466 THE AMERICAN NATURALIST [Vol. LII 



lution. 2 Iii view of the recent concentration of interest 

 on heredity, my subject has the flavor of an old-fashioned 

 one, which calls back to the days when Darwin and Wal- 

 lace were living, and when Wallace's "Island Life" was 

 frequently read with enthusiasm, and when there was 

 possibly a more general belief that natural selection was 

 one of the large factors in evolution. But progress has 

 not been limited to the studies of heredity, for with the 

 rapid rise of certain phases of general physiology, ani- 

 mal behavior and animal ecology, a newer orientation is 

 now possible with regard to the migration of animals by 

 both the active and passive methods. For our knowledge 

 of animal responses, as well as the influence of the vege- 

 tational and physical environment, have made consider- 

 able progress, and we now probably see more clearly than 

 ever before the intimate relation existing between the 

 animals and the conditions which influence their migra- 

 tions. The present occasion has thus furnished an op- 

 portunity to make a preliminary reorganization of the 

 accumulated materials from a somewhat different stand- 

 point than was formerly current in discussing migration. 

 And although some of these ideas are widespread and 

 even commonplace in certain limited fields, yet they are 

 not yet in as general use as is desirable, and they are in 

 urgent need of extended application and critical study. 



In the following discussion of migration as an evolu- 

 tionary factor, I wish to emphasize two points in particu- 

 lar. One is the discussion of the process of analysis and 

 the other is to suggest some methods of applying this 

 method to the problem of migration. It may seem aside 

 from the main thesis to give this emphasis to the process 

 method of evolution, but after striving several years for 

 the conscious application of this method in an allied Held 

 (Adams '13, '15), and seeing its beneficial results there, 



^ 2 By evolution, I mean to use the term in the broadest possible sense-to 



