521 Rev. K. St. Aubyn Rogers' Bionomic Notes on 



Taveta (May 8, 1905— Jan. 30, 1906) : 7 ^ and 4 $ of 

 montana, 2 of the females with the pale markings of a 

 cream tint instead of white : 6 A. csehria, of which 2 

 resemble the males of montana and possess fulvous 

 markings, the others pale ochreous. 



Kilimanjaro (Jan. 26-81, 1906): 1 $ montana: 1 $ 

 Acrma carmentis. The latter is white-marked and re- 

 sembles the much larger female of montana. 



In looking through the fine collection of butterflies from 

 the Congo State in the Brussels Museum I was surprised 

 to find that the form montana was abundantly represented 

 from this area. 



In Mr. St. Aubyn Rogers' experience Acraja csebria is 

 less abundant than the Planema, and the above figures 

 support this conclusion. In Southern Africa, on the other 

 hand, the AcTcVa appears to be much commoner than 

 P. aganice. There is however a similar mimetic relation- 

 ship, — and the same is true of the representative forms of 

 Acrasa and Planema on the West Coast. Everywhere 

 the Acrxa seems to exist with the Planema and to act 

 as a variable and unstable mimic. The far greater con- 

 stancy of the colours of the Planema leads to the 

 inference that it is the model and the Acrxa the mimic. 

 Varieties of the latter commonly diverge and become 

 rough but undoubted mimics of Danaida chrysippus. 

 There can be no doubt that the usual strong superficial 

 resemblance between these two Acrxinx, combined with 

 the divergence of esehria from the ordinary colouring and 

 pattern of the genus Aerxa, led to its erroneous inclusion 

 for a time in Planema. 



It is interesting to attempt to answer the question why 

 Planema aganice acts as the model although it is, pro- 

 oably for the most part, a less abundant species. The 

 reason is probably to be found in its greater constancy and 

 also in its larger size. There are several other instances 

 of mimetic associations between Planema and Acrma : in 

 all that I am acquainted with the Planema is the larger 

 insect and appears to act as the model. The dominance 

 of a butterfly in the environment is affected by size as 

 well as by numbers and other qualities : cMeris jxirihits, a 

 large butterfly is likely to act as model for a small one. 

 In a parallel instance from tropical America, the larger 

 Nymphaline, Colienis julia, Fab., appears to act as model 

 for the smaller Heliconine, Eucides ali]jliera, Godt., both 



