]\ii-:lanis.m and melanochuoism. 55 



would probabl}" be i^rcater. But some years ago (1877) there 

 was a discussion {Entojii., vol. x., pp. 92-96), in which some of 

 our leading lepidopterists took part. With all due respect to the 

 opinion of the others who took part in the discussion, I think 

 Dr. Buchanan White and Mr. Nicholas Cooke (so far as the 

 discussion in the Entomologist was concerned) took up the two 

 essentially strong sides of the question. Taking it up from a 

 purely insular point of view, however, neither of these gentle- 

 men appear to have come to any strong or satisfactory 

 conclusions. Dr. White took up the view of " natural 

 selection " and " protection." Mr. Cooke went against the 

 view of " natural selection " (which he seems to have made up 

 his mind was nothing more than a modified form of " sexual 

 selection," although I doubt whether anyone saw it in the 

 light he presented it), and argued that melanism was caused 

 by fumes, etc., acting chemically on the food, and physio- 

 logically on the larva. I cannot myself imagine smoke or 

 fumes, by means of food, affecting the organisation of any 

 animal in such a way as to produce melanism, and I doubt 

 whether melanism can be produced or ever has been produced 

 in this way ; but combining Dr. White's and Mr. Cooke's 

 theories, I can understand that smoke and fumes would darken 

 the objects in the localities where they are poured out in such 

 excessive quantities, and then by Dr. White's argument of 

 "natural selection" and "protection," I can understand how 

 melanic forms are perpetuated and intensified. Mr. Birchall 

 {Ent. Mo. Mag., vol. xiii., p. 131) took up the view of deficient 

 amount of sunlight owing to the " excessive moisture," as 

 being the exciting cause in Ireland, Scotland and the Isle of 

 Man, and deficient sunlight due to " exhalations from furnaces 

 and chemical works " in manufacturing districts, and further 

 states that " the sun is obscured by the clouds of coal smoke, 

 and the vegetation defiled and destroyed by the deposits of 

 soot." He then argued that having obtained dark forms, " the 

 dark forms have greater strength of constitution, etc., and that 

 the light forms become eliminated." The larva of Agrotis ripce 

 lives underground all day, pupates underground, and yet the 

 imago is often pale ochreous or silvery white in certain 

 localities, never black ; yet as far as this argument goes, this 

 species (and all underground feeding larvse, etc.) should 

 produce specimens which ought to be specially black. Of 

 course, the white colour is in my opinion, due to the pale 

 colour of the sand in the localities where these forms are 



