Opalina mitotica. 53 
nucleus. These authors do not say if the ring formation is as 
frequent and as marked in freshly taken individuals. 
In Opalina mitotica, as in all other Opalinae studied, the nuclear 
membrane persists, not disappearing at any stage of mitosis. 
None of the material studied shows the formation of chromatin 
spherules from the chromosomes, as I have described for O0. intesti- 
nalis and O0. caudata. This is probably due to the methods of 
preparation. The nuclei, being in a late anaphase, are past the 
stage in mitosis when the chromatin spherules are most distinct. 
Most should by this time be dissclved, but often in other species 
one finds a few chromatin spherules that for some reason persist a 
little longer, even as late as the anaphases. None of the nuclei in 
my specimens are sufficiently deeply stained to bring out these 
bodies if present. | 
No nucleolus appears in any nucleus in my specimens. This 
may very probably be due to the methods of preparation, for in 
O. intestinalis and O. caudata the nucleolus is not brought out by 
many of the common fixing fluids and stains. Some careful students 
have denied its presence in those species, though some methods 
demonstrate it with great clearness and though ZELLER had 
accurately described it in 1877. “Lichtgreen” after sublimate-acetie 
brings it out very clearly, so does acetic acid alone (ZELLER’s method). 
In 0, intestinalis and 0. caudata the nucleolus persists throughout 
the mitosis, going undivided into one of the daughter nuclei, the 
other daughter nucleus acquiring a new nucleolus. It is therefore 
improbable that the nucleoli in these specimens are absent because 
they have disappeared during mitosis, since in other species the 
nucleolus does not so disappear. 
Both longitudinal and transverse division occurs in Opalina 
mitotica. None of the eight hundred and thirthy-three, individuals 
in my slides show the body really in process of division, but there 
is one which is slightly constrieted in the middle, as if beginning 
to divide transversely, and another which is broadened and furrowed 
preparatory for longitudinal division, and there are present in the 
slides twenty or more individuals that have just been formed by 
longitudinal division (Fig. 6), and there is at least one individual!) 
1) There are in the slides two other individuals which are very short 
and stocky and seem to have been recently formed by transverse division. 
Both have recovered from the division and show an even contour and 
complete ciliation (Fig. 10). 
6* 
