SOUNDS PRODUCED BY FISH. 
157 
will be obtained by cuttiDg the fish through transversely. The ner- 
vous cord is seen to lie above the vertebral column, the nervous canal 
being formed by the interarching spinous process. Below the ^«rte- 
bral column is the large cavity containing the 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 (Fig. 
201, Sy S^)y though different kinds of noises are made acci- 
dentally or involuntarily by the lips or the bones of the 
mouth, as in the 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 bleak; oe, 
CBSophag:us; Z, air-passage of the 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 forcing the air from 
the swimming-bladder into the oesophagus. In the sea- 
horse, the sounds are caused by the vibrations of certain 
small voluntary muscles. 
The mud sun-fish {AcanfliarcTius pomotis) utters a deep 
grunting sound; the gizzard shad {Dorosoma cepediannm, 
Fig. 202) makes ^^an audible whirring sound;" the chub- 
sucker or mullet {Enmyzon oilo7igic7n) utters a single 
prolonged note accompanied by a discharge of air-bubbles;" 
the cat-fish produces ^^a gentle humming sound;" eels 
