A Guide To The Study 

 Fresh- Water Biology 



With Special Reference to Aquatic Insects and Other 

 Invertebrate Animals and Phyto-Plancton 



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By 



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James G. Needham, Ph.D. 



Professor of Limnology, Emeritus, in Cornell Univer. 



AND 



Paul R. Needham, Ph.D. 



Associate Biologist, U. S. Bureau of Fisheries 



FOURTH EDITION 

 Revised and Enlarged 



ITHACA • NEW YORK 

 COMSTOCK PUBLISHING COMPANY, INC. 



1941 



^BOSTON UNIV£K;::)mY 

 COLLEGE OF LIBERAL ARTS 



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