CO 
EMBRYOLOGY OF THE TURTLE. Part III. 
or 
cr 
of capillaries, evidently evincing a high state of vascular organization and activity. 
As regards the other parts of the embryo, we have but little to notice that is 
new, except to point out the already minute ramifications of bloodvessels in the 
head, a feature not represented in the two embryos last mentioned. At this 
stage, the so-called vena terminalis also merits particular notice, inasmuch as it has 
now become as distinctly a vessel as it ever will be. In Turtles’ embryos this 
vein never becomes a single perfect circular channel, as is the case among Birds. 
Wherever there appears to be a single large current, it will be found, upon close 
examination, to be made up of an infinite number of minute anastomozing ves- 
sels. (See Pl. 17, fig. 6, which, although a little older, exhibits the same appear- 
ance.) It will soon be seen that this peculiarity becomes a more prominent and 
readily noticeable feature in further advanced stages. 
At this age, the diameter of the vascular area of this species, and of all 
the other species with oval eggs, is broader in one direction than in the other, 
its greater breadth correspondmg to the longer axis of the egg. In globular 
eggs there are no such differences; but the vascular area always continues more 
or less circular. In their younger stages of development, oval eggs also have a 
circular vascular area, as is shown in the case of Nanemys guttata (Pl 18, fig. 
7). We have mentioned previously the growing tendency of the vessels of the 
vascular area to trend m a direct line from the point of their origin towards 
the vena terminalis. This tendency is now carried out to the utmost in this 
eg, so as to give to the vessels a stiff and rigid appearance (PI. 16, fig. 6). 
The next older stage (Pl. 14, fig. 2, 2a; Pl. 18, fig. 8; Pl 18a, fig. 6-10; 
Pl. 24; fig: 2, "2ae BL 9e;. fig. .8, 8a,.9, 9a; Pk dQ digs 4.5 Pls 22) figs 9), \offexs 
some new and remarkable features in addition to a further development of the 
different organs. 
The brain of this embryo (Pl. 14, fig. 2a; Pl 18a, fig. 9; Pl. 22, fig. 9, 0, 
b') has become strongly lobed, especially in the region above the eyes, where it 
is so prominent as to give the head a crested appearance. The lower side also 
projects downwards between the eyes, (PI. 22, fig. 9, ¢,) where it constitutes the 
optic lobe. The dorsal vertebrae reach to the tip of the tail (Pl. 14, fig. 2a). 
They have so approximated their opposite halves (Pl. 9e, fig. 8, f, fig. 8a, f) as 
almost to inclose the spinal marrow (fig. 8, e, fig. 8a, e) in a perfect tube. The 
chorda dorsalis (fig. 8, g, 8a, g, 9, g, 9a, g) is still very conspicuous, and appears 
to have increased in diameter. The musculo-cutaneous layer (Pl. 9e, fig. 8, p. p', 
fig. 8a, p, p') is separated ito two portions, namely, an outer (fig. 8, 8a, p) or 
dermal layer, and an inner (fig. 8, 8a, p') or musculo-costal layer. The end of the 
head below the eyes is quite pointed (Pl. 14, fig. 2a). The eyes are very prominent 
(PL 14, fig. &; PL 18a, fig. 7, % and fig. 9; Plu 22, fig; 9, ec) The netina (Bb 
