CLASS PISCES 471 



principal inducements which led England to establish colonies in 

 America." (Jordan and Evermann.) The total weight of the 

 codfishes landed at Boston and Gloucester in 1908 was 41,615,- 

 277 pounds, valued at $1,042,683. The Bureau of Fisheries 

 distributes millions of fry every year (see Table XV). 



Subclass II. Dipnoi. The Lung-fishes. — The lung-fishes, 

 of which there are only three living genera, are said to be inter- 

 mediate between the fishes and amphibians. They possess 

 certain structural features not found in other fishes, but char- 

 acteristic of Amphibia. On the other hand, they are in many 

 respects like the Holocephali and Crossopterygii. Among 

 their important characters are their acutely lobate, paired fins 

 (Fig. 405), an opening between the nasal sac and the mouth 

 cavity, a persistent, unconstricted notochord, and an air-bladder 

 which opens into the pharynx and functions as a lung. 



Family Ceratodontid^e. — The Australian lung- fish, Neocera- 

 todus fosteri (Fig. 405), is the only living species belonging to this 



Fig. 405. — The Australian lung-fish, Neoceratodus fosteri. (From Sedg- 

 wick's Zoology, after Giinther.) 



family. It lies on the bottom of stagnant pools and feeds on 

 worms, mollusks, crustaceans, and other small animals that it 

 gathers from the vegetation. Occasionally it comes to the sur- 

 face in order to change the air in its single lung. Because of 

 this lung it can exist in water unfit for fishes that breathe 

 entirely with gills. Such an environment may have led to 

 the evolution of lung-breathing Amphibia from gill-breathing 

 fishes. 



Family Lepidosirenid^e. — This family contains two genera 

 of living fish. The three species of the genus Protopterus (Fig. 



