VENOM, ELECTRICITY, LIGHT, AND SOUND 141 



serrated spine (Fig. 36e) is a tract of tissue, glistening white in 

 colour, which may be difficult to detect unless cross-sections 

 of the 'spine be prepared and examined under the microscope. 

 Similar tissue has been found associated with the dorsal fin- 

 spines of the Spiny Dog-fishes (Fig. 6oa), Bull-headed Sharks 

 (Fig. 52B), and Chimaeras (Fig. 80), and the cells of which it 

 is composed secrete a virulent venom capable of causing painful 

 or even dangerous wounds. 



Among the Bony Fishes poison glands of a rather more 

 elaborate structure occur in a number of forms, of which the 

 Cat-fishes, Weevers, Scorpion-fishes, and Toad-fishes may be 





Fig. 58. — POISONOUS FISHES. 



A a'. Greater Weever {Trachinus draco),'X\; B. Poison-fish {Synanceia verrn- 

 ' cosa), X I. 



specially mentioned. Certain Cat-fishes of the rivers of North 

 America known locally as Stone-cats or Mad-toms {Noturus, 

 Schilbeodes), have the outer rays of each pectoral fin modified to 

 form a stout, flat spine, generally serrated along one or both ot 

 its edges, and capable of inflicting nasty jagged wounds. ^ At 

 the base of each spine is a sac with a more or less wide opening, 

 and this is beheved to contain fluid of a venomous nature, 

 which is poured out when the spine is brought into action. 



In the Weevers [Trachinus), of which two species occur on our 

 own coasts, the glands are associated with the long, sharp spine 

 with which each gill-cover is armed, as well as with the five or 

 six spines supportingthe first dorsal fin (Fig. 58A) . The opercular 

 spine is ensheathed by an extension of the skin, only its tip 



