Interpretive tracing adapted from left half of freeze-etch replica of a transverse fracture of a Trichuris suis eggshell from fig. 9 of Wharton and Jenkins (1978) [120]. Note: (1) in the original imagery the distinct difference in texture between the Outer and Inner Chitinous Layers; (2) the thick band of tightly packed parallel fibrils (labeled “LL”) appears to be the Spatio Externum, with parallel fibrils oriented circumferentially; (3) careful inspection of the boundary between the Spatio Externum and the Chitinous Layer in the original reveals a distinct band of finely stippled texture that was unmentioned and unlabeled by the authors – most likely the Electron-dense Parietal Coating; (4) the broken dark line near the lower margin of the Spatio Externum would then be the Permeability Barrier Membrane but was not mentioned in the description; (5) beneath (internal to) the Permeability Barrier Membrane would be the Spatio Internum, which is shallow equatorially (as in Figure 22). Labels revised from original to reflect proposed new scheme.