The Development of the Alligator 327 
(lu), which here consist of several thick-walled 
tubes, surrounded by lobes of mesoblast. The 
other features of the figure need no special mention. 
Figure 207 is through the base of the posterior 
appendages (pa), in which the cartilages are already 
being outlined by condensations of mesoblast. The 
intestine (z) is cut in two regions—at a more an- 
terior point, where it is seen as a small, circular 
hole surrounded by mesoblast and hung by a 
narrow mesentery, and through the cloacal region, 
the larger and more ventral cavity, into which the 
Wolffian ducts (wd) open a short distance caudad 
to this section. The blood-vessels present a rather 
curious appearance. A short distance anterior to 
this point the aorta has divided into three, or it 
might be said that it has given off two, large 
branches. These two branches, one on either side 
near the posterior cardinal vein, pass toward 
the ventral side of the embryo on each side of the 
cloaca and end at about the region represented by 
the present figure. The small portion of the aorta 
that remains after the giving off of the two 
branches just described continues, as the caudal 
artery (ca), into the tail; it is a small vessel just 
under the notochord, and gives off small, paired 
branches at regular intervals toward the vertebral 
region. The posterior cardinal veins (pc), posterior 
to the openings of the Wolffian ducts into the 
cloaca, unite to form a large caudal vein lying just 
ventral to the caudal artery. 
