BIOLOGICAL RELATIONS OF AQUATIC FORMS 197 



Conclusions. 1. Do you conclude that its sight is keen ? 



2. How does its range of vision compare with that of man ? 



3. Why should a fish have sensory (sense) organs ? 



d. External Adaptations 



Note. Use preserved specimens. 



Observations. 1. With what is the body covered ? 



2. What is the general arrangement of the covering ? Note. 

 - The scales and horny rayed fins constitute what exoskeleton 

 there is present. Is there another skeleton ? If so, where ? 



Conclusions. 1. How is the exoskeleton of scales adapted 

 to protect the fish ? 



2. How is the sliminess or slippery character of the scales of 

 advantage ? 



3. How are the scales adapted to gain flexibility of the body ? 

 Drawing (Optional). Sketch a side view of a fish. Label: 



head, eyes, dorsal fin, pectoral fin, anal fin, caudal fin, and gill 

 cover. 



e. Internal Adaptations (Optional) 

 1. SKELETON 



Note. Use prepared skeleton or a chart. 



Observations. 1. Notice a column of bones (the vertebral column, or 

 backbone) running the full length of the fish. Is it solid or flexible ? 



2. Where are the ribs attached ? 



Conclusions. 1. Since this skeleton is inside the body, it is called an 

 endoskeleton. What do you think is its general purpose ? 



2. Of what advantage that it be constructed of so many parts, rather 

 than a rigidly formed framework of few parts ? 



3. Why should fishes have internal skeletons ? 



4. What is meant by the term " adaptation of structure to function " ? 



5. In what different ways does the skeleton of a fish show adaptations 

 of structure to functions ? 



2. INTERNAL ORGANS 



Note. Use preserved specimens with ventral body wall cut away. 

 Observations. 1. Push a slender probe down the throat, into the 



