41 



fines the phenomenon to the higher latitudes of the British 

 Isles, and to high altitudes. 



" Lord Walsingham's theory of melanism in Lepidoptera 

 was embodied in his address as President of the Yorkshire 

 Naturalists' Union, delivered on 3rd March, 1885, an ^ was 

 commented upon by me in the ' Entomologist,' Vol. xviii., 

 pp. 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 ex- 

 panse 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 p. 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 moun- 

 tains, 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 which I thought to be but four miles distant, was 

 sixteen. 



" In the mountains of Switzerland and the Tyrol the clear- 

 ness 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 rapes var. bryonice may be given as an example of the 

 former, and the male of Melitoea cynthia of the latter. 



" This uncertain condition of the weather is characteristic 

 of the climate of the British Isles ; the result is, that our in- 

 digenous Lepidoptera are, as a rule, darker in colour than the 

 Continental ; and the tendency to melanism increases north- 

 wards, till it may be said to culminate in the Shetlands. 



