396 SEXUAL SELECTION. Part II. 



colours would not be visible during: the nig^ht: 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 Zygaenidae, various Sphingidaa, 

 Uraniidae, some Arctiidse and Saturniidaa, 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 Argijnnis 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. H33 and 392 ; 

 also Harris, ' 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 liegiou, 

 in ' Transact. Linn. Soc' vol. xxv. part i. 1865. 



