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- 
