CELL DIVISION 



75 



distribution of daughter chromosomes to the two new cells about to be 

 formed, and the end of the phases is not definitely marked. In the late 

 anaphase there may sometimes be found a slight indentation of the cell 

 membrane on either side of the coll in the plane of the equator of the 

 spindle. These indentations mark the beginnings of the division of the 

 cytoplasm into two portions. At this time in some cells it may be possible 

 to note small granules on the spindle fibers in the plane of the equator. 

 The new cell membrane when formed passes through these granules. 

 The division of the cell into two is completed by the gradual tightening of 

 the constriction about the equator of the cell. In plant cells, a cell plate 

 is usually formed at the plane of the equator of the spindle as the result 

 of thickenings on the spindle fibers, and there is no constriction of the cell 

 at its middle. 



Fig. 43. Fig. 44. 



Fig. 43.- — Dividing cell exhibiting a constriction of the cell membrane in the equa- 

 torial region and a massing of the chromosomes at the poles in late anaphase. 



Fig. 44. — Late telophase, or the completion of cell division. The centrosomes have 

 divided as if preparatory to the next division, and the nuclei are again in the resting 

 condition. 



The Telophases. — In these concluding phases (Fig. 44) occurs the re- 

 construction of the cells and nuclei after division. The new cell membrane 

 in the plane of division is completed by a constriction of the membrane in 

 the equator of the cell, whose beginning at the surface is shown in Fig. 43. 

 The chromatin becomes diffuse, in some cells retracing the prophases, 

 that is, undergoing changes in inverse order, often through an apparent 

 loose and close spireme which finally assumes the condition of a network 

 with net-knots. In other cells the chromosomes become inflated vesicles 

 which fuse to form the nucleus. A nuclear membrane is formed but the 

 source of the material of which it is formed is not known with surety. It 

 is believed in some cases to be of the same material as linin. Sooner or 



