552 EMBRYOLOGY OF THE TURTLE. Part III. 
already described. The dorsal artery, which runs along the middle line of the 
body, (Pl. 18, fig. 7,) forks as it reaches its posterior termination. Each limb 
of the fork doubles outwardly upon. itself in a horizontal plane, and then passes 
forward parallel to, and in the same layer with, the dorsal artery, forming thus an 
abdominal vein, till it reaches the vena afferens, into which it empties, at a point 
a little posterior to the heart. That part of the dorsal artery which runs forward 
and forms a cephalic artery (PI. 18a, fig. 11, 7) branches and anastomoses extensively 
with return currents, the cephalic veins. These veins empty into the vena afferens, 
near the point where the abdominal veins discharge their contents into the heart. 
At the middle third of the body, the substance of the subsidiary layer is very 
much thickened around and above each abdominal vein, the thickening being 
shaped into a semicylindrical band, with the convex side downwards. LKach thick 
band lies principally between the abdominal vein and the dorsal artery, and is 
peculiar from its having dark, obliquely transverse striz along its whole length.’ 
The relations of these two bands, one on each side, to the dorsal artery and the 
abdominal veins, and the peculiar transverse zigzag strize within their thickness, 
correspond so closely in their relations and appearance to the organs, which, in a 
more advanced embryo, may be recognized as the Wolffian bodies, that we have 
no hesitation in identifying the former with the latter, both in name and in fune- 
tion. The sides of the abdominal cavity are more constricted than we have known 
to obtain before. The branchial fissures (Pl. 18a, fig. 15, m) extend through the 
musculo-cutaneous layer, and open into the cavity of the pharynx. The subsidiary 
layer, by folding together along the axis of the body and bringing the faces of 
its two opposite halves in contact, forms a double pendent curtain, the height of 
which equals the thickness of the body above it. The double lower edge of this 
curtain still remains in connection with the rest of the subsidiary layer, the 
latter expanding horizontally as heretofore, but at a lower level. In a_ trans- 
verse section (Pl. 9e, 7) of the posterior third of the body, we do not find the 
least trace of a curtain; but, on the contrary, the subsidiary layer (xz, o') expands 
directly outwards from its basis of attachment. This layer, excepting that the 
dorsal artery, the abdominal veins, the Wolffian bodies, and the pendent curtain 
have been formed by it, appears to have undergone no other change than 
to adopt the shape which the approaching sides of the body have impressed 
upon it. 
Another embryo of the same species, Nanemys guttata, (Pl. 18a, fig. 14,) although 
one day younger than the one just described, is more advanced” The whole body 
1 See an older phase for the peculiar appearance 2 The amnios in this figure is represented as torn 
of this band (Pl. 18a, fig. 8, 9). open along the middle region of the body. 

