and descends to the ventral side only in the vicinity of the sex pore. As a 

 rule the senninal duct is single, however, in Paradiclybothrium pacificum, 

 described by us and A. V. Gussew there are two of them (Bychowsky and 

 Gussew, 1950). From the testis, starting at first along the ventral and 

 then closer to the dorsal side, emerge two ducts lying along the sides of 

 the body parallel to the intestinal trunks, now closer to the middle, now 

 directly over them, and in front they merge into one. The reasons for the 

 formation of two seminal ducts instead of one are not clear; however, there 

 is no doubt that this phenomenon is secondary and quite possibly connected 



nsuM 



Fig. 88. Octoplectanocotyle trichiuri Fig. 89. Protomicrocotyle pacifica 

 Yamaguti, adult worm (According to Meserve. (Combined from two 

 Yamaguti, 1937). drawings of Meserve, 1938). 



with the very powerful development of the uterus which, so to speak, 

 divides the middle part of the duct. 



The histological structure of the seminal ducts has been poorly 

 studied. They are sharply delineated from the parenchyma by a special 

 membrane toward the inside of which is located the epithelial layer with a 

 few rounded nuclei. Apparently, at least in a number of types, there also 

 exists a circular musculature independently under the membrane. This 

 can be observed in Polystoma integerrimum Froelich (Fig. 91) and in a 

 number of other forms, fresh water as well as marine. 



56 



