96 THE BIOLOGY OF STENTOR 



sections of the membranellar band is shown by the observation 

 that late regeneration primordia grafted into the backs of non- 

 differentiating cells can and frequently do break into the oral ring 

 through a localized resorption of the membranellar band (c). This 

 interpolation also occurs in reorganizing stentors in which the 

 head has been rotated 180° in place, but now the mouthparts are 

 also resorbed though on the far side of the cell (d). 



There are other evidences that oral resorption is a separate and 

 predetermined part of the reorganization process. In one interesting 

 case the stentor was transected and the anterior half rotated 180° 

 on the posterior. This specimen then reorganized. Because of the 

 disarrangement of the striping, the anlage remained for a long 

 time in a diagonal position across the center of the cell yet the 

 mouthparts and adjacent membranellar band were resorbed long 

 before the primordium moved forward (e). It is also pertinent 

 that mid-stage reorganizers can induce transient primordium 

 formation in non-differentiating cells to which they are grafted; 

 reorganization goes to completion on the reorganizer side and the 

 mouthparts of the other component are also resorbed although 

 there is not a new set to take their place (f). 



On the contrary, it appears that in the state of division or 

 regeneration there is little predisposition for the feeding organelles 

 to be resorbed. When two stage-2 dividers were grafted together 

 in homopolar parabiosis division did not continue, the two 

 primordia moved forward but the original mouthparts remained 

 intact (g). True reorganization then followed, in which all four of 

 the existent oral parts were resorbed. 



These experiments suggest that in reorganization the mouth- 

 parts are somehow invisibly dissociated, or cut off morphologically, 

 and therefore usually predestined to dedifferentiation. This 

 interpretation seems to be supported by the fact that if re- 

 generation is induced by excising the head and a new head is then 

 grafted back into place later, then, if the primordium continues 

 developing, reorganization ensues and the old mouthparts are 

 resorbed (see Fig. 37B). Also if the heads of non-differentiating 

 stentors are circumscribed and rotated 180° in place, reorganiza- 

 tion follows in the majority of cases. So in both types of experi- 

 ment it would seem that isolating the whole set of feeding organ- 

 elles has the same effect as the hypothetical disjunction of the 



