"'Oh, they are of different sizes. Generally they are small. But they are not at all disagreeable to eat. I was told about them when I went down to visit the Fountain of the Samaritan, a very pretty, good-sized spring in the Ossuary.' "'Is it far from here?' he said eagerly. "'I cannot tell you at the moment. All I know is that this fountain was built in 1810 by M. Héricourt de Thury, Engineer of Subterranean Passages. As a matter of fact, this fountain is frequented by copepodes (Cyclops Fimbriatus)...' "'Ah! Copepodes! Are they fishes?' "'Yes; and they present modifications of tissue and coloration peculiar to themselves. They have a beautiful red eye.' "'What? One eye?' "'Yes; that is why they are called cyclops. But you need not be astonished that this fish has only one eye, for the Asellus Aquaticus, which also lives in the running streams of the Catacombs, a little aquatic isopode, as its name indicates, often has no eyes at all.' "'Impossible!' cried M. Longuet. 'How do they see?' "'They have no need to see, since they live in darkness. Nature is perfect. She is perfect in giving eyes to those who need them; she is perfect in taking away eyes from those who do not need them.' "M. Longuet appeared to reflect a little; then he said: 'Then, if we continued to live in the Catacombs, we should end by no longer having eyes?' "'Evidently: we should begin by losing the use of our sight and then our sight itself. Our descendants would soon lose their eyes altogether.' "'Our descendants!' he cried. "We laughed at this little slip; and then he pressed me to continue my description of the fishes of the Catacombs. "I discussed at length the modification of organs, their excessive development or their atrophy, according to the environment in which the species lives. I described the different kinds of fishes also at length. "But at last he said: 'All this about their organs is very interesting. But how do you catch them?' "'I can only tell you that the Catacombs which contain all these millions of bones cannot offer us a single maggot in the way of bait.' "'No matter,' said Theophrastus. 'There are more ways of killing a dog than hanging him. An angler has more than one trick in his basket; and the Asellus Aquaticus had better look out.' "That day and the days which followed it were very much alike. Whenever we came to a stream we stopped and drank. Always M. Longuet wanted to stop and fish. This was not wholly hunger; the sportsman's ardour burned in his soul. But I represented to him that, for anything we knew, we had the whole three hundred and ten miles of Catacombs to traverse before we came to the exit, and that it was our first duty to walk and walk. We might have fallen into them at the furthest end.