45 
But what new facts does Mr. Robson give us relating to melanism ? 
Not one that has not been noticed before. What new theory does Mr. 
Robson bring forward to replace the ideas he vainly tries to overthrow ? 
None ! Not one single original idea of any description. He certainly 
offers a warmed-up, second-hand edition of Lord Walsingham’s theory, 
from which the latter has more than half withdrawn. “ Absence of 
sunlight! ” This, then, accounts for the effusive praise g ; ven to Mr. 
Birchall’s elementary paj^er of so many years ago. That gentleman 
casually mentioned that “ the clouds in Ireland ” and “ the smoke in 
Lancashire ” intercepted some of the sunlight, and this accounts for 
Mr. Robson’s appraisement of Mr. Birchall’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 paper 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 Lepidoptera 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 
white 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 sjitecies 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 by 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 with 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 
ground again, until some new facts can be brought to support 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 Lond. 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 proved to the hilt, that his own ignorance 
equals, or even exceeds, my own. 
The puzzles of Mr. Robson are amusing. Mr. Barrett mentions a 
tendency to dark variation, and associates it with moisture, but this 
