DARWIN AND DESCENT. 223 



■ Tlie words "on my theory" were cut out in 1869. 



" A slow southern migration of a marine fauna 

 . . . will account, on the theory of modification, for 

 many closely allied forms," &c. (p. 372). 



Again : — 



" But the existence of several quite distinct species, 

 belonging to genera exclusively confined to the 

 southern hemisphere, is, on my theory of descent with 

 modification, a far more remarkable case of diflSculty " 

 (p. 381). 



"My" became "the" in 1866 with the fourth 

 edition. This was the most categorical claim to the 

 theory of descent with modification in the " Origin of 

 Species." The " my " here is the only one that was 

 taken out before 1 869. I suppose Mr. Darwin thought 

 that with the removal of this " my " he had ceased to 

 claim the theory of descent with modification. Nothing, 

 however, could be gained by calling the reader's atten- 

 tion to what he had been done, so nothing was said 

 about it. 



Again : — 



" Some species of fresh-water shells have a very 

 wide range, and allied species, which, on my theory, 

 ■are descended from a single source, prevail throughout 

 the world" (p. 385). 



" My theory " became " our theory " in 1 869. 



Again : — 



"In the following remarks. J shall not confine 

 myself to the mere question of dispersal, but shall 

 consider some other facts which bear upon the truth 



