nical movements are those in which the
stored energy of a living body is not involved. Similarly dynamite may
be exploded, thereby displaying its characteristic properties, or may
(with due precautions) be carted about like any other mineral. The
explosion is analogous to vital movements, the carting about to
mechanical movements.

Mechanical movements are of no interest to the psychologist, and it has
only been necessary to define them in order to be able to exclude them.
When a psychologist studies behaviour, it is only vital movements
that concern him. We shall, therefore, proceed to ignore mechanical
movements, and study only the properties of the remainder.

The next point is to distinguish between movements that are instinctive
and movements that are acquired by experience. This distinction also is
to some extent one of degree. Professor Lloyd Morgan gives the following
definition of "instinctive behaviour":

"That which is, on its first occurrence, independent of prior
experience; which tends to the well-being of the individual and the
preservation of the race; which is similarly performed by all members
of the same more or less restricted group of animals; and which may be
subject to subsequent modification under the guidance of experience." *

* "Instinct and Experience" (Methuen, 1912) p. 5.

This definition is framed for the purposes of biology, and is in
some respects unsuited to the needs of psychology. Though perhaps
unavoidable, allusion to "the same more or less restricted group
of animals" makes it impossible to judge what is instinctive in the
behaviour of an isolated individual. Moreover, "the well-being of
the individual and the preservation of the race" is only a usual
characteristic, not a universal one, of the sort of movements that, from
our point of view, are to be called instinctive; instances of harmful
instincts will be given shortly. The essential point of the definition,
from our point of view, is that an instinctive movement is in dependent
of prior experience.

We may say that an "instinctive" movement is a vital movement performed
by an animal the first time that it finds itself in a novel situation;
or, more correctly, one which it would perform if the situation were
novel.* The instincts of an animal are different at different periods of
its growth, and this fact may cause changes of behaviour which are
not due to learning. The maturing and seasonal fluctuation of the
sex-i