498 MR. F. E. BEDDARD ON THE 
trunks two or three branches are given off to the walls of the intestine. 
These trunks with their branches are displayed in Plate XXYV. fig. 3. Behind 
the 13th segment the dorsal vessel is ampullated, and appears to give off three 
branches in each segment. 
The supra-intestinal vessels run back for some considerable distance, but 
they appear to unite into a single trunk, as has been already stated in the 
account of the alimentary tract, where also the details of the intestinal circula- 
tion are given. 
The two lateral vessels at first run beneath the intestine, and are closely 
adherent to it (Plate XX, VI. figs. 1, 2) ; ineach segment a branch is given off to 
the mesentery. In Plate X XV. fig. 5 the distribution of the vessels in the anterior 
part of the body is shown, including the 7th, 8th, and 9th segments ; the lateral 
vessel (/) has here moved from the under surface of the intestine, and occupies 
a lateral position ; it gives off one mesenteric branch in the 9th segment and 
two in the 8th ; in the 7th and 8th segments a branch is given to the vascular 
plexus on the surface of the gizzard, the ultimate ramifications of which are 
connected by direct anastomosis with the branches given off from the first of 
the transverse trunks uniting the dorsal and ventral vessels, and which haye 
been already described. In the same figure the two anterior hearts (/) are 
shown; each before joining the supra-nervian vessel (v) gives off a trunk 
which supplies the body wall and mesentery. In fig. 6 the further course 
forward, and the termination of the lateral and supra-nervian trunks, is shown; 
they each give off corresponding branches to the mesenteries, which have the 
relation to each other of artery and vein; the lateral trunks terminate among 
the muscles of the pharynx, and the supra-nervian following closely the course 
of the nerve cord ends on the upper surface of the anterior part of the pharynx 
near to the cerebral ganglia. 
The lateral vessels seem chiefly concerned with the blood supply of the 
mesenteries. I was unable to trace them further back than the 18th segment, 
which is no doubt owing to the fact that in this part of the body the mesenteries 
are supplied with blood by the supra-nervian trunk. 
The supra-nervian vessel runs continuously from one end of the body to the 
other, lying just above the ventral nerve cord; in each segment it gives off a 
branch on either side, which supplies the body wall and mesentery ; in the 
region of the hearts, however, this branch is not given off, the mesenteries 
being supplied from the dorsal and lateral vessels ; in the anterior part of the 
body the ventral vessel runs between the spermathece, giving off two main 
branches on each side, which have been already described as corresponding to 
branches of the lateral vessels. 
These are the chief facts in the circulatory system of Pleurochwta; a 
general scheme of the whole circulation is shown in Plate XXV. fig. 4. 
