Cortical granules in hamster eggs

The presence is recorded of large numbers of granules at the surface of the vitellus in the hamster egg before spermatozoon penetration. The granules were mostly between 0.1 and 0.5 μ in diameter and occurred at a density of between 50 and 100 per 100μ2. Spermatozoon penetration resulted in almost complete disappearance of the cortical granules, and this change took place before the activation of the egg as indicated by the resumption of the second polar meiosis. Activation alone, on the other hand, whether spontaneous or artificially induced, had no noticeable effect on the granules. Disappearance of cortical granules was associated with a distinct decrease in the light-refracting power of the vitelline cortex. Disappearance of cortical granules in the hamster egg is therefore concluded to be an early and specific response to spermatozoon penetration. It may not, however, be associated with the formation of a block to polyspermy in the surface of the vitellus.