CELL MULTIPLICATION 



21 



achromatic spindle begin to contract, and thus separate the halves of the 

 chromosomes in such a way that one-half of each is turned toward one pole, 

 and the other half toward the other. As this continues, the two groups, 

 which are equal in size, draw away from each other and from the equator, 

 each group being formed of daughter chromosomes. 



FIG. 1 6. Monaster Stage of Karyokinesis. (Rabl.) 



Anaphase. The two groups (daughter chromosomes) now gradually ap- 

 proach their respective poles, or centrosomes, and the equator becomes free. 

 On reaching the pole, each group gathers in a form which is similar in arrange- 

 ment to the monaster and is known as the diaster. During this time the cell 

 body becomes slightly constricted by a circular groove at its equatorial plane. 



Telophase. Soon afterward the fibrils of the chromatic spindle which 

 connect the two groups begin to grow dim and finally disappear. The daugh- 



FIG. 17. Stages of Karyokinesis. A. Commencing separation of the split chromo- 

 somes. B. The separation further advanced. C. The separated chromosomes passing 

 along the fibers of the achromatic spindle. (Rabl.) 



ter chromosomes assume the form of threads twisted in a coil and develop 

 each a nuclear membrane and a nucleolus, forming a daughter nucleus. 

 The nuclei enlarge and the nuclear threads assume the appearance of the 

 resting state of the nucleus. Meanwhile, the constriction about the body 

 of the cell cytoplasm has become deeper and deeper until the protoplasm is 

 divided into two equal parts, or daughter cells, each with its daughter nucleus, 

 and the process of karyokinesis is completed. 



