312 Action of the Genetic Material 



fact in favor of the idea that genie action occurs during the resting 

 stage of the nucleus. Assuming the general facts of experimental 

 embryology as known, we may formulate the questions posed by that 

 basic situation thus: 



1. Is the series of determining processes which take place in 

 development, from the first establishment of polarity to the last bit of 

 histological differentiation, under genie control? Or does the genie 

 control initiate cytoplasmic diflFerentiation which afterward continues 

 under its own steam? 



2. What does genie control mean? 



3. Why does the proper genie material act only at its proper time 

 and place and others do not act at all, though all of them are always 

 present simultaneously? 



a. Basic deliberations 



The answer to the last question contains much of the answers to 

 the others. The question has been called the problem of the "activation 

 of the genes," the idea being that all the genes are present all the time 

 without acting, but that at the proper moment, say when some 

 epidermis cells of a Drosophila embryo are being determined to form 

 a wing bud, the "wing genes" alone begin to become active in the 

 respective cells and only in these. In the discussions of this major 

 problem there was never a doubt that during development the cyto- 

 plasm in some way underwent a differentiation of a chemical type, 

 chemodifferentiation, which made it specifically different in cells or 

 cell groups located in the individual parts of the embryo. It does not 

 make any difference whether this distribution of specificity is a 

 primary one, as in the mosaic type of development, or a secondary 

 one, by means of evocators and inductors in the inductive type of 

 development ( with all transitions between the two known ) . However, 

 this distribution of specificity of the cytoplasm is itself under genie 

 control, as proved by the transplantation experiments with inductors 

 between different genera and families of Amphibia (Schotte, Holt- 

 freter). Adapting an old expression of Boveri, I called the result of 

 such a chemodifferentiation of embryonic regions a "stratification" in 

 order to emphasize both the chemical diversification and the tri- 

 dimensional arrangement of the different layers. The so-called acti- 

 vation of the genes, then, meant ( Goldschmidt, 1927, 1938) that the 

 genie material (as I prefer to say, for reasons discussed before), 

 which is always present and functioning, produces its primary 

 products (and probably releases them into the cytoplasm) all the 



