302 Action of the Genetic Material 



beads of the macronucleus may be isolated and the cut half animals 

 with these partial nuclei may be tested for regeneration or for remain- 

 ing differentiated. In early stages after fission all macronuclear nodules 

 are found to be equipotent, each being able to sustain morphogenesis 

 (regeneration) and morphostasis (continuation of detailed differen- 

 tiations of the body). As the vegetative cycle progresses, the differ- 

 entiation potential of posterior nodes gradually declines and the more 

 so, the more posterior the location. Midway through the vegetative 

 cycle, the posterior nodules no longer support full regeneration. 

 Toward the end of the vegetative cycle, posterior nodules do not sup- 

 port any regeneration, and intact individuals dedifferentiate the entire 

 oral apparatus. But mid-nodules still support some regeneration, and 

 the anterior nodules never cease to be fully active. During fission the 

 macronucleus is reorganized, and the two fission products are again 

 fully active in their entire length. Relocation experiments (by micro- 

 dissection methods ) show that whatever subnucleus becomes posterior 

 by chance will show the progressive deterioration. Once begun, it 

 cannot be reversed by being put into an anterior position, but it can 

 be reversed by coalescence with normal nodes and re-formation of 

 new ones from the mass. Weisz thinks that it is the cytoplasm with 

 its constant differentiations (the kinetosomes, etc., discussed in I 2 A) 

 which makes the nodes behave as described. (See Sonneborn's work, 

 1955, on the cytoplasmic positional control of the fertilization nucleus, 

 and Nanney's work on the macronuclear differentiation in Tetrahy- 

 mena, 1953a, where anterior or posterior location determines macro- 

 and micronuclear differentiation. Compare Lwoff on similar control of 

 kinetics in our earlier discussions.) 



It is very important that Feulgen reactions show the macro- 

 nucleus to be constant in all stages in regard to DNA. However, with 

 the new measuring methods of Pollister and Leuchtenberger, it was 

 found that variations in DNA exist and that near the time of fission a 

 gradient develops anteroposteriorly. Thus it is assumed that depoly- 

 merization of DNA takes place in this direction, which is reversed 

 when the nodules coalesce during fission. "In substance, therefore, the 

 data imply that in each somatic cycle, initial subnuclear equivalence 

 gradually gives way to patterned genetic divergence." 



Weisz assumes that the autonomous kinetosomes of the adoral 

 zone influence the behavior of the macronucleus. He goes so far as to 

 state that the genie activity of the macronucleus depends upon the 

 function of definite kinetosomes. In the macronuclear gradient just 

 described, the only visible differences of the anterior body part which 



