358 THE DESCENT OF MAN. 



up their wings. Hence the lower surface of the wings 

 being brighter than the upper surface in certain moths is 

 not so anomalous as it at first appears. The Saturniidse 

 include some of the most beautiful of all moths, their wings 

 being decorated, as in our British Emperor moth, with fine 

 ocelli; and Mr. T. W. Wood* observes that they resemble 

 butterflies in some of their movements; "for instance, in 

 the gentle waving up and down of the wings as if for dis- 

 play, which is more characteristic of diurnal than of 

 nocturnal Lepidoptera." 



It is a singlar fact that no British moths which are 

 brilliantly colored, and, as far as I can discover, hardly any 

 foreign species, differ much in color according to sex; 

 though this is the case with many brilliant butterflies. The 

 male, however, of one American moth, the Saturnia Io, is 

 described as having its fore wings deep yellow, curiously 

 marked with purplish-red spots; while the wings of the 

 female are purple-brown, marked with gray lines. \ The 

 British moths which differ sexually in color are all brown, 

 or of various dull yellow tints, or nearly white. In several 

 species the males are much darker than the females, J and 

 these belong to groups which generally fly about during 

 the afternoon. On the other hand, in many genera, as 

 Mr. Stainton informs me, the males have the hind wings 

 whiter than those of the female of which fact A gratis 

 exclamationis offers a good instance. In the Ghost Moth 

 (Hepialus humuli) the difference is more strongly 

 marked; the males being white and the females yellow 



*"Proc. Ent. Soc. of London," July 6, 1868, p. 27. 



f Harris, "Treatise," etc., edited by Flint, 1862, p 395. 



\ For instance, I observe in nay son's cabinet that the males are 

 darker than the females in the Lasiocampa quercus, Odonestis pota- 

 toria, Hypogymna dispar, Dasychira, pudibunda and Cycnia mendica. 

 In this latter species the difference in color between the two sexes is 

 strongly marked; and Mr. Wallace informs me that we here have, as 

 he believes, an instance of protective mimicry confined to one sex, as 

 will hereafter be more fully explained. The white female of the 

 Cycnia resembles the very common Spilosoma mentkrasti, both sexes 

 of which are white; and Mr. Stainton observed that this latter moth 

 was rejected with utter disgust by a whole brood of young turkeys, 

 which were fond of eating other moths; so that if the Cycnia was 

 commonly mistaken by British birds for the Spilosoma, it would es- 

 cape being devoured, and its white, deceptive color would thus be 

 highly beneficial. 



