Stereoscopic vision within the schizochroal eye of trilobites

Abstract

MOST trilobites had holochroal eyes which were probably analogous with the compound eyes of most living arthropods¹. Trilobites of the suborder Phacopina had schizochroal eyes, in which comparatively few large separate lenses are distributed over the eye surface. Clarkson and Levi-Setti² showed that the schizochroal eye is unique in structure, in that each lens is biconvex and is made of two calcitic elements of different refractive indices, separated by an aspherical surface with a configuration such that the lens was corrected for spherical aberration. A modified interpretation by Campbell³ suggests that the e and o rays were transmitted through the calcite lens to focus in the same plane. Since chromatic aberration is not important in seawater more than a few metres deep, either interpretation implies that each lens of the schizochroal eye was capable of forming an accurate image of its field of vision^2,3.