Homozygotes and ss^ax/ss^aP88 flies show transformation of the arista to distal mesothoracic tarsus. Expressivity of the phenotype is generally higher in ss^ax/ss^aP88 flies than in ss^ax homozygotes. The expressivity of the phenotype decreases with increasing temperature in ss^aB/ss^ax flies. Homozygous or ss^ax/ss^aP88 flies do not generally produce an ectopic tarsal response to chemical stimulation. ss^ax/ss^aP88 flies usually cannot fly, although homozygous ss^ax flies show variable flight ability.