No. 576] 



MUTATIONS IN DROSOPHILA 



700 



causal connection. 1 Nevertheless, I have been quoted as 

 having produced the first mutants by the use of radium. 

 I may add that repetition of the experiment on a large 

 scale both with the emanations of an X-ray machine and 

 from radium salts has failed to produce any mutations, 

 although the flies were made sterile for a time. Loeb and 

 Bancroft also tried the effect of radium. 2 They found a 

 black mutant type after treatment with radium but since 

 the same type appeared in the control they do not believe 

 that its appearance had any connection with the radium. 

 They also state that after treatment a white-eyed female 

 appeared in the first generation, and suggest that a white 

 eyed male may have existed in a previous generation that 

 escaped notice, but if it had been found in a previous gen- 

 eration, the mutation or the contamination must have 

 been earlier than the one that produced the white-eyed 

 female ; for, a white-eyed male takes two generations to 

 reappear again. Pink-eyed flies were also found both in 

 the control and in the treated flies. In regard to another 

 mutant tvpo. thev state: 



But although "two hundred different cultures" were 

 subsequently treated with radium and no short-winged 

 (miniature) flies appeared, I get the impression that 

 Bancroft and Loeb must have had stock that was already 

 contaminated bv some recessive mutant factors. All of 

 these mutants had been obtained and described by us, and 

 the stock used bv Bancroft and Loeb was obtained m part 

 at least from my friend Dr. Frank E. Lutz, who had at 

 that time in his possession, as a letter I have from him 

 states, certainly two of these mutants, black and imma- 

 ture, that he had received from me. It seems to me not 

 improbable that the collector, who got the stock from Dr. 



