MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 
139 
doctrine of the derivation of cave animals. Of the facts we have ourselves observed or which have 
been observed by others we will briefly summarize: 
1. The variations in Pseudotremia cavernarum and Tomocerus plumbeus, found living near the 
entrance of caves in partial daylight. 
2. The bleaching of Polydesmus and Machilis found living in small caves; the blindness of 
Neotoma, or the wood-rat of Mammoth Cave; of fish found in wells and subterranean streams; 
the atrophy of the mole’s optic nerves induced in one generation. 
3. The larger size of the eyes of the young than in the adult Troglocaris of Europe and the 
blind crayfish of American caves; Semper’s history of the atrophy of eyes in the parasitic Pin 
notheres; eyes of Gammaruspulex affected after living in darkness; the eyes of Gammaridse in 
Lake Baikel becoming smaller the deeper they live; the instability in the eyes of Csecidotsea. 
Since this paper was written a few additional instances have come to our knowledge, and 
others are reported in periodicals bearing on this subject. While the eyeless and abyssal forms 
(both fresh-water and deep-sea) may have existed for many generations, for periods of hundreds 
and possibly thousands of years, yet the following facts tend to show that the bleaching of the 
body and atrophy of the eyes, as well as the adaptations to a life in darkness, may have been 
induced after but a few generations, perhaps but one or two only, resulting in the comparatively 
rapid evolution of cave species. 
Thus, in a small cave near White’s Cave, and at a point about 60 feet from the mouth, occurred 
a salamander ( Spelerpes longicaudatus Green) which was apparently bleached, being nearly white, 
with dark-brown blotches. The common Cambarus. bartonii occurs somewhat bleached in Mam¬ 
moth Cave, and this may not be the result of inheritance, but occurs in young hatched without 
the cave and afterwards carried in, so as not to be exposed to the light, the shell remaining pale, 
as in the very young. Perfectly white, bleached specimens of the common Polydesmus granulatus 
Say occurred in Indian Cave. The pale variety of Tomocerus plumbeus is possibly the product of 
a single or at least very few generations ; the white and blind Porcellio found by Mr. Hubbard in 
Little Wyandotte Cave, though possibly a true cave form, has not yet been found elsewhere, and 
may have been the young of a normal epigean species. But the most striking instance is the 
bleached specimen of Asellus communis from Lost River, referred to on pp. 15 and 33, which, 
though white, had eyes of normal size; there is good reason to suppose that these specimens 
were hatched in epigean waters, and that being carried into Lost River when young, the pigment 
in its skin owing to absence of light had failed to assume its normal dark color. 
A parallel case is that mentioned by R. Schneider* 
The author gives an account of the subterranean variety of G-ammarus pulex which is found at Clausthal. The 
first point of interest is its pale color, pigment being so completely absent from its body that it is milk-white and 
transparent; even the fat-cells, which are intensely red or orange-yellow in the ordinary G. pulex, are quite white. 
In the second place the eye is not normally developed, but is in the first stage of reduction ; the crystalline cones 
show signs of degeneration, and the whole eye exhibits that “ megalophthalmy” or proportionately greater size 
which is often the first indication of loss. The pigment has also begun to be reduced, and is of a dirty black, instead of 
a brownish color. The anterior pair of antennae exhibit elongation, owing to the increase in the number of the joints. 
r l’hcompared with the ordinary forms, a considerable increase in the amount of calcareous deposits; and 
there is always a considerable amount of iron oxide in the contents of the intestine whence the iron makes its way to 
various parts of the body. 
Friesf suggests that experiments should be made on the effects of rearing normal, eyed Gam- 
mari in darkness, and refers to Humbert’s statement, that in the greater depths of Lake Baikal 
with an increase in depth of their habitat there is an increasing lack of development of the eyes in 
some Gammaridm. Fries also states that he himself had previously observed a decrease in the 
pigment of the eyes in young examples of Gammarus pulex living in darkness. 
Here should be cited the observations of Anton Stecker, who states that— 
Chernes usually said to be eyeless, has rudimentary eyes, represented by clear, somewhat transparent spots, the 
chitine forming them being devoid of the granulations covering the rest of the shield. Each cornea is supplied by a 
large and well developed optic nerve, proceeding from an optic ganglion in connection with the brain. But the 
layer of crystalline rods was wholly absent. About 30 to 35 per cent,, of the specimens of Chernes cimicoides examined 
# Unterirdische Gammarus von Clausthal. P. B. Ak. Berlin, 1885, p. 1087. Also: Abh. z. Programm k. Real- 
Gymnasiums Berlin, Ostern. Abstr. in: Journal Roy. Micr. Soc. (2), vi, p. 243. 
tZool. Anzeiger, Aug., 1879, pp. 36, 37. 
