44 
AN EARLY HUMAN OVUM 
It will be recollected that in Leopold’s ovum both layers of the tropho- 
blast are represented in the irregular villi, and that in Peters’ specimen 
the epithelial villi are broader bands composed of Langhans’ cells and 
covered by an endothelium-like layer of syncytium bounding the blood 
lacunae. Our specimen seems to represent a phase hitherto unknown, in 
which the ovum is largely unattached and the villi are wholly plasmodial. 
Leopold’s ovum is a stage in which attachment is proceeding and the 
plasmodial villi are becoming replaced by cyto-trophoblastic processes or 
villi, while Peters’ ovum represents a stage in which attachment is taking 
place, and the necrotic zone having largely disappeared, there is a 
mingling of foetal and maternal tissues; in short, formation of a placenta 
has begun. In the later stages destruction of decidua no doubt continues, 
but far less actively. 
With regard to the manner in which the purely plasmodial masses 
become replaced by processes containing both cyto-trophoblast and plasmodi- 
troph oblast, three possible explanations present themselves : 
(1) The trophoblast may from the beginning be plasmodial and the 
cell-layer may arise by differentiation within the plasmodium. Such a 
possibility has been suggested, among others, by one of us (Dr. Teacher 
in his studies on Chorion-epithelioma), but it is very difficult to reconcile 
with the characters of the spun-out and vacuolated plasmodium in the 
present ovum. 
(2) In terms of the view expressed by Leopold and already 
referred to, the broad processes seen in Peters’ ovum may arise by the 
formation of buds of the cyto-trophoblast which grow outwards into the 
plasmodial strands, much in the same way as the mesodermic processes 
grow into the primitive epithelial villi. Much of the plasmodium would 
thus be reduced to the endothelium-like lining of the blood lacunae. 
This explanation also presents difficulties in view of the characters of 
the early plasmodium. It is difficult to picture the process imagined, and 
therefore we are inclined to fall back on a third possibility, viz. : 
(3) That the cjffio-trophoblast grows out as cellular masses and 
columns, not ' so much into the plasmodial strands, but into the spaces 
between the strands. 
