THE OVUM IN THE AMPHIBIA. 
179 
not be mistaken for the germinal vesicle arrived at the surface. There is a similar 
spot, and that too of an elevated form, on the egg of each of the Lissotritons. But 
independent of the fact that the germinal vesicle has entirely disappeared from the 
interior of the egg before it escapes from the ovary, this spot is shown not to be the 
vesicle, both in the fact that in the egg of Rana temporaria the dark portion of the 
yelk is unchanged, while in each case the spot is perforated, and leads into the canal 
that passed originally to the vesicle. I regard the spot as simply a protrusion outwards 
of the edges of the canal while closing, after the vesicle has disappeared. I shall 
presently show that a similar white spot is formed on the under surface of the egg of 
the Frog soon after deposition, and which might equally well be mistaken for the ger- 
minal vesicle. 
Mode of disappearance of the Vesicle. — The mode in which the vesicle disappears 
may be inferred from the facts of its structure. Being filled with a progeny of cells 
which we may regard as of different periods of growth, and these again containing 
others, it is fair to conclude that this process of cell formation is that by which the 
parent vesicle is ultimately destroyed. At the time when the germinal vesicle has 
nearly attained its full size, the peripheral cells are smaller than those nearer to its 
centre, while the yelk cells that surround the vesicle are still smaller than either, and 
are of a dark colour. When, therefore, the vesicle has acquired its full size, by the 
simple vegetative endogenous growth of the contained celts, we may fairly presume 
that the death of the parent mother-cell, or germinal vesicle, takes place as the result 
of their enlargement, by the diffluence of its investing membrane ; and the enclosed 
daughter cells, thus gradually set free in the midst of those of the yelk, as in the ideal 
(fig. 7)5 form one mass with the latter, and the moment of the actual disappearance of 
the vesicle thus escapes direct observation, its previous existence being indiccited only 
by the unbroken outline of the investing membrane. 
These views lead me to agree with Wagner and Barry in regard to the structure 
and mode of growth of the germinal vesicle, but not as to that by which it disappears. 
Dr. Barry indeed believes that the vesicle only becomes changed by its mode of de- 
velopment, and does not cease to exist. But most certainly it does disappear in the 
Amphibia, and, as I believe, through the growth of the young cells in its interior. I 
cannot therefore agree with Dr. Barry that the changes in the vesicle end in the pro- 
duction of two cells in the centre of the yelk, that give immediate origin to the em- 
bryo ; but rather believe that it is from one of the central cells of the germinal vesicle 
that the future embryo vesicle takes its origin, while the remainder of the liberated 
cells are distributed with this through the substance of the yelk, when the segmenta- 
tion of this body takes place. This opinion is in accordance with that of Vogt*, who 
found that in the ova of Alytes ohstetricans the germinal spots increase in number, 
and that a few hours after fecundation small vesicles, similar to these spots, are scat- 
tered through the yelk. I have myself found similar vesicles in the fecundated egg 
* Untersuchungen iiber die Entwicklungsgeschichte der Geburtshelfer-Krsete {Alytes ohstetricans), 4to, 1842. 
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