REGENERATION II9 



primordium formation was exceedingly variable, ranging from 

 5 to 12 hours (Tartar, 1956a). 



It is relevant here that in doublet stentors, with only one set of 

 feeding organelles removed, regeneration is usually prompt 

 (Tartar, 1958b), again indicating that the remaining set of intact 

 organelles offer no inhibition to a primordium site which is not 

 subtended by one of its own. In single animals, however, the time 

 for beginning anlage formation does vary inversely with the extent 

 of oral ablations, recalling a similar rule by Zeleny (1905) for 

 metazoa. Thus Morgan found that the more of the membranellar 

 band removed the sooner regeneration followed, and Weisz (1948a) 

 confirmed this. A similar relationship was demonstrated in the 

 hypotrichous Ur onychia by Taylor (1928). Even w^hen there are 

 no ablations, re-regeneration occurs if for any reason the differen- 

 tiation of the oral primordium is incomplete, and the more 

 incomplete the sooner (Tartar, 1957c). I also noted the time 

 relation in regard to the length of membranellar band removed 

 and found in addition (Tartar, i959d) that if the gullet, buccal and 

 oral cavity are neatly removed so as to leave almost the entire length 

 of membranelles intact regeneration is still retarded. These experi- 

 ments indicate that any portion of the feeding organelles is partially 

 inhibitory of primordium formation, but all are required to prevent 

 this formation entirely. 



Sokoloff and others believed that the ratio between volume of 

 nucleus and volume of cytoplasm cannot vary too greatly if re- 

 generation is to be possible, but Weisz (1948a) found that re- 

 generation times are the same in comparable fragments regardless 

 of the number of nuclear nodes included, provided of course that 

 at least one was present. He therefore discounted the idea of 

 necessary nucleo-cytoplasmic ratios. With this I can agree in 

 regard to the range of differences in the ratio which one finds in 

 fragments from a single animal, yet it will be shown later (p. 306) 

 that the extreme decrease in the ratio of nucleus to cytoplasm 

 which is made possible by grafting exp^eriments does indeed result 

 in very tardy regeneration.* 



*Uhlig (i960) emphasized the correlation between " age " and regenera- 

 tion time : this period was shortest in young, post-fissional animals which 

 were also more reactive in producing primordium formations at multiple 

 primordium sites from disturbances of cell patterns. 



I 



