1. Arbacia punctulata eggs have been broken into "halves" with centrifugal forces ranging from 4,000 x g to 100,000 x g, the higher forces being obtained with the air turbine. 2. The relative size of the two halves varies with the centrifugal force used; the higher the force the larger is the (heavy) red half, and the smaller the (light) white half. With low forces, the white half is larger than the red; with high forces, the reverse holds. 3. The degree of stratification of the eggs just prior to breaking also varies with the force used. With low forces, applied for a long period (20 min.), the eggs are very well stratified. With high forces, the egg breaks apart (½-1 min.) before the materials are completely segregated into layers. 4. The red half obtained with the highest force available (100,000 x g), is only slightly smaller than the whole egg and contains some of all the materials in the original egg except the nucleus. It develops much better, both fertilized (fertilized merogone) and parthenogenetic (parthenogenetic merogone), than the red half obtained with lower forces previously used.