324. A. A. W. HUBRECHT. 
perforated by these blood-spaces, can best be appreciated by 
comparing transverse sections, as figs. 2 and 3, with each 
other. From the moment that the trophospongia is formed 
the maternal decidual tissues may be said to develop and 
to undergo histological modifications along two different lines. 
That which constitutes the trophospongia can be studied quite 
separately from that which remains outside of the outer 
boundary line of the trophosphere. 
We will successively study the alterations which these two 
regions undergo during the course of pregnancy, and conclude 
by the examination of the changes occurring in that part of 
the mucosa which has taken no conspicuous part in the 
decidual proliferation, which is situated opposite the decidua 
reflexa, and which might—topographically !—be compared with 
the decidua vera of the Primates. 
Beginning with the trophospongia, we notice that its outer 
boundary line (being at the same time that of the trophosphere), 
though not yet sharply marked off in the stage of figs. 40 and 
41, is well defined in that of fig. 42. There is a rather sudden 
passage from the cell-mass of the trophospongia to the exter- 
nal decidual tissues where the blood-spaces have still an endo- 
thelium, and where the constituent cells are more fusiform, 
being generally arranged with their long axis perpendicularly 
to the radius of the trophosphere. This arrangement increases 
and becomes more and more conspicuous in the later stages 
when the fusiform shape is distended into a fibriform, when 
the nuclei become at the same time more elongated, and when 
in consequence the cellular constituents of that portion of the 
decidual tissues more and more assume the aspect of a circular 
fibrous layer (fig. 44). Closer examination always renders it 
possible to distinguish clearly between this layer, which assumes 
that fibrillar aspect, and the circular muscular coat, which is out- 
side of it, and which was fibrillar from the outset. I have been 
obliged to make this digression concerning a tissue which will 
be more fully described lower down, because for a full under- 
standing of the modifications in the outer regions of the tro- 
phospongia it is desirable to picture to ourselves the character 
