UNIFORMITY IN NAUSEOUS GROUPS 277 



simply childish to appeal vaguely to the direct action of 

 like forces as the explanation of the remarkable resem- 

 blance which runs through the group. The environing 

 forces are not like but extremely unlike, because of the 

 very diverse conditions under which various members of 

 the group live and grow. 



All the butterfly Sub-Families which furnish the chief 

 models for Mimicry are remarkable for the uniformity of 

 colour and pattern throughout groups of species in each 

 of the countries they inhabit. These Sub-Families are 

 the Danainae, found all over the tropics, and the allied 

 Ithomiinae {Neotropinae) of tropical America, the Acrac- 

 ifiae, almost confined to Africa and tropical America, and 

 the allied Heliconinae, practically restricted to the latter. 

 A very strong family likeness runs through long series of 

 species, as any one may see by a glance at the successive 

 drawers of a collection of African Acraeinae or Oriental 

 Ettploeini and comparing them with an equal number of 

 species in any Sub-Family which does not provide nume- 

 rous models for Mimicry. Compare, for instance, our 

 European Vanessidae with sets of local species belonging 

 to any of the four above-named Sub-Families. The species 

 of Vanessa do indeed possess homologous markings,' and 

 many of the gaps between them can be filled up, but we 

 have to hunt the world in order to do it, and even then 

 we only obtain a partial continuity between extreme 

 differences, whereas in the specially protected Sub- 

 Families there is not only continuity but uniformity in 

 large groups of species. Mr. A. G. Mayer '^ has found 

 that among 450 species of Neotropical Ithomiinae and 

 Heliconinae there are only fifteen shades of colour, whereas 

 among 200 species of Neotropical Papilioninae there are 

 thirty-six shades. And this is not by any means due to 

 the scarcity of variation in the former, for individual 

 differences in each locality, and geographical differences, 

 as we pass from one district to another, are very prevalent. 

 Combined widi the uniformity within these Sub-Families 

 is a marked tendency to resemble other protected Sub- 



^ See F. A. Dixey in Trans. Ent. Soc. Lofid., 1890. p. 89. 

 ^ Bull. Mtis. Comp. Zool. at Harvard Coll., Feb. 1&97, p. 167. 



