THE CELLULAR BASIS 129 



division to embryonic differentiation? In this 

 process of mitosis, or indirect cell division, two 

 important things take place: (1) Each 

 chromosome, chromomere and centrosome is 

 divided exactly into two equal parts so that 

 each daughter structure is at the time of its 

 formation quantitatively one-half the size and 

 qualitatively precisely like its mother struc- 

 ture. (2) Accompanying the formation of 

 radiations, which go out from the centrosomes 

 into the cell body, diffusion currents are set 

 up in the cytoplasm which lead to the localiza- 

 tion of different parts of the cytoplasm in 

 definite regions of the cell, and this cytoplas- 

 mic localization is sometimes of such a sort 

 that one of the daughter cells may contain one 

 kind of cell substance and the other another 

 kind. Thus while mitosis brings about a 

 scrupulously equal division of the elements of 

 the nucleus, it may lead to a very unequal and 

 dissimilar division of the cytoplasm. In this 

 is found the significance of mitosis, and it sug- 

 gests at once that the nucleus contains non-dif- 

 ferentiating material, viz., the idioplasm or 

 germ-plasm, which is characteristic of the race 



