78 
LABORATORY EXERCISES 
of the head with that of the remainder of the body. Note the 
position of the eyes. Does the fish close its eyes? Explain. Note 
the position, shape, and size of the mouth. Watch the movements 
of the mouth. Find the gill openings on either side of the body. 
The covering of each is an operculum. Note the form and the 
movement of the operculum. Does the operculum move in unison 
with the mouth? 
III. Respiration in the Fish. 
1. In a preserved (or freshly killed) fish, examine the gills. 
Note the four pairs of bony arches which act as supports for the 
delicate gill filaments. Water enters the mouth and passes out 
through the gills. As it passes through the gills, some of the oxygen 
which is in solution is removed by the blood circulating through 
the gill filaments. Review the method by which the human body 
obtains its supply of oxygen. Compare this with what takes place 
in the gills of a fish. 
2. Slowly heat a beaker of cold water. Note the bubbles which 
form during the heating. These are air bubbles. What becomes 
of them? From this experiment determine which holds the more 
dissolved air, cold or warm water. Why do fish come near the 
surface in warm water? Why is ice packed about or placed in the 
minnow buckets used by fishermen? 
3. In the process of photosynthesis, what gas is used by the 
plant? What is released? Why, then, can green water plants and 
fish live together in an aquarium to the great advantage of each 
other? 
IV. Make a drawing of a side view of a sunfish. 
EXERCISE 78 
THE FROG 
Capture one or more live frogs and bring them into the labora¬ 
tory. 
I. The Living Frog. Observe in the water and out of it. When 
quiet in the water, what is the frog’s position? What is its rela- 
