542 EMBRYOLOGY OF THE TURTLE. Part III. 
larger outer, amniotic sacs, the latter no longer keeping the embryo suspended, this 
falls on its left side, (PI. 15, fig. 2,) where it remains till a late period (PI. 15, 
145, -15;.16). 
As the embryo increases in age and the body bends more and more upon 
itself, the amnios gradually follows less and less the contours of the lower side, 
and reaches across broader sinuses, namely, from the top of the head to the 
ventral opening, (Pl. 13, fig. 3; Pl. 14, fig. 4, 5; PL 18a, fig. 8, a1; fig. 13, a) 
and from the caudal region to the posterior edge of the same opening (PI. 13, 
fig, 2; Pl. 18a, fig. 8, a).* This separation from the surface, against which it 
formerly pressed, grows still more conspicuous, and soon the dorsal portion begins 
to raise itself above the back of the embryo, (Pl. 15, fig. 12,) and then the 
whole amniotic sac swells out, (Pl. 9c, fig. 3; Pl. 14, fig. 1, 3; Pl. 15, fig. 4, 5, 12; 
Pl. 18, fig. 9a,) as if distended with fluid, far beyond the outlines of the body, and 
thus becomes very conspicuous. ere then it is evident, that, at this age, the 
embryo remains in a curved position, by its own natural tendencies irrespective of its 
amniotic envelope. The distension of the amnios by the action of the infiltrated 
fluid would seem to indicate that there is a difference, at least in density, between 
the latter and that which is exterior to it, outside of the sac; else why should 
this endosmotic action take place? Unfortunately no investigation of these fluids 
has been made. Subsequently, im the latter stages of incubation, this distension 
subsides, and the amnios again closely embraces the body. In this condition it 
remains till the animal leaves its shell (Pl. 15, fig. 1, 2, 8, 8a, 9, 11; Pl 18) 
fig. 10, 10a, 10b, 10c). 
Synchronically with the changes described above, the lower opening of the 
body gradually narrows, and bears along with it the basis of the amnios, till 
finally the latter is attached to the ventral surface by a narrow isthmus, (PI. 9c, 
fig. i339 VP WAS figoals Pl oy fig. 4)0d,° 126). Ple ae iatie S7o;) Aspringim syurom athe 
trumpet-shaped abdominal projection. 
The peripheric portion of the germinal amniotic layer still persists after its 
separation from its imner fold, the “amniotic sac,’ and may be observed even 
to the latest moment before the period of hatching of the little Turtle. It is 
recognizable not only by its relation to the other membranes, the embryonal 
membrane and the allantoidian sac, but also by its characteristic cellular structure, 
(compare Pl. 9a, fig. 28 with fig. 31, 4, 31a, 6,) which will be described in 
another place, in connection with the histology of the various organs and of other 
parts of the body. 
Growth of the Embryo. Immediately after the first steps are taken to bring out 
1 The largest figure of Pl. 18a marked 2, ought to bear the number 8. 




