Fig. 1.

Arrangement of chitin in the cuticle of arthropods. In 1965, Bouligand presented a model to explain the arrangement of chitin microfibrils in the arthropod cuticle (a). Laminae (alternating in white and grey) of parallel chitin microfibrils (black and red lines) are stacked, with respect to the orientation of the microfibrils, in a helicoidal manner. In each sheet, one microfibril is highlighted in red to demonstrate that, in ultra-thin oblique sections, the illusion of a parabolic texture is provoked, as shown in a transmission electron micrograph of the Drosophila larval cuticle (b). Bar 500 nm