RE-FERTILIZATION OF THE FERTILIZED EGGS OF THE SEA URCHIN

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Abstract
If the fertilized eggs of sea urchins (Strongylocentrotus pulcherrimus, Pseudo-centrotus 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 cleavage of re-fertilized eggs is irregular and characteristic of polyspermy. Refertilization can occur without removing the membrane mechanically if the eggs have been treated with a Ca-Mg-free medium immediately after the 1st insemination. Refertilization can take place at any stage of the first cell division and even at the 2-cell stage. 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.

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