. Biology of the vertebrates : a comparative study of man and his animal allies. Vertebrates; Vertebrates -- Anatomy; Anatomy, Comparative. Ports of Entry 813 7,000,000 cones and 100,000,000 or more rods, all packed closely together like matches in a box, each one registering a single point of reflection from outside illumination. In the human eye, rods and cones differ more in size than in shape, yet their names are still descriptive of their form. First position +. o â¢' / â 1 1 ; / / Second position + >A ,' i 1. ' Third position + I'q. Fig. 712. The blind spot of the eye. Hold the black
. Biology of the vertebrates : a comparative study of man and his animal allies. Vertebrates; Vertebrates -- Anatomy; Anatomy, Comparative. Ports of Entry 813 7,000,000 cones and 100,000,000 or more rods, all packed closely together like matches in a box, each one registering a single point of reflection from outside illumination. In the human eye, rods and cones differ more in size than in shape, yet their names are still descriptive of their form. First position +. o â¢' / â 1 1 ; / / Second position + >A ,' i 1. ' Third position + I'q. Fig. 712. The blind spot of the eye. Hold the black figure straight in front of the eyes about a foot distant. Close the left eye and look at the white cross. You will see the round white spot also. This corre- sponds to the first position in the diagram. Now gradually move the page toward your eye. When you reach the second position the round spot will disappear, because the rays of light from it now fall upon the place where the optic nerve enters the eyeball and not upon the rods and cones of the retina. If the page is moved still nearer, the round spot will reappear, because light reflected from it now strikes the retina on the other side of the optic nerve, as shown by position 3. Vision is dependent upon photosensitive pigments found in the outer segments of rods and cones. The existence of such a substance, called visual purple or rhodopsin, has been known since 1876. It is abundant in rods and was at one time thought to occur in small quantities in cones. It is now believed that cones have a somewhat different pigment, visual violet or. 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 Walter, Herbert Eugene, b. 1867; Sayles, Leonard Perkins, 1902-. New York : Macmillan Co.
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Keywords: ., bookcentury1900, booksubjectanatomycomparative, booksubjectverte
