vi PREFACE 
following pages, so that I will now quote to the reader 
a few lines from the writings of others. 
Prof. C. S. Minot, in a review of Prof. C. Lloyd 
Morgan’s “ Habit and Instinct,” writes thus :— 
“As a naturalist, it has seemed to me that the 
naturalist’s method has an immense future in Psy- 
chology. The method includes two main factors: 
the observation of details, and the comparison of 
homologous phenomena in different forms of life ; and 
the method starts from the standpoint of evolution. 
There need be no restriction, of course, upon the three 
aspects of Psychology which have heretofore prevailed 
—the metaphysical, introspective, and experimental, 
but there should come soon, and with revolutionary 
power, not merely enlarged interest in, and sympathy 
with, Comparative Evolutional Psychology, but more 
than that—eagerness to enter this field of enquiry and 
to share in harvesting it” (Psych. Rev., vol. iv. No. 3, 
p. 313). 
Those who do me the honour of reading the pages of 
this book will learn for themselves how completely 
I share Professor Minot’s views, and that my convic- 
tions have been followed by corresponding action. 
But one may well ask: Who is able for so great a 
task ? I know of no higher ideal of the requirements 
for the worker in Comparative Psychology than that 
set forth by Prof. Groos in his “ Die Spiele der 
Thiere.” He well says: “The author of a psychology 
of animal play should have, in reality, not alone two, 
but many souls within his breast.” He would have 
