of the Moluccas, or even larger. The difference of form is, however, the
most remarkable feature, as it is altogether a new thing for a whole
set of species in one country to differ in exactly the same way from the
corresponding sets in all the surrounding countries; and it is so well
marked, that without looking at the details of colouring, most Celebes
Papilios and many Pieridae, can be at once distinguished from those of
other islands by their form alone.
The outside figure of each pair here given, shows the exact size and
form of the fore-wing in a butterfly of Celebes, while the inner one
represents the most closely allied species from one of the adjacent
islands. Figure 1 shows the strongly curved margin of the Celebes
species, Papilio gigon, compared with the much straighter margin of
Papilio demolion from Singapore and Java. Figure 2 shows the abrupt bend
over the base of the wing in Papilio miletus of Celebes, compared with
the slight curvature in the common Papilio sarpedon, which has almost
exactly the same form from India to New Guinea and Australia. Figure
3 shows the elongated wing of Tachyris zarinda, a native of Celebes,
compared with the much shorter wing of Tachyris nero, a very closely
allied species found in all the western islands. The difference of form
is in each case sufficiently obvious, but when the insects themselves
are compared, it is much more striking than in these partial outlines.
From the analogy of birds, we should suppose that the pointed wing
gave increased rapidity of flight, since it is a character of terns,
swallows, falcons, and of the swift-flying pigeons. A short and rounded
wing, on the other hand, always accompanies a more feeble or more
laborious flight, and one much less under command. We might suppose,
therefore, that the butterflies which possess this peculiar form were
better able to escape pursuit. But there seems no unusual abundance of
insectivorous birds to render this necessary; and as we cannot believe
that such a curious peculiarity is without meaning, it seems probable
that it is the result of a former condition of things, when the island
possessed a much richer fauna, the relics of which we see in the
isolated birds and Mammalia now inhabiting it; and when the abundance
of insectivorous creatures rendered some unusual means of escape
a necessity for the large-winged and showy butterflies. It is some
confirmation of this view, that neither the very small nor the very
obscurely coloured groups of butterflies have elongated wings, nor is
any modification perceptible in those strong-winged groups which already
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