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 Reptiles. 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 
