14 



HANDBOOK OF PHYSIOLOGY. 



A ccmstriction develops at the centre of the nucleus, possibly preceded 

 by division of the nucleoli, and gradually divides it into two equal 

 daughter nuclei. A similar constriction of the protoplasm of the cell 

 occurs between the daughter nuclei and divides it in two parts. 



a 



Fig. 12. Akinesis, amitosis, or direct cell division. A, Constriction of nucleus; B, division 

 of nucleus and constriction of cell body; C, daughter nuclei still connected by a thread, division 

 being delayed ; Z>, division of cell body nearly complete. (After Arnold.) 



Indirect division, mitosis (/^TOC, a thread), or karyokinesis 

 a kernel), is the almost universal method, and consists of a series of 



Fig. 12A. Karyokinesis, mitosis, or indirect cell division (diagrammatic). ^4, Cell with rest- 

 ing nucleus; B, wreath, daughter centrosomes and early stage of achromatic spindle; C, chromo- 

 somes; Z>, monaster stage, achromatic spindle in long axis of nucleus, chromosomes dividing; 

 E, chromosomes moving toward centrosomes; F, diaster stage, chromosomes at poles of nucleus, 

 commencing constriction of cell body ; <?, daughter nuclei beginning return to resting state; H, 

 daughter nuclei showing monaster and wreath; 1, complete division of cell body into daughter 

 cells whose nuclei have returned to the resting state. (After Bo'hm and von Davidoff.) 



changes in the arrangement of the intranuclear network, resulting in 

 the exact division of the chromatic fibres into two parts, which form the 



