298 PROFESSOR TURNER ON THE 
their vessels were larger than ordinary capillaries. Compared with the capil- 
laries of the foetal villi they were from twice to four times as big, so that they 
may be regarded as indicating an early stage of a dilatation into maternal 
sinuses, such as is still more clearly seen in the sloth, and reaches its maximum 
development in the human placenta. Many of these vessels ran vertically 
through the placenta, so that when horizontal sections were made through the 
organ they were seen in transverse section. In many cases these transversely 
divided vessels were surrounded by a ring of cells, the epithelial investment of 
the process of maternal tissue in which the vessel lay, which showed that the 
process only contained a single dilated capillary (fig. 16). The epithelial cells 
investing the intra-placental prolongations of the decidua were remarkably large 
and distinct, and on the average about ith or even 34d as large as the correspond- 
ing cells in the bitch. The fox, therefore, like the bitch, has no continuous layer 
of modified mucosa, such as is seen in the cat, on the uterine face of the 
separated placenta. The villi of the chorion had an arborescent arrangement, 
and gave off both lateral and terminal offshoots, in which a network of capillaries 
ramified. 
The placenta of the Seal has a closer affinity in its arrangement and structure — 
to that organ in the canine, than in the feline Carnivora. In the seal, as in the 
dog and fox, the decidua serotina, or mucous membrane of the placental zone, 
does not form a continuous layer on the uterine face of the separated organ. A 
definite layer is, however, left on the uterine zone itself, when the placenta is shed, 
which is subdivided into pits or trenches, by projecting folds. When the organ is 
in situ, these folds dip into the substance of the placenta, but are torn through 
in the process of separation, so that the only portions of the maternal tissue 
which are shed in the act of parturition, are the intra-placental prolongations 

of the mucous membrane. That the membrane left on the inner surface of — 
the uterus in the placental zone is the mucous membrane, is proved by its 
vascular structure, by the layer of columnar epithelial cells on its free ‘ 
surface, and by the presence of utricular glands. But the intra-placental 
prolongations, whilst consisting of the columnar epithelium, and of vascular 
sub-epithelial connective tissue, contain no utricular glands. The serotina, 
therefore, both in its deciduous and non-deciduous portions, is nothing more 
than the modified mucous membrane. In the feline Carnivora, again, as illus- 
trated by the common cat, the mucosa not only sends prolongations into the 
substance of the placenta, but forms a continuous layer on the uterine face of 
the shed placenta, and there is a consequent deficiency in the corresponding 
zone in the uterus itself. 
Hence, thoughall the Carnivora part with a considerable portion of the 
maternal mucosa in the separation of the placenta, yet they exhibit differences 

