SEX RATIOS IN DROSOPHILA AMPELOPHILA. 



ELIZABETH RAWLS, 

 COLUMBIA UNIVERSITY. 



As a rule there is an excess of females amongst the fruit flies 

 that first hatch. It seemed that this must be due to the more 

 rapid development of the females since the total output gives 

 approximately an equal number of males and females. It was 

 possible, although improbable, that more females are actually 

 produced at first and more males later. In order to test this 

 possibility five pairs of wild flies from stock that had been 

 a year in confinement were placed in bottles and after two 

 days removed to new bottles. Then after two days each pair 

 was removed to a third bottle, etc., as long as the pair lived. 

 Counts were made of all the flies produced in each bottle. The 

 results showed that on an average about equal numbers of males 

 and females came from each batch. This result occurred in the 

 case of three of the five pairs of flies studied, as the following 

 figures will show: 



TABLE I. 



The fourth pair began very early to show a somewhat different 

 sex ratio. Each day twice as many females as males hatched out, 

 so that of the 340 individuals obtained from this pair, 222 were 

 females and 118 were males, making a sex ratio of 2 : i. 



The fifth pair proved to be even more unusual than the fourth 

 in its excess of females for each day two, three and even four 

 times as many females as males would hatch out. The total 



