BEDROCK 



between the eastern and western females of alciope are found on the 

 western island of Fernando Po. It is to be hoped that we shall soon 

 be in possession of the same full and careful records of Planema 

 Models and Acrcea Mimics, from this part of the range and from 

 the opposite coast of the Cameroons, that are now available from 

 Lagos and Entebbe. 



If the appearance of the white bar were sufficient to transform 

 " alicia " (Fig. 12) into " aurivillii " (Fig. 14) it is not unlikely that 

 a single sudden step might produce the change. But it is by no 

 means sufficient. The uncoloured figures indicate, although they 

 cannot show, that the fulvous markings of the fore wing in Fig. 12 

 gain a deeper tinge in Fig. 14, and that those of the hind wing are, 

 outside the band, more or less replaced by the dusky ground- 

 colour. Furthermore, the base of the hind wing under surface of 

 " aurivillii " is marked with a warm umber triangle bearing the 

 black spots which are found in this position in " alicia." Now all 

 these points of difference between the butterflies represented in 

 Figs. 12 and 14 are characteristic features of the Model — the male 

 of Planema macarista. 



If it be unreasonable to suppose that all these mimetic features 

 arose spontaneously and together, what is the probable explanation 

 of their origin ? It is probable that by spontaneous variation a 

 white band like that shown in Fig. 13 appeared in the ancestral 

 form (Fig. 12), and that this was from the very first sufficient to 

 confer some advantage by suggesting the appearance of a dominant 

 Model (Fig. 6). From this point Natural Selection acting on further 

 variations produced the detailed likeness which we see in the white 

 band itself and in the other mimetic features. 



If this be a valid interpretation, we ought, by studying sufficient 

 material, to find variations corresponding to that shown in Fig. 13 — 

 variations which might form the starting-point of new mimetic 

 patterns if suitable Models happened to exist in the locality. We do 

 find such variations, and a good example occurred among the 249 

 alciope females bred by Mr. Lamborn. The fulvous bar crossing 

 the fore wing was transformed into white in a single one of these 

 (Fig. 11), and a slight indication of the same change was seen in a 

 second specimen. Both individuals belonged to the same family. 



Now if there existed in the locality a dominant Planema or other 



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