Class. of Insects, vol. ii. p. 390) seems surprised at this case. On
the relative colours of diurnal and nocturnal Lepidoptera, see ibid.
pp. 333 and 392; also Harris, Treatise on the Insects of New England,
1842, p. 315.)
There is evidence of another kind in regard to display. Butterflies, as
before remarked, elevate their wings when at rest, but whilst basking
in the sunshine often alternately raise and depress them, thus exposing
both surfaces to full view; and although the lower surface is often
coloured in an obscure manner as a protection, yet in many species it
is as highly decorated as the upper surface, and sometimes in a very
different manner. In some tropical species the lower surface is even
more brilliantly coloured than the upper. (15. Such differences between
the upper and lower surfaces of the wings of several species of Papilio
may be seen in the beautiful plates to Mr. Wallace s Memoir on the
Papilionidae of the Malayan Region, in Transactions of the Linnean
Society, vol. xxv. part i. 1865.) In the English fritillaries
(Argynnis) the lower surface alone is ornamented with shining silver.
Nevertheless, as a general rule, the upper surface, which is probably
more fully exposed, is coloured more brightly and diversely than the
lower. Hence the lower surface generally affords to entomologists the
more useful character for detecting the affinities of the various
species. Fritz Muller informs me that three species of Castnia are
found near his house in S. Brazil: of two of them the hind-wings are
obscure, and are always covered by the front-wings when these
butterflies are at rest; but the third species has black hind-wings,
beautifully spotted with red and white, and these are fully expanded
and displayed whenever the butterfly rests. Other such cases could be
added.
If we now turn to the enormous group of moths, which, as I hear from
Mr. Stainton, do not habitually expose the under surface of their wings
to full view, we find this side very rarely coloured with a brightness
greater than, or even equal to, that of the upper side. Some exceptions
to the rule, either real or apparent, must be noticed, as the case of
Hypopyra. (16. See Mr. Wormald on this moth: Proceedings of the
Entomological Society, March 2, 1868.) Mr. Trimen informs me that in
Guenee s great work, three moths are figured, in which the under
surface is much the more brilliant. For instance, in the Australian
Gastrophora the upper surface of the fore-wing is pale
344