244 HOW DO WE CLASSIFY ANIMALS? 



of the scales, overlapping in a backward direction, are other 

 adaptations for life in water. 



The paired fins are called pectoral and pelvic fins because they 

 are attached to the bones forming thetiTuctoral and pelvic girdles. 

 These fins are homologous to the foxelimbs and hindlimbs of 

 higher animals. The dorsal, anal, and caudal fins are not paired. 



A fin is composed of a thin membrane or skin stiffened by long 

 slender spines of bones or cartilage called rays. The caudal fin 

 is light and strong, and, as powerful muscles are attached to it, 

 can push against the water with sufficient force to move the body 

 forward. The flattened, muscular body of the fish, tapering I 



^ostri^ 



,-firs-t dons-al fin 



,. second 

 ^« cCprs-ocl 



.Caudal fin 



i i. » *• jJ$rf// ' t'wi/ ,- second: 



lateral * m &/i ill /. trlt'fmr ^ ' ccons-ocl 



uJm ... ■-■ IK v^HbL f in. 



I mouth \V\^ -pelvic fin i — anal fin 



Name all the adaptations you can find in the body of this fish and show how each 

 is an adaptation. 



toward the caudal fin, is moved from side to side with an undulating 

 motion which results in the rapid forward movement of the fish. 

 The caudal fin is the principal fin of locomotion. The paired fins 

 are used for turning and balancing. 



The sense organs. The eyes, globular in shape, are on each 

 side of the head. They are unprotected by eyelids, but their 

 tough transparent outer covering and their position in the sides 

 of the head afford some protection. A fish becomes aware of the 

 presence of food by smelling it rather than by seeing it. The 

 nostrils, small pits unconnected with the mouth cavity, contain 

 organs for smelling. In the catfish, the barbels, or horns, receive 

 sensations of feeling, smell, and taste. 



