. Comparative animal physiology. Physiology, Comparative; Physiology, Comparative. Photoreception 403 land and are seen through the window. A variety of devices in deep-sea fishes tend to increase visibility at low intensities. Some of these are relatively larger eyes, relatively larger lenses and pupils, a greater concentration of rods, tubular eyes which sacrifice peripheral vision for a more effective central vision, and various patterns of bioluminescence to illuminate the objects to be seen. Aerial Vision. The dioptric differences between eyes adapted to vision in air and in water are pro
. Comparative animal physiology. Physiology, Comparative; Physiology, Comparative. Photoreception 403 land and are seen through the window. A variety of devices in deep-sea fishes tend to increase visibility at low intensities. Some of these are relatively larger eyes, relatively larger lenses and pupils, a greater concentration of rods, tubular eyes which sacrifice peripheral vision for a more effective central vision, and various patterns of bioluminescence to illuminate the objects to be seen. Aerial Vision. The dioptric differences between eyes adapted to vision in air and in water are pronounced and are discussed above. Another group of differences include those pertaining to protection of the cornea, especially from drying. In man and many other animals this is accomplished by blink-. Fig. 113. Diagram showing the upward visual field of a fish, a, The aerial window as seen from below; h, explanation of the aerial window, assuming calm water. Light rays striking the water surface within the window are refracted, while those striking outside the window are reflected. From Walls.^*' ing. In birds and many mammals, however, there is an additional structure, the nictitating membrane, which probably covers the cornea most of the time during flight and prevents drying by the rapid air stream to which the eye is exposed. Air- and Water-Vision. Animals which live in both air and water must have an exceptional range of accommodation in order to see v\'ell in both media. A fish, when placed in air, is automatically subject to myopia, and any air-living vertebrate, when under water, to hypermetropia. Aimhleps, the so-called "four-eyed fish," has two pupils for each eye, and two retinas, one. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Prosser, C. Ladd (Clifford Ladd), 1907-; Bishop, David
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