136 



THE AMERICAN NATURALIST 



[Vol. XLVII 



may differ much among themselves as to habitat, habits, 

 plumage markings, etc., yet as places of residence and 

 providers of food for their external parasites they are all 

 much alike. The temperature is the same, the feathers 

 as food are about the same. Although the parasite's 

 host may live in the water, the parasite itself, safely 

 tucked away next the skin or among the feathers, lives on 

 dry land in free air, for the water, even where it con- 

 tinually covers part of the plumage, as in swimmers, or 

 occasionally all of the plumage, as in divers, only touches 

 the plumage surface. Beneath this surface it is always 

 dry and there is always free air. 



Thus despite an isolated life for the inhabitants of each 

 host island, and the great variety of these islands as re- 

 gards name and relation to phyletic mainlands, the actual 

 life conditions are monotonously alike on all these 

 islands. So that there is, for the Mallophaga, no such 

 variety of conditions of habitat and food and food-getting 

 and mate-seeking and egg-concealing and young-rearing 

 as would tend sharply to select and promote variations, 

 with a result of genus and family making. There is no 

 external influence at work promoting wide divergence. 

 The generic and family distinctions tend to be few; the 

 varietal and specific tend to be many. 



IV 



As a direct outcome of these conditions of life of the 

 Mallophaga there arises an extremely interesting state 

 of affairs concerned with their host and geographic dis- 

 tribution, a state of affairs which reveals, I think, a prin- 

 ciple or fundamental consideration concerning the dis- 

 tribution of wingless ecto-parasites in general. This 

 special subject may be introduced by a swift resume 

 of our present knowledge of the facts of the distribution 

 of the Mallophaga. In this resume I include some par- 

 ticular illustrations, by examples, of certain special dis- 

 tributional conditions. 



As Mallophaga have been taken so far from but a 



