Optical and histological studies have been carried out on the eye of the Mediterranean mantis shrimp Squilla mantis (Linnaeus), with emphasis on correlation of observations based on the different methodologies. The ommatidia have acceptance angles of 2.4°, comparable to those of other compound eyes, but the wide apertures, 20°, of the cornea-cone units apparently are an adaptation to the dimly lit natural habitat of the species. Skewing of optical axes in the ommatidia of the double cornea suggests that each eye is capable of distance perception. Three systems of tangential nerve fibers in the lamina connect sets of cartridges in specific arrays. Giant fiber trees extend throughout the medulla externa. The medulla interna also contains large, extensively branched, integrating fibers. All ganglia, at least up to the medulla interna, are structurally divided into an upper and a lower half and contain large integrating fibers connecting the two halves. Optical findings are correlated with histological findings. OFFICIAL PUBLICATION DATE is handstamped in a limited number of initial copies and is recorded in the Institution's annual report, Smithsonian Year. SERIES COVER DESIGN: The coral Montastrea cavernosa (Linnaeus). Library of Congress Cataloging in Publication Data Schiff, Helga. Optics, range-finding, and neuroanatomy of the eye of a mantis shrimp, Squilla mantis (Linnaeus) (Crustacea, Stomatopoda, Squillidae).

The anatomy of the eye of Squilla mantis and the geometrical optics derived from it are briefly described. The shape and size of the electroretinogram (ERG) are dependent on a) position where it is picked up, b) the light intensity, and c) the change of intensity. Single-fiber analysis confirms the results obtained by the anatomy and the ERG of the eye. Frequency of response of a single secondary fiber to intensity changes of light is proportional to the derivate dI/dt ( I = intensity; t = time). The Squilla sees a moving object as the sum of the intensity changes caused by that object, varied in time and space. The eyes have a maximum of sensitivity for light of 535–555 mµ wavelength, and a second maximum in the near ultraviolet light, the latter partly seen as green fluorescence due to an eye pigment. Anatomy, physiology, and the environmental conditions have been combined to explain the vision of this animal, adapted to his life in the blue-violet twilight of the deeper Mediterranean sea.

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