86 THE entomologist's record. 



specimens being much more protected from their enemies by 

 their greater resemblances to objects rested upon, have by 

 '* natural selection " gradually assumed their present state. Note 

 also, the wood has been much collected of late years, and the 

 light specimens naturally are taken in much greater numbers 

 than dark ones." This really is my own view, except that I 

 think the darkening of the trunks arises perhaps less from the 

 shutting out of light, than to the natural increase of humidity 

 due to increase of age of trees and greater condensation, and 

 to the gradual increase of Derby as a manufacturing centre. 



Another extreme case, almost on all fours with this, is a most 

 extraordinary development of extreme melanism in Boarmia 

 repandata, near Huddersfield {Ent. Mo. Mag.,vo\. xxv., p. i6i). 

 Mr. G. Porritt, F.L.S., in 1888, bred from a wood in that dis- 

 trict some black forms of this species. So intensely black are 

 these extreme specimens, that insects commonly called black, 

 appear brownish beside them. The larvae from which these 

 specimens were bred came from an intensely dark fir wood, in 

 the midst of what is one of the largest manufacturing districts 

 in Britain, and where the vapour must hold in suspension large 

 quantities of carbon and other impurities. An almost parallel 

 case was cited by Mr. N. Cooke {Entom. x., p. 94) in a dis- 

 cussion of this subject, where he writes: — "The most interesting 

 case of melanism that has come under my observation — and 

 my friend Mr. Greening, of Warrington, can say if I exaggerate 

 the facts — is the total change in the colour of TcpJirosia biundu- 

 laria, in Delamere Forest. Some thirty years since, when he 

 and I visited Petty Pool Wood, this species was very abundant, 

 appearing in March, and was to be found through April and 

 May, but all were of a creamy white ground colour ; dark 

 varieties were so scarce that they were considered a great 

 prize. Now it is the reverse, all are dark, smoky brown, 

 approaching black ; a light variety is very rare. The same 

 change, and nearly to the same extent as regards numbers, 

 has come over AmpJiidasys betularia. Throughout the district, 

 from Petty Pool, including Warrington, to Manchester, the 

 black form is now usually found. I am inclined to suspect 

 that climate and manufactures have done more to bring about 

 this change than anything else. During the past thirty years, 

 what large towns have sprung up to the west of this district ! 

 Runcorn, Widnes, St. Helens, Earlstown, Wigan, etc ; all 

 pouring forth from their tall chimneys chemical fumes and 

 coal smoke, which emanations are carried over our collecting 



