Page:Popular Science Monthly Volume 92.djvu/375

 Popular Science Alonfhly

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��probability developed in zones of semi-darkness.

Glands Furnish Light

It makes no difference where these lamps may be found or on what part of the body they may be carried. All are evolved from glands. In its simplest form the gland is a sack, the walls of which give off a lumin- ous substance which is ignited when it comes in contact with the water. The action is there- fore chemical. On the other hand, some fish have an inclosed organ which is lighted up within the body. The construction of the organ is very complicated. First, there is a covering which prevents the light from entering the body. In front of this is a silvered or brightly colored re- flector which acts as a search- light, in that it tends to throw the light outward. Often there is a lens present to concentrate the light, thus making it seem much brighter. Besides all this, many fish have dimmers which can be used at will, so that they can prevent light from escaping outward.

They Look Like Moving Signs

In addition to the principal organ of light, many deep-sea fish have minor ones, often arranged symmetrically, forming many beautiful patterns which emit a

����This fish is decorated along its whole length with lamps, which flash and dim like an electric sign which bids for notice

��A fish with fish "lamps" beneath the eyes. These eyes are large and round, but apparently almost sightless

��varied colored light. The purpose of these is in all probability to distinguish one variety of fish from another and male from female. But the use of those organs of light which have reflectors, len- ses and dimmers, can only be conjectured. Some are, undoubtedly, real lanterns used to illuminate dark sur- roundings ; others, which are attached to the tip of a long, movable stem, and carried not at all unlike an electric bulb, may be used as decoys to lure in unwary prey; other organs again are of a protective nature, lighting up when the fish is attacked. All these organs emit a per- fectly cold light — some- thing that man has not yet invented.

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