Kikk. — Heptatrema cirrata Forster. 243 



sinus is shown to communicate with the right jugular — indeed, to form 

 the anterior part of it; but there is no reason to suppose that that is 

 the case in Heptatrema. 



When the right jugular of Heptatrema gets as far back as the gill- 

 clefts its ventral position becomes more pronounced, as it has to pass 

 below the incurrent branchial tubes. After passing the posterior end 

 of the lingual mass it receives a vein that serves a considerable part of 

 that mass, especially the left side. This may be referred to as the 

 anterior lingual vein. There next enters a vein formed by the union 

 of a left jugular and another vein from the lingual mass. This latter 

 vein, which may be called the posterior lingual vein, is formed by two 

 veins, one from the lower and right portions of the mass, the other from 

 its upper portion. The left jugular vein is formed by two somewhat 

 slender parallel branches lying below the incurrent tubes of the left gill- 

 sacs. They unite T5 cm. before the posterior lingual vein is reached. 

 After the vein formed by the union of the left jugular and the posterior 

 lingual has entered, the combined jugular vein passes backward towards 

 the heart. It receives the inferior jugular, a median vessel of consider- 

 able size. This vein is itself formed by the union of two veins running 

 in the ventral body-wall below the lingual mass. After entry of the 

 inferior jugular the jugular trunk passes to the posterior end of the 

 sinus venosus, which it enters in close conjunction with the right hepatic 

 vein. 



Anterior Cardinal System. — The right anterior cardinal sinus starts 

 beside the notochord at the base of the cranium. It runs backward in 

 the body-wall until it comes abreast of the first gill-sac; then it tends 

 towards the middle line, coming to lie beside the dorsal aorta, which, 

 from the fifth gill-sac backwards, lies between it and the left anterior 

 cardinal sinus. It receives many lateral veins. It ends in the portal 

 heart. No part of it communicates with the sinus venosus. 



The left anterior cardinal sinus commences in a position correspond- 

 ing to that of the right. It early receives a large branch from below 

 and beside the pharynx. This suggests that the anterior part of the 

 left jugular may perhaps join the sinus. Posteriorly the left anterior 

 cardinal sinus joins with the posterior cardinal trunk to enter the sinus 

 venosus. 



Posterior Cardinal Sinuses, Right and Left. — A median sinus origin- 

 ates just below the notochord in the tail. A right sinus presently 

 separates from this, runs parallel to it for a little way, and rejoins it. 

 This may be repeated once or twice. Finally the two sinuses are well 

 established, and communicate with each other by several wide connecting 

 branches below the dorsal aorta. As the sinus venosus is reached the 

 richt sinus gives off a small branch, which crosses the left sinus and 

 runs to the portal heart. The right sinus then joins the left, and the 

 combined trunk, with the left anterior cardinal sinus, joins the sinus 

 venosus. 



Segmental veins running from the body-wall enter the corresponding 

 posterior cardinal sinus. Usually there is one such vein to two myo- 

 meres. Sometimes the renal vein running from a glomerulus enters 

 one of these segmental veins, but more often it runs direct to the pos- 

 terior sinus of its side. The renal veins leave the glomeruli on the 

 ventral aspect. The segmental veins pass over the nephridial system 

 dorsallv. 



