150 



A HISTORY OF FISHES 



which manufacture a kiminous slime, to elaborate and powerful 

 structures with lens and reflector. Some fishes seem to have 

 the power of emitting Hght without possessing any definite 

 light organs, but, in some forms at least, this is due to the 

 presence of luminous bacteria in the tissues of the fish, or to the 

 luminous properties of the slime exuded from the skin. A species 

 of Smooth-head [Leptoderma) captured in the Bay of Bengal has 

 been described as having the skin covered all over with a thick, 

 opalescent, and uniformly luminous epidermis, and was said 

 to ghmmer hke a ghost as it lay dead at the bottom of a pail 

 of sea- water. The Bummalow (Harpodon), the Myctophoid fish 

 of the Indian Ocean, which in a dried and salted condition 



Fig. 63. — LUMINOUS ORGANS. 



A. Lantern-fish (Diaphus metopoclampus),Xi \ b. Ipnops murrayi,x\\ c. 

 Anomalops katopron, X |. (In the upper figure the luminous organ is retracted and 



therefore invisible.) 



forms the well-known "Bombay Duck," is brilHantly phos- 

 phorescent all over when freshly caught, but there are no special 

 light-producing organs (Fig. 62B). 



Certain sharks, most of them inhabitants of deep water and 

 belonging to the family (Squalidae) which includes our own 

 Spiny Dog-fish, have the power of emitting light. This has 

 been described as a vivid and greenish phosphorescent gleam, 

 and has been shown to be due to the presence of numerous 

 tiny light organs of very simple structure scattered over the 

 skin. The Spinax of the Atlantic and Mediterranean, known 

 to fishermen as "Darkie Charhe," has been kept aHve in the 

 Naples aquarium and the production of light carefully observed. 

 Another form found near Ceylon was placed on the deck of a 



