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Show 396 SEXUAL SELECTION. PAnT 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 Zygrenidre, various Sphingidre, Uraniidm, some Arctiidre and Saturniidre, fly about during the day or early evening, and many of these are extremely beautiful, being far more brightly coloured than the strictly nocturnal kinds. A few exceptional cases, hmrever, of brightly-coloured nocturnal 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..: nor. In some tropical species the lower su·rface is even more brilliantly coloured than the upper.U In one English fritillary, the Argynnis aglaia, the lower surface 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 tho lower. Hence the lower surface generally affords 10 For instance, Lithosia; but Prof. Westwood (' Modern Class. of Insects,' vol. ii. p. 3UO) seems surprised at thi:; case. On the relative colours of diurnal and nocturnal Lepidoptera, sec ibid. p. B33 and 392 ~ al so Harris, 'Treatise on the Insects of New England,' 1812, p. 315. u 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. Wallac~.J's Memoir on tho Papilionidro of tho Malayan Begion) in' Transact. Linn. Soc.' vol. xxv. part i. 1SG.J. CIIAP. XI. BUTTERFLIES AND MOTHS. 397 to entomologists the most useful character for detecting the affinities of the various species. Now if we turn to the enormous group of moths, which do not habitually expose to full view the under surface of their wings, this side is very rarely, as I hear from Mr. Stainton, coloured more brightly than the upper side, or even with equal brightness. Some exceptions to the rule, either real or apparent, must be noticed, as that of Hypopira, specified by Mr. Vv ormaldP 1\fr. R. r_rrimen informs me that in Guenee's great work, three moths are figured, in which the under surface is much the most brilliant. For instance, in the Australian Gastrophora the upper surface of the fore-wing is pale greyish-ochreous, while the lower surface is magnificently ornamented by an ocellus of cobalt-blue, placed in the midst of a black mark, surrounded by orange-yellow, and this by bluish-white. But the habits of these three moths are unknown ; so that no explanation can be given of their unusual style of colouring. Mr. Trimen also informs me that the lower surface of the wings in certain other Geometrre 13 and quadrifid N octure are either more variegated or more brightly-coloured than the upper surface; but some of these species have the habit of'' holding their wings quite erect over their "backs, retaining them in this position for a considerable "time," and thus exposing to view the under surface. Other species when settled on the ground or herbage have the habit of now and then suddenly and slightly lifting up their wings. Hence the lower surface of tho wings being more brightly-coloured than the upper sur- 12 ' Proc. Ent. Soc.' 1\'larch 2nd, 1868. 13 See also an account of the S. American genus Erateina ( ono of -the Geometrre) in 'Transact. Ent. Soc.' new series, vol. v. pl. xv. and. xvi. |