igO THE SENSES OF ANIMALS 



has any sound been heard in the wild from a whalebone 

 whale, and there was no evidence that this was being used 

 in echo-location. But when one remembers the necessity of 

 avoiding collision with the bottom and submerged objects 

 when travelling at high speed, or in great depths where it 

 is completely dark, or at night, the probability that the 

 whalebone whales, too, have a sonar system is high. Much 

 yet remains to be discovered, not only about whales, but 

 about other sea creatures; it has just been found that some 

 seals have a sonar system, and they also can earn their 

 livings in turbid water where no light can penetrate. 



A few years ago a "tame" dolphin appeared off one of 

 the New Zealand bathing beaches and fraternized with the 

 swimmers ; it even permitted small children to ride astride 

 its back. The legends of the ancients about the affection of 

 the dolphin for mankind may not have been without founda- 

 tion. Whales have no facial muscles and consequently they 

 are unable to alter their expression. In view of the intelli- 

 gence and playfulness revealed by the study of dolphins in 

 oceanaria one wonders if it is entirely fortuitous that the 

 dolphin's mouth is so curved that it appears to human eyes 

 to be set in a fixed and slightly mischievous grin. (See 

 Plate 15.) 



The skull of the whales difTers widely from the usual 

 pattern in mammals ; the relative sizes and positions of the 

 bones forming it are much modified, and in many species 

 they show a high degree of asymmetry. There is also a 

 complicated system of air spaces situated around the base 

 of the skull and connected through the Eustachian tube with 

 the mouth and lungs. The bones of the middle ear are much 

 modified in shape, as is also the membrane of the ear-drum. 

 All these structures are so unlike those in the other mammals 

 that zoologists formerly thought that the middle ear in these 

 animals could not function for the transmission of sounds, 

 and that whales and dolphins heard by bone conduction, that 

 is, that sound waves penetrated the body of the creatures 

 and set up vibrations in the bones of the skull from which 

 they were transmitted directly to the inner ear. Fraser and 

 Purves have recently made a detailed study of the hearing 

 sense of whales, and have shown that the bone-conduction 



