THE CELL. 39 



linear enlargements of the lines of the achromatic spindle appear 

 in its equator, and through these a plane of cleavage, dividing the 

 two new cells from each other, is finally established. 



It is rarely that any biological process assumes such mathemat- 

 ical precision as is displayed in karyokinesis. The purpose of that 

 mode of cell-division appears to be an exactly equal partition of 

 all parts of the chromoplasm between the young cells. Whether 

 the amount of cytoplasm given to the daughter-cells is the same 

 or different, the division of the chromoplasm is exactly equal, not 

 only in its whole bulk, but each chromosome, which appears to be 

 the morphological unit of the chromoplasm, is split into exactly 

 equivalent halves, one of which is contributed to the formation of 

 each daughter-nucleus. It is for this reason that the chromoplasm 

 is looked upon as the carrier of hereditary peculiarities. 



After the formation of the daughter-nuclei, the centrosome 

 usually passes from it into the cytoplasm. It may divide earlier 

 than has been described, the division taking place while it exists 

 as the polar body, or even earlier (Fig. 16). 



A cell nearly always divides to form two new cells, but some- 

 times three or more cells may be produced, the chromosomes being 

 distributed among them (Fig. 19). Such cases are probably 



FIG. 19. 



Epithelial cell from a carcinoma. (Galeotti.) The centrosome has divided into four portions, 

 and the chromosomes are arranged with reference to these. The figure represents the meta- 

 kinetic phase of karyokinesis, which will result in the formation of four imperfect 

 nuclei. 



always morbid, and the resulting cells are not wholly the equiv- 

 alents of the parent cell. 



It occasionally happens that the cytoplasm fails to divide after 

 the formation of the daughter-nuclei, and cells with two or more 

 nuclei result. When the nuclei continue to multiply and the 



