GEROULD: CAUDINA. 178 
(nucleoli) lying close against the nuclear membrane; but the nuclei 
of the future ova are many times larger than those of the follicular 
cells. The cells are all irregularly polyhedral, owing to mutual 
pressure. "The cytoplasm at this stage is homogeneous, the nucleus 
finely granular. 
The cells which are to form the follicle gradually lose cytoplasm 
and flatten out against the ovum (Plate 6, figs. 87-91). Eventually 
the nucleus itself becomes flattened, and the cell body transparent. 
The boundaries of the cells in the well-developed follicle, as made out 
with silver nitrate (Plate 6, fig. 85), are sinuous. Whether the 
sinuosity of the cell outline is here due to a contracted condition of 
the underlying tissue, as Muscatello (94) found to be the case with 
endothelium of vertebrates, I have not had an opportunity to decide 
by experiment. The cells have a greater diameter than that of any 
other epithelial cells in Caudina. 
As the incipient ova grow, the chromatie bodies of their nuclei 
(the nucleoli) increase in size, and a network of less deeply staining 
substance makes its appearance in the nucleus (Plate 6, figs. 87-91, 
86). Meanwhile the cytoplasm, hitherto homogeneous, becomes 
differentiated into a peripheral, deeply staining layer and a central, 
circumnuclear portion, which takes the stain less deeply (Figs. 86, 
89, 91). The two layers are from the beginning separated by a 
membranous protoplasmic structure, ¿ntravitelline membrane, which 
under a high power presents in sections a broken outline; from 
this fact it may be inferred that the membrane is probably a 
network, not a continuous sheet. 
At an early stage in the growth of the immature ovum, even before 
a definite folliele is formed, this membranous structure is found to be 
attached to the periphery of the ovum on the side next the lumen of 
the tubule (Figs. 86, 88, 89), being thus drawn out, as it were, into 
a funnel-shaped prolongation or neck. At this point the micropyle 
is subsequently formed. It is probable that this funnel-shaped portion 
of the membrane becomes perforated at its apex and that the lips of 
the perforation become continuous with the adjacent cells upon the 
surface of the ovum, which are becoming flattened and are presently 
to form the follicle, 
When the ovum has attained a diameter of perhaps 80-124 u with 
a germinative vesicle of 44 u by 53 m, a zona radiata begins to be 
secreted between the yolk and the follicle. This is interrupted at 
only one point, the place where the funnel-shaped membrane comes 
