56 FIRST LESSONS IN ZOOLOGY 



part of soft rays jointed and branched, both sphies anc' 

 rays being connected by and supporting a thin skin. At 

 the end of the tail is the caudal 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 correspond 

 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 bod}' ; pass a rubber band back over the 

 head and around these fins to keep them so. Keep the 

 fish under water while attempting to depress the pectoral 

 spines, for in air it will keep them rigidly erect. Pass 

 another rubber band about the ventral fins. Then liber- 

 ate 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 without the use 

 of these fins. What kind of a course does it take through 

 the water .■' 



Examine the eyes. Are there eyelids.? 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 



