1 68 ANIMAL BIOLOGY 



air bladder of fishes is frequently regarded as homologous 

 with the lungs of higher vertebrates, and in the Dipnoi 



FIG. 136. Protopterus annectens, lung fish. (From Boas.) 



the air bladder approaches more closely to the structure 

 and function of true lungs than in any other group of 

 fishes. 



FIG. 137. Flying fish. (After Jordan.) 



