276 THE VERTEBRATE ANIMALS 



with the paired limbs of a man. Note the Figure on page 326 

 and locate the paired pectoral and pelvic fins. (These are so called 

 because they are attached to the bones forming the pectoral and 

 pelvic girdles. See page 426.) Find, by comparison with the 

 Figure, the dorsal, anal, and caudal fins. How many unpaired 

 fins are there? 



The flattened, muscular body of the fish, tapering toward the 

 caudal fin, is moved from side to side with an undulating motion 

 which results in the movement forward of the fish. This movement 

 is almost identical with that of an oar in sculling a boat. Turning 

 movements are brought about by use of the lateral fins in much 

 the same waj- as a boat is turned. AVe notice the dorsal and other 

 single fins are evidently useful as balancing and steering organs. 



The Senses. — The position of the eyes at the side of the head 

 is an evident advantage to the fish. Why? The eye is globular 

 in shape. Such an eye has been found to be very nearsighted. 

 Thus it is unlikely that a fish is able to perceive objects at any great 

 distance from it. The eyes are unprotected by eyelids, but the 

 tough outer covering and their position afford some protection. 



Feeding experiments with fishes show that a fish becomes aware 

 of the presence of food by smelling it as well as by seeing it. The 

 nostrils of a fish can be proved to end in little pits, one under each 

 nostril hole. Thus they differ from our own, which are connected 

 with the mouth cavity. In the catfish, for example, the barbels, 

 or horns, receive sensations of smell and taste. The sense of per- 

 ceiving odor is not as we understand the sense of smell, for a fish 

 perceives only substances that are dissolved in the water in which it 

 lives. The senses of taste and touch appear to be less developed 

 than the other senses. 



Along each side of most fishes is a line of tiny pits, provided with 

 sense organs and connected with the central nervous system of the 

 fish. This area, called the lateral line, is believed to be sensitive 

 to mechanical stimuli of certain sorts. The " ear " of the fish is 

 under the skin and serves partly as a balancing organ. 



A fish must go after its food and seize it, but has no structures 

 for grasping except the teeth. Consequently we find the teeth 

 small, sharp, and numerous, well adapted for holding living prey. 

 The tongue in most fishes is wanting or very slightly developed. 



