RELATION OF VESICULAR MOLE TO CHORION CARCINOMA 135 
a means of nourishment by the absorption by osmosis of certain elements from the 
maternal blood in which it is bathed. This cellular condition of the trophoblast is 
only seen in the very earliest stages, and, as shown in the above specimen, is soon 
replaced by the plasmodial form, especially in the outer layers of the reticulum where 
the process first begins. In these places the cells were seen to have lost their definite 
outline. 
It has been suggested that this is due to the pressure of the blood, and to 
some chemical action of its plasma, and it is not difficult to recognize in these 
cellular masses the syncytium of the fully formed villus. 
Peters also noticed that the trophoblast was somewhat more abundant on the 
side facing the decidua basalis than on the outer side. Even at this very early stage 
the differentiation of the outer layer of the chorionic vesicle into villi had begun, and 
this precocity of development of the human chorion has been one of the greatest 
factors in misleading embryologists, who have based their observations on the 
conditions found in the chick. 
Coste, in 1847, was t' ie ^ rst to observe the role of the epithelium of the 
chorionic vesicle. In his description of an ovum, fifteen to eighteen days old, he 
shews the chorion to consist of two layers : an inner membrane passing continuously 
over the inner surface of the chorion, and an outer, which alone formed the hollow 
villi, so that in looking on the inner surface of this layer, numerous small openings 
were seen which did not penetrate the inner membrane. Coste believed these villi 
to be the pathfinders for the blood vessels of the fully formed villi serving 
temporarily to anchor the ovum to the uterus, but he did not describe the histological 
appearance of the layers. Kolliker, in 1 861, had an opportunity to examine the 
chorion, and he found that the outer membrane was epithelial, with cells of the same 
character as in the epithelium of older vascularized villi, and that the inner layer 
consisted of developing connective tissue and carried fine blood vessels. (Minot). 
In Schawbe's embryo, thirteen to fifteen days old, the chorionic villi were 
considerably branched and entirely filled with mesoderm. Their tips had little 
thickenings of epithelium by which they were attached to the decidua, and this was 
the only connexion between the foetal and maternal tissues. 
According to Minot, the reason for this is that the uterine mucosa does not 
grow in between the villi, nor do the villi penetrate the cavities of the uterine glands, 
' only the tips of the villi touch the surface of the decidua either at first or sub- 
sequently, except, of course, over the chorion laeve during the abortion of the villi. 
The tips of the villi are attached to the uterine surface, they penetrate the decidua 
for a short distance, but even in the placental area at the close of gestation the pene- 
tration is slight and the villi make their way only into the surface stratum of the 
decidua serotina. There is no evidence of any sort that the villi penetrate the glands 
at any period. 
