as to push the pollen on to
the stigmatic surface. Hence, again, if humble-bees were to become rare in
any country, it might be a great advantage to the red clover to have a
shorter or more deeply divided tube to its corolla, so that the hive-bee
could visit its flowers. Thus I can understand how a flower and a bee might
slowly become, either simultaneously or one after the other, modified and
adapted in the most perfect manner to each other, by the continued
preservation of individuals presenting mutual and slightly favourable
deviations of structure.

I am well aware that this doctrine of natural selection, exemplified in the
above imaginary instances, is open to the same objections which were at
first urged against Sir Charles Lyell's noble views on "the modern changes
of the earth, as illustrative of geology;" but we now seldom hear the
action, for instance, of the coast-waves, called a trifling and
insignificant cause, when applied to the excavation of gigantic valleys or
to the formation of the longest lines of inland cliffs. Natural selection
can act only by the preservation and accumulation of infinitesimally small
inherited modifications, each profitable to the preserved being; and as
modern geology has almost banished such views as the excavation of a great
valley by a single diluvial wave, so will natural selection, if it be a
true principle, banish the belief of the continued creation of new organic
{96} beings, or of any great and sudden modification in their structure.

_On the Intercrossing of Individuals._--I must here introduce a short
digression. In the case of animals and plants with separated sexes, it is
of course obvious that two individuals must always (with the exception of
the curious and not well-understood cases of parthenogenesis) unite for
each birth; but in the case of hermaphrodites this is far from obvious.
Nevertheless I am strongly inclined to believe that with all hermaphrodites
two individuals, either occasionally or habitually, concur for the
reproduction of their kind. This view was first suggested by Andrew Knight.
We shall presently see its importance; but I must here treat the subject
with extreme brevity, though I have the materials prepared for an ample
discussion. All vertebrate animals, all insects, and some other large
groups of animals, pair for each birth. Modern research has much diminished
the number of supposed hermaphrodites, and of real hermaphrodites a large
numb