trips. The final processing of the drawings was made by the brigade of artists 

 of the Zoological Institute, primarily by N. Liahovi and E. D. Samenskia. 



I beg all my friends who cooperated in my work to accept my heart- 

 felt gratitude. 



All the drawings which illustrate the present work were nriade from 

 the ventral views of the whole mounts of the worms. The exceptions are de- 

 scribed in the legends. Borrowed drawings are acknowledged with references 

 to the author and the year of publication. The references to location of hosts 

 of monogenetic trematodes are made in the legends of the drawings to permit 

 verification of the correctness of classification, and also in this connection 

 because many of these references will widen the scope of the information 

 about the widespread locations of the hosts of the different types of parasites. 



The work was completed in December 1955, and all the literature 

 available to me which had been published up to the middle of 1955 was utilized 

 for it. Unfortunately, certain important works were known to me only by 

 abstracts. Likewise, I was unable to include those papers which appeared 

 during the year and a half which passed from the time of completion to the 

 time of publication. In doing so I missed a certain number of references 

 which cited new data concerning the distribution and biology of monogenetic 

 trematodes, and also which described certain new types and species. The 

 inclusion of all of these references in the present work was impossible. 

 Comnnents on more important publications were added during the course 

 of reading the proofs, but only as special footnotes. Nevertheless, I believe 

 the existing irritating omissions will not seriously influence the basic con- 

 clusions. 



B. Bychowsky 



XVI 



