Chap. XL BUTTERFLIES AND MOTHS. 411 



Mimickry. — This principle was first made clear in an 

 admirable paper by Mr. Bates, 24 who tlms threw a flood 

 of light on many obscure problems. It had previously 

 been observed that certain butterflies in S. America 

 belonging to quite distinct families, resembled the Heli- 

 conidee so closely in every stripe and shade of colour 

 that they could not be distinguished except by an 

 experienced entomologist. As the HeliconidaB are 

 coloured in their usual manner, whilst the others depart 

 from the usual colouring of the groups to which they 

 belong, it is clear that the latter are the imitators, and 

 the Heliconidse the imitated. Mr. Bates further observed 

 that the imitating species are comparatively rare, whilst 

 the imitated swarm in large numbers ; the two sets 

 living mingled together. From the fact of the Heli- 

 conidae being conspicuous and beautiful insects, yet 

 so numerous in individuals and species, he concluded 

 that they must be protected from the attacks of birds 

 by some secretion or odour ; and this hypothesis has 

 now been confirmed by a considerable body of curious 

 evidence. 25 From these considerations Mr. Bates in- 

 ferred that the butterflies which imitate the protected 

 species had acquired their present marvellously decep- 

 tive appearance, through variation and natural selection, 

 in order to be mistaken for the protected kinds and 

 thus to escape being devoured. No explanation is 

 here attempted of the brilliant colours of the imi- 

 tated, but only of the imitating butterflies. We must 

 account for the colours of the former in the same 

 general manner, as in the cases previously discussed in 

 this chapter. Since the publication of Mr. Bates' paper, 

 similar and equally striking facts have been observed 



24 ' Transact. Linn. Soc.' vol. xxiii. 1862, p. 495. 



25 ' Proc. Ent. Soc' Dec. 3rd, I860, p. xlv. 



