( i ) 



species towards a stronger and never in an opposite direction ; 

 further, that when the relative dominance of the two species 



[xxi 

 was equal the mere operation of iNlUller's factor would produce 

 no mimetic effect, until some other factor had first j)roduced a 

 condition of inequality. On this view mimetic interchange 

 would never be mutual and simultaneous, but would only re- 

 sult from a complete reversal of the relative dominance of the 

 two species during the production of the mimetic resemblance. 

 For this process he had suggested the name of " Alternate 

 Mimicry." The ai^thor was also compelled to reject entirely 

 Dr. Dixey's new hypothesis as to the " function of the double 

 aposeme," because it completely left out of consideration the 

 differences and resemblances between the various forms 

 regarded from the standpoint of general facies ; he contended 

 that resemblance in general effect was of the first importance 

 in considering mimetic relationship, and that this new 

 hypothesis was liable to be extremely misleading on account 

 of the exaggerated significance which it attached to the merely 

 partial resemblance which might be said to exist between two 

 species possessing a single conspicuous feature in common but 

 differing markedly in other respects. Moreover, not only was 

 the theoretical position of Reciprocal Mimicry very unsatis- 

 factory and unconvincing, but further, the cases which had 

 been cited as proving its actual occurrence in nature appeared 

 open to serious criticism. For while in some cases the facts 

 did not appear to justify the assertion that an interchange had 

 taken place, in the others such an interpretation involved 

 many difficulties which disappeared when the mimetic phe- 

 nomena were interpreted as being due to the simple mimicry 

 of one form by another. 



In illustration of his contentions Mr. Mahshaf.l exhibited 

 a number of butterflies, the great majority of which had been 

 kindly lent for the purpose by Mr. W. J. Kaye, the remainder 

 having been kindly supplied by Dr. K. Joudan and Mr. 

 Hamilton Druce. 



Dr. DiXBY then stated that he did not consider the 

 Presidential Chair to be a proper place in which to reply to 

 Mr. Marshall's criticism, and that he would therefore deal 

 with the points at issue on some future occasion. Mr. C. J. 



