flock over the farm-walls and fences. From this ram was descended
the breed of ancon, or otter, sheep. Now the stimulus which had
excited this variation must have been applied early in embryonic
life, or perhaps during the formation or maturing of the germ-cells
themselves. Such a variation we call a congenital variation.

These cases are merely illustrations of the general truth that in
every variation there are two factors concerned: the living being
with its constitution and inherent tendencies and the external
stimulus.

The courses of the different balls in a charge of grape-shot, hurled
from a cannon, are evidently due to two sets of forces--1, their
initial energy and the direction of their aim; 2, the deflecting
power of resisting objects or forces--or the different balls might
roll with great velocity down a precipitous mountain-side. In the
first case velocity and direction of course would be determined
largely by initial impulse; in the second, by the attraction of the
earth and by the inequalities of its surface.

In evolution, environment, roughly speaking, corresponds to these
deflecting or attracting external objects or forces; inherent
tendencies to initial impulse. If we lay great weight on initial
tendencies, inherent in protoplasm from the very beginning, we shall
probably lay less stress on natural selection as a guiding,
directing process.

The great botanist, Nägeli, has propounded a most ingenious and
elaborate theory of evolution, as dependent mainly on inherent
initial tendency. We can notice only one or two of its salient