Fig. 1. Summary model and results. (A) Pattern formation in the abdomen. Two segments are shown, each with an A and a P (blue) compartment stratified into different types of cuticle (shown at bottom of the panel). The Hh and Wg gradients pattern the cuticle (Struhl et al., 1997b; Lawrence et al., 2002). The gradient of `X' may have opposing slopes in A and P; its vector determines the orientation of the hairs in A (up the gradient) and P (down the gradient) as shown by the arrows. Anterior is to the left. (B) A field guide to the main results; the genotypes of clones are shown inside the ellipses. Genotype symbols outside the clone, say, fz^–, indicate the genetic background in which the clone was induced (fz^–). Red arrows mark where polarity is reversed or normalised. Anterior is up.