490 



THE AMERICAN NATURALIST 



[Vol. LII 



and operate in botli short and long cycles, the various 

 cycles traveling at diverse rates and mutually influencing 

 one another in their adjustments to pressure. In these 

 wonderful moving systems of cycles can be visualized the 

 essence of modern scientific conceptions. From electrons, 

 atoms, molecules, chemical compounds, colloids, cells, tis- 

 sues, organs, individuals, and culminating in the com- 

 munity and association, is seen in each a dynamic center 

 or microcosm, about which revolves other systems, in 

 turn revolving as a part of a larger system in ever widen- 

 ing expansion, each in turn subordinated to a higher or- 

 der of dominance, the culmination of interacting systems. 



I have now completed an outline of the fundamental 

 dynamic principles which are necessary as a background 

 for my discussion of animal migration. These general 

 principles appear to underlie all processes of animal reg- 

 ulation internal and external, and are expressions of 

 these laws of interacting systems. 9 



9 Although the preceding discussion is intended to bear mainly on migra- 

 my belief that these general principles are of relatively wide application. 

 (To be continued) 



