vi PREFACE 



between animals and the sum total of their environ- 

 ments, one may fairly consider that they are of 

 ecological worth. 



In the arrangement of the references I have tried 

 to group related papers, but many defy any single 

 system. Some of the publications deserve to be in 

 several lists, but little duplication has been made, 

 as this would unduly prolong the lists. The anno- 

 tations will supplement the titles and their grouping 

 in indicating the contents and importance of the 

 papers for our purpose. It has often been difficult 

 to select from several almost equally valuable and 

 useful papers. Others with different interests, aims, 

 and experience would doubtless make a different 

 choice. It will therefore be a favor, if those who 

 use this handbook and feel that important papers 

 have been excluded, will communicate this fact to 

 the author. 



This book is not intended as a treatise on the sci- 

 ence of ecology; its aim is primarily educational. 

 This is the justification, if any were necessary, for 

 placing emphasis upon the point of view and the 

 importance of an understanding of explanatory pro- 

 cesses and of the methods of scientific investigation. 

 Any adequate treatment of this subject would ex- 

 ceed the space of this volume and it is reserved for 

 future elaboration. 



At present ecology is a science with its facts out 

 of all proportion to their organization or integration. 

 There is thus an immediate need of integration, and 

 this above all requires a clear conception of the sci- 



