SEX-RATIO IN DROSOPHILA AMPELOPHILA. 371 



ratios were more frequently in favor of the females and in only 

 one case was there any evidence that a sex-linked lethal mutation 

 had occurred. 



In conclusion, I wish to express my thanks to Professor Fer- 

 nandus Payne for the suggestion of this problem and also for 

 many helpful suggestions and criticism while the work was in 

 ^progress. I am also greatly indebted to my wife, Elmira Shierling 

 Warren, for help, both in the carrying out of the experiment and 

 in the preparation of the manuscript. 



SUMMARY. 



1. The sex-ratio in Drosophila ampelophila is 100 females to 

 95 males. 



2. The age of the parent has no effect upon the sex-ratio of its 

 offspring. 



3. The difference which Moenkhaus found between his two 

 strains, and which he attributed to selection, was probably due 

 to the fact that his male strain was a normal one and his female 

 strain was a lethal bearing one. 



4. The sex-ratio in Drosophila ampelophila is not readily, if at 

 all, modifiable by selection. 



5. There was probably one sex-linked lethal mutation in the 

 writer's selection stocks. 



BIBLIOGRAPHY. 

 Doncaster, L. 



'14 The Determination of Sex, pp. xi + 172. Cambridge University Press, 



Cambridge. G. P. Putnam's Sons, New York. 

 Moenkhaus, W. J. 



'n The Effects of Inbreeding and Selection on Fertility, Vigor and Sex-Ratio in 



Drosophila ampelophila. Jour. Morph., 22: 123. 

 Morgan, T. H. 



'12 The Explanation of a New Sex-ratio on Drosophila. Science, 36: 718. 

 '143 Two Sex-linked Lethal Factors in Drosophila and their Influence on the 



Sex-ratio. Jour. Exp. Zool., 17: Si. 

 'i4b A Third Sex-linked Lethal Factor in Drosophila. Jour. Exp. Zool.,. 



I?: 325- 

 Morgan, Sturtevant, Muller, and Bridges 



'15 The Mechanism of Mendelian Heredity, pp. xiii + 262. New York, 



Henry Holt and Co. 

 Rawles, Elizabeth 



'13 Sex-ratios in Drosophila. BIOL. BULL., 24: 115. 

 Stark, A. H. 



'15 The Occurrence of Lethal Factors in Inbred and Wild Stocks of Drosophila. 

 Jour. Exp. Zool., 19: 531. 



