292 Action of the Genetic Material 



typical, such as could also occur in the development of Metazoa, thus 

 making erbunglcicJie Tcilung a phenomenon to reckon with in the 

 study of genetic control of development. Another possibility is that 

 the processes described are specific for Infusoria, owing to the neces- 

 sities of the non-cellular organization of the complicated organism. 

 The erbungleiche division may be analogous here to any process of 

 segregation of differently determined material in metazoan develop- 

 ment. This means that what is accomplished in the metazoan embryo 

 by separating groups of cells differently determined on the basis of 

 cytoplasmic differentiation, is accomplished in the non-cellular organ- 

 ism by intranuclear differentiation, because the lack of cellular sub- 

 division prevents the use of the method chosen in embryonic differ- 

 entiation. I think that this possibility should be realized when it 

 comes to drawing general genetic conclusions from the facts found in 

 Paramecium. 



But it must not be forgotten that Nanney ( 1953Z? ) and Sonnebom 

 (1955) showed that in certain cases the location of the nuclei in 

 definite cytoplasm decides their fate as a micro- or a macronucleus, 

 respectively. Even centrifugation can change this fate, obviously by 

 changing the cytoplasmic surroundings. Thus we cannot speak of 

 differential division but only of division products made different 

 secondarily. This would tend to nullify the foregoing argument. 



We return now to the problem whether progressive differentiation 

 in development under control of the genie material can be the result 

 of changes of this material within the nucleus, accomplished either 

 by erbungleiche Teilung, as discussed, or by some kind of intranuclear 

 differentiation affecting differentially the diverse parts of the genie 

 material, for example, by destroying or inactivating some or by sev- 

 erally augmenting another part, thus narrowing down step by step 

 the possible genie actions. 



There is, in my opinion, a group of facts which may be inter- 

 preted, after a fashion, in this sense, though this has never been tried, 

 if I am not mistaken. These are the facts relating to polyteny and 

 endomitosis. Since Jacob] (1925) discovered and interpreted the 

 presence in tissues of nuclei of sizes varying according to a 2° series, 

 and Geitler (1938) found and explained the process of endomitosis 

 resulting in polytene chromosomes, this phenomenon has attracted 

 much attention. (See Geitler's new monograph, 1954.) Apart from 

 chromatin diminution and other specific features of heterochromatin, 

 discussed above, it is the only type of visible nuclear differentiation in 

 Metazoa connected with processes of differential determination. One 



