290 



THE SECOND-CHROMOSOME GROUP 



(2866), and, as expected, gave no lethal result (table 133, not separated 

 for plexus). 



The third culture, 2867, gave 40 black curved and 41 black flies and 

 seemed to be the type to be used. Accordingly several of the black 



curved males, supposed to be of the constitution were out-crossed 



I c 



to TT— females to give the required stable stock. It was well that 



three Fo cultures were raised at the same time, for these test cultures 



Table 133. — Pi, black cf X black purple curved plexus speck 9 ; Fi black 



9 + Fi black &. 



(table 134) proved that the male was not carrying lethal and had in 



6 4- c 

 fact been an F2 double cross-over of the constitution . 



+ + t. 

 After this failure to secure stock from flies of the original F2, the 



attempt was repeated successfully with black flies of the derived 



culture (F2) which had the same constitution as the original F2, but 



in which flies of the succeeding overlapping generations were known not 



Table 134. — Pi, black cf^ X black purple curved plexus speck 9 ; Pi black 



curved 9 -f- Pi black curved cf. 



to be present. Two such black males by tt — females gave as expected 

 black and black curved offspring (3112: 6 = 81,5 c =67; 3197: 5 = 67, 

 5 c = 53). A stock from this source was turned into the stock-room 

 after tests had shown that it was carrying the lethal. The tests (table 

 135) consisted of inbreeding some of the black curved males and females, 



which proved to have the required constitution { ^^ ^"^ ^ 1 . 



\h-\-lnC++/ 



