DARKNESS AND BLINDNESS. 



83 



to none but entomologists. I owe my own knowledge of 

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

 species of the cave beetle, ^fachcerites, 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 ineffective on the males ; hence the 



Fig. 23.— Blind Cymothoe in fresh -n-ater (sninll 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 (Chcetog aster), Crus- 

 tacea [Oyclopidce), 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 



