DISCUSSION 
87 
tissue within the follicle. Van Tussenbroeks ovum must have lain to 
one side of the central coagulum, as she herself concluded ; in its growth 
it disturbed the outer part of the corpus luteum and to a great extent 
broke it up, while the inner portion remained intact. 
On the other hand, if it be admitted, as we believe it must, that the 
primary and essential factor in determining the effective implantation of 
the ovum be a rich supply of blood, the conditions just external to the 
layer of lutein tissue are still more favourable, and accordingly it appears 
that in the present case and that of Franz the ovum has burrowed out 
of the follicle into this lamella, and lies separated from the corpus luteum 
by a narrow zone of ovarian stroma except at one point. Here the wall 
of the gestation sac is directly continuous with the interior of the corpus 
luteum by a band of tissue of doubtful character and more or less in a 
state of necrosis. This strand is perfectly comparable with the cone of 
fibrinous material occupying the point of entrance in the Teacher-Bryce 
ovum (Plate hi, Fig. 3), and may, as has been already explained, be 
interpreted in the same way. AVhether this point of perforation correspond 
to the region of rupture of the follicle or to some other point is 
immaterial, because we know that the process of imbedding cannot begin 
till at least seven days after fertilization, by which time the follicle would 
be again closed. While this interpretation satisfactorily explains the position 
of the ova in these cases, another possibility may be admitted, viz., that 
the ovum was arrested between the lips of the wound in the follicle, 
was there fertilized, and was then imbedded in the vascular stroma outside 
the follicle. If this were so the fibrinous and necrotic tissue occupying 
the gap in the follicle wall might be due to the destructive process 
extending inwards towards the heart of the follicle. The imbedding in the 
case of Thompson’s ovum, which lay in the splayed-out mouth of the 
follicle with no lutein tissue either on its free surface or between it and 
the corpus luteum, may have occurred in this way. 
The fact that in our younger stage the chorionic vesicle lies wholly 
without the follicle is in favour of the first alternative, which moreover 
presents a more complete analogy to the conditions in a uterine im¬ 
plantation. The further growth of the ovum and extension of the 
