determined phases of the life cycle of the parasites to a determined circle 

 of hosts, " and in another place of this work--more briefly: "The adapta- 

 bility of the parasite to life only on a determined circle of hosts is called 

 specificity. " 



From our point of view, all the "new" definitions (in relation 

 to the definition of V. A. Dogiel) suffer from excessive "erudition" 

 (scholarship) and attempt to include such aspects which could successfully 

 be excluded as self-understood. We believe that whatever be the definition 

 of the meaning of specificity it should be considered as a potential aptitude 

 for determined relations with the host, or, in other words the ability 

 (aptitude) to exist on this host. We consciously underline the word "ability, " 

 contrasting it with the very fact of existence on or in a determined host. 

 As is well known, the transformation of the aptitude into reality is a 

 complex, contradictory process, taking place only in specific conditions. 

 Consequently one must consider that specificity is a potential possibility 

 toward definite correlations between the parasite and a certain circle of 

 hosts; whereas the realization of this possibility leads to the phenonnenon 

 observed in nature or experimentally--occurrence of the parasite on a 

 certain host. In other words, the occurrence of the parasite is the reali- 

 zation of its possibilities of existence on a given host under given concrete 

 historical conditions (which, as is self-evident, are determined by definite 

 ecological conditions). 



Let us show by an example the difference between specificity 

 and occurrence. Experiments on B. melleni (MacCallum) show that this 

 species is specific for (or, as he means by specificity, is actually limited 

 physiologically to, nobis) three orders--Beryciformes, Perciformes, and 

 Tetrodontiformes and in nature they are encountered only on a small 

 number of species of three families of Perciformes (see pages 223-225 ), 

 that is, the specificity of the given species is far from being fully realized. 

 We can cite a considerable number of examples of similar type but this is 

 hardly necessary as the basis for the difference between the definitions of 

 "specificity" and "occurrence" is quite clear from what has been said above. 



When we speak about "the ability of a parasite to exist, " under 

 this expression is given a whole number of aspects which are determined 

 by the existence of the animal and determining its existence. Just as any 

 ability toward existence of living organism it is also determined among the 

 parasites by an intricate complex of peculiarities which are historically 

 formed and hereditarially transmitted and arise under the influence of 

 internal and external factors which are in uninterrupted interaction with 

 each other. There isn't the slightest necessity to explain this complex 

 phenomenon in each separate case because it is understood by the very 

 word "existence, " and consequently to introduce the different aspects which 

 characterize the existence of the parasites into the definition of specificity 

 is unnecessary. For this reason it seems to us that "new" complex 



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