EDITOR'S PREFACE* 



Ix this Yolume Professor Groos makes a contribu- 

 tion to three distinct but cognate departments of in- 

 quiry : philosophical biology, animal psycholog}^, and the 

 genetic study of art. Those who have followed the be- 

 ginnings of inquiry into the nature and functions of 

 play in the animal world and in children will see at 

 once how much light is to be expected from a thor- 

 ough-going examination of all the facts and observations 

 recorded in the literature of animal life. This sort of 

 examination Professor Groos makes with great care and 

 thoroughness, and the result is a book which, in my 

 opinion, is destined to have wide influence in all these 

 departments of inquiry. 



I wish, before speaking of certain conclusions which 

 are of especial interest, to make some running comments 

 on the contents of the book, without, of course, forestall- 

 ing the reader's ovm. discovery of its riches. Chapter I 

 is an examination of Mr. Spencer's " surplus-energy '' 

 theory of play; the result of which is, it seems, to put 

 this theory permanently out of court. The author's 



♦ In this preface certain passages are repeated from a review 

 of the German edition of Professor Groos' book, printed in Sci- 

 ence, February 26, 1897. . ^ 0£? '" /I 



