With our beautiful English butterflies, the admiral, peacock, and
painted lady (Vanessae), as well as many others, the sexes are alike.
This is also the case with the magnificent Heliconidae, and most of the
Danaidae in the tropics. But in certain other tropical groups, and in
some of our English butterflies, as the purple emperor, orange-tip,
etc. (Apatura Iris and Anthocharis cardamines), the sexes differ either
greatly or slightly in colour. No language suffices to describe the
splendour of the males of some tropical species. Even within the same
genus we often find species presenting extraordinary differences
between the sexes, whilst others have their sexes closely alike. Thus
in the South American genus Epicalia, Mr. Bates, to whom I am indebted
for most of the following facts, and for looking over this whole
discussion, informs me that he knows twelve species, the two sexes of
which haunt the same stations (and this is not always the case with
butterflies), and which, therefore, cannot have been differently
affected by external conditions. (5. See also Mr. Bates s paper in
Proc. Ent. Soc. of Philadelphia, 1865, p. 206. Also Mr. Wallace on
the same subject, in regard to Diadema, in Transactions, Entomological
Society of London, 1869, p. 278.) In nine of these twelve species the
males rank amongst the most brilliant of all butterflies, and differ so
greatly from the comparatively plain females that they were formerly
placed in distinct genera. The females of these nine species resemble
each other in their general type of coloration; and they likewise
resemble both sexes of the species in several allied genera found in
various parts of the world. Hence we may infer that these nine species,
and probably all the others of the genus, are descended from an
ancestral form which was coloured in nearly the same manner. In the
tenth species the female still retains the same general colouring, but
the male resembles her, so that he is coloured in a much less gaudy and
contrasted manner than the males of the previous species. In the
eleventh and twelfth species, the females depart from the usual type,
for they are gaily decorated almost like the males, but in a somewhat
less degree. Hence in these two latter species the bright colours of
the males seem to have been transferred to the females; whilst in the
tenth species the male has either retained or recovered the plain
colours of the female, as well as of the parent-form of the genus. The
sexes in these three cases have thus been rendered nearly alike, though
in an opposite manner. In the allied genus Eubagis, both sexes of some
of the species are plain-coloured and nearly alike; whilst with the
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