Opalina. 279 
308, 309), I have often seen one or two compact chromatin spheres 
already extruded and lying in the cytoplasm, or in the process of 
being extruded (Fig. 302, Pl. XX VIII, O. dimidiata). In animals which, 
without being encysted, have been ingested by the tadpoles and have 
passed unencysted through the whole alimentary canal to the rectum, 
one often finds the extrusion of great masses of chromatin from the 
nuclei. ‘These masses, sometimes before, but generally just after 
their extrusion, become reticulated, with lighter areas in the meshes 
of the heavily stained chromatin net (Figs. 237—247, Pl. X XVI). 
In some cases the nuclei from which the chromidia have been ex- 
truded show very distinct chromosomes (Fig. 238, 239, 241). In 
other cases irregular chromatin masses are left in the nuclei 
(Fig. 240). In still other instances the chromatin left in the nucleus 
is very finely granular (Fig. 245). In Fig. 241, in the posterior 
end of the body, is shown a hollow sphere of net-like chromatin 
surrounding an unstained central sphere. In many degenerating 
nuclei of O. obtrigona exactly similar structures were found (Figs. 104 
—109, 111—115, Pl. XXI). In a few instances, when the staining 
was exactly right, I have seen that the chromatin spheres in the cysts 
were composed of a net-like, darkly staining envelope surrounding a 
central sphere (Fig. 133, Pl. XXII: the central sphere was present 
but is not indicated in the drawing which shows the reticulated sur- 
face of the sphere). I have not yet attempted to test microchemi- 
cally the nature of these central spheres. The unencysted ingested 
animals just described showed very clearly that the chromatin spheres 
fragment and scatter through the cell, there disappearing. It is 
not quite certain that always two chromatin spheres are extruded, 
but that there are usually two appears certain from the phenomena 
observed. It seems altogether probable that we have in these pheno- 
mena a throwing away of nutritive chromatin similar to that describ- 
ed by Herrwic, Scuavupinn and others for numerous Plasmodroma. 
IT have described the formation of chromatin spherules during 
the course of each mitosis throughout the year (except perhaps just 
before and after copulation) and have suggested that these chro- 
matin spherules are nutritive — comparable to the granules of the 
macronucleus of higher Ciliata. Their formation and extrusion is 
positively useful, being probably connected with nutrition and per- 
haps with the formation of the refractive spherules of the endosare. 
The formation and extrusion of the large chromatin spheres before 
copulation is apparently negatively useful, leaving the nuclei in the 
right condition for copulation. It seems likely that the chromatin 
