MECHANICAL PROPERTIES OF PERIVITELLINE FIBERS OF SEA URCHIN EGGS AS STUDIED BY APPLICATION OF CENTRIFUGAL AND ELECTROPHORETIC FORCES

¹ Department of Biology, Faculty of Science, Toho University, Miyama, Funabashi, Chiba 274, Japan

Fertilized sea urchin eggs are concentrically located in the perivitelline space. However, after centrifugation or treatment with Ca-free sea water, most eggs came to rest on the bottom of the perivitelline space, and few fibers were detected within the perivitelline space by differential interference microscopy. In normal fertilized eggs with the fibers, the egg shifted to the anode under an electric field and returned to its original position after the field was shut off. In centrifuged eggs without the fibers the recovery to the concentric position was not achieved. Such invariable coincidence of the perivitelline fibers and the concentric position of the eggs shows that the fibers are the structure supporting the egg in the central portion of the perivitelline space.

The mechanical properties of these fibers were studied by application of centrifugal and electrophoretic forces. The results indicate that: 1. the fibers show an internal viscous resistance against stretching and 2. tension of the fibers is about 0.9 x 10^-5 dyne which is large enough to support the fertilized egg in the pervitelline space.