SOCIETIES. 163 



deposited ; and the leaf closes over the ova when the appendages are 

 withdrawn. The discussion on the two similar species, Plebius argus 

 and P. argyrognomon was resumed and concluded. — Mr. H. St. J. 

 Donisthorpe read a paper " On the Origin and Ancestral Form of 

 Myrmecophilous Coleoptera." — Mr. W. L. Distant communicated a 

 paper on " Ehynchota Malayana." — Mr. J. B. Collin communicated a 

 paper by Mr. Wesche " On the Antennae of Diptera, and the Present 

 Classification of the Nemocera, with two subsidiary sections bearing 

 on the latter subject." — Mr. G. A. K. Marshall then read a paper en- 

 titled " On Eeciprocal Mimicry. A Eejoinder to Dr. F. A. Dixey." 

 Dr. Dixey had taken the view that within the limits of a Miillerian 

 association every species exercises a mimetic influence upon every 

 other, the amount of the influence depending upon its dominance, 

 which is determined by its numbers, distastefulness, and general 

 notoriety. Thus, as between any two species, the mimetic approach 

 would be mutual and result in an interchange of characters. This 

 interchange would be proportionate to the relative dominance of the 

 two species ; where this is unequal, the weaker species would take 

 on, to a considerable extent, the superficial appearance of the 

 stronger, while the latter would adopt only some small characters 

 from its mimic ; but where the dominance is equal, the interchange 

 would be equal, so that this would constitute the optimum condition 

 for the production of reciprocal mimicry. On the other hand, Mr. 

 Marshall contended that this gravitational conception of mimicry was 

 really based on a false analogy and was at variance with the real 

 principle of Miiller's theory. While admitting the theoretical possi- 

 bility of mimetic interchange, he urged that a logical application of 

 Miiller's argument would lead to the view that mimetic approach 

 would be one-sided only, that is, from a weaker species towards a 

 stronger and even in an opposite direction ; further, that when the 

 relative dominance of the two species was equal, the mere operation 

 of Miiller's factor would pi-oduce no mimetic effect until some other 

 factor had first produced a condition of inequality. On this view 

 mimetic interchange would never be mutual and simultaneous, but 

 would only result 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." 

 Mr. Marshall said also that he was 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 re- 

 semblances 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 difl'ering 

 markedly in other respects. Moreover, not only was the theoretical 

 position of Eeciprocal Mimicry very unsatisfactory 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 



