THE ROLE OF FERTILIZIN IN THE FERTILIZATION OF EGGS OF THE SEA-URCHIN AND OTHER ANIMALS

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Abstract
1. It has been shown in the sea-urchin that the presence of fertilizin, in the form of the jelly coat of the egg, serves as an aid to fertilization. In solution it acts as a barrier to fertilization. 2. Confirmation is presented of Lillie's finding that sea-urchin sperm cannot be re-agglutinated after reversal of an initial agglutination. It is also shown that the reversed sperm are incapable of fertilization. 3. Appropriate heat treatment converts fertilizin into a substance that does not cause sperm agglutination but still combines with the sperm as shown by the inability of the sperm to be subsequently agglutinated by ordinary fertilizin and by loss of fertilizing power. In accordance with the assumption of multivalency in the lattice theory of agglutination, the modified fertilizin is assumed to be univalent. It is found to be non-dialyzable. 4. In the starfish and in Urechis the egg water is shown to contain a specific sperm-combining substance (univalent fertilizin) that is incapable of causing iso-agglutination of sperm. 5. Of various interpretations of the spontaneous reversal of agglutination in the sea-urchin, a splitting of the fertilizin into univalent fragments is considered the most likely. 6. Reasons are presented for holding open the possibility that fertilizin plays an indispensible part in fertilization. Various possible explanations as to the manner in which it serves as an aid to fertilization are discussed and that involving trap action is considered the most likely. 7. It is suggested that some species of animals produce upon immunization only, or principally, univalent antibodies and a method of determining this point is offered.