pattern in the distribution of separate species on their hosts. Specifically, 

 the representatives of the genus Dactylogyrus basically are en- 

 countered on one species of host or on the species of one genus, and if on 

 a second species of different genera, then the representatives of the latter 

 (host genera) can cross-breed (hybridize, nobis). This conclusion, which 

 was made on relatively small material, was later substantiated by more 

 detailed observations. The proposed generalization was accepted by a 

 number of researchers and is widely used in a number of theoretical 

 works (Knorre, 1937; Ass, 1939; Rubtzov, 1940; Kirchenblat, 1941; 

 Dogiel, 1947; Koratha, 1955a; and others). Very interesting data as well 

 as the considerations of the subject are found in the work of Nybelin 

 (Nybelin, 1936). Judging our work in 1933, he writes that in principle he 

 agrees with the theory proposed by Bychowsky and attempts to give it a 



_ 



To call the proposed generalization, which mainly bears a private 

 character a "theory" is at least an exaggeration; at best it deserves a 

 name of a rule as it is accepted in Russian literature. 



certain theoretical basis. His considerations can be briefly summed up 

 as follows. Since it is knov/n that the infection of fishes takes place 

 through the free -swimming larva, one must accept the fact that the 

 searches for the corresponding hosts are based in a positive haemotaxis 

 which apparently provokes albiginous (?, sic ) substances specific for 

 each species of fishes. For parasites which are encountered on only one 

 host bear only one positively haemotaxic substance determined for each 

 species of host, and for the ones encountered in two, three or more hosts, 

 two, three or more "related" substances act on the larva. In the opinion 

 of Nybelin this explanation refers not only to Monogenoidea but also to the 

 miracidia of digenetic trematodes and also to all parasitic worms the 

 larva of which actively seek their host. As will be apparent from what 

 follows, these considerations of Nybelin coincide with ours in considerable 

 measure (see page 289). Further, Nybelin establishes names for the 

 forms which are enumerated on the one, two, three or many hosts. He 

 proposes for them the terms, "monokapalisch, " "di--", "tri--," 

 "polykapalisch, " corresponding to the number of the hosts on which the 

 different species are encountered. These terms are hardly possible in 

 the Russian language. Our "one--, two--, three-hosted, and so forth, 

 parasites fully and distinctly replace the terms proposed by him. Nybelin 

 quite truthfully underscores that for the studies on the subject of con- 

 sanguinous relations of parasites and correspondingly their hosts, it is 

 necessary to have a very precise classification of both. Unfortunately, 

 he is also right saying that the old data are very often uncertain in this 

 respect. As is seen from the above-mentioned this refers also to many 

 contemporary materials in equal degree. Most interesting in the work of 

 Nybelin are the data about his examination of the hybrids between separate 



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