Dynamics of Delta across two cycles of expression during stage 3. Embryos are aligned from top to bottom according to developmental age, indicated on the left by the last formed morphological segment visible in each embryo (mx2: second maxilla, mxp: maxilliped, 1LBS: first leg-bearing segment). On each row the same embryo is viewed laterally with florescent nuclear staining (SYBR green) to show the morphology (A1, B1, C1, D1, E1), in normal light from the same view (A2, B2, C2, D2, E2), and from a posterior orthogonal view (A3, B3, C3, D3, E3). Within this period, Delta expression around the proctodeum is dynamic, showing an oscillation of expression in each region of the peri-proctodeal area. Arrows of the same color mark a single cycle of expression, from its initiation as bilateral patches around the proctodeum (black asterisk) to its resolution as a primary pair-rule stripe. Magenta arrowhead marks the second LBS in lateral views: red asterisk marks artefactual breaks in the epithelium. Scale bar: 400 μm.