The ultrastructure of cortical granules in sea urchin eggs (Hemicentrotus pulcherrimus) was investigated electron microscopically following block staining with phosphotungstic acid (PTA).
The lamellar substance of the components of cortical granules showed intensive affinity for PTA, while non-lamellar substance was not stained. The origin and chemical components of the cortical granules were discussed from the point of their affinity for PTA.