DARWIN AND DESCENT. 209 



in 1872. It is obvious, therefore, that "the theory" 

 means " my theory ; " it is not so obvious why the 

 change should have been made at all, nor why the one 

 "my theory" should have been taken Sind the other 

 left, but I will return to this question. 



Again, Mr. Darwin writes : — 



" Although we must be extremely cautious in con- 

 cluding that any organ could not possibly have been 

 produced by small successive transitional gradations, 

 yet, undoubtedly, grave cases of difficulty occur, some of 

 which will be discussed in my future work " (p. 192). 



This, as usual, implies descent with modification to 

 be the theory that Mr. Darwin is trying to make good. 



Again : — 



"I have been astonished how rarely an organ can 

 be named towards which no transitional variety is 

 known to lead. . . . Why, on the theory of creation, 

 should this be so ? . . . Why should not nature have 

 taken a leap from structure to structure ? On the 

 theory of natural selection we can clearly understand 

 why she should not ; for natural selection can act only 

 by taking advantage of slight successive variations ; 

 she can never take a leap, but must advance by the 

 slowest and shortest steps" (p. 194). 



Here " the theory of natural selection " is opposed 

 to " the theory of creation ; " we took it, therefore, to 

 be another way of saying " the theory of descent with 

 modification." 



Again : — '- 



"We have in this chapter discussed some of the 

 difficulties and objections which may be urged against 



o 



