

The apertures of the vaginal tracts are often complicated. 

 Thus, among a number of species they form sucker -shaped funnels or a con- 

 ven pad, very often instead of one opening there are a number of small ones, 

 forming in their combination so to speak a small grill (grid, nobis) as is 

 observed for instance in Polystoma integerrimum Froelich (Fig. 71). 

 Among many forms there is a special chitinous armature of the vaginal 

 aperture, as for instance among many Microcotylidae (Fig. 105). Finally, 

 among many of the lowest Monogenoidea the terminal portion, which is 

 sometimes a very significant part of the entire vaginal duct, has the shape, 

 of a small chitinous pipe or funnel (Fig. 106). 



OJmm 



Fig. 105. Microcotyle sp. 

 from the gills of Sebastodes 

 schlegeli (Hilg. ) from the 

 region of Yablochnoii 

 (Southern Sakhalin, Sea of 

 Japan). 



Fig. 106. Ancylodiscoides magnus Bychowsky 

 and Nagibina, from the gills of Silurus glanis 

 L. from the Delta of the River Volga. Chiti- 

 nous armature of the vaginal duct. 



The genito -intestinal canal (canalis genito-intestinalis) exists 

 in Polystomatidae, Sphyranuridae and all Oligonchoinea. In its structure 

 this duct is somewhat reminiscent of the vitelline glands and also equipped 

 with a ciliated epithelium and circular musculature, starts from the ovi- 

 duct and extends, having greater or less length, and because of this being 

 more or less curved, toward one of the intestinal trunks into which it 

 opens. Sometimes however, the canalis genito-intestinalis opens into one 

 of its transverse branches and not directly into the intestinal trunk. Among 

 Protogyrodactylidae one observes a very odd-shaped peculiarity in the 

 structure of the female sex system which appears as a distinguishing sign 

 of that family. According to the description of Johnston and Tiegs (Johnston 

 and Tiegs 1922), the vitellaria of these forms have a junction with the in- 

 testinal trunks near the anterior end of the body which can be designated 

 as the vitello-intestinal duct (canalis vitellario-intestinalis). This forma- 

 tion undoubtedly is completely unique and cannot be considered homologous 

 to any duct of the other Monogenoidea (see however page 360 ). 



p. 71 



67 



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