ch results from each man trying to keep the
best dogs without any thought of modifying the breed.

Even without any change in the proportional numbers of the animals on
which our wolf preyed, a cub might be born with an innate tendency to
pursue certain kinds of prey. Nor can this be thought very improbable;
for we often observe great differences in the natural tendencies of our
domestic animals; one cat, for instance, taking to catch rats, another
mice; one cat, according to Mr. St. John, bringing home winged game,
another hares or rabbits, and another hunting on marshy ground and
almost nightly catching 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 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