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. The fins, or paddles, were very curious, and much like those of the whale; they consisted of above a hundred small bones strongly united together, in a sort of pavement enclosed in a strong skin, and not divided into toes, as you may observe in this representation of the entire skeleton. [Illustration] You may see many specimens of the skeleton itself in the British Museum. The Icthyosaurus was a great tyrant, and used to prey on every creature that came within his reach; this is known by the fossil remains found in the inside of his body. He used at times even to act the cannibal, and eat his own relations, for a large one has been dug out of the cliff at Lyme Regis, with part of a small one in his stomach undigested; he must have been altogether a very unamiable character. But as his family has been so long extinct, and we are told that we ought to say nothing but what is good concerning the dead, I shall not say any more about him, leaving you to form your own conclusions from what I have related to you. THE PLESIOSAURUS. Those still more strange looking animals with very long necks, which are represented swimming in the water, have been named _Plesiosauri_, a word signifying, _related to_, or _closely resembling_, a lizard. There are some nearly perfect specimens in the British Museum, and this is a representation made up by taking the uninjured parts of several, so as to make up a perfect whole. [Illustration] Taking it altogether, there is not one of the fossil animals so much unlike anything at present known to exist. Its usual length was from 9 to 15 feet, but it was at times very much larger. The head was much shorter in proportion than that of the Icthyosaurus, being more like that of the guana, the lizard which people eat in the West Indies. The neck must have been longer than that of any living animal, not even excepting the swan; it contained thirty-three bones, or _vertebræ_, while the whole of the rest of the back-bone in the body and tail, contained only fifty-seven.