Structural basis of the activation wave in the egg of Xenopus laevis.

A series of changes in the surface of activated Xenopus eggs was observed. Within a few seconds of prick activation a light area appears near the pricking point and expands as a circular light zone (light wave). Some 60 s later this is followed by a dark area expanding as a circular dark zone (dark wave). Both waves travel at a rate of about 9 micron/s at 21 degrees C. In the light zone, cortical granules are breaking down, microvilli are elongating, and the egg surface is expanded. On the other hand, the elongated microvilli are reshortening to become globular and the egg surface is contracted in the dark zone.