FERTILIZATION OF FERTILIZED SEA URCHIN EGGS

Fertilized, mechanically demembranated, eggs of the sea urchins Lytechinus pictus and Lytechinus variegatus can be re-fertilized when heavily re-inseminated at a half-hour or more (17° to 22° C.) after the initial fertilization. The re-fertilization occurs more readily the earlier the second insemination is performed. The reinseminated eggs tend to become heavily polyspermic. Concentrations of sperm that give 100 per cent re-fertilization do not cause any significant polyspermy when used as a first inseminate on normal unfertilized eggs. The results show not only that the demembranated fertilized egg is capable of accepting additional sperm but also that it lacks the ability to propagate a fast block to all but one sperm. Treatment of the unfertilized eggs with trypsin, so as to suppress membrane formation, or with papain at the time of fertilization, so as to cause reversal of membrane elevation, also permits re-fertilization upon re-insemination without further treatment. The results are interpreted in terms of the possible presence of fertilizin-like sperm receptors on the surface of the denuded fertilized egg.