variation and natural selection, in order to be mistaken for the
protected kinds, and thus to escape being devoured. No explanation is
here attempted of the brilliant colours of the imitated, but only of
the imitating butterflies. We must account for the colours 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. (31. Wallace, Transact. Linn. Soc. vol. xxv. 1865 p. i.;
also, Transact. Ent. 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 s theory.)
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 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 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 differ 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
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