StoryImage( ‘/Images/Story//Auto-img-117753178313459.jpg’, ”, ‘Eyestalks Snails have eyes on the ends of retractable stalks. Eyesight in most snail species is poor, so they often rely on more highly developed senses of hearing, smell and taste. ‘);
StoryImage( ‘/Images/Story//Auto-img-117753169613168.jpg’, ”, ‘Pinhole eyes The eyes of the nautilus work just like adjustable pinhole cameras, without lenses.>’);
StoryImage( ‘/Images/Story//Auto-img-117753175220920.jpg’, ”, ‘Third eye Some animals have a parietal eye on top of their skulls. This eye doesnt see, but it can trigger hormone production (including reproductive hormones), and it helps in regulating body temperatures. Also, if a shadow passes over this eye, it often triggers a flight response in the animal.‘);
StoryImage( ‘/Images/Story//Auto-img-117753166919735.jpg’, ”, ‘Prehistoric eyes The trilobite, a sea crustacean living during the Paleozoic Era (600 to 250 million years ago) may have had the earliest complex vision. Oddly, its faceted compound eyes were filled with calcite crystals that served as lenses, sometimes even set in pairs to better bend and focus light.‘);
StoryImage( ‘/Images/Story//Auto-img-117753172713476.jpg’, ”, ‘Binocular vision Having a pair of eyes instead of just one eye allows us to judge object depth and distance with remarkable accuracy. Other advantages of two eyes: a wider field of view, having twice the power for viewing faint objects, and having a spare in case one eye is damaged. ‘);
StoryImage( ‘/Images/Story//Auto-img-117753184628103.jpg’, ”, ‘Blind, but light-sensitive Earthworms lack sight, but they have light receptors all over their bodies. You can test this yourself by using a flashlight to search for earthworms in your back yard at night. Move the light slowly across the grass. As soon as the ring of light reaches an earthworm, the creature will dive into the soil. ‘);
The sense of sight gives us a spatial understanding of our surroundingsthe ability to form a mental picture of our environment.
In nature, sight provides animals with two of the most important advantages in the game of survivala means of finding food, and a means of avoiding predators. Of course, sight offers many other advantages as well, for example, in locating mates or finding shelter.
The simple building blocks necessary for sight are actually found in most of the worlds living things, including plants. These are photoreceptive cells, which are capable of detecting, absorbing, and using light.
In plants, when light falls on photoreceptive cells, it might trigger such responses as bending the plants toward the light, or germination, or production of sugar (photosynthesis).
Without nervous systems, of course, plants dont have the ability to form any kind of mental pictures. In animals, photoreceptive cells are the basis of eyesight, and may also be found in photosensitive patches on their bodies.
Following are some facts about sight in nature:
from the April 25-May 2, 2007, issue