Il6 YORKSHIRE NATURALISTS' UNION. 



VI. Atmospheric electricity has also been called into 

 requisition to account for certain changes. 



VII. Mr. Geo. Lewis has argued* that exposure to more 

 or less direct action of the sun's rays may influence colour by 

 acting mechanically upon the tissues of the scales, and so pro- 

 duce an actual modification of their structure, enabling them to 

 absorb and reflect to us certain rays. 



VIII. And lastly, the same author suggests, but only to 

 dismiss the idea as ''probably incorrect,' 'That blackness arises 

 from the invigorating energy derived from warmth, as blackness 

 absorbs heat rays ; but [he adds] in that case it would not 

 properly be a protective colour, but an incident in another line 

 of evolution.' f 



If we examine these various theories with a view to 

 ascertain how far they can be made to account for that par- 

 ticular tendency to melanism which we propose to consider, 



First, it would I think be open to some doubt whether the 

 dark varieties of the northern or Alpine regions are indebted to 

 their colouring for any appreciable measure of protection. In 

 the north of Scotland, and perhaps in the Shetland Islands, the 

 black peaty soil and some few dark lichens growing on the rocks 

 might serve to conceal an insect approaching them in tint. 



It has been observed that Gnophos obscurata and other 

 insects vary decidedly in colour according to the nature of the 

 soil on which they occur, but if we admit that this cause may 

 have some influence where peaty soil is found, it could not be 

 held to account for the like inclination in the Alpine insects to 

 assume a partial melanism, although it has been called into 

 requisition to explain the melanochroic race of certain Lepidop- 

 tera occurring in the manufacturing districts of this country, to 

 which I shall have occasion again to allude.* 



* Transactions of Entomological Society, London, 1882, p. 503, 

 t Loc. cit., p. 517. 



Trans. Y.N.U., 1883 (pub. 1885). Series D 



