424 ELEMENTARY GEOLOGY 
By the Permian, or upper stage of the Carboniferous, 
reptiles of rather high type have appeared upon the 
earth. It seems probable that the order of succession 
of development was from the fish to the amphibia, then 
to the reptile. What the ancestors of the true fishes 
Fig. 244. 
Ideal landscape of the Carboniferous period. (After Haushofer.) 
were, cannot be predicted with certainty, but they are 
probably to be found among some of the invertebrates, 
perhaps the worms. The gap between the fishes and 
lower animals is a large one, and until we have learned 
more about this ancient life we can form no very satis- 
factory conclusion upon this interesting point. 
