Pap A. A. W. HUBRECHT. 
uterus horn. A transverse section of this longitudinal inci- 
sion, the lips of which coalesce when the decidua reflexa 
comes to be established, and shows the aspect given in 
Figs. 2, 3, 87 of my paper of ’89. The cavity is thus not so 
much a cylindrical one (as it would seem to be if only one 
section is examined) but a slit-like one.! 
And the swelling itself is evidently one of interglandular, 
non-epithehal vascular tissue of the mucosa. Numerous 
fine capillaries transverse the swollen region in which the 
uterine glands and their lumen rapidly degenerate and dis- 
appear (cf. Hubrecht, ’89, figs. 37 and 38), sometimes even 
(l.c. fig. 39) the remains of the glands being phagocytically 
disposed of by the activity of the trophoblast cells. The 
endothelium of these maternal capillaries is generally swollen ; 
their opening up and the extrusion of the blood-fluid into 
the trophoblastic lacunee after their having been eroded by 
the action of the trophoblastic cells has already been described 
above. ‘The swelling continues to enlarge simultaneously 
with the enlarging blastocyst inside of it. The part of it 
which will contribute towards the constitution of the reflexa 
is the part which protrudes in the uterus lumen; it becomes 
thinner and its elements more stretched and fibrous as preg- 
nancy goes on; finally it becomes, together with the tropho- 
blast, a thin membrane, which ruptures at birth, 
The remaining saucer-shaped portion of the maternal 
trophospongia takes part in both these successive phenomena 
of growth and of distension, but as it is applied against the 
antimesometrical wall of the mucosa it does not share the 
vicissitudes of the reflexa, but constitutes what has been 
called in human embryology the decidua serotina. It flattens 
1 It will be very interesting to learn whether in man the closure of the 
decidua capsularis comes about in the same way. It has as yet not been 
definitely established, although it seems very probable, N.B.—This footnote 
was already in print when, during the proof correction, I became acquainted 
with Bryce’s and ‘Teacher’s sections of a very early human blastocyst (’08) 
which, even more than Peters’ specimen, establishes the similarity which in 
this respect exists between man and the hedgehog, a similarity which I have 
ventured to predict in an earlier publication (’89). 
