Fish Study 151 



sal fin is usually higher in front than behind and can be lifted or shut down 

 like a fan. This fin when it is lifted gives the fish greater height and it 

 can be twisted to one side or the other and thus be made a factor in 

 steering. The anal fin on the lower side acts in a similar manner. The 

 tail fin is the propeller and sends the body forward by pressing backward 

 on the water, first on one side and then on the other, being used like a 

 scull. The tail fin varies in shape very much in different species. In the 

 goldfish it is fanlike, with a deeply notched hind edge, but in some it is 

 rounded or square. 



The paired fins correspond anatomically to our arms and legs, the 

 pectorals representing the arms, the ventrals the legs. Fins are made up 

 of rays, as the bony rods are called which support the membrane; these 

 rays are of two kinds, those which are soft, flexible, many jointed and 

 usually branched at the tip; and those which are bony, not jointed and 

 which are usually stiff spines. AVhen the spines are present in a fin they 

 precede the soft rays. 



Fishes' eyes have no eyelid but the eyeball is movable, and this often 

 gives the impression that the fish winks. Fishes are necessarily near- 

 sighted since the lens of the eye has to be spherical in order to see in the 

 water. The sense of smell is located in a little sac to which the nostril 

 leads; the nostrils are small and often partitioned and may be seen on 

 either side of the snout. The nostrils have no connection whatever with 

 breathing, in the fish. 



The tongue of the fish is very bony or bristly and immovable. There 

 is very little sense of taste developed in it. The shape, number and 

 position of the teeth vary according to the food habits of the fish. The 

 commonest type of teeth are fine, sharp and short and are arranged in 

 pads, as seen in the bullhead. Some fish have blunt teeth suitable for 

 crushing shells. Herbivorous fishes have sharp teeth with serrated edges, 

 while those living upon crabs and snails have incisor-like teeth. In some 

 specimens we find several types of teeth, in others the teeth may be 

 entirely absent. The teeth are borne not only on the jaws but also in the 

 roof of the mouth, on the tongue and in the throat. 



The ear of the fish has neither outside form nor opening and is very 

 imperfect in comparison with that of man. Extending along the sides of 

 the body from head to tail is a line of modified scales containing small 

 tubes connecting with nerves; this is called the lateral line and it is 

 believed that it is in some way connected with the fish's senses, perhaps 

 with the sense of hearing. 



Since fishes must push through water, which is more difficult than 

 moving through air, they need to have the body well protected. This 

 protection is, in most fishes, in the form of an armor of scales which are 

 smooth and allow the body to pass through the water with little friction. 

 These scales overlap like shingles in a roof and are all directed backward. 

 The study of the fish scale shows that it grows in layers. 



In order to understand how the fish breathes we must examine its gills. 

 In front, just above the entrance to the gullet are several bony ridges 

 which bear two rows of pinkish fringes; these are the gill arches and the 

 fringes are the gills. The gills are filled with tiny bloodvessels, and as the 

 water passes over them, the impurities of the blood pass out through the 

 thin skin of the gills and the life-giving oxygen passes in. Since fish 

 cannot make use of air unless it is dissolved in water, it is very important 



