# The How and Why Library/Life/Animals-Section XIII
#### XIII. The Oyster-Fish that Climbed on Shore

Why we can almost see him do it. What? Why see Mr. Frog change into himself from a fish!
Right under our eyes, if we have him in an aquarium, where we can watch him, he changes from a water animal that swims just like a fish, to a land animal that jumps like a rabbit, a robin or a kangaroo.
So, if we ever wonder whether all the different kinds of insects and other animals could have grown out of one common cell, we have only to think of the strangely different parts that frog plays on the stage of life, in his one little lifetime; and how he came to get into the habit of changing himself like that.
It isn't the frog alone that goes through such wonderful changes. Isn't that change from a lump of jelly in a limy shell into a downy beautiful creature with little wings and little feet and a little " chirp, chirp" just as strange? Or the change from the flower-seed to flower, and back to seed again, just as strange as either the frog's life story or a chicken's life story?
In the growth of everything in the world—all plants and all animals—there is this beginning in a lower form of life, and a growing up through higher forms. And all plants and all animals begin with the lowest form of life—with a single cell. This is the way of growth of everything: Flower seed to flower, and back again; little egg to little bird and back again to egg; egg to tadpole, tadpole to frog and back again to egg. Egg to caterpillar, caterpillar to butterfly, then to egg again.
And back again, and back again; always "saying it over" as if Mother Nature were afraid we would miss this wonderful story of the ages, and the great lesson of it all.
"You can change. You can be what you want to be. You can change your bones and muscles, but best of all, and fastest of all, you can change your minds and your hearts. You can do good things and great things today and better tomorrow, and all your life."
What has Mr. Frog to say about all this?
He says he agrees to every word of it. He says this by his actions—and actions speak louder than words. Like most otherpeople he seems happiest when he is young; when he is a lively little tadpole. See him flirt and flip and flash through the water, playing with his little brother and sister tadpoles, as boys and girls play with each other, in the sunshine. Later, when he puts legs on his body and teeth in his mouth, hops out into the hard world and earns his living, he has many sober moments.
It would be better for Mr. Frog if he could stay longer with his mama—or even if he knew he had a mama to stay with! And Mama Frog would learn to be much brighter and to bring up brighter sons and daughters if she stayed with her little ones and brooded them and fed them, for awhile, as the birds do.
For, as we know, it is the animals that stay longest with their mamas and brothers and sisters that are the brightest and best of all. This whole group of animals to which the frog belongs are named "ver'-te-brates"—which means they have backbones. You're a ver'-te-brate. All Mama Frog ever does for her little ones is to find a nice, warm shallow place in which to lay her eggs. This she does in the spring. These eggs she covers with a thick coat of jelly that helps protect them from fish and other water animals that like a breakfast of fresh frog eggs.
After while, lying in this warmed shallow water, the frog's egg begins to grow long and narrow. A tadpole is on the inside stretching himself, after a sound sleep. And, sure enough, pretty soon, out wriggles a baby tadpole.
He doesn't seem to know yet that he is a baby frog. He seems to think he's an oyster; for he first fastens himself to a water weed or something of that sort, with a sucker fastener like the oyster's foot. Later, this sucker foot turns into a mouth—or rather he lets go, and begins to swim around and uses for a mouth what he had been using for a foot.
It is as if he said to himself: "No, come to think of it, I'm not an oyster. I'm a fish."
And so he goes plowing himself through the water like a fish, not backing himself through the water like a crawfish. But he still carries his lungs, that is, his gills, on the outside, very much as the lobster does all his life. So, for a while, it looks as if he had "half a notion" to be, not a fish, but a crawfish.
"But no," he says. "I think it will be more fun to play fish." So he soon gets rid of the outside gills and grows a new set that he puts inside, under a lid—just as the fish does.
This picture shows how a frog grows: I, the eggs are fastened to the underside of a leaf in shallow water; 2 and 2a, tadpoles when first hatched, showing feather-like gills; 3, the gills have disappeared; 4, full-grown tadpoles; 5, hind legs begin to grow; 6, four legs appear; 7, the tail grows shorter; 8, the tail has disappeared, the tadpole has grown into a frog.
Then it seems as if he gets tired of playing fish, and thinks it would be still nicer to get up on land and hop about. Maybe he thinks about flying, too. Goodness only knows what goes on inside the heads of "little tads." They change their minds and their bodies so often, and so surprisingly, they keep you guessing. Now the tadpole seems to be thinking most about hopping. He starts to grow two pair of legs. After the legs first come he has "lots of fun" with them, kicking himself through the water as a boy swims. Yet he still uses his tail in swimming, as if he hadn't quite given up the idea of being a fish.
Finally away goes his tail! And in the strangest way. For when he's about two months old, he begins to eat a great deal less and just hangs around in the water—not swimming as much as he did, but just keeping still—thinking and thinking. His tail keeps growing smaller and smaller—shorter and shorter. He absorbs it into his body until finally he hasn't any tail at all. No wonder he didn't eat much else—he's been living on his tail!
And now he isn't a fish any more at all—he's a frog. There He goes, hopping about on the shore, very lively and very happy. He keeps close to his old home in the water though, and every now and then plumps back into it; as if he wanted to keep up an acquaintance with his water friends.
Or, perhaps, he goes back to look for his lost tail!
I wonder if the kitten remembers when he was a tadpole. He seems to be wondering about his tail, anyhow. See how he keeps chasing it around and around. He doesn't know as much about tadpole tails as we do—does he?