287] NORTH AMERICAN POLYSTOMIDAE—STUNKARD 



INTRODUCTION 



The knowledge of the trematodes of North America is very scanty. 

 Information at hand consists largely of brief and scattered papers and 

 comprehensive studies on the morphology of the larger groups are want- 

 ing. Such studies are needed as contributions to the knowledge of adult 

 forms, and it is apparent also that knowledge of the anatomy and tax- 

 onomy of the adult is demanded in the solution of life history problems. 



This paper contains the results of a study on the structure 

 and classification of North American representatives of the families 

 Polystomidae, Aspidcgastridae, and Paramphistomidae. Because of cer- 

 tain structural and developmental featnres these three families are of 

 particular interest and importance not only in the taxonomy but also in 

 the phylogeny of the trematodes. The Polystomidae differ from all other 

 known Heterocotylea in that they are endoparasitic ; the Aspidcgastri- 

 dae are both ectoparasitic and endoparasitic, develop both directly and 

 by means of an intermediate host, and in the adult condition are para- 

 sites of both vertebrates and molluscs ; while the Paramphistomidae are 

 the only forms retaining a primitive posterior sucker. These facts are 

 significant and it is probable that further study into the structure and 

 life history of these forms will throw considerable light on the general 

 problems of development and taxonomy of the trematodes. 



During the past three years the writer has made parasitological 

 examinations of over three hundred North American fresh-water turtles. 

 These comprise sixteen species collected from widely scattered localities. 

 For assistance in securing this material, grateful acknowledgments are 

 due Dr. N. A. Cobb of Washington, D. C, Professor A. W. Orcutt of 

 Denison University, Professor W. E. Burge of the University of 

 Illinois, Professor J. E. Ackert of Kansas State Agricultural College, 

 and Professor W. W. Cort of Macalester College. The material of 

 Alassostoma parvum was collected and turned over to me by Mr. T. B. 

 Magath. A type specimen of Polystoma coronatum Leidy from the U. S. 

 National Museum was placed at my disposal for study. The work was 

 begun at the suggestion of Professor Henry B. Ward and carried on 

 under his direction. Part of the material used in the investigation 

 came from his private collection, and for this material as well as for 

 criticisms and suggestions in the course of the work the writer wishes to 

 express his appreciation. 



