216 M. M. Mercaur 
foam-like alveolar ‘nature can hardly be discerned. Occasionally 
one finds individuals whose endosare clearly shows the alveoles, 
especially when stained i toto with Drwarreyy’s haematoxylin 
(Figs. 15, Pl. XIV, 87, Pl. XX), or in section by Enrutcn’s triacid 
mixture. Mayer’s haemalum after Fuemmrne’s fluid shows the same 
structure but less clearly. The clearest pictures of the alveoles of 
the endosare are found in very small individuals of O. dimidiata 
and 0. obtrigona. The structure in O. intestinalis is the same, but 
is a little less clearly seen. 
The endoplasma differs markedly from the ectoplasma in the 
very much smaller size of its alveoles, which are very minute. The 
nodal granules of the endosare (Fig. 15, Pl. XIV) resemble in size 
the granules which lie at the nodes and along the films of the ecto- 
sarc foam. The endoplasmic alveoli are usually so minute that one 
is unable to see if any granules lie along their walls at other points 
than the nodes of the foam. When however one finds an animal 
in whose endoplasma some of the alveoles are enlarged, the walls 
of the alveoles are seen to bear frequent granules. 
The endoplasma in 0. intestinalis is more dense in the anterior 
end of the body, in front of and near the anterior nucleus. In all 
other species studied a similar greater density of the endoplasm in 
the anterior end of the body is observed, though it is less noticeable 
in the flattened species, especially in O. ranarum. 
Endosare spherules (Figs. 4, 5, 6, 10, 11, 12, 13, 16, Pl. XIV). 
In the endosare are many refractive bodies which I have called 
endosarc spherules (Mercatr 1907a). They have been observed 
by most of those who have studied Opalina. ZeuuER describes little 
refractive bodies in the “parenchyma” of each of the five species of 
which he treats. These he says are slightly flattened and disc- 
shaped, and show a central dark spot which may be due to the 
presence of a central cavity or to a hollow in each face of the disc. 
He says their diameter is about 0°004 mm. 
BarrurtH (1885) describes for O. ranarum certain masses of 
“olycogen” which stain brown with iodine, and near them many 
light yellow strongly refractive drops of another substance (“fat?”). 
The latter were probably the refractive spherules. 
TénniGEs (1898) describes minutely the structure of the spherules 
as they appear in sections of 0. ranarum stained with iron-haema- 
toxylin. I can confirm his statements that they are disc-shaped, 
