150 THE MIDDLE PAST. 



with the fauna : we rise (speaking in general terms) from 

 a world of cold-blooded air-breathers in the palaeozoic to 

 cold-blooded air-breathers in the mesozoic, and from these 

 again to the warm-blooded air-breathers of the cainozoic 

 era. If fishes were the dominant vertebrates in paleozoic 

 times, reptiles were undoubtedly so during the mesozoic ; 

 and now, in the cainozoic, the mammals (so feebly repre- 

 sented in the past) are about to assume the chief import- 

 ance. The great march of life is not only ever forward, but 

 ever upward. It is not merely that creation is concomi- 

 tant with extinction, but the new creations are ever as- 

 suming more exalted ordinal forms of the same primal 

 patterns. 



