Fig. 1.

Precambrian postgastrular embryo (4F10) from the Weng'an Phosphate Member of the Doushantou Formation showing external view from right side (A) and ventral side (E), and digital internal sections (B, C, D, and F) and the same sections (B, C, D, and F) with drawings of cell boundaries (in reduced size) along the a-p axis. (A) External view from right side along the anterior (right) and posterior (left) axis with lines C and D showing the locations of the internal digital sections seen in Fig. 2. (B) Digital internal section and the same section with drawing of cell boundaries at reduced size cut half way into the embryo from the right surface (Fig. 1A), showing maximal dorso-ventral asymmetry and ectodermal cells. (C) Digital internal section and the same section with drawing of cell boundaries at reduced size along the same (a–p) axis as Fig. 1B with 30° rotation top down away from the observer showing transition from asymmetry (Fig. 1B) to bilateral subsymmetry (Fig. 1D). (D) After 90° rotation from Fig. 1B, internal section and the same section with drawing of cell boundaries at reduced size showing the plane of left-right bilateral subsymmetry. (E) External digital view from the ventral side, revealing exposed, putative endodermal cells. (F) Internal section and the same section with drawing of cell boundaries at reduced size cut inward 23% from ventral surface (Fig. 1E), showing left-right, bilateral subsymmetry of the massive internal cells. (Scale bar, 250 μm.) Key: A, anterior; P, posterior; D, dorsal; V, ventral; R, right side; L, left side; ED, ectodermal cell.