NEW DATA. 



69 



CLUB. 



In May 191 3 there were observed in a certain stock some flies which, 

 although mature, did not unfold their wings (text-fig. Ha). This con- 

 dition was at first found only in males and suspicion was aroused that 

 the character might be sex-linked. When these males were bred to 

 wild females the club-shaped wings reappeared only in the F2 males, but 

 in smaller number than expected for a recessive sex-linked character. 

 The result led to the further suspicion that not all those individuals that 

 are genetically club show club somatically. These points are best illus- 

 trated and proven by the following history of the stock: 



Club females were obtained by breeding F2 club males to their F2 

 long-winged sisters, half of which should be heterozygous for club. 



Fig. H. — Club wing, a shows the unexpanded wings of club flies; c shows the absence of the two 

 large bristles from the side of the thorax present in the normal condition of the wild, b. 



When the F2 club females and club males were bred together, instead of 

 only clubs being produced, long-winged flies also appeared. In fact, 

 only about a third of the oflFspring showed the club character. 



Club females bred to wild males gave some club males in Fi (although 

 most of the males had long wings), and in F2 some of the females and 

 some of the males were club. In all essential points club shows the 

 characteristic features of a sex-linked recessive, except that it is realized 

 in only a small proportion of the individuals that are genetically club. 



These general statements are substantiated by the following data: 

 Club male by wild female gave in 20 F2 mass cultures, wild-type 9 , 



