I'll' Transactions. 



With regard to the forking of the ventral aorta, it is perhaps worthy 

 of note that in two preparations that carry much injection the right 

 division of the aorta appears as though it sprang from the left. 



Dorsal Aorta. — As in Bdellostoma, the efferent branchial arteries do 

 not run direct to the dorsal aorta, but those of each side run to a vessel 

 that may, for the sake of convenience, be called a lateral aorta. This 

 occupies a dorso-lateral position parallel to the dorsal aorta, to which 

 it sends regular communicating vessels. These communicating vessels 

 are three in number on each side. The most anterior of these vessels are 

 .behind the second pair of gill-sacs.' In "A Treatise on Zoology " (Ray 

 Lankester) Goodrich represents in diagram the circulatory system of 

 Bdellostoma, the diagram being based on the figures of Muller, Jackson, 

 and Klinckowstrom, to ^hich figures I have no access. The diagram 

 shows that the lateral aortae of Bdellostoma have more connecting: 

 branches to the dorsal aorta than those of Heptatrema, and that in 

 Bdellostoma there is communication anteriorly to the first gill-sacs. In 

 front of the gill-sacs the lateral aortae of Heptatre?na can be traced 

 forward nearly to the head. Posteriorly they turn inwards about abreast 

 of the last gill-sacs to join the dorsal aorta, which has, of course, received 

 all its blood through them. The turn inwards is made at a noticeable 

 angle, and the last efferent branchial vessel of either side may not be 

 received until after the turn is made (see Plate XVII, fig. 1). 



The efferent branchial arteries leave the gill-sacs on the anterior 

 aspect. Those of the anterior pair always, and those of the second pair 

 nearly always, branch just as they leave the gill-sac, the two branches 

 entering the lateral aorta separately. The third, and sometimes even the 

 fourth, efferent artery of one side, or both, may branch in like fashion. 

 In the preparation figured in Plate XVII, fig. 1, the second efferent 

 branchial artery of the left side has a distinctly double origin. 



From the median dorsal aorta vessels are given off to supply the 

 notochordal sheath, the pharynx, and the body-wall. These last, the 

 segmental arteries, often alternate with each other, but posteriorly to 

 the heart a more or less regular arrangement in pairs becomes evident. 

 One segmental artery often suffices for two myomeres. 



I have not been able to observe the blood-suppl}' of the pro-nephros. 

 With regard to the nephridial system, each segmental artery that crosses 

 the system sends, typically, a branch to the corresponding glomerulus. 

 In cases — and they are frequent — in which there is no segmental artery 

 corresponding to a glomerulus, a renal artery runs direct from the 

 aorta (see Plate XVI, fig. 2). One case was observed in which a segmental 

 artery sends branches to two glomeruli. 



Posteriorly to the heart splanchnic arteries run from the dorsal aorta 

 to the intestine; the splanchnic arteries are numerous, and appear to 

 be one in each segment. 



Numerous slender arteries pass from the dorsal aorta to the gonads. 

 These arteries are much more noticeable in cases in which there are 

 many ova forming. 



Jugular System.- — There is a large right jugular vein lying above 

 the lingual mass and beside the pharynx. It arises well forward, abreast 

 of the fifth slime-gland. The vessels that contribute to it come from 

 the body-wall, the lingual mass, and the pharynx. Anteriorly to the 

 gill-sacs it resembles a sinus rather than a vein. In the diagram for 

 Bdellostoma already referred to, the anterior part of the right cardinal 



