vi PREFACE TO THE REVISED EDITION. 



But there has been a further reason for this change of 

 method. An invalid who is nearly eighty cannot with pru- 

 dence enter upon work which will take long to complete. 

 Hence I have thought it better to make the needful altera- 

 tions and additions in ways requiring relatively moderate 

 time and labour. 



The additions made to this volume are less numerous and 

 less important than those made to the first volume. A new 

 chapter ending Part V, on " The Integration of the Or- 

 ganic World," serves to round off the general theory of 

 Evolution in its application to living things. Beyond a new 

 section (§ 289a) and the various foot-notes, serving chiefly 

 the purpose of elucidation, there are notes of some signifi- 

 cance appended to Chapters I, III, IY, and V, in Part IY, 

 Chapters Y and VIII, in Part V, and Chapters IX, X, and 

 XII in Part VI. Moreover there are three further appen- 

 dices, D 3 , F, and G, which have, I think, considerable sig- 

 nificance as serving to make clearer some of the views 

 expressed in the body of the work. 



Turning from the additions to the revisions, I have to 

 say that the aid needed for bringing up to date the contents 

 of this volume, has been given me by the gentlemen who 

 gave me like aid in revising the first volume : omitting 

 Prof. Perkin, within whose province none of the contents 

 of this volume fall. Plant-Morphology and Plant-Physi- 

 ology have been overseen by Mr. A. G. Tansley. Criti- 

 cisms upon parts dealing with Animal Morphology I owe 

 to Mr. J. T. Cunningham and Prof. E. W. MacBride. 

 And the statements included under Animal Physiology 

 have been checked by Mr. W. B. Hardy. 



