Expression of <i>engrailed</i> in embryos of the onychophoran <i>E. rowelli</i> at subsequent developmental stages.

<p>Anterior is left in A, B, E, F and up in C, D. Leg-bearing segments and corresponding limbs are numbered. Note the repeated stripes along the body and the lack of expression in the dorsal and ventral extra-embryonic tissue. Double-arrowheads in A, B, E and F indicate the dorsally located domain of <i>engrailed</i> in the cephalic lobe. Arrowheads in C and D point to the transverse ectodermal furrows, which lack <i>engrailed</i> expression. (A) Early stage II embryo in lateral view. (B) The same embryo as in A in ventral view. Note the lack of expression in the posterior region and around the proctodaeum (black arrow). (C) Confocal micrograph of the posterior end of the same embryo as in A labelled with the DNA marker SYBR Green. (D) Light micrograph of the same embryo as in C. (E) Early stage III embryo in lateral view with eleven <i>engrailed</i> stripes along the body and a spot-shaped domain in the developing antenna (arrowhead). (F) Late stage III embryo in lateral view with 15 <i>engrailed</i> stripes along the body (13 within the trunk) and an additional domain in the developing antenna (arrowhead). Abbreviations: <i>at</i>, developing antenna; <i>cl</i>, cephalic lobe; <i>de</i>, dorsal extra-embryonic tissue; <i>js</i>, jaw segment; <i>ss</i>, slime papilla segment; <i>ve</i>, ventral extra-embryonic tissue. Scale bars: 250 µm (A, B, E, F), 100 µm (C, D).