vi Preface 



It has seemed best to leave the texts unaltered except 

 for the correction of typographical errors, renumbering 

 of tables and figures, and redrawing the latter. In a 

 few places, where the original text has been found likely 

 to be misunderstood, brief notes have been added. It is 

 hard to resist the impulse to temper the style, especially 

 of the ' Animal Intelligence,' with a certain sobriety and 

 restraint. What one writes at the age of twenty-three 

 is likely to irritate oneself a dozen years later, as it doubt- 

 less irritated others at the time. The charitable reader 

 may allay his irritation by the thought that a degree of 

 exuberance, even of arrogance, is proper to youth. 



To the reports of experimental studies are added two 

 new essays dealing with the general laws of human and 

 animal learning. 



JANUARY, 1911. 



