is 



PUYSlol.tiCK \L GENETICS 



Leave the lasl Bpecific consideration out of account, it is obvious 

 thai these tacts and their interpretation fall completely in line 



with the result- of the analysis of the phenocopies. 



There is another interpretation of these results by Child (1925) 

 and his student Hinriehs (1925) which seems at first sight to be 

 different. According to Child, pattern is determined by a 

 metabolic gradient which begins with a dominating high level 



Fig. 16. — Semidiagrammatic representation of the main series of grades of 

 otocephaly in the guinea pig. {From Wright, 1934, Genet. 19, Fig. 1.) 



spreading to adjacent regions of a lower level. In general, the 

 anterior end of an embryo is supposed to be the highest level. 

 According to Child, high levels are more susceptible to injuries 

 than lower levels, and therefore the reported experiments are 

 bound to injure mostly the anterior end of the embryo, which is 

 supposed to control the pattern. This interpretation (which, by 

 the way, does not agree with the results of experimentation by 

 the Spemann school) is, however, only a specific way of express- 

 ing in terms of metabolic level the same thing that Stockard 

 expressed in more general terms of inhibition and velocities. 



