EXPLANATION OF THE PLATES. 627 
of the allantois; the green to the venous system of the 
allantois. a, the shell; 6, shell membrane; ¢, zona pel- 
lucida (see p. 485); d, embryonal membrane ; e, outer 
peripherie portion of the amnios (see p. 541); f, h, m, 1, 
the allantois; m, m, edges of its superior folds; h, its 
lower border; /, its peduncular base ; — + —-—-,its pos- 
terior portion next to the yolk on the right side; 4, X’, 
amnios; (4,) its umbilicus; . . . . embryonal membrane 
lining the amniotic sac, (x, k’,) and covering the shield 
of the embryo, here represented by a transverse, trian- 
gular section; g, vascular area; i, its lower border; 7, 
subsidiary layer, in which run the omphalo-meseraic ar- 
teries (q’); j, yolk; n, intestine ; 0, allantoidian arteries ; 
o!, the same passing close to the body, and then more 
outwardly ; p, ventricle with aorta (darker red) in the 
middle ; p!, branchial arteries; p!’, dorsal artery fore- 
shortened ; p!! to q, single omphalo-meseraic artery pass- 
ing down behind the heart (p,7); g, two branches of 
the same; g', omphalo-meseraic arteries of the yolk, 
which anastomoze with the veins at 7; 7, the double ven- 
tricle ; 7/, omphalo-meseraic veins ramifying through the 
mass of the yolk; s, abdominal veins foreshortened, in 
part, and turned in to enter the auricles (7); ¢, allantoi- 
dian veins, foreshortened in part, which run along the 
sides of the body, and pass in behind, and into the ven- 
tricle (rv) ; ¢/, allantoidian veins, which run on the outer 
folds; ¢/’, the same as ¢/, running along the inner folds, 
close against the body, and then on the outer folds. 
Chelydra serpentina, about 4 diam., corresponds to Pl. 
15, fig. 4, 5, 5a, and to Pl. 16, fig. 2, 2a, 2b. 
Fig. 9, 10, 11, 12, 15, 16, 17, 13, 14, 4, 5, and 6 represent a 
series of embryos of Chelydra serpentina, from the time 
the shield begins to be distinct to the moment of hatch- 
ing. Fig. 6 represents a young just breaking through 
the ega-shell. All in their natural size. 
Fig. 7, and 8. 
fig. 8, young breaking through the ege-shell; nat. size. 
Ozotheca odorata ; fig. 7, head from below ; 
Fig. 22, 23,18, 19, 20, and 21, represent a series of embryos 
of Chrysemys picta; nat. size. 
PLATE IXd. 
[Drawn by H. J, Clark.] 
Fig. 1. 
diam. 
An actual longitudinal section of an embryo, 40 
The embryo is nearer to the yolk (yk) than is 
natural. The two opposite sides of the lateral halves of 
the yolk are approximated here for want of room, but 
the level of the vitelline surface is kept in its proper 


relation to the position of the embryo. a, a’, a’, a°, a’, 
the amnios; a, its peripheric part; a’, a? above, the edge 
of its dorsal aperture; a’ at the tail, to a® above, the 
caudal hood; a’, a’, a', the cephalic hood; a’, a‘, the 
area pellucida of the subsidiary layer (n, o'); c, c, the 
area pellucida; d, d, its periphery; e, e', e, e, e, &, 
spinal marrow; e, edge of the channel of the spinal mar- 
row ; €’, floor of the same ; ¢', e*, edge of the broad chan- 
nel of the brain; e*, point where the edges touch; e’, 
lower floor of the brain; e*, posterior end of the ger- 
mino-spinal layer; /', vertebral layer; f, vertebrie ; g, 
anterior end of the chorda dorsalis; g', its posterior end ; 
h, heart; 7, incipient vena terminalis; j*, cavity be- 
tween the vertebra (/') and the subsidiary (n) layer; 
n, intestino-subsidiary layer; o', peripherie part of the 
subsidiary layer ; —-—.—- , point where the lower half 
of the egg joins the segment of the upper part; yk, 
the yolk (its cells are magnified just as much as the em- 
bryo) ; al, albumen; vs, yolk sac, or rather zona pellu- 
. ., embryonal membrane. 
cida; . . Chelydra serpen- 
tina; the same as PI. 12, fig. 1, la. 
Fig. 2. An actual section of the walls of the Graafian fol- 
licle, and of a full-grown egg, 500 diam. a, a’, the two 
walls of the stroma; 4, tunica granulosa; c, zona pellu- 
cida; vs, vitelline or yolk sac; d', embryonal membrane ; 
e, yolk cells about the Purkinjean vesicle (g); ve, yolk 
cells from the centre of the yolk. 
Compare fig. 11b, Pl. 9. 
Chrysemys picta. 
Fig. 3. View from above of fig. 2, Pl. 9¢; the letters are 
the same. 
Fig. 4. Profile of an ege of Ozotheca odorata, nat. size ; 
the shell broken open at the side to expose the yolk; e, 
embryonic disc. 
Fig. 5. The albumen of a hen’s egg, at the point where 
resorption is going on, showing the exposed edges of all 
the layers of albumen, down to the yolk. 
PLATE IXe. 
[Drawn by H. J. Clark.] 
Fig. 1 to fig. 9a are, longitudinal and transverse sections of 
the embryo. The same parts are lettered alike in all; 
. ., embryonal membrane ; al, albumen; yk, yolk; a, 
germinal layer; a’, fold of the cephalic hood; a, fold 
of the caudal hood ; a’, the subsidiary layer in the area 
pellucida about the head; a‘, the same about the tail ; 
a’, cephalic hood ; a’, base of attachment of the cephalic 
hood; , primitive furrow; c, area pellucida; c', cavity 
