362 WILLIAM A. HILTON 
21, there is some evidence of anastomosis between these clear 
areas. Very soon after the first anastomosing vessels are formed, 
others are added with great rapidity and soon clear lines run over 
most parts of the yolk. In some embryos the pattern is of one 
sort, in others it has a slightly different character, but all show at 
an early stage certain vessels which are larger and clearer than the 
rest and some of these indicate where the earlier vessels were. 
Parts of these earlier blood islands and early vessels may remain 
for a time not completely connected with the rapidly forming 
network (figs. 22-25). Very soon the first vessels extend ventrally 
and laterally in every direction and in still later stages the yolk 
is covered by only a thin layer of ectoderm and a thin sheet of 
mesoderm, and the body-wall has not begun to grow over it to 
any degree. 
After the formation of a network of clear lines, and about the 
time of the first development of pigment in the embryo, a slight 
pink color appears in the larger vessels and soon the heart begins 
to beat slowly, before there is much color in the blood and before 
there is any circulation. 
At first there are two general systems of capillary network 
over the surface of the yolk, corresponding roughly with the two 
blood areas on the right and left sides, but as circulation becomes 
established these are all fused into one system,with a varying num- 
ber of branches having many anastomoses, which reaches across 
the yolk and underneath the body of the embryo. Branches 
penetrate the body a little before the blood becomes red. 
Fig. 14 Desmognathus embryo showing first indication of blood islands. > 10. 
Fig. 15 Desmognathus embryo just beginning to have pigment. Side-view 
showing a vitelline circulation. 12. 
Fig. 16 Later stage, Desmognathus embryo, showing yolk vessels. 12. 
Fig. 17 Embryo of Desmognathus before hatching, showing lateral cutaneous 
and yolk vessels. X 5. 
Fig. 18 Embryo of Desmognathus just before hatching; two parallel vessels 
have been formed in the body-wall. 5. 
Fig. 19 Larva of Desmognathus just after hatching, with three parallel vessels; 
the yolk vessel is reduced. X 5. 
Fig. 20 Larva of Desmognathus some time after hatching but still with the 
mother. This shows a ventral abdominal vessel and cutaneous vessels connected 
with it, the last shown only on the left side. 5. 
