SKOT. 4] SOUND PKOnUCTION BY MARINE ANIMAI.S 553 



(Dijkgraaf, 195;"); Moultoii, 1957). This includes a ridged membrane on the 

 basal portion of the antenna and a toothed surface on the shell of the head near 

 the base of the antenna. There are mechanisms for engaging and keeping 

 engaged the two rough surfaces as the antenna is raised. In the so-called 

 snajDping shrimps (family Alpheidae), which are famous as noise makers, the 

 sound is produced as the movable "finger" of the enlarged "claw" is brought 

 down agahist the immovable "thumb" (Johnson, Everest and Young, 1947). 

 This apparently simple arrangement is actually quite elaborate. The "finger" 

 is fitted with a knob which fits into a groove on the "thumb". The base of the 

 "finger" is provided with a small suction cup, which, when the "finger" is 

 raised, meets another suction cup on an immovable portion of the "claw". 

 Considerable muscular force is required to break this connection, so that 

 the mechanism is, in effect, spring-loaded. 



C. Cetaceans 



Fishermen and some other seamen from remotest antiquity have been 

 aware that the smaller cetaceans produced audible sounds. With the develop- 

 ment of civilization this awareness has faded, until in 19th-century Europe 

 most zoologists confidently called the cetaceans mute, discounting sailors' tales 

 of squealing porpoises on the insufficient grounds that the animals lack vocal 

 cords. This is an anatomical fact, yet sounds may be produced in the larynx, 

 as has been repeatedly demonstrated, not merely by the animals themselves, 

 but also by men pumping air through dead cetacean larynges [two such recent 

 experiments were by Eraser and Purves {in litt., 1953) and Schevill and Law- 

 rence (MS., 1949), in all cases on small delphinids]. 



The cetacean larynx has been described rejDeatedly (e.g. Murie, 1870, 

 1873; Turner, 1872; Boenninghaus, 1902; Hosokawa, 1950; Kleinenberg and 

 Yablokov, 1958; etc.). The considerable difference between mysticetes (baleen 

 whales) and odontocetes (toothed whales) is refiected here. It will suffice for 

 our purposes to point out that, although vocal cords as such are lacking, there 

 are projections and thin membranous parts in the laryngeal cartilages which 

 may be made to vibrate as air is passed through the larynx. (The sounds 

 resulting from the artificial excitation do not duplicate the animal's vocaliza- 

 tions, but are still not entirely unlike some elements of the natural phonation.) 



To confine ourselves for the moment to the odontocetes, we are concerned 

 with two basic sounds, a whistle-like squeal of limited frequency range and an 

 impulsive click of broad (almost "white") frequency range. The squeal is what 

 is usually heard as air-borne sound in non-instrumental listening. A number of 

 biologists (e.g. Matthews, 1950) have supposed that all or some of the cetacean 

 sounds are formed at the nasal orifice (blowhole), presumably because one often 

 sees a stream of bubbles issuing therefrom. Our experience has been that a 

 squeal always accompanies the bubbles, although the converse is not true. 

 Since the squeal is the most intense of the two types of sound, it has seemed to 

 us that it requires the passage of more air through the sound source than does a 



