320 THE DESCENT OF MAN. 



are the imitators, and the Heliconidae the imitated. Mr. Bates 

 further observed that the imitating species are comparatively 

 rare, whilst the imitated abound, and that the two sets live 

 mingled together. .From the fact of the HeliconidEe being con- 

 spicuous and beautiful insects, yet so numerous in individuals 

 and species, he concluded that they must be protected from the 

 attacks of enemies by some secretion or odor; and this conclusion 

 has now been amply confirmed,'" especially by Mr. Belt. Hence 

 Mr. Bates inferred that the butterflies which imitate the protected 

 species have acquired their present marvelously deceptive ap- 

 pearance through variation and natural selection, in order to be 

 mistaken for the protected kinds, and thus to escape being de- 

 voured. No 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' paper, similar and equally striking 

 facts have been observed by Mr. Wallace in the Malayan region, 

 by Mr. Trimen in South Africa, and by Mr. Riley in the United 

 States." 



As some writers have felt much difficulty in understanding 

 how the first steps in the process of mimicry could have been 

 effected through natural selection, it may be well to remark that 

 the process probably commenced long ago between forms not 

 widely dissimilar in color. In this case even a slight variation 

 would be beneficial, if it rendered the one species more like the 

 other; and afterwards the imitated species might be modified to 

 an extreme degree through sexual selection or other means, and if 

 the changes were gradual, the imitators might easily be led along 

 the same track, until they differed to an equally extreme degree 

 from their original condition; and they would thus ultimately 

 assume an appearance or coloring wholly unlike that of the 

 other members of the group to which they belonged. It should 

 also be remembered that many species of Lepidoptera are liable 

 to considerable and abrupt variations in color. A few instances 

 have been given in this chapter; and many more may be found 

 in the papers of Mr. Bates and Mr. Wallace. 



With several species the sexes are alike, and imitate the two 

 sexes of another species. But Mr. Trimen gives, in the paper 

 already referred to, three cases in which the sexes of the imitated 



30 'Proc. Bnt. Soc' Dec. 3rd, 1866, p. xlv. 



=^ Wallace, 'Transact. Linn. Soc' vol. xxv. 1865, p. 1; also 'Transact. 

 Bnt. Soc' vol. iv. (3rd series), 1867, p. 301. Trimen, 'Linn. Transact.' 

 vol. xxvi. 1869, p. 497. Riley, 'Third Annual Report on the Noxious 

 Insects of Missouri,' 1871, pp. 163-168. This latter essay is valuable, as 

 Mr. Riley here discusses all the objections which have been raised 

 against Mr. Bates' theory. 



