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 possess great strength and
rapidity of flight.
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