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XVIII. On the first Changes in the Ova of the Mammifera in consequence of Impregna- 
tion, and on the Mode of Origin of the Chorion. By Thomas Wharton Jones, Esq. 
Communicated by Richard Owen, Esq. F.R.S. 
Received March 16, — Read April 27, 1837. 
Part I . — On the Changes in the Envelopes. 
HAVING previously described the structure of the ovum of mammiferous animals, 
as it exists in the ovary before impregnation*, I now proceed to relate some facts re- 
specting the changes which it undergoes in consequence of that act. 
My observations in reference to this point are the following. 
Observation 1. — On Wednesday the 16th, and Thursday the 17th September, ]835, 
I examined the internal organs of generation of a Rabbit, which had been impreg- 
nated on the afternoon of the Saturday preceding, and which was killed on the after- 
noon of Tuesday. The ovaries of both sides presented corpora lutea. 
In the Fallopian tube of the right side, near where it enters the horn of the uterus, 
I found six ova. Iti the same place on the left side there were only two. They dif- 
fered very remarkably from the ova as they exist in the ovaries before impregnation, 
inasmuch as the former presented, in addition to the component parts of the ovum of 
the ovary, a thick gelatinous matter surrounding it, similar to what is observed in 
the ovum of the Frog. The addition of this gelatinous envelope made the diameter 
of the whole body about T vth of an inch. Plate XVI. fig. 1. represents one of these 
ova magnified 40 diameters, and fig. 2. the ovum of the Frog when recently laid, 
magnified 2 diameters. 
I could not detect the germinal vesicle in the ova in question. The granulary 
matter of the yelk was coherent. The application of weak vinegar to the ova ren- 
dered the yelk transparent. Dilute nitric acid made the superadded gelatinous en- 
velope contract, but by the addition of more water it gradually expanded again. 
The question which this observation suggests is, “ Where do the ova acquire the 
additional gelatinous envelope; in the Fallopian tubes or in the ovaries?” The two 
following observations give the answer, “ In the ovaries.” 
Observation 2. — March 6, 1236. Examined a female Rabbit to-day, 41 hours and 
40 minutes after impregnation. There were no ova in the horns of the uterus, nor 
in the Fallopian tubes. 
The right ovary presented on its surface a very large and prominent Graafian ve- 
* See Lond. and Edin. Phil. Mag. vol. vii. p. 209. 
2 Y 
MDCCCXXXVII. 
