DAItKHESS AND BLINDNESS. 



83 



to none but entomologists. I owe my own knowledge of 

 it to my friend Dr. Hagen of Cambridge, U.S. In all the 

 species of the cave beetle, Machcerites, the females only are 

 blind, while the males have well-developed eyes ; in spite of 

 this they both live together in absolute darkness. This proves 

 that the same result — total blindness — may come from dif- 

 ferent causes ; for we may fairly regard it as impossible that 

 in the last-named case the darkness of the cave has affected 

 the females alone, and been ineflPective on the males ; hence the 



Fig. 23. — Blind Ciiiiotlioe in fresh water (sraall pools) at Pelelew, Pelew Islands. 

 About ten diameters. 



blindness of the former cannot be caused by the darkness. In 

 confirmation of this statement I may also adduce the fact that 

 there are many blind or half-blind animals which live in well- 

 illuminated situations, where the moderate intensity of the light 

 would allow them the full use of eyes ; this is the case, for 

 instance, with many Bivalves — all fresh-water bivalves and 

 many sea bivalves — with various Annelida {ChcRtog aster), Crus- 

 tacea [Gyclopiolce), and others. I myself have found a perfectly 

 blind small species of Cymothoe (fig. 23) living in slightly 

 brackish water in a basin overshadowed by limestone rock, but 



