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 pioint 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 1 Transact. Linn. Soc.’ vol. xxv. 1865, p. 1 ; also 4 Transact. Ent. 
Soc.’ vol. iv. (3rd series), 1867, p. 301. 
27 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. 
