THE CELLULAR BASIS 103 



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, the 

 function of which is the "transmission" of her- 

 editary properties from generation to genera- 

 tion, and the chief characteristics of which are 

 independence of the general protoplasm, con- 

 tinuity from generation to generation and ex- 

 treme stability in organization. This is the 

 idioplasm of Nageli, the germ-plasm of Weis- 

 mann. But there is no reason to suppose that 

 germ-plasm is anything other than germinal 

 protoplasm, which is found in all cells in the 

 earliest stages of development but which be- 

 comes 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 small- 

 est unit of living matter which is capable of 

 independent existence. Neither the nucleus 



* See pp. 183-184 for a more complete statement. 



