Knobs contain spiral structures seen in sections through 3-D reconstructions. (A-C) Sections (averages of 3-4 slices) taken at different heights through knobs in a tomogram of a negative-stained schizont skeleton, showing a spiral structure. White arrows in (A) indicate some examples of radiating connections between turns; yellow arrows in (C) indicate diffuse coating material with a radiating pattern. (D-E) Handedness and depth of knob spirals: models of 2 adjacent knobs from opposite sides of the skeleton, which have been collapsed onto one another during lysis and staining, viewed face-on (D) and from the side (E). (F) Section through the tomogram tilted to cut through the coating layer of one side of a knob cone, showing coating material over at least 5 turns in curved layers (yellow arrows). Some stain-excluding membrane material (marked in [F] by a dashed line; see Figure 4B) remains after detergent extraction.