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 Æneas 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. ascanius_, the males and females are alike; in others the males are a little or very much more superbly coloured than the females. The genus Junonia allied to our Vanessæ 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. œnone_, the male is rather more brightly coloured than the female, and in a few (for instance _J. andremiaja_) 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 Theclæ, in which both sexes are nearly alike and wonderfully splendid; in another, the male is coloured in a similarly gorgeous manner, whilst the whole upper surface of the female is of a dull uniform brown. Our common little English blue butterflies of the genus Lycæna, illustrate the various differences in colour between the sexes, almost as well, though not in so striking a manner, as the above exotic genera. In _Lycæna agestis_ both sexes have wings of a brown colour, bordered with small ocellated orange spots, and are consequently alike. In _L. œgon_ the wings of the male are of a fine blue, bordered with black; whilst the wings of the female are brown, with a similar border, and closely resemble those of _L. agestis_. Lastly, in _L. arion_ both sexes are of a blue colour and nearly alike, though in the female the edges of the wings are rather duskier, with the black spots plainer; and in a bright blue Indian species both sexes are still more closely alike.