The Bionomics of South African Insects. 491 



which one alone is found in any part of the total range of 

 the species. Hence the polymorphism, although partially a 

 distributional phenomenon, is not entirely so. On the 

 other hand, I know of no example among the Lepidoptera 

 in Avhich a species is at the same season divided into two 

 sub-equal sections throughout its range, each containing 

 both males and females, and each section mimicking 

 a very different model. Among Diptera, the European 

 Volucella homhylans and its form mystaeea supply good 

 examples; and now Mr. Marshall has collected evidence 

 which makes it in the highest degree probable that the 

 Lepidoptera are not without such cases. He brings 

 convincing support for the belief that Eitralia toahlhergi 

 and E. mivia are the two forms of a single species. It is 

 greatly to be hoped that Mr. Marshall may be as success- 

 ful in establishing this interesting and unique case, as he 

 has been in the marvellous seasonal transformation of 

 Precis. His evidence is set forth in the following quota- 

 tions from his letters : — 



" UmJcomccas 3Iouth, Netted ; Sept. 3, 1897. — In my own 

 mind I am pretty well convinced that EuraJia mima and 

 vjcihlbcrgi are one and the same species which has developed 

 two mimetic I'orms as in Papilio ccnca, but that in this case 

 both sexes are concerned. My reasons for so thinking are 

 that they have been taken in coitu several times, that 

 specimens occur presenting intermediate coloration, and 

 also that the two forms are always found together whenever 

 they are met with in any number. I have not often been 

 fortunate enough to see these congregations, but I re- 

 member seeing some thirty or forty specimens, comprising 

 about equal numbers of each form, collected together on 

 the side of a steep shady kraantz along the Palmiet River. 

 Mr. A. I). Miller, who has collected for many years in 

 Durban, tells me this is by no means uncommon, and 

 that they congregate particularly in the afternoon when 

 going to roost. Mr. C. N. Barker tells me that some years 

 ago he came across a large number of both forms on a 

 large tree on which they had evidently bred, for many of 

 them had only just emerged, and some had not their 

 wings fully developed. This shows that they are also 

 associated in their earlier stages." 



About the time Avhen this passage was written Mr. 

 Marshall presented to the Hope Department a set of 

 eight individuals of these Euralias, viz. four of E. mima (2 $, 



