of easy passages between sensory and motor nerves in
centres lower than the cortex.

CHAPTER XXI

INSTINCT

=Definition of Instinct.=--In a foregoing section, it was seen that our
bodily movements divide into different classes according to their
source, or origin. Among them were noted certain inherited spontaneous,
but useful, complex movements which follow, in a more or less uniform
way, definite types of stimuli presented to the organism. Such an
inherited tendency on the part of an organism to react in an effective
manner, but without any definite purpose in view, whenever a particular
stimulus presents itself, is known as instinct, and the resulting action
is described as an instinctive act. As an example of purely instinctive
action may be taken the maternal instinct of insects whose larvae require
live prey when they are born. To provide this the mother administers
sufficient poison to a spider or a caterpillar to stupefy it, and then
bears it to her nest. Placing the victim close to her eggs, she incloses
the two together, thus providing food for her future offspring. This
complex series of acts, so essential to the continuance of the species,
and seemingly so full of purpose, is nevertheless conducted throughout
without reference to past experience, and without any future end in
view. Instinct may, therefore, be defined as the ability of an organism
to react upon a particular situation so as to gain a desirable end, yet
without any purpose in view or any previous training.

=Characteristics of Instinct.=--An instinctive act, it may be noted, is
distinguished by certain well marked characteristics:

1. The action is not brought about by experience or guided by
intelligence, but is a direct reaction on the part of the organism to
definite stimulation.

2. Although not the result of reason, instinctive action is purposeful
to the extent that it shows a predisposition on the part of the organism
to react in an effective manner to a particular situation.

3. An instinctive movement is a response in which the whole organism is
concerned. It is the discomfort of the whole organism, for instance,
that causes the bird to migrate or the child to seek food. In this
respect it differs from a mere reflex action such as the winking of the
eye, breathing, coughing, etc., which involves only some particular part
of the organism.

4. Although not a consciously purposed action, instinct nevertheless
involves c