BLOOD AND VITELLINE VESSELS IN AMPHIBIA 361 
dally the heart leads into a large sinus, which in early stages has 
a duct of Cuvier connected with it on each side. Veins empty 
into these from somatic vessels and also a little later from yolk 
vessels. The caudal region of the sinus is divided into a right and 
a left part and thus becomes connected with right and left vitel- 
lines so that these veins have their origin from the lower part of 
the sinus, and from vessels which develop on the surface of the 
yolk, including the region of the blood masses. As the right 
vitelline loses its yolk connections, the left vessel drains the yolk. 
With the development of the liver, the forward end of this vessel 
comes to run into it. As the intestine develops and changes its 
position the cephalic portion of the portal comes to be situated 
more dorsally. ‘The caudal portion forms the subintestinal, while 
branches are given off from the cephalic end in the liver to form 
hepatic veins. 
7. Well marked cutaneous vessels are developed in rather late 
embryos; branches from these extend down into the body-wall 
and the veins retain their early connections with the region of the 
duct of Cuvier. Branches grow down, and developed fromsome 
of these or in connection with them, a mid-ventral vessel, the ven- 
tral abdominal, is formed in the somatopleure. This arises rather 
late and is connected with the lateral cutaneous vein and with the 
liver. 
DEVELOPMENT OF THE BLOOD AND VITELLINE CIRCULATION IN 
DESMOGNATHUS 
The first external indication of the development of blood is 
found in embryos some little time before hatching. At such a 
time the outline of the body is well shown above the surface of the 
yolk, the head end is well differentiated and limb buds are formed, 
but no pigment has yet made its appearance. The earliest blood 
stage recognized was in an embryo of about thirteen somites 
(fig. 14). On the dorso-lateral surface of the yolk sac of such an 
embryo, a series of rather small, clear specks of blood islands made 
their appearance. These were more or less isolated from each other 
and appeared as clearer areas on the surface of the large white 
yolk mass (fig. 14). In a little later stage, such as shown in figure 
