The slow block to polyspermy occurs when polar bodies discharge their contents, thereby altering the egg coats.

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The slow block to polyspermy is primarily achieved through the release of calcium ions within the egg, which triggers changes in the egg's zona pellucida (or vitelline layer in non-mammalian species), making it impermeable to additional sperm. This process does not involve the discharge of contents from polar bodies.

The Slow Block to Polyspermy Occurs When Polar Bodies Discharge