PREFACE 



The investigations of recent years have added so much to 

 our knowledge of the activities of animals that any adequate 

 account of the whole field of animal behavior would require 

 several volumes. The present work is confined to certain 

 topics which bear upon the evolution of animal intelligence, 

 and our treatment of even this part of the subject has been 

 of necessity fragmentary. It has been our aim to give a 

 fairly clear conception of the activities upon which intelli- 

 gence is based, to show how intelligence is'related to these 

 activities, and to sketch the general course of the evolution of 

 intelligence hi the animal kingdom. No effort has been 

 made to deal with all the classes of animals in which intelli- 

 gence is manifested, and some groups which were not 

 essential to the development of our theme have received 

 little attention. 



I wish to express my thanks to Prof. L. J. Cole and Prof. 

 H. B. Torrey for their helpful criticisms of the manuscript of 

 this book before it went to press. To Prof. L. T. Hobhouse, 

 Prof. E.'L. Thorndike and Dr. L. Witmer I am indebted for 

 permission to reproduce the figures which are attributed to 

 these writers in the text, and I am also indebted to the 

 Macmillan Company for kindly allowing me to reproduce 

 figures 15 and 16 from their publications. My greatest debt 

 is to mv wife for helo and encouragement in many ways. 



S. J. H. 



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