Perciformes, which thus are their basic hosts. In addition to that, separate 

 representatives of this family of monogenetic trematodes, which is the 

 largest in volume, are encountered on nine orders of fishes which have no 

 genetic links with each other or with both of the above-mentioned orders 

 or which have genetic relations with them. 



Let us summarize everything that has been said before about 

 the occurrence of families of Monogenoidea on orders of fishes. 



1. The occurrence either on one order of fishes or on several „ 278 

 orders which, however, are genetically linked with each other, is charac- 

 teristic for 21 families of Monogenoidea (Amphibdellatidae, Anthocotylidae, 

 Bothitrematidae, Chimaericolidae, Diclybothriidae, Diclidophoridae, 

 Diplectanidae, Dionchidae, Gastrocotylidae, Hexabothriidae, Hexostomatidae, 

 Loimoidae, Mazocraeidae, Microbothriidae, Microcotylidae, Monocotylidae, 

 Plectanocotylidae, Protogyrodactylidae, Protomicrocotylidae, Tetraonchidae 

 and Tetraonchoididae). 



I 



If one does not take into consideration the data about the single finding 

 on Clupeiformes (see page 275 ). 



2. The parasitizing on one order of fishes, or as a single 

 exception on a second order not related to the first, is characteristic for 

 one family (Acanthocotylidae). 



3. The finding on a group of related orders in a large majority 

 of genera and species and also a normal parasitizing in a small number of species 

 and genera on nvo orders not related to each other or to tlie first group is charac- 

 teristic for one family (Capsalidae). 



4. Parasitizing two orders of fishes which have no genetic 



links, is characteristic for two families Discocotylidae and Calceostomatidae. 



5. The occurrence on many orders of fishes, related as well as 

 unrelated with each other, is characteristic for two families (Dactylogyridae 

 and Gyrodactylidae). 



Thus, it becomes clear that of 27 families of Monogenoidea, 

 for 23 generally the presence of normal links between the character of 

 their occurrence andftie phylogenetic interrelations of the host is typical, 

 and this was not observed only in four ot them. The reasons for the latter 

 lie, as we shall attempt to show later, in that part of these families are 

 artifical on the one hand and on the other that here appear other causal 

 relationships. 



318 



