Correspondence on Biology, etc. 



if you will read it carefnlly, and, if you can, " hold a brief " 

 for me at the British Association in this matter. You will 

 see that a considerable part of my paper is devoted to a 

 demonstration of the fallacy of that part of " Romanes " 

 which declares species to be distinguished generally by use- 

 less characters, and also that *' simultaneous variations '' 

 do not usually occur. 



On the question of sterility, which, as you well observe, 

 is the core of the question, I think I show that it could not 

 work in the way Eomanes puts it. The objection to Belt's 

 and your view is, also, that it would not work unless the 

 " sterility variation " was correlated with the " useful 

 variation." You assume, I think, this correlation, when you 

 speak of two of your varieties, B. and K., being less fertile 

 with the parent form. Without correlation they could not be 

 so, only some few of them. Romanes always speaks of his 

 physiological variations as being independent, " primary," 

 in which case, as I show, they could hardly ever survive. At 

 the end of my paper I show a correlation which is probably 

 general and sufficient. 



In criticising Romanes, however, at the British Associa- 

 tion, I want to call your special attention to a point I have 

 hardly made clear enough in my paper. Romanes always 

 speaks of the *' physiological variety " as if it were like any 

 other simple variety, and could as easily (he says more easily) 

 be increased. Whereas it is really complex, requiring a re- 

 markable correlation between different sets of individuals 

 which he never recognises. To illustrate what I mean, let 

 me suppose a case. Let there occur in a species three in- 

 dividual physiological varieties — A, B and C — each being 

 infertile with the bulk of the species, but quite fertile with 

 some small part of it. Let A, for example, be fertile with 

 X, Y and Z. Now I maintain it to be in the highest degree 

 improbable that B, a quite distinct individual, with distinct 



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