ACKNOWLEDGMENTS 



We are indebted to the American publishers of the following 

 books or periodicals for permission to use figures or other illustrations 

 which are reproduced in this book. In a few cases these have been 

 slightly modified by the contributors. Also we are under obligation to 

 numerous foreign publishers who, for obvious reasons, we have been 

 unable to ask for permission. 



American Journal of Hygiene 



Figures 188, 191, 192 

 Biological Bulletin 



Figures 5, 10, 13, 74, 81, 82, 84, 96, 104, 181, 183, 185, 186, 187, 

 199A, 199B, 223 

 Biology of the Protozoa by G. N. Calkins, 1933. Lea and Febiger Co. 



Figures 1, 2, 3 A, 3B, 9 

 Genetics 



Figures 166, 168 

 Journal of Animal Behavior, Henry Holt and Co. 



Figure 103 

 Journal of Cellular and Comparative Physiology, Wistar Institute 



of Anatomy and Biology 



Figures 119, 120, 121, 122, and Table 2 

 Journal of the Elisha Mitchell Scientific Society 



Figures 202A, 202B 



Journal of Experimental Medicine, Rockefeller Institute for Medical 



Research 



Figures 189, 190 

 Journal of Experimental Zoology, Wistar Institute of Anatomy and 



Biology 



Figures 14, 94, 97, 98, 102, 105, 106, 149, 156, 162, 164, 179, 182 

 Journal of Morphology, Wistar Institute of Anatomy and Biology 



Figures 83, 91, 93, 154, 157, 160, l6l, 163 



