324 Dr. Frederick A. Dixey on 



footing, any departure from which might be attended with 

 danger to itself; while the only part played by the former 

 is to shelter itself under as close an approximation to the 

 aspect of the model as circumstances permit. 



We may now take the case of a species possessing 

 a nauseous flavour, and requiring some means of adver- 

 tisement in order to make its inedibility available for 

 purposes of protection. Two courses may be said to lie 

 open for such a species. First, it may seek advertise- 

 ment by acquiring a conspicuous and easily recognised 

 aspect of its own, distinct from that of any others ; or, 

 secondly, it may obtain a share in the notoriety already 

 attaching to some dominant inedible form by assimilating 

 its aspect to that of the latter, instead of striking out a 

 new line for itself. An examination of the lepidopterous 

 fauna of such a region as the neotropical makes it certain 

 that the latter of these methods, viz., the method of 

 " Mtillerian mimicry," has been very extensively fol- 

 lowed. Its advantages, as compared w^ith the former 

 method, are obvious. In the first place it assists the 

 memory of predaceous foes by keeping at a low figure the 

 number of distinct inedible types to be learned and so 

 avoided, and in the second place it benefits at least two 

 species at the same time instead of one, and both have 

 therefore an interest in keeping it up ; for inasmuch as in 

 this case, as distinct from that of Batesian mimicry, the 

 mimic is inedible as well as the model, the results of 

 experimental tasting will be uniformly the same, and will 

 be favourable to the immunity of both species. It 

 follows that (1) there is no such limit as exists in 

 Batesian mimicry to the number either of individuals or 

 species forming a Mtillerian group. An assemblage of 

 this latter kind is only strengthened, not weakened, by 

 fresh accessions ; all being alike inedible, and so all 

 contributing to the common safety. (2) The benefit 

 of Mtillerian association being mutual, there is a distinct 

 reason, which we saw does not exist in the case of 

 Batesian mimicry, for the model to help on the process of 

 assimilation by itself advancing to meet the mimic. 



To summarise the foregoing. Every conspicuous and 

 distasteful form is a centre of attraction for other forms, 

 whether edible or inedible ; but in the former case 

 (Batesian mimicry) the mimetic attraction is limited in 

 operation, and acts only in one direction, influencing 



