56 THE ENTOMOLOGlhT S KECOKD. 



found, and in which the imago hides by day. But Dr. 

 Chapman {Ent. Mo. Mag., vol. xxv., p. 40), by some obser- 

 vations which he had made, and which he there related, 

 has given us another clue, and opened up a new phase of 

 the question. He suggested that a darkening of the surfaces 

 of trees and similar objects was produced by rain, and hence 

 the darkening of many species might be due to this cause 

 for the purpose of protection. But this appears only to 

 touch the fringe of the question as the surfaces are not made 

 permanently darker by rain. How does rain permanently 

 darken the tree-trunks and other objects on which insects rest? 

 It is well known to the most elementary student of chemistry 

 that rainwater rarely occurs pure, and that in large towns the 

 quantity of impurities is very great. The vast quantity of 

 smoke, gases, fumes, etc., in manufacturing towns, brought 

 down by rain, is scarcely credible, and it is from these 

 impurities I consider the permanent darkening comes. When 

 the water evaporates, the solid matter is left behind, and as a 

 result the impurities are left to darken the surfaces to which 

 they have been carried by the rainwater. The theories of 

 "natural selection" and "protection" now apply in their fullest 

 sense, the insects become darkened, "hereditary tendency" 

 perpetuating and intensifying the melanism. I believe from 

 this (and it appears to be a fair deduction), that Lancashire 

 and Yorkshire melanism is the result of the combined action 

 of the "smoke," etc., plus humidity, and that the intensity of 

 Yorkshire and Lancashire melanism produced by humidity and 

 smoke, is intensified by "natural selection " and " hereditary 

 tendency." As example I would cite the species AmpJiidasys 

 betularia, I'ephrosia biundularia, Boarniia rhomboidaria, B- 

 repandata, Diuni(za fagella and Hiberiiia viarginaria {pro- 

 geinmaria), which, occurring on trees, fences and similar 

 objects would thus be affected. Taking this view, I consider 

 the melanism of these counties "extraordinary ; " I also con- 

 sider it due to "humidity." The melanism of Staffordshire, 

 Derby, and other localities of a similar character, I consider, 

 is produced much in the same way, and the protective 

 melanism of London lepidoptera and of other large towns I 

 would refer to the same cause. Probably no better instance 

 of this kind occurs among London lepidoptera than Eiipithecia 

 rcctangulata var. nigrosericeata (another species which in the 

 imago state frequents tree-trunks). 



(To be continued.^ 



