order and even more--of the genus (species) of fishes. For that reason 

 this case can be interpreted differently, but at any rate it would be more 

 correct to judge the occurrence of subspecies and not of the species as a 

 whole, especially since they could be considered species (which are, nobis) 

 close to each other. If we accept this, then the subspecies of G. arcuatus 

 do not form any exception from the general rule. As has already been 

 pointed out, A. manilensis is apparently encountered in artificial conditions p. 244 

 and not in nature, hence, it is difficult to speak about its natural occurrence. 

 It is possible that here takes place infection of unusual hosts sinailar to the 

 one which we have seen from Benedenia melleni (MacCallum), We cannot 

 fail to note that all the families of the hosts of this species are related in 

 some (true, farther removed) degree. As has already been pointed out, 

 the data about Trochopus tubiporus and Squalonchocotyle abbreviata provoke 

 great doubts and probably in both cases there must be a mistake. It is 

 possible that Heterocotyle minima actually is encountered only on Trigonidae 

 and the indication of its finding on the shark is erroneous; until the data of 

 Price are substantiated, it is difficult to solve this problem either way 

 convincingly. Finally, the data of MacCallum on Microcotyle pomacanthi 

 demand verification (as do the majority of his data on occurrence). If one 

 should consider that the indication of the finding of this species on Labridae 

 is faulty, then the remaining four families are close to each other as we 

 indicated. As a result, the data about the six species enumerated before 

 cause doubts to some degree and demand further substantiation and re- 

 examinations. Thus, only Calicotyle affinis, Pseudaxine indicana, and 

 Ancyrocephalus mogurndae are fully authenticated as occurring on un- 

 related species, that is, all in all, 0. 3% of the total number of the Mono- 

 genoidea. 



We examined the question about the occurrence of species of p. 245 



monogenetic trematodes on their hosts without taking into account the 

 quantitative side of the question, i.e. , without taking into consideration 

 the frequency of occurrence of any given species of parasite on any given 

 species of fishes, but nevertheless, the corresponding data substantiate 

 the established normalities (generalities or principles, see above, nobis) 

 (certain materials on this subject can be found in the preceding text. ), 

 One can consider that in the case of the occurrence of any species on a 

 number of hosts, it is encountered, as a rule, in a considerably greater per- 

 centage on one of them and the number of individual parasites on this 

 species of the host is more numerous than on all the others. This can be 

 illustrated by the following table based on our data with . V. A. Dogiel 

 and those of A. P. Markevlch (Table 6). From it we see that the percentage of 

 infection and the number of parasites in one "basic" host is immeasurably 

 larger than among others --the "secondary" host. Similarly the same can 

 be seen from the data of Hargis (Hargis, 1953) concerning the occurrence 

 of certain American monogenetic trematodes (Table 7). 



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