DR. MARTIN BARRY’S RESEARCHES IN EMBRYOLOGY. 
563 
quently expresses the opinion that the germinal vesicle is “the nucleus of the ovum- 
cell -j\” 
423. Bischoff. “ All the ova [of the Dog] which I found in the oviduct, still re- 
sembled in a remarkable manner the ovarian ova, viz. they always had a granular 
disc, just as those in the ovary, and the yelk is always still dark and untransparent. 
Those of the earliest age presented also scarcely any change in size or in the appear- 
ance of the yelk. With all imaginable care and pains I sought in all for the germinal 
vesicle, but in vain. The disappearance of this structure therefore in mammals also 
(where hitherto it has been admitted only hypothetically), I believe myself enabled 
to pronounce as a decided fact. In an impregnated bitch, which I examined 19 
hours after the first coitus, and where I found the ova still in the ovary, the germinal 
vesicle was present. It thus probably disappears just on the exit of the ovum from 
the ovary. What becomes of it, I cannot tell. I decidedly believe that it bursts, and 
that its contents, mixed with the semen, form the spot, from which the development 
of the embryo proceeds;};.” 
Existing views regarding “ Cells .” 
424. The nucleus of the vegetable cell received but little notice until its import- 
ance was conceived by our celebrated fellow-countryman Robert Brown, who was 
the first to denominate this structure the nucleus of the cell. “This areola,” says 
Dr. Brown, “which is more or less distinctly granular, is slightly convex, and although 
it seems to be on the surface is in reality covered by the outer lamina of the eell§.” 
“ It is often nearly spherical, more or less firmly adhering to one of the walls, and pro- 
jecting into the cavity of the cell§.” 
425. Schleiden, struck with the constant presence of the nucleus in the cells of the 
very young “embryo” and of the newly- formed albumen, conceived it to be intimately 
connected with the origin of the cell. “In consequence of which,” says the same ob- 
server, “ I directed my attention to this point, and was so fortunate as to see my 
labours crowned with success ||.” “This structure,” says Schleiden, “varies in its 
outline between the oval and the circular, as well as in its form it appears to do from 
the lenticular to the perfect sphere *f[.” After giving the dimensions of this object in 
various instances, he proceeds, “ yet upon the whole these measurements are of little 
importance as they [the nuclei] grow and decrease [in size], and it cannot be deter- 
mined at what period of life it is that the cytoblast [nucleus] is found — “ In very 
large well-developed cytoblasts, ##: *there is observed (whether in the interior or sunk 
into the surface is not yet clear to me) a minute sharply circumscribed body which, 
judging by the shadow, appears to present a thick ring or a thick-walled hollow glo- 
t L. c., p. 259. + R. Wagner’s Lehrbuch, &c., p. 95, 1839. 
§ Transactions of the Linnean Society, vol. xvi. p. 710, &c., to which I refer for further information com- 
municated by the same author, on the Nucleus of the cell. 
|| Beitriige, &c., Muller’s Archiv, 1838, Heft II. p. 139. Ibid. pp. 139. 140. 
tf Beitrage, &c., Muller’s Archiv, 1838, Heft II. p. 140. 
4 c 2 
