Advancement of the cleavage furrow from the outside of the cell inward towards the center of the cell. The cleavage furrow acts as a 'purse string' which draws tight to separate daughter cells during cytokinesis and partition the cytoplasm between the two daughter cells. The furrow ingresses until a cytoplasmic bridge is formed.
Comment:
Consider also annotating to 'contractile ring contraction involved in cell cycle cytokinesis ; GO:0000916'.