320 The Descent of Man. Part II. 



the green patch on the fore-wings, and in the occasional ap- 

 pearance of the small crimson stripe on the hind-wings, 

 borrowed, as it wonid seem, from its own female ; for the females 

 of this and of many other species in the iEneas group possess 

 this crimson stripe. Hence between the brightest specimens 

 of P. sesostris and the dullest of P. childrence, there was but a 

 small interval ; and it was evident that as far as mere varia- 

 bility is concerned, there would be no difficulty in permanently 

 increasing the beauty of either species by means of selection. 

 The variability is here almost confined to the male sex; but 

 Mr. Wallace and Mr. Bates have shewn 24 that the females of 

 some species are extremely variable, the males being nearly 

 constant. In a future chapter I shall have occasion to shew 

 that the beautiful eye-like spots, or ocelli, found on the wings of 

 many Lepidoptera, are eminently variable. I may here add 

 that these ocelli offer a difficulty on the theory of sexual 

 selection ; for though appearing to us so ornamental, they are 

 never present in one sex and absent in the other, nor do they 

 ever differ much in the two sexes. 25 This fact is at present 

 inexplicable ; but if it should hereafter be found that the for- 

 mation of an ocellus is due to some change in the tissues 

 of the wings, for instance, occurring at a very early period of 

 development, we might expect, from what we know of the laws 

 of inheritance, that it would be transmitted to both sexes, though 

 arising and perfected in one sex alone. 



On the whole, although many serious objections may be 

 urged, it seems probable that most of the brilliantly coloured 

 species of Lepidoptera owe their colours to sexual selection, 

 excepting in certain cases, presently to be mentioned, in which 

 conspicuous colours have been gained through mimicry as 

 a protection. From the ardour of the male throughout the 

 animal kingdom, he is generally willing to accept any female ; 

 and it is the female which usually exerts a choice. Hence, if 

 sexual selection has been efficient with the Lepidoptera, the 

 male, when the sexes differ, ought to be the more brilliantly 

 coloured, and this undoubtedly is the case. When both sexes 

 are brilliantly coloured aud resemble each other, the characters 

 acquired by the males appear to have been transmitted to both 



24 Wallace on the Papilionidae of tomolog. Soc' Nov. 19th, 1866. p. 



the Malayan Region, in ' Transact, xl. 



Linn. Soc' vol. xxv. 1865, pp. 8, 25 Mr. Bates was so kind as to 



36. A striking case of a rare lay this subject before the Entomo- 



variety, strictly intermediate be- logical Society, and I have received 



tween two other well-marked female answers to this effect from several 



varieties, is given by Mr. Wallace. entomologists. 

 See also Mr. Bates, in ' Proc. En- 



