CH. II.] 



KARYOKINESIS 



19 



5. The stage of metakinesis. The sister threads separate, one set 

 going towards one pole, and the other to the other pole of the spindle 

 (fig. 24) : these form the two daughter nuclei. The chromosomes are 

 probably pulled into their new position by the contraction of the 

 spindle fibres attached to them. 



6. Each daughter nucleus goes backwards through the same series 



Ml : j Fine uniting 



filaments. 



FIG. 24. Metakinesis. A. Early stage. B. Later stage, c. Latest stage formation of diaster. B. and 

 c. show how the sister threads disentangle themselves from one another. (Waldeyer.) 



of changes ; the diaster or double star is followed by the dispirem or 

 double skein, until at last two resting nuclei are obtained (fig. 25). 



A new membrane forms around each daughter nucleus, the spindle 

 atrophies, and the attraction sphere becomes less prominent. The 

 division of the cell protoplasm into two parts around the two nuclei 

 begins in the diaster stage, and is complete in the stage represented 

 in fig. 25. 



-- Remains of spindle. 



Line of separation of the __.J 



two cells. 

 Antipole of daughter ,.--, 



nucleus. 



, "v^ Lighter substance of the 

 \ _..--* nucleus. 



Cell protoplasm. 



Hilus. 





FIG. 25. Final stages of karyokinosis. In the lower daughter nucleus the changes are still more 

 advanced than in the upper. (Waldeyer.) 



The karyokinetic process has been watched in all its stages by 

 more than one observer. The time occupied varies from half an hour 

 to three hours; the details, however, must be studied in hardened 

 and appropriately stained specimens. They are most readily seen 

 in cells with large nuclei, such as occur in the epidermis of 

 amphibians. 



The process varies a good deal in different animal and vegetable 



