Ill GENERAL SUMMARY 743 



Some of the conclusive observations on these problems can be made now and are 

 being made; others must await more specific direction l)y biological observation 

 at a higher level of organization. 



ACKNOWLEDGEMENTS 



The author gratefully acknowledges permission by Dr. J. Lee Kavanau and the 

 editors of J. Exptl. ^ool. and Exptl. Cell Research to use Figs. 2 and 3, and by 

 Dr. Philip Grant to use Fig. i . I wish also to express thanks to Dr. C. Albert Kind 

 and Dr. Arthur Chovnick for a critical reading of the manuscript and several 

 valuable suggestions. 



Lileralure p. 744 



