PREFACE TO THE SECOND EDITION 



The advance of comparative psychology during the 

 past nine years has been remarkable. In preparing a 

 second edition of this book I have tried to include every 

 newly discovered .fact of the first importance, but the 

 literature is now so extensive that in order to keep the 

 bibliography within reasonable limits, I have had to exer- 

 cise more selection than I did in preparing the bibliography 

 for the first edition. For like reasons, the text of the book 

 does not enter so fully into detail in describing the results 

 of a particular investigation as was possible when the 

 material at hand was so much less in amount. 



More than half the book has been completely rewritten, 

 including the chapters on Vision, on Spatially Determined 

 Reactions, and on The Modification of Conscious Pro- 

 cesses by Individual Experience. I hope that the edition 

 represents an advance upon its predecessor, not only by 

 including many newly ascertained facts, but also by pre- 

 senting its subject matter in more logical form. 



M. F, W. 



Vassar College, Poughkeepsie, N.Y., 

 April, 1917. 



