DR. MARTIN BARRY’S RESEARCHES IN EMBRYOLOGY. 
555 
pellucid. The free portion of the spot resolves itself into cells ; and the foundations 
of other cells come into view in its interior, arranged in layers around the central 
cavity; the layers being 1 pushed forth by the continual origin of new cells in the 
interior. The latter commence as dark globules in the pellucid fluid of the central 
cavity. Every other nucleus met with in these researches has seemed to be the seat 
of changes essentially the same. The appearance of the central portion of the 
nucleus is, from the above process, continually varying; and the nature of the 
nucleolus of Schleiden may perhaps be thus explained. The germinal vesicle, en- 
larged and flattened, becomes filled with the objects arising from the changes in 
its spot ; and the interior of each of the objects filling it, into which the eye can pene- 
trate, presents a repetition of the process above described. The central portion of 
the altered spot, with its pellucid cavity, remains at that part of the germinal vesicle 
which is directed towards the surface of the ovum, and towards the surface of the 
ovary. At the corresponding part, the thick transparent membrane of the ovum in 
some instances appears to have become attenuated, in others also cleft. Subsequently, 
the central portion of the altered spot passes to the centre of the germinal vesicle ; 
the germinal vesicle, regaining its spherical form, returns to the centre of the ovum, 
and a fissure in the thick transparent membrane is no longer seen. From these suc- 
cessive changes it may be inferred that fecundation has taken place ; and this by the 
introduction of some substance into the germinal vesicle from the exterior of the 
ovary. It may also be inferred, that the central portion of the altered germinal spot 
is the point of fecundation. In further proof that such really is the case, there arise 
at this part two cells, which constitute the foundation of the new being. These two 
cells enlarge, and imbibe the fluid of those around them, which are at first pushed 
further out by the two central cells, and subsequently disappear by liquefaction. 
The contents of the germinal vesicle thus enter into the formation of two cells. The 
membrane of the germinal vesicle then disappears by liquefaction. 
402. Each of the succeeding twin cells presents a nucleus, which, having first 
passed to the centre of its cell, resolves itself into cells in the manner above described. 
By this means the twin cells, in their turn, become filled with other cells. Only two 
of these in each twin cell being destined to continue, the others, as well as the mem- 
brane of each parent cell, disappear by liquefaction, when four cells remain. These 
four produce eight, and so on, until the germ consists of a mulberry-like object, the 
cells of which do not admit of being counted. Nor does the mode of propagation 
continue the same with reference to number only. The process inherited from the 
germinal vesicle by its twin offspring, reappears in the descendants of these. Every 
cell, whatever its minuteness, if its interior can be discerned, is found filled with the 
foundations of new cells, into which its nucleus has been resolved. Together with a 
doubling of the number of the cells, there occurs also a diminution of their size. 
The cells are at first elliptical, and become globular. 
403. The above mode of augmentation, namely the origin of cells in cells, appears 
4 b 2 
