NATVRE-STUDY LESSONS. 53 



16. (a) Observe the movement of the lower jaw and 



gills. 



{b) Discover the connection between the rhythmi- 

 cal arching of the gills and the opening of 

 the mouth. 



(c) Why are these actions connected ? 



17. Remove a fish from the water for a short time and 

 observe how this affects the fish. 



18. (a) Fill test-tubes with well water, rain water, creek 



water, unshaken boiled water, boiled water 

 well shaken or stirred with an egg-beater, 

 and label them. Let them stand side by 

 side several hours and then examine them 

 for air-bubbles. 



(J?) If air is necessary for the respiration of fish, in 

 which of the above kinds of water would a 

 fish live longest .' 



(r) Make a list of the samples of water in the order 

 of their capacity for supporting the respira- 

 tion of fish. 



E. The Body. 



19. {a) Note the outline of the body as seen from 



above, from the sides, and from below. 



(b) Make sketches showing these outlines. 



(c) Mark the lateral line. 



20. (a) Observe the covering ; note the arrangement 



of the scales ; their size ; their thickness j 



their shape and color. 

 (^) Sketch a scale. 

 (f) Infer the advantage to the fish of having the 



scales arranged as they are. 



