314 A. A. W. HUBRECHT. 
the fact that the intensity of the proliferation is not equally 
distributed in the swollen part of the mucosa, and hardly 
affects the mesometrical region, a folding of the opposite 
surface being the natural consequence. It is in the middle of 
this gutter-like depression that the earliest blastocyst is found 
(Pl. XV, fig. 5, and Pl. XX, fig. 37). My preparations do not for 
the present allow me to give a definite answer to the question, 
whether it is the blastocyst that first induces, by its presence 
in a certain part of the uterus lumen (where it stops on its way 
from the oviduct outwards), the decidual proliferation of the 
mucosa just described; or whether this proliferation and the 
swellings, with the gutter-like depression on the top that 
appears in consequence of it, are already on their way of being 
formed before the blastocysts have yet arrived on the spots 
where they will then definitely be lodged. The question is one 
that can only be answered by the finding of stages between the 
segmented ovum with two segmentation spheres (such as were 
noticed by Keibel in the oviducts close to the uterus lumen), 
and the earliest stages (Pl. XV, figs. 2, 4, 5, and 6) that have 
come under my own observation. I wish to point to this 
question as one to which further investigations will have to 
attend.! 
Once the blastocyst safely lodged in the bottom of the 
groove which is figured in figs. 2 and 5 of Pl. XV, and in fig. 37 
of Pl. XX (see also diagram, fig. 28), the processes of occlusion 
of the groove go hand in hand with the further development of 
the vascular arrangements in the proliferating decidual region. 
It was noticed that at the commencement the blastocyst 
reposes at the bottom of a groove, which in the figures just 
referred to is still seen to be in free communication with the 
uterus lumen. This communication is soon interrupted by 
1 | have observed a few cases in which a decidual swelling, with its gutter- 
shaped depression, was present and normally constituted, but in which there 
was no blastocyst. As, however, other swellings of the same uterus did 
contain embryos with the layers fully formed, I cannot look upon these cases 
as quite normal, and can thus only accord to them a very relative importance 
with respect to the question above referred to. 
