14 
AN EARLY HUMAN OVUM 
correspond to the dimple seen on the surface of the lobule; that is repre¬ 
sented by a shallow depression which appears on the surface immediately 
over the centre of the blastocyst, and is seen in Plate II, Fig. 2. The 
blood-vessels of the decidua are greatly dilated, more especially on the deep 
aspect of the blastocyst, where they form the same “ blood cushion ” seen 
in the ova of Peters, Ercole Cova, and Graf v. Spee (1905). The glands 
are enlarged and irregular. Beneath the blastocyst there is great extra¬ 
vasation of blood and deposit of fibrin, while the upper part of the tubercle 
is seen to be occupied by a haemorrhage. 
The implantation cavity is clearly marked off all round, but more 
especially at its outer part, by a darker staining band which, as will be 
seen presently, represents a layer of necrotic tissue. The cavity is occupied 
by very irregular strands of tissue, the spaces of which are densely packed 
with blood corpuscles. Above, the space is encroached on and the zone 
of necrotic tissue broken up by the haemorrhage already alluded to. 
Under a higher power (100 d) the blastocyst wall (Plate in, Fig. 3) is 
seen to be composed of a lightly staining lamella of protoplasm, in which 
the cell outlines are indistinctly defined, while the very irregular mesh- 
work occupying the space in the decidua is observed to have plasmodial 
characters. 
In describing the histological details of the several parts, we shall first 
take the decidua, then the trophoblast, and lastly the embryonic rudiment. 
THE DECIDUA. 
The surface epithelium has completely disappeared. Whether this be 
the result of maceration, or is a normal feature, it is not possible to 
determine. The fact that it is also absent from the outlying parts of 
the decidua, while it is present in the cases of Peters and Leopold, 
suggests that it is due to superficial maceration. 
There is no coagulum or organised thrombus adhering to the surface 
over the ovum. The mucous membrane shows all the well known 
characters of the menstrual decidua. The cells are clear and swollen, the 
tissue spongy; the vessels are greatly dilated; the glands are enlarged, 
