Opalina. 297 
shape lie at the nodes of the foam. ‘hese are highly refractive in 
the living nucleus (Pl. XVI). Their reaction to stains shows them 
to be of achromatic, not chromatic, material. The granules not only 
differ in size in the same nucleus, their average size in different 
nuclei varies perceptably. They seem largest in nuclei in which 
the spindle is forming preparatory to mitosis (Fig. 47, Pl. XVIII). 
The lines uniting these granules (optical sections of the walls of 
the alveoli) generally show very clearly in well-stained nuclei both 
in preparations of total objects and in sections. The lines are 
not discernable in living nuclei, at least with the illumination I 
have used. 
Nucleolus (Figs. 18, 19, 22, 25, 27, 29, Pl. XV; 55, 56, Pl. XVIII: 
Fig. 73, Pl. XIX). 
The always spherical, or nearly spherical, nucleolus belongs to 
the achromatic group of nuclear structures. It is always present 
in fully formed nuclei and lies near the axis of the nucleus, never 
at the surface. It is held in an alveolus of the achromatic foam 
(Fig. 55, Pl. XVIII), completely filling this alveolus, so that the 
films of the foam are seen radiating from its surface. Where these 
strands touch the surface of the nucleolus they are seen to enlarge 
to form typical nodal granules, triangular in optical section, as are 
many of the other nodal granules. 
The nucleolus stains strongly with plasma stains. One does 
not find it in total preparations stained with borax-carmine, but in 
many DeLarreLp haematoxylin preparations it shows very distinctly 
and is sharply distinguished from the chromatin by its fainter color 
and browner tone. In other Dearie haematoxylin preparations, 
which are not so well decolorized, one often cannot distinguish the 
nucleolus from the chromatin. The most selective and distinctive 
stain for the nuclear structures is safranin followed by light green 
(Lichtgriin). The chromatic elements take the safranin strongly 
while the achromatic elements are green. With this stain the 
nucleolus is a clear bright green and is a very conspicuous object, 
for it is large (Figs. 22, 25, 27, 29, Pl. XV). Often with light 
green, and still better with DeLarreLy’s haematoxylin, one sees that 
the nucleolus is not homogeneous, from one to ten or more circular 
lighter areas being visible within it (Figs. 55, 56, Pl. XVIII; 73, 
Pl. XIX). Generally the more central light spot appears the larger. 
These vacuoles (?) are generally of different sizes in the same 
