MELANIC VARIATION IN LEPIDOPTERA. 1 33 



clearly the tendency to suifusion of colouring in the perfect 

 insects, and the resemblance between arctic and alpine variation. 



We should expect to find varieties tending to assume 

 absorbent colouring not only in the Arctic and Alpine regions, 

 where the amount of cloud and mist must greatly diminish the 

 incidence of direct sunlight, but also under any conditions 

 which would limit it in an artificial manner. Dr. J. Hann * 

 strongly insists upon the chemical energy and potentiality of 

 diffused sunlight; corroborating and supplementing Tyndall's 

 observations to this effect. The smoke of our furnaces in the 

 manufacturing districts, and of our chimneys in large towns, 

 undoubtedly deprive the urban population of their fair share of 

 undiffused sunlight within the radius affected by them. Ac- 

 cordingly we find several instances of more or less melanic forms 

 occurring in such situations. I have in my own collection an 

 almost black variety of Hemeivphila abruptaria taken by Mr. 

 Sidney Olliff in London, and Boletobia fuliginaria in this country 

 is essentially a London insect. In the neighbourhood of Man- 

 chester, as I am informed, the dark variety of Aniphydasis betu- 

 laria has become not uncommon of late years. 



Other instances, such as the black variety of Abraxas 

 grossulariaia from Lancashire, Folia chi, the suffused form, 

 olivacea, from Newcastle, and Tephrosia crepuscularia and 

 biundularia from Barnsley, are probably familiar to you. 



We should expect insects occurring in dense forests to be 

 darker than those of the open country, and so far as my Cali- 

 fornian experience goes this is undoubtedly the case. Mons. 

 Bellier de Chavagnerie remarks that chrysalids in dark caves 

 produce darker specimens. All fishes from the very deep sea 

 inaccessible to the sun's rays are either colourless or entirely 

 black. 



* ' Handbuch der Klimatologie, ' 1883, p. 73. 



