Royal Society Publishing  Reflecting optics in the diverticular
eye of a deep-sea barreleye fish (Rhynchohyalus natalensis)  J.
C. Partridge, R. H. Douglas, N. J. Marshall, W.-S. Chung, T. M.
Jordan, H.-J. Wagner   We describe the bi-directed eyes of a
mesopelagic teleost fish, Rhynchohyalus natalensis, that
possesses an extensive lateral diverticulum to each tubular eye.
Each diverticulum contains a mirror that focuses light from the
ventro-lateral visual field. This species can thereby visualize
both downwelling sunlight and bioluminescence over a wide field
of view. Modelling shows that the mirror is very likely to be
capable of producing a bright, well focused image. After
Dolichopteryx longipes, this is only the second description of
an eye in a vertebrate having both reflective and refractive
optics. Although superficially similar, the optics of the
diverticular eyes of these two species of fish differ in some
important respects. Firstly, the reflective crystals in the D.
longipes mirror are derived fro