tine posterior part of the disc retains very inconsequential remnants of the 

 clampsT their chitinous parts acquire even greater similarity with the 6- 

 suckered forms, basically in contrast to the first family. This process 

 is especially advanced in Paradiclybothrium in which, as is known, the 

 posterior part of the disc almost does not develop and the entire disc has 

 a distinct appearance of 6-clamped or rather of the 6-suckered one. An 

 analogous process, it is true not extending very far, is observed also in 

 Hexostomatidae. But by chance the name of the order does not corre- 

 spond to the actual nunnber of the attaching clamps! Thus, with certain 

 differences in the processes of reduction, all 3 families acquire common 

 traits in the structure of the attaching disc and become similar to Poly- 

 stomatidae. This similarity already bears the nature of a more coarse p. 468 



convergence which, however, was utilized in the systems preceding ours for 

 the evaluation of the systematic status of Diclybothriidea. Let us remember 

 also that in Polystomatidae and Sphyranuridae, which represent the highest 

 link of development of Polyonchoinea, the ductus genito-intestinalis appears 

 completely independently as a result of special conditions of reproduction 

 similar to the ones of Oligonchoinea among which this characteristic is 

 peculiar to the entire group as a whole. 



There is still one more genus among the highest monogenetic 

 trematodes in which, for reasons completely unknown to us, one pair of 

 clamps is absent and this results again in converging similarity with the 

 above-mentioned families. This genus, Plectanocotyle , pertains to a 

 special family and what is especially interesting is that the genus Octo- 

 plectanocotyle , which is the closest to it and unusually close in structure, 

 has a completely normal development of the attaching apparatus and in 

 addition to that lives on the same host and is encountered in the same 

 location as Plectanocotyle . On the basis of the structure of both genera, 

 one may think that an insufficient development of the fourth pair of clamps 

 takes place in the latter. The opposite example of considerable growth of 

 the anterior pair of clamps among two genera independent of each other, 

 Anthocotyle and Pseudoanthocotyle was described by us with L. F. Nagibina 

 relatively recently (Bychowsky and Nagibina, 1954). 



Returning to the cases of progressive development of homologous 

 and homodynamic organs, one must consider one more example. 

 As was indicated before, the 4 normal pairs of clamps peculiar to the basic 

 mass of Oligonchoinea are developed on the base of the part of the edge hooks 

 which in corresponding cases enter differently into the composition of the 

 chitinous base of the clamp. Along with this, within the limits of Mazocraeidae 

 (Mazocraeidea ?, nobis) two groups, Microcotylidae and Gastrocotylidae, are 

 observed, in which a new progressive formation of another rOAv of pairs of 

 clamps takes place. The fact that this is a new formation was correctly 

 indicated by V. A. Dogiel in his work on oligomerization (Dogiel, 1954a). 

 Nevertheless, all the clamps of these worms are homodynamic and homo- 

 nymous to each other and to the clamps of the remaining Mazocraeidae 



561 



