Studies in Artificial Parthenogenesis

The unfertilized Arbacia egg consists essentially of fluid proteins, surrounded by a stiff membrane (the vitelline membrane), which is the plasma membrane of the egg cell. This membrane is a protein gel with little or no admixture of lipoids. 2. There are two types of cortical change, membrane swelling and membrane elevation. In the former, the membrane absorbs water and increases in thickness; in the latter, the normal process, it becomes lifted away from the egg surface. 3. The vitelline membrane only loses its semipermeable properties several minutes after elevation, and the increase of permeability that then ensues is best regarded as a result rather than as a cause of the process. 4. Artificial membrane elevation is produced only by substances which lower the surface tension of the vitelline membrane. This is explainable on the basis of a theory that considers the various forces at play on the membrane. After its surface tension is lowered, the forces exerted outward are stronger than those balancing them, and the membrane is as a result pushed away from the egg. 5. Cytolysis is not due to a simple swelling of egg proteins for these can be shown to coagulate rather than to swell, it is due to a continuation of the same process as that which results first in membrane elevation. 6. The sperm produces membrane elevation by lowering the surface tension of the vitelline membrane. This it accomplishes by causing the membrane to swell at the point where it strikes the egg. 7. Experimental evidence is presented to show that this membrane swelling produced by the sperm is due to the action of an acid. 8. The fact that potassium cyanide does not prevent initiation of development by hypertonic sea-water, is taken as evidence against the oxidation theory of artificial parthenogenesis. 9. All initiation of development involves the gelatinization or coagulation of some substance within the egg. This coagulative change can be demonstrated to take place before the egg interior shows any other signs of the approach of development.