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 cells, 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), form one mass with the latter, and the moment of the actual disappearance of 

 the vesicle thus escapes direct observation, its previous existence being indicated 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 obstetricans 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 uber die Entwicklungsgeschichte der Geburtshelfer-Kraete (Alytes obstetricans), 4to, 1842. 



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