86 THE ENTOMOLOGIST. 



Union, delivered on March 3rd, 1885, and was commented upon 

 by me in the 'Entomologist' (Entom. xviii. 81-87), to which I 

 beg a reference. 



It appears to me that Mr. Dobree has misunderstood Lord 

 Walsingham's theory of melanism, viz., " that a large expanse of 

 white snow tends to produce it." Such was not my reading of 

 the author's theory in 1885. 



I have refreshed my memory and carefully re-read the 

 address, and as I understand the theory put forth, it was, 

 shortly, that the dark coloration of Lepidoptera from both high 

 latitudes and altitudes was of service to them, because in such 

 localities " they require rapidly to take advantage of transient 

 gleams of sunshine " {vide page 10 of the Address). 



I have myself travelled in the Netherlands, Belgium, France, 

 Germany, Switzerland, the Tyrol, Bohemia, Spain, and Italy, 

 and in all these countries, except in the mountains, I have been 

 struck by the extreme clearness of the atmosphere. In Bohemia, 

 Italy, and Spain I found this to be the case in the greatest 

 degree ; in fact in Bohemia I found to my sorrow, one very hot 

 day, that the town I could plainly see and I thought to be but 

 four miles distant was sixteen miles away. 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 

 rather the rule than the exception ; many of the topomorphic 

 varieties are melanic, and many of the alpine species are very 

 dark ; Pieris rupee var. hryonice may be given as an example of 

 the former, and the male of Melitcea cyntJiia of the latter. This 

 uncertain condition of the weather is characteristic of the climate 

 of the British Isles. The result is that our indigenous Lepi- 

 doptera 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. 



If I am correct in my views, and I think the facts I have 

 brought forward are in accordance with Mr. Dobree's, then it 

 follows that, in the British Isles and in the mountains of Europe, 

 it is essential to the imagines of Lepidoptera that they should 

 rapidly take advantage of transient gleams of sunshine, and this, 

 the darkening of their coloration, enables them to do. I have 

 myself seen Vanessa urticce fall helpless in its flight when the sun 



