98 MODERN IDEAS OF EVOLUTION 



the same principles, and filling the same places in 

 nature. 



If we inquire as to the history of this swarming 

 marine life of the early Palaeozoic, we find that its 

 several species, after enduring for a longer or a 

 shorter time, one by one became extinct, and were 

 replaced by others belonging to the same groups. 

 Thus there is in each great group a succession of 

 new forms, distinct as species, but not perceptibly 

 elevated in the scale of being. In many cases, in 

 deed, the reverse seems to be the case ; for it is not 

 unusual to find the successive dynasties of life in any 

 one family manifesting degradation rather than ele 

 vation. New, and sometimes higher, forms, it is true, 

 appear in the progress of time, but it is impossible, 

 except by violent suppositions, to connect them 

 genetically with any predecessors. The succession 

 throughout the Palaeozoic presents the appearance 

 rather of the unchanged persistence of each group 

 under a succession of specific forms, and the intro 

 duction from time to time of new groups, as if to 

 replace others which were in process of decay and 

 disappearance. 



In the latter half of the Palaeozoic we find a 

 number of higher forms breaking upon us with the 

 same apparent suddenness as in the case of the early 

 Cambrian animals. Fishes appear, and soon abound 

 in a great variety of species, representing types of no 

 mean rank, but, singularly enough, belonging, in 



