Fig. 2. Metrics for quantifying gastrulation. (A) Blastopore closure: ratio of the blastoporal surface area (yellow) to the surface area of the vegetal hemisphere (green) of the embryo. (B) Convergent extension: length-to-width ratio of the Xnot domain (red outline). (C) Spherical approximation to the embryonic surface visualized by reprojecting the 2D image into 3D. White lines in B and C indicate the dorsal midline. (D) Archenteron measurement: distance in degrees between the dorsal lip of the blastopore (blue line) and the anterior limit of the archenteron (white line); degrees of arc between the anterior limit of the Xnot domain (pink line) and the anterior limit of the archenteron (white line); degrees of arc between the dorsal mesendodermal mantle (orange line) and the center of the blastopore. (E) Archenteron inflation: area of the archenteron at the mid-sagittal plane divided by the area of the embryo at that plane.