A Criticism of the Cell-Theory; being an Answer to Mr. Sedgwick's ...

A CRITICISM OP THE CELL-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 Coeloblastse,
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 apparently
a mere prelude to division. Take the single instance
of Opalina ranarum. Because this organism is microscopic,
and may be described, without offence to our sense of proportion,
as a corpuscle, it is invariably called unicellular. Yet in
essential features it resembles one of the Coeloblastee. 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,—presumably
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 Coeloblastae, 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 macrouucleus and micronucleus as two
separate nuclei. But putting aside this phenomenon, the
significance of which we do not yet clearly understand, there