170 Transactions of the South African Philosophical Society. 



The blood flowed away from each side of the lophophore. from the 

 right by a vessel which passed round by the oral region and joined 

 that from the left to form the large vessel on the left side of the 

 descending limb of the alimentary canal. In all these there was 

 observed to be an almost continuous stream of blood downwards 

 away from the lophophoral region. 



As in some other species, the efferent vessel at a little distance 

 from the lophophoral region gives off a number of blind vessels into 

 the body cavity. These were occasionally very distinctly seen in the 

 living animal, and were then observed to be contractile, receiving 

 blood from the main vessel and expelling it exactly as in the case of 

 the tentacular vessels. 



The tentacular vessels apparently expelled the blood by con- 

 traction. It would be difficult to say if the circular vessels were 

 contractile. The vessels by which the blood leaves the lophophoral 

 region were not contractile (i.e., the vessel on the left side of the 

 alimentary canal and its two branches). 



The centrally placed vessel between the ascending and descending 

 limbs of the alimentary tract showed, however, a very marked con- 

 traction from below upwards. This was observed to occur, always 

 in the same direction, through the entire course of so much of the 

 vessel as could be seen (sometimes 10 mm.) under normal conditions, 

 without removing the animal from its tube, in which case the move- 

 ment was abnormal. A large volume of blood (corpuscles and 

 plasma) was seen to be thus conveyed to the lophophoral region 

 and to pass to either side by two short branches of the main vessel. 

 Each of these branches opened directly into a vessel which seems 

 capable of great expansion, and is lodged in a cavity of the lopho- 

 phore very apparent in section. The blood passed into the tentacles 

 in its immediate neighbourhood, and to the tentacles further removed 

 by the circular vessels. There was no evidence of any true circula- 

 tion through the tentacles nor of circular distributing and recipient 

 vessels, the whole of the blood-vessels of the lophophoral region 

 being merely a complex form of the simple blind vascular diverticula 

 seen on the large vessel within the body. The greater part of the 

 stream of blood thus never entered the tentacles, but passed on 

 directly to the two branches of the efferent vessel which joined 

 each other to form the single vessel situated in the left side of the 

 descending limb of the alimentary canal. There was thus a true 

 circulation, the blood being driven forward by a vessel lying over 

 what in Phoronis corresponds to the dorsal aspect of the alimentary 

 canal. On reaching the anterior end it passes by two vessels round 

 the alimentary canal (cf. the "hearts" of annelids) which join to- 



