i54 



THE BRITISH NATURALIST. 



[August 



Also (b ) species restricted in range to such localities are generally 

 melanic in coloration. 



(2) Certain species of Lepidoptera and possibly of Coleoptera 1 , in 

 districts influenced by the atmospheric pollution caused by manufac- 

 tures, mining operations, &c, have, within recent years, assumed a 

 distinctly melanic character, which has apparently arisen and become 

 intensified synchronously with the establishment and increase of such 

 atmospheric pollution. 



Now it is obvious that we have here two entirely distinct classes 

 of phenomena. The factors which induced them need not necessarily 

 have been the same or even similar, the theory by which one kind 

 of melanism may be explicable need not of necessity solve the other. 



Mr. Tutt may have kept this distinction clear in his own mind, 

 but he has hopelessly confused the readers of his " Melanism ," by 

 attempting to explain both classes, by his theory of humidity similarly 

 applied. Before pointing out the utter inconsistency of such a line of 

 argument, let us consider for a moment the differing nature of the two 

 forms of melanism as defined above, and which I have called 1 and 2. 



It will be seen that a and b of No. 1 may be considered as 

 equivalent, the only real difference being in whether we call a special 

 form, species or variety. 



Considering, then, archaic melanism (No. 1), the first and most 

 obvious remark is, that we have no right to assume the present 

 environment, whether of cold, deficient sunlight, humidity, any of the 

 characteristics in fact, of the localities where such cases occur, to 

 have been the actual cause of their normal variation taking the melanic 

 direction. We may say that their melanism is adapted to the environ- 

 ment, but not that it has been necessarily caused by it. - The distinction 

 is an important one. Let us take an instance. The Shetland male 

 of Hepialus humuli is Melanochroic, our common form pure white, but 

 is it safe to assume the latter to be the type ? By type I mean earlier 

 form ; preponderance of individuals does not indicate it, otherwise we 

 should have now to regard the form doubledayaria as the type of 

 Ampliidasys betularia. Antiquity is doubtless the test ; but from what 

 evidence we have (comparison with other members of the genus), we 

 might with some justice infer that the dark northern form of H. 

 humuli 6 was the original, and our white male the result of a later 

 evolution. 



Now hereby it is apparent how this class of melanic phenomena 

 differs in essence from No. 2, viz., that we have no evidence of origin of 



1. I was unaware of any instance of this class of melanism among Coleoptera till I 

 recently discovered that the form of Bradycellus cognatus, at Lindow, near 

 Manchester, was distinctly melanic, but I have no evidence as to how long 

 this form has occurred there. 



