THE CELLULAR BASIS 135 



generation to generation; whereas the cell 

 body contains the differentiating substance, 

 the personal plasm or somatoplasm which 

 gives rise to all the differentiations of cells, 

 tissues and organs in the course of ontogeny. 



Weismann supposed that the mitotic divi- 

 sion of the chromosomes during development 

 was of a differential character, the daughter 

 chromosomes differing from each other at 

 every differential division in some constant 

 and characteristic way, and that these differ- 

 entiations of the chromosomes produced the 

 characteristic differentiations of the cytoplasm 

 which occur during development. But there 

 is not a particle of evidence that the division 

 of chromosomes is ever differential; on the 

 contrary, there is the most complete evidence 

 that their division is always remarkably equal 

 both quantitatively and qualitatively. If 

 daughter chromosomes and nuclei ever become 

 unlike, as they sometimes do, this unlikeness 

 occurs long after division and is probably the 

 result of the action of different kinds of cyto- 

 plasm upon the nuclei, as is true, for example, 

 in the differentiation of the chromosomes in 



