10 THE ANIMALS AND MAN 



fin; in front of the tail on the under surface is the anal fin, 

 while still in front of this is the pair of ventral fins, and on 

 the sides of the body back of the mouth are the pectoral fins. 

 How is each of these fins composed? The ventral fins cor- 

 respond to the hind legs of other backboned animals, while 

 the pectoral fins correspond to the forelegs, wings, or arms. 

 Watch the fish swim and determine the use of each kind of 

 fin. Professor Needham gives the following directions for 

 doing this: "To learn the use of the pectoral and ventral 

 fins catch the fish with the hand, avoiding the sharp spines 

 at the front of the pectoral and anterior dorsal fins; fold the 

 pectoral fins backwards, flat against the sides of the body; 

 pass a rubber band back over the head and around these 

 fins to keep them so. Keep the fish under water while at- 

 te^npting to depress the pectoral spines, for in air it will 

 keep them rigidly erect. Pass another rubber band about 

 the ventral fins. Then liberate the fish and watch it. What 

 position does its body assume ? Release the paired fins and 

 fasten down the dorsal and anal fins with rubber bands. 

 Liberate the fish again, and observe how it gets along with- 

 out the use of these fins. What kind of a course does it take 

 through the water?" 



Examine the eyes. Are there eyehds? In front of the 

 eyes are two pairs of nostrils. Examine the inside of the 

 mouth. Is there a tongue? Where are the teeth situated, 

 and in what direction do they point? What advantage to 

 the fish is it to have the teeth pointing as they do ? 



Lift up the flap, called opercular flap, in front of one of 

 the pectoral fins and bend it forward. Under it are four 

 gill arches, each with a double fringe of gills. The cavities 

 enclosed by the gills are called gill-pouches. Note the gill- 

 rakers, short and blunt, on the first gill arch. Note also, on 

 the under side of the flaps turned back, delicate red gill-like 

 structures covered by a membrane. These are the false 

 gills. The true gills are organs by means of which the fish 



