Segmentation last phase: loss of oscillation and shift from double to single-segment periodicity. Embryos are aligned as in Figure 1. In all but F3, the view is from the posterior pole - anterior on top. Columns 2 to 6 depict the expression of a single gene, or pair of genes, as indicated on top. Column 1 presents the same view as column 2, but under fluorescent light (SYBR green nuclear staining) (A1, F1, O1, T1). In A1, F1 and F3 eve2 expression in red is overlaid on the nuclear staining. F3 presents the same embryo as F1, but in lateral view, to clarify orientation for all embryos: eve2: Expression in primary “pair-rule” rings (A2) is lost around the 34 LBS stage (F2, O2, T2). eve1: Stripe intercalation is still visible at the 27 LBS stage (B). By the 34 LBS stage, all visible stripes are at single segment intervals (G, K, P, U), as shown by the coincidence of eve and Delta staining (H, L). The embryo in P is asymmetric, with one more stripe resolved on the left. Delta: Stripe intercalation is lost by the 43 LBS stage; the broader peri-proctodeal expression (D, I) is reduced (M), to a single stripe at its anterior margin (Q, R, V), eventually completely disappearing (W). engrailed expression appears segmentally immediately anterior to the single Delta stripe (S). knirps (E) is up-regulated in the peri-proctodeal zone around the 34 LBS stage (J) and is persistently on thereafter (N, Y). Black (white in F3 and S) arrows: proctodeum; purple arrows: Delta expression; magenta arrows: eve1 expression except in S where it marks en expression. Arrowheads: background staining commonly observed at the periphery of late germ bands. Scale bar in C, H, L, Q and S: 100 μm, in all other panels: 200 μm.