REORGANIZATION 95 



for an excised part, but they resemble reorganization because the 

 mouthparts are replaced. Both Schwartz (1935) and Weisz (1951b, 

 1954) called this reorganization, and this may be permissible; for 

 if, in such cases, the well-formed primordium at stage 4 is removed 

 by a minimal excision or caused to be resorbed, the mouthparts are 

 still completely resorbed, the animals then regenerating later 

 (unpublished). The same occurs with true reorganizers, bearing 

 complete feeding organelles (b). It would appear that in reorgani- 

 zers and regenerators with mouthparts, these structures are pre- 

 determined to be resorbed. In contrast, an adaptive resorption of 



B. Primordium of reorganizer excised at stage 4, before visible 

 resorption of mouthparts has begun. Oral structures neverthe- 

 less subsequently resorbed though there are no new ones to take 



their place. Regeneration follows. 



C. a: Stage-5 primordium grafted to a non-differentiating 

 host, b: Developing anlage breaks into the oral zone, joining 

 with the original membranellar band, a section of which is 

 resorbed to permit incorporation of the new mouthparts. This 

 imitates band resorption in reorganization, but the host mouth- 

 parts are not resorbed and a doublet stentor results (c). 



D. Stage-5 reorganizer with head circumscribed and rotated 

 180°. Original mouthparts are resorbed, although now on side 

 opposite to primordium. Anlage breaks into the peristome, free 



ends of same join on far side and a normal stentor results. 



E. Specimen reorganizing after anterior was rotated on the 

 posterior half. The primordium formed far down on the side of 

 the cell yet the old mouthparts and adjacent section of mem- 

 branellar band were resorbed as if the anlage were normally 

 located. Later the new organelles moved forward, joined with 

 the original membranellar band and produced a normal stentor. 



F. Stage-4 reorganizer grafted to non-differentiating stentor. 

 a: By stage 6, the reorganizer (right) had induced a transient 

 reorganization primordium in its partner. Both original sets of 

 mouthparts were resorbed, as also the out-of-phase accessory 

 anlage. c: Partner left without oral structures now regenerating, 

 with induced re-reorganization in the other animal. Oral resorp- 

 tion may therefore extend to other mouthparts present in the 



graft systein. 



G. a: Parabiotic graft of two stage-2 dividers, b: No 

 division occurred, and the anlagen moved forward instead but 

 the original mouthparts were not resorbed as in reorganization. 

 c: Specimen then produced two reorganization primordia and 

 all four pre-existing sets of mouthparts were resorbed as the 



usual doublet was formed {d). 



