PREFACE xix 



gested readings include materials dealing with Science in general, 

 some of which are so advanced as to be of use almost solely to ad- 

 vanced students. Titles appear here that may occasion surprise in a 

 text of this sort. The writer remembers that in very many cases this 

 is the only course in Science which the student undertakes during 

 his college career; he also remembers that many students have asked 

 him for just this sort of reference material. 



Acknowledgment is made of obligations to Professor W. C. Allee, 

 of the University of Chicago, who read a copy of the manuscript 

 as it was being developed and offered encouragement and valuable 

 suggestions. Advantage was also taken of criticisms made by Mr. 

 Henshaw Ward, who was kind enough to read an earlier copy. No 

 small credit for such values as this volume may possess is due to the 

 cooperation and active assistance of the writer's wife, Pearle Oliver 

 Buchanan; its preparation was made possible by her assistance in 

 discussions and her part in the tedious task of correcting proof. The 

 practical suggestions and efficient handling of copy by Miss Ona 

 Cunningham, Secretary of the Department of Zoology, were valu- 

 able aids. The writer also appreciates the generous help of the 

 publishers, Harper and Brothers, and their care in the manufacture 

 of the book. Finally, an indebtedness that cannot be redeemed here 

 is acknowledged to former and present colleagues, and to former 

 students, whose opinions, either by positive suggestion or by the 

 friendly clash of ideas that is so often fruitful, have aided the 

 writer in formulating his course. 



For the preparation of the figures it was indeed fortunate that 

 the services of Miss Maudjean Gail were available and the writer is 

 indebted to her for much assistance and careful work. In general, 

 the figures are those which the writer at one time or another has 

 found valuable in his course. Emphasis is placed on diagram^rather 

 than reproductions. We prepared a considerable number of dissec- 

 tions and had at our disposal many histological preparations. Many 

 of the figures were drawn from such dissections and preparations 



