ring themselves for the
serious onset of adult responsibilities. On this theory each play
becomes a beautiful case of adaptation to nature. The kitten plays
with the ball as the old cat handles the mouse; the little dogs
wrestle together, and so learn to fight with teeth and claws; the deer
run from one another, and so test their speed and learn to escape
their enemies. If we watch young animals at play we see that not a
muscle or nerve escapes this preliminary training and exercise; and
the instinctive tendencies which control the play direct the
activities into just the performances which the animal's later
life-habits are going on to require.

On this view play becomes of the utmost utility. It is not a
by-product, but an essential part of the animal's equipment. Just as
the infancy period has been lengthened in the higher animals in order
to give the young time to learn all that they require to meet the
harsh conditions of life, so during this infancy period they have in
the play-instinct a means of the first importance for making good use
of their time. It is beautiful to see the adults playing with their
young, adapting their strength to the little ones, repeating the same
exercises without ceasing, drilling them with infinite pains to
greater hardihood, endurance, and skill.

On this theory it is also easy to see why it is that the plays are
different for the different species. The actual life conditions are
different, and the habits of the species are correspondingly
different. So it is only another argument for the truth of this theory
that we find just those games natural to the young which train them
in the habits natural to the old.

This view is now being very generally adopted. Many fine illustrations
might be cited. A simple case may be seen in so small a thing as the
habit of leaping in play; the difference, for example, between the
mountain goat and the common fawn. The former, when playing on level
ground makes a very ludicrous exhibition by jumping in little
up-and-down leaps by which he makes no progress. In contrast with this
the fawn, whose adult life is normally in the plains, takes a long
graceful spring. The difference becomes clear from the point of view
of this theory, when we remember that the goat is to live among the
rocks, where the only useful jump is just the up-and-down sort which
the little fellow is now practising; while the deer, in his life upon
the plains, will always need the