154 



INSECTS 



on vertebrate blood 

 exceedingly simple 



But the parasitism here is of an 

 character, and means only the 

 adaptation of the external form 

 to a life among fur, hair or 

 feathers, and the development 

 of some sort of structures to 

 hold on with. 



Most hairy animals, from the 

 little field mouse through all the 

 ruminants to man himself, are 

 subject to the attacks of sucking 

 lice. Now, while man cannot be 

 strictly ranged as a hairy animal 

 nowadays, some of his anthro- 

 poid allies come conveniently 

 under such a definition, and the 

 few species that infest humanity 

 are some of the remaining dis- 

 advantages of a former closer 

 relationship with ape-like forms. 

 That man has been in this com- 

 paratively hairless condition for 

 a long time is shown by the fact 

 that one of his parasites has be- 

 come especially adapted to life 

 under such conditions, and that 

 another has undergone an even 

 more profound modification in 

 habit since he was a clothed 

 animal. 



These sucking lice are, in 

 general, small flattened creat- 

 ures, gray, whitish or yellowish 

 in color, with an elongate oval body or abdomen cov- 

 ered with short hair or spines, and a more or less 



Fig. 63. — Mouth parts of a 

 sucking louse. 



