Art. 19 LICE OF THE GENUS PEDICULUS EWING 25 



Although the writer has examined many lots of Pediculus from 

 man he has seen no other lot that he would refer unqualifiedly to 

 this variety, although some taken from an Eskimo in Greenland 

 are near it and not at all of the type of P. humanus americanus or 

 P. humanus angustus. 



Head lice commonly found in America are of various types. 

 Most of them appear to be either hybrids between the American 

 Indian head louse, and the Caucasian head louse; or between the 

 Caucasian head louse, and the Caucasian body louse, or the louse of 

 the American negi'o ; our American negro apparently has no distinc- 

 tive head or body louse. 



GEOGRAPHICAL AND HOST DISTRIBUTION OF THE GENUS PEDICU- 

 LUS IN THE NEW WORLD 



The problem of the host distribution of Pediculus in America is 

 the most interesting, in the writer's opinion, of that of any genus of 

 any group of ectoparasites. In this genus are found species so 

 closely allied in their structural characters that more than one au- 

 thority has claimed that they belong to a single species, yet the hosts 

 of these closely related species are so far separated that not only 

 are they regarded as belonging to different families but to families 

 that are held by mammalogists to have no immediate phylogenetic 

 relationships. 



As has been shown in previous pages of this paper, the Ateles- 

 infesting species and those infesting man are in reality not so nearly 

 related structurally as has been supposed, and in fact are amply dis- 

 tinct in regard to the shape of the typical pleural plates. Yet, grant- 

 ing these essential differences, the conviction still remains that by 

 comparison with other Anoplura of primates all species of Pediculus 

 are remarkably alike. 



As previously stated, different theories may be advanced to ex- 

 plain this unusual diversity of the two kinds of hosts. Kellogg 

 (1913) believed that the close relationship shown by the Pediculi 

 themselves indicated some sort of phylogenetic relationship of the 

 hosts. 



The writer's suggestions (Ewing, 1924) in regard to the signifi- 

 cance of tlie host distribution of Pediculus in America, are two: 

 First, it may be that here we have a case of a crossing over of the 

 parasites from their original and favored hosts to another distantly 

 related host group. In other words, it would appear that the spider 

 monkeys obtained their pediculids from man, when the latter reached 

 tropical America in his dispersion from the Old World. That 

 such a crossing over from one host group to another with no near 

 phylogenetic relationhip has taken place appears very probable in 

 the case of the biting lice of the family Gyropidae (Ewing, 1924). 



