STERILIZATION OF DROSOPIIILA. 



193 



TABLE II. 



FLIES STERILE AT 32. REMATED AND CONTINUED AT 32. 

 The numbers given refer to individual flies. 



Plough and Strauss, by Strauss (3), and by the unpublished work 

 of Young mentioned above, that stocks show differences in their 

 reactions to high temperature, some being much more tolerant 

 than others. In the most tolerant stocks Porto Rico and 

 Canton there is a clear differential effect such that the males 

 are rendered completely sterile while the females are unaffected. 

 In less tolerant stocks like the Prague and Amherst cultures the 

 females show some effect, though it is not so great as in the case 

 of the males. In mutant stocks like spineless and brown there 

 is much less resistance and both sexes are rendered completely 

 sterile. From these and other data there is evidence that at a 

 temperature somewhat lower than 32 degrees even these stocks 

 show the same differential sterilization of the males without any 

 effect on the females. 



Turning now to experiments designed to test the length of 

 time required for flies sterile at 31 degrees to recover fertility 

 when returned to 24 degrees, we find this selective effect of high 

 temperature on the male flies again clearly demonstrated. This 

 recovery of fertility first noted by Northrop as indicated above 

 was shown by removing cultures from the 31 degree incubator 

 at intervals and placing them in new bottles at 24 degrees. 

 Controls were furnished by cultures of normal flies bred con- 

 tinuously at 24 degrees, and also by females from the sterile 31 

 degree cultures mated to normal males. In all cases the bottles 



