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 

 mitosis by W. Schleicher (1878), karyokinesis by W. Flem- 

 ming (1882), or indirect cell division. The appearances 

 vary according to the simplicity or complexity 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 growth 

 with actual increase of the 'essential substances of the 

 cell. 



It will be convenient for our present purposes to divide 

 the mitotic changes into the following phases: 



1. The Prophase, or 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 

 filamentous deposit of chromatin. The remainder of the 

 nucleus is brilliant and clear, with scattered threads of 

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