Vol. XXXIII. December, 1917. No. 6. 



BIOLOGICAL BULLETIN 



SELECTION FOR HIGHER AND LOWER FACET 



NUMBERS IN THE BAR-EYED RACE OF 



DROSOPHILA AND THE APPEARANCE 



OF REVERSE MUTATIONS. 1 



H. G. MAY. 



CONTENTS. 



The Experiments of Zeleny and Mattoon. . . . . 361 



The Experiments of MacDowell . . 362 



The Present Experiments ... 363 



Material and Methods 363 



Selections in the Vestigial-winged Stock 368 



Selections in the Long-winged Stock 373 



The Appearance of Full-eyed Males and Heterozygous Females 385 



Discussion and Conclusions 387 



Summary 393 



Literature . 395 



THE EXPERIMENTS OF ZELENY AND MATTOON. 



In 1915 Charles Zeleny and E. W. Mattoon published their 

 results obtained by selecting for higher and lower facet numbers 

 in the bar-eyed race of Drosophila. Three lines were selected 

 for higher numbers and three lines for lower numbers. Indi- 

 vidual pairs were mated and the selection w r as carried on for 

 three generations in each direction. 



They counted the facets in 250 flies at the beginning of the 

 experiment and found the average number to be 98.04 for males 

 and 65.06 for females. Counts made on 250 more flies from the 

 stock at the end of the experiment gave the same results. From 

 the ratio between numbers from males and females they com- 

 puted a factor for converting the female number to the male 

 number and published all numbers on the male standard. With- 

 out exception each generation produced successively higher 



1 Contribution from the Zoological Laboratory of the University of Illinois, 

 No. 97. 



361 



