230 M. M. Mercaur 
time of extrusion of the vegetative chromidia and copulation, 
though I have stained sections of all of these forms with safranin 
and light green, which gives such clear pictures of the nucleolus. 
In at least some zygotes which have grown a little since copulation, 
the nucleoli are seen. Its apparent absence from those nuclei which 
have recently cast off vegetative chromidia, and are probably but 
slightly active in nutrition, seems of much interest, though I would 
not venture to suggest what may be the real meaning of this 
relation. In the case of large dividing individuals in the summer, 
fall and winter, the new nucleolus appears in the anterior daughter 
nucleus at the time when this nucleus is forming the chromatin 
spherules, which seem to be essentially vegetative chromidia. These 
phenomena will soon be described. It seems probable that the 
nucleolus has some connection, not necessarily causal, with the 
nutritive activities of the nucleus. 3) In the third place I would 
emphasize that the new nucleolus, when it arises, seems to come 
from some substance in liquid form in the nucleus, and not from 
the immediate transformation of any previously visible structures. 
4) The old nucleolus does not grow beyond a certain size, though 
it may persist for nearly a year. The new nucleolus, after each 
division, grows to the same size as the old and then stops its 
erowth. This suggests that there is some balance between the 
nucleolus and the other structures of the nucleus (or cytoplasm ?) 
which requires the presence in an ordinary fully-formed nucleus of 
a nucleolus of a given size. The diminution of the vegetative 
chromatin, preceeding and during the period of conjugation, seems 
to do away with the necessity of a nucleolus during that time, or 
to remove something which if present would have caused a nucleolus 
to form. 
The various stages in the growth of the new nucleolus are of 
oreat assistance in determining the sequence of phenomena in the 
telophases of mitosis. Until this criterion was found it was almost 
impossible to be certain of the relative order in mitosis of several 
of the stages observed. 
This description of the condition and behavior of the nucleolus 
in O. intestinalis is based upon series of preparations of animals from 
many different hosts. I have since studied a series of preparations 
of apparently normal Opalinas from an apparently normal Bombinator, 
in which the nucleolar relations are quite different. These Opalinas 
were killed at once upon opening the rectum of the host so that 
the divergent condition of the nucleolus is not due to degenerative 
