184 SURVEY OF CELL-LIFE. 
the microscope. We cannot, at present, lay down any general 
law respecting the circumstances under which such a coalescence 
occurs; it presupposes that the cell-membrane and intercellular 
substance are homogeneous structures, and may perhaps always 
take place when such a state exists. 
As regards the subdivision of the cells, we have already seen 
how a jutting out of the cell-membrane may be produced by 
its more vigorous growth in certain situations. But a jutting 
inwards into the cavity of the cell may also result from the 
very same process. Now, if we imagine this jutting inwards to 
take place in a circular form around a cell, as the consequence 
of a partial increase in the force of its growth, it may proceed 
to such an extent, that one cell may be separated into two, 
connected together only by a short peduncle, which may after- 
wards be absorbed. This would illustrate the most simple form 
of subdivision in a cell. In the animal cells, however, which 
undergo subdivision, that is, the fibre-cells, the process is more 
complicated; firstly, because when an elongated cell subdivides, 
it splits into many fibres; and, secondly, because the cells are so 
very minute. The process, therefore, cannot for these reasons 
be accurately traced, and the following is all that we can de- 
tect : a cell becomes elongated on two opposite sides into several 
fibres ; from the angle, which the fibres on either side form with 
each other, a striated appearance gradually extends over the 
body of the cell ; this formation of strize becomes more and more 
distinct, until the body of the cell splits entirely into fibres. 
The coalescence of several primary cells to form a secondary 
cell is, to a certain extent, the opposite process to the last. 
Several primary cells, of muscle for instance, are arranged close 
together in rows, and coalesce into a cylinder, in the thickness 
of which lie the nuclei of the primary cells. This cylinder is 
hollow and not interrupted by septa, and the nuclei lie upon the 
internal surface of its wall. These are the facts of the process, 
so far as they have as yet been observed. One can form a 
conception of so much as is yet required to render them com- 
plete. If two perfectly-developed cells coalesce together, their 
walls must first unite at the poimt of contact, and then the 
partition-wall between the cavities must be absorbed. Nature, 
however, does not by any means require that these acts should 
occur at precisely defined periods. The coalescence may take 
i 
