THE DEVELOPMENT OF ORGANISMS 



809 



channel of expression. Young creatures mimic in play what they 

 sec their seniors doing in earnest. Here, again, there is some truth, 

 and a corroboration may be found in the imitativeness of certain 

 forms of playing in children. But Spencer's theory will not cover 

 the facts. Thus it has been shown experimentally that an isolated 

 yoimg animal, such as a kitten, will play, and will play true to type, 

 provided that an appropriate liberating stimulus, apart from imita- 

 tion, is supplied at an appropriate time. But if a kitten reaches a 

 certain age — usually about two or three months — ^without having 

 had any experience of mice, it will not afterwards show any "mousing 

 instinct", nor any capacity for playing with a mouse. 



(3) A third idea has some relevance, namely, the close correlation 

 between pleasant emotions and bodily movements. It is a familiar 

 fact of experience, elaborately studied by the physiologists and 

 psychologists, that pleasant feelings reverberate in various parts of 

 the body, such as the heart, the lungs, the larynx, the food-canal, 

 and the bladder. The correlation of emotional excitement and the 

 activity of the suprarenal bodies is well known. But to the internal 

 movements there may be added movements of the body as a whole, 

 and these will be naturally specific for different types. The child 

 dances with joy; the otter cub gambols exuberantly. This simple 

 movement -play may be a useful safety-valve, but it is also a 

 natural expression of overflowing joie de vivre. 



(4) To Karl Groos we owe the illuminating suggestion that play 

 is especially important as an irresponsible apprenticeship to the 

 subsequent business of life. It is the young form of work, and this 

 accounts for its specificity. The young Carnivore has its sham hunt, 

 and the young Ungulate its amateurish race, neither involving 

 serious responsibilities. Under the shelter of parental or communal 

 care the playing animal educates powers that are essential in its 

 after-life, and is afforded opportunities without the serious conse- 

 quences which are involved whenever the struggle for existence sets 

 in keenly. As Groos puts it, animals do not play because they are 

 young, they continue young in order that they may play. No doubt 

 non-plajdng young animals also educate their capacities, but the 

 point is that the interpolation of the play-period is an additional 

 advantage which some plastic and well-endowed creatures have 

 been able to secure for themselves. It is interesting to notice that 

 most of the mammals that man has succeeded in domesticating are 

 playing mammals. 



(5) Another aspect of the play-period is that it affords opportu- 

 nity for testiag new variations before the day-by-day sieve of the 

 struggle for existence becomes too close in the mesh. Play affords 

 elbow-room for new departures; and its value is particularly clear 

 when the adult life is very varied, like an otter's, demanding 

 plasticity and resourcefulness. Here there is a marked contrast 



