Reactions of Isopods to Light 245 



It seemed desirable, therefore, to carry on a critical study of 

 closely related species, one living within caves, the other outside 

 of caves, subjecting both species to the same conditions and com- 

 paring their reactions. Such a study ought to show whether 

 or not the cave species and its out-door relative are physiologi- 

 cally similar. So far as known to me, writers on cave species who 

 have made any mention of the sense organs of these animals have, 

 with one exception, noted m cave species, as compared with epigeal 

 forms, better developed tactile organs, but less efficient organs of 

 vision. But no extensive detailed observations on the relative 

 sensitiveness to light and other stimuli of a cave animal and an 

 outdoor animal of a similar sort had been made; such a compari- 

 son seemed worth making. 



Among the many who have mentioned the better development 

 of the tactile organs in subterranean animals as compensation for 

 the loss of eyes may be mentioned the following: Packard ('88, 

 pp. 123-130) reviewed the literature and cited many illustrations 

 of this compensation, particularly in American cave animals. 

 Hamann ('96) found the same to be true of European cave ani- 

 mals in general : likewise Chilton ('94, pp. 261-263 ) and Vire ('99) 

 in discussing the subterranean animals of New Zealand and 

 France, respectively, found evidence of this compensation. An 

 exception to this theory ol compensation is pointed out by Vej- 

 dovsky ('05, p. 12), who says that in Bathyonyx de Vismesi^ 

 Vejdovsky, from the depths of Lough Mask in Ireland, which 

 has extremely degenerate eyes, the other sense organs of the head 

 (Sinnespinsel und Sinneskapseln) are also less numerous and less 

 well developed than in the common fresh-water amphipods. 



As regards the isopods in particular, this increased develop- 

 ment of other sense organs in compensation for the loss of eyes was 

 noted by de Rougemont ('76) and subsequently by Leydig ('83, 

 p. 36). Vire ('97, pp. 131-132) calls attention to a striking series 

 of Asellidae showing stages in the hypertrophy of these organs; 

 first, the Asellus aquaticus which lives in brooks about Paris; 



' This is a deep-water form, to be sure, but it deserves consideration in this connection, since the modi- 

 fi cations of animals Uving in the depths of fresh water lakes are in general like those of subterranean 

 animals. 



