End of gastrulation through neurula stages showing embryonic disk. (A, B) Fixed embryo cut in half at the late gastrula stage illustrating internal structures. (A) Low magnification. Dorsal region of embryo is towards the top. (B) High magnification. Arrows delineate the small size of the yolk plug. (C-E) Illustration of the embryonic disk in living Ensatina embryos. The two embryos are at an early neurula stage. Arrows indicate the lateral edges of the neural plate. Arrowheads point to closed blastopore. (C) Low magnification view of whole dorsal surface of embryo. Blastopore is towards the top. (D) High magnification of same embryo. (E) Low magnification view of a different embryo with the blastopore toward the top right corner (arrowhead). Ar = Archenteron; Bl = Blastocoel. Scale bar = 1.0 mm.