G. D. Hanna, H. H, Haskir., J. W- Hedgpeth, A. E. Hopkins, H. J. Humm, 

 C. E Jenner, Mrs. van der Feen -van Benthem Jutting, P. Korringa, C E 

 Lindsay, V. L. Loosanoff, G. R. Lunz, I. D. Marriage, J. L. McHugh, M, N. 

 Mistakidis, J. R Nelson, T. C Nelson, H. G. Orcutt, HA. Pilsbry, L. R. 

 Pomeroy, H. G. Richards, J. E. Rogers, LA. Stauber, andD. E Wallace. 

 My sincere thanks are extended to them . 



My genuine appreciation is expressed to J D. Andrews, A. F. Chestnut, 

 J B. Engle, H. A. Cole, H. H, Haskir, V. L. Loosanoff, J. L. McHugh, J. R. 

 Nelson T , C . Nelson, P . S . Galtsoff, L . A . Stauber, and B H . Willier for 

 generously checking the entire manuscript of this paper, in particular for errors 

 and misinterpretations of data. All commentary has been written by the author. 



Library research for this paper was performed in the libraries of Rutgers 

 University, Princeton University, the American Museum of Natural History, and 

 the University of North Carolina at Chapel Hill . May I acknowledge with thanks 

 the genial cooperation of the staffs in these libraries . A preliminary draft of this 

 review was prepared while I was a member of the Department of Zoology, Rutgers 

 University, New Brunswick, New Jersey. Final writing and revision and publishing 

 was accomplished after I joined the staff of the Department of Zoology, University 

 of North Carolina, Chapel Hill, North Carolina . I acknowledge my appreciation 

 to both institutions for the many courtesies extended to me during the long prepara- 

 tion of this monograph . 



What measure of accuracy and completeness this synthesis attains is in 

 large part the product of the cooperation which has been extended so generously by 

 so many. It is a pleasure to acknowledge this support. 



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