activity to its
real end is prevented by incapacity or by ignorance; in the other, it is
prevented by a deliberate exercise of will. The former occurs in
children; the latter, often enough in adults. Whatever view we hold
regarding this matter, the sexually differentiated love-games of young
animals must be regarded as a manifestation of the sexual life. None the
less, in sexually immature animals, just as in the case of children,
sexual differentiation is not always so marked as it is in adults; and
it may happen that the sexes may exchange their roles. Cases observed by
Seitz have been published by Groos and also by myself.[46] I have myself
watched a young cow which repeatedly attempted to mount another young
cow; I have also on several occasions seen young bitches attempt to
cover dogs. To this part of our subject belongs the observation of
Exner, that when dogs are playing wildly with one another one hardly
ever sees a bitch among them. But if an exception should occur, the
bitch is usually a young one. In animals, sexual differentiation is not
complete until sexual maturity is attained, and the same is true of the
human species, although, as I have shown above, children already
manifest sexual differentiation in their games, their inclinations, and
their general conduct.

I have thought it desirable to refer to the play of animals in this
place, as well as to treat of the subject in its direct relationship to
the sexual impulse. What is true of play is true also of the other
interests and inclinations of the child, many of which are also
associated with the sexual life; these have been described earlier, so
that here I need merely allude to the matter in passing.

Hitherto I have described the sexual life of the child in so far as it
is the subject of direct observation or can be recalled to memory. But
it was explained at the outset that there is still another way of
gaining clear knowledge of the subject, namely, by experiment; and it
was shown that castration may be regarded as such an experiment.
Although the reproductive capacity of the male is not developed prior to
the formation of spermatozoa in the testicles, nevertheless we learn
from the effects of castration that the testicles exhibit important
functional activity much earlier in life. This fact was long overlooked,
and its importance is even to-day largely underestimated, because we
have been accustomed to regard the provision of an external secre