ELEVATION AND RETRACTION OF THE FERTILIZATION MEMBRANE OF ECHINODERM EGGS FERTILIZED IN PAPAIN SOLUTIONS

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Abstract
When eggs of sea urchins and starfish are added to a suspension of sperm in papain solutions (0.02 to 0.04%), a fertilization membrane is elevated in the normal time and, after reaching full separation, retracts to the surface of the egg. This process is completed in approximately 5 minutes in the case of sea urchins (Strongylocentrotus purpuratus and Lytechinus pictus) and 25 minutes in the case of starfish (Asterias forbesii). It is not visible during subsequent development after removal of the eggs from the solution, and development to late stages is normal. Treatment of unfertilized eggs with papain prevents membrane elevation upon fertilization, as reported for other proteolytic enzymes. Treatment of eggs with fully formed fertilization membranes shows no effect on these. It is suggested that the retracted membrane, obtained by fertilization in papain solution, fuses with the egg surface, and that, in general, the question remains open as to whether or not proteolytic enzymes dissolve the vitelline membrane of the unfertilized egg.