THE BRITISH NATURALIST. 



65 



Mr. J. Jenner Weir replied to this paper, and with very good 

 reason, intimated that Mr. D'Obree had not properly understood 

 Lord Walsingham's theory. Mr. Weir spoke of the extreme clearness 

 of the atmosphere in the Netherlands, Belgium, France, Germany, 

 the Tyrol, Bohemia, Spain, and Italy, except in the mountains. " In 

 the mountains of, Switzerland and the Tyrol the clearness of the 

 atmosphere was nearly as great, but constantly interrupted by dense % 

 mists and clouds, and it is precisely in these altitudes that melanism 

 becomes the rule rather than the exception ; many of the topomorphic 

 varieties are melanic, and many of the Alpine species are very dark ; 

 Pievis rapce (an error for napi) v. Bryonia may be given as an example 

 of the former, and the males of Melitcea cynthia of the latter. This 

 uncertain condition of the weather is characteristic of the climate of 

 the British Isles. The result is that our indigenous Lepidoptera are, 

 as a rule, darker in colour than the continental, and the tendency to 

 melanism increases northwards, till it may be said to culminate in the 

 Shetlands." 



Mr. Cockerell continued the discussion, and though he admits the 

 suggestiveness of, some of Mr. D'Obree's facts, he thinks "the 

 deductions he draws from them are perhaps open to question. From 

 the presence of melanic forms in mountain regions, and in the West of 

 Ireland and Scotland, it see«TS , "fmly natural to suppose that the 

 peculiar features of these regions are responsible for the variation ; 

 and of all causes that seem probable from this point of view nothing- 

 comes more prominently before us than the extreme mistiness and 

 dampness of the atmosphere." • ';Jf 



Mr. Dale in the Introduction to his British Butterflies gave a 

 brief note on the subject, and contended that light colours rather than 

 dark absorb heat. He says " the dry chalk soils of the south absorb 

 a greater amount of heat than the wet peaty soils of the north, and to 

 that, in conjunction with the fact that there is more rain and conse- 

 quently less sunshine in the north is melanism entirely due." 

 Lord Walsingham replied to this in the succeeding part of the "Young 

 Naturalist," and contended that Mr. Dale's arguments supported his 

 theory, and that differing from "birds and other animals, which require 

 to retain heat rather than to absorb, and as quickly radiate, or loose 

 it, insects, on the contrary, require rapidly to take advantage of 

 transient gleams of sunshine during the short summer season, and may 

 be content to sink into a dormant condition so soon as they have 

 secured the reproduction of their species." 



The next to write upon the subject was Dr. Chapman, who said 

 he considered Melanism to be " a western rather than a northern form 

 of variation ; to be associated with a wet rather than a cold climate ; 

 and it has certainly been more common of recent years, which may be 



