ON RECIPROCAL MIMICRY. lo3 



done the necessary amount of feeding, whereas under the scythe the 

 process would often be more prolonged, and portions would remain long 

 enough for the larvae to mature. 



The mowing machine, however, appeared about 1850, and the dis- 

 appearance of the species had then made much progress, so that we 

 must look to the first half of the nineteenth century for the primary 

 agencies. 



I have tried to ascertain various dates as to the practical treatment 

 of the red clover crop without much success ; the introduction of red 

 clover extensively as an arable crop goes back to the end of the 

 eighteenth century-, but with what rapidity it became general I do not 

 know. 



If someone versed in the history of English agriculture during the 

 last 150 years would find precisely how clover was treated and to what 

 extent it was cultivated in different parts of England from its intro- 

 duction as an arable crop in the middle of the seventeenth century 

 down to the extinction of tiemianjus, it would probably throw some 

 light on the subject. The two leading points appear to be the great 

 extension of tillage (including clover) about the beginning of the 

 19th century and the introduction of the mowing machine about the 

 middle of that century. 



On Reciprocal Mimicry. 



Summary of Paper read before the Ent. Soc. of Lomlon, April 7th, 1909 

 (Extracted from Report). 



At the meeting of the Entomological Society of London, on April 7th, 

 1909, Mr. G. A. K. Marshall read a paper with this title, and 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 resemblances might be stated as follows. The latter gentle- 

 man considers 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 w^ould take on, to a considerable extent, the super- 

 ficial appearance of the stronger, while the latter would adopt onl}' 

 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 con- 

 ception 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 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 

 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 produce no mimetic effect, 

 until some other factor had first produced a condition of inequality. 



