DR. MARTIN BARRY’S RESEARCHES IN EMBRYOLOGY. 
557 
subsequently disappear by liquefaction, and are succeeded by a new set, arising in 
the interior, and likewise becoming circumscribed by a proper membrane, and so on. 
This explains why some observers have never seen a membrane in this situation. 
After the fecundation of the ovum, the cells of the tunica granulosa, that is, part of 
the so-called “ disc,” are found to have become club-shaped, greatly elongated, filled 
in some instances with cells, and connected with the thick transparent membrane by 
their pointed extremities alone. 
407- That the thin membrane described in the Second Series of these researches as 
rising from the thick transparent membrane in the Fallopian tube, and imbibing fluid, 
is really the incipient chorion, was then shown by tracing it from stage to stage, up 
to the period when villi form upon it. There remained, however, two questions 
undecided ; viz. whether the chorion is formed of cells, and if so, whether the cells 
are those of the so-called “disc,” brought by the ovum from the ovary. It may now 
be stated that the chorion is formed of cells, which gradually collect around the thick 
transparent membrane, and coalesce ; and that the cells in question are not those of 
the “disc” brought with the ovum from the ovary. The cells which give origin to 
the chorion are to be more particularly described in a future paper. 
408. The existing view, namely, that a nucleus, when it leaves the membrane of its 
cell, simply disappears by liquefaction, is inapplicable to any nucleus observed in the 
course of these investigations. The nucleus resolves itself into incipient cells in the 
manner above described. In tracing this process, it appears that the nucleus, and 
especially its central pellucid cavity, is the seat of changes which were not to have 
been expected from the recently advanced doctrine, that the disappearing nucleus has 
performed its entire office by giving origin at its surface to the membrane of a single 
cell. It is the mysterious centre of a nucleus which is the point of fecundation ; and 
the place of origin of two cells constituting the foundation of the new being. The 
germinal vesicle, as already stated, is the parent cell, which, having given origin to 
two cells, disappears, each of its successors giving origin to other two, and so on. 
Perpetuation, however, at this period, consists, not merely in the origin of cells in 
cells, but in the origin of cells in the pellucid centres of the nuclei of cells. 
409. Neither the germinal vesicle, nor the pellucid object in the epithelium-cell, is 
a “ cytoblast.” The cells into which the nucleus becomes resolved, may perhaps enter 
into the formation of secondary deposits — for instance, spiral fibres ; and they may 
contribute to the thickening which takes place, in some instances, in the cell-mem- 
brane. 
410. The germ of certain plants passes through states so much resembling those 
occurring in the germ of mammiferous animals, that it is not easy to consider them 
as resulting either from a different fundamental form, or from a process of develop- 
ment which, even in its details, is not the same as what has been above described ; the 
fundamental form in question in Mammalia, and therefore it may be presumed in 
Man himself, being that which is permanent in the simplest plants, — the single iso- 
lated cell. 
