CELL DIVISION 



103 



DIAGRAM OF HOMOTYPE MITOSIS (Karyokinesis) . 



The division of all of the somatic and all of the germinal cells is 

 accompanied by changes more or less corresponding with the fol- 

 lowing diagrams, except the reduction divisions of the germinal cells, 

 which occur by heterotype mitosis, which will be made clear by a 

 subsequent diagram. 



festinj nucleus 



Proph, 



asc 



Any somatic or germinal cell. 



Stage preliminary to multiplication of 



any somatic or germinal cell, 

 a. Formation of the spirem; disap- 

 pearance of the nuclear mem- 

 brane, etc. 



6. Formation of enumerable chro- 

 mosomes; appearance of cen- 

 trosomes and nuclear spindle. 



c. Formation of the polar and hypo- 

 polar fields, and the gathering 

 of the chromosomes, apex 

 toward the center, to form the 

 equatorial plate and "aster." 



Each chromosome splits longitudinally, 

 the corresponding parts maintain- 

 ing their normal positions in the 

 equatorial plate. The half-chro- 

 mosomes are of equal valence. 



a. The halves of each divided chro- 

 mosome separate and turn 

 toward opposite polar fields. 

 Thus the future nuclei receive 

 exactly one-half of the chro- 

 matin, in the form of one-half 

 of each chromosome. 



6. The separated chromosomes 

 gather at opposite ends of the 

 cell about the polar and hypo- 

 polar fields to form the "amphi- 

 aster." 



The division of the cytoplasm after 

 separation of the daughter-nuclei, 

 and the loss of the star-like arrange- 

 ment of the chromosomes. 



Complete division of the cell into two 

 of equal size and value. 



Fia. 31. 



