CONCLUSIONS ON MIMICEY AND SEX 139 



in the chemical and physical constitution of pig- 

 ments. 



(8) Female Mimicry is not by any means always 

 a question of colour and pattern alone. Thus, 

 the mimetic females of some Papilionidae lose the 

 ' tails ' which are retained by the non-mimetic 

 males (e. g. P. dardanus = merope), and the females 

 of the tropical American Nymphaline genus 

 Eresia and Pierine genus Dismorphia and its 

 allies, are not only better mimics in colour and 

 pattern but also in shape of the wings. 



SEXUAL SELECTION (EPIGAMIC CHAEACTEKS) 



We do not know the date at vN^hich the idea 

 of Sexual Selection arose in Darwin's mind, but 

 it was probably not many years after the ' sudden 

 flash of insight ' which, in October, 1838, gave to 

 him the theory of Natural Selection. An excel- 

 lent account of Sexual Selection occupies the 

 concluding paragraph of Part I of Darwin's 

 Section of the Joint Essay on Natural Selection, 

 read July 1, 1858, before the Liunean Society. ^ 

 The principles are so clearly and sufficiently 

 stated in these brief sentences that it is appro- 

 priate to quote the whole : 



' Besides this natural means of selection, by which those 

 individuals are preserved, whether in their egg, or larval, or 

 mature state, which are best adapted to the place they fill in 

 nature, there is a second agency at work in most unisexual 

 animals, tending to produce the same effect, namely, the 

 struggle of the males for the females. These struggles are 

 ^ Journ. Proc. Linn. Soc, iii. 1859, 50. 



