Dr Barry's Besearches in Embryology. 85 



alone do not suffice in researches of this nature, unless extended 

 to the very earliest stages, he again specially directed his at- 

 tention 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 immediately 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 antici- 

 pated by any of the numerous conjectures which have been pub- 

 lished. 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 opaque. 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 physiology 

 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 exceedingly pellucid. The outer 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 outer layers being pushed forth by the 

 continual origin of new cells in the interior. The latter 

 commence as dark globules in the pellucid fluid of the cen- 

 tral cavity. Every other nucleus met with in these re- 

 searches 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, presents a repetition of the pro- 

 cess 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, 



