Clones of kis165A1 mutant cells induced between wing veins L2 and L5 engender ectopic vein formation close to the position of longitudinal veins in both the anterior and posterior compartments and broadening of the L3-L4 intervein region. When mutant kis165A1 clones occupy the entire wing, this results in a reduction in wing size, loss of the L2 vein and increase in the distance between the L3 and L4 veins.