The lice, Anoplura, are small, soft-bodied, wingless insects 

 having the mouth parts of a suctorial type but unjointed and with 

 the appendages ending in hooks. The human lice belong to a 

 family of the Pediculidae. Pediculus humanus, the head-louse, lives 

 on the hairy parts of the head, and the eggs or "nits" are deposited 

 upon the hairs. The body or clothing louse, hitherto classified as 

 P. vestimenti, has been shown not to be separable as a species from 

 the foregoing one. It lives, however, on the neck and trunk, the 

 eggs being deposited upon the clothing. Phthirius pubis, the pubic 

 or crab-louse, lives on the hairy portions of the body, especially in 

 the pubic region. As in the case of other surface parasites attacking 

 the skin the organisms are less significant from their immediate 

 presence than from the secondary effects for which they are account- 

 able; for example, the results of bleeding, or scratching of the skin 

 on the part of the individual affected, eczematous conditions and 

 surface infections by extraneous organisms being not uncommon. 

 They are also the most important, if not the sole agents, in the 

 transmission of the virus of typhus fever. 



The fleas, Siphonaptera, of which there are many species 

 attacking various animals, are well, though peculiarly, segmented 

 laterally compressed insects in which the mouth parts are suctorial, 

 and in which the limbs, especially the hinder pair, are strongly 

 developed. The thinness of the body enables them to pass through 

 very narrow spaces, while their jumping capabilities are well 

 known. The adults are blood-suckers, and some are important as 

 carriers, notably the rat-flea, Xenopsylla cheopus, now recognized 

 as the transmitting organism of bubonic plague. The penetrating 

 flea "jigger" or "chigoe", Dermatophilus penetrans, occurs in the 

 West Indies, Central and South America, and elsewhere. The 

 female burrows with the head into the human skin, the body 

 increasing greatly in size and assuming a spherical form. The 

 human flea, Pulex irritans, lives in human habitations, usually 

 under unsanitary conditions. It is said to be chiefly European, 

 the dog flea, Ctenocephalus cants, which also attacks man, being of 

 more general distribution. The eggs of fleas are deposited in the 

 dirt of cracks in the floor and similar situations. 



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