328 



TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



2. The Supra-intestinal Vessel is always attached to 

 the dorsal wall of the intestine, and is invested by a layer 

 of chloragogen cells continuous with those which form 

 the outermost layer of the intestinal wall (PL III, 

 fig. 9, si.v.). It originates in segment 5 as an offshoot of 

 the dorsal vessel which lies above it, and it extends 

 through the body to a short distance behind the segments 

 containing the reproductive organs. Nomura (1913) 

 states that w Limnodrilus gotoi this vessel opens into the 

 dorsal vessel again at the posterior part of the body. 

 Although I have carefully examined many serial sections, 

 I have not been able to find this second opening of the 

 supra-intestinal into the dorsal vessel in Tuhifex 

 rivulorum. The vessel seems rather to diminish gradually 

 in size, and finally to disappear. In those segments of the 

 mature worm which contain the reproductive organs, the 

 supra-intestinal vessel is slightly displaced and lies a 

 little to one side of the mid-dorsal line. This is probably 

 due to the pressure exerted by the reproductive organs on 

 the other organs in the body. 



Text-Fig. 1. Diagram of segments V — IX showing the positions of 

 the principal blood vessels with their connections in these segments. 

 d.v. dorsal vessel, si.v. supra-intestinal vessel, in. intestine, v.v. ventral 

 vessel, pv.v. perivisceral vessel, in. v. intestinal vessel, hi. heart. 



3. The Ventral Vessel extends through the whole 

 length of the body, and lies beneath the alimentary canal 

 between it and the nerve cord (PI. I, fig. 1, v.v.). It 



