No. 3.] UTERUS AND EMBRYO. 379 
centa, g, f, f, and down between the lobes, g: the epithelium 
therefore corresponds entirely with the placental mesothelium 
of the rabbit. The upper portion of the placenta, /, corresponds 
to the meshwork of degenerated glands in the rabbit’s placenta. 
The layer of epithelium, 2, z, #, covering the side of the placenta, 
corresponds to the foetal ectoderm in a similar position in the 
rabbit ; at an earlier stage it resembles very closely in appear- 
ance what I find in the rabbit (Creighton, 77a, p. 560, Pl. XIX., 
Fig. 0, ¢, c, c,). Deep down under the space between the lobes of 
the placenta comes the sub-placenta, Ercolani’s cotyledonary 
organ, O, which was compared above with the sub-placenta of 
the rabbit ; the thick pedicle of the placenta, e, x, x, corresponds 
to the sub-glandular layers of multinucleate decidual cells, which 
has encroached upon and apparently replaced the outer zone 
of uninucleate decidual cells, which is present earlier, as it is in 
the rabbit. At the side of the placenta is the peri-placental 
thickening, ¢.d, and springing from it the so-called reflexa, c, 
which is probably only the peri-placenta hypertrophied. The 
reflexa is entirely absent in the rabbit. In regard to what I 
suppose to be the glands, P, neither the descriptions nor the 
figures of Ercolani suffice to indicate their character. 
The interpretation offered differs in nearly every respect from 
Ercolani’s own; and yet though I have no preparations of the 
Guinea pig’s placenta, and am acquainted with the organ only 
through the publications of others, I think the homologies drawn 
may be accepted with considerable security; but let me add 
that I am well aware that their actual justification can come 
only from the specimens. 
Sections of the rat’s placenta near full term show that the 
structure in that species is strictly comparable to what exists in 
the rabbit. The surface is covered by a thin epithelium over- 
laying a vascular connective tissue layer ; the vacuolated tubular 
glands, very much degenerated, occupy the greater part of the 
placenta, leaving only a thin vascular zone from which the outer 
zone is lost, and which is therefore occupied solely by the much 
altered sub-glandular zone of multinucleate cells. There are 
many differences in details of structure from the rabbit, but the 
fundamental likeness is self-evident. 
As the similarity of the placentz of various rodents has been 
noted by previous authors, it is probable that the type of 
placental organization is the same throughout the class. 
