304 Action of the Genetic Material 



specific substances produced by the nuclei are enzymatic, permitting 

 proper substrate utilization on (he part of the kinetosomes. Vice 

 versa, the same would be true for the kinetosomally produced sub- 

 stances needed for genie synthesis. Inactivation of the subnuclei would 

 then mean inability to produce characteristic metabolites. 



Let us now compare these facts and interpretations with the 

 genically controlled, consecutive determination in metazoan develop- 

 ment. The most important points for such a comparison are: (1) in 

 the Infusoria, regeneration of exact ectoplasmic morphology with its 

 intricate pattern is equivalent to a restoration of the hierarchy of 

 differential kinetosomes; (2) this is possible only if part of the original 

 hierarchy is left; (3) the necessary specific nuclear substances must be 

 available. An application of these facts to Metazoa must take into 

 consideration the non-cellular nature of the ciliates, as expressed by 

 Lwoff (see I 2 B b aa) in the dictum: "A multicellular organism has 

 differentiated cells, a ciliate has differentiated parts." The comparison 

 correctly assumes that each somatic metazoan cell nucleus corresponds 

 to a subnucleus of a ciliate; and the germ-track nuclei, to the micro- 

 nuclei. Weisz asks now whether it is not possible that the successive 

 segregation of potencies in development might be paralleled by a 

 correlated segregation of nuclear potencies through a mechanism of 

 the type described for ciliates, that is, the interaction of peripheral 

 with nuclear products. It is assumed that in the metazoan cells a 

 similar reduction of genie activities may be followed by reactivation. 

 Finally, also, certain important genes may be completely activated. 



We reported this most interesting work in detail because it seems 

 to be the only experimental attack upon the problem of intranuclear 

 differentiation. We note that the author could not convince himself 

 that in the course of morphogenesis the genome is altered by in- 

 activation of individual "genes." The alteration concerned a com- 

 plicated interrelation between peripheral and nuclear products, the 

 observed changes during "development" being in the nature of quanti- 

 ties in regard to thresholds. Thus we conclude that so far there is no 

 evidence of intranuclear differentiation in development, meaning 

 sorting out and differential activation of genie material. The solution 

 of the problem is clearly one of nucleo-cytoplasmic interaction in- 

 volving quantities, substrates, and thresholds rather than intranuclear 

 changes within the genome. This, of course, does not exclude the 

 complete inactivation of the entire genome as a consequence of 

 endomitotic polyteny, in itself not a cause but a consequence of dif- 



