PROFESSOR W. TURNER ON THE PLACENTATION OF THE APES. 
533 
fied arrangement of cells, which from their position may appropriately be called the sub- 
chorionic cells (figs. 7, 8). They formed a yellowish' white membrane, sufficiently thick 
to be seen with the naked eye and to be peeled off’ with a pair of forceps, which was 
continued over the whole surface of the chorion. I examined microscopically these sub- 
chorionic cells, both in vertical sections through the chorion and in preparations made 
by cutting away the stems of the villi and looking at the placental surface of the 
chorion. The layers of cells were not uniform in number, but varied from four or five 
to eight or ten, or even more. The cells in the most superficial layers were flattened 
and irregularly polygonal, and two or three times larger than the intra-chorionic cells 
just described. The cells in the deeper layers were elliptical, or even elongated into 
small spindles, not unlike in shape, but larger than, the fusiform corpuscles of the 
connective tissue of the chorion. In the more superficial cells the nucleus was very 
distinct, and in the whole the protoplasm was granulated. When seen in mass these 
cells had a yellowish colour, which contrasted with the white connective tissue of the 
chorion. They differed also very materially in appearance from the amniotic epithe- 
lium in relation to the opposite surface of the chorion. In some of the sections 
through the chorion the line of demarcation between the sub-chorionic cells and the 
proper tissue of the chorion seemed to be as definite as that between the cuticle and 
cutis in a section through the skin. But when thin sections were made and 
examined with a magnifying power of 350 diameters, the proper tissue of the chorion 
seemed to pass between the cells of the deeper layers, so as to give one the impression 
that they were derived from the chorion and were not cells superadded upon its free 
surface, but not arising from it. 
The stems of the villi at their origin from the chorion were invested by a stratified 
arrangement of cells similar to, and continuous with, the sub-chorionic cells ; and at 
the angle between the place of origin of the villus and the adjacent part of the chorion 
a great crowd of these cells was collected, for as many layers of cells enveloped the 
base of the villus as were situated on the immediately-adjacent part of the chorion. 
The layers diminished in number as the villous stem was traced farther away from the 
chorion. The cellular covering was also prolonged on to the larger branches of the villi, 
but with a considerable reduction in the number of layers. On the smaller branches 
of the villi, and on the terminal and lateral buds, the cellular covering of the villi was 
reduced to a single layer of somewhat flattened, though not squamous, cells, rectangular 
in outline and closely applied to each other by then- margins. 
The decidua placentalis or serotina formed a thick well-defined layer between each 
lobe of the placenta and the corresponding part of the muscular coat of the uterus. 
Opposite the intervals between the lobelets into which each lobe was divided, the 
modified mucous membrane was thicker than opposite the lobelets, and approached 
more closely to the chorion ; and the villi which grew from the chorion, corresponding 
to these intervals, were much shorter than those entering into the substance of the 
lobelets. At the margin of the placental lobes the decidua serotina was directly 
