98 THE STORY OF THE LIVING MACHINE. 



their appearance. Between the two stars or 

 asters a set of fibres can be seen running from 

 one to the other (Fig. 29). These two asters and 

 the centrosomes within them have been spoken 

 of as the dynamic centre of the cell since they 

 appear to control the forces which lead to cell 

 division. In all the changes which follow these 

 asters lead the way. The two asters, with their 

 centrosomes, now move away from each other, 

 always connected by the spindle fibres, and finally 

 come to lie on opposite sides of the nucleus (Figs. 



FIG. 29. FIG 30. 



FIG. 29. The centrosomes are separating but are connected by 



fibres. 

 FIG. 30. The centrosomes are separate and the equatorial plate of 



chromosomes, cr, is between them. 



29, 30). When they reach this position they are 

 still surrounded by the radiating fibres, and con- 

 nected by the spindle fibres. Meantime the mem- 

 brane around the nucleus has disappeared, and 

 thus the spindle fibres readily penetrate into the 

 nuclear substance (Fig. 30). 



During this time the chromosomes have been 

 changing their position. Whether this change in 

 position is due to forces within themselves, or 

 whether they are moved around passively by 

 forces residing in the cell substances, or whether, 



