Page:Popular Science Monthly Volume 36.djvu/404

39 animals, the eyes are wanting from causes of the same nature as have induced their absence in true cave animals. No animal or series of generations of animals, wholly or in part, lose the organs of vision unless there is a physical appreciable cause for it. "While we may never be able to satisfactorily explain the loss of eyes in certain deep-sea animals from our inability to personally penetrate to the abysses of the sea, we can explore caves at all times of day and night, of winter and summer; we can study the egg-laying habits of the animals, and their embryonic development; we can readily understand how the caves were colonized from the animals living in their vicinity; we can nicely estimate the nature of their food, and its source and amount, as compared with that accessible to out-of-door animals; we can estimate with some approach to exactitude the length of time which has elapsed since the caves were abandoned by the subterranean streams which formed them and became fitted for the abode of animal life. The caves in southern Europe have been explored by more numerous observers than those of this country, and the European cave fauna is richer than the American, but the conditions of European cave life and the effects of absence of light and the geological age of the cave fauna are like those of American caves. Moreover, the cave life of New Zealand and the forms there living in subterranean passages and in wells show that animal life in that region of the earth has been affected in the same manner. The facts seem to point to the origin of the cave forms from the species now constituting a portion of the present Quaternary fauna; hence they are of very recent origin.

The result of cave exploration shows that no plants, even the lowest fungi, with the exception of Oozonium auricomum Link, and perhaps one or two other kinds of fungi common to Europe and America in and out of caves, can so adapt themselves as to live and propagate their species in the total darkness of caverns. They are far more dependent on the influence of light than animals.

"We will now briefly rehearse the facts relating to the changes in structure and color undergone by animals adapted to a life in total darkness in caves, premising that, so far as we know, the Protozoa detected in subterranean waters do not essentially differ from those living in the light. It appears from the following facts that eyeless animals change their color as well as those having eyes:

1. A sponge (Spongilla stygia) found by Dr. Joseph in the waters of Carniolan grottoes, instead of being green, is pellucid and bleached.

2. The Hydra (H. pellucida), also found by Dr. Joseph in the subterranean lakes of Carniola, was, as its name indicates, neither