( 29) 
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 throughout. 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 
the deepest interest. 
The remarkable forms of the females of the Papilio merope 
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. 19), but is now wellknown. 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 cenew form yielded a 
synepigonic group, including a large majority of forms like the 
parent, but also examples of the very different Aippocoon form. 
Still more recently seven eggs from the rarest of the forms, 
trophonius, 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 are commonly equalled or 
exceeded. 
IL. Seasonal 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 dimorphism 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 pattern exists, 
in combination with others which are far more deep-seated, 
