( cxlvi ) 



This apparent irregularity in the development of the eye 

 among Ectoparasites is, no doubt, explained by some difference 

 in habits, although much still remains a mystery to us. 



Is the absence of eyesight in these insects due to parasit- 

 ism ? Only to a certain extent, I think. We know that the 

 insects which in the imago state are totally or partially blind 

 are found among those which live in caves, deep under stones, 

 or in other places where there is little or no light. The 

 Ectoparasitic insects whose eye-sight is lost or reduced are 

 those living on hosts that frequent similar dark places. Al- 

 though not invariably true, the parasites of mammals which 

 conceal themselves or dwell in burrows, hollow trees, caves, 

 etc., are blind. Most of the fleas, for instance, which live 

 on burrowing mammals are blind, while the bird- fleas have 

 the eyes well developed. Bat parasites have no eyes or 

 only remnants of them, with the exception of the Cimicidae. 

 This exception is instructive. The Cimicidae or bed-bugs, 

 some of which feed on bats (text-fig. 6) are closely allied to 

 the Polyctenidae (text-fig. 7), likewise found on bats, but 



Fig. 6. Head of Loxaspis villosus Stal (1865). 

 ,, 7. ,, ,, Polyctenes molossu-i Gigl. (1864). 



totally blind. The Cimicidae are usually found where bats 

 sleep, only visiting their hosts in order to take nourishment, 

 as they are temporary parasites. The Polyctenidae, on the 

 other hand, live in the fur of bats, not leaving the host. 

 They are more intensely parasitic and exist in almost uni- 

 formly dark surroundings. Is it the intensity of parasitism 

 or the darkness which has caused the loss of eyes in Poly- 





