Based on whether the daughter cells are completely separated or not. Formation of mesomeres, macromeres, micromeres in the 16 cell embryo. More layers are formed in the next two rounds of cell division. Because of the concentration of yolk in the vegetal hemisphere the formation of the cleavage furrow in the yolk-containing ventral portion is slower and lags behind that in the animal hemisphere. E-cadherin is important in adhesion between blastula cells.
Cleavage occurs at oblique angles with daughter cells either moving to the right or to the left.
DD or Dd mother, all offspring had coils which opened on the right.