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

184 THE MALAYAN PAPILIONIDIE AS
A, B,) has acquired exactly the same peculiarity of
having red spots instead of yellow. Lastly, in the
island of Timor, the female of P. CEnomaus (a species
allied to P. Memnon) resembles so closely P. Liris
(one of the Polydorus-group), that the two, which
were often seen flying together, could only be distinguished by a minute comparison after being captured.
The last six cases of mimicry are especially instructive, because they seem to indicate one of the processes by which dimorphic forms have been produced.
When, as in these cases, one sex differs much from
the other, and varies greatly itself, it may happen
that occasionally individual variations will occur having
a distant resemblance to groups which are the objects
of mimicry, and which it is therefore advantageous to
resemble. Such a variety will have a better chance of
preservation; the individuals possessing it will be multiplied; and their accidental likeness to the favoured
group will be rendered permanent by hereditary transmission, and, each successive variation which increases
the resemblance being preserved, and all variations
departing from the favoured type having less chance
of preservation, there will in time result those singular
cases of two or more isolated and fixed forms, bound
together by that intimate relationship which constitutes them the sexes of a single species. The reason
why the females are more subject to this kind of
modification than the males is, probably, that their
slower flight, when laden with eggs, and their exposure
to attack while in the act of depositing their eggs