266 PSEUDACRAEA EURYTUS 



of the basal umbre indicating influence by hohleyi or its 

 female tirikensis. It would seem as if hohleyi and tiri- 

 Tcensis are the strongest and most stable forms, influencing 

 the other two. 



These abundant forms of Pseudacraea eurytus that 

 have been captured on the islands of Lake Victoria have 

 a very important bearing on the explanation of mimicry 

 by Natural Selection. As is abundantly evident from 

 letters quoted, Professor Poulton believes that here is 

 strong evidence of the efficacy of Natural Selection in 

 at least keeping the mimics up to the mark. When models 

 are scarce no one form of Pseudacraea has any particular 

 survival value over another, and all kinds of non-mimetic 

 transitional forms are preserved which, when the models 

 are superabundant, are presumably destroyed by enemies 

 so that they do not appear in collections. 



It would be of the very greatest interest at the present 

 time to obtain offspring from the mimetic forms on the 

 mainland and ascertain whether they will produce transi- 

 tional offspring. Indeed, we know that they do produce 

 a certain proportion of these, for two examples have 

 been captured at Entebbe and have been alluded to 

 before. 



The table on p. 265 shows by comparison the difference 

 between collections made without prejudice at localities 

 where Planema outnumbers Pseudacraea, and where the 

 latter are predominant. 



The chart on p. 267 shows very graphically how the 

 figures vary and the manner in which the numbers of 

 Planemas and of intermediate Pseudacraeas vary inversely. 



A most remarkable thing is the complete change in 

 the proportion of Planema to Pseudacraea on Kome 

 Island and its near neighbours to the west in the period 

 between 1914 and the end of 1918 and commencement 

 of 1919. When I was on Kome for several months in 

 1914, Planemas far outnumbered Pseudacraeas, which 



