BLOOD AND VITELLINE VESSELS IN AMPHIBIA BT iA 
its communication with somatic vessels, it may be followed into a 
right yolk vessel and this may be considered to be either a continu- 
ation of the right vitelline or the anastomosis of the somatic with 
the yolk system. In this specimen blood has penetrated into the 
aorta but not into the somatic veins. 
In another specimen of the same length the left vitelline branch 
of the sinus venosus is very large, with both somatic and visceral 
connections marked, while the right is small and with much less 
evident communications. In this specimen it is hard to trace the 
early blood masses because there are now a number of lacunae 
on the surface of the yolk, more or less connected with the earlier 
ones, and the corpuscles from the original blood masses have 
largely escaped from the earlier spaces and are found in some of the 
other channels. These cavities are not yet lined with endothe- 
lium to any great extent; that is, the blood is not inclosed in vessels 
and the corpuscles are free on the surface of the yolk (figs. 8 and 9). 
A few cavities alone show the beginnings of the formation of capil- 
lary walls, either from some of the earlier cells or from some of the 
cells of the blood masses. Individual cells change their bodies 
into thin plates while the nuclei remain large. In this specimen 
blood can be seen in the gills. 
In a specimen 7.5 mm. long the right vitelline connection has 
been lost, but branches from the somatopleure communicate on 
the right side with the sinus venosus. On the left the vitelline 
vein connects with the blood spaces on the yolk and the sinus is in 
communication with the lateral vessels of the somatopleure. 
Farther along a vitelline vein may be seen on the right side, com- 
municating with the vessels on the yolk, not with the sinus. Ves- 
sels over the surface of the yolk are prominent, with blood in 
them; a right and left ventral may be seen, these are united farther 
back and then lost, although there may be others more caudad. 
Down near the sinus there is a single small ventral vessel and back 
of it a small cavity with no blood. Other specimens of the same 
length showed practically the same condition. 
In a number of specimens 8 mm. long, with 27 or more somites, 
the liver encroaches upon the sinus venosus and forms cords of 
