TENSION AT THE HIGHLY STRETCHED SURFACE OF SEA-URCHIN EGGS

Unfertilized eggs of the sea urchin, Paracentrotus lividus, were placed between two parallel plates and flattened by a definite force to 20% of their original diameter, with two-fold increase in their surface area. The resulting tension at their surface was calculated from the relation of force and deformation. In spite of this extensive stretching, the tension was found to be not more than 0.2 dyne/cm, while under conditions involving mild stretching (3%) the tension still amounted to 0.12 dyne/cm. These results do not support Mela's theory (7, 8), which predicts a transition of the mechanical properties of the egg surface from a 'subelastic' to 'elastic' state when the surface is stretched to beyond 34% of its initial area.