DR. MARTIN BARRY’S RESEARCHES IN EMBRYOLOGY. 
593 
scribes as being “ originally scattered-fN” In the Annelida, “the germinal vesicle is 
furnished with a minute, opake, single germ-nucleus or spot, which sometimes pre- 
sents an accumulation of grains. In Clepsine bioculata*** the germinal vesicle presents 
numerous, minute, pale, scattered spots, as in the Batraciiians|.” In some of the 
Mollusca, “the germ-nucleus or spot is usually a single, opake mass, which is some- 
times granular, and in some instances surrounded by minuter appendages, or has the 
appearance of being invested by a membrane^.” 
442. With reference to ova in general at the period of their ripening, R. Wagner 
remarks: “In the contents of the germinal vesicle, hitherto transparent, there takes 
place a coagulation ; new globules present themselves near the single or manifold 
germinal spot (which is to be considered as the nucleus of the germinal vesicle), — - 
or there are formed accumulations of granulated masses which sometimes constitute 
even membrane-like layers, as in many Insects. The germinal spot disappears as a 
single nucleus, or is no longer to be found among the other grains. # **As soon as the 
ova have left the ovary ### the germinal vesicle is no longer to be found. It has sud- 
denly or at least rapidly disappeared. Whether it suddenly bursts, or quickly col- 
lapses, is doubtful. The latter, from observations on the ova of Frogs and other 
animals, appears to me the more probable. The thinly fluid contents are observed to 
diminish in quantity, while there arise more solid granular coagulations ||.” 
443. A spot was described in mv “ First Series’’^ on the inner surface of the mem- 
brana vitelli in the ovum of the Frog. In the course of recent examinations it has 
seemed to me that the black layer — known to form at the periphery of the yelk in 
this ovum — comes into view as the spot in question disappears. The spot is composed 
of flat, elliptic objects such as those which become resolved into minuter objects, of 
the same kind, in the substance surrounding the germinal vesicle in the mammiferous 
ovum'f-'i~. 
f Is there not an earlier period in these, as probably in all other ova, when there is present only one spot or 
nucleus ? 
t “Ei,”p. 5. $ Ibid. 11 “Ei,”pp. 7.8. 
Philosophical Transactions, 1838, Part II., p. 313. par. 40. Plate VI. fig-. 28 d l . 
ft When I communicated my last memoir (“ Second Series,” l. c., par. 292. Note), the presence of this spot, 
in connexion with the new doctrine of “ cells,” seemed to require a modification of some of the conclusions in 
my “First Series,” as to the order of formation of the several parts of which the ovum is composed. For, pre- 
suming the spot in question to be the nucleus of a cell — and (following Schleiben’s views) necessarily existing 
before the membrane of its cell — I stated that if such spot were present in the corresponding membrane of 
other ova, the formation of this membrane is doubtless earlier than that of the germinal vesicle itself. — I have 
now to add, that later observations induce me to believe that the spot in question does not correspond to the 
nucleus of a cell, but seems (as above) to denote the commencement of the formation of the black layer, sucli 
formation appearing to begin in one of the discs by which the germinal vesicle is surrounded ; which disc then 
presents the appearance of a lenticular and usually elliptic spot. — The existence of this spot, therefore, does 
not affect my conclusions as to the order of formation of the several parts of the ovum ; nor do I see that the 
doctrine of cells — modified as it must be by the facts made known in this memoir — affects those conclusions. 
MDCCCXL. 4 G 
