Hyalin is a protein released from the cortical granules of a fertilized animal egg. The released hyalin modifies the extracellular matrix of the fertilized egg to block other sperm from binding to the egg, and is known as the slow-block to polyspermy. All animals have this slow-block mechanism.
Hyalin is a large, acidic protein which aids in embryonic development. The protein has strong adhesive properties which can help with cell differentiation and as a polyspermy prevention component. It forms the hyaline layer which covers the surface of the egg after insemination.