THE CRAB-LOUSE 79 



them. As a result of his studies he has taught 

 us much about the pest. 



Just as the head-louse is usually confined to 

 the head but may establish itself on other parts, 

 so the crab-louse usually frequents the hair of the 

 pubis and peri-anal region, but may be found also, 

 or alternatively, in the armpits, where it is fairly 

 common ; on the scattered hair of the trunk and 

 limbs ; on the beard and moustache ; on the 

 eyebrows and eyelashes ; and on the scalp hair. 

 The preceding positions are mentioned in the 

 order of frequency with which the lice are found 

 upon them. On the hair of the head it is very 

 rare indeed, probably because this has such very 

 different qualities from the body hair, such as 

 abundance and calibre. 



The eggs (Fig. 6) are laid cemented on to the 

 hairs in a manner similar to those of the other 

 species ; but from these they may be distinguished 

 easily, by means of a lens of low power, by their 

 slightly smaller size, their darker colour, and the 

 character of the cap or operculum, which in this 

 species is more conical and symmetrically sculp- 

 tured by prominent round nodules which cover 

 its whole surface. The cement also covers a 

 larger length of the hair, running considerably 

 below the base of the egg. The eggs hatch in 

 from six to eight days. The newly emerged louse 

 moves at once to the base of the hair on which it 

 was hatched out, and, clinging to this hair alone, 

 buries its mouth parts in the skin and begins to 



