It is long since the compound eyes of these Trilobites, as illustrated by Burmeister, gave Buckland the opportunity to infer that the laws of light and of vision were the same from the first as now. But what does this imply? Not only that the light of the sun penetrating to the depths of the Cambrian sea, was regulated by the same laws as to-day, but that a series of cameras was perfected to receive the light as reflected from objects, to picture the appearance of these objects on a retinal screen as sensitive as the film of the photographer, and thereby to produce true perceptions of vision in the sensorium of these ancient animals. I have before me a fragment of the eye of a Trilobite (_Phacops_), in which may be seen the little radiating tubes provided for the several ocelli of the compound eye, just as we see in the modern Limulus; and each of these ocelli must have been a perfect photographic camera, and more than this, since absolutely automatic, and probably having the power to represent colour as well as light and shade. We know also, from the recent experiments of an Austrian physiologist on the eyes of insects, that such compound eyes are so constructed as to present a single picture, just as we can see the whole landscape in looking through the many little panes of a cottage window. In our own time the king-crab and lobster no doubt see just as their predecessors did millions of years ago, and with precisely similar instruments. But the eyes of the modern Crustaceans have to compete with eyes of a dissimilar type, constructed on the same general optical principles, but quite different in detail. These are the simple or single eyes of the cuttle-fishes and the true fishes. The same rivalry existed in the oldest seas, when the competition of Crustaceans and cuttles was just as keen as now. Though the eyes of the latter have not been preserved, or at least have not yet been found, we have a right to infer that the cuttles of the Cambrian and Silurian seas must have been able to see as well as their Crustacean foes and competitors. If so, the other type of eye must have been perfected for aquatic vision as early as the compound type. In any case we know that a little later, in the Carboniferous period, we have evidence that the eyes of fishes conformed to those of their modern successors. I have myself described[152] a carboniferous fish (_Palæoniscus_) from the bituminous shales of Albert County, New Brunswick, in which the hard globular lens of the eye had been sufficiently firm and durable to retain its form, and to be replaced by calcite, showing even that like the lens of the eye of a modern fish it had been constructed of concentric laminæ. In the Carboniferous period also, both types of eye, the compound and the single, experienced the further modifications necessary to fit them for vision in air, the compound eye in insects, the simple eye in Batrachians.[153] The original photographic cameras, strange though