96 EXTINCT MONSTERS 



One of the most primitive, and at the same time one of the 

 earliest known Labyrinthodonts, is the Archegosaurus, of which 

 we must now give a short account. 



It resembled the modern Proteus and other amphibians that 

 retain their lungs throughout life. 



Some of the specimens acquired since Sir R. Owen published 

 his conclusions on this creature are now in the Natural History 

 Museum. There are certain fishes of the present day that have 

 their backbones in an incomplete or unfinished state ; that is to 

 say, the bones consist partly of cartilage, like an unfinished 

 house which is only built up to a certain level, the upper 

 stories being merely indicated by scaffolding. An example of 

 this kind of fish is furnished by the existing mud-eel, or Lepido- 

 siren, a highly interesting form of life to the geologist, because 

 it tends to fill up the gap between the two distinct classes of 

 Fishes and Eeptiles. Now, in this respect, the old Carboniferous 

 amphibian we are now considering resembles the mud-fish. The 

 latter leads a partly amphibious life, burying itself in the mud 

 during the hot season, and breathing air by means of its air- 

 sack. It is believed by evolutionists that, in the course of ages, 

 lungs were developed from the air-sacks of " ganoid " fishes. 

 After detailing certain other characters, in which Archegosaurus 

 resembles the higher ganoid fishes, Sir Richard Owen says, " All 

 these characters point to one great natural group, peculiar for 

 the extensive gradations of development, linking and blending 

 together fishes and reptiles within the limits of such group." 

 The salamander-like ganoids, Lepidosteus of North America 

 and Polypterus of the Nile, are the most fish-like; the true 

 Labyrinthodonts are the most reptilian or saurian of the group ; 

 Archegosaurus conducts the march of development from the 

 fish proper to the labyrinthodont type ; Lepidosiren conducts 



