( 3 ) 



flies in tropical South America, and Commander J. J. Walker 

 gave similar testimony with regard to the many Australasian 

 and other oversea localities visited by him. 



Wednesday, April 7th, 1909. 



xviii] 



Mr. E. Shelford exhibited a case containing a number of 

 examples of mimetic Oriental Blattidae, the models being 

 Coleoptera, principally CoccineUidae and Ghrysomelldae. 



xx] Papers. 



Mr. G. A. K. Marshall read a paper entitled " On 

 Reciprocal Mimicry. A Rejoinder to Dr. F. A. Dixey." In 

 the course of his remarks the author explained that the main 

 difference between his views and those of Dr. Dixey as to the 

 development of Miillerian I'esemblances might be stated as 

 follows. The latter gentleman considers that within the 

 limits of a Miillerian association every species exercises a 

 mimetic influence upon every other, the amount of the in- 

 fluence 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 inter- 

 change 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 

 Midler's theory. While admitting the theoretical possibility 

 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 



