No. 605] 



ANIMAL COLORATION 



259 



been alleged that very many types from the same region 

 show the influence of one or another of the dominant 

 Miillerian aggregations. Miiller's hypothesis, however, 

 has not attained preeminence solely by extension to newly 

 discovered cases of resemblance, but has prospered in 

 many instances at the direct expense of the Batesian con- 

 ception. Its changed fortune depends largely upon 

 Dixey's*^ discovery of mimetic attraction, or reciprocal 

 mimicry. 



This relation, which it is held exists between many in- 

 sects previously considered typical Batesian couples, sug- 

 gests that the observed resemblance involves mutual ad- 

 justment. But the idea that each species introduces into 

 its own pattern elements characterizing that of the other, 

 and thus contributes actively to the development of a 

 common type of coloration, is intelligible in terms of the 

 mimicry hypotheses, only if the superficial resemblance 

 so attained is mutually advantageous. Whatever justi- 

 fies change in the interpretation of fact lies here; for, if 

 it be assumed in the beginning that the likeness noted 

 must have arisen either through the action of Batesian or 

 Miillerian factors, it must be admitted that the notion of 

 mutual advantage seems more fitly associated with the 

 latter: two species, each of which enjoys marked immu- 

 nity, seem better able to force reciprocal concessions in 

 their achievement of resemblance, than they should, if 

 there were great disparity in their means of defence. 



Perhaps the most obvious suggestion from Dixey's 

 research is not, after all, that a closer approximation to 

 truth may possibly be attained through reclassification of 

 mimetic resemblances, but that an intergrading series of 

 alleged Batesian and Miillerian mimics is perfectly con- 

 ceivable, in which no known test could possibly determine 

 the occurrence of a natural break. Hence there would 

 seem to be only historical reasons for maintaining tlie 

 two categories. 



It is notewortliy tlml iicitlu'i- liyp..tl;(".i. to wlilri, ivf 



