duction which man shares with the lower
animals. It is true that much discussion has taken place concerning the
proper use of the term "instinct," and some definitions of instinctive
action would appear to exclude the essential mechanism of the process
whereby sexual reproduction is assured. Such definitions scarcely seem
legitimate, and are certainly unfortunate. Herbert Spencer's definition of
instinct as "compound reflex action" is sufficiently clear and definite
for ordinary use.

A fairly satisfactory definition of instinct is that supplied by
Dr. and Mrs. Peckham in the course of their study _On the
Instincts and Habits of Solitary Wasps_. "Under the term
'instinct,'" they say, "we place all complex acts which are
performed previous to experience and in a similar manner by all
members of the same sex and race, leaving out as non-essential,
at this time, the question of whether they are or are not
accompanied by consciousness." This definition is quoted with
approval by Lloyd Morgan, who modifies and further elaborates it
(_Animal Behavior_, 1900, p. 21). "The distinction between
instinctive and reflex behavior," he remarks, "turns in large
degree on their relative complexity," and instinctive behavior,
he concludes, may be said to comprise "those complex groups of
co-ordinated acts which are, on their first occurrence,
independent of experience; which tend to the well-being of the
individual and the preservation of the race; which are due to the
co-operation of external and internal stimuli; which are
similarly performed by all the members of the same more or less
restricted group of animals; but which are subject to variation,
and to subsequent modification under the guidance of experience."
Such a definition clearly justifies us in speaking of a "sexual
instinct." It may be added that the various questions involved in
the definition of the sexual instinct have been fully discussed
by Moll in the early sections of his _Untersuchungen ueber die
Libido Sexualis_.

Of recent years there has been a tendency to avoid the use of the
term "instinct," or, at all events, to refrain from attaching any
serious scientific sense to it. Loeb's influence has especially
given force to this tendency. Thus, while Pieron, in an
interesting discussion of the question ("Les Problemes Actuels de
l'Instinct," _