( xlii ) 



facts from any attempt — in this cuse peculiarly difficult — to 

 explain the causes. 



The minutiio of an aposematic pattei'n such as that of 

 Xf'ptis may well be kept up by selection on an area where 

 two or more species exist together, and where o.g. an elaboi'a- 

 tion of the marginal markings is common to all. Under these 

 circumstances, too, elaboration would probably bo gained by a 

 species with simpler pattern bi'ought by migration into the 

 area in question. When, however, an aposematic species 

 with elaborate pattern becomes isolated, we should expect, on 

 the very same principles that are believed to account for the 

 growth of Miillerian resemblances generally, that enemies 

 would continue to test with especial severity largo departures 

 fi'om the average specilic pattern. But in this case the 

 numbers composing the average, being made up of the majority 

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

 inlluence 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 oft' 

 large and conspicuous departures from the average. Thus, 

 perhaps, may be explained the simplification in detail and 

 pei'sistence 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 ])r. T. A. 

 Chapman, Mr. G. A. K. Marshall, the liev. G. Wheeler, 

 Col. N. Manders and other Fellows participated. 



IMiMicRY 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 

 ho 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 



