STUDIES IN MAMMALIAN EMBRYOLOGY. 335 
formation of the decidual swelling. The first effect of the 
appearance of this marked swelling, opposite the mesometrium, 
is a stretching of the mucosa at the mesometrical side, where, 
as was noticed above (p. 311), it is less thick ab origine. 
Whereas the uterine epithelium that covers the folds of the 
reflexa shows distinct signs of commencing degeneration 
(fig. 87), the epithelium opposite is in no way similarly 
affected. But in consequence of the stretching just referred 
to, the depth of the glands that for the most part are very wide- 
mouthed in this region (fig. 37) diminishes. In the early stage 
of diagram fig. 30, this phenomenon of passive stretching has 
reached its height; during the further course of pregnancy 
more active phenomena are seen to occur in this epithelium on 
the mesometrical surface of the uterus lumen. Proliferation 
sets in, and indications of the rejuvenescence of this epithelium 
are not wanting. Clear, flask-shaped and cubic cells, with 
distinct rounded nuclei, are the elements that constitute it. 
Instead of the stretching which was noticed at the com- 
mencement, projecting folds are gradually noticed that protrude 
into the uterine lumen. They prove that the formation of 
new epithelial cells is even ahead of the stretching process, 
which of course goes on with inevitable regularity during all 
the consecutive phases of pregnancy. The position of these 
folds is influenced by the position of the decidual swelling with 
respect to the uterine lumen. Although the diagrams 28—36 
indicate the normal condition which is noticed in the majority 
of cases there were sometimes noticed slight irregularities in 
the position of the lumen, and these cases are specially in- 
structive to show that the folds of the proliferating uterine 
epithelium are very variable, and that their position is largely 
influenced by similar causes. In many preparations, especially 
when the lumen is more and more diminishing, I findthem pressed 
against the opposite surface of the decidua reflexa, and in con- 
sequence of the different reagents the proliferated epithelium 
is then often detached from the underlying muscularis, and ad- 
heres against the degenerating epithelial surface of the reflexa. 
This is certainly not the normal condition, and was not noticed 
