36 
MONICA TAYLOK. 
blood from the heart to the dorsal aorta. The mandibular 
aortic arch has completely disappeared. The anterior ends 
of the aortic roots are prolonged forward to the head as dorsal 
carotids, and each of these is joined by a vessel from the 
hyoid arch. A coeliaco-meseuteric artery is present, as has 
already been explained in connection with the excretory 
system. 
Text-fig. 2. 
Diagram of the vascular system of a larva of Stage 26. a. Anus. 
a. c. Alimentary canal, a. c. v. Anterior cardinal vein. c. a. 
Carotid artery, c. m. a. Cceliaco-mesenteric artery, c. v. Caudal 
vein. d. a. Dorsal aorta, d. c. Ductus Cuvieri. h. v. Yitel- 
line vein. i. r. v. Inter-renal vein. 1. Liver, p. c. Pericardium. 
p. c. V. Posterior cardinal vein. s. i. v. Suhintestinal vein. u. h. 
Urinary bladder, y. Yolk. 
At this stage the anterior cardinals are fully developed. 
The ductus Cuvieri are long, since the sinus venosus is still 
topographically the most anterior part of the heart. The 
vitelline vein enters the sinus anterior to the ductus Cuvieri. 
The paired portions of the posterior cardinals, now fully 
formed, are very short, the inter-renal vein commencing in the 
seventh segment. Posteriorly, especially in the neighbour- 
hood of the developing urinary bladder, however, the inter- 
renal vein shows its double nature. Blood from the yolk- 
