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

A THEORY OF BIRDS' NESTS. 259
most readily obtained, since no other character is subject to such numerous and rapid variations. The case I
have now endeavoured to illustrate is exactly analogous
to what occurs among butterflies. As a general rule,
the female butterfly is of dull and inconspicuous colours,
even when the male is most gorgeously arrayed; but
when the species is protected from attack by a disagreeable odour, as in the Heliconidcl, Danaidie and
Aerceide, both sexes display the same or equally brilliant hues. Among the species which gain a protection by imitating these, the very weak and slow-flying
Leptalides resemble them in both sexes, because both
sexes alike require protection, while in the more active
and strong-winged genera-Papilio, Pieris, and Diadema-it is generally the females only that mimic the
protected groups, and in doing so often become actually
more gay and more conspicuous than the males, thus
reversing the usual and in fact almost universal characters of the sexes. So, in the wonderful Eastern leafinsects of -the genus Phyllium, it is the female only
that so marvellously imitates a green leaf; and in all
these cases the difference can be traced to the greater
need of protection for the female, on whose continued
existence, while depositing her eggs, the safety of the
race depends. In Mammalia and in reptiles, however
brilliant the colours may be, there is rarely any difference between that of the sexes, because the female is
not necessarily more exposed to attack than the male.
It may, I thinlk, be looked upon as a confirmation of
this view, that no single case is known either in the
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