A favorite saying of Jean Baer is that textbooks perpetuate errors by copying them 

 from one to another. I have tried to avoid this by going to the original papers as much 

 as possible, but in so doing I may well have introduced some errors of my own. I should 

 appreciate having these called to my attention also. 



Papers are appearing so fast that, unless one is forced to it, he cannot take the 

 time to read and ponder those outside his own immediate field of interest and to try to 

 integrate them into a coherent whole. Writing this book has made me do so, and the 

 process has taught me a great deal. Not only have I learned many things which I did not 

 know, but I have come to realize more clearly how much information we still lack, even 

 about parasites which have been studied extensively. This book reflects that situation. 

 The reader will find at least one question, one gap in our knowledge on each page. Each 

 is a challenge for future research which I hope will be accepted by many who read this 

 book. 



I should like to express appreciation to Drs. Carl A. Brandly, John O. Corliss, 

 William R. Horsfall, Francis J. Kruidenier, R. N. Mohan and Miss Virginia Ivens for 

 reading and commenting on various chapters; to Mrs. Helen V. Olson for preparing fig- 

 ures 6, 13A, 18, 19, 20K-1, 24 and 31; to Miss Ada Price for typing the greatest part of 

 the manuscript; to Mesdames Marion Corzine, Mardell Harris, Kathryn Hill, Janet 

 Manning, Lucille Rice, Carolyn Seets and Misses Eileen Bourgois and Beverly Seward 

 for proof-reading the manuscript; to Drs. E. R. Becker, J. F. Christensen, H. Christl, 



F. P. Filice, D. M. Hammond, C. A. Hoare, R. R. Kudo, J. Ludvik, E. R. Noble, 



G. A. Noble, Muriel Robertson, R. M. Stabler, E. E. Tyzzer and D. H. Wenrich, to 

 Balliere, Tindall & Cox, Cambridge University Press, Charles C Thomas, the Common- 

 wealth Agricultural Bureaux, Gustav Fischer Verlag, Iowa State University Press, Johns 

 Hopkins Press, Springer-Verlag, University of California Press, Williams & Wilkins Co. 

 and The Wistar Institute, and to the Annals of Tropical Medicine and Parasitology, Iowa 

 State Journal of Science, Journal of Morphology, Journal of Parasitology, Journal of 

 Protozoology, Parasitology, Quarterly Journal of Microscopic Science, Quarterly Re- 

 view of Biology, University of California Publications in Zoology, Veterinary Reviews 

 and Annotations, Zeitschrift fur Parasitenkunde, and Zentralblatt fur Bakteriologie for 

 permission to reproduce some of their illustrations; and, not the least, to the Burgess 

 Publishing Company for its patience and understanding during the time this manuscript 

 was in preparation. 



NORMAN D. LEVINE 



University of Illinois 

 Urbana 

 November, 1960 



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