ust 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 transmitted to the females: because with
these they would be exposed to too great elimination by enemies.
Wallace was the first to point out that in species with concealed
nests the beautiful feathers of the male occurred in the female also,
as in the parrots, for instance, but this is not the case in species
which brood on an exposed nest. In the parrots one can often observe
that the general brilliant colouring of the male is found in the
female, but that certain spots of colour are absent, and these have
probably been acquired comparatively recently by the male and have not
yet been transmitted to the female.

Isolation of the group of individuals which is in process of varying
is undoubtedly of great value in sexual selection, for even a solitary
conspicuous variation will become dominant much sooner in a small
isolated colony, than among a large number of members of a species.

Any one who agrees with me in deriving variations from germinal
selection will regard that process as an essential aid towards
explaining the selection of distinctive courtship-characters, such as
coloured spots, decorative feathers, horn