The Dawn of Mind 211 



especially for moving objects. Except in gristly fishes, the ex- 

 ternal opening to the ear has been lost, so that sound-waves and 

 coarser vibrations must influence the inner ear, which is well 

 developed, through the surrounding flesh and bones. It seems 

 that the main use of the ear in fishes is in connection with balanc- 

 ing, not with hearing. In many cases, however, the sense of hear- 

 ing has been demonstrated ; thus fishes will come to the side of a 

 pond to be fed when a bell is rung or when a whistle is blown by 

 someone not visible from the water. The fact that many fishes 

 pay no attention at all to loud noises does not prove that they are 

 deaf, for an animal may hear a sound and yet remain quite indif- 

 ferent or irresponsive. This merely means that the sound has no 

 vital interest for the animal. Some fishes, such as bullhead and 

 dogfish, have a true sense of smell, detecting by their nostrils very 

 dilute substances permeating the water from a distance. Others, 

 such as members of the cod family, perceive their food in part 

 at least by the sense of taste, which is susceptible to substances 

 near at hand and present in considerable quantity. This sense of 

 taste may be located on the fins as well as about the mouth. At 

 this low level the senses of smell and taste do not seem to be very 

 readily separated. The chief use of the sensitive line or lateral 

 line seen on each side of a bony fish is to make the animal 

 aware of slow vibrations and changes of pressure in the water. 

 The skin responds to pressures, the ear to vibrations of 

 high frequency; the lateral line is between the two in its 

 function. 



Interesting Ways of Fishes 



The brain of the ordinary bony fish is at a very low level. 

 Thus the cerebral hemispheres, destined to become more and more 

 the seat of intelligence, are poorly developed. In gristly fishes, 

 like skates and sharks, the brain is much more promising. But 

 although the state of the brain does not lead one to expect very 

 much from a bony fish like trout or eel, haddock or herring, illus- 



