presence of individuals of the other sex, but it soon became an excitant,
and as the individuals which caused the greatest degree of excitement were
preferred, it reached as high a pitch of perfection as was possible to it.
I shall confine myself here to the comparatively recently discovered
fragrance of butterflies. Since Fritz Muller found out that certain
Brazilian butterflies gave off fragrance "like a flower," we have become
acquainted with many such cases, and we now know that in all lands, not
only many diurnal Lepidoptera but nocturnal ones also give off a delicate
odour, which is agreeable even to man. The ethereal oil to which this
fragrance is due is secreted by the skin-cells, usually of the wing, as I
showed soon after the discovery of the SCENT-SCALES. This is the case in
the males; the females have no SPECIAL scent-scales recognisable as such by
their form, but they must, nevertheless, give off an extremely delicate
fragrance, although our imperfect organ of smell cannot perceive it, for
the males become aware of the presence of a female, even at night, from a
long distance off, and gather round her. We may therefore conclude, that
both sexes have long given forth a very delicate perfume, which announced
their presence to others of the same species, and that in many species (NOT
IN ALL) these small beginnings became, in the males, particularly strong
scent-scales of characteristic form (lute, brush, or lyre-shaped). At
first these scales were scattered over the surface of the wing, but
gradually they concentrated themselves, and formed broad, velvety bands, or
strong, prominent brushes, and they attained their highest pitch of
evolution when they became enclosed within pits or folds of the skin, which
could be opened to let the delicious fragrance stream forth suddenly
towards the female. Thus in this case also we see that characters, the
original use of which was to bring the sexes together, and so to maintain
the species, have been evolved in the males into means for exciting the
female. And we can hardly doubt, that the females are most readily enticed
to yield to the butterfly that sends out the strongest fragrance,--that is