CHAPTER VI. 

 CELL DIVISION. 



The most simple form of reproduction or multiplica- 

 tion takes place through the separation of the cell 

 into two or more segments of fairly uniform size and 

 appearance. 



It is usually preceded or accompanied by remarkable 

 changes in the nucleus which have led to its being called 

 karyokinesis, karymitosis or indirect cell division. The 

 appearances vary according to the simplicity or com- 

 plexity of the cellular structure so that one description 

 cannot apply to all cases, though an account of what 

 takes place in a typical cell may be accepted as a type 

 of the process. 



The cell that is about to divide is distinctly larger than 

 its fellows and its nucleus contains an excess of nuclein 

 or chromatin hyperchromatosis. The cells formed by 

 division are smaller than the normal, so that both before 

 and after division we see examples of true cell growin 

 with actual increase of the essential substances of the 

 cell. 



It will be convenient for our present purposes to 

 divide the karyokinetic changes into the following 

 phases : 



1. The Preparation of the Nucleus for Division. 

 When an ordinary resting nucleus stained by the usual 

 methods is carefully observed it will be found that the 

 nuclear membrane is quite distinct, and that just within 

 it there is a more or less well marked, slightly filament- 

 ous deposit of chromatin. The remainder of the nucleus 

 is brilliant and clear, with scattered threads of chroma- 

 tin. If a nucleolus be present it appears as a minute 



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