THE TRUE FISHES. 167 



been seen so packing a river three hundred and sixty feet wide and 

 twenty-nine feet deep, that the backs of the upper ones were out of 

 the water. 



Order II. Lung-Fishes (Dipnoi). The lung-fishes 

 are eel-shaped, and covered with large scales. Some, as 

 the Lepidosiren, have two perfect lungs, as well as gills. 

 When left dry in pools, they form cases in the mud, which 

 they line with a mucus, and lie dormant until the return of 

 the water. The Ceradotus of Australia (Fig. 206), discov- 



FlG. 206. The Ceradotus of Queensland, Australia, an air-breathing and 

 water-breathing mud-fish of the ancient type, with paddle-fins. 



ered in 1870, attains a length of six feet When under 

 water the heart pumps the blood to the gills, but when 

 they are deprived of it the gases from the air-chamber are 

 expelled with a loud noise, and fresh air taken in, the 

 blood being now carried the other way, or toward the 

 chambered, lung-like air-bladder, to become freshened. 



NOTE. The Protopterus, a lung-fish of Africa, has plume-like fins, 

 and is also noted for its burrowing habits, forming burrows a foot from 

 the surface. One, sent to England in its earthen case, came to life 

 months after, when soaked in water. Some remain in their dry nests 

 for several seasons. Many of the family have the faculty of reproduc- 

 ing lost fleshy parts of their fins, etc. 



Order III. Branchioganoidei. This order is repre- 

 sented by the Polypterus of the Nile. The dorsal fin is 

 broken up into numerous points, each being supported by 



