OUR FACE FROM FISH TO MAN 



However, the fact that even the true nature of 

 nerve currents is as yet very imperfectly known 

 does not prevent us from realizing the value of 

 even a homely face to all animals that navigate 

 the waters or move upon the land or in the 

 air. 



Not the least important of the shark's detecting 

 and navigating instruments are the very numerous 

 "ampullae" that are so thickly scattered all over 

 the surface of the head. Each of these pits is con- 

 nected with a nerve tendril and thousands of 

 these nerves run together into larger tracts, which 

 finally run into the brain itself. Possibly these 

 ampullae detect vibrations of low frequency in 

 the water and in some way cooperate with the 

 olfactory nerves in giving stimuli proportional to 

 the nearness of the source. 



Then there are the taste organs scattered over 

 the mouth cavity, all wired most carefully and 

 elaborately and connected with the appropriate 

 brain centers. 



The so-called "internal ears" embedded in the 



cartilage on either side of the hindbrain, consist 



chiefly of the ingenious semi-circular canals (see 



pages 202-6, Fig. 104), arranged like our own in 



16 



