Divisions of Life and Time 



entire orders, died out long ago, and are known 

 only from fossils. The Amphibia include not 

 only such creeping and crawling things as 

 newts, salamanders, and mud-puppies, but frogs 

 and toads, a small number of curious little 

 snake like creatures, and a large number of ex- 

 tinct species, including very many of almost 

 gigantic size. These last form an order by 

 themselves, which was of no little importance 

 in the ancient world. So far as size, number, 

 and distribution are concerned, the reptiles and 

 amphibians of to-day are a degenerate lot, and 

 it is difficult to imagine that they were succes- 

 sively the dominant forms of life, as common 

 and as widely spread over the world as mam- 

 mals are to-day. 



Under the comprehensive term Fishes are 

 really included three divisions or classes of 

 equal rank in classification, though very un- 

 equal in the number of species. One of these 

 is represented by the lowly little lancelet, 

 which has no skull even, and can barely be 

 considered a vertebrate ; another contains the 

 lampreys and their relatives, more or less dis- 



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