A yellow crescent is formed in the area which will later become larval muscle cells. After fertlization the surface layers of the animal hemisphere rotate 30 o toward the point of sperm entry. The newly exposed surface area will later invaginate during gastrulation. Polymerization of microtubules is involved. Cleavage The site of the first cleavage furrow is determined by the point of sperm entry and the subsequent cytoplasmic movements of the newly fertilized egg.
Cytoplasmic factors influence the angle and timing of the formation of the mitotic spindle.
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.