BEHAVIOR AND FUNCTIONS OF THE NUCLEUS 299 



this assertion later. Both Gruber and Morgan were pointing to the 

 high probabihty that the action of the nucleus is indirect and that 

 what is crucial is not the physical presence of the nucleus but of 

 something it produces. 



Prowazek (1904) made more of a case for regeneration in 

 Stentor without the nucleus, though he too regarded nuclear 

 derivatives as indispensable. That enucleated dividing stentors can 

 complete fission and oral differentiation of the posterior daughters, 

 he also observed. In addition, he reported that elevated tempera- 

 tures in *' warm cultures " could supply the conditions for regenera- 

 tion without the nucleus. Yet he cited only one case and he did 

 not claim that the oral differentiation was complete. Ishikawa 

 (19 1 2) thought he confirmed this result in Stentor " in some cases ". 

 Sokoloff (1924) made similar experiments on Bursar ia truncatella 

 in w^arm culture and reported that eight out of thirty enucleated 

 animals regenerated the feeding organelles and were able to ingest 

 normally; but Schmahl (1926) denied this, though he did not say 

 specifically that he tried high temperatures. Returning to 

 Prowazek's studies, his strongest statement was that if stentors 

 are cut and recut so that they are repeatedly compelled to 

 regenerate, then in a few cases (3) oral regeneration could occur 

 in enucleate pieces, and he did not say that the regeneration was 

 incomplete. Regeneration in the absence of the nucleus, whether 

 in warm cultures or by repeated cutting, he explained as due to 

 the presence of chromidia, substituting for the nucleus. Before w^e 

 smile at this, we should remember that just as the Feulgen staining 

 anticipated the modern DNA doctrine, so the old chromidial 

 hypothesis is a sort of pre-vision of the RNA story which is 

 developing today; and Prowazek's exploratory study may contain 

 the germ of new techniques. 



8. Reconstitution of shape in relation to the nucleus 



Though stentors cannot redifferentiate oral structures without 

 the nucleus or its products, may they not at least recover their 

 normal form after injuries? Cutting operations usually have two 

 effects: the symmetrical, conical shape of a stentor is distorted, 

 and the lateral striping if not the membranellar band is disturbed 

 and misaUgned. Cutting also produces a wound, with exposure of 

 the endoplasm, and we can assert categorically that all investigators 



