72 



THE ANIMALS AND MAN 



the antennae or feelers (fig. 29), a single pair of which is borne 

 on the head of every insect. That many insects have an 

 amazingly keen sense of smell has been shown by numerous 

 experiments, and is constantly proved by well-known habits. 

 Hearing is the perception of cer- 

 tain vibrations of bodies. These vi- 

 brations give rise to waves — sound- 

 waves as they are called — which 

 proceed from the vibrating body in 

 all directions, and which, coming to 

 an animal, stimulate the special au- 

 ditory organs, which transmit this 

 stimulation along the auditory nerve 

 to the brain, or nerve ganglion, 

 where it is translated as sound. These 

 sound-waves come to animals usu- 

 ally through the air, or, in the case 

 of aquatic animals, through water, or 

 through both air and water. The 

 organs of hearing are of very com- 

 plex structure in the case of man and 

 Fig. 29. The antenna of ^-J^g high- 

 a carrion beetle, with 

 the terminal three seg- ^^ verte- 

 ments enlarged and flat- b r a t e S . 

 tened and bearing many Qur ears 

 " smelling-pits. " (Much 

 enlarged; photo-micro- 

 graph by Geo. O. Mitch- 

 ell.) 



(fig- 30), 

 which are 

 adapted 

 for perceiving or being stimu- 

 lated by vibrations ranging from 

 16 to 40,000 a second — that is, 

 for hearing all those sounds pro- 

 duced by vibrations of a rapidity 

 not less than 16 to a second nor 

 greater than 40,000 to a second 



Fig. 30. Diagram of the in- 

 ternal part of the human ear; 

 o, external opening; b, bones 

 of the ear; /, labyrinth; c, 

 cochlea or "snail shell"; », 

 auditory nerve. (After Head- 



ly.) 



