

NEW-WORLD SCIENCE SERIES 

 Edited by John W. Ritchie 



ZOOLOGY 



A TEXTBOOK 



FOR COLLEGES AND 



UNIVERSITIES 



BY 

 T. D. A. COCKERELL 



Professor of Zoology 

 University of Colorado 



ILLUSTR AT ED 



Yonkers-on-Hudson, New York 



WORLD BOOK COMPANY 



1920 



