No. 576] VARIATION IN DROSOPHILA 739 



generations of selection, and now gives approximately 100 

 per cent. Beaded offspring, though no selection has been 

 practised for nearly a year. This stock has been used in 

 one series of crosses to supplement another series in 

 which Pink and Beaded enter the cross from opposite 

 parents. The results in each case are essentially similar, 

 and show that when Beadedness enters with Eed it comes 



TABLE XXV 

 E 2 Eesults of the Cross Pink Beaded' X Wild 



17 1 1 2 13 366 964 12 1 41 7 



out more with Bed than with Pink. They show that in 

 the Fj female crossing over occurs almost independently 

 of Pink, so that almost the same percentage of Beaded- 

 winged individuals appears in each class, though usually 

 the class that is similar to the Beaded parent is consider- 

 ably the "largest. In Table XXVII, however, a record 

 is given in which a very considerable " repulsion" oc- 

 curred, and the high Beaded class is not Pink Beaded, 

 as is there expected, but Red Beaded. The results from 

 back-crosses of the brothers of these females to Pink 

 normal stock show that no mistake was made in record- 

 ing the cross, which therefore, though somewhat surpris- 

 ing, must stand. 



TABLE XXVI 



The tables show also that in the males, crossing over is 

 of very rare occurrence, if, indeed, it occurs at all. The 

 records show that out of 566 Beaded flies (Tables XXVII 

 and XXIX) which occurred as the offspring of an Fj male 



