18 
AN EARLY HUMAN OVUM 
clearly clue to the haemorrhage into the upper part of the implantation 
chamber. The effect of the blood extravasation comes out rather more clearly 
in Plate ir, Fig. 2, in which the plasmodial meshwork can be observed to 
be pressed down to some extent on the wall of the blastocyst, while the 
layer of large cells elsewhere lying immediately within the necrotic zone 
is displaced inwards. The larger masses and bands have, as might be 
expected, resisted the pressure, and one process remains applied to the 
decidua as what appears to be an anchoring strand (Plate m, Fig. 3). 
The inner part of the plasmocli-trophoblast has the appearance of irregular 
branching lamellae laid down round the wall of the blastocyst. In no 
section, or part of a section, is any portion of the wall of the vesicle 
left uncovered by a plasmodial layer. Here and there in the formation 
there are masses of what appears to be eoagulum, but it is not impos¬ 
sible that some of these, at any rate, represent portions of necrosed 
plasmodium. 
The distinctive dusky-red colour of the plasmodium is brought out in 
Plate v, Fig. 5. At this magnification a granular structure is revealed in 
the protoplasm which is absent from the cyto-trophoblast, and under a 
still higher power this appearance is discovered to be due to an alveolar 
structure in the protoplasm. 
The whole appearances presented by the plasmodium lead one to infer 
that the extraordinary irregularity in the disposition of the layer is due 
to a process of vacuolation which has broken up the larger solid masses 
into a sponge-work, and that the trabeculae of this sponge-work have 
broken down so as to allow the blood shed into the implantation space 
by the opening of the vessels, to pass into its meshes. 
We thus reach a conception of the origin of the primitive blood 
lacunae in the trophoblast not unlike that of Peters, but it will be 
observed that the spaces are produced, in the first instance, entirely in 
the plasmodi-trophoblast. In this respect our ovum reveals a condition 
of the human blastocyst hitherto unsuspected; its walls are at this early 
stage almost wholly plasmodial, with the exception of a thin germinal 
layer or mother-zone of cyto-trophoblast forming the immediate wall of 
the vesicle. 
