310 



THE WORLD OF ANIMAL LIFE 



FISHES 



While Fishes as a class are easily distinguished from all other 

 animals, they show their relationship to certain of the amphibians 

 in the fact that a few of their members possess lungs as well as gills. 

 These are styled Lung-Fishes; and they are not only allied to 

 the newts and salamanders by the possession of lungs, but they are 

 also somewhat like them in build. As a rule, however, fishes 

 breathe by means of gills. 



Instead of legs and arms, fishes are provided with fins, thin filmy 

 webs stretched on a number of little bones. Sometimes these fins 



are very small, and 

 sometimes they are 

 developed to a won- 

 derful extent, as in 

 the case of the flying- 

 fish. 



The fishes are all 

 cold-blooded, and as 

 a rule possess hearts 

 of only two chambers. 

 The heart of the lung-fishes, however, is a three-chambered organ. 



Like the reptiles, the fishes are usually clothed with scales, but 

 in some cases the skin is quite unprotected. Some few species are 

 covered with bony plates. 



Just as birds are specially built for flying through the air, 

 so the form of a fish is perfectly adapted for moving through the 

 water. The head is sharp, and the body is oval in form and 

 narrow. The scales are placed somewhat like the slates on the 

 roof of a house, but fixed towards the head, and directed back- 

 wards so that the water slips over them easily. 



Perhaps the most interesting part of a fish is its breathing 

 apparatus. If you open the gill-covers of a fish you will see a 

 number of reddish arches. These are the gills; and they are red 

 because all the blood is sent there from the heart, in order that 



Skeleton of a Fish 



