225 



ova, and their size, locality, or age. The variation with regard to 

 size is referable chiefly to a difference in the quantity of fluid im- 

 bibed in different instances by the incipient chorion. Vesicles filled 

 with transparent fluid are frequently met with in the Fallopian tube, 

 very much resembling the thick transparent membrane of the ovarian 

 ovum. These vesicles are probably uniinpregnated ova, in the 

 course of being absorbed. The so-called " yelk" in the more or 

 less mature ovarian ovum, consists of nuclei in the transition state 

 and exhibiting the compound structure above described. The mass 

 of these becomes circumscribed by a proper membrane. They and 

 their membrane subsequently disappear by liquefaction, and are 

 succeeded by a new set, arising in the interior, and likewise be- 

 coming circumscribed by a proper membrane, and so on. This ex- 

 plains why some observers have never seen a membrane in this 

 situation. After the fecundation of the ovum, the cells of the 

 tunica granulosa, that is, part of the so-called " disc," are found to 

 have become club-shaped, greatly elongated, filled in some instances 

 with cells, and connected with the thick transparent membrane by 

 their pointed extremities alone. 



That the thin membrane described by the author in his second 

 series as rising from the thick transparent membrane in the Fallo- 

 pian tube, and imbibing fluid, is really the incipient chorion, was then 

 shown by tracing it from stage to stage, up to the period when 

 villi form upon it. There remained, however, two questions unde- 

 cided ; viz., whether the chorion is formed of cells, and if so^ 

 whether the cells are those of the so-called " disc," brought by the 

 ovum from the ovary. The author now states that the chorion is 

 formed of cells, which gradually collect around the thick transparent 

 membrane, and coalesce ; and that the cells in question are not those 

 of the "disc" brought with the ovum from the ovary. The cells 

 which give origin to the chorion are intended to be more particularly 

 described in a future paper. 



The existing view, namely, that a nucleus, when it leaves the 

 membrane of its cell, simply disappears by liquefaction, is inappli- 

 cable to any nucleus observed in the course of these investigations. 

 The nucleus resolves itself into incipient cells in the manner above 

 described. In tracing this process, it appears that the nucleus, and 

 especially its central pellucid cavity, is the seat of changes which 

 were not to have been expected from the recently advanced doctrine, 

 that the disappearing nucleus has performed its entire office by giving 

 origin at its surface to the membrane of a single cell. It is the 

 mysterious centre of a nucleus which is the point of fecundation ; 

 and the place of origin of two cells constituting the foundation of 

 the new being. The germinal vesicle, as already stated, is the 

 parent cell, which, having given origin to two cells, disappears, 

 each of its successors giving origin to other two, and so on. Per- 

 petuation, however, at this period, consists, not merely in the origin 

 of cells in cells, but in the origin of cells in the pellucid central 

 part of what had been the nucleus of cells. 



The author shows that neither the germinal vesicle, nor the pel- 



