1891.] Embryology. 381 
EMBRYOLOGY.! 
On the Foetal Membranes of Testudinata.—Dr. K. Mitsukuri 
has published an elaborate paper in the Journal of the College of 
Science, Imperial University of Japan (Vol. IV., pt. 1), on the feetal 
membranes of the, turtle. The contribution is a paper of fifty pages, 
with ten excellent plates. The amnion arises from an anterior and 
two lateral folds,—there is no posterior fold,—and these extend grad- 
ually from before backwards.’ The lateral folds meet above the embryo, 
but their cavities do not unite across, so that a connection between the 
amnion (proper) and the serous envelope—sero-amniotic connection 
—always remains along the line of union. The backward growth of 
the amniotic folds over the embryo does not stop at the posterior end, 
but continues to grow backward, although diminished in width, until 
finally there is produced a tube extending from the posterior end of 
the embryo, reaching a length as great as the embryo itself, and placing 
the cavity of the amnion into communication with the exterior, 
In the Testudinata the allantois arises as a diverticulum from the 
posterior region of the midgut, and is from the first continuous with 
it. The later stages of the foetal membranes are more complicated. 
The allantois is obstructed in its growth over the embryo by the sero- 
amniotic connection. Ultimately the allantois surrounds the yolk by 
means of its three lobes. ‘‘ There is always, even in very much ad- 
vanced eggs, a small mass of the white just at the point where the three 
lobes of the allantois meet at the lower pole.” It seems that we have 
here, in a very primitive condition, the structure described by Duval 
as the placenta of birds. The yolk-sac passes into the interior of the 
body in hatching, where it lies for a long time, and may be found in 
young tortoises late in the spring of the year following. 
Mitsukuri thinks that if the embryology of the groups of reptiles and 
birds are carefully gone over again many structures which are highly 
significant in the light of facts now obtained will be found to have 
hitherto escaped notice; for instance, the sero-amniotic connection 
and the posterior tube of the amnion. The amnion was probably de- 
veloped originally by mechanical causes. In Testiudinata, when the head 
fold is produced, there are two reasons why it should sink into the 
yolk ; ‘* first, the yolk is very large and liquid, especially beneath the 
blastoderm ; and, in the second place, the white disappears from over 
* Edited by Thomas H. Morgan, Johns Hopkins University, Baltimore, Md. 
