Aet. 19 



LICE OP THE GENUS PEDICULUS EWING 



27 



Brazil. In this vast area, in which the monkeys are found only in 

 the forests, the genus is broken up into geographical species, as for 

 example; Ateles pan is found from the state of Vera Cruz, Mexico, 

 south into Guatemala; Ateles fusciceps is found in Trans- Andean 

 Ecuador, and Ateles hyhridus is limited to the valley of the Magda- 

 lena, Colombia. Species differentiation in this group appears to 

 have followed dispersion, and this dispersion shows a spread over 

 an immense area several thousands of miles in extent. 



If the first suggestion, the "cross-over theory," is rejected, we then 

 find that the solution of the distribution problem of Pediculus and 

 the problem of the origin of the genus in the Americas become de- 



FiG. 8. — Map showing the distribution of spider monkeys (ateles), based chiefly on 



KECOUDS GIVEN BV ELLIOTT 



pendent upon that of the distribution and origin in this continent 

 of the hosts. The problem then hinges upon the work of the mam- 

 malofirist more than on that of the entomoloijist. 



SUMMARY 



1. In America two distinct groups of Pediculus exist, one of them 

 confined to man and one to monkeys. 



2. The forms infesting man are apparently largely hybrid races 

 of head lice, the pure strains of which were originally found on the 

 white, black, red, and yellow races of man living in their original 

 geographic range. 



