( cix ) 



unceasing selection. Comparatively brief isolation of a group 

 of individuals may lead to a departure from the specific type 

 of apparatus prevalent in other areas, and may thus mechanic- 

 ally prevent syngamy if from any cause members of the 

 group became again sympatrio with those of the parent 

 species. 



A very different but exceedingly interesting oi'igin of 

 asyngamy is suggested by observations which support the 

 conclusion that varietal forms may show a tendency towards 

 preferential inter-breeding. 



H. W. Bates believed that he had strong evidence for the 

 existence of this tendency in the races of certain tropical 

 American butterflies. He stated this in his epoch-making 

 paper on the butterflies of the Amazon valley,* and it is 

 interesting to observe in the published 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, Nov. 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." f 



Then a few days later we find Darwin still thinking of the 

 subject, and writing to Hooker [1862, Nov.] 24 : — " I have 

 now finished his [Bates'] paper . . . ; it seems to me admir- 

 able. To my mind the act of segregation of varieties into 

 species was never so plainly brought forward, and there are 

 heaps of capital miscellaneous observations." | 



He also again wrote to Bates, probably on the following 

 day, Nov. 25 [1862 1], asking for the solid facts which are so 

 greatly wanted : — 



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



■■ Trans. Linn. Soc, vol. xxiii (1862), p. 495. 



t " Life and Letters," vol. ii, p. 392. 



+ "More Letters," vol. i, p. 214, Letter 147. 



