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 ("The Evolution Theory", London, 1904, I. page 219.)
pointed out that decorative colouring and sweet-scentedness may replace one
another in Lepidoptera as well as in flowers, for just as some modestly
coloured flowers (mignonette and violet) have often a strong perfume, while
strikingly coloured ones are sometimes quite devoid of fragrance, so we
find that the most beautiful and gaily-coloured of our native Lepidoptera,
the species of Vanessa, have no scent-scales, while these are often
markedly developed in grey nocturnal Lepidoptera. Both attractions may,
however, be combined in butterflies, just as in flowers. Of course, we
cannot explain why both means of attraction should exist in one genus, and
only one of them in another, since we do not know the minutest details of
the conditions of life of the genera concerned. But from the sporadic
distribution of scent-scales in Lepidoptera, and from their occurrence or
absence in nearly related species, we may conclude that fragrance is a
relatively MODERN acquirement, more recent than brilliant colouring.

One thing in particular that stamps decorative colouring as a product of
selection is ITS GRADUAL INTENSIFICATION by the addition of new spots,
which we can quite well observe, because in many cases the colours have
been first acquired by the males, and later transmitted to the females by
inheritance. The scent-scales are never thus transmitted, probably for the
same reason that the decorative colours of many birds are often not