Opalina. 233 
to be arranged in the form of an alveolated foam, but are in the 
form of masses and fibrils. It is difficult with most dyes to distinguish 
the chromatic fibrils from the achromatic, but double staining with 
safranin and light green gives a very clear demonstration of the 
distinctness of the two sorts of fibrils, the chromatin being red, the 
linin green. Care must, however, be taken not to extract the light 
green too much. The slides must be left in absolute alcohol but a 
moment, else the light green may be extracted from the nucleus 
and the whole endoplasma as well, remaining only in the ectoplasma. 
The chromatin masses are not homogeneous, but contain many 
granules which after staining with safranin (Fig. 31, Pl. XV) iron- 
haematoxylin (0. caudata, Figs. 83, 84, 86, Pl. XX), or DrLarrenn’s 
haematoxylin (Fig. 69, Pl. XIX), decolorize more slowly than the rest 
of the chromatin mass. The character of these granules can best 
be discussed in connection with the later stages of mitosis. 
In the preliminary notice of this work (Mercanr 1907 a) I wrote 
“The chromatin net in the ‘resting’ nucleus consists of large and 
small chromatin masses and their branching anastomosing pseudo- 
podia-like processes. In certain conditions of the nucleus no such 
processes are found”. After further study, it seems that the last 
statement is mistaken and that more or less of a network of chromatin 
is always present, though in some conditions of the nucleus it may 
be very delicate and difficult to distinguish from the achromatic 
foam even with differential stains. 
Prophases of mitosis. 
One sees from the study of total preparations and of sections 
that, as the nucleus prepares for mitosis, the longitudinal fibres of the 
chromatin net become emphasized and the transverse fibrils become 
fainter (Figs. 45—52, 57, Pl. XVIII). One imagines that the latter are 
drawn in and that their substance is added to the longitudinal fibres. 
At this time the nodes that lie along the longitudinal fibres are 
especially emphasized (Fig. 50). While the chromatic spindle is thus 
forming, the longitudinal films of the achromatic foam thicken and 
the transverse films become fainter (left side of Fig. 47, Pl. XVIII), 
the whole nucleus at the same time becoming elongated. 
The spindle is never regular and is hardly well enough formed 
to be comparable to the spindle in the mitosis of metazoan cells. 
Figs. 49 to 52, Plate XVIII, show it in its fullest development. The 
thicker fibres in the whole nucleus are seen to have an irregularly 
