2f!R DE. C. CHILTON ON THE SUBTEERANEAN 



all, even of those mentioned by Semper, can be thus explained. Thus Packard appears to 

 make no reference to the Pinnotheres mentioned by Semper [99, p. 80], the zogeaof which 

 has well-developed eyes of the typical character, while the full-grown animals which live 

 in the " water-lungs " of Holothurians " gradually become blind or half-blind ; the brow 

 grows forward over the eyes, and finally covers them so completely that, in the oldest 

 individuals, not the slightest trace of them, or of the pigment, is to be seen through the 

 thick skin ; while at the same time the eyes seem to undergo a more or less extensive 

 retrogressive metamorphosis " [99, p. 81]. 



Cases like this certainly seem to indicate, as Semper observes, " that the influence of 

 darkness is proved to be direct in each individual, and not hereditary." Here we see that 

 the eyes are preserved in the free swimming zosea, where they are of service to the animal, 

 but are gradually lost in the adult, where they are no longer required ; and while this 

 shows the powerful effects of disuse in the individual, it does not show that these effects 

 are inherited without the intervention of Natural Selection, as appears to be assumed by 

 Packard and others, who account for the blindness of cave animals by the direct effect of 

 the darkness and the consequent disuse of the organs. If the characters thus acquired 

 through disuse were necessarily inherited, we should expect to find the eyes of the zosea of 

 the Pinnotheres more or less imperfect. 



Packard, who discusses the bearing of cave life on the Theory of Descent at con- 

 siderable length, is thoroughly Neo-Lamarckian in his views, and sees little or no room for 

 the operation of Natural Selection. Thus, on p. 121, he remarks : — 



" Given great changes in the physical surroundings, inducing loss of eyes through 

 disuse, the abolition in some cases of the optic ganglia and optic nerves, the elongation of 

 the appendages, isolation from out-of-door allies, and the transmission by heredity owing 

 to close in-and-in breeding within the narrow fixed limits of the cave, are not these 

 collectively verce causae ? Do they not fully account for the original variations and their 

 fixation ? In short, can we not clearly understand the mode of origin of cave species and 

 genera ? What room is there in a case like this, or in that of parasitic animals, for the 

 operation of natural selection ? The latter principle only plays, it has seemed to us, a 

 very subordinate and final part in the set of causes inducing the origin of these forms " 

 [83, p. 121]. 



If these modifications, however, were the direct inherited eff'ect of the environment, 

 i. e. darkness &c., should we not expect to find them similar in all animals subjected to 

 the same conditions ? The modifications might be greater in some instances than in others, 

 in accordance with the varying lengths of time that the animals had lived under these 

 conditions, but we should certainly expect that the development in all cases would be 

 proceeding uniformly and in the same direction. Now it seems to me that we do not 

 find this process demonstrated even in the facts adduced by Packard himself, but that 

 there is a certain apparent capriciousness which is inconsistent with the constant and 

 uniformly acting causes that he sets forth. Thus, in the case of the eyes, instead of 

 the degeneration proceeding on similar lines in all individuals, we may have — : 



(1) Total atrophy of optic lobes and optic nerves, with or without the persistence in 

 part of the pigment or retina and the crystalline lens ; 



