418 Action of the Genetic Material 



E. SYNOPSIS 



In view of the mass of details reported and analyzed, and the 

 variety of genically controlled processes involved, a synopsis of the 

 whole may be attempted. Many of the authors mentioned with their 

 specific work have tried to develop a generalized picture of genie 

 control of development — usually with emphasis on the special group 

 of facts and ideas with which the author is preoccupied. Many of 

 these discussions have already been mentioned, like my own pioneer- 

 ing books of 1920a and 1927, and the numerous general papers of 

 Sewall Wright. Many embryologists have taken part in such dis- 

 cussions: Brachet (1950a), De Beer (1951), von Ubisch (1952, 1953), 

 Dalq (1941), Weiss (1950), Baltzer (1952), F. E. Lehmann (1945), 

 Holtfreter (1951), and physiological geneticists like Waddington 

 (1950), Stern (1939, 1954), Hadorn (1948), Serra (1949). In all these 

 attempts at synopsis, the individual facts and points of view con- 

 tained in the foregoing chapters are marshaled with preference given 

 to one or the other aspect. We shall try to apportion the roles of the 

 different views to whatever proved or imagined genie actions may 

 enter the total picture. 



The general problem is one of pattern formation, a tridimensional 

 pattern resulting from four-dimensional processes, and this problem is 

 the same for genetics and experimental embryology. I have tried re- 

 peatedly to use a simpler, two-dimensional model for the general 

 processes involved (e.g., the pattern on the insect wing; Goldschmidt, 

 1920a, 1927, 1938a). The genically controlled actions involved were 

 order, timing and threshold conditions of the decisive processes, 

 centers of diffusion (outlets) of determining stuffs, their path (the 

 determination stream), and relation with growth processes. Many 

 detailed facts have since been added (especially by Henke and his 

 students; see 1935, 1948Z7, 1953), but the general picture, that is, the 

 processes which can be used as a general model for genie interaction, 

 has not changed much. Henke, who has contributed so much to the 

 descriptive, experimental, and genetical analysis of the subject, has 

 drawn the following picture (discussion by Henke in Waddington's 

 1950 paper ) . Comparative morphology has led to the conclusion that 

 chains of consecutive processes of diversification occur comparable to 

 the chains of induction in organ development. The first link, the 

 primary patterning in an otherwise undifferentiated blastema, requires 

 definite ideas involving colloid chemistry. ( This is what I called strati- 

 fication and compared to the production of Liesegang rings, which is 



