MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 117 



day and night, of wiuter and summer ; we can study the egg-laying habits of the animals, and 

 their embryouie 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 

 aud 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 subterrauean 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, aud the European cave fauna is richer than the American, but the conditions of Euro- 

 pean cave life and the effects of absence of light and the geological age of the cave fauna are a 

 nearly exact parallel with those presented in the foregoing pages. Moreover, the cave life of 

 New Zealand and the forms there living in subterrauean passages and in wells show that 

 animal life in that region of the earth has been effected 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 excep- 

 tion 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 aud 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 under- 

 gone 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 {R. pellucida), also found by Dr. Joseph in the subterranean lakes of Carniola, 

 was, as its name indicates, neither green nor brown, like the two species of the upper world, but 

 pellucid, bleached out, or colorless. 



Such was also found by Dr. Joseph to be the case with the smaller Crustaceans, such as cer- 

 tain cave species of Cypris, Leptodera, Estheria, and Branchipus (B. pellucidus Jos.). 



3. As regards change of color, we do not recall au exceptiou to the general law, that all cave 

 animals are either colorless or nearly white, or, as in the case of Arachnida and insects, much 

 paler than their ouc-of-door relatives. 



The worms (planarians and earth-worms) are somewhat paler than their allies living out of 

 caves, but as the normal environment of most planarians and earth-worms is much like those of 

 cave animals, the difference is not so marked, though both of our cave planarian worms are white 

 and eyeless. 



All the cave Crustacea, both aquatic and terrestrial, are colorless or whitish, more or less 

 vitreous, and pellucid, the pigment cells being degenerate and functionless. The effects of total 

 darkness seem quite different from the influence to which the eyeless deep-sea Crustacea are 

 exposed, since they, like their fellows with eyes normal or bypertrophied, are said to be of the 

 same flesh and reddish tints common to deep-sea animals. 



In the case of thecavernicolous Myriopods the bleaching of the body is very marked. In out- 

 of-door Myriopods the normal tint of the integument is brown or rarely amber-brown ; but the 

 color of the cavernicolous species is white or flesh-white, like a freshly-molted Myriopod of 

 normal habitat. 



The cave species of Arachnida are usually pale whitish or pale amber-colored, or pale horn, 

 with a reddish tint. Of the mites, some are white, others horn-color, or chitiuous. In the 

 family Chernetidse the cave species are "dull white," or "pale horn with a reddish tint," or " pale 

 yellowish." 



We will now briefly note the effects upon the eyes and optic lobes of a life in total darkness; 

 these are, as more fully stated in the previous chapter : 



