nce in the female sex as compared with the male. They
have believed with Wallace that the greater dangers of the female, with
slower flight and often alighting for oviposition, have been in part
met by the high development of this special mode of protection. The fact
cannot be doubted. It is extremely common for a non-mimetic male to be
accompanied by a beautifully mimetic female and often by two or three
different forms of female, each mimicking a different model. The male
of a polymorphic mimetic female is, in fact, usually non-mimetic (e.g.
Papilio dardanus = merope), or if a mimic (e.g. the Nymphaline genus
Euripus), resembles a very different model. On the other hand a
non-mimetic female accompanied by a mimetic male is excessively rare. An
example is afforded by the Oriental Nymphaline, Cethosia, in which the
males of some species are rough mimics of the brown Danaines. In some
of the orb-weaving spiders the males mimic ants, while the much larger
females are non-mimetic. When both sexes mimic, it is very common in
butterflies and is also known in moths, for the females to be better and
often far better mimics than the males.

Although still believing that Wallace's hypothesis in large part
accounts for the facts briefly summarised above, the present writer has
recently been led to doubt whether it offers a complete explanation.
Mimicry in the male, even though less beneficial to the species than
mimicry in the female, would still surely be advantageous. Why then is
it so often entirely restricted to the female? While the attempt to find
an answer to this question was haunting me, I re-read a letter
written by Darwin to Wallace, April 15, 1868, containing the following
sentences: "When female butterflies are more brilliant than their males
you believe that they have in most cases, or in all cases, been rendered
brilliant so as to mimic some other species, and thus escape danger. But
can you account for the males not having been rendered equally brilliant
and equally protected? Although it may be most for the welfare of
the species that the female should be protected, yet it would be some
advantage, certainly no disadvantage, for the unfortunate male to enjoy
an equal immunity from danger. For my part, I should say that the female
alone had happened to vary in the right manner, and that the beneficial
variations had been transmitted to the same sex alone. Believing in
this, I can see no improbability (but from analo