II. On the modifications of the simple and compound eyes of insects

The simple eyes of insects have been so accurately described by previous observers, that little need be said on their structure. I have described the simple eye of Eristalis , chiefly for comparison with the compound and aggregate eyes. The close relation of the recipient rods to the inner surface of the cornea in this insect is most noteworthy, since, combined with the great convexity of the cornea and the highly refractive nature of the rods themselves, this renders the formation of an optical picture impossible. These facts with the small number of recipient rods shew that it is most probable that the function of the ocelli is rather the perception of the intensity and the direction of light than of the actual disposition and colours of surrounding objects.