Agassiz on the Embryology of the Turtle. 351 
Ee oat or nodule consisting of concentric layers of columnar 
stals 
The absorption of Albumen.—The albumen is absorbed into the 
yolk sac in a very peculiar manner; the outer layers are re- 
moved first, at a point always above the embryonic disc, so that 
mthe end an inverted conical hole is formed. From this hole 
the absorption spreads centrifugally till all the albumen is drawn 
into the yolk sac, or zona pellucida now, and the latter has dis- 
tended so as to completely fill the shell. At or near the time 
that the absorption of the albumen commences, the segmentation 
of the yolk begins; and the embryonic dise is formed, in some 
Species, before the clear hyaline space appears under the embryo. 
Self-division of the Mesoblast.—Before we describe the segmen- 
We refer to the self-division of the mesoblast of the yolk cell. 
This takes place, at least to a certain extent, without the influ- 
yolk mass, and in fact is a forerunner, as if to prepare the way 
for the latter change 
‘8410 into two more till the ectoblast is filled by an innumerable 
host of mesoblasts. This process goes on slowly, and lasts as 
long as the young turtle is within the shell. It is completed 
first in those ectoblasts which enter into the formation of the 
rabryonic disc, and afterwards in those which are added to the 
! al layer. : ; 
e The great point gained by these last observations, 1s to pr« 
that these self-divided. mesoblasts become the original cells, “the 
: Segmentati the yolk.—The segmentation of the yolk 
_ Mass ay been ald g a yan of only one species of turtle, viz: 
¢JPtemys (Emys) insculpta. i 
time on the 27th of May, 1854, and afterwards during the two 
— « eeding days, i ies of 
. ‘dividuals, Te ecco of segmentation is not so regular, and 
