CHAPTER XXVII 



FISHES 



Vocabulary 



Aquatic, pertaining to the water. 



Cartilaginous, made of cartilage, a gristle-like tissue. 



Nasal, pertaining to the nose. 



Operculum, the covering over the gills in fishes. 



Filaments, any thread-like organs. 



Prehension, the function of grasping. 



Visceral, pertaining to the viscera or abdominal organs. 



Pectoral, pertaining to chest or shoulders. 



Pelvic, pertaining to the hips. 



Fishes are aquatic vertebrates, with either a cartilaginous or 

 bony skeleton ; they breathe by means of gills; are usually covered 

 with scales; and have limbs in the form of fins. 



External Structure. The body can be divided into three regions, 

 the head, trunk, and tail. There is no narrowing to mark the 

 neck, since the smoother outline is better fitted for passing through 

 the water. The general outline of the body is spindle shaped, 

 flattened more or less at the sides to aid in locomotion by displacing 

 the water as easily as possible. 



Scales. The whole body, except the head and fins, is covered 

 with scales overlapping toward the rear, giving protection and at 

 the same time allowing great freedom of motion. They are supplied 

 with a slimy secretion which aids in locomotion and in escape from 

 enemies. In some fish, such as the trout and catfish, the scales 

 are minute or lacking, but in any case, the color of the skin corre- 

 sponds to the fish's surroundings and is therefore a protection. 



Head. The head is usually pointed, protected by plates instead 

 of scales, and attached directly to the trunk. The lack of a neck 

 is no disadvantage, as the fish can turn its whole body as quickly 

 as most animals can turn their heads. 



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