FISHES 



223 



from the Gulf of St. Lawrence to Texas and Mexico. Their 

 habits are imperfectly known, but this much seems true. The 

 young eels are born in the sea from eggs deposited by the 

 mature female. In the spring these young eels ascend the 

 rivers and streams, in \\hicli they remaui until they are two 

 or three years okl. When grown and ready to spawn, 

 they return to the sea. 



Fig. 159. — tel. 



The electric eels, so-called, belong to another order of 

 fishes. They are eel-like m shape but are not true eels. 

 They possess powerful electric batteries. 



Lung fishes. —All of the sharks, rays, and bony fishes 

 breathe by means of gills. The air bladder, when present 

 in these fishes, seems to function only as a hydrostatic 

 apparatus. But in the ganoids, represented by the bowfin, 

 gar pike, sturgeon, and spoonbill, the air bladder certainly 

 functions, to some extent, as an organ of respiration. So 

 we find that the ganoids foreshadow, as it were, fishes which 

 possess true lungs in which the blood is purified by the ex- 

 change of gases. There are, at least, three very interesting 

 species of fishes, known as the lung fishes, in which the air 

 bladder is modified into a fairly well-developed lung. One 

 species is found in the fresh waters of Queensland, Australia, 

 and is called Ceratodus, or "Burnett Salmon," It grows 



