REGENERATION I07 



the membranellar band suffers ablation, the old mouthparts are 

 resorbed as the new ones take their place. Regeneration has been 

 staged according to visible changes in the primordium (Tartar, 

 1957c) as in Fig. 24. 



Just as regeneration can occur in starving metazoa, so in Stentor 

 the process imposes no nutritive demand. Weisz (1949a) remarked 

 that in regeneration of coeruleus there is an extensive loss of pigment 

 granules which he presumed to be utilized in supporting primor- 

 dium formation, since this occurred in posterior and middle 

 fragments but not in anterior pieces which do not have to produce 

 a new set of feeding organelles. I too have often noticed a fading 

 in the animals, which seems to be correlated in degree with the 

 number of times they undergo primordium formation, though 

 this is not always apparent. Carbohydrate reserve granules may 

 be utilized in regeneration, if this can be dissociated with their 

 employment in mere survival; and Weisz (1948b) claimed that 

 oral regeneration could not occur in the absence of these reserves 

 or their potential equivalent in the form of food vacuoles, but this 

 could not be confirmed (Tartar, 1959a). Regeneration or further 

 development of a regeneration primordium already begun can, 

 however, be greatly delayed by cold (Morgan, 1901a). 



Apart from the necessity for the presence of a segment of the 

 macronucleus, the character of cutting injuries and ablations im- 

 poses few limitations on regeneration potentialities. Central-disc 

 fragments with widely exposed endoplasm folded upon themselves 

 to cover the wound surfaces and neatly regenerated (Fig. 25A). 

 Collapsed stentor "skins" from which almost all the endoplasm 

 has been squeezed out easily regenerated and recovered the 

 normal plump form (b), quite as in similar tests with Condylostoma 

 (Tartar, 1941b). When almost all the ectoplasm was sliced off, the 

 patch remaining greatly stretched to cover the exposed endoplasm 

 and regeneration was consummated (c). But endoplasmic spheres 

 completely bereft of ectoplasm never regenerated, though they 

 remained intact and alive (insofar as they resisted bacterial attack) 

 for two days (Tartar, 1956c). 



These tests effectively dispose of the notion (Prowazek, 1913; 

 Sokoloff, 1924; Weisz, 1948a) that the ratio of ectoplasm to endo- 

 plasm (how measured ?) cannot be altered far from an optimum if 

 regeneration is to be possible, as well as the opinion that wound 



