Fedotov hardly corresponds to reality. The attentive reader of the first 



part of our work, knowing the structure of digenetic trennatodes, can easily 



conclude that there are many more differences than similarities between 



Monogenoidea and Trematoda and in the first place in the most important 



systems of organs--nervous and sex. As regards the real similarity, they 



have a more general nature which embraces not only these two classes but 



also the remaining groups of flatworms, including the free-living ones. 



However, in addition to this, one must not base himself only on the nnorpho- 



logical structure of one mature phase of the development of animals inasmuch 



as the appearance of a number of similarities and differences which are 



caused by the conditions of existence of these phases is possible. A much p. 473 



greater significance should be attributed to larval phases and particularly 



to the entire life cycle. Comparing monogenetic and digenetic trematodes 



in this connection, one can be surprised, not by the fact that we divide 



these two groups, but that until very recently they were attributed to one 



class. 



Among contemporary Rhabdocoela, there are some species which 

 strikingly resemble monogenetic trematodes and others --digenetic, so that 

 one can say almost with certainty from which each descends. Reference to 

 digenetic trematodes with a simplified cycle of development, as for instance 

 Aspidogastridae also cannot be taken into consideration because this very 

 aberrant group has not yet been sufficiently studied, and their larval stages 

 are structurally very far from the larvae of monogenetic trematodes. Thus, 

 the independence of the origin of Monogenoidea and Trematoda, it is true 

 from ancestors very close to each other, cannot be subjected to serious 

 doubt, which is recognized at the present time by all researchers of flat- 

 worms. The second, and properly speaking, the basic moment of doubts of 

 D. N. Fedotov is actually a misunderstanding. He supposes that it is in- 

 admissible to consider Monogenoidea, a very specialized group (with which 

 we completely agree), as ancestors also of the very specialized tapeworms. 

 Such a formulation of the question seems to us fully justifiable but the present 

 conclusion does not follow at all from the text of our work, on the contrary 

 it completely contradicts it. According to our considerations the monogenetic 

 trematodes, just as the tapeworins, descend from common primitive mono- 

 genetic-like ancestors, which doesn't mean at all that Monogenoidea gave rise 

 to Cestoidea. 



Furthermore^ it seems strange to us that while recognizing more 

 or less the plausibility of our considerations about the connections between 

 Monogenoidea and Gyrocotyloidea, D. N. Fedotov considers it possible to 

 speak about the inadmissibility of comparison of the internal structure of 

 monogenetic trematodes and tapeworms. In the first place if one is to accept 

 that the divergence of both of these classes is sufficiently great then a 

 comparison of their internal organization should be considered only in very 

 general traits; and in the second, if there exists a group close on one hand 

 to one class and on the other --to another, it would be correct to draw 

 attention not to the links but to the 



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