OF EVOLUTION. 



the Devonian, they become very abundant, so much 

 so that this period has been aptly designated the 

 "Age of Fishes." But neither here, nor in the 

 period preceding, the Silurian, has there ever been 

 found a vestige of an animal higher in the scale of 

 organization than a fish. In the rocks of the Car- 

 boniferous period do the first of the more highly 

 organized animals appear, but only in forms, as far 

 as it is possible to determine from our knowledge 

 of recent animal life, whose early existence is 

 passed in an ichthyic or fish-condition. These are 

 the amphibians, the group to which the frogs and 

 toads, the newts and salamanders belong animals, 

 as we all know, and as we see exemplified in the tad- 

 pole, whose larval forms breathe the oxygen of the 

 water by means of exposed gills, and which in their 

 advanced or adult stage, develop true lungs, and 

 thus approximate the reptilian condition. But we 

 meet as yet with no true reptiles. These appear 

 for the first time in the rocks of the succeeding 

 period, the Permian. 



We have now passed through about two-thirds 



