66 MINUTE STRUCTURE OF CELLS less. 



nucleus is seen to contain a spindle shaped body {s/>) formed 

 of excessively delicate fibres which converge at each pole 

 to the corresponding astrosphere. The precise origin of 

 this nuclear spindle is uncertain : it may arise either 

 from the nuclear matrix or, more probably, from the 

 protoplasm of the cell : it is not affected by colouring 

 matters. 



At the same time each chromosome splits along its whole 

 length so as to form two parallel rods or loops in close 

 contact with one another (b) : in this way the number of 

 chromosomes is doubled, each one being now represented 

 by a couple. 



The divided chromosomes now pass to the equator of the 

 spindle (d) and assume the form of more or less V-shaped 

 loops, which arrange themselves in a radiating manner so as 

 to present a star-like figure when the cell is viewed in the 

 direction of the long axis of the spindle. Everything is now 

 ready for division to which all the foregoing processes are 

 preparatory. 



The two chromosomes of each couple now gradually pass 

 to opposite poles of the spindle (e, f), two distinct groups 

 being thus produced (g) and each chromosome of each 

 group being the twin of one in the other group. Perhaps 

 the fibres of the spindle are the active agents in this 

 process, the chromosomes being dragged in opposite 

 directions by their contraction : on the other hand it is 

 possible that the movement is due to the contractility of the 

 chromosomes themselves. 



After reaching the poles of the spindle the chromosomes 

 of each group unite with one another to form a network (h) 

 around which a nuclear membrane finally makes its appear- 

 ance (i). In this way two nuclei are produced within a 

 single cell, the chromosomes of the daughter-nuclei, as well 



