INTRODUCTION 
5 
proof regarding the plasmodial investment of the villi, or syncytium. 
Certain authors have maintained that it owes its origin to the maternal 
tissues—some deriving it from the epithelium either of the surface or of 
the glands of the decidua, others holding that it represents maternal endo¬ 
thelium spread over the villi in the interlocking of foetal and maternal 
tissues, which has long been considered to take place in the development 
of the placenta. 
The idea that uterine epithelium is necessary for the production of 
the plasmodium was finally excluded by Catherine Van Tussenbroek when 
she demonstrated the existence of a syncytial layer on the villi of a 
chorionic vesicle imbedded in the ovary, and her observation has been 
confirmed by several investigators. It is just conceivable, however, that 
if a fertilized ovum developed in the interior of the Grafiian follicle, the 
follicular epithelium might be responsible for the production of the plas¬ 
modium ; but this cannot be the case if it be proved that the blastocyst 
may be imbedded in the ovarian stroma outside the corpus lutemn. In 
the second communication embodied in this publication further proof will 
be provided that such a case may occur. 
The theory that the plasmodial layer on the villi is derived from 
maternal endothelium has become practically untenable in view of the 
characters of the earl} 7 ova described in recent years, but it is not quite 
so certain that it may not owe its origin to the maternal connective tissue 
in which the ovum is imbedded, altered by the biochemical activities of 
the ectodermic cells of the blastocyst. 
In this connection earlier stages in the development of the plasmodium 
than have been hitherto available in the human subject, are required for 
the complete demonstration of its foetal origin in the human placenta. 
Our young uterine ovum, in virtue of its stage of development, and our 
case of ovarian pregnancy, being a crucial experiment both on the nature 
of the imbedding process and on the origin of the plasmodium, bring 
critical evidence to bear on this question. 
