Figure 2.

Stages 5 and 6: Anterior–posterior axis reads left to right in both images. Scale bar = 1 mm. Stage 5 (30 h). Stage 6 (36 h). Abbreviations: am, anterior margin of mesoderm; anp, anterior neural pore; ap, area pellucida; hn, Hensen’s node; hp, head process; mfh, margin of free head; nf, neural fold; no, notochord, notochord mesoderm; pf, primitive fold, lateral lip; pg, primitive groove, blastopore; po, proamnion, anterior blastopore; ps, primitive streak; zj, zone of junction. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]