274 M. M. Mercatr 
remains minute and hardly shares in the activities of growth. The 
divergence must have occured in a binucleated (or multinucleated) 
condition. We have in Opalna such a binucleated (or multinucleated) 
form. In what way could its condition with similar nuclei be chan- 
ged into a condition with dissimilar nuclei? 
First let us note again the fact that the nuclei of the bi- 
nucleated Opalinae are often slightly dissimilar in regard to mitosis, 
one being often in a slightly more advanced condition than the other. 
There is a similar divergence in regard to the formation of the prob- 
ably nutritive chromatin spherules, one nucleus showing these in 
a more advanced stage of formation. The exact balance of the two 
nuclei seems already somewhat disturbed in Opalina. 
May we conceive this divergence as going further, the nutritive 
chromatin becoming hypertrophied in one nucleus and not in the 
other, the second nucleus ultimately giving up almost all its con- 
nection with nutrition and becoming, much smaller, giving us ulti- 
mately the condition seen in higher Cilzata with very divergent 
micro- and macronuclei? 
One thing seems to stand in the way of such an interpretation 
so far as Opalina is concerned: in the division of Opalena one whole 
nucleus, and not two half nuclei, is given to each daughter cell. 
The condition in Opalina is not a true binucleated condition. We 
have merely a delayed division of the body, which causes two 
daughter nuclei to lie for a long time in one cell, indeed even until 
they have entered upon the next mitosis. Division of the cell when 
it does occur is not associated with the mitosis in the nuclei which 
is taking place at the same time, but is really the delayed cell- 
divion that belonged with the last nuclear mitosis. Division of the 
cell-body lags one step behind the division of the nuclei. To get a 
proper understanding of the real meaning of this division we must 
bring together that division of the body and that division of the 
nucleus which really belong together. 
In attempting to do this we see at once that the direction of 
division of either nucleus or body must be changed. At present 
the long axes of nuclei and body coincide and remain constantly in 
this relation. The nucleus divides transversely and the body gen- 
erally longitudinally.1) Can we find a plausible scheme which will 
get around this difficulty? 
') Longitudinal division of the body is characteristic of Flagellata and is 
doubtless, primitive for Opalina. Many Flagellata show nuclei which when dividing 
elongate at right angles to the plane of division of the body and then divide 
