Opalina, 259 
polarity is seen not only in the shape of the nucleus but also in 
the fact that the chromatin network is attached to each pole of 
the nucleus. This attachment is very clearly seen during mitosis 
and apparently persists through the “resting period”. The orientation 
of the nuclei is constant and unchanging, their long axis being 
about parallel with, usually coincident with, the long axis of the 
body. The nuclei never rotate, except possibly upon their long axes, 
which would be without significance in this connection. This con- 
stancy of orientation may be due in part to the fact that the two 
nuclei are generally connected by a thread. The longitudinal axis 
of a daughter nucleus always remains in the same position as that 
of the parent nucleus. This enables us to clearly see the interesting 
fact that the nuclei of the binucleated species of Opalina always 
divide in the same direction and that they do so whether the ac- 
companying division of the body is longitudinal or transverse. 
In Metazoa and plant cells and in most Protozoa in which the 
relations are clearly discerned, the plane of division of the cell-body 
is parallel to the plane of division of the nucleus, both being per- 
pendicular to the long axis of the mitotic spindle. The binucleated 
Opalinae show the same relation in the case of the unusual trans- 
verse divisions, but in the more frequent longitudinal divisions the 
plane of division of the body is parallel with the long axis of the 
nuclear spindle. A similar discrepancy between the directions of 
the division of the body and of the nucleus is seen in the Trypano- 
somes, but there the nuclear relations are not so clear, there being, 
especially, no certain indication that the orientation of the parent 
and daughter nuclei remains constant generation after generation. 
The constancy in the direction of the division of the nuclei and the 
variability in the direction of the division of the body in Opalina 
show that there is a lack of coordination between the direction of 
division of the nucleus and of the body. This lack of coordination 
is much more marked in the multinucleated species. 
The conditions are interesting to consider frow the point of view 
of phylogeny. If the anterior end of Opalina is homologous with 
the anterior end of a Flagellate, and doubtless it is so, we see that 
the two agree in dividing longitudinally. In most Flagellata we have 
only longitudinal divisions.?) Probably in Opalina the longitudinal 
division is primitive and the unusual transverse division secondary. 
The latter is probably comparable to the transverse division char- 
') Oxyris marina is said to divide transversely. 
