No. 2.] COMPARATIVE CYTOLOGICAL STUDIES. 531 
of the nucleolar substance is probably different in different 
objects. 
We have found above that in the simplest though secondary 
nuclear divisions, the amitotic, the nucleolar substance of the 
parent-cell is transported into the daughter-nuclei by the me¬ 
chanically simplest process, namely, by a direct division of the 
parent-nucleolus ; this is very frequently the case in amitosis, 
though it does not always occur. But in most mitotic divisions 
the nucleolus first disappears, i.e. y there would seem 'to be an 
indirect mode of transference of its substance corresponding to 
the indirect mode of transference of the chromatin and linin ele¬ 
ments. Now all mitotic divisions do not proceed on exactly the 
same plan, for we find differences in regard to the presence of a 
central spindle, in regard to the number of the chromosomes, etc. 
Accordingly, one would expect also different modes of transfer¬ 
ence of the nucleolar substances. Thus in some cases, as 
Wager (’93) suggests, the chromosomes may serve as mechan¬ 
ical vehicles for the transportation of this substance. In many 
other cases it is very probable that this substance, after the 
disappearance of the nuclear membrane, becomes dispersed in 
the cytoplasm ; and then each of the daughter-nuclei may 
either take up this substance from the cytoplasm again, or may 
produce its own nucleolus from a new substance, owing to the 
primitive nucleolar substance having been assimilated by, or 
even discharged from, the cytoplasm. There are observations 
in support of each of these three modes of re-formation of 
nucleoli in the daughter-nuclei. But since when the nuclear 
membrane disappears the cytoplasm probably comes into con¬ 
tact with the substance of the nucleoli, it is most probable that 
it would produce either a physical or a chemical change in the 
latter, and hence the second and third modes would appear 
the more probable. Accordingly, I agree with Humphrey (’94) 
that there is no substantial basis for Zimmermann’s (’93) con¬ 
clusion “omnis nucleolus e nucleolo,” or more strictly speaking, 
that the nucleolus in most cases is not derived from a previously 
existing one. But the third mode of diffusion of the nucleolar 
substance is in reality not a transference of this substance at 
all, since it probably becomes lost in the cytoplasm ; and hence, 
