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THE AMERICAN NATURALIST [Vol. XLVII 



closely massed resting cormorant, pelicans and gulls, all 

 of them bird kinds whose individuals are practically 

 always well parasitized. When a bird dies or is killed 

 some of its Mallophagous parasites will sometimes wan- 

 der off of the cold body, but usually they remain on the 

 body and die there within a few days. Before dying they 

 frequently grasp a feather barbule with their strong 

 mandibles and are found there firmly fixed after death. 



That they can not live, except unusually, for more than 

 a few days off the body of the warm-blooded host I have 

 proved by keeping them on feathers in ovens at the tem- 

 perature of the bird body or on feathers in vials next my 

 own body. They die in from two or three to six or seven 

 days off the host body, or on it after death of the bird. It 

 may be that the normal life of the adult Mallophagan is 

 but a week long, but the fact that the young die off the 

 host, or on it after its death, just as soon as the adults, 

 indicates that the parasites are simply unable to live 

 apart from their live hosts, for the only two apparent 

 conditions peculiar to life on a bird's body, namely, a cer- 

 tain constant temperature and feathers for food, are cer- 

 tainly not difficult to reproduce off the body. 



At times of actual contact of the bodies of their hosts 

 they undoubtedly migrate from bird to bird. Thus they 

 can move from male to female, or vice versa at mating, 

 from mother and father to fledglings in the nest, and from 

 individual to individual of the same species in the case 

 of gregarious birds perching together. 



The Mallophaga are, then, true, permanent ecto-par- 

 asites, of simple development, some degradation and 

 adaptive modification of body, which occur in the num- 

 ber of one to several species on probably all kinds of 

 birds and mammals, and on practically all bird and mam- 

 mal individuals, but which, except in special and rather 

 uncommon cases of unusual abundance, cause little seri- 

 ous injury to their hosts. The familiar constant search- 

 ing of the plumage with the bill by birds is almost always 

 due to the slightly irritating influence of these small para- 



