884 PROFESSOR W. ©. M‘INTOSH AND MR E. E, PRINCE ON 
be less complex, and finally they form simple twigs towards the termination of the 
chorda. The arterial branches along the sides of the body appear (in optical section) to 
be more deeply situated than the veins. 
At this time no blood-vessel extends beyond the line of the muscle-plates—including 
those of the tail; indeed, it is not till the third day that three or four loops of capillaries 
(Pl. XXVIII. fig. 8, aa) pass from the distal ends of the vertical vessels in the region of 
the adipose fin. They increase in number about the tenth day, yet at this period none 
occur in any other fin, except the tail. This is a noteworthy feature, though it is in 
consonance with what ALEx. AGassiz has generally observed, viz., that the posterior 
dorsal is the first to be differentiated. * 
In the wolf-fish the anterior region of the intestine (Pl. XXVL. fig. 2) is supplied by a 
large artery (mesenteric) d, which leaves the aorta on the right side, proceeds towards the 
intestine, and bifurcates after a short course. The superior branch runs along the posterior 
third of the upper part of the gut to inosculate with the main artery from the posterior end, 
as formerly mentioned. ‘The other trunk passes to the lower side of the gut, and gives 
twigs anteriorly as previously seen, and these terminate in veins passing upward to the 
intestinal (portal) vein. A hepatic branch is also sent to the liver. Another branch (the 
subclavian) is given off by the aorta in front to each pectoral. In the salmon, again, besides 
this branch, the aorta sends twigs to the right and left sides of the yolk-sac. These, how- 
ever, were not noticed in Anarrhichas, though they may have been present. When about 
a week old, moreover, minute branches occurred in the salmon in the space between the 
yolk-sac and the ventral fin. Some of these seem to come from the arterial twigs of the 
sac, others from the oblique twigs on the side of the body. In the newest and most 
minute capillaries in the developing fish (salmon) the blood-discs pass edgewise, and at 
intervals, the rest being simply a flow of pale fluid: nothing else at least could be observed. 
Caudal Circulation.—The circulation in the tail of Anarrhichas, at the stage shown 
in Pl. XXVIL. fig. 2, may very well be contrasted as regards the arrangement of the 
vessels with that in the salmon two or three days old (Pl. XXVIII. fig. 1), though it 
has to be borne in mind that the presence of the fairly formed cartilaginous hypural 
elements in Anarrhichas has an influence on the relations of the parts. The aorta (ao) in 
the wolf-fish leaves the notochord just at its dorsal bend, a twig passing up, over the 
chorda, a little beyond the point of departure. The course of the vessel is backward and 
downward between the upper and lower hypurals. The next branch is a slender twig 
(cad) which passes, with a nearly equal interval on each side at its origin, almost to the 
tip of the notochord, where a few coils occur. It then enters the venous system. It is, 
probably, the representative of the small artery which, about a fortnight before, went 
upwards along the notochord and returned by a similar vein, as in the salmon. 
At the posterior termination of the hypural fissure the artery splits 
proceeding dorsally and another ventrally—the two lying nearly in a continuous line. 

a branch 
From these a series of more or less parallel loops pass outward and obliquely downward 
* Proc. Amer. Acad. Arts and Sci., vols. xiii. and xvii. 
