THE ANATOMY OF SCALIBREGMA INFLATUM. 261 



subintestinal sinuses situated one on each side of tlie ventral 

 groove of the intestine (figs. 14 — 16). These may be traced 

 from beliind forwards as far as the level of the fifteenth setfe, 

 then they taper rapidly and disappear. Anterior to this 

 point the stomacli receives blood only from the six median 

 vessels above referred to. In each segment, from the fifteenth 

 to the end of the body, a pair of vessels collecting blood from 

 the nephridia and setal sacs opens into the subintestinal 

 sinuses. 



On the walls of the stomach and first part of the intestine 

 there are numerous fine blood-streams, which carry blood 

 from the ventral portion of the gut into the dorsal vessel. 

 These are not distinguishable on the posterior part of the 

 intestine, as this portion of the gut is surrounded by a sinus, 

 by means of which blood is conveyed from the subintestinal 

 sinuses to the dorsal vessel. The Avhole of the blood in the 

 walls of the stomach and intestine is contained in sinuses; 

 the intestine, as seen in section, appears to be quite enclosed 

 in a blood-sinus. The subintestinal sinuses are somewhat 

 specialised parts of the general sinus. The dorsal vessel is 

 not distinct from the sinus in the posterior part of the animal, 

 but from the level of the twelfth setfe (i.e. a point a little 

 behind the blood-reservoir) it is distinct, and has a wall of 

 its own. 



In Areiiicola the blood in the walls of the stomach and 

 intestine is apparently contained in vessels in young speci- 

 mens, but in sinuses in old specimens (Gamble and Ash- 

 worth, 1900, p. 460) ; but even in the latter it is sometimes 

 difficult to determine whether the gastric plexus is formed of 

 vessels or sinuses. In Scali bregma the blood in the walls of 

 the stomach and intestine is certainly contained in sinuses, 

 which in the posterior part of the intestine are large. 



The body-wall and nerve-cord are very sparingly supplied 

 with blood. No vessels are distinguishable in the body-wall, 

 except in immediate proximity to the setal sacs, and these 

 vessels are few and small. 



The walls of the heart and blood-reservoir are very thin, 



