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^ ACKNOWLEDGMENTS 



The studies upon which this thesis is based have been prosecuted 

 under the direction of Professor S. x\. Forbes and Professor J. W. 

 Folsoni, the "Biological Studies" having been carried on under the 

 direction of the former and the "Embryological Studies" under the di- 

 rection of the latter. To both Professor Forbes and Professor Folsom, 

 my sincerest thanks are due for their advice, encouragement, and as- 

 sistance throughout the progress of the work. I wish also to acknowl- 

 edge the aid of Mr. W. C. Matthews and Mr. Alvah Peterson in the 

 preparation of the drawings. 



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ILLINOIS LIBRARY 



nr UK'HANA CHAMPAIGN 



