Fig. 2. An abdominal segment and effects of omb^– clones. Left-hand panel shows a normal segment with nomenclature for the types of cuticle (Struhl et al., 1997b). Right-hand panel is a memorandum for both vectorial and scalar effects of omb^– clones (surrounded by red dashed lines) in different positions in both the A and P compartments. The scalar is shown by the colour of the cuticle and the red arrows show the observed polarity of the hairs (which normally point posteriorly), near and within the clones. We imagine the polarity to be a consequence of the concentration landscape for X. For clarity, the hairs have been removed from part of the A compartment on the right. Compare Fig. 3 and Fig. 7.