tensive family of the Nymphalidae, however, we find that several of
the larger species, of comparatively feeble structure, have their wings
modified (Cethosia, Limenitis, Junonia, Cynthia), while the large-bodied
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 an insectivorous bird;
but it is a remarkable fact that most of the genera of Fly-catchers
of Borneo and Java on the one side (Muscipeta, Philentoma,) and of
the Moluccas on the other (Monarcha, Rhipidura), are almost entirely
absent from Celebes. Their place seems to be supplied by the
Caterpillar-catchers (Graucalus, Campephaga, &c.), of which six or seven
species are known from Celebes and are very numerous in individuals. We
have no positive evidence that these birds pursue butterflies on the
wing, but it is highly probable that they do so when other food is
scarce. Mr. Bates has suggested to me that the larger Dragonflies
(AEshna, &c.) prey upon butterflies; but I did not notice that they were
more abundant in Celebes than elsewhere. However this may be, the fauna
of Celebes is undoubtedly highly peculiar in every department of which
we have any accurate knowledge; and though we may not be able
satisfactorily to trace how it has been effected, there can, I think, be
little doubt that the singular modification in the wings of so many of
the butterflies of that island is an effect of that complicated action
and reaction of all living things upon each other in the struggle for
existence, which continually tends to readjus