62 



THE BRITISH NATURALIST. 



TMarch 



those where black did not form a portion of the original colouring, 

 then the scales of the darkest hue increased in the same way and the 

 wings became suffused with this darker shade. For this phenomenon 

 the term Melanism was adopted, and after a little time it was restricted 

 in its application to those species which had become blacker, and the 

 term Melanochroism was applied when the species had become darker 

 in hue without a suffusion of black scales. The Doubledayaria of 

 Betularia will serve as an illustration of one, and the variety U 11 i color 

 of Xerampelina as an example of the other. Believing that both these 

 forms of variation are produced by- the same exciting cause, I propose 

 to avoid needless repetition by using the word Melanism as a generic 

 term including the whole. 



The late Mr. Edleston was the first person to call attention to this 

 remarkable phenomenon. Rather more than 50 years ago he wrote 

 to " Newman's Entomologist " in reference to the increasing numbers 

 of what he called the " negro aberration '" of Betularia. He had 

 exposed some virgin females in his garden and was surprised to find 

 most of the visitors were of this " negro aberration/' He said this 

 fLrm was almost unknown sixteen years before, and, contrasting it 

 with its increased numbers when he wrote, said " if this goes on for 

 a few years the original type of Betularia will be extinct in this 

 district."' 



I do not find any further allusion to what was going on until 1876, 

 when the late Edwin Birchall wrote a very remarkable paper, " On 

 Melanism," in the " Entomologist's Monthly Magazine," Vol. XIII., 

 p. 131. In this paper Mr. Birchall condensed into less than three 

 pages, almost everything that has been said on the subject from that 

 time to the present. He spoke in general terms of the localities 

 where Melanism prevailed, viz., the Highlands of Scotland, Ireland, 

 the Isle of "Man, Durham, South Lancashire and the West Riding of 

 Yorkshire ; and pointed out that where it prevailed there was also 

 but a meagre lepidopterous fauna. He suggested "as not improbably 

 among the causes at work in limiting the numbers of Lepidoptera in 

 Scotland, Ireland, the Isle of Man, and the North of England: — The 

 peculiarities of the climate of Ireland and the Isle of Man being 

 deficient sunshine, excessive moisture, and the almost entire absence 

 of frost, it may be suggested that under such conditions the hiberna- 

 tion of larvae and the sleep of pupae are incomplete and that damp and 

 mould make many victims. Over wide districts of Yorkshire, 

 Lancashire and Durham — those very districts where Melanism 

 occurs — the air is polluted by mephitic exhalations from furnaces and 

 chemical w T orks, the sun is obscured by clouds of coal smoke, and the 

 vegetation defiled and destroyed by deposits of soot ; in some of the 

 worst districts, such as St. Helens and Bradford, lepidoptera scarcely 



