MELANIC VARIATION IN LEPIDOPTERA. II9 



Mr. MacLachlan, in the paper above referred to,* regards this 

 as a powerful factor in explaining the causes of variation, 

 although he thinks that a ' still more potent one is to be found 

 where the condition of isolation or segregation necessarily 

 exists, resulting in the production of local forms, which in 

 extreme cases are worthy of the term species.'' 



Edwards' experiments with pupge of Phyciodes tharos in a 

 refrigerator f seem to prove that long exposure to cold in this 

 stage does tend to a suffusion or blending in the markings of 

 the perfect insect. 



Dorfmeister believes that temperature exerts the greatest 

 influence during the turning into pupa, but nearly as much 

 shortly after the same period \ when, however, one or other 

 direction has been taken, it may through the action of the 

 temperature be accelerated or retarded, but cannot be any more 

 changed. J And the Rev. J. Green, who has had considerable 

 experience in forcing pupae, endorses this opinion. § But even 

 if retarded development is sufficient to account for the produc- 

 tion of some of our northern varieties, it fails to suggest any 

 reason for this result or to enlighten us as to the natural law, if 

 any, by which it is produced. Bearing in mind the sombre 

 grey of the perfect insects of the genus Cossus, the brilliant 

 hues of certain of the longicorn Coleoptera, both possessing 

 larvae which are not developed in a single season, and the 

 growth of many plants whose seeds lie dormant for long periods, 

 the rule is certainly not one of general application. 



M. Nicolas Wagner^ found that electricity applied in 



the pupal stage turned red to orange and black to red in the 

 • 



* Journal of Linnean Society (Zoology), xiv, p. 105. 



t Canadian Entomologist, ix, p. 205. 



+ Canadian Entomologist, vii, p. 232. 



§ Entomologists' Monthly Magazine, iii, p. 255. 



II ' Bulletin des Seances de la Societe Entomologique de France, ' vol. 

 xlvii, 1865. 



