DR. MARTIN BARRY’S RESEARCHES IN EMBRYOLOGY. 
531 
Preparatory Changes in the Germinal V ssicle and Germinal Spot. 
325. The germinal vesicle (c) does not “burst,” “dissolve away,” or “become 
flattened,” on or before the fecundation of the ovum, as hitherto supposed. It ceases 
to be pellucid ; and this perhaps is one cause of the mistaken views regarding it. 
But another cause is possibly a less transparent state assumed by the surrounding 
substance ; and a third is doubtless the almost entire absence of observations on 
mammiferous ova at this period. 
326. The germinal vesicle fills with cells, and these become filled with the foun- 
dations of other cells ; so that the germinal vesicle is gradually rendered nearly opake 
(Plate XXII. fig. 164. c.). The mode in which this alteration takes place, is the fol- 
lowing ; and it is one which, if confirmed by future observation, must modify the 
views recently advanced on the mode of origin, the nature, the properties, and the 
destination of the nucleus in the physiology of cells. Some minute details are un- 
avoidable ; but their introduction here will save future repetition. 
327. The germinal spot ( h ) is known to present in some instances a dark central 
point'f-. I find that such a point always makes its appearance at a certain period ; 
that it enlarges, resembles a dark globule or ring, and contains a cavity filled with 
fluid, which is exceedingly pellucid. That which originally constituted the germinal 
spot assumes the appearance of incipient cells | (Plate XXII. fig. 156. h.). These, 
enlarging, gradually come to occupy the whole of the interior of the germinal vesicle, 
except that part from which they rose. In the ovum, fig. 157, that which had been 
a dark point presented a finely granular appearance, with a central pellucid cavity. 
In a subsequent condition (fig. 159.), the part corresponding to that just referred to, 
as finely granular, had distended, and presented a layer of incipient cells ; while in its 
interior there had arisen another object having a finely granular appearance, and 
likewise a central cavity. In the more advanced ovum of figs. 160 and 161, the 
germinal vesicle contained no less than four concentric layers, arisen in the order 
just mentioned, and surrounding a pellucid central space, which was exceedingly 
minute. The germinal vesicle in the ovum, fig. 162, presented an appearance of the 
same kind, but seemed to be in a condition yet more advanced. Besides three con- 
centric layers of cells, a space was seen in the interior (included by the dotted line, 
fig. 163.) ; and in this space were two other concentric layers of cells, in a still more 
incipient state, — these also surrounding a pellucid centre §. 
+ R. Wagner, Prodromus Historise Generationis, 1836. Schwann, l. c., p. 54. 
J My friend R. Wagner with reference to the ova of squamous Amphibia and cartilaginous Fishes, remarks, 
“ Also where the germinal spot is single only, and in riper ova, there are sometimes found to arise granula- 
tions, in the form of minute scattered globules on the inner surface of the germinal vesicle, whereupon the ori- 
ginal larger and opaker germinal spot becomes less distinct and disappears.” (Lehrbuch der Physiologie, 
Erste Abtheilung, p. 33, 1839. Prodromus, &c., figs. 24. and 27.) This eminent observer appears also to 
have seen the external portion of the germinal spot in the mammiferous ovum undergoing the change I have 
above described (Lehrbuch, &c.. Tab. II. fig. viii.), though the nature of that change remained concealed. 
§ The changes above described, as taking place in the germinal spot, may assist to explain its altered ap- 
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