DIVISION OF CELLS. ii 



varieties of elements by a complicated series of changes, collectively known as kar- 

 yokiiiesis, or mnosis, especially affecting the nucleus. As already pointed out, in 

 addition to presiding over the nutritive and chemical changes, the nucleus is par- 

 ticularly concerned in the process of reproduction ; further, of the several morpho- 

 logical constituents of the nucleus, the chromatin displays the most active change, 

 <;ince this substance is deeply concerned in transmitting the characteristics of the 

 parent cell to the new elements. So essential is this substance for the perpetuation 

 of the characteristics of each specific kind of cell that the entire complex mitotic 

 cycle has for its primary purpose the insurance of the equal division of the chroma- 

 tin of the mother cell between the two new nuclei, such impartial distribution of the 

 chromatin taking place irrespective of any, or even very great, dissimilarity in the 

 size of the daughter cells, the smaller receiving exactly one-half of the maternal 

 chromatin. 



Mitotic Division. — The details of karyokinesis, or mitosis, sometimes also 

 spoken of as iyidirect division^ include a series of changes involving the centrosome, 



Fig. 9. 

 ABC 



^r -,. ^^^ \ 



ft 



/■■■. . •  



D 



<■-« 





G H I 



\ 



Chromatic figures in dividing cells from epidermis of salamander embryo. X 960. Ay resting stage ; B, close 

 spireme ; C, loose spireme ; Z>, chromosomos {" wreath " ), seen frcm surface ; £, similar stage, seen in profile ; F^ 

 longitudinal cleavage of chromosomes; G, beginning migration of segments towards ceiitrosomes ; //^separating 

 groups of daughter segments ; /, daughter groups attracted towards poles of new nuclei, cytoplasm exhibits begin- 

 ning cleavage. 



the nucleus, and the cytoplasm, which are conveniently grouped into four stages ; 

 (i) the Prophases, or- preparatory changes; (2) the Metaphase, during which the 

 chromatin is equally divided ; (3) the Aiiaphases, in which redistribution of the 

 chromatin is accomplished ; (4) the Telophases, during which the cytoplasm under- 

 goes division and the daughter cells are completed. 



