111 . 
arity of climate likely to effect these species, is its excessive moisture, 
and that the tendency is (as suggested) to deepen or intensify the colour 
and markings, but that there is not, with this abundance of rain, an 
excessive decrease of light, since the rain falls rapidly and heavily ; 
there are comparatively few cloudy days without rain in proportion to 
what are experienced in drier districts ; and the frequent and brilliant 
sunshine, and exquisitely clear and pure blue sky, affords a striking 
contrast to that of the Metropolitan and manufacturing districts in 
which cases of melanism are so frequent, and consequently cases of 
pure melanism appear to be very rare here.” 
In 1885 , Lord WaLingham took for the subject of his presidential 
address to the Yorkshire Naturalists’ Union “ Some probable causes 
of a tendency to melanic variation in Lepidoptera of high latitudes." 
In this paper he proved, as the result of actual experiment that dark 
coloured Lepidoptera absorbed heat more rapidly than did those of 
paler hues. He showed how great an advantage was derived by 
darker insects under special climatic conditions. From their power 
of more quickly absorbing invigorating warmth, they de\'eloped 
more rapidl}-’ and were able to take advantage of any transient gleam 
ot sunshine. As this important pamphlet is no doubt familiar to 
most, I need not quote from it at length, but it sought to 
establish the fact that wherever the direct ra 3 's of the sun are 
interrupted, whether through the mist and cloud of Alpine regions, or 
from any other cause, that there we might reasonably expect to find - 
melanic forms, and did so. “ The smoke of our furnaces in the 
manufacturing districts, and of our chimneys in large towns, un¬ 
doubtedly deprive our urban population of their fair share of undiffused 
sunlight within the radius affected by them. Accordingly we find 
several instances of more or less melanic forms occurring in such 
situations." The illustrations I need not quote. He then goes on 
“ We should expect insects occurring in dense forests to be darker 
than those of the open country, and so far as my Californian experiences 
go this in undoubtedly the case.” He also tells us that All fishes 
from the very deep sea, inaccessible to the sun’s rays are either 
colourless, or entirely black.” 
This was the first attempt to show why melanic forms obtained a 
preference in the struggle for existence, and gave us another step 
towards a knowledge of the causes of variation. Two years later Mr. 
D'Obree published a paper on the subject in the “ Entomologist " 
(Vol. XX, p. 25 ), in which he claimed to have destroyed Lord 
Walsingham’s argument. But Mr. D’Obree was a student of noctuse 
only, and no conclusion based on study of an entire order could be 
upset by reference to one portion onty of such order. Mr. D’Obree’s 
conclusions were that “ melanism is primarily due to the peculiar 
