Opalina. 931 
changes caused by living in cultures. In all of these animals, when 
binucleated, one nucleus contains a nucleolus and the other does not. 
Generally the nucleolus is in the posterior nucleus, but in 8°), of 
the binucleated forms the nucleolus is in the anterior nucleus. All 
of the forms found with the nucleolus in the anterior nucleus were 
anterior daughter cells formed by transverse division indicating 
probably that about 16°), of the divisions are transverse. 
The conditions in these Opalinas show that the old nucleolus 
does not persist. It diminishes and disappears just before, or during, 
or some times just after, the spireme stage, which in these animals 
is less marked than usual. It reappears generally at about the 
time the spindle is forming for the next division, or before. 
Occasionally it does not appear until the spindle is formed. We 
find therefore some animals with no nucleolus in either nucleus 
(spireme stage), some (8°/,) with a nucleolus in the anterior nucleus 
only, and the rest with a nucleolus in the posterior nucleus only. 
The discrepancy between the different series of preparations as 
to the condition of the nucleoli necessitates more careful study of 
this subject. My notes upon the several sets of preparations do not 
say whether the hosts had been starved for a time or not. Until 
this relation has been carefully, observed one cannot be certain which 
of the nucleolar phenomena are normal and which abnormal. Possibly 
all are normal, varying with the conditions of nutrition. It is but 
a surmise that the conditions of nutrition explain the divergent 
conditions of the nucleoli, but it seems the most probable explanation 
Opalina must be very sensitive to surrounding conditions, and it is 
possible that in this genus we have an opportunity to study, with 
unusual hope of some success, the problem of the function of the 
plasmosome nucleolus. 
ZELLER saw and clearly described and figured nucleoli in all 
stages from the cysts to the full grown forms, in all five of the 
species he studied. He even figures a central dot in the nucleolus, 
which he calls a central vacuole. It is barely possible that in the 
cysts and in certain small forms he has mistaken certain chromatin 
masses for the true nucleoli, but there is no doubt that, at least in 
the case of full grown forms, he has described the true plasmosome 
nucleolus. This is easily demonstrated with acetic acid, which is the 
reagent he chiefly used. 
Since ZELLER, no student of the Opalinae has observed the true 
nucleolus. PrrrzNer (1886), TOnnieEs (1899) and Léger & Dusosce 
(19040) refer to certain chromatin masses as nucleoli, but make no 
