ON MELANISM IN LEPIDOPTEKA. 93 



Both are of opinion that "natural selection" solves a great 

 part of the difficulty there is in arriving at knowledge of 

 the cause of melanism. I cannot understand, for my own 

 part, what natural selection has to do with it. 1 boldly deny 

 there is any such influence at work amongst either SphingidcB, 

 Bombf/cida, GeometrcB, or Noctuce. The Diurni which do 

 not pair soon after they emerge from the pupa may, to some 

 degree, select their mates ; but the other classes above 

 named, as far as I have observed, pair without any selection 

 whatever. The female, as soon as she is mature, and some- 

 times before maturity, exercises an irresistible influence over 

 the males, which, as soon as perceived by them, brings them 

 in search of the object of attraction; and the first male 

 which reaches the female, no matter if a cripple, is allowed 

 by the female to pair with her. I have seen Notodonta 

 trepida, in Delamere Forest, paired before the female was 

 fully developed. Was there any selection there ? Mr. 

 Greasley and I, when hunting for Cheimatohia horeata last 

 November, in the above locality, repeatedly found females of 

 C. horeata paired with miserable little males, whilst a dozen 

 or more far better developed males were hanging to the twigs 

 in the vicinity, having evidently arrived too late. 



I could multiply the evidence on this point, but I feel sure 

 that every one of experience will grant that natural selection 

 does not exercise any influence in causing melanism in most 

 classes of Lepidoptera. I wrote to Mr. Birchall with regard 

 to this point, and he admitted that "sexual selection" did 

 not appear to have so much to do with melanism as the 

 "survival of the fittest" larvae. 1 grant that the fittest larvae 

 survive — and what is the consequence } We find the fittest 

 larvae of certain species here produce a darker variety than 

 the fittest larvae in another locality, and vice versa; other 

 species are here produced of a lighter variety than in the 

 other locality ; for instance, we take Hadeiia adusta here in 

 abundance, but they are all light-coloured ; in Glen Spean 

 this species occurs in profusion, but no light varieties can be 

 met with. In this neighbourhood we ioke Acromjcta leporina 

 of a tolerably deep gray colour; at Loch Laggan it is 

 beautifully white, with the characteristic marks dark. Here, 

 we have Pieris napi white ; at Roy Bridge, Inverness-shire, 

 I took several very dark ones : all 1 saw were dark, and 1 



