No. 3.] UTERUS AND EMBRYO. 399 
Kastschenko. The inner layer, S¢v, is called the Gallertschicht 
by many German writers, and seems to be what Kolliker (Zvt- 
wickelungsgeschichte, 2te Aufl., p. 322) designates as “ Gallert- 
gewebe zwischen Chorion und Amnion”’; it usually contains a 
considerable number of large granular wandering cells. Jung- 
bluth, 106a, describes a network of capillaries, which exist 
during the first half of pregnancy, apparently in the upper part of 
the stroma, —z.e. next the amnion — but I fail to findany. Where 
the amnion comes into contact with the chorion the adjacent parts 
of the two membranes are more or less loosened, forming a net- 
work of strands by which the membranes are united: most of 
the uniting strands appear to belong rather to the chorion than 
to the amnion. This loose tissue is perhaps that which Kolliker 
designates as a Gaclertgewebe distinct from the chorion. 
Although the chorion bounds the ccelom, I have observed no 
mesothelium upon its mesodermic surface; but I have not made 
search for it by any special methods. In the rabbit, it will be 
remembered, the mesothelium is very evident over the placenta, 
but the rabbit differs from man by the absence of union between 
the amnion andchorion. Nor have I been able to find any base- 
ment membrane, properly so called, under the chorionic ecto- 
derm. As to the appearance which suggests it, I accept Kast- 
schenko’s explanation, 107, 455. 
The mesoderm in the villi is differentiated otherwise than 
that of the membrane of the chorion. In the youngest stage 
I have examined there is some of the primitive matrix present 
in the villi; and I presume that earlier the whole mesoderm has 
the same character. In my specimen (three weeks) the change 
is progressing.» I have not succeeded in satisfying myself as to 
the process of change which takes place, but I think it probably 
essentially as follows: The cells gradually develop large bodies 
and acquire a more decided affinity for coloring-matters; mean- 
while vacuoles appear in the matrix, presumably by its modifica- 
tion into a new substance; the vacuoles increase in size and 
number, transforming the matrix into a network and ultimately 
causing its total disappearance, leaving the intercellular spaces 
filled entirely with the new substance, which has come from a 
metamorphosis of the original matrix; probably this new sub- 
stance is more or less fluid, since wandering cells are scattered 
freely through it. Leaving this half-hypothetical history, let us 
