an insect visit these flowers." And
he shows how this species is even wonderfully and specially modified to
effect self-fertilization.

In the work just referred to Mr. Darwin gives a series of the most
wonderful and minute contrivances by which the visits of insects are
utilized for the fertilization of orchids,--structures so wonderful {56}
that nothing could well be more so, except the attribution of their origin
to minute, fortuitous, and indefinite variation.

The instances are too numerous and too long to quote, but in his "Origin of
Species"[47] he describes two which must not be passed over. In one
(_Coryanthes_) the orchid has its lower lip enlarged into a bucket, above
which stand two water-secreting horns. These latter replenish the bucket
from which, when half-filled, the water overflows by a spout on one side.
Bees visiting the flower fall into the bucket and crawl out at the spout.
By the peculiar arrangement of the parts of the flower, the first bee which
does so carries away the pollen-mass glued to his back, and then when he
has his next involuntary bath in another flower, as he crawls out the
pollen-mass attached to him comes in contact with the stigma of that second
flower and fertilizes it. In the other example (_Catasetum_), when a bee
gnaws a certain part of the flower, he inevitably touches a long delicate
projection, which Mr. Darwin calls the antenna. "This antenna transmits a
vibration to a certain membrane, which is instantly ruptured; this sets
free a spring by which the pollen-mass is shot forth like an arrow in the
right direction, and adheres by its viscid extremity to the back of the
bee!"

Another difficulty, and one of some importance, is presented by those
communities of ants which have not only a population of sterile females, or
workers, but two distinct and very different castes of such. Mr. Darwin
believes that he has got over this difficulty by having found individuals
intermediate in form and structure[48] between the two working castes;
others may think that we have in this belief of Mr. Darwin, an example {57}
of the unconscious action of volition upon credence. A vast number of
difficulties similar to those which have been mentioned might easily be
cited--those given, however, may suffice.

There remains, however, to be noticed a very important consideration, which
was brought forward in the _North British Review_ for June 1867, p. 286,
namely, the necessity for the sim