RE-FERTILIZATION OF THE FERTILIZED EGGS OF THE SEA URCHIN

¹ The Sugashima Marine Biological Station, Nagoya University, Sugashima, Shima-gun, Mie-ken, Japan

1. If the fertilized eggs of sea urchins (Strongylocentrotus pulcherrimus, Pseudocentrotus depressus, Heliocidaris crassispina, Temnopleurus toreumaticus) are inseminated again after removal of the fertilization membrane and washing with a Ca-Mg-free medium for a few minutes, re-fertilization can take place. Spermatozoa not only penetrate into the previously fertilized eggs but also take part in the formation of the mitotic figure, so that the cleavage of re-fertilized eggs is irregular and characteristic of polyspermy.

2. Re-fertilization can occur without removing the membrane mechanically if the eggs have been treated with a Ca-Mg-free medium immediately after the first insemination.

3. Re-fertilization can take place at any stage of the first cell division and even at the 2-cell stage.

4. It is justifiable to consider that there is a sperm-excluding substance on the surface of fertilized eggs. This substance is stable in sea water but is easily lost in Ca-Mg-free media.