PREFACE ix 



In an endeavor to avoid as many errors as possible, the 

 manuscript of most of the chapters has been read by zoologists 

 who are authorities in the special field treated therein. It is 

 a great pleasure to thank these gentlemen in this place for the 

 invaluable assistance they have rendered. I am indebted to 

 Professor A. S. Pearse for reading Chapters I-IX ; to Mr. Peter 

 Okkelberg for reading the entire manuscript ; to Professor G. N. 

 Calkins for reading Chapter II ; to Professor H. V. Wilson for 

 reading Chapter IV ; to Professor Charles W. Hargitt for read- 

 ing Chapters V and VI; to Professor W. C. Curtis for reading 

 Chapters VII and IX ; to Dr. G. R. La Rue for reading Chapter 

 VII ; to Dr. B. H. Ransom for reading Chapter VIII ; to Dr. 

 Hubert Lyman Clark for reading Chapter X ; to Professor 

 J. Percy Moore for reading Chapter XI ; to Mr. H. B. Baker 

 for reading Chapter XII ; to Professor A. E. Ortmann for read- 

 ing the part of Chapter XIII relating to the Crustacea, Ony- 

 chophora, and Myriapoda ; to Professor Vernon L. Kellogg for 

 reading the part of Chapter XIII relating to Insecta ; to Mr. J. H. 

 Emerton for reading the part of Chapter XIII relating to the 

 Arachnida; to Professor Alexander G. Ruthven for reading 

 Chapters XIV-XIX ; to Professor B. M. Allen for reading Chap- 

 ter XIV ; to Mr. R. E. Richardson for reading Chapters XV- 

 XVII ; to Professor Lynds Jones for reading Chapter XX ; and 

 to Mr. Marcus W. Lyon, Jr., and Mr. N. Hollister for reading 

 Chapter XXI. I am also indebted to Dr. A. F. Shull for read- 

 ing a large part of the proof, and to my wife for her especially 

 valuable assistance in reading proof and preparing the index. 



ROBERT W. HEGNER. 



May 14, 1912. 



