Page:Popular Science Monthly Volume 46.djvu/837

Rh Schioldte, of Copenhagen, and Dr. Gustave Joseph, of Breslau, have made curious studies of the transitions in gradual atrophy of vision from aërial animals to their cave-inhabiting congeners. M. Joseph believes that when the light is diminished in the animal's habitat, dislocation of the eyes takes place, and that the intermediate species are especially domiciled in caves where a twilight prevails, or where a little light enters at noon or in summer. While the Proteus and the Amblyopsis of the Mammoth Cave have the eyes simply covered by a membrane, some mollusks appear not to have even a place for the most rudimentary ocular globe. We might, however, ask if these different degrees of blindness do not proceed in a measure from differences in the length of time that has elapsed since the species were buried. On the one side, some animals have been found in caves having their eyes preserved in full vigor; on the other side, artesian wells have thrown to the surface, and some subterranean lakes have yielded to the collector, living beings in no wise modified from those living above ground. It has been reasonably concluded from this that these beings have been drawn in by the water that feeds the lakes coming from unknown distant points, and that their abode underground has not been long enough continued to make them blind. It would be interesting to compare atrophy of vision in cave-inhabiting animals or in those of subterranean waters with those remarkable creatures specially adapted to enormous sea depths which, have been collected in the expeditions of the Challenger, Talisman, and others of like purpose.

It is perhaps possible to attach too much importance to the blindness of subterranean animals as a peculiarity. A considerable number of species living in surface waters are destitute of vision.

M. Joseph is of the opinion that "the presence or absence of organs of vision always corresponds with the conditions of existence of the animals." So far as concerns the heredity of atrophies, Hovey says, in his Celebrated American Caverns, that Dr. Hayden witnessed the birth of eight little blind amblyopses.

What we have said is only the present indication of some of the questions raised by underground zoölogy. An ample harvest of facts heretofore not observed may be anticipated from the exploration of the numerous caves of the Causses in France—such as have been made in the caves of Carniola and the United States—or of any caves as yet virgin to scientific examination. The subject is full of interest, and all the more attractive because so much still remains to be found out about it.

The outfit for hunting cave-inhabiting animals includes an