Variations in the Structure and Design of Compound Eyes

Abstract

At first glance the compound eyes of insects and crustaceans seem to be spherical structures with a more or less uniform distribution of facets. A second look, however, often reveals that the eye is really not symmetrical. There may be regional variations in its curvature, in the sizes of the facet lenses and consequently their packing density. These are reflected in the size and shape of the pseudopupil — the dark spot which marks the part of the eye that images the observer (Stavenga 1979). Even closer observation shows that as the eye is rotated the pseudopupil moves at different speeds in different parts, showing that in some regions the same angle in space occupies more of the eye surface than it does in others. Gordon Walls (1942) wrote that “everything in the vertebrate eye means something”, and although our subjects here are exclusively invertebrate, the same dictum is just as valid. The small variations I have mentioned are not haphazard developmental oddities; they all reflect the way in which the eye samples its environment. Properly interpreted, they tell us a great deal about the role of vision in the animal’s life.