THE MUTATED GENE 193 



nucleated ones of the other in both directions. In this case, the 

 nucleated part controlled the differentiation: a mediterranea 

 stem upon a nucleated Wettsteinii rhizoid forms a typical 

 Wettsteinii umbrella. This shows that actually the genes 

 within the nucleus control the production of a specific formative 

 stuff (not unspecific, as in the hormonic type) which diffuses 

 through the cytoplasm to the place of its form-controlling 

 action. 



It might be added finally that Gregory and his collaborators 

 (1933-1936) have tried to trace the actual product of genie action 

 responsible for hereditary size. As reported before (see page 

 54), hereditary size differences in mammals and birds (Castle 

 and Gregory; Gregory et at.) as well as in insects (Goldschmidt) 

 are based upon a different rate of cell division from the very 

 start of development. According to a number of physiological 

 investigations (Hammett, 1931), the concentration of gluthatione 

 in the body is somehow correlated with cell proliferation. Greg- 

 ory therefore tested the gluthatione content of embryos of large 

 and small breeds of rabbits and of fowl and found them propor- 

 tional to the adult size of the race. As it is believed that a high 

 concentration of disulfides favors protein synthesis, the size genes 

 might act via such intermediate steps. 



4. The Determination Stream. — There is one series of facts 

 that allows the forging of another interesting link between genetics 

 and experimental embryology. When Goldschmidt (19206) first 

 developed his theory of gene action, he considered certain cases 

 of pigment patterns in Lepidoptera with which he was familiar. 

 There were especially cases of melanism which he had analyzed 

 genetically, and which showed that the amount of pigment 

 production, and also the arrangement of this pigment, was 

 dependent upon a number of Mendelian genes. In some cases, 

 it seemed that pigmentation started from one point (the wing 

 base) and spread from there in different genie combinations 

 across the wing in a definite path. In others, there seemed to be 

 a number of predetermined centers at definite points from which 

 this flow took place. Therefore the terms outlet of pigment and 

 -pigment stream, were used, a movement not of pigment, but of 

 pigment-determining substance being meant. 



Later, another remarkable case was studied which led to a 

 more definite statement (Goldschmidt, 19236). Intersexual 



