BIOLOGY 



type represented in Figure 36, the number of chromosomes 



is invariably four. 



ce The second part of the 



X""~ ~^X first stage consists of the 

 .en / \ separation of the two gran- 



ules of the centrosome as 

 shown at B. As these parts 

 separate, they are seen to 

 be connected by fibers form- 

 ing what is called the spin- 

 dle. The granules continue 

 to move away from each 

 other until they finally 

 come to lie at opposite 

 poles of the nucleus, form- 

 ing the amphiaster (Gr. am- 

 phi = both + aster = star) 

 as shown at D. They are 

 still connected by the fibers 

 of the spindle, which now 

 pass into the nucleus itself; 

 the nuclear membrane in 

 the meantime has disap- 

 peared. At the end of this 

 phase the chromosomes 

 have assumed a position 

 midway between the two 

 granules, lying on the mid- 

 dle of the spindle, and at 

 right angles to the line con- 

 necting them, at E. They 

 thus form a sort of plate be- 

 tween the two poles of the 



spindle, known as the equatorial plate. The formation of the 



chromosomes and the separation of the centrosomes may take 



FIG. 36. DIAGRAM SHOWING THE 

 SUCCESSIVE STAGES IN THE PROCESS 



OF KARYOKINESIS 



A, the resting cell before it enters into the 

 process of cell division; H, the completed proc- 

 ess after the cell has divided into two parts; 

 ce, the centrosome; ch, the chromatin. For 

 description of the different stages, see text. 



