FISHES AND FISHERIES 255 



and such others, as the curious sea-horses and the remarkable 

 flying-fish, and the fishes that leave the water and wander 

 over the land, the student must go to some of the detailed 

 works on fishes, as Jordan's "Guide to the Study of Fishes." 

 Jordan & Evermann's "American Food and Game Fishes" 

 is a most excellent treatise, popular enough so that anyone may 

 enjoy reading it. 



The Lung-fishes (sub-class Dipneusti}. This sub-class, 

 formerly called Dipnoi, is represented by only a few living 

 species, occurring in Australia, South America and Africa. 

 They are of particular interest to the naturalist not only be- 

 cause they are the sole survivors of a once numerous group of 

 fishes, but because several things about their structure seem 

 to 'indicate that they must be closely allied to the ancestral 

 type from which both the bony fishes and the Amphibia, or 

 frogs, salamanders, etc., have descended. The gills in most 

 of them remain functional and are used while the animals are 

 in the water, but at other times, when they burrow into the 

 wet mud or elsewhere, they breathe by means of lungs, which 

 are spongy sacs, represented in most fishes by the air bladder. 

 The paired fins, too, have an elongated jointed axis with rays 

 which resemble the limbs of some of the Amphibia as much 

 as the fins of fish. 



