41 
With regard to the other notes referred to by Mr. Robson, that referred 
to by Mr. Cockerell supports my view, but that of Mr. Dale {Brit. Nat., 
p. 65), is really not deserving criticism. Really, it is difficult to get 
down to the level of a man who denies the primary laws of physics. 
Now, with regard to Mr. Robson’s remarks on my own pamphlet, I 
must begin by thanking that gentleman for his kind intimation to the 
entomological public that the pamphlet has attracted a good deal of 
attention, although his way of announcing the fact certainly leaves some¬ 
thing to be desired. His reference to the early part of my papers as 
containing “a clearly-defined and intelligible theory,” leads me to suggest 
that so long as I was only explaining the very elementary facts connected 
with melanism, Mr. Robson was able to follow them, but when I went 
off into the secondary and more indirect causes bearing on the subject, 
which required a more complete grasp of general scientific principles, 
my theory becomes “ dim and obscure,” and “ so many side issues are 
raised and discussed that the original idea is almost, if not entirely, lost 
sight of.” That is, I presume, Mr. Robson wanted something very 
straightforward to be presented to him, something that would be easier 
to criticise, and this was managed so long as I kept within the confines 
presented by an elementary physical geography text-book, but when 
I get beyond these limits, the paper becomes “ dim and obscure ” to 
Mr. Robson. But even in physical geography Mr. Robson is behind 
the times, for he talks of the increased humidity caused by the Gulf 
Stream as “ assumed.” This is a matter of fact, not assumption. His 
knowledge, too, of the distribution of melanic forms in Britain is shaky, 
for he speaks of my “ attempting to show that these are the districts 
where melanism most prevails.” This, again, is a matter of fact, and 
not of attempt. 
If Mr. Robson had understood what I had written on the subject, 
he would not have given me credit for restricting nature’s action to such 
narrow lines as he does. The breadth of my views, and the considera¬ 
tion of possible contingencies, seem to be the great blot in the paper, 
according to my critic. I pointed out broadly, that where there was 
excessive moisture, or excessive smoke, or both combined, rock-resting 
and tree-frequenting species, became melanic. This form of melanism I 
considered due to two things: (1) Moisture (or smoke, or both com¬ 
bined), which in some way, acted physiologically on the larvas, affecting 
them in such a manner as to make the species vary in a general way; 
(2) “ Natural selection,” which selected the dark forms produced by the 
general variation, and formed a race, suitable by constitution, to its en¬ 
vironment. I still suppose “ moisture ” is the great factor in inducing 
or producing the primary physical change in the larvae in Britain 
(although many other causes may have a similar effect elsewhere), re¬ 
sulting in this instance, in a melanotic development, and nothing as yet 
has been urged against this opinion. On the contrary it seems to have 
been very generally accepted. With regard to this, I might perhaps go 
a step further, and point out that although the final result of the action 
of moisture and smoke is much the same, the effect has been rather 
different. Moisture has acted slowly through ages on the constitution 
of the larva, and has thus brought about a certain amount of general 
variation; the secondary action of moisture, due to “ natural selection,” 
has likewise been slow, but always in the direction of melanism, by 
selecting the dark forms (or races) most protected by darker environ- 
F 
