Bristles small. Body small. Eclosion delayed. Viability excellent. Female sterile; eggs rarely found and only in a few ovarioles (Perrimon and Gans, 1983). Yolk formation in oocytes inhibited (King and Burnett, 1957). Follicular cells form abnormal derivatives of endoplasmic reticulum and migrate abnormally or form excess of normal endoplasmic reticulum derivative (King and Vanoucek, 1960; Falk and King, 1964). ty ovaries in ty+ host develop autonomously (King and Bodenstein, 1965). The heteroallelic combination ty/ty2 exhibits the visible phenotypes described for ty homozygotes (Schalet, 1986), and, in addition, may show a reduction in thoracic hairs and abnormally-shaped rough eyes; viability severely reduced in some cultures. RK2.