No. 576] MUTATIONS IN DROSOPHILA 



707 



the chromosomal material are the basis for mutation it 

 would seem perhaps a priori unlikely that the same 

 changes should occur at the same time in both members of 

 a pair, and if not the effect would not appear in the next 

 generation, and not until two flies of the later progeny 

 each carrying one mutant factor met. Whatever weight 

 may be attached to this argument— we know really nothing 

 as to the origin of mutations— it seemed necessary to 

 carry some stocks to another generation; and this was 

 done. 



The following are the totals of offspring produced by 

 flies from larvae that had been etherized twice daily from 

 the time of hatching to the winged state : 



In the next case fewer drops of ether were used— four 

 or five throughout larval and pupal life. The parent flies 

 were changed to new bottles quite often to prevent crowd- 

 ing and abundant food was supplied: 



The following data are from the offs] 

 that had 8 and 10 drops of ether twice ( 



The next data are the records of the offspring of 



