Fig. 7. Segment formation in Tc'Kr^jaws is not re-established during later stages of development. Embryos are doubly labelled for Tc'eve (brown) and Tc'wg RNA (blue). Numbers relate to canonical Tc'wg stripes, i.e. starting with the mandibular segment. (A-F) Wild-type embryos of increasing developmental age, stage-matched to Tc'Kr^jaws embryos (G-L; staging is based on the dynamic Tc'wg head expression). Compared with wild type (A-C), Tc'eve expression becomes irregular and prematurely fades in Tc'Kr^jaws embryos (G-I). Initially, only the seven anteriormost wg stripes (md to A1) are properly formed in Tc'Kr^jaws. Posterior to A1, several irregular or fragmentary wg stripes form (G-K), which then reorganize such that in more mature embryos (L) normal Tc'wg stripes 8-10 are frequently observed, consistent with the 10 differentiated segments in Tc'Kr^jaws larvae. No new Tc'eve or Tc'wg activity is evident at later stages, when in wild-type embryos the last Tc'wg stripes form (15 and 16 in our notation, which correspond to abdominal segments A9 and A10) (D-F). A non-segmental Tc'wg domain is present in the growth zone throughout development. This domain represents terminal fates and eventually becomes part of the proctodeum.