CHAPTER VI 



THE HEAD-LOUSE (PEDICULUS CAP1T1S) 



THE head-louse is the commonest of the three 

 lice of man in the more cultured countries. It 

 is rather smaller and more slender than the 

 body-louse, with slightly deeper constrictions at 

 the sides of the abdomen, but is otherwise so 

 much like it that it is very difficult to say whether 

 an isolated specimen is one or the other. The 

 distinction between them is rather one of habit 

 than of structure, and entomologists are begin- 

 ning to regard the two as biological races of one 

 species rather than as distinct species. Probably 

 primitive man, who was much more hairy than 

 his modern descendants, was infested by a louse 

 more resembling the head-louse of to-day than 

 the other, and this was the ancestor of the two 

 races, which split off from one another at some 

 time after the adoption of skins as clothing. 

 Evidence of this is that the claws and gonopods 

 are specially adapted for dealing with hair, not 

 cloth. These two forms of lice will, as Bacot(l) 

 showed, interbreed readily, the males of one 

 variety crossing with the females of the other, 



