228 ENTOMOLOGY 



butterflies of a distasteful species before it becomes recognized 

 as such, and that there exist in this region 2,000 individuals 

 of species A and 10,000 of species B ; then, if they are different 

 in appearance, each will lose 1,200 individuals, but if they are 

 deceptively alike, this loss will be divided among them in pro- 

 portion to their numbers, and A will lose 200 and B 1,000. A 

 accordingly saves 1,000, or 50 per cent, of the total number 

 of individuals of the species, and B saves only 200, or 2 per 

 cent. Thus, while the relative numbers of the two species are 

 as i to 5, the relative advantage from their resemblance is as 

 25 to i. 



If two or more distasteful species are equally numerous, 

 their resemblance to one another brings nearly equal advan- 

 tages. In cases of this kind and many are known it is 

 sometimes impossible to distinguish between model and mimic, 

 as all the participants seem to have converged toward a com- 

 mon protective appearance, through an interchange of features 

 the " reciprocal mimicry " of Dr. Dixey. 



From this explanation, the superior value of Mullerian as 

 compared with Batesian mimicry is evident. 



The fourth condition that the imitators differ from the 

 bulk of their allies holds true to such a degree that even the 

 two sexes of the same species may differ extremely in colora- 

 tion, owing to the fact that the female has assumed the like- 

 ness of some other and protected species. The female of 

 Papilio merope, indeed, occurs (as was just mentioned) under 

 three varieties, which mimic respectively three entirely dissim- 

 ilar species of Danainse, and none of the females are any- 

 thing like their male in coloration (Frontispiece, Figs. 5-11). 

 The specific identity of these four South African varieties of 

 merope has been established by Trimen, Marshall and other 

 investigators. 



The generally accepted explanation for these remarkable 

 but numerous cases in which the female alone is mimetic, is 

 that the female, burdened with eggs and consequently sluggish 

 in flight and much exposed to attack, is benefited by imitating 



