562 
DR. MARTIN BARRY’S RESEARCHES IN EMBRYOLOGY. 
globuleux au moment de la ponte, preisente bientot apres des taches arrondies et 
claires. qui ne surpassent gueres 4 ; elles resultent de la disposition particulikre des 
granules qui remplissent son interieur, et qui se retirent de la circonference vers le 
centre-f'-.” 
421. T. Wharton Jones. “ It is known that in birds and reptiles the germinal 
vesicle disappears before impregnation. In the ova of the Frog, contained in the 
oviduct, and also in the more advanced of those contained in the ovary, no trace of 
the germinal vesicle is to be observed. ** # In the furthest advanced ova contained in 
the ovary of the Newt, the blastoderma was formed, and I think I perceived the place 
where the germinal vesicle had been. As to the ova of the Mammifera, I have found 
many in which there was no germinal vesicle, and which certainly had not been im- 
pregnated. It is to be remarked that in such ova the vitelline grains were for the 
most part coherent and formed the vesicular blastoderma. It being determined that 
the disappearance of the germinal vesicle is prior to impregnation and not dependent 
on it, the next question which arises is ‘ how does the germinal vesicle disappear?’ 
My observations on the ova of the water Newt are the only ones I have which bear 
upon this question. From what I have observed in them I think the mode of disap- 
pearance is the following : The vesicle at first imbedded in the substance of the yelk, 
approaches more and more the surface of it, until it comes to lie immediately under- 
neath the vitellary membrane, in the manner represented in fig. 12. The coat of 
the vesicle having become very soft and weak gives way, and the contained fluid is ef- 
fused on the surrounding surface of the yelk. The coat of the vesicle being of extreme 
tenuity cannot be seen after it has given way. The small depression in which the 
vesicle was situate now forms the cicatricula, fig. 13. I think that the fluid contained 
in the germinal vesicle being effused gives a degree of consistence to the matter 
composing the surface of the yelk, and thus promotes the formation of the blasto- 
dermal” 
422. Schwann. “ It is of great importance to decide the question, what is the 
import of the germinal vesicle. Is it a young cell arising within the yelk-cell, or is 
it the nucleus of the yelk-cell ? If the first, it is very probably the most essential 
foundation of the embryo; but if it be the nucleus of the yelk-cell, its importance 
ceases with the formation of the yelk-cell, and according to the analogy of most 
cell-nuclei it must subsequently be either entirely absorbed, or continue for a time, 
without forming any new essential object §.” — “It is worth while to a certain extent, 
from the import of the germinal vesicle [in the physiology of cells] to determine a 
priori its subsequent destiny, and thereby to be able to give at least a clue to the 
much more difficult observations on the impregnated ovum||.” Schwann subse- 
t L. c., p. 660. 
J On the first Changes in the Ova of the Mammifera in consequence of Impregnation, and on the Mode 
of Origin of the Chorion. Philosophical Transactions, 1837. Part II. pp. 343. 344. 
§ L. c., pp. 49, 50. || L. c., p. 51. 
