CHARLES ZELENY 71 



SO close to bar as to act as a unit with it for all demonstrable cases. 

 The present case is then an instance of a second mutation in the same 

 germinal material and in the same direction as a previous mutation. 

 The ultra-bar mutant adds to the series of germinal changes 

 which have been made out in the case of eye-facet number. As 

 previously reported germinal changes have been obtained which in- 

 volve accessory factors in other than the sex chromosome, some of 

 these producing an effect of large degree and others of small degree. 

 Reverse mutations of the bar stock to full have also been observed. 

 The case described in the present paper is a further step in the same 

 direction as bar. In addition to the further decrease in facet number 

 ultra-bar has a much greater degree of dominance than bar. Fur- 

 thermore it occurred in the direction of selection, appearing in the 

 low and not in the high selection line. 



