152 THE BIOLOGY OF STENTOR 



readily extend themselves into new primordium sites. Another 

 possibility is that somehow the anlage does receive morphogenetic 

 guidance from the surrounding ectoplasm which acts as a unit, 

 and that the ectoplasm as a whole gives "information" only one 

 step at a time, instead of a single command to make a primordium. 

 However this may be, we see again that the cell makes a strong 

 attempt to act together in all its parts as a single integrated unit. 



6. Activation in reorganizers and dividers 



It is natural to suppose that the state of activation which is not 

 of the nucleus but of the cytoplasm and can be transmitted from 

 one cell to another, or from a host cell to a grafted patch, is to be 

 found whenever an oral primordium develops. Therefore re- 

 organizers and dividers should also be in this state. This can be 

 tested by determining whether they continue to support oral 

 differentiation in regeneration primordia grafted to them, in the 

 same way that regenerating cells do. They do. Reorganizers 

 support regeneration primordia (Tartar, 1958b), likewise for 

 dividers. But in the case of dividers the intact feeding organelles 

 seem to exert a greater effect than in reorganizers and the mouth- 

 parts usually have to be excised if a grafted anlage is not to be 

 resorbed along with the host's, following the injury of cutting. 

 Conversely, both division and reorganization primordia are 

 resorbed when grafted to non-differentiating cells. We may con- 

 clude that oral primordia arising under any circumstance require 

 the same type of cytoplasmic as well as nuclear support. 



7. Rerouting the oral primordium 



This state of activation, or readiness to support primordium 

 development which is common to all re-differentiating stentors, 

 points to a basic similarity of dividers, reorganizers, and regener- 

 ators which has often been remarked. It was Gruber who first 

 noted that oral regeneration is accomplished through the formation 

 of a lateral primordium like that appearing in the normal course of 

 division. The unique characteristic of fission is not anlage 

 formation but the development and constriction of a division 

 furrow, and this aper9u of Johnson's is amply confirmed by the 

 fact that dividers as early as stage 3 can proceed to complete 

 separation after the primordium is excised. Otherwise, events in 



