The vaginal duct can be present or absent. In a naajority of 

 cases it is a single duct starting from the oviduct, however, among many 

 forms we can observe two vaginal ducts emerging, not from the oviduct, 

 but from the vitelline ducts. 



p. 68 



The apertures of the vaginal ducts are variously located among 

 the different species (Fig. 101). Thus among Dactylogyridae , Tetraonchidae 

 and other lower monogenetic trematodes, if this duct exists, it is always 

 single and its opening lies either on the dorsal or ventral side or, most p. 



frequently, more or less laterally. Among the types studied by A, V. 

 Gussew "Dactylogyridae of the Hanka Lake" there is one species Dactylogyrus 

 obscurus Gussew, among which one can suppose the presence of two vaginae; 

 if this is so, then the secondary origin of this species is certain. 



69 



Fig. 102. Benedenia derzhavini (Layman), 

 left edge of the anterior end of the body 

 showing the common opening of the copula - 

 tory organ, uterus and vagina. Adult worm 

 from the gill chamber of Sebastodes schlegeli 

 (Hilg. ) from the region of Vladivostok (Sea 

 of Japan). 



Among the Mono- 

 cotylidae the vagina is single 

 with a ventral opening in a 

 number of forms, however, 

 it is divided into two ducts 

 which open independently. 

 Capsalidae either have a 

 single vagina or it is often 

 absent. Its opening is 

 located for the most part 

 laterally in the vicinity of 

 the sex atrium and often 

 it even opens into the 

 latter in the direct vicinity 

 of the penis and the opening 

 of the uterus (Fig. 102). 

 Among Microcothriidae the 

 vagina is single or double. 

 It is interesting that in the 

 bifurcated duct of Lepto- 

 bothrium pristiuri Gallien 

 (Fig. 103 ) both of its 

 apertures open into the 

 special organs of the sex 

 atrium. Acanthocotylidae 



and Gyrodactylidae do not 

 have vaginal ducts. As a rule they are also absent among Mazocraeidae 

 and Discocotylidae, and if they exist they are usually single. Among 

 Acanthocotylidae the openings are paired. It is noteworthy that in Acantho- 

 cotyle merlucci Beneden and Hesse there are two commisures uniting both 

 vaginal ducts (Fig. 104); such a peculiarity has not been noticed in any other 

 species of Monogenoidea. Annong Microcotylidae, Hexostomatidae, and 

 Polystomatidae the paired vaginae start from the vitelline ducts. They 



65 



