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numbers composing the average, being made up of the majority 

 of the individuals of but a single species, would exert an 

 influence less powerful than that of the far larger number 

 •contributed by two or more species. If this reasoning be 

 sound we should expect that a less searching selection would 

 permit departures in minute detail, while it would still cut off 

 large and conspicuous departures from the average. Thus, 

 perhaps, may be explained the simplification in detail and 

 persistence of general effect. It would furthermore follow as 

 a general conclusion that after isolation aposematic patterns 

 would tend to be kept more constant than others. Against 

 this tendency must be set the special liability of aposematic 

 species to enter fresh combinations — a tendency of course 

 held in check in these small outlying islands. 



A discussion on the change of coloration in insular forms 

 of this and other lepidoptera followed, in which Dr. T. A. 

 Chapman, Mr. G. A. K. ]Marshall, the Rev. G. Wheeler, 

 Col. X. Manders and other Fellows participated. 



Mimicry in Bourbon Butterflies. — Lieut.-Colonel N, 

 Manders exhibited a collection of butterflies from Bourbon 

 demonstrating examples of mimicry and the effects of the 

 interaction of species. At a previous meeting of the Society ' 5 

 he had exhibited a series of the nireus group of Papilios from 

 Africa, Madagascar and the neighbouring islands, in which he 

 pointed out that whereas both sexes were of some shade of green 



and therefore resembled each other, in Bourbon the female of 

 the indigenous species (P. phorbanta) was brown and quite un- 

 like the male. He attributed this to the effects of mimicry, 

 Eujilcea goudoti being the model. It had since been suggested 

 to him by Professor Poulton and Mr. Trimen that Euploea 

 ^iqyhon resembled both P. phorhanta and Salamis augustina far 

 more closely than E. goudoti, and they were of opinion that 

 this had been the model for the two species. Against this 

 view was the fact that E. euphon was strictly confined to 

 Mauritius, and no record of its occurrence in Bourbon was 

 forthcoming. This undoubtedly closer resemblance of euphon 

 had led him to further investigate the matter, and there ap- 

 peared to be two hypotheses to account for its disappearance : 



