DEVELOPMENT AND LIFE-HISTORIES OF TELEOSTEAN FISHES. 779 



be traced from the liver posteriorly to the caudal region, and it contains numerous large 

 round corpuscles, though these do not seem to occur anterior to the liver (PL XV. fig. 1). 

 Again the venous trunks immediately in front of the pectoral fins send prolongations 

 downward, and communicate with the venous end of the heart, which at this time shows 

 the broad auricle directed upward and backward, and a spacious sinus venosus (sv, 

 PL XII. fig. 8). The large venous tube thus passing to the sinus on each side is the ductus 

 Cuvieri, which, in addition to the posterior (cardinal) vein, also receives the anterior 

 (jugular) trunk. Around the two anterior veins the cellular tissue of the pronephros 

 grows (prn, PL XL figs. 9, 11), and venous ramifications are developed in the midst of 

 the renal matrix. Before the end of the first week after hatching — generally on the 

 fourth or fifth day in Gadoids — a simple circulation can be detected. The anterior 

 bulbous end of the heart driving the blood upwards behind the eyes — probably by the 

 artery of the hyoid arch, whence it courses by the great subnotochordal trunk (dorsal 

 aorta) to a point a little posterior to the root of the tail, and, passing round by a minute 

 loop, returns by a large venous trunk which anteriorly divides into the two cardinals 

 already mentioned. The two subnotochordal trunks with the anterior branchial artery 

 constitute the simple vascular system in its earliest condition. A day or two later a 

 venous branch leaves the vena vertebralis at a point about midway along the trunk — 

 above the mesenteron, and passes down to the lower side of the alimentary canal — and 

 forward along the margin of the liver to the sinus venosus. This must be the 

 subintestinal vein, which is, however, usually described as passing along the intestinal 

 portion of the alimentary canal. Its course, however, is at this stage very short. Not 

 so in the case of the intestinal artery (coeliaco-mesenteric) which leaves the dorsal 

 aorta in the pectoral region, traverses the mesenteron in descending, then courses 

 beneath the rectum, but ascends before reaching the anus, and passes along the anterior 

 margin of the urinary vesicle to join the caudal vein. The caudal vein is lengthening 

 simultaneously with the caudal artery ; thus, in a cod on the seventh day both reached 

 barely a quarter the length of the caudal trunk, while on the fourteenth day they 

 extended almost to the tip of the tail. The force of the arterial current seems to hollow 

 out the yielding channel, and causes it to become longer, but the afferent venous trunk 

 has the appearance of a somewhat irregular ill-defined sinus. During the second week 

 great advances take place in the haemal circulation. Lereboullet noticed, in Perca 

 about two weeks old, that blood was passing along two of the gill-arches ; and in the 

 Gadoids and other forms described in this paper two arches likewise develop arterial 

 channels. There is considerable variation in the details of this development ; thus a 

 haddock, on the fourteenth day after extrusion, showed arterial blood passing along 

 two (apparently the anterior) branchial arches, whereas another embryo of the same 

 species, on the eleventh day, showed three branchial arteries and a fourth artery, which 

 runs apparently within the opercular fold, possibly, however, the hyo-opercular. The 

 mandibular artery is a well-marked trunk coursing along the outer margin of the 



