One of the consequences of the massive increase in surface area of cleaving embryos is the need to add additional material to the surface of the embryo as cleavage continues. At the right, unpigmented material (arrows) has been added to the region immediately adjacent to the cleavage furrow in this two-cell amphibian embryo (photo from deLaat and Bluemink, 1974, J. Cell Biol. 60:529-540).
Addition of new surface material at the cleavage furrow