INSECTS. 363 



sex; but Mr. Wallace and Mr. Bates have shown * that the 

 females of some species are extremely variable, the males 

 being nearly constant. In a future chapter I shall have 

 occasion to show 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, f This fact is at present inexplicable; but if it 

 should hereafter be found that the formation 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 inherit- 

 ance, 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-colored 

 species of Lepidoptera owe their colors to sexual selection, 

 excepting in certain cases, presently to be mentioned, in 

 which conspicuous colors have been gained through mimicry 

 as a protection. From the ardor 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 colored, and this undoubtedly is the 

 case. When both sexes are brilliantly colored and resemble 

 each other the characters acquired by the males appear to 

 have been transmitted to both. We are led to this conclu- 

 sion by cases, even within the same genus, of gradation 

 from an extraordinary amount of difference to identity in 

 color between the two sexes. 



But it may be asked whether the differences in color 

 between the sexes may not be accounted for by other means 



* Wallace on the Papilionidse of the Malayan Region, in "Trans- 

 act. Linn. Soc.," vol. xxv, 1865, pp. 8, 36. A striking case of a rare 

 variety, strictly intermediate between two other well-marked female 

 varieties, is given by Mr. Wallace. See also Mr. Bates, in " Proc. 

 Entomolog. Soc.," Nov. 19, 1866, p. 40. 



f Mr. Bates was so kind as to lay this subject before the Entomo- 

 logical Society, and I have received answers to this effect from several 

 entomologists. 



