218 FAUNAL DIVISIONS OF EASTERN NORTH AMERICA. 



In concluding this outline on the distribution of faunas in Eastern North 

 America in relation to areas of vegetation I might briefly restate my belief that 

 the present aspects of dispersal are a result of past conditions ; that a fauna is 

 the expression of certain adjustments between organisms and their environments, 

 and that the most important direct factor in any environment is the nature of 

 the vegetation which is conditioned by soil and by the climatic factors of heat 

 and moisture. The faunal divisions outlined in this paper seem to me to accord 

 more nearly with the observed facts. They at least rest on a natural relation of 

 animal species to their present habitats and to the geological history of the land 



Trotter, The Auk, vol. XXVI, July, 1909, pp. 221-233. Also an article in The Auk for April, 



1 



l 



Areas: and in Cassinia 



Carolinian Fauna in the Lower Delaware Valley. The above papers by the w 

 of faunal distribution that directly concern the matter of the present memoir. 



with 



V 





