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.
