452 
MONTGOMERY. 
[Vol. XV. 
the nucleolus is usually nearer the center of the nucleus than 
in those more mature stages where the nucleus lies near the 
periphery of the cell. But in the more mature stages the 
nucleolus may lie at the animal pole, or the vegetal pole, or 
at one side of the nucleus, so that no coincidence between 
the position of the nucleolus and the age of the nucleus can be 
determined. Thus the nucleolus stands, eg., in no relation to 
the animal pole of the more mature nucleus, that pole where 
amoeboid processes are produced (Figs. 204 and 209). The 
ground substance of the nucleolus is dense and homogeneous, 
and stains quite deeply; the nucleoli of the smaller germinal 
vesicles stain, as a rule, less intensely. In the ground sub¬ 
stance of all the nucleoli more or less numerous fluid globules 
occur, which stain very faintly or not at all, and their presence 
gives a vacuolated appearance to the nucleolus ; those within 
the same nucleolus are of unequal size, and among them two 
or three usually occur which far exceed the others in size. 
Occasionally there is one large central vacuole (Fig. 206), but 
as a rule the larger ones are peripheral, and may produce prom¬ 
inences of the surface of the otherwise perfectly smooth and 
spherical nucleolus (Figs. 209 and 212). In one large vacuole 
(Fig. 212) a finely granular mass was found, though this may 
have been an artefact. Since in the smaller nucleoli these 
vacuoles are less numerous and smaller in size, it would seem 
probable that in stages antecedent to those found by me the 
nucleolus may be wholly devoid of such vacuoles. The nucleo¬ 
lus has no enveloping membrane, for what at first view appears 
to be such a structure careful study shows to be merely the 
result of refraction. 
In addition to the single large nucleolus described, there are in 
the most mature nuclei also from about one to five minute nuclei 
(Fig. 209). These vary somewhat in size, are perfectly spher¬ 
ical and homogeneous, without vacuoles, and stain more deeply 
than the larger one. Sometimes they are found in close con¬ 
tact with the nuclear filaments (cf. the nucleoli of the second 
generation in Tetrastemma catenulatum and the observations 
of Riickert (’ 92 ) on the germinal vesicles of Selachii). These 
probably have no genetic relation to the large nucleolus, since 
