MECHANICAL PROPERTIES OF SEA URCHIN EGGS III. VISCO-ELASTICITY OF THE CELL SURFACE

When a sea urchin egg was compressed between two parallel plates, the force required to keep the distance between the plates constant gradually decreased with time. The contours of the compressed egg were different from the contours expected from the assumption that the surface forces are uniform over the entire surface. The surface forces of the egg without deformation computed from the area of the cell surface in contact with the substratum, the density of the egg and its size were 0.02–0.04 dynes/cm in Hemicentrotus pulcherrimus. Larger values were obtained in eggs during compression. Surface forces, which were computed from measurements of the form of the egg and the applied force when the egg was deformed by a rod and a plate supporting the egg, increased as the deformation increased.
From these results, it was concluded that the cell surface is visco-elastic in sea urchin eggs.