Expression of onychophoran Hox genes (ventral views). In all cases anterior is to the left. Arrows in A and B point to up-regulated expression of lab and pb in the ventral nervous system. The asterisk (*) in A indicates damage of ventral tissue as a result of the hybridization procedure. See text for further information. Abbreviations; av, anal valves; fap, frontal appendage; hl, head lobe; j, jaw, L1-L15, first to fifteenth walking limb; sp, lime papilla, vee, ventral extraembryonic ectoderm.