52 



STUDENTS HISTOLOGY 



The effect of these changes is to separate the chromatin into 

 masses called chromosomes. The number of chromosomes varies in 

 different species, but is probably constant in the same species. 

 Fig. 29 shows the main events in karyokinesis in a diagrammatic 

 manner. It represents the process as it occurs in the starfish, 

 where the process is less complicated than in some cases. Each 



C D 



FIG. 29. KARYOKINESIS AFTER WILSON. 



chromosome becomes split lengthwise into two halves. One group 

 of halves moves to one end or pole of the cell, the other group to 

 the other pole. The two groups of chromosomes give rise to two 

 new nuclei. 



The separation of the groups of chromosomes is accomplished 

 by delicate filaments, which radiate from the two poles to which the 

 chromosomes are to travel. Some of these filaments meet at the 

 equator of the cell to form what is called the nuclear spindle. The 



