538 Proceedings of the Royal Society 
drawn out of the maternal pits without removing any of the mater- 
nal substance along with them, just as the fingers are drawn out of 
a glove without any portion of the substance of the glove accom- 
panying them, so that the placenta is non-deciduate. 
Having been engaged in the study of the structure of the pla- 
centa in the undelivered cow and sheep, it seemed to me, from the 
mode in which the foetal villi divided into branches, and from the 
consequent subdivision of the maternal pits into smaller branching 
compartments, that the interlocking of the foetal and maternal 
tissues with each other was so great as to render it difficult, if not 
impossible, for the foetal villi to be forcibly expelled from the 
maternal cotyledons, without carrying away with them some of the 
uterine tissue. With the object of testing the accuracy of this sup- 
position, I procured, in the spring of the present year, the foetal mem- 
branes, separated in normal parturition, both of the cow and sheep, 
and submitted the foetal cotyledons to microscopic examination. 
Before describing the microscopic appearances, it may be advis- 
able to say a few words on the general arrangement of the cotyle- 
dons, both foetal and maternal, in these animals. 
I shall first describe the arrangements in the sheep from a 
specimen where the cotyledons were well developed. 
In this animal the maternal cotyledons projected as cup-shaped 
mounds from the uterine wall. They were covered on the outer 
convex surface by the uterine mucosa, which was prolonged as far 
as the free inverted edge of the cup. The inner surface of the coty- 
ledon was composed of a soft, spongy material, containing numerous 
pits, which extended almost vertically, and divided as they passed 
deeper into its substance, into smaller compartments, which radiated 
towards the outer wall of the cotyledon, without diverging much 
from each other. The pits were lined by well-marked cells, most 
of which were irregular in shape, polygonal, ovoid, or even some- 
what caudate, and of considerable size, though some few were like 
modified columnar cells. They consisted of granular protoplasm, 
in which one, two, or sometimes three, well-defined ovoid or elliptical 
nuclei were imbedded, but without a cell- wall. Not unfrequently 
the outline of the individual cells was very indistinct, and they 
seemed as if composed of a layer of protoplasm studded with nuclei. 
The cells rested on a highly vascular sub-epithelial connective 
