We will return to the question of the origin of the fauna of 

 Monogenoidea and of their systematic groups (see further), and now we 

 must deal briefly with the data of the nature of the faunas of the nnono- 

 genetic trennatodes of separate orders of Teleostei represented in 

 Figure 265. This diagram represents a further deciphering of the 

 preceding one and gives us a number of important materials explaining p. 319 

 at the same time, that which has been expressed above. First of all it 

 distinctly shows that a number of orders of fishes does not have its own 

 independent fauna because on them are encountered only separate species 

 of genera of worms characteristic for these orders which have just trans- 

 ferred from the fishes of other orders. In a majority of the cases, how- 

 ever, we deal here with separated independent species which permits us 

 to speak about the beginning of the process of the formation of an in- 

 dependent fauna which at the present time descends from the contempo- 

 rary fauna of other orders. At the same time, let us note that when we 

 speak about contemporary faunas we mean, of course, not the present 

 historical nnoment but the Quarternary period and in separate cases 

 perhaps even the end of the Tertiary. To the orders of fishes having 

 precisely such faunas one should ascribe Echineiformes, Polynemi- 

 formes, Macruriformes, Ophiocephaliformes, Cyprinodontiformes, 

 Gasterosteiformes and Scopeliformes, i.e., 7 of 17 orders of 

 Teleostei, ^ on which monogenetic trematodes were discovered. Thus, 



_ 



Excepting Acipenseriformes. 



only 10 orders have their own independent faunas and the relations here 

 within the limits of separate orders are quite different. Thus, the 

 faunas of Monogenoidea of Beloniformes, Mugiliformes, Dactylopteri- 

 formes, Anguilliformes and Tetrodontiformes, even though they contain 

 independent genera and in some cases there are several of them, are 

 nevertheless secondary, deriving from the fauna peculiar to Perci- 

 formes and becoming independent in this fashion also relatively early, it is true 

 more likely at a more ancient time than the faunas of the first seven 

 orders. The situation is different with the other five orders. Along 

 with the groups which transferred to them from other orders of 

 Teleostei, they contain also the groups of different taxonomic significance 

 appearing on them primarily, which is clearly visible from the diagram 

 under study. At the same time , two orders, Pleuronectiformes and 

 Gadiformes, basically have faunas which clearly transferred to them 

 frona the Percifornnes and only an insignificant number of species is 

 primary for the given fishes. 



372 



