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, it is obvious that there is no possible
explanation except through selection. This brings us to the last kind of
secondary sexual characters, and the one in regard to which doubt has been