THE FISH 137 



Can you identify the subopercle, preopercle, interopercle? 

 Under the opercles on the ventral side is the branchiostegal 

 membrane and the branchiostegal rays which support the 

 membrane. How many are there? Raise the operculum 

 and examine the gills, their number and arrangement and 

 method of support. On the anterior margin of the gill 

 arches are teeth called gill rakers. What function can you 

 suggest for them? Press down the tongue and observe 

 the effect upon gills and gill rakers. How does the fish 

 breathe? What motions are involved? Watch a fish in 

 the aquarium to find an answer to these questions. 



6. Lateral Line. A series of raised, dot-like markings 

 along the sides of the body. Examine one of the scales 

 which has on it one of the dots and see what it is like. The 

 lateral line has a sensory function. 



7. Openings. Just in front of the anal fin look for open- 

 ings of the anus and genital organs. 



Make a drawing of the fish as seen from the side. 



m. Internal Anatomy. 



Make a median incision just in front of the anus and carry 

 it forward to the hinder border of the gills, being careful 

 not to injure the underlying organs. Make cuts at right 

 angles so that the flaps may be pressed to one side. Place 

 the fish on its side and work out the internal organs. Com- 

 pare the body cavity with that of the frog. Is there a 

 thoracic cavity distinct from an abdominal? 



1. Liver. This is a reddish organ of considerable size. 

 How is it held in place? Is there more than a single lobe 

 in it? Is a gall-bladder present as in the frog? 



2. Stomach. Raise the liver and push it to one side to 

 expose the stomach. From the stomach the esophagus 



