REGENERATION 131 



generate and that these then became able to regenerate without 

 the nucleus. This surprising result was explained in terms of the 

 then-popular chromidial hypothesis, whereby a nucleus can be 

 stimulated to extrude chromidia, which can then substitute for it 

 (see p. 299). 



Hartmann (1922) posed the question of whether division could 

 be indefinitely postponed by repeated cutting ablations on a 

 feeding cell. That this is the case, he demonstrated for Amoeba 

 and the fresh water worm Stenostomum, as well as for Stentor 

 coeruleus. Stentors were fed on Colpidium and allowed to grow but 

 were cut before they attained division size. Hartmann noted that 

 a cut could produce either oral or headless remainders and, 

 although his account is not clear in this regard, I assume from his 

 statement that regeneration occurred and that this was oral 

 regeneration and not merely holdfast renewal or recovery of normal 

 shape. In one tabulated case a stentor regenerated 25 successive 

 times during 52 days, without fission, while the controls divided 

 35 times. These results indicated, that if there is an accumulation 

 of some factor disposing the cell to fission, this factor is reduced by 

 excisions ; as well as that indefinitely repeated regeneration seems 

 to be possible within one individual if fed, and that frequent fission 

 is not essential to survival. 



9. Blockage of regeneration 



Although stentors regenerate with the greatest regularity and 

 can even re-regenerate repeatedly or exhibit a succession of re- 

 organizations in starved fusion complexes, I have encountered a 

 half-dozen cases among thousands in which, for some un- 

 accountable reason, otherwise healthy appearing coeruleus failed 

 to regenerate the feeding organelles though surviving for many 

 days. A similar number of instances were found among starving 

 animals, which is enough to give the impression that stentors 

 cannot form regeneration primordia without carbohydrate reserves 

 as Weisz (1948b) asserted. Yet a direct pursuit of this question 

 showed that even the most pellucid animals without food vacuoles 

 or demonstrable glycogenoid granules were still quite able to 

 regenerate (Tartar, 1959a). On the other hand, it is common 

 enough to find that necrotic stentors or animals which have an 

 apparently decreased vitality from being long isolated on slides 



