IV. 
geographical position of these islands. This wave of migration was 
arrested on reaching our most northern shores, with the natural out¬ 
come of stunted forms, and melanism became the result of the want 
of the accustomed succulent food, and of a climate, warmer certainly 
than that within the Arctic circle, but still sufficiently cold and with 
sufficiently short summers to arrest the development capable in the 
milder climate of the insects’ original home. The appearance of 
melanism in the high mountainous regions of continental Europe, 
where the same causes obtain as in our extreme north, helps to 
support this view. Yorkshire melanism ” (in which I suppose he 
includes that from Lancashire and Durham also), “ may be treated 
as a merely local aberration not affecting the general position.” 
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 ; 
Pieris rapce (an error for napi) v. Bryonice 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 seems only 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.” 
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.” 
