A simple example of a collimated beam of light being split into two parallel beams by a birefringent material. The various beams are explained in the link but the important thing to understand is that this unexpected optical phenomenon is being produced by one monochromatic source of light incident on one geometrically simple but birefringent object. A trichinelloid eggshell is much more complex with thousands of protein “pipes” surrounding a birefringent core of chitin and with the pipes arranged parallel in layers and each layer rotated around a perpendicular axis by about 10° relative to the next. Adapted from Jan Pavelka: Fluorescence and birefringence of 445 nm blue laser in calcite crystal https://en.wikipedia.org/wiki/File:Fluorescence_in_calcite.jpg.