THE SPECIAL SENSES 



235 



or gnats, undoubtedly hear by means of numerous delicate 



hairs borne on the antennae. The male mosquitoes (Fig. 



149) have many hundreds of these long, fine antennal hairs, 



and on the sounding of a tuning-fork these hairs have been 



observed to vibrate strongly. In the base of each antenna 



there is a most elaborate organ, 



composed of fine chitinous 



rods, and accompanying nerves 



and nerve cells whose function 



it is to take up and transmit 



through the auditory nerve to 



the brain the stimuli received 



from the external auditory 



hairs. 



123. Sound-making. The 

 sense of hearing enables ani- 

 mals not only to hear the 

 warning natural sounds of 

 storms and falling trees and 

 plunging avalanches, but the 

 sounds made by each other. 

 Sound-making among animals 

 serves to aid in frightening 

 away enemies or in warning 

 companions of their approach, 

 for recognition among mates 



and members of a band or species, for the attracting and 

 wooing of mates, and for the interchange of information. 

 With the cries and roars of mammals, the songs of birds, 

 and the shrilling and calling of insects all of us are familiar. 

 These are all sounds that can be heard by the human ear. 

 But that there are many sounds made by animals that 

 we can not hear that is, that are of too high a pitch for 

 our hearing organs to be stimulated by is believed by nat- 

 uralists. Especially is this almost certainly true in the case 

 of the insects. The peculiar sound-producing organs of 



FIG. 149. A male mosquito, showing 

 auditory hairs (a. h.) on the an- 

 tennae. 



