210 GEOEGE JOHN EOMANES mi- 



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 



