. At its front it fits closely to the vertebral column. The anterior vertebrÆ are much enlarged, twisted together, and through them passes a chain of bones which connect with the hidden cavity of the air. The air bladder therefore assists the ear of the catfish as the tympanum and its bones assist the ear of the higher animals. An ear of this sort can carry little range of variety in sound. It probably gives only the impression of jars or disturbances in the water.

The catfish lays her eggs on the bottom of the brook, without much care as to their location. She is not, however, indifferent to their fate, for when the little fishes are hatched she swims with them into shallow waters, brooding over them and watching them much as a hen does with her chickens. In shallow ponds the young catfishes make a black cloud along the shores, and the other fishes let them alone, for their spines are sharp as needles.

Up the brooks in the spring come the suckers, large and small—coarse, harmless, stupid fishes, who have only two instincts, the one to press to the head of the stream to lay their eggs, the other to nose over the bottom of the stream wherever they go, sucking into their puckered, toothless mouths every organic thing, from water moss to carrion, which they may happen to find. They have no other habits to speak of, and when they have laid their eggs in a sandy ripple they care no more for them, but let go of life's activity and drop down the current to the river whence they came. There are black suckers and white suckers, yellow ones, brown ones, and mottled, and there is more than one kind in every little brook, but one and all they are harmless dolts, the prey of all larger fishes, and so full of bones that even the small boy spits them out after he has cooked them.

Then come the minnows, of all forms and sizes, the female dull colored and practical, laying her eggs automatically when she finds quiet water, and thinking no more of them afterward. The male, feeble of muscle, but resplendent in color, with head and fins painted scarlet or purple, or silver white, or inky black, as may be most pleasing to his spouse. His mouth is small and without teeth, for he feeds on creatures smaller than fishes, and his head in the spring is covered with coarse warts, nuptial ornaments, which fall off as soon as the eggs are properly disposed of. In the little brook which comes to my mind as I write two kinds of minnows come up the stream together before the others realize that it is verily spring. The one is small, dainty, translucent, and active, swimming free in the water near the surface and able to take care of itself when pursued by a sunfish or bass. Along the side of its body are two black stripes not quite parallel, and between and below them the silvery scales are flushed with fiery scarlet. The fins are all yellow, with scarlet at base, and as the male passes and repasses before the female all these colors, which she has not, grow brighter than ever.

The next is a larger fish, clumsy in form, hugging the bottom as he swims. The whole body of the male is covered with coarse white warts, and across each fin is a bar of black, white, and orange. This minnow feeds on mud, or rather on the little plants which grow in mud, and his intestines are lengthened out proportionally. In fact, they are so long that, to find room for them, they are wound spool-fashion about the air bladder in a way which happens to no other animal.

Of the other minnows, the one attracts his female by a big, jet-black head; another by the painted fins, which shine like white satin; another by his deep-blue sheen, which is washed all over with crimson. In fact, every conceivable arrangement of bright colors can be found, if we go the country over, as the adornment of some minnow when he mates in the spring. The only exception is green, for to the fishes, as to the birds, green is not a color. It only serves to cover one, while the purpose of real color is to be seen.

And there are fishes whose colors are so placed that they are hidden from above or below, but seen of their own kind which looks on them from the side.

The brightest fishes in the world, the "Johnny darters," are in our little brook. But if you look at them from above you will hardly see them, for they are dull olive on the back, with dark spots and dashes like the weeds under which they lie. The male is only a little fellow, not so long as your finger and slim for his size. He lies flat on the bottom, half hidden by a stone, around which his tail is twisted. He will stay there for hours, unseen by other fishes, except by his own kinsmen. But if you reach down to touch him with your finger he is no longer there. The tail straightens out, there is a flash of blue and scarlet, and a foot or two away he is resting quietly as before. On the bottom is his place, and he seems always at peace, but when he moves his actions are instantaneous and as swift as possible to a creature who lives in the water. On the bottom, among the stones, the female casts her spawn. Neither she nor the male pays any further attention to it, but in the breeding season the male is painted in colors as beautiful as those of the wood warblers. When you go to the brook in the spring you will find him there, and if you catch him and turn him over on his side you will see the colors that he shows to his mate, and which her choice through ages has tended to develop in him. But do not hurt him. He can only breathe for a moment out of water. Put him back in the brook and let him paint its bottom the colors of a rainbow, a sunset, or a garden of roses. All that can be done with blue, crimson, and green pigments in fish ornamentation you will find in some brook in which the darters live. It is in the limestone brooks that flow into the Tennessee and Cumberland where they are found at their brightest, but the Ozark region comes in for a close second.

There will be sticklebacks in your brook, but the other fishes do not like them, for they are tough and dry of flesh, and their sharp spines make them hard to swallow and harder still to digest. They hide beneath the overhanging tufts of grass, and dart out swiftly at whatever passes by. They tear the fins of the minnows, rob the nests of the sunfish, drag out the eggs of the suckers, and are busy from morn to night at whatever mischief is possible in the brook.

The male dresses in jet-black when the breeding season is on, sometimes with a further ornament of copper-red or of scarlet. The sticklebacks build nests in which to hide their eggs, and over these the male stands guard, defending them with courage which would be dauntless in any animal more than two inches long. Very often he has to repel the attacks of the female herself, who, being relieved of all responsibility for her offspring, is prone to turn cannibal. Even the little dwellers of the brook have their own troubles and adversities and perversities.

Last of all comes the blob, or miller's thumb, who hides in darkness and picks up all that there is left. He is scaleless and slippery, large of head, plump of body, and with no end of appetite. He lurks under stones when the water is cold. He is gray and greenish, like the bottom in color. He robs the buried nests of eggs, swallows the young fishes, devours the dead ones, and checks the undue increase of all, not forgetting his own kind. When he has done his work and the fall has come and gone, and the winter and the spring return, the brook once more fills with fishes, and there are the same kinds, with the same actions, the same ways, and the same numbers, and one might think from year to year, as the sun is said to do, that these were the selfsame waters and the selfsame fishes mating over and over again and feeding on the selfsame food.

But this is not so. The old stage remains, or seems to remain, but every year come new actors, and the lines which they repeat were "written for them centuries before they were born." But each generation which passes changes their lives just a little, just as the brook and the meadow itself is changing.