THE OVA OF LEOPOLD AND PETERS 29 
of larger granular cell-masses with one or several nuclei, having thus the 
characters of plasmodium. The cells of the inner layer he distinguishes 
as Langhans’ cells. Here and there the layer thickens into buds of 
Langhans’ cells covered by plasmodiuin. These buds stretch out into 
long processes containing cells of both types, but there is never any 
outgrowth of mesoblast into them. Both cell layers are certainly of 
ectodermic origin, indeed Leopold regards any separation of them as 
inconceivable in light of the appearances in his specimen. The processes 
are attached here and there to the decidua, the terminal cells insinuating 
themselves among the tissues of the latter. The implantation cavity is a 
globular space filled with maternal blood in which the ovum floats freely, 
being anchored only by the tips of the trophoblastic processes. 
There are distinct points of resemblance between our ovum and that 
of Leopold, but the differences are also strongly marked. The first 
striking point of contrast, apart from the absence of an embryonic 
rudiment, is that in our case the trophoblastic processes are entirely 
plasmodial; any cells which could bear comparison to Langhans’ cells 
are confined to the thick wall of the vesicle, and the anchoring strands 
of plasmodium are fewer in number. The undifferentiated condition of 
the blastocyst wall in our ovum, and the absence of a cellular layer 
in the trophoblastic processes, lead one to infer that it is probably 
younger than Leopold’s. 
While the characters of the blastocyst, the haemorrhage into its 
interior, and the absence of an embryonic rudiment are abnormal features 
in Leopold’s ovum, on the other hand, in respect of the trophoblast it 
very possibly represents a normal intermediate stage between the present 
specimen and Peters’ ovum. It is known that in later stages the villi 
develop practically normally in the absence of an embryo, and doubtless 
the trophoblast may also do so at this early stage. 
The blastocyst wall in Leopold’s ovum, while it has a general likeness 
to that in the present ovum, is a less definite and a thinner structure, 
and has a greater resemblance to the layer of cells, with commencing cubical 
arrangement, covered by endothelium-like syncytium, which constitutes 
the greater part of the blastocyst wall in Peters’ specimen (cf. Leopold, 
