MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 
117 
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 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 subterranean 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 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 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 (71. pellucidus Jos.). 
3. As regards change of color, we do not recall an exception 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 out-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 hypertrophied, are said to be of the 
same flesh and reddish tints common to deep-sea animals. 
In the case of the cavernicolous 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 Chernetidae 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: 
