THE PRODUCTION OF SOUNDS 225 



evidence points to the fact that whales and dolphins locate objects by a 

 method akin to asdic, at any rate unless and until experiments in which 

 hearing and sound production are excluded - and it has not yet been 

 possible to do this - prove the contrary. 



The fact that Cetacean orientation principally relies on echo-location 

 may explain why mass-strandings occur in some species (seepage 199). 

 Dudok van Heel has demonstrated that these strandings nearly always 

 occur on very slightly sloping or on muddy coasts. In both cases the echo 

 either comes from everywhere or there is no echo at all, which causes 

 complete lack of orientation. 



We must now ask how and where all these supersonic vibrations are 

 produced, particularly since, as we have seen in Chapter 4, Cetaceans lack 

 vocal chords. Actually, animals can produce sounds not only by means of 

 vocal chords but also by vibrating the air in other folds in the lining of their 

 larynx and throat. Various research workers, including F. C. Fraser, have 

 shown that noises are produced whenever air is pumped through the 

 larynx of a dolphin. Moreover, we have already seen that when air 

 escapes or is sucked in through the blowhole and the diverticula beneath 

 it, definite sounds are produced, and that air bubbles are released from 

 the blowhole even when the animal is submerged. While it is questionable 

 whether these bubbles are directly connected with the production of 

 sounds since, as we have seen, Mysticetes have no diverticula, the diverti- 

 cula of Odontocetes with their numerous folds could certainly act as 

 excellent vibrating membranes. Possibly the laryngeal diverticulum of 

 Mysticetes (see p. 147) may play a similar part, but this question awaits 

 further examination. In any case, we have seen that Cetaceans have a 

 wide enough range of organs to produce all the sounds we have discussed, 

 and that echo-locating is very likely to be an important reason why they 

 produce them. 



