120 T. H. MORGAN 



In No. 39 (ratio of 115:33), seven out of fourteen females mated 

 gave no offspring. One lot in table 1 shows a ratio of 116 9 9 to 

 46crd'. Out of 319 9 tested, four produced nothing. Out 

 of 14cfcf, seven were sterile. 



One lot (xvii) of table 1 had a sex-ratio of 969 9 to SOd'd'. 

 Out of thirty-nine females mated, only one gave no offspring. 

 Six males tested were sterile. 



No. 12 of table 1 had a sex-ratio of 122 9 9 to 32d^cf'. Out 

 of forty-three females mated, twelve produced nothing. Out 

 of five males tested two produced nothing. 



Summing up the results for the males, we get: 



males males 



sex ratio tested sterile 



78:16 16 16 



116:46 14 7 



96:30 6 6 



122:30 5 2 



Total 41 31 



AN HYPOTHESIS TO ACCOUNT FOR THE EXCEPTIONALLY HIGH 



RATIOS 



The following very high sex-ratios have been recorded for 

 Drosophila : 



Quackenbush' 



' Quackenbush, L. S. Unusual broods of Drosophila. Science, N.S., vol. 32, 

 p. 183, August 5, 1910. 



