ch. v] SOME CRITICISMS 51 



(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. 



In offering certain criticisms of the mimicry ex- 

 planation it will be convenient to do so in connection 

 with these five conditions which Wallace regarded as 

 constant for all cases of mimetic resemblance. 



(1) That the imitative species occur in the same 

 area and occupy the very same station as the imitated. 



This on the whole is generally true. It is well shewn 

 in some of the most striking cases such as those of 

 the Old-World Papilios that mimic Danaines, or of 

 the Dismorphias and their Ithomiine models. In 

 many of these cases the range of neither model nor 

 mimic is a very wide one, yet the mimic is found 

 strictly inside the area inhabited by the model. Papilio 

 agestor, for instance, is only found where Caduga tytia 

 occurs, nor is P. mendax known outside the area 

 frequented by Euploea rhadamanthus. Even more 

 striking in this respect are some of the Ithomiine- 

 Dismorphia resemblances in the New World. The 

 Ithomiine models are as a rule very local though 

 very abundant. Two hundred miles away the pre- 

 dominant Ithomiine often bears quite a distinct 

 pattern, and when this is the case tbe mimicking 

 Dismorphia is generally changed in the same sense. 



4—2 



