Chitin fibril helicoidal structural motif within the periodic region. (A) three dimensional model of a helicoid, (B) with an SEM fractograph, (C) a polished surface from a transverse cross section, (D) the chitin fiber orientations from the x-ray scattering analysis, (E) Three representative c plots of the α-chitin reflection, A charge contrast scanning electron micrograph from a damaged coronal cross section (F) with false color (G) and a model of a helicoidal slice (H), which accurately reproduces the fracture patterns.