*00990- Transactions.— Zoology. 
Each fetus lay coiled up in its compartment (fig. 1), some part of its 
— body, in many cases, pushing one of the partition walls and causing it to 
 bulge out into the adjacent compartment. In the specimen figured, for 
instance, the head of fetus m encroaches upon compartment c; the 
trunk of e encroaches upon compartment m, and its head upon r. The 
foetuses are thus packed as closely as if they were not oce: in separate 
chambers. 
In the specimen figured there were eight foetuses in the uterus, but the 
usual number seems to be five. In some cases one fetus was considerably 
less developed than the rest: this is the case with a in fig. 1: in one 
instance there was in the anterior end of the oviduct a mass of = evi- 
dently an egg which had undergone no development. 
The precise anatomical relations are as follows:—The wall of the 
uterus, as mentioned above, is very thin: it consists of an outer peritoneal 
investment (fig. 2, p), then of a remarkably thin muscular layer (m), and 
finally of the mucous membrane (m.m.). The latter is produced into a 
series of reduplications which extend across the cavity to the opposite wall, 
and in this way the fetal compartments are formed. 
From this it is evident that the outer walls of the foetal compartments 
are simply portions of the uterine walls, and are lined with epithelium, but 
that the party walls (ps. ch.) consist of mucous membrane only, covered 
with epithelium on both sides. The mucous membrane has a yellowish 
colour, is raised on its free surface into numerous folds, and is abundantly 
süpplied with blood-vessels, so that each fetus is surrounded with a 
vascular membrane. 
From the inner surface of the mucous membrane, a thin colourless 
transparent non-vascular layer (fig. 2, ps. am.) can be readily dissected off. 
From the relations of the mucous membrane, as just described, it follows 
that this non-vascular membrane must occur in the form of a series of 
closed sacs, forming the actual lining of the several compartments. 
As a consequence of this arrangement, when the peritoneal and muscular 
layers of the uterus are stripped off—which ean be done with great ease— 
and the Fallopian tube and cloacal end of the uterus removed, the mucous 
membrane of the uterus proper is obtained in the form of a single perfectly 
closed sac, but on removing the mucous membrane itself, a number of 
closed sacs are obtained, each enclosing a fœtus with the surrounding finid, 
and consisting of the non-vascular membrane just described. 
It will be seen at once that the transparent non-vascular sac in which 
each foetus is directly enclosed, has the same general relation to the foetus 
as the amnion of Sauropsida and Mammalia, from which it differs in being 
a product, not of the foetal but of the maternal tissues. I propose, there- 
