bees visiting the
flowers, if humble-bees were to become rare in any country, it might be
a great advantage to the plant to have a shorter or more deeply divided
corolla, so that the hive-bees should be enabled to suck 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 to each
other in the most perfect manner, by the continued preservation of all
the individuals which presented slight deviations of structure mutually
favourable to each other.

I am well aware that this doctrine of natural selection, exemplified in
the above imaginary instances, is open to the same objections which
were 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 agencies which we see still at work, spoken of as trifling and
insignificant, when used in explaining the excavation of the deepest
valleys or the formation of long lines of inland cliffs. Natural
selection acts only by the preservation and accumulation of 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 banish
the belief of the continued creation of new organic 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 there is
reason to believe that with all hermaphrodites two individuals, either
occasionally or habitually, concur for the reproduction of their kind.
This view was long ago doubtfully suggested by Sprengel, Knight and
Kolreuter. 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 number pair; that is, two individuals regularly
unite for repr