(fortmtous, nobis) predisposing factors which actually were conditioned 

 historically. In this connection the expression of V. A. Dogiel about the 

 "potential" of parasites (Dogiel, 1947, page 62 ) is more correct. For 

 pleurocercoids of the broad tapeworna the presence of wide adaptive 

 peculiarities which resulted in (during, nobis) the process of evolution and 

 which allowed them to exploit many of the lowest coldblooded vertebrates as hosts, 

 or in other words that the process of adaptation of the larvae of the broad 

 tapeworm to the hosts was formed historically in such a way that it did not 

 lead to narrow specificity to determined hosts, is beyond any doubt. Con- 

 sequently, to speak about "fortuitous coincidence of peculiarities" in the 

 present case is completely incorrect. One can speak about chance of the 

 parasitizing of different hosts by pleurocercoids of the broad tapeworm but 

 not in making a medium (permanent?, nobis) of a certain organism as a 

 host, because this process, we repeat, is historically conditioned by the 

 diapason of adaptive peculiarities of the parasite (which do not develop 

 suddenly, but which were formed gradually earlier). The fact that the 

 given process in its present stage does not represent anything new is 

 substantiated by the retention of the morphobiological peculiarities of 



pleurocercoids without any changes. It is possible that later with the i 



establishment of relatively constant new links between tha "old" parasite 

 and the "new" host, new evolutionary potentials will also appear but this 

 is not observed in the present phase of the process. Thus, as "fortuitous" 

 appear not the factors which predispose (**) the parasite toward becoining 

 established in the host organism (here Bychowsky actually says, "by the I 



host, " nobis) , but the factors which determine this, and among them basically 

 the biocoenotic links between certain animals and conditions of the medium. ] 



Summarizing what has been said before, we think that the 

 research of E. N. Pavlovsky undoubtedly has a progressive significance 

 for the understanding of the process of the establishment (**) of the 

 parasite in the host organism; however, his conclusions demand further 

 reworking and, in certain cases, changes. 



Analyzing the process of the coming into being (**) of the bio- p. 289i 

 coenotic pair, host-parasite, one must draw attention to those sides of ! 



this problem which were not reflected by E. N. Pavlovsky. This, first of , 



all, is a question about ways and means of infection of the future host to i 



which, from our point of view, relatively little attention was allotted, | 



whereas for the analysis of the historical development of the inter- 

 relations, parasite-host, this question has paramount significance. 



A long tinne ago K. I Skriabin and R. S. Schultz (1931) pro- 

 posed to divide the parasitic worms into two groups on the basis of their , 

 penetration into the final host. To the first of these groups, which received 

 the name Geohelminths, they ascribed those worms which the host received 

 directly from the surrounding nnedium and, predominantly, they are parasites 

 which do not have intermediary hosts. To the second group, Biohelminths, 



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