264 Voice of Animals [THIRD WEEK 



number of sounds by gritting the teeth, and when the 

 male fish is attempting to charm the female by dashing 

 round her, spreading his fins to display his brilliant 

 colours, this gritting of the teeth holds a prominent place 

 in the performance, although whether the fair finny one 

 makes her choice because she prefers a high-toned grit 

 instead of a lower one can only be imagined! But vibra- 

 tions, whether of sound or of water pressure, are easily 

 carried near the surface, and fishes are provided with 

 organs to receive and record them. One class of such 

 organs has little in common with ears, as we speak of 

 them; they are merely points on the head and body 

 which are susceptible to the watery vibrations. These 

 points are minute cavities, surrounded with tiny cilia or 

 hairs, which connect with the ends of the nerves. 



The ears of the frogs and all higher animals are, like 

 the tongue-bone and the lower jaw, derived originally from 

 portions of gills, which the aquatic ancestors of living 

 animals used to draw the oxygen from the water. This is 

 one of the most wonderful and interesting changes which 

 the study of evolution has unfolded to our knowledge. 



The disproportionate voices are produced by means of 

 an extra amount of skin on the throat, which is distensible 

 and acts as a drum to increase the volume of sound. In 

 certain bullfrogs which grow to be as large as the head of 

 a man, the bellowing power is deafening and is audible 

 for miles. In Chile a small species of frog, measuring only 

 about an inch in length, has two internal vocal sacs which 

 are put to a unique use. Where these frogs live, water is 

 very scarce and the polywogs have no chance to live and 



