The How and Why Library/Life/Animals-Section XII
XII. The Oyster Learns to Swim
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Of course no oyster ever did learn to swim, because when he did learn he was no longer an oyster. It looks more as if he once knew how to swim and then forgot. You see his near cousins, the crawfish and the lobster could swim. To swim again he had to turn into something better than an oyster.
You can't imagine him coming out of his shell and turning into a fish, can you? Well, if you had never seen it you could not imagine a perfectly quiet egg coming out of its shell and turning into a beautiful bird; or a plant bursting out of a little brown seed and turning into an apple blossom. But it really wasn't just like that about the oyster and the fish. It was more like fairy fungi turning into a fern. The oyster improved himself into a fish, very, very slowly.
An egg has a shell of lime on the outside. So has the oyster. When the egg hatches the chicken has bones of lime on the inside. When the oyster improved himself into a fish he used the lime of his shell to make inside bones. He already had muscles, a stomach, blood vessels and nerves. But where did he get the idea of a jointed backbone? Where did he get the idea of swimming? Why, all plant and animal life began in the water. Living things were natural born swimmers. The oyster just forgot how. He was a water hermit. The angle or earthworm made ring muscles, and the lobster and crawfish jointed shells. The fish combined these old ideas of nature and made jointed ring bones for a backbone.
Perhaps the oyster got tired of lying as still as a bump on a log. He noticed the crawfish swimming and, inside, the crawfish was not nearly so well made as he. So he ought to be able to swim still better. He wasn't a bit ashamed of learning of his inferiors. So he opened his shell and his mind to his poor relation, Mr. Crawfish.
"Dear Mr. Crawfish," he said—for you can even make a crawfish good-natured and obliging if you call him "Dear Mr.;" "Dear Mr. Crawfish, teach me how to swim."
"Oh, I'm not much of a swimmer," said Mr. Crawfish, "I can only swim backward," for Mr. Crawfish, like the rest of us, is more modest and, in other ways more polite, when he is good-natured. He doesn't feel so boastful as he does when he is in a fighting mood."Well, you might swim better, dear Mr. Crawfish," said polite Mr. Oyster, "but you have wonderful legs and claws. Now I have always led a quiet, peaceable life, and I don't want any claws to fight with. And I have so much better insides—pardon me for saying so, Mr. Crawfish—that I don't need those claws to tear up my food before I swallow it. But I do want to swim.
"Now, it seems to me, that if we would take that horny stuff your shell is made of, I could divide it up into little pieces, to shingle the outside of my soft body to protect it. Then I wouldn't be afraid to come out of my shell house."
"Yes," said Mr. Crawfish, becoming enthusiastic over his friend's plans, "and when you got to be a bird you could use these same shingles for scales on your legs and feet, and to make the beak of your nose and your feathers and quills. Then, if you should happen, later on, to turn into a little boy you could use that material for finger nails and hair."
"And these scales," says Mr. Oyster, "will need to be tough and smooth and round at the edges like a boy's finger nails, so they won't get broken easily."
"But what are you going to do with that bony shell of yours?" asked Mr. Lobster. "It seems a great pity to throw it away. Mother Nature tells us never to throw anything away. And it's a perfectly good shell."
"You're right. Just let's think. I have got to fasten these strong muscles of mine to something. I notice you can't move anything, unless you have something to rest the lever on."
Of course Mr. Oyster is right. A boy can't pry up a stone unless he has something to rest the pryer or lever on. There was a man a long time ago who said he could move the world if he had something big and strong enough to rest a lever on. And he was right.
"I can pry myself through the water backward," says Mr. Lobster, "but if I tried to swim by moving my tail to right and left I'd break in two. Besides, my flipper tail would have to be set up on edge for the rudder to steer myself with, and I would have to have paddles on the sides to swim forward as well as backward."
"Oh, I get the whole idea now," declared Mr. Oyster, getting quite excited, "I'll take this limy shell of mine and put it on the inside, then I will have just the thing to fasten my muscles to. You see I fasten hinge muscles to it now, so I know how. I will have to divide it into jointed rings like the earthworm's muscle rings, or mybackbone would be as stiff as a—well as an iron poker. Then 111 make paddles on the sides, of the same horny substance that your shell is made of, but mixed with a softer substance so that I can furl and unfurl them like boat sails when I want to move through the water, and back up and turn and twist. The wings of those dragon-flies are made of just such stuff, but they aren't thick and tough enough for flying through the water—those beautiful gauzy wings.
So the oyster keeps his improved insides, shingles himself with scales made of the lobster's shell, changes the claw legs into fins, sets his tail on edge for a rudder, makes an inside backbone of his limy, outside house, but jointed like the crawfish's shell, and ringed like the muscles of the earthworm. He swallows some extra mouth-fuls of air in a little bag called his "swim bladder" to make himself lighter, and away he goes through the water!
When he gets to be a bird you will see him twist his tail back again, and carry it in the same position the lobster does. It will lie flat on the air pressing it down, just as the lobster's tail lies flat on the water!
What will he do that for?
That is the very first question we will take up when we come to birds—why does a bird have his tail set on like a crawfish?
But why not watch the next bird you see; notice how he uses his tail as a crawfish does. You can easily see this because he uses it in this way just when you can watch him best—when he drops to a perch.