162 VERTEBRATES. 



a distance, when this is necessary. Specimens are often 

 seen alive in the markets, in cool weather, twenty-four 

 hours or more after they have been taken from the water. 



Aquarium Study. Study a live specimen that has 

 been placed in an aquarium, or tank, or tub of water. 

 Observe its form, its coloration, its markings, its method 

 of getting about. What adaptations can you discover in 

 its form to locomotion in water ? To living on the muddy 

 bottoms in river channels ? 



Observe the large eyes, the mouth' opening directly for- 

 ward, the long barbels at the corners of the mouth, a 

 pair of smaller barbels above and behind the mouth, and 

 two pairs below and behind the mouth. 



Observe on either side of the head, where it joins the 

 body, a wide strip of membrane overlapping a long ver- 

 tical slit. Notice the regular opening and closing of this 

 aperture, and also of the mouth, and note the concerted 

 action between the two. Place a drop of ink in the water, 

 close in front of the mouth, to discover the direction of 

 the current of water through these openings. 



I. Fins. Four of these are paired fins, the pair at 

 the sides of the body, just back of the head, are the 

 pectoral fins ; the pair low down on the sides of the body, 

 much farther back,- are the ventral fins, the others are 

 single or unpaired fins. The two fins on the median dorsal 

 line are dorsal fins. The one on the median ventral line is 

 the anal fin. The large one at the posterior end of the 

 body is the caudal fin. 



As the fish swims about, watch it to discover the use of 

 each of these fins. That the large caudal fin is the one 

 principally concerned in locomotion will be seen at once. 

 To learn the use of the pectoral and ventral fins, catch the 

 fish with the hand, avoiding the sharp spines at the front 

 of pectoral and anterior dorsal fins ; fold the pectoral fins 



