552 SCHEVILL, BACKUS, AND HERSEY [CHAP. 14 



sounds ascribable to cetaceans are splashings at the surface (of course some of 

 these must be classed as purposeful, like "lobtailing" — whacking the surface 

 with the flukes from above). The vocal sounds are ordinarily louder. 



6. Sound-Producing Mechanisms 



A. Fishes 



Considerable attention has been paid to the sound-producing mechanisms of 

 fishes and crustaceans, but relatively little is known about them in whales and 

 porpoises. The mechanisms in fishes are generally of one of two sorts, or a 

 combination of the two. The loudest sounds originate with the swim-bladder, 

 which is made to resonate, the process being somewhat analogous to drum- 

 beating. This is commonly accomplished by the contraction of special "drum- 

 ming" muscles which are applied to the surfaces of the swim-bladder as in 

 Prionotus and Opsanus as well as in some sciaenids, zeids, macrourids and 

 many others (Jones and Marshall, 1953). In still others the musculature 

 causing the resonance of the swim-bladder is not highly specialized, but 

 simply the normal axial musculature in a most intimate contact with the swim- 

 bladder. In the trigger-fishes, Batistes and Metichthys, the body-wall under the 

 pectoral is exceedingly thin and the swim-bladder is beaten directly by rapid 

 vibrations of the fin (Moulton, 1958). In some fishes the interior of the swim- 

 bladder is intricately partitioned in a way as to suggest that it is an adaptation 

 to sound-production, as in Prionotus carolinus (Fish, 1954). 



The second sort consists of mechanisms producing stridulatory sounds by 

 the rubbing of one hard part against another. In most cases stridulatory 

 sounds are made by rubbing the teeth together. The teeth may or may not 

 have obvious specializations for sound production. In the filefish, Monocanthus 

 hispidus, the teeth are so modified, the upper median incisors are ridged ; 

 sound is also produced by the rapid elevation and lowering of the first dorsal 

 spine, which grates against its articulating surface (Burkenroad, 1931). In 

 other fishes, elements of the pectoral girdle may be rubbed against one another. 

 In still others, parts of the vertebral column are used in such a way. In some 

 cases stridulatory sounds are amplified by the resonant swim-bladder, as in 

 the Haemulidae or, as they are sometimes known, grunts (Burkenroad, 1930), 

 in which the anterior end of the swim-bladder lies against the pharyngeal 

 teeth — the primary sound-producers in this case. Other modes of sound produc- 

 tion in fishes may be discovered. In the goby, Bathygobius soporator, and the 

 blenny, Chasmodes bosquianus, the exact manner of sound generation remains 

 unknown, but the observed faint sounds appear to result from the spasmodic 

 escape of water out of the gill openings (Tavolga, 1958, 1958a). 



B. Crustaceans 



In marine crustaceans, sounds are made by stridulation or, in some cases, by 

 rapping one hard part against another. In the langoustes, Palinurus vulgaris 

 and Panulirus argus, a very elaborate stridulatory mechanism has evolved 



