First cleavage begins at the animal pole and travels to the vegetal pole. It is meridional and bisects the grey crescent, occurring approximately 2.5 hours post-fertilization. It is also meridional and occurs at approximately 3.5 hours post-fertilization. It occurs at approximately 4 hours post-fertilization. At its completion, there are now eight cells total, four micromeres and four macromeres.
Cleavages follow synchronously and rapidly.
Amphibian embryos, when they are between 16 and 64 cell stages, are called a morula. 5. Subsequent cleavage cycles begin to lost their synchrony due to the lengthening of the cell cycle in the cells of the vegetative hemisphere. The blastocoel, a prominent cavity in the animal hemisphere above the mass of the yolk, is seen after the morula stage. When the embryo has completed the cell cycle which takes it from the 64 to 128-cell stage, it is called a blastula, and remains a blastula until the cell numbers are between 10,000 and 15,000. Effect of yolk on cleavage.