normalities (rules, norms, principles, see other interpretations on page 

 220 , nobis) which will be discussed later. However, taking into consider- 

 ation the wide ability for hybridization among Cyprinidae, which appear 

 to be the main hosts of Dactylogyrus , one cannot fail to recognize the 

 necessity of preserving this "rule" because in its initial form it can be 

 useful in some measure for the ichthyologists in their works on hybrid- 

 type fishes and for parasitologists during their evaluation of peculiarities 

 of infection of a determined circle of hosts within a particular region. 

 As a matter of fact, these questions extend beyond the limits of the problems 

 which interest us at the present time. Let us pass again to the factual 

 material. Of the 40 species of Dactylogyrus encountered on two or more 

 genera of one family of fishes, 30 are discovered on fishes of two genera 

 (24 species on two species; four--on three; and two species on four species 

 of fishes), two species each on three species of three genera of fishes 

 and finally eight species of Dactylogyrus each on a number of fishes be- 

 longing to four or more genera. Of the 24 species found on two species 

 of fishes of different genera, ten are encountered on fishes which pro- 

 duce hybrids [D actylogyrus crassus Kulwiec, D. falcatus Diesing, D. 

 alatus Linstow, D. haplogonus Bychowsky, D. parvus Wagener, D. 

 wunderi Bychowsky, D. zandti Bychowsky, D. grislaginis Alarotu, D. 

 gracilinneinatus Alarotu, D. acus (Mueller)]. 12 on fishes of genera very 

 close to each other which were not differentiated until recently (D. acutatus 

 Mueller, D. gussevi Achmerov, D. navicularis Gussew, D. gobioninum 

 Gussew, D. markewitschi Gussew, D, facetus Gussew, D. tendibulus 

 Gussew, D. rimsky-korsakowi Gussew, D. curvicirrus Achmerov, D. 

 parabramis Achmerow, D. palliatus Gussew, D. vancleavi Monaco and 

 Mizelle), and only the finding of two species causes certain perplexity. 

 The first of thena is D. megastoma Wagener- -it is indicated in the literature 

 on Rhodeus sericeus (Pall. ) and Blicca bjoerkna (L. ). The considerable 

 separation of these hosts forced us to doubt the correctness of these data. 

 During their verification it was clarified that in the first place D. megastoma 

 was found only by the author of this species and wasn't discovered by any- 

 one after him, and in the second place that the indication of its presence 

 on Blicca bjoerkna is based on the legend to the figure of the egg of D. 

 megastoma from the gills of Blicca bjoerkna (Wagener, 1857a, page 109 ). 

 In conclusion one can consider with large measure of probability that the 

 given species is encountered only on one host--Rhodeus sericeus. 



The second species--D. ramulosus Malewitskaja--is known 

 from numerous findings on the gills of Leuciscis idus (L. ) and is indicated 

 from Rutilis rutilis (L. ) fronn the single finding of several samples of p. 240 



worms on one sample of fish from the middle -flowing (mid-stream?, nobis) 

 of the river Tissa (Zakhvatkin, 1951). The latter indication undoubtedly 

 is erroneous and is based on an incorrect determination either of the host 

 or the parasite. We do not doubt this because many time s during the 

 verification of preparations by V. A. Zakhvatkin we became convinced 

 of the inaccuracies of his determinations. Thus, both species of Dactylogyrus 



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