398 SEXUAL SELECTION. [Part II. 



light on many obscure problems. It had previously been 

 observed that certain butterflies in South America, belong- 

 ing to quite distinct families, resembled the Heliconi- 

 dae so closely, in every stripe and shade of color, that 

 they could not be distinguished except by an experi- 

 enced entomologist. As the Helieonidse are colored in 

 their usual manner, while the others depart from the usual 

 coloring of the groups to which they belong, it is clear 

 that the latter are the imitators, and the Heliconidas the 

 imitated. Mr. Bates further observed that the imitating 

 species are comparatively rare, while the imitated swarm 

 in large numbers; the two sets living mingled togeth- 

 er. From the fact of the Heliconidse 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 odor ; and this 

 hypothesis has now been confirmed by a considerable 

 body of curious evidence. 26 From these considerations 

 Mr. Bates inferred that the butterflies which imitate the 

 protected species had acquired their present marvellously 

 deceptive appearance through variation and natural se- 

 lection, in order to be mistaken for the protected kinds 

 and thus to escape being devoured. ISTo explanation is 

 here attempted of the brilliant colors of the imitated, but 

 only of the imitating butterflies. We must account for the 

 colors of the former in the same general manner as in 

 the cases previously discussed in this chapter. Since 

 the publication of Mr. Bates's paper, similar and equally 

 striking facts have been observed by Mr. Wallace 26 in the 

 Malayan region, and by Mr. Trimen in South Africa. 

 As some writers 27 have felt much difficulty in under- 



25 ' Proc. Ent. Soc.' Dec. 3, 1866, p. xiv 



86 ' Transact. Linn. Soc' vol. xxv. 1865, p. 1; also ' Transact. Eut. 

 Soc' vol. iv. (3d series), 1867, p. 301. 



,1 See an ingenious article entitled " Difficulties of the Theory of Nat- 



