534 
PROFESSOR W. TURNER ON THE PLACENTATION OF THE APES. 
continuous with the decidua vera, and the spongy character of the serotina was 
prolonged into the vera immediately continuous with it. 
When the placenta was carefully stripped off the uterus, the decidua placentalis 
split into two portions, the one adhered to the uterine surface of the placenta, the 
other remained on the uterus, and the latter was considerably thicker than the former. 
The separation into the two layers was effected by tearing through delicate bands 
and flakes of the decidual tissue, which were continuous with the septa between the 
loculi to be immediately described, in the uterine layer of the decidua serotina. 
The layer of decidua which remained attached to the uterine surface of the placenta 
was thin, and of a fawn colour. Its placental surface was very irregular owing to 
numbers of hillock-like prolongations of its substance, which projected into the interior 
of the placenta in a manner not unlike that in which stalagmites project from the floor 
of a cavern (fig. 10). These hillocks were usually somewhat conical in form, and 
were set so closely together that narrow intervals only intervened between the bases 
of adjacent hillocks. The arrangement of the hillocks was examined both in vertical 
sections through the placental decidua and in preparations made by detaching the villi 
from the decidua and examining its placental surface. In both these modes of pre- 
paration the terminal parts of the stems of the villi were seen to be intimately 
attached to the hillocks of decidua ; so close, indeed, was the union that some force 
had to be used to draw them asunder, and in the act of separation it was usual for 
either a portion of the decidua to be drawn away with the villus, or for a fragment of 
the villus to remain attached to the decidua. To carry out the comparison which I 
have already made, if the hillocks of decidua resemble stalagmites projecting from the 
floor of a cavern, the villi of the chorion are like stalactites depending from its roof, 
and the attachment of the villi to the decidua is due to the mutual growth and fusion 
of the two structures. 
When examined microscopically this layer of the decidua placentalis was seen to be 
chiefly composed of irregularly polygonal, somewhat flattened cells, composed of a large 
and distinct nucleus surrounded by a granulated protoplasm. These cells had a strati- 
fied arrangement and a yellow colour when seen in mass. They closely resembled, 
both in appearance and arrangement, the superficial layers of sub-chorionic cells. 
Although, as a rule, the cells were compactly arranged in the several strata, they at 
times, in the deeper strata, were surrounded by a delicate, translucent, faintly fibril - 
lated matrix, apparently an imperfectly differentiated connective tissue. Groups of 
fusiform cells were also occasionally seen. 
The hillocks of the decidua possessed a very similar structure. The greater part of 
their thickness was composed of a stratified arrangement of the irregularly polygonal, 
somewhat flattened, granulated and nucleated cells ; but the axis of the hillock was 
not so richly cellular, but consisted mainly of delicately filamentous connective tissue 
containing fusiform corpuscles. The end of a villus attached to a hillock was com- 
pletely surrounded by the stratified cells of the decidua, so that the villus was 
