Cuap. II. FOLDINGS OF THE EMBRYONIC DISC. 563 
from the same point (fig. 4 and 5, 7°) at which the double dorsal artery (fig. 4 
and 5, j*) unites to form a single channel in the abdominal region, between the 
Wolffian bodies (fig. 4, g). The abdominal veins (fig. 4, 7?) are more distinct 
from the Wolffian bodies (g); the zigzag lines on the Wolffian bodies appear to 
be in direct communication with the abdominal vein, and, moreover, have a strong 
red tinge, from which we should judge that they are the bloodvessels of the body 
in which they are situated. The liver (PI. 18a, fig. 4 and 5, 7) is hollowed on its 
upper side, and on its lower and posterior side a dark body (fig. 5, w) is imbedded, 
which, from its position and green color, must be the gall bladder. The Wolffian 
bodies (fig. 4, g) are not quite so long as heretofore. The abdominal parietes are 
now closed over, with the exception of a small opening for the passage of the 
neck of the allantois, and the connection of the intestine and the yolk sac. 
The allantois not only covers the whole body, but spreads almost as far as 
the vascular area (PI. 16, fig. 3). It is most extended on that side which faces 
the ventral surface of the embryo, and its vessels have attained to a very large 
size, much exceeding, in this respect, any of those in the vascular area, even 
the vena afferens (7). The allantois of one of the figures (Pl. 15, fig. 13) 
representing this stage of development is very much shrunk by being withdrawn 
from its area of expansion and crowded up near the embryo. It will be noticed 
how highly vascular the whole surface of the embryo is; from the end of the 
head to the tip of the tail, the animal appears like a great vascular organ _per- 
forming respiratory functions. This peculiarity remains permanent in some adult 
Turtles, namely, in the family of Trionychide.’ The vascular area, as far as it 
extends superficially, covers about one half the yolk sac, and the vena afferens 
(Pl. 16, fig. 3, 71) is plunged deeper than ever into the yolk mass. At the 
exterior edge of the superficial extension of this area, the downward bend of 
the vessels resembles very much an irregular vena terminalis, but that part of 
the area is altogether plunged beneath the surface of the yolk. 
The paddle-like shape of the legs is no longer recognizable here ; but both 
the anterior and posterior limbs are now divided into a cylindrical and distinctly 
jointed leg, and a terminal, rounded, and expanded foot, yet without the least 
sign of toes. This obtains not only among the higher families of Turtles, (PI. 
15, fig. 15,) but even among the lowest, the Chelonioide, as the next phase will 
show more distinctly (Pl. 6, fig. 24). This is rather remarkable as regards the 
Chelonioidee, since in them the foot and leg become eventually, by a gradual 
metamorphosis, (Pl. 6, fig. 24, 22, 21, 20, 18, 13, 15, 14, 16,) apparently fused 
into one very large elongated paddle. A comparison of the feet of an advanced 
1 Comp. p. 284. 
