viii PREFACE 



for the editor to write short chapters on certain topics that were not 

 presented in the available literature in sufficiently brief compass or 

 in sufficiently non-technical language. 



The one-man textbook is only too often written to emphasize 

 the author's pet theories and is likely to be unduly biased. The 

 present work is completely non-partisan. It consists of the writ- 

 ings of many authors and presents many diverse theories. The 

 student is left to balance the various views one against another and 

 to form his own judgment. 



It is very unfortunate, but none the less true, that even in these 

 scientific days, the subject of evolution has a bad name in many 

 communities and in many educational institutions with religious 

 affiliations. The mistake is made of supposing that evolution and 

 religion are diametrically opposed. The present writer has been at 

 some pains to make it clear that evolution and religion are strictly 

 compatible. We teachers of evolution hi the colleges have no sinister 

 designs upon the religious faith of our students. 



While this book is intended primarily for a college textbook, 

 we have also had in mind the general reader. Apart from a few of 

 the more technical details, the text seems to us very readable. The 

 language of the great classic writers Darwin, Wallace, Romanes, De 

 Vries, Le Conte is simple and lucid. Among recent biological books 

 few are written so freshly and vividly as those of Professor J. Arthur 

 Thomson. The clearness and scientific accuracy of Conklin, Saleeby, 

 Guyer, Walter, Lull, Osborn, the Coulters, Downing, Shull, Tayler, 

 Popenoe, Johnson, and others, are familiar to American biologists. 



Scrupulous care has been taken to verify all passages quoted, 

 but it is hardly likely that, in so large a mass of material, all errors 

 shall have been avoided. The author and the publishers would 

 welcome as a favor any suggestions or corrections submitted by 

 interested readers. 



A list of fifty books from which material has been quoted is given 

 on pages 510-512. To the authors and publishers of these books and 

 monographs we wish herewith to tender our grateful a'cknowledg- 

 ments for their generosity and co-operation. A considerable amount 

 of material for which permission to reprint had been granted fails 

 to appear in the present volume. It is hoped to incorporate this 

 material in an appendix to a later edition, or else to use it in the form 

 of a small volume of supplementary readings. 



H. H. N. 



August 15, 1921 



