CHAPTER VIII 

 VENOM, ELECTRICITY, LIGHT, AND SOUND 



Poison glands in Selachians. In Bony Fishes: Cat-fishes, Weevers, Scorpion- 

 fishes, Toad-fishes. Effects of venom. Treatment. Fishes with poisonous 

 flesh. Electric organs: Torpedo, Electric Eel, Electric Cat-fish, Skates 

 and Rays, Mormyrids, Star-gazers. Origin of electric organs. Nature 

 of the discharge. Uses of electric organs. Luminous fishes. Photo- 

 phores. Other light organs. Production of light. Purpose of luminous 

 organs. Production of sound: by the air-bladder, by stridulation, 

 by elastic spring mechanism. Sound-producing fishes. 



As has been explained in an earlier chapter {cf. p. 68), the 

 spines arming the gill-covers, or those which support the fins, 

 may form usefiil weapons of offence or defence, and their 

 eflfectiveness may be further increased by the development of 

 poison glands in association with them. Such poison organs 

 are more common in fishes than was formerly supposed, but 

 they seem to be used almost entirely for defensive purposes, 

 instead of playing a part in securing food as in the snakes. 

 They are, for the most part, of rather simple structure, often 

 composed merely of strips or bunches of specialised cells, and 

 appear to owe their origin to the modification of certain 

 portions of the epidermal layer of the skin. 



Among the Selachians poison organs are found in the Spiny 

 Dog-fishes (Squalus), Bull-headed Sharks (Heterodontus) , Sting 

 Rays (Trygonidae) , Eagle Rays {Myliobatidae) and Chimaeras 

 [Holocephali) . Until quite recent years the presence of definite 

 glands was denied by many, and the acute inflammation 

 resulting from a wound caused by the tail-spine of a Sting Ray 

 was believed to be due merely to the action of the mucous 

 covering the spine on the lacerated flesh. Pliny alone among 

 classical writers seems to have suspected the presence of venom 

 in this fish. "Nothing is more terrible," he writes, "than the 

 sting that arms the tail of Trygon (the Sting Ray of the Medi- 

 terranean), called Pastinaca by the Latins, which is five inches 

 long. When driven into the root of a tree it causes it to 

 wither. It can pierce armour like an arrow, it is as strong as 

 iron, yet possesses venomous properties." It has now been 

 shown that in the groove running along either edge of the 



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