24 THE BOOK OF NATURE STUDY 



The Senses. The sense of touch is situated in the skin of the 

 body generally, but is especially acute in the lips, the end of the 

 snout, and the extremities of the limbs. In many animals it is 

 further assisted by long, stiff hairs arranged around the mouth, 

 as in the so-called " whiskers " or " vibrissae " of the cat. 



While in most mammals the sense of sight is well developed, 

 there are many species which are almost blind ; the bat and the 

 mole, for example, having eyes so small as to require careful search 

 for their discovery. 



Similarly, the sense of smell is possessed by all the Mammalia, 

 except perhaps the toothed whales. In some beasts it is 

 extremely well developed. Dogs, for example, have so acute a 

 power of scent that they can trace odours quite unappreciable 

 to the human nose. Most of the hoofed animals, too, have a keen 

 sense of smell. This sense is of great importance, for thereby 

 many animals have to depend thereon to find their prey or to avoid 

 their enemies. 



Hearing is generally well developed among mammals. As an 

 aid thereto many have developed very large external ears, which 

 are capable of being turned in various directions to catch the 

 sounds, as in the ass and horse. In the antelopes the ears are 

 sometimes of great length, but the African elephant holds one of 

 the highest places in this matter, since the ears in some races may 

 attain a length of as much as six feet. But the animal with the 

 longest ears, relatively to its size, is the little long-eared bat of our 

 country-side, for herein this most useful sound conductor is longer 

 than the whole body ! (see p. 45). 



Those species which live entirely in the water, such as seals and 

 whales, and the mole among the land-dwellers, have no external 

 ears whatever ; and probably for the following reasons. To the 

 mole external ears would be much in the way, for it spends nearly its 

 whole life in underground burrows ; while to sea-dwellers, like seals 

 and whales, projecting ears would be of little or no value ; on the 

 contrary, they would be rather in the way during rapid movement 

 through the water. Such sound as it may be necessary for these 

 creatures to perceive is conveyed through a very small tube 

 leading from the surface of the head to the organ of hearing within 

 the skull (Fig. 14, p. 49). 



