ACTIVATION AND INHIBITION: ORAL PRIMORDIUM 157 



embarked upon any one of these courses is not irrevocably deter- 

 mined to pursue no other. 



The experimental analysis reviewed in this chapter demonstrates 

 that stentors alternate through at least two cell states involving 

 some pervasive aspect of the cell. A prolonged state of inhibition 

 of oral primordium formation which maintains the status quo of 

 the formed organism alternates with another and more transitory 

 state promoting redifferentiation of feeding organelles which 

 prevails during regeneration, reorganization, and division. 

 Moreover, the stimulus to regeneration appears to be another 

 condition separable from the subsequent activation, transmissible 

 to any grafted partner regardless of size and resulting in its 

 parallel reorganization. Whether there is a " division state " or 

 predisposition to fission which is Hkewise transmissible in fusion 

 complexes is still obscured by contradictory evidence. 



Besides clarifying the question of division, we next need to know 

 in what parts of stentor these cell states reside. Present evidence 

 suggests that the nucleus is not involved, since macronuclei can 

 be exchanged between regenerators and non- differentiating 

 stentors without effect. A nucleus or some nucleus is essential for 

 primordium formation and development but this organelle 

 apparently does not take the lead. Enucleated non-differentiating 

 stentors are as capable of inducing anlagen resorption as nucleate. 

 Preliminary tests in which stentors bereft of the endoplasm show 

 the same inhibitive influence suggest that cell states reside in the 

 cortical layer. If so, these states characterize the entire ectoplasm 

 because the effect is quantitative and depends on the relative sizes 

 of the joined stentors. Every part of this or some other pervasive 

 feature of the cell may be involved in the cell states of activation 

 and inhibition and somehow capable of affecting what occurs 

 locally at the primordium site, as indicated by the quantitative 

 relationships. 



After those parts of stentor which "carry" or take the lead in 

 establishing cell states are identified, the next step according to 

 conventional procedure would be to obtain a biochemical 

 characterization of the changes in these parts. It is natural to 

 suppose that intercellular transmission in grafts would occur via 

 the semi-fluid endoplasm which flows and mixes between the two 



