Formerly novel optics: a collection of optical tidbits

Thefirst birefringent optical element was the calcite trilobite eye, 540,000,000 years ago. One type was a hexagonal array of from one to several thousand lenslets of calcite crystals, oriented to produce no double images. At each molt new eyes were grown. Some trilobite eyes were calcite with spherical aberration correction resulting from a gradient index. (Some trilobites were blind.) Reference: Richard Fortey, Trilobite!, Knoff, New York, 2000