MELANISM AND MELANOCHROISM. 33 
exhibit a decidedly lighter deviation of colours from the normal 
types. 
“ By way of adding a few facts in support of these remarks, 
I may state that even in the most favourable seasons, lepidop- 
tera collected on the plains here are invariably paler than 
individuals of the same species occurring on the lower hills or 
in wooded districts near the Ranges. The rainfall is in all 
seasons much greater on and around the base of the Ranges 
than out on the open plains. The higher we ascend the Alps 
the more humidity we meet with, and the greater the darken- 
ing of the lepidoptera, until we reach the summit, when they 
become perfectly black. P eixnodaimon pluto, Erebiola butleri, 
and occasionally Ltathmonyma hectori are cases in point, and 
doubtless many more species that yet remain to be discovered. 
Most entomologists will naturally suppose that all mountain 
forms of lepidoptera are endowed with a more hardy constitu- 
tion than other or allied species occurring at lower altitudes ; 
but the cause of melanism at high altitudes is not so much a 
question of cold or heat as its great advantage over other 
colours in a wet or humid region. Doubtless Lord Walsing- 
ham’s theory of the greater absorption of heat by dark- 
coloured lepidoptera would occasionally be advantageous to 
certain melanic forms as well as in a protective sense, but as 
Mr. Tutt has shown {Ent. Record, vol. i., 232), it leaves the 
origin of melanism wholly unexplained. Again, we know that 
melanism is prevalent in some seasons that are at the same 
time both mild and moist. A certain degree of moisture is 
necessary in the egg, larval, and pupal stages to perpetuate the 
typical colours of a species, and we know it is only in exceptional 
seasons or under exceptional conditions that lepidoptera vary 
most. Still, we must allow that in hot, dry seasons, the colours 
of many species of lepidoptera are rendered paler, or obsolete, by 
the sun’s absorption, or bleaching of the colours affected ; but we 
are not so much interested in this question at present as we are 
in the origin and causes of melanism. One remarkable instance 
which would appear to oppose Lord Walsingham’s theory 
occurs in the habits of Nyctemera annidata, a jet-black diurnal 
moth with two white marks on each forewing and one on the 
hindwing. The moth in a natural state, or when bred, almost 
invariably emerges from the cocoon and flies about on dull and 
drizzly days. It may sometimes be seen soaring in the cool 
early morning, but at all times it shuns the hot sunshine. It 
would therefore appear that the theory of absorption of heat 
c 
