Genie Control of Development 311 



interesting work we are, as geneticists, still where we were before: 

 the cytoplasm must become differentiated into regions which in some 

 way are competent for specific genie actions, based upon primary or 

 secondary genie products removed from the nuclei. This is, I reaHze, 

 an unpopular conclusion, since we all long for biochemical solutions 

 of our problems. But when we have hardly learned how to walk, we 

 are simply not yet ready for flying. 



B. THE CYTOPLASMIC SUBSTRATE OF GENIC ACTION 



We discussed the possibility that genie action in development 

 could acquire its specificity and order in time and space by intra- 

 nuclear changes which may be described as successive inactivation of 

 no longer needed genie substances, possibly by an inherent cycle of 

 stability and instability, or by the entrance of deactivating products of 

 former genie activity into the nucleus from the cytoplasm. We saw 

 that there is nothing known to support such assumptions and much to 

 discredit them. All facts of regeneration and restitution are opposed 

 to them. The fact that individual cells at the end of development still 

 react typically to new genetic changes like introduction of lethals or 

 mutant loci through somatic crossing over (Stern, 1936; Demerec, 

 1943 ) shows the continued activity of at least those genie loci studied. 

 Thus it seems that all the genetic material is present in all differenti- 

 ating cells, with probably only one exception, namely, the stoppage of 

 all genie activity and potential activity in cells which change to a 

 unique function of mass synthesis through one of the endomitotic 

 processes. Thus we must conclude, with the majority of students of 

 this field, that it is the interaction of the genie material with the 

 cytoplasm which results in orderly, genetically controlled develop- 

 ment. 



We know from our earlier discussion that genie control of 

 developmental processes has been established (by the finding of 

 mutants) for every step of development from characters of the egg 

 to the very last processes of differentiation. It is true (see the former 

 discussion, II 2 C c) that the first stages of development are little 

 influenced by the nucleus, which seems to show no discernible influ- 

 ence in the diverse experiments on merogony and development of 

 hybrids up to the time of gastrulation. However, it is also known that 

 the nucleus controls even prefertilization differences in the egg, and 

 therefore the lag until gastrulation does not mean more than pre- 

 servicing of this period of quick cell division, in respect to the deter- 

 mining actions of the genie material, which, by the way, is another 



