SEXUAL SELECTION 417 



As sexual selection primarily depends on variability, 

 a few words must be added on this subject. In respect to 

 color there is no difficulty, for any number of highly vari- 

 able Lepidoptera could be named. One good instance will 

 suffice. Mr. Bates showed me a whole series of specimens 

 of Papilio sesosiris and P. cMIdrence; in the latter the males 

 varied much in the extent of the beautifully enamelled 

 green patch on the fore- wings, and in the size of the white 

 mark, and of the splendid crimson stripe on the hind- wings; 

 so that there was a great contrast among the males between 

 the most and the least gaudy. The male of Papilio sesosiris 

 is much less beautiful than of P. childrence; and it like- 

 wise varies a little in the size of the green patch on the 

 fore-wings, and in the occasional appearance of the small 

 crimson stripe on the hind-wings, borrowed, as it would 

 seem, from its own female; for the females of this and of 

 many other species in the ^neas group possess this crimson 

 Stripe. Hence, between the brightest specimens of Papilio 

 sesosiris and the dullest of P. childrence, there was but 

 a small interval; and it was evident that, as far as mere 

 variability 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 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. " This fact is at present inexplica- 



^ Wallace on the Papilionidse of the Malayan Region, in "Transact. Linn. 

 Boc," 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. xl. 



»' Mr. Bates was so kind as to lay this subject before the Entomological 

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



