Contributions to the theory of natural selection. A series of essays ... By Alfred Russel Wallace ...

ILLUSTRATIVE OF NATURAL SELECTION. 155
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 Anthribidce, (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 5Mr. Darwin showed how it could
in many cases be explained by the principle of