DISCUSSION 
89 
and retention of the ovum within the Graafian follicle, or in its immediate 
neighbourhood, until such time as it becomes capable of imbedding itself 
by its own activities, when it may do so in any patch of connective tissue 
which is sufficiently large to accommodate it and sufficiently vascular to 
meet the demands of its nutrition. 
In the present case, as in all others recorded, there is no formation 
resembling decidua. In this matter the early uterine ovum sheds light 
on the facts of ovarian pregnancy. It has revealed a stage in the process 
of imbedding in which destructive changes exceed, or perhaps better 
precede, constructive decidual changes. The formation of a decidua in 
the immediate neighbourhood of the ovum is not essential to its 
imbedding. The blastocyst implants itself in the tissue of all others 
best capable of reacting to the stimulus of an irritant or foreign body, 
viz., connective tissue. In uterus, tube and ovary alike, the reaction is 
manifested, in the first instance, by enlargement of the vessels. In the 
uterus there is soon extensive formation of decidua, but in the ovary the 
actively destructive changes persist to a later stage than in the uterus. 
This fact, along with the absence of a decidua, points to the conclusion 
that decidua formation is a provision of .a conservative nature, by which 
during the early months the activities of the trophoblast are limited 
and controlled until such time as placentation is complete. 
Lastly, ovarian pregnancy finally excludes the theory that the uterine 
epithelium can have any part in the formation of the plasmodium. The fact 
that neither the membrana granulosa nor the lutein tissue has any part in 
the formation of the investment of the villi in an ovum imbedded in the 
ovary, limits the possibilities of a maternal origin of the layer of syncytium 
to the connective tissue. The wholesale destruction of tissue in the ovary 
and the characters of the early stages of an ovum imbedded in the 
uterus cjuite put out of court any theory which has as its basis the idea 
of an interlocking of foetal and maternal tissue, and with it the deriva¬ 
tion of the plasmodial layer from maternal endothelium. The fact that 
the tissue round the chorionic vesicle in the ovary is everywhere clearly 
recognisable as necrotic connective tissue, while it is strong presumptive 
evidence in favour of the wholly embryonic origin of the plasmodium, 
M 
