Optical Changes in the Membranes of the Sea-Urchin Egg at Fertilization, Mitosis and Cleavage

Abstract
1. Changes in birefringence and light scattering of the sea-urchin egg membranes at fertilization, mitosis and cleavage are described and illustrated. 2. There is a close similarity between the changes in the cortex at fertilization and at cleavage. 3. The changes in the cortex at cleavage start at the poles of the cell, and only later spread to the equator.