RELATION OF VESICULAR MOLE TO CHORION CARCINOMA 137 
epithelioid cells, having a very slight attachment at one point only to the chorionic 
vesicle. Close to this area, and apparently in contact with it, is a small cavity, 
believed to be the amnion. 
(It may be noted, in passing, that from the appearances found in the above 
specimen, the statement made by Peters, that the amnion does not form by free folds 
as has hitherto been taught, but by an inclusion of epiblastic cells in the form or a plug, 
by the breaking down of which the embryo, body cavity and amnion are formed, receives 
confirmation). 
It is a significant fact that at no point in the decidua which the chorionic villi 
had not touched was there any syncytial tissue, a point which has been much 
emphasized by Minot in discussing the foetal origin of the syncytium. 
That the early ovum is thus only anchored and not adherent to the maternal 
tissues was also demonstrated in another specimen which came under observation. 
A small ovum, measuring about 4 cm. in diameter, almost completely sur- 
rounded by decidua, was expelled by a patient who had missed one menstrual period. 
This was floated out in water, and with great care the decidual tissue was 
gently stripped away. No force was used or required, the villi detaching themselves 
without any apparent damage, the ovum then presenting the appearance of a shaggy 
spheroid. The amnion and chorion were separated and pieces were stained 
and mounted on the fiat. The amnion consisted ot two distinct layers, the inner 
being formed of flat epithelial cells with oval nuclei, many in a state of active 
division (epiblast) ; the outer of young connective tissue, long spindle and branching 
cells varying greatly in size and shape (mesoblasf). The chorion, with which we are 
chiefly concerned, also consisted of two layers, the inner mesoblastic lay r er corres- 
ponding with that seen in the amnion. The outer layer was also formed of flat 
epithelial cells, but here the cells were of more than one layer, two were seen in some 
places, but the arrangement was not uniform. Here and there over the membrane 
buds ot the outer layer were seen, some branched giving off smaller buds and having 
a mesoblastic core, others apparently hollow buds of epithelium. The tips ot the 
villi were found to be quite complete, ending in each case by a solid mass of cells, 
giving to the villus a clubbed appearance. 
Sections were then cut of the decidua (see Fig. 4, Plate VIII). These shewed 
typical decidual tissue, flat, polygonal spindle and round cells with large round nuclei. 
The free surface to which the ovum had been attached was reticulated, deep recesses and 
spaces running up into the compact layer, but the importance which is attached to the 
specimen consists in the fact that no trace of foetal structure, such as syncytial cells 
or other parts of villi were seen in any of these spaces, some ot which were filled 
with blood, or in any other part of the section, and it is not unreasonable to conclude 
that in these spaces, bathed in maternal blood, the clubbed ends of the villi were 
previously situated. 
T 
