9 6 



THE STORY OF THE LIVING MACHINE. 



Cell Division or Karyokinesis. We will begin 

 with a cell in what is called the resting stage, 

 shown at Fig. 23. Such a cell has a nucleus, with 

 its chromatin, its membrane, and linin, as already 

 described. Outside the nucleus is the centrosome, 

 or, more commonly, two of them lying close to- 

 gether. If there is only one it soon divides into 

 two, and if it has already two, this is because a 

 single centrosome which the cell originally pos- 

 sessed has already divided into two, as we shall 

 presently see. This cell, in short, is precisely like 

 the typical cell which we have described, except 

 in the possession of two centrosomes. The first 



FIG. 27. FIG. 28. 



FIG. 27. This and the following: figures show stages in cell divi- 

 sion. Fig. 27 shows the resting stage with the chromatin, cr, 

 in the form of a network within the nuclear membrane and 

 the centrosome, ce, already divided into two. 



FIG. 28. The chromatin is broken into threads or chromosomes, cr. 

 The centrosomes show radiating fibres. 



indication of the cell division is shown by the 

 chromatin fibres. During the resting stage this 

 chromatin material may have the form of a 

 thread, or may form a network of fibres (see Fig. 

 27), But whatever be its form during the resting 



