( xcvii ) 



the range of dorippus — the occasional appearance of single 

 individuals in the swarms of the type form. And if the two 

 are syngamic on the outskirts, the gradual transition in pro- 

 portions towards the metropolis of dorippus suggests that 

 they are syngamic throughovit. Common as the species is — 

 probably the commonest butterfly in the world, — the evidence 

 from epigony has never been obtained, although from the 

 point of view of heredity the investigation promises to be of 

 tlie deepest interest. 



The remarkable forms of the females of the Papilio rnerope 

 group already alluded to afford another excellent example, 

 although in this case good transitional series can be constructed. 

 The evidence of syngamy was first obtained by Hewitson (see 

 p. Ixxxvii), but is now well known. The evidence of epigony has 

 fortunately been obtained in 1902 and again within the last 

 few weeks by one of our Fellows at Durban, Mr. G. F. Leigh. 

 Eggs from a female of the commonest cenea form yielded a 

 synepigonic group, including a large majority of forms like the 

 parent, but also examples of the very different Mpijocoon form. 

 Still more recently seven eggs from the rarest of the forms, 

 tropJionius, produced, in addition to males, two females of the 

 cenea variety, and not one resembling the parent. 



These differences, although only of colour and pattern, 

 greatly exceed those between ordinary close species. When we 

 deal with other kinds of dimorphism or polymorphism involv- 

 ing important structural differences, such as those of the social 

 Hymenoptera and Neuroptera, the discriminating characters 

 between nearly related genera ai-e commonly equalled or 

 exceeded. 



II. Seasoned Dimorphism : — In certain exceedingly interest- 

 ing examples of dimorphism the relation between the forms is 

 epigonic and not syngamic ; for rare and occasional inter-breed- 

 ing is not syngamy. I refer to the most strongly-marked cases 

 of seasonal dimoiphism in butterflies, especially the wonderful 

 examples proved to be epigonic by Guy A. K. Marshall. In 

 .some of the forms the two seasonal phases were not even 

 regarded as closely related species. In these extraordinary 

 cases, where the widest difference in colour and pattei-n exists, 

 in combination with others which are far more deep-seated, 



PROC. ENT. see. LOND., V. 1903. H 



