THE CELLULAR BASIS 97 



versible, so that they do not again become 

 germinal cells, the differentiations of the sex 

 cells are reversible, so that these cells, after 

 their union, again become germinal cells. 



In many theories of heredity it is assumed 

 that there is a specific "inheritance material," 

 distinct from the general protoplasm, of which 

 the function is the "transmission" of hereditary 

 properties from generation to generation, and 

 of which the characteristics are independence 

 of the general protoplasm, continuity from 

 generation to generation and extreme stability 

 in organization. This is the idioplasm of 

 Xageli, the germ-plasm of Weismann. But 

 there is no reason to suppose that "germ- 

 plasm" is anything other than germinal proto- 

 plasm, which is found in all cells in the earliest 

 stages of development but which becomes 

 limited in quantity or altered in quality in 

 tissue cells. A "germ-plasm" which is abso- 

 lutely distinct from and independent of the 

 general protoplasm is a mere fiction which 

 finds no justification in reality. 



4. The Units of Living Matter. The en- 

 tire cell, nucleus and cytoplasm, is the ulti- 



