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 striae 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 point 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 



