38 PKOCEEDINGS OF THE NATIONAL MUSEUM. vol.63, 



with clinging organs in the form ol' liair chispers, there must be a 

 close approximation in the physical element of the louse environment 

 as is afforded by the pelage. Finally, the food requirements and 

 other elements of the environments for the lice of the two host 

 groups must approximate. A superficial examination of these con- 

 ditions shows that in some of tliese respects some of the primates 

 and ungulates do approximate the Caviidae and Octodontidae. 

 Former existing species of these groups probably did so even to a 

 greater degree. 



The pelage of some mammals is of such a nature as to constitute 

 a physical barrier to the transfer to them of such hair-clasping lice 

 as the Gyropidae. The fur of a mole or shrew, for example, is so 

 fine and the hairs so dense that such lice would find it physically 

 impossible either to progress between the hairs or to clasp them effec- 

 tively with their modified hair-clasping legs. Other mammals, the 

 porcupines or some of the larger ungulates, for example, have the 

 pelage so coarse as to present a great obstacle to the crossing over of 

 small lice with their hair-claspers adapted for holding only medium- 

 sized hairs. 



Although the different mammalian groups through the processes 

 of their development have arrived at their present day positions of 

 great diversity in morphology and habits, anyone who has examined 

 the skins of these mammalian groups has noted cases of most excel- 

 lent convergence in regard to the pelage type. Take the echidnas and 

 the porcupines and certain of the spiny rats, for example, they all 

 have developed the long, rigid, exceedingly sharp-pointed, quill 

 type of pelage, each quill being only a modified hair of enormous 

 proportions. Undoubtedly these quills serve in the main the same 

 purpose in all three groups, and they have in each instance been de- 

 veloped in the same way, yet from what diverse phylogenetic groups. 

 If there is such remarkable convergence in the physical elements of 

 the fur environment, why not in the other elements ? Data in respect 

 to these other elements unfortunately as yet have not been obtained 

 in any comprehensive way. However, it should be noted that in 

 the physical and chemical properties of the blood, mammalian 

 species of diverse groups frequently show an unusual similarity. 



As the forest is to a monkey, the pelage of a mammal is to a louse. 

 Both furnish the physical background for these two respective kinds 

 of inhabitants. In these environments are to be sought food, shelter, 

 and the necessaries for grow^th, reproduction, and dissemination. 

 Given a convergence in different forest environments a possibility 

 is presented of their being inhabited by the same groups of forest 

 mammals. Similarly, given a convergence in different pelage en- 

 viionments on the backs of mammals we would expect, and sometime? 



