412 SEXUAL SELECTION. Part II. 



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- 

 standing how the first steps in the process of mimickry 

 could have been effected through natural selection, it 

 may be well to remark that the process probably has 

 never commenced with forms widely dissimilar in colour. 

 But with two species moderately like each other, the 

 closest resemblance if beneficial to either form could 

 readily be thus gained ; and if the imitated form was 

 subsequently and gradually modified through sexual 

 selection or any other means, the imitating form would 

 be led along the same track, and thus be modified to 

 almost any extent, so that it might ultimately assume 

 an appearance or colouring wholly unlike that of the 

 other members of the group to which it belonged. As 

 extremely slight variations in colour would not in many 

 cases suffice to render a species so like another pro- 

 tected species as to lead to its preservation, it should 

 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 ; but 

 under this point of view Mr. Bates' original paper on 

 mimickry, as well as Mr. Wallace's papers, should be 

 consulted. 



In the foregoing cases both sexes of the imitating 

 species resemble the imitated ; but occasionally the 



26 ' Transact. Linn. Soc' vol. xxv. 1865, p. 1 ; also ' Transact. Ent. 

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



2 ' See an ingenious article entitled, " Difficulties of the Theory of 

 Natural Selection," in the ' Month,' 1869. The writer strangely sup- 

 poses that I attribute the variations in colour of the Lepidoptera, by 

 which certain species belonging to distinct families have come to 

 resemble others, to reversion to a common progenitor ; but there is no 

 more reason to attribute these variations to reversion than in the case 

 of any ordinary variation. 



