jo Practical Zoology. 



In the following directions, relative and not absolute measure- 

 ments are intended. Instead of using a foot rule, take a strip of 

 paper and mark the entire length, head, depth, etc., either by 

 pencil or by folding. Compare these so as to be able to say 

 whether the head is one third, one fourth, or what part, of the 

 length of the body. 



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 qf 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 the depth of 

 the fish. 



2. The fins on the back are the dorsal fins ; spread them out 

 to their fullest extent, and study them thoroughly ; their framework 

 consists of fin rays, some of them spinous rays, or spines (un- 

 jointed, or inarticulated) , others soft rays (jointed, or articulated). 

 Study carefully one of the soft rays, using a lens ; spread the fin 

 and hold it between you and the light to see the joints, which ap- 

 pear as fine cross lines on the soft rays ; 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 parts 

 within the fold. 



Measure along the base of each fin ; this is the length of the 

 fin ; extend the fin fully, and measure the length of its longest 

 ray ; this is the hight of the fin. Compare the length and the hight 

 of the fin. In some fishes the dorsal fin is single ; in others it is 

 divided, forming two or more dorsal fins. 



The tail fin is the caudal fin; is it symmetrical? The fin in 

 front of and below the caudal is the anal ; compare this fin with 

 the dorsal. The fins above named, being in the middle line, an 

 called median, or vertical, fins. 



