THE LIFE OF AN ANIMAL 293 



Experiments in feeding fishes show that they become 

 aware of the presence of food by smelling it as well as by 

 seeing it. The nostrils of a fish are sensitive to substances 

 dissolved in the water in which the fish lives, as our nos- 

 trils are sensitive to gases carried by the air. Their 

 nostril openings end in little pits which do not connect with 

 the throat, as do ours. 



The sense of taste is located on the tongue of the fish, 

 and the sense of touch is located in the skin. Both of 

 these appear to be less developed than the other senses. 



The fish has an ear under the skin back of each eye and 

 lying wholly within the skull. It is like the internal parts 

 of our ears, and is sensitive to vibration in the water, just 

 as the ears of land animals respond to vibrations of the 

 air. (LABORATORY MANUAL, Exercise XXXI.) 



340. The Relation of Sensation to Motion. In order 

 to live and reproduce its kind, an animal must be able to 

 protect itself from danger and to secure food. Therefore it 

 is provided with the means of defense or the means of 

 escape from enemies, and with the power of motion. When 

 any change of surroundings affects the sense organs, the 

 nerves send impulses to the brain or spinal cord, and they 

 in turn send impulses to the muscles. 



341. Useful Responses. If animals respond to external 

 conditions in a way advantageous to themselves, they will 

 succeed in getting food and in escaping from danger. Hence 

 they are the more likely to live long and to leave descendants. 

 There is a probability that the young will inherit from the 

 parents the inclination to respond in the same way. As a 

 result, instincts may originate and be perpetuated. 



Instinct may be defined as an inherited habit. For 

 example, a little kitten that has never seen a mouse is 

 at once on the alert at the sound of a slight scratching. 

 It sits motionless watching the point from which the 

 sound comes. The kitten is trying to catch its prey in the 



