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 (D7xoi).—The lung-fishes 
are eel-shaped, and covered with large scales. Some, as 
the Lepidosiven, 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- 
Fic. 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 
