490 THE GENERAL PRINCIPLES OF ZOOLOGY 



into the air as she follows it ; or, crouching stealthily, she ad- 

 vances first one foot and then the other, with eyes fixed on her 

 mother's gently swaying tail, finally pouncing upon it only to 

 receive a box on the ear from her parent. The calf or the colt 

 kicks up his heels and gambols about the pasture. Such kinds 

 of behavior we recognize as play ; they are of no immediate ad- 

 vantage to the individual ; the animal appears to indulge in them 

 merely for the pleasure derived from such a form of activity ; 

 they do not seem in any way necessary to the satisfactory per- 

 formance of the various functions of animal life. 



Psychologically it is doubtless the pleasure derived from play 

 which prompts the animal to indulge in it. When, however, we 

 seek for the underlying biological end which play is to accom- 

 plish in the economy of the individual or of the race, we find two 

 theories in the field. According to one the animal plays 

 when stimulated by a superabundance of health and strength ; 

 he works off his surplus energy, as we say in popular language. 

 But while the instinct to play may be called into action by a 

 condition of physical well-being, it is scarcely probable that the 

 biological end is to reduce a superfluous amount of energy. If 

 animals played only when in a condition of exuberant health and 

 strength, we might be led to this conclusion, but this seems far from 

 being the case. Any one who has observed a couple of dogs at play 

 will have seen them start up again and again after they have lain 

 down from sheer exhaustion ; the moment they have recovered 

 breath, as it were, they are at it again. Superfluous energy must 

 long have been used up ; they must rest until they have regained 

 sufficient for the next attack. Animals will even play to some ex- 

 tent when they are ill, at a time when phvsical energy is below 

 the normal. Taking such facts into consideration, the first theory 

 of play does net appear entirely satisfactory. 



The second theory considers that the biological end of play is 

 the training of the individual for the future requirements of life. 

 Hence play is most manifest in the young animal ; the kitten 

 springing at her mother's tail is training her muscles and nerves 

 for their later use in the process of catching birds and mice; 

 there is necessary the same coordination of movements and the 

 same concentration of attention, and the skill attained at this 

 time of life will save her from losing many a desirable meal later 





