1890 PHYSIOLOGICAL SELECTION 217 



visions for cross-fertilisation in other species.) Xow, 

 I believe most of all in what I have called ' collective 

 variation ' of the reproductive system in the way 

 of physiological selection, whereby, owing to some 

 common influence acting on a large number of indi- 

 viduals similarly and simultaneously, they all become 

 sexually co-adapted intei- se while physiologically 

 isolated from the rest. This essential featm-e of the 

 theory seems to me entirely to remove the difi&culty 

 about in-breeding, as well as that which Wallace 

 urged about the chances against a suitable m.eeting 

 of ' physiological complements.' 



As for my having attributed too much to the 

 swamping efiects of intercrossing (Panmixia), this, I 

 am convinced, is the one and only particular wherein 

 I have at all departed from the judgments of Darwin ; 

 though, curiously enough, it is the particular on 

 which my critics have laid least stress when accusing 

 me of Darwinian heresy. But it is too big a question 

 to treat in correspondence. Guhck's recently pub- 

 lished paper at the Linnean Society seems to me a 

 most important one in this connection, and I have 

 a large body of other evidence. 



To F. Darwin, Esq} 



18 Cornwall Terrace, Begent's Park, X.W. . January 8, 1889. 



Dear Darwin, — Hate you, indeed ! A^Tiy, I can- 

 not imagine any better service than that of stopping 

 a fellow from making a fool of himself, and I most 

 cordially thank you for having done so in this case. 



' Mr. F. Darwin had pointed out some erroneous conclusions in a pro- 

 jected scientific paper. 



