SEX-RATIO IN DROSOPHILA AMPELOPHILA. 



353 



experiment was made somewhat difficult. This might have 

 been overcome by isolating some males and females from each 

 mating and then, after the counts for that generation were com- 

 pleted, mating the offspring of the pair giving the most extreme 

 ratio. This would have prolonged the experiment, so to avoid 

 delay, at about the eighth or ninth day after the young had 

 begun to emerge, fifteen pairs were mated from among the off- 

 spring of each mating which was being examined. In this way, 

 by the time one generation was finished, the next was almost 

 ready to begin to emerge. Since ten matings in each strain were 

 examined, this necessitated the mating of about3OO pairs of flies 

 in each generation. A control was also carried in each experi- 

 ment in which a few hundred flies were examined each generation. 



PRELIMINARY EXPERIMENT. 



This experiment was to test whether the age of the parents 

 would in any way influence the relative number of males and 

 females produced. Several matings were made and the adults 



TABLE I. 



Showing Results of Experiment to Test the Effect of Age of Parent Upon the Sex-Ratio. 



were transferred to new bottles every eight days as long as they 

 both lived. The age of the parents does not influence the sex- 

 ratio as is shown by the results given in Table I. 



