136 MIMICRY AND VARIATION [ch. 



Batesian or Miillerian sense. Batesian mimics are such 

 genera as Dismorphia and Protogo7iius, to which there 

 are no reasons for attributing disagreeable properties. 

 Of the nature of Miillerian mimics on the other hand are 

 the various Heliconines and Ithomiines which enter 

 into the combination. In each case the whole assem- 

 blage is a great "mimicry ring," of which the pattern 

 is dictated by the Ithomiine that predominates in point 

 of numbers. It is, however, very doubtful whether 

 this can be accepted as a satisfactory explanation. The 

 four groups which we have considered are all character- 

 ised by a peculiar and distinctive coloration, and in 

 each case the pattern must on the theory of mimicry 

 be regarded as a highly efficient warning pattern. One 

 or other of these patterns must doubtless be looked upon 

 as the most primitive. If so the question at once 

 arises as to why a distasteful genus should change from 

 one efficient warning pattern to another quite distinct 

 one. If the newer pattern affords better protection 

 we should expect it to have spread and eventually to 

 have ousted the older one. That it has not done so 

 must probably be attributed to the old pattern being 

 as efficient as the new one. But if this is so we are 

 left without grounds for assuming the change to have 

 been brought about by natural selection through the 

 agency of enemies to whom warning colours appeal. 

 For natural selection can only bring about a change 

 that is beneficial to the species. Hence we must 

 suppose the change on the part of the dominant model 

 to have been independent of natural selection by 



