On the Progress of Embryology in the Year 1840. 339 



aborted ova. In like manner, parts of the [Graafian] follicle 

 which usually remain in the ovary, for example, portions of 

 Barry's ovisac, may be found in the oviducts. 



5. Neither the place to which the ova in the tubes and uterus 

 have advanced, nor the size of the same, nor the time that has 

 elapsed since they left the ovary, affords an exact criterion for 

 the degree of their internal development. This position fur- 

 nishes only a confirmation of what was already known******. 



6. The germinal vesicle does not disappear nor burst through 

 fecundation, but fills with cells, the formation of which proceeds 

 from the germinal spot : and this takes place by no means in a 

 peculiar manner, but according to a normal mode which mani- 

 fests itself elsewhere. These circumstances, which really ex- 

 tend our knowledge, have been made known by the laborious 

 researches of Barry. The general process is as follows; — It is 

 known that in the interior of the germinal spot there exists a 

 central body, which often becomes surrounded by concentric 

 traces. This body now enlarges and fills with a pellucid fluid. 

 That part of the germinal spot which is directed towards the 

 interior of the germinal vesicle passes into cells, arranged 

 like pill-boxes one within the other, yet so that the pellucid 

 central vesicle remains near to the periphery [of the ovum]. 

 Within the cells thus arisen there are formed new cells. This 

 cell-formation proceeds in layers from the centre towards the 

 periphery. The outer strata of cells are thus pushed further 

 out, and the most external disappear while new inner strata 

 form, so that the middle ones advance to the outer part. In 

 this manner the germinal vesicle becomes filled with masses 

 of cells, while its membrane disappears. But in the situation 

 of what was originally the centre of the germinal spot there 

 are formed two cells, distinguished by their larger size : and 

 out of these two larger cells new cells arise, as before through 

 the formation of cells in cells, — 4, 8, 16, and so on, — the num- 

 ber doubling every time. These two cells of the central part 

 of the germinal spot, with their succeeding cells, form the 

 foundation of the germ. In it, the germ, again, there is to 

 be seen a cell distinguished by its larger size. The nucleus 

 of this latter cell generates, through further development, the 

 foundation of the embryo. It may hence be conceived, that 

 the seminal fluid taken up by imbibition, arrives at what was 

 originally the central part of the germinal spot ; first gives a 

 stimulus to the cell-formation in the peripheral part of the 

 germinal spot, and to the consequences of the same ; then, 

 through the formation of cells, becomes itself the germ ; and 

 that, subsequently, within the germ the nucleus of a principal 

 cell gives the stimulus to the formation of the embryo. Fe- 



