PREFACE TO SECOND EDITION 



IN the years that have elapsed since the first edition 

 was published, the subject of Comparative Psychology 

 has undergone a great change. It is hardly too much to 

 say that, owing to the activity of a group of workers 

 in the American Universities, the investigation of the 

 animal mind has, roughly within this period, established 

 for itself a place among the recognised sciences. Hence 

 much that was within the hands of pioneers when this 

 book was first written, has now been thoroughly 

 examined. Much, of course, still remains undetermined. 

 In some material respects I have found it necessary to 

 modify opinions formed on the data available in 1900. 

 In particular, the observations of Mr. H. S. Jennings 

 have shown me that something of the nature of mind 

 is to be carried further down in the organic world than 

 I supposed. His results, together with other work in 

 general psychology, have led me, however, to extend 

 rather than to narrow the view taken in the first edition 

 of the function of mind in evolution, and even to raise 

 the question whether mind (in the infinitely varied forms 

 of its activity from the groping of unconscious effort to 

 the full clearness of conscious purpose) may not be the 

 essential driving force in all evolutionary change. In 



