404 



THE ANIMAL PARASITES OF MAN 



of bristles on the dorsal aspect, and small hairs directed back- 

 wards at the posterior margin. The barrel-shaped white eggs are 

 deposited in cracks in the boards, sweepings, spittoons, &c. ; they 

 produce legless larvae consisting of fourteen segments, which, after 

 about eleven days, are transformed into pupae ; after another 

 eleven days the flea emerges. 



FIG. 257. Pulex irritans. 14/1 



FIG. 258. Larva of 

 flea, enlarged. (After 

 Railliet.) 



^ 259. Pulex serraticeps. 22/1. 



Fleas live in human dwellings all over the worid. and periodically 

 pass on to persons to suck their blood. They may deposit their eggs on 

 very uncleanly individuals, and even undergo development, therefore it is 

 possible to find larvae and pupae on such persons. 



The dog flea, Pulex serraticeps, is easily distinguished from the flea of 

 man by the large thick bristles on the posterior margin of the first 

 thoracic ring (fig. 259). 



