396 
SEXUAL SELECTION. 
Paet IL 
colours would not be visible during the night; and 
there can be no doubt that moths, taken as a body, are 
much less gaily decorated than butterflies, all of which 
are diurnal in their habits. But the moths in certain 
families, such as the Zygscnidae, various Sphingidse, 
Uraniidse, some Arctiidas and Saturniidae, fly about 
during the clay or early evening, and many of these 
are extremely beautiful, being far more brightly 
coloured than the strictly nocturnal kinds. A few 
exceptional cases, however, of brightly-coloured noc- 
turnal species have been recorded . 10 
There is evidence of another kind in regard to display., 
Butterflies, as before remarked, elevate their wings 
when at rest, and whilst basking in the sunshine often 
alternately raise and depress them, thus exposing to full 
view both surfaces ; and although the lower surface is 
often coloured in an obscure manner as a protection, 
yet in many species it is as highly coloured as the 
upper surface, and sometimes in a very different man- 
ner. In some tropical species the lower surface is even 
more brilliantly coloured than the upper . 11 In one 
English fritillary, the Argynnis aglaia , the lower sur- 
face alone is ornamented with shining silver discs. 
Nevertheless, as a general rule, the upper surface, 
which is probably the most fully exposed, is coloured 
more brightly and in a more diversified manner than 
the lower. Hence the lower surface generally affords 
10 For instance, Lithosia ; but Prof. Westwood (‘ Modern Class, of 
Insects/ vol. ii. p. 390) seems surprised at this case. On the relative 
colours of diurnal and nocturnal Lepidoptera, see ibid. p. 333 and 392 ; 
also Harris, 4 Treatise on the Insects of New England/ 1842, p. 315. 
11 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 Papilionidse of the Malayan Kegion, 
in ‘ Transact. Linn. Soc.’ vol. xxv. part i. 1865. 
