Birds that go much into the water have an oil about their feathers which keeps them from being soaked; for this reason, a duck, when it comes out of the water, is almost as dry as before it went in. But if a hen should go into the water in the same way, she would be wet through her feathers to her skin. She was not made to go into the water, and so has neither the oily feathers nor the webbed feet which are given to the duck.
Why fishes have scales, and why they are oily.
Why is it that fishes have scales? It is because they need a smooth covering in order to get along easily in the water. A covering which is rough, or which would soak in water, would be bad for them. The scales, you know, lap over one upon another, as you see here in the herring. They thus make quite a firm coat of mail, and at the same time do not hinder the bending motions of the fish. If the same covering were all in one, instead of being made up of many scales, it could not bend as easily as it does now in turning its course in the water. The scales are kept oiled, and this helps the fish to glide along swiftly. It is this that makes the fish so slippery that it is difficult to hold it in its struggles when it is first taken out of the water.
How the hermit-crab guards his naked tail.
I have told you, in another chapter, about the coverings of such animals as lobsters and crabs. There is one kind of crab, called the hermit-crab, that has no covering over his tail as he has over the other parts of his body. It is therefore very liable to be injured unless it is guarded in some way. And how do you think he guards it? He just puts it into some shell that he finds, as you see here, and then goes about, dragging it after him. As he grows the tail becomes too large for the shell, and as soon as he feels the shell beginning to pinch, he pulls his tail out and goes in search of another shell. It is amusing to see him try one after another till he finds one that fits well. Sometimes two of these crabs come to the same shell, and then they have a fight about it. Very foolish must a crab feel when he has driven another one off, and finds, after all, that the shell he has been fighting for does not fit his tail.
Questions.—What is said about our skin as a covering? What is said about its fitting well? Where are there wrinkles, and why? How is the covering of man’s body different from that of other animals, and why? What is said about animals in cold climates? What about those that live in warm countries? What about the elephant, the monkey, and the horse? What about the fur of the cat? What about the covering of birds? How are the feathers of the wing different from those of the breast, and why? Why are the feathers of some birds oily? Tell about the duck and the hen. Why do fishes have scales? Why are they kept oiled? Tell about the hermit-crab.