EXTERNAL PARTS 



107 



the head next to the trunk is protected by a piece of bone 

 that covers the gills (gill cover or operculum, 6-peV- 

 ku-liim), and the openings leading into the nostrils, which 

 do not connect with the mouth cavity. 



The trunk bears a number of fins. Each fin is fur- 

 nished with several bony fin-rays covered by a thin fold 

 of skin. On the shoulder and 

 hip regions of the trunk, the 

 fins occur in pairs and are called 

 the pectoral and pelvic fins. 

 Several fins are found that are 

 not in pairs. These are the 

 median fins of the trunk. 



The caudal or posterior re- 

 gion of the fish ends in a large 

 median fin. The tail region is 

 chiefly important in locomotion, 

 but the fins also help in balanc- 

 ing and steering. 



Scales cover the trunk and tail, each one overlapping 

 like the shingles of a house. The skin is full of mucous 

 glands that keep the fish covered with slime. Both the 

 slime and the scales protect the fish (Figure 109). 



Figure 109. — Scales of 

 Fishes. (Magnified.) 



LABORATORY STUDY 



Study living fish such as goldfish or perch. Place one or two in an 

 aquarium and observe their behavior. Fill out the report below. 



