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An elementary text book of fresh-water 

 biology for students 



By 

 JAMES G. NEEDHAM 



Professor of Limnology in Cornell University 

 and 



J. T. LLOYD 



Formerly, Instructor in Limnology in Cornell University 



SECOND EDITION 



1930 



CHARLES C THOMAS • PUBLISHER 



SPRINGFIELD, ILLINOIS BALTIMORE, MARYLAND 



