Teacher's Corner 



The goldfish seems to be made especially for the teacher to use in demon- 

 strating the fish's wonderful adaptations to a life in water. 



First of all we look at the shape of the fish. Looked at from above it is 

 wedge-shaped or rounded in front ; looked at from the side the shape is a smooth 

 oval. Thus its form in every way is adapted for moving through the water 

 swiftly. A little exercise to prove this might be as follows: Cut a model of a 

 fish from a piece of shingle or a thin piece of wood, submerge it by holding it 

 down, and then move it lengthwise and crosswise; even a little child can see 

 the effect of this experiment. Next we note the fish's covering, which is an 

 armor of scales as smooth as glass, overlapping like shingles on a roof; they are 

 directed backward and thus by the smoothness of these scales the fish is 

 enabled to move more swiftly through the water. 



Dorsal f i 



Qhil fi 



Cill e*v«r 

 'Pe«t©*al fin 



( GiUof« a Ug 



Ventral fir 



Goldfish with the parts named. 

 This figure should be copied on the blackboard for reference. 



The next point of observation naturally is how does the fish move? Why 

 does it not have legs and arms like ours? The answer is that no man, however 

 expert in swimming, can swim so rapidly as a fish. The fish's fins are specially 

 adapted to drive it swiftly through the water. The goldfish has seven fins: 

 One pair just back of the gill openings, which morphologically represents our 

 arms or the front legs of an animal — these are called the pectoral fins; below 

 and back of them is another pair of fins which may be compared to our legs or 

 the hind legs of an animal, and are called ventral fins; along the back is a fin 

 that may be raised or flattened at will — it is called the dorsal fin; the fish's 

 tail is the tail fin, and on the lower side just in front of the tail is the anal fin. 



The reason we take any interest in all these seven fins of the fish is because 

 they help the fish to move and therefore we are as interested in them as we are 

 in a bird's wings. The dorsal fin, when lifted, can be twisted to one side or the 

 other. This helps to steer the fish just as the rudder helps to steer the boat. 

 The anal fin on the lower side helps in a similar manner. The tail fin is the 

 propeller. It is pushed first this way and than that against the water and thus 

 sends the fish forward. The two pairs of fins help the fish to keep its balance 



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