1 4 FOREWORD 



In addition to the personal aid received from my 

 scientific associates, many of whom will be named in 

 the text, the kindly criticism of Professor Alfred E. 

 Emerson has been particularly helpful in developing 

 the work and in shaping the content and implica- 

 tions of these lectures. My thanks are given also to 

 Professor Sewall Wright for his criticism of Chapter 

 IV, to Mr. Kenji Toda for preparing the illustra- 

 tions and to Marjorie Hill Allee, whose command of 

 the written word has been a constant resource. 



W. C. Allee 

 The University of Chicago. 



