78 LICE AND THEIR MENACE TO MAN 



roughened surfaces of pliers strengthen so greatly 

 their grip on a piece of wire. They are, in fact, 

 the sloths of the insect world ; for just as the legs 

 of these animals have become so adapted for 

 moving from branch to branch in the thick South 

 American forests that they are helpless on the 

 ground, so the crab-louse has become even more 

 modified for its progression in a forest of hair and 

 cannot progress on any other medium. It is 

 ~ indeed one of the most specialised of parasitic 

 insects. To continue the comparison of this with 

 the body-louse, its head is larger in proportion to 

 its body, and there is less distinction between the 

 thorax and the abdomen, there being no " waist " 

 at all. There are three protuberances on each 

 side of the abdomen, two pairs of which bear long 

 hairs, and the insect is altogether more hairy- 

 looking than the body-louse. Often these lice 

 are so thickly encrusted with the dried salts of 

 sweat, which quite obscure them, that they look 

 more like small masses of dirt than insects. 



Until very recently indeed little was known 

 about the habits of the crab-louse beyond a few 

 very obvious facts as to the parts they frequent 

 and where their eggs are laid. They cannot be 

 reared in boxes covered with chiffon, as are the 

 other two species, for laboratory work ; but Pro- 

 fessor Nuttall (1) has recently shown that it is 

 possible to rear them by confining them to the 

 hairs of the leg on a space enclosed by a silk 

 stocking with an elastic garter above and below 



