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MONTGOMERY. 
[Vol. XV. 
contain vacuoles ; and in every respect the nucleolar changes 
during this stage are the very reverse of the preceding. 
Fourth nucleolar stage. — This is characterized by the gradual 
degeneration and disappearance of the nuclei (Fig. 235). Small 
vacuoles arise in them, and these increase numerically, while at 
the same time the nucleolar substance stains less intensely. 
Fusion of neighboring nucleoli is very frequent at this time, or 
perhaps a little time before the nucleoli lose their staining 
power ; accordingly, in the largest germinal vesicles it is the 
rule to find a small number of large nucleoli. The nucleoli 
are not evenly distributed along the periphery of the nucleus, 
and are often flattened against the nuclear membrane. This 
nucleolar stage is found only in the largest ovarial eggs, where 
the nucleus is perfectly regular in outline, without amoeboid 
processes, and its membrane has attained its greatest thickness. 
Since this species is a protandric hermaphrodite, in which 
male and female sexual products ripen successively in each 
gonad, I found it at first difficult to determine whether a young 
nucleus in a given gonad corresponded to a male or to a female 
cell. But after comparing briefly the spermatogenesis of the 
other metanemerteans mentioned in this paper, and finding in 
them that no nucleus in any stage of spermatogenesis was larger 
than any of the smallest germinal vesicles here figured, I con¬ 
cluded that also in Stichostemma no male nuclei can attain the 
dimensions of even the smallest nuclei of our second nucleolar 
stage, and hence that all these nuclei were correctly concluded to 
be germinal vesicles, and not nuclei of spermato-genetic stages. 
We notice in the succession of the nucleolar stages described 
the rhythmic sequence in regard to (1) the position of the 
nucleoli, (2) their states of fusion and division, and (3) the 
absence and presence of vacuoles in them ; these successive 
changes may be expressed as follows : 
Nucleoli, 
a. 
t \ 
Position. Vacuoles. Fusion, division. 
peripheral . . . absent.fusion ? 
central . . . present . . . division, then fusion. 
peripheral . . . absent.division. 
peripheral . . . present . . . fusion, then division. 
Stage. 
First 
Second 
Third 
Fourth 
