Eggs of the sea urchin, A. punctulata, were centrifuged and then cut into 2 equal sized fragments, one containing practically all of the pigment and other granules, the other almost devoid of granular material. The time lapse from fertilization to the beginning of cleavage was the same, at the same temp., as in comparable fragments of non-centrifuged eggs; i.e., the presence or absence of granules was without effect. The actual passage of the cleavage furrow, however, was retarded in the granular fragments, which are more viscous than the normal egg, and accelerated in the granule-free fragments. Since some fragments contained an egg nucleus they were diploid after fertilization whereas others were haploid. The ratio of the amount of nuclear material to the amount of cytoplasm was a determining factor in the time lapse to cleavage.