musical instruments have been acquired through sexual selection. In
four other Orders the members of one sex, or more commonly of both
sexes, are provided with organs for producing various sounds, which
apparently serve merely as call-notes. When both sexes are thus
provided, the individuals which were able to make the loudest or most
continuous noise would gain partners before those which were less
noisy, so that their organs have probably been gained through sexual
selection. It is instructive to reflect on the wonderful diversity of
the means for producing sound, possessed by the males alone, or by both
sexes, in no less than six Orders. We thus learn how effectual sexual
selection has been in leading to modifications which sometimes, as with
the Homoptera, relate to important parts of the organisation.
From the reasons assigned in the last chapter, it is probable that the
great horns possessed by the males of many Lamellicorn, and some other
beetles, have been acquired as ornaments. From the small size of
insects, we are apt to undervalue their appearance. If we could imagine
a male Chalcosoma (Fig. 16), with its polished bronzed coat of mail,
and its vast complex horns, magnified to the size of a horse, or even
of a dog, it would be one of the most imposing animals in the world.
The colouring of insects is a complex and obscure subject. When the
male differs slightly from the female, and neither are
brilliantly-coloured, it is probable that the sexes have varied in a
slightly different manner, and that the variations have been
transmitted by each sex to the same without any benefit or evil thus
accruing. When the male is brilliantly-coloured and differs
conspicuously from the female, as with some dragon-flies and many
butterflies, it is probable that he owes his colours to sexual
selection; whilst the female has retained a primordial or very ancient
type of colouring, slightly modified by the agencies before explained.
But in some cases the female has apparently been made obscure by
variations transmitted to her alone, as a means of direct protection;
and it is almost certain that she has sometimes been made brilliant, so
as to imitate other protected species inhabiting the same district.
When the sexes resemble each other and both are obscurely coloured,
there is no doubt that they have been in a multitude of cases so
coloured for the sake of protection. So it is in some instances when
both are brightly-coloured, for they thus imitate protected species, or
resemble surrounding objects such as flowers; or they give notice to
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