48 CALIFORNIA ACADEMY OF SCIENCES. 



and, on the other hand, have collected live parasites from 

 a bird skin seven days old. The death of the parasites 

 can hardly be caused by starvation, in view of their feed- 

 ing habits, but rather must be attributed to the lack of 

 animal heat which they have been accustomed to during 

 the life of the host. 



Mallophaga which infest swimming and diving birds 

 are not furnished with special contrivances for their 

 pseudo-aquatic life. They, in fact, never come, neces- 

 sarily, into contact with the water, living, as they do, at 

 the roots of the feathers where the water can never pen- 

 etrate, and where they have a constant and sufficient sup- 

 ply of air for the longest submergence possible to the 

 host. 



The origin of the parasitic habit among the Mallophaga 

 and its influence on their structure are questions of much 

 interest, but ones which cannot be touched on here. 



Some of the phenomena of the relations of parasites to 

 hosts, the migration of the parasites, and the influence of 

 their peculiar habits on the rapid establishing of varia- 

 tions, are considered in the following paragraphs under 

 the head of "Distribution." 



Distribution. 



The Mallophaga are parasites which live for their whole 

 life on the body of the host; only in rare instances are the 

 insects to be found off the host's body. The common 

 louse of the hen, Menopon pallidum, has been found 

 walking on the roosts or elsewhere in the chicken houses. 

 But the Mallophaga are not "stationary parasites" of 

 that extreme type in which the organs of locomotion are 

 lost; and the infesting of new hosts is accomplished by 

 actual migration of individuals from one bird to another. 

 It is obvious that for any one bird -species this migration 



