belonging to different tissues more or less akin.
In both cases there are manifold variations on one and the same theme.
The constancy of the theme is manifest, however, and the variations only
fit it to the diversity of the circumstances.

Now, in both cases, in the instinct of the animal and in the vital
properties of the cell, the same knowledge and the same ignorance are
shown. All goes on as if the cell knew, of the other cells, what
concerns itself; as if the animal knew, of the other animals, what it
can utilize--all else remaining in shade. It seems as if life, as soon
as it has become bound up in a species, is cut off from the rest of its
own work, save at one or two points that are of vital concern to the
species just arisen. Is it not plain that life goes to work here exactly
like consciousness, exactly like memory? We trail behind us, unawares,
the whole of our past; but our memory pours into the present only the
odd recollection or two that in some way complete our present situation.
Thus the instinctive knowledge which one species possesses of another on
a certain particular point has its root in the very unity of life, which
is, to use the expression of an ancient philosopher, a "whole
sympathetic to itself." It is impossible to consider some of the special
instincts of the animal and of the plant, evidently arisen in
extraordinary circumstances, without relating them to those
recollections, seemingly forgotten, which spring up suddenly under the
pressure of an urgent need.

No doubt many secondary instincts, and also many varieties of primary
instinct, admit of a scientific explanation. Yet it is doubtful whether
science, with its present methods of explanation, will ever succeed in
analyzing instinct completely. The reason is that instinct and
intelligence are two divergent developments of one and the same
principle, which in the one case remains within itself, in the other
steps out of itself and becomes absorbed in the utilization of inert
matter. This gradual divergence testifies to a radical incompatibility,
and points to the fact that it is impossible for intelligence to
reabsorb instinct. That which is instinctive in instinct cannot be
expressed in terms of intelligence, nor, consequently, can it be
analyzed.

A man born blind, who had lived among others born blind, could not be
made to believe in the possibility of perceiving a distant object
without first perceiving all the objects in betwee