How Cells Divide — Indirect Cell Division 65 



the spindle^ known as the equatorial plate. The latter lies approximately 

 equidistant between the two centrosomes. 



B. Metaphase (Gr. meta, between or after; phasis, appearance) (Fig. 20, 

 E) 



This stage Is known as the equilibrium phase with the chromosomes 

 lined up across the middle of the equatorial region and balanced between 

 the two opposing forces of the opposite centrosomes. Each chromosome 

 now splits lengthwise into two equal parts. This Is very necessary If the 

 linear arrangements of the hereditary genes contained within the chromo- 

 somes are to be equally divided between the two future cells. The chromo- 

 somes which have each divided lengthwise now separate into two exactly 

 similar groups. 



C. Anaphase (Gr. ana, up; phasis, appearance) (Fig. 20, F-G) 



In this stage the two equal halves of each chromosome migrate from 

 the equatorial region along the spindle toward the opposite centrosomes. 

 Some of the newly formed chromosomes move slowly, while others go 

 rapidly. The part of the spindle to which the chromosomes are attached 

 is known as the attachment fibers of the spindle. The part of the spindle 

 over which the chromosomes have already traveled Is known as the used 

 spindle or interzonal connecting fibers which are visible between the two 

 groups of migrating chromosomes. In later anaphase stages the cell mem- 

 brane constricts, still later to divide the cell proper into two parts. In 

 certain cells, at least, a plate of small granules appears at the position of 

 the former equatorial plate. This plate becomes more pronounced and 

 may play a part In dividing the cell at that point (Fig. 20) . 



D. Telophase (Gr. telos, end; phasis, appearance or aspect) (Fig. 20 H-I) 



This stage Is a reconstruction stage. The entire cell now Is divided 

 at the equatorial plate of the spindle. Each half cell (daughter cell) 

 eventually becomes entire and normal with the characteristics of the 

 original parent cell. The nucleus again becomes spherical. The nuclear 

 membrane reappears. The asters disappear completely. The chromo- 

 somes change Into an Irregular network of chromatin granules again as 

 found in the original nucleus. The spindles disappear by the end of this 

 stage. Each daughter cell now grows to approximately the same size as 

 the original parent cell. Later, the process of mitosis will repeat Itself 

 in each of the two previously formed daughter cells. 



