These shells--particularly the shells of the largest species of crabs--not only contain a great deal of lime but carbon and phosphorus, also, and these are splendid soil stuff, too. In the smaller kinds of crabs--of crustaceans, generally--these shells are mostly chitin, the stuff that the coverings of insects is made of. The crustaceans, by the way, are closely related to the insects. You may _suspect_ this by comparing their shapes, but then you'll see there isn't any doubt about it when I tell you that in getting born from the egg, the crabs and their kin don't come out dressed in their final shape, but change after they are born, first into one shape and then into another, just as insects do. Each shape, as it comes along, looks funnier than the rest; that is, it looks funny to us, but not, naturally, to the crabs. It must seem just the thing to them, for they always dress the same way and look as solemn about it as a man does when he wears a monocle. In fact, they do something almost as funny as wearing a monocle. For many of them carry their eyes about, not on the end of a cord, to be sure, but on the end of a stick. These "sticks" are called foot stalks. And they're not a bad idea either--for a crab. By moving them around the crabs can keep much better posted on what is going on about them than they could otherwise; particularly as a crab always moves sidewise or backward. What good a monocle does, though, nobody knows. III. THE STRANGER THAT MADE LONDON LAUGH But if we can hardly look a crab in the eye and keep a straight face, what would we do if we met a duck-billed mole? We'd laugh right out! I'm sure of it, for that's what even the men of science did when they saw the first one that came to England. This strange foreigner--it came to London all the way from Australia--had a body like a mole. But you couldn't call it a mole. For one thing, it had a bill like a duck. Yet no more could you call it a duck; for, besides having a body like a mole, it had a tail like a beaver. Still I'm afraid the beavers wouldn't have owned it--hospitable as they are--even if they could have overlooked that bill. For--can you believe it?--this duck-billed, mole-bodied, beaver-tailed creature lays eggs! [Illustration: THE ANIMAL X FROM THE ANTIPODES A mole's body, a duck's bill, a beaver's tail, this strange citizen of that land of strange animals, Australia, lays eggs like a bird and suckles its young like a pussy-cat! Do you wonder that the wise men of London laughed at the idea that there is any such creature--even when they were looking right at one?]