FRESH-WATER 

 BIOLOGY 



BY 



HENRY BALDWIN ^[ARD, PH.D. 



PROFESSOR OF ZOOLOGY IN THE UNIVERSITY OF ILLINOIS, SPECIAL INVESTIGATOR 

 FOR THE UNITED STATES BUREAU OF ^FISHERIES, ETC. 



AND 



GEORGE CHANDLER WHIFFLE 



PROFESSOR OF SANITARY ENGINEERING IN HARVARD UNIVERSITY AND THE 

 MASSACHUSETTS INSTITUTE OF TECHNOLOGY 



WITH THE COLLABORATION OF A STAFF 

 OF SPECIALISTS 



FIRST EDITION 



NEW YORK 



JOHN WILEY & SONS, INC. 



LONDON: CHAPMAN & HALL, LIMITED 



1918 



