it becomes so accustomed to this turmoil that it
will expand its tentacles in search of food, just as it does when placed
in calm water. If now one of the expanded tentacles is gently touched
with a solid body, all the others close around that body, in just the
same way as they would were they expanded in calm water. That is to say,
the tentacles are able to discriminate between the stimulus which is
applied by the turmoil of the water and that which is supplied by their
contact with the solid body, and they respond to the latter stimulus
notwithstanding that it is of incomparably less intensity than the
former."[26]

[26] Romanes, _Mental Evolution in Animals_, pp. 48, 49.

When a stimulus passes over a nerve to a ganglion, it leaves upon it an
impression which remains for a shorter or longer time as the stimulus is
great or small. Now, when a stimulus is again applied to the nerve, the
impression wave follows in the footsteps, as it were, of the first
impression wave, and the ganglion reflects or transfers it just as
before, thus showing that nerve has another peculiar quality--that of
_memory_.

Again, when two or more reflexes are excited by the same stimulus or
stimuli, the ganglion learns to associate one with the other, thus
showing that it possesses another quality--that of the association of
ideas (stimuli and reflexes).

All of these operations are, in their beginnings, exceedingly simple;
yet, as organisms increase in complexity, these simple beginnings become
more complex and more highly developed.

Heretofore, the operations described have been entirely ganglionic
(reflex) and utterly without that which we call consciousness. Now, since
consciousness, as I understand it, is simply a knowledge of existence, and
since this knowledge of existence is only to be had through sensual
perceptions, and, since sensual perceptions are excited undoubtedly by
cooerdinated stimuli, then, "there cannot be cooerdination of many stimuli
without some ganglion through which they are all brought into relation.
In the process of bringing these into relation, this ganglion must be
subject to the influence of each--must undergo many changes. And the quick
succession of changes in a ganglion, implying as it does perpetual
experiences of differences and likenesses, constitute the raw material of
consciousness."[27]

[27] Spencer, _Principles of Psychology_, Vol. I. p. 435.

However quick this succession of changes may