Segmentation dynamics of Delta across mid-late stage 4. Flat mounted embryos are aligned from top to bottom according to developmental age (A, B, C, D), indicated on the left by the number of the last formed LBS. During this interval the distance from the stomodeum (red dotted line) to the proctodeum (magenta dotted line) is almost constant. The appearance of new stripes/rings of Delta expression and their forward movement is associated with the convergence of the germ band toward the anterior/cephalic region, as shown by black dotted lines marking the 1st and the 16th leg-bearing segment (LBS). Note, though, that the length of the germ band from the 16th to the 35th LBS (or the primary stripe that precedes it) is, if anything, expanding during this interval. The punctate expression of Delta in medial regions of anterior segments marks neural precursors arising in each segment. Scale bar: 200 μm.