MR. JONES ON THE IMPREGNATED MAMMIFEROUS OVUM. 
341 
The ovum of the Newt differs from that of the Frog, inasmuch as the gelatinous- 
like matter which surrounds the yelk and its membrane is of an oval form, and is 
somewhat hardened on the surface, so as to form a kind of shell, inside which is a 
fluid substance, in which the yelk and its membrane can freely revolve and glide 
from one end to the other. The vitellary membrane is thinner in the Newt than in 
the Frog. Fig. 3. is the ovum of a Newt, in which development has commenced ; 
magnified rather more than twice. 
But what I wish particularly to insist on, in regard to the ova of the batrachian 
reptiles, and especially of the Newt, is, that when the embryo of the latter has attained 
a certain size, but still at an early period, the vitellary membrane gives way, and then 
the embryo is only contained within the cavity of the substance, which is added to 
the ovum in the oviduct, fig. 4. 
In the case of the Frog the vitellary membrane does not give way, until about the 
time the Tadpole is ready to burst all its envelopes. With the development of the 
embryo the cavity circumscribed by the vitellary membrane increases to as much as 
one fifth of an inch in diameter, and always retains its spherical form. There is a 
limpid fluid in the interior of the vitellary membrane, which seems to serve the pur- 
pose of an amniotic fluid, fig. 5. 
Observation 4. — March 18 and 19, 1836. Examined a female Rabbit seven days 
after impregnation. The right ovary presented four corpora lutea, the left ovary two. 
I found only one ovum in each horn of the uterus ; they were about -'o4ti of an inch 
in diameter*. Fig. 6, magnified 40 diameters. 
No vitellary membrane was to be seen. The gelatinous-looking envelope consti- 
tuted the only covering of the yelk, which now formed a vesicular blastoderma. The 
cavity of the gelatinous-looking envelope was much larger than the vesicular blasto- 
derma. The inner surface of the gelatinous coat presented what I supposed to be 
fragments of the vitellary membrane adhering to it. 
In both ova the vesicular blastoderma was irregular on one side, that on which I 
supposed the embryo was about to be developed. It was beginning to present the 
separation into layers, and had the same peculiar friable globular structure as the 
blastoderma of the hen’s egg. 
Observation 5.— This observation, which refers to the human ovum, agrees with 
that just related in regard to the ovum of the Rabbit. 
In the spring of 1836 I examined a small human ovum sent to me to Cork, where 
I then was, from Glasgow, by Dr. Mackenzie. In his letter to me, dated November 
29, 1835, he describes it thus : “ A very small human ovum. It came along with the 
entire decidua from a patient of mine. It lay in the middle of one of the parietes of 
* The reason I found but two ova is, perhaps, that from their great transparency they may have escaped 
notice. The gelatinous coat was so transparent that I could with difficulty see the outline of it under the 
glass when it was observed by transmitted light. The vesicular blastoderma being opaque was the only cir- 
cumstance that enabled me to detect the ova at all. 
2 Y 2 
