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THE AMERICAN NATURALIST [Vol. XL1II 



form and structure of many other organs, external as 

 well as internal. And further that these hormones are 

 in some cases absolutely essential to the continuance of 

 life. In short we must consider the interior of every 

 organism as exhibiting an environment to which every 

 organ probably contributes and by which every organ 

 is more or less influenced. The hormones of this en- 

 vironment are the mechanisms of correlation and by 

 means of them one organ influences another. It is no 

 longer necessary to describe organic correlation as an 

 unknown law of growth. It is the dependence of one 

 organ on another through the hormones that the in- 

 fluencing organ produces. 



Granting this condition, it follows that natural selec- 

 tion may well be conceived to modify an internal hormone- 

 producing organ, if this organ is of vital significance, and 

 incidentally thus to establish a new internal environment 

 that would so influence the form and external configura- 

 tion of a given organism that it would be called a new 

 species and yet none of the new external features by 

 which this organism would be described might show the 

 least usefulness. 



