24 1 



THE AMERICAN NATURALIST [Vol. XLIX 



in regard to the character of these females. Three pairs 

 of factors are involved which should give the following 

 classes of males: 



Non-cross-overs Single Cross-overs Double Cross-overs 



Red, rud., round. Red, long, bar. Red, long, round. 



White, long, bar. White, rud.., round. White, rud., bar. 



Red, rud., bar. 



White, long, round. 



It will be observed that the rudimentary males run far 

 behind their schedules, due beyond doubt to their poor 

 viability. 



Double crossing-over took place four times in the ex- 

 periment. If the two X chromosomes that carry respec- 

 tively the factors for red rudimentary round and white 

 long bar are represented as twisted once around each 

 other, as in text-fig. 1, a, the result of fusion and recom- 

 bination at the crossing points would give the two chromo- 

 somes shown in 1, b. One chromosome now carries the 

 factors for red, long, round, and the other the factors for 

 white, rudimentary, bar. As the tables show there are 



