NEW MALLOPHAGA. 



49 



may be readily accomplished: (a) from male to female, 

 or vice versa, during copulation: (b) from parent to 

 young, during the nesting season. In both of these 

 cases there is actual contact of the hosts. If at other 

 times in the life of the host it comes into actual contact 

 with other birds of its own species migration of parasites 

 can take place. Such cases must occur among birds of 

 gregarious habits: the crowding together of gulls on 

 small masses of floating sea -weed, or on masses of food, 

 or on the rocks of the shore, must bring about actual con- 

 tact of the bodies of the birds. But, as common observa- 

 tion shows, there are in the crowding groups of gulls in- 

 dividuals of di fit' rent species. Thus in these cases there 

 is possible a migration of parasites from one bird -species 

 to another, these species in the case of the gulls beino- 

 closely related ones — species belonging, in fact, to one 

 genus. But on the " roosts " of maritime birds, the cliffs 

 of the shore and the outlying rocks, birds of very differ- 

 ent kinds sit huddled together. Along the rocky shores 

 of Point Pinos on the Bay of Monterey, pelicans, cormo- 

 rants and gulls gather in great numbers and perch side by 

 side on favorite '-roosts." It seems as if migration of 

 parasites from one to another of these bird-species could 

 here, and elsewhere under similar conditions, often be 

 accomplished; and I have found Lifeurus toxoceras, de- 

 scribed by Nitzsch from a cormorant, on both a cormo- 

 rant and a pelican shot on this shore. Other cases of 

 contact occur between birds of prey and their victims (I 

 have noted a Physostomum, a genus confined normally to 

 passerine birds, on a sparrow-hawk); and in those few- 

 groups of closely allied forms among which hydridization 

 occurs, as with the ducks. Still other opportunities for 

 accidental or normal contact between birds of different 

 species will suggest themselves to the student. 



Pkoc. Cal. Acad. Sci., 2d Ser., Vol. VI. (4) March 9, 1896. 



