SURVEY OF CELL-LIFE. 185
place before the cell-wall and cell-cavity exist as distinct structures, somewhat in the following manner: the nuclei are formed
first, around them a new stratum of substance is deposited, the
external portion of which, in accordance with the course of
formation of an ordinary simple cell, would become condensed
into a cell-membrane. But in this instance the nuclei lie so
close together, that the strata forming around them and corre-
sponding to the cells, flow together, to form a cylinder, the ex-lternal portion of which becomes condensed into a membrane,
just in the same manner as in simple cells, where merely the
external portion of the stratum formed around the nucleus,
becomes hardened on the outside into a membrane, in consequence of the reception of new molecules. There is, therefore,
nothing in this which differs so very materially from the course
of development of a simple cell; indeed, we seemed to be compelled to assume a similar process for the formation of the nuclei
furnished with two or more nucleoli. (See page 176.) It is
possible that there may be stages of transition between the
ordinary simple cell and these secondary cells. It has been
already mentioned at pages 117-118, that fat-cells occur in the
cranial cavity of fishes, many of which contain two nuclei.
It is possible that only one of them is the cytoblast of the
cell, and that the second is a nucleus which has formed subsequently; but they resemble one another so completely in their
characteristic position on the cell-membrane (see pl. III, fig.
10,) that perhaps they may both be cytoblasts of a cell which
has been formed around both nuclei, in consequence of the external stratum of the precipitate having become condensed in
such a manner that the membrane enclosed both nuclei. Meanwhile observation affords no demonstrative proof on the subject, and the similarity in the position of these two nuclei may
be explained in another way. Fat thrusts all bodies which have
imbibed water towards the outside of the cell, in order that it
may assume its own globular form. If now a second nucleus
should form in one of these fat-cells, it will be thrust towards
the outside, and must gradually raise the cell-membrane into a
prominence. It may also be observed, that opportunities of
demonstrating the actual absorption of the fully-developed
partition-wall between two cells do occur in the spiral vessels of
plants.
