i34 THOMPSON YATES AND JOHNSTON LABORATORIES REPORT 
As an alternative hypothesis, it was suggested by Hart that the fertilized 
ovum had the power of making its way through the uterine epithelium, as has been 
observed in the development of the guinea-pig. (Hubrecht). 
This latter view is now thought to be the true one, especially since it has been 
confirmed by the observations of Peters, who maintains that the epibiast of a fertilized 
ovum has an inherent phagocytic action, and by its means is able to attach itself to 
the maternal wall by burrowing downwards and laterally into the mucous membrane, 
and so coming to lie embedded in a cavity of its own formation. 
The following is a brief summary of the description of the early ovum from 
which the above theory was deduced : — 
Peters found the ovum on the second or third day, lying in a deep cavernous 
space with overhanging walls, in which no maternal epithelium was seen. Except at 
the point of entrance to the cavity where a plug of fibrin occupied the opening, the 
epithelium on the surface of the mucous membrane was completely intact. The 
rest of the mucosa was found to be congested and oedematous, with some degenera- 
tion of the epithelial cells in the neighbourhood of the ovum, while in the deeperlayers 
there was slight hypertrophy of the glandular elements. Decidual cells were first 
noted at some little distance from the ovum, being formed by the enlargement and 
rapid proliferation of the connective tissue cells of the stroma. 
The ovum is described as containing an embryonic area composed of a few 
cylindrical cells, an amniotic cavity completely closed, lined in the outer portion by 
flat cells, and surrounding all the chorionic vesicle. Between the amnion and the 
chorion there were several layers of mesoblast, the amniotic cavity being, in fact, em- 
bedded in mesoblast. The chorionic vesicle was lined by a thin layer of mesoblast, 
a slight space, however, separated it from the outer layer, which consisted of an 
irregular meshwork of epiblastic cells, forming a delicate reticulum between the ovum 
and the tissue in which it is embedded. The spaces in this network were filled by 
maternal blood. 
It is important to emphasize the fact that the earliest chorionic epithelium is 
cellular and not plasmodial in nature, as usually described. For it the name ' tropho- 
blast ' has been suggested by Hubrecht, who speaks of it thus : — 
' The first new name of which I want definitely to establish the significance is 
the name trophoblast. I propose to confer this name on the epibiast of the blastocyst, 
as far as it has a direct nutritive significance, as indicated by proliferating processes, 
by immediate contact with maternal tissue, maternal blood, or secreted material. The 
epibiast of the germinal area, the formative epibiast, and that which will take part in 
the formation of the inner lining of the amnion cavity is, ipso facto, excluded from the 
definition.' 
As indicated in the above definition, these cells take no part in the formation 
of the embryo, but they serve to anchor the ovum to the maternal tissues, and act as 
