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 in 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 my wife for help and encouragement in many ways. 
8. J. H. 
