506 
MONTGOMERY. 
[Vol. XV. 
3. Position of the Nucleolus in the Nucleus. 
Where a single nucleolus is present it almost always lies 
excentrically, though not against the nuclear membrane. Those 
cases where it regularly occupies the center of the nucleus must 
be regarded as exceptional ; thus I am unable to agree with 
Macfarlane that the nucleolus is either the morphological or 
the tropic center of the cell. At the time of its origin, and 
often at the time of mitosis, the nucleolus may be in contact 
with the nuclear membrane. Where a number of nucleoli are 
present they may be scattered irregularly through the nucleus, 
or grouped at one point in it, or be concentrically arranged ; 
their position is often dependent upon the stage of the develop¬ 
ment of the nucleus. Thus in the metanemerteans examined 
by me they lie at the periphery in the smallest germinal 
vesicles, then wander towards its center, and finally migrate to 
the periphery again. 1 
The nucleoli lie in the nuclear sap, as a rule not in any close 
connection with the chromatin reticulum. But in those cases 
where the nucleolus may be unusually large it appears to be 
suspended by the fibers of this reticulum, but not in such a way 
that the fibers penetrate into its substance, but become simply 
wound around its surface ; thus it appears that when the 
nucleolus increases in size it forces apart the fibers of the 
nuclear network in such a way that the latter gradually pro¬ 
duce a latticework on its surface. In this way the nucleoli 
may be more or less held in position in the nucleus, but 
Herrick’s observations on the gravitation of the nucleolus 
show that it is not firmly held by the chromatin fibers. The 
nucleolus is, as it were, a ball lodged in the branches of a 
tree, its movements hindered by the intervening branches, but 
nevertheless not immovable. Various views on the mode of 
suspension of the nucleolus : Pfliicke (’95), Heidenhain (’92), 
Rosen (’95), Jensen (’83), Zimmermann (’96). Note also its 
peculiar position in Synapta (Leydig, ’52). 
1 For the opinions of other authors, cf. the reviews of the papers of Pfliicke 
(’95), Heidenhain (’92), Rosen (’95), Jensen (’83), Leydig (’52), Zimmermann 
(96), Schneider (’91). 
