large Morphinae of Brazil.
In a great many cases, though not by any means in all, the male
butterflies are "more beautiful" than the females, and in the Tropics
in particular they shine and glow in the most superb colours. I really
see no reason why we should doubt the power of sexual selection, and I
myself stand wholly on Darwin's side. Even though we certainly cannot
assume that the females exercise a conscious choice of the
"handsomest" mate, and deliberate like the judges in a court of
justice over the perfections of their wooers, we have no reason to
doubt that distinctive forms (decorative feathers), and colours have a
particularly exciting effect upon the female, just as certain odours
have among animals of so many different groups, including the
butterflies. The doubts which existed for a considerable time, as a
result of fallacious experiments, as to whether the colours of flowers
really had any influence in attracting butterflies have now been set
at rest through a series of more careful investigations; we now know
that the colours of flowers are there on account of the butterflies,
as Sprengel first showed, and that the blossoms of Phanerogams are
selected in relation to them, as Darwin pointed out.

Certainly it is not possible to bring forward any convincing proof of
the origin of decorative colours through sexual selection, but there
are many weighty arguments in favour of it, and these form a body of
presumptive evidence so strong that it almost amounts to certainty.

In the first place, there is the analogy with other secondary sexual
characters. If the song of birds and the chirping of the cricket have
been evolved through sexual selection, if the penetrating odours of
male animals,--the crocodile, the musk-deer, the beaver, the
carnivores, and, finally, the flower-like fragrances of the
butterflies have been evolved to their present pitch in this way, why
should decorative colours have arisen in some other way? Why should
the eye be less sensitive to _specifically male_ colours and other
_visible_ signs _enticing to the female_, than the olfactory sense to
specifically male odours, or the sense of hearing to specifically male
sounds? Moreover, the decorative feathers of birds are almost always
spread out and displayed before the female during courtship. I have
elsewhere[44] pointed out that decorative colouring and
sweet-scentedness may replace one another in Lepidoptera as well as in
flowers, for j