288 THE HISTORY OF CREATION, 
into the cavity of the mouth) into air passages. The series 
of the ancestors of man which breathed air through lungs 
began at this stage. Their organisation may probably in 
many respects have agreed with that of the still living 
Ceratodus and Protopterus, but at the same time may 
have been very different. They probably lived at the 
beginning of the Devonian period. Their existence is 
proved by comparative anatomy, which shows the Dipneusta 
to be an intermediate stage between the Selachii and 
Amphibia. 
THIRTEENTH STAGE: Gilled Amphibians (Sozobranchia), 
Out of those Mud Fish, which we considered the primary 
forms of all the Vertebrata which breathe through lungs, 
there developed the class of Amphibia as the main line 
(pp. 205, 216). Here began the five-toed formation of the 
foot (the Pentadactyla), which was thence transmitted to 
the higher Vertebrata, and finally also to Man. The gilled 
Amphibians must be looked upon as our most ancient 
ancestors of the class of Amphibia; besides possessing 
lungs they retained throughout life regular gills, like the 
still living Proteus and Axolotl (p. 218). They originated 
out of the Dipneusta by the transformation of the paddling 
fins into five-toed legs, and also by the more perfect dif- 
ferentiation of various organs, especially of the vertebral 
column. In any case they existed about the middle of the 
paleeolithic, or primary period, possibly even before the Coal 
period; for fossil Amphibia are found in coal. The proof 
that similar gilled Amphibians were our direct ancestors, is 
given by the comparative anatomy and the ontogeny of 
Amphibia and Mammals, 
