A Quantitative Description of Protoplasmic Movement During Cleavage in the Sea-Urchin Egg

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Abstract
1. Protoplasmic movements during cleavage in the eggs of the heart-urchin Clypeaster japonicus have been followed by tracing the movements of cytoplasmic granules and of carbon particles adhering to the surface. 2. These movements are quantitatively described in normal eggs and in eggs whose mitotic apparatus has been destroyed by colchicine. 3. The results obtained are qualitatively similar to those obtained by Spek and by Dan and his collaborators. 4. Endoplasmic movement and changes in the length and shape of the astral rays are readily explained by the contracting-ring (band) theory. 5. The location of the motive force of cell division is discussed.