ARCHEAN AND PALEOZOIC LIFE 423 
By evolutionary processes of development, the am- 
phibia (the group to which the frogs belong) and rep- 
tiles appear to have developed from the Devonian fishes. 
At first they were water animals, breathing with gills, 
and in this respect they resembled the true fishes. 
Carboniferous plants, —the bark of trees. 
The amphibia first appear in the Carboniferous, and there is 
a closer resemblance between the young of the present amphibia 
and the adults of these ancient species, than between the adults of 
the present and Carboniferous. The tadpole of to-day, which has 
gills, but no feet, probably resembles the earliest amphibia. In 
the process of development the tadpole form changes to that of 
the frog, which moves over the land and breathes air. 
1 Since this was written the discovery of amphibian footprints in the 
upper Devonian rocks of Pennsylvania is announced. 
