The Authors 



ELSBETH KROEBER is First Assistant in Biological Science; Adminis- 

 trative Assistant at the Midwood High School, Brooklyn, New York. She 

 was formerly Chairman of the Department of Biology^ at James Madison 

 High School, Brooklyn, New York. 



WALTER H. WOLFF is Principal of the William CuUen Bryant High 

 School, Queens, New York. Among his former positions are the follow- 

 ing: Instructor, School of Education, The City College, College of the 

 City of New York, and Chairman of the Department of Biology and 

 General Science, DeWitt Clinton High School, Bronx, New York. 



THE ILLUSTRATIONS 



The cover design for this book was executed by Richard Bartlett from a 

 drawing by W. A. Dwiggins, the frontispiece and title page ^^'ere painted 

 by Else Bostelmann, the text drawings were made by Paul Wenck and 

 Joseph Lenhard, and the diagrams by iMagnuson and Vincent. The photo- 

 graphs reproduced in the text are acknowledged where they occur. The 

 montage on page z was assembled with the professional assistance of 

 Marion Howe. 



Copyright, /(}-^S, Kjyo by D. C. Heath and Company 



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