"What?" said Jack, with a certain amount of eagerness. "They struck me as being those great lizard things which they find turned into fossils out Swanage and Portland way. I dare say you've seen specimens of them in the British Museum." "No," said Jack, colouring a little, "I have never taken any interest in such things." "No?" said the captain wonderingly. "Ah, well, perhaps you will. Now it struck me that these things were--were--Do either of you gentlemen remember the name of them?" "Plesiosaurus. Lizard-like," said Sir John. "That's it, sir," cried the captain, glancing at the speaker, and then looking again at Jack. "And I tell you how it struck me, and how I accounted for their being so seldom seen." "Yes!" said Jack, who had laid down his knife and fork, and was leaning forward listening attentively. "How did you judge that?" "From its large eyes." "What had that to do with it?" "It meant that it was a deep-sea living creature. You'll find, if you look into such matters, sir, that things which live in very deep water generally have very large eyes to collect all the light they can." "But yours were living on the top of the water," said Jack. "To be sure," cried the doctor, giving Sir John a sharp glance. "Come, captain, that's a poser for you." "Well, no, sir," replied the captain modestly, and with a quiet smile; "I think I can get over that. Perhaps you know that fish which live in very deep water, where the pressure is very great, cannot live if by any chance they are brought to the surface. The air-vessels in them swell out so that they cannot sink again, and they get suffocated and die." "But if it was their natural habit to live in deep water," said Jack, "they would not come to the surface." "If they could help it, sir," said the captain; "but when a creature of that kind is ill it may float toward the surface, and turn up as you see fishes sometimes. I fancy that my great lizard things are still existing in some places in the mud or bottom of the sea, that they are never seen unless they are in an unnatural state, and then they soon die, and get eaten up by the millions of things always on the look-out for food, and their bones sink." "I should like to see one," said Jack thoughtfully. "And I should like to show you one, sir," said the captain. "There's no knowing what we may see if we cruise about. Well, I'll promise you sea-snakes and whales and sharks. I can take you too where there are plenty of crocodiles for you to practise at with a rifle. Good practice too to rid the world of some of its dangerous beasts." Jack shuddered, and wanted to say that he did not care to see anything of the kind, but he did not speak, and just then the captain rose from the table, drew up the blind, and looked out. "There you are, sir," he said. "Come and look. The lads were ready enough when I told them to light up to-night. Looks nice, don't she?"