Fig. 5. Plate XVI. represents a small portion of the cornea of a lobster; here each of the eyes are small squares, not hexagons; a conformation which admits a smaller number in the same surface; so great a number was not necessary in this instance, as the eyes of the lobster are moveable. Fig. 6. the same of its natural size. OF THE EYES OF THE MONOCULUS POLYPHEMUS. The monoculus polyphemus, or king crab, has four eyes, two large and two small ones; the large eyes are formed of a great number of transparent amber-like cones, the small ones of a single cone, “The internal surface of the large eyes, examined with the microscope, is found to be thick set with a great number of small transparent cones, of an amber colour, the bases of which stand downward, and their points upward next the eye of the observer. The cones in general have an oblique direction, except some in the middle of the cornea, about thirty in number, the direction of which is perpendicular. The center of every cone being the most transparent part, and that through which the light passes, on that account the perpendicular or central cones always appear beautifully illuminated at their points. In a word, they are all so disposed, as that a certain number of them receive the light from whatever point it may issue, and transmit it to the immediate organ of sight, which we may reasonably suppose is placed underneath them. The cones are not all of the same length; those on the edges of the cornea are the longest, from whence they gradually diminish as they approach the center, where they are not above half the length of those on the edges. “The structure of the small eyes being less elaborate, their internal appearance, when placed in the microscope, will be described in a few words. They consist of an oval transparent horny plate, of an amber colour, in the center of which stands a single cone, through which and the oval plate the light passes.”[55] [55] See Mr. André’s paper with a plate, in the Phil. Trans. for 1782, page 440. OF THE EYES OF A SPIDER.