538 
DR. MARTIN BARRY’S RESEARCHES IN EMBRYOLOGY. 
eventually liquefy, and thus the contents of the germinal vesicle (c) — again reduced to 
fluid — enter into the formation of the two central cells, these being destined to succeed 
it. The membrane of the germinal vesicle (c), distended to a large size, — and still 
present in the ova, figs. 193. 195. 198 — disappears by liquefaction. This vesicle is 
thus, not a “ cytoblast,” as supposed by Schwann, but a parent cell : and of the nu- 
merous progeny of cells which arise within it, only two remain as its successors'!'. 
350. While the changes just described are in progress within the germinal vesicle, 
membranes (e) continue to form and then disappear successively around the layers 
of discs or cells, by which this vesicle is surrounded (par. 339.). Those membranes 
present at this period a high refracting power (Plate XXIV. fig. 193, Plate XXV. 
fig. 194. e.), and in some instances resist considerable pressure without being ruptured 
Very soon, however, the substance they invest has wholly disappeared, and its place 
is occupied by colourless transparent fluid. In this fluid there are often found soli- 
tary cells, the remains of the substance just referred to (Plate XXVI. fig. 206 .). It 
is also very common to meet with these solitary cells in previous conditions of the 
ovum (Plate XXIV. figs. 187- 193.), before the last of the membranes e has disap- 
peared §. 
351. An appearance frequently met with as the cells which surround the germ 
attain their greatest size, is represented in Plate XXIV. fig. 188, and more highly 
magnified in fig. 189. It seems to be produced in the following manner. Every cell 
within the ovum, which attains a size admitting of examination, appears to be filled 
with the foundations of other cells, arisen in the manner before described, and 
arranged in concentric layers around a pellucid cavity. The outer layers liquefy, 
leaving the central ones as dark isolated objects in a comparatively transparent fluid 
(fig. 189.). The membrane of the cell remains. Between the membranes of these 
cells there are also minute cells present in great number, which also have a high re- 
f In my “Second Series” (/. c., par. 317.) I erroneously applied the term “parent cell” to the mem- 
brane e. 
t “ Second Series,” l. c., par. 171, Plate VI. fig. 103. (3. 
§ The membranes e, instead of liquefying, may perhaps contribute to the thickening of the thick transpa- 
rent membrane /. Some observations mentioned in my “First Series” (l. c., Plate V. fig. 17./, e.) suggest, 
indeed, the consideration whether the membrane f may not be formed by a succession of the membranes e. 
The membrane of the ovisac (/<) was stated in that memoir (/. c., par. 23.) to appear to form around a mass of 
granules, since found to be cells. I have now to add, that these cells seem to coalesce for the formation of 
that membrane; and not only for its formation, but for its thickening also (compare in my “First Series” the 
thickness of this membrane ( h ) in certain figures of Plate VIII. with its original condition in Plate V.) ; the mem. 
brana granulosa appearing to be the medium through which the latter part of the process is effected. It would 
thus appear that the ovisac (the foundation of the Graafian vesicle) is a great cell, as well as possibly the thick 
transparent membrane /. The substance surrounding the germinal vesicle in certain states, exhibits changes 
similar to those presented by a nucleus ; namely, a succession of discs or incipient cells in concentric layers, 
and the formation of a membrane, or rather a succession of membranes, e, at the surface of those layers (par. 
339.). So that the substance in question seems to be a great “ cytoblast.” 
