^6 The Life Story of the Fish 



It can open and shut its gill covers. It can open and shut its 

 jaws, and some fishes can protrude the upper lip in a startling 

 but not particularly endearing fashion. There are muscles to 

 perform these operations. There are also muscles to move 

 the various fins. All of these muscles, however, are compara- 

 tively insignificant. Both in bulk and in strength, they are 

 as nothing compared to the great mass which forms the 



Figure io. BODY MUSCLES OF THE FISH 



Drawn from a model by Dr. W. K. Gregory in the American Museum 

 of Natural History. 



main part of the fish's muscular system. This is the series 

 of W-shaped segments adjoining and fitting into one another 

 along the whole length of each side of the body, which form 

 the part of the fish which you eat. You can verify this struc- 

 ture the next time a whole fish is served to you by stripping 

 off the skin and examining the meat. 



The fish's principal motive force is concentrated in this 

 compact mass in the body wall, and each muscle is limited 

 in its action to the region immediately surrounding it. In the 

 higher animals, including ourselves, the situation is very 

 different. The body wall plays practically no part in move- 

 ment. The principal motive force is decentralized. It is 

 broken up into separate units, the long muscles of the limbs. 



