Stages 7 and 8 of C. salei. Sytox staining, a-g; SEM, h. All scale bars 200 μm. a-d, Stage 7, Germ band. a: Posterior view of the growth zone (GZ), a dense region that is continuous with the primary thickening (PT) in stage 6, Figure 3h. The dorsal field (DF) is extended to its maximum. b: Same egg as in a rotated by 90 degrees, such that the embryo is in lateral view. The embryonic tissue (early germ band) extends along the ventral curvature between the two arrows. Between the two white arrow heads is the equator, which is the sharp change in cell density that marks the border of migration of mesendodermal cells from the primary thickening. c: Postero-lateral view of an embryo that is slightly more developed than the one in a and b. d: Lateral view of the same embryo as shown in c. The embryonic tissue (early germ band) extends along the ventral curvature between the two white arrows. This region has more cells and a much higher density than the dorsal field (DF). The equator is no longer visible. e-h, Stage 8, Segmented germ band. e: Lateral view. Evident are all future prosomal segments: cheliceres (Ch), pedipalps (P) and four walking legs (white arrow heads). At the posterior end, the growth zone (GZ) exhibits a higher density of cells. f: Frontal view of the same embryo as in e. g: Slightly more advanced embryo than e. Anterior to the cheliceral segment (Ch) the precheliceral region (Pc) is separated by a clear margin from the surrounding extra-embryonic (mainly yolk) tissue. All prosomal segments (cheliceres, Ch; pedipalps, P; four walking legs, L1-L4) are distinct. h: Lateral view. An embryo comparable to e. Evident are the germ band (GB) and yolk (Y). The yolk is located in the regions labelled earlier as the dorsal field (DF) and the extra-embryonic (Ee) region.