260 Proceedings of the Royal Physical Society. 
identical in many respects with those seen in this early embryo of Myrmeco- 
phaga jubata. There is, for instance, a well-marked asymmetry of the 
pharynx in both cases. 
The placenta! is almost circular, and the false amnion? has been cut away 
so as to expose the true amnion containing the embryo. The head and neck 
bend is almost right-angled, and the hind part of the body slopes away at 
an obtuse angle to the back. The umbilical cord and tail extend up on the — 
right side of the head. The limb rudiments are distinct, the fore limb 
rudiment being divided into a narrower proximal and a wider distal portion, 
whereas the hind limbs are undifferentiated. 
Myotomes are visible from a point slightly tailwards of the fore limbs. 
There is no trace of the cerebral hemispheres apart from a slight notching 
of the wall of the fore brain, but the mid brain is indicated and the thin 
roof of the medulla oblongata is clearly visible. The rudiment of the eye 
and three visceral arches can be made out. 
The embryo is completely enclosed in the amnion. On the right hand 
side there is seen a whitish projection lying inside the amnion, close to the 
embryo. This bears a superficial resemblance to the yolk sac, but on 
examination of the sections it is seen to be only a proliferation of the cells 
of the amniotic wall. It springs from the point where the amnion leaves 
the umbilical cord, and is in the form of a large irregular sac which has no 
definite lining epithelium. The cavity does not extend into the amniotic 
wall and contains small masses of proliferating cells, as well as some 
coagulum. 
The question as to whether this is a normal feature of the development 
of M. jubata, and, if so, what its morphological nature is, can only be 
decided when further material of the early stages become available. 
The ventral wall of the alimentary canal is completely closed (except for 
the point of entrance of the allantois) and there is no trace of a yolk sac or 
yolk stalk. 
The sections of the embryo are cut at 20, and most of the following 
work was done by means of reconstructions by the glass plate méthod. 
The notochord is small in cross-section, and its anterior end is hook- 
shaped and lies just behind the pituitary diverticulum from the buccal 
1 T understand that the investigation of the minute structure of the placenta was 
entrusted by Professor Agar to another worker, but in any case the attempt to interpret 
minute details without access to the earlier stages of development involves so much risk 
of error that it seems advisable to postpone it for the present. 
* Tagree with those embryologists who think that the term “chorion,” in spite of the 
archzeological interest that attaches to its having come down from the ancient Greeks, 
should be dropped from use owing to its having lost all precision of meaning, 
