Seasonal Dimorphism in certain African Butterflies. 



times, and is, in each case, regarded as the principal 

 character for distinguishing two otherwise similar species. 

 Comparing the under surfaces, one sees either no 

 difference whatever, or only such as has a purely 

 individual value ; whilst, occasionally, individuals come 

 to hand in which the apical black patch of the upper 

 surface varies between the two extreme types, clearly 

 proving it to be valueless as a specific character ; 

 A. acrita indeed is only one of those intermediate grades 

 itself, for the black apex is still more largely developed 

 in A. chderibula. 



These differences in Acrsea I believe to be seasonal ; the 

 examples with the black apical patch being the wet- 

 season forms. Supposing this to be a correct explanation 

 of this curious and certainly inconstant difference, the 

 species will stand as follows : 



Dry-season form. Wet-season form. 



1. Acrssa anacreon, Trimen. *AcrsBa bomba f H. G. Smith. 



2. Acrsea guillemei, Oberth. Acrsea periphanes, Oberth. 

 y. Acrsea doubledayi, Guer. Acrsea dircsea, Westw. 



4. Acrsta stenobsea, Wallgr. Acrssa caldarena } Hewits. 



5. Acrsea pudorina, Staud. Acrsea chseribula, Oberth. 



With regard to the above associations, it must be 

 borne in mind that a species which, in a variable climate, 

 is dimorphic, ceases to be so in a uniform climate, and 

 thus it does not follow, because a species does not vary in 

 one part of Africa, that it therefore shows equal constancy 

 in another part : indeed, we now know that some of the 

 Southern species which appear to breed from generation 

 to generation true to type, break up into two widely 

 different types in Central Africa. Then, again, in a 

 climate neither unusually dry nor wet, an intermediate 

 type may prevail, to the exclusion of the extremes. 

 Hitherto we have not received typical A. pudorina from 

 Nyasa-land, but we have a form so near to it, that no 

 Lepidopterist would have the temerity to describe it as a 

 distinct species ; secondly, we have typical A. acrita ; and, 

 lastly, A. chseribula^ from Zomba. 



Climatic modifications and seasonal forms result 





c ' I cannot distinguish A . induna as a species, from this, 

 t I consider this the same as A. ambigua, Trimen. 



