Dedicated to the memory of 



Professor Donald Walton Davis 



late Professor of Biology at the College of 

 William and Mary. His devotion to aca- 

 demic and scientific principles and his human 

 qualities represented a continuous inspiration 



(R. E. ALSTON). 



PRENTICE-HALL INTERNATIONAL, INC., London 

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© 1963 by Prentice-Hall, Inc., Englewood Cliffs, N.J. 



All rights reserved. No part of this book may be reproduced in any form, by mim- 

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Library of Congress Catalog Card Number: 63-14907 



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