' The morphologist, when comparing one organism with 

 another, describes the differences between them point by point, 

 and " character " by " character." If he is from time to time 

 constrained to admit the existence of " correlation " between 

 characters (as a hundred years ago Cuvier first showed the 

 way), yet all the while he recognizes this fact of correlation 

 somewhat vaguely, as a phenomenon due to causes which, 

 except in rare instances, he cannot hope to trace ; and he falls 

 readily into the habit of thinking and talking of evolution as 

 though it had proceeded on the lines of his own descriptions, 

 point by point, and character by character. But if, on the 

 other hand, diverse and dissimilar fishes can be referred as a 

 whole to identical functions of very different co-ordinate 

 systems, this fact will of itself constitute a proof that a com- 

 prehensive " law of growth " has pervaded the whole structure 

 in its integrity, and that some more or less simple and recog- 

 nizable system of forces has been at work.' — D'Arcy Thompson 

 (Growth and Form, p. 727). 



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