GENE MUTATIONS 



tic of stumpy is the extreme reduction of tar- 

 sal segments (Fig. 9). The appendages appear 

 otherwise normal. Stumpy may be called a re- 

 cessive, but a large proportion of heterozygous 

 females bear a spur at the tip of their protho- 

 racic metatarsi. More or less irregularity oc- 

 curs in tarsal segments of all legs so that 

 heterozygotes are not as sure footed as pure 

 wild-type. No metatarsal spur has ever been 

 found on middle or hind legs of heterozygoteS' 

 nor has a prothoracic metatarsal spur ever been 

 found in wild-type females. This spur closely 

 resembles the spur normally occurring at the 

 end of the prothoracic tibia. It may be pres- 

 ent on either or both front legs, but many het- 

 erozygotes fail to show it. Even in its ab- 

 sence it is usually possible to identify het- 

 erozveotes by tarsal irregularity. Stumpy is) 

 of normal viability and fertility except that 

 females have difficulty in feeding from cater- 

 pillars and consequently may die without pro- 

 ducing eggs. Apparently they cannot brace them- 

 selves well enough to insert their stings for 

 puncturing in order to feed. 



TWISTED, tw (legs). A male of wild-type stock 

 was X-rayed in January, 1930 (dosage about 3560 

 R units), and then mated to four females. In 

 the offspring of one of these females there ap- 

 peared fourteen males v/ith twisted legs. Legs 

 of twisted show much malformation and irregular 

 bending. Many individuals fail to eclose, prob- 

 ably on account of mechanical difficulties . Males 

 are of normal fertility, but females are almost 

 sterile (P. W. Whiting, 1934b). (Discarded) 



63 



