ble blue, while the female is orange-brown with black spots and
stripes--we find the explanation in the fact that the female mimics an
uneatable Danais, and thus gains protection while laying its eggs on low
plants in company with that insect. In the allied species, Diadema
bolina, the females are also very different from the males, but are of
dusky brown tints, evidently protective and very variable, some
specimens having a general resemblance to the uneatable Euplaeas; so
that we see here some of the earlier stages of both forms of protection.
The remarkable differences in some South American Pieridae are similarly
explained. The males of Pieris pyrrha, P. lorena, and several others,
are white with a few black bands and marginal spots like so many of
their allies, while the females are gaily coloured with yellow and
brown, and exactly resemble some species of the uneatable Heliconidae of
the same district. Similarly, in the Malay Archipelago, the female of
Diadema anomala is glossy metallic blue, while the male is brown; the
reason for this reversal of the usual rule being, that the female
exactly mimics the brilliant colouring of the common and uneatable
Euplaea midamus, and thus secures protection. In the fine Adolias
dirtea, the male is black with a few specks of ochre-yellow and a broad
marginal band of rich metallic greenish-blue, while the female is
brownish-black entirely covered with rows of ochre-yellow spots. This
latter coloration does not appear to be protective when the insect is
seen in the cabinet, but it really is so. I have observed the female of
this butterfly in Sumatra, where it settles on the ground in the forest,
and its yellow spots so harmonise with the flickering gleams of sunlight
on the dead leaves that it can only be detected with the greatest
difficulty.

A hundred other cases might be quoted in which the female is either
more obscurely coloured than the male, or gains protection by imitating
some inedible species; and any one who has watched these female insects
flying slowly along in search of the plants on which to deposit their
eggs, will understand how important it must be to them not to attract
the attention of insect-eating birds by too conspicuous colours. The
number of birds which capture insects on the wing is much greater in
tropical regions than in Europe; and this is perhaps the reason why many
of our showy species are alike, or almost alike, in both sexes, while
they are prot