58 THE OVUM AND 
hours’ incubation be folded in the same manner, its margin at 
many points is found to be no longer dark and even, but to be 
composed of extremely pale transparent cells. These cells pre- 
sent every variety of size, some being as large and even larger 
than the primitive globules of the germinal membrane. They 
either project forward in the form of half-spheres, or the greater 
portion of their spherical surface juts out in some instances, and 
they may be completely separated by pressure. They contain a 
pellucid fluid, but no nucleus. ‘The following fact shows them 
to be cells; some of them contain very minute, isolated, black 
granules, which resemble the molecules described by Brown, 
and exhibit molecular motion within the cell. This fact proves 
that the contents of the cell must be fluid. A fluid which is 
miscible with water cannot, however, preserve any definite form, 
unless it be encompassed by a membrane. Such a structure must, 
therefore, exist in this instance. It is not altogether easy to con- 
vince one’s self that these granules, exhibiting molecular motion, 
do actually le within the cells ; but it may be concluded from the 
fact, that they do not flow away when the surrounding fluid is 
allowed to escape, and that they are not moved beyond the 
limits of the cell, but only to its walland back again. Beneath 
this stratum of cells lie the globules of the unincubated germinal 
membrane, which, however, appear to have become still more 
clear and minutely granulous than those of the membrane ex- 
amined after four hours’ incubation. In addition to these, se- 
parate cell-nuclei may be observed, such as occur in the cells 
of the serous layer at a subsequent period, and may be seen in 
plate I], fig. 6. Still more internally than this layer, we meet 
with perfectly dark globules. The serous and mucous layers of 
the germinal membrane are perfectly formed in the egg after 
sixteen hours’ incubation. If the membrane at that period be 
folded so that its external surface may be seen, it will be found 
any degree of certainty to any precise hour of incubation. The periods cited should 
therefore only be taken as being near about the true determinations of the time. 
The cells in the germinal membrane, before incubation even, do not appear to be al- 
ways at the same stage of development; thus, plate IJ, fig. 4, ec, and fig. 4, a, 0, re- 
presents cells from two different membranes. A great portion of the germinal mem- 
brane from which ¢ was taken consisted of such cells as that delineated, and I thought 
I perceived molecular motion in the granules contained in some of them, which, if 
correct, would clearly prove them to be cells. 
