Cuap. II. FOLDINGS OF THE EMBRYONIC DISC. 567 
more convoluted than those of the Wolffian bodies (a). Already there are numer- 
ous pigment cells upon the surface of the Wolffian bodies (Pl. 18a, fig. 3, ). 
A white and narrow band, of dense substance, tapering at each end, (wood-cut 2, x,) 
runs along the under-side of the Wolffian body, (wood-cut 2, a,) and presses closely 
against its surface. All the relations which this body bears to the surrounding 
organs mark it as the genital organ, whether of a male or female is not yet 
determinable, but probably that figured here is a male, if the long, slender, back- 
ward prolongation (wood-cut 2, /) may be considered a vas deferens. The mouth 
of the embryo is open as far back as the base of the jaws. The upper jaw, in 
Chelydroidx at least, is pointed (Pl. 18a, fig. 3) and slightly hooked. The feet 
have well marked and movable toes. 
inthe: next. phase: (Pl. 13,: fig. 1 3+ Pl. -1,. fig..4, .5,-5a, 6; PL. 16, figs 2, 2a, 
2b; Pl. 18, fig. 9, 9a; Pl. 25, fig. 2, 6, 6a, 6b, 8) the proportions of the body are 
about the same as in the last. The shield is more projecting at its edges, and 
the large dermal scales are quite conspicuous (Pl. 25, fig. 8). The ventral side 
of the body shows a new feature: the sternum or breastbone (Pl. 16, fig. 2b ; 
Pl. 25, fig. 8) has made its appearance, and extends longitudinally from the ante- 
rior edge of the fore legs to the anus, and laterally, between the anterior and 
posterior pairs of legs, almost to the edge of the shield. The head is more 
elongated, especially in front of the eyes, and the upper jaw and nasal region are 
less curved, being more on a line with that part which lies behind the eyes, so 
that, on the whole, the head very much resembles that of a bird. 
The heart (Pl. 25, fig. 2, 4) has increased to such a size, that, when filled 
with blood, it appears very dark and opaque. The vascular area (Pl. 13, fig. 1; 
Pl. 15, fig. 5; Pl. 16, fig. 2a, 2b) covers four fifths of the yolk mass. The dor- 
sal artery (Pl 25, fig. 6, A, fig. 6a, h, fig. Gb, h) gives off several vessels (fig. 
6, 7) to the kidneys, (,) and’ the abdominal veins (fig. 6, and 6a, d, fig. 6b, a’) 
distribute numerous venous currents (fig. 2, a) to the under-side of the Wolffian 
bodies. The omphalo-meseraic afferent vessel, (Pl. 16, fig. 2a, 71, fig. 2b, 71,) soon 
after it leaves the body, plunges in a direct line through the yolk mass, and 
joins the exterior boundaries of the vascular area on the lower side (fig. 2a). Even 
at this late age there is sometimes an exception to this, when the vena afferens 
(Pl. 13, fig. 1, 77) does not sink into the yolk mass till it has reached the peri- 
phery of the yolk mass. The allantoidian arteries and veins (Pl. 13, fig. 1, 0; 
Pl. 16, fig. 2; Pl. 18, fig. 9) are very conspicuous ; their main stems running par- 
allel, side by side. The liver (Pl. 25, fig. 2, 7) evinces a high degree of vascular- 
ity, very large vessels running from its under-side and branching upon its upper 
surface. The gall bladder (fig. 2, w) is larger and darker. The Wolffian bodies 
(Pl. 25, fig. 2, a, fig. 6, a, fig. 6a, a, fig. 6b, a) are considerably shortened and_hol- 
