The sequence of images at the right is a computer morph of still images of Xenopus zygotes labeled with the fluorescent dye trypan blue to visualize yolk platelets during the 60 min period after fertilization (Danilchik and Denegre, 1991). Development 111, 845-856). Since it is a morph, the dynamics should not be taken too literally. Nevertheless, the sequence does demonstrate the dynamic changes in the deep cytoplasm of the animal pole that result from subcortical rotation movements. For reference, the future ventral side of the embryo is on the left. This is also the side where the sperm entry point (SEP) is visible after fertilization.