ST?UDIES on the BCTOPAfeASITIC TREMATODES OF JAPAN. gg 



a vessel is given off on each side to the posterior part of the body and 

 the sucker (PI. XVII, fig. 2). Finally in Tristomum, the two main 

 vessels are much more separated from each other than in the other 

 genera ; and the larger vessel runs about midway between the in- 

 ternal and the external ventral nerve, and becomes continuous with 

 the smaller vessel a short distance in front of the posterior sucker. 

 Anteriorly the larger vessel becomes continuous at the base of the 

 terminal vessel (vesicle) already described with another vessel, which 

 proceeds anteriorly and unites with an exactly similar vessel of the 

 other side just in front of the pharynx on the dorsal side of the brain. 

 The median vessel thus constituted proceeds for a short distance for- 

 wards, and then divides right and left into two branches, the rami- 

 fications of which supply the anterior suckers and the anterior parts 

 of the body proper. 



From the two main excretory vessels above described, numerous 

 branches are given off at various points apparently without any 

 regularity. These branches divide again and again, and the smaller 

 branches anastomose variously with each other and with those coming 

 from the opposite side of the body. I have not been able to observe 

 the terminal funnels of the excretory capillaries in any of the marine 

 species I have hitherto studied. It should however be mentioned to 

 avoid misunderstanding that I have not as yet had as much op- 

 portunity for observing these funnels as I could wish ; and consider- 

 ing their wide distribution among the Plathelminthes, it is scarcely to 

 be doubted that they would be found also in all ectoparasitic 

 Trematodes. In Tristomum sinuatum, however, I have observed the 

 excretory capillaries form a close network just inside the muscular 

 layer of the body. So far as I have observed, the transition from the 

 capillaries to the ordinary excretory vessels does not seem to be so 

 sudden as in those forms whose excretory systems have been so 



