n and
Dixey from Africa, and we may expect to learn many more interesting
facts in this connection. Here again the preliminary postulates of the
theory are satisfied. And how much more that would lead to the same
conclusion might be added!

As in the case of mimicry many species have come to resemble one another
through processes of selection, so we know whole classes of phenomena
in which plants and animals have become adapted to one another, and have
thus been modified to a considerable degree. I refer particularly to the
relation between flowers and insects; but as there is an article on "The
Biology of Flowers" in this volume, I need not discuss the subject, but
will confine myself to pointing out the significance of these remarkable
cases for the theory of selection. Darwin has shown that the originally
inconspicuous blossoms of the phanerogams were transformed into flowers
through the visits of insects, and that, conversely, several large
orders of insects have been gradually modified by their association
with flowers, especially as regards the parts of their body actively
concerned. Bees and butterflies in particular have become what they
are through their relation to flowers. In this case again all that is
apparently contradictory to the theory can, on closer investigation, be
beautifully interpreted in corroboration of it. Selection can give rise
only to what is of use to the organism actually concerned, never to what
is of use to some other organism, and we must therefore expect to find
that in flowers only characters of use to THEMSELVES have arisen, never
characters which are of use to insects only, and conversely that in the
insects characters useful to them and not merely to the plants would
have originated. For a long time it seemed as if an exception to this
rule existed in the case of the fertilisation of the yucca blossoms by
a little moth, Pronuba yuccasella. This little moth has a sickle-shaped
appendage to its mouth-parts which occurs in no other Lepidopteron,
and which is used for pushing the yellow pollen into the opening of
the pistil, thus fertilising the flower. Thus it appears as if a new
structure, which is useful only to the plant, has arisen in the insect.
But the difficulty is solved as soon as we learn that the moth lays
its eggs in the fruit-buds of the Yucca, and that the larvae, when they
emerge, feed on the developing seeds. In effecting the fertilisation
of the flower the moth is at