Popular Science Alonfhly 



359 



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. 



