76 PHYSIOLOGICAL GENETICS 



these temperature effects. An analysis of these facts was made 

 by trying to fit them to the different formulas for temperature 

 action upon chemical processes. They did not fit either of 

 them, and Driver therefore concludes that the series of Bar 

 genes affect different simultaneous reactions differentially — 

 either retarding the rate of facet formation or changing the limits 

 of the effective periods or both more or less — and that these 

 changes, in addition, do not parallel the simultaneous changes of 

 rates of general developmental processes (differences in tem- 

 perature coefficient). Within the sensitive period, the rate of 

 facet formation seems to progress evenly. Altogether, then, 

 the facts point to an action of the mutant gene upon the rates 

 of closely interwoven but simultaneous reactions, as postulated 

 in Goldschmidt's theory of development. A better knowledge 

 of the development of the Bar eye might help to a better under- 

 standing of the processes involved. Chen's (1929) findings that 

 the very young Anlage of the Bar eye is not smaller than a 

 Wild-type eye points to a process parallel to the one reported 

 for vestigial. We shall meet the same set of facts many times 

 in later chapters, where additional facts will be reported. 



But one more recent investigation is to be mentioned because 

 it will possibly reduce the Bar case to the same type of processes 

 that we described for vestigial. In a paper dealing with the 

 action of the t>o-gene upon the expression of the Bar series, 

 Margolis (1935a) finds evidence that actually the effect of the 

 5-gene may have nothing to do with the process of formation 

 of ommatidia but is concerned rather with the production of 

 something that destroys the material for ommatidia (see also 

 Wolsky, page 32), which would bring the Bar case into line with 

 the vestigial case. He found that the presence of vg, which, 

 as we know, retards development, decreases the number of 

 facets. This would be the case if a facet-destroying action of 

 Bar were prolonged by lengthening the time of its action. All 

 the data presented above would be interpreted in terms of a sys- 

 tem of reactions in time, which Margolis develops tentatively 

 along lines similar to those developed by Goldschmidt in his 

 analytical work. 



In a quite recent paper (Margolis and Robertson, 1937), 

 Margolis modifies his interpretation somewhat. Certain irregu- 

 larities in the behavior of the sensitive period in Wild flies are 



