340 
MR. JONES ON THE IMPREGNATED MAMMIFEROUS OVUM. 
side, quite transparent, except at its most projecting point, where there was a spot 
of blood. I perceived nothing peculiar in the ovum contained in this vesicle. I did 
not detect a germinal vesicle in it. 
Besides this large and prominent Graafian vesicle there were on the surface of the 
right ovary other five prominent vesicles filled with coagulated blood. At the most 
projecting point of each of these there was a small whitish mammillary elevation, 
within which was contained the ovum, surrounded by a transparent gelatinous sub- 
stance, the same as that described in the preceding observation ; only it is to be re- 
marked, that in the Fallopian tubes this gelatinous looking substance had swelled out 
and acquired a greater diameter than it presented in the ovary. I did not detect a 
germinal vesicle in the ova forming the subject of this observation. 
In the left ovary I found only one vesicle, containing the coagulated blood and the 
ovum surrounded by the gelatinous looking envelope. 
Observation 3. — A Rabbit 48 hours after impregnation presented appearances much 
the same as the above. 
Is any trace of the gelatinous looking envelope of the ovum to be observed before 
impregnation ? In the ova of the Rabbit, &c., before impregnation, the proligerous 
disc, in which the ovum is imbedded, is observed to be composed of a gelatinous 
substance interspersed with grains, but as yet there appears no distinctly circum- 
scribed envelope*. 
The gelatinous looking envelope of the ovum I have just described must not be 
confounded with the vitellary membrane of the ovum, which was fully considered in 
my former paper. The former appears to be analogous to the cortical membrane 
surrounding the ovum of the Ornithorhynchus paradoxus , &c. while still in the ovary, 
described by Mr. OwEN'f'. That it, and not the vitellary membrane, as I formerly 
imagined, forms the chorion, will be made evident by the following observations. 
I would, however, premise some remarks on the ova of the batrachian reptiles, in 
order to place in a more striking point of view the circumstances I am about to re- 
late in regard to the ova of the mammifera. 
Fig. 2. exhibits the ovum of the Frog magnified 2 diameters. It is composed of a 
yelk, black on its surface, and whitish inside. The yelk is surrounded by a vitellary 
membrane, thicker than that of the bird’s egg, but thinner in proportion than that of 
the ova of the mammifera. Outside the vitellary membrane is a gelatinous envelope, 
which is added in the oviduct, the two preceding parts being formed in the ovary. 
When the ova are laid the gelatinous envelope rapidly absorbs water, and swells out 
to great thickness. 
* Dr. Karl Krause of Gottingen, however, in a late Number of Muller’s Archiv., speaks as if the gela- 
tinous substance really formed a well defined envelope. From his observations on the ovum before impregna- 
tion he has been led to form much the same opinion regarding the origin of the chorion as is recorded in this 
memoir. 
f Philosophical Transactions, 1834, p. 561. 
