20 
AN EARLY HUMAN OVUM 
The nuclei of the eyto-trophoblast are clearly in very active division. 
Mitotic figures are not numerous, nor are they very well preserved, but 
their presence indicates that the ovum was in all probability in active 
growth shortly before being cast off. The cell characters are best made 
out in the tangential sections which cut the poles of the blastocyst. 
Plate vm, Fig. 11, is a photograph of one pole and Plate vn, Fig. 7, is 
a drawing of the other. A great many of the cells have either double, 
triple or even multiple nuclei. This may be observed both in the drawing 
and photograph. In the photograph (Plate vm, Fig. 11) the cell outlines 
are clearly distinguishable ; there is evidence of cell division; and it may 
be pointed out that the large dividing cells belong to the innermost layer 
of the cyto-trophoblast. The absolute continuity of the cyto-trophoblast 
and plasmodi-trophoblast is brought out (dearly in Plate vn, Fig. 7. The 
appearances here, and all round the blastocyst wall, altogether preclude 
any other conclusion than that the cyto-trophoblast, by active and con¬ 
tinuous proliferation of its cells, is gradually differentiated at its outer 
margin into plasmodi-trophoblast. The cyto-trophoblast is, in short, the 
germinal zone of the trophoblast. 
At one or two places the cyto-trophoblast shows minute buds extend¬ 
ing from its outer aspect. In one situation the bud has taken the form 
of a narrow cell column, on each side of which, but separated from it 
by a space, is a strand of plasmodium. The space does not contain blood, 
but corresponds to the clefts seen elsewhere between the cell-layer and 
plasmodium. These buds, though very rare, we take to indicate a com¬ 
mencing proliferation of the cellular layer, which will ultimately lead to 
the formation of the cellular villi of Peters’ stage. The grounds on which 
this opinion is based wifi be discussed later; meantime it may be stated 
that these buds are clearly outgrowths of the cell-layer, and not plasmodial 
strands which have reverted to a cellular condition. 
At no point does the cyto-trophoblast show any such columnar 
disposition of its cells as would indicate the presence of a layer of 
embryonic ectoderm in any part of the wall of the blastocyst, nor any 
thickening which could represent the formative cell mass continuous with 
the trophoblast. 
