PREFACE ix 



articles in the leading medical journals of all countries, and 

 reviews many of them. Any of these periodicals will be lent 

 by the Association library, at the average cost of postage, to 

 any member of the Association. These three publications, on 

 account of their scope and thoroughness, are of inestimable 

 value to anyone who attempts to keep pace with the progress 

 of the medical sciences. There are, however, few if any of the 

 journals or books listed under " Sources of Information " which 

 have not been drawn upon either for illustrations or infor- 

 mation or both. All of these, collectively, have made this book 

 possible, and to them, and to the workers who contribute to 

 them, are due, therefore, not only the thanks of the author but 

 also the thanks of everyone who may profit in any way by this 

 book. 



The writer is very deeply indebted to the authorities who have 

 been kind enough to read the manuscript, and who have freely 

 given the benefit of helpful suggestions and criticisms. Pro- 

 fessor Gary N. Calkins, Professor of Protozoology at Columbia 

 University, Dr. B. H. Ransom, Zoologist of the U. S. Bureau of 

 Animal Industry, and Dr. L. 0. Howard, Chief of the U. S. 

 Bureau of Entomology, have helped materially to round off 

 the rough corners, and fill in the chinks, of the sections on Pro- 

 tozoa, " worms," and arthropods, respectively. 



Hearty thanks is also due my wife, Belle Clarke Chandler, 

 for the invaluable assistance she has given by her constant and 

 efficient cooperation in the editorial part of the work. 



