60 THE OVUM AND 



layer of the germinal membrane of an egg after sixteen hours' 

 incubation, we find it to be composed of globules, which vary- 

 greatly both in size and appearance, (see plate II, fig. 7.) The 

 large globules, which form the greater proportion, may be proved 

 to be cells, and Baer has already named them vesicles. The 

 molecular motion, which is frequently visible in isolated globules 

 within them, although much slighter in these instances than 

 in the cells of the serous layer, affords sufficient evidence of 

 their cellular character. They contain a transparent fluid and 

 granules of various kinds. One particular globule, having very 

 dark outlines, resembling those remarked in the cells of the 

 yelk-cavity, may be observed in almost every cell. Several of 

 the globules, and of all gradations of size, are frequently seen 

 in a cell. In addition to the above, a minutely granulated 

 substance is present in many of them. These cells lie some- 

 what loosely together in a structureless, tenacious, intercellular 

 substance, which is their cytoblastema, so that at this stage 

 they are but slightly flattened against one another. This in- 

 tercellular substance contains, in addition, perfectly dark glo- 

 bules and smaller granules, but I do not know what relation 

 they bear to the cells. A portion of them may, perhaps, be 

 nuclei of new cells. Yet I could not decide whether the one 

 dark globule, which is generally so very prominent in the cells 

 of the mucous layer, had actually the signification of a cell- 

 nucleus. It differs in form from the usual cell-nucleus very 

 materially. During the progressive development of the ger- 

 minal membrane, the quantity of intercellular substance, and 

 of those globules the cellular nature of which is not demon- 

 strable, diminishes very much, so that at a subsequent period 

 the cells lie close together, and present the appearance of ve- 

 getable cellular tissue. The description here given applies 

 only to the mucous layer on the outside of the area pellucida. 

 Within that the cells have quite a different appearance. They 

 are very much smaller, of pretty equal size, very transparent, 

 and contain no coarse granules, but only very small globules. 

 They do not appear to have any nucleus, and this fact dis- 

 tinguishes them from the cells of the serous layer, which pos- 

 sess a nucleus even within the area pellucida. 



The first rudiments of the embryo appear to be formed from 

 the cells of the serous and mucous layers of the germinal mem- 



