THE CELL 



29 



A. Mitotic Division. — In a cell about to divide, the first 

 change is a general enlargement of the nucleus. At the 

 same time the centrosome becomes double, and the two 

 portions travel from one another, but remain united by 

 delicate lines to form a spindle-shaped structure (fig. 4 (1)). 

 The spindle passes into the centre of the nucleus, and seems 

 to direct the changes in the reticulum. The nuclear mem- 

 brane disappears, and the nucleus is thus not so sharply 



(3) 



Fig. 4. — Nucleus in Mitosis. (1) Convoluted stage ; (2) Monaster 

 stage ; (3) Dj'aster stage ; (4) Complete division. 



marked off from the cell protoplasm. The nucleoli and 

 nodal points also disappear, and with them all the finer 

 fibrils of the network, leaving only the stouter fibres, which 

 are now arranged either in a skein, or as loops with their 

 closed extremity to one pole of the nucleus and their open 

 extremity to the other. The nucleus no longer seems to 

 contain a network, but appears to be filled with a convoluted 

 mass of coarse fibres, and hence this stage of nuclear division 

 is called the convoluted stage. 



The spindle continues to grow until it occupies the whole 



