168 FIRST LESSONS IN ZOOLOGY. 



It lives on the dead leaves of aquatic grasses,, etc. The lo- 

 cal English name is " flat-head/' the native name being 

 "barramundi." 



The African lung-fish (Fig. 172) has two lungs. It lives 

 on leaves in the White Nile, the Niger, and Gambia rivers, 

 where it buries itself in the mud a foot deep. A similar 



FIG. 171. Ceratodus, or Australian Lung-fish. (The tail in nature ends in a 



point.) 



lung-fish (Lepidosiren) lives in the rivers of Brazil. These 

 three lung-fish, with their amphibious habits, whose allies 

 began to exist in Devonian times, long before the coal 

 period, unmistakably point to the appearance of a new and 

 higher type of vertebrate life, the Amphibians, or Sala- 



^^ 



FIG. 172. Protopterus annectens, a Lung-fish of Africa. (One third natural 



size.) 



manders, etc. If their limbs were stronger, jointed, and 

 divided into toes like those of a frog's, they would be able 

 to walk and live on land. The transition from a swimming 

 to a walking air-breathing animal is a remarkable one; yet 

 we should bear in mind that at first the tadpole is without 

 limbs and breathes by gills. 



