Sie WILLIAM A. HILTON 
In specimens a little later than those figured for the earliest 
blood masses, the heart is well formed, the mesoderm encircles 
most of the yolk, blood vessels within the embryo are without 
blood and the lateral channels are to some degree lined with endo- 
thelium (figs. 48 and 44). The early blood vessels are largely 
dorso-lateral in position as regards the rest of the yolk; right and 
left vitelline veins connect with the heart, the left being larger. 
In later stages the left vitelline remains, the vessels on the yolk are 
prominent, the corpuscles are well formed and there are communi- 
cations of the aorta with the yolk vessels by a number of small 
vitelline arteries. 
Some little time before hatching and before the embryo has un- 
coiled from the yolk and shortly after pigment is evident along the 
sides of the body, the lateral cutaneous vein is seen as already 
described. Sections of embryos of 10 mm. or less and before 
hatching show the lateral cutaneous on either side, a little ventral 
to the nervous system and near the surfaces of the body. It is 
not seen in later stages from the surface because of the develop- 
ment of pigment over it. In successively older embryos, as the 
extra cutaneous vessels develop as seen in surface views, sections 
show them extending down into the body-wall as it comes to 
encircle the yolk (fig. 36). These blood vessels, as could be seen 
to some extent from living specimens, were in the somatopleure. In 
sections of very much later larvae (those 18 to 20 mm. in length) 
the yolk is very much reduced, the vitelline system has in part 
become the hepatic-portal, the lateral cutaneous vessels have 
extended down ventrally into all parts of the body-wall. Con- 
nected with these cutaneous vessels, near the middle line ventrally, 
are two vessels partly fused into one. These evidently represent 
Fig. 34 Section of the head end of an embryo of Desmognathus, showing the 
two vitelline vessels within the body and the beginnings of blood islands (b) on the 
Violen >< 25. 
Fig. 35 Later embryo of Desmognathus, showing blood islands (b) on the 
surface of the yolk. X 25. 
Fig. 36 Larval Desmognathus, about 14 mm. long showing the position of blood 
vessels in the body wall (/) and on the surface of the yolk (v)._ X 25. 
Fig. 37 Section of a Desmognathus larva of about 20 mm., showing the position 
of the lateral cutaneous vessels (/) and the ventral abdominal vein, (a). X 25.* 
