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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 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, 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, 

 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. 



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 ceUs. Only two of these in each 

 twin cell being destined to continue, the others, as well as the 

 membrane 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 



