l6o VEKTEBRATES. 



of miles from the ocean and are oftentimes two years old 

 or more when they reach the ocean. Small eels are found 

 in nearly all the streams tributary to the Mississippi river. 

 Summary. — (i) Watch a fish in water. Can it turn its 

 eyes? Can it lower and raise itself in the water? Can it 

 swim in a definite straight line? Observe the use that it 

 makes of its fins. When the fish is swimming slowly does 

 it use the same method as when moving rapidly ? Of what 

 use is the dorsal fin ? The anal ? Of what use are so many 

 fine bones found in many fishes ? 



(2) Does a fish swim with the current or against it? 

 If it should go down a stream which direction must its 

 head be? Why? 



(3) What constitutes the principal food of fishes? In 

 order to catch a fish what kind of bait must be used? Can 

 the same bait be used for all fishes? Can a fish be deceived 

 with things that are not food? How does that deception 

 take place? What is a game fish? 



(4) How do fishes spend the winter? Can they be 

 caught in the winter? How? What is the source of oxy- 

 gen that the fish gets from the water? Could fishes live in 

 places where the water is frozen over all the year? Why? 



Classification. — (i) Notice that the fish has disclosed 

 an entirely new structure to us. As in the arthropods tht 

 nervous system extends along the longitudinal axis, but 

 instead of lying down on the ventral skeleton, it lies on the 

 dorsal side and is held up by a succession of large bones 

 articulating with one another so as to form a strong frame- 

 work, or backbone. This framework forms a support for all 

 the organs of the body, and to it are attached bones which 

 form the internal skeleton. 



