KARYOKINESIS 



57 



The essential fact is the exact partition of the nuclear material 

 between the two daughter cells. It may be added that these various 

 complexities of structure can be seen in living cells as well as in fixed 

 and stained material. 



Flemming gives the following summary of karyokinesis : — 



Mother Nuclei's Daughter Nucleus 



(progressive changes). (regressive changes). 



a Resting stage. Resting stage. g ^ 



b Coil. Coil. / 



c Astroid. Diastroid. e 



i d Division of Astroid and its loops ^ 



(Prophases) (Aletakinesis) (Anaphases). 



c c 



C'C 



Fig. 29. — Karyokinesis. — After Flemming. 



1. Coil stage of nucleus ; ex., central corpuscle. 



2. Division of chromatin elements into U-shaped loops, and longitudinal 



splitting of these chromosomes (astroid stage). 



3. 4. Recession of chromosomes from the equator of the cell (diastroid). 



5. Nuclear spindle, with chromatin elements at each pole, and 



achromatin threads between. 



6. Division of the cell completed. 



Besides the ordinary indirect divisipn just described, the 

 net result of which is that each of the two daughter cells 

 gets the normal number of chromosomes, a precise half of 

 each of the chromosomes in the original cell, there is 

 another kind of cell division (meiotic or reducing division) 

 which occurs only in the maturation of the ovum and 

 spermatozoon, and has for its net result the reduction of the 

 number of chromosomes to a half of the normal number. 



