102 



What is the cause of Melanism in the Scotch Specimens 

 of Triphaena Comes, Hb. (Orbona, Fb.) ? 



By R. Adkin, F.E.S. Read December xoth, 1896. 



In the early part of the present year I read some notes on 

 Triphana comes. At the following meeting Mr. Tutt read a paper 

 entitled " Is Cold the cause of Melanism in Scotch Specimens of 

 Triphcena orbona, Hufn. {comes, Tr.)?" the opening sentence of 

 which reads thus: — "At the last meeting of the Society it will be 

 remembered that I took exception to the following statement in 

 Mr. Adkin's paper : ' I consider that all the evidence points to cold 

 being the chief factor in the darkening of the species {Triphcena 

 orbona [comes] ) in its northern localities.' " 



I may say at once that, on referring to my paper, I could not find 

 any such statement as that adverted to by Mr. Tutt ; nor do I think 

 that any portion of the paper, or the paper as a whole, is capable of 

 this construction ; but lest anything in it conveyed such an impres- 

 sion to the meeting, I gladly accept the opportunity thus offered to 

 revert to the subject. 



My object in writing the paper was to record the forms of this 

 interesting species occurring in the various districts of its known 

 geographical range, rather than to assign any particular cause for the 

 assumption by it of any special form, and I think Mr. Tutt must 

 have based his idea of the conclusions at which I arrived, on a de- 

 sultory conversation which followed the reading of the paper ; the 

 chief topic of which was, I believe, the question of the comparative 

 times of the blooming of the "sallows" in various parts of Scotland 

 and England, a point which is likely to be very incorrectly stated 

 when given from memory alone, as was the case on that occasion. 



A large portion of Mr. Tutt's paper is taken up with quotations 

 from various magazines to show that the blooming time of the 

 " sallows" is about the same in the "warm Moray and Sutherland 

 districts," where the melanic forms of comes occur, as in the south of 

 England, and that Orkney also has a mild climate ; and he concludes 

 with the remark that he will be greatly interested to hear what I 

 now consider the " motive power " in the production of melanism in 

 T. orbona {comes), and suggests that " the excessive humidity is more 

 likely to be the prevalent meteorological factor " in these districts. 



If Mr. Tutt had said quite as likely instead of juore likely, we 

 should, I think, have been entirely in accord, but it may be well to 

 briefly review the question. 



In the first place it must be remembered that we are not dealing 

 with a boreal or an alpine species. On the contrary, all the obtain- 

 able information points clearly to its being one that inhabits districts 



