

ADAPTIVE COLORATION 203 



So much for that kind of mimicry but how is the following kind to 

 be explained? The Ithomiinae of the Amazon valley have the same 

 form and coloration -as the Heliconiinse, but the Ithomiinae themselves 

 are already highly protected. The answer is that this resemblance is of 

 advantage to both groups, as it minimizes their destruction by birds- 

 these having to learn but one set of warning signals instead of two. 

 This is the essence of Miiller's famous explanation, which will presently 

 be stated with more precision. There are two kinds of mimicry, then: 

 (i) the kind described by Bates, in which an edible species obtains 

 security by counterfeiting the appearance of an inedible species; (2) that 

 observed by Bates and interpreted by Mliller, in which both species are 

 inedible. These two kinds are known respectively as Batesian and 

 Miillerian mimicry, though some writers prefer to limit the term mimi- 

 cry to the Batesian type. 



Wallace's Rules. The chief conditions under which mimicry occurs 

 have been stated by Wallace as follows: 



"i. That the imitative species occur in the same area and occupy 

 the very same station as the imitated. 



"2. That the imitators are always the more defenceless. 



"3. That the imitators are always less numerous in individuals. 



"4. That the imitators differ from the bulk of their allies. 



"5. That the imitation, however minute, is external and visible 

 only, never extending to internal characters or to such as do not affect 

 the external appearance." 



These rules relate chiefly to the Batesian form of mimicry and need 

 to be altered to apply to the Miillerian kind. 



The first criterion given by Wallace is evidently an essential one and 

 it is sustained by the facts. It is also true that mimic and model occur 

 usually at the same time of year; Marshall found many new instances 

 of this in South Africa. In some cases of mimicry, strange to say, the 

 precise model is unknown. Thus some Nymphalidae diverge from their 

 relatives to mimic the Euplceinae, though no particular model has been 

 found. In such instances, as Scudder suggests, the prototype may exist 

 without having been found; may have become extinct; or the species 

 may have arrived at a general resemblance to another group without 

 having as yet acquired a likeness to any particular species of the group, 

 the general likeness meanwhile being profitable.- 



The second condition named by Wallace is correct for Batesian 

 but not for Miillerian mimicry. 



The fulfilment of the third condition is requisite for the success 



