EXPLANATION OF THE PLATES. 
Fig. 8. From the right side ; the shell is removed ; 7, edge 
of the vascular area; fig. 8a, the same as fig. 8, from the | 
left side, on the right the allantois is cut away to show | 
the edge of the shield more distinctly, 2 diam.; period of | 
laying unknown, opened Aug. 22, 1852. 
Fig. 9. From above, the shell partially removed, 2 diam. ; 
period of laying unknown, opened Aug. 21, 1852. 
Fig. 10. 
the oviduct, July 20, opened Sept. 19, 1855. 
Twins, nat. size; the shell is removed; taken from 
Fig. 11. From above, the shell mostly eut away; laid June 
20, opened Aug. 2, 1855. 
Fig. 12. 
the same as fig. 12, the embryo from behind, to show the 
From above, the allantois drawn back ; fig. 12a, 
extent of the vascular area on the lower side of the 
yolk; laid June 10, opened Aug. 1, 1855. 
Fig. 13. Embryo with its allantois, taken out of the shell, 
about 3 diam.; laid June 18, opened July 31, 1855. 
PLATE XVI. 
[Fig. 4 from nature, by H. J. Clark, the others by A. Sonrel.] 
Fig. 1. The allantois and amnios removed... Chrysemys 
picta, nat. size. Laid June 21, opened Oct. 23, 1855. 
Fig. 2. From above, the shell cut away, nat. size; fig. 2a, 
the same as fig. 2, from below, about 2 diam., the shell 
being removed to show the superficial extent of the vas- 
cular area; 7', vena afferens; fig. 2b, the same as fig. 2, 
and 2a, the allantois and amnios cut away, and the em- 
bryo turned back and exposed from below; 7’, the point 
where the vena afferens enters the yolk mass. Chryse- 

mys picta. Laid June 21, opened Sept. 1, 1855. 
Fig. 3. 
mys picta. Laid June 16, opened Aug. 1, 1855. 
Fig. 4. 
2 diam. Period of laying unknown, opened Sept. 17, 
1852. Ch. picta. 
Fig. 5. From above, a little more than 3 diam. The allan- 
tois is drawn back. Ch. picta. Date of laying unknown, 
From above, 5 diam.; r', vena afferens. Chryse- 
Seen obliquely from above and to the right, about 
opened Aug. 2, 1855. 
Fig. 6. From above and to the right; fig. 6a, the same from 
the left, without the vascular area; about 4 diam. Laid 
June 20, opened July 17, 1855. Nanemys guttata. 

PLATE XVII. 
[All the figures of this Plate are drawn from specimens of Chelydra 
serpentina; fig. 5, by A. Sonrel, the others by H. J. Clark.]} 
Fig. 1. Portion of the intestine and of the adherent yolk sac, 

about 5 diam. The vena afferens on the right; in 
the middle the omphalo-meseraic artery. Hatched in 
October. 
Fig. 2. 
the yolk sac, 5 diam. On the right the afferent vein; in 
Portion of the intestine to show its opening into 
the middle the omphalo-meseraic artery. Taken from 
the oviduct, July 20, opened Sept. 19, 1855. 
Fig. 3. 
The large vessel on the left is an omphalo-meseraic 
Portion of the vascular area, just below the surface. 
artery, the others are omphalo-meseraic veins; the 
arrows indicate the course of the blood, 250 diam. ; fig. 
3a, large, transparent cells from fig. 3, 500 diam. Laid 
June 10, opened Sept. 18, 1855. 
Fig. 4. 
of the same as fig. 4, 40 diam. Period of laying un- 
Portion of the allantois, 20 diam. ; fig. 4a, portion 
known, opened Sept. 17, 1855. 
Fig. 5. Part of the edge of the vascular area, 5 diam. 
Period of laying unknown, opened Aug. 6, 1852. 
Fig. 6. Strip of the vascular area, from the first part of the 
omphalo-meseraic artery to the vena terminalis, 5 diam. 
Taken from the oviduct, July 20, opened Sept. 17, 1855. 
Fig. 7. Portion of the nearly parallel omphalo-meseraic 
arteries, and the very crooked omphalo-meseraic veins, 
5 diam. Laid June 10, opened Sept. 18, 1855. 
PLATE XVIII. 
[Fig. 1, 2, 3, 4, 4a, 5, 7, 9, 11, 11a, 11b, from nature, by H. J. Clark. 
Fig. 6, 8, 9a, 10, 10a, 10b, 10c, 10d, 10e, 10f, by A. Sonrel.] 
Fig. 1. Omphalo-meseraic vein with a very thick wall, 500 
diam.; the same as PI. 17, fig. 3, and 7. Ch. serpentina. 
Fig. 2. Omphalo-meseraic artery, 500 diam. Embryo just 
hatched. 
Fig. 3. Piece of the allantois with a bloodvessel, 500 diam. 
Period of laying unknown, opened Aug. 27, 1852. 
Fig. 4. Mesh of bloodvessels covered by yolk, 20 diam. ; 
fig. 4a, a single vessel in its sheath of yolk, 500 diam. 
Ch. serpentina. Just hatched. 
Fig. 5. 
boring omphalo-meseraic arteries. Magnified from fig. 7. 
Laid July 11, opened July 22, 1852. 
Ce | 
Fig. 6. The fork of the vena terminalis, 12 diam.; the same 
Posterior ‘end of the dorsal artery and the neigh- 
Nanemys guttata. 
as fig. 7. 
Fig. 7. From below, 5 diam.; the same as fig. 5, and 6. 
Fig. 8. From above, 3} diam. Nanemys guttata. Period 
of laying unknown, opened Aug. 21, 1852. 
Fig. 9. Ozotheca odorata. Period 
of laying unknown, opened Aug. 23, 1852; fig. 9a, the 
From above, 2 diam. 
same as fig. 9. The embryo and allantois drawn to one 
side. 
