432 



ORGAN SYSTEMS OF MAN 



Fig. 16-28. This is a comb-jelly {Mnemiopsis leidyi) found along Cape Cod. The combs are luminescent and this 



photo was taken using their own light. 



that reason it is a highly efficient Hght. It 

 has been said that if man could learn how to 

 produce light as efficiently, a small boy could 

 turn a generator that would light a moder- 

 ately-sized city. Most of the energy in an 

 electric light or any other kind of light is 

 lost in the production of heat. 



It is interesting to note how widespread 

 among living things is the ability to pro- 

 duce light (Fig. 16-28). Indeed luminous 

 species occur in all the major phyla, ex- 

 cept the Platyhelminthes and the Nema- 

 thelminthes. The sea is teeming with lumi- 

 nescent bacteria, Protozoa, and a large 

 variety of Metazoa. Luminous bacteria may 

 cause a carcass or rotting log to glow in 

 the forest on a dark night. They and other 

 organisms may cause a brilliant display of 

 light in the wake of a ship on the ocean at 

 certain times of the year. The intermittent 

 light of the common firefly has inspired the 

 artistically inclined to describe it in verse 



and music. Deep sea forms as well as other 

 animals are endowed with luminescent or- 

 gans which provide light in an otherwise 

 eternally dark world. 



Luminescent bacteria usually glow con- 

 tinuously as long as they have sufficient 

 oxygen, whereas the firefly flashes its light 

 intermittently from an especially designed 

 organ. Luminescence depends on the pres- 

 ence of two substances, luciferase, an 

 oxidative enzyme, and luciferin, an organic 

 substance present in specific luminescent 

 organs. If these two substances are ex- 

 tracted from the animal and mixed in a test 

 tube in the presence of free oxygen, lumi- 

 nescence occurs. Stimulation of the lumi- 

 nescent organs is apparently under the 

 control of the animal that possesses it, at 

 least in some instances. For example, the 

 male firefly flashes its light during the mat- 

 ing season, a fact which may have some- 

 thing to do widi attracting the female. 



