26 PEOCEEDINGS OF THE NATIONAL MUSEUM Vou 68 



That these Gyropid lice have as their favored hosts certain groups of 

 rodents appears almost certain, since it is on rodents that nearly all 

 the species are found, and it is on certain rodents that those mem- 

 bers of the family with the most generalized structures occur. Yet 

 several species of Gyropidae occur in nature on American ungulates 

 and upon these ungulates are unusually prolific. 



In regard to the theory that Ateles species have acquired their 

 Pediculids from man, it is important to note that the pelage of the 

 monkey -hosts is very similar to that of the head of man in coarse- 

 ness and abundance, also that the blood of Ateles is physiologically 

 more nearly like that of man than the blood of most monkeys. 



On the skins of their hosts lice find themselves in a portable habi- 

 tat, and, in the case of mammal-infesting lice, one that differs from 

 that of free-living species in that its temperature is uniform or 

 nearly so. Except for these two elements, portability and uniform- 

 ity of temperature, the pelage environment of a louse is to be com- 

 pared exactly to the grass environment of a grasshopper or the forest 

 environment of a sloth. Having two similar environments in nature 

 for a certain free-living species, we observe that the breaking down 

 of a natural barrier between them causes the inhabitants of the one 

 to spread and occupy the other. Having similar environments for 

 Pediculus in the head of man and in the fur coat of Ateles it is 

 conceivable that the breaking down of the natural barriers by the 

 invasion by man of the territory of the monkeys and by his intimate 

 association with them, might cause some of his lice to spread to a 

 simian environment. 



The second explanation advanced by the writer (Ewing, 1924) is 

 that in Pediculus we have one of those generalized types which is to 

 an unusual degree free from the influences of its environment. If 

 this is true we would expect it to be a very old type and one which 

 is now found on widely diversified host groups. Some of the Mallo- 

 phagan genera, Philopterus for example, are found on a great many 

 bird groups, both land and acquatic. If this be the true explanation 

 we must expect Pediculus to be eventually recorded from several 

 diverse groups of primates.. In this connection it should be noted 

 that Fahrenholz (1913 and 1917) reports Pediculus from various 

 species of gibbons (Ilylobates) of the Old World. 



If the phylogeny of the ^^eZes-infesting Pediculids has followed 

 that of their hosts it is observed from our knowledge of them that 

 tlie lice have been in America for a long geological period. Accord- 

 ing to Elliot (1913), the genus Ateles has a very great area of distri- 

 bution (fig. 8) extending from south central Brazil to as far north 

 as the state of Vera Cruz, Mexico, and on the continent of South 

 America from the Pacific slope of Ecuador to the Atlantic coast of 



