Chap. VII.] 



PL A TYHELMINTHES. 



249 



glandular, and these glands, we may suppose, act on 

 the contents of the blood-vessels which are richly 



distributed to the nephridium. 

 wider portion, the walls of 



are muscular, may be 



upon as 



The terminal and 



analogous to a 



which 



looked 



ureter. 



Bearing in mind that we 

 have in the earthworm to do 

 with a form in which meta- 

 meric segmentation is most 

 markedly expressed, and that 

 this metamerism has clearly 

 affected the nephridia, we are 

 prepared to find a very much 

 simpler condition of things 

 among the Platylielniintlies, 

 and, at the same time, to find an 

 arrangement which is more dif- 

 fused. InMonoccelis (Fig. 104), 

 for example, there is a plexus of 

 fine canals, which communicate, 

 on the one side, with large 

 principal canals, of which there 

 are two pairs, one external 

 and one internal, and on the 

 other with funnel-shaped pro- 

 cesses, the entrance to which is 

 guarded by a long cilium ; the 

 principal canals are connected 

 with one another by anastomo- 

 sing branches. In the Deii- 

 droccela, as represented by 

 Polycoelis, the fine canals appear to be absent. 



If we take the liver fluke as a type of the 

 TTrematoda, we again find that the system of 

 excretory vessels is diffused throughout the whole 



Fig. 103. A single Kephri- 

 dium of ;l?iac7iajtt(. 



a, Internal orifice, funnel- 

 shaped and surrounded by 

 cilia. It opens into one 

 segment, passes through 

 the septum () into the 

 next segment, and opens to 

 the exterior by e, external 

 oriflce. (After Vejdovsky.) 



