INFLUENCE OF ENVIRONMENT ON EXPECTED CLASSES. 215 



the following offspring were obtained. The expectation is for 

 equality in all four classes: 



Long 9 ... .52? 



Long cf 489 



Rudimentary 9 . 7 



Rudimentary d 31 31 



There is an enormous deficit in the classes of rudimentary 

 flies. Instead of equality there are only 1/27 as many as ex- 

 pected. 



When on the other hand the FI females were back-crossed in 

 pairs the following totals were obtained : 



Long 9 ... 1.717 



Long cf 1,545 



Rudimentary 9 . . 1,120 



Rudimentary cf ... 1,179 



There is an approach to equality in the last case (i : .7), and, 

 in consequence, the contrast with the preceding data is striking. 

 For purposes of more detailed comparison the data for the two 

 mass cultures and for the 20 pairs is given: 



TABLE I. 



BACK-CROSS PAIRS. 



