570 EMBRYOLOGY OF THE TURTLE. Part III. 
developed, and, starting from a transverse vessel (e, e) near the base of the third 
joint, go in pairs to each finger. In this phase the allantois has almost com- 
pletely enveloped the yolk mass (Pl. 16, fig. 1). 
In the next phase, (Pl. 15, fig. 1, 2, 3; Pl. 9a, fig. 30, 30a; Pl 18, fig. 3; 
Pl. 19, fig. 9-12, 16b, 16c, 18, 18a, 19, 20, 21, 23, 24, 25, 26, 26a, 32; Pl. 20, 
fig.» 1jx 1a, Tb, :.6, -6,. Ty -8,.9pn9ay lO) Te Pie iol, By 3564, koG ear 
14, 14a, 14b, 14c, 14d, l4e, 14f, 14g, 15, 15a, 16, 16a, 16b, 20 to 20d, 29, 31, 
32 to 32d, 34, 34a; Pl. 24, fig. 6; Pl. 25, fig. 1 to 1d, 5,) the whole contents of the 
ege are surrounded by the allantois, (Pl. 15, fig. 2,) and no part of the organ- 
ization, except the blood, is in a loose, mobile state. Even the yolk forms a 
tenacious sheath about the .bloodvessels, (this is figured for the next stage, Pl. 
18, fig. 4, 4a,) which anastomoze with each other throughout the whole yolk sae. 
The yolk sac is nearly as small as when the embryo is hatched. The propor- 
tions of the body are about the same as when the embryo is born; the head 
is quite pomted, and the neck proportionally shorter than heretofore. The folds 
of the skin are more marked and numerous. The lower jaw is pointed (Pl. 25, 
fig. la, x). In Chelydroide (Pl. 15, fig. 5) the shield is marked with a median 
and two lateral rows ef large tubercles, and numerous smaller ones all over the 
surface, while among Emydoide the shield is minutely granulated. The head, 
neck, legs, and tail are covered with small and rather stiff scales. The thick, 
transparent layer covering the terminal jomts of the toes in the last phase is 
here developed into horny sheaths, forming sharp claws (Pl. 21, fig. 20, a). 
The brain is composed of large, globular, transparent cells, each. containing a sin- 
gle mesoblast; and those of the hemispheres, (Pl. 19, fig. 16b, 16c, a, b, 6, ¢, ©) 
of the olfactory lobes, (fig. 18, a,) of the Schneiderian membrane, (fig, 19, a, 0,) of 
the medulla oblongata, (fig. 20, a, 6,) and of the spinal cord, (fig. 21,) have all 
one common physiognomy. Already there are a few slightly caudate cells, (fig. 
18, a, fig. 19, a,) and those of the Schneiderian membrane (fig. 19) are mutually 
pressed agaist each other. The eyes have fully developed eyelids (Pl. 15, fig. 
3). The crystalline lens (Pl. 21, fig. 29) is covered in front by a large layer 
of polygonal cells, (a,) the “membrana pupillaris,’ which is overlapped by the 
anterior edge of the membrana hyaloidea, the zonula Zinnii (¢). The zonula 
Zinnii (¢) has the longitudinal plications, the ciliary processes of the membrana 
hyaloidea, as fully developed perhaps as in the adult. At the anterior edge of 
the zonula, the pigment layer (4) is quite thick. The cells (Pl. 21, fig. 52a, a, 
b, c, d) of the fibres of the crystalline lens are so excessively transparent and 
closely adherent to each other, that it is difficult to recognize each separately ; 
and, in fact, in some parts of the lens, their walls appear to be obliterated at 
the point of contact, so that they form a continuous ribbon (PI. 21, fig. 32b, 
