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 Jitst imcleolar 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. 



