No. 2.] COMPARATIVE CYTOLOGICAL STUDIES. 
449 
covered by the chromatic filament or by lying in a part of the 
nucleus outside of the plane of the section. In this stage, 
further, two nucleoli are never present; accordingly, in the 
spirem there is neither a disappearance nor a division of the 
nucleolus. In the dispirem stage each daughter-nucleus contains 
one nucleolus (Fig. 171), the two nucleoli being, however, often 
unequal in size. I found very few aster stages, and these were 
either so unfavorably placed for study or the chromosomes so 
densely entangled that I could not determine whether a nucleo¬ 
lus is present in this stage and whether a division of it takes 
place at this time. The facts determined are (1) that no divi¬ 
sion of the nucleolus occurs in the typical spirem stage, since 
here only one nucleolus is present ; and (2) that each nucleus 
of the daughter-spirem has one nucleolus. But I cannot show 
whether a division of the nucleolus occurs in the time between 
these two stages or whether the original nucleolus passes over 
into one of the daughter-nuclei, while in the other one a new 
nucleolus is produced. In these various mitotic stages the 
nucleolus usually lies at the periphery of the nucleus, and it is 
most frequently the case that it is not in contact with the 
chromatin filament ; it preserves its former shape and staining 
intensity, and apparently does not decrease in size during the 
mitosis. To be sure, in the karyokinetic stages under considera¬ 
tion it usually appears small in proportion to the size of the 
particular nucleus, but then it is usually the case in most 
mitoses, and probably so here, that before the disappearance 
of the nuclear membrane the volume of the nucleus greatly 
increases. 1 
Two nucleoli, never quite equal in size, are frequently found 
in certain small nuclei, which the distribution of the chromatin 
would show to be in a stage at the commencement of the 
prophasis of the mitosis or at the conclusion of the metaphasis 
(Figs. 163, 164-167, 170, 172). As the figures show, all these 
nuclei which contain two nucleoli are more or less of the same 
size. Nuclei which are a little smaller than these, as well as 
those which are larger, invariably contain a single nucleolus. 
1 The chromatin filament has considerable thickness and is apparently a con¬ 
tinuous thread ; it is looped around the inner surface of the nuclear membrane. 
