Genie Control of Development 419 



a colloidal phenomenon. ) The next link in the chain is the use of the 

 differentiated areas as centers for further substratiflcation. Diffusible 

 determining stuffs are more or less involved with all-or-none effects 

 upon cells. (This is what I called the determination stream leading 

 to final determination directly or by way of a labile period.) There 

 might be a third link, when the subterritories of the second link work 

 once more as a center ( I called it points of outlet ) for still another set 

 of determinations. To this system may be added growth processes of 

 a different kind. (For a detailed analysis see Goldschmidt, 1938a; 

 and Henke, 1935.) 



This model certainly contains some of, the main elements of any 

 genie action in control of pattern, and it leaves room for all the 

 individual types of collaborating processes studied before. If we try to 

 form a picture of the entire process, we should first emphasize one 

 important point. The genie control of patterning must not mean that 

 there is genie interference with every single observable process of 

 diversification, as is postulated in some of the more naive ideas of 

 statistically minded geneticists, who introduce particular genes plus a 

 modifier system for the control of any differentiating action. Actually, 

 in the process of patterning, a great role is played by what we called 

 short cuts, meaning over-all consequences of a single genically con- 

 trolled process, working like an avalanche when started. These short 

 cuts are found at different levels of development. In most eggs a 

 stratification of cytoplasmic materials of different prospective potency 

 occurs even before fertilization under genetic control (see II 2 A). 

 This predetermination is clearly a self-perpetuating process which 

 lasts for some time in development without further genie interference, 

 as experimental embryology, especially of echinoderms, has shown 

 (e.g., Boveri, Runnstrom, Hoerstadius, von Ubisch, Baltzer). Wad- 

 dington has called this the epigenetic momentum. It is this type of fact 

 which led to attributing predetermination to the action of cytoplasmic 

 genes, a concept which was criticized previously, and which is indeed 

 not more than a circumscription of our ignorance. There is no doubt 

 that in later development such self-propelling processes, initiated only 

 by genie action, take place, thus, I might say, alleviating the burden 

 of the genie material in controlling developmental processes. Forma- 

 tion of areas of diversification in the process of organ formation might 

 repeat such processes of epigenetic momentum. The same role of 

 short cut is played by inductors ( evocators ) and embryonic hormones, 

 as we have seen. 



Regulation is another short-cut action the role of which in normal 



