What animals build nests?

And lay eggs in the spring and early summer?

And go in large companies with their mates from one part of the world to another, at certain seasons, following the sun?

And float through the air—as the hawk does when he is sailing?

And fly, as the hawk does, when he "swims" through the air?

"Birds do all these things," you say. So they do. But they are not the only animals that do them. As you know they are not the only animals that lay eggs either. Fish and frogs and snakes lay eggs also. Some fish build nests. Many migrate—going from one part of the water world to another, in the spring or early summer, to lay their eggs.

The fish not only foretells the birds in these habits, but even in their differences in these habits. For, curiously enough, they have different ideas about where to build their nests, just as birds do. Some, like the beautiful little sunfish, that you know so well, lay their eggs on the ground—or beds of rivers—as the meadow-larks do. Others, like the stickle-back, build in the tops of water weeds. Red wing blackbirds build up in cat-tails and rushes.

As if still further to hint that they too are related to our " little brothers of the air," these fish that build nests in little water trees, also guard the eggs. It is only the fish that lay their eggs in the tops of water weeds that are bright enough to guard them. So it will be interesting for you to find, by noticing and inquiring, whether birds that build their nests on the ground are as bright as those that build in bushes or trees. More kinds of enemies get at a nest on the ground. The brighter bird as a rule chooses the better place. But you must not expect to find all birds of the trees wiser than all birds of the ground ; for there are the same kind of exceptions among the families of animals as there are among families of men. The meadow-lark is very clever about hiding its ground nest.

And there are fish that fly, just as there are birds that swim. Flying fishes are found in all the warmer waters of the world. It is in the warm countries that many queer animals, that are part one thing and part like another, are found. You know a fish has a pair of fins that he wears on each side of his back in the same place that the bird wears his wings. The back fins of the flying fish are much longer than those of the ordinary fish, with long ribs like a bat's wings.

These long, stout fins help the fish to jump out of the water— much as you may have seen a seal jump and climb up on a rock by means of his leg-fin-flippers. Then, once in the air, Mr. Flying Fish goes on flapping his fin wings and so manages to fly about three hundred yards—or the length of two city blocks.

As a frog seems to loan his webbed feet to the swimming birds, because he tried them first and found them "handy" for paddles or oars, so fish seem to have been the inventor of wings. Later, other animals adopted the wing idea, flying frogs, flying bats, flying birds, flying squirrels. The flying frog is found in one of these warm places of the earth—the East Indies. He has much larger feet than our frogs have, and he uses the webs between his toes to help hold himself in the air as he leaps from tree to tree ; for he's a tree-frog.

When men first tried to learn to fly—isn't it curious?—they did just as the flying frog and flying squirrel do. They got up on some high place, spread out something against the air to hold them up, and then jumped off. Just as little boys do when they jump from shed roofs, and try to sail down with umbrellas—only little boys mustn't do this because it's bad for the umbrella—and worse for the little boys—because it's so easy to get hurt. In the same way an aeronaut jumps from a balloon, with an umbrella-like parachute to break the fall.

If you have ever noticed a flying squirrel leap from tree to tree you have seen how useful those long thin strips of skin between his legs are to him. He can jump much farther than the ordinary squirrel because these extra strips of skin make a kind of wings to hold him up, just as the tree-frog's little umbrella feet help to support him and just as the bird's wings, not only act as sails to send him through the air, but help to support him as he flies.

Notice the flying squirrel. See, he jumps—not straight across but downward, in a slanting direction. And just before he lights he does just what a bird does before lighting—he turns and goes up again. Do you know what he does this for? If he didn't do it he would strike on his nose, against the tree—and real hard, too, because he is going pretty fast. Then he'd get a nose-bleed! As it is, by turning upward in his flight, he checks himself, as a boy does when, in skating, he turns up his foot and sticks the heel of his skate into the ice. He is also in a position to light on all four legs instead of "lighting" on his little nose.

You will notice that a bird spreads his tail much wider when he comes to light than he does when he is flying. Also notice that he curves upward, much as the crawfish does when he swims backward. See how his tail used in this way checks his flight?

As we also saw, his quills, his beak and his " toe nails" are made of the same stuff as the shell of the lobster. His bones are made of the same stuff as the shell of the oyster, and these bones and quills are hollow—like the reeds that grow by the water's edge. Remember too, that the bird, as well as the fish, has scales ; and these scales on his legs are of the same shape and made of the same kind of material as the fish's scales. Its feathers, too—as you can plainly see is true of the quills—are made of the same scale stuff. And, as if to remind us of the bird's relation to the fish, on the side of his scales—these scales, when the chicken or other little bird is young, look much like feathers.

While the bird, both in form and action, is related to the fish and the crawfish on one side by his scales, his wings—which are only flying fins—and his tail, we will find that in these and other ways he is related to all four-footed things—and to two-footed and two-armed creatures. Examine the leg of a chicken and you will find there a thigh, a shin, and, of course, feet. In the ankle you will find what is left of seven bones There are seven bones in your ankle, too ; but in the bird some of these bones have disappeared and some have grown together, because the bird doesn't use his feet enough to make so many bones necessary. If you had to keep your ankle still for a long time, say in a plaster cast, the bones would grow together, and doctors are very careful to see that joints are exercised just as soon as possible, in such cases.

So, as we say that certain kinds of birds are pigeons, although they differ so much from one another; that a hawk and a duck are both birds, although they differ so much more; and that the fish, the pigeon, and the horse and the man are all alike in having backbones, so we find, the more we study men and animals, that they are alike in more and more ways than we would ever imagine, just by looking at them.

Particularly if we are thinking how different they are, which is very easy. Try, instead, to see in what ways they are like each other. That is harder, but is ever so much more interesting.