No. 2.] COMPARATIVE CYTOLOGICAL STUDIES . 411 
which appear at only a certain stage of the cell. The true 
nucleolus may be considered first, then these other structures, 
or “ pseudonucleoli.” 
There is always one true nucleolus to each nucleus, and in 
only two cases out of hundreds of ova examined have I seen 
two nucleoli (Figs. 57 and 61). The position of the nucleolus 
within the nucleus is in most cases excentric, seldom central, 
and never apposed to the nuclear membrane; it apparently lies 
free in the caryolymph, and is not supported by the chromatin 
threads. In the youngest, most immature germinal vesicles 
(I have not studied it in the ovogonia) it is apparently wholly 
homogeneous, dense, not noticeably refractive, and usually 
spherical (Figs. 57-61) ; sometimes, however, it shows an oval 
or more elongate form, and in the latter case its long axis 
usually coincides with that of the nucleus (Fig. 58) ; it is 
never irregular in outline. 
The nucleolus always colors differently from the chromatin, 
when treated with double stains, as follows : 
Stain. Nucleolus. Chromatin. 
Ehrlich-Biondi . . maroon . . . green. 
Haematoxylin, eosin . orange red . . blue. 
Acid carmine, nigrosine blue .... red. 
Haematoxylin, fuchsine purple . . . blue. 
Flemming’s stain . . yellow . . . violet. 
With the increase in size of the nucleus the nucleolus 
enlarges, and in such a way that the size of the latter usually 
preserves its proportion to that of the former ; but as the 
figures show, this proportion is quite frequently not preserved. 
What may be termed the first stage of this nucleolar growth 
consists merely in an increase in the amount of the homogene¬ 
ous substance, and between the largest homogeneous nucleoli 
(Fig. 65) and the smallest (Fig. 57) there is no difference 
except one of size. 
The second period of nucleolar growth is introduced when 
vacuoles commence to appear in the substance of the nucleolus 
(Fig. 62). Since my observations show that these nucleolar 
vacuoles are derived from small fluid globules which first appear 
