Читать книгу Peter Parley's Wonders of the Earth, Sea, and Sky онлайн

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You have now seen the points in which the Icthyo-saurus chiefly resembled a crocodile or lizard; from which the latter half of its name is derived, saurus, a lizard. I must now tell you something of those parts in which it is like a fish, from which it takes the other part of its name, icthy, for icthus, a fish.

You know that crocodiles live a good part of their time on land, and they therefore have feet and a back-bone like land animals, which enable them to walk better, but do not allow them to swim so well as fish. The back-bone is heavy and firm, and each of the bones composing it has one side slightly hollow, and the other side swelling out to fit into the hollow in the one that comes next to it. But in fish both sides of the bones are hollow, and they are joined together by gristle, as you can easily see in the fish that are commonly eaten; this renders the back-bone much more flexible and lighter, and therefore better adapted for an animal always swimming. That of the Icthyosaurus was formed in the same manner, and we therefore judge that he spent his whole life in the water; for a back-bone so formed, would not have been able to support such a great heavy body when walking on the land.