VI PREFACE 



of Chicago; Dr. A. G. Mayer, Director of the Marine Biological Lab- 

 oratory, Tortugas, Fla.; James H. Emerton of Boston, Mass.; Dr. and 

 Mrs. G. W. Peckham of Milwaukee, Wis.; Dr. William Trelease, Director 

 of the Missouri Botanical Garden'; Dr. Henry Skinner, as editor of " En- 

 tomological News"; and the editors of "The American Naturalist." 



Acknowledgments are further due to the Boston Society of Natural 

 History, the American Philosophical Society and the Academy of Science 

 of St. Louis. 



Courteous permission to use certain figures was given also by The 

 Macmillan Co.; Henry Holt & Co.; Ginn & Co.; Prof. Carl Chun of 

 Leipzig; F. Dummler of Berlin, publisher of Kolbe's Einfiihrung; and 

 Gustav Fischer of Jena, publisher of Hertwig's Lehrbuch and Lang's 

 Lehrbuch. 



In the revised edition much new matter has been added ; particularly, 

 an entire chapter on the transmission of diseases by insects. A few new 

 illustrations have been introduced and several of the old figures improved. 

 The bibliography has been increased by the addition of about one hun- 

 dred titles of important works. 



