correlation between the male sex opening and the opening of the uterus in 

 Dionchidae (see page 372 ) is completely analogous to the one existing in 

 tapeworms. 



We consider the difference 

 in the structures of the copulatory 

 organ as an important difference be- 

 tween Monogenoidea and Cestoidea; 

 however, during the study of Dicly- 

 bothriidae we found that actually the 

 copulatory organ of these worms 

 should be evaluated more as a cirrus 

 than as a penis (Bychowsky and 

 Gussew, 1950), consequently the sharp 

 difference caused by this characteristic 

 between Monogenoidea and Cestoidea 

 s. str. is effaced. 



Fig. 315. Diagram of the corre- 

 lations of the classes of flatworms. 

 Microbothriidae are set apart to 

 show the problematic status of their 

 position. 



Relatively recently an in- 

 teresting study on Gyrocotylidae 

 (Lynch, 1945) was published. The 

 author studied the morphology of 

 these interesting animals in detail and in the section on taxonomic position 

 of genus Gyrocotyle indicates that they are undoubtedly close to monogenetic 

 trematodes, but that they can be ascribed to tapeworms only provisionally. 

 The author was not acquainted with our work which undoubtedly is interesting 

 on the one hand because Jiis conclusions are completely Independent, but on the 

 other hand this did not allow him to express a more definite judgment. 



Thus, newer research apparently confirms the idea advanced 

 by us about the great independence of Gyrocotylidae and their intermediary 

 position between Monogenoidea and Cestoidea more and more. At the same 

 time one cannot fail to note that their proximity to the first class perhaps 

 is considerably larger than to the second. 



In the analysis of the interrelations of parasitic flatworms, as 

 is known, we have attributed enormous deciding significance to the cerco- 

 mere and its chitinous armature. In 1952 A. V. Ivanov published a study on 

 Udonellidae, which was conducted by him at our suggestion for the establish- 

 ment of their position in the system of flatworms. As a result of very 

 meticulous analysis A. V. Ivanov clarifies that this group descended from 

 Turbellaria quite independently he separates it into a separate class. The 

 basic criterion for such a conclusion apparently was precisely the absence 

 in Udonellidae of a larva equipped with a cercomere and its chitinous 

 armature. Agreeing with the point of view advanced by us, A. V. Ivanov, 

 in the concluding part of his work, cites the diagram of phylogenetic relations 

 between the main groups of flatworms. This scheme is principally very p. 



477 



570 



