THE DIPXEUSTA. 2 1 



O 



has lately been discovered in Australia. During the dry 

 season, that is in summer, these strange animals bury 

 themselves in a nest of leaves in the dry mud, and then 

 breathe air through lungs like the Amphibia. But during 

 the wet season, in winter, they live in rivers and bogs, 

 and breathe water through gills like fish. Externally, they 

 resemble fish of the eel kind, and are like them covered 

 with scales ; in many other characteristics also — in their 

 internal structure, their skeleton, extremities, etc. — they 

 resemble Fish more than Amphibia. But in certain features 

 they resemble the Amphibia, especially in the formation 

 of their lungs, nose, and heart. There is consequently an 

 endless dispute among zoologists, as to whether the Mud- 

 fish ai'e genuine Fish or Amphibia. Distinguished zoologists 

 have expressed themselves in favour of both opinions. 

 But in fact, owing to the complete blending of character- 

 istics which they present, they belong neither to the one 

 nor to the other class, and are probably most correctly 

 dealt with as a special class of Vertebrata, forming the 

 transition between Fishes and Amphibians. The still living 

 Dipneusta are probably the last surviving remains of a 

 group which was formerly rich in forms, but has left no 

 fossil traces on account of the want of a solid skeleton. 

 In this respect, these animals are exactly like the Monor- 

 rhina and the Leptocardia. However, teeth are found in 

 the Trias which resemble those of the living Ceratodus. 

 Possibly the extinct Dipneusta of the palgeolithic period, 

 which developed in the Devonian epoch out of primaeval 

 fish, must be looked upon as the primary forms of the 

 Amphibia, and thus also of all higher Vertebrata. At 

 all events the unknown forms of transition — from Primaeval 

 fish to Amphibia — were probably very like the Dipneusta. 



