No. 576] 



TMUATIOX IX DROSOPIIILA 



725 



tests made of F 1 flies whether of matings to "Wild stock 

 or of matings to other mutants such as Black, Pink, Arc, 

 Ebony, etc. Table XXVI shows these two types as they 

 appeared in back crosses to normal Pink males of normal 

 and Beaded females of the cross Pink Beaded by Wild. 

 Here it was found that more of the normal than of the 

 Beaded F 1 flies were of Type X, and conversely that more 

 of the Beaded than of the normals were of Type Y. 



It has not been possible to distinguish with certainty 

 between these two types even by their offspring because 

 of the large amount of fluctuation that occurs in the per- 

 centages of Beaded offspring. For example it would be 

 difficult to say whether a fly giving five per cent, of its 

 offspring Beaded would belong to Type X or Type Y. 



It would be expected that Type Y would be given by 

 those flies that carried both factors for Beaded, and 

 Type X by those that lack the lethal factor, and it will 

 be seen later that on the whole the evidence supports 

 this view. 



B. Crosses between Beaded Flies and Other Mutants 

 1. The F, Generation 

 If we examine the F, generation when Beaded flies are 

 crossed to other mutants, i. e., to flies of a stock that is 



which is unlike tlio normal Wild flies in some other wing 

 character, or in eye color or body color, etc., we find an 

 even greater amount of variability in the percentage of 

 Beaded-winged offspring than in the F, generation of 

 Beaded by Wild. (See Tables I and IX; also Charts 



The details may be gathered from Table IX, where it 

 can be seen that there is a certain specificity in the per- 

 centage of Bonded offspring that appear in any specific 



For instance, it appears that more of the offspring 

 have Beaded wings if a cross is made with Vermilion- 

 eyed flies than when Beadeds are mated to Pink-eyed 



