ootype must be designated as the female sex duct (ductus communis). Such 

 a division is much more satisfactory because of the fact that it can also be 

 applied to Rhabdocoela. In passing, we would also like to indicate that 

 among various groups the number of ducts entering the oviduct varies: 

 often the vaginal and genito-intestinal ducts or one of them can be absent. 



p. 67 



The vitelline ducts represent the most powerfully developed 

 part of the female sex system. These are the follicular glands; as a rule 

 there are two , less often one or three. They are usually powerfully 

 developed and occupy almost the entire body starting from the head end 

 and extending to the attaching disc, and often even extending into it; the 



vitellaria are located be- 

 tween the intestines, the 

 sex glands and the ducts 

 and alnnost completely dis- 

 place the parenchyma of 

 the body. When the vitellaria 

 are very strongly developed, 

 they unite along the median 

 line of the body in such a 

 way that they have the shape 

 of a single organ. However, 

 even in these cases the 

 double origin of the vitellaria 

 is easy to establish by the 

 presence of two efferent 

 vitelline ducts. The latter 

 emerge from each vitellar- 

 ium one by one starting on 

 the sides of the body; they 

 extend mostly along the 

 ventral side or more or 

 less close to the medial 

 line of the body and unite 

 into a common vitelline 

 duct which opens into the oviduct. Very often this unpaired or common 

 vitelline canal forms a widening --a vitelline reservoir along its extension. 

 The latter, however, for the most part does not reach significant dimensions. 



The vitellaria are arranged in similar fashion in all monogenetic 

 trematodes with a few exceptions. Thus, among Diplozoon, there is only 

 one vitelline gland and correspondingly one vitelline duct (Fig. 231) because 

 of the peculiar Structure of its sex system connected with the presence of 

 two worms grown together in its adult stage. This phenomenon is secondary. 

 In the odd genus Trivitellina (Protogyrodactylidae) the vitellaria are divided 

 into three groups of which each has its own independent vitelline duct, which 

 then unites into a common one (Fig. 99, see however, page 360). 



Fig. 99. Trivitellina subrotunda Johnston 

 and Tiegs, adult worm. Natural size 

 about 0. 2 mm. (According to Johnston 

 and Teigs, 1922). 



63 



