346 Action of the Genetic Moterial 



TABLE 3 



Before discussing this result for genie action as revealed in dosage 

 experiments, I must report that DeMarinis and Hersh (1943) have 

 arrived at the same conclusions by the ingenious method of measuring 

 eye mosaics produced by somatic crossing over. They found that the 

 ratio of the white facets to the total number conforaied to the relative 

 growth function. The analysis of the data led to the conclusion that 

 the Bar factors control an activator of cell division in the optic disc; 

 the number of facets is the resultant of these divisions. They consider 

 that the additive inhibiting effect may be produced in three ways: 

 secondary destruction of an anlage, which is excluded by Steinberg's 

 (1941) embryological work; or by a failure of size increase in the 

 individual facets, which disagrees with the observed facts; or by lack 

 of formation of facets. From the behavior of the mosaics, in which 

 the time of change by crossing over can be ascertained, this last 

 possibility is explained as a postponement of the time of onset of 

 divisions under the influence of Bar action. Recently DeMarinis ( 1952) 

 has extended these conclusions by the further use of the mosaic 

 technique. He finds that the anterior portion of the eye anlage con- 

 tributes a proportionally larger number of cells to the final size of the 

 eye. This happens either by increased rate of cell division or by the 

 prolongation of the period of cell division, which is under control of 

 the Bar series, acting according to dosage. However, the influence of 

 Bar does not reduce the eye anlage as a whole, but affects, quanti- 

 tatively, a definite number of embryonic cells in the anterior portion 

 of the anlage. The increasing dosages thus reduce the eye from anterior 

 to posterior, and the effect is proportionally greater on the anterior 

 dorsal lobe. 



Leaving aside these details, we have Hersh's idea of a different 



