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Show 388 SEXUAL SELECTION. PART II. other tropical groups, and with some of .our English butterflies, as the purple emperor, orange-tip, &c. (~~atu? ·a I1·is and Anthocharis cardamines), the sexes dtffer either greatly or slightly in colour. No language su~ces to descriLe the splendour of the males of some tropical species. Even within the same genus we often find species presenting an extraordinary difference be:ween the sexes whilst others have their sexes closely alike. Thus in the South American genus Epicalia, Mr. Bates, to whom I am much 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 (ancl this is not always the case with butterflies), and therefore cannot have been differently affected by external conditions.3 In n~n~ of these species the males rank amongst the most bnllmnt of all butterflies, and differ so greatly from the comparatively plain females that they were forme:·ly plac~d in distinct genera. The females of these nme species resemble each other in their general type of coloration, and likewise resemble both sexe8 in several allied genera, found in various parts of the world. Hence in accordance with the descent-theory 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 mn,nner. 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 type of colouring which 1 Sco also Mr. Datrs' paper in 'Proc. Ent. Soc. of Philadelphin,' 18li5, p. 206. Also l\lr. Wallace on the same subject, in regard to Diaclema, in ' 'framad. Entomolog. Soc. of London,' 1869, p. 278. BUTTERFLIES AND MOTHS. 389 is usual with their sex in this genus, for they are gaily decorated in nearly the same manner as the males, but in a somewhat less degree. Hence in these two species the bright colours of the males seem to have been transferred to the females; whilst the male of the tenth species has either retained or recovered the plain colours of the female as well as of the parent-form of the genus ; the two sexes being thus rendered in both cases, though in an opposite manner, nearly alike. In the allied genus Eubagis, both sexes of some of the species are plain-coloured and nearly alike; whilst with the greater number the males are decorated with beautiful metallic tints, in a diversified manner, and differ much from their females. The females throughout the genus retain the same general style of colouring, so that they commonly resemble each other much more closely than they resemble their own proper males. In the genus Papilio, all the species of the JEneas group are remarkable for their conspicuous and strongly contrasted colours, and they illustrate the frequent tendency to gradation in the amount of difference between the sexes. In a few species, for instance in P. ascani~~s, the males and females are alike ; in others the males are a little or very much more superbly coloured than the females. The genus J unonia allied to our V anessoo offers a nearly parallel case; for although the sexes of most of the species resemble each other and are destitute of rich colours, yet in certain species, as in J. amone, the male is rather more brightly coloured than the female, and in a few (for instance J. andrem1:a}a) the male is so different from the female that he might be mistaken for an entirely distinct species. Another striking case was pointed out to me in the British museum by Mr. A. Butler, namely one of the Tropical American Thecloo, in which both sexes -·---·- -· --- - ... - ---- |