11 . 
Scotland, Ireland, the Isle of Man, and the North of England:—the 
peculiarities of the climate of Ireland and the Isle of Man being, 
deficient sunshine, excessive moisture, and the almost entire absence 
of frost. It may be suggested that under such conditions the hiberna¬ 
tion of larvae, and the sleep of pupae are incomplete, and that damp 
and mould make many victims. Over wide districts of Yorkshire, 
Lancashire, and Durham—those very districts where melanism 
especially occurs—the air is polluted by mephitic exhalations from 
furnaces and chemical works, the sun is obscured by clouds of coal 
smoke, and the vegetation defiled and destroyed by deposits of soot ; 
in some of the worst districts, such as St. Helen’s and Bradford, 
Lepidoptera scarcely exist at all. In the Highlands of Scotland, 
although the air be purity and the sunshine brightness, the long, cold, 
wet winter, and the late spring, can hardly fail to check the multiplica¬ 
tion of those forms of life which have their metropolis in warmer 
southern lands.” Mr. Birchall then goes on to show by quotations 
from Darwin and Wallace that black and dark colours are advantageous 
to animals, and concludes his arguments thus “ As it appears certain 
that greater strength of constitution and more powerful and acute 
perceptive faculties are, from some yet unknown cause, associated with 
dark colours in the Vertebrata, may we> not presume that insects are 
subject to the same law, and that dark varieties of Lepidoptera are 
able to spread and increase under adverse conditions, whilst the lighter 
coloured types fail to do so, and are consequently eliminated in the 
struggle for life, and that the occurrence of melanic forms may be thus 
reasonably explained as a simple case of the survival of the fittest.” 
He then enumerated between thirty and forty species of Lepidoptera 
in which melanism had been observed, a list which could now be very 
largely added to. 
A long and interesting discussion ensued, both in the “ Entom¬ 
ologist’s Monthly Magazine ” and in the “ Entomologist,” in which 
many points only briefly touched on by Mr. Birchall were en¬ 
larged upon and discussed at length. The only one of the various 
papers which then appeared, from which I need trouble you with 
quotations is by Mr. Barrett “ On the degree of tendency to variation 
exhibited by the Lepidoptera of Pembroke and neighbourhood.” He 
referred first to the fact that “ Lepidoptera whose larvae feed in trees 
are almost totally absent.” This, he thinks arises from the mildness 
of the winters, and in a far larger degree from their extreme humidity, 
but he thinks the principal cause of the exclusion of the tree-feeding 
species, is the furious violence of the storms, which, coming across the 
Atlantic rush upon this coast from the south-west, with a fury which 
the trees themselves can barely resist.” He then comments on the 
little variation he has observed, and concludes “ that the special peculi- 
