THE CYTO-TROPHOBLAST 
19 
While our specimen speaks for the production of the blood lacunae 
by the formation of spaces in the trophoblast into which the extravasated 
blood is shed, it cannot be concluded that they are formed in the first 
instance in a uniformly thick lamella of plasmodium constituting a toler¬ 
ably regular wall to the blastocyst. The plasmodi-trophoblast from its very 
nature is probably highly irregular from a very early stage, and therefore 
the blood lacunae may in part represent spaces intervening between out¬ 
growing plasmodial masses—between what may, in fact, be termed primitive 
plasmodial villi. 
THE CYTO-TROPHOBLAST. 
The cyto-trophoblast constitutes a relatively thin lamella which forms 
the immediate wall of the vesicle. The lamella is sharply differentiated 
from the plasmodi-trophoblast by its staining reactions. It is tinted, in 
haemal urn and eosin preparations, a delicate blue-pink colour. The cell 
outlines are nowhere sharply defined, but they can be readily made out 
in sections in which the blastocyst wall has been tangentially cut. Else¬ 
where the appearance is rather that of a zone of protoplasm with embedded 
nuclei. As has been already mentioned spaces* occur between the cyto- 
trophoblast and the inner laminated layer of the plasmodium, but between 
the spaces the two formations are directly continuous. While at these 
points the cell-layer and plasmodial layer are distinguished in histological 
characters, the transition from the one to the other is not sharp and 
defined; the cell-layer changes its tone to pink, and passes uninterruptedly 
into the dusky-red plasmodial layer. The nuclei are extraordinarily irre¬ 
gular in size, though all show the same loose character of the chromatin 
reticulum, with one or two chromatin nucleoli (Plate vn, Fig. 7). They 
differ markedly, as already stated, from the nuclei of the plasmodium, 
which stain deeply and have a granular appearance. Here and there the 
innermost nuclei tend to be arranged in a row for a short distance, as 
if the cells next the cavity were assuming the epithelial disposition which 
characterises this zone in Peters’ ovum. This arrangement of the nuclei 
is also seen in Leopold’s youngest ovum, but in our specimen it is much 
less definite even than in that extremely early stage. 
