316 THE INFLUENCE OF INANIMATE SURROUNDINGS. 



It follows from all this — as it seems to me — that the action 

 of marine currents, as means of separation and amalgamation in 

 the distribution of organic life, must be made to bear a larger 

 part than it has hitherto done, in inquiries as to the origin 

 of the present fauna of the globe from those of former periods. 

 For if we conceive of this course of development as a mechanical 

 process and make it our jsurpose to trace those determining 

 causes which have been merely mechanically operative, this can 

 never be done by propounding a more or less plausible hypo- 

 thesis, but only by methodical investigation ; nay, only by the 

 method of modern physiology — as much by a due reference to 

 all the factors together which must be taken into consideration, 

 as by successively identifying the influence which each of them, 

 separately, may or must have had. 



