that spread Disease. 39 



The clothes-louse is larger than the head-louse, and the sides 

 of the abdomen are less deeply cleft between the segments. The 

 antennae are slightly thinner in the clothes-louse than in the 

 head-louse, and the front border of the thorax is less rounded. 

 Other differences occur in the female sexual organs. In the crab- 

 louse the body is shorter than in the two former species, and the 

 thorax is broader than the abdomen ; along each side of the 

 abdomen are projections which at their tips carry pencils of 



FIG. 12. CLOTHES-LOUSE OB BODY-LOUSE, 

 Pedievlufs humanus, female, X 18 ; largely responsible for the spread of typhus fever. 



hairs. In the louse of the chimpanzee the lateral margins of 

 the abdomen are straight in front, but behind they present the 

 appearance of a saw. 



A female louse lays four or five eggs a day for about a month, 

 and then dies. There is no caterpillar or maggot stage ; the 

 young, on hatching out, differ from the adults only in their smaller 

 size and in certain trifling differences'- of structure. As they grow 

 they moult the skin three times before arriving at the adult 



