80 ANIMAL ECOLOGY 



every hypothesis. He is conducted to the places where the trans- 

 itions of nature are most perceptible, and where the absence of 

 former, or the presence of new circumstances, excludes the ac- 

 tion of imaginary causes. By this correction of his first opinion, 

 a new approximation is made to the truth ; and by the repetition 

 of the same process, certainty is finally obtained. Thus theory 

 and observation mutually assist one another; and the spirit 

 of system, against which there are so many and such just com- 

 plaints, appears, nevertheless, as the animating principle of 

 inductive investigation. The business of sound philosophy is 

 not to extinguish this spirit, but to restrain and direct its efforts." 

 J. PLAYFAIR, "Illustrations of the Huttonian Theory of 

 the Earth," Edinburgh, 1802, pp. 524-525. 



THE facts and ideas with which the animal ecolo- 

 gist needs to become acquainted are so widely scat- 

 tered that a large amount of selective reading is 

 necessary. The ecologist must read, select, and 

 become an organizing center of things ecological. 

 All of the facts and conceptions which he needs are 

 not even confined to zoological or biological literature. 

 In seeking an understanding of any problem, conven- 

 tional groupings of the sciences and their arbitrary 

 boundaries must not bar one from fertile fields. 

 Many of the conceptions of the physical sciences, 

 due to their more advanced stage of development, 

 anticipate the future development of biology. This 

 is particularly true of their dynamic conceptions. 

 For this reason we should not hesitate to utilize and 

 deliberately strive to secure development along 

 similar lines in animal ecology. Elsewhere I have 

 stated (An Ecological Survey in Northern Michigan, 

 1906, pp. 11, 12) that: "It is thus very apparent 



