20 THE STORY OF FISH LIFE. 



fish, sometimes it is but a temporary phase, as in 

 the higher animals. 



Fish, then, are gill-breathing animals, and these 

 gills are, it has just been hinted, in some way 

 connected with the tube into which the food 

 is taken. Let us now look closer into this 

 connection. 



Everybody knows, of course, that a fish's gills 

 are to be found in its head. Many will be 

 further able to point out that they can readily 

 be seen by raising a bony flap or plate lying 

 on either side of this head, but that they have 

 anything to do with the food-pipe, or, as we 

 prefer to call it, the alimentary canal, is a fact 

 which doubtless will be new to many. Let us 

 make clear, then, the nature of this association 

 at once. Food is taken in at the mouth, and 

 thence, as everybody knows, passes down a tube 

 into a more or less extensive and sometimes com- 

 plicated bag called the stomach. This is true 

 equally of the fish, and of ourselves. But fish, 

 and some other lowly backboned animals, have 

 a series of slits in the wall of this tube, situated 

 at the back of the mouth, just before the region 

 where the tube suddenly narrows to become the 

 gullet, the passage leading to the stomach. The 

 wall of the tube in the fish, between every slit, 

 becomes strengthened by a solid support, which 

 takes the form of a half-hoop, and from every 

 one of these half-hoops there arises a series of 

 slender rods, closely packed, so as to form a 

 kind of fringe to the hoop. These rods support 

 closely plaited folds of skin richly supplied with 

 .a series of fine blood-vessels, through which the 



