VEETEBEATA. 79 



2. Identify the gills. (Dem.) 



a. Observe that each gill consists of a row of fringes 



(gill filaments). 

 6. How many gills are there on each side ? 



c. Observe that each gill is supported and kept in 



place by an arch of bones (gill arch). 



d. Sketch a gill. 



3. When the mouth of the fish opens, do the opercula 



open at the same time ? 

 Why does the fish open its mouth so frequently ? 

 Explain how a fish breathes. 

 Does a fish drink ? How do you know ? 



F. The Scales. Exoskeleton. 



1. Show by a sketch the arrangement of the scales. 



2. What advantages are there to the fish in having 



these scales ? 



3. Sketch a scale. (Dem.) 



4. Compare a scale from the lateral line with an 



ordinary scale. Sketch. 



5. Do the scales give the color to the fish ? 



6. Are the scales ctenoid or cycloid ? Ctenoid scales 



have teeth on one edge while cycloid scales have 

 no teeth. 



Gr. Suggestive Questions. 



1. Does a fish sleep ? (Watch a goldfish at home.) 



2. What is the "swim-bladder" of a fish ? (Dem.) 



3. On which one of its senses does a fish depend the 



most to warn it of approaching danger ? 



4. Is there anything peculiar about the way in which 



a dead fish floats ? 



5. Make a list of the principal fishes which are found 



alive in your neighborhood. 



