324 The Descent of Man. Part Ji. 



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. Triinen in South 

 Africa, and by Mr. Eiley in the United States. 31 



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 colour. 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 modi- 

 fied 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 colouring 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 

 colour. 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 

 form diffr?r from each other in colour, and the sexes of the 

 imitating, form differ in a like manner. Several cases have also 

 been recorded where the females alone imitate brilliantly- 

 coloured and protected species, the males retaining "the 

 " normal aspect of their immediate congeners." It is here obvious 

 that the successive variations by which the female has been 

 m. '"'ified have been transmitted to her alone. It is, however, 

 probable that some of the many successive variations would 

 have been transmitted to, and developed in, the males had 

 not such males been eliminated by being thus rendered less 

 attractive to the females; so that only those variations were 

 preserved which were from the first strictly limited in their 

 transmission to the female sex. We have a partial illus- 

 tration of these remarks in a statement by Mr. Belt; 32 that 



31 Wallace, 'Transact. Linn. Sec' 163-168." Tnis latter essay is A T alu- 



rol. xxx. 1865, ]». 1 ; also ' Transact. able, ns Mi. Riley here discusses all 



&nt. Soc* vol. iv. (3rd series), 1867, the objections which have been 



p. 301. Trimen, ' Linn. Transact.' raised against Mr. Bates' theory, 

 vol. xxvi. 1869, p. 497. Kiley, 32 ' The Naturalist in Nicaragua 



f Third Annual Report on th ? Noxi- 1874, p. 385. 

 ous Insects of Missouri.' 1871, pp 



