hills (and they have a hankering even after these), at any rate as
the amoeba.

To repeat in other words. All enduring forms establish a modus
vivendi with their surroundings. They can do this because both they
and the surroundings are plastic within certain undefined but
somewhat narrow limits. They are plastic because they can to some
extent change their habits, and changed habit, if persisted in,
involves corresponding change, however slight, in the organs
employed; but their plasticity depends in great measure upon their
failure to perceive that they are moulding themselves. If a change
is so great that they are seriously incommoded by its novelty, they
are not likely to acquiesce in it kindly enough to grow to it, but
they will make no difficulty about the miracle involved in
accommodating themselves to a difference of only two or three per
cent. {72a}

As long as no change exceeds this percentage, and as long, also, as
fresh change does not supervene till the preceding one is well
established, there seems no limit to the amount of modification
which may be accumulated in the course of generations--provided, of
course, always, that the modification continues to be in conformity
with the instinctive habits and physical development of the organism
in their collective capacity. Where the change is too great, or
where an organ has been modified cumulatively in some one direction,
until it has reached a development too seriously out of harmony with
the habits of the organism taken collectively, then the organism
holds itself excused from further effort, throws up the whole
concern, and takes refuge in the liquidation and reconstruction of
death. It is only on the relinquishing of further effort that this