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516 EMBRYOLOGY OF THE TURTLE. Part III. 
the progress of this process to its completion. The egg of Chelydra serpentina 
is that in which we have followed most carefully the successive steps of the 
absorption of albumen, up to the period when the yolk sac is more than half 
full of clear fluid. At this last-mentioned stage of the resorption of albumen, the 
ege had been laid about three days and six hours. In an egg of Ozotheca 
odorata a week old, the albumen was all within the yolk sac. This also 
obtained in eggs of Thalassochelys Caouana of the same age (PI. 9b, fig. 8). 
In both these cases, however, the embryo was not so far advanced in devel- 
opment as at the last stage to which we have traced this process in the egg of 
Chelydra serpentina. After the yolk sae is filled, the yellow part of the yolk 
mass continues to lessen in size, and the space above it, containmg the clear 
fluid and the cerebro-spinal part of the embryo, to increase in magnitude, until 
the period when the Turtle leaves the shell. The older the egg, the more dis- 
tended does the shell appear, so that, when a mere pinhole is opened in it, a 
portion of the contents protrude through the aperture. This becomes very trouble- 
some when investigating those eggs which have a flexible and elastic shell, like 
that of Chelydra; for, in such cases, the moment an opening is made, the con- 
fined fluid tears open the embryonic envelopes’ and rushes out in a forcible jet, 
causing the embryo to assume an unnatural position. 
SHO TION S1Vs 
THE TRANSFORMATIONS OF THE YOLK IN THE FECUNDATED EGG. 
In the preceding chapter? we have described the mode of formation of the 
yolk, and its successive changes prior to the last copulation. We have now to 
consider the changes which it undergoes after this period. 
The yolk cells continue to grow, in certain respects, after the egg has entered 
the oviduct. There is, at this stage, something unprecedented in the unceasing 
enlargement of the mesoblast, until it finally so fills the ectoblast that the wall 
(Pl. 9a, fig. 35b) of the latter is hardly to be distinguished from the encroaching 
surface of the former. To an unprepared eye, especially if one had not seen 
the intermediate steps, (Pl. 9, fig 11f, llg; Pl. 9a, fig. 2d, 53a, 53b,) the mes- 
oblast would appear destitute of any wall beyond its own (fig. 59a-39e); but 
1 This tearing of the egg membranes may be pre- in instances when it is not desirable to keep the latter 
vented by making a hole in the lower side of the intact for further investigation. 
ege and letting out a portion of the yolk, especially ? See p. 458-476. 
