Fifteen families reinain unstudied- -Protogyrodactylidae, 

 Monocotylidae , Loimoidae, Dionchidae, Microbothriidae, Acanthocotylidae, 

 Amphibdellatidae , Bothitrematidae , Hexabothriidae , Chimaericolidae, 

 Hexostomatidae , Anthocotylidae , Plectanocotylidae, Protomicrocotylidae, 

 and Gastrocotylidae. 



The study of representatives of these families is a problenn of 

 first priority and above all Microbothriidae, Bothitrematidae, Hexabothriidae 

 and Hexostomatidae should be studied because their location in the system is 

 doubtful and information about larval stages must play a deciding role in 

 the final elucidation of this question. 



Because the number of unstudied families is larger than those 

 studied, it appears at first sight that it is premature to make generalizing 

 conclusions; however, this is not true, inasmuch as we can also judge the 

 structure of the larvae in the majority of the unstudied families from the 

 existing data. We cannot expect principal differences among the larvae of 

 Protogyrodactylidae and Dactylogyridae,and (judging by, nobis) the structure 

 of the adults we can say with great accuracy what the larvae must be in this 

 aberrant family. The same can be said about Monocotylidae, Loimoidae 

 and Dionchidae, the larvae of which must be very close to those of Capsalidae, 

 The structure of the larvae of Acanthocotylidae is clear, because the adult 

 individuals have an unchanged larval disc. The larvae of Amphibdellatidae 

 and Tetraonchidae are undoubtedly very close. There are no special doubts^ 

 either about the larvae of Anthocotylidae, Plectanocotylidae, Protomicro- 

 cotylidae, or Gastrocotylidae because the structure of the adult indi- 

 viduals provides the basis for a sufficiently precise idea about the nature 

 of their larvae. In such a fashion the material which exists on the subject 

 of the development of the 13 families gives fully sufficient data for the 

 general representation about the larval stages of the overwhelming majority 

 of Monogenoidea. It is understandable that separate details of the structure p. 96 

 remain unknown, but this concerns mainly the secondary peculiarities from 

 the point of view of the analysis of the phylogeny of the group. 



All the data on the subject of the development of separate species 

 are placed by us into a separate appendix (pages 138 to 216 ) to which we 

 refer those who are interested. Here is expressed only generalized material 

 about the character and peculiarities of the postembryonic period and the 

 development of monogenetic trematodes. 



The presence of the free -swimming larva equipped with a 

 c iliated covering is characteristic for all Monogenoidea. Representatives 

 of Gyrodactylidae appear as exceptions, inasmuch as they are viviparous. 

 We consider the data of Alvey (Alvey, 1936) about the absence of the ciliated 

 coverings among free-swimming larvae of Sphyranura oligorchis Alvey as 

 erroneous (see page 192). 



97 



