majority they are arranged one after the other, 

 of the uterus is similar to that of the oviduct. 



The histological structure 



For the convenience of description the structure of the eggs is 

 described in the chapter on embryology (Fig. 89). The only viviparous 

 family, Gyrodactylidae, sharply distinguishes itself from all other Mono- 

 genoidea by the structure of the female sex system. The most stuffied sex 



system is that of Gyrodactylus 

 (Fig. 12). This genus is charac- 

 terized by presence of the ovo- 

 vitellaria C'Keimdotterstock" of 

 the German authors) and the 

 absence of vitelline glands. Also 

 in connection with this, the egg 

 cells of Gyrodactylus, in con- 

 trast to all other nnonogenetic 

 trematodes, are fairly richly 

 supplied with yolk although the 

 feeding of the embryo which is 

 developing within the uterus takes 

 place apparently basically by way 

 of the liquid alimentary substances 

 which penetrate from the body of 

 the wornn into the uterus. Besides 

 the indicated peculiarities , among 

 Gyrodactylus the vaginal and genito- 

 intestinal canals are also absent. 

 Undoubtedly the simplified structure 

 of the sex System of these species 

 is a secondary phenomenon and 

 even the presence of the "ovo- 

 vitellaria" which often occurs 

 among Turbellaria, should not be 

 considered as a primary primitive 

 peculiarity. 



Fig. 107. Chimaericola leptogaster 

 (Leuckart), diagram of the structure 

 of the sex system (According to Brink- 

 mann, 1942). 



In conclusion, it is neces- 

 sary to note with regret that the 

 level of the morphological study of monogenetic trematodes is still very low 

 which undoubtedly hampers attempts at formulating a system to a signifi- 

 cant measure. 



70 



