A ORITICISM OF THE CELIL-THEORY. 157 
growth without division into cells, because there are not in 
the animal kingdom any such striking instances of massive 
growth without cell division as are exhibited by the Ceeloblastz, 
especially if we leave out of consideration the Mycetozoa, as 
belonging to the debateable territory between the two kingdoms. 
Nevertheless, we have instances of growth and mitotic nuclear 
division, unaccompanied by cell division, which are not ap- 
parently a mere prelude to division. Take the single instance 
of Opalinaranarum. Because this organism is microscopic, 
and may be described, without offence to our sense of propor- 
tion, as a corpuscle, it is invariably called unicellular. Yet in 
essential features it resembles one of the Celoblaste. It 
contains numerous nuclei, which divide mitotically, and their 
division is an accompaniment of the growth of the mature 
organism. Themultinucleate mature condition is of considerable 
duration. In the reproductive process this multinucleate 
corpuscle divides repeatedly, until a number of small offspring 
are formed, each containing several, usually four or five, nuclei. 
The minute product of fission then encysts, and it is remarkable 
that either during or immediately after encystment the several 
nuclei break up, and a single new nucleus is formed,—pre- 
sumably it is constituted out of the chromatin of the several 
nuclei. The form which emerges from the cyst grows, and 
growth is accompanied by repeated mitotic division of the 
nucleus till the mature condition is reached. The whole 
history reminds one of that of a Mycetozoon, except that the 
young do not fuse to form a plasmodium, but simply grow up; 
in this respect Opalina resembles the Ceeloblaste, differing from 
them, however, in the fact that the whole organism is concerned 
in reproduction, not a special part. Although it has, as he 
remarks, a distinct “‘ development,” Zeller, who first followed 
its life history, has no doubt that Opalina is a single cell. 
Now the multinucleate condition is far from uncommon in 
the Protozoa, and it may almost be said to be the rule in the 
Ciliata, if we regard macronucleus and micronucleus as two 
separate nuclei. But putting aside this phenomenon, the 
significance of which we do not yet clearly understand, there 
