Ntl and myoD expression in swr, snh, pgy and laf mutant embryos. Animal pole or anterior is left or up, except where noted. A dorsal view of whole-mount anti- Ntl antibody stainings at the bud stage of wild type (A); swr (B) where the Ntl notochord domain is about twice as broad as in wild type; snh (C) where the Ntl domain is about 50% broader than in wild type; and pgy (D) where the Ntl domain is about 25% broader than in wild type. In EH, S,T the yolk was removed and then the axis of the embryo flattened onto a slide in order to visualize the entire axis of the embryo (a ‘spread’). Spreads of myoD in situ hybridizations of bud stage embryos in wild type (E,E′), swr (F,F′), snh (G,G′), and pgy (H,H′) mutant embryos. Higher magnifications of the posterior expression (E′-H′) show the mediolateral expansion of myoD expression. Lateral view of a whole-mount myoD staining at the 18- somite stage in wild-type (I) and laf mutant (J) embryos. An arrowhead indicates the enlarged somitic expression of myoD in laf. Dorsal (K,M,Q) and lateral (L,N,R) views of whole-mount myoD stainings of wild-type, swr and snh embryos at the 6-7 somite stage. From a dorsal view of snh (Q) 7 somites are visible. In a lateral view of the same snh embryo (R), it is apparent that only the 5 most posterior somites extend around the circumference of the embryo. Spreads of myoD staining at the 5-6 somite stage in wild type (S) and pgy (T). The wild-type embryo (K) is shown from the vegetal pole (O). In P a vegetal pole view of the swr embryo in M shows the first two somites extending around the circumference of the embryo. The more posterior somites also extend to the ventral side and fuse, but are not in the plane of focus.