884 SEXUAL SELECTION. [Part IL 



Butterflies, as before remarked, elevate their wings when 

 at rest, and while basking in the sunshine often alternately 

 raise and depress them, thus exposing to full view both 

 surfaces ; and, although the lower surface is often colored 

 in an obscure manner as a protection, yet in many species 

 it is as highly colored as the upper surface, and sometimes 

 in a very different manner. In some tropical species the 

 lower surface is even more brilliantly colored than the 

 upper. 11 In one English fritillary, the Argynnis aglaia, 

 the lower surface alone is ornamented with shining silver 

 disks. Nevertheless, as a general rule, the upper surface, 

 which is probably the most fully exposed, is colored more 

 brightly and in a more diversified manner than the lower. 

 Hence the lower surface generally affords 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, colored 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 Hypo- 

 pyra, specified by Mr. Wormald. 12 Mr. R. Trimen 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 grayish-ochreous, while 

 the lower surface is magnificently ornamented by an ocel- 

 lus of cobalt-blue, placed in the midst of a black mark, 

 surrounded by orange-yellow, and this by bluish-white. 



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 Papilionidae of the Malayan Region, in ' Trans- 

 act. Linn. Soc' vol. xxv. part i. 1865. 



12 ' Proc. Ent. Soc' March 2, 1868. 



