126 THE ENTOMOLOGIST. 



slightly lighter in colour than the leaf itself, which it resembles 

 in structure and in the amount of pubescence: it is single- 

 celled ; but Giraud says it contains " Un grand norabre de 

 petites cellules disposees sans ordre." This specimen was 

 unmistakably inhabited by the inquilines; but whether all 

 were so it would be difficult to say. For this addition to our 

 Fauna we are indebted to Mr. W. C. Boyd, who found the 

 gall at Topley Pike, near Buxton, Derbyshire, in the autumn 

 of 1875, and kindly sent me the specimen from which I bred 

 the producer. Dr. Giraud says it appears to be very local ; 

 but should it be again met with I should be very thankful for 

 fresh specimens, as there is much about the species which is 

 still unsatisfactory. 

 Maldon, Essex. 



MELANOCHROISM, &c., IN LEPIDOPTERA. 

 By F. Buchanan White, M.D., F.L.S. 



I AM happy to meet so gallant a knight as Mr. Nicholas 

 Cooke upon a field affording so much scope for discussion as 

 that of variation in Lepidoptera, and gladly accept his 

 challenge. 



In the first place — if I read his remarks aright, and their 

 meaning seems certainly plain enough — Mr. Cooke uses the 

 term "natural selection" in a sense in which no one else 

 does, namely, the selection of their partners by the female 

 insects. This, if Mr. Cooke likes, is "sexual selection"; 

 "natural selection" it certainly is not. 



" Natural selection" may be defined as the weeding out of 

 all but those individuals who are best fitted to survive in the 

 struggle for existence, and this weeding ((or the most part — 

 like the majority of the universal mother's operations — a 

 gradual process) is carried out by many and various agencies. 

 It may happen that in certain districts dark forms of certain 

 species have some advantages over their lighter-coloured 

 brethren. By their more obscure colour they may escape 

 detection by their enemies, and hence have a greater chance 

 of being the means of continuing the species than the more 

 conspicuous lighter-coloured individuals ; or, in another 

 district the very reverse of this may occur, and the advantage 



I 



