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

176 IHE MALAYAN PAPILIONIDE AS
of Danaidae are in the same position: they are slow
and weak fliers; yet they abound in species and individuals, and are the objects of mimicry. The Satyridma
have also probably a means of protection —perhaps their
keeping always near the ground and their generally
obscure colours; while the Lycemnidae and HIesperidme
may find security in their small size and rapid motions.
In the extensive family of the Nymphalidm, however,
we find that several of the larger species, of comparatively feeble structure, have their wings modified
(Cethosia, Limenitis, Junonia, Cynthia), while the largebodied powerful species, which have all an excessively
rapid flight, have exactly the same form of wing in
Celebes as in the other islands. On the whole, therefore, we may say that all the butterflies of rather large
size, conspicuous colours, and not very swift flight have
been affected in the manner described, while the smaller
sized and obscure groups, as well as those which are
the objects of mimicry, and also those of exceedingly
swift flight have remained unaffected.
It would thus appear as if there must be (or once
have been) in the island of Celebes, some peculiar
enemy to these larger-sized butterflies which does not
exist, or is less abundant, in the surrounding islands.
Increased powers of flight, or rapidity of turning, was
advantageous in baffling this enemy; and the peculiar
form of wing necessary to give this would be readily
acquired by the action of " natural selection" on the
slight variations of form that are continually occurring.
Such an enemy one would naturally suppose to be