THE CARP. 117 



tion of the body acts as a sort of oar, whose rapid mo- 

 tions play the principal part in progression. The actions 

 of the median fins and of the tail are combined to deter- 

 mine the direction of the motion. The lateral fins appear 

 to have their most important function in maintaining 

 equilibrium. 



If we open a carp in order to examine its internal 

 structure, we find before us an organization quite dif- 

 ferent from anything we have observed in the animals 

 already studied. 



At first we notice that a large portion of the abdomen 

 is filled with a capacious bladder, tightly contracted in 

 the middle, and communicating with the oesophagus by 

 a long canal. This is the swimming-bladder, which exists 

 in a large number of the species of fishes, and contributes 

 in an efficacious manner to simplify the mechanism of 

 locomotion. This bladder is filled or emptied of air at 

 the will of the fish, so that the body, being decreased or 

 increased in density, rises or sinks in the water without 

 any effort of the fins. The gas in the swimming-bladder 

 does not come from the exterior : it is secreted by the 

 walls of the membrane. There is no swimming-bladder 

 in those species that constantly remain at the bottom 

 of the water near the mud in which they seek their 

 food. 



The digestive apparatus also occupies a considerable 

 portion of the abdominal space. The intestinal canal of 

 the carp, indicating an essentially vegetable diet, is long, 

 folded, and partly hidden among the numerous lobes of 

 the liver. The mouth has no teeth in its jaws ; the palate 

 is thick and fleshy ; the tongue is largely developed, as 

 it is indeed in all fishes. 



The respiratory apparatus presents important peculi- 



