358 WILLIAM A. HILTON 
cells. The blood corpuscles are abundant in the sinus and rest 
on the liver cords in some places, while in others there is the begin- 
ing of a development of an endothelial covering formed by expan- 
ded cells, some of them perhaps derived from the blood mass. 
The lateral veins on each side come down but communicate with 
the sinus over the liver in its caudal regions, virtually with the 
liver itself after the sinus is passed. ‘The vitelline veins are now 
represented by the left only, which comes into the left side of the 
liver. There are a number of vessels in the body-wall as described 
in earlier stages, while in the connective tissue at the sides of the 
body the lateral cutaneous vessels are first seen as small rather 
isolated tubes just under the skin. Through part of its length in 
the caudal region a connection with some of the lateral vessels 
was seen. The yolk vessels are very numerous, and many of 
them, especially the smaller, have endothelial linings. In the 
caudal regions of the aorta especially, there are connections with 
the yolk vessels, which have here, as farther towards the head, 
penetrated well under the body of the embryo. Many of the 
blood corpuscles in this stage are undergoing division, especially 
within the cavities of the liver. These and others are now almost 
without yolk granules, the protoplasm of the cell varying from 
a light to a dark pink with eosin stain. Within the cytoplasm of 
some of the larger cells, lighter spaces seem to indicate where 
yolk granules have been absorbed or have dropped out. In the 
liver and in some of the vessels, the corpuscles are crowded to- 
gether in masses and blood is found in the gills. 
In a specimen 9 mm. long the liver is much larger; into it or 
into the ducts of Cuvier, which may be recognized on its dorsal 
and cephalic surface, empty the two large lateral head or somatic 
veins. These are continued down a short distance on each side 
as large lateral somatic vessels and have branches communicating 
with the lateral cutaneous. The connections with the head 
vessels were higher up. The lateral cutaneous becomes larger 
as it runs down, or at least it has more blood, and beyond the 
forelimbs, branches from it may be seen in the body-wall. In 
this stage, as in several earlier ones, a vestige of the right vitelline 
vein remains, situated somewhat more dorsally than the left. 
