LIVING LIGHTS 



Wide Occurrence of Luminescence 



A noteworthy fact in regard to luminescence is its 

 wide distribution in the sea. When the oars drip 

 sparks on a summer night we see the luminescence 

 of Noctiluca ; and there are many open -water 

 animals some Radiolarians, some Medusae, most 

 Ctenophores, some " worms," many crustaceans, 

 a few molluscs, Tunicates like the splendid Pyro- 

 soma, and various surface fishes which are lumines- 

 cent. In the shore area there are luminescent 

 Echinoderms, especially Brittle-stars ; the boring 

 Pholads with their miners' lamps ; and various 

 members of the alliance of Stinging Animals. In 

 the great abysses luminescence is common, e.g. 

 among Alcyonarians, Medusae, Echinoderms, Crus- 

 taceans, Cuttle-fishes, and true fishes. On land 

 we know it best in glow-worms, fire-flies, and other 

 insects, but it also occurs in some Myriopods (e.g. 

 Geophilus electricus), and in some earthworms 

 (e.g. Photodrilus). It is usually said to be quite 

 absent in freshwater animals, but we have some 

 suspicions as to the accuracy of this generalization, 

 bearing in mind a freshwater relative of the 

 glow-worm and allegations of luminescence in 

 the larvae of some Harlequin flies. That there 

 are phosphorescent Bacteria is well known every 

 one can see them on fish hung up to dry and it is 

 probable that reports of luminous birds are due to 

 luminescent fungi on the plumage. 



In a case like the luminescence of Bacteria, no one 

 even looks for any utility. The luminescence is a 



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