232 M. M. Metcatr 
reference to the plasmosome nucleolus. Neresnermer (1907) says 
he has not seen a true nucleolus, not accepting the name nucleolus 
as applicable to the masses of chromatin described by Prrrzner, 
Téonnices, and Licer & Dusosca. NeresHermer is surely right in 
not applying the name nucleolus to the chromatin masses so charac- 
teristic of the nuclei of Opalina. They seem so entirely unrelated to 
the true plasmosome nucleoli that no one term should be applied to 
both. One must admit, however, that in some other animals it is not 
easy to distinguish clearly between plasmosome nucleoli and bodies 
related to chromatin, so that in general the word nucleolus must be 
allowed to have the broader meaning. 
Chromatin. 
The chromatic material of the nucleus in O. intestinalis, and all 
other species studied, lies near the surface of the nucleus just beneath 
the membrane (Fig. 59, Pl. XVIII).1) This seems to be true of all con- 
ditions of the nucleus except just before, during, and after encystment, 
when, in the multinucleated species, the chromatin contracts toward 
the centre of the nucleus. One sees in the resting nucleus that 
there are irregular masses of chromatin, of larger and smaller sizes, 
scattered here and there beneath the nuclear membrane (Figs. 23, 27, 
Pl. XV; 45—48, Pl. XVIII; 76, 77, Pl. XX). These chromatin masses 
are drawn out into numerous points each of which connects with a 
fiber of chromatin which runs over the surface of the nucleus beneath 
the membrane. These fibres branch and the branches anastomose 
with one another and with the branches of similar fibres from other 
chromatin masses (Figs. 27, Pl. XV; 46, Pl. XVIII). In other words, there 
is just beneath the nuclear membrane a network of chromatin fibrils, 
the chromatin masses described lying upon and being in connection 
with the network. One could say that the fibres seem like delicate 
reticulate pseudopodia from the chromatin masses. 
The fibres of chromatin are sometimes quite even (Fig. 46, Pl. XVIII); 
again one finds them considerably enlarged at the nodes (Fig. 27, PI. XV); 
in other nuclei one sees them as rows of different sized granules strung 
on a thread (cf. Fig. 50, Pl. XVIII, a nucleus in mitosis). These difte- 
rences cannot be wholly due to differences in staining, but represent 
real divergent conditions of the chromatin threads during the so-called 
resting stage. The chromatic structures of the nucleus never seem 
") Cf. Tonyiezs (1899), Bovert (1900). 
