194 THE SEAS 



crustaceans and squids. They may occur on almost any 

 part of the animal, and are often arranged in rows along the 

 sides of the body (see Plate 72) though they are frequently 

 found in the head region, as in the case of the deep-sea 

 anglers with their waving lamps for the attraction, possibly, 

 of prey. One very remarkable fish has no eyes but instead 

 a large light organ under the frontal bones within the 

 skull. 



The reason for the production of light in these different 

 marine animals is in most cases a complete mystery. We 

 can only hazard a guess as to what part it plays in the life 

 of the animal. Thus it is difficult to see what use lumines- 

 cence can be to bacteria, Noctiluca, jellyfish, or the Sea 

 Pens, it is probably merely a by-product of the normal 

 activities of these creatures. The case of the concealed 

 animals, such as the Piddock or the Tube-worm, Chce- 

 topteriis, presents almost equal difficulties though it may 

 be that the light serves to attract to their burrows the tiny 

 animals on which they feed. In other cases the light may 

 help members of the same species to recognize one another 

 or assist the females in attracting the males during the 

 mating season. It appears that luminous secretion may 

 be discharged into the water to distract a pursuing enemy, 

 while in other cases the sudden flashing of light from the 

 more complicated light organs may perhaps protect the 

 animals by giving warning that it is harmful or distaste- 

 ful as food, in much the same way as the brilliant colours 

 of some terrestrial animals are said to afford warning of 

 the unpleasantness of their owners. Of course it is possible 

 that there is truth in the old belief that the light organs 

 of the deep-sea animals which look so much like little 

 lanterns are actually used for the same purpose and help 

 them in their search for food. But we can be certain of 

 nothing and the production of animal light is, and seems 



