84 THE SENSES OF ANIMALS 



with a very high degree of accuracy. This mobility, com- 

 bined with the extreme sensitivity of the structure of the 

 inner ear, is used for many purposes : to alert the mammal 

 to danger ; to find its way about, as in the bats ; and to aid 

 in the capture of prey, as in the bush-babies. 



In order to appreciate the use of the external ear, observa- 

 tions of a very simple kind may be carried out just by visiting 

 a good zoo and noting carefully the variations in the size 

 and shape of the ears of the mammals to be seen. It does 

 not necessarily follow that because an elephant has huge 

 ear-flaps it is able to hear any better than — say — a harvest 

 mouse; but the elephant requires to hear sounds over 

 much greater distances than a mouse of any kind which 

 is largely concerned with sounds comparatively close at 

 hand. 



Nearer to home, the way in which our own dogs and cats 

 twitch or cock their ears shows very well how much these 

 organs are used in daily life. A dog can recognize the sound 

 of its owner's motor car even when another car of similar 

 make is also moving in the vicinity. It can also separate out 

 the footsteps of each member of the household and will react 

 differently towards one member or another. Similarly, a dog 

 which will respond to its owner's footsteps with a welcoming 

 bark will stiffen its tail if the footsteps of a stranger can 

 also be heard at the same time. 



Try a small experiment for yourselves. Make sure your 

 dog knows that you have left the house, having first shut it 

 up in a room where it cannot see your eventual return, but 

 where you can hear it when it barks. After a while, start 

 walking up your path or drive with your normal pace and 

 gait. The dog will almost certainly give its welcoming bark. 

 Stop still for a moment and then continue your progress 

 but alter your step — perhaps shuffling your feet. The dog's 

 tone will change at once. This will demonstrate how very 

 acute and discriminating a dog's hearing is. 



A cat's ears are peculiarly sensitive, and have most delicate 

 adaptations of the inner ear. There is no doubt that a 

 domestic cat uses its ears to aid in hunting, whether the prey 

 be a young bird in undergrowth or a mouse or vole in 

 amongst thick vegetation. Good nocturnal vision is, of 



