Fig. 4. Cortical torsion occurs in parthenogenetically activated eggs. (A-F) Eggs were parthenogenetically activated and, from 75 minutes post-activation (0.79 NT) onward, bathed continuously in 20 mmol/l BDM. Activated egg, viewed from the side through two cleavage cycle equivalents (frames approximately 10 minutes apart), developed a spiraled pigment pattern in the animal hemisphere as the surface rotated left to right (counterclockwise).