Researches in Embryology : Third Series. 527 
these delicate objects ; and has thus had ample opportunity of con- 
firming the principal facts therein stated. He has now procured in 
all 230 ova from the Fallopian tube. But being aware that repeated 
observations alone do not suffice in researches of this nature, unless 
extended to the very earliest stages, he again specially directed his 
attention to the ovum while it is still within the ovary, with a view 
to discover its state at the moment of fecundation, as well as imme- 
diately before and after that event. 
The almost universal supposition, that the Purkinjian or germinal 
vesicle is the essential portion of the ovum, has been realized in 
these investigations ; but in a manner not anticipated by any of the 
numerous conjectures which have been published. The germinal 
vesicle becomes filled with cells, and these again become filled with 
the foundations of other cells ; so that the vesicle is thus rendered 
almost opake. The mode in which this change takes place is the 
following, and it is one which, if confirmed by future observation, 
must modify the views recently advanced on the mode of origin, the 
nature, the properties, and the destination of the nucleus in the physi- 
ology of cells. It is known that the germinal spot presents, in some 
instances, a dark point in its centre. The author finds that such a 
point is invariably present at a certain period ; that it enlarges, and 
is then found to contain a cavity filled with fluid, which is exceed- 
ingly pellucid. The outer portion of the spot resolves itself into 
cells ; and the foundations of other cells come into view in its in- 
terior, arranged in layers around the central cavity ; the outer layers 
being pushed forth by the continual origin of new cells in the in- 
terior. 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 author believes that the 
nature of the nucleolus of Schleiden is to be thus explained. The 
germinal vesicle, enlarged 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 penetrate, pre- 
sents 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 cor- 
responding part, the thick transparent mem.brane 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, regain- 
ing its spherical form, returns to the centre of the ovum, and a 
fissure in the thick transparent membrane is no longer seen. From 
these successive 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. 
