422 
MONTGOMERY. 
[Vol. XV. 
a yolk substance, either of the yolk-ball fragments or a sub¬ 
stance equivalent to that out of which the latter are differen¬ 
tiated, and this substance, then penetrating osmotically the 
nuclear membrane, becomes deposited or precipitated in the 
nucleus in the form of spherical globules, which are the nucleoli. 
From this yolk substance taken into the nucleus the chroma¬ 
tin, linin, and nuclear sap might derive the nourishment neces¬ 
sary for their growth, and those nucleoli which remain through 
the fourth nucleolar stage might represent either a reserve supply 
of this nourishment, or chemically changed portions of it, from 
which all nutritive substances have been extracted ; the latter 
view would seem substantiated by the fact that the nucleoli 
stain somewhat differently in the third and fourth stages. 
The nuclear membrane is present during all these stages. 
The nucleus is always regular in outline, usually oval, except 
during the third stage, when it may become slightly irregular, 
though it never becomes noticeably lobose or amoeboid. 
In the first nucleolar stage (Figs. 140 and 141) the chromatin 
appears as a network of delicate fibers, which stain with haema- 
toxylin. Towards the end of the second stage (Figs. 146-150) 
it assumes the form of irregular masses, and the fibers become 
less numerous. In the largest ovarial nuclei (Figs. 154 and 
157) it is finely distributed throughout the nucleus in the form 
of minute microsomes ; traces of fibers may be found only at 
the periphery of the nucleus, though I have not determined 
whether these are fibers now for the first time forming, as is 
the case in the other nemerteans. The nucleoli are never 
suspended by the chromatin fibers. 
This species is characterized by the formation of a mem¬ 
branous structure in the cytoplasm, during the second and 
third nucleolar stages, which is present in none of the other 
nemerteans. This is a membrane within the cytoplasm, 
separated from the nucleus, as well as from the cell membrane 
by cytoplasm; it lies close to the nucleus (Figs. 146 and 155, 
Iv. Mb.). It is thicker than the nuclear membrane, though 
not so dense, and differs in no wise structurally from the 
cytoplasm, except in its greater density, the cytoplasmic gran¬ 
ules in it lying closer together (these granules appear to be 
