42 
AN EARLY HUMAN OVUM 
is necessarily associated with the destruction of vessel walls and the 
opening up of glands. Haemorrhage occurs into the cavity, but the blood 
does not coagulate. It serves to nourish the ovum, and after a time 
it begins to circulate among the trophoblastic processes. Up to this stage 
the ovum has not become attached to the decidua. It now becomes fixed, 
first by anchoring strands of plasmodium and later by the development 
of primitive cellular villi. Our, specimen shows the very initial stages of 
attachment. 
We may here digress for a moment to point out a very suggestive 
analogy with the normal ovum in respect of its influence on adjacent 
maternal tissues, presented by an embolus of chorion-epithelioma in its 
development into a secondary tumour . 1 The embolus, usually somewhat 
larger than the imbedding ovum, lodges in the fork of a blood-vessel, the 
wall of which soon shows degenerative changes identical in character with 
those seen in the decidua around the present ovum. These occur prior to the 
invasion of the tissues by the tumour cells. The injured blood-vessel dilates 
into a more or less globular aneurismal cavity, and there may be con¬ 
siderable growth of the embolus in its interior before invasion begins. 
The blood in the neighbourhood of the embolus does not coagulate, until 
secondary changes, which need not be discussed here, bring about that 
result. After a time the tumour elements invade the maternal tissues 
and the embolus becomes attached. At this stage appearances may be 
found very similar to those around the margin of Peters’ ovum. 
The formation of the aneurism with its necrotic wall, round the 
embolus finds a parallel in the behaviour of the decidua round the human 
ovum. We may assume that, as in the case of the guinea-pig ovum, there 
is primarily destruction of a fairly wide zone of tissue, which draws away 
from the ovum partly, at least, on account of the swelling which accompanies 
coagulation necrosis. The shed blood must further stretch the soft decidua 
just as the wall of the vessel is stretched into the wall of an aneurism, 
and the necrotic zone of the decidua is removed, like the necrotic wall 
of the aneurismal sac, before attachment can take place. Also, as in the 
1 “ On the Development and Natural Healing of Secondary Tumours of Chorion-epitlielioma,” 
by John II. Teacher, Jour. Path, and Bad. vol. xii. part iv. 1908. 
