acteristic 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 to say, that excites them to the highest
degree. It is a pity that our organs of smell are not fine enough to
examine the fragrance of male Lepidoptera in general, and to compare it
with other perfumes which attract these insects. (See Poulton, "Essays
on Evolution", 1908, pages 316, 317.) As far as we can perceive them
they resemble the fragrance of flowers, but there are Lepidoptera
whose scent suggests musk. A smell of musk is also given off by several
plants: it is a sexual excitant in the musk-deer, the musk-sheep, and
the crocodile.

As far as we know, then, it is perfumes similar to those of flowers that
the male Lepidoptera give off in order to entice their mates, and this
is a further indication that animals, like plants, can to a large extent
meet the claims made upon them by life, and produce the adaptations
which are most purposive,--a further proof, too, of my proposition
that the useful variations, so to speak, are ALWAYS THERE. The flowers
developed the perfumes which entice their visitors, and the male
Lepidoptera developed the perfumes which entice and excite their mates.

There are many pretty little problems to be solved in this connection,
for there are insects, such as some flies, that are attracted by smells
which are unpleasant to us, like those from decaying flesh and carrion.
But there are also certain flowers, some orchids for instance, which
give forth no very agreeable odour, but one which is to us repulsive
and disgusting; and we should therefore expect that the males of such
insects would give off a smell unpleasant to us, but there is no case
known to me in which this has been demonstrated.

In cases such as we have discussed, i