Science / Medicine : New Way of Seeing Discovered in Spiders

Crabs and spiders use a method of seeing unlike any of the eight ways previously identified in animals, and researchers believe that complex process may help answer questions concerning the evolution of the eye.

Scientist D. E. Nilsson of Lund University in Sweden discovered the ninth way of seeing after studying the eyes of arthropods such as crabs, insects and spiders. He said the principal difference between the arthropod visual system and that of other animals is the manner in which it handles light.

“Imaging is accomplished by a remarkable combination of ordinary lenses, cylindrical lenses, parabolic mirrors and light-guides,” he said, adding that the lens-mirror combination is equivalent to the lens structure in a classical telescope. Furthermore, the compound eyes of arthropods are made up of hundreds of separate units that construct an image much like a television picture made of dots.

The arthropod visual system does not experience the world much differently than humans, he said, but the resolution is much worse.

Nilsson said the new optical system will help scientists determine the evolution of the eye, from the more complicated visual systems to the single-lens method of seeing, which humans have.