152 ■ VERTEBRATES 



Where is the tongue attached? For what is it used? 



(7) Note the location, size and color of the eyes. Are 

 they simple or compound? Do you find eyelids? Can a 

 living fish change the direction of its vision? How many 

 nostrils? Are they connected with each other or with the 

 mouth ? Probe with bristle to find out. 



(8) Lift up the gill cover, operculum, which lies flat on 

 the surface of the body in front of the pectoral fin. What is 

 the nature of the gill cover ? How many bones in it ? What 

 is its covering ? Of what use is it ? 



Look just under the gill cover for a membrane which 

 lies close to the edge of the cover and is attached to it fur- 

 ther back. How does this membrane compare with a fin? 

 This is the branchiostegal membrane. 



(9) B.eneath the branchiostegal membrane are the red 

 gills. Raise them with the needle. How many? How 

 attached? Are they separate from one another? Note 

 shape of each. Note that the gill consists of the bony frame- 

 work, or arch, the filaments on the posterior edge, and the 

 gillrakers on the anterior side. How do the filaments and 

 the rakers differ from one another? Open the mouth and 

 depress the tongue. How does it affect the gills? What 

 do you think about the principal uses of the gill rakers ? Of 

 the filaments? 



Explain the process of passing water through the gills of 

 the living fish. 



Remove the first gill below the operculum by loosening 

 it carefully at the ends. Is it fastened by a true joint or 

 is it merely a continuation of the arch into the framework 

 of the body? Study the filaments. What gives them their 

 red color? Pick out a single filament. Is its color as red 



