LUMINESCENCE IN THE SEA 225 



makes Pyrosoma one of the most brilliantly luminescent 

 animals of tropical seas. 



As in Pennatula and many other cases, any stimulation 

 serves to excite luminescence in Pyrosoma, and Moseley, 

 in his Notes of a Naturalist, states that, when the " Chal- 

 lenger " expedition captured a specimen over 4 feet in 

 length, " I wrote my name with my finger on the surface 

 of the giant Pyrosoma as it lay on deck in a tub at night, 

 and my name came out in a few seconds in letters of 

 fire." 



Fishes. — Deep-sea luminous fishes have been weU known 

 since the time of the " Challenger " expedition. A few of 

 the more notable forms belong to the genera Scopelus, 

 Chauliodus, Astronesthes, and Photostomias. The Ught-organs 

 may be in various positions on the head, on the gill-covers, 

 along the sides of the body, or on the ventral surface. 

 Ipnops murrayi has two very large photogenous organs 

 occupying most of the flattened upper surface of the head. 

 Melanocetus johnsoni has the light on the extremity of a 

 long flexible process from the top of the head, so as to form 

 a lure which may attract prey to the wide-open, formidable 

 mouth below. There is also much variety in the structures. 

 The essential glandular parts of the organs are probably 

 in all cases enlargements and differentiations of the mucous 

 glands of the skin, and the reflectors and other accessory 

 layers are developed from the surrounding integumentary 

 tissues. All these Hght-producing organs of fishes are well 

 supplied with nerves. 



It is possible that luminescence in deep-sea fishes may 

 serve a number of useful purposes, such as general illumina- 

 tion of the surrounding water, the attraction of prey, pro- 

 tection and warning, and it has even been suggested that 

 the specific arrangement of the lights facflitates recognition 

 by other members of the same species, Hke colour-schemes 

 in terrestrial animals. Murray and Hjort have shown that 

 many of the tropical luminous fishes do not come from the 



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