IV. On the structure and functions of the eyes of arthropoda

Abstract Three distinct forms of eye exist in the Arthropoda j the Compound eye, the Simple- Ocellus, and the less known Compound Ocellus common in larval insects, first described by Dr. Landois. The relationship of the Compound eye to the Simple Ocellus is shown to be very distant, although I believe that these two types have been evolved from a common but very rudimentary primitive type. On the other hand, that between the Compound eye and the Compound Ocellus of a larval insect, is very close, the Compound eye being merely an aggregation of a great number of these ocelli, variously modified in the more highly differentiated Insects and Crustaceans. A fourth form of eye exists, in which the Ocelli are less closely united ; this forms a connecting link between the compound eye and the’ compound ocellus. It is found in the Isopods, and may be conveniently termed the Aggregate eye.