SURVEY OF CELL-LIFE. 185 
place before the cell-wall and cell-cavity exist as distinct struc- 
tures, 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 mstance 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- 
ternal 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 conse- 
quence 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 com- 
pelled 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 subse- 
quently ; 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 ex- 
ternal stratum of the precipitate having become condensed in 
such a manner that the membrane enclosed both nuclei. Mean- 
while observation affords no demonstrative proof on the sub- 
ject, 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. 
