SOUI^BS PBOBVCED BY FISH. 



157 



will be obtained by cutting the fish through transversely. The ner- 

 vous cord is seen to lie above tlie vertebral column, the nervous canal 

 being formed by the interarcbing spinous process. Below the ''<;rte- 

 bral column is the large cavity containing tlie heart, stomach, 3tc., 

 while the rest of the section is occupied by muscles. (C. S. Minot.) 



The noises produced by certain fishes are due to the 

 action of the pneumatic duct and swimming-bladder (Pig. 

 301, S, 8'), though different kinds of noises are made acci- 

 dentally or involuntarily by the lips or the bones of the 

 mouth, as in tlie tench, carp, and a large number of other 

 fishes. Over fifty species of fish are known to produce 

 sounds of some sort. The swimming-bladders of Trigla and 





Fig. 201. — Swimming bladder {S, anterior, S', posterior division) of the blealc; ce, 

 oesophagus; Z, air-passage of tile air-bladder leading into the oesophagus. 

 From Semper, 



Zeus have a diaphragm and muscles for opening and clos- 

 ing it, by which a murmuring sound is made. The loudest 

 sounds are made by the drum-fish. In some minnows, 

 pouts, and eels the sound is made by foi'cing tlie air from 

 tlie swimming-bladder into the resophagus. In the sea- 

 horse, the sounds are caused by the vibrations of certain 

 small voluntary muscles. 



The mud sun-fish {Acantharchus poviotis) utters a deep 

 grunting sound; the gizzard shad (Dorosoma cepedianum, 

 Fig. 202) makes "an audible whirring sound;" the chub- 

 sucker or mullet {Erwiyzon oUongum) "utters a single 

 prolonged note accompanied by a discharge of air-bubbles;" 

 the cat-fish produces "a gentle humming sound;" eels 



