In conclusion, justaposing one group of facts with the other, we 

 obtained the possibility of establishing basic ways of the phylogenetic develop- 

 ment of the Monogenoidea. We believe, although numerous errors are 

 unavoidable, that, nevertheless, basically the constructed phylogenetic scheme 

 corresponds to all contemporary facts. Any attempt to build it otherwise 

 will inevitably lead to contradiction with one or the other of the groups of 

 facts mentioned above. Whether or not we were able to show this con- 

 vincingly is another matter>and we leave this to the readers to judge. 



In the process of research, we had to touch upon a number of 

 general questions along with those specific ones, Thus, during the discussion 

 of the conclusions in the chapter about occurrence the question about p, 480 



specificity is especially examined. We have attempted to show that speci- 

 ficity, although it is a more general phenomenon in relation to occurrence, 

 nevertheless the latter is not determined only by specificity but also by a 

 number of completely different biological factors. With such an approach 

 many phenomena connected with the process of the origin and evolution of 

 parasitism become understandable. Hence, a somewhat different evaluation 

 of the known "triad" of factors of the formation of the biocoenotic pair, 

 parasite-host, of E, N. Pavolosky; of the "triad" which as a whole is very 

 important for philosophical evaluation of correlations between the fortuitous 

 and the unavoidable in the process of evolution of parasitism. Further the 

 research on occurrence led us to the necessity of reexamination of the contemporary 

 evaluation of the so-called "law" of Fuhrmann and the reestabllshment of its correctness, 

 but only as a particular case of the relations between the occurrence of the 

 parasitic wornns with the phylogenetic links of the latter and the phylogenesis 

 of the hosts. Certain considerations, which seem to us not without interest, 

 are cited also in the chapter about phylogenetic parallelism, which in our 

 opinion can be determined only as a particular case of evolutionary changes 

 of the biocoenotic pair, parasite-host. 



During the analysis of the phylogenetic scheme of Monogenoidea 

 we were obliged to dwell on certain evolutionary questions and first of all 

 on tlie general directions of the evolutionary progress (Severtsov, 

 1939). Certain cases of the evolutionary development of Monogenoidea 

 cannot be included into the well-known directions by way of aromorphoses, 

 ideoadaptions and coenogenesis, and regress as our data show. To these 

 one must attribute the gradual, very sharp 



qualitative change of the organization of the parasite which accompanied a 

 considerable increase in the life level and morphological level, but without 

 rapid change of the conditions of its existence. In some measure these 

 changes can be compared with telomorphosis according to I. I. Schmalghauser 

 (1940 and 1946); however, this is a special type of evolution which demands 

 special study. 



The study of the processes of evolution of monogenetic trematodes 

 forced us also to turn our attention to the phenomenon of convergent simi- 



575 



