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MONTGOMERY. 
[Vol. XV. 
classed as germinal vesicles, yet it seems so probable that the 
substance out of which the nucleoli are formed is extranuclear, 
that I would conclude, a priori , that no nucleoli are present 
in stages of the germinal vesicle much earlier than those which 
have been here described. Those small nucleoli of a second 
generation, which are first produced in the third and fourth 
nucleolar stages, may represent yolk globules assimilated by 
the nucleus, since in these stages the cytoplasm is filled with 
such globules. 
On the other hand, the yolk cannot be considered as having 
its origin in nucleoli which have wandered out of the nucleus, 
since in none of these stages are nucleoli found in the cyto¬ 
plasm. And if such were the case, one certainly should be 
able to observe the large nucleoli of the third nucleolar stage 
in the cell substance, for it is at this period that the yolk first 
appears. I conclude that the yolk globules have their origin 
in some substance contained in the cytoplasm, and that the 
nucleolar substance also has its origin in some cytoplasmic 
substance. But whether the primitive nutritive substance of 
the yolk globules and that from which the nucleolar substance 
is derived are identical, is of course open to question ; how¬ 
ever, judging from the similarity in appearance, we might con¬ 
clude that the primitive cytoplasmic substance was the same 
in both cases, and especially if we consider, which seems plaus¬ 
ible, the nucleoli to represent the nutritive substance of the 
nucleus, as the yolk globules certainly represent that of the 
cell body. 
In the first nucleolar stage the nuclear membrane is usually 
very thin, but always perceptible ; in the later stages it becomes 
thicker. The nucleus is never noticeably irregular or amoe¬ 
boid in outline. Might this be explained by the absence of 
yolk balls in the cytoplasm ? 
In the second and at the beginning of the third nucleolar 
stages, the central mass of nucleoli is usually surrounded by a 
clear space, in which space few or no chromatin microsomes 
occur, though it may be transversed by a few achromatic fibers 
(Figs. 239 and 240). This space was found in most of the egg 
cells of this stage in the three individuals sectioned, though it 
