STERILIZATION OF DROSOPHILA. 



EXPERIMENTS. 



The Drosophila stocks used for the tests were for the most 

 part taken from a wild stock culture collected at Canton, Ohio, in 

 September 1924, but for certain of the experiments other stocks 

 were used as indicated. They showed a varying degree of 

 toleration of high temperature as recorded by Plough and Strauss, 

 but even though the critical temperature was different for 

 different stocks each could be rendered sterile at some particular 

 temperature. Even when a culture showed sterility it was 

 observed that copulation between. the flies takes place, and that 

 eggs were laid in numbers roughly equal to those from similar 

 flies at normal temperature. Since these eggs appear to be nor- 

 mal and since virgin females are known to lay eggs under normal 

 temperature conditions, the conclusion is again suggested that 

 the sterility at high temperature is caused by some failure to 

 function on the part of the males. 



Further data similar to those of Plough and Strauss were 

 first collected. A series of lines of Canton stock were being run 

 at 31 degrees. Since this temperature is close to the limit at 

 which this stock can be bred, it was found that several strains 

 usually showed sterility in each generation. There was a high 

 degree of constancy in the reaction to temperature of these 

 strains, some failing regularly after one generation, others running 

 along for several generations normally. Matings were made at 

 31 degrees between both males and females from a number of 

 these lines and flies of the opposite sex from the same strain 

 carried continuously at 24 degrees. Normal flies of this stock 

 are always fertile for at least one generation at 31 degrees. If a 

 culture of the 31 degree stock showed sterility, then it might be 

 supposed that the mating of sibs of this strain to the 24 degree 

 stocks would indicate whether one sex rather than the other was 

 responsible for the failure. The cultures in all cases contained 

 five pairs of flies each, and a summary of the tests is given in 



Table I. 



A comparison of the totals in this table emphasizes the sug- 

 gestion of the summaries of the similar tests of Plough and 

 Strauss, namely that most of the males from a culture at 31 

 degrees are sterile, while most of the females are fertile. This 



