In order to understand the nature of the distribution of the 

 Monogenoidea on their hosts correctly and to evaluate the degree of their 

 adaptability to the latter, we consider it useful to conduct an analysis of 

 the occurrence of monogenetic trenaatodes on their hosts, and first of 

 all, on the basic group--fishes. This analysis can be more easily con- 

 ducted, starting from the evaluation of the occurrence of the species of 

 Monogenoidea on the species and genera of their hosts--fishes, and only p. 220 

 then to transfer our attention to the characteristic correlation of larger 

 taxonomic units of parasites with the large systematic subdivisions of 

 their hosts. Such continuity will enable us to approach the question under 

 consideration, and will further help to show the existing normal relations. 



It is necessary to make a few preliminary remarks. The term 

 "occurrence" as used by us is adopted in order to underline the principle 

 difference between the natural distribution of parasites on their hosts 

 which is observed in nature, and those potential possibilities toward the 

 infection of "different" animals by parasites which can be discovered in 

 experimental conditions or during certain disruptions of the natural pro- 

 cess in nature (Pavlovsky, 1946). The term "specificity" so widely used 

 at the present time in all cases of finding the parasite only on one host in 

 nature without taking into consideration the repetition and of potential 

 possibilities of infection should, in our opinion, be used with great reserve. 

 Thus, we do not juxtapose occurrence with specificity but we consider that 

 it is inadvisable to place the sign of equality between these two phenomena 

 and that it is only the analysis of the nature of occurrence, as we shall 

 further attempt to demonstrate, that can lead to the establishment of the 

 degree, of specificity of various parasites in relation to their hosts. 



The data about all the known monogenetic trematodes up to 1953 and 

 certain supplemental data from recent times, serve as material for the composition 

 of the following chapters. Also, in spite of a number of their shortcomings, the resimies 

 of Sproston, (Sproston, 1946) and Price (Price, 1936-43) are basically used and they are 

 supplemented by subsequent works, particularly by Russian and American researchers. 

 Unfortunately, it Is difficult to take Into consideration a number of works for very dif- 

 ferent reasons, and thus undoubtedly there Is a certain amount of data which has not 

 been considered in our analysis, and because of this there are certain Inevitable gaps. 

 However, considering the total amount of factual data, the gaps are not so numerous, 

 and further supplements and corrections cannot alter the general picture of the nor- 

 malities (the dictionaries give normal, natural, law-governed, and, development in 

 conformity with natural laws, as equivalents of the root of this Russian word. Its 

 ending makes It a noun. We have translated it variously as generalization, principle, 

 normality or regularity, depending on the sentence. See Foreword, nobis) which are 

 obtained as a result of this analysis. 



240 



