iv THE PLAY OF ANIMALS. 



main contention is that play, so far from being "by- 

 play," if I may so speak, is a matter of serious moment 

 to the creature. Play is a veritable instinct. This 

 view is expanded in Chapter II, where we find a fine 

 treatment in detail of such interesting topics as imita- 

 tion in its relation to play, the inheritance of acquired 

 characters apropos of the rise of instincts, and the place 

 and function of intelligence in the origin of these pri- 

 mary animal activities. This chapter, dealing with the 

 biological theory of play, is correlated with Chapter V, 

 in which the Psychology of Animal Play is treated. 

 Together they furnish the philosophical and theoretical 

 basis of the book, as the chapters in between furnish the 

 detailed data of fact. I shall return to the biological 

 matter below. Chapters III and IV go into the actual 

 Plays of Animals with a wealth of detail, richness of 

 literary information, and soundness of critical interpre- 

 tation which are most heartily to be commended. In- 

 deed, the fact that the first book on this subject is at the 

 same time one of such unusual value, both as science and 

 as theory, should be a matter of congratulation to work- 

 ers in biology and in psychology. The collected cases, 

 the classification of animal plays, as well as the setting 

 of interpretation in which Professor Groos has placed 

 them — all are likely to stand, I think, as a piece of 

 work of excellent quality in a new but most important 

 field of inquiry. 



With this general and inadequate notice of the divi- 

 sions and scope of the book, I may throw together in a 

 few sentences the main theoretical positions to which the 

 author's study brings him. He holds play to be an in- 

 stinct developed by natural selection (he gives good rea- 

 sons for not accepting the inheritance of acquired char- 

 acters), and to be on a level with the other instincts 



