152 Handbook of Nature-Study 



that the water in the aquarium jar should often be replenished. The gill 

 arches also bear a series of bony processes called gill-rakers. Their 

 function is to prevent the escape of food through the gills while it is being 

 swallowed, and they vary in size according to the food habits of the fish. 

 We note that the fish in the aquarium constantly opens and closes the 

 mouth; this action draws the water into the throat and forces it out over 

 the gills and through the gill openings; this then, is the act of breathing. 



LESSON XXXVI 

 A Study of the Fish 



Leading thought — A fish lives in the water where it must breathe, move 

 and find its food. The water world is quite different from the air world 

 and the fish have developed forms, senses and habits which fit them for 

 life in the water. 



Method — The goldfish is used as a subject for this lesson because it is 

 so conveniently kept where the children may see it. However, a shiner 

 or minnow would do as well. 



Before the pupils begin the study, place the diagram shown on p. 150 

 on the blackboard, with all the parts labelled; thus the pupils will be able 

 to learn the parts of the fish by consulting it, and not be compelled to 

 commit them to memory arbitrarily. It would be well to associate the 

 goldfish with a geography lesson on China. 



Observations — i. Where do fishes live? Do any fishes ever live any 

 part of their lives on land like the frogs? Could a salt-water fish live in 

 fresh water, or vice versa? 



2. What is the shape of a fish when seen from above? Where is the 

 widest part? What is its shape seen from the side? Think if you can in 

 how many ways the shape of the fish is adapted for moving swiftly through 

 the water. 



3. How many fins has the fish? Make a sketch of the goldfish with 

 all its fins and name them from the diagram on the blackboard. 



4. How many fins are there in all? Four of these fins are in pairs; 

 where are they situated? What are they called? Which pair corres- 

 ponds to our arms? Which to our legs? 



5. Describe the pectoral fins. How are they used? Are they kept 

 constantly moving? Do they move together or alternately? How are 

 they used when the fish swims backwards? 



6. How are the ventral fins used? How do they assist the fish 

 when swimming? 



7. Sketch a dorsal fin. How many spines has it? How many soft 

 rays are there in it? What is the difference in structure between the stiff 

 spines in the front of the dorsal fin and the raj^s in the hind portion? Of 

 what use to the fish are these two different kinds of fin supports? 



8. Sketch the anal fin. Has it any spines in front? How many 

 rays has it? How is this fin used when the fish is swimming? 



9. With what fin does the fish push itself through the water? 

 Make a sketch of the tail. Note if it is square, rounded, or notched at the 

 end. Are the rays of the tail fin spiny or soft in character? 



10. Watch the goldfish swim and describe the action of all the fins 

 while it is in motion. In what position are the fins when the fish is at 

 rest? 



