Science: Face of the Future

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Frogs, toads and other amphibians have tears. Many amphibians "have fair color vision, but . . . their sight is in general poor."

Most snakes "see hardly anything except objects in motion. Most snakes are nearly deaf too, so that their knowledge of the outer world reaches them largely by way of the little forked tongue, which is probably the most wonderful tactile organ in existence."

Birds' eyes "are the finest and most remarkable of all the eyes on earth, being often both telescopic and microscopic. . . . Visual acuity is almost incredible, being in some instances 100 times as great as that in men. . . . Birds do not see blues and violets at all. This helps in their distance vision because the haze which hangs about distant objects and which, for our eyes, renders them more or less invisible, for birds does not exist. Birds, on the other hand, see infra-red radiations which, for us, affect only the temperature sense of the skin and not the retinas at all. . . .

"Nearly all birds have eyes on the sides of the head. Such birds, of course, can have no binocular vision. Many nevertheless possess stereoscopic vision which they get by virtue of the fact that they have two maculae ... in each eye. This gives in the one eye the two pictures from two different angles which constitutes the sine qua non for stereoscopic vision."

Primates (monkeys, apes, men) are the only creatures who have both binocular and stereoscopic vision. "Only in man, of all the mammals, does there seem to be continuous easily kept, binocular and stereoscopic vision. Even in the human child, however, the eyes do not as a rule move in perfect unison with each other till about three months after birth, because stereoscopic vision, in the history of life on this planet, is an extremely recent appearance. The same fact explains the ready loss-of-binocularity (cross-eyes) in many persons as the result of optical errors (eye-strain). ... I should add that the eye-grounds of all monkeys and apes are almost exactly the same as those of the black race of mankind."

Few animals other than primates have their eyes in the front of their faces (the young human fetus also has its eyes at the sides of its head). Because their visual fields do not overlap, they do not have binocular vision. The visual fields of hares and rabbits overlap behind their narrow heads, an essential for such hunted creatures. But they do not have stereoscopic vision. Their brains are insufficiently developed for that refinement.

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