370 Pruf. Valentin's Beport on the Progress of Embryology, 



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

 the degree of their internal development. This position fur- 

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

 6. The germinal vesicle does not disappear 7ior hurst through 

 fecundation^ but fills with cells, the formation of ivhich 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 con- 

 centric traces. This body now enlarges and fills with a pel- 

 lucid 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 be- 

 fore, through the formation of cells in cells, 4, 8, 16, and so 

 on, the number 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 de- 

 velopment, the foundation of the embryo. It may hence be 

 conceived, that the seminal fluid, taken up by imbibition, ar- 

 rives at what was originally the central part of the germinal 

 spot ; first gives a stimulus to the cell-formation in the peri- 

 pheral 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 



