It is thus that we arrive at the importance of the play-function, and
thus, also, we realise that while it extends beyond the sexual sphere it
yet definitely includes that sphere. There are at least three different
ways of understanding the biological function of play. There is the
conception of play, on which Groos has elaborately insisted, as
education: the cat "plays" with the mouse and is thereby educating
itself in the skill necessary to catch mice; all our human games are a
training in qualities that are required in life, and that is why in
England we continue to attribute to the Duke of Wellington the saying
that "the battle of Waterloo was won on the playing fields of Eton."
Then there is the conception of play as the utilisation in art of the
superfluous energies left unemployed in the practical work of life; this
enlarging and harmonising function of play, while in the lower ranges it
may be spent trivially, leads in the higher ranges to the production of
the most magnificent human achievements. But there is yet a third
conception of play, according to which it exerts a direct internal
influence--health-giving, developmental, and balancing--on the whole
organism of the player himself. This conception is related to the other
two, and yet distinct, for it is not primarily a definite education in
specific kinds of life-conserving skill, although it may involve the
acquisition of such skill, and it is not concerned with the construction
of objective works of art, although--by means of contact in human
relationship--it attains the wholesome organic effects which may be
indirectly achieved by artistic activities. It is in this sense that we
are here concerned with what we may perhaps best call the play-function
of sex.[19]

[19] The term seems to have been devised by Professor Maurice Parmelee,
_Personality and Conduct_, 1918, pp. 104, 107, 113. But it is understood
by Parmelee in a much vaguer and more extended sense than I have used