No. 2 .] COMPARATIVE CYTOLOGICAL STUDIES. 419 
mitosis), I could find no nucleoli ; but one or two small minute 
nucleoli might nevertheless be present within these nuclei, but 
escape detection, owing to their small size and to the compara¬ 
tively great amount of chromatin. These nuclei are usually 
elongated and irregular in form (Figs. 144 and 145, C. T. N.). 
The smallest germinal vesicles, which are recognizable as 
such by slightly larger dimensions and more regular, spherical 
shape, show likewise no recognizable nucleoli. 
In what may be termed the first nucleolar stage , the nuclei 
have grown still larger, and in them are to be seen from one to 
about twelve small nucleoli. These are all peripheral in posi¬ 
tion, being flattened against the inner surface of the nuclear 
membrane, which results in their not being spherical, but more 
or less flattened, lens-shaped, or hemispherical (Figs. 140 and 
141). 
Second nucleolar stage. — The peripheral nucleoli commence 
to wander towards the center of the nucleus, at the same time 
growing larger and increasing in number (Figs. 142-145, 152). 
This process goes on until a considerable number of quite large 
nucleoli are present, none of which are any longer in contact 
with the nuclear membrane. As a rule they are not evenly 
distributed throughout the nucleus, but groups of them occur 
at different points in the nucleus (Figs. 153, 146-150). This 
period of differentiation, then, consists in the grouping of most 
or all of the nucleoli at or near the center of the nucleus, 
accompanied by their increase in size. There is no ground for 
supposing that at this stage they fragment into smaller nucleoli; 
but very frequently groups of two or three nucleoli may be seen 
in close contact with one another, and these would represent 
states of fusion rather than of division, since they are found to 
be flattened at the point of contact, and not attenuated. Thus 
the increase in the size of the nucleoli would be due, in part at 
least, to fusion of contiguous ones. While some of the nucleoli 
have left the periphery of the nucleus, others are at the same 
time forming there, which in their turn eventually reach the 
center, so that a continual process of formation of nucleoli, and 
wandering of those already formed towards the center, takes 
place at this stage. 
