Il6 THE BIOLOGY OF STENTOR 



regeneration will then ensue (Tartar, 1957c). Causin (1931) found 

 neither primordium formation nor nuclear changes in coeruleus 

 which were cut into repeatedly. Yet (if a repetition be allowed for 

 completeness of this account) he remarked, without giving further 

 details, that when so cut the '' sectioned myofibrils degenerate and 

 new ones appear in the pigment bands to replace them." Weisz 

 (1949a) also spoke of an extensive reorganization of "contractile 

 equipment " during regeneration and these hints deserve pursuing. 

 Causin likewise considered that alteration of the nucleo-plasmic 

 ratio would be a sufficient stimulus to regeneration, but whatever 

 anticipations he may have had in this direction are probably 

 covered by Schwartz's demonstration that reorganization follows 

 excision of major parts of the macronucleus. 



Even substantial portions of the lateral body wall and endoplasm 

 can be removed without inciting regeneration, but removal of any 

 portion of the feeding organelles is a sufficient stimulus to re- 

 generation. Excision of all mouthparts of course produces prompt 

 primordium formation. If the gullet or the oral pouch only is 

 removed regeneration also occurs, or if in morphogenesis mouth- 

 parts are produced which lack either of these organelles, or are in 

 any other way incomplete, they will be replaced by a new set 

 through regeneration (Tartar, 1957c). The mere act of primordium 

 formation therefore does not satisfy the requirements of re- 

 generation, for there seems to be a feedback mechanism which 

 informs the cell whether the resulting differentiation has been 

 complete. 



When only the aboral half of the membranellar band is removed 

 regeneration is much delayed as a rule but does occur eventually. 

 The only exception is that, if division intervenes, the abbreviated 

 feeding organelles, now on the proter, may be approximately of 

 right proportions for this smaller cell and then regeneration does 

 not always occur. These results are reminiscent of Taylor's (1928) 

 studies on Uronychia, in which he found that the removal of one 

 cirrus, or the sectioning of critical neuromotor fibrils which could 

 then not rejoin, constituted sufficient stimulus for regeneration. 



Long ago Johnson observed that a double monster stentor 

 regenerated doubly, on both sides, though it needed to renew only 

 one of the mouths. Such observations were greatly extended with 

 the technique of grafting two stentors together. In doublet animals 



