LIVING SUBSTANCE 



61 



as the -delicate Stentor Roeselii (Fig. 6, A\ which lives in fresh 

 water and is especially adapted for this experiment, be divided into 

 two parts in such a manner that each possesses a piece of the long 

 rod-like nucleus, the same phenomenon appears as in Hydra : the 

 two pieces regrow into small complete Stentors (Fig. 6, B and C) 

 and continue to live in all respects normally. In such an experiment 

 the cell, an individual of the lowest order, has become divided into 

 two individuals, and can even be divided into more, if the opera- 

 tion be performed so that each piece possesses some protoplasm as 



FIG. 6. Stentor Roeselii, a trumpet-shaped infusorian ; A, cut across at * ; B and C, the two pieces, 

 which have become regenerated into complete Stentors. The clear extended mass in the 

 interior is the nucleus. 



well as a piece of the nucleus. This fact is of fundamental im- 

 portance, and we shall have occasion to recall it frequently. In the 

 present case it stands only apparently in contradiction with the 

 idea of the cell as the elementary individual ; for by the cutting 

 operation there are obtained, not new stages of individuality, but 

 complete Stentors, i.e., individuals of the value of a cell. In all 

 such divisions of cells, wherever protoplasm and nucleus are present 

 in the pieces, the latter have the value of cells ; in the process we 

 do not go below the cell. If, however, the cut be made so that 

 one piece contains protoplasm and nucleus, and the other only 

 protoplasm, the former continues to live and represents a complete 

 cell, while the latter, possessing no longer the individuality of a 



