72 'WHAT IS A SPECIES?' 



excellent example, although in this case good transitional 

 series can be constructed. The evidence of Syngamy was 

 first obtained by Hewitson (see p. 57, footnote 1), but is 

 now well known. The evidence of Epigony has fortu- 

 nately been obtained in 1902 and again within the last 

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

 Leigh. Eggs laid in 1902 by a female of the commonest 

 South African form, cenea, yielded a synepigonic group, 

 including a large majority of forms like the parent, but 

 also examples of the very different hippocoon form. In 

 the more recent example seven eggs from the rarest of 

 the South African forms, trophonius, produced, in addition 

 to males, two females of the cenea variety, and not one 

 resembling the parent. 1 



These differences, although only of colour and pattern, 

 greatly exceed those between ordinary close species. 

 When we deal with other kinds of dimorphism or poly- 

 morphism involving important structural differences, such 

 as those of the social Hymenoptera and Neuroptera, the 

 discriminating characters between nearly related genera 

 are commonly equalled or exceeded. 



b. Seasonal Dimorphism : — In certain exceedingly in- 

 teresting examples of dimorphism the relation between 

 the forms is epigonic and not syngamic ; for rare and 

 occasional interbreeding 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. 2 In some of the 

 forms the two seasonal phases were not even regarded as 

 closely related species. In these extraordinary cases, 



1 Trans. Ent. Soc. Lond., 1904, pp. 677-88, Plate XXXI. Still later, 

 in 1904, Mr. G. F. Leigh bred from the eggs laid by a trophonius female, 

 six males, four females of the cenea form, and one female of the trophonius 

 form (Trans. Ent. Soc. Lond., 1906, pp. 281-3, Plate XVII). Finally, 

 within the last few weeks I have received from the same keen naturalist 

 a splendid synepigonic group of twenty-eight specimens bred from a hippo- 

 coon parent — the first time that offspring have been reared from this form 

 of female. Of the twenty-eight, fourteen are males, eight are cenea females, 

 three are hippocoon females, and three are trophonius females [December 2, 

 1906]. 



2 Trans. Ent. Soc. Lond., 1902, pp. 414-60. 



