THE FISH. 71 



Use the dissecting-pan described under " The Crayfish," 

 or put the fish on a large plate. 



1. Notice the shape of the fish as a whole ; hold the fish, 

 with the belly down and the tail toward you, and 

 observe that there is an anterior and a posterior 

 part, a dorsal and a ventral surface, and that it is 

 bilaterally symmetrical. A fish whose body is flat- 

 tened from side to side, is said to be " compressed " ; 

 the word " flat," when used in describing a fish, 

 means flattened from above downward, and is applied 

 to such a fish as the flounder. 



Close the mouth of the fish, and measure from the 

 foremost point of the head, the tip of the snout, to 

 the front edge, the base, of the tail-fin ; this is the 

 length of the fish. Measure from the tip of the 

 snout to the hinder point of the hard part of the flap 

 which covers the side of the head ; this is the length 

 of the head. How many times is the length of the 

 head contained in the length of the fish? Measure 

 from above downward at the deepest part ; this is the 

 depth of the fish. How many times is it contained in 

 the length ? Compare the width and depth of the fish. 



2. The fins on the back are the dorsal fins j spread them 

 out to their fullest extent, and study them thoroughly ; 

 their framework consists of fin-rays; some of them 

 spinous rays, or spines (unjointed, or inarticu- 

 lated), others soft rays (jointed, or articulated) ; 

 study carefully one of the soft rays, using a lens; 

 count each kind of rays; observe the membrane 

 connecting the rays. This membrane is double ; the 

 fin is really a fold of the skin, with supporting [tarts 

 within the fold. 



