( Ixv ) 



this powerful combination seemed more satisfactory than 'Sh\ 

 Trimen's supposition in 1868 that it " is possibly an instance 

 of special modification in imitation of some gigantic Acraea as 

 yet unknown, or perhaps extinct" (Trans. Linn. Soc, vol. 

 xxvi, 1870, p. 503). Professor Poulton suggested that it was 

 possible that the remarkable bluish-grey patches on the under- 

 side of the fore-wing of antiraachus were traces of descent from 

 an ancestor common to it and the other equally extraordinary 

 and equally isolated species of the genus Drurya, — D. zalmoxis. 

 In the discussion which followed the exhibit Professor 

 PouLTOX suggested that the struggle for existence against the 

 attacks of young, inexperienced enemies, — the kind of selective 

 attack to which ex hyyothesi Miillerian (synaposematic) resem- 

 blance was due — was in reality far more severe than appeared 

 at first sight because of the pressure of the struggle upon the 

 enemies themselves. This pressure was chiefly felt by the young, 

 and it was so excessive that comparatively few individuals in 

 the fresh wave sent forth at each breeding season, survived 

 to become mature and experienced. It followed from this fact 

 that the amount of selective pressure exerted by inexperienced 

 enemies of insects was ten, twenty, a hundred, at any rate 

 many times as great as that which was due to the educational 

 period of the mature enemies existing at any moment. 



With reference to the Pkesidext's remarks, on the great 

 size of Drurya antiraachus compared to that of the other 

 members of the synaposematic group, Mr, P. A, Herox sug- 

 gested that, in the recognition of prey by sight, size, — within 

 considerable limits, — might be of minor importance to color- 

 ation, — the term being used to cover every kind of pattern 

 and marking. The size of an insect, as correlated with the 

 idea of its distance, was, in natural surroundings, under 

 varying atmospheric conditions, extremely difficult of exact 

 estimation, though it might be easily observable in a group 

 of other insects of known size in a standard cabinet drawer. 

 Distance, and its correlative size, might perhaps be especi- 

 ally hard of determination by animals which, like the 

 majority of insect-hunting birds, had their eyes placed 

 somewhat laterally and not frontally, as in the anthropoids 

 in carnivora and in owls and similar predatory birds, 



PROC. EXT. soc. LOXD., V. 1903. F 



