Knobs in the membrane of a P falciparum–infected erythrocyte have an underlying electron-dense layer. Average of 20 slices from a tomogram of a high-pressure-frozen, freeze-substituted schizont, showing knobs in the erythrocyte membrane and underlying electron-dense material. cyt, erythrocyte cytoplasm; mem, erythrocyte membrane; TVN/MC, tubulovesicular network/Maurer's cleft.