SURFACE CHANGES DURING CELL DIVISION

¹ Colby College and The Marine Biological Laboratory, Woods Hole, Mass.

1. A study of cell surface changes during cell division has been made, using echinochrome granules as natural markers rather than adherent bits of clay or dye.

2. The polar surface of the sea urchin egg stretches symmetrically in all radii from the pole during the first two-thirds of furrowing, and either remains at maximum stretch or shrinks somewhat during the latter third.

3. The furrow surface shrinks in two dimensions in the plane of the surface during earliest furrowing to the cylinder stage; it shrinks latitudinally in a degree which is proportional to the distance from the equator and it expands longitudinally from the cylinder stage on; the cortex undergoes plastic deformation at the peak of the furrow; there is no liberation of cortical echinochrome granules to the endoplasm at any stage of division.

4. All of the cortex is relatively rigid throughout division. The first signs of softening occur at the poles during late furrowing.