$6 'WHAT IS A SPECIES?' 



letters how Darwin instantly fixed upon the point and 

 tried to elicit the data upon which the conclusion was 

 formed. Thus he wrote to Bates, November 20, [1862]: — 

 ' No doubt with most people this [viz. the interpretation 

 of Mimicry] will be the cream of the paper ; but I am not 

 sure that all your facts and reasonings on variation, and 

 on the segregation of complete and semi-complete species, 

 is not really more, or at least as valuable, a part. I never 

 conceived the process nearly so clearly before ; one feels 

 present at the creation of new forms. I wish, however, 

 you had enlarged a little more on the pairing of similar 

 varieties ; a rather more numerous body of facts seems 

 here wanted.' : 



Then a few days later we find Darwin still thinking of 

 the subject, and writing to Hooker [1862, November]24 : — 

 ' I have now finished his [Bates'] paper . . . ; it seems to 

 me admirable. To my mind the act of segregation of 

 varieties into species was never so plainly brought for- 

 ward, and there are heaps of capital miscellaneous obser- 

 vations.' - 



He also again wrote to Bates, probably on the following 

 day, November 25, [1862 ?], asking for the solid facts 

 which are so greatly wanted : — 



' Could you find me some place, even a footnote (though 

 these are in nine cases out of ten objectionable), where 

 you could state, as fully as your materials permit, all the 

 facts about similar varieties pairing, — at a guess how 

 many you caught, and how many now in your collection ? 

 I look at this fact as very important ; if not in your book, 

 put it somewhere else, or let me have cases.' 3 



Remembering that Mr. Roland Trimen, F.R.S., had 

 expressed the same opinion as the result of his wide and 

 long experience of South African butterflies, I asked him 

 if he would kindly furnish me with a statement. His 

 reply, dated December 28, 1903, is as follows: — ' I have 

 noticed the tendency of the sexes of a variety to pair 

 together rather than with other varieties in the numerous 



1 Life and Letters, vol. ii, p. 392. 



2 More Letters, vol. i, p. 214, Letter 147. 

 s Ibid. vol. i, p. 215, Letter 148. 



