Quarterly journal of microscopical science . The lint \ isible sign thai fertilization has occurred, i althe surface of the egg. [n the case of the eohinoderm or annelidegg, fertilization is attended bj the formation <d a fertilizelion membrane*. H must be remembered, however, that theessential ohange al the egg-surface is oompleted long befonany visible ohange is possible. What is the nature of thefertilization membrane? In the case of the egg of Nereisu- certain (Lillie, 20) that fins membrane is the vitellinemembrane of the unfertilized i gg, which is pushed awaj from• lie egg-surface by
Quarterly journal of microscopical science . The lint \ isible sign thai fertilization has occurred, i althe surface of the egg. [n the case of the eohinoderm or annelidegg, fertilization is attended bj the formation <d a fertilizelion membrane*. H must be remembered, however, that theessential ohange al the egg-surface is oompleted long befonany visible ohange is possible. What is the nature of thefertilization membrane? In the case of the egg of Nereisu- certain (Lillie, 20) that fins membrane is the vitellinemembrane of the unfertilized i gg, which is pushed awaj from• lie egg-surface by the disintegration and hydration oi the 424 J. GRAY egg-surface immediately under the vitelline membrane. Inthe case of the echinoderm egg it seems probable that essen-tially the same change takes place. Many years ago Loeb (25) showed that the fertilizationmembranes collapsed when placed in sea-water containingalbumen, and that on transference to normal sea-water themembrane regained its normal spherical shape. He concluded Test-fig. Diagram illustrating the origin of the fertilization membrane ofEchinus mi liar is. A. Unfertilized egg. B. Fertilized , Zona pellucida containing an electro-positive Vitelline membrane of unfertilized Fertilization membrane formed by the interaction of a, and an electro-negative colloid, d, which is set free when b is emulsified. that the extrusion of the membram was therefore due to thei \i-tence of an osmotically active colloid (proteid) within thefertilization membrane. Now the osmotic properties of sucha colloid are markedly affected by the presence of hydrogenand hydroxy] ions ; hence, it Loebs conclusion be correct,the degree to which the fertilization membrane is extrudedshould be altered by altering the acidity or alkalinity of thesea-water. This is actually the case. If the water be made acid STUDY OF FERTILIZATION 425 the membrane remains close to the egg; the higher thealkalinity the more water is absorbed
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