VENOM, ELECTRICITY, LIGHT, AND SOUND 155 



"bark" of the Conger Eel, may perhaps be ascribed to this 

 cause. The characteristic breathing or murmuring sounds 

 made by the members of the Carp family {Cyprinidae) may be 

 similarly accounted for, but the noises of a like nature made by 

 the Loaches (Cobitidae) are said to be due to the rapid expulsion 

 of air-bubbles through the anus. 



In a number of fishes characteristic sounds are made by 

 stridulation; that is to say, by the rubbing or friction of one 

 surface against another. For example, the Horse Mackerel 

 (Trachurus), the Sun-fish {Mola), and certain species of Trigger- 

 fishes (Balistes) produce harsh noises by grating together the 

 upper and lower pharyngeal teeth. The Bull-head {Cottus) 

 uses a portion of the gill-cover for stridulation; the Flying 

 Gurnard (Bactylopterus) the hyomandibular bone; the Trigger- 

 fish {Balistes), ¥i\e-fish {Monacanthus), Bodtr-fish. {Capros), Surgeon- 

 fish {Acanthurus), Stickleback (Gasterosteus) , and some of the 

 Cat-fishes (Siluroidea), the spines of the dorsal, anal, pectoral or 

 pelvic fins. 



In the "Drumming" Trigger-fish {Balistes aculeatus) of 

 Mauritius the noise is said to be due to the friction of certain of 

 the bones of the arch supporting the pectoral fin against one 

 another, and since these are more or less intimately associated 

 with the air-bladder, the latter acts as a sort of amplifier 

 and intensifies the sound vibrations. Professor Cunningham, 

 who has made a special study of a species of Trigger-fish 

 {B. buniva) abundant at Ascension Island, describes the pro- 

 duction of sound as follows. "Just behind the pectoral fin is 

 an area of skin resembUng a drum, a portion of the air-bladder 

 being immediately beneath it. . . . When the drumming 

 sound was produced the pectoral fin was moved rapidly to and 

 fro and the membrane of the drum could be seen to vibrate. 

 It certainly seemed as though the sound was due to the vibra- 

 tions of the drum itself, and as though these vibrations were 

 due to the striking of the drum by the fin, but it was impossible 

 to decide whether the friction of the internal bones of the 

 pectoral girdle was necessary to produce the sound. . . ." 

 Mention may be made of an Indian Cat-fish {Callomystax) which 

 possesses a most elaborate stridulating organ involving the 

 vertebral column and the dorsal fin. The sounds are produced 

 by the scraping of the first interspinous (radial) bone of the 

 dorsal fin between two thin ridged plates representing the 

 hinder portion of a bony ridge formed by the fusion of the spmes 

 of the fourth and fifth vertebrae. When the fish flexes its body 



