MELANOCHROISM IN BRITISH LEPIDOPTERA. 147 



Mr. Eobson's appraisement of Mr. Bircliall's intellect. Further, one 

 might think that Lord Walsingham was the best man to elaborate a 

 theory of his own. The paper on which Mr. Robson's hopes of salvation 

 are based I have already criticised, and Lord Walsingham himself 

 says : — " Mr. Tutt, referring to a j^aper of my own, in which I called 

 attention to the tendency to melanism exhibited by Arctic and Alpine 

 Lepidoptera, points out that insects from high latitudes are not gener- 

 ally melanic. I think I may at once admit that I had used the term 

 ' melanic ' somewhat incorrectly in this connection ; what I desired to 

 point out was the general tendency of Arctic Lejiidoptera to a certain 

 suffusion of markings, and to an increase in the proportion of dull or 

 dingy scales, calculated more rapidly to absorb heat than the purer 

 Avhite of more southern varieties. Such a tendency will, I think, be 

 admitted to exist, but I am aware it is far more conspicuous in many 

 insular and Alpine districts; and, while I cannot agree that the 

 arguments put forward in that paper are in any way undermined by 

 this admission, or that the advantage secured to the species by the 

 development of colour capable of rapidly absorbing heat has been in 

 any way disproved, I am quite willing to accept Mr. Tutt's assertion 

 that melanism does not habitually occur unless lower temperature is 

 accompanied hj increased humidity : qualifying the acceptance only by 

 suggesting that anything which would have the same effect as increased 

 humidity in diminishing the action of sunlight would probably be found 

 to produce the same results." The advantage of a dark coloration may, 

 in a small degree, be admitted, although the active character of the 

 absorbing influence of the wings is not at all clear or proven, but we 

 have to deal Avith the origin of such dark coloration. This idea of 

 Lord Walsingham's I criticised at the time (Ent. Record, vol. ii., pp. 3-4), 

 as well as his elaboration of the idea that partially intercepted sunlight, 

 was probably a cause of melanism. It is useless to travel over the 

 gi-ound again, until some new facts can be brought to supjiort the idea, 

 and this, I venture to state, will probably never be done. Lord 

 Walsingham also suggested experiments to be carried out on these lines, 

 by Messrs. Poulton and Merrifield. Both these gentlemen conducted 

 experiments (recorded in the Trans, of the Ent. Society of Loud, for 1892), 

 and they resulted in failure, so far as they went, and fully bore out my 

 prophecy that there was no effect in this direction. Mr. Robson appears 

 to have clutched at the point on which I publicly expressed my ignorance 

 and want of knowledge, as the best means of attacking my paper, but 

 I am afraid that he has j)roved to the hilt, that his own ignorance 

 equals, or even excels, my own. 



The puzzles of Mr. Eobson are amusing. Mr. Barrett mentions a 

 tendency to dark variation, and associates it with moisture, but this 

 puzzles him, because Mr. Barrett mentions the " blue sky and bright 

 sunshine of Pembroke ; " so also does the pure air and bright sunshine 

 of parts of Scotland, for Mr. Birchall says, that in some of these melanic- 

 producing districts " the air is purity, and the sunshine brightness ; " 

 he is puzzled at the sunlessness of Ireland and the Isle of Man, and the 

 want of influence of the Gulf Stream on the coast of France. In fact, 

 many things puzzle Mr. Eobson, but these he nobly leaves to the meteor- 

 ologists of Ireland. " Sufficient unto the day is the evil thereof," and 

 Mr. Eobson showed his evident pleasure when he reached the end of his 

 paper, probably at having pulled through a task which he set himself 



