woodcocks or snipes. The tendency to catch rats rather than mice is known
to be inherited. Now, if any slight innate change of habit or of structure
benefited an individual wolf, it would have the best chance of surviving
and of leaving offspring. Some of its young would probably inherit the same
habits or structure, and by the repetition of this process, a new variety
might be formed which would either supplant or coexist with the parent form
of wolf. Or, again, the wolves inhabiting a mountainous district, and those
frequenting the lowlands, would naturally be forced to hunt different prey;
and from the continued preservation of the individuals best fitted for the
two sites, two varieties might slowly be formed. These varieties would
cross and blend where they met; but to this subject of intercrossing we
shall soon have to return. I may add, that, according to Mr. Pierce, there
are two varieties of the wolf inhabiting the Catskill Mountains in the
United States, one with a light greyhound-like form, which pursues deer,
and the other more bulky, with shorter legs, which more frequently attacks
the shepherd's flocks.

Let us now take a more complex case. Certain plants excrete a sweet juice,
apparently for the sake of eliminating something injurious from their sap:
this is {92} effected by glands at the base of the stipules in some
Leguminosae, and at the back of the leaf of the common laurel. This juice,
though small in quantity, is greedily sought by insects. Let us now suppose
a little sweet juice or nectar to be excreted by the inner bases of the
petals of a flower. In this case insects in seeking the nectar would get
dusted with pollen, and would certainly often transport the pollen from one
flower to the stigma of another flower. The flowers of two distinct
individuals of the same species would thus get crossed; and the act of
crossing, we have good reason to believe (as will hereafter be more fully
alluded to), would produce very vigorous seedlings, which consequently
would have the best chance of flourishing and surviving. Some of these
seedlings would probably inherit the nectar-excreting power. Those
individual flowers which had the largest glands or nectaries, and which
excreted most nectar, would be oftenest visited by insects, and would be
oftenest crossed; and so in the long-run would gain the upper hand. Those
flowers, also, which had their stamens and pistils placed, in relation to
the size and habits of t