SEXUAL SELECTION 411 



surface alone is ornamented with shining silver. Never- 

 theless, as a general rule, the upper surface, which is prob- 

 ably more fully exposed, is colored more brightly and 

 diversely than the lower; hence the lower surface gener- 

 ally 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 South 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 colored 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. " Mr. Trimen informs me that in Guen^e's 

 great work three moths are figured, in which the under sur- 

 face is much the more brilliant. For instance, in the Aus- 

 tralian Gastrophora the upper surface of the fore- wing is 

 pale grayish-ochreous, while the lower surface is magnifi- 

 cently 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 coloring. Mr. Trimen also informs 

 me that the lower surface of the wings in certain other 

 Geometrse" and quadrifid Noctuas are either more varie- 

 gated or more brightly colored than the upper surface ; but 



several species of Papilio may be seen In the beautiful plates to Mr. Wallace's 

 "Memoir on the Papilionidse of the Malayan Eegion," in "Transact. Linn. 

 Soc," vol. XXV. parti., 1865. 



•« See Mr. Wormald on this moth: "Proc. Ent. Soc," March 2, 1868. 



" See also an account of the S. American genus Erateina (one of the Geome- 

 trse) in "Transact. Ent. Soc," new series, vol. v. pi. xv. and xvi. 



