disc of Microbothriidae acts differently than the one among all remaining 

 Monogenoidea and represents a formation which serves for tight attach- 

 ment to the body of the host. The attaching disc among Udonella, which 

 was separated not long ago to an independent class of flatworms (Ivanov, 

 1952), has an analogous nature. This forces us to consider with great 

 doubt the systematic status of the Microbothriidae. However, this does p. 387 



not exhaust the peculiarities of the structure of this group. First of all, 

 the coverings of the body are singular. Thus, in our preparations it is 

 apparent that the cuticule has a very thin granular layer on its exterior 

 surface which stains unevenly. It is difficult to say because of relatively 

 poor fixation what the nature of this peculiarity is. A powerful layer of 

 circular musculature which covers the entire body of the animal from the 

 anterior end to the attaching disc without any interruptions is located under 

 and tightly against the cuticule. We do not encounter any single species of 

 monogenetic trematodes known to us which has such a distribution and 

 thickness of the layer of circular musculature. As regards the internal 

 organization and primarily the sex system, we do not observe any special 

 peculiarity here with the exception that the copulatory organ and the vagina 

 are equipped with a very powerful musculature which is very similar in 

 structure to the circular musculature of the coverings. On the whole the 

 sex system resembles the ones of the lowest monogenetic trematodes just 

 as in many straight-intestined Turbellaria. As regards other genera of 

 Microbothriidae we do not have any materials about their structure but 

 judging by the literary data they basically resemble Leptocotyle. The 

 isolation of Pseudocotyle into a special subfamily because of the presence 

 of numerous testes in this genus is hardly supported and this genus 

 apparently is very close to Microbothrium in which, although there is only 

 one gonad, the testis consists of numerous follicles which, although united 

 by a common connective tissue envelope, are separated from each other. 



All in all^we can doubt the fact that Microbothriidae is a group 

 belonging to the class of Monogenoidea. If subsequent research and primarily 

 the study of the development of embryology shows the absence of the 

 chitinous hooked armature of the attaching disc in all phases of development 

 one may be able to speak with certainty that it is an independent group 

 standing close to Rhabdocoela and perhaps even belonging to the order of 

 Turbellaria. If it appears that this is not so and Microbothriidae are 

 designated Monogenoidea then it will be more probable that they should be 

 ascribed to Monopisthocotylinea to which they bear the greatest resemblance. 

 Consequently until further studies we leave the present family in the group 

 indicated as it is done in all contemporary resumes'T 



463 



