mimicry; and it is interesting to find his observations confirmed by examples on the other side of the globe. The remarkable genus _Drusilla_, a group of pale-coloured butterflies, more or less adorned with ocellate spots, is also the object of mimicry by three distinct genera (_Melanitis_, _Hyantis_, and _Papilio_). These insects, like the _Danaidæ_, are abundant in individuals, have a very weak and slow flight, and do not seek concealment, or appear to have any means of protection from insectivorous creatures. It is natural to conclude, therefore, that they have some hidden property which saves them from attack; and it is easy to see that when any other insects, by what we call accidental variation, come more or less remotely to resemble them, the latter will share to some extent in their immunity. An extraordinary dimorphic form of a female _Papilio_ has come to resemble the Drusillas sufficiently to be taken for one of that group at a little distance; and it is curious that I captured one of these Papilios in the Aru Islands hovering along the ground, and settling on it occasionally, just as it is the habit of the Drusillas to do. The resemblance in this case is only general; but this form of _Papilio_ varies much, and there is therefore material for natural selection to act upon so as ultimately to produce a copy as exact as in the other cases. The eastern Papilios allied to _Polydorus Coon_ and _P. Philoxenus_, form a natural section of the genus resembling, in many respects, the _Æneas_-group of South America, which they may be said to represent in the East. Like them, they are forest insects, have a low and weak flight, and in their favourite localities are rather abundant in individuals; and like them, too, they are the objects of mimicry. We may conclude, therefore, that they possess some hidden means of protection, which makes it useful to other insects to be mistaken for them. The Papilios which resemble them belong to a very distinct section of the genus, in which the sexes differ greatly; and it is those females only which differ most from the males, and which have already been alluded to as exhibiting instances of dimorphism, which resemble species of the other group. The resemblance of _P. Romulus_ to _P. Hector_ is, in some specimens, very considerable, and has led to the two species being placed to follow each other in the British Museum Catalogues and by Mr. E. Doubleday. I have shown, however, that _P. Romulus_ is probably a dimorphic form of the female _P. Pammon_, and belongs to a distinct section of the genus[9]. Footnote 9: See Plate II. fig. 6.