Vlll PREFACE 



and for this book little claim to originality can be made. 

 The author has attempted to present the subject in the way 

 that seemed simplest and most natural to him, realizing that 

 in so doing he would almost necessarily follow in large meas- 

 ure the authors who have influenced his thinking upon the 

 subject. He is especially indebted to his former instructor, 

 Professor W. K. Brooks, than whom there is no clearer 

 thinker in the field of evolution. 



There are a number of very valuable books which treat 

 of the evolution theory. Most prominent among these are 

 the writings of Darwin and Wallace, and Romanes' Dar- 

 win and After Darwin. The author does not intend that 

 this volume shall be accepted by any reader as a substitute 

 for those more important books, but rather that it shall serve 

 as an introduction to the subject, giving a comprehensive 

 outline of the theory, with just sufficient illustration to invite 

 the reader to seek fuller knowledge of the great number of 

 most interesting phenomena which are related to the theory. 

 At the end of this book will be found a list of a few of the 

 more important volumes treating of the theory of evolution 

 and the phenomena which it explains. 



In the preparation of this book, especially in securing or 

 preparing the pictures, the author has received much assist- 

 ance and many courtesies. It is a pleasure to him to 

 acknowledge his indebtedness: 



For the gift or loan of photographs or material for illus- 

 tration, to the authorities of the United States National 

 Museum, the American Museum of Natural History, the 

 United States Department of Agriculture, the United States 

 Fish Commission, to A. Radcliffe Dugmore, Rev. Dr. John 

 T. Gulick, Mr. C. L. Allen, and especially to his friend, 

 Horace W. Britcher, whose untimely death has removed one 

 of our keenest students of living spiders ; 



For assistance in the identification or in the preparation 

 of material for illustrations, to Dr. Harrison G. Dyar, 



