No. 2 .] COMPARATIVE CYTOLOGICAL STUDIES. 
443 
be more freely fluid. Further, at this period we usually find 
vacuoles within some of the nucleoli of each germinal vesicle 
(Figs. 217, 218, 226, 229-231) ; sometimes no vacuoles are 
present in any of the nucleoli of a nucleus, but it is the rule that 
at least one of them, and that usually the largest, contains one 
or several vacuoles. Sometimes four or five of the nucleoli, 
which may be very unequal in size, may each have vacuoles. 
Occasionally a nucleolus contains only one vacuole, and in the 
latter there may be one or several small solid bodies, which 
stain like the ground substance of the nucleolus, and may be 
termed nucleololi; one of the latter may be fused with the inner 
surface of the nucleolar ground substance (Figs. 217, 218, 230, 
231). These nucleololi vary in number and size, and are 
absent in the greater number of the vacuoles ; so no particular 
significance should be attached to them, since they are probably 
nothing more than portions of the ground substance of the 
nucleolus which have become detached from the surrounding 
substance and have come to lie within the vacuole. During 
this period the nuclear membrane is thinner than at any other 
stage, and the nucleus is very noticeably amoeboid in form, the 
amoeboid processes being much more pronounced than in any of 
the other nemerteans examined; these processes in reality repre¬ 
sent changes in the form of the nucleus, and are not artefacts, 
since they are seen equally well after preservation in the most 
diverse fixing fluids (Figs. 226, 227, 230, 232, 233). The nu¬ 
clear membrane is always particularly thin around these nuclear 
processes, but, as far as I could make out, never becomes broken. 
Third nucleolar stage. — The large nucleoli which were 
present at the end of the preceding stage now commence to 
fragment into smaller nucleoli, which are more or less equal in 
size, and then the latter wander towards the periphery of the 
nucleus ; at the conclusion of this period, which must take 
place in a very short time, since I found only a few germinal 
vesicles exhibiting it, there are a large number of rather small 
nucleoli close to the nuclear membrane (Fig. 234). At this 
time the nucleoli attain their maximum staining intensity ; the 
nucleus usually shows no traces of an amoeboid form, and its 
membrane has increased in thickness. None of the nucleoli 
