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