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BIOLOGY 



!. IBRARY 

 G 



COPYRIGHT. 



First Edition, 1891. 



Second Edition, Revised, 1893- 



Third Edition, Revised and Enlarged, 1897. 



Reprinted, 1898, 1900, 1901, 1905. '97 i99. 



1911, 19141 i9 20 - 





