fishes. Thus he examined 7 samples of Rutilis rutilis x Abramis brama 

 and in 5 cases discovered representatives of the genus Dactylogyrus, 

 8 samples of Scardinius erythropthalmus x Blicca bjberkna on 4 of which 

 appeared Dactylogyrus; three individuals of Abramis bram x Blicca p_ 237 



bjoerkna of which 2 were infected and finally one sannple of Rutilis rutilis 

 X Blicca bjoerkna on which there wasn't anything. The results obtained by 

 him are presented in Table 5 composed by us. Nybelin thinks that because 

 it is difficult to detect the identity of the parents of the hybrids the presen- 

 tation of parasitological data for this would have been very interesting. He 

 supposes that the finding of the parasites of one host on the hybrids would 

 give sufficient basis to the establishment of one of the parasitic forms 

 (parent species, nobis). Of all the one-hosted species encountered by him 

 on the on the hybrids he considers Dactylogyrus crucifer , D. nanus , D. 

 difformis, D. auriculatus, D. falcatus, D. cornu , and D. distinguendu s, 

 (as the only ones belonging to one host?, nobis). Evolving from this, he 

 analyses his findings and comes to the conclusion about the possibility of 

 utilizing Dactylogyrus for the determination of the parental forms of the 

 hybrids. In addition to that, he considers that the findings of Dacty logyrus, 

 which are peculiar to Abramis brama on Blicca bjoerkna are not correct and is the 

 result of a mistake- -a mistake for a Blicca bjoerkna o f the hybrid individuals very 

 similar to it which are actually mixtures between Abramis brama and Blicc a bjoerkna. The 

 analysis of Nybelin is undoubtedly interesting; however, as numerous 

 researchers have shown, ours just as those of collaborators of our labo- 

 ratory, he unfortunately was mistaken in the determination of one and 

 naany-hosted parasites, being carried away to excess in the direction of 

 a very strict adaptability of one species to one species of host. Neverthe- 

 less, the general trend of Nybelin seems to us to be completely truthful 

 and it seems fully justifiable to utilize peculiarities of the pattern of 

 parasitism displayed by the species of Dactylogyrus for determining the 

 parental forms of hybrid fishes. Thus for instance, the hybrid nature and p. 238 

 its origin in sample no. 8 in Table 5 is fully understood because of the 

 composition of the species of Dactylogyrus encountered on it. 



Coming back to the question concerning the occurrence of rep- 

 resentatives of the genus Dactylogyrus on fishes forming hybrids, one 

 must underscore that we are speaking here about viable hybrids, that is 

 about those which underline close phylogenetic relations of the hybridizing 

 fishes and which are related to different genera (Nikolukin, 1952). In 

 other words, the ability to form hybrids is only an indication of the con- 

 sanguinous relations of the host and the "rule" proposed by us can be 

 formulated in a much simpler fashion--separate representatives of the 

 genus Dactylogyrus are encountered either on one species of fishes or on 

 several belonging to different but closely related genera, as is evident 

 from the analysis which is conducted by us concerning the occurrence 

 of species of nnonogenetic trematodes. This condition can, with different 

 reservations which are, however, not numerous, be referred to all the 

 Monogenoidea and in this fashion it represents a reflection of more general 



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