40 
AN EARLY HUMAN OVUM 
of imbedding in the case of the human ovum is in all probability 
similar to that which Graf v. Spec describes as occurring in the guinea- 
pig rather than to that which occurs in the mouse or hedgehog, though it 
is not impossible that the ovum settles into one of the slight hollows 
which are present on the surface of the normal endometrium. This opinion 
is of course no new one ; it has been advocated by Peters, Graf v. Spee, 
Leopold and many others, but our case enables us to amplify the con¬ 
ception in some particulars. 
We would describe the imbedding of the human ovum as follows : 
The ovum having attained the stage of an early blastocyst, and 
measuring about '2 mm. in diameter (i.e. approximately the size of the 
mature oocyte), comes to rest in a slight depression, but neither a crypt 
nor a fissure, in the endometrium, destroys the surface epithelium, and 
continuing its destructive activity passes into a space in the decidua which 
has thus been produced. Necrosis followed by solution (digestion) of a 
considerable mass of the endometrium follows, resulting in the formation 
of an implantation cavity. So far we agree with the views expressed by 
Graf v. Spee regarding the human ovum in 1905. Changes leading to 
the production of decidua begin immediately after the solution of the 
epithelium, and the elevation is formed which is the characteristic resting- 
place of all the four earliest ova at present known. The mouth of the 
implantation chamber is probably blocked by a mass of blood clot, the 
cavity having meantime been filled by blood shed from the opened-up 
maternal capillaries. The present specimen shows a narrow orifice only 
T mm. in diameter, and the sealing substance is rather thrombus-like 
material than blood clot. The relatively-wide gap ("8 mm.) in the 
surface of the mucosa closed by blood clot and fibrin, which characterises 
the ova of Peters, Jung, Stolper and Graf v. Spee, is here entirely 
absent. If we have proved our thesis that the present ovum is the 
earliest yet recorded, we must conclude that this gap is not the portal of 
entrance properly so called—it is much too large—but is a secondary 
formation, being produced by the subsequent destructive activity of the 
trophoblast threatening to destroy the roof of the implantation chamber. 
The smaller extent of the fibrine cap in Leopold’s ovum, and the fact 
