210 GEOEGE JOHN EOMANES i88i- 



summary of what I regard as the very backbone of 

 my evidence. 



If your large knowledge of geographical distribu- 

 tion should enable you to supply me with specific 

 cases of the general principle mentioned by Darwin in 

 the quotation given on page 392 (' Origin of Species,' 

 6th ed., pp. 134-5), I should much like to try experi- 

 ments on the sterility which I should expect to find 

 between these interlocking species. 



It seems comical to ask a scientific opponent for 

 assistance, but the fact of being able to do so 

 proves the superiority of science to politics. 



18 Cornwall Terrace, Regent's Park, N.W. : December 27, 1888. 



I am most glad that in your last letter you deal 

 with what I consider the real ' question ' — viz. not 

 whether degrees of sterility obtain among a large 

 proportional number of species, but whether there is 

 any such correlation between them and absence of 

 isolation of other kinds as my theory would expect. 

 And in dealing with this question you hit upon 

 precisely the two greatest difficulties which I have 

 myself concluded lie against the theory. The first 

 is about areas now discontinuous having been once 

 continuous, and our being so often unable to say 

 whether or not such has been the case. But this 

 difficulty is one that lies against verification of the 

 theory, not against the theory itself. It was in view 

 of this difficulty that I mentioned oceanic islands as 

 furnishing the best flora for trying experiments upon ; 

 but since I published the paper, I have not been able to 



