Hemitergite development and <i>engrailed</i> expression in flat mounted stage 7 embryos of <i>Strigamia maritima</i>.

<p>All images orientated with anterior to the left. Images with the same letter indicate same specimen; A, B, B2, C: fluorescent nuclear staining (Sytox Green) to show the morphology; A1, B1, B3 and C2 respectively same view as A, B, B2, C, under transmitted light, showing pattern of <i>en</i> expression. <b>A–A1.</b> Lateral view of most of the left half of a germ band, showing developing hemitergites extended along the dorsal side only for 30% in the anterior half of the trunk, and the presence of developing tracheal pits (<i>tp</i>). For most of the germ band only the laterodorsal part is visible; note the lack of gene expression in the undifferentiated dorsal epithelium (<i>ude</i>). <b>B–B1.</b> Ventral view of middle trunk region. <b>B2–B3.</b> Close-up of panel B, showing developing hemitergites with weakly formed intercalary furrow (<i>if</i>). <b>B3.</b> Shows correspondence between the extent of the laterodorsal <i>engrailed</i> stripe and the hemitergite extension. <b>C–C1.</b> Ventral view of posterior trunk of nuclear stained embryo. At this stage a thin undifferentiated epithelium, not expressing <i>engrailed</i>, is interposed between the medial and lateral parts of the germ band (<i>arrowhead</i>). <b>C1.</b> Shows posterior correspondence between <i>engrailed</i> expression and hemitergite coverage. The last leg-bearing segment (<i>llb</i>) features the only dorsoventrally uniform <i>engrailed</i> stripe. Other abbreviations: <i>htb,</i> semicircular dorsal border of the hemitergites; <i>mxp</i>, maxilliped. Scale bars: 200 µm for A, A1, B, B1, D, D1; 100 µm for insert in A, C, C1.