lie in the fact that within the linnits of the orders of Monogenoidea the 

 evolutionary process took place in two ways--by way of a greater and 

 greater specialization and of the breaking in with the adaptation toward 

 parasitizing the sanne host during the period of prolonged existence of the 

 parasite on the given, little -changing host and by way of a relatively rapid 

 species and genus formation during the location of the parasite on quickly 

 evolving progressive groups. In the last type of evolutionary process that p. 462 

 height of organization which was peculiar to the ancestral forms as a rule 

 is preserved and the important morphological structures are not touched, 

 whereas in the first type a slow change and transformation into the form 

 sharply different fronn the initial ancestral organism takes place as has 

 been indicated. If the second group of evolutionary changes does not provoke 

 special doubts and corresponds sufficiently distinctly to the ideoadaptations, in 

 the understanding of A. N. Severtsov (1922b, 1925), then the first cannot 

 be evaluated either as an ideoadaptation or as an aromorphosis,but represents 

 something different. We shall note preliminarily, so as not to come back 

 to the aromorphoses, that the latter undoubtedly take place in the evolution 

 of Monogenoidea and by them one can explain both the appearance of new 

 orders and of new families, which in the vast majority of cases, and 

 especially in the lowest Monogenoidea, sharply differ from each other by 

 the degree of sophistication of the organization and the origin of new pro- 

 gressive peculiarities. 



The fact that the gradual qualitative change in the organization 

 of the first type of parasite does not represent an ideoadaptation is fully 

 apparent from the fact that in this process takes place not a mere change 

 but a considerable elevation of the life and morphological level which is 

 characteristic for aromorphous changes. However, this is not aromorphosis 

 in the pure state, for rapid reconstructions of the organization under the 

 influence of sharp changes in the condition of existence are characteristic 

 for the latter, a circumstance which is absent in our case. However, the 

 very fact of the presence of such changes demands considerable supple- 

 mentary confirmation. For that reason, let us permit ourselves to depart 

 from our basic theme and dwell on certain general questions. 



It is commonly accepted at the present time that the process of 

 species formation bears an adaptive character and takes place as a result 

 of interrelations between the exterior and the interior factors of development 

 in which selection plays an important role in the formation of the new. How- 

 ever, if this is basically accepted by all, when it comes to the evaluation 

 of the meaning of the separate factors, the opinions sharply diverge. Hence 

 the exaggeration of the role of one of the factors and the unde revaluation of 

 the rest or even practically their denial. We are inclined, however, to think 

 that for the correct evaluation of each factor one must pay greater attention 

 to the organism as a morphophysiological whole and not to its separate 

 structures which represent it neither separately nor totally. 



554 



