early placenta of Macacus nemestrinus. 
303 
(2) The changes in the uterine wall determined by the 
arrival of the blastocyst. 
As already remarked, the block of’ tissue removed with the 
fragmentary blastocyst consists entirely of decidua compacta. 
Some of the changes herein have been already noticed (cf. (1) 
supra). Thus the general appearances are best compared to those 
attendant upon an inflammatory process. 
The decidua compacta is composed of “ stroma cells ” in the 
interstices of which widespread oedema has occurred. The 
capillary vessels do not appear unusually numerous or large 
however. The exudation is most marked in the tissues im- 
mediately underlying the surface epithelium, and at this level 
the exudation is so plentiful as to form distinct patches (cf. 
Fig. 4). In these patches there are not many leucocytes, and 
the exudation appears to be coagulated, owing no doubt to the 
action of the fixing reagent. 
The stroma cells give no clear evidence of proliferation and 
increase, save in some of the more central sections, and then the 
appearance is very local. 
The glands are not remarkable for tortuosity, but some dis- 
tinctly shew enlargement towards their mouths. Into some of the 
glands, as will be shewn in the sequel, haemorrhage has taken 
place and then the epithelial lining cells tend to degenerate and 
to disappear '*'. 
I have not been able to identify the cell-nests described by 
Selenka*f* and referred by that author to proliferating uterine 
epithelial cells. 
In the more central sections, the blastocyst and uterine wall 
are firmly coherent. Here one can distinguish regions which are 
either indubitably embryonic or maternal respectively, and between 
these comes an intermediate area wherein the constituent cells 
appear at first sight to be inextricably confused and intermingled 
(Figs. 5 and 6). This intermediate area, shewn better in Fig. 6, 
(the “ Placentar-polster ” of Selenka) is characterised on the 
maternal aspect in the following way. First the stroma cells tend 
to separate and thus wider intercellular spaces are left. The 
capillary vessels become more distinct being more fully distended 
than elsewhere. Extravasation of red-blood cells occurs and these 
are found (cf. Fig. 5) making their way towards the embryonic 
tissues. Rarely, larger arterial capillaries or arterioles of spiral 
form are cut, and there is some evidence that the glands tend to 
assume a slightly spiral course. 
* This agrees with the description provided by JFrassi [op. cit.). 
f Placentaranlage, p. 7. 
