tern Lepidoptera,
the Pieridae; and but few occur in the Lepidoptera of other countries.
The spring and autumn broods of some European species differ very
remarkably; and this must be considered as a phenomenon of an analogous
though not of an identical nature, while the Araschnia prorsa, of
Central Europe, is a striking example of this alternate or seasonal
dimorphism. Among our nocturnal Lepidoptera, I am informed, many
analogous cases occur; and as the whole history of many of these has
been investigated by breeding successive generations from the egg, it is
to be hoped that some of our British Lepidopterists will give us a
connected account of all the abnormal phenomena which they present.
Among the Coleoptera Mr. Pascoe has pointed out the existence of two
forms of the male sex in seven species of the two genera Xenocerus and
Mecocerus belonging to the family Anthribidae, (Proc. Ent. Soc. Lond.,
1862); and no less than six European Water-beetles, of the genus
Dytiscus, have females of two forms, the most common having the elytra
deeply sulcate, the rarer smooth as in the males. The three, and
sometimes four or more, forms under which many Hymenopterous insects
(especially Ants) occur, must be considered as a related phenomenon,
though here each form is specialized to a distinct function in the
economy of the species. Among the higher animals, albinoism and melanism
may, as I have already stated, be considered as analogous facts; and I
met with one case of a bird, a species of Lory (Eos fuscata), clearly
existing under two differently coloured forms, since I obtained both
sexes of each from a single flock, while no intermediate specimens have
yet been found.

The fact of the two sexes of one species differing very considerably is
so common, that it attracted but little attention till Mr. Darwin showed
how it could in many cases be explained by the principle of sexual
selection. For instance, in most polygamous animals the males fight for
the possession of the females, and the victors, always becoming the
progenitors of the succeeding generation, impress upon their male
offspring their own superior size, strength, or unusually developed
offensive weapons. It is thus that we can account for the spurs and the
superior strength and size of the males in Gallinaceous birds, and also
for the large canine tusks in the males of fruit-eating Apes. So the
superior beauty of plumage and special adornments of the males of so
ma