FRESH-WATER 

 BIOLOGY 



BY 



HENRY BALDWIN WARD, Ph.D. 



Professor of Zoology in the University of Illinois, Special Investigator 

 FOR THE United States Bureau of Fisheries, Etc. 



AND 



GEORGE CHANDLER WHIPPLE 



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 



