vi PREPACK 



portions of the text. The author desires to express his especial 

 indebtedness to his good friend, Mr. H. O. Hanson, for the 

 preparation of many of the illustrations; to Mr. W. A. Andrews, 

 for microscopical studies from which drawings have been made, 

 and to Miss Mary L. Williams, for the execution of many of the 

 studies. Special mention is also made of the author's indebted- 

 ness to the assistance and collaboration of his former pupils and 

 present associates, Drs. E. Altenburg and H. J. Muller. 



CARLTON C. CURTIS. 

 COLUMBIA UNIVERSITY, 

 Juiu-, 1914. 



