(Mazocraeidea ? , nobis). However, the numerous consecutive inceptions 

 of the clamps takes place independently of each other in both families, for 

 Gastrocotylidae, as is apparent from the phylogenetic diagram, descends 

 from Plectanocotylidae, and Microcotylidae from the ancestors of Disco- 

 cotylidae--Anthocotylidae. Exceedingly interesting was the discovery of 

 the representatives of the new genus ^ on the flying fish Prognicthis agoo 



1 ~~~ 



The description of this genus and the elaboration of its systematic status 

 will be given in a special work. 



(Schleg. ) during the expedition on the Vityaz in 1955 in the Pacific Ocean 

 which is close to the typical Diclidophoridae in its structure but has an 

 attaching disc equipped not with eight clamps, as is characteristic for the 

 present family, but with 18. Thus, the tendency toward the new formation 

 of a larger number of clamps appears within the limits of one more branch 

 of Mazocraeidae (Mazocraeidea?, nobis ), again completely independently 

 of both preceding cases. 



Drawing certain conclusions about the questions under consider- 

 ation concerning convergent sinnilarities within the limits of the group of 

 monogenetic trematodes we can note that, in the first place, only those 

 cases have undoubtedly phylogenetic significance where convergencies arise 

 within the limits of homologous and homonymous structures, and in the 

 second place the appearance of convergent peculiarities of characteristics 

 in closely related groups leads to wide parallelism which is conditioned p. 469 



both by common conditions of existence as well as the internal potentialities 

 for the development of specific structures. It seems to us that the study of 

 the convergencies, in the wide sense of this phenomenon, and especially 

 the study of parallelisms must give very valuable and important results 

 both in the study of phylogeny of separate groups of animals and in the under- 

 standing of common principles of the evolutionary process. The materials 

 which have been expressed above, it seems to us, give certain support to 

 the present conclusions. 



In closing we must underline that a whole number of our opinions 

 demand further refinement and corrections. Nevertheless, we think that the 

 basic traits of the proposed phylogenetic schenie and the evaluation of 

 phylogenetic tendencies in Monogenoidea will remain relatively unchanged in 

 the future. 



562 



