136 THE BIOLOGY OF STENTOR 



I. The course and spectrum of cell interactions 



Enlarging upon these statements, we shall at first and for the 

 most part confine our account to regenerators and their parts 

 interacting with non-differentiating stentors (Tartar, 1958b). 

 When a sector bearing the primordium and a few macronuclear 

 nodes is cut out of a regenerator, development of the anlage con- 

 tinues as the fragment regenerates a small stentor; or when the 

 sector is grafted into the back of another regenerator, both host 

 and donor primordia continue differentiating and produce a 

 doublet or bistomial stentor. These tests show that such sectors 

 contain all that is necessary for anlagen development and that the 

 grafting operation itself has no effect on this process. But if a 



B 



Fig. 34. A. Induced primordium resorption. Sector of a stage-3 

 regenerator grafted to a non-differentiating host (a), b: Anlage 

 is promptly resorbed, but not the multiplied fine striping 

 encompassed by it. c: Specimen undergoes regeneration- 

 reorganization because added primordium site does not subtend 

 mouthparts, and a doublet is formed (d). 

 B. Accelerated reformation of primordium after excision. 

 a: Primordium and site removed, b: Rift soon appears in 

 previously closed line of heal, c: Primordium appears in rift 

 within an hour after operation and there is no multiplication of 

 adjacent lateral stripes, d: Only relatively few and broad stripes 

 are hence carried into the frontal field. 



